AR 500/1000 Rheometer Manual

Table of Contents

TA INSTRUMENTS AR RHEOMETERS i

AR 500/1000Rheometers

Hardware Manual

PN 500017.001 Rev. B (Text and Binder)PN 500017.002 Rev. B (Text Only)Issued January 2000

Table of Contents

ii TA INSTRUMENTS AR RHEOMETERS

©1996, 2000 by TA Instruments109 Lukens DriveNew Castle, DE 19720

Notice

The material contained in this manual isbelieved adequate for the intended use of thisinstrument. If the instrument or procedures areused for purposes other than those specifiedherein, confirmation of their suitability must beobtained from TA Instruments. Otherwise, TAInstruments does not guarantee any results andassumes no obligation or liability. Thispublication is not a license to operate under or arecommendation to infringe upon any processpatents.

TA Instruments thermal analysis and rheologysoftware, including operating system, module,data analysis, and utility software, and theirassociated manuals are proprietary and copy-righted by TA Instruments, Inc. Purchasers aregranted a license to use these software programson the instrument with which they werepurchased. These programs may not beduplicated by the purchaser without the priorwritten consent of TA Instruments. Eachlicensed program shall remain the exclusiveproperty of TA Instruments, and no rights orlicenses are granted to the purchaser other thanas specified above.

NOTE: The operation and proceduresassociated with the AR 500 and AR 1000Rheometers are essentially identical. Onlythe ranges of operation are different (seespecifications on page 4-2). Therefore, theterm “AR Rheometers” as used throughoutthis manual, refers to both instruments.

Table of Contents

TA INSTRUMENTS AR RHEOMETERS iii

Table of Contents

Chapter 1: Introducingthe AR Rheometers ................................ 1-1

Overview.................................................. 1-1

Safety and EMCConformity Specifications ....................... 1-2

Lifting and Carrying Instructions...... 1-3Electrical Safety ................................ 1-4

Wiring Instructions (UK only).... 1-4Usage Instructions ............................. 1-5

Maintenance and Repair .......................... 1-6

Chapter 2: Description of theAR Rheometers ...................................... 2-1

Overview.................................................. 2-1

A Brief History of Controlled-Stress Rheometers.................................... 2-1

TA Instruments AR Rheometers.............. 2-3Schematics of the AR Rheometer ..... 2-4Instrument Components .................... 2-6

Chapter 3: TechnicalDescriptions ............................................ 3-1

Overview.................................................. 3-1

The Air Bearing ....................................... 3-1Rotational Mapping........................... 3-3

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iv TA INSTRUMENTS AR RHEOMETERS

Auto Gap Set Mechanism ........................3-4Closing the Gap .................................3-4Thermal Compensation......................3-5

The Peltier Plate .......................................3-5

Normal Force Transducer (optional)........3-8

Chapter 4: TechnicalSpecifications ..........................................4-1

Overview ..................................................4-1

Specifications ...........................................4-1

Chapter 5: Installation..........................5-1

Overview ..................................................5-1

Removing the Packaging andPreparing for Installation..........................5-1

Installation Requirements.........................5-3

Connecting the System Together .............5-5Connecting the Rheometer tothe Electronics Control Box ..............5-5Connecting the Computer tothe Electronics Control Box ..............5-6Connecting the Water Bath................5-7

Leveling the Rheometer ...........................5-8

Checking Your System.............................5-9

Shut-down Procedure .............................5-10

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TA INSTRUMENTS AR RHEOMETERS v

Chapter 6: Measuring Systems............ 6-1

Overview.................................................. 6-1

General Description ................................. 6-2Geometry Materials........................... 6-2

Stainless Steel ............................. 6-2Aluminum ................................... 6-3Plastic.......................................... 6-3

Cone and Plate ......................................... 6-4

Parallel Plate ............................................ 6-6

Concentric Cylinders ............................... 6-8

Using the Stress and Shear RateFactors.................................................... 6-11

Choosing the Best Geometry ................. 6-12Cone and Plate/Parallel PlateSystems............................................ 6-12

Angles ....................................... 6-13Diameters .................................. 6-14Material..................................... 6-15

Preventing Solvent Evaporation ............ 6-16

Preventing Slippage atSample/Geometry Interface ................... 6-17

Chapter 7: AR RheometerEnhancements/Options.......................... 7-1

Overview.................................................. 7-1

Normal Force Transducer (optional) ....... 7-1

Gap Setting Validation (optional)............ 7-3

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vi TA INSTRUMENTS AR RHEOMETERS

Inertial Correction ....................................7-4

Air Bearing Friction Correction ...............7-6Determining the CorrectionFactor .................................................7-6

Chapter 8: How Do I... ..........................8-1

Overview ..................................................8-1

...Clean theFilter Regulator Assembly?......................8-2

...Remove the Air Bearing Clamp? ..........8-4

...Attach a Geometry?...............................8-5

..Set Up the ConcentricCylinder System? .....................................8-6

Changing the Cup Size ......................8-7Controlling Temperature with aConcentric Cylinder System..............8-8

...Ensure the Sample is LoadedCorrectly? .................................................8-9

...Calibrate the Rheometer? ....................8-11

Chapter 9: Do’s and Don’ts..................9-1

Overview ..................................................9-1

Do .............................................................9-1

Don’t.........................................................9-2

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TA INSTRUMENTS AR RHEOMETERS vii

Appendices

Appendix A: Useful Information........ A-1

Moments of Inertia.................................. A-1Calculations forMoments of Inertia ........................... A-2

Cone........................................... A-2Cylinder ..................................... A-2

Appendix B: Symbols and Units......... B-1

Appendix C: GeometryForm Factors ......................................... C-1

Cone/Plates ............................................. C-1

Dimensions ............................................. C-2

Appendix D: LCD DisplayMessages ................................................ D-1

Initializing Transducer............................ D-1

Pressure Too Low................................... D-1

Peltier Overheat ...................................... D-1

Index.........................................................I-1

Table of Contents

viii TA INSTRUMENTS AR RHEOMETERS

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TA INSTRUMENTS AR RHEOMETERS 1–1

CHAPTER 1: Introducing the ARRheometers

OverviewIntroducing the TA Instruments AR (and AR-Nwith Normal Force) Rheometers—controlledstress/controlled rate rheometers capable ofhandling many different types of samples, usinga range of geometry sizes and types.

This manual relates to all hardware aspects ofthe AR and AR-N Rheometers. For completeinformation on the operation of the instrument,you may also have to refer to the relevantsoftware manuals supplied with the instrument.

Should you find that something in this manual isunclear, or if you feel that certain informationshould be added, please do not hesitate tocontact us directly at our Leatherhead, UKoffice. The numbers you should use are:

Tel: +44-1372-360363Fax: +44-1372-360135

Alternatively, please contact your local officedirectly or speak to your area salesrepresentative.

This chapter describes some important safetyinformation. Please read this informationthoroughly before proceeding.

Introduction

1–2 TA INSTRUMENTS AR RHEOMETERS

Safety and EMC ConformitySpecifications

In order to comply with the European CouncilDirectives, 73/23/EEC (LVD) and 89/336/EEC(EMC Directive), as amended by 93/68/EEC;the AR has been tested to the followingspecifications:

• Safety:

EN 61010-1:1993

• Emissions:

EN 55011: 1991, CISPR 11:1990 Group 1Class B (30–1000 MHz) Radiated

EN 55011: 1991, CISPR 11:1990 Group 1Class B (0.15–30 MHz) Conducted

• Immunity:

EN 50082-1: 1992, ElectromagneticCompatibility-Generic immunity standardPart 1. Residential, commercial, and lightindustry.

• IEC 801-2: 1991, ESD.

• IEC 801-3: 1984, Radiated RF Immunity.

• IEC 801-4: 1988, EFT/B. Electrical fasttransients/burst.

CAUTION: This instrument must only beconnected to an earthed (grounded) powersupply. If this instrument is used with anextension lead, the earth (ground)continuity must be maintained.

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Lifting andCarrying Instructions

Please follow these recommendations when youmove or lift the instrument and its accessories:

• When moving the rheometer, the air bearingclamp should always be in place, ensuringthat the bearing cannot be moved. SeeChapter 5 for information on the air bearingclamp and how it is attached.

• Use two hands to lift the instrument, keeping

your back straight as you lift, to avoidpossible strain on your back. You may wantto use two people to lift the instrument.

• Treat the AR with the same degree of care

you would take with any scientificlaboratory instrument.

Introduction


Electrical Safety

Before connecting the main electrical supply,check the voltage rating against the voltageselector switch.

Supply Voltage 230 Vac 5 amps120 Vac 10 amps

Frequency 50 to 60 Hz

Power 800 Vac

Always unplug the instrument before performingany maintenance.

WARNING: Because of the high voltagesin this instrument, maintenance andrepair of internal parts must beperformed by TA Instruments, Inc. orother qualified service personnel only.

Wiring Instructions(UK only)

The mains leads supplied with this instrumentare color coded in accordance with the followingcode:

Green and yellow Earth (Ground)Blue NeutralBrown Live

Please seek advice from your local TA officeoutside of UK.

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Usage Instructions

Before connecting the rheometer to auxillaryequipment, you must first disconnect theinstrument from the main power supply and readthe Installation chapter. Safety of the rheometermay be impaired if the instrument:

• shows visible damage• fails to perform the intended measurements• has been badly stored• has been flooded with water• has been subjected to severe transport

stresses.

Introduction


Maintenanceand Repair

Adjustment, replacment of parts, maintenanceand repair should be carried out by trained andskilled TA personnel only. The instrumentshould be disconnected from the mains beforeremoval of the cover.

WARNING: The cover has a tamperproofseal and should only be removed byauthorized personnel. Once the cover hasbeen removed, live parts are accessible.Both live and neutral supplies are fused,therefore, a failure of a single fuse couldstill leave some parts live. Theinstrument contains capacitors that mayremain charged even after beingdisconnected from the supply.

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CHAPTER 2: Description of theAR Rheometers

OverviewThis chapter describes the main components ofthe rheometer and provides technicalinformation on performance and design. Pleaseread this chapter thoroughly to become familiarwith the nomenclature used throughout thismanual.

A Brief Historyof Controlled-StressRheometers

Sir Isaac Newton (c.1700) was the first toformulate a mathematical description of a fluid’sresistance to deform or flow when a stress wasapplied to it. He described this resistance as theviscosity. It is mathematically described as theshear stress divided by the shear rate or strain.Until Couette developed the first rotationalviscometer (c.1890), viscosity was measuredusing stress driven (gravity) flow. Many oftoday’s techniques still use this principle, suchas flow cups, U-tubes, capillaries, etc.

The development of an electromechanicalinstrument, using synchronous motors, and theelectronic versions, using controlled speedservo-motors, made controlled rate the widelyused technique for versatile rheologicalinstruments for many years.

Description


The first controlled-stress instrument, capable ofcontinuous rotation, was developed by Davis,Deer, and Warburton (1968 J.Sci. Instr. 2, I,933-6) at the London School of Pharmacy. Thisinstrument used an air turbine and an air bearing.In the early 1970’s, a second generation ofinstruments was developed, using an inductionmotor drive to avoid the problems associatedwith the air turbine. These, however, wererestricted to a maximum torque of5000 µNm.

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TA InstrumentsAR Rheometers

The TA Instruments AR Rheometers are fifth-generation instruments, which functions aseither a controlled-stress or controlled-rateinstrument.

The rheometers are designed to fulfill therequirements of measurement as implied by thefull meaning of the term rheology—defined asthe “study of the deformation and flow ofmatter.”

Deformation is measured in the non-destructiveregion of elastic or visco-elastic deformation.This can give invaluable information concerningthe microscopic interactions in the test material,as well as measuring the shear stress/shear raterelationships at higher stresses.

In the controlled-stress technique, the stress canbe applied and released at will, and the actualbehavior of the sample can be measured directly.This is not usually possible with conventionalcontrolled-shear rate instruments. In addition,most real-life situations can be simulated moreaccurately using controlled-stress measurements.

Description


Schematics ofthe AR Rheometer

Figure 2.1 shows a schematic of the front of therheometer. Figure 2.2, on the next page showsthe rear.

Figure 2.1The AR Rheometers (Front)

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Figure 2.2The AR Rheometers (Rear)

Description


Instrument Components

The instrument consists of a main unit mountedon a cast metal stand, with the electronic controlcircuitry contained within a separate electronicscontrol box. Figure 2.3 shows the front and rearof the electronics control box.

Figure 2.3Electronics Control BoxFront (Left) and Rear (Right)

The AR Rheometer contains an electronically-controlled induction motor with an air bearingsupport for all the rotating parts. The drivemotor is equipped with a hollow spindle, with adetachable draw rod inserted through it. The

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draw rod has a screw-threaded section at thebottom, which allows the geometry to besecurely attached.

The measurement of angular displacement isdone by an optical encoder device. This candetect very small movements down to 0.6 µrad.The encoder consists of a non-contacting lightsource and photo-cell, arranged either side of atransparent disc attached to the drive shaft. Onthe edge of this disc are extremely fine, accuratephotographically-etched radial lines. Therefore,this is a diffraction grating. There is also astationary segment of a similar disc between thelight source and encoder disc. The interaction ofthese two discs results in diffraction patterns thatare detected by the photo cell. As the encoderdisc moves when the sample strains under stress,these patterns change. The associated circuitryinterpolates and digitizes the resulting signal toproduce digital data. This data is directly relatedto the angular deflection of the disc, and,therefore, the strain of the sample.

The main electronics are housed in a separatecontrol box. The interplay between therheometer/electronics and controller areexplained in more detail in Chapter 5.)

Temperature control is achieved in the standardconfiguration via a Peltier plate system. This isexplained in more detail in Chapter 3.

Description


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CHAPTER 3: Technical Descriptions

OverviewIn order to fully utilize the advanced capabilitiesavailable with the AR Rheometers, some of theimportant components require a more detailedexplanation. This chapter describes in detail thedesign and functions of the:

• Air bearing• Auto gap set device• Peltier plate• Normal force transducer• Independent gap validation

The Air Bearing

As its name suggests, an air bearing uses air asthe lubricating medium. This allows virtuallyfriction-free application of torque.

The design of an air bearing is a compromisebetween several characteristics such as airconsumption, friction, stiffness, and tolerance tocontamination and misuse.

The amount of air consumed is related to thepressurized bearing clearance. To minimize airconsumption, a small clearance (<10µm) isneeded. However, as air has a finite viscosity(0.0018 mPa.s), small gaps give rise to highshear rates, and correspondingly the frictionincreases.

Technical Description


If large gaps are used, the shear rate is loweredand friction is reduced, but the stiffness of theair bearing is also reduced.

Thus, a compromise in the design of an airbearing is needed for optimal performance.

The air bearing used in the AR Rheometers usesa mixture of proven bearing techniques withnovel materials. The surfaces can be easilymachined to tolerances of less than 1µm,providing an extremely smooth finish.

A schematic of the Air Bearing and the othermain components of the rheometer head isshown in Figure 3.1 below.

Optical Encoder

Upper Radial Bearing

Thrust Bearing

Drag-cup Motor

Motor Housing

Lower Radial Bearing

Figure 3.1The Rheometer Head

The bearing is designed to be virtually friction-free, so that it moves under the smallest of

• Drag Cup

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forces. Even turbulent flow in the assembly issufficient to make the bearing rotate. Thisknown as the windmill effect. To ensure that thebearing is steady, a process called RotationalMapping, which is explained in the next section,is carried out.

Rotational Mapping

As a result of the micron tolerances needed tomake an air bearing work, any real bearing willhave small variations in behavior around onerevolution of the shaft.

By combining the absolute angular position datafrom the optical encoder with microprocessorcontrol of the motor, these small variations canbe mapped automatically and stored in memorysince the variations are consistent over time,unless changes occur in the air bearing.

The microprocessor can allow for theseautomatically by carrying out a baselinecorrection of the torque. This results in a verywide bearing operating range, without operatorintervention; i.e., a confidence check in bearingperformance.



Auto GapSetMechanism

The auto gap set facility has three majorfunctions, as follows:

• automatic setting of gaps via software• programmed gap closure• thermal gap compensation

These features are described in more detail onthe following pages.

Closing the Gap

When you load a structured sample onto arheometer, there is always a danger that theloading process will destroy the very structureyou are trying to measure.

Once you have set the gap and loaded thesample, the head is lowered. The speed of thehead as it is lowered is controlled via the‘automatic gap options’ set in the TAInstruments rheology software. There are threeclosure option available with an ARRheometer—standard, linear, and exponential.An additonal Normal Force closure option isavailable if an AR-N is used. The optionsavailable are described in detail in the onlinehelp for the rheology software.

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ThermalCompensation

When a wide temperature range is used for anexperiment, the metallic rheometer parts and themeasurement geometries can heat or coolcausing expansion or contraction of themeasurement system gap. The auto gap setfacility takes this into account and compensatesfor these changes. Therefore, regardless oftemperature, you can be confident that the gapremains constant. A typical value for stainlesssteel geometries is 0.5 µm°C-1

The Peltier Plate

Temperature control in the standardconfiguration is via a Peltier plate, which usesthe Peltier effect to rapidly and accuratelycontrol heating and cooling. The Peltier systemuses a thermo-electric effect. This functions as aheat pump system with no moving parts, and isideally suited to rheological measurements. Bycontrolling the magnitude and direction ofelectric current, the Peltier system can provideany desired level of active heating or coolingdirectly in the plate.

• Standard Peltier System range: -10°C to99°C.

• Extended Peltier System range: -20°C to

180°C.

WARNING: Extended use above 150°C isnot recommended, as this will reduce thelife of the Peltier elements.



This provides very fast temperature control,however, it is unable to control the temperatureof very large sample masses such as largeconcentric cylinder systems.

A schematic of the Peltier plate is shown inFigure 3.2.

Peltier Elements (x4)

Pt100

TOP

UNDERSIDE

Heat Exchanger

Figure 3.2The Peltier Plate

Since the Peltier system operates as a heat pump,it is necessary to have a heat sink available. Theheat sink removes unwanted waste heat from theplate. This heat sink is normally in the form of areservoir, containing a few liters of water, plus asmall pump which can provide a sufficient flowrate through the Peltier heat exchanger jacketbuilt into the plate. The reservoir fluid will

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become warm with the prolonged use of thePeltier at high temperatures.

If your temperature range is 20°C below and60°C above ambient, the water bath should be atroom temperature. If, however, you wish towork at lower or higher temperatures, thewaterbath temperature needs to be alteredaccordingly (i.e., the Peltier plate will work mostefficiently at a temperature range that is 15°Cabove and below the water bath temperature.).

However, if you are using the Extended Peltiersystem, we recommend that you connect thesystem to a main water supply, especially if youexpect to routinely operate for extended periodsabove 100°C.

The flow rate through the Peltier plate does notneed to be high. A flow rate of at least 0.5 litremin-1 is adequate. If this flow rate is notmaintained, the temperature control system willlose control and the plate will heat or coolcontinuously.

CAUTION: The Peltier Plate may bedamaged by operating the instrumentwithout a flow of water through thePeltier system. There is a PeltierOverheat protection device whichshould become active if no flow isdetected. A ‘Peltier Overheat’ messagewill be displayed on the computermonitor and the LCD of the electronicscontrol box.



Normal Force Transducer (optional)

When a viscoelastic liquid is sheared, a forcecan be generated along the axis of rotation of acone or parallel plate geometry. For this tohappen, the structure responsible for theelasticity must not be completely disrupted bysteady shear. For this reason, colloids,suspensions, etc., although elastic at rest,become effectively inelastic under steady shear,and can, in fact, show negative normal forcesdue to inertial effects.

However, polymer solutions and melts, andproducts incorporating them, are typically elasticunder shear because of the long lifetime of themolecular entanglement.

Normal force measurements are usually madewith cone and plate or parallel plate geometries,therefore, it is important that you use a methodto detect the force that does not allow significantchanges in the gap. This would result in theactual shear rate varying with normal force, dueto deflections of the force-detecting component.

The AR Rheometers keep the upper geometrypositioned as accurately as possible with an airbearing, and movement is kept to an absoluteminimum. This ensures good bearingperformance.

The force is detected on the static lower plateusing high sensitivity load cell technology,which is essentially deflectionless.This results in a fast response, wide range signal,which is easy to calibrate, and has a genuineNormal force-measurement capability.

Normal force range: 1 g to 5000 g

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WARNING:During sample loading andmeasurement, the normal forcetransducer is protected from overload.However, take care when cleaning orattaching accessories to the lower platethat you do not exceed the maximumnormal force.

CAUTION: Keep hands and fingersaway from the plate during headmovement.



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CHAPTER 4: Technical Specifications

OverviewThis chapter contains the technical specificationsfor the AR Rheometers. You can obtain furtherinformation from your local SalesRepresentative.

Specifications

The following specifications apply to the TAInstruments AR Rheometers:

Table 4.1AR RheometerDimensions

AR-N Instrument Section (Casting):

Width 9 in. (22 cm) Height 23.5 in. (60 cm) Depth 10 in. (25 cm)

Weight 48.5 lbs (22 kg)

AR-N Controller:

Width 7.5 in. (18.5 cm) Height 14.5 in. (37 cm) Depth 17 in. (43 cm)

Weight 46.2 lbs (21 kg)

Technical Specification


Table 4.2AR RheometerSpecifications

Supply Voltage 230 Vac 5 amps120 Vac 10 amps

Frequency 50 to 60 Hz

Power 800 Vac

Torque 0.1 µNm to 100 mNm (AR 1000)Range 1µNm to 50mm (AR 500)

Shear Stress 0.0008 to 508,000 Pa (AR 1000)Range (Geometry 0.008 to 254,000 Pa (AR 500)Dependent)

Frequency 0.1 mHz to 100 Hz (AR 1000)Range (0.628 mrad s-1 to 628 rad s-1)

0.1 mHz to 40 Hz (AR 500)

Angular Controlled Stress:Velocity 10-8 to 100 rad s-1

Range Controlled Strain:10-2 to 100 rad s-1

Angular 0.62 µradsDisplacementResolution

Shear Rate Range 10-6 to 11,000 s-1

(Geometry, materialand techniquedependent.)

(table continued)

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Table 4.2AR RheometerSpecifications (cont’d)

Minimum strain 0.00006

Normal force Range: 1 g to 5000 g

Table 4.3Peltier SystemSpecifications

Peltier Standard: -10 °C to 99 °C System Extended: -20 °C to 180 °C Range

NOTE: Extended use of the extended Peltier plate is not recommended above 150 °C. Also, the lower temperature ramps can be significantlyreduced by circulating an appropriate refrigerant.

Ramp Rate 20 °C min-1

(Standard) (Typical) Ramp Rate (20 to 100 °C) 50 °C min-1

(Extended) (100 to 150 °C) 25 °C min-1

Internal 0.016 °C Resolution of Pt100

Technical Specification


Table 4.4Optional AccessorySpecifications for ExtendedTemperature Module (ETM)

ETM Temperature Range -100 °C to 400 °C Ramp Rate (Typical) 120 °C min-1

InternalResolution 0.025 °C

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CHAPTER 5: Installation

OverviewNormally the installation of your new systemwill be carried out by a member of the TAInstrument’s sales or service staff, or theirappointed agents, and it will be ready for you touse. However, should you need to install orrelocate the instrument, this chapter provides thenecessary instructions.

Removing the Packagingand Preparing forInstallation

If needed, the first step is to carefully remove allitems from any and all packaging. Werecommend that you retain all packagingmaterials in case the instrument has to beshipped to a TA Instruments service depot atsome point in the future (for example, in thecase of some upgrades).

Please follow these recommendations when youmove or lift the instrument and its accessories:

• When moving the rheometer, the air bearingclamp should always be in place, ensuringthat the bearing cannot be moved. Figure5.1 shows the air bearing clamp and how itis attached.

• Treat the AR Rheometers with the same

degree of care you would take with anyscientific laboratory instrument.

Installation


Airbearingclamp

Drive shaftand drawrod

Screw in the draw rod from here

Airbearingclamp insecureposition

Figure 5.1Air Bearing Clamp Attachment

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InstallationRequirements

It is important to select a location for theinstrument using the following guidelines.Choose a location that is...

In . . . a temperature-controlled area.

. . . a clean environment.

. . . an area with ample working andventilation space around the instru-ment, approximately 2 meters inlength, with sufficient depth for acomputer and its keyboard.

On . . . a stable, vibration-free work surface.

Near . . . a power outlet. Five to sevenavailable electrical sockets,depending upon theaccessories being used.

. . . your computer loaded with theTA Instruments rheology software.

. . . sources of compressed lab air andpurge gas supply for use duringcooling and subambient experiments.A compressed air supply that iscapable of supplying clean, dry, oil-free air at an approximate pressure of37.5 psi (for AR 500) or 30 psi (forAR 1000) at a rate of 50 liters/min.The dew point of the air supply shouldbe -20 °C or better. See Chapter 8 forinformation on the air filter regulatorassemby.

Installation


Awayfrom. . . dusty environments.

. . . exposure to direct sunlight.

. . . direct air drafts (fans, room air ducts).

. . . poorly ventilated areas.

After you have decided on the location for yourinstrument, refer to the next several sections tounpack and install the AR Rheometers.

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Connecting theSystem Together

Connecting the system together should presentno problems, as long as you use instructionsfound in the next several sections.

Connecting the Rheometerto the Electronics Control Box

The Electronics Control Box forms the linkbetween the rheometer and the computer. All therequired processing is done within the controlbox, which can be regarded as the heart of thesystem. Refer to Figure 5.2 on the next page.

1. Push the male end of the Power cable intothe Power port on the back of the rheometerand the other end in the Power port on theback of the control box.

2. Push the D-type cable into theAnalogue/Digital port on the back of therheometer and connect the other end to theAnalogue/Digital port on the back of thecontrol box.

Installation


Figure 5.2Cable Connections

Connecting the Computerto the Electronics Control Box

The electronics control box and computer areconnected via a single RS232 cable, which issupplied with the system. One end of the cablehas a 9-pin female connector, and the other endhas a 9-pin male connector.

1. Push the 9-pin female connector into the 9-pin socket marked "Computer" on the backplate of the controller.

2. Push the 9-pin male connector into the serialport socket on the back of the socket on thecomputer.

NOTE: Remember you must configurethe software for the appropriatecommunications port—refer to the onlinehelp for instructions on how to do this.

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Connecting theWater Bath

NOTE: A water bath is not needed if youhave purchased the rheometer with ablank sample plate.

The rheometer is supplied with two lengths ofwater pipe. To connect the water bath, followthese directions:

1. Take each pipe separately. Push one endonto one of the outlets on the rear of thewater bath.

2. Connect the other end of the pipe to the pushfittings on the back of the rheometer.

3. Repeat the process using the other waterpipe to connect the second outlet on thewater bath to the second push fitting on theback of the rheometer.

4. Check for leaks by turning on the waterbath.

NOTE: If you are using the rheometerregularly at temperatures above 120°C,you will need to connect your instrumentto a main water supply. See the sectioncalled “The Peltier Plate” in Chapter 3 forinformation.

Installation


Leveling theRheometer

Optimum performance depends upon theinstrument being level and in a sturdy position toavoid the possibility of rocking. To check andsee whether your instrument is level, simplyplace a bubble spirit level on the Peltier plate.

If the instrument is not level, screw theadjustable feet (located at each corner of theinstrument) either in or out, as necessary. Checkthe spirit level after each adjustment. Once youhave the instrument leveled correctly, press eachcorner of the instrument to check that all fourfeet are in contact with the laboratory bench.Any movement caused by pressing should berectified by adjusting the feet, and thenrechecking the level of the Peltier plate.

If the spirit level is the circular type, it should beplaced in the middle of the Peltier plate. If thespirit level is the bar type, place it along adiameter of the Peltier plate. Check the level byplacing it along another diameter of the Peltierplate at 90° to the first position.

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Checking YourSystem

After installation has been completed, start theinstrument to check to make sure everything isworking and that all parts of the system arecommunicating with each other. Use thefollowing steps to check your system:

1. Turn on the air supply to the instrument.

2. Turn on the water supply to the instrument.

3. Remove the air bearing clamp.

4. Turn on all electrical parts of the system(rheometer, PC, etc.). A system check willbe initiated as shown by the LCD on theelectronics control box.

5. Start the rheology software.

6. Select the Instrument Status screen in thesoftware.

7. If everything is installed correctly, theinstrument will display continually updatingfigures.

8. Lower the head. If the installation is OK,the head will operate.

9. Input a temperature slightly different to thatdisplayed. If the installation is OK, thetemperature will change to the new one youhave just input.

10. Raise the head.

Installation


If all of these actions result in the correctresponse, you can be confident that you haveinstalled the system correctly and it is ready foruse. If you have problems, please contact yourlocal TA Instruments office or their appointedagent.

Shut-down Procedure

When you have finished your experiments andare ready to turn the instrument off, it isimportant that you follow the steps listed belowin the correct order.

1. Raise the head and remove the geometry.

2. Exit the software package that you arecurrently running.

3. Turn off the rheometer and the computer.

4. Replace the air bearing clamp.

5. Turn off the water supply to the instrument.

6. Turn off the air supply to the instrument.

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CHAPTER 6: Measuring Systems

OverviewThis chapter describes the geometries currentlyavailable from TA Instruments and providesguidelines to choose the optimum geometry (ormeasuring system) for each application. Acomplete geometry catalog is available whichdescribes in detail each geometry and typicalapplications. Contact your local TA Instrumentsoffice or their appointed agent for further details.Some theoretical considerations are given thatwill provide guidance and help you maximizethe use of the AR Rheometers.

TA Instruments offers a range of geometries.The geometries are divided into the followinggroups, each with a range of sizes available:

• Cone and plate• Parallel plate• Concentric cylinders.

The next several pages describe the types ofgeometries and provide details on how to attachthe geometry to the rheometer.

Measuring Systems


General Description

The measuring system is defined as those partsthat are in direct contact with the sample ormaterial.

A measuring system consists of two parts:

• One is the fixed member (or Stator), whichis either the Peltier plate, or a systemattached to the Peltier plate (in the case ofconcentric cylinders or when the ExtendedTemperature Module is in use).

• The second part (the geometry) is attachedto the driving motor spindle, where it islocked in position using the draw rod. Thedraw rod is detachable and passes throughthe center hole bored in the spindle. Thegeometry constitutes the moving member ofthe system (the Rotor).

Geometry Materials

Geometries are usually constructed fromstainless steel, aluminum, or acrylic. The rotorshould ideally be as light as possible tominimize inherent inertia effects. It should alsobe chemically compatible with the test sample inorder to avoid corrosion problems.

Stainless SteelStainless steel is relatively heavy, but it has alow coefficent of thermal expansion. It iscompatible with most test materials and is robustenough to withstand heavy use, even if you are aless experienced operator.

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AluminumAluminum has a higher thermal coefficient ofexpansion and is limited because of its chemicalcompatibility. As it is lighter, inertial effects arenot as great.

PlasticEngineering grade acrylic, polycarbonate, andrigid PVC are all suitable materials for geometryconstruction. These are transparent so the visualbehavior of the sample can be observed. Plasticgeometries are also much lighter than metallicgeometries.

Acrylic and polycarbonate have less inertialproblems as they are relatively light, but theyhave limited chemical compatibility. You shouldnot use plastic geometries above 40°C.

Measuring Systems


Cone and PlateA schematic of a cone and plate system is shownbelow in Figure 6.1. It is important to knowhow to calculate the stress and shear rate factorsfor each geometry before deciding on thegeometry dimensions.

Torque (M)

Angular

ω rad s -1

αTruncationT

R

Velocity

Figure 6.1The Cone and Plate

Shear stress Pa F M

where FR

( ) =

=

σ

σ π3

2 3

The standard diameters available are 20 mm,40 mm and 60 mm with cone angles of 0.5° to4° in 0.5° increments.

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Cone and plate geometries are generally used forsingle phase homogeneous samples or sampleswith sub-micron particles. Samples containingparticulate matter are usually unsuitable for coneand plate geometries as the particles will tend tomigrate to the apex of the cone and will getjammed in the truncation area. Erroneous datawill result.

The angles and truncation values of each coneare individually calibrated. A calibrationcertificate is available. The serial number, angleand truncation are all inscribed on the stem ofeach cone.

Measuring Systems


Parallel Plate

The parallel plate system allows samplescontaining particles to be effectively measured.You can set the gap to any distance, therebyeliminating the problems due to particles size.Generally samples that have particles need tohave a gap size set at least 10 times greater thanthe largest particle size. For example, if themaximum particle size is 100 µm, you shouldset the gap to at 1000 µm.

The main disadvantage of a parallel plate systemis that the stress is not uniform across the entirediameter. However, the software compensatesfor this fact. The shear stress and shear ratefactors given are with respect to the rim.

A schematic of a parallel plate is shown inFigure 6.2 below.

R

Torque (M)

AngularVelocityω rad s-1

D = gap

Figure 6.2The Parallel Plate

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Shear rate s F

where FR

D

( )− =

=

1 γ

γ

ω

Shear stress Pa F T

where FR

( ) =

=

σ

σ π2

3

.

.

Measuring Systems


Concentric Cylinders

Concentric cylinder systems (or cup and bob)are generally used for lower viscosity samplesthat would otherwise not be constrained withinthe gaps of cone and plate or parallel platesystems. (See Chapter 8, “Setting Up ConcentricCylinder Systems.”)

There are several different types including:

• Recessed end• Conical end (DIN)• Vaned• Double concentric.

See the following figures for examples ofconcentric cylinder geometries.

Torque (M)AngularFrequencyω rad s-1

HR1R2

Figure 6.3Recessed End

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NOTE: The following equations are alsoused for the Vaned system.

Assuming no end effects.

Shear stress Pa F M

where FH

R RR R

( ) =

=+

σ

σ π1

2

2

2

1

2

2

24

Torque (M)AngularVelocityω rad s-1

HR1R2

Figure 6.4Conical End

The shear stress and shear rate factors are thesame as the geometry shown in Figure 6.3 onpage 6-8. The conical end aids penetration andeven distribution of stiffer samples.

Measuring Systems


Torque (M)AngularVelocityω rad s-1

HR1R2R3R4

Figure 6.5Double Concentric

The ratio R1:R2 = R3:R4. The shear rate is thencalculated as in Figure 6.3 using either R1 and R2

or R3 and R4.

Shear stress Pa F M

where FH

R RR R R

( )

( )

=

=+

+

σ

σ π1

2

2

2

2

2

1

2

3

24

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Using the Stressand Shear Rate Factors

The TA Instruments operating system softwarecalculates the stress and shear rate factors,which are used by the software in all subsequentcalculations.

However, there may be occasions when you willneed to enter these factors manually. If you do,follow the sequence given below:

1. Multiply the angular velocity (ω) by theshear rate factor (Fγ ) to obtain the shearrate (s-1).

2. Multiply the angular displacement by thesame factor to obtain the strain(dimensionless).

3. Multiply the torque (T) (µNm) by the shearstress factor (Fσ ) to obtain the shear stress(Pa).

.

Measuring Systems


Choosing theBest Geometry

If you are an inexperienced rheologist, you willprobably have initial difficulty selecting theoptimal geometry. It is important that youunderstand the following...

...exactly what type of experiment do you wishto carry out,

...what is the sample behavior like—does thesample contain particles, and

...probably most importantly, what is the real-life situation are you trying to recreate?

Sometimes the answers to all of the abovequestions are not known, but there are somebasic guidelines that will help you. However, itis also important to remember that you aremeasuring the bulk properties of the materialitself, and this should be independent of the typeof geometry used (within reason!).

Cone and Plate/ParallelPlate Systems

The cone and plate and parallel plate systemsboth need small sample volumes, are easy toclean, have low inertia, and can potentiallyachieve high shear rates. The additionaladvantage to using a cone and plate is that theshear rate is uniform throughout the sample, andthe parallel plate can accommodate largeparticles.

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Generally the cone and plate or parallel platesystems can be used for almost any sample.They are easy to set up and use, making one ofthese systems the best choice for optimumresults.

They are both available in different sizes,therefore, it is important to understand how tochoose the system with the correct dimensions.

AnglesCones are supplied by TA Instruments in anyangle from 0° to 4°, usually in 0.5° increments.The 4° cone is the largest available, as thesample velocity profile becomes unpredictable athigher angles and the mathematical expressionof α ~ tan α is no longer valid.

The 4° cone is ideal for creep measurements,because a longer displacement is required perunit strain.

The smaller the angle (or gap in a parallel platesystem), the higher the maximum shear rateobtainable.

Measuring Systems


Diameters

The smaller the diameter of a cone or parallelplate system, the larger the shear stress factor.This means that a small (e.g., 20 mm) diametergeometry should be used with stiffer materials ormedium to high viscosities. A 40 mm geometryis more versatile and it usually allows themajority of medium viscosity materials to bemeasured.

A large diameter geometry (e.g., 60 mm) is moresensitive to stress changes and is used tomeasure low viscosity samples.

Be sure to load the sample correctly and becareful not to under or overfill the geometry. Ifthis occurs, it would effectively change thediameters of the cones and, hence, adverselyaffect the shear stress factors.

The following figure summarizes theinformation given above on the choice of angle(or gap) and diameter.

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20 mm (suitable for

high viscosities)

40 mm

60 mm (suitable for

low viscosities)

StressIncreases

angle (or gap) decreases

shear rate increases

Figure 6.7Choosing GeometryAngle and Diameter

Material

Stainless steel is relatively heavy, has a lowcoefficient of thermal expansion, is compatiblewith most samples, and is very robust.

Aluminum geometries are lighter than steel, buthave a larger coefficient of thermal expansion.They will go to temperatures greater than 40°C,but are still heavier than acrylic.

Acrylic geometries are very light and are,therefore, most suitable to use with low viscositysamples. However, you should not use acrylicgeometries above 40°C.

See the beginning of this chapter for moredetails on materials.

Measuring Systems


Preventing SolventEvaporation

If you are using samples that contain volatilesolvents or are water-based, evaporation cancause problems during measurements. TAInstruments has overcome this problem by usinga solvent trap cover, which sits over thegeometry (but does not touch it).

Solvent trap version geometries have a well ontop of the geometry. Place a small amount ofthe relevant solvent into this well. The solventtrap cover has a lip that sits in the solvent,allowing the free space around the sample tobecome saturated with the solvent vapor, whichprevents evaporation.

A schematic of a solvent trap cover andgeometry is shown in Figure 6.8 below.

Solvent trap version geometry

Solvent well

Solvent vapour saturated free space

SAMPLE

Figure 6.8Solvent Trap Coverand Geometry

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Preventing Slippage atSample/Geometry Interface

Some samples, such as hydrogels, contain a lotof water that can migrate to the surface of thesample. This can cause a film layer to formbetween the bulk of the material and thegeometry surface, causing slippage at thisinterface. To alleviate this problem, use specialcross-hatched geometries, which, in effect, havethe measuring surface slightly roughened.(However, when you use these cross-hatchedgeometries, there is a trade-off between absoluteaccuracy and repeatability.)

Measuring Systems


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CHAPTER 7: AR RheometerEnhancements/Options

OverviewThis chapter provides information on some ofthe enhanced features of the AR Rheometers.These include the following features:

• Normal force (AR-N)• Gap validation• Flow inertial correction• Air bearing friction correction.

Normal Force Transducer (optional)

If you have purchased the normal force option,your rheometer will be marked as an AR-N.

When a viscoelastic liquid is sheared, a forcecan be generated along the axis of rotation of acone or parallel plate geometry. For this tohappen, the structure responsible for theelasticity must not be completely disrupted bysteady shear. For this reason, colloids andsuspensions etc., although elastic at rest, theirstructure is immediately disrupted when shearedand can, in fact, show negative forces.

Polymer solutions and melts, and productsincorporating them, however, are typicallyelastic under shear due to the long lifetime of themolecular entanglements largely responsible forthe elasticity.

Enhancements


Because normal force measurements are usuallymade with cone and plate or parallel plategeometries, it is important that the method usedto detect the force does not allow significantchanges in the gap. This would result in theactual shear rate varying with normal force, dueto deflections of the force-detecting component.

The AR-N keeps the upper geometry positionedas accurately as possible with an air bearing.This is designed to keep movement to anabsolute minimum, which is consistent withgood bearing performance. The force isdetected on the static lower plate using highsensitivity load cell technology, which isdeflectionless for most practical purposes.

This results in a fast responding, wide rangesignal which is easy to calibrate giving agenuine Normal force measuring systemcapability.

Normal force range: 1 g to 5000 g

Using the TA Instruments rheology softwareyou can monitor normal forces generated whileloading samples, as well as close the gapmeasurement and load under normal forcecontrol.

CAUTION: Keep hands and fingersaway from the plate during headmovement.

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Gap SettingValidation (optional)

Independent gap confirmation or validation isavailable as an option. A Mitutoyo digitalgauge, accurate to 1 µm, is attached to the sideof the rheometer to allow a direct reading of theactual gap.

Enhancements


Inertial Correction

When a stress is applied to a sample, the samplewill move, and continue to move, while thatstress is applied. If the stress is then removed,the sample will stop moving, but notinstantaneously. It requires a finite time torespond to this change in stress. This lag time isdue to inertial effects, and its magnitude dependsupon the sample, measuring geometry, and testprocedure.

In flow experiments, the effect of inertia is morepronounced when you use low viscosity fluids.Inertial effects in flow experiments appear asapparent thixotropic loops when a standard UPand DOWN flow curve is carried out.

Consider Figure 7.1. which shows anexaggerated effect of inertia.

Figure 7.1Flow Curve WithoutInertial Correction

You could interpret this graph as a flow curve ona thixotropic sample, highlighted by thepresence of the hysteresis loop. However, thefact that the the DOWN curve (B) crosses the xaxis alerts us to the fact that this apparent

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thixotropy is actually an inertial artifact and thatthe down curve intercepts the y-axis below theorigin.

The inertial correction feature available in theAR Rheometer eradicates such artifacts. It is astraight-forward toggle ON/OFF option that youcan access using the software. (See the onlinehelp available for the software.)

Using the same sample as above, but measuringwith the inertial correction ON, yields the resultsshown in Figure 7.2.

Stress

Shear rate

Stress

Shear rate

Figure 7.2Flow Curve withInertial Correction

This now shows a Newtonian response, which isas expected.

This inertial correction only needs to be activewhen low viscsoity materials are beingmeasured.

Enhancements


Air BearingFriction Correction

As explained in Chapter 3 (TechnicalDescriptions), an air bearing is used to providevirtually friction-free application of torque to thesample. However, there will always be someresidual friction. With most samples this isinsignificant; but, in about 1% of low viscositysamples, this inherent friction causesinaccuracies in the final rheological data. Toovercome this problem, TA Instruments hasintroduced an air bearing friction correction thatyou can choose to activate.

Each air bearing is custom designed andengineered, therefore, they are all unique. Thismeans that the correction factor will also beunique to each bearing.

Determining theCorrection Factor

If you wish to apply the air bearing frictioncorrection, you must first calibrate your bearing.The calibration procedure should be carried outmonthly, if you use the option frequently.Ensure that your air supply is stable, because thebearing can be affected by changes in the airsupply.

To determine the air bearing friction correctionfactor, follow the procedure beginning on thenext page. (You may need to refer to thesoftware manual or online help for furtherguidelines.)

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1. Attach the geometry of choice to therheometer.

2. Enter the relevant geometry details using thesoftware.

3. Set the gap in the usual way.

4. Set up a PEAK HOLD flow procedure usingthe parameters below:

Hold torque 10 µNmTime 5 minutesSample Interval 2.0 secsTemperature 25°C

All other parameters can be set to zero.

5. Start the experiment and save the data whenit has finished.

6. Display the data using the axes as shown inFigure 7.3 below. This also shows theexpected result.

Figure 7.3Air Bearing Friction Correction

Enhancements


7. Check your results. A plateau should havebeen reached within this time. Read off thevalue for the plateau angular velocity.

8. Calculate the friction correction factor usingthe equation given below:

Bearing frictioncorrectionNm

rads

Applied torque

Plateauangular velocity

µ−

=1

9. Enter the resultant value in the “bearingfriction correction” option found in thesoftware.

For the Advantage program:

a. Select Options on the menu.b. Select Instrument.c. Click on the Miscellaneous tab.d. Enter the friction factor value in the

Bearing friction correction field.e. Click OK.

This routine can also be used to check thecondition of your air bearing. If this iscarried out monthly, and the plateau angularvelocity recorded, any deterioration in thebearing performance can be seen. This willmanifest itself as a significant change in theplateau velocity with time. (Particularly ifthe plateau velocity becomes lower andlower.)

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CHAPTER 8: How Do I...

OverviewThis chapter covers the “How do I...” typequestions that you are mostly likely to ask whenyou first use your rheometer. Areas coveredinclude:

• Attaching a geometry• Undoing the air bearing clamp• Choosing the right geometry• Checking the operation of the air bearing• Setting up the concentric cylinder system• etc.

In most cases these topics are covered in greaterdetail in the preceding chapters.

How Do I...


...Clean the FilterRegulator Assembly?

The air bearing requires a very clean supply ofair regulated to a stable pressure of between 25to 40 psi, dependent upon the air bearing. Thefilter regulator assembly is an important part ofyour rheometer system. It is designed to meetthe required standards of cleanliness (99.9999%of particles above 0.01µm retained) and regu-lation, given that the source of air is dry and pre-filtered.

The maximum inlet pressure is 147 psi (10 bar).The maximum pressure to the rheometer is 42psi (3 bar).

The filter regulator assembly is shownschematically in Figure 8.1.

Figure 8.1The Filter RegulatorAssembly

PressureGauge

From air supply

To Rheometer

Filter bowelscontainingfilter elements

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If you use the filter regulator, you will need tocheck routinely (i.e., at least monthly) for anysigns of contamination (i.e., water, oil or dirt)collecting in the filter bowls. If you see a buildup of water, follow these steps:

1. Turn off the air supply and disconnect theassembly from the rheometer. Rememberto put the airline plug into the back of therheometer.

2. Unscrew the filter bowl plug and dry theinside thoroughly.

3. Replace the plug and purge with air prior toreconnection to the rheometer. The filterelements must be replaced similarly whenthere is a visible build up of dirt.

How Do I...


... Remove theAir Bearing Clamp?

You should never remove the air bearing clampuntil the air supply is connected and switchedon.

Once the air supply is switched on, and you canhear the air through the rheometer, the clampcan be safely removed.

To remove the clamp, simply firmly hold theclamp and unscrew the draw rod in theappropriate direction.

CAUTION: Never hold the draw rodand unscrew the clamp!

Draw rod

Air bearingclamp

Figure 8.2Air Bearing Clamp

The clamp is replaced in exactly the same way.The air must not be switched off until the clampis in place.

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...Attach a Geometry?

This procedure is carried out using the sametechnique as described for the air bearing clamp:

1. Switch on the air and remove the air bearingclamp by turning the draw rodcounterclockwise.

2. Push the geometry up the drive shaft andhold it while placing the draw rod in thescrew thread of the geometry.

3. Screw the draw rod upwards (clockwise). Itshould be screwed finger tight, but notforced.

Attaching a geometry Removing a geometry

Clockwise Counterclockwise

Figure 8.3Attaching/Removing A Geometry

To remove the geometry, use the reverseprocess.

How Do I...


...Set Up theConcentric CylinderSystem?

As explained in Chapter 6, the concentriccylinder system requires the use of an externalwater jacket. This houses the adapter, whichcontains the cup of the system. Figure 8.4shows how the the adapter and cup arepositioned in the jacket.

To set up the concentric cyliner system, followthese steps:

1. Place the water jacket on top of the Peltierplate (or blank sample plate if you have thisoption) (see a in Figure 8.3).

The Peltier plate has three indents aroundsits rim. The lip of the water jacket containsthree ball screws that are designed to fit inthe indents in the Peltier plate.

2. Rotate the water jacket until the you feel theball screws fit firmly (see b in Figure 8.3).The system is self-centering.

ba

Figure 8.3Attaching the Water Jacket

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Changing the Cup Size

If you need to change the size of the cup you areusing, you need to change the adapter size aswell.

To change adapter follow these steps:

1. Undo the silver screw collar of the jacketand lift out the adapter already in place.(You must ensure the jacket is removedfrom the water supply and is empty beforeproceding.).

2. Replace the required adapter and replace thescrew collar tightly. The new cup can nowsit in the new adapter. You will need tochange the adapter when changing the cupsize.

The water jacket set is shown in Figure 8.4below. The water jacket can then be reattachedto the Peltier plate as explained above.

Collar

Cup

Adapter

WaterJacket

Figure 8.4Water Jacket Arrangement

How Do I...


Controlling Temperaturewith a Concentric CylinderSystem

If accurate temperature control is desired whenusing a concentric cylinder system, you need touse an external fluid circulation system. Thesystem recommended by TA Instruments uses aComputer Controlled Fluid Circulator (CCFC),which can be interfaced with the software. Itcontrols the circulating fluid temperature to givethe exact sample temperature required. Thisinvolves the use of an external Pt100 placed inthe cup of the concentric cylinder system. Theuse of such a system is detailed in a separateinstruction booklet available from TAInstruments.

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...Ensure the Sampleis Loaded Correctly?

Ensuring that the sample is loaded correctly andthe gap is properly filled is probably one of themost important points to consider in anyrheological experiment.

You will find that you will become quite adeptat judging the right amount of sample to use,depending upon the geometry diameter and gapsize. You can either calculate the exact volumeor weight of sample needed. However, caremust be taken if you intend to use a pipette orsyringe to deliver the correct amount. Samplesthat are delicately structured will be adverselyaffected by the high shear rate regimeencountered in syringes or pipettes.

If the gap is not filled correctly, there are certaintypes of errors that can occur. The magnitude ofthe errors will be entirely sample dependent, butgenerally over filling is less of a problem thanunder filling. Such errors are called edge effectsFigure 8.5 shows the different types of fillingencountered.

• If the gap is overfilled, some of the excesssample may migrate to sit on top of thegeometry. If, however, the sample is of lowviscosity, this is not likely to happen and theerrors are much reduced.

• If the gap is underfilled, you are effectivelyaltering the diameter of the geometry. Thiswill inevitably introduce large errors andyou should definitely avoid this situation.

How Do I...


Correct

Overfilled

Underfilled

Figure 8.5Loading the Sample

Loading the sample correctly is a skill that youwill learn with time. It may help you to spendsome time initially simply loading and reloadinga sample. The correct loading is vital toaccurate and meaningful results.

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...Calibrate theRheometer?

Strictly speaking, you cannot calibrate yourrheometer yourself. You can check that theinstrument is functioning properly by measuringthe viscosity of a certified standard Newtonianoil. If you get a greater than 4% error in thereading, there is a possibility that yourrheometer needs some attention from a TAInstruments Service Engineer.

Carry out the following experiment.

1. Attach a 60 mm 2° cone to the rheometer.(This is the preferred geometry, if you donot have one use the largest cone that you dohave.)

2. Set the zero gap and measurement systemgap in the usual way.

3. Carefully load the sample ensuring correctfilling.

4. Carry out a 2-minute flow test over as widea range as possible.

5. Determine the Newtonian viscosity. If thisvalue is more than 4% different from thecertified value, repeat the experiment. Ifthere is still an error, call your local TAInstruments office for advice.

There are several sources of operator error thatcan give erroneous answers. This does notnecessarily mean that your instrument is notworking properly. These include errors in

How Do I...


setting the gap, incorrect temperatures used, orover- or under-filling of the gap. Thiscalibration check needs to be carried outmonthly.

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CHAPTER 9: Do’s and Don’ts

OverviewPlease read this chapter thoroughly before usingyour rheometer. It may be helpful to prepare acopy of these points and place them in aprominent position near the instrument.

DO... ensure the air supply is always very clean at

a stable pressure (50 psi). A coarse filter anddesiccant dryer system and double filterregulator assembly should be used.

... look out for water collection in the filterbowls before and during use of theinstrument. Drain the filter bowls whenevernecessary. (See Chapter 8.)

... look for visible signs of dirt on the filterelements in the filter regulator before use.Replace whenever necessary.

... replace the air bearing clamp when the air inON, and always ensure it is in place whenthe instrument is moved or when the air isswitched off.

... refit the air connector plug supplied with theinstrument whenever the air line isdisconnected.

... disconnect and blast air through the air linewhenever starting up after any period whichair has been switched off. (Not necessaryevery morning, unless you know your airsupply tends to accumulate water overnight.)

Do’s And Don’ts


DO... connect and switch on air supply before

switching the instrument on.

... switch on water supply to the Peltier platebefore switching the instrument on.

... use good laboratory practice when using theinstrument. Wear safety glasses andprotective clothing where necessary.

DON’T... operate the instrument without the correct

air supply.

... remove the air connector plug until ready toattach purged air supply.

... unnecessarily touch the air bearing spindleunless the air is on. This includes attachingand removing geometries.

... use the rheometer head as a lifting point.

... operate the instrument without a watersupply if you have a Peltier System.

... disconnect or connect any cables, leads etc.while the power is on.

... be frightened of using the instrument for thefirst time.

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TA INSTRUMENTS AR RHEOMETERS A–1

APPENDIX A: Useful Information

Moments of Inertia

The inertia of each geometry can bemeasured directly via TA Instrumentsrheology software. Below is a table whichshows the approximate inertia values for coneand plate and parallel plate systems. You areadvised to measure the inertia directly eachtime. (See the online help for information).

Units µNm s2.

Stainless Steel Acrylic

Diameter (mm) Standard SolventTrap

Standard SolventTrap

20 1.06 2.80 0.45 0.4340 4.35 6.92 1.39 1.3460 17.70 23.32 4.77 3.03

Apppendix A

A–2 TA INSTRUMENTS AR RHEOMETERS

Calculations forMoments of Inertia

Sometimes it may be necessary for you tomanually calculate the moment of inertia.Below are the relevant equations you willneed.

ConeAxis through vertex and center of circularbase.

inertia r=110

5p a r

r radiusα angle of cone (degrees)ρ density

CylinderAxis through center of cylinder

inertia h r=1

24

p r

h height of cylinder

The approximate densities (x 109 µNm-4s2)

are

Steel 7.83Acylic 1.19Aluminium 2.71

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TA INSTRUMENTS AR RHEOMETERS B–1

APPENDIX B: Symbols and Units

The following symbols are used throughout. Theinstrument can be used with either cgs or SIunits depending upon the preference.

Measurement CGS Unit Symbol SI Unit Symbol Conversionfrom CGSto SI

Area squarecentimeters

cm2 squaremeters

m2 104cm2 = 1m2

Force dyne dyne Newton N 105dyne = 1N

Length centimeter cm meter m 102cm = 1m

Mass gram g Kilogram Kg 1000g = 1Kg

Plane Angle Radian rad Radian rad No change(360° = 2πrad)

Temperature degreeCelsius(Centigrade)

°C Celsius °C No change

Time second s second s No change

Volume cubiccentimeter

cm3 cubicmeters

m3 106cm3 = 1m3

Appendix B

B–2 TA INSTRUMENTS AR RHEOMETERS

Parameter Symbol CGS Unit SI Unit Conversion CGSto SI

AngularDisplacement

ω rad rad No change

Angular Velocity ϖ rad s-1 rad s-1 No change

Compliance J cm2 dynes m2 N x 10-1

Cone Angle α degrees degrees No change

Elastic ShearModulus

dyne cm-2 rad-1 N m-2

rad-1

x 10-1

Shear Rate γ s-1 s-1 No change

Shear Strain γ no change

Shear Stress σ dyne cm-2 N m-2

(Pa)x 10-1

Torsional Force τ dyne cm N m x 10-7

Viscosity η Poise (P) Pa.s 1 cP = 1 mPa.s

.

.

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TA INSTRUMENTS AR RHEOMETERS C–1

APPENDIX C: Geometry Form Factors

Cone/Plates

Dimensions Form Factors

Angle(°)

Diam.(mm)

Truncation(approx.)(µm)

Samplevolume(ml)

Shearrate

Shearstress

Viscos.(Pa.s)

00.51.01.52.04.0

202020202020

13263952105

0.030.060.090.120.24

114.657.338.1628.6514.33

0.47740.47740.47740.47740.4774

0.004160.008330.012510.016660.03331

0.00.51.01.52.04.0

404040404040

13263952105

0.150.300.450.601.20

114.657.338.1628.6514.33

0.05960.05960.05960.05960.0596

0.000520.001040.001560.002080.00416

0.00.51.01.52.04.0

606060606060

13263952105

0.601.201.802.44.8

114.657.338.1628.6514.33

0.01770.01770.01770.01770.0177

0.000150.000310.000460.006180.00124

Appendix C

C–2 TA INSTRUMENTS AR RHEOMETERS

Concentric Cylinder Dimensions

Rotor Type RotorRadius

R1 (mm)

Stator RadiusR2 (mm)

ImmersedHeight (mm)

Gap(microns)

DIN (conical) 14 15 42 5920Recessed 14 15 42 4000Vaned 14 15 42 4000

Rotor Type StatorOuterRadius

R1 (mm)

Rotor InnerRadius

R2 (mm)

Rotor OuterRadius

R3 (mm)

ImmersedHeight(mm)

Gap(microns)

Double Gap 20 20.38 21.96 59.5 500

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TA INSTRUMENTS AR RHEOMETERS D–1

APPENDIX D: LCD Display Messages

The LCD display on the front of the rheometerelectronics box displays some useful informationand some error messages. The most common ofthese are explained below with suggestedremedies.

Initializing TransducerThis message is usually displayed momentarilywhen the instrument is first switched on. If themessage persists, it means that the air bearing isnot free to move. This usually occurs if youhave forgotten to remove the air bearing clamp.

Pressure Too Low

This is displayed if the air supply has beeninadvertently switched off while the rheometerwas on, or the supply pressure has droppedbelow the minimum operating pressure.

Peltier Overheat

This is displayed if the flow of water through thePeltier plate has dropped or stopped completely.Check the flow of water through the plate.There may be a blockage. Clear the blockagebefore using the rheometer again.

Appendix D

D–2 TA INSTRUMENTS AR RHEOMETERS

Hardware

TA INSTRUMENTS AR RHEOMETERS I–1

Index

A

adapterchanging, 8-7

air bearing, 3-1clamp removal, 8-4description, 3-1friction correction, 7-6schematic, 3-2

air bearing clamp, 1-3, 5-1, 9-1

air bearing friction correction, 7-1

air supply, 5-3, 9-1, 9-2

Analog portinstalling cable, 5-5

angles, 6-13

angular displacement, 2-7, 6-11

angular displacement resolution, 4-2

angular velocity, 6-11

angular velocity range, 4-2

AR Rheometersair supply, 5-3angular displacement resolution, 4-2angular velocity range, 4-2components, 2-5cone and plate, 6-4

Index

I–2 TA INSTRUMENTS AR RHEOMETERS

AR Rheometers (continued)description, 1-1electronics control box, 5-5enhancements, 7-1ETM temperature range, 4-4geometries, 6-1, 6-2installation, 5-1internal resolution of Pt100, 4-3introduction, 2-3leveling, 5-8measuring system, 6-1minimum strain, 4-3motor, 2-6moving, 1-3, 5-1normal force range, 4-3Peltier system range, 4-3ramp rate, 4-3, 4-4schematic, 2-4shear rate range, 4-2shear stress range, 4-2shutdown, 5-10specifications, 4-1torque range, 4-2unpacking, 5-1upper geometry, 3-8

AR-N, 7-1, 7-2

auto gap set mechanism, 3-4

automatic gap setclosing, 3-4

C

calibrate, 8-11

Index

TA INSTRUMENTS AR RHEOMETERS I-3

CE Compliance, 1-2

components, 2-6

Computer Controlled Fluid Circulator (CCFC), 8-8

concentric cylinderconical end, 6-9double concentric, 6-10recessed end, 6-8setup, 8-6

cone and plate, 6-4

conesangles of, 6-13diameter of, 6-14

contamination, 8-3

controlled-stress technique, 2-3

cupchanging, 8-7

D

deformation, 2-3

Digital portinstalling cable, 5-5

draw rod, 2-6

E

edge effects, 8-9

Index


elasticity, 7-1

electricalsafety, 1-4

electronics control box, 2-6, 5-5connecting to computer, 5-6

environment, 5-4

error messagePeltier overheat, D-1Pressure too low, D-1

ETM temperature range, 4-4

European Council Directive, 1-2

evaporation, 6-16

F

filter regulator assembly, 9-1cleaning, 8-2

flow inertial correction, 7-1

forcenormal force measurements, 3-8normal, transducer, 3-8

fuses, 1-6

G

gap, 8-9setting, 6-6, 7-3

Index


gap validation, 7-1

geometries, 3-8, 6-2, 9-2aluminum, 6-3attaching, 8-5choosing, 6-12concentric cylinder, 6-8cone and plate, 6-4diameter of, 6-14interface with sample, 6-17material, 6-15materials, 6-2parallel plate, 6-6plastic, 6-3slippage, 6-17solvent trap version, 6-16stainless steel, 6-2

Geometry Form Factors, C-1

H

hysteresis loop, 7-5

I

inertial correction, 7-5

inertial effects, 3-8

installation, 5-1

instructionswiring, 1-4

Index


instrumentfuses, 1-6grounding (earthing), 1-2maintenance, 1-6power requirements, 5-3repair, 1-6

L

LCD display, D-1

M

maintenance, 1-6

measuring system, 6-2fixed part (Strator), 6-2moving part (Rotor), 6-2parts of, 6-2

Motor portinstalling cables, 5-5

N

Newtonian viscosity, 8-11

normal force, 7-1geometries, 7-2measurement, 7-2

normal force measurements, 3-8

Normal force range, 3-8, 4-3

Index


O

optical encoder, 2-6

Pparallel plate

diameter of, 6-14schematic, 6-6

Peltier overheat, D-1

Peltier platedescription, 3-5flow rate, 3-7heat sink, 3-6leveling, 5-8schematic, 3-6

Peltier portinstalling cables, 5-5

Peltier system range, 4-3

power requirements, 5-3

power supply, 1-2

Pressure too low, D-1

R

ramp rate, 4-3, 4-4

repair, 1-6

rheologydefinition, 2-3

Index


rheometercalibrating, 8-11controlled-stress, 2-2do’s and don’ts, 9-1leveling, 5-8moving, 1-3, 5-1

rheometershistory, 2-1

Rotational Mappingdefinition, 3-3

S

safetyelectrical, 1-4

sampleloaded, 8-9loading, 8-10

shear rate, 2-3, 3-8equation, 6-4

shear rate factorusing, 6-11

shear rate range, 4-2

shear stress, 2-3equation, 6-4

shear stress range, 4-2

slippage, 6-17

solvent trap cover, 6-16

Index


Specifications, 1-2EMC Directive, 1-2

strain, 6-11

stress rate factorusing, 6-11

symbols, B-1

systemcheck, 5-9concentric cylinder, 6-8cone and plate, 6-4, 6-12installation, 5-5parallel plate, 6-6, 6-12shutdown, 5-10

T

temperature control, 2-6

thermal compensation, 3-5

thermal expansion, 6-15

thixotropic loops, 7-4

thixotropy, 7-5

torque, 6-11

torque range, 4-2

U

units, B-1

unpacking, 5-1

Index


V

viscosity, 2-1

W

water bathconnecting, 5-7

water jacket, 8-7

windmill effect, 3-3

wiring instructions, 1-4

work surface, 5-3

Documents

AR 500/1000 Rheometer Manual