Gasket Compounds, Silicone, Viton, EPDM, Aflas, Butyl, Ethylene

Gasket Compounds

o-ring compounds

Seal and Design offers a wide range of rubber compounds also know as elastomers. Elastomers consist of both synthetic and natural materials, and are formulated to have a wide array of physical properties. Different compounds are better suited for a variety of applications, depending primarily on the compound's exposure to fluids, heat, and pressure.

General compounds exist for applications with typical environments, while highly engineered compounds exist for the most demanding environments and applications. When a gasket is required in automotive, aerospace, chemical processing, or pharmaceutical application, Seal & Design has access to the best compound for the job.

Nitrile (Buna-N, NBR)

Nitrile rubber is the general term for acrylonitrile butadiene terpolymer. The acrylonitrile content of nitrile sealing compounds varies considerably (18% to 50%) and influences the physical properties of the finished material. The higher the acrylonitrile content, the better the resistance to oil and fuel. At the same time, elasticity and resistance to compression set is adversely affected. In view of these opposing realities, a compromise is often drawn, and a medium acrylonitrile content selected. Nitrile has good mechanical properties when compared with other elastomers and high wear resistance. Nitrile is not resistant to weathering and ozone.

EPDM (Ethylene Propylene)

EPDM is a copolymer of ethylene and propylene. Ethylenepropylene-diene rubber (EPDM) is produced using a third monomer and is particularly useful when sealing phosphate-ester hydraulic fluids and in brake systems that use fluids having a glycol base. With an broad operating temperature range of 300°F to –65°F, this elastomer is also used in many steam, and lower temperature applications.

Neoprene (Chloroprene, CR)

Neoprene was the first synthetic rubber developed commercially and exhibits generally good ozone, aging and chemical resistance. It has good mechanical properties over a wide temperature range. This material is used for sealing refrigerants, and many applications where the product will be exposed to UV and Sunlight. It is a low cost elastomer, and can be found in rubber, grommets, boots, and bellow products. The Temperature range on the elastomer is 250°F to –40°F.

Viton (Fluorocarbon, FKM)

Viton® Gasket Information Page

Fluorocarbon rubber has excellent resistance to high temperatures, ozone, oxygen, mineral oil, synthetic hydraulic fluids, fuels, aromatics and many organic solvents and chemicals. Low temperature resistance is normally not favorable and for static applications is limited to approximately –15°F (–26°C) although in certain situations it is suitable down to –40°F (–40°C). Under dynamic conditions, the lowest service temperature is between 5°F and 0°F (–15°C and –18°C). Gas permeability is very low and similar to that of butyl rubber. Special fluorocarbon compounds exhibit an improved resistance to acids, fuels, water and steam.

Silicone (VMQ)

The term silicone covers a large group of materials in which vinyl-methyl-silicone (VMQ) is often the central ingredient. Silicone elastomers as a group have relatively low tensile strength, poor tear and wear resistance. However, they have many useful properties as well. Silicones have good heat resistance up to 450°F (232°C), good cold flexibility down to –75°F (–59°C) and good ozone and weather resistance as well as good insulating and physiologically neutral properties.

Polyurethane (AU, EU)

One must differentiate between polyester urethane (AU) and polyether urethane (EU). AU type urethanes exhibit better resistance to hydraulic fluids. Polyurethane elastomers, as a class, have excellent wear resistance, high tensile strength and high elasticity in comparison with any other elastomers. Polyurethane is used in a majority of hydraulics seals, and high pressure o-rings. Permeability is good and comparable with butyl rubber.

Fluorosilicone (FVMQ)

Fluorosilicone rubber contains trifluoropropyl groups next to the methyl groups. The mechanical and physical properties are very similar to silicone rubber. However, fluorosilicone offers improved fuel and mineral oil resistance but poor hot air resistance when compared with silicone. The elasotmers wide temperature range (350°F to –100°F) make it an excellent seal for lower pressure fuel seals where low temperature is a concern.

Aflas (Tetrafluoroethylene Propylene, FEPM)

Aflas® Datasheet (PDF)

AFLAS® is the tradename for a fluoroelastomer based upon an alternating copolymer of tetrafluoroethylene and propylene ( TFE/P ). The rubber compound has excellent heat resistance with continuous service temperature capability of 230°C. Aflas also has excellent chemical resistance, and is used in many down hole applications, due to it's excellent resistance to sour gas, and hydrocarbons.

Perfluoroelastomer (Chemraz, Kalrez, Simriz, Perlast, FFKM)

The name "perfluoroelastomer" is somewhat misleading. An actual perfluorinated material with a high molecular weight is polytetrafluoroethylene or PTFE which has the chemical formula "(CF2)n." The molecular carbon chain is shielded by the chemical inertness of the large bonded fluorine atoms. Perfluoroelastomer is produced by the copolymerization of tetrafluoroethylene (TFE) and a perfluorinated ether, e.g. perfluoromethylvinylether (PMVE). The differing resistance to volume swell of the different perfluoroelastomers is due to the perfluorinated ether element, where the side-chain can consist of up to four perfluorinated carbon atoms. The extraordinary chemical resistance is partly due to the fluorine atoms shielding the carbon chain, and partially due to the vulcanization system.

SBR (Styrene-Butadiene)

SBR probably is better known under its old names Buna S and GRS (government rubber styrene.) SBR was first produced under government control between 1930 and 1950 as a replacement for natural rubber. The basic monomers are butadiene and styrene, with styrene content approximately 23.5%. About one third of the world output of SBR is used in tire production. SBR is mostly used in seals for non-mineral oil based brake fluid applications. SBR is used in many grommets, and has been replaced by many of the new elastomers available today.

Butyl (IIR)

Butyl rubber is produced by many companies in different types and varies widely in isoprene content. Isoprene is necessary for proper vulcanization. Butyl has a very low permeability rate and good electrical properties. Heat resistance. Butyl Rubber is used in many acid, and brake applications. The material has a wide temperature range from 250°F down to –75°F.

Hypalon (Chlorosulfonated Polyethylene, CSM)

The polyethylene polymer contains additional chlorine and sulfur groups. Chlorine gives the material resistance to flame and mineral oil and also improves the cold flexibility. This elastomer is used in many acid, and outdoor applications. Hypalon has an operating temperature range of 250°F to –20°F.

Polyacrylate (ACM)

ACM or simply acrylate rubber consists of a polymerized ester and a curing monomer. Ethyl acrylate rubber has a good resistance to heat and mineral oil; on the other hand butyl acrylate has a better cold flexibility. Polyacrylate has a good resistance to mineral oil, oxygen and ozone even at high temperatures. The water compatibility and cold flexibility of ACM are significantly worse than with NBR. The material is used in many ATF fluid applications in the automobile industry.

Ethylene Acrylic (AEM, Dupont VAMAC®)

Developed as a lower temperature version of Polyacrylate. The temperature range is -40°F to 325°F. It typically has higher swell than Polyacrylate in automatic transmission fluids and power steering fluids.