The thermal wedge effect in hydrodynamic lubrication

The' 'thermal wedge' effect in hydrodynamic lubrication has been studied both theoretically - and experimentally. The friction theory has been refined to take into consideration the effect on friction of a variation of temperature across the film from the bearing to the disk surface. The theoretical pressure and temperature equations formulated by Currie were used in conjunction with the friction equation to obtain theoretical performance curves. Tests were carried out on a set of bearings having three, four and five pad configurations. Two different bearing materials were used, namely, babbitt, and Delrin A.F. fiber/resin. Circumferential oil rings were fitted into the assembly to restrict the radial flow of oil, thereby ensuring full lubrication of the bearings. Experimental observations proved that a thermal gradient across the film did exist, thus justifying the basic assumption in the variable viscosity analysis. Experimental coefficients of friction compared favourably with predicted values. The agreement was better than by-earlier theories. The results indicate that bearing performance is improved by the use of oil restrictor rings (actual load carrying capacities were more than doubled). The optimum bearing .configuration was that of a four-pad babbitt bearing. Although the Delrin A F bearing performed much better than the babbit bearings, differential thermal expansion of the Delrin produced a geometric wedge, and a bearing of this material could not be considered-as a thermal wedge bearing.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat