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PTFE
The first
coating material applied by Caw was PTFE, which stands for
poly-tetra-fluoro-ethylene. In
South Africa this is often referred to by the Du Pont trade
name of TEFLON 8. In the early stages it was mainly applied
for use in the textile industry. Today it is applied to a
wide variety of articles in the manufacturing industry where
its non-stick, heat resistant properties are of use. For
the best results with regard to these two properties, the article has to
be baked at 400° C.
Although the PTFE is
present as a continuous film it is not often useful as a
corrosion resistant coating as it is micro-porous.
Other systems where the PTFE is present as a pigment in the
resin, can be applied at a lower temperature. These may have
better abrasion and corrosion resistance than the high-bake
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Special Coating
Some
plastics not available in paint systems can be applied
using powder coating techniques. E.g. Gun Coat, Nylons, polyethylene and
PVDF These have good corrosion resistance and can be
more than half a millimeter thick
provided the substance has sufficient heat capacity. PCDF
coatings have
exceptional abrasion resistance.
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Non-stick
Very few solid substances will
permanently adhere to a "Teflon"
finish. And while tacky
materials may show some
adhesion, almost all substances release easily.
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Low
coefficient of friction
The
coefficient of friction of "Teflon"is generally in the range of 0.05 to
0.20,
depending on the load, sliding
speed and particular "Teflon" finish used.
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Non-wetting
Since "Teflon" surfaces are both
oleophobic and hydrophobic, they
are not readily wet.
Clean-up is easier, more thorough and in many cases
self-cleaning.
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Heat-resistance
There is no decomposition of PTFE below
205° C (400° R;
insignificant decomposition between 205° C
and 290° C (400° F and 550° F) which requires no special
precautions. Between 290° C and 315° C (550° F and 600° F)
intermittent service is possible with adequate ventilation. |
Unique
electrical properties
Over a wide range of frequencies,
"Teflon" has high dielectric strength,
low dissipation factor, and very high
surface resistivity. By special techniques,
it can even be made conductive
enough to be used as an
anti-static coating.
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Cryogenic
stability
Many "Teflon" finishes will withstand
severe temperature extremes without
loss of physical properties. "Teflon" may
be considered for use at
temperatures as low as —270° C (-450° F).
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