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An Elastomer is a material that
can be, or already is, modified to a state exhibiting little plastic
flow and has quick and nearly complete recovery from an extending force.
Such material before modification is called, in most instances, a raw
or crude rubber, and, by appropriate processes, can be converted into
a finished product.
When the basic elastomer is converted to an essentially
non-plastic state and tested at room temperature, 15° to 30†
C (60° to
90† F), it must meet the following test requirements, according to
ASTM:
- Capable of being stretched 100%.
- After being stretched 100%, held
for 5 minutes and then released, it is capable of retracting to within
10% of its original length
within 5 minutes after release.
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Neoprene rubber is a homopolymer of chloroprene. It is more resistant
than natural rubber to gasoline, sunlight, ozone and oxidation. It
is also flame resistant and will not support combustion. It has good
resistance to corrosive action of chemicals, bacterial enzymes, and
its water resistance is as good as natural rubber. It has good resistance
to heat and does not soften as does natural rubber, but where increased
resistance to heat, ozone, weathering, gasoline or oil is required.
The temperature range is -40° to +135°C (-40° to 275° F) |
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Buna-N is known as Nitrile or NBR, it is a copolymer
of butadiene and acrylonitrile. It has excellent resistance to petroleum,
fuel and other petroleum products. It has good low temperature flexibility
and is superior to most elastomers in compression set, cold flow and
abrasion resistance. However, it does not possess good resistance to
ozone, sunlight or weather. Buna-N has a temperature range of -40ƒ to+135ƒ C
(-40ƒ to 275ƒF) |
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Buna-S or SBR is a copolymer of styrene and butadiene and has properties
similar to natural rubber. It has greater abrasion resistance than
natural rubber, better wear resistance and better low temperature flexibility.
Though superior in water resistance to natural rubber, it has about
the same resistance to solvents and chemicals. It has better heat resistance
and heat-aging qualities than natural rubber, and in excess heat it
hardens and becomes brittle instead of softening as does natural rubber.
The temperature range of SBR is -55ƒ to +70ƒC (-67ƒ to158ƒF). |
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Butyl (IIR) rubber is a copolymer of isobutylene. It has exceptionally
low gas and moisture permeability and outstanding resistance to heat
aging, weather, ozone, chemical attack, flexing, abrasion and tearing.
It has good resistance to phosphate ester based hydraulic fluids, and
has excellent electrical insulation performance. Butyl is not recommended
for use when in contact with petroleum oils and fluids. The temperature
range is -55ƒ to 120ƒC (-67ƒ to +248ƒF). |
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Ethylene Propylene (EPDM) rubber is a copolymer of ethylene and propylene and
also contains a small amount of a third monomer, diene. It has outstanding
resistance to aging, weathering, ozone, oxygen and many chemicals. It has high
and low temperature stability, as well as steam and water resistance. Its dynamic
and mechanical properties are between those of natural rubber and SBR. It has
excellent resistance to phosphate ester based hydraulic fluids, but is not
recommended for use in contact with petroleum oils or fluids. The temperature
range is -55ƒ to +135ƒC (-67ƒ to +275ƒF). |
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Hypalon is Chlorosulfonated polyethylene. It has outstanding resistance
to ozone attack and color retention during light exposure. It has
excellent flame and oil resistance, as well as excellent heat, weather,
acid,
chemical, and abrasion resistance. Hypalon has a temperature range
of -40ƒ to+160ƒC (-40ƒ to +320ƒF).
Hypalon® is a Registered Trade Mark of DuPont Dow Elastomers |
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Natural rubber is a ready-made organic elastomer. It offers the optimum balance
of properties necessary for high performance in demanding mechanical applications.
it has high resilience, has very good tensile and tear properties over a wide
range of durometers and has excellent resistance to cold flow. The abrasion
resistance of natural rubber is good, and it has better low temperature flexibility
than most synthetics. However, natural rubber does not age well, nor is it
chemically inert. It is inferior to many synthetics in heat aging, resistance
to sunlight, oxygen, ozone, solvents and oil. The temperature range of natural
rubber is -55ƒ to +50ƒC (67ƒ to +122ƒF).
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Silicone (SI) rubber is a semi-organic elastomer made from silicone,
oxygen, hydrogen and carbon. It has outstanding resistance to temperature
extremes. Under normal operating conditions, temperatures as high as
260ƒ C (500ƒ F) and as low as -75ƒ C (-103ƒ F) have little effect on
the physical and electrical properties. At temperatures between -85ƒ C
(-121ƒ F) and +260ƒ C (+500ƒ F), it is superior in its resistance to
compression set, compared with all other available elastomers. At moderate
temperatures, it has poor tensile strength, tear resistance and abrasion
resistance. However, at extreme temperatures, where other materials
have failed, the physical properties of silicone remain unchanged.
Silicone has outstanding resistance to sunlight, ozone, oxygen, gases
and moisture. It has a temperature range of -100ƒ to +315ƒ C (-148ƒ to
+599ƒ F). |
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Polyurethane (AU, EU) elastomers are formed from the reaction of isocyanates
with hydroxyl compounds. The have outstanding abrasion resistance at
moderate temperatures, greater than most rubbers and plastics. Urethanes
have exceptionally high tensile strength, tear strength, and load bearing
capabilities, higher than any conventional rubbers. They are resistant
to oils, solvents, fats, greases, gasoline, ozone, sunlight and weather.
A wide range of hardnesses are available to urethane from a soft 15
duro., Shore A to a hard 80 duro., Shore D. Urethane remains flexible
at low temperatures or where there is a possibility of heat build-up
from friction. The temperature range is -40ƒ to +95ƒ C (-40ƒ to +203ƒ F). |
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Viton rubber is a copolymer of vinylidene fluoride and hexafluoropropylene. It
has good resistance to most chemicals and commercial fluids. It has an outstanding
ability to retain strength at elevated temperatures and to withstand embrittlement
during long-term heat aging. It has outstanding compression set with the ability
to recover following deflection at 150ƒ to 230ƒ C (302ƒ to 446ƒ F). The temperature
range is -30ƒ to +230ƒ C (-22ƒ to +446ƒ F), but will withstand temperatures
up to 315ƒ C (599ƒ F) for short periods of time.
Viton® is a Registered Trade Mark of DuPont Dow Elastomers |
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