Friction wear and acoustic emissions of some plastics sliding against Si3N4

The friction, wear and acoustic emission properties of POM, PA 66, torlon, PP, PTFE, HDPE and PVC sliding against silicon nitride, Si3N4, were studied using a ball-on-flat-rotating-disc tribometer. The friction and normal forces were measured in real time to accurately determine the dynamic coefficient of friction COF. Wear of the weaker material was quantified by the loss in volume ww. Additionally, AE signal due to stress waves arising from the interaction of the surfaces in dynamic contact was detected. Low COF was found for HDPE, POM and PTFE, the latter showing a decrease to 0.08 at higher load. Torlon generated extremely high friction. For the remaining plastics, the COF was comparable to that found in similar experiments conducted against SAE 52100 steel counterface. Wear levels were found to be low or acceptable except for PTFE. The wear equation developed by Rhee [S.K. Rhee, Wear equation for polymers sliding against metal surfaces, Wear 16 (1970) 431–445] was used to relate ww to the following operating parameters: sliding duration, sliding speed and normal load. These results were then expressed in the form of wear depth. Finally, ∫AE dt∫AE dt increased with ww for all plastics and a linear relationship was found between ∫Ff ds∫Ff ds, the integrated friction force over the sliding distance (friction work), and ∫AE dt∫AE dt.