Vacuum Three-Ball Tribometer for Testing Liquid Lubricants

A three-ball tribometer has been developed for use in evaluating the performances of oils and greases as lubricants in a vacuum at room temperature. This apparatus differs from the one described in "Vacuum Four-Ball Tribometer for Testing Liquid Lubricants" (LEW-16194), NASA Tech Briefs, Vol. 21, No. 4 (April 1997), page 64. The present apparatus is designed especially for experiments on the tribodegradation of liquid lubricants under conditions similar to those observed in preloaded angular-contact ball bearings operating in the boundary-lubrication regime in a vacuum. Tribodegradation can include both physical and chemical changes caused by a combination of contact stresses and aggressive ambient conditions. The chemical changes typically involve chemical reactions between lubricants and bearing surfaces, decomposition of lubricants, and darkening of lubricants associated with the formation of products denoted generally as "friction polymers."