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FKM(by ASTM D1418 standard) (equivalent to FPM by ISO/DIN 1629 standard) is the designation for about 80% of fluoroelastomers as defined in ASTM D1418. Other fluorinated elastomers are ''perfluoro-elastomers'' (FFKM) and ''tetrafluoro ethylene/propylene rubbers'' (FEPM). All FKMs contain vinylidene fluoride as a monomer. Originally developed by DuPont (Viton), FKMs are today also produced by Daikin Chemical (Dai-El), 3M's Dyneon (Dyneon Fluoroelastomers), Solvay Specialty Polymers (Tecnoflon) and HaloPolymer (Elaftor). Fluoroelastomers are more expensive than neoprene or nitrile rubber elastomers. They provide additional heat and chemical resistance. FKMs can be divided into different classes on the basis of either their chemical composition, their fluorine content or their crosslinking mechanism. ==Types == On the basis of their chemical composition FKMs can be divided into the following types: *Type 1 FKMs are composed of vinylidene fluoride (VDF) and hexafluoropropylene (HFP). Copolymers are the standard type of FKMs showing a good overall performance. Their fluorine content typically ranges around 66 weight percent. *Type 2 FKMs are composed of VDF, HFP, and tetrafluoroethylene (TFE). Terpolymers have a higher fluorine content compared to copolymers (typically between 68 and 69 weight percent fluorine), which results in better chemical and heat resistance. Compression set and low temperature flexibility may be affected negatively. *Type 3 FKMs are composed of VDF, TFE, and perfluoromethylvinylether (PMVE). The addition of PMVE provides better low temperature flexibility compared to copolymers and terpolymers. Typically the fluorine content of type 3 FKMs ranges from 62 to 68 weight percent. *Type 4 FKMs are composed of propylene, TFE, and VDF. While base resistance is increased in type 4 FKMs, their swelling properties especially in hydrocarbons are worsened. Typically they have a fluorine content of about 67 weight percent. *Type 5 FKMs are composed of VDF, HFP, TFE, PMVE, and Ethylene. Type 5 FKM is known for base resistance and high temperature hydrogen sulfide resistance.〔http://www.swjagels.com/uploads/Base_Resistant_FKM_Technology_in_Oilfield_Seals.pdf〕 A useful overview of different types of FKM-compounds is listed (here ). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「FKM」の詳細全文を読む スポンサード リンク
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