Rubber Hardness

Elastomeric materials are usually measured with either a Shore A Scale Durometer or an IRHD dead load system. These tests are designed for use with samples approx 6mm thick, and a surface area sufficient to permit at least 3 test points 5mm apart, 13mm from any edge.

Microhardness testers, Shore "A" Micro (M), or IRHD Micro (M), are utilised to measure samples which are too small for testing with macro instruments.

Shore

The Shore type instrument is a spring loaded indentation device, in which values are obtained as a function of the viscoelastic property of the material. The truncated cone indentor, extends 0.098inch (2.5mm)) and is pressed onto the sample against an 822g spring. Each 0.001 inch of deflection of the indentor is shown as 1 degree Shore (A), therefore, the harder the material, the more the deflection, the higher the number.

Materials reading below 10 degrees and above 90 degrees can be tested using Shore O & D scales respectively. The scales "OO" is designed to read materials less than 10 Shore "O". Scales "B" & "C" are intermediate scales and the specifications are hybrids of the "A" & "D".

The microhardness tester reading Shore "A" Micro is basically a combination of "OO" Spring and "D" Indentor (set at 0.050inch (1.25mm)). The instrument is comparative and is supplied with a set of reference blocks which enable calibration to the macro "A" value.

IRHD

The IRHD (International Rubber Hardness Degrees) instrument has a spherical indentor which indents the sample under a minor and major Load. The differential indentation depth is measured and tabulated to read directly in "IRHD" degrees. The displacement/IRHD degrees conversion table is published in ISO 48 : 1994. The standard shows three different combinations of Ball & Loadings, (N) Normal, (H) High and (L) Low.

Aplications

Standards