Microasperity Lubrication

Abstract

Large load-supporting capability has been observed between parallel surfaces of a rotary-shaft face-seal when one of the surfaces contains microasperities in the form of circular cylinders with 12 × 10−3-in. dia and 100-microin. height, covering about one third of the surface. A theory is presented in which the load support is attributed to small tills on the tops of the asperities. The experimental data of lubricant film thickness versus applied load are correlated well by this theory assuming an average till of 0.86 microin. for the 12-mil-dia asperities investigated. Torque data obtained by a thermal technique are also correlated by this theory in the form of a plot of coefficient of friction versus Hersey number. Although direct evidence of the presence of small tilts on the asperity tops is lacking, it has been demonstrated that the load support is even further increased when the tops are purposely rounded. It is concluded that the theory developed correlates well the experimental data and, further, that the use of planned microasperities is an effective method for lubricating the parallel surfaces of face seals and thrust-bearing surfaces.