Elastohydrodynamic lubrication of real surfaces

Abstract

The paper describes recent experimental and theoretical work on scuffing using a two disc machine. The machine was designed to simulate the operating conditions of high speed, high temperature aerospace gears. A key feature of the rig is the use of axially finished discs to simulate the orientation of finish on real gears, and crowning which avoids the complications of misalignment and unquantifiable edge effects. Scuffing has been studied using both conventionally ground and superfinished surfaces. The latter process is found to give a significant improvement in scuffing load together with reduced friction and bulk temperatures. Corresponding theoretical work is aimed at directly simulating the experimental conditions with the eventual objective of predicting circumstances under which failure of the physical mechanism of micro elastohydrodynamic lubrication (micro EHL) will occur. A line contact micro EHL analysis of typical disc machine conditions shows the mechanism to be extremely robust in theory, but a more recent model which takes account of film thinning at the edges of a real contact due to sideways leakage of oil in valley features of roughness shows promise as a means of explaining film collapse and scuffing failure.