FLUOROSILICONE (FSi)
Typical Trade Name:
Silastic L.S…………………….Dow
Corning Corp.
Fluorosilicone combines the good high and low temperature
properties of silicone with basic fuel and oil resistance.
The primary uses of fluorosilicones are in fuel systems at
temperatures up to 350·F (177·C) and in applications where
the dry-heat resistance of silicone is required, but the seal
may be exposed to petroleum oils
and/or hydro-carbon fuels. In some fuels and oils, however,
the high temperature limit is more conservative because temperatures
approaching 350·F may degrade the fluid, producing acids which
attack fluorosilicone elastomers.
On the other end of the temperature scale, fluorosilicones
typically seal at temperatures as low as -100·F (-73·C). High
strength type fluorosilicones are available.
Certain of these exhibit much improved resistance to compression
set.
ISOPRENE RUBBER-SYNTHETIC
(IR)
Typical Trade Name:
Natsyn……………………………Goodyear
Tire & Rubber Co.
Polyisoprene has the distinction of being a synthetic elastomer
which has the same chemical composition as natural rubber.
For a guide to its chemical and physical properties, refer
to Natural Rubber below.
NATURAL RUBBER -- NATURAL
POLYISOPRENE (NR)
Crude natural rubber is found in the juices of many plants,
including the shrub guayule, Russian dandelion, goldenrod
and dozens of shrubs, vines and trees. The
principal source is the tree Hevea Brasiliensis which is native
to Brazil. Petroleum oils are the greatest enemy of natural
rubber compounds. The synthetics have all but
completely replaced natural rubber for seal use.
NR IS RECOMMENDED FOR:
Automotive brake fluid.
NR IS NOT RECOMMENDED FOR:
Petroleum products.
NEOPRENE RUBBER (CHLOROPRENE,
CR)
Typical Trade Name:
Neoprene (formerly E. I. DuPont de Nemours Company)
Butaclor…………………………..…………………Distain
Denka……………………….………..Denka
Chemical Co.
Neoprenes are homopolymers of chloroprene (chlorobutadiene)
and were among the earliest of the synthetic rubbers available
to the seal manufacturers.
Neoprene can be compounded for service at temperatures of
-65· to +300·F (-54· to +149·C). Most elastomers are resistant
to deterioration from exposure to either petroleum lubricants
or to oxygen, but not both. Neoprene is unusual in having
limited resistance to both. This, combined with broad temperature
range and
moderate cost, accounts for its desirability in many seal
applications.
CHLOROPRENE IS RECOMMENDED FOR:
Refrigerants (Freon, ammonia)
High aniline point petroleum oils
Mild acid resistance
Silicate ester lubricants
CHLOROPRENE IS NOT RECOMMENDED
FOR:
Phosphate ester fluids
Ketones (MED, acetone).
NITRILE OR BUNA-N (NBR)
Typical Trade Names:
Chemigum…………………..Goodyear
Tire & Rubber Co.
Paracril………………………………………………Uniroyal
Hycar……………….………………Goodrich
Chemical Co.
Krynac…………………………………………..Polysar,
Ltd.
Ny Syn…….…………..Copolymer Rubber
& Chem. Corp.
Nitrile, chemically, is a copolymer of butadiene and acrylonitrile.
Acrylonitrile content is varied in commercial products from
18% to 48%. As the nitrile content increases, resistance to
petroleum base oils and hydrocarbon fuels increases, but low
temperature flexibility decreases.
Due to its excellent resistance to petroleum products, and
its ability to be compounded for service over a temperature
range of -65· to +275·F (-54· to +135·C), nitrile is the most
widely used elastomer in the seal industry today. Most military
rubber specifications for fuel and oil resistant MS and AN
O-rings require nitrile base compounds. It should be mentioned,
however, that to obtain good resistance to low temperature
with nitrile compounding, it is almost always necessary to
sacrifice some high temperature fuel and oil resistance.
Nitrile compounds are superior to most elastomers with regard
to compression set or cold flow, tear and abrasion resistance.
Inherently, they do not possess good resistance to ozone,
sunlight or weather, but this can be substantially improved
through compounding. However, since ozone and weather resistance
are not always built in, seals from nitrile bases should not
be stored near electric motors or other equipment which may
generate ozone, or in direct sunlight.
NITRILE IS RECOMMENDED FOR:
General purpose sealing
Petroleum oils and fluids
Cold water
Silicone greases and oils
Di-ester base lubricants (MIL-L-7808)
Ethylene glycol base fluids (Hydro lubes)
NITRILE IS NOT RECOMMENDED FOR:
Halogenated hydrocarbons (carbon tetrachloride, trichloroethylene)
Nitro hydrocarbons (nitrobenzene, aniline)
Phosphate ester hydraulic fluids
(Skydrol, Fyrquel, Pydraul) Ketones (MEK, acetone)
Strong acids
Ozone
Automotive brake fluid.
POLYPHOSPHAZENE FLUOROELASTOMER
(FZ)
Typical Trade Name:
EYPEL-F……………………………….Ethyl
Corp.
EYPEL-F elastomer should effectively solve many difficult
sealing problems due to its combination of physical properties,
fluid resistance and temperature range.
The base polymer was developed for the U.S. Army by Firestone
Tire and Rubber Company, and it has much the same temperature
range (-85· to 325·/350·F) and fluid resistance (especially
petroleum products) as fluorosilicone elastomers but physical
properties are definitely better – enough so that polyphosphazene
compounds have performed adequately in dynamic and extrusion
tests. Major disadvantage is its resistance to water which
is only fair to poor.
POLYACRYLATE RUBBER
(ACM)
Typical Trade Names:
Cyanacryl…………………………….American
Cyanamid Co.
Hycar……………………………..B.F.
Goodrich Chemical Co.
This material has outstanding resistance to petroleum fuel
and oil. In addition, it possesses complete resistance to
oxidation, ozone and sunlight, combined with an ability to
resist flex cracking. Compounds from this base polymer have
been developed which are adaptable for continuous service
in hot oil over the temperature
range 0· to +350·F (-28· to +177·C). Resistance to hot air
is slightly superior to nitrile polymers, but strength, compression
set and water resistance are inferior to many of the other
polymers.
There are several polyacrylate types available commercially,
but all are polymerization products of acrylic acid esters.
Greatest usage of polyacrylate is by the automotive industry
in automatic transmissions and power steering gears using
Type A fluid.
POLYSULFIDE RUBBER (T)
Typical Trade Name:
Polysulfide Rubber……………………..Thiokol
Chemical Corp.
Polysulfide Rubber was one of the earliest commercial synthetic
polymers and is prepared form dichlorides and sodium polysulfide.
It has a remarkable combination of solvent resistance, low
temperature flexibility, flex-crack resistance and oxygen
and ozone resistance. However, heat resistance, mechanical
strength and compression set are not outstanding. Other seal
compounds are more versatile from the performance standpoint,
hence polysulfide rubber is recommended by Parker only for
specific applications which cannot be satisfied by any other
elastomer. Temperature range is -65· to 225·F (-54· to +107·C).
Seals of polysulfide are recommended for service involving
contact with solutions of petroleum solvents, ketones and
ethers.
POLYURETHANE RUBBER
(AU, EU)
Typical Trade Names:
Texin……………………………..Mobay
Chemical Co.
Adiprene…………………E.I. DuPont
de Nemours Co.
Cyanaprene………………….American
Cyanamid Co.
Pellethane………………………..…………Upjohn
Co.
Roylar………………………………………….Uniroyal
Polyurethanes exhibit outstanding mechanical and physical
properties in comparison with other elastomers. Over a temperature
range of -65· to +200·F, resistance to petroleum oils, hydrocarbon
fuels, oxygen, ozone and weathering is good. However, polyurethanes
quickly deteriorate when exposed to acids, ketones and chlorinated
hydrocarbons.
SILICONE RUBBER (Si)
Typical Trade Names:
Rhodia………………………….….Rhone
Poulenc
Silastic…………..…………..….Dow
Corning Corp.
No trade name…………………….General
Electric
No trade name………Stauffer Chemical Company
The silicones are a group of elastomeric materials made from
silicone, oxygen, hydrogen and carbon. As a group, the silicones
have poor tensile strength, tear resistance and abrasion resistance.
Special compounds have been made which have exceptional heat
and compression set resistance. High strength compounds have
also been developed, but their strength does not compare to
conventional rubber. Silicones possess excellent resistance
to temperature extremes. Flexibility below-175(F (-114(C)
has been demonstrated and Parker has compounded silicone materials
which will resist temperatures to 700(F (371(C) for short
periods. The maximum temperature at which silicones are recommended
for continuous service in dry air is 450(F (232(C). Silicone's
retention of properties at these high temperatures is superior
to other elastic materials.
Silicone compounds are not normally recommended for dynamic
sealing applications due to relatively low strength and high
coefficient of friction.
Most silicone compounds have a higher than normal mold shrinkage
that results in finished parts being undersize when produced
in standard molds. Contact us for more information about the
effects of mold shrinkage on seal compounds.
SILICONES ARE RECOMMENDED FOR:
Dry heat
High-aniline point oils
Chlorinated di-phenyls.
SILICONES ARE NOT RECOMMENDED
FOR:
Most petroleum fluids
Ketones (MEK, acetone)
Water and steam.
