Comparative evaluation of metal and polymer ball bearings

Abstract

The usage of polymers in bearings has been increasing in recent years due to certain valuable tribological properties, including their ability to self-lubricate and their resistance to corrosion. These advantages encourage manufacturers to use polymer bearings in corrosive and lubricant-free work environments as well as applications in which weight reduction is desirable. The objective of this study is to compare the performance of polymer with metal in rolling contact. This is carried out by monitoring the acoustic emission, vibration and operating speed of metal and polymer bearings during their operation.A set of tests was conducted on 8mm radial bearings comprising polymeric inner race, outer race, and cage as well as 52mm thrust bearings comprising polymeric top race, bottom race and retainer. These bearing components were manufactured using two different polymers: polyetheretherketone (PEEK) and polytetrafluoroethylene (PTFE). The rolling elements used in these bearings were made of alumina. The performance of these materials in both radial and thrust bearings was evaluated.A second set of tests was conducted to compare the performance of these polymers with stainless steel in similar bearings. 8mm polymer ball bearings and 8mm metal bearings under dry lubrication conditions were used in these tests. Performance is compared using vibration, acoustic emission as well as changes in the rotational speed. A lower level of vibration is observed with the usage of PEEK in the bearing elements when compared to that of PTFE and metal. However the transfer film formation in PEEK bearings resulted in unstable operating speed of the bearing. Stable operating speeds after an initial running-in period is observed due to transfer film formed in carbon-filled PTFE bearings. However a higher level of vibration is observed in this material when compared to that of the PEEK bearings.