Elasto-Hydrodynamic Lubrication of Rolling-Contact Surfaces

An X-ray technique is described for the measurement of the thickness and shape of thin oil films (from 5 to 50 millionths of an inch thick) formed between the rolling and rolling-sliding surfaces of hardened steel rollers as in rolling bearings and gears. The film thickness with white mineral oil, diester-base, and silicone lubricants was found to vary with temperature (viscosity), speed, and load in much the same way as expected from elasto-hydrodynamic considerations. The shape of the elastically flattened contact regions on the rollers appeared to change with rolling speed in such a way as to explain why ball bearings and gears have longer fatigue life (in revolutions) at high speed than at low speed.

The experimental results are compared with lubrication theory in which the elastic deflections of the bearing surfaces are combined with the viscous flow of the lubricant under pressure. Although there is general agreement between theory and experiment, possible modifications to the theory to account for the increasing discrepancy with experiment at high speed, load, and viscosity are discussed.