Teflon®
Virgin TFE is almost
universally inert as a result of the molecular structure of the resin.
Components made of
this material exhibit excellent impermeability to most corrosive liquids,
vapors and gases, even at elevated temperatures, as well as under pressure
and vacuum. They are affected only by molten alkali metals, fluorin and
chlorine trifluoride at elevated temperatures and pressure.
Virgin TFE has exceptional
electrical and dielectric properties, but can be somewhat limited for
mechanical applications. It will creep or cold flow when a compressive
load is applied. Since it is a soft material, it can also experience a
high rate of wear when used in a dynamic situation.
The addition of inert
fillers will increase resistance to wear, deformation and creep. It will
also improve stiffness, thermal conductivity, hardness and dimensional
stability. However, the fillers decrease properties such as tensile strength,
elongation, and dielectric values.
GLASS FIBERS
Milled glass fibers
are the most widely used filler for TFE. They have the least effect on
chemical and electrical properties and add greatly to the mechanical properties
of unfilled TFE. (Addition of glass improves compressive properties by
as much as 40% and improves wear resistance manyfold.) These compounds
resist acids and oxidation but can be attacked by alkali.
BRONZE POWDER
This filler has better
warp and creep resistance and better thermal conductivity than the glass
fiber with TFE. The compound is easily machined, but has poor chemical
resistance in the presence of acids and alkali. It is especially useful
in applications which undergo higher mechanical loads or are subject to
high speed rubbing contacts where the bronze-filler supplies the strength
and conductivity to carry away excess, unwanted heat.
CARBON & GRAPHITE
These fillers are
used both separately and together in TFE compound. They have good chemical
resistance to corrosive environments. They also exhibit good initial wear
and rubbing or sliding contact characteristics, both dry and in water.
They are frequently used in piston rings to reduce cylinder wall wear
by entrapping abrasive foreign particles in their relatively soft surfaces.
MOLYBDENUM DISULFIDE (MoS2)
This filler is used,
frequently in combination with others, to increase surface hardness, stiffness
and to reduce the starting coefficient of friction and steady-state wear.
Its effect on electrical and chemical properties is negligible.
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