Study on the tribological properties of Polyamide 66-Polyamide 66 sliding combination in Hertzian contact under grease-lubricated conditions

Polyamide 66 (PA66) exhibits excellent mechanical properties and high temperature resistance, rendering it a prevalent material for gear transmission. This study investigates the influence of lubrication, contact pressure, sliding speed and PV value (the product of pressure and velocity) on the tribological performance of PA66 gear materials under Hertzian contact using a pin-on-disc test rig. The results show that grease lubrication can significantly increase the tribological properties at high PV values. At a PV value of 30 MPa·m/s, the friction coefficient under grease lubrication is 86.9% lower compared to that under dry conditions, and the wear rate is reduced by 96.1%. The friction coefficient and wear rate of PA66 decrease with increasing PV values under dry friction conditions. However, at a PV value of 4 MPa·m/s, the wear rate of PA66 pins is highest when lubricated with grease, which is about 18 times that of dry condition. This is due to the grease reducing the surface mechanical strength of PA66. The wear mechanisms of PA66 primarily include adhesive wear and abrasive wear. At low PV values, abrasive wear dominates under lubrication conditions, whereas adhesive wear is predominant under dry conditions. Conversely, at high PV values, abrasive wear is more prevalent under dry friction conditions, and adhesive wear is more prominent under grease lubrication conditions.