The Effect of PTFE Content on Tribological Properties of Polyoxymethylene Composites

Polyoxymethylene (POM) and its composites with excellent mechanical properties are often used as alternative materials in gear transmission design. This paper considers the practical application scenario of POM gears, using a pin-on-disk tribometer to simulate the Hertzian contact and sliding part of gear mesh. The effects of polytetrafluoroethylene (PTFE) content (0%, 5%, 10%, and 15%), maximum contact pressure (40 MPa and 60 MPa), sliding speed (0.1 m/s and 0.5 m/s), and ambient temperature (room temperature and 70 °C) on the tribological properties of POM composites under self-mated contact are investigated. The results show that the tribological properties of the composites tend to improve with the increase of PTFE content under the two ambient temperature conditions, reaching the optimum at 15% PTFE content. However, the addition of PTFE does not improve the tribological properties of the composites under the most severe conditions of 70 °C and a pressure–velocity (PV) value of 30 MPa m/s. At two ambient temperatures, pure POM and its composites exhibit the lowest friction coefficient at a PV value of 6 MPa m/s and the smallest specific wear-rate at a PV value of 20 MPa m/s. The friction coefficient of composites decreases with an increase in ambient temperature from room temperature to 70 °C at a sliding speed of 0.1 m/s but increases at a sliding speed of 0.5 m/s. Analysis of variance (ANOVA) results indicate that all factors are significant, except for temperature which does not have a significant effect on the friction coefficient. Additionally, this paper analyzes the wear mechanisms of composites.