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Tetrafluoroethylene/propylene copolymers (FEPM)
These are usually recognised by the Asahi Glass trade name of Aflas®, and have base polymers that differ in viscosity and molecular weight.
Chemical properties
Aflas® compounds have resistance to oils, lubricants and some fuels approaching that of fluoroelastomer dipolymers. In addition, they exhibit excellent resistance to steam, amines, hydrogen sulphide (sour gas), and bases. They also have excellent ozone/weathering resistance, and exhibit the best radiation resistance of all elastomers.
Typical operating temperatures
Steam duties: up to +260°C.
Other media: +0°C to +200°C continuous, or +230°C intermittent.
Fluid sealing duties
FEPM compounds are very useful, if specialised, fluid sealing materials. Their usefulness for general applications are limited by high compression set, poor extrusion resistance especially at high temperatures, and rapid stiffening below +5°C.
James Walker standard grades
AF85: available in hardnesses of 70, 80 and 90 IRHD.
AF69/90: compounded for rapid gas decompression (RGD) resistance.
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