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VKRT Seminar 10-02-2011Rubber Hardness: Gibitredevelopments and technicalmarket tendenciesEng. Mauro Belloni

About HardnessThe hardness is the measure of the penetration of anindentor in a sample under defined conditions.The measurement will depend upon:a) the elastic modulus of the rubber,b) the viscoelastic properties of the rubber,c) the thickness of the test piece,d) the geometry of the indentor,e) the pressure exerted,f) the rate of increase of pressure,g) the interval at which the hardness is recorded.The hardness test is correlated with other methods fortesting visco-elastic properies and is widely usedbecause it is: Low cost, quick, non distructive.

Instrument Construction:About Hardness - IRHD•Constant forces are applied to thesample (pre-load for 5 s, Mainforce for 30 s)•Indentor have Spherical ShapeStandards: ISO 48, ASTM D 1415

Gibitre Technology for irhdThe hardness unitsproduced by Gibitre havesome unique features

Gibitre Technology for irhdThe sample holder isconnected to a ballrecirculationscrew andmoved up and down using amicro-motor.The position of the sampleholder is controlled with 0.1Micron resolution

Gibitre Technology for irhdThe indentor is connected to aload cell.Ruby Spere for the indentorDuring the test the forces (preload and main load) applied tothe sample are controlledmoving the sample holderupwards.A High speed controller withclosed loop regulation hasbeen specifically designed toensure stable forceapplication.

Gibitre Technology for irhdA High speed controller withclosed loop regulation hasbeen specifically designed toensure stable forceapplication.

Advantages if GibitreConstruction• Modular Construction• ease of maintenance,• ease of calibration• No Moving parts in themeasuring part• improved repeatability• Direct calibration process• Solid Construction• Ball Recirculation Screw• Load cell with overloadprotection• Indentor with RubySphere

Gibitre Products

Digital Manual Shore Tester• Shore Units (Shore A, Shore D, Shore A0, Shore 00)• Interchangeable units with the same console• Use with support or for direct measurement• PC Connection for Data and Curves direct acquisition

Automatic Shore and Irhd Units• This solution is ideal when each unit must be available atthe same time.• Single units can be connected to the same pc usingindependent usb ports and can be used at the same time.• Test Results and Curves are stored in the same database

Automatic Multi-Unit Tester• This solution is ideal for research labs or when one measureis used with higher frequence• The multi-unit configuration permits to install up to 4 selectedtypes of shore or irhd hardness units.• The unit to be used is placed in the front position and isautomatically recognized by the software.

Rubber Samples

SoftwareHardnessRelaxationcurves for eachtestStatisticAnalysisTestIdentificationResults and comparisonwith tolerances

Data Analysis - Hardness at set time• The test timecan be set•Calculation ofhardness atspecific timecan be setindependently.

Data Analysis - Hardness Relaxation• The curve ofHardness Relaxationversus time isdisplayed and stored.• Regression line of thecurve in logarithmicaxes is calculatedand the relative anglecoefficient iscalculated.• Angle coefficient isan indicator of viscoelasticbehaviour andhas correlation withthe level of curing fora defined compound.This measure can beused for a quick andnon-distructive testfor moulding processcontrol.

Data Analysis - Hysteresis Curve (IRHD)After the standard irhd test the main load can be removed fromthe sample (only pre-load is kept on the sample) to check thehysteretic behaviour of the sample. The % of the positionrecovery of the indentor is calculated at the set test time.Positive correlation has been found between % finaldeformation and compression set results

Data Analysis – Raw data exportAll gibitre programs provide the possibility toexport row data of curves. This is useful forspecific investigation needs.

Studies and DevelopmentsInteresting studies have been done during 2010 regarding the relationshipbetween IRHD hardness reading and sample thickness.The research project has been done in cooperation among GibitreInstruments, Pirelli Automotive Milan Research Laboratory,Bridgestone Rome Research Laboratory, University of Physics ofNaples.The aim of the project was the investigation of mathematical models to correcthardness reading according to the real thickness of the sampleThe starting point for the research has been the UNI 7319 standard developedin 1974 by Dr. Bassi. The Standard provided empiric correction curves.The study has identified mathematical models which provide successfulcorrection within limited sample variations and can provide interestingpossibilities to incorporate in future software version the correction fortests on non-standard samples.

Sample manipulationprovides the realadvantages in the useof the instrumentsSample manipulationStandard Gibitre sampleholder provides auseful way toautomatically performtests in different pointsof the sample.The sample holder movesup and down androtates automaticallybetween one test andthe next one.

Diaphragm centring device for O-rings• The device is used in combination with theMicrometric Slide (code 8-HS0-44-000-0) andenables automatic multiple tests to be carried outon O-ring or round parts with external diameterup to 75 mm.• The use is very simple:• 1) set on the manual gauge-meter of the slidingsystem the dimension of the o-ring to be tested(internal diameter + cord)/2 to centre it correctly.• 2) put the o-ring on the Diaphragm centring andfix the o-ring slightly using the open-closeleverage• 3) Start a multiple test session to makeautomatically tests in different points of thesample.• When you test different o-rings of the same kind,no regulation is required between one o-ring andthe next one• The distance between the plate and thediaphragm can be regulated according to thecross-section of the o-ring.• The Y axe position is automatically centred dueto the mechanical construction of the instrument

Microcylinder centring device for O-rings• The device is designed for the quick centring ofO-rings or cylindrical parts independently fromthe diameter. This device permits to make onetest on the sample and requires manual repositioningof the sample between one tests andthe next.• This device is mounted directly on the standardplate of the instrument.• The use is very simple:• 1) the sample is placed between the verticalmicro-cylinders.• 2) The position of the micro-cylinders isregulated using the handle to fix the sample inthe middle.• 3) The middle position of the micro-cylinders isthe correct centring point for the test.• The height of the micro-cylinder can be regulatedusing the regulation ring according to the crosssectionof the sample.• The Y axe position is automatically centred dueto the mechanical construction of the instrument

Centring device for tubesThe device positions a piece of tubingfor testing.Note: this device permits to make onetest on the sample and requiresmanual re-positioning of thesample between one tests and thenext.Extension of sample holderAluminium extension to be applied tothe sample holder for the testingof hardness of big samples.

Laser Centring DeviceThe device includes:• -Class 1 laser Sensor thatdetects the maximum thicknesspoint of the part being tested• -Motor-controlled slide thatmoves the sample to performthe test in the optimum testposition.• For the performance of the testthe user must simply place thesample on the sample holder inthe test area and press start.The instrument:• -finds automatically theoptimum test point of thesample• -measures the thickness of thesample in the test point.• -moves the sample in the testposition• -performs the hardness test inthe optimum test point• -moves back to the start point toprepare for the next test.

The test report refers to 10tests on the same O-Ringwith 1.5 mm crosssection.The tests have been doneusing laser positioningsystem.Laser Centring Device

HD0 – Multi-sample hardness testerThe instrumentautomatically handles up to20 samples placed on thesample holder and performshardness tests (Shore, IRHDor micro-IRHD) in differentpoints of the sample andthen a density test.

Comparison of resultsThe possibility to compare resultsamong different instruments is relatedwith:• Calibration of the devices• Repeatability of the device• Interlaboratory comparisons

Calibration of the hardness testers• Gibitre Instruments provides calibration service both forown produced and for other brands of instruments andhas issued up to now about 450 SIT calibrationcertificates for all models and brands of instruments• Interesting features of the service offered are:• Comparison with pre-calibration and post-calibrationresults with standard samples.• Pre-calibration regulation of the instrument(depending from the model)• Calibration service within 24 hours from instrumentreceiving• No charge in case an instrument cannot be calibrated(transportation excluded)• Support for packaging and transportation (re-usablemulti-layer cardboard packing)

Repeatability oftest resultsGibitre performscontinuous verificationof repeatability andcontrol capability ofthe instruments toevaluate theperformances oftechnical changes onthe instruments.

Interlaboratory TestsGibitre Instruments takes part to systematic Interlaboratory test programssince yearsSince 2011 the participation to the Interlaboratory Test programorganized by LRCCP has been added to the yearly Gibitre Testprogramme.

Requests for hardness testsat controlled temperatureare continuously increasing.Gibitre is presentlydeveloping thermalchambers to enable hardnesstest at high and lowtemperaturesDifferent possibilities will beavailable for small-scaleresearch needs and forproduction control withautomatic sample loadingsystem.The new applications will beshown at Milan Plast2012exibition.Developments

Thank You for your AttentionMr Bert Haring from AVOKAL and myself willbe at your disposal for further informationabout this topic or any other Gibitre productand service.