Materials Guide
AFLAS™
Trade Names(s): Aflas . . . Asahi Glass Co., Ltd.
ASTM D1418 Designation: FKM
ASTM D2000/SAE J200 Type, Class: HK
Standard Color: Black
Description: A copolymer of tetrafluoroethylene/ propylene, Aflas can offer a combination of high temperature and chemical resistance.
Key Use(s): Seals for oil field, aerospace, chemical and general industrial environments.
Temperature Range: Standard Compound: -23° to +400°F. (Dry Heat Only)
Hardness (Shore A): 60 to 95.
Features: With good resistance to sour gases and oils, as well as amine corrosive inhibitors, Aflas has outperformed other elastomers in oil field applications. It has also outperformed them in automotive applications involving the new types of oils and fluids that have been developed for higher temperatures.
Limitations: Tests have shown that other FKM elastomers are recommended for automotive fuels since they have less volume swell than Aflas. Also, Aflas has shown to have less than desirable results when exposed to toluene, ethers, ketones, and acetic acid.
NITRILE - BUNA-N (NBR, Acrylonitrile-Butadiene Rubber)
Trade Names(s):
Chemigum . . . Goodyear
Hycar . . . B. F. Goodrich
Krynac . . . Polysar, Ltd.
Nysyn . . Copolymer Rubber
Paracril . . . Uniroyal
Perbunan . . . Mobay
ASTM D1418 Designation: NBR
ASTM D2000/SAE J200 Type, Class: BF, BG, BK, CH
Standard Color: Black
Description: Presently the seal industry’s most widely used and economical elastomer, Nitrile combines excellent resistance to petroleum-based oils and fuels, silicone greases, hydraulic fluids, water and alcohols, with a good balance of such desirable working properties as low compression set, high tensile strength, and high abrasion resistance.
Key Use(s): Oil resistant applications of all types. Low temperature military uses. Off-road equipment. Automotive, marine, aircraft fuel systems. More than 50% of the O-Rings sold are Nitrile O-Rings, commonly used in hydraulic/pneumatic motors, cylinders, pumps and valves. Technical moldings of all kinds, e.g. seals, sleeves, membranes, bellows, valves, buffers, vibration dampers and footwear soles. Also suitable for roll covers, printing blocks, printing blankets, conveyor belting, rubberized fabrics (e.g. for flexible silos), hoses, cable sheathing, brake and clutch linings, open and closed cell rubber, punching blocks and gloves. Can be compounded for FDA applications.
Temperature Range: Standard Compound: -40° to +250°F. (Dry Heat Only)
Hardness (Shore A): 40 to 90.
Features: Comprised of the copolymer butadiene and acrylonitrile, in varying proportions. Its performance characteristics may be varied over a working temperature range of -65°F to +300°F. Increasing acrylonitrile content gives Nitrile its better resistance to petroleum-based oils and hydrocarbon fuels, enhancing resistance to the degrading effects of heat, at a cost of reduced low temperature performance. It is also good with silicone greases and oils.
Conversely, decreasing acrylonitrile, while increasing butadiene content, provides better low temperature flexibility a characteristic most often required by Air Force-Navy (AN) and Military Standard (MS) O-ring specifications.
Carboxylated Nitriles (CNBR or XNBR) are NBR compounds with an additional group cross link in the polymer. This addition to the NBR polymer provides benefits such as improved abrasion resistance and fluid resistance. Carboxylated Nitrile has excellent toughness, wear resistance and resistance to fluids. Carboxylated Nitriles have very good high temperature resistance but are not well suited to use in cold weather. Recommended application range is 0 °F to + 275 °F.
Limitations: Precautions should be taken to avoid exposure of Nitrile to such highly polar solvents as acetone, MEK, chlorinated hydrocarbons and nitro hydrocarbons, which are known to cause rapid and extreme deterioration. It should not be used in the presence of strong acids or brake fluids.
Additional limitations on Nitrile use include applications with direct exposure to ozone and sunlight. Not recommended for exposure to ethers, esters, ketones, or chlorinated hydrocarbons.
ETHYLENE-PROPYLENE
Trade Names(s):
Nordel . . . DuPont Dow Elastomers
Epcar . . . B.F. Goodrich
Vistalon . . . Exxon Chemical Co.
Epsyn . . . Copolymer Rubber
Royalene . . . Uniroyal, Inc.
ASTM D1418 Designation: EPDM
ASTM D2000/SAE J200 Type, Class: AA, BA, CA, DA
Standard Color: Black
Description: A copolymer of ethylene and propylene (EPR), combined with a third comonomer adiene (EPDM), Ethylene Propylene has gained wide seal industry acceptance for its excellent ozone and chemical resistance characteristics.
Key Use(s): Outdoor weather resistant uses. Automotive brake systems. Automobile cooling systems. Water applications. Low torque drive belts.
Temperature Range: Standard Compound: -60° to +300°F. (Dry Heat Only)
Hardness (Shore A): 40 to 90.
Features: With a working temperature range of -60°F to +300°F, depending upon the compound, EPR/EPDM excels in its resistance to the very same chemical agents that cause rapid and extreme deterioration in Nitriles.
In particular, EPR/EPDM features good resistance to such polar solvents as ketones (MEK and Acetone). It is also highly recommended for effective resistance to steam (to 400°F), hot water, silicone oils and greases, dilute acids and alkalis, alcohols and automotive brake fluids.
EPR/EPDM further features excellent resistance to aging by both ozone and sunlight.
Limitations: With the exception of resistance to polar solvents, EPR/EPDM is not recommended for its overall solvent resistance. And, unlike Nitriles, this elastomer performs poorly when exposed to petroleum oils, diester-based lubricants (MIL-L-7808), or aromatic fuels.
FLUOROCARBON (Viton®)
Trade Names(s):
Viton . . . DuPont Dow Elastomers
Fluorel . . . 3M Company
Technoflon . . . Montedison, USA
ASTM D1418 Designation: FKM
ASTM D2000/SAE Type, Class: HK
Standard Color: Black
Description: Combining high temperature resistance with outstanding chemical resistance, Fluorocarbon-based compounds approach the ideal for a universal O-ring material.
Key Use(s): Seals for aircraft engines. Seals for automotive fuel handling systems. High temperature/low compression set applications. Wide chemical exposure situations. Hard vacuum service.
Temperature Range: Standard Compound: -20° to +400°F. (Dry Heat Only)
Hardness (Shore A): 50 to 95.
Features: Excellent resistance to petroleum products and solvents, with good high temperature compression set characteristics. Fluorocarbon O-rings make ideal seals for aircraft, automobile and other mechanical uses.
Fluorocarbons are highly resistant to swelling in gasoline and gasoline/alcohol blends, as well as resistant to the degrading effects of light and ozone. They are also resistant to acids, silicone fluids and greases, and have a broad chemical compatibility.
With low gas permeability, they are also well suited for hard vacuum service.
Limitations: Fluorocarbons are not recommended for exposure to ketones, amines, low molecular weight esters and ethers, nitro hydrocarbons, hot hydrofluoric or chlorosulfonic acids, or Skydrol® fluids. They are also not recommended for situations requiring good low temperature flexibility.
STYRENE BUTADIENE
Trade Names(s): Too numerous to list.
ASTM D1418 Designation: SBR
ASTM D2000/SAE J200 Type, Class: AA, BA
Standard Color: Black
Description: Also known as Buna S, or GR-S (Government Rubber-Styrene), Styrene Butadiene was the elastomer substituted for Natural Rubber during World War II. Compounded properties are similar to those of Natural Rubber.
Key Use(s): Sealing of automotive brake systems.
Temperature Range: Standard Compound: -50° to +212°F. (Dry Heat Only)
Hardness (Shore A): 40 to 90.
Features: The main use for Styrene Butadiene today is in the manufacture of automobile tires because it exhibits excellent resistance to brake fluids. SBR is still used in some brake applications.
Limitations: SBR is not recommended for exposure to petroleum oils, most hydrocarbons, strong acids, or ozone.
This material is seldom used in modern sealing applications. It has been replaced by better performing materials.
FLOURO-SILICONE
Trade Names(s):
Silastic LS. . Dow Corning Corporation
FSE . . . General Electric
ASTM D1418 Designation: FVMQ
ASTM D2000/SAE J200 Type, Class: FK
Standard Color: Blue
Description: Fluorosilicone combines the good high and low temperature stability of Silicones with the fuel, oil, and solvent resistance of Fluorocarbons.
Key Use(s): Aerospace fuel systems. Auto fuel emission control systems. Primarily for static sealing applications.
Temperature Range: Standard Compound: -75° to +400°F. (Dry Heat Only)
Hardness (Shore A): 50 to 80.
Features: Fluorosilicone is most often used in aerospace applications for systems requiring fuel and/or diester-based lubricant resistance up to a dry heat limit of 400° F.
Although generally specified for aerospace use, due to its excellent fuel resistance and high temperature stability, Fluorosilicone is becoming an increasingly popular material for a wider range of sealing applications.
Featuring good compression set and resilience properties, fluorosilicone compounds are suitable for exposure to air, sunlight, ozone, chlorinated and aromatic hydrocarbons.
Limitations: Due to limited physical strength, poor abrasion resistance, and high friction characteristics, Fluorosilicone elastomers are not generally recommended for dynamic sealing. They are predominately designed for static sealing use. They are also not recommended for exposure to brake fluids, hydrazine, or ketones.
NEOPRENE® (CHLOROPRENE)
Trade Names(s):
Neoprene . . . DuPont Dow Elastomers
Baypren . . . Bayer
ASTM D1418 Designation: CR
ASTM D2000/SAE J200 Type, Class: BC, BE
Standard Color: Black
Description: One of the earliest of the synthetic materials to be developed as an oil-resistant substitute for Natural Rubber, Neoprene is a homopolymer of chloroprene (chlorobutadiene).
Key Use(s): Numerous component uses in the transportation field. Recommended for exposure to weathering. Preferred sealing material for refrigeration industry. FDA approved for food & beverage industry use.
Temperature Range: Standard Compound: -45° to +250°F. (Dry Heat Only)
Hardness (Shore A): 40 to 90.
Features: Neoprene can be used in innumerable sealing applications due to its broad base of such desirable working properties as: good resistance to petroleum oils; good resistance to ozone, sunlight and oxygen aging; relatively low compression set; good resilience; outstanding physical toughness; and reasonable production cost.
Due to its excellent resistance to Freon® and ammonia, Neoprene is also widely accepted as a preferred material for refrigeration seals.
Limitations: Neoprene is generally attacked by strong oxidizing acids, esters, ketones, chlorinated, aromatic and nitro hydrocarbons. Because Nitrile is economically competitive with Neoprene, and generally has superior performance characteristics in most situations, it has largely replaced Neoprene in the O-rings of today.
KALREZ®
Trade Names(s): Kalrez . . . DuPont Dow Elastomers
ASTM D1418 Designation: FFKM
ASTM D2000/SAE J200 Type, Class: No Designation at Time of Publication
Standard Color: Black
Description: Kalrez parts are made from a perfluoro elastomer possessing exceptional resistance to degradation by aggressive fluids and/or gases.
Key Use(s): Seals for use in the chemical and petroleum industries as well as for the manufacturing of semiconductors and analytical and process instruments. It is also used for high temperature applications and for paint and coating operations.
Temperature Range: Standard Compound: -35° to +600°F. (Dry Heat Only)
Hardness (Shore A): 65 to 95
Features: Kalrez combines the toughness of an elastomeric material with the chemical inertness of Teflon™. It resists attack by nearly all chemical reagents and provides long-term service where corrosive additives can cause other elastomers to swell or degrade. In addition, Kalrez parts are less likely to cold flow than Teflon seals.
Limitations: Withstanding degradation by virtually ALL chemicals, Kalrez can swell significantly when exposed to some fluorinated solvents, fully halogenated freons and uranium hexafluoride. In addition, Kalrez parts should not be exposed to molten or gaseous alkali metals.
As the thermal coefficient of expansion for Kalrez is stated by the manufacturer to be “about 50% greater than for fluoro-elastomers”, gland volume may have to be increased to allow for this expansion in elevated temperature situations. Because of its high cost, Kalrez is generally used when no other elastomer is appropriate.
HYPALON®
Trade Names(s): Hypalon . . . DuPont Dow Elastomers.
ASTM D1418 Designation: CSM
ASTM D2000/SAE J200 Type, Class: CE
Standard Color: Black
Description: A chlorosulfonated polyethylene, Hypalon offers outstanding resistance to attack by oxygen and ozone, high resistance to degradation by corrosive chemicals, good to excellent heat resistance, and fair to excellent oil resistance.
Key Use(s): For resistance to corrosive or oxidizing chemicals (acids & alkalis). For enhanced weather resistance (when compounded with protective pigments). For resistance to Freon® refrigerants (when compounded with a high chlorine content).
Temperature Range: Standard Compound: -50° to +275°F. (Dry Heat Only)
Hardness (Shore A): 50 to 90.
Features: Depending upon chlorine content, the heat resistance, oil resistance and low temperature flexibility
properties of Hypalon compounds can be widely varied to meet specific application needs.
At low chlorine levels, Hypalon compounds exhibit their best heat resistance and low temperature flexibility properties, with fair oil resistance. At high chlorine levels, Hypalon compounds feature excellent oil resistance, with less heat resistance and less low temperature flexibility.
In general, Hypalon compounds are highly resistant to degradation by corrosive chemicals, and are very resistant to oxidation. Taken as a group, CSM compounds are more resistant to corrosive and oxidizing chemicals than are Neoprenes or Nitriles. They are also considered to be tougher than Silicone or Ethylene-Propylene elastomers.
Limitations: Resistance of Hypalon compounds to solvents is limited more by swelling than actual degradation. They are not recommended, however, for exposure to aldehydes, esters, ethers, ketones, aromatic, chlorinated or nitro hydrocarbons. Hypalon has poor compression set.
NATURAL RUBBER
ASTM D1418 Designation: NR
ASTM D2000/SAE J200 Type, Class: AA
Standard Color: Black
Description: Natural Rubber is the vulcanized product of the juice of the Hevea tree (latex).
Key Use(s): Seals in brake systems. Seals in food & beverage applications.
Most popular material for non-hydraulic sealing applications.
Temperature Range: Standard Compound: -60° to +220°F. (Dry Heat Only)
Hardness (Shore A): 40 to 90.
Features: Natural Rubber features low compression set, high tensile strength, high resilience, high abrasion and high tear resistance properties, with a good friction surface and excellent adhesion to metals.
Until the invention of synthetic elastomers in the 1930’s, Natural Rubber was the only polymer available for O-ring manufacture.
Still used today in FDA applications for food and beverage seals, Natural Rubber features good resistance to organic acids and alcohols, with moderate resistance to aldehydes.
Limitations: The poor resistance of Natural Rubber to attack by petroleum oils was the primary reason for the research and development of synthetic rubbers beginning in the 1930’s.
Also readily deteriorated by exposure to sunlight and ozone, Natural Rubbers have been predominantly replaced by “use specific” synthetic rubbers in the seal industry of today.
TEFLON® Virgin
Trade Names(s): Teflon . . . DuPont Dow Elastomers
ASTM D1418 Designation: FEP
ASTM D2000/SAE J200 Type, Class: No Designation At Time Of Publication
Standard Color: White
Description: Teflon is a tough, chemically inert polymer possessing an incredible working temperature range.
Key Use(s): Seals for wide chemical exposure situations, with special emphasis on temperature extremes. For static and SLOW INTERMITTENT dynamic situations.
Temperature Range: Standard Compound: -300° to +450°F. (Dry Heat Only)
Hardness (Shore A): 98.
Features: Teflon is inert to virtually all industrial chemicals, even at elevated temperatures. Seals fabricated from this material feature outstanding weather resistance, high resistance to ozone, and high resistance to the degrading effects of exposure to such solvents as acetone, MEK, and xylene.
Possessing average elastomer characteristics of 2,500 to 3,500 psi tensile strength, and 300% elongation, they are tough, impact resistant, low friction, non-twisting performers over an extremely wide temperature range.
Limitations: Teflon is hampered by very poor elastic memory at room, or low temperatures. This presents problems in O-ring installation, requiring extra care to be taken in control over O-ring I.D. stretch. Heating Teflon in boiling water, or in a controlled oven, to 200°F is said to enable an O-ring stretch of 10 to 20% to be achieved, thereby assisting installation, and helping to assure a tight fit.
Because of its poor tear resistance, during O-ring installation particular care should be taken to avoid nicking or scratching Teflon, as imperfections will cause O-ring leakage.
Finally, the tendency of virgin Teflon to cold flow over time, when used in gasket type applications, may require special material compounding (with fillers) to control such “creep” in critical sealing situations.
POLYURETHANE, Cast
Trade Names(s):
Vibrathane . . . Uniroyal
Cyanaprene . . . American Cyanamid
Polathane . . . Polaroid
ASTM D1418 Designation: No designation at time of publication.
ASTM D2000/SAE J200 Type, Class: No designation at time of publication.
Standard Color: Amber
Description: Cast Polyurethane is outstanding over other O-ring elastomers in abrasion resistance and tensile strength. Additionally, Cast Polyurethane surpasses the performance of Millable Polyurethane in its higher tensile strength, greater elongation, wider temperature range, and lower compression set characteristics.
Key Use(s): Seals for high hydraulic pressures. Situations where highly stressed parts are subject to wear. Used for wheels, rolls, slurry parts, bumpers, couplers, and shock absorbers. Wiper seals for axially moving piston rods.
Temperature Range: Standard Compound: -60° to +225°F. (Dry Heat Only)
Hardness (Shore A): 70 and 90.
Features: With tensile strength of up to 6,000 psi, elongation of 350 to 650%, compression sets of 10 to 25%, and exceedingly high abrasion resistance, the physical properties of Cast Polyurethane are among the best of all O-ring elastomers.
The heat resistance of standard compound Cast Polyurethane (to 225°F) shows a decided improvement over the lesser heat resistance of standard compound Millable Polyurethanes (to 175°F).
Although they swell slightly upon exposure, Cast Polyurethane compounds feature excellent resistance to mineral-based oils and petroleum products, aliphatic solvents, alcohols and ether. They are also compatible with hydraulic fluids, weak acids and bases, and mixtures containing less than
80% aromatic constituents.
Limitations: Cast Polyurethanes are not recommended for exposure to concentrated acids and bases, ketones, esters, very strong oxidizing agents, pure aromatic compounds and brake fluids. With the exception of special compounds, they are also not recommended for exposure to hot water or steam.
SILICONE
Trade Names(s):
Baysoline … Bayer Corp.
Silastic … Dow Corning
Silplus … General Electric
ASTM D1418 Designation: MQ, PMQ, VMQ, PVMQ
ASTM D2000/SAE J200 Type, Class: FC, FE, GE
Standard Color: Red
Description: A group of elastomers, made from silicon, oxygen, hydrogen and carbon, Silicones are renowned for their retention of flexibility and low compression set characteristics, within one of the widest working temperature ranges for elastomers.
Key Use(s): Static seals in extreme temperature situations. Seals for medical devices, compatible with FDA regulations.
Temperature Range: Standard Compound: -94° to +450°F. (Dry Heat Only)
Hardness (Shore A): 25 to 80
Features: Especially resistant to high, dry heat, special Silicone compounds have been manufactured to resist up to 600°F heat for short periods of time in primary static applications. Also, Silicones are noted for their high resistance to fungus and aging effects of both sunlight and ozone attack, and are non-toxic with neutral odor and taste.
Limitations: Generally, low abrasion and tear resistance, and high friction characteristics preclude silicones from effectively sealing some dynamic applications.
Many Silicones compounds also exhibit higher than normal mold shrinkage, resulting in undersized, molded finished parts (from standard molds). Unless especially compounded, Silicones swell considerably in aliphatic and aromatic hydrocarbon fuels.
They should also be considered Non- resistant to petroleum oil, although they can be used in high aniline point oils. Silicones are also highly permeable to gases and are generally not recommended for exposure to ketones (MEK, acetone) or concentrated acids. Heat aging of LSR results in an accelerated reduction in physical properties compared to that of conventional silicone.