AGARD-LS-201 AGALC,&RD - dtic.mil · Processes for Paint Removal (Procedes efficaces et ecologiques pour l'enlevement des peintures) This publication was prepared at the request of

AGARD-LS-201

AGALC,&RDa ADVISORY GROUP FOR AEROSPACE RESEARCH & DEVELOPMENT

7 RUE ANCELLE, 92200 NEUILLY-SUR-SEINE, FRANCE

DTICSELECTE WV

JUL 1 9 19951,

AGARD LECTURE SERIES 201 G

Environmentally Safe and EffectiveProcesses for Paint Removal(Procedes efficaces et ecologiques pour l'enlevementdes peintures)

This publication was prepared at the request of the Structures and Materials Panel and under thesponsorship of the Consultant and Exchange Programme of AGARD and will be presented on

27-28 April 1995 in Lisbon, Portugal, 1-2 May 1995 in Eskisehir, Turkey, and 4-5 May 1995 inOttobrunn, Germany.

19950718 003NORTH ATLANTIC TREATY ORGANIZATION

\1 DSTRIBUTION STATKEM AApJparoved for pub~la remlec

Db~trdbutiowz Um~ited

Published April 1995

Distribution and Availability on Back Cover

Canada Groupe 45 Sacr6-Cocur Blvd. 45, boul. Sacr6-(oeur

Communication Communication Hull, Qudbec Hull (Qudbec)K1A 0S7 KIA 0S7

Group Canada

Printing ServicesServices d'imprimerie

April 20, 1995

TO THE RECIPIENT OF AGARD PUBLICATION LS-201:

Please be advised that the title for Paper #10 does not appear on the first a e of the aper (page10-1). The title of this paper is:

Selective Chemical Stripping

Sincerely,

Kelly EdwardsA/Project ManagerAGARD Publications

tdISBUTI 1NSTAtEtýApproved for public release;

Distribution Unlimited

Government Gouvernement Printed on ImpriCisur m dnof Canada du Canada reo'cledpaper papier relctci

AGARD-LS-201

ADVISORY GROUP FOR AEROSPACE RESEARCH & DEVELOPMENT

7 RUE ANCELLE, 92200 NEUILLY-SUR-SEINE, FRANCE

Accesion For

NTIS CRA&IDTIC TABUnannounced IIJustification

AGARD LECTURE SERIES 201 By--Environmentally Safe and Effective Distribution I

Availability Codes

Processes for Paint Removal Avail and/or(Proc~d6s efficaces et 6cologiques pour l'enlvement Dist Special

des peintures)

This publication was prepared at the request of the Structures and Materials Panel and under thesponsorship of the Consultant and Exchange Programme of AGARD and will be presented on27-28 April 1995 in Lisbon, Portugal, 1-2 May 1995 in Eskisehir, Turkey, and 4-5 May 1995 inOttobrunn, Germany.

" - North Atlantic Treaty Organization- Organisation du Trait6 de lAtlantique Nord

EDIS77tMrnON STA A

Approred for public release;Distribution, Unlimited

The Mission of AGARD

According to its Charter, the mission of AGARD is to bring together the leading personalities of the NATO nations in thefields of science and technology relating to aerospace for the following purposes:

- Recommending effective ways for the member nations to use their research and development capabilities for thecommon benefit of the NATO community;

- Providing scientific and technical advice and assistance to the Military Committee in the field of aerospace research

and development (with particular regard to its military application);

- Continuously stimulating advances in the aerospace sciences relevant to strengthening the common defence posture;

- Improving the co-operation among member nations in aerospace research and development;

- Exchange of scientific and technical information;

- Providing assistance to member nations for the purpose of increasing their scientific and technical potential;

- Rendering scientific and technical assistance, as requested, to other NATO bodies and to member nations in

connection with research and development problems in the aerospace field.

The highest authority within AGARD is the National Delegates Board consisting of officially appointed seniorrepresentatives from each member nation. The mission of AGARD is carried out through the Panels which are composed ofexperts appointed by the National Delegates, the Consultant and Exchange Programme and the Aerospace ApplicationsStudies Programme. The results of AGARD work are reported to the member nations and the NATO Authorities through theAGARD series of publications of which this is one.

Participation in AGARD activities is by invitation only and is normally limited to citizens of the NATO nations.

The content of this publication has been reproduceddirectly from material supplied by AGARD or the authors.

Published April 1995

Copyright © AGARD 1995All Rights Reserved

ISBN 92-836-1017-2

Printed by Canada Communication Group

45 Sacre-Cfeur Blvd., Hull (Qudbec), Canada KIA 0S7

Abstract

Environmentally Safe and Effective Processes forPaint Removal

Paint stripping and repainting of aircraft surfaces are required periodically during the operating lifetime of an aircraft.Historically, paint removal has been achieved using chemical strippers, involving materials which contain toxic componentsand which create hazardous working conditions. The process generates large amounts of hazardous waste from the chemicalsused. Alternative methods for aircraft paint removal are now being investigated within the NATO nations with regard to theirenvironmental safety and effective application. These processes include: Plastic Media Blasting, Wheat Starch Dry MediaBlasting, Carbon Dioxide Pellet Blasting, Sodium Bicarbonate Blasting and Thermal Decomposition Methods (Laser, FlashLamps/Carbon Dioxide). The Lecture Series will review these current state-of-the-art alternative methods with regard toenvironmental effects and related health hazards, costs, process controls, practicality of operation and their effects on.properties of aircraft structural materials.

Abrege

Procedes efficaces et ecologiques pour l'enlevementdes peintures

L'enlbvement des peintures et la remise en peinture des surfaces ext6rieures d'un a6ronef sont demand6s p6riodiquement toutau long de la vie op6rationnelle de l'appareil. Traditionnellement, ces op6rations sont r6alis6es t 1'aide de d6capantschimiques qui contiennent des ingr6dients toxiques, et qui cr6ent, par cons6quent, des conditions de travail dangereuses. Leproc6d6 g6nbre des volumes importants de d6chets nocifs.

Des m6thodes alternatives pour l'enlbvement des peintures a6ronautiques sont en cours d'examen an sein des pays membresde 1'OTAN du point de vue du danger qu'ils repr6senteraient pour l'environnement et de l'efficacit6 de leur application. Cesproc6d6s comprennent: le d6capage 4 sec par projection de grenailles plastiques, le grenaillage ý boulettes de dioxyde decarbone, le grenaillage au bicarbonate de soude et les m6thodes bas6es sur la d6composition thermique (laser, feux t6clair/dioxyde de carbone).

Ce cycle de conf6rences fera le point de ces m6thodes alternatives avanc6es actuelles en ce qui concerne leur impact6cologique et les risques sanitaires associds, les coots, les contr6les en cours de fabrication, la faisabilit6 de l'op6ration et lescons6quences de l'adoption de ces m6thodes pour les caract6ristiques des matdriaux structuraux a6ronautiques.

Hii

List of Authors/Speakers

Lecture Series Director: Dr. Jeffrey WALDMANNaval Air Warfare CenterAircraft Division Warminster4.3.4.2. M/S 08 (Code 6063)P.O. Box 5152Warminster, PA 18974-0591USA

Authors/Speakers

Dr. Terry FOSTER Mr. Olivier MALAVALLONHead Materials Technology AMrospatialeEsquimalt Defence Research Detachment Direction des EtudesFMO Victoria A/DET/CG-MPVictoria, BC Canada Toulouse Est.VOS 1B0 316 route de BayonneCANADA 31060 Toulouse Cedex 03

FRANCE

Author

Mr. S. VISAISOUKIce Blast International Corp.627 John St.Victoria, BCCANADA V8T 1T8

iv

Contents

Reference

Abstract/Abr~g6 iii

List of Authors/Speakers iv

Introduction Iby Dr. Jeffrey WALDMAN

Overview of Paint Removal Methods 1by Dr. Terry FOSTER

Paint Removal Principles 2by Mr. Olivier MALAVALLON

Background to Plastic Media Blasting 3by Dr. T. FOSTER

Dry Media Blasting with Wheat Starch 4by Mr. 0. MALAVALLON

Water Blasting Paint Removal Methods 5by Dr. T. FOSTER

Paint Removal and Surface Cleaning Using Ice Particles 6by Dr. T. FOSTER and Mr. S. VISAISOUK

Stripping with Dry Ice 7by Mr. 0. MALAVALLON

Aquastrip 8by Mr. 0. MALAVALLON

Stripping by Laser 9by Mr. 0. MALAVALLON

Selective Chemical Stripping 10by Mr. 0. MALAVALLON

Facilities used for Plastic Media Blasting 11by Dr. T. FOSTER

Treatment of Plastic Media Waste 12by Dr. T. FOSTER

Bioremediation of Wheat Starch Media Waste 13by Mr. 0. MALAVALLON

Operational Parameters and Material Effects 14by Dr. T. FOSTER

Process Evaluation 15by Mr. 0. MALAVALLON

Standardization Work 16by Mr. 0. MALAVALLON

Future Prospects 17by Mr. 0. MALAVALLON

Bibliography B

vi

1-1

Introduction

Paint removal and repainting of aircraft surfaces are required periodically during the operating lifetime of an aircraft.Historically, paint removal has been achieved using chemical paint removal methods. These methods use materials whichcontain toxic components and which create hazardous working conditions. These processes also generate large amounts ofhazardous waste from the chemicals used.

Alternative methods for aircraft paint removal that are environmentally safe are now being investigated within the NATOnations. These processes include: Plastic Media Blasting and other abrasive blasting methods (Wheat Starch, Water Jet, IceParticles, Carbon Dioxide Pellets, Sodium Bicarbonate) as well as Thermal Decomposition Methods (Laser, FlashLamps/Carbon Dioxide).

In October 1992 the Structures and Materials Panel of AGARD held a workshop on Environmentally Safe and EffectiveProcesses for Paint Removal from aircraft. The purpose of the workshop was to review the state-of-the-art of the newtechnologies for paint removal and their effects on the properties of aircraft structural materials. The practicality of operation,environmental effects, cost and process controls were also discussed in that these factors strongly influence theimplementation of alternate paint removal processes.

As a result of the workshop, it was decided to present a Lecture Series on Environmentally Safe and Effective Processesfor Paint Removal for aircraft. Two experts in the field (Dr. T. Foster and Mr. 0. Malavallon) will present a series of lectureson this subject. The lectures will cover in detail the principles of paint removal and various environmentally safe paintremoval processes including plastic media blasting and other abrasive blast removal methods as well as environmentally safethermal and chemical paint removal processes. The treatment of waste disposal and work on standardization of the variousalternate paint removal processes will also be presented. The Lecture Series will review these current state-of-the-artalternative paint removal methods with regard to environmental effects and related health hazards, costs, process controls,practicality of operation and their effects on properties of aircraft structural materials.

Paper presented at the AGARD SMP Lecture Series on "Environmentally Safe and Effective Processes for Paint Removal"held in Lisbon, Portugal, April 27-28, 1995; Eskisehir, Turkey, May 1-2, 1995 and Ottobrunn, Germany, May 4-5, 1995

and published in LS-201.

1-1

OVERVIEW OF PAINT REMOVAL METHODS

Dr. Terry FosterEsquimalt Defence Research Detachment

FMO VictoriaVictoria, B.C., Canada VOS IBO

SUMMARY sensitive surfaces such as composite materials and strictcontrol of blast parameters and conditions are required.

As an introduction to environmentally safe and Optical methods can be slow, leaving paint residues, andeffective methods of paint removal, the following is an chemical methods may not remove all of the coating oroverview of the various methods available. Many of require special coating formulations to be effective.the methods introduced in this paper will be discussedin further detail during this lecture series. The purpose 2. PLASTIC MEDIA - VARIOUS TYPESof this overview is to introduce the various paintremoval methods available. Plastic media was the original media developed as a

replacement for chemical strippers. This media will be the1. INTRODUCTION focus of a series of lectures in this series and only a brief

summary will be given here.With the introduction of strict environmentalregulations governing the use and disposal of Plastic media is made from a variety of polymericmethylene chloride and phenols, major components of materials, depending on the hardness of the blast mediachemical paint strippers, there have been many new required, and is produced in a variety of grit sizes. Theenvironmentally safe and effective methods of paint main plastic media are based on acrylic, urearemoval developed. The new methods developed for formaldehyde, melamine-formaldehyde, polyester andremoving coatings from aircraft and aircraft polyallyl diglycol carbonate. The properties of the variouscomponents include: mechanical methods using plastic media are shown in Table 1.abrasive media such as plastic, wheat starch, walnutshells, ice and dry ice, environmentally safe chemical Since its development in the early 1980's, PMB hasstrippers and paint softeners, and optical methods developed into a process used routinely in many areas ofsuch as lasers and flash lamps. aircraft refinishing, especially military aircraft. The US,

Canadian, German and other air forces worldwide haveEach method has its advantages and disadvantages, approved some form of plastic media stripping for aircraft.and some have unique applications. For example, Many studies have been carried on the effects of themechanical and abrasive methods can damage various plastic media and the operating parameters (media

TABLE 1 -- BLAST MEDIA PROPERTIES

MEDIA CHEMICAL HARDNESS DENSITYCOMPOSITION

(Moh scale) (W/cm')

Type I Polyester 3.0 1.25Type II Urea Formaldehyde 3.5 1.5Type III Melamine Formaldehyde 4.0 1.5Type IV Phenol Formaldehyde 3.5 1.5Type V Acrylic 3.5 1.2Type VI Polyallydiglycol carbonate 3.0 1.3



1-2

flow rate, media type, blasting pressure and standoff two mechanisms, vaporization and combustion. Fordistance) on material properties of aluminum, example, if a stream of air is directed at the paintedtitanium, and various composite materials (esp. surface during laser stripping, the paint removal isgraphite epoxy composites), more efficient than if a stream of inert gas, which

prevents combustion, is directed at the paint surface.

3. STARCH BASED MEDIA The stream of air allows the paint to combust as wellas vaporize whereas the stream of inert gas only

Wheat starch blasting media will also be discussed in allows the paint to vaporize.much more detail in subsequent lectures and only abrief summary will be included here. Wheat starch Care must be taken when using laser stripping becausewas developed by Ogilvie Mills Ltd (now a subsidiary the substrate surface can reflect or absorb the laserof CAE Canada Ltd.), Montreal, Canada as a radiation, and the nature of the surface also affects thebiodegradable, non-toxic, non-petroleum based, rate of paint removal. On an anodized aluminumnatural polymer abrasive grit for paint removal, surface, the radiation from a CO 2 laser is absorbed by

the oxide layer and the parameters required to stripWheat starch has several advantages over paint must be more closely controlled than on aconventional plastic media. This medium is softer reflective surface such as aluminum metal. After laserthan Type 1] or Type V media and thus the possibility paint removal, there is no residual paint film left onof damage to delicate substrates is reduced. It is much the anodized surface whereas there is always a residualeasier to remove one coating layer at a time with wheat paint film left on the aluminum surface. On astarch than with other plastic media. Wheat starch is reflecting surface, as the paint film is reduced ina natural material and there are minimal disposal thickness during laser stripping, the amount of laserproblems. energy absorbed by the thin paint film is reduced as

more of the radiation is reflected from the substrateWheat starch is under consideration by the CF as a surface. At some point, vaporization of the thin paintpossible blasting media. Research is currently under film no longer occurs.way to investigate the parameters necessary forefficient paint removal and to determine the benefits of Laser stripping of a coated carbon steel, which also iswheat starch over Types V and VI plastic media. a reflecting surface for CO, laser radiation, resulted inWheat starch is also under consideration for special visual damage to the steel surface. Microscopicapplications such as stripping decals and removing examination of the steel surface revealed a change inpaint from sensitive substrates, such as Kevlar based microstructure to a depth of 150 pm at 800 J/cm2 andmaterials. 100 kW/cm2 of laser energy and power. At lower

energy and power, 40 J/cm2 and 60 kWcm

Economic and environmental concerns about the respectively, no damage was observed but, as with thedisposal of other types of used media could also bring reflective aluminum, a thin layer of paint remained onwheat starch into more serious consideration in the the surface.future.

In practice, laser stripping would require a robotic4. LASER PAINT STRIPPING system to ensure that the partially de-focused laser

beam was moved across the surface in a controlledLaser paint stripping is being investigated as a method manner to prevent surface damage and to maintainof paint removal because it requires no abrasive media paint removal efficiency. Laser stripping is less costlythat requires disposal and the amount of residue than chemical stripping.remaining after laser stripping is quite small.

International Technical Associates in the USA are

Paint removal by laser radiation is by one or both of developing an Automated Laser Paint Stripper

1-3

(ALPS). This system will consist of the following * only paint debris to removeeight components: * low capital investment

"* Laser 5-1 Medium Pressure With Paint Softeners"• Robot"* Multi Spectral Camera Medium pressure water jets utilizing chemical"• Rastering System softeners is a commercial process owned by"* End Effector or Manipulator LUFTHANSA calledAQUASTRIP. The blast head for"• Waste Management System this process consists of two nozzles integrated into a* Cell Controller rotating head. The head rotates at 2000-6500 rpm and

"• Safety System is driven by an impulse from the water jets due to theeccentric alignment of the nozzles. The typical

A pulsed (1000 Hz) CO2 laser (6 kW) is mounted on parameters used for this process are:a robot (supplied by Vadeko) that is track mounted,pedestal type with seven degrees of freedom. The • maximum operating pressure - 7,250 psicamera is used to decide if the coating has been * water velocity - 320 m/secremoved. The rastering system is required to ensure # water flow rate - 20 I/minthe laser moves around the aircraft and does not dwell * traversal speed - 50 mm/secfor extended periods in one position. The material 0 standoff distance - 30 - 150 mmremoved from the aircraft is vacuumed up as it iscreated and then processed through particle and The LUFTHANSAAQUASTRIP study has shown thatvapour separators to ensure the waste conforms to up to 60% of all stripping jobs require the use oflocal regulations. The cell controller is a computer softeners. The softeners used are most effective withsystem (UNIX operating system) interfaced to the polyurethane coatings and the dwell times must berobot, laser, waste system and safety system. The determined for each coating system. A dwell time ofsafety system meets the requirements for laser and 2-4 hours is normal and a water rinse is used torobot operation. remove the paint softener prior to water blasting. Two

water softeners are currently used: Turco 1270-5 and5. WATER BLASTING Brent LB2020 and both are based on biodegradable

solvents such as benzyl alcohol.Two methods of paint removal using high pressurewater have been developed. The first method uses A research program was carried out to determine theonly high pressure (28,000 psi) water and the second effects of the AQUASTRIP process on the long termmethod employs medium pressure water blasting (up integrity of aircraft structures. These tests showedto 7,250 psi) in combination with paint softeners. that the two softeners did not induce pitting or etchingAlthough paint softeners add an extra step in the of aluminum (2024-T3) components and noremoval process, lower blasting pressures (7,250 psi) degradation of elastomers was observed.are required to remove coatings. High and mediumpressure water blasting offers several advantages: During dynamic operation for over 20 cycles no

damage was found to clad or anodized layers but"* water is usually readily available damage to these surfaces could occur if the nozzle was"* inexpensive and easy to handle stationary for 5-10 seconds. Cadmium plating on"• selective stripping feasible fasteners was not removed by this process. Residual"• no storage problems stress measurements using Almen Arc Heights showed"* readily available technology for treatment and deflections of less than 10 pm well below the

disposal allowable limit of 150 pm for 2024-T3 aluminum.* readily recyclable Fatigue test results indicated that under the above

1-4

blast conditions there was no change in the fatigue life • maximum operating pressure - 24,000 psiof the material. ° water flow rate - 20 1/min

• traversal speed - 25 mm/secWater migration during blasting can occur into • standoff distance - 37 mmcavities directly accessible for the water jet. Neutron • stripping rate - 1.25 ft2/min per nozzleradiography has shown that intact bonded or sealedsurfaces are not affected by the AQUASTRIP process. Using the above parameters residual stressThe AQUASTRIP process can be quite destructive on measurements using the Almen Strip method gaveseals and the seal removed if the jet is directed at the Almen arc heights of less than 75 pm for 2024-T3edge of the sealer. aluminum alloy. Surface roughness measurements

under the same blasting conditions resulted in surfaceUse of the AQUASTRIP process on composite roughness increasing from 23, 36, 67, 126 pin throughsurfaces requires further refinement and it is four blast cycles on Al 2024-T3 alclad. Furtherrecommended that each composite material requires a process validation studies are planned to includecomplete test matrix prior to use of the AQUASTRIP composite surfaces (glass fibre and graphite fibre),process. The application of the paint softeners used in aluminum and fibre honeycomb structures and joints,the AQUASTRIP process to composite surfaces has lap joints and fasteners to investigate sealant integritybeen approved by LUFTHANSA in prior test and water intrusion.procedures.

6. ICE PARTICLES5.2 High Pressure Water

Ice blasting will be discussed in more detail in aThe USAF (Wright Laboratory, Aeronautical Systems subsequent lecture. Ice blasting was developed byDivision (AFMC)) and United Technologies, USBI RETECH (now Ice Blast International), under contractCo. are developing a Large Aircraft Robotic Stripping to Defence Research Establishment Pacific, as a dustSystem (LARPS) using a high pressure water process free blasting technique for confined spaces such asas an environmentally safe and effective paint removal ship bilges and machinery spaces. More recently itsystem. has been shown to have further application in paint

removal from delicate substrates that can be damagedThe robotic system is being developed independently by conventional blasting techniques and as a cleaningof the high pressure water system. The robotic system technique for soiled or contaminated surfaces.will be designed to handle large military aircraft suchas the Boeing C-135, B-52, and E-3 and the Rockwell Ice particles offer several advantages as a blastingB- I B. Hanger, aircraft preparation and system medium. They are not abrasive and fracture under amapping may be different for each aircraft but the high load such as impact with a substrate, thussystem will be essentially the same. limiting the impact force and thereby preventing

damage to delicate substrates. Ice is also a dust freeThe procedure for qualifying a high pressure water media that melts to water. The spent medium, namelyblasting system has been broken down into three parts, water, can be easily removed from the coating debrisI) Process Optimization, ii) Process Validation and can be disposed of leaving the debris to beTesting, and iii) Additional Materials testing. As of handled as a known hazardous waste disposal1992 the process optimization has been completed and problem.the process validation testing has begun.

The use of ice blasting is also being considered by theThe process optimization study resulted in the CF as a method for cleaning soiled aircraft coatings,following parameters for use in the high pressure removing decals from aircraft, removing paint fromwater process: delicate surfaces such as Kevlar and graphite epoxy

1-5

composites, and as a possible method to clean aircraft There are several disadvantages with the dry icecomponents such as gas turbine blades. blasting process including:

Concerns about the environmental aspects of the • the requirement to store compressed liquid CO2

disposal of the spent media from plastic media on siteblasting or traditional grit blasting could lead to more 0 the use of very high air pressures (up to 250 psi)serious consideration of ice blasting for the stripping that require large compressorsand cleaning of entire aircraft or other equipment. • the process is noisy because of the compressors

and cryogenic equipment used in the process7. CARBON DIOXIDE (DRY ICE) PARTICLES

The cleaning rates of CO2 alone are quite low and a7-1 Ila Ice Particles process combining CO 2 and flash lamps shows more

promise.The major advantage of carbon dioxide (CO2 ) pelletsis that there is no media residue after blasting. One 7.2 Xenon Flash/Dry Icedisadvantage is that it must be removed from enclosedspaces to ensure the safety of personnel and an The development of a combined xenon flashadequate source of breathable air. lamp/carbon dioxide pellet blasting by Warner

Robbins Air Logistics Center (WR-ALC) andTwo German companies have investigated dry ice McDonnel Douglas Aircraft Company (McAIR)pellets (Deutsche Airbus, Domier and Messer carries the trademark FLASHJETTM.Grieshiem Company). Dry ice blasting alone was notfound to be particularly effective in removing well A xenon flash lamp emits sufficient energy to ash theprepared paint systems with stripping rates of 1 m2/hr. paint coating and the carbon dioxide blast is used toIf used in combination with paint softeners, rates of up remove the residue.to 15 m2/hr were observed, but this rate only occurredif the paint system was completely blistered by the The FLASHJEjTM process can selectively removesoftener. polyurethane coatings down to the epoxy primer

leaving the primer intact. This process therefore doesThree US companies have been or are also developing not damage the substrate or affect the followingdry ice blasting processes. Research and testing of dry properties:ice blasting for aircraft is ongoing. A Boeing 707 atthe Smithsonian Museum was stripped using dry ice • mechanical properties of thin, structuralblasting and the process has been evaluated for F- 15, aluminumC- 141 and C- 130 aircraft. • mechanical properties of graphite epoxy

• adhesive bond strengthImpact of CO2 particles can do considerable damage. * repaint adhesion or corrosion resistanceFor example, in the German study, anodized and * fatigue life of Al 2024-T3 or Al 7075-T6alclad layers show micro-ruptures and micro-fissures, • Almen test results indicate deflection of less thanmicro-fissures were observed on composite surfaces 0.0005 inches.along with upper-layer delaminations and in somecases the coating on the backside of the panel was The process is capable of stripping at rates of up toremoved during blasting. From this study it was 2.8 ft2/min down to bare substrate and 4 't /min toconcluded that CO2 blasting needed more refinement remove only the topcoat (polyurethane/epoxy coatingand should only be used in combination with paint system).softeners.

The FLASHJETTM process is now a commercially

1-6

available production process for coating removal from Experience has shown that different polyurethaneaircraft components. coating formulations react differently with softeners.

Some blister at room temperature after 30 minutes8. BICARBONATE OF SODA exposure while others require higher temperatures (up

to 40 •C) and longer exposure times (up to 24 h).

Crystalline sodium bicarbonate is an odourless, non-

flammable, water soluble abrasive material. Sodium The major concern with all paint softeners is thebicarbonate is used in food and pharmaceutical possibility of a reaction between the softener and theapplications. The blast particles are crystalline with base material. Exposure of aluminum alloys to acidsharp and jagged edges but produce a dusty based softeners for eight hours at 40"C resulted inenvironment unless water (2 L/min) is injected into the weight loss in the range of 0.1-0.3%. SEMblast stream. The material is soluble in water and this observation noted the loss of the oxide layer and thecan be used as a method of separating the blast media initiation of corrosion on the surface. No weight lossfrom paint particles, or changes in the surface was noted with alcohol based

softeners (benzylalcohol containing). No reduction inSodium bicarbonate has been under evaluation for fatigue behaviour or strength was observed with eitherpaint removal from aircraft for a number of years and type of softener.has been shown to be effective.

No change in flexural strength or interlaminar shearConcerns about the possible corrosive effects of strength were observed using either type of softener onsodium bicarbonate on aluminum structures have been duroplast composites. Benzylalcohol based softenersaddressed by the manufacturer. An inhibitor has been reduced the interlaminar shear strength of aadded to reduce the corrosive effect and it has been thermoplast composite to an unacceptable level.demonstrated the sodium bicarbonate is no morecorrosive than previously used chemical strippers. 10. STRIPPABLE COATINGS

Sodium bicarbonate has been used in the following By design and formulation, a coating can be madeapplications: strippable chemically in a short period of time using

environmentally friendly paint strippers (methylene"* remove grease, contamination and coatings from chloride-free and phenol-free).

a variety of structures"* remove baked-on-food and other residue from Selectively strippable coatings are based on one of two

baking equipment principles:"* remove coatings from wood and fibreglass marine

structures • intermediate coating that is easily removed, or* cleaning of circuit boards, and ° a barrier coat not removed in the stripping process• cleaning automotive parts The disadvantage of the barrier coating method is that

coating thickness builds up in multiple stripping and9. PAINT SOFTENERS repair procedures. It has also proven difficult to

obtain a good balance between adhesion andAs an alternative to blasting methods, paint softeners strippability in the barrier coating and the barrierhave been developed that do not use chlorinated coating makes it more difficult to detect cracks in thehydrocarbon solvents. The softeners are generally anti-corrosive primer.alcohol (alcalic) or acid based and are considered lesspolluting than paint strippers based on chlorinated ICI has developed an intermediate coat systemsolvents; they are also biodegradable. consisting of an epoxy primer, intermediate coat II and

a modified polyurethane topcoat. It has been

1-7

independently shown that this coating system can beremoved in under two hours using non-chlorinatedchemical strippers (pH neutral).

Experience with this system on the Airbus A320showed that after three years, the polyurethane topcoatand intermediate coat could be removed with a non-phenolic stripper. Topcoat lifting occurred after 5minutes and complete removal down to the epoxyprimer occurred within 30 minutes, leaving an intactepoxy primer.

2-1

Paint Removal Principles

Mr. Olivier MalavallonA6rospatiale

Direction des EtudesA/DET/CG-MP

Toulouse Est. 316 route de Bayonne31060 Toulouse Cedex 03

FRANCE

On the question of paint removal, the number of listed Nevertheless, for each of the three basic physical

processes - in use, under development and under study - phenomena, it is possible to identify the main mechanisms

appears very high and very varied, brought into play in material removal leading to paintstripping.

In order to better understand this situation, it is useful togroup these processes into families. 3 STRIPPING PROCESSES

3.1 Chemical stripping1 CLASSIFICATION

In the case of chemical stripping, the operating methodFrom among the various types of listed classifications, the used is as described in § 2 and requires the carrying out ofclassification chosen is the one taking the physical all identified steps.phenomena involved in the material removal process intoaccount. Although the operating methods and the physico-chemical

mechanisms are almost the same, the use and efficiency ofThe physical phenomena allowing material removal to these products vary. They depend mainly on the type ofachieve paint stripping are as follows: chemical strippers used. These can be classed by their- chemical, known compositions structured around one or more active- mechanical, chemical constituents.- thermal. These chemical constituents are as follows:

These principles can be used either one by one in theelaboration of a process which is then considered as - methylene chloride,«simplex» or they can be combined to obtain better results. - phenolic compounds,Today, the main combinations are of the <<duplex»> type, - activated acids or activated bases free from phenols,

such as: chromates or methylene chloride.

- chemical + mechanical,- thermal + mechanical. Originally, the physico-chemical mechanisms used by

most strippers were based on the action of methylene

2 DESCRIPTION chloride. This molecule has high polarity and a highsolvent power. When this molecule is used, the following

It is possible to define an operating method for all paint reactions are generated:stripping processes independent of the process studied:

- migration of the solvent molecules (CH2 C12) through

a) cleaning, degreasing, drying and masking, the layers of paint which are similar to a macromoleculenetwork,

b) application of the stripping process to the surface, accumulation of the migrating particles as soon as theyencounter a modification in the macromolecular

c) paint stripping, network,- solvation leading to a swelling of the paint,

d) removal of paint residues (by scrapping, rubbing down, loss of cohesion between the various layers of paint by

water jet, etc.), electrostatic reaction of the methylene chloride moleculewith the small-size molecules.

e) if necessary, complete or local reapplication (repeat ofb) + c) + d)), For products in which phenolic compounds replace

methylene chloride, the mechanisms brought into play aref) demasking and final cleaning, the same.

g) recovery and processing of waste. Lastly, a new generation of chemical strippers, free fromchromates, methylene chloride and phenolic compounds,

According to type of physical phenomenon and process has been engineered from activated acids or activatedused, note that: bases. The physico-chemical reactions generated are similar

to those generated by methylene chloride. However, the- steps a) and f) are more or less reinforced and increased, molecules used are less active and their solvent power is- steps b) and c) can be carried out almost simultaneously lower. To improve the chemical kinetics, «<active>» elements

or completely dissociated, are introduced into the composition of these products.- phase d) and e) depend mainly on the efficiency of the

process.



2-2

3.2 Mechanical stripping Schematic diagram:

This family of stripping processes includes technologiesusing mechanical phenomena based on erosion. Erosion vi vi V2

can be generated by friction of tools such as sanders or A

brushes. Erosion can also be achieved by blasting small- ang A

size particles onto the surfaces to be treated. 0

For mechanical stripping, if operating method is asdescribed in § 2, steps a), e), f) and g) can be significantly a = stripping anglereduced and steps b) and c) carried out simultaneously. V2 = blasting speedV2 = rebound speed

3.2.1 Friction (where V1 > V2)A = particle

These processes are mainly manual. The operator exerts B = substrate

pressure on the surface to be treated either directly or usingmechanical assistance. Movement of the tool used is The main parameters influencing these types of processesassociated with this pressure. The aim of these movements are:

is to homogenize the surface under treatment, avoid localheating and control work progress. - type of media,

- media flow rate,

3.2.2 By blasting particles - carrier fluid pressure (inducing speed),- type of nozzle,

Initially manual, these processes have undergone sustained - angle between nozzle centerline and substrate.

industrial research and are now either semi-automated orcompletely automated. 3.3 Thermal stripping

This type of technology consists in blasting particles onto These fairly recent processes are based on sophisticatedthe surface to be stripped by means of a carrying fluid. The technologies making extensive use of electronics andcarrying fluids generally used are water and air. automation.

These particles, also called media, can be of differentphysico-chemical types: At present, the principles of the processes developed are

mainly based on supplying of thermal energy. The energy- mineral («hsand» scrunadum), transmitted to the paint substrate under certain conditions- organic (wheat starch media, nut shells, etc.),

- synthetic (plastic media), allows the internal molecular bonds of the paints to be

- crystalline (H20 ice, dry ice), broken.- liquid (water, etc.). Energy is supplied by radiation. According to type of

radiation used, different paint degradation modes areAlso, these particles can be characterized by a grain size observed.and a density.

Generally, the media are introduced into the carrier fluid at In the case of thermal stripping, if the operating method isthe level of a subassembly called «nozzle>> then accelerated as described in § 2, steps a), e), f) and g) can be significantlyin the nozzle. reduced and steps b) and c) carried out simultaneously.

When the media hit the surface, there is a sudden transfor- 3.1 Thermal modemation in its kinetic energy:

- in the form of work dissipatedby the erosion phenomenon, This stripping mode is suitable for certain wavelengths.- in the form of a new rebound kinetic energy. The radiation is emitted in the direction of the substrate to

be treated. It accumulates locally on the surface in the formIn addition, for certain media, this mechanical shock can of heat.cause crackingof the superficialpaintlayers.This sustained This accumulation of energy then allows the molecularcracking allows the infiltration of the media and causes bonds to be thermally broken.lack of cohesion between paint coats.

2-3

The accumulation required for stripping depends mainly 4.2 Selective strippingon the energy of the photons used, the paint absorptioncoefficient and the frequency of the energy pulses. 4.2.1 Definition

3.3.2 Photoablation When a process is capable of achieving continuous anduniform stripping removing a certain paint thickness -

In this case, the stripping mode used is photochemical. The without however removing the entire paint system -radiation emitted generates protons whose energy is greater stripping is said to be selective.than that of the molecular bonds. In theory, each protonemitted can directly break one of these bonds. In practice, for an external paint scheme, this consists in

being able to remove certain layers located on the surface4 - STRIPPING LEVELS (such as varnish, decorative paint, top coat) without

removing or damaging the underlying coats (such as wash4.1 Reminders primer or primer).

On aircraft, external paint schemes are applied to almost 4.2.2 Benefitsall external surfaces, independentofthe substrates, whetherthese are metallic or composite. This type of stripping, when it can be performed, can be

used to brighten up or change the livery of an aircraft.However, these substrates are never bare, but almost Potentially, it allows cycles tobe reduced, avoids increasesalways covered by appropriate surface treatments mainly in weight whilst limiting structural inspections beforeto protect them against corrosion phenomena or electrostatic repainting.phenomena. In reality, the paint schemes are applied tothese protected substrates. Diagram: selective stripping

These external paint schemes in general consist of a stackof different layers. Each of these layers is defined and used Selectivefor a precise purpose and meet specific technical stippingrequirements. Also, on account of this stack, each paint derti p .. leve

decorative paint .....

coat interfaces with at least another coat in the paint system top coat _ _

considered primer Adjustablewash primer • ''' ... H• .. H'''4 • / lmt

An external paint scheme generally consists of the following o / // ##//

paint coats: bare substrate

- wash primer,- primer, 4.3 Complete stripping- top coat,

4.3.1 Definitionto which the following can be added for certain applica-tions: If a stripping process is capable of totally removing the

- decorative paint, external paint scheme without damaging or modifying the- varnishv substrate and its protection, stripping is called complete.

Note: If the stripping reachs the bare substrate, that isThe situation can be summarized as shown on the diagram removing all protections covering it, the operation is calledbelow: conversion.

General paint diagram 4.3.2 Benefits

This type of stripping, when it can be performed, can bew1irh used to make repairs to or inspections of the aircraftdecorative paint C 1 Complete structure. It also allows the paint scheme to be changed

Pop coa Paint without incurring weight penalties.primer - Schemewash pi e .•"'''''',,.•>''',,) > >

protectio m - • ."er . . . . Protected

bare 41 Ptratetbare substrate/ / / / jsbtre

2-4

Complete stripping diagram - external paint scheme considered,

- stripping principle or principles retained and used bywamish |the process,d e c o ra tiv e p a in t C o m p l et etop oat ..... • •complete

t stripping - type of substrate to which the paint is applied,primer _._•

wash primer -boprotectn -.. ................... Limit - technologies used and control of stripping parameters.

bare substrate Lastly, it appears that certain processes can intrinsicallyonly perform selective stripping or complete stripping

4.4 Comments operations.

The capacity of a process to achieve selective stripping orcomplete stripping (otolerance>> notion) depends on severalcriteria:

3-1

BACKGROUND TO PLASTIC MEDIA BLASTING


FMO VictoriaVictoria, B.C., Canada VOS IBO

1. INTRODUCTION PMB due to the possibility of damage to the aluminumalloy (2024-T3) used on most commercial aircraft.

Chemical strippers based on active phenoliccomponents in a chlorinated solvent have been the There are also limitations on the use of plastic media ontraditional method for removing of paints and coatings aircraft written into many specifications. The followingfrom aircraft. With the recent recognition of the are situations and conditions that may restrict orenvironmental and health concerns of chlorinated preclude the use of plastic media:solvents and the problem disposing of phenols therehave been some major developments in paint removal - nature of the substrate - thin section aluminum ortechnology. One of the first techniques developed to composites such as kevlarreplace chemical strippers and now one of the most 0 type of coating, especially hard or resilient typeswidely used techniques for paint removal from aircraft that are difficult to removewas plastic media blasting (PMB). ° the need to mask part of the aircraft to prevent

ingress of media into the structureThe PMB technique is similar to traditional grit • the dust must be contained during blasting andblasting (slag, sand alumina or Carborundum) must be controlled to prevent health problems fortechniques used on steel and other metals based on workersgrits) but using polymer based media that are softer • the media must be recycled to be cost effectiveand less aggressive. Plastic media are ranked by • the media and paint are generally considered ahardness and density as well as chemical composition. hazardous waste and must be disposed inPlastic media are also available in a variety of mesh accordance with local regulations.sizes ranging from 20 to 60 mesh or a selecteddistribution of sizes. A list of the various media types 2. PLASTIC MEDIA TYPES ANDand their physical properties are shown in Table 1. The CHARACTERISTICSclassification is based on the US MIL SPEC MiI-P-85891. The following descriptions of the various plastic media

are based on the US Military Specification Mil-P-While the Type II, urea formaldehyde, was the first 85891. The descriptions are taken from the technicalmedia in general use in many applications and facilities, data sheets produced by the manufacturers, from theit has recently been replaced by the Type V, acrylic, Composite Materials Co. Inc, Technical Data Sheetsmedia. This is the media currently specified by the and from the AFSC Design Handbook "Paint StrippingCanadian Department of National Defence (DND) for Technologies - Plastic Media Blasting (PMB) andstripping Canadian Forces (CF) aircraft and is specified Other Abrasive Grits".at many US Air Force (USAF) facilities. The othermedia are used for specific applications but do not find 2.1 Type I. Polyesterwidespread application in aircraft stripping.

Polyester is a thermoset resin usually produced in castThere are still restrictions on the use of PMB, sheets and unlike the other phenolic resins is producedespecially on commercial aircraft. For example, the in the unfilled form. Because of its low density andIATA Taskforce on Paintstripping did not recommend sharpness it removes coatings through a chipping rather



3-2

than abrasive process. The advantage of this is

TABLE 1 -- BLAST MEDIA PROPERTIES

MEDIA CHEMICAL HARDNESS DENSITYCOMPOSITION

MOH Barcol (I/cm",)

Type I Polyester 3.0 34 - 42 1.04 - 1.46

Type II Urea Formaldehyde 3.5 54 - 62 1.47- 1.54Type III Melamine Formaldehyde 4.0 64- 72 1.47- 1.52Type IV Phenol Formaldehyde 3.5 54-62 1.38- 1.42Type V Acrylic 3.5 46-54 1.17- 1.20Type VI Polyallydiglycol Carbonate 3.0 30- 40 1.3 - 1.4

that very little residual stress is produced in Al been observed for Type IH media on Al 2024-T3.2024-T3 Almen tests but the coating removal Type 1 media can have a pronounced peening effectprocess is considerably slower than for Types II and of some aluminum surfaces such as Al 6061 and ism. generally not used on thin aluminum or composite

components.Type I media has not found general application inthe aircraft industry but is used extensively in the 2.3 Type III, Melamine Formaldehydeelectronics industry and to remove coatings fromfibreglass and composite materials. Melamine formaldehyde resin is produced in a

similar manner to the urea formaldehyde resin2.2 Type IL Urea Formaldehyde except there is increased chemical cross-linking that

produces a harder resin. The material used in paintUrea formaldehyde is a thermoset resin produced by stripping is generally recycled media containingthe controlled reaction of formaldehyde with amino alpha cellulose and not from sheet produced(NH 2) resins. The media is generally made from specifically for blasting media. As this media isurea molding compounds to which alpha cellulose harder than Type II, it has not found much generalfibres have been added to increase strength rather purpose use in the aircraft industry. Almen arcthan from virgin material produced specifically for heights as high as 0.014 inches have been found onplastic media. This media was one of the original Al 2024-T3.developed in the early 1980s for paint stripping andwas studied extensively by both the US and German 2.4 Type IV. Phenol FormaldehydeAir forces. More recently this media has beensuperseded in many applications and specifications Thermoset phenolic resins are produced by theby the Type V, acrylic media. polymerization of formaldehyde and phenol. This

media is generally cellulose filled similar to TypesThis media is generally used on Al 7075-T6 under 1I and 11. Very little data is available on this typethe following blasting conditions: of media due to the extensive early use of Types II

and Ill."* blast pressure 30 - 40 psi"* standoff distance 18 - 24 inches 2.5 Type V. Acrylic"* blast angle 45 - 90

Acrylic polymers are formed by the free radicalAlmen arc heights of 0.002 - 0.010 inches have initiated polymerization of methyl methyl

3-3

methacrylate (MMA). The acrylic media used in When ground this material gives sharper edges thanPMB is generally produced by cryogenic grinding. Type V and in some cases can be effective at lowerThis reduces heat buildup during the grinding operating pressures than Type V media. The allylprocess and results in a sharper more aggressive media lies between Type II and Type V in densitymedia. but is of similar hardness to Type I.

Type V media is becoming the workhorse of PMB This media has applications similar to Types I andwith physical properties between Types I and IH. V. For example it has been used to strip compositeThe acrylic media has been used successfully on and fibreglass surfaces as well as magnesium andthin section aluminum (less than 0.016 inches) and aluminum surfaces. This media has not beenon graphite epoxy surfaces. As the acrylic media is studied to the same extent as the other types andan unfilled polymer there is very little dust produced thus its effects on various materials has not beenduring blasting. Almen arc heights in normal completely characterized.blasting conditions are generally less than 0.005inches on Al 2024-T3.

2.6 Type VI. Polyallydiglycol Carbonate

Allyldiglycol carbonate is a cross-linked (allyl withunsaturated polyester) thermoset polymer. Thismaterial is used for its optical transparency andlight weight in lenses for eyewear. The materialused for plastic media is unfilled.

4-1

Dry Media Blasting with Wheat Starch


FMO VictoriaVictoria, B.C., VOS IBO

CANADA

1 - ORIGINS 2 - FACILITIES AND INSTALLATIONS

1.1 Development The brand name TECHNOSTRIP registered by CENTREIndustrie in 1993 covers several types of installations and

First, we must recall that a particle blasting stripping facilities. These were developed mainly to meet thesystem schematically consists of several entities. These requirements of customers in the aeronautic field.

are as follows:This range of products includes:

- a media conditioning and processing assembly,- a media acceleration, blasting and recovery assembly, - complete self-supporting and semi-automated system

- a monitoring/control/travel assembly, (including all subassemblies) for aircraft stripping,- a carrier assembly allowing installation, - large-size blasting booth for semi-automatic stripping,- and lastly, the media used. - manual blasting booth,

- sealed and portable manual stripping head.In the case studied, the origins are various.Thus, by purchasing and conducting studies on patents 2.1 TECHNOSTRIP'S complete self-supporting systemfiledby theCanadian company COMPUSTRIP, theFrenchcompany CENTRE Industrie and its Canadian subsidiary This system was developed to strip external surfaces ofINTECH Aeronautic Int. developed the TECHNOSTRIP aircraft using a fairly basic and available infrastructure

scheme at the end of 1992. Their work mainly concerned such as a maintenance hangar. By design, the systemthe improvement of the carrier assembly, the media integrated, from the outset, all subassemblies allowingacceleration/blasting/recovery assembly and the autonomous operation. Only theelectricity andcompressedmonitoring/control/travel assembly. air supplies are to be provided.

In addition to this activity, wheat starch media was In this version (see diagram 1), the system is self-propelleddeveloped by the Canadian company ADM-OGILVIE and can be dismantled for transport to a geographicallywhich tested and industrialized it for this type of applica- remote maintenance site. It consists of:tion. Finally, it is on the basis of standard plastic mediaconditioning and processing equipment that a specific a modified self-propelled carrier (GROVE), equippedassembly was developped by CENTRE Industrie. with a telescopic arm the end of which accommodates

a horizontal beam along which the articulated arm (seeFurthermore, CENTRE Industrie has leda specific research diagram 2), supporting the stripping head, moves.and development program in order to optimize the efficiency To this, we must add a control station equipped with allof nozzles conventionally used for stripping. By correlation positioning, control, adjustment and safety systems.between two-phase flow simulations on computer andstripping tests using nozzles with new forms, CENTRE a movable trailer including all the media conditioningIndustrie elaborated and filed an international patent for a and processing subassemblies and the waste recoverynozzle called «flat nozzle>> (end of 1993). system (see diagram 3). The media are fed to the

stripping head through flexible hoses and waste1.2 Partnership and improvements recovered after stripping is returned via flexible hoses

for processing on the trailer.Already during thedevelopmentof the COMPUTERSTRIP2000 demonstrator, AEROSPATIALE and AIRFRANCE The stripping head has been constantly studied andcooperated with the Canadian company. This gave rise to improved.technical demonstrations in Toulouse and Paris-Orly. This subassembly contains in a compact volume (see

diagram 4):AEROSPATIALE and AIR FRANCE cooperated fromlate 1992 with CENTRE Industrie. This technical - theblastingnozzlesforthemediaconveyedandprojectedcooperation was achieved mainly in the form of applied by compressed air,research and development contracts and also technical - the stripping waste suction device,exchanges and information relevant to the aeronautic field. - the computer-assisted display system,

- the sealing devices preventing all leaks (of air andThe main concrete results from this cooperation are waste) when movements are made during stripping,

described in § 6 and 8. - the head/surface bearing and positioning compensationsystems,



4-2

- and the safety systems. The paint waste and starch media are recovered and fed tothe trailer via a hose for conditioning and processing. A

For the starch media treatment, ADM Ogilvie and then window on the upper part of the stripping head allows theCENTRE Industrie demonstrated that it can be used several operator to check stripping obtained (see diagram 8). Thetimes and that its optimum operating range is between 5 operator triggers blasting and moves the head by pressingand 15 cycles (see diagram 5). it onto the surface to be stripped.This characteristic allows an optimized volume of mediato be carried in the tank installed on the trailer allowing Depending on travel rate controlled by the operator, thissufficient autonomy while minimizing the weight and tool can perform complete or selective stripping.dimensions of the trailer's subassemblies.

3-USThe positioning and travel system of this motorized instal-lation allows it to be positioned in space with regard to the On account of its innovative aspect, we will mainly dealaircraft and then with regard to the surface to be stripped with thecomplete self-supporting system TECHNOSTRIP.in a reliable and operational manner (see § 4). Utilization methods for the other systems are, by design,

either based on the self-supporting system or conventional.2.2 - Large-size blasting booth for semi-automatic

stripping The processing to be applied to the aircraft or to allelements removed from an aircraft is as follows:

By design this cabin of modular length uses most of thesubassemblies developed for the self-supporting system. - step 1 : cleaning and visual inspection,In a closed and ventilated chamber, a flat nozzle is used in - step 2 : degreasing,open jet mode. Travelis acheivedby means ofa suspended - step 3 : maskingarm adjustable vertically on OZ axis which itself is carried (and, if necessary, zoning of substrates),on a gantry on which travel is controlled along transverse - step 4 : positioning,axis OY. The gantry itself moves along booth longitudinal - step 5 : semi-automated stripping,axis OX. Nozzle travel canbeprogrammed and supervised - step 5a : manual stripping and finishing,from outside the booth or a computer-assisted display - step 6 : cleaning,installation can be used to optimize stripping performance. - step 7 : demasking and visual inspection.

3.1 - Cleaning and visual inspectionThe starch media and the stripping waste are collected viathe floor specially designed for this purpose. They are then The aim of this step is to inspect the external surfaces of thetransferred to the conditioning and processing installa- aircraft before performing the stripping operations. Alltions located outside of the booth (see diagram 6). surface defects or anomalies must be identified, marked on

the drawing and, if necessary, treated or protected for2.3 - Manual blasting booth repair at a later stage.

This is a conventional manual blasting booth (volume of 3.2 - Degreasingaround I M3) equipped with a pair of flexible gloves. Thenozzle used is a flat nozzle supplied with media and After cleaning of the external surfaces of the aircraft,compressed air via a flexible hose. This hose is connected contamination may remain due to products such as greases,to the starch media conditioning and processing installa- oils, fuel, hydraulic fluid, silicones, etc.. Ifresidualproductstion and to a media metering, acceleration and recovery of these types remain on the surface of the aircraft they mayassembly. Blasting is in open jet mode within the volume hinder the repainting of the aircraft after stripping.of the booth.

They must therefore be eliminated, on the one hand, toThe blasted media and stripped paint residues are collected prevent them from being embedded into the surface and,via the bottom of the working surface (see diagram No. 7). on the other hand, so that they will not contaminate the

recycled media.

2.4 - Manual stripping head 3.3 - Masking

The manual stripping head is designed to complement the By design, the stripping head is almost completely tight.

semi-automated self-supporting system. It is supplied via Dust, paint residues and media are confined underneath

a connection provided for this purpose on the trailer. This this head. However, all areas which may be damaged,

head consists of a flat nozzle supplied with compressed air either intrinsically or in their function, by the stripping

and starch media via a flexible tube. process must be masked.

4-3

Thus, certain parts such as windows and window frames Oncepositionedinits <<sector),,theTECHNOSTRIP systemmay require protection. Also, cavities, seals, drain holes, maps the surfaces to be stripped into «sections>>. To goair inlets, etc. must be masked to avoid retention oraccumu- from one section to another, the position of the telescopiclation of media detrimental to their correct operation. arm of the carrier must be changed and the beam moved

with regard to the surface so that it remains flat against andNote that, if the stripping head movements are adequately parallel to the next surface to be stripped. The «panels>> areprogrammed, all these precautions can be significantly then positioned within each of these «sections>>. A «panel>reduced. corresponds to the maximum surface area that can be

stripped by the stripping head driven by the arm withoutNote: having to move the beam.Surfaces with metallic substrates (and associatedthicknesses) and surfaces with composite substrates Diagram:(together with their type of protection and structure) mustbe checked and, if necessary, identified on the aircraft by SeciSection A i Section B

zoning.Panel Al Panel Bi Fuselage

This step is required as the qualified stripping conditions

may be limited to certain thicknesses or require additional Panel A2 Panel B2

maintenance operations after stripping. 00 00000 00 0 000

3.4 - Positioning

To use the processing power and accuracy that automatedand/or computerized systems offer to the full, they mustfirst of all be correctly positioned with regards to thesurfaces to be stripped. However, as aircraft never have the Once the area to be stripped has been selected, the strippingsame weight or same attitude, the self-supporting systemmust be initialized with regard to the aircraft reference head positions itself over the panel by appropriatesystem before all stripping operations are startled. movements. Then, by a slow approach movement, it

comes into contact with the surface, positions itself by

CENTRE Industrie has developed a triangulation method means of its actuators so that it continuously and tightly

which, by data processing, allows the system to be positioned bears on the surface.

or allows it to know its position with regard to the aircraft. 3 - Semi-automated strininaThis method is covered a patent.

The position is acquired thanks to a dimensional data bank When the stripping head is tightly in contact with the

available in the TECHNOSTRIP system computer rele- surface to be stripped, the compressed air and media arevant to the aircraft configuration. Thanks to the various blasted through the nozzles at stripping head level. Thesensors installed on the carrier, the beam and the arm, the metallic masks installed in front of the nozzles protecting

position of the stripping head can be permanently known the surface retract and the head moves.

and controlled.

To perform stripping, the aircraft surface access regions are The head moves longitudinally and parallel to aircraftToliperform4 sectori , tsurface. When the length of the <<panel>> has been covered,

the arm moves the head laterally through a distance equal

Diagram: to stripping trace.

During this operation, the metallic masks installed in front

of the nozzles protect the surface.

2The stripping parameters are defined to strip the surface8 •without damaging it, The parameters, distance and angle

are fixed by the shape of the stripping head. In addition,media grain size is kept constant by a filtering and stirringsystem.

4-4

The air pressure and media flow rate parameters can be 3.7 - Cleaningadjusted if applicable without, however, exceeding themaximum allowed reference value. Only travel speed is After thepainted surfaces havebeen stripped, the light filmreally variable, of dust covering the upper surfaces of the aircraft must be

removed. This can be achieved by cleaning with equipmentDiagram: of the water jet type.

3.8 - Demasking and inspectionThe last step in the stripping operation consists in demasking

the previously protected areas. A visual inspection can becarried out to check that these masked areas have not been

angle .damaged or soiled by the stripping operation.

3.9 - Stripping level

By the optimization work carried out on the strippingparameters for the various painted substrates, selective

Legen_: stripping and complete stripping can be performed in ad nozzle/substrate distance reliable and reproducible manner on both metallic anda nozzle centerline/substrate plane angle composite substrates. Optimum working conditions haveV nozzle/substrate travel speed been identified for metal substrates alone (complete and(1) nozzle selective stripping) and others for composite material(2) substrate substrates (complete and selective stripping) which can

also be used on metallic substrates. For metallic substrates,Travel speed is adjusted by a computer-assisted display the complete stripping conditions are quite different fromsystem which continuously allows the readjustment of the the selective stripping conditions; however, for compositeposition of the stripping front, materials, they are relatively similar.

The stripping parameters, optimized for the flat nozzle, 4 - USE OF AUTOMATED FACILITIESallow a uniform stripping trace to be obtained with analmost straight front with very clearly-marked lateral In order to obtain optimized results and best possibleedges. performance, automation and data processing were

implemented at the design stage of the TECHNOSTRIPHowever, on account of its dimensions and certain obsta- semi-automated system. The movements, positioning,cles or access difficulties, only 80% of the external surfa- strippingandcheckofthe system'sparameters arethereforeces can be stripped in semi-automated mode. automated and computerized and supervised by the

technician using the system from his booth. Only the3.6 - Manual stripping and finishing operations which allow the operator to be relieved of long

and tricky tasks and that the machine can perform moreWhilst a semi-automated system is working in a sector rapidly and more reliably have been computerized. Thearound the aircraft, stripping operations or, if applicable, other operations use conventional methods (mainlyfinishing re-work operations can be performed manually. mechanical and manual).To achieve this, the operator equipped with the manual Theautomation of thestripping operation and its monitoringstripping head, can gain access and strip the designated by computer-assisted display allows stripping with stablesurfaces from an aerial platform or a working platform. and optimized operation which cannot be achieved by a

conventional manual process without the risk of damagingThis head is also equipped with a flat nozzle. However, its the stripped structure.parameters are slightly reduced to avoid all damage to thesubstrate. 5 - RELIABILITYThe operator places the head on and moves it over thesurface to be stripped. He checks the result obtained When repetitive operations must be performed on thevisually through a window installed on the top of the structure of an aircraft worth several tens of millions of USstripping head. dollars, preventive measures must be taken beforehand.By its size, this type of nozzle allows almost all the surfacesof the aircraft not accessible by a semi-automated system First of all, a semi-automated concept was favored during(15%) to be treated. the definition stage (see § 4). Then, reliability and operating

safety were implemented when elaborating and chosingthe solutions.

4-5

The flat nozzle offers, by design, uniform energy distribu- 6 - EFFECTS ON MATERIALStion over the complete surface of the trace and presents nomaxima. 6.1 - Selective stripping

Finally, selective stripping can be performed on metallicEnergy substrates and on composite material substrates.

On metallic substrates, the paint system is strippeddown to the primer with good productivity. Surfacefinish Ra obtained is around 3 microns.Deflection on aluminium type-C Almen test specimensis very low. Adherence of residual paint on the substrate

is perfect.width of trace Overlapping of two traces, either laterally or crossed,

does not damage the selectively stripped surface onmetallic substrates.

Also, the design of the stripping head fixes the angular and On composite material substrates, selective stripping

distance parameters guaranteeing high precision. As for can be achieved down to the primer on carbon, glass!media flow rate and compressed air pressure, they are carbon hybrids, monolith or sandwich structure Kevlarfixed by the operator and cannot exceed allowable limitst using epoxy resins. Selective stripping can also be

achieved on substrates protected electrostatically by

bronze mesh.

Thetravelspeedisadjustedbyacomputer-assisteddisplay Surface finish Ra obtained is around 8 microns. Nosystem which continuously allows the stripping front damage to the substrates has been observed eitherposition, visualized by a camera, to be readjusted with visually or by non-destructive testing. Adherence ofregard to thetheoretical stripping frontposition materialized residual paint on the substrate is perfect.by a line on camera's sight. Thus, if the real stripping frontis a head of the theoretical front, travel speed is increased. 6.2 - Complete strippingOn the other hand, if the real stripping front is behind thetheoretical front, the travel speed is reduced. - On metallic substrates, in particular aluminium alloys,

complete stripping can be achieved without damagingAlso, a device installed in the stripping head, and which their corrosion protections. Surface finish Ra obtainedcan be positioned between the nozzle and the surface, can is 3 microns. Deflection curve on aluminium alloy type-be used to prevent the blasted media from reaching the C Almen test specimens fulfills the IATArequirements.surface. This device is used: Fatigue tests show no reduction in fatigue for alumi-

nium alloys (unclad test specimens).- to set up the pass (lateral movement, see § 3.5),

- On carbon/epoxy and glass-carbon/epoxy hybrid com-- when travel speed is too slow (safety), posite materials, complete stripping can be achieved

but requires additional control and precautions. Surface- to pass over a surface not to be treated, finish obtained is around 7 microns.

- when head stops on detecting of an obstacle (safety).7 - EFFECTS ON ENVIRONMENT

Lastly, an anti-collision system has been specially designedto detect any obstacles at level of the stripping head and its In operation, the TECHNOSTRIP installation, consistingsupporting arm. This system also calculates the position of of the stripping plate and the starch media conditioning andall elements which move with regard to the aircraft struc- processing assembly, does not exceed a noise level of 75ture. dBa.

To finish, optimized operating points, defined by precise Also, in order to avoid all risks of possible explosions duestripping parameters, have been tested and validated with to the accumulation of very fine particles in suspension,success under conditions considered as unfavorable for the the grain size used and the filtering systems have beenaircraft structure, defined and tested to never reach a potentially critical

zone.

4-6

In addition, the sealing of the stripping head has been - CFM 56 engine fancarefully studied to reduce risks of compressed air, mediaand stripping residue leaks to a minimum. . in manual booth

Lastly, dry stripping by blasting wheat starch media offers . O.G.U. substratethe same advantages for the environment as plastic mediablasting (P.M.B.) with, in addition, the fact that it uses . stripping to remove initial paintorganic biodegradable media.Stripping waste can be processed by a procedure called - Hydraulic casing for helicopterbioremediation (see wheat starch bioremediationpresentation) allowing 95% of theresidues to be eliminated.The only substances which remain are the inorganicelements and the heavy metals contained in the paints and magnesium substrateprotections on the surface of aircraft. removal of sealant joints.

8 - UTILIZATION EXAMPLES 8.2 - Composite material substrates

8.1 - Metallic substrates - Elevator repair

- AIRBUS A300/A310 fuselage . in 10 m x 3 m booth, installed andusedatAEROSPA-

* semi-automated TECHNOSTRIP system TIALE, Nantes facilities,

* stripping ofclad and unclad aluminium alloy substrates . stripping of external protection applied to carbonon fuselage fiber epoxy sandwich substrate,

MSN 079 and MSN 129 belonging to AIR FRANCE . process qualified by AIRBUS Industrie.

process authorized by NTO by AIRBUS following aspecial test program.

4-7

UCA

V) rCL'

Zu E

00

2: 0

a::0-

>i E .-.13 M i,

0-

U)U) U~ -'.:C *5 *

00

~CDr

C)

~Cl

LC0-c

4-8

Shoulder

i, • Elbow

\\ Head

"BLATIN AD RWrist

BLASTING AND RECOVERY HEAD

4-9

PAINT STRIPPING EFFICIENCY OF ENVIROSTRIP STARCH MEDIA

st

at

at-c

I

14 IS 13 2i

0 OF CYCLES ULM

PAINT STRIPPING EFFICIENCY OF ENVIROSTRIP STARCH MEDIA

NEW MEDIA AUTOMATIC ADD

lot

a 2 4 4 1 15 12 14. 16 1 20

50 F CYCLE I. •W

AINCDOSuTRif

4-10

TECHNOSTRIP : BLAST ROOMOUST COLLECTOfi

'iN blast room allow proOKEin forA lagOUSTet wihca dsmnld

wihlreuiOri UST c eedn nth ati ilb possibTle C atoJ useABINETosem-oi 2---essi1-

PRESURE OT TR~lEY ITHTURNAB5

4-11

ID TECHNOSTRIP:

PORTABLE UNIT FOR MANUAL STRIPPINGThe equipment allows manual closed circuit stripping for all surfacesthat cannot be reached by the automatic system.

TEClNOI--

FINISHING OFF: MANUAL BLAST HEAD

TO THE RECLAIMER

VIEWING WINDOWSAC T sWINDOW '

SURFACE TO BE STRIPPED .........

5-1

WATER BLASTING PAINT REMOVAL METHODS


FMO VictoriaVictoria, B.C., Canada VOS 1BO

SUMMARY * water is usually readily available* water is inexpensive and easy to handle

Water blasting is a paint removal technique that has • selective paint stripping feasiblebeen used for cleaning and paint removal for many • no media storage problemsyears. The major disadvantages until recently were the * technology readily available for treatment andslow rate of paint removal and the possibility of damage disposalto the substrate from the high pressures used. With the • media is readily recyclableimprovement in nozzle design that allows for higher • only paint debris to remove in waste treatmentoperating pressures and the use of environmentally processcompliant paint softeners or strippers, water blasting is • low capital investmentbecoming a recognized technique for paint removal inthe aircraft industry. 2. MEDIUM PRESSURE WATER BLASTING

USING PAINT SOFTENERS1. INTRODUCTION

Medium pressure water jets utilizing chemical softenersWith the restriction and banning of most of the phenolic- is a commercial process owned by LUFTHANSA calledbased paint strippers, high and medium pressure water AQUASTRIP®. The blast head for this process consistsblasting are being developed as two of the possible of two nozzles integrated into a rotating head. The headreplacement coating removal techniques. The medium rotates at 2000-6500 rpm and is driven by an impulsepressure water blasting uses water pressures of 7,250 psi from the water jets due to the eccentric alignment of thein combination with paint softeners. The high pressure nozzles. The typical parameters used for this processwater blasting is at pressures up to 28,000 psi but are:requires robotic control.

9 maximum operating pressure - 7,250 psiThe medium pressure water blasting process utilizing • water velocity - 320 m/secchemical softeners is a commercial process owned by • water flow rate - 20 1/minLUFTHANSA calledAQUASTRIP®[1]. Although paint • traversal speed - 50 mm/secsofteners add an extra step in the removal process, lower • standoff distance - 30 - 150 mmblasting pressures (7,250 psi) are used to removecoatings. The lower pressures mean a reduced The LUFTHANSA AQUASTRIPO program developmentpossibility of impact damage to the substrate from the findings has shown that up to 60% of all stripping jobsblasting process. require the use of softeners. The chemical softeners are

most effective with polyurethane coatings and the dwellThe Large Aircraft Robotic Paint Stripping System times must be determined for each coating system. A(LARPS) using high pressure water (up to 28,000 psi) dwell time of 2-4 hours is normal and a water rinse isis a process being developed by the USAF (Wright used to remove the paint softener prior to water blasting.Laboratory, Aeronautical Systems Division (AFMC)) in Two paint softeners are currently used Turco 1270-5conjunction with United Technologies, USBI Co. [2]. and Brent LB2020 and both are based on biodegradable

solvents such as benzyl alcohol.High and medium pressure water blasting offers severaladvantages: A research program was carried out to determine the



5-2

effects of the AQUASTRIP® process on the long term Boeing C-135, B-52, E-3 and the Rockwell B-lB.integrity of aircraft structures. These tests showed that Hanger type, aircraft preparation and system mappingthe two softeners did not induce pitting or etching of may be different for each aircraft but the system will bealuminum (2024-T3) components and no degradation of essentially the same.elastomers was observed.

The procedure for qualifying a high pressure waterDuring dynamic operation for more than 20 cycles, no blasting system has been broken down into three parts,damage was found to clad or anodized layers but damage 1) Process Optimization, ii) Process Validation Testing,to these surfaces could occur if the nozzle was stationary and iii) Additional Materials Testing. As of 1992, thefor 5-10 seconds. Cadmium plating on fasteners was not process optimization has been completed and theremoved by this process. Residual stress measurements process validation testing has begun.using Almen Arc Heights showed deflections of lessthan 10 pm, well below the allowable limit of 150 pm The high pressure water blasting system underfor 2024-T3 aluminum. Fatigue test results indicated development uses blast nozzles designed by USBI thatthat under the above blast conditions there was no provide a uniformly distributed waterjet intensity that ischange in the fatigue life of the material, sufficient to remove primer and topcoat but does not

roughen the aluminum substrate to an unacceptableWater migration during blasting can occur into cavities degree. The mechanism of coating removal is similar todirectly accessible for the water jet. Neutron that from rain erosion and modelling studies areradiography has shown that properly bonded or sealed underway to characterize the waterjet impact propertiessurfaces are not affected by the AQUASTRIP® process. and allow refinement of the blasting parameters basedThe AQUASTRIP® process can be quite destructive on on coatings characteristics.seals and the seal removed if the jet is directed at theedge of the sealer. The process optimization study resulted in the following

parameters for use in the high pressure water process:Use of the AQUASTRIP® process on composite surfacesrequires further refinement. It is recommended that a * maximum operating pressure - 24,000 psicomplete test matrix be developed for each composite • water flow rate - 20 I/minmaterial, prior to use of the AQUASTRIP® process. The * traversal speed - 25 mm/secapplication of the paint softeners used in the • standoff distance - 37 mmAQUASTRIP® process to composite surfaces has been * stripping rate - 1.25 ft2/min per nozzleapproved by LUFTHANSA in prior test procedures.

Using the above parameters residual stress3. HIGH PRESSURE WATER BLASTING measurements using the Almen Strip method gave

Almen arc heights of less than 75 pm for 2024-T3The USAF (Wright Laboratory, Aeronautical Systems aluminum alloy. Surface roughness measurements underDivision (AFMC)) and United Technologies, USBI Co. the same blasting conditions resulted in surfaceare developing a Large Aircraft Robotic Paint Stripping roughness increasing from 23, 36, 67, 126 pin throughSystem (LARPS) using a high pressure water process as four blast cycles on Al 2024-T3 alclad.an environmentally safe and effective paint removalsystem. Further process validation studies are planned to include

composite surfaces (glass fibre and graphite fibre),The robotic system is being developed independently of aluminum and fibre honeycomb structures, lap joints andthe high pressure water system. The robotic system will fasteners to investigate sealant integrity and waterbe designed to handle large military aircraft such as the intrusion.

5-3

4. CONCLUSIONS 791) held during the 75th meeting of the AGARDStructures and Materials Panel in Lindau, Germany

The low pressure water blasting process in conjunction from 7th-8th October 1992.with paint softeners is an environmentally friendlytechnique for removing coatings. The technique also 6. REFERENCESimparts no significant substrate damage on either clad oranodized Al 2024-T3 alloys. 1. J. Volklmar, "AQUASTRIP® - An Innovative Paint

Removal Technology", Paper #13 presented at theThe LARPS system looks promising for an automated AGARD Workshop on Environmentally Safe andhigh pressure water blasting system. The robotic system Effective Processes for Paint Removal, AGARD Reportcould also be used for various NDT inspection methods 791, Lindau, Germany 7th-8th October 1992.such as X-ray, ultrasonic or eddy current.

2. D.W. See, S.A. Hofacker, M.A. Stone and D.5. ACKNOWLEDGEMENT Harbaugh, "Large Robotic Paint Stripping (LARPS)

System and the High pressure Water Process", PaperThe information provided in this paper was taken from #11 presented at the AGARD Workshop ontwo reports (see references 1 and 2) presented at the Environmentally Safe and Effective Processes for PaintAGARD Workshop on Environmentally Sqfe and Removal, AGARD Report 791, Lindau, Germany 7th-Effective Processes for Paint Removal (AGARD Report 8th October 1992.

6-1

PAINT REMOVAL AND SURFACE CLEANING USING ICE PARTICLES

T. FosterDefence Research Establishment Pacific

FMO VictoriaVictoria, BC, Canada VOS IBO

S. VisaisoukIce Blast International Corp.

627 John St.Victoria, BC, Canada V8T 1T8

SUMMAIY 1. INTRODUCTION

Research into the possibility of using ice particles as a 1.1 History of Ice Blastingblast medium was first initiated at Defence ResearchEstablishment Pacific (DREP) in an effort to develop Ice blasting as a process for paint removal was firsta more environmentally acceptable paint removal studied at DREP in the late sixties and early seventies.method. A paint removal process was also required Initial experiments showed that ice particles could bethat could be used in areas where normal grit blasting accelerated by high pressure air and could be effectivecould not be used due to the possibility of the residual in removing paint from coated surfaces. A moreblasting grit contaminating machinery and other systematic study of the effects of ice particle size, iceequipment. As a result of this research a commercial temperature, rate of mass flow, standoff distance andice blasting system was developed by RETECH. This air pressure by G.W. Vickers"2 showed that icesystem is now being used to remove paint from blasting could be used to remove a variety of differentsubstrates that cannot be easily blasted by coatings from metal surfaces.conventional techniques and also to clean soiled orcontaminated surfaces. In 1984 DREP contracted with RETECH to

investigate developing the concept of ice blasting.The problems involved in the development of an ice During a series of contracts withblast system, and its components and their functions RETECH the effects of nozzle design, ice particle size,are described. Due to the complexity of paint removal ice particle size distribution and ice particleusing ice blasting, parameters such as air pressure, ice temperature on the rate of coating removal wereparticle size and ice particle flow rate were studied and studied and the ice blasting process refined. In 1988,adjusted to suit the nature of the particular coating and using Defence Industrial Research (DIR) funding, asubstrate of interest. commercial ice blasting system was developed by

RETECH. Refinements since then have led to the

The mechanism of paint remove by ice particles has current commercial ice blasting system.

also been investigated. A theoretical model has beendeveloped to explain the different paint removal 1.2 Advantages of IceBlastingmechanisms such as erosion by abrasion and erosion Ice blasting was conceived as a dust-free coatingby fracture as they relate to ice blasting. removal technique for confined spaces (tanks or void

fice blasting to removal paint from a spaces) or areas where conventional blasting could notriney te substtes o be used due either to safety considerations or the

variety of substrates is presented as well as examples possibility of damage to equipment by the ingress ofof surface cleaning and surface decontamination. blast media (eg. bilge areas of ships). More recently

ice blasting has developed into a coating removal andcleaning technique for substrates that could bedamaged by conventional paint removal techniques



6-2

such as paint strippers and grit blasting. velocity of the impact is too low to cause fracture.The erosion of coatings by hard and abrasive particles

The advantages of using crystalline ice as a blasting normally is the result of plastic deformation. Somemedia as compared to other abrasive media such as newer coatings are chip resistant and thus quite elasticgrit, alundum or plastic are as follows: and difficult to remove by any method.

1) ice is not abrasive and masking of most delicate In abrasion, a particle impinges on the coating at ansurfaces is not necessary, oblique angle. On impact, it creates a crater and a lip

or rim of displaced material as shown in Figure 1.2) no dust is produced by ice breakdown thereby Further impacts remove the lip material and/or createreducing the environmental impact of coating large craters. As abrasion relies on brute force, it isremoval, non-discriminating and either some of the coating

remains or some of the underlying substrate is

3) ice melts to water which can be readily separated removed or damaged (Figure 1).from the coating debris thus simplifying disposal,

Substrate erosion is not necessarily a negative effect.4) ice is easily made on site from water and For example, its provides the surface profileelectricity, reducing dependence on media suppliers, necessary for good paint adhesion, especially for highand build coatings on steel. Substrate erosion also

removes chemically bound corrosion products prior to5) ice particles do not damage machinery or other re-coating. However, in some other situations,equipment if contamination occurs. substrate erosion or damage can lead to serious

problems of structural integrity.

1.3 Mechanism of Coating Removal Using Ice

Blastin The fracture theory of coating removal is shownpictorially in Figures 2 and 3. On impact at normal

Conventional blast media such as sand, grit or velocities ice particles transfer energy to the coatingalundum rely on the abrasive quality of the blast producing conical cracks. At higher velocities, radialmedia to erode the coating from the substrate. Ice is a and lateral cracks are also formed. Loss of coatingnon-abrasive blast media which fractures the coating material from the volume element defined by therather than abrades. intersection of the various cracks produces

"sombrero" structures (Figure 2). Further ice particle

How a coating is removed from a substrate depends impacts tend to further the extension of the fractureupon the nature of the particles used (hard or soft, lines along the coating/substrate interface (Figure 3)blunt or angular) and the nature of the coating (brittle instead of creating more "sombreros". This isor ductile, thick or thin). because crack propagation in this plane requires

overcoming the adhesive force (mechanical bonds,Blunt particles have an elastic impact at low hydrogen bonds, or van der Waals forces) which isvelocities, and an elastic-plastic impact as the velocity much lower than the cohesive force (covalent bonds,

increases. Angular particles have an elastic-plastic ionic bonds or cross-linking) existing in the coatingimpact. With hard or abrasive particles the elastic- material or the substrate. Similarly creating newplastic damage occurs primarily on the coating, while cracks in the coating or substrate requires morewith soft or non-abrasive particles it occurs primarily energy than extending the cracks along the plane

on the particles - they disintegrate. between the coating and the substrate.

Coatings can be brittle or elastic. When subject to Evidence of the fracture mechanism came fromparticle blasting, coatings generally behave as brittle microscopic examination of an ice blasted surface andmaterials. The erosion of coatings by soft or non- the observation that during ice blasting, coatings wereabrasive particles occurs through fracture or through removed in large pieces the size of the nozzleplastic deformation or through abrasion when the diameter, or larger, rather than by methodical

6-3

abrasion of the coating. Microscopic examination of transport hose to the blast nozzle which can be up toa coated surface after ice impact, but before complete 80 m away. High pressure air is injected at the nozzlecoating removal, showed that the coating was covered at pressures up to 200 psi.with small cracks and in some small areas no coatingremained (Figure 4). These observations led to the Accelerating the ice particles at the nozzle reduces thetheory that ice particles remove coatings by way of a volume of high quality air, (refrigerated and dried)fracture mechanism rather than by abrasion. The required for ice blasting. This reduces the overalltheoretical considerations of ice blast phenomenon energy required for ice blasting drastically. The highhave been described in two previous reports.4'5 pressure air and the ice particles are only in contact

for a short period of time and little ice particle1.4 Mechanism of cleaning using Ice Particles degradation has been observed.

As ice is non-abrasive, it is ideally suited for cleaning 3. EXAMPLES OF COATINGS REMOVALapplications where surface contaminants are to be AND CLEANING BY ICE BLASTINGremoved from substrates, particularly delicate andfragile ones. The ice blasting equipment was operated in two

modes, low pressure and high pressure. The blastAlthough ice particles are non-abrasive, they provide parameters used in the following examples are shownphysical agitation on impact. This mechanical in Table 1.rubbing action is sufficient to remove most non-bonded foreign matter. On melting the water serves 3.1 Coating Removal From Graphite Epoxyto flush the surface free of debris. CompQsites

Ice particles have also been found to be superior in A graphite epoxy panel was coated with the standardremoving surface contaminants from surface cracks Canadian Air Force coating system, 25 pm of aand voids. This is likely attributable to the force strontium epoxy primer and 50 pin of a polyurethanedeveloped by the physical deformation of the ice topcoat. The coating was allowed to cure at 202C forparticles on impact. one week. This coating was readily removed from the

substrate at both high and low pressures with no2. ICE BLASTING APPARATUS visual damage to the substrate. Coating removal rates

of between 225 cm2/min and 450 dm /min wereA schematic of the ice blasting equipment, consisting recorded. A scanning electron microscope (SEM)of an air conditioning module, ice making module and examination of the substrate after blasting alsoan ice conditioning module is shown in Figure 5. revealed that there were no broken or exposed

graphite fibres and the top layer of resin was stillAir from a compressor fitted with an aftercooler is intact. The sharp edges of the paint are indicative of adiverted to two streams: about 15% of the air is dried brittle fracture in the paint.and cooled down to -20 ':C and the remaining isutilized unimproved. A single ice maker supplies ice 3.3 Cleaning Of An Aircraft Polyurethane Topcoatat 90-115 kg/h; if more ice is required then several icemakers can be utilized. The ice is sized according to The aircraft epoxy/polyurethane coating system wasapplication. The size distribution is particularly also applied to an aluminum panel. The coatingdependent on the coating/substrate combination to be system was cured for one week at 20 'C and for onestripped. A precision metering fluidizer controls the week at 65 "'C. The coating was then soiled with aice particle flow rate. The instantaneous and mixture of hydraulic fluid and carbon black whichcontinuous production, sizing, metering and fluidizing was cured in an oven at 75 nC for one hour. Theof the ice particles are constantly monitored and excess soil was removed with a rag leaving a stainedoptimized by the ice management system to prevent surface (Figure 6). The stains were easily removedice packing, clogging and interrupted flow. The using low pressure blasting with no visual damage tofluidized ice is delivered through an insulated the coating surface (Figure 7).

6-4

3.4 Cleaning of Engine Components metallized coating. More recently ice blasting hasbeen used to clean tire and composite molds used in

Compressor blades, 7th stage, and turbine blades, 1st manufacturing, and has been used to clean foodstage, from a JT9D engine from a commercial airliner processing equipment.were cleaned using ice blasting. All of the corrosionproducts and combustion products (Figure 8) were 5. REFERENCESreadily removed by ice blasting, thus increasing theefficiency of the engine. There was no damage to the 1. Vickers, G.W. and G. Galecki, "Development ofunderlying coating during the ice blasting process. Ice Particle Entrained Air Jets For Cleaning

Purposes", DREP Contractors Report Series CR 83-5. CONCLUSIONS 30, April 1981.

Ice blasting has been shown to have several 2. Foster, T., and G.W. Vickers, "Use of Ice Particleadvantages over conventional blasting processes. The Entrained Air Jets for Cleaning Purposes", 7thamount of blast media used is small (-100 kg/h or Internaval Corrosion Workshop, Canberra, Australia,100 litres of water), and clean up and media April 1984.contamination are either greatly reduced oreliminated. There is no need to store large volumes of 3. Foster T., S. Visaisouk and R. Rowe, "Alternatecontaminated media when removing toxic materials or Blasting Materials: Plastic Grit and Ice Particles", 8thhazardous coatings. The water can usually be Internaval Corrosion Conference, Plymouth, U.K.,separated from the coating quite readily and the water April 1988.remaining can be further processed if required byreverse osmosis to reduce the volume of hazardous 4. Visaisouk S., and S. Levine, "Theoreticalwaste. Considerations of Impact Damage by Ice Blast: An

Overview", DREP Contractors Report Series CR 89-Ice is much softer and less abrasive than conventional 31, December 1988.media, and ice blasting can be used to remove paintfrom surfaces that would not tolerate conventional 5. Visaisouk S., and S. Levine, "Theoreticalblasting media and processes. Ice blasting can also be Considerations of Ice Blast Phenomenon withused with little risk of damage or contamination of Experimental Correlation", Contractor Report Seriesadjacent structures or equipment, due to the non- CR 91-30, November 1991.abrasiveness of the ice particles. For this same reasonminimal safety equipment is required for personnel. 6. Benson, C.E., R.G. Grubb, R.C. Heller, B.D.

Patton and G.L. Wyatt, "Crystalline Ice BlastIce blasting has been developed as a commercial Decontamination Technology Demonstration",process and has been used successfully to remove presented at the Nuclear and Hazardous Wastegraffiti from polyurethane coating systems, to remove Management International Topical Meeting", Boiseaircraft coatings from graphite epoxy composite Idaho, August 23-27, 1992.structures and to clean soiled aircraft coating. Iceblasting has also been successfully used to cleancorrosion and combustion products from gas turbineblades without damaging the underlying ceramic or

6-5

< oz0

(0D wa/ I- / :I 0

I - I Q -

w

o -

8- 0-o 0.)L.CJ Lo Lo0 o I~CC) R0 0.0.0 O00: (Y o -D

w .2CJ--;5 - ,

< & LL 1 j 00

CL FnOO 'UJ) LOO00-0- LO Q. o 0 r-- CD

o 0) oo fl'otq2Loo6

I-cCD )

a) 0 U) c

F--

Fn S Fn c m

6-6

. . . . . . . . ....... . ........

.. .....o. . . . . . ...

.. . .. . .. . . ... . . . . . . .

.......

.. .. .. .

( 1ý

......

... . ......

. . . . . . . . .. .-

.......... 0 ... .. .... . .. . .. .

... .. ..

F:-J.

o 0o

w- a: 0

6-7

0 z ucc0o N

m 0c ccw U-J m

_cc u

__ ______z z -

-~ 20

_ 4

zz 0z

z z z IP Mc c u

50 WQ Q Q c

6 0 ccW L N 0L >

cc cci w)- E

cc U) a-

2 x~

00

.la

4Cu

itQ

6-8

Figure 6 -- Soiled Aircraft Coating System Before Ice Blasting.

Figure 7-- Soiled Aircraft Coating System After Ice Blasting.

6-9

UC)

0,

4-.

4)

0aD

coW)

7-1

Stripping with Dry Ice




FRANCE

1 - GENERAL PRINCIPLE OF PROCESS 3.1 Blast nozzle

Mechanical-typestripping using dry ice (solidCO2) consists Several types of nozzles exist. They differ by theirin blasting particles of dry ice onto the painted surface. geometriesanddimensions.TheresultsobtainedcandependThis surface can be used alone or in duplex according to on the type of paints or protections removed. However,type of substrate to be treated, nozzles with flat outlet sections seem to offer better per-

formances.2 - PRINCIPLES OF PROCESS

3.2 Nozzle travel speedAccording to operating conditions, three physicalmechanismsmaybeinvolvedwhenblastingdryiceparticles Stripping efficiency is reduced when travel speed isonto a paint system. increased. If speed is too low or even null, the substrates

may be damaged especially if they are of the composite2.1 Thermal shock type. Consequently, stops are prohibited.

The thermal shock generated by a sudden change in the 3.3 Blast angletemperature on the surface compared with the temperaturewithin the thickness of the part, creates a tensile stress The blast angle affects the mechanical shock. The forceproportional to the temperature difference. applied to the surface is higher as the angle tends towards

90'. However, best results are obtained for angles ofIf this stress is greater than the breaking stress of the paint, between 600 and 800.a crack network develops on the surface and the paintbecomes fragile. 3.4 Stripping distance

2.2 Differential thermal contraction The lower the distance, the higher the shock. However, inorder not to damage composite substrates, a minimum

If two materials are cooled to same temperature and distance is to be observed.subjected to movements, a difference in stress may appearat the interface between the two materials (for example at 3.5 Compressed air pressure and media flow ratesubstrate/paint interface).

The flow rate is not measured at nozzle outlet but at iceNote: particle storage tank outlet.Most organic materials become vitreous at low Thehigherthepressureandflowrate,thehigherthekinetictemperatures, this makes the combined actions of thermal energy of the particle jet.shock and differential thermal contraction more efficient.

4-0SE2.3 Mechanical shock

The process and equipment studied are industrialized inThe dry ice particles are blasted by a pressurized air jet the USA by COLDJET and in France by SIAC.onto the surface to be treated. The results obtained depend,on the one hand, on the characteristics of the media 4.1 Equipment and technology(temperature, grain size, hardness, density, etc.) and, onthe other hand, on the blasting parameters (angle, distance, A heat exchanger is used to cool the liquid C02. It is storedparticle speed, nozzle, flow rate, etc.). in a buffer register then transferred to the ice particle

production unit (pelletizer). The pressure of the liquid CO2The efficiencyofthisstrippingisreinforcedwhenthepaint is reduced to produce solid C02 and gaseous C02has been previously made fragile. (exhausted into the atmosphere).

3 - PARAMETERIZATION The ice is compressed and stored in a hopper, adjusted inheight, at a temperature of -80'C at atmospheric pressure.

The following parameters influence the stripping quality The C02 pellet valve is located under the hopper.and, in particular, the uniformity and efficiency obtained.



7-2

4.2 Stripping 6- RESULTS

When performed manually, this process requires accurate 6.1 - Simplex confi gurationhandling by the operator. In effect, the operator adjusts thefollowing parameters by his movements and position: Stripping of a completely cured paint was almost impossi-

ble irrespective of the substrate. However, risks of damaging- travel speed of nozzle over the surface, composite structures exist in certain configurations.- blast angle,- stripping distance. Forfresh orrecently appliedpaint (several hours), complete

stripping can be obtained irrespective of the substrate.Note: However, certain precautions mustbe taken forcomposites.Duplex-type industrial configurations exist where theparameters are previously set or controlled by automated 6.2 - Duplex configurationsystems (FLASHJET).

Prior application of chemical products such as paint5 - TESTS PERFORMED softeners allow the upper coats to be made fragile and

damaged. According to the paint schemes considered,5.1 - Test specimens partial stripping can be obtained.

- For metallic substrates, the test specimens were made of However, observed productivity was low and severalclad 2024 T3 aluminium alloy painted with a currently hours were required to apply softeners.used scheme.

6.3 - Comments- For composite substrates, the test specimens were made

of monolith epoxy carbon (6 tape plies), sandwich The equipment used generated a lot of noise (> 90 dB) and(4 fabric plies for skin), painted with standard schemes high amounts of gaseous C02 were given off and had to bedifferent for each type of structure. The paints applied exhausted.were aged to different stages.

Also, in the configurations tested, the equipment handledThe surface areas of these test specimens ranged from by the operator was heavy, cumbersome and unsuitable forseveral hundreds of cm' to 1 M2. stripping surfaces on civil transport aircraft.

5.2 Operating processes 7 - CONCLUSION

During the stripping tests, the materials and the settings Used alone and under the conditions in which it was tested,were made by specialists from SIAC. the characteristics and results of C02 pellet blasting

stripping were very poor. However, certain applicationsFrom experience acquired, two configurations were such as surface preparations or fresh paint stripping meritretained: further examination.- one simplex configuration, the process alone,- one duplex configuration with previous application of

a chemical product.

5.3 Inspections

Monitoring and inspections performed were visual or usedmagnification means. Their aim was to assess the followingcriteria :- efficiency,- quality obtained,- selectivity,- damage to substrate,- substrate.

8-1

Aquastrip

Mr. Olivier MalavallonA~rospatiale



FRANCE

The AQUASTRIP stripping process is a mechanical 3- PARAMETERIZATIONprocess. It consists of applying a high-pressure water jet bymeans of a rotating stripping head with two water jets. The parameters used are those conventionally retained to

parameterize mechanical particle blasting strippingThe efficiency of these water jets is improved in certain processes.cases by using a paint softener before applying the waterjet process. The main parameters influencing jet efficiency are as

follows:This process has been developed and is industrialized bythe German airline Lufthansa. Simplex mode process (mechanical effect alone)

1 - PRINCIPLE OF PROCESS - nozzle/part distance (around 30 mm),- water pressure (100 to 600 bar),

The AQUASTRIP stripping principle consists in -water temperature (20 to 80'C),periodicallyapplying(frequency 150to220Hz)pressurized - blast frequency (150 to 200 Hz),water by means of a rotating nozzle. - blast angle is fixed at 300.

The physical high-pressure water jet paint stripping Duplex mode process (combined chemical and mechanicalmechanism consists in mechanical shock and infiltration effects)of the water between the various coats of the paint system.

The parameters relevant to softener application must beThe higher the kinetic energy of the jet, the higher the considered:mechanical shock. Speed and water pressure must thereforebe sufficiently high. - application temperature: 15 to 25°C,

- application time: 1 to 4 h,The mechanical shock (periodic in this application) causes - type of softener: - TURCO 1270-5the paint to crack and become fragile. - BRENT LB2020

The water then infiltrates into these cracks and causes lack Several comments are required concerning certainof cohesion between the coats of paint, parameters.

2 - STRIPPING HEAD PRINCIPLE Blasting freuuency

Stripping head principle The jet applied to the surface by nozzle design can beadjusted to produce a contraction/expansion phenomenon

The stripping head includes two nozzles through which of varying frequency.two water jets are blasted. The head is rotated by thepressure of the jets (or by its reaction force). This leads to Stripping distanceperiodic application of the pressure on the surface to bestripped. The lower the distance, the higher the impact of the jet on

the paint and the easier the stripping.Diageram

A variation of 10% in stripping distance is sufficient tochange the stripping characteristics.

Pressure

This pressure acts:

on the force exerted by the jet on the paint; the higher thepressure, the more aggressive the stripping,

are sreduedwhng quality: ssuripping inreityased.uiomt

sB SBZ



8-2

Nozzle travel speed 2nd configuration

The nozzle travel speed influences: An automated hangar allowing maintenance operations isequipped with 6 automatic working platforms. A motorizedmanipulator is equipped with 6 stripping heads consisting

- stripping selectivity: paint thickness removal is reduced of faired rotating heads designed along the same principle

when speed is increased. Speed is therefore lower for as the manual head.stripping down to substrate than when stripping downto primer, This stripping assembly is installed on a telescopic platform

allowing access to the greater part of the surface of an

- stripping uniformity: reduced when speed is increased. aircraft. A semi-automatic device controlledby theoperatorallows remote-control of head/substrate distance.

4- USE High-pressure system

4.1 - Installation Water is supplied by the urban network and initially

The installation available at Lufthansa allows the pressurized to a pressure of 6 bars. An 8-piston pump then

AQUASTRIP process to be used with two equipment pressurizes it to 500 bars.

configurations. Retreatment system

1st configuration A special drainage system allows separate treatment of

water contaminated by softener and water used with theA stripping room equipped with a manual stripping system AQUASTRIP process alone. The waterusedby this processwith two rotating water jets. is directly treated in a separator/settler and stored in a

reservoir for reuse. The water can be recycled around threeDiagram times.

4.2 - Operating method

The AQUASTRIP process uses a specific operating process.

Step 1: Measurement of paint thicknesses on aircraft

The procedure consists in measuring the thickness-- -of the paint coat over the complete surface of the

. aircraft. The measurement points are accuratelylocated and a separate measurement is made forfuselage, wings and tailplane.

Step 2: Masking

The aim of the masking operation is to protect:

- parts which must be protected when applyingsoftener:

The inclination of the water jets with regard to nozzle . composite parts,

centerline allows rotational speeds of around 3500rev/min . edges of metallic bonded seals,

to be obtained. . all moving parts,the electrical equipment, etc.,

- the water is recovered at floor level by a channeldrainage system. - substrates or composites which must not bestripped by the AQUASTRIP process.

-a retreatment system filters the water by eliminating thepaint waste obtained. Step 3: AQUASTRIP stripping process

- a water circulation system recycles the water which is Step 4: Cleaning of the surface

used in closed-circuit configuration. Step 5: Demasking

8-3

5-RESULTS - the process has no effects on paint adherence,

The AQUASTRIP process has been subject to many - the process does not damage bonded seals,studies conducted by Lufthansa in relation withmanufacturers BOEING and AIRBUS Industrie. - selective stripping and complete stripping are possible,

- the softeners used have no effects on aluminium substrate

5.1 - Evaluation on metallic substrates corrosion.

The test specimens were as follows: 5.2 - Restrictions in the use of AOUASTRIP

- clad 2024 material, thickness: 0.83 and 1.3 mm, - Operators using AQUASTRIP mustbe highly qualified

- paint system: epoxy primer + polyurethane top coat. in the use of this process.

Test conditions for optimized process were: - Composite material parts must not be stripped with theAQUASTRIP process.

- water pressure : 500 bar- water temperature : 20 0C - The substrate is extensively damaged by prolonged- nozzle/part distance: 30 mm stripping caused by a stop in stripping head movement.- travel speed : 50 mm/s

5.3 - Approval of process by manufacturersThe analyses of the various studies showed that undercertain conditions: At present, the AQUASTRIP process is authorized by

BOEING («No technical objection» document of 1990).- the process does not reduce fatigue life, AIRBUS Industrie has defined application limits for the

AQUASTRIP process (Basic Process Definition).- repeated stripping is possible up to 5 cycles without

damaging the substrate (with a thickness of 0.83 mm), This process can be used on aluminium, steel and titaniummaterial parts and on metallic parts with bonded seals.

- the process has no effects on permanent deformation,

9-1

Stripping by Laser




FRANCE

1 - PRINCIPLE OF PROCESS Two types of YAG LASER were evaluated

1.1 - Laser beam Make Maximum Wavelenfth Frequency Pulse____ power duration

Radiation) are monochromic electromagnetic wave Quantel 20W 1,06 pm (IR) 30Hz 10 ns

generators whose directivity, intensity and phase IQL 30 900 W 1,06 prin (IR) 100 Hz 1HY 106A s

coherence characteristics have special properties.

A LASER beam generator consists of the following The power of the Quantel YAG LASER is low (20 W) butit has the advantage of being compact and light (3 kg).

- an active material: solid, gaseous or liquid,-aluminousorelectricalsystemexcitingtheactivematerial, The IQL YAG LASER has a power compatible with

-an optical system consisting of two mirrors, one reflecting industrial applications such as stripping or welding. Use of

by 100%, the other semi-reflecting (R - 98%) optical fiber allows this LASER to be combined with arobotized arm.

Diaram1.3 - CO2 TEA LASER

Excitation system

R= 100% R=98% The active material is CO 2 gas, This material is excited byan electronic discharge within the gas.

ACHVE IATERLASER

AcrrvE RSEon The performance or the CO2 TEA LASER used are given

in the table below:Miror I Miror

Excitatio, System

Make Maximum Wavelength Maximum Maximum PulseThe excitation system places the active material in a power energy frequency duration

condition which causes LASER emission. When triggered, Coherent- 60W 10,6 pm 51 12Hz 90 nsthe light moves to and for in a cavity with two mirrors in Hull (IR)LASER axis. As one of the mirrors is semi-reflecting, apart of the light passes through it. This is the usable LASERbeam. 1.4 - Excimer LASER

Three types of laser beam generators were evaluated. The active material is gaseous, composed of a noble gas(Xe, Ar) and a halide (Cl, F).

1.2 - YAG LASER

The active material consists of a Yttrium-Aluminium- Once excited by an electric discharge, these atoms group

Garnet bar supporting neodymium Nd3+ ions which together to form excimers (EXCIted diMERs). These

generate the LASER effect, dissociate and generate the LASER effect.

The bar is generally cylindrical (dia. 7 x L 210) and is Diagram

excited by flash lamps (similar to photoflash units).

Diagram Active MaterialExiao eemission

Excitation Flash Laop

Miror Miror

(R = 98%)

Active rnaterial = Ytreir Atlrniniumn Orenat

Paper presented at the AGARD SMP Lecture Series on "Environmentally Safe and Effective Processes for Paint Removal"held in Lisbon, Portugal, April 2 7-28, 1995; Eskisehir, Turkey, May 1-2, 1995 and Ottobrunn, Germany, May 4-5, 1995


9-2

The performance of the evaluated Xe Cl gas LASER are 2.3 - Stripping with Excimer LASERgiven in the table below: (193, 248 or 308 mm)

Excimer LASER stripping can be explained by aMake Maximum Wavelength Maximum Pulse photochemical model. The phenomenon involved is called

power frequency duration <<photoablation>>.

Lumonics 100 W 308 nm 500 Hz 20 ns(UV) The radiation emitted is in the ultra-violet range (308 nm

for the XeCl LASER). As the energy of a photon is greaterthan that of the molecular bonds, each photon emitted canin theory break one of these bonds. The material is thenovaporized» layer by layer.

The Excimer LASER is the latest generation LASER. Thepowers available today do not exceed 150 W. However, 3 - PARAMETERIZATIONwork is in progress on a 500 W to 1 kW LASER which willallow their application fields to be extended. 3.1 - Travel speed

2 - STRIPPING This is the travel speed of the test specimen in front of theLASER beam.

The main aim of stripping is to break the molecular bondsof the paint in order to separate it from the substrate. The higher the speed, the lower the time the beam remains

at a given location on the test specimen. Energy density is2.1 - Stripping with YAG LASER (1.06 tim) therefore lower and stripping intensity reduced. To obtain

selective stripping, stripping speed must therefore beYAG LASER stripping can be explained by a thermal increased.model. As this type of laser emits infrared radiation (1.06ýtm), the energy of the photons is lower than the energy of Also, speed is directly related to the efficiency of thethe molecular bond. They must therefore be accumulated process.(in the form of heat) in order to break the bonds. This leadsto a thermal effect and the heat propagates through the 3.2 - Pulse frequencymaterial.

The number of pulses per second affects the efficiency andThe duration of the pulse also has an effect. The thermally not the stripping quality. If the parameters are optimized,affected thickness is proportional to: both frequencyand speedcanbedoubledand same stripping

result will be obtained without changing the othere = f (\Kt) parameters.

where: 3.3 - Energy

e : thickness of material treated Proton energy E = hv, where v is radiation frequencyK : material diffusivity emitted by the LASER.t : irradiation time

Radiation energy increases with the number of photonsThus, the longer the pulse, the higher the thermally affected emitted by the active material of the LASER during firing.depth.

The chance of breaking the molecular bonds are increased2.2 - Stripping with CO2 TEA LASER (10.6 t1m) when the number of photons is increased. Thus, the higher

the radiation energy, the better the stripping efficiency.CO2 TEA LASER stripping can also be explained by athermal model. The advantage of this type of LASER lies 3.4 - Form of LASER spotin its high paint absorption coefficient at 10.6 4tm (greaterthan 90%) and therefore a LASER-to-thermal energy Depends on the lens used and the lens-part distance.conversion rate much higher than that of a YAG LASER.

With the YAG LASER, the lens used had been cut intofour then rebonded (see diagram).

9-3

It allows a uniform and square spot to be obtained at the This type of installation is highly automated and thefocal point. A lens of this sort is used to produce a commands and the information relevant to the variousuniform spot on the specimen. sensors are displayed on computer screens.

At present, only automated LASER stripping can beThe specimen is then placed at the focal point of the lens achieved on account of the accuracies and movementsand the lens-part distance must not vary. required.

Diagram 5 -TESTS CONDUCTED

5.1 - Test specimens{7~~7A> Apoint4

scof )0)h 5o The metallic test specimens were made of clad 2024K •• _aluminium alloy. They were protected by chromic

, 5- •anodizing and a polyurethane primer.5- •The polyurethane paint system applied was of the wash

primer, primer and top coat type.

With theExcimerLASER, the lens used was cylindrical. - The composite test specimens were made of T300/914It allowed an energy line to be obtained, monolith carbon protected by a colored primer plus a

When the lens-part distance is moved towards the lens polyurethane top coat.

focal distance, the beam converges to form a thin line. The top coatpaints were aged in hotandwetatmospheresThis distance will be selected greater than the lens focal before the tests were conducted.distance to strip paint over a larger area.

5.2 - Choice of LASERGAS:During the tests, a blowing test was performed to increase After various preliminary feasibility tests on test specimens,stripping efficiency; but the effect of the blown gas was using YAG, C02 TEA and Excimer LASERs, the YAGnegative. LASER was selected on account of the results obtained.

4 - M The test configuration retained was as follows:

A LASER beam stripping installation consists of several Diagracomponents as follows:

- a LASER source,LASER

- a LASER beam guide system, emission

- a focussing head, AsýZ.c- a gas and residue suction and filtering system, Aspiritio

- a stripping head travel system.

Air blowat 6 bar

Diagram: pessureangleP%, Seie

V M travel speed

S~a = 300Le :f=150 mm (focal distance)

d = stripping distance - available power = 1 kilowatt

V = travel speedM1,M2,M3 = reflecting mirrors

9-4

5.3 - Results

- For the metallic test specimens, it was possible to show For selective stripping, productivity obtained was verytheexistenceofan operatingpointforcomplete stripping poor and surface finish Ra was 3 microns.for which we obtained very low productivity and a verylow Ra =0.3 gim. Visual observation showed that the coat of blueAfter the stripping operation, the surface had a residual polyurethane primer absorbed less LASER radiationlayer of paint dust. We therefore had to clean the surface than the top coat. The primer therefore acts as a barrierwith alcohol to eliminate this coat. This operation could protecting the substrate.be avoided by improving plasma blowing duringstripping. 5.4 - ConclusionAfter stripping, the surface was homogeneous but notuniform: energy distribution was not sufficiently LASER beam stripping can be achieved using severaluniform. active materials: YAG, C02 TEA or Excimer.It was not possible to perform selective stripping. The YAG LASER appears to be the most efficient LASER

assessed. However, the results obtained, productivity,For the composite test specimens, it was possible to quality and type of stripping, were very poor.

show the existence of an operating point for completestripping and one for selective stripping. Also, for stripping and on account of its specificities, the

LASER beam can only be used in an automated manner.For complete stripping, productivity was very low andthe surface finish value Ra obtained was 7 microns. In spite of these results, it seems that certain companies in

Europe have recently developed technical solutionsThe energy distribution of the LASER spot was not allowing better results to be obtained.sufficiently homogeneous to allow complete stripping.Visual observation revealed zones where the compositewas damaged.

10-1




FRANCE

1 - REOUIREMENTS

At the end of the 80's, some of the large European airlines Diaeram:expressed a wish for paint systems with improvedstrippability on their aircraft allowing the possibility tostrip down to the primer without altering it using «mild»chemical strippers based on methylene chloride.These improvements were initially intended to reduce L27/ 7 top coat

costs and stripping cycle times whilst facilitating rapid 11111111111111 - barrier coat

repainting, and this without the need to change the i- primer

conventionally used industrial facilities. The level of in- - substrate protectionservice performance of these paint systems was to be the 4..- substrate

same as the previous ones. Requirements related to hygiene, stripping repainting

safety and the environment were added to these initialrequirements.

2- DEVELOPMENT- in the second case, this coat acts as a screen which is

To meet customers' expectations, AEROSPATIALE, consumed by the effect of the stripper; this degradationwithin the AIRBUS Industrie GIE, formed a work group. may be partial or total. Repainting is therefore requiredThis group was given the task of specifying, following up to restore the damaged coat, by reapplication of thethe elaboration and qualifying the paint systems allowing product, followed by application of top coat.requirements to be met, in relation with the paint suppliers In this case, this coat is called the intermediate coat.and the airlines.

2.1 - Conceot 4-. top coat

The analysis made showed the interest of transferring as 4- intermediary coat

far upstream as possible (to paint conception level) most of 4- primerthe technical constraints related to stripping. 4-, protection

4- substrate

Thus, the concept retained for the paint system, allowing stripping , repainting

selective chemical stripping, is a 3-coat system withcharacteristics as near as possible to the previously used 2.3 - Technical specificationpaints.

A technical specification was drawn up (TN A007.10028)Diagram: from the existing technical specifications for external

paints andprimers (TN A.007.10012 andTN A007.10113).4-. top coat This specification repeats the main requirements in order

selectively strippable coat to guarantee same performance levels.

primer This specification mainly requires a flexible top coat with4- substrate protection very good resistance to UV radiation, good intrinsic" , substrate adherence of the system on protections appliedon substrates

(metallic and composite) of external surfaces, good fluid2.2 - Mechanism resistance, very good resistance to impact and bending and

very good corrosion resistance behavior.The innovation of this concept lies in the integration intoa paint system of a specific coat acting as a barrier against 2.4 - Industrial facilities and processesthe chemical strippers used. This type of coat can have twobehaviors according to its chemical nature: The industrial facilities used both for paint application and

stripping are the same as those conventionally used.- in the first case, this coat acts as a screen for the stripper The stripping product application methods are the same.

and is not altered or consumed; repainting only requires Rigourous selection of the products to be used is requiredthe reapplication of the top coat. and the operators must be trained.

In this case, this coat is called a barrier coat.



10-2

3 - WORK 4 - EXPERIENCE ACOUIRED

3.1 -Fine-tuning 4.1 - Industrial application

Work has been undertaken by AEROSPATIALE in close Application tests on aircraft have allowed the workingcooperation with the aeronautical paint suppliers. The test methods used to be adapted to suit and the operatingresults obtained and the methods used have allowed to method, the parameters used and the associated documentsvalidate and, in certain cases, adapt the requirements to be validated.specified in the AIRBUS technical specification.

Correlations between laboratory tests and workshop appli-This fine-tuning and validation work included, on the one cations have highlighted the importance of the parametershand, demonstration tests on forms representative of the related to the operating method, such as repainting times.aircraft and, on the other hand, very complete laboratory Their effects have been quantified and taken into accounttests. These were completed by full scale application tests in the industrial process to guarantee the quality andon AIRBUS A320 and AIRBUS A340 aircraft allowing reliability of the paint systems whilst taking industrialthe paint system to be validated for use in the workshop. requirements into account.

3.2 - Oualified paint systems 4.2 - In-service fleet

The first research work began in cooperation with the At present, the in-service aircraft fleet used by AIRBUSFrench company MAP Aero with technical and financial Industrie's customer airlines consists of around twentybacking from STPA. It allowed us to qualify, at the start of aircraft including AIRBUS A320s, AIRBUS A330s andthe 90"s, the following scheme: AIRBUS A340s.

- anti-corrosion primer: ISOMAP P23 Their in-service behavior and the associated maintenance- barrier coat: MAPSTRIP S15 operations are subject to regular follow-up between a- flexible UVR top coat: AEROMAP 1000 group of AIRBUS Industrie partner specialists and the user

airlines.Following this, the international group COURTAULDSAerospaceand its French subsidiary International Celomer 5 - FUTURE OUTLOOKSqualified the following scheme at the beginning of 1994:

5.1 - Painting policy- anti-corrosion primer: INTERGARD 90- barrier coat: CA 30.000 AIRBUS Industrie and its partners have elaborated a- flexible UVR top coat: CA 40.000 painting policy allowing the customers' requirements to

be met as far as possible. These requirements varyA third paint system for selective chemical stripping was significantly according to the size of the airlines and thedeveloped by the AKZO-DEXTER Aerospace Finishes economical and technical constraints to which they aregroup but for which the qualification work could not be submitted. Several alternatives therefore had to beoffered.started.

Among these technical alternatives, the selectively3.3 - Chemical strippers strippable paint systems, offered with all guarantees, allow

the use of stripping products which have very limitedDevelopment and fine-tuning work on products containing effects on the environment and guaranteeing efficient andno chromates orphenol and, if possible,no methyl chlorides, economically viable industrial cycles.has been started by certain manufacturers. The first resultsshow that the efficiency of these products depends in part 5.2 - Technical developmentson repainting times, type of coat (barrier or intermediate)and chemistries used to elaborate them. However, The technical improvements to be made to the selectiveencouraging results have been obtained, chemical stripping paint systems mainly concern the new

environmental and hygiene - safety requirements. The aimof these developments is to limit the investments requiredto achieve conformity with new legislation.

10-3

The possible improvements are: 5.3 - Change in demands

- low VOC technologies and chemistries, The possibility of stripping down to the primer (external- stripping products free from substances harmful or paint system), without altering it, with «mild» strippers

highly polluting for the environment and which do not without chromates or phenols and, possibly, based onlead to extra costs for processing waste. methylene chloride, corresponds to the requirements made

by certain airlines in the early 90's.It is also possible that certain improvements or adaptationscan be recommended subsequent to in-service use. These requirements are very closely related to the

operational requirements and environmental constraints.Their changes will dictate the future outlooks for thisconcept which specifically associates the paint system andthe stripping process.

11-1

FACILITIES USED FOR PLASTIC MEDIA BLASTING



1. INTRODUCTION The volume of the air supply will depend on the size ofthe facility, number and size of blast nozzles and the

The equipment used for plastic media blasting (PMB) is recovery and recycling system used. All blast facilitiesgenerally independent of the media and is similar to require dry compressed air to avoid clumping of theequipment used in traditional abrasive blasting. PMB media and to ensure an even flow of media during theequipment is usually modified to enable the close control blasting process.of the media flow and the operation at low pressures(30-40 psi). Because of the delicate nature of some of 2. BLAST CABINETSthe stripping procedures, the nozzles used for PMB havebeen redesigned to improve cleaning rates, give an even A small blast cabinet for PMB is listed and identified bydistribution of particles and reduce the variation in a US National Stock Number NSN 4940-01-225-3845.particle velocity across the blast stream. This results in This type of cabinet is available from many suppliers ofa more equal distribution of particles and impact plastic media and these suppliers should be consultedenergies at the substrate. prior to purchase of a PMB Cabinet.

There are three types of blast facilities available: Blast cabinets generally use 1/8" or 3/16" blast nozzlesand require up to 100 ft3/niin of air per nozzle to operate

"* Blast Cabinets for small components at pressures up to 40 psi. Cabinet manufacturers should"* Blast Booths which will accommodate larger be consulted as to air requirements prior to purchase of

components but may be used for purposes other a blast cabinet.than blasting, and

"* Blast Rooms which are designed for complete A typical blast cabinet has a working area of 5 feet by 4vehicles or aircraft and are generally not used for feet. Although this area limits the size of componentsother purposes that will fit in a blast cabinet, the standoff distance

(usually 12-18 inches) from the component should alsoSome components are common to all three types of be taken into consideration in the choosing size of blastfacilities and only vary in scale depending on the size of cabinet.the facility. A blast facility for PMB will usually includethe following components: Some problems associated with blasting components in

a cabinet include the following:"* air compressor"• pressurized feed hopper for media . working volume and the need to control the blast"* media flow control valve angle and standoff distance can restrict the size and"* blast nozzle complexity of the component to be stripped"* recovery system for spent media * due to the confinement of the media, visibility for"• magnetic separator to remove magnetic particles complex operations can be difficult at times"* recycling system to clean media and remove dense • flexibility and manipulation can be restricted due to

particles, and the use of rubber gloves which restrict reach, sense"* hoses to transport the media of touch and movement.



11-2

3. BLAST BOOTHS below that for combustion or explosion* fire suppression system to protect the personnel, the

Blast booths offer the flexibility of size and allow access aircraft, and the facility

to all sides during blasting of large structures and * plastic media blast system with sufficient blast

components. The actual configuration of a blast room nozzles and blast pots and media storage capability

will vary from site to site and depend on the space to meet the desired level of productivity

available and the equipment to be stripped. * classification and cleaning system (cyclone airwashes, vibratory screens, dense particle separators,

The booth can either be a temporary enclosure made of and magnetic separators) capable of processing the

plastic sheeting in a larger area or a metal enclosure volume of media required to maintain continuous

placed in a hanger or other work space. operation* recovery system to automatically remove the media

Most of the blasting equipment used in a blast booth is from the floor of the blast room

similar to that used in a blast cabinet except scaled to 0 crane or scaffolding system to allow operatorssuit the size of the booth and the number of blast nozzles access to all parts of the aircraftin operation. Ventilation of the blast booth area and an * an additional feature may be a robotically controlled

air supply for the blast personnel will place an extra load blasting systemon the air supply system and could require a separate airsystem. The most significant component of a blast To install and operate a blast room input from all

booth is the media recovery system. A floor recovery personnel involved in the process is required along withsystem will automate the recovery and recycling of the consultation with the manufacturer of the media and

media and prevent build up of spent media in the booth. blasting equipment (turnkey systems are available fromA manual vacuum recovery system can also be employed some manufacturers).to remove the spent media from the floor of the booth.A manual vacuum system may require blasting to stop 5. PMB EQUIPMENTwhile the used media is recovered.

5A. Media Delivery Systems

It is also recommended that a dense particle separator(DPS) be an integral part of a blast booth. The DPS All three types of blasting facility require a mediaremoves any heavy particles from the recycled media delivery system consisting of the following components:

such as pieces of metal, fasteners, sand, and other non-ferrous particles. These particles may have been brought * pressurized blast potinto the booth by blasting personnel or be dislodged - media flow control valve

from components during blasting. If dense particles are • media storage vesselnot removed, damage to blasted surfaces may occur. 9 safety control devices

• blast nozzles and hoses4. BLAST ROOMS AND AUTOMATED BLAST

SYSTEMS The media flow in a blast cabinet can be controlled witheither a microprocessor controlled flow valve or the

A blast room is designed to accommodate a complete valve on the feed hopper (pinch valve) is calibrated.aircraft and is dedicated as a blasting facility. Its sizewill be determined by the maximum size of aircraft After the media has passed through the recovery system,

expected to use the facility, it then flows to a media storage hopper directly aboveA blast room requires the following components: the pressure vessel. When blasting is stopped for any

reason, the media in the storage hopper flows into the

* adequate ventilation to meet local health standards pressure vessel for use. Depending on the media flowfor personnel exposure and to maintain dust levels rate, the pressure pots should contain up to a thirty (30)

11-3

minute supply of blast media. This can vary with each hopper above the pressure vessel. Whenever themanufacturer's design. blasting process stops, the media from the storage

hopper is automatically transferred to the pressureAs a safety precaution all of the pressurized systems vessel.have pressure relief valves that are activated in case ofa blockage of media flow that could cause a pressure As the media breaks down it must be replaced. Hencebuildup. As a safety precaution, most operating systems regular additions to compensate for media breakdownhave a release switch ("deadman") at the nozzle that, must be scheduled into the blast process. Similarly aswhen released, causes the system to stop and the media is used a number of times it will no longerdepressurize. have the cleaning efficiency of new media and it should

then be replaced. The rate at which the media breaksProper selection of blast hoses and couplings is down will depend on the types of coatings removed, theimportant from at least two points of view. Air leaks hardness of the substrates and the age and difficulty ofneed to be minimized with good fittings to ensure removing certain coatings. When cleaning efficiencyefficient operation of the system. Proper hose selection drops significantly the media should be replaced.will ensure proper media flow and eliminate mediacontamination due to hose breakdown. Manufacturers 5-3 Dense Particle Separatorsrecommendations should be followed in the selection ofhoses and couplings. In blast booths and rooms a heavy particle separator

should be employed. Experience has shown that denseBlast nozzle designs are generally proprietary but particle contamination can occur in these type of blastinclude a regular venturi nozzle used for many years in facilities. Dense particles can include any or all of thetraditional sand blasting operations, a double venturi following:nozzle designed for increased blasting efficiency and anew "flat" nozzle for use with newer, softer media that • sand, glass and other silicate materialsgives a better impact profile on the blast surface. • non-ferrous (aluminum, magnesium and zinc) and

ferrous metal particles5-2 Media Recovery Systems • high density plastics.

In a blast cabinet the media falls to the bottom of the If these particles are not removed from the blast stream,cabinet and is vacuumed into the media reclamation damage can occur to blasted components.system. In a blast booth the media can either be vacuumrecovered from the floor of the booth or an automated There are three types of heavy particle separationrecovery system can remove the media from a floor grid technique:system similar to that in a blast room.

• fluidized bedIn the reclamation process the fine or dust particles are * air wash systemremoved in a dust collector and the remaining media and - inclined vibrating deckcontaminants are transported into a cyclonic chamber.In the cyclonic chamber the heavy re-usable media is The fluidized bed system is the most popular and mostthrown to the outer walls where it spirals down through readily available DPS. Manufacturers should bean air wash which removes any remaining debris from consulted as to which type of dense particle separator isthe reusable media. The media then passes over a available with their equipment. No matter which DPS isvibrating hopper to remove any oversize particles and chosen, its efficiency should be routinely checked usingcorrectly size the reusable media. The reusable media the Boeing test method (Boeing D6-54707 Heavythen passes over a magnetic detector to remove any Particle Contaminants Test Method). A level of lessmagnetic debris and subsequently flows into a storage than 200 ppm measured using this test method is the

11-4

accepted level of both the US and Canadian military and • the cleaned plastic media is then recombined andBoeing. In this method, several samples of the recycled mixed by the air stream and returned to the storageblasted media are weighed and placed in containers of a hopper.solvent more dense than the blast media (usually aFreon). The plastic media will float on the surface of the Air wash systems using screens of thirty inches insolvent and the dense particles will fall to the bottom of diameter are capable of processing up to 1,000 lbs perthe container and can be weighed and examined. hour of plastic media.

The air wash cleaning system is usually an off-line The inclined vibrating deck system was developed by thesystem but may be configured to operate as part of a grain industry to separate similar sized grains that differcontinuos PMB system. in density. This type of system has been evaluated at

several USAF bases but is not in general use in the PMBThe air wash system consists of the following six steps industry.some of which may be combined:

6. CONCLUSIONS"• a vibrating screen (0.125 inch mesh) is used to

remove the gross contaminants There are three types of PMB facilities available; blast"• a cyclone separator is used to remove fine paint cabinets, blast booths and blast rooms. Individual

particles and dust requirements will be the leading factor in choosing the"• a large powerful magnet is used to remove any type and size of facility required.

ferrous contaminants"• a multiple stage vibrating screen is used to sort and

classify the media by mesh size"• after classification into three or four preselected

mesh sizes, the media then falls through an airchannel, where it is subjected to an air separationprocess to remove any dense particles

12-1

TREATMENT OF PLASTIC MEDIA WASTE



Although plastic media itself is not generally Protection Agency (US EPA) and various localconsidered a hazardous waste, the paint particles agencies as an approved recycling process for plasticcontaining chromate pigments contaminating the spent media.media are considered a hazardous waste product. Thereare currently four approaches under investigation More recently a method of recycling Type V (acrylic)aiming to reduce the volume of hazardous waste plastic media has been developed jointly by Sacramentoproduced during paint stripping: Air Logistics Center (SM-ALC) and Battelle.' A pilot

project has been initiated to convert spent acrylic media"• elimination of the chromate containing pigments or into pellets that can be re-ground into blasting media.

other hazardous pigments from primers and As any hazardous materials in the spent blast media arecoatings encapsulated during this process, the pellets meet the

"• separation of the paint or hazardous materials from leaching rate standard of the US EPA. The recycledthe plastic or other media media has been shown to have similar stripping rates,

"• encapsulation or recycling of the contaminated aggressiveness and breakdown rates as new media. Amedia to make it safe for disposal or reuse full scale prototype is under development and should be

"* produce a biodegradable media. operational by 1995.

Research to develop new pigments and primers that A final and more attractive method to reduce both thewill result in the elimination of hazardous pigments volume of hazardous waste and the need for recyclingsuch as strontium chromate and into developing is to formulate a biodegradable media. One alternativealternative anti-corrosive surface treatments to replace media which will be discussed at some length duringcadmium plating is continuing. Contamination of the this lecture series is wheat starch. As wheat starch isspent media will remain a problem because the a natural product it is completely biodegradable and anhazardous pigments and surface treatments will still be enzymatic biodegradation process has been developedused on aircraft and their components for the for this media. A second media currently underforeseeable future. Therefore, the only realistic development is based on modified corn starch.alternatives at the moment to reduce the volume of Research on this media is still at the preliminary stageshazardous waste produced by PMB are to re-cycle or but some progress has been made.re-use the media in some form or remove the hazardousmaterials from the media. References

Complete separation of the paint particles from the 1. R.F. Williams, "PMB - Hazardous Wasteplastic media is difficult and time consuming and is not Alternatives", paper presented at the 1994currently an economic approach to solving the problem DoD/Industry Advanced Coatings Removalof hazardous waste. The dust and fines recovery Conference, New Orleans, USA, May 1994.process of plastic media blasting does remove some ofhazardous waste particles and therefore, this dust must 2. A.O. Rockswold, S.K. Mayer, H.N. Conkle and D.M.be treated as a hazardous waste products. Bigg, "Repelletization of Spent Type V Plastic Blasting

Media", paper presented at the 1994 DoD/IndustryThe US Technologies Corp.[l] has developed a Advanced Coatings Removal Conference, Newrecycling technique to recycle spent media and paint Orleans, USA, May 1994.residue. The technology utilizes the media and paintresidue as an ingredient in the manufacture of plumbing 3. R. Kovar, K. Blizard and L. Rubin, "Biodegradablefixtures such as sinks, showers and vanities. This Plastic Media Blast Materials", paper presented at theencapsulates the hazardous waste in a non-leachable 1994 DoD/Industry Advanced Coatings Removalform which is acceptable under environmental Conference, New Orleans, USA, May 1994.regulations. This is a proprietary process which isawaiting patent approval. This process has received therequired approvals from the US Environmental



13-1

Bioremediation of Wheat Starch Media Waste

Mr. Olivier Malavallon Mr. John OestreichAdrospatiale Soc. C.A.E. Electronics Ltd.

Direction des Etudes Montreal, QuebecA/DET/CG-MP Canada


FRANCE

1 - REMINDS - Step 1: The starch waste must first be liquified. Thestarch waste is automatically dispersed into

The development of a bioremediation process is designed pre-heated water (96 - 98TC). The starch willto minimize most of the waste generated with dry media be fully hydrated at this temperature. A heatpaintremoval. The bioremediation method was developed stable alpha-amylase enzyme then breaksby DOT Technologies in Canada. down the starch, solubilizing the starch

polymers. The enzymes require 60 minutes toWhen paint is removed with wheat Starch Media, a dust completely liquify the starch waste. Then thewaste is produced containing both starch and paint. The waste is cooled to 30 - 33°C and afterwardswaste will also contain a percentage of inorganic materials transferred to the bio-reactor.from the starch, the paint waste and contaminants from theaircraft (sealants, tapes, ... ). - Step 2: The starch waste is continuously circulated

from the bio-storage vessel, through an air2 - PRINCIPLE tower, to the bio-chamber, and then returned

to the bio-storage tank. Bacteria and nutrientsThis disposal method first uses enzymes to render the are added to the bio-reactor and the waste isstarch component soluble in water, converting the starch to then allowed to digested for several days.various sugars. Specially bred bacteria then digest the During digestion, the temperatureof the wastesugars, and some of the hydrocarbons in the paint. At this is maintained at 30 - 33°C, air is supplied viastage, the primary end products are carbon dioxide and the air tower, and the pH is monitored andwater. This bioremediation method reduces the waste adjusted to a neutral level.generated by dry paint removal by approximately 95%.

- Step 3: As the digestion of the starch sugars proceeds,The bacteria, bred by natural selection, tolerates high the sugar level decreases. To maintain opti-levels of heavy metals, and toxic hydrocarbons. mum bacterial action, a quantity of liquid

waste is automatically transferred from theThe basic chemistry of bioremediation, as well as the biostorage unit to the evaporator. In themanagement of bacteria in this application are summarized evaporator, the volume of waste is reduced byhereafter. 50%. The concentrated waste is then returned

to the bio-chamber. A newly dispersed volume3 --TRIALS of waste, equal to the volume of water lost

through evaporation, is automatically addedThe process is based on research performed on a semi- to the bio-chamber to maintain a constantcommercial size pilot unit. This unit, operated by DOT waste volume level.Technologies, processes up to 70kg per batch, and digeststhe starch waste at a rate of over five kg of waste per hour. - Step 4: Once digestion of several batches has been

completed over a period of several weeks, theMore than one tonne of waste has been processed in residual waste is collected in the evaporationprototype trials. Waste starch media has been supplied by unit. This is concentrated into a paint sludgevarious North American companies including BOEING, and is removed from the system. In this way,NORTHROP GRUMMAN, BEECH AIRCRAFT, the inorganic materials are removed.CANADIAN HELICOPTERS and the CAE Test Center.The source of the waste, type of paint removed, and mesh - Step 5: The water produced during digestionsize of the waste had no discernible effect on the evaporates and is vented to the atmospherebioremediation process. through an activated carbon filter. The water

evaporated during concentration of the waste4- PROCESSING can be recovered and reused, minimizing any

effluent to the environment.The following operational sequence is used either for thepilot unit operation or for a 100 MT/year facility.



13-2

5 - MONITORING 6 - ECONOMICS AND CONCLUSION

In order to ensure a good functionment and the follow up Today's commonly used methods are primarily land-fillof the bio-rem6diation system, tests are performed. For and incineration. It appears after analysis that the bioexample, if the sugar levels increase as indicated by a remediation costs are in France at the same level of costspecific gravity reading, the bacteria may have become than for land-fill or incineration. Since the costs of theseinactive during the digestion cycle. The waste solution pH, methods are expected to rise in the future, bioremediationtemperature, andairsupplyshouldbeverifiedandcorrected offers an efficient alternative method of protecting theif necessary. If all equipment is operational, a new bacteria environment, and controlling disposal costs over the long-and a nutrient package are added to restart and to insure the term.digestion cycle.

14-1

OPERATIONAL PARAMETERS AND MATERIAL EFFECTS

Dr. Terry FosterEsquirnalt Defence Research Detachment


1. INTRODUCTION surface can effect the surface in two ways: I) the peeningeffect of the particles can induce residual surfaces

Although there are six types of plastic media, the focus stresses (peening), and ii) the surface can be roughenedon operational parameters and materials effects of PMB or eroded.will be on the Type V acrylic media with some referenceand comparisons to Type II media. The other four Roughening of the surface during plastic media blastingplastic media are not used extensively in general aircraft is most notable with alclad alloys. As the clad layer isstripping and will not be discussed in this paper. There much softer than the underlying aluminum substrate theare several military and commercial documents impinging media will smear and roughen the alcladavailable with detailed procedures for plastic media surface. This effect is also dependant on the angle ofstripping of aircraft and some of these are shown in impingement of the blast particle. An example ofTable 1. The actual choice of blasting parameters will surface erosion is the removal of the anodizing layer onto a great extent depend on the media chosen and the the surface of aluminum alloys.substrate to be stripped.

The surface of composite materials can also be damagedCountry Document Title during PMB. Broken or exposed fibres are usually the

most obvious indication that PMB has damaged theUSA Technical Order 1-1-8 Application of composite surface.

Organic Coatings, Aerospace Equipment,Sections 2-7 and 2-14 The effect of induced compressive stresses on the

Canada surface of aluminum alloys is distortion and warpage ofMcDonnel CSD #4 Oct 19 1988 the structure or test specimen and in some cases a loss ofDouglas mechanical properties. This warpage is measured as theAirbus SIL 51-007 Sept 6 1989 and AUPS 02-100 Almen Arc height using the test described later. High

Jan 30 1990 Almen arc heights indicate that a high residual surfacestress has been produced. Increased surfaces stresses are

The effects of various blasting conditions on materials unacceptable on aircraft structures and is one of thecan be evaluated using visual, optical microscopy, reasons why PMB is not used on all aircraft materials.scanning electron microscopy (SEM) and mechanical The Almen arc height is also used as a method ofand corrosion test methods. The American Society for determining the acceptable blasting conditions for theTesting and Materials (ASTM) test methods, relevant to various types of media.PMB, for metals and composites are listed in Table 2.In some test methods up to twelve specimens are 3. MECHANICAL PROPERTIES OF METALSrequired to give meaningful results, therefore statistical AND COMPOSITESanalysis tools are also required to interpret the resultsdue to the scatter in some of the data. Fatigue of metals is a major concern in aircraft structural

integrity and as PMB can effect the surface properties of2. SURFACE EFFECTS OF PMB a metal (e.g. increased roughness and residual stress)

increased fatigue crack growth rates have been aThe impact of plastic media particles on a substrate concern. There has been no evidence to date of reduced



14-2

fatigue life as a result of PMB for aluminum alloys of or SEM. Inspection of the surface for broken fibres,greater than 0.06 inches thickness. cracks in the resin, lack of surface resin or missing fibre

layers are indications that damage has occurred.In alloys of less than 0.06 inches thickness fatigue can Interlaminar or subsurface damage must be detectedbe reduced by as much as 66% (0.032 inch, notched Al using non-destructive means such as x-ray or ultra-2024-T3). In general, fatigue crack growth rates are sound or microscopic examination of cross-sections.affected by the following blast parameters and materialsproperties: Unless harsh blasting parameters are used (high

pressures and close stand-off distances) that result in• increasing blasting pressure visible fibre damage or matrix cracking, there has been* increased dwell time or number of blasting cycles no observed degradation in the mechanical properties* reduced specimen thickness (tensile, flexural, compressive, interlaminar shear• presence of dense particle contaminants in the strength, or fatigue properties) of fibre composites from

media PMB.the type of aluminum alloy, with Al 2024-T3showing a greater increase in fatigue crack growth 4. ALMEN ARC HEIGHTS AND BLASTINGrate than Al 7075-T6. PARAMETERS

To reduce the effects of PMB on fatigue crack growth In the Almen Arc Test a strip, 3" x 0.75" x 0.032", ofrates blasting parameters must be chosen that reduce the 2024-T3 aluminum (or other alloy as required) islevel of induced surface stresses or peening. securely fastened to a steel plate with four fasteners as

shown in Figure 1. The aluminum strip is then blastedFor composite surfaces, erosion or damage to the surface for various periods of time (usually 2.5, 5, 10, 20, 30,can lead to degradation of mechanical properties (tensile, 40, 50 or more seconds). The Almen strip is removedflexure, fatigue life and compression). The blasting from the holder and the warpage or arc height isparameters used on composite surfaces are generally less measured after each blast time. The Almen Arc heightsevere than those chosen for metal surfaces. The factors is then plotted as a function of blast time as shown inthat can result in surface damage to composites include: Figure 2. Saturation has occurred when a doubling of

the blast time results in a change in arc height of less• long dwell times or repeated stripping of a surface than 10%. Once saturation occurs no further blasting is* choice of media, generally media with a hardness required.

of 3.5 Moh (Type II) are more damaging thanmedia with a hardness of 3.0 Moh (Type V, The Almen arc test is useful in obtaining the bestacrylic) combination blast parameters for each media, (pressure,blast angle, the more shallow the blast angle the standoff, blast angle, and media flow rate) that result ingreater the chance of surface damage the least residual stress while maintaining an acceptablelower blast pressures and increased standoff coating removal rate. In many blasting specifications adistances reduce the possibility of surface damage maximum Almen arc height for a given number of blastbut also result in slower stripping rates, these two cycles is specified, usually 0.006 inch (0.15mm) usingfactors must be balanced in choosing blast inch Al 2024 (0.032 inch thick). This means that for theparameters any given blast parameters and media, the Almen arcremoving only the topcoat of a coating system and height must be less than that specified after blasting forleaving the primer intact will also result in the set number of blast cycles.reduced surface damage

Two examples of the effects of various blast parametersThe easiest and most direct method of determining on the Almen arc height are shown in Figures 2 and 3.surface damage on composite is by optical microscopy

14-3

From Figure 2 it can be seen that both blast angle and Moh).media flow rate can effect the Almen arc height. Higherflow rates, more media impacts per second, and a 90W Standoff distance will also obviously have an effect onblast angle, more efficient transfer of energy to the the Almen arc height as shown in Figure 3 for asubstrate surface, both result in increased Almen arc magnesium alloy at standoff distances of 12 and 18heights. inches, similar effects are seen for Al 2024-T3.

The effect of the hardness of the various media types can 5. CONCLUSIONSbe seen in Figure 2. The harder more dense media, Type"I (3.5 Moh, 1.5 gm/cm2), gives significantly higher When used with attention to the choice of blastAlmen arc heights than the less dense media, Type V parameters and with an understanding of the possible(1.2 gm/cm2), or the softer media, wheat starch (3.0 effects on material properties, plastic

media blasting is a safe and effective method for qualifying procedure whenever a new PMB process is toremoving coatings from aircraft structures. The effects be qualified.of PMB on materials have been well documented overthe last several years and are well documented ( see There are several specifications (military andbibliography), commercial) available to the new user of PMB. This

will enable the user to reduce the time required to get aThe Almen arc height test is also a useful test for PMB facility operational and help provide a thoroughdetermining the effects of various combinations of blast background knowledge of PMB.parameters on materials. It can also be used as a

TABLE 2 - TEST METHODS FOR EVALUATIONEFFECTS OF PMB ON MATERIALS

Test Method TitleMetalsASTM E206 Fatigue Testing and Statistical Analysis of Fatigue DataASTM E647 Measurement of Fatigue crack Growth RatesASTM E466 Conducting Constant Amplitude Axial Fatigue Tests of Metallic Materials

CompositesASTM D790 Flexural Properties of Unreinforced and Reinforced Plastics and Electrical

Insulating Materials (Method II: Four Point Flexure)ASTM D2344 Apparent Interlaminar Shear Strength of Parallel Fibre Composites by Short

Beam MethodASTM D3039 Tensile Properties of Fibre Resin CompositesASTM D3410 Standard Test Method for Compressive Properties of Uni-Directional or

Crossply Fibre-Resin CompositesCorrosionASTM B 117 Salt Fog TestingASTM G31 Laboratory Immersion Corrosion testing of MetalsASTM G34 Standard Test Method for Exfoliation Corrosion Susceptibility in 2XXX and

7XXX Series Aluminum AlloysASTM G46 Standard Recommended Practice for Examination and Evaluation of Pitting

Corrosion

14-4

SPECIMEN

DIAL GAUGECC

[ I I

I !! SPECIMEN HOLDERI. 0 , o

CONTACT SURFACE

ALMEN ARC HEIGHT BEFORE BLASTING

AFTE BLASTING

Figure I Almen Test Gauge and test specimen.

14-5

0.01 -

U-J 0.00

S0.00

/0 30 60 90 120 5 8 1Timie (seconds) 15-IOi1----* 480 Ib/ 90 deg 480 lb/45 deg

Fiur 650 lb/45 deg -- e---- - 650 lb/90 degFiue2ComParison Of Aimen arc data for Type V media at toblast angles and mediaI ~ flow rates using a 1 2" standoff distance (AL 2024-T3).

/ ~0.03~

S0.015

I 0.005

/0 30 60 90 120 I50 190 210

T ype 11/45 deg Type V/4 e ' ~ - Starch/4 OFiue3Compai-ison Of the Almen arc data for Type 11, Type V and Wheat Starch mediaat 45 0 and 90' at a media flow rate of 480 lb/hr and 12'" standoff distance (Al 2024-T3).

14-6

0.05 -

0.04-

"- 0.03 -

0-

S0.01

-|I I I

0 30 60 90 120 150 180 210

Time (seconds)

S490 Ibs/ 18" 90 - 4 0 lbs/12" SO

Figure 4 Comparison of the effects of standoff distance on the Almen arc data for Type Von magnesium alloy at 90 deg and 30 psi.

15-1

Process Evaluation

Mr. Olivier MalavallonAdrospatiale



FRANCE

1 - CURRENT SITUATION This is the CELOMER International paint system(COURTAULDS Aerospace group), qualified to

It is not always easy to conduct a study and implement a specification TN A.007.10013. This paint system is assystematic policy in the aeronautical paint stripping field, follows:The situations to be studied are complicated by extensivetechnical data, material conditions and financial unknowns. -Wash primer (P99) + primer (PAC 33) + top coat (PU66).To these are added demands both in the civil and militaryfields to increase the performance obtained, optimize These are flexible polyurethane paints.cycles, reduce recurrent costs, quickly amortize investmentsand now increasing respect for the environment. 2.3 - Processes

Toreplycorrectly, thevariouspossibilitiesmustbeassessed The processes selected are those which are liable to stripusing, if possible, identical criteria and reference systems. thepaint systems applied to the external surfaces of transport

aircraft.The only criteria which apply to all the processes andmethods is the overall stripping cost. It is not sufficient for These processes are as follows:a process to meet the related technical requirements (forexample <JATAguidelines>),itmustalsobeeconomically solvent-based, non-phenolic, slightly chlorinatedjustifiable. The overall costs take into account therefore strippers (associated with the barrier coat system),the costs and materials, labor and also the downtime of the activated acid strippers,aircraft, amortization and maintenance of the installations PMB + type II media,and processing of waste, etc.. DMB + starch media,

water ice pellet blasting,2 - AEROSPATIALE EVALUATION CO2 ice pellet blasting,

Xenon lamp + CO2 ice pellet blasting,For many years now, AEROSPATIALE has undertaken very high-pressure water jet,research and development programs to find and evaluate high-pressure water jet,alternatives to theconventional chemical stripping process. chemical stripping + high-pressure water jet,This work has led itto carry out comparative analyses from LASER,technical elements enhanced as the work progressed. Xenon lamp.

2.1 - Substrates 2.4 - Evaluation criteria

The substrates taken into account in the evaluations are The evaluation criteria selected take into accountthose used on the external surfaces of civil transport requirements from different fields. They can be groupedaircraft. They can be divided into two families: into the following categories:

- metallic materials, mainly consisting of cladand unclad - Hygiene & Safety. Environment:aluminium alloys, . hygiene and safety protections and requirements,

volume of hazardous waste.- composite materials, made up of different types of

structures (sandwich, monolithic) using different types - Technical aspects:of fibers (glass, kevlar carbon) and epoxy resins (120'C . media intrusion,and 180TC). . potential corrosion,

potential damage on metallic substrates,These substrates are very often protected with different . potential damage on composite substrates,typesof surface treatments (such as anodizing) orprotective . potential damage to adjacent parts,materials (such as bronze mesh). . ability for selective stripping,

reliability.2.2 -Paints

- Industrial aspects:The paints applied to the surfaces of these protective . masking and precleaning,substrates are conventional external paint systems. The final cleaning,paint system retained is the one the most often used. . productivity,

cycle time.



15-2

04J OD 0D w w , ~U C

LU

A 2: 0S0 ul -j 0

a: ai u , u9 LU U, 00 a a a a a

2: UL

Uj Lu LU LU em_/ : U) m 0 0 300 U, 02 0 U,0 c: 2:2 , , U

Uo w (w r- U f- Lo

0 M

0 , - LU ,.i LU L L LU l(D ,3 U) 0 U () U) / ) U) w : 0 0 2:0 0 0

7: wi 0 LiU LUJ LU LUj LU LU 0 29 0 0 0 0 05. >-J >- > - > J LU- . 5 2 5 - .-

ro a a) C/ (n C13 <n m * . N , . 0 U

0l LL LU LU LUI

3LU LU LJ u LCL~~ 0

c'j aU N. , 0 U, -i 0 0 C 0 0) 0) U

.Ž)LUI LU U

2: ~. z.2. P-0

_ u 0 0 Ž 0 0 0 00. a- : 2 9 9 5o 2: OU2: 2 : 55

aLU LU wF--F

co LU L LU2: :

- 0 0 0 2: 0: -

a- -n 3 7 U, N. U ) 0 N Ja o N , o

LU ,w LU LU ai

wU LUL LU LU LU2: - 3: U) m- 'Mn0 fn

u 0 0 0 0 00 0 0~

oLU LUui LU .w w

LUui u u

R- -m >- F-

LU 0i 0 0 LU =_U>- ~ ~ ~ ~ ~ ~ F a_ 5. - -U - 5 :5. 5 .

U)) cn 3: w w: CD 2: :2LU LU LUI LL LU Li 0 02 ~ Ž0

LUG 2:) 0l 0. o ..J :

CL U) 'aU Z 5

U) 0,

LUA. U,

~~I C.', oU

o' E ca a3 > -2 Cl ;z -S~ .- 2: 0 ;L

cc: a- (n a Lli 5 a 0 1 C 0 m C 4'r E

15-3

- Financial aspects: Other aircraft manufacturers have made evaluations of this

* development costs, type.* investment costs, From available information, it seems that the results of

* operating costs, AEROSPATIALE's and BOEING's evaluations are similar

* waste processing costs. and often oppose the results obtained by Mc DONNELLDOUGLAS.

2.5 - EvaluationNevertheless, the results obtained can be considered as

The method chosen consisted in evaluating each process fairly reliable for the first 5 processes. Their classification

for the criteria retained. This evaluation was made, on the may change as results from various research programs

one hand, from available information and results and, on become available. As for the other processes, follow-up

the other hand, from incomplete or partial information due must be continued in order to benefit from any

to lack of results or simply because the tests are still in improvements which may be made.

progress.2.6 - Conclusion

The values allocated to each criterion range from 0 to 10;0 corresponds to the best result, 10 to the worst result. From an overall cost-type approach, it is possible to

conduct a comparative evaluation of the various existing

After evaluating all the criteria, the values obtained were stripping processes or those under development.

added together. The sum obtained represents the scoreobtained by the process. The best process is supposed to be However, the economical conditions, social legislation

one with the lowest score. and means available are not the same for everyone.

However, processes with a characteristic or a specificity To this, we must add the strategies and policies specific to

incompatible with stripping aircraft external paint systems each company which, for some, make it more advantageous

were eliminated from the final classification, to invest and perform the work in-house whereas, forothers, it is more advantageous to outsource and benefit

The results obtained show that the 5 processes which from more advantageous conditions.obtained the best scores were in decreasing order:

- DMB + starch media,

- PMB + type II media,- solvent-based, non-phenolic, slightly chlorinated

strippers (associated with the barrier coat system),- Xenon lamp + CO2 ice pellet blasting,- LASER.

16-1

Standardization Work

Mr. Olivier MalavallonA~rospatiale



FRANCE

1 - ORIGINS For composite material substrates, their behaviors were

studied visually and mechanically using, in particular, theFor several years now, the main civil aircraft manufacturers tensile test.(AIRBUS and its partners, BOEING, FOKKER, Mc This IATA Paint Stripping TaskForce completed its workDONNELL DOUGLAS) have been working jointly on the in June 1993.writing of technical recommendations and the drawing upof an international standard. This work concerns the 3 - ISO STANDARDIZATIONevaluation of the processes and products used to stripaeronautical paint systems. When the IATA Guidelines had been published, it was

decided to continue the work by creating an internationalThis procedure was initiated on request from the main standard. Thus, in September 1993, a working group wasairlines. In effect, the airlines are faced with situations in formed under the ISO organization (ISO/TC20/WG8).which the financialand operational objectives arebecoming The composition of this work group is more or less theincreasingly important. same as that of the IATA Task Force.The need was felt to rationalize and, if possible, harmonizethe criteria and technical requirements of the various civil The aim of this work group is to produce an internationalaircraft manufacturers in order to facilitate in-service standard which can be used as reference for evaluating andmaintenance of the fleets of airlines operating AIRBUS, qualifying stripping products and processes.BOEING, DOUGLAS aircraft, etc..

This standard is being drawn up on the basis of the IATA2 - IATA TASK FORCE Guidelines and care is being taken to minimize modifi-

cations. However, the aircraft manufacturers realized thatIn December 1990, a task force was set up within IATA, the section relevant to composite materials would have toincluding mainly aircraft manufacturers and airlines. This be reconsidered and redone.commission was given the objective of encouraging thedevelopment of alternatives for stripping coatings applied Today, the draft standard concerning metallic substratesto the structures ofcommercial aircraft. The clearly defined has been finalized and distributed. As for the compositeaim is to obtain stripping processes meeting economical, material section, the first draft drawn up by the aircraftenvironmental and technical requirements. manufacturers has been distributed and is now in the

finalization stage.In January 1993, a document entitled <IATA guidelinesfor evaluation of aircraft paint stripping materials andprocesses>> was edited.This document first of all summarizes the technicalrequirements for the stripping of paint. It then details thetechnical specifications for each substrate family (metallicor composites) specifying the test methods, the testspecimens and the requirement levels to be reached.For metallic substrates, this mainly concerns:

-paint adherence,cladding,

- permanent deformation,- fatigue strength,

crack detection,corrosion (sandwich, immersion, galvanic, H2embrittlement).



17-1

Future Prospects




FRANCE

The technical presentations made within the scope of these - The third category«Lecture Sdries N' 201 >> allow us to have an overall view is halfway between the two previous categories. Althoughof the work and achievements relevant to the stripping the limits of this category are imprecise, it very clearlyprocesses which must be both efficient and ecologically- concerns regional transport and liaison aircraft orfriendly, medium-size transport aircraft such as those

manufactured by:

Concerning the destiny of these processes and their use inthe future, it would be desirable to identify and take the - ATR,main influencing factors into account. - British Aerospace,

- CASA,1 - MARKETS - DORNIER

- FOKKER, etc...During the last ten years, the number of military or civilaircraft in service has been steadily increasing. Today, 3 - PROCESSESthere are around several tens of thousands. Althoughairlines have used subcontractors for many years now, it is Certain processes are more appropriate than others. Thisonly recently that the armed forces have began to depends on the surfaces to be treated, the dimensions,subcontract stripping and painting work to specialized accessibilities, forms and substrates.companies which, in certain cases, can operate in-situ.

Thus, for the second category (large aircraft), semi-Recourse to specialized subcontracting can be explained automatised processes seem overall to be the most efficient.by the cost and cycle gains thus obtained which, today,increasingly influence decisions taken. However, for the first category (small aircraft), manual

procedures seem to be the mostpractical and most efficient2 - AIRCRAFT pending, perhaps, the development of high-performance

and (very) costly automated equipment which could, inSeveral types of aircraft are to be considered. They can be part, replace the work done by man.split into 3 main categories.

Lastly, for the third category (medium aircraft), choice of- The first category processes and methods are not so obvious and depend on

Includes small-size aircraft, with highly developing external criteria such as:forms, generally with many inspection doors on theexterior, in certain cases with special coatings and often investments and equipment available,using composite material structures. additional presence of category 1 or category 2 aircraft

in the fleet considered,This category mainly includes: hygiene and safety constraints,- helicopters, etc ...- small liaison and touring aircraft,- executive aircraft, 4 - INVESTMENTS- fighters.

On account of the current economic situation, it seems- The second category difficult and risky to invest millions of US dollars in the

mainly concerns large-size aircraft with surfaces of developmentand fine-tuning of newtechnologies andnewfairly regular and continuous forms, with metallic or stripping facilities.composite substrates.

The validation costs for current solutions are relatively

This category includes: high. The number of developments and processes willtherefore probably remain constant or fall.

- Civil transport aircraft such as those manufactured byAIRBUS, BOEING, DOUGLAS, etc., In addition, the potential customers - airlines, specialized

- Military transport aircraft, patrol aircraft, tanker aircraft, companies and air forces - are also faced with highlyetc., regulated investment credits and reduced amortization

times.



17-2

Lastly, choices and industrial policies concerning, for Also, on account of foreseeable developments in ecologicalexample, recourse to subcontracting, relocating activities, sensitivities, the brand name and the reputation of such oretc., are and will be governed by social, economic and such a user may be placed in jeopardy if he is known aslegislative constraints, being a polluter.

5 - LEGISLATION Nevertheless, today, a certain amount of caution is requiredand even a certain wait-and-see policy is being pursued.

In the future, it seems probable that European, NorthAmerican and Asian legislations will impose (very) severeconstraints for the environment and hygiene-safety.Emissions of volatile polluants, discharges, waste andstorage may reach processing coats such that certain so-lutions will have to be abandoned.

B-I

Bibliography

This bibliography has been prepared by the NASA Center for AeroSpace Information (CASI)1, tosupport the Lecture Series 201: 'Environmentally Safe and Effective Processes for Paint Removal.'It includes selected reports, papers, books, and other items entered in the NASA STI Database from1973 through 1994.

1 Identification numbers 93A (or N) 12345, are NASA accession numbers and may be used to order

copies of the cited documents from NASA CASI, via address, phone, fax, or Internet as follows: 800Elkridge Landing Road, Linthicum Heights, MD 21090-2934 USA, (301) 621-0390, (301) 621-0134or [email protected].

B-2

B-3

Biological treatment of T-38 paint stripping Improved paint removal techniquewastes 84N1958073N74723 MANK, J. F.; DICK, R. J.; ABRAMS, H. C.;MUELLER, J. A.; HEINEMANN, J. M. 46 pages NOWACKI, L. J. 151 pages Avail: CASI HCAvail: CASI HC A03/MF AOI A08/MF A02

The project was initiated with a brief visit to RobinsCompatibility of aircraft operational fluids with a Air Force Base to review their aircraft paint strippinggraphitepoxy composite: Development of an operation. After that project initiation visit, Battelleexterior coating system and remover contacted commercial airlines, aircraft manufacturers,81N11120 military bases, contract stripping companies, andCLARK, K. G. 43 pages Avail: CASI HC A03/MF stripping chemical manufacturers to determine whatA01 the state-of-the-art is in the field of stripping paintThe objective of this investigation is the identification from aircraft. Many personal visits to strippingof aircraft operational and specialty chemical which facilities were made to get first-hand informationare potentially detrimental to the integrity of organic from the people involved with stripping aircraft andmatrix composites. In this report, results of several to see the actual stripping facility. A summary of thestudies made with the graphitepoxy Hercules information obtained from these contacts is providedAS/3501-6 are disclosed. Several alternatives to the in the appendix of this report. The complete strippingproblem of paint removal are discussed. It is con- of a C141 at Robins Air Force Base and the partialcluded that water and maintenance fluids containing stripping of a KC-135 at Tinker Air Force Base werewater produce significant plasticization of graphit- observed. The intent was to identify specific itemsepoxy, while most solvents, oils, hydraulic fluids, and and practices in the Warner Robins ALC operationfuel cause no significant mechanical losses. Paint that could be improved in order to decrease theremoval was found to be a significant problem due to amount of time required to strip an aircraft andthe activity of chemical removers. Removal is com- therefore increase throughput. It was concluded thatplicated by the fact that stripping thermoset coatings Warner Robins is essentially up with the state-of-the-from graphitepoxy is more difficult than stripping art of airplane paint stripping that has been observedfrom aluminum. A 'weak link' coating system using a at other stripping facilities.nitrocellulose primer is, thus far, the best strippablecomposite coating if used with the simple methylene Laser paint removalchloride remover designated 4-70-1. It is recom- 85N 11989mended that confirmational testing with tensile, MALLETS, T. In Defense Systems Managementflexure, compression, fatigue and dynamic mechan- Coll. DoD Robotics Appl. Workshop Proc. (SEEical specimens of graphitepoxy and possibly some N85-11978 03-01) 4 pages Avail: CASI HCadhesive, be made. Following these tests, the AO1/MF A04nitrocellulospolyurethane coating system should be The Laser Paint Stripper program is a three phasefield tested on graphitepoxy aircraft substrates. effort which includes: feasibility demonstration;

prototype optimization; and implementation at ourSelf resonating pulsed water jets for aircraft Air Logistic Centers (depots) by FY88. Majorcoating removal: Feasibility study technical areas that make up the automated system83N 13292 include: (1) laser device with power and uptime toCHAHINE, G. L.; JOHNSON, V. E., JR.; handle the number and size of aircraft (F-16 vsFREDERICK, G. S. 90 pages Avail: CASI HC C-5A); (2) the beam transport and manipulationA05/MF AOl system; (3) controls for beam/aircraft safety, align-The objective of this project was to investigate the ment, and surface condition sensors; (4) integrationfeasibility of disrupting a high pressure water jet into software; and (5) cleanup of residue products.a discrete train of well organized slugs throughpassive acoustic self-excitation of the jet, and as a Plastic media blast best for strippingresult to enhance the ability of the jet to remove 86A26274aircraft coatings and to prepare surfaces for recoating. BULLINGTON, J. B. (U.S. Army, ProductionThis innovative technique takes advantages of the Engineering Div., Corpus Christi, TX) ManTechwater hammer pressures produced by the slugs' Journal, vol. 10, no. 4, 1985. 8 pagesimpact (which are much higher than the stagnation A new cost-effect technique for paint stripping, whichpressures generated by a continuous jet), without the complies with nonpollution and safety standards isdrawbacks of having a mechanical rotating inter- examined. The plastic media blast (PMB) process ofrupter. In addition this technique provides larger removing acrylic and lacquer topcoats from epoxyworking standoff distances, wider areas of impact and prime surfaces, which is applicable to airframes, tailthus greater control of the energy imparted to a target rotors, and composites, is analyzed; the advantages ofthan a cavitating jet. It is therefore capable of over- the PMB technique are discussed. The need tocoming the drawbacks of existing water jet methods prevent media and dust contamination of specificin preparing aircraft surfaces for repainting and of aircraft components is investigated. The design of theproviding a primary supplement if not a practical standard cabinet-type continuous-flow dry air blastingreplacement for chemical removal methods. machine used in the PMB process is described.

B-4

Stripping and painting a plane - Technological Paint removal processand economic aspects 86N2643686A47614 ROBERTS 13 pages Avail: CAST HC A03/MFCAVALLINI, A. (Alitalia, Rome, Italy) IN: A01AIRMEC '85 - Aviation equipment servicing: A process of stripping paint from aluminum employsAircraft and helicopter maintenance; International plastic particulate having sharp edges, having aExhibition and Conference, 4th, Duesseldorf, West hardness of about 3.5 on the mohs' scale and having aGermany, February 26-March 3, 1985, Conference range of sizes from about 30 to 40 U.S. standardReports (A86-47601 23-01). Duesseldorf, West sieve. This media strips aluminum without abrasion atGermany, Duesseldorfer Messegesellschaft mbH, a pressure of about 25 to 40 pounds per square inch at1985. 30 pages the nozzle. Other substrates other than soft plastic canA correct stripping operation is an absolute pre- be stripped without damage.requisite for achieving good results in an aircraftrepainting job. The nature of stripping agents, Localized coating removal using plastic mediaproduction of toxic fumes, and the disposal of the blastingstripping residuals are discussed, together with the 88A52369construction specifications of a special stripping/ NOVAK, HOWARD L.; WYCKOFF, MICHAELpainting hangar and the means of reducing the ground G.; ZOOK, LEE M. (NASA, Kennedy Spacetime for the aircraft to the essential minimum. To Center; USBI Booster Production Co., Cocoa Beach,achieve good adhesion of paint and finish, the FL) IN: Space Congress, 25th, Cocoa Beach, FL,installation of an air conditioning system capable of Apr. 26-29, 1988, Proceedings (A88-52317 23-12).maintaining strictly controlled temperature and Cape Canaveral, FL, Canaveral Council of Technicalhumidity was found to be a necessity. Correct thick- Societies, 1988. NASA-supported research. 8 pagesness and good finish characteristics were achieved Steps taken to qualify the use of plastic mediausing airless electrostatic applicators, which could be blasting for safely and effectively removing paint andpositioned over each platform and could be inter- other coatings from solid rocket booster aluminumconnected and moved along the fuselage. The structures are described. As a result of the effort, anconditions of drying, when no operator is allowed improvement was made in the design of surfaceinside the hangar, could be controlled from the finishing equipment for processing flight hardware, incontrol center. A dual-color TV system permits a addition to a potentially patentable idea on improvedsupervisor to control and coordinate the entire plastic media composition. The general arrangementstripping/painting operation. of the blast equipment and the nozzle configuration

are presented.

Evaluation of the effects of a plastic bead paint Plastic media blasting recycling equipment studyremoval process on properties of aircraft 89N21987structural materials 81 pages Avail: CAST HC A05/MF AOl86N26384 Plastic Media Blasting (PMB) is a new technologyCHILDERS, S.; WATSON, D. C.; STUMPFF, P.; introduced as a candidate to replace wet chemicalTIRPAK, J. 151 pages Avail: CAST HC A08/MF paint stripping of airframes and component parts.A02 This report documents the physical testing,An abrasive blasting process using plastic beads has observations, and laboratory analyses used tobeen proposed for removing organic coatings from evaluate the effectiveness of plastic media recyclingaircraft surfaces and component parts. During the equipment at three PMB sites. Different systems forprototype development of the plastic bead blasting recycling plastic media were evaluated for opera-process for paint removal many concerns surfaced tional performance, losses, efficiency, and metalrelative to the potential effects of the process on removal. An optimum recycling system was selectedmetal and composite aircraft structural materials. This which included a cyclone for gross air/mediaevaluation of the plastic bead blasting paint removal separation, a vibrating screen to remove extra largeshowed that it removed protective metal coatings and extra small particles, and a self-cleaning magneticsuch as aluminum cladding and anodize coatings from separator for ferrous particle removal.aluminum alloys and cadmium plating from steelstructure. Surface roughness resulted on clad The effects of plastic media blasting paint removalaluminum alloys. Warpage as a result of surface cold on the microstructure of graphitepoxy compositeworking occurred on unsupported thin skin metal materialsmaterials. The bond strength of thin skin adhesive 89N22688bonded structure was not affected. The process is less KOZOL, JOSEPH; THOMAN, STEVEN; CLARK,damaging in fatigue to 7075-T6 aluminum structure KENNETH 45 pages Avail: CAST HC A03/MFblasted at 60 psi nozzle pressure than at 38 psi nozzle A01pressure. Epoxy/graphite composite structure which Plastic media blasting (PMB) was assessed as a paintwas plastic bead blasted showed statistically removal method for AS4/3501-6 and IM6/3501-6significant losses in the matrix dominated properties. graphite epoxy (Gr/Ep) composite materials.No significant reductions occurred in the fiber Microstructural effects on these composite materialsdominated mechanical properties. were evaluated after repeated paint/blast cycles.

B-5

Polyester (type 1) and urea formaldehyde (type 2) UT); (Pauli and Griffin Co., Vacaville, CA) SAE,plastic media materials were used in a variety of blast Annual AerospacAirline Plating and Metal Finishingconditions. Ultrasonic inspection, optical microscopy Forum and Exposition, 25th, New Orleans, LA, Mar.and scanning electron microscopy were used to assess 27-30, 1989. 12 pagesthe damage induced during paint removal. After one The development of an automaterobotic strippingpaint/blast cycle, most of the blast conditions caused process for F-4 and F-16 aircraft is discussed. Thelittle or no visual damage to the composite substrates. selection and optimization processes involved theAfter four paint/blast cycles, several of the conditions evaluation of various stripping methods prior tocaused minimal visual damage. Paint removal by selecting the plastic media blast procedure. Thesanding caused more visual damage after one paint design and requirements for the Robotic Paintremoval cycle than any of the repeat blast conditions Stripper Cell (RPSC) and the testing of a prototypethat were evaluated. are described. The installation and verification phase

of the project is examined. Diagrams of the RPSCAccustrip - The next generation in nontoxic low are provided.impact stripping90A24686LEE, RICK C.; KIRSCHNER, LARRY SAE, Automating and controlling dry paint strippingAnnual AerospacAirline Plating and Metal Finishing 90A24702Forum and Exposition, 25th, New Orleans, LA, Mar. CUNLIFFE, F. R., III (Aerolyte Systems,27-30, 1989. 14 pages Burlingame, CA) SAE, Annual AerospacAirlineAccustrip: a new 'wet stripping' process that allows Plating and Metal Finishing Forum and Exposition,depainting in existing chemical stripping facilities 25th, New Orleans, LA, Mar. 27-30, 1989. 11 pagesutilizes a proprietary blend of sodium bicarbonate as The key parameters which affect the efficiency anda media along with a mixture of air and water. The success of the dry paint-stripping process aremedia is manufactured and blended as food grade discussed, including pressure at the nozzle, the size ofquality. The process has several major benefits. It has the nozzle, the angle of blasting, the distance from thevery low dust emissions, removes oil and grease, and work-piece, the hardness and the size of the media,has ability to remove surface corrosion from metal and the media flow. It is pointed out that, by automat-substrates during stripping without additional steps or ing the dry paint stripping process, many of thesematerials. The blended sodium bicarbonate is parameters can be controlled, making it possible tonontoxic to the worker and environment. Economics reproduce the same result, time and again. Attentionof the media do not require costly reclaim facilities or is given to a recently developed automated aircraftdust collecting systems. Disposal costs are minimal, wheel stripping machine, whose units are operated by

joy stick controls from outside the cabinet. The wheelRobotic dry stripping of airframes - Phase II can be rotated and moved forward and backward in90A24691 order to gain access to all of the surfaces; the operatorPAULI, ROBERT A.; WITTENBERG, ART M. also controls the nozzle manipulator which is a five-(Pauli and Griffin Co., Vacaville, CA); (Air Canada, axis unit. At present, robotic systems are being devel-Quebec) SAE, Annual AerospacAirline Plating and oped for small aircraft and for the jumbo jets in useMetal Finishing Forum and Exposition, 25th, New throughout the commercial airline fleets of the world.Orleans, LA, Mar. 27-30, 1989. 10 pagesThis paper describes a program for the developmentof a dust-free closed-cycle robotic system for dry Determination of effects of plastic medium blaststripping of airframes, designed to insure dust-free on surface-crack detection by fluorescentwork environment and reduce plastic-media loss, the penetrant inspection in wrought aluminum alloyscontamination risk, and the media inventory require- 90A45224ment. Phase I of the program involved building a CONRAD, D. A.; CAUDILL, G. R. (U.S. Navy,prototype of the proposed robotic arm and its dust Materials Engineering Div., Norfolk, VA) Materialsenclosure to prove basic automation concepts, Evaluation (ISSN 0025-5327), vol. 48, Aug. 1990.showing reasonable paint removal rate from a curved 7 pagessurface, and establishing that the process is dust-free The effect of plastic medium blasting (PMB) on theand recovers plastic media in a closed-cycle fashion. deformation of preexisting surface cracks wasThis paper contains calculations on the effect of investigated using fluorescent penetrant inspectiondifferent blasting parameters in order to determine (FPI) process to measure the crack length. It wasoptimum values required for the completion of Phase found that, when PMB was used to remove coatings,I. Also presented is the progress achieved by the subsequent etching was critical to effective surface-Phase II of the program, which is to prove the total crack detection by FPI. The observed changes inconcept by building the complete system and crack lengths were found to be due to two phenom-demonstrating its capability, end: the intrusion of medium into the crack and the

closure. Restoration of cracks was demonstrated byAutomated aircraft paint strip cell subjecting the blasted surface to an etching process.90A24699 The relative detectability of surface cracks after PMBBYERS, THOMAS EDWARD; PAULI, ROBERT paint removal was compared with that for chemical(USAF, Ogden Air Logistics Command, Ogden AFB, paint removal.

B-6

Plastic media blast (PMB) paint removal from is projected to be a serious threat to PMB's domi-composites nance. Second, PMB's process and parameters must90A50162 be further researched to optimize the method'sBUTKUS, LAWRENCE M.; MEUER, GARY D.; effectiveness. Third, the worker's safety can beBEHME, ARTHUR K., JR. (USAF, Materials further enhanced by both protective equipment that isLaboratory, Wright-Patterson AFB, OH); (Dayton, available today, and facility construction that isUniversity, OH) IN: International SAMPE specifically designed for the given removal method.Symposium and Exhibition, 35th, Anaheim, CA, Apr. Fourth, facility design is the major consideration2-5, 1990, Proceedings. Book 2 (A90-50056 23-23). when defining a paint removal's environmentalCovina, CA, Society for the Advancement of Material effects. Lastly, it is undeterminable if robotics willand Process Engineering, 1990. 13 pages replace human labor. Equipment that safely appliesPlastic media blasting (PMB) for use on graphitepoxy PMB is available today, while the equipment thatcomposites was compared with the manual sanding further the method's effectiveness of separating heavymethod to determine the possible darnage to surfaces. particles will be accessible in 1 year.It was shown that, using PMB on metal andcomposite airframe surfaces could streamline Mechanical paint removal techniques for aircraftstripping operations, reduce health hazards, and structureseliminate the possible damage chemical strippers may 90N25254cause. PMB was found to be a viable, less damaging AMRO, J. P. 97 pages Avail: CASI HC A05/MFpaint removal method than manual sanding, provided A02some precautions are taken. Nondestructive evalua- Paint removal was studied by mechanical means, i.e.,tion, mechanical testing, and scanning electron blasting, from aluminum structural aeronauticalmicroscopy of stripped and unstripped (baseline) materials (2024-T3) and the changes on the surfacegraphitepoxy panels was performed to determine the morphology introduced by the paint removal processeffects caused by a single application of PMB and are examined. The principal experimental parameters"hand" sanding. Experiments identified safe com- are particle velocity, and particle angle of incidence.bination of PMB parameters, including: media size An ideal combination of these parameters could yieldand hardness, standoff distance, angle of incidence, a stripped aircraft skin substrate with minimal or noand nozzle pressure. damage. Three types of plastic particles were used

are: Polyextra, Polyplus, and Type III. ScanningUltrasonic assisted paint removal method electron microscopy has shown that a potentially90N 16479 damaging surface morphology is formed on theREINHART, THEODORE J. Filed 7 Jul. 1987 surface of the structural material. MultipleSupersedes US-Patent-Appl-SN-070499 9 pages microcracks or fissures generated by the strippingAvail: US Patent and Trademark Office could reduce the life and/or change the engineeringThis abstract discloses paint or other protective properties of the material. It as also found thatcoating removal method involving the use of aluminum material stripped using plastic mediareciprocal motion ultrasonic frequency mechanical particles has a very rough surface that may affect theenergy applied to the coating by a variety of tool and aerodynamic flow of an airplane. The number ofabrasive substrate members in the company of surface microcracks and degree of surface roughness varypreparation agents, such as coolant, heating, with the particle impact angle and velocity. Tosoftening, and/or abrasive agents. The invention is minimize or eliminate the damage done to the surfaceparticularly applicable and disclosed in terms of, during the plastic particle stripping, it was necessaryprotective coating removal from aircraft such as is to change the blasting media to softer and smalleroften necessary for replacement or in the reutilization particles. Commercial wheat flour was selected forof aircraft with different identification markings. The this purpose. With the substitution of these naturalcoating removal method is environmentally and particles, the scanning electron microscopyhuman operator safe in comparison with presently observations of the stripped surface revealed noused coating removal methods such as abrasive potential damage (microcracks or fissures) on theblasting and chemical solvent removal, structural material, and the surface roughness was

also reduced.The future of aircraft paint removal methods90N16936 Mechanical paint removal techniques for aircraftTHEN, MICHAEL J. 169 pages Avail: CASI HC structuresA08/MF A02 90N26166The purpose of this study was to develop a qualitative AMRO, JOE P.; TALIA, JORGE E. Presented atforecast for predicting aircraft paint removal the 1990 AIAFAA Joint Symposium on Generalmethods. A Delphi methodology was used to create a Aviation Systems 20 pages Avail: CASI HCtechnical forecast, combining the expectations of A03/MF A01individuals who work with the related technologies on Paint removal by mechanical means, i.e., blasting,a daily basis. The Delphi results yielded five major from aluminum structural aeronautical materialsconclusions. First, the projected paint removal (2024-T3) was examined alone with the changes onmethod that will suit future paint removal needs is the surface morphology introduced by the paintPlastic Media Blasting (PMB), and no other method removal process. Three types of plastic particles were

B-7

used in this research: Polyextra, Polyplus, and Type attention is given to the paint sensor which is theIII. Scanning electron microscopy has shown that a feedback element for determining the state of thepotentially damaging surface morphology is formed stripping process.on the surface of the structural material. Multiplemicrocracks or fissures generated by the stripping Paint stripping in the aerospace industrycould reduce the life and/or change the engineering 91A49159properties of the material. It was also found that WOLF, KATY (Institute for Research andaluminum material stripped using plastic media Technical Assistance, Los Angeles, CA) IN:particles has a very rough surface that may affect the International SAMPE Technical Conference, 22nd,aerodynamic flow of an airplane. The number of Boston, MA, Nov. 6-8, 1990, Proceedingsmicrocracks and degree of surface roughness vary (A91-49101 21-23). Covina, CA, Society for thewith the particle impact angle and velocity. To Advancement of Material and Process Engineering,minimize or eliminate the damage done to the surface 1990. 7 pagesduring the plastic particle stripping, it was necessary Methods available for paint stripping of aerospaceto change the blasting media to softer and smaller structures and other industrial equipment areparticles. Commercial wheat flour was selected for discussed. Special attention is given to the followingthis purpose. With the substitution of these natural alternatives: methylene chloride-based chemicalparticles, the scanning electron microscopy observa- strippers, cryogenic striping, plastic media blasting,tions of the stripped surface revealed no potential sodium bicarbonate stripping, and not painting at all.damage (microcracks or fissures) on the structuralmaterial, and the surface roughness was also reduced. Proceedings of the 2nd E-3 AWACS Corrosion

Prevention Advisory Board (CPAB)Automatic aircraft paint stripping 91N1515091A36895 Meeting held at Tinker AFB, OK, 12 Jul. 1990 141STURDIVANT, VERNON R. (Southwest Research pages Avail: CASI HC A07/MF A02Institute, San Antonio, TX) Society of Two environmental issues in particular are affectingManufacturing Engineers, Conference on Aerospace all USAF weapons systems and is being felt by FMSAutomation and Fastening, Arlington, TX, Oct. 9-11, weapons systems as well (particularly in Germany).1990. 12 pages These are volatile organic compounds (VOCs), andPaint must be removed from aircraft to allow detailed non-chemical paint removal. Topics include:surface inspection, to perform repair operations, and problems with waterborne primers, MIL-P-85582;to keep weight at acceptable levels after many coats comparison of plastic materials, MIL-P-85891of paint have been applied. Southwest Research (Dupont lease agreement); use of high solidsInstitute is presently constructing a robotic system for polyurethane topcoat, MIL-C-85285; andautomatically removing paint from fighter aircraft for qualification of materials.the United States Air Force. The process removespaint by plastic media bead blasting. The blast The effect of paint removal by natural beadnozzles are positioned over the aircraft surface with a blasting on the surface morphology of compositerobot. The system consists of two, 9 degree-of- materialsfreedom (DOF) robots together with two robot 91N 15335controllers, one cell control computer, paint sensors, GUY, THU-HA; LANKARANI, HAMID M.;and bead blasting equipment. TALIA, JORGE E. 19 pages Avail: CASI HC

A03/MF AOIRobotic sensors for aircraft paint stripping Paint removal by blasting and its effects on the91A36896 surface morphology of the composite material wereWENIGER, RICHARD J. (Southwest Research investigated. Plastic media blasting (PMB), usedInstitute, San Antonio, TX) Society of extensively by many as a paint removal method,Manufacturing Engineers, Conference on Aerospace showed potential microstructural damage. However,Automation and Fastening, Arlington, TX, Oct. 9-11, natural particles seemed to be a better choice for paint1990. 12 pages removal by blasting since they were softer andAircraft of all types need to have paint routinely smaller in size; thus, minimizing the amount ofremoved from their outer surfaces. Any method needs damage to the surface of the composite. The variationto be controlled to remove all the paint and not of the degree of roughness and amount of brokendamage the surface of the aircraft. Human operators fibers were correlated with the parameter of impactget bored with the monotonous task of stripping paint angle to obtain an optimum environment for paintfrom an aircraft and thus do not control the process removal by blasting.very well. This type of tedious operation tends itselfto robotics. A robot that strips paint from aircraft Design of a wall-scaling robot for inspection andneeds to have feedback as to the state of the stripping maintenanceprocess, its location in respect to the aircraft, and the 91N15557availability of stripping material. This paper describes BAHR, BEHNAM; MAARI, SAMI M. 10 pagesthe sensors used on the paint stripping robot being Avail: CASI HC A02/MF AOldeveloped for the United States Air Force's The design of a new wall-scaling robot for theManufacturing Technology Program. Particular inspection and maintenance of various structures,

B-8

such as aircraft or nuclear power plants, is described, mechanical techniques, specifically by the impinge-This robot is capable of climbing straight or curved ment of solid particles, a technique that would notsurfaces in two directions, up/down or left/right in leave structural damage on the treated material andstrokes of 55 mm. The load carrying capability of this would not effect the environment.robot is about 100 kg. Thus, it can carry a variety ofnon-destructive testing devices for inspection, paintremoval, and de-riveting devices for maintenance. The evaluation of the effects of a plastic beadThe robot uses vacuum suction cups for sticking to blasting paint removal process on graphite-epoxythe surface of an object and can be integrated with a compositesvision sensor system for guidance and visual 92A10150inspection. The positioning of the robot is achieved WIDAUF, DAVID P. (Utah State University,by the use of a joy-stick or a PC computer. With this Logan) IN: International SAMPE Symposium andportable robot it is possible to: (1) inspect areas that Exhibition, 36th, San Diego, CA, Apr. 15-18, 1991,are within easy reach; (2) program the robot to follow Proceedings. Book I (A92-10126 01-23). Covina,a specified path while inspecting or maintaining the CA, Society for the Advancement of Material andstructures; and (3) remotely guide it to desired Process Engineering, 1991. 11 pageslocations. This robotic system will minimize human Experiments were carried out on 12-ply graphitepoxyerror, increase the productivity of an inspector, and panels to investigate the effect of paint removal byreduce the cost of inspection and maintenance, plastic bead blasting on the physical properties of the

composite. The evaluation included tensile testing,flexural testing, and SEM and ultrasonic examina-

Use of natural particles for the removal of paint tions. The graphitepoxy composites exhibited statis-from aeronautical composite materials tically significant losses in the matrix-dominated91N18015 properties while no significant losses were observedGUY, THU-HA; LANKARANI, HAMID M.; in the fiber-dominated properties. No significantTALIA, JORGE E. In its Proceedings: Techfestl4 differences were found in strength and modulus(SEE N91-18004 10-01) 1 pages Avail: CASI HC among the panels.AO1/MF AOlPaint removal by blasting and its effects on thesurface morphology of aeronautical composite The operational status of automated aircraftmaterials are investigated. An ideal combination of washing systemthe parameters for mechanical paint removal by 92A56087blasting such as particle type, size, velocity and angle SOGA, TOMOKATSU (Japan Airlines Co., Ltd.,of incidence yields a stripped aircraft skin substrate Tokyo) IN: Aircraft Symposium, 29th, Gifu, Japan,with minimal or no damage. Natural particles, Oct. 7-9, 1991, Proceedings (A92-56001 24-01).specifically white corn flour, seem to be a good Tokyo, Japan Society for Aeronautical and Spacechoice for paint removal by blasting. Since they are Sciences, 1991. In Japanese. 4 pagessofter as well as smaller in size than other particles The performance and configurations of an automatedused for paint removal, they minimize the amount of aircraft washing facility are presented. The brushingdamage to the surface of the composite. They are also area, the operation time, and rinsing are controlled incheaper and produce no harm to environment. The this computerized washing system.variation of the degree of surface roughness and theamount of broken fibers were correlated with somestripping parameters, such as particle impact angle Paint removal using cryogenic processesand velocity. This defined an optimum environment 92N28912for paint removal by blasting. KIRTS, RICHARD E.; STONE, PHILIP L. 44 pages

Avail: CASI HC A03/MF AOlThe use of a high-pressure jet of cryogenic fluid (e.g.,

Mechanical paint removal techniques for liquid nitrogen at -320 F) to remove paint and othercomposite aircraft protective coatings from Navy aircraft and ships was91N24163 studied. The objective of the work was to explore theTALIA, JORGE E.; BAHR, BEHNAM; BECKER, feasibility of developing a paint removal method thatWAYNE; LANKARANI, HAMID M. In its is less harmful to the environment than the chemicalProgram Plans for Aviation Safety Research (SEE paint stripping methods presently in use. It wasN91-24157 16-03) 6 pages Avail: CASI HC learned that only thick (t greater than 0.020 inch)A02/MF AOl films of paint can be effectively removed by theThe use of conventional paint removal on composite mechanism of thermal shock. Aircraft paint is too thinmaterial can lead to a fast deterioration or weakening and flexible to be removed by cryogenic methods.of the material due to the absorption and chemical Cryogenic methods are not recommended for use onattack of the solvent which may result in a catastro- ships because of the danger of steel embrittlement byphic failure of the structure. Moreover, recent EPA low temperatures. It was demonstrated that a jet ofregulations ban the use of solvents for paint removal liquid nitrogen can effectively remove certain paintson land and sea military bases. The objective is to (regardless of thickness) by the mechanism ofinvestigate the possibilities of paint removal by differential thermal contraction. The process may

B-9

have application where control of paint waste is 28th, San Diego, CA, Apr. 20-23, 1992. 14 pagesessential, for example, removal of thick films of lead Various coating removal technologies are discussedbase paint, from the viewpoint of the process and delivery, with

emphasis placed on the mobile Large Aircraft RobotLaser paint stripping Paint Stripping (LARPS) concept. LARPS is a92N29581 combined and integrated package of a deliveryHEAD, J. D.; NIEDZIELSKI, J. PETER 102 pages system and the process media, representing theAvail: CASI HC A06/MF A02 alternative to the fixed-frame or gantry robot styleA study to assess the utility of high powered C02 delivery systems. The paper describes details of thepulsed laser depainting methods was conducted on LARPS system design and performance, and presentsaluminum and graphite epoxy composites. The design diagrams of LARPS.various tests were designed to detect potential formsof damage or loss of properties of various aircraft Starch media blasting for aerospace finishingstructural materials during removal of paint with applicationspulsed laser energy. Tests for changes in physical 93A14091properties, paint adhesion and corrosion protection of OESTREICH, JOHN; PORTER, TODD (Ogilvierepainted materials showed no detectable adverse Mills, Ltd., Montreal, Canada) SAE, Annualchanges in any of the samples studied. AerospacAirline Plating and Metal Finishing Forum

and Exposition, 28th, San Diego, CA, Apr. 20-23,Automated laser depainting of aircraft survey of 1992. 9 pagesenabling technologies A wide range of starch blast media coating removal92N70886 applications for the aerospace industry are reviewedKOPF, PETER W.; PICHON, DEAN 261 pages with particular attention given to the coating removalAvail: CASI HC A12/MF A03 technologies used in commercial and military aircraftThe requirements needed to integrate a laser maintenance. For commercial aircraft, these coatingdepainting system into the Oklahoma City Air removal processes include processes for removingLogistics Center Depainting Facility were identified coatings from clad aluminum and from composites,and evaluated to determine if the enabling tech- removal of interior finishing coatings, and removal ofnologies were available to reasonably expect a large structural and bonding adhesives. For military aircraftrobotic laser depainting system could be made and maintenance, the processes discussed include theoperated in a production environment. Robotic, laser, coating removal from aluminum clad surfaces, andsensor, and computer control systems were examined, from composite parts. Consideration is also given totested, and evaluated. the removal of coatings and bonding adhesives as part

of aircraft manufacture procedures,Dry ice blasting93A14084 Water instead of chemical corrosives againstLONERGAN, JEFFREY M. (U.S. Navy, Naval aircraft paint - Environment-friendlyAviation Depot, San Diego, CA) SAE, Annual paint-stripping methods could mean drastic costAerospacAirline Plating and Metal Finishing Forum reductions for the aircraft industryand Exposition, 28th, San Diego, CA, Apr. 20-23, 93A218501992. 8 pages New-Tech News (ISSN 0935-2694), vol. 3, 1992.As legal and societal pressures against the use of 3 pageshazardous waste generating materials has increased, This paper describes an environmentally friendlyso has the motivation to find safe, effective, and alternative for removing aircraft paint. The techniquepermanent replacements. Dry ice blasting is a utilizes a thin stream of water to strip paint offtechnology which uses C02 pellets as a blasting surfaces. Rotating nozzles fan out the stream so thatmedium. The use of C02 for cleaning and stripping the aircraft surface remains undamaged despiteoperations offers potential for significant environ- enormous water pressure.mental, safety, and productivity improvements overgrit blasting, plastic media blasting, and chemical Dry-ice blastingsolvent cleaning. Because C02 pellets break up and 93A30768sublime upon impact, there is no expended media to Aerospace Engineering (ISSN 0736-2536), vol. 13,dispose of. Unlike grit or plastic media blasting which no. 3, March 1993. 3 pagesproduce large quantities of expended media, the only Dry-ice blasting technology that uses carbon dioxidewaste produced by C02 blasting is the material pellets as a blasting medium is discussed. It is notedremoved. The quantity of hazardous waste produced, that the use of C02 for cleaning and stripping opera-and thus the cost of hazardous waste disposal is tions may provide significant environmental, safety,significantly reduced, and productivity improvements over grit blasting,

plastic-media blasting, and chemical-solvent cleaning.Coating removal systems - Mobile or fixed?93A14087 The role of paint systems in aircraftMANGOLD, VERNON L., JR. (Kohol Systems, maintainabilityInc., Dayton, OH) SAE, Annual AerospacAirline 93A30962Plating and Metal Finishing Forum and Exposition, GARDNER, GREGORY A.; BAUMGARDNER, L.

B-10

K. (McDonnell Douglas Corp., Saint Louis, MO); aimed at designing and fabricating two mobile(Bridge Associates, Frankfurt am Main, Germany) robot-based laser stripping systems for removingAIAA, AHS, and ASEE, Aerospace Design paint from metallic and composite substrates ofConference, Irvine, CA, Feb. 16-19, 1993. 6 pages fighter-sized aircraft. Emphasis is placed on the majorAircraft paint systems are extremely long-lived and cell elements of the ALPS system which include aeffective. This robust design means that, when they laser, a robot, a multispectral camera, a rasteringmust be removed, these systems present significant system, an end effector, a waste management system,difficulties to the maintenance centers facing the task. a cell controller, and a safety system.A summary of the paint-stripping processes availableto aircraft overhaul centers shows that relatively cost The effects of high-pressure water on the materialeffective processes can be selected, but that even the integrity of selected aircraft coatings andbest present problems. The conclusion is that the real substrateshope for alleviating this problem involves a redesign 93A40668of the paint systems to make them more maintainable, HARBAUGH, DARCY J.; STONE, M. A. (USBInot the development of better stripping processes for Co., Huntsville, AL) Society of Manufacturingexisting coatings. Engineers, Maintaining and Supporting an Aircraft

Fleet Conference, Dayton, OH, June 9-11, 1992.Ultra-high pressure water jet technology - An 6 pagesoverview of a new process for aerospace paint USBI is developing high-pressure water as anstripping alternative technology to replace the current chemical93A40661 stripping process for aircraft. A critical componentJOHNSON, SPENCER T. (Jet Edge, Inc., for the high-pressure water process is the nozzleMinneapolis, MN) Society of Manufacturing assembly. An extensive evaluation of both commer-Engineers, Maintaining and Supporting an Aircraft cially available and in-house designed nozzle config-Fleet Conference, Dayton, OH, June 9-11, 1992. urations has been done to select nozzles which meet13 pages the stringent paint stripping requirements. This paperNew technology used to develop water pressures of presents the results of the nozzle optimization workover 50,000 psi is reviewed. The technology uses and the materials evaluations performed.ultra-high pressure waterjet equipment capable ofremoving the toughest coating from delicate sub- Intelligent control of robotic paint stripping usingstrates without damage, using only water. color vision feedback

94A12324Sensor-adaptive control for aircraft paint HARVEY, D. N.; ROGERS, T. W. (MTS Systemsstripping Corp., Eden Prairie, MN); (Pratt & Whitney Waterjet93A40663 Systems, Huntsville, AL) In: Intelligent robots andWENIGER, RICHARD J.; FRANKE, ERNEST A. computer vision XII: Algorithms and techniques;(Southwest Research Inst., San Antonio, TX) Proceedings of the Meeting, Boston, MA, Sept. 7-9,Society of Manufacturing Engineers, Maintaining and 1993 (A94-12322 02-63). Bellingham, WA, SocietySupporting an Aircraft Fleet Conference, Dayton, of Photo-Optical Instrumentation Engineers, 1993.OH, June 9-11, 1992. 10 pages 9 pagesThe difficulty of removing paint from aircraft varies The paper describes a color-based machine visiongreatly due to factors such as the number of coats, system which is capable of functioning as a real-timeage and condition of paint, and the presence of other process control system for a robotic work cellcoverings such as decals. Efficient automation of currently being developed for stripping paint frompaint stripping requires adaptive process control both large and small aircraft. The system is based onbased on sensors that can distinguish between sub- hue, saturation, and intensity representation of thestrate and coating material. This paper describes a image data and on rapid analysis techniques and issensor for identification of the type and condition capable of differentiating between painted, primed,of aircraft materials based on the analysis of optical stripped, and roughened aircraft surfaces. Thesereflectance spectra. The performance of a recently techniques were tested on a large number of aircraftinstalled robotic depainting system using this paint schemes under actual stripping conditions, andsensor for adaptive control of the paint stripping were found to be fast and robust enough for real-timealso is described. process control.

Automated Laser Paint Stripping (ALPS) Environmentally Safe and Effective Processes for93A40667 Paint RemovalBARONE, PHILIP A. (International Technical 94N 10613Associates, Santa Clara, CA) Society of The 75th meeting was held in Lindau, Germany, 7-8Manufacturing Engineers, Maintaining and Oct. 1992 133 pages Avail: CASI HC A07/MF A02Supporting an Aircraft Fleet Conference, Dayton, Paint stripping and repainting of aircraft surfaces areOH, June 9-11, 1992. 18 pages required periodically during the operating lifetime ofAn Automated Laser Paint Stripping program an aircraft. Historically, paint removal has beendeveloped by International Technical Associates, achieved with chemical strippers. These materialsSanta Clara, California is described. The program is often contain toxic components and create hazardous

B-11

working conditions. It is necessary to ensure that N94-10613 01-31) 6 pages Avail: CASI HCalternate paint removal techniques are available that A02/MF A02can be performed in a cost effective, environmentally The text presents a synthesis of the activities andsafe manner without causing damage to aircraft subjects of French interest in new techniques for thesurfaces. For individual titles, see N94-10614 removal of paint in the civil and military air trans-through N94-10629. port sector.

Paint removal activities in the US Navy94N10614 Paint removal activities in GermanyKOZOL, JOSEPH In AGARD, Environmentally 94N 10617Safe and Effective Processes for Paint Removal (SEE HOLBEIN, R.; ARNOLDS-MAYER, G. InN94-10613 01-31) 5 pages Avail: CASI HC AGARD, Environmentally Safe and EffectiveAOI/MF A02 Processes for Paint Removal (SEE N94-10613 01-31)Use of methylene chloride and phenol based chemical 5 pages Avail: CASI HC AO1/MF A02strippers for aircraft paint removal generates large To replace paint removing chemicals containingquantities of hazardous waste and creates health and chlorinated hydrocarbons several alternative paintsafety problems for operating personnel. This paper stripping methods have been developed or arepresents an overview of the U.S. Navy's activities in under study in Germany: high pressure waterthe investigation and implementation of alternate stripping; plastic media blasting; use of alcalic andpaint stripping methods which will minimize or acid activated softeners; C02 pellet blasting; andeliminate hazardous waste and provide a safe operat- laser application.ing environment. Alternate paint removal methodsunder investigation by the Navy at the present timeinclude use of non-hazardous chemical paint remov- The development of alternative paint removalers, xenon flashlamp/C02 pellets, lasers and plastic techniques in the RAFmedia. Plastic media blasting represents a mature 94N 10618technology in current usage for aircraft paint stripping HARTLEY, M.; WEEDING, M. In AGARD,and is being investigated for determination of its Environmentally Safe and Effective Processes foreffects on Navy composite aircraft configurations. Paint Removal (SEE N94-10613 01-31) 8 pages

Avail: CASI HC A02/MF A02Paint removal activities in Canada Personnel safety and environmental legislation is94N 10615 forcing the removal of chemical removers. The RAFFOSTER, TERRY In AGARD, Environmentally chose the Plastic Media Stripping process as theirSafe and Effective Processes for Paint Removal (SEE alternative. During testing of the process a number ofN94-10613 01-31) 3 pages Avail: CASI HC problem areas and additional advantages wereAO1/MF A02 highlighted. Solution to the problems are discussedPaint removal activities currently under way in and the advantages quantified.Canada include: research and development of laserpaint stripping; development and commercializationof a new blasting medium based on wheat starch; Operational aspects of F.16 plastic media blasting,commercialization of a new blasting medium and as carried out by Fokker Aircraft Servicesprocess using crystalline ice blasting for paint 94N 10619removal and surface cleaning; and the development of POT, FRANK In AGARD, Environmentally Safeautomated and robotic systems for paint stripping and Effective Processes for Paint Removal (SEEapplications. A specification for plastic media N94-10613 01-31) 3 pages Avail: CASI HCblasting (PMB) of aircraft and aircraft components is AOI/MF A02currently being drafted by NDHQ for use by the In 1987, Fokker Aircraft Services started F. 16Canadian Armed Forces (CAF) and contractors air-intake paint removal by means of Plastic Mediainvolved in coating removal for the CAF. Defense Blasting (PMB). Especially for this process, a robotResearch Establishment Pacific (DREP) is studying has been developed. In a later stage, completethe effects of various blast media on coating removal exterior PMB-paint removal has been tested andrates, and minimizing the possibility of damage to successfully adopted. The paint removal is carried outsubstrates other than aluminum such as graphite in the scope of a thorough corrosion control program.epoxy composite and Kevlar. The effects of plastic The requirement that all the paint must be removed inmedia blasting on liquid penetrant detection of fatigue order to allow this control program to be carried outcracks is also under investigation, properly, leads to severe masking complications. The

process parameters are relatively conservative,Procedures without danger to the environment because of the requirement that absolutely no anodicand efficiency (PSDEE) for the removal of paint, layer damage is permitted. Following PMB paintPoint on the French activities concerning the removal, corrosion is removed using aluminum oxideremoval of paint blasting. Finally, a highly flexible polyurethane paint94N 10616 system is applied, based upon TT-P-2760 KoroflexGAUTHIER, PIERRE In AGARD, Environmentally primer. To summarize the process, it can be statedSafe and Effective Processes for Paint Removal (SEE that the plastic media blasting itself is straight-

B-12

forward. Proper masking is difficult to perform Plastic media blasting activities at Hill Air Forcethough, compounded by special customer Baserequirements such as open panel edges. 94N 10622

CHRISTENSEN, J. D. In AGARD,Environmentally Safe and Effective Processes forPaint Removal (SEE N94-10613 01-31) 2 pages

Use of robots for aircraft dry stripping via plastic Avail: CASI HC A0l/MF A02media blasting Hill Air Force Base in Utah developed plastic media94N 10620 blasting (PMB) paint removal process for removingGILLARD, E. In AGARD, Environmentally Safe paint from Air Force aircraft. The development of theand Effective Processes for Paint Removal (SEE process involved extensive testing of various abra-N94-10613 01-31) 6 pages Avail: CASI HC sives and subsequent parameters to end up with anA02/MF A02 approved production process. Hill AFB has beenIn order to meet constant financial and reliability using PMB in a production mode since 1985, andconcerns, European manufacturers have introduced completely discontinued chemical stripping of air-more and more composite materials on their aircraft. frames in 1989. We have recently installed andIn addition to fairings for which the use of composites began operating a fully automated PMB facilityhas become absolutely necessary, composites are that utilizes two nine-axis robots to strip an aircraft.used on each new program for structures which are This system has enabled us to further reduce themore and more highly loaded and sophisticated. manhours required to strip an aircraft, and alsoSimilarly to metallic structures, an external paint allowed us to remove the employee from the blastingscheme is applied to these composite structures to atmosphere into a control room. We have, and willprotect them from ultraviolet rays, provide general continue to realize, significant environmental andcorrosion resistance and allow the airlines to economic savings by using PMB. Hill is also activelycustomize their aircraft. Conventional stripping involved with the development of future paintmethods using chemical strippers cannot be used as stripping technologies.many impregnation resins do not resist chemicalstrippers. Aerospatiale has endeavored to find newefficient methods that are easy to implement, cause nodamage and are applicable both to metallic and Large Aircraft Robotic Paint Stripping (LARPS)composite structures. Dry stripping via plastic media system and the high pressure water processblasting has formed the subject of many tests. These 94N 10623tests proved that such stripping was compatible with SEE, DAVID W.; HOFACKER, SCOTT A.;the objectives but required automation of the process STONE, M. ANTHONY; HARBAUGH, DARCYfor large airframe stripping. (United Technologies Corp., Huntsville, AL.);

(United Technologies Corp., Huntsville, AL.);(United Technologies Corp., Huntsville, AL.) InAGARD, Environmentally Safe and Effective

German Air Forces experiences with plastic media Processes for Paint Removal (SEE N94-10613 01-31 )blasting and future requirements 21 pages Avail: CASI HC A03/MF A0294N 10621 The aircraft maintenance industry is beset by newSTOERMER, MATTHIAS In AGARD, Environmental Protection Agency (EPA) guidelinesEnvironmentally Safe and Effective Processes for on air emissions, Occupational Safety and HealthPaint Removal (SEE N94-10613 01-31) 14 pages Administration (OSHA) standards, dwindling laborAvail: CASI HC A03/MF A02 markets, Federal Aviation Administration (FAA)German Air Force (GAF) has been researching a safety guidelines, and increased operating costs. Inmethod of paint removal for a couple of years to light of these factors, the USAF's Wright Laboratoryreplace the chemical method still in use. This is to Manufacturing Technology Directorate and theimprove corrosion prevention, environmental Aircraft Division of the Oklahoma City Air Logisticsprotection and health care. With the support of Center initiated a MANTECH/REPTECH effort toGerman aerospace company MBB and the University automate an alternate paint removal method andof the Armed Forces in Munich GAF selected Plastic eliminate the current manual methylene chlorideMedia Blasting (PMB) as the most suitable method. chemical stripping methods. This paper presents someHaving a stripping facility for the entire aircraft at of the background and history of the LARPS pro-MBB Manching already in existence, GAF decided gram, describes the LARPS system, documents thethat the next step forward to gain more experiences is projected operational flow, quantifies some of theto establish a smaller 'stripping cabin' at an air force projected system benefits and describes the Highbase. This cabin is suitable for stripping removable Pressure Water Stripping Process. Certification of anparts and components of aircraft and equipment with alternative paint removal method to replace thethe max. size of a half dismantled TORNADO wing. current chemical process is being performed in twoWith these gained experiences GAF will be in phases: Process Optimization and Process Validation.position to formulate the specific requirements for an This paper also presents the results of the Processentire on-base aircraft stripping plant which will be Optimization for metal substrates. Data on the coatingsuitable for F-4's, TORNADO's and EFA's, too. removal rate, residual stresses, surface roughness,

B-13

preliminary process envelopes, and technical plans AGARD, Environmentally Safe and Effectivefor process Validation Testing will be discussed. Processes for Paint Removal (SEE N94-10613 01-3 1)

10 pages Avail: CASI HC A02/MF A02Automated Laser Paint Stripping (ALPS) update Research into the possibility of using ice particles as a94N10624 blast medium was first initiated at Defence ResearchLOVOI, PAUL In AGARD, Environmentally Safe Establishment Pacific (DREP) in an effort to developand Effective Processes for Paint Removal (SEE a more environmentally acceptable paint removalN94-10613 01-31) 12 pages Avail: CASI HC method. A paint removal process was also requiredA03/MF A02 that could be used in areas where normal grit blastingTo date, the DoD has played a major role in funding a could not be used due to the possibility of the residualnumber of paint stripping programs. Some technolo- blasting grit contaminating machinery and othergies have proven less effective than contemplated. equipment. As a result of this research a commercialOthers are still in the validation phase. Paint stripping ice blasting system was developed by RETECH. Thisis one of the hottest issues being addressed by the system is now being used to remove paint from sub-finishing industry since the Environmental Protection strates that cannot be easily blasted by conventionalAgency (EPA) has mandated that chemical stripping techniques and also to clean soiled or contaminatedusing methylene chloridphenolic type strippers be surfaces. The problems involved in the developmentstopped. The DoD and commercial aircraft com- of an ice blast system, and its components and theirpanies are hard-pressed to find an alternative, functions are described. Due to the complexity ofAutomated laser paint stripping has been identified as paint removal using ice blasting, parameters such asa technique for removing coatings from aircraft air pressure, ice particle size and ice particle flow ratesurfaces. International Technical Associates (InTA) were studied and adjusted to suit the nature of thewas awarded a Navy contract for an automated laser particular coating and substrate of interest. Thepaint stripping system (ALPS) that will remove paint mechanism of paint removal by ice particles has alsofrom metallic and composite substrates. For the been investigated. A theoretical model has beenprogram, which will validate laser paint stripping, developed to explain the different paint removalInTA will design, build, test, and install a system for mechanisms such as erosion by abrasion and erosionfighter-sized aircraft at both the Norfolk and North by fracture as they relate to ice blasting. Finally, theIsland (San Diego) Aviation Depots. use of ice blasting to removal paint from a variety of

substrates is presented as well as examples of surfaceAquastrip TM: An innovative paint removal cleaning and surface decontamination.technology94N 10625 Paint removal using wheat starch blast mediaVOLKMAR, J. In AGARD, Environmentally Safe 94N10627and Effective Processes for Paint Removal (SEE FOSTER, TERRY; OESTREICH, JOHN (OgilvieN94-10613 01-31) 10 pages Avail: CASI HC Mills Ltd., Montreal, Quebec.) In AGARD,A02/MF A02 Environmentally Safe and Effective Processes forEnvironmental, safety and health issues, forced Paint Removal (SEE N94-10613 01-31) 9 pagesoperators to search for an alternative paint removal Avail: CASI HC A02/MF A02process. High pressure water jetting and new A review of the Wheat Starch Blasting technology isintegrated paint and stripper systems are Lufthansa's presented. Laboratory evaluations covering Almenanswer to this challenge. AQUASTRIP complies Arc testing on bare 2024-T3 aluminum andwith the specification requirements. In order to magnesium, as well as crack detection on 7075-T6receive approval from airframe manufacturers and bare aluminum, are discussed. Comparisons withauthorities the process has undergone an extensive Type V plastic media show lower residual stresses areresearch program since 1988. An operation window achieved on aluminum and magnesium with wheatwas established, to enable maximum of safety during starch media. Dry blasting effects on the detection ofoperation on metal and composite surfaces. Even cracks confirms better crack visibility with wheatthough AQUASTRIP is a hybrid process and requires starch media versus Type V or Type II plastic media.technological investment, it is well on the way to Testing of wheat starch media in several compositeprove its innovative, ecological and economical test programs, including fiberglass, Kevlar, andcharacter in first large scale applications under graphite-epoxy composites, showed no fiber damage.realistic conditions. Its potential has already been Process developments and production experience atreflected by patents and trademarks, which were the first U.S. aircraft stripping facility are alsoregistered in conjunction with the development of reviewed. Corporate and regional aircraft are beingAQUASTRIP and the vital interest for cooperative stripped in this three nozzle dry blast hangar.work on the process development and other poten-tial utilization. IATA TaskForce: Paintstripping

94N 10628Paint removal and surface cleaning using ice MOOY, THOMAS In AGARD, Environmentallyparticles Safe and Effective Processes for Paint Removal 5 p94N10626 (SEE N94-10613 01-31) 5 pages Avail: CASI HCFOSTER, TERRY; VISAISOUK, S. (Ice Blast A01/MF A02International Corp., Victoria, British Columbia.) In In 1990 the International Air Transport Association

B-14

(IATA) established a task force to stimulate the recycling systems. In addition the facilities have todevelopment of alternatives for chemical stripping of contain proper recovery equipment, because plasticcommercial aircraft. The IATA TaskForce Paintstrip- media can be reused, even 20 times. In recyclingping objectives are: to identify the most promising, systems plastic media is cleaned, too large and toocurrent alternatives for short term implementation; to small particles are removed, hard and magneticprepare a document containing requirements for the particles are removed from reusable media and dustdevelopment of alternatives; to stimulate the infor- is separated from media. In addition to paint strippingmation exchange. After the September 1992 meeting PMB can successfully be used for cleaning of sur-the TaskForce will report back to IATA. The most faces from contamination and to some extent fortangible result of the TaskForce is the IATA Guide- polishing, grinding and roughening. Paint strippinglines containing requirements for the qualification of has been the main application so far, but there maystripping processes. be many other possibilities to apply the method in

the future. However the PMB is not the only newSelectively strippable paint schemes technology for stripping problems. Some interesting94N 10629 investigations were performed for using frozenSTEIN, R.; THUMM, D.; BLACKFORD, ROGER carbon dioxide, soda or high pressure water jet forW. (Imperial Chemical Industries Ltd., Slough, paint stripping.England.) In AGARD, Environmentally Safe andEffective Processes for Paint Removal 4 p (SEE Effects of plastic media blasting on aircraft skinN94-10613 01-31) 4 pages Avail: CASI HC 94N26488AOI/MF A02 CHEN, CHARLES C.; MULLER, MARK;In order to meet the requirements of more environ- REINHARDT, JOHN W. 113 pages Avail: CASImentally acceptable paint stripping processes many HC A06/MF A02different removal methods are under evaluation. The use of methylene chloride chemical solvents inThese new processes can be divided into mechanical aviation paint removal is becoming increasinglyand chemical methods. ICI has developed a paint unacceptable in view of restrictive Environmentalscheme with intermediate coat and fluid resistant Protection Agency (EPA) regulations. A readilypolyurethane topcoat which can be stripped available alternative, plastic media blasting (PMB),chemically in a short period of time with methylene must be examined for its effects on the thin aluminumchloride free and phenol free paint strippers, used as skin material in civilian aircraft. This study

examines the effects of plastic media blasting or theDry stripping as a surface treatment method crack propagation rates of 2024-T3 aluminum in94N17544 alclad of 0.032, 0.040, 0.050 inch thickness, and inNIEMINEN, ILKKA Sponsored by Finnish anodized of 0.032, 0.040, and 0.050 inch thickness. AIndustry, and Technical Research Centre of Finland, technical search was performed for the followingEspoo 72 pages Avail: CASI HC A04/MF AO topics: (1) fatigue crack growth (FCG) rate compari-High environmental and safety standards as well as son between PMB and chemical stripping, (2) effectsuse of new paint and substrate materials have created of heavy particulate contamination on the fatigue lifethe need for developing stripping methods to sub- of aircraft skin, (3) acceptable level of contaminationstitute chemical and mechanical methods and on the in the plastic media, (4) effects of multiple strippingsother hand for expanding the applicability of blasting on FCG, (5) maximum number of strippings allowed,as a surface treatment. Plastic Media Blasting (PMB) and (6) specifications of controlled parameters to(alternatively Dry Stripping System (DSS)) is an safely operate a PMB system. Fatigue crack propa-emerging technology first used in aircraft mainte- gation tests, Almen strip tests, Scanning Electronnance for paint stripping. Traditionally this task is Microscope (SEM) photography, and surface tough-performed by brushing and grinding or by using ness measurements were conducted. The results of thechemical solvents. With plastic media it is possible to technical search and the tests performed are present-remove thick paints with high adhesion without ed, as well as supplementary Alnen strip arc heightdamaging the substrate and even layer by layer. If data. This study also presents an overview of ninesuitable type of plastic media, blasting pressure low alternative aviation paint stripping methods in termsenough, media concentration high enough and on the of paint stripping effectiveness, substrate damage,other right blasting time, blasting distance and environmental impact, health impact, and cost.blasting angle are chosen, the effectiveness of PMBcan be varied to a large extent. In regard to the The effect of mechanical paint stripping onhardness of media plastic particles are situated the fatigue and fracture of thin aluminumbetween some organic materials and shots used in airplane skinsand blasting. Therefore composite materials can be 94N29900treated without damaging the substrate or thin metal AMRO, JOE P. 150 pages Avail: Univ. Microfilmsplates without causing any deformations. The Order No. DA93 11975principle of plastic media blasting equipment is An experimental investigation has been carried out tosimilar to traditional blasting equipment. Never- evaluate the affects of dry stripping (paint removal bytheless the properties of plastic media are different to plastic particle blasting) on aluminum aircraft skinsharder particles used in shot peening resulting in (2024-T3). Analytical procedures were carried out forhigher demands for filtration, ventilation and determining changes in fatigue life and relevant

B-15

fracture resistance parameters such as number of identical to those used in a previous FAA program.cycles required to generate a surface crack of certain Almen strips tests were performed to quantify thelength, crack propagation rate, and number of cycles blast intensity. A fatigue testing program wasto failure while indicating the dependence of these conducted on both the 'as received' and the PMBparameters on the surface condition (morphology). treated material. Reductions in mean fatigue life wereThe surface morphology dependence on deformation, observed for all materials tested after PMB treatment.fracture resistance properties, and defects presented These reductions were statistically significant for theon the surface were characterized using scanning 0.032 alclad and 0.040 anodized specimens.electron microscopy, optical microscopy, and othermodern metallographic techniques. The resultsindicated that all the parameters of plastic media Diode array alternative to paint removalblasting had significant effects on the fatigue life of solid-state cw laserthe specimens. Minor changes in the blasting 94N37203parameters may reveal different results. All fatigue COMASKEY, BRIAN 5 pages Avail: CASI HCsamples were found to exhibit a general decrease in AO1/MF AO0life of 10 to 46 percent after being subjected to four The purpose of this memo is to highlight an alterna-cycles of paint removal. The samples were cyclically tive to the approach for cw laser paint removal. Theloaded to 20,000 cycles then stripped and repainted point to be made is that a direct diode design isfour times; 20,000 cycles represents approximately feasible and can be far more competitive than a solid-5 years of life. The initial stress ratio for loading was state laser based system. Through by-passing the use0.1 with stresses varying from 20 to 65 ksi. of a solid-state laser media, we immediately gain a

factor of about five in system efficiency based onmeasured optical-to-optical efficiencies of our

Evaluation of corrosion protecting properties of average power diode pumped lasers. This permits amodern aircraft paint systems massive reduction in system cooling requirements.94N30420 It should be noted that cooling system size was theTHART, W. G. J.; BOOGERS, J. A. M. Presented greatest concern voiced by Gordon McFadden atat the Aerospace Corrosion Control Symposium, Hobart Lasers with regards to his Nd:YAG laserAmsterdam, Netherlands, 23-25 Mar. 1992 systems operated in field applications. Furthermore,Sponsored by Royal Netherlands Air Force 32 pages with direct diode use far fewer diode packages willAvail: CASI HC A03 be needed to deliver a given amount of wattage onThe flexibility, adhesion and corrosion protecting the target. This will largely eliminate the intimidat-properties of several modern paint systems were ing sticker shock and shorten (proportionally by theexamined. Since paint cracking around fasteners diode count) the required run-to-fail times demandedunder operational conditions usually occurs at low of the system.temperatures, this was examined by tensile testing ofpainted metal strips at -50C. After tensile testing thedegree of paint delamination (loss of adhesion) wasestablished, and cross sections were made to examinethis delamination on a microscopic scale. The corro-sion protecting capability of paint systems was deter-mined by exposing specimens with a precracked paintsystem and crossed scribe lines to an acceleratedcorrosion test (MASTMAASIS). In this investigationthe different paint systems had the same topcoat,Aerodur HF A 132. Since Plastic Media Blasting(PMB) is a potential method for replacing the chemi-cal paint stripping procedure, PMB and variouscleaning operations were also considered.

Fatigue testing of 2024-T3 material after fourcycles of PMB stripping94N3223758 pages Avail: CASI HC A04/MF A01The goal of this program was to determine the effectof plastic media blasting (PMB), an alternative tochemical paint removal, on the fatigue life of2024-T3 aluminum. Two surface treatments,anodized and alclad, of three thicknesses: 0.032 inch,0.040 inch, and 0.050 inch were considered. Anumber of alclad and anodized aluminum panels ofthe alloy and thicknesses specified were subjected tofour cycles of PMB. The blast parameters were

REPORT DOCUMENTATION PAGE

1. Recipient's Reference 2. Originator's Reference 3. Further Reference 4. Security Classificationof Document

AGARD-LS-201 ISBN 92-836-1017-2 UNCLASSIFIED/UNLIMITED

5. Originator Advisory Group for Aerospace Research and Development

North Atlantic Treaty Organization7 rue Ancelle, 92200 Neuilly-sur-Seine, France

6. TitleEnvironmentally Safe and Effective Processesfor Paint Removal

7. Presented at/sponsored by27-28 April 1995 in Lisbon, Portugal,1-2 May 1995 in Eskisehir, Turkey, and4-5 May 1995 in Ottobrunn, Germany

8. Author(s)/Editor(s) 9. Date

Various April 1995

10. Author's/Editor's Address 11. Pages

Various 104

12. Distribution Statement There are no restrictions on the distribution of this document.

Information about the availability of this and other AGARDunclassified publications is given on the back cover.

13. Keywords/Descriptors

Paint removers Ice particle blastingAbrasives Dry icePaint stripping Laser applicationsCleaning agents EvaluationPlastic media blasting Environmental impactStarch media blasting Waste treatmentWheat BiodegradationWater blasting

14. Abstract

Paint stripping and repainting of aircraft surfaces are required periodically during the operatinglifetime of an aircraft. Historically, paint removal has been achieved using chemical strippers,involving materials which contain toxic components and which create hazardous workingconditions. The process generates large amounts of hazardous waste from the chemicals used.Alternative methods for aircraft paint removal are now being investigated within the NATOnations with regard to their environmental safety and effective application. These processesinclude: Plastic Media Blasting, Wheat Starch Dry Media Blasting, Carbon Dioxide PelletBlasting, Sodium Bicarbonate Blasting and Thermal Decomposition Methods (Laser, FlashLamps/Carbon Dioxide). The Lecture Series will review these current state-of-the-art alternativemethods with regard to environmental effects and related health hazards, costs, process controls,practicality of operation and their effects on properties of aircraft structural materials.

NATO -•- OTAN

7 RUE ANCELLE ° 92200 NEUILLY-SUR-SEINE DIFFUSION DES PUBLICATIONS

FRANCE AGARD NON CLASSIFIEES

T616copie (1)47.38.57.99 e T61ex 610 176

Aucun stock de publications n'a exist6 ý AGARD. A partir de 1993, AGARD d6tiendra un stock limit6 des publications associ6es aux cyclesde conferences et cours speciaux ainsi que les AGARDographies et les rapports des groupes de travail, organis6s et publi6s A partir de 1993inclus. Les demandes de renseignements doivent 6tre adressees ý AGARD par lettre ou par fax A l'adresse indiqu~e ci-dessus. Veuillez nepas tWlphoner. La diffusion initiale de toutes les publications de 1'AGARD est effectu6e aupres des pays membres de l'OTAN parl'interm~diaire des centres de distribution nationaux indiqu~s ci-dessous. Des exemplaires suppl~mentaires peuvent parfois etre obtenusaupr~s de ces centres (Ai l'exception des Etats-Unis). Si vous souhaitez recevoir toutes les publications de I'AGARD, ou simplement cellesqui concement certains Panels, vous pouvez demander .6tre inclu sur la liste d'envoi de 1'un de ces centres. Les publications de I'AGARDsont en vente aupr~s des agences indiqu~es ci-dessous, sous forme de photocopie ou de microfiche.

CENTRES DE DIFFUSION NATIONAUXALLEMAGNE ISLANDE

Fachinformationszentrum, Director of AviationKarlsruhe c/o FlugradD-76344 Eggenstein-Leopoldshafen 2 Reykjavik

BELGIQUE ITALIECoordonnateur AGARD-VSL Aeronautica MilitareEtat-major de la Force adrienne Ufficio del Delegato Nazionale all'AGARDQuartier Reine Elisabeth Aeroporto Pratica di MareRue d'Evere, 1140 Bruxelles 00040 Pomezia (Roma)

CANADA LUXEMBOURGDirecteur, Services d'information scientifique Voir BelgiqueMinistbre de la Defense nationale NORVEGEOttawa, Ontario KIA 0K2 Norwegian Defence Research Establishment

DANEMARK Attn: BiblioteketDanish Defence Research Establishment P.O. Box 25Ryvangs A116 1 N-2007 KjellerP.O. Box 2715 PAYS-BASDK-2100 Copenhagen 0 Netherlands Delegation to AGARD

ESPAGNE National Aerospace Laboratory NLRINTA (AGARD Publications) P.O. Box 90502Pintor Rosales 34 1006 BM Amsterdam28008 Madrid PORTUGAL

ETATS-UNIS Forga A~rea PortuguesaNASA Headquarters Centro de Documentaqi5o e InformagdoCode JOB-1 AlfragideWashington, D.C. 20546 2700 Amadora

FRANCE ROYAUME-UNIO.N.E.R.A. (Direction) Defence Research Information Centre29, Avenue de la Division Leclerc Kentigern House92322 Chdtillon Cedex 65 Brown Street

GRECE Glasgow G2 8EXHellenic Air Force TURQUIEAir War College Milli Savunma Ba~kanligi (MSB)Scientific and Technical Library ARGE Dairesi Balkanligi (MSB)Dekelia Air Force Base 06650 Bakanliklar-AnkaraDekelia, Athens TGA 1010

Le centre de distribution national des Etats-Unis ne detient PAS de stocks des publications de I'AGARD.D'6ventuelles demandes de photocopies doivent 6tre formul~es directement aupr~s du NASA Center for AeroSpace Information (CASI)

Jl'adresse ci-dessous. Toute notification de changement d'adresse doit 6tre fait 6galement auprbs de CASI.

AGENCES DE VENTE

NASA Center for ESA/Information Retrieval Service The British LibraryAeroSpace Information (CASI) European Space Agency Document Supply Division

800 Elkridge Landing Road 10, rue Mario Nikis Boston Spa, WetherbyLinthicum Heights, MD 21090-2934 75015 Paris West Yorkshire LS23 7BQEtats-Unis France Royaume-Uni

Les demandes de microfiches ou de photocopies de documents AGARD (y compris les demandes faites auprbs du CASI) doiventcomporter la d6nomination AGARD, ainsi que le num6ro de sdrie d'AGARD (par exemple AGARD-AG-315). Des informationsanalogues, telles que le titre et la date de publication sont souhaitables. Veuiller noter qu'il y a lieu de sp6cifier AGARD-R-nnn etAGARD-AR-nnn lors de la commande des rapports AGARD et des rapports consultatifs AGARD. respectivement. Des r~f~rencesbibliographiques compl~tes ainsi que des r~sumn6s des publications AGARD figurent dans les journaux suivants:

Scientific and Technical Aerospace Reports (STAR) Government Reports Announcements and Index (GRA&I)publi6 par la NASA Scientific and Technical publi6 par le National Technical Information ServiceInformation Division SpringfieldNASA Headquarters (JTT) Virginia 22161Washington D.C. 20546 Etats-UnisEtats-Unis (accessible 6galement en mode interactif dans la base de

donn6es bibliographiques en ligne du NTIS, et sur CD-ROM)

Imprimý par le Groupe Communication Canada

45, boul. Sacrt-Cawur, Hull (Qudbec), Canada KJA 0S7

NATO OTAN

7 RUE ANCELLE - 92200 NEUILLY-SUR-SEINE DISTRIBUTION OF UNCLASSIFIED

FRANCE AGARD PUBLICATIONS

Telefax (1)47.38.57.99 e Telex 610 176

AGARD holds limited quantities of the publications that accompanied Lecture Series and Special Courses held in 1993 or later, and ofAGARDographs and Working Group reports published from 1993 onward. For details, write or send a telefax to the address given above.Please do not telephone.AGARD does not hold stocks of publications that accompanied earlier Lecture Series or Courses or of any other publications. Initialdistribution of all AGARD publications is made to NATO nations through the National Distribution Centres listed below. Further copies aresometimes available from these centres (except in the United States). If you have a need to receive all AGARD publications, or just thoserelating to one or more specific AGARD Panels, they may be willing to include you (or your organisation) on their distribution list.AGARD publications may be purchased from the Sales Agencies listed below, in photocopy or microfiche form.

NATIONAL DISTRIBUTION CENTRESBELGIUM LUXEMBOURG

Coordonnateur AGARD- VSL See BelgiumEtat-major de la Force adrienneQuartier Reine Elisabeth NETHERLANDSRue d'Evere, 1140 Bruxelles Netherlands Delegation to AGARD

National Aerospace Laboratory, NLRCANADA P.O. Box 90502Director Scientific Information Services 1006 BM AmsterdamDept of National DefenceOttawa, Ontario KIA 0K2 NORWAY

DENMARK Norwegian Defence Research EstablishmentDanish Defence Research Establishment Attn: BiblioteketRyvangs A116 1 P.O. Box 25P.O. Box 2715 N-2007 KjellerDK-2100 Copenhagen 0 PORTUGAL

FRANCE Forga A6rea PortuguesaO.N.E.R.A. (Direction) Centro de Documentaqdo e Informaqdo29 Avenue de la Division Leclerc Alfragide92322 Chntillon Cedex 2700 Amadora

GERMANY SPAINFachinformationszentruh INTA (AGARD Publications)Karlsruhe Pintor Rosales 34D-76344 Eggenstein-Leopoldshafen 2 28008 Madrid

GREECEHellenic Air Force TURKEYAir War College Milli Savunma Ba§kanliji (MSB)Scientific and Technical Library ARGE Dairesi Ba~kanliji (MSB)Dekelia Air Force Base 06650 Bakanliklar-AnkaraDekelia, Athens TGA 1010 UNITED KINGDOM

ICELAND Defence Research Information CentreDirector of Aviation Kentigern House/o Flugrad 65 Brown Street

Reykjavik Glasgow G2 8EXITALY

Aeronautica Militare UNITED STATESUfficio del Delegato Nazionale all'AGARD NASA HeadquartersAeroporto Pratica di Mare Code JOB-100040 Pomezia (Roma) Washington, D.C. 20546

The United States National Distribution Centre does NOT hold stocks of AGARD publications.Applications for copies should be made direct to the NASA Center for AeroSpace Information (CASI) at the address below.

Change of address requests should also go to CASI.

SALES AGENCIESNASA Center for ESA/Information Retrieval Service The British Library

AeroSpace Information (CASI) European Space Agency Document Supply Centre800 Elkridge Landing Road 10, rue Mario Nikis Boston Spa, WetherbyLinthicum Heights, MD 21090-2934 75015 Paris West Yorkshire LS23 7BQUnited States France United KingdomRequests for microfiches or photocopies of AGARD documents (including requests to CASI) should include the word 'AGARD'and the AGARD serial number (for example AGARD-AG-315). Collateral information such as title and publication date isdesirable. Note that AGARD Reports and Advisory Reports should be specified as AGARD-R-nnn and AGARD-AR-nnn,respectively. Full bibliographical references and abstracts of AGARD publications are given in the following journals:

Scientific and Technical Aerospace Reports (STAR) Government Reports Announcements and Index (GRA&I)published by NASA Scientific and Technical published by the National Technical Information ServiceInformation Division SpringfieldNASA Headquarters (JTT) Virginia 22161Washington D.C. 20546 United StatesUnited States (also available online in the NTIS Bibliographic

Database or on CD-ROM)

LPrinted by Canada Communication Group

45 Sacrý-Cceur Blvd., Hull (Qudbec), Canada KJA 0S7

ISBN 92-836-1017-2

Documents

AGARD-LS-201 AGALC,&RD - dtic.mil · Processes for Paint Removal (Procedes efficaces et ecologiques pour l'enlevement des peintures) This publication was prepared at the request of