A study of wear chemistry and contact temperature using a microsample four-ball wear test

This study demonstrates that insight into the tribological reactions taking place in mixed and boundary lubrication can be provided by combining micro sample four-ball wear tests with chemical analysis using gel permeation chr omatography (GPC) as the principal analytical tool. At the end of the micro sample four-ball wear test the lubricant turns into a grease-like mixture p reventing the liquid lubricant from recirculating into the wear track and t hus causing failure. Analyses of the various lubricant samples after their failure in the microsample test all show a relatively small amount of insol uble deposits and a large quantity of unreacted fresh lubricant. Virtually no intermediate reaction products were found. Combining this information wi th lubricant stability and the fact that a large quantity of lubricant flow ed through the sliding junction while only a small portion was oxidized sug gests that two very different thermal environments exist in the concentrate d contact. The insoluble deposits are typical of thermal oxidative reaction s that require temperatures of 400 degrees C or above. The unreacted lubric ant found at failure indicates that this portion of the lubricant sample wa s maintained at temperatures of 150 degrees C or below. The formation of gr ease-like mixture with as little as four percent reacted material indicates the remaining liquid lubricant and its insoluble reaction deposits were we ll mixed throughout the test. These findings suggest that the hot Zones cau sing severe lubricant degradation are in the immediate vicinity of the aspe rity-asperity contacts while the low temperature zone - the valleys between asperities which are in the majority - are much cooler.