Disclosure to Promote the Right To Information

Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public.

इंटरनेट मानक

“!ान $ एक न' भारत का +नम-ण”Satyanarayan Gangaram Pitroda

“Invent a New India Using Knowledge”

“प0रा1 को छोड न' 5 तरफ”Jawaharlal Nehru

“Step Out From the Old to the New”

“जान1 का अ+धकार, जी1 का अ+धकार”Mazdoor Kisan Shakti Sangathan

“The Right to Information, The Right to Live”

“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता है”Bhartṛhari—Nītiśatakam

“Knowledge is such a treasure which cannot be stolen”

“Invent a New India Using Knowledge”

है”ह”ह

IS 11232 (1985): Chromate conversion coatings on aluminium[MTD 24: Corrosion Protection]

IS : 11232 - 1985

Indian Standard

SPECIFICATION FOR

CHROMATE CONVERSION COATINGS ON ALUMINIUM

Corrosion Protection Sectional Committee, SMDC 29

Chairman Representing

SHRIC. P.h Naval Chemical & Metallurgical Laboratory, Bombay

MemJers

Dlt S.N. PANDEY ( Alternate I to Shri C. P. DC )

Dn M. B. Dss~navlc~ ( Alternate II to Shri C. P. De )

DR M. BALAKRIRHNAN Pyrene-Rai Metal Treatments Ltd, Bombay Smtr A. D. INAMDAR ( Ahrnate)

SHRI B. G~SWAMY l‘ata Engineering & Locomotive Co Lid, Jamshcdpur

SHRI N. K. NAO ( Allernafe ) SHRI V. K. JAIN Oil 8: Natural Gas Commission, Dehra Dun

SHRI K. S. BIIATIA ( Altermzte ) JOINT DIRECTOI~ STANUAI~US Research Designs & StandaIds Organization,

( CARRIAQE 1 ) Lucknow DY DIRECTOR ( MET-~ ) ( Alternate )

SHRI R. L. KAPOOIL Ministry of Shipping & Transport ( Roads \\‘mg ) DR V. M. KI~:LKAR Engineers India Ltd, New Delhi DR M. D. MAHESRWAI~I The Indian Tube Co Ltd, Jamshedpur

SHIU K. R. NATARAJ~N ( Alternate ) SHILI K. P. MUKH~I~JICE National Metallurgical Laboratory, Jamshedpur

DR INDEI~ SINGH ( Alternate ) SHI~I R. C. MUKHERJEF. Steel Authority of India ( Rourkela Steel Plant ),

Rourkela SHRI NIRANJAN DASH ( Alternate )

SIIKI R. P. NACAR Tata Consulting Engineers, Bombay SHRI D. B. MEHTA ( Alternate )

SHRI M. M. NATH Lloyds Tar Products Ltd, New Delhi SHRI L. PvOAZHENTHY Indian Lead Zinc Information Centre, New Delhi DR K. S. RAJA~OPALAN Central Electra-chemical Research Institute,

Karaikudi Dlt K. BALAKRISIINAN ( Alternate )

SIIRI S. RAMAJAY~M Indian ‘I’elephone Industries Ltd, Bangalore SHRI N. S. NANJVNI~A RAN ( Alternote )

( Continued on page 2 )

@ Copyright 1985

INDIAN STANDARDS INSTITUTION This publication is protected under the Indian Copyright Act ( XIV of 1957 ) and reproduction in whale or in part by any means except with written permission of the publisher shall be deemed to be an infringement of copyright under the said Act.

IS:11232-1985

( Continued from page 1 )

DR N. I?. RAO SI~SI J. HANERJEE ( Alternate )

DR SANI~IP KUMALC ROY SHRI A. K. SAHTJ

SHRI D. K. ROY ( Alternate ) SIJRI s. R. SaIIu

Repesenting

Ministry of Dcf’ence ( R & D )

Indian Explosives Ltd, Rishra National ?‘est House, Calcutta

SHW K. ANN.&IA~L ( Alternate )

Steel Authority of India Ltd ( Bokaro Steel Plant ), Bokaro Steel City

SHIU D. SEN SHKI D. SIN GTJPT~ SIIICI 1>. K. SINOl1

Ministry of Defence ( DGOF ) Oil India Ltd, Calcutta Bharat Heavy Electricals Ltd

SJIEI R. M. SINGHAL ( Alternate I ) SHIU R. N. MISHRA ( Alternate II )

SRIU K. S. SIUNIVASAN National Buildings Organization, New Delhi SJXIU S~IAWI KANT ( Alternate )

SHRI G. K. T2\~crax Fibreglass Pilkington, Bombay Strtc~ A. S~nulw ( Alternate )

DB K. M. Veitnra SIIRI R. K. SINIIA ( Alternate )

Fertilizer ( P & D ) India Ltd, Sindri

SHJLI I<. ~<A<:IIAVENURAN, Director General, IS1 ( Ex-o$cio Member ) Director ( Strut & Met )

Secretary

SI~I~I B. K. MU~HOPADIIYAY Assistant Director ( Metals ), IS1

.

IS : 11232 - 1985

Indian Standard

SPECIFICATlON FOR CHROMATE CONVERSION COATINGS

ON ALUMINIUM

0. FOREWORD

0.1 This Indian Standard was adopted by the Indian Standards Institution on 14 March 1985, after the draft finalized by the Corrosion Protection Sectional Committee had been approved by the Structural and Metals Division Council.

0.2 Aluminium and aluminium alloys are chromate treated in order to retard corrosion; as a base for organic films including paints, plastics and adhesives; and as a protective coating having a low electrical contact impedance/resistance.

0.3 For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accord- ance with IS : 2- 1960*. The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard.

1. SCOPE

1.1 This standard specifies requirements relating to rinsed chromate conversion coatings on aluminium alloys. It is intended to give protection against corrosion and to act as a base for other coatings. Coatings that require no rinsing after application are not covered by this standard.

2. METHOD OF APPLICATION OF CHROMATE COATINGS

2.1 Chromate conversion coatings are applied by dipping, spraying and brushing. Chromating solutions arc usually acidic and contain hexavalent chromium salts together with other salts which may be varied

*Rules for rounding off numerical values ( rwised ).

IS:11232 - 1985

to affect the appearance and hardness of the film. The colour of the film, and, therefore, the type of conversion coating depends on the composition of the chromating solution, hut it is also affected by the /JH and temperature, the duration of the treatment, and the nature and surface condition of the alloy being treated.

2.2 These coatings receive a final water rinse. If hot water is used as the final rinse after the chromating process, it is essential that the time of rinsing should be kept as short as possible in oder to prevent the dis- solution of the liexavalent chromium. The drying of the coating shall be carried out at a temperature not exceeding 60°C to prevent cracking due to dehydration of the chromate coating.

3. CLASSIFICATION

3.1 Finishes can be applied ranging in colour from brown, thick coatings providing maximum corrosion protection to yellow, intermediate thickness coatings suitable as an organic film base or to colourless, thin coatings suitable for low electrical contact resistance.

3.2 Finishers can seldom guarantee to supply exact shades of colour with chromate conversion coatings. If it is necessary to have exact shades of colour, it is possible to dye chromate coatings to obtain a wide range of coIours, but they can only be expected to give an order of added corrosion resistance similar to that provided by the undyed coatings. It should be noted that colour and colour uniformity will be somewhat between one alloy and other and from a polished surface to an etched surface. Iridescence and variations in colour density from one area of the surface to another are normal and shall not be considered a sign of poor quality.

The finishes are divided into three classes and their.most important characteristics are as follows:

ClllSS Appearance Coating Weight Corrosion Protection

1. Yellow to brown More than Maximum corrosion resistance 0.4 g/m2 generally ussd as final finish

2. Colourless to 0.1 to Moderate corrosion resistance, yellow O-4 g/m2 used as a paint base and for

bonding to rubber

3. Colourless Less than Decorative, 0.1 g/m2

slight corrosion resistance low electrical con- tact resistance

4,

IS : 11232 - 1985

4. REQUIREMENTS

4.1 General - Chromate conversion coatings harden with age by gradual dehydration. They should, therefore, be handled carefully for the first 24 hours after treatment, and any tests ( including corrosion tests ) shall be deferred until the expiry of that period.

4.1.1 The basis metal should be free from visible defects, such as blisters, gouges, non-metallic inclusions, pits or porosity which will be detrimental to the appearance and performance of the film.

4.2 Adhesion - The coatings shall be adherent and non-powdery. When specified, the chromate conversion coating shall pass the organic coating adhesion test in Appendix A.

4.3 Corrosion Resistance - When subjected to the neutral salt spray test ( see IS : 9844-l 98 L * ), two separate panels of the coating shall with- stand exposure for the hours shown in Table 1, without giving evidence, to the unaided eye, of more than a total of eight isolated spots or pits, not larger than 1 mm in diameter. Each individual panel shall not have more than five isolated spots or pits, none larger than 1 mm in diameter on their respective surfaces. Spots within 10 mm of the edges of the panels are not counted.

TABLE 1 EXPOSURE TINIE

COATINO NON-I&AT-TREATABLE HEAT-TREATABLE ALLOYS CAST ALLOYS WITH CLASS WROLEKT ALLOYS AND CAST ALLOYS WITH A A NOMWAL SILIOON

NOMINAL SILICON CON- CONTENT OF MORE TENT LESS THAN 1 PERCENT THAN 1 PERCENT

Hours Hours Hours

1 500 336 48

2 250 168 24

3 168 120 12

Nom - The exposure times are indicative of the relative corrosion resistance of the various coating classes on the different alloys, but no direct relationship exists between performance in the neutral salt spray test and performance in service.

-_--

4.4 Coating Weight - The weight of the coating per unit area of coated surface shall conform to the values given in 3.2 when tested in accordance with the method given in IS : 9838-1981t.

‘Methods of testing corrosion resistance of electroplated and anodized aluminium coatings by neutral salt spray test.

tMethod for determination of coating mass per unit area of conversion coatings on metallic materials by gravimctric method.

5

IS : 11232 - 1985

4.4.1 It should be recognized that heavier coating weights do not always provide better performance, particularly when using the coating for an organic film or adhesive base.

4.4.2 The presence of a Class 3 coating shall be confirmed by the spot test ( see Appedix B ).

4.5 Test Specimens and Sampling

4.5.1 Test specimens should be of the same alloy and surface condition as the articles represented. Panels should be 75 x 250 x 0.8 mm.

4.5.2 The sampling plan for testing the coatings shall be as agreed to between the interested parties.

APPENDIX A

( Clause 4.2 )

ORGANIC COATING ADHESION TEST

A-l. SCOPE

A-l.1 The chromated specimen shall be coated with the organic coating system specified by the purchaser. The coating shall be between 25 and 125 micrometres in thickness.

A-2. APPARATUS

A-2.1 Cutting Tool - Sharp razor blade, scalpel, knife or other cutting device having a cutting edge angle between 15 and 30 degrees that will make either a single cut or several cuts at once. It is of particular importance that the cutting edge be in good condition.

A-2.2 Cutting Guide - If cuts are made manually ( as opposed to a mechanical apparatus ) a steel or other hard metal straightedge or template to ensure straight cuts.

A-2.3 Rule - Rule graduated in 0.5 mm.

A-2.4 Tape - Semi-transparent pressure sensitive tape, 25 mm wide with an adhesive strength of 40 & 2.8 g/mm width. The tape shall be capable of maintaining that strength f 5 percent for 1 year. An adhesive composed of resin and 100 percent crude rubber is reported to meet these characteristics. The backing of the tape may consist of fibre-reinforced cellulose acetate, unplasticized polyvinyl chloride, or polyester film.

A-2.5 Rubber Eraser - On the end of a pencil.

6

IS : 11232 - 1985

A-2.6 Illumination - Normal reading light.

A-2.7 Magnifying Glass - 2 x to 10 X.

A-3. PROCEDURE

A-3.1 Place the coated specimen ( panel or part ) under the magnified glass with suitable illumination. For organic coatings up to 50 pm thick. Make eleven parallel cuts 1 mm apart. The cuts should penetrate through to the base. The cuts shall be 20 mm long. Brush the area with a soft brush or tissue to remove any flakes or loose particles.

Make an additional number of cuts at 90” to and centred on the original cuts. Brush the area as before and inspect the incisions to make certain that all have reached the base material.

Remove two complete laps of tape from the roll and discard. Remove an additional length at a steady rate and cut a piece about 75 mm long. Place the centre of the tape over the grid of cuts and smooth into place with a finger. To ensure good contact with the film rub the tape firmly with the eraser on the end of a pencil. Observe for uniform contact.

Within 90 f 30 s of application, remove the tape by grasping the free end rapidly and smoothly pulling it off as close to an angle of 180” as possible.

A-3.2 Inspect the grid area for removal of coating from the substrate using the illuminated magnifier. Rate the adhesion according to the following scale:

5.

4.

3.

2.

1.

0.

The edges of the cuts are completely smooth; none oft he squares of the lattice are detached.

Small flakes of the coating are detached at the intersections; less than 5 percent of the area is affected.

Small flakes of the coating are detached along edges and at intersections of cuts. The area affected is 5 to 10 percent of the lattice. The coating has flaked along the edges and on parts of the squares. The area affected is 15 to 33 percent of the lattice.

The coating has flaked along the edges of cuts in large ribbons and whole squares have detached. The area affected is 35 to 65 percent of the lattice.

Flaking and detachment worse than Grade 1.

A-3.3 Repeat the test in two other locations on the panel or part.

A-4. REPORT

A-4.1 Report the number of tests, their mean and range.

7

IS : 11232 - 1985

APPENDIX B ( Clause 4.4.2 )

SPOT TEST FOR CHROMATE CONVERSION COATING

B-l. OUTLINE OF THE TEST

B-l.1 A solution of ferric nitrate, hydrochloric acid and potassium ferricyanide reacts with untreated aluminium to give blue green colour. Chromated aluminium takes time to develop this colour, and this time depends upon the thickness of chromate coating or film formed.

B-2. REAGENTS

B-2.1 Solution I - Dissolve 2 g of ferric nitrate ( AR ) in 20 ml of reagent grade hydrochloric acid and dilute with 473 ml of distilled water.

B-2.2 Solution II - Dissolve 2 g of potassium ferricyanide in 473 ml of distilled water.

B-2.3 The two solutions should be stored separately in brown bottles and mixed together in equal volumes before use. The storage life of the mixed solution is limited to only 7 days.

B-3. PROCEDURE

B-3.1 Take a piece of untreated aluminium plate, without any chromate conversion coating and remove the oxide layer by dipping it for about half a minute in 2 N sodium hydroxide solution. This shall be used as a reference plate for comparison purposes.

B-3.2 Place a drop of mixed solution ( see B-2.3 ) by means of a glass rod on both, the untreated plate, and the treated aluminium plate with chromate conversion coating. The solution will turn blue green immediately on the untreated plate, while the time to change the colour to blue green on the treated plated will vary with the thickness of conversion coating.

8