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Nitrite, Buna N, or NBR
Nitrite is the most widely used elastomer in the seal Industry. The popularity of nitrite is due to its excellent resistance to petroleum products and its ability to be compounded for service over a temperature range of -67ºF to 257ºF (-55ºC to 125ºC).

Nitrite is a copolymer of butadiene and acrylonitrile. Variation in proportions of these polymers is possible to accommodate specific requirements. An increase in acrylonitrile content increases resistance to heat plus petroleum base oils and fuels but decreases low temperature flexibility. Military AN and MS O-ring specifications require nitrite compounds with low acrylonitrile content to insure low temperature performance.

Nitrite provides excellent compression set, tear, and abrasion resistance. The major limiting properties of nitrite are its poor ozone and weather resistance and moderate heat resistance.

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Polyurethane, AU, or EU
Polyurethane compounds exhibit outstanding tensile strength and abrasion resistance in comparison with other elastomers. Fluid compatibility is similar to that of nitrite at temperatures up to approximately 158ºF (70ºC). At higher temperatures, polyurethane has a tendency to soften and lose both strength and fluid resistance advantages over other elastomers. Some types are readily damaged by water, even high humidity. Polyurethane seals offer outstanding performance in high pressure hydraulic systems with abrasive contamination, high shock loads, and related adverse conditions provided temperature is below 158ºF (70ºC).

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Chloroprene, Neoprene, or CR
Neoprene is a polymer of chlorobutadiene and is unusual In that it is moderately resistant to both petroleum oils and weather (ozone, sunlight, oxygen). This qualifies neoprene for O-ring service where many other elastomers would not be satisfactory. It is also used extensively for sealing refrigeration fluids. Neoprene has good compression set characteristics and a temperature range of -67"F to 284ºF (-55ºC to 140ºC).

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Fluorocarbon, Viton, Fluorel, or FKM
Fluorocarbon combines resistance to a broader range of chemicals than any of the other elastomers. It constitutes the closest available approach to the universal O-ring elastomer. Although most fluorocarbon compounds become quite hard at temperatures below -4ºF (-20ºC), they do not easily fracture, so they are serviceable at much lower temperatures. Fluorocarbon compounds provide a continuous 437"F (225ºC) high temperature capability.

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Fluorosilicone or FVMQ
Fluorosilicones combine most of the attributes of silicone with resistance to petroleum oils and hydrocarbon fuels. Low physical strength and abrasion resistance combined with high friction limit fluorosilicone to static seals. Fluorosilicones are used primarily in aircraft fuel systems over a temperature range of -85ºF to 347ºF (-65ºC to 175ºC).

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If you are looking for VITON gaskets or EPDM gaskets feel free to contact Seal Dynamics to get more information about how we use EPDM and VITON in our process.

Hydrogenated Nitrile (HNBR)
Hydrogenated nitrile is a synthetic polymer that results from the hydrogenation of nitrile rubber (NBR). In this process the molecular "double bonds" in the NBR primary polymer chain undergo a hydrogenation process and therefore the term "hydrogenated nitrile" (HNBR). The allowable temperature range extends to 149ºC (300ºF) with short periods at higher temperature possible. By following design guidelines effective sealing can be achieved at -32ºC (-25ºF) for static applications. For dynamic applications however, operating temperatures are limited to above 23ºC (-10ºF). HNBR compounds possess superior mechanical characteristics, particularly their high strength. For sealing applications up to approximately 159ºC (300ºF), this is an advantage as it prevents extrusion and wear.

Chemical resistance

Not compatible with:

Perfluoroelastomer (FFKM)
The name "perfluoroelastomer" is somewhat misleading. An actual perfluorinated material with a high molecular weight is polytetrafluoroethylene or PTFE. 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.

Heat resistance

Chemical resistance

Not compatible with:

Silicone or PVMQ
Silicone is a semi-organic elastomer with outstanding resistance to extremes of temperature. Specially compounded, it can provide reliable service at temperatures as low as -75ºF (-59ºC) to as high as 450ºF (232ºC) continuously. Silicone also has good resistance to compression set.

Low physical strength and abrasion resistance combined with high friction limit silicone to static seals. Silicone is used primarily for dry heat static seals. Although it swells considerably in petroleum lubricants, this is not detrimental in most static sealing applications.

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Seal Dynamics is a custom manufacturer of gaskets using EPDM, Fluorel and VITON gasket materials. Contact us if you would like more information.