Investigation Of Tribological Properties Of POM Filled With PTFE And Inorganic Particles

Polyoxymethylene (POM) is a high-crystalline engineering plastic, which has high mechanical strength, good stability, corrosion resistance and wear resistance as well as anti-fatigue properties. So POM is widely used in automobile, electrical appliance, precision apparatus, etc. However, pure POM against steel exhibits a high coefficient of friction, and which is not suitable for sliding components. So far, the most effective way to reduce coefficient of friction of POM is to prepare the PTFE-POM composites filled with polytetrafluoroethylene (PTFE). In order to increase the applicability of the POM in the bearing industry, the graphite, glass fiber, kaolin and PTFE, which was acted as a solid lubrication, were selected for the modifying agents, then the POM composites were prepared. A commercial POM-20%PTFE composite was chosen to carry out a comparative investigation. It is expected to further improve the tribological properties of POM.The different contents of the PTFE-graphite, PTFE-GF and PTFE-kaolin, respectively, were added into POM, then they were extruded with a single-screw extruder.The POM-PTFE-graphite, POM-PTFE-GF and POM-PTFE-kaolin composites were hot-molded into slab specimens.Wide angle x-ray diffraction (WAXD) patterns were taken on a Bruker D8 ADVANCE diffract-meter (Germany) with Cu-filtered Cu kαradiation at room temperature. The crystalline area and the amorphous area were calculated with a software of this apparatus, then the mass fraction crystallinity of the POM composites were obtained.For the POM-PTFE-graphite and POM-PTFE-GF composites, the friction and wear tests were carried out in a reciprocating tribometer under two different loading conditions. These composites were tested against a 45 carbon steel track, at room temperature in ambient atmosphere (60±3)%RH. The conditions were a reciprocating frequency of 1.0 Hz. Results show that by comparison to a POM+20%PTFE composite, a POM+20%PTFE+5%graphite composite exhibited a relatively low coefficient of friction under loading conditions of 3.3 Mpa and a POM+20%PTFE+10%GF composite exhibited a relatively low specific wear rate under loading conditions of 6.2 Mpa.For the POM-PTFE-kaolin composites, the friction and wear tests were also carried out in a reciprocating tribometer. It is found that a POM+20% PTFE+7.5%kaolin composite exhibited a relatively low coefficient of friction and high wear resistance compared to a POM+20%PTFE composite.