ABSTRACT
The subject of polymer-polymer pair interaction is highly important, bearing in mind that such pairs are used in the construction of machines and equipment, among other uses. Considering that the characteristics of polymer-polymer sliding pairs (e.g., the load limit value and advantageous parameter, PV) differ from those of polymer-metal pairs, the subject is particularly interesting and has been little explored so far. Hence, the present study presents one of the areas of the effects of standstill time (intrinsically characteristic of polymeric materials) on the startup parameters in sliding pairs where the sample and the countersample were made of a polymeric material. Pairs of same-type polymers, POM-POM, PET-PET, and PA6-PA6, were subjected to tests. A test rig dedicated to static friction coefficient determination, whose principle of operation is based on the interdependences between the force characteristics of an inclined plane, was used for this purpose. The sliding pair was successively loaded with 25 N, 50 N, and 75 N, and the standstill time ranged from 0 to 10 min. The determined tribological characteristics were analysed with regard to the standstill time under load, unit pressure, and polymer pair material. An optical profilometer and a scanning electron microscope were used to qualitatively evaluate the effects of standstill time and unit pressure on the surfaces of the interacting elements. Complex interrelationships between the test results and the set experimental parameters were noted. SEM micrographs revealed post-friction changes in the sliding surfaces.
ABSTRACT
This article concerns the tribological properties of three selected polymer materials: polyamide PA6, polyethylene PE-HD and polyetheretherketone composite PEEK/BG during sliding against aluminium alloy EN AW-2017A in the presence of hydraulic oil HLP 68. The tests were carried out under contact pressure p of 3.5-11 MPa at ambient temperature T ranging from -20 °C to +20 °C. The dependence of kinetic friction coefficient µk on the two parameters was determined through tribological tests carried out using a pin-on-disc tribometer. A five-level central composite rotatable design (CCRD) was adopted for the experiment. All the test results were statistically analysed. The microhardness of the surface of the polymeric material was measured before and after the friction process. The surface was also examined under SEM. Temperature and contact pressure have been found to have a significant effect on the tribological properties of the tested sliding pairs. Relative to the applied friction conditions, the surfaces after friction showed rather heavy signs of wear.
