Rubber Hardness: Gibitredevelopments and technical

market tendencies

Eng. Mauro Belloni

VKRT Seminar 10-02-2011

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 HardnessThe 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 fortesting visco-elastic properies and is widely used because it is: Low cost, quick, non distructive.

Instrument Construction:

• the force is applied to the indentor using a spring

• The hardness is measured after defined times (typically1, 3, 10, 15 seconds)

• Sample thickness: 6 mm

Standards: ISO 868, ISO 7619-1, ASTM D 2240

About Hardness - Shore

Thin RubberISO 7619-1, ASTM D 2240Shore M

Cellular RubberASTM D 2240Shore 00

Cellular RubberISO 7619-1, ASTM D 2240Shore A0

Hard RubberISO 868, 7619-1, ASTM D 2240Shore D

Normal RubberISO 868, 7619-1, ASTM D 2240Shore A

ApplicationStandardType

Most used Types of Instruments:

Indentor

Spring

Presser Foot

Instrument Construction:

• 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

About Hardness - IRHD

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 ball-recirculation 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 irhdThe indentor is connected to a load cell.

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.

Ruby Spere for the indentor

Gibitre Technology for irhdA 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

Statistic Analysis

• The test time can be set •Calculation of hardness at specific time can be set independently.

Data Analysis - Hardness at set time

• 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 visco-elastic 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 - Hardness Relaxation

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

Data Analysis - Hysteresis Curve (IRHD)

Studies and DevelopmentsInteresting 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 re-positioning 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 cross-section 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 re-positioning 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 DeviceThe 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.

Laser Centring DeviceThe 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.

HD0

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.

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 SITcalibration 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 TestsGibitre Instruments takes part to systematic Interlaboratory test programs since years

Since 2011 the participation to the Interlaboratory Test programorganized by LRCCP has been added to the yearly Gibitre Test programme.

DevelopmentsRequests 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.

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.