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Rubber Engineering-Physical Testing
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.
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.
he 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.
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