Influence of load, sliding speed and heat-sink volume on the tribological behaviour of polyoxymethylene (POM) sliding against steel

This work focuses on a tribological and contact-temperature investigation of unreinforced polyoxymethylene (POM) sliding against steel (DIN 100Cr6) under a wide range of loads and sliding speeds. We have investigated a wider range than is commonly studied, along with different heat-sink volumes of the steel counter-body (3-fold variation). Four empirical contact-load criteria, i.e., wear-change factor, mechanical load factor, thermal load factor, and critical temperature factor, were introduced to complement the evaluation of the tribological behaviour and the contact temperature. Moreover, these factors are not limited to current materials, but provide general methodological approach. Irrespective of the heat-sink volume, even with an 8-fold increase in the p ∙ v value (0.6–4.8 MPa.m/s), the wear mechanism does not change significantly. This beneficial behaviour is mainly due to the synergistic interplay of the mechanical and thermal loads, which mutually suppress the domination and critical state of a single wear mechanism, either mechanical-based or thermal-based, which was understood through novel empirical factor analyses. Another key parameter for maintaining stable and beneficial tribological performance was the large thermal mass, i.e., the heat-sink volume of all the steel samples that suppressed the commonly observed high-temperature rise under severe contact conditions. Thus, the tribological performance was notably enhanced compared to previous studies under similar conditions, since the heat-sink volume was large enough and the balance between the thermal and mechanical loads was maintained.