Fluorocarbon rubber FKM FPMIn the United States fluorocarbon rubber is well known by its trade name of Viton (for
other trade names see section 2.4). Based on vinylidene fluoride and hexafluoro-propylene
the grades available differ in the chemical building blocks which were used to construct the
polymer. Like silicone rubber, FKM has excellent high temperature resistance with an upper
continuous heat aging temperature limit of 205 "C. DuPont literature [24] quotes continuous
dry heat service to be >3,000 hours at 232 "C decreasing to >48 hours at 316 "C.
At the opposite end of the scale Nagdi [25] points out that conventional FKM is usually
serviceable at temperatures down to -20 "C in dynamic applications, while for static use
the temperature can be lower, although this will depend on the grade chosen. A primary
variable in FKM grades is the level of fluorine in the elastomer molecule, FKMs being
fluorohydrocarbons. Terpolymers tend to have a higher fluorine content than copolymers
and therefore have better resistance to various media. In general, fluoroelastomers have
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