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
creep-resistant
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.
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