VKRT Seminar 10-02-2011 Rubber Hardness: Gibitre developments and technical market tendencies Eng. Mauro Belloni
Index Introduction about rubber hardness measure Available Instrument Configurations Technology used for IRHD Software and Calculation Studies Centring Devices and sample manipulation Certification and Comparison of results Hardness Test at controlled Temperature
About Hardness The hardness is the measure of the penetration of an indentor 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 for testing visco-elastic properies and is widely used because it is: Low cost, quick, non distructive.
About Hardness - Shore Instrument Construction: the force is applied to the indentor using a spring The hardness is measured after defined times (typically 1, 3, 10, 15 seconds) Sample thickness: 6 mm Standards: ISO 868, ISO 7619-1, ASTM D 2240 Spring Indentor Presser Foot Most used Types of Instruments: Type Standard Shore A ISO 868, 7619-1, ASTM D 2240 Shore D ISO 868, 7619-1, ASTM D 2240 Shore A0 ISO 7619-1, ASTM D 2240 Shore 00 ASTM D 2240 Shore M ISO 7619-1, ASTM D 2240 Application Normal Rubber Hard Rubber Cellular Rubber Cellular Rubber Thin Rubber
Instrument Construction: About Hardness - IRHD Constant forces are applied to the sample (pre-load for 5 s, Main force for 30 s) Indentor have Spherical Shape Standards: ISO 48, ASTM D 1415
Gibitre Technology for irhd The hardness units produced by Gibitre have some unique features
Gibitre Technology for irhd The sample holder is connected to a ballrecirculation screw and moved up and down using a micro-motor. The position of the sample holder is controlled with 0.1 Micron resolution
Gibitre Technology for irhd The indentor is connected to a load cell. Ruby Spere for the indentor During the test the forces (pre load and main load) applied to the sample are controlled moving the sample holder upwards. A High speed controller with closed loop regulation has been specifically designed to ensure stable force application.
Gibitre Technology for irhd A High speed controller with closed loop regulation has been specifically designed to ensure stable force application.
Advantages if Gibitre Construction Modular Construction ease of maintenance, ease of calibration No Moving parts in the measuring part improved repeatability Direct calibration process Solid Construction Ball Recirculation Screw Load cell with overload protection Indentor with Ruby Sphere
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 at the same time. Single units can be connected to the same pc using independent 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 measure is used with higher frequence The multi-unit configuration permits to install up to 4 selected types of shore or irhd hardness units. The unit to be used is placed in the front position and is automatically recognized by the software.
Certified Rubber Samples Gibitre provides certified samples for hardness verification. Available samples are for Shore (A, D) and IRHD (Micro, Normal) hardness
Software Hardness Relaxation curves for each test Statistic Analysis Test Identification Results and comparison with tolerances
Data Analysis - Hardness at set time The test time can be set Calculation of hardness at specific time can be set independently.
Data Analysis - Hardness Relaxation The curve of Hardness Relaxation versus time is displayed and stored. Regression line of the curve in logarithmic axes is calculated and the relative angle coefficient is calculated. Angle coefficient is an indicator of viscoelastic behaviour and has correlation with the level of curing for a defined compound. This measure can be used for a quick and non-distructive test for moulding process control.
Data Analysis - Hysteresis Curve (IRHD) After the standard irhd test the main load can be removed from the sample (only pre-load is kept on the sample) to check the hysteretic behaviour of the sample. The % of the position recovery of the indentor is calculated at the set test time. Positive correlation has been found between % final deformation and compression set results
Studies and Developments Interesting studies have been done during 2010 regarding the relationship between IRHD hardness reading and sample thickness. The research project has been done in cooperation among Gibitre Instruments, Pirelli Automotive Milan Research Laboratory, Bridgestone Rome Research Laboratory, University of Physics of Naples. The aim of the project was the investigation of mathematical models to correct hardness reading according to the real thickness of the sample The starting point for the research has been the UNI 7319 standard developed in 1974 by Dr. Bassi. The Standard provided empiric correction curves. The study has identified mathematical models which provide successful correction within limited sample variations and can provide interesting possibilities to incorporate in future software version the correction for tests on non-standard samples.
Sample manipulation Sample manipulation provides the real advantages in the use of the instruments Standard manipulation tool Specific Manipulation devices Automatic sample changer
Diaphragm centring device for O-rings The device is used in combination with the Micrometric Slide (code 8-HS0-44-000-0) and enables automatic multiple tests to be carried out on O-ring or round parts with external diameter up to 75 mm. The use is very simple: 1) set on the manual gauge-meter of the sliding system 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 and fix the o-ring slightly using the open-close leverage 3) Start a multiple test session to make automatically tests in different points of the sample. When you test different o-rings of the same kind, no regulation is required between one o-ring and the next one The distance between the plate and the diaphragm can be regulated according to the cross-section of the o-ring. The Y axe position is automatically centred due to the mechanical construction of the instrument
Microcylinder centring device for O-rings The device is designed for the quick centring of O-rings or cylindrical parts independently from the diameter. This device permits to make one test on the sample and requires manual repositioning of the sample between one tests and the next. This device is mounted directly on the standard plate of the instrument. The use is very simple: 1) the sample is placed between the vertical micro-cylinders. 2) The position of the micro-cylinders is regulated using the handle to fix the sample in the middle. 3) The middle position of the micro-cylinders is the correct centring point for the test. The height of the micro-cylinder can be regulated using the regulation ring according to the crosssection of the sample. The Y axe position is automatically centred due to the mechanical construction of the instrument
Centring device for tubes The device positions a piece of tubing for testing. Note: this device permits to make one test on the sample and requires manual repositioning of the sample between one tests and the next. Extension of sample holder Aluminium extension to be applied to the sample holder for the testing of hardness of big samples.
Laser Centring Device The device includes: - Class 1 laser Sensor that detects the maximum thickness point of the part being tested - Motor-controlled slide that moves the sample to perform the test in the optimum test position. For the performance of the test the user must simply place the sample on the sample holder in the test area and press start. The instrument: - finds automatically the optimum test point of the sample - measures the thickness of the sample in the test point. - moves the sample in the test position - performs the hardness test in the optimum test point - moves back to the start point to prepare for the next test.
The test report refers to 10 tests on the same O-Ring with 1.5 mm cross section. The tests have been done using laser positioning system. Laser Centring Device
The instrument automatically handles up to 20 samples placed on the sample holder and performs hardness tests (Shore, IRHD or micro-irhd) in different points of the sample and then a density test. HD0
Comparison of results Calibration of the devices Repeatability and Reproducibility of the results Interlaboratory tests
ISO 17025 Accreditation Since 2005, Gibitre Instruments is accredeted ISO 17025 laboratory for the calibration of IRHD (N, M, L, H) and Shore (A, D) hardness testers
Calibration of the hardness testers Calibration system is the main issue for ensuring the correct reading of the instruments The calibration includes the verification of: Dimensions of the indentor Forces applied to the sample Relationship between hardness measure and Indentation Gibitre Instruments provides calibration service both for own produced and for other brands of instruments and has issued about 400 SIT calibration certificates for all models and brands of instruments Interesting features of the service offered are: Comparison with pre-calibration and post-calibration results with standard samples. Pre-calibration regulation of the instrument (depending from the model) Calibration service within 24 hours from instrument receiving No charge in case an instrument cannot be calibrated (transportation excluded) Support for packaging and transportation (re-usable multi-layer cardboard packing)
Repeatability of test results
Interlaboratory Tests Gibitre Instruments takes part to systematic Interlaboratory test programs since years Since 2011 the participation to the Interlaboratory Test program organized by LRCCP has been added to the yearly Gibitre Test programme.
Requests for hardness tests at controlled temperature are continuously increasing. Gibitre is presently developing thermal chambers to enable hardness test at high and low temperatures Different possibilities will be available for small-scale research needs and for production control with automatic sample loading system. The new applications will be shown at Milan Plast 2012 exibition. Developments
Thank You for your Attention Mr Bert Haring from AVOKAL and myself will be at your disposal for further information about this topic or any other Gibitre product and service.