Effect of Clearance on Rotary Rock Bit Journal Bearing Contact Stress

Abstract

This paper presents a numerical method for analyzing the effect of clearance on closely conforming rotary rock bit journal bearings. The modified Boussinesq point-force displacement influence function and the modified profile function are introduced in conjunction with the discretization of the integral equation. Automatic mesh generation is employed to redefine a new pressure area boundary and therefore round-off errors normally found while solving a large-scale linear system of equations can be avoided. The numerical method has been implemented in a computer program and has been applied to the problems of misaligned and perfectly aligned conformal contact. There is a close agreement with the Persson’s analytical solution at the center of the aligned bearing length. However, owing to a high stress concentration at the bearing edge, the edge pressure distribution will differ significantly from the Persson’s plane stress model. The conformal contact will have a comparatively higher peak pressure and lower contact-angle than the Hertzian line contact prediction. The results of the analysis provides a design tool for improving drill bit life.