Sliding cooperation of materials with different hardness (deformability), e.g., a polymeric material cooperating
with metallic materials, occurs in machine elements in one of the following two variants: a conventional pair
or a reverse pair.
In the case of the conventional sliding pair, the deformation area (contact area) of the sliding materials does
not move on the surface of the polymer element during their cooperation. In the case of reverse pairs, the
contact surface changes its position when moving on the surface of the polymer element. Depending on
the variant of the sliding pair, the differences in the friction and wear process of polymer material can be
observed.
Tribological investigations of chosen sliding pairs (elastomer on steel or steel on elastomer) in the static friction
were carried out on the rig. The polymeric materials selected for the tests were thermoplastic elastomers TPU,
PUR, and silicone rubber SI. These materials co-operated with C45 steel in the different contact pressures
(p = 0.1 – 0.26 MPa) under dry friction or mixed lubrication conditions (hydraulic oil Hipol HLP-68). Based
on the recorded value of the friction force Ft, the values of static coefficients of friction μstat were determined.
The test results showed a significant influence of the variant of the combination of materials (metal-polymer
or polymer-metal) on the value of the friction coefficient. In all tested pairs in which steel sample (pin) slid
against elastomeric plates, the friction coefficient was higher than in the case when the elastomeric sample
(pins) cooperated with steel counterfaces (plates). The main reason is the considerable value of the deformation
component of the friction force. This is probably due to the displacement of the elastomer deformation area in
its surface layer and energy dissipation as a result of stress-strain hysteresis in the elastomeric material, as in
the case with reversed pairs.
Effect of loading time on the static friction polymer-metal sliding pairs at low temperature
