Quantitative measurements of film thickness in a radially loaded deep-groove ball bearing

The evaluation of the lubricant film thickness in machine elements working in elastohydrodynamic conditions is essential for the design aimed at improving their performance and durability. Among electrical methods for measuring the lubricant film thickness in these contacts the electrical capacitance is convenient to use because it relates directly to the film thickness by an inverse proportional relationship. Simultaneous measurements of optical film thickness and electrical capacitance have allowed the authors to perform quantitative evaluation of the film thickness in a model glass/steel contact, and develop a testing procedure which can be applied to steel/steel contacts. In the current paper a novel approach to film thickness measurements in rolling element bearings is presented. By replacing all but one steel ball with electrically insulating, ceramic balls evaluation of the lubricant film thickness in a radially loaded ball bearing has been achieved. The current procedure provides a valuable research tool for in-situ monitoring of lubrication condition, allowing studying the influence of operating parameters as well as the lubricant's chemistry.