Factors Affecting Surface Roughness Measurement Results, and the Impact on Predicted Life of Elastohydrodynamic Lubricated Rolling-Element Bearings

This work investigates the sensitivity of the surface roughness lubricant life adjustment factor for rolling-element bearings to variations in measured roughness. Roughness measurement results using different values of stylus tip dimension and short wavelength cutoff filter were obtained for several bearing raceway surfaces and used as the inputs for a lubricant life adjustment factor based on the lambda ratio—the ratio of elastohydrodynamic lubrication (EHL) film thickness to the composite surface roughness. The effect on predicted bearing life is shown to be significant. As one means of verification of surface roughness measurements, an ISO type D random/repeating precision roughness specimen was also investigated and shown to have excellent sensitivity to stylus tip dimension, demonstrating its effectiveness as a tool for assessment of stylus radius and condition.