Thermal Wedge Lubrication of Parallel Surface Thrust Bearings

The parallel surface thrust bearing has been studied both theoretically and experimentally. The general equations governing the laminar flow of a Newtonian fluid are presented and suitably reduced to describe the flow of lubricant through a plain collar bearing with sector pads. A computer solution of the resulting equations has been obtained in which the variations of density and viscosity with temperature are accommodated and the circumferential leakage of oil from the bearing is recognized. The resulting performance curves indicate that useful load-carrying capacities, produced by a “thermal wedge” effect, are possible with a parallel surface thrust bearing. The effect of the inlet oil temperature and bearing speed on the performance is shown. Tests were carried out on three, four, and five-pad bearings operating at 15,000 rpm. It was found that circumferential oil seals were required to insure stable operation. The results confirm that hydrodynamic lubrication may be achieved with a parallel surface thrust bearing. However, it was found that some practical limitations are imposed by high temperatures. A comparison between the theoretical load capacity of an optimum tilting pad bearing and that of a parallel surface bearing for equivalent pad dimensions, speed, and lubricant conditions revealed that the tilting pad bearing had the superior performance. Comparison of friction results with the findings of other workers shows good agreement.