The classification of FKM is based upon the content of fluorine or their
mechanism of crosslinking, as well as their chemical composition. Resistance
to chemicals and heat is an added feature of FKMs. Companies that produce
FKMs include Dyneon Fluoroelastomers (3M), HaloPolymer (Elaftor) Solvay
Specialty Polymers, Daikin Chemical as well as a number of manufacturers
from China. The price of Flooroelastomers is higher than that of nitrile
rubber or neoprene.
The following classification of FKMs is based according to their chemical composition.
Type 1 FKMs is characterised by a 66 weight percentage of content in flourine. They display excellent performance in most areas of applications. Composition of Type 1 FKMs is that of VDF (Vinylidene fluoride) and HFP (hexafluoropropylene).
Type 2 FKMs is typifed by an enhancement in thermal and chemical resistance. Negatively affected are properties of flexibility at low temperatures as well as compression set.
Type 3 FKMs. Generally, the content of fluorine averages from 62 percent to 68 percent. Flexibility at low temperatures is enhanced for Type 3 FKMs as a result of the addition of PMVE (perfluoromethylvinylether)Type 3 FKMs are made up of PMVE, TFE AND VDF.
Type 4 FKMs generally have a 67 percent by weight of fluorine content .Type 4 FKMs have enhanced base resistance. However, swelling characteristics are worsened particularly in contact with hydrocarbons. The composition of Type 4 FKMs are VDF, TFE AND propylene.
Type 5 FKMs. High temperature resistance to hydrogen sulphide as well as base resistance are known properties of Type 5 FKMs. Composition of Type 5 FKMs are PMVE (perfluoromethylvinylether), TFE, HFP, VDF and ethylene.
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