On the Evaluation of the Service Life of Shaft-Bushing Tribosystems at low speed

This work presents the results of a set of endurance tests performed on steel to steel shaft/bushing tribosystems, without re-lubrication after start-up. The experimental procedure was designed in order to provide simulation for the operative conditions of earthmoving machinery. For this purpose, a new testing machine was specifically manufactured so as to accommodate shaft/bushing assemblies up to a nominal coupling diameter of 90 mm, with a maximum radial load capability of 300 kN. The machine was operated in alternating rotation, with a span angle of 180 degrees, at an angular speed of 10 rpm. The effects of contact pressure intensity were investigated, as well as the effects of grease lubrication type and of the geometry of grease breeding grooves that were located on the bushings inner surface. The tribology behaviour of the tested assemblies was quantified by means of the transmitted torque, grease temperature at the surface of contact and the metallographic analysis of wear out surfaces.