Low
The low coefficient of friction with PTFE has been widely
known, first published in 1949 when K.V. Shooter and P.H.
Thomas measured coefficient of friction using a Bowden-Leben
machine.39 With loads of between 1 and 4 kg (2.2 and 8.8 lb.)
and sliding velocities of 0.1 and 10 mm/s (0.02 to 2 ft/min.),
they reported that the coefficient of friction was 0.04. It is significant
that a coefficient of 0.01 was reported with a load of
1360 kg (3000lb.) in a later test.40
Slide
When PTFE comes in contact with another surface, it provides
lubrication by sliding. The PTFE does not peel off, but
simply slides along on its own surfaces. Also, the orientation of
the resins plays a role in reduced friction. When the polymers
slide along the chain, coefficient is lowered by 39%, as compared
to sliding across the chain.41
Increase = decrease
Another critical factor is that static friction of PTFE decreases
with an increase in load.42 Static coefficient of friction is lower
than the dynamic coefficient and avoids stick-slip problems.43
Oil
When oil comes in contact with PTFE, it slides off because of
the low coefficient of friction. PTFE uses this property to advantage
by reducing energy loss to oil drag. Oil flows more
readily over lubricated components, increasing oil’s capacity