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Selecting PTFE Compounds

SELECTING THE RIGHT PTFE COMPOUND

PTFE fluorocarbon resin performs well in many applications without filler. In fact, fillers can lessen its outstanding electrical and chemical properties. In mechanical applications, however, compounds of PTFE and inorganic fillers offer improved wear resistance, reduce creep and initial deformation, and increased stiffness and conductivity. Hardness is increased, and the coefficient of thermal expansion is decreased. Compounds can therefore make it possible to gain the advantages of PTFE in applications where the unfilled resin cannot be used.

Glass Fiber Glass in the form of short fibers is the most widely used filling material. The most popular compounds are 15% or 25% glass (by weight). It is sometimes combined with graphite or MoS2. Glass has little effect on most of the electrical properties of PTFE. It resists acids and oxidation, but it can be attacked by alkali.

Carbon A typical carbon filler is high-purity coke powder. It is often used in combination with graphite in concentrations of 25% to 35% glass (by weight). Compounds of PTFE and carbon have excellent wear resistance, both dry and in water. They are compatible with most chemicals and can carry heavy loads under rubbing contact.

Graphite This crystaline form of carbon is used alone or in combination with glass or amorphous carbon. A typical compound is 15% graphite by weight. The addition of graphite helps reduce the wear of soft metal mating parts and improves frictional and wear properties when mixed with other fillers. Like
other forms of carbon, it serves well in corrosive environments.

Bronze Round or irregularly-shaped bronze particles are often used at 60% by weight, or 55% with 5% MoS2. Compounds of bronze and PTFE are creepresistant and easily machined. They deliver good wear performance, low friction, and relatively high thermal conductivity.

MoS2 Used in concentrations of approximately 5% by weight in compounds with glass or bronze, MoS2 can increase surface hardness and lower coefficient of friction and wear rate.