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Elastomer selection guide 1

Find the Right Elastomer for Your Application Selecting seal materials can be an intimidating task There are many types of elastomers and each is available in many di ?erent compounds There are nine popular elastomers used in seals This selection guide surveys popular elastomers intended for service at pressures up to psi Detailed information on compounds of each elastomer may be found in Parco ? s material selection guides If you believe your application may require a special compound not listed please contact a Parco customer service representative Elastomer Selection Criteria of retraction re ects the ability of an elastomer to retract that is behave like rubber at low temperatures ? Fluid may penetrate the seal and act as a plasticizer e ?ectively lowering the brittle point below the value observed in dry air In such cases the seal may operate e ?ectively below its rated service temperature This must be con ?rmed on a case-by-case basis Fig Service Temperatures of Popular Elastomers Temperature Capabilities Elastomer performance becomes less predictable when a seal operates near the limits of its service temperature range Consider the e ?ects of temperature extremes when selecting an O -ring material At low temperatures ? Elastomers become harder and less exible until at the brittle point or glass transition the seal may crack ? Elastomers lose their rubber-like properties as the temperature drops The TR- temperature Silicone Fluorocarbon A as Fluorosilicone Polyacrylate HNBR Ethylene Propylene Nitrile Neoprene - - Temperature F Compounding a ?ects performance at both high and low temperatures Not all compounds of a given elastomer have the same temperature range The temperature limits in the chart span the range of the compounds of each elastomer CFig Common Fluids ASTM D Designation Acids dilute Alcohols Alkalis dilute Brake uid non-petroleum Fuel oil Hydraulic oil phosphate- ester Hydrocarbons aliphatic Hydrocarbons aromatic Ketones Mineral oil Solvents chlorinated Steam to F Water Fluid Compatibility by Elastomer Nitrile FluorocarEbPoDnM Silicone NeoprenePolyacrylaFtlueorosilicHoNnBeR A as NBR FKM EPDM VMR CR ACM FVMR HNBR FEPM Examples Hydrochloric acid Methanol ethanol Sodium hydroxide Wagner B Dextron Diesel oils - Skydrol Hyjet Gasoline kerosene Benzene toluene Acetone MEK ?? Trichloroethylene ?? ?? Legend Recommended Minor-to-moderate e ?ect useful in some static applications only Moderate-to-severe e ?ect Not recommended ? Changes in elastomers due to low temperature are physical not chemical and are generally reversible However if the geometry of the gland changes while the seal is cold the seal may be too sti ? to adapt to the new shape and may fail Movement may damage the seal while it is cold and in exible At high temperatures ? As temperatures approach the upper service limit elastomers often undergo irreversible chemical changes The polymer backbone may break or adjacent polymer molecules may crosslink causing seals to become more rigid reducing their resistance to compression set ? The rate of many chemical reactions doubles with each increase of C F The relationship between reaction rate and temperature of these ?rst- order reactions can be