Lubricant Films in Rolling Contact of Rough Surfaces

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Abstract
An experimental and mathematical study of elastohydrodynamic film formation is described for a rolling four-ball configuration utilizing steel bearing balls. Wear rates are determined in the microgram range, using a radiotracer tagged ball. Existence and interruptions of elastohydrodynamic films are observed by measurement of electrical conductivity through the Hertzian contact. Surface microgeometry of the rolling tracks on the balls is statistically analyzed by processing electrical analogs of surface profiles through on-line computing equipment. Defining electrical contacts as asperity approaches through a separating film, the average duration and frequency of such approaches is computed from surface microgeometry statistics. A comparison of computed and observed values of contact conductivity parameters shows good order of magnitude agreement and yields estimates of average film thickness as a function of speed and load which agree, satisfactorily with the order of film thickness predicted by elastohydrodynamic theory. Significant wear is shown to occur only in regimes where the film is interrupted and to become progressively more rapid as the severity of asperity contacts increases with decreasing speed.

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