08/10/2003
CT104 Manual
Tri-M Engineering
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8
3.2 Rubber Mounting Materials
Compound
- High Grade EPDM 80 extruded rubber
Rating
- ULHB94 Horizontal Burn Test, compound # 295-104-02-90
ETHYLENE PROPYLENE COPOLYMER
(EPM/EPDM) Elastomers prepared from ethylene and propylene
monomers , at times with a small amount of a third monomer (Etlylene Propylene Terpolymer). Excellent
resistance to phosphate ester type hydraulic fluids.
Specific gravity..........................................86
Tensile Strength.........................................3,000
Elongation, max.........................................6x
Hardness, Shore A.....................................30-90
Brittle Point (F)..........................................-90
The hardness testing of plastics is most commonly measured by the Shore (Durometer) test or
Rockwell hardness test
.
Both methods measure the resistance of the plastic toward indentation. Both scales provide an empirical hardness value
that doesn't correlate to other properties or fundamental characteristics. Shore Hardness, using either the Shore A or
Shore D scale, is the preferred method for rubbers/elastomers and is also commonly used for 'softer' plastics such as
polyolefins, fluoropolymers, and vinyls. The Shore A scale is used for 'softer' rubbers while the Shore D scale is used for
'harder' ones.
The Shore hardness is measured with an apparatus known as a Durometer and consequently is also known as
'Durometer hardness'. The hardness value is determined by the penetration of the Durometer indenter foot into the
sample. Because of the resilience of rubbers and plastics, the hardness reading my change over time - so the indentation
time is sometimes reported along with the hardness number. The ASTM test method designation is ASTM D2240 00.
Related methods include ISO 7619 and ISO 868; DIN 53505; and JIS K 6301, which was discontinued and superseded
by JIS K 6253.
The results obtained from this test are a useful measure of relative resistance to indentation of various grades of
polymers. However, the Shore Durometer hardness test does not serve well as a predictor of other properties such as
strength or resistance to scratches, abrasion, or wear, and should not be used alone for product design specifications.
As seen in the charts below, the correlation between the two Shore Durometer hardness scales is weak; attempts at
conversion between the scales are therefore discouraged. The correlation is higher for materials with similar resiliency
properties, but is still too low for reliable conversions. Likewise, conversion between Shore Hardness and Rockwell
hardness is discouraged.
