The Effect of Journal Surface Finish on Journal Bearing Load Capacity - A Radiometric Method

Radiometric wear measurement techniques have been applied to determine the effect of journal surface finish on journal bearing load capacity. Bearing load capacity was measured by using a test machine that applies a linearly increasing unidirectional load to a radioactive test bearing. The onset of bearing wear provides a direct measurement of fluid-film breakdown, which is used to define hydrodynamic bearing load capacity. By use of a journal that can be located at two different positions on the shaft, the relative difference in load capacity between two journal surface finishes can be measured without the need to disturb the geometry of the bearing. The effect of journal surface finish on bearing load capacity was thereby quantified. In this study, nodular iron journals were prepared to have test surfaces with different levels of surface roughness. Results of the radiometric measurements indicate that roughness average, R_a, and core roughness depth, R_k, are the best predictors of load capacity. An increase in the value of either parameter results in a proportional decrease in load capacity. These studies also show that when the journal is ground opposite to the direction of shaft rotation, load capacity decreases by 33%. This work has demonstrated the capability of the radiometric wear technique to quantify the relative performance of journal surfaces and journal geometry.