A quick guide to the most common compounds:
Both Kalrez® & Viton® are registered trademarks of Dupont Dow Elastomers
BUTADIENE RUBBER (BR)
Typical Trade Name:
Ameripol CB.……..….……....BF.Goodrich
Budene.….……..Goodyear Tire & Rubber
Diene….….…Firestone Synthetic Rubber
Trans 4 or Cis 4…....Philips Chemical Co.
Polybutadiene is an elastomer with properties very similar to natural rubber. Its physical properties are not quite up to natural rubber; however, in some cases its low temperature characteristics are better. Butadiene is primarily a tire polymer.
BUTYL RUBBER (BR)
Typical Trade Names:
Bucar Butyl……………Columbian Chemicals Co.
Exxon Butyl……………Exxon Chemical Co. USA
Polysar Butyl…………………………..Polysar LTD.
Butyl rubber is an all petroleum product made by co-polymerizing isobutylene and just enough isoprene to obtain the desired degree of unsaturation necessary for vulcanization. Brominated and chlorinated butyl rubber are also available and are prepared by select replacement of hydrogen with bromine or chlorine.
Until the introduction of ethylene propylene rubber, butyl was the only elastomer which was satisfactory for Skydrol 500 service over a temperature range of -65 to +225·F (-54 to +107·C).
In addition, butyl has excellent resistance to gas permeation which makes it particularly useful for vacuum applications and accounts for its wide use in the manufacture of inner tubes and the inside layer of tubeless tires.
Butyl is recommended for:
Phosphate ester type hydraulic fluids (Skydrol, Fyrquel, Pydraul)
Ketones (MEK, Acetone)
Silicone fluids and greases.
Butyl is not recommended for:
Petroleum oils
Di-ester base lubricants
CHLORINATED POLYETHYLENE (CM)
Typical Trade Name:
CPE…………………………Dow Chemical Co.
Chlorinated polyethylene is made from a high density polyethylene. Its saturated backbone and its chlorine content give it limited resistance to petroleum oils and good resistance to oxidation. Unlike neoprene, the chlorination of CPE is random and can be varied. As the chlorine content is increased, resistance to petroleum oils improves but low temperature flexibility becomes poorer. CPE can be blended with other polymers to improve their flame and impact resistance. In fact, it is seldom used alone, the bulk of the product being used for blending purposes.
CHLOROSULFONATED POLYETHYLENE (CSM)
Typical Trade Name:
Hypalon……………….E.I. DuPont de Nemours
The ethylene monomer with some of the hydrogen replaced by chlorine and sulphur groups is the main constituent of this elastomer.
It is useful over a temperature range of -65 to +250· (-54 to +121· C), but its mechanical properties, compression and permanent set characteristics are less than is desired for both dynamic and static sealing applications.
Chlorosulfonated Polyethylene has good acid resistance.
EPICHLOROHYDRIN RUBBER (CO, ECO)
Typical Trade Names:
Herclor…………………………..Hercules, Inc.
Hydrin………………………B.F. Goodrich Co.
Epichlorohydrin is a recent addition to the oil resistant polymer class. Compounds of this type are aliphatic polyethers with chlorofunctional side chains. Two basic classes, homopolymers (CO) and copolymers (ECO) are available. Both have excellent resistance to hydrocarbon oils, fuels and ozone. High temperature resistance is good, but compression set at 300·F is only fair. This property, plus the corrosive nature of epichlorohydrin, are limiting factors in some applications.
Copolymers give very good low temperature properties, providing a temperature range of -65· to +275·F (-54· to +135·C) under the same conditions.
ETHYLENE ACRYLIC
Typical Trade Name:
VAMAC………………………….E.I. duPont de Nemours
Ethylene acrylic compounds are considered "medium performance elastomers," having a useful temperature range extending from approximately -30· to +350·F. Resistance to weathering, ozone and air aging is very good, and they have sufficient resistance to petroleum oils and automatic transmission fluids to make them look attractive for automotive applications.
ETHYLENE PROPYLENE RUBBER (EPM, EPDM)
Typical Trade Names:
Nordel…………………………….E.I. duPont de Nemours
Royalene……………………………………………Uniroyal
Vistalon………….……………..Exxon Chemical Co. USA
Epsyn………………Copolymer Rubber & Chemical Corp.
Epcar……………………..………………B.F. Goodrich Co.
Ethylene propylene rubber is an elastomer prepared from ethylene and propylene monomers (ethylene propylene copolymer) and at times with a small amount of a third monomer (ethylene propylene terpolymers). It was introduced to the rubber industry in 1961 and quickly won broad acceptance in the sealing world because of its excellent resistance to Skydrol and other phosphate ester type hydraulic fluids.
Ethylene propylene has a temperature range of -65· to +300· F (-54· to +149·C) for most applications.
EP IS RECOMMENDED FOR:
Phosphate ester base hydraulic fluids (Skydrol, Fyrquel, Pydraul)
Steam to 400·F (204·C)
Water
Silicone oils and greases
Dilute acids
Dilute alkalis
Ketones (MEK, acetone)
Alcohols
Automotive brake fluids.
EP IS NOT RECOMMENDED FOR:
Petroleum oils
Di-ester base lubricants.
FLUOROCARBON RUBBER (FKM)
Typical Trade Names:
Fluorel………………………………..……….3M
Kalrez…………..……E.I. duPont Nemours Co.
Kel-F…………………..…3M (formerly Kellogg)
Viton………………….E.I. duPont Nemours Co.
Fluorocarbon elastomers were first introduced in the mid-1950's. Since then they have grown to major importance in the seal industry. Due to its wide spectrum chemical compatibility and temperature range and its low compression set, fluorocarbon rubber is the most significant single elastomer development in recent history.
Its working temperature range is considered to be -15· to +400·F (-29· to +204·C), but it will take temperatures up to 600·F (316·C) for short periods of time, and duPont's Kalrez is normally recommended up to 500·F (260·C). On the low temperature end, Parker's compound V835-75 will seal down to -40·F in a static seal. Though the standard compounds have been known to seal at -65·F (-54·C) in some special static applications, the normal low temperature limit is -15·F (-26·C).
Special formulations having extra chemical resistance are also available, and new types are being developed constantly.
Fluorocarbon O-rings should be considered for seal use in aircraft, automobile and other mechanical devices requiring maximum resistance to elevated temperature and to many functional fluids.
FKM IS RECOMMENDED FOR:
Petroleum oils
Di-ester base lubricants (MIL-L-7808, MIL-L-6085)
Silicate ester base lubricants (MLO 8200, MLO 8515, OS-45)
Silicone fluids and greases
Halogenated hydrocarbons (carbon tetrachloride, trichloroethylene)
Selected phosphate ester fluids
Acids.
FKM IS NOT RECOMMENDED FOR:
Ketones (MEK, acetone)
Skydrol fluids
Amines (UDMH), anhydrous ammonia
Low molecular weight esters and ethers
Hot hydrofluoric or chlorosulfonic acids.
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…………………………..…………………Distugil
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 (Hydrolubes)
NITRILE IS NOT RECOMMENDED FOR:
Halogenated hydrocarbons (carbon tetrachloride, trichlorethylene)
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.
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