Aspects of thrust cone tribology: Part 2: Surface failure in thrust cones and the influence of rolling and sliding speeds in concentrated contacts

Abstract

This paper outlines relevant aspects of the operation of thrust cones and describes salient features of an unexpected form of failure encountered in small-scale thrust cone simulation tests. Interpretation of the thrust cone simulation test results in the light of related twin-disc tests at the relevant low slide-roll ratio leads to two conclusions. Rather than scuffing, the limiting surface failure mechanism in small-scale thrust cone tests was general plastic deformation with cold pressure welding promoted by the lack of support at the cone edges and the prolate epicycloidal path followed by the contact. The limiting surface failure mechanism in full-scale thrust cone bearings, which have markedly lower curvature and higher rolling speed than used in small-scale simulation tests, was predicted to be scuffing delayed to relatively severe operating conditions by prior running-in. Further development of the insights gained from the related twin-disc work results in two recommendations. Future work should be directed to assessing the surface modification that follows transition from EHL to mixed lubrication and redefining the conditions in which transition to micro-EHL occurs in order to quantify the potential enhancement of scuffing resistance offered by controlled running-in. It should also concentrate on evaluating the combined effects of microgeometry conducive to lubricant film formation and material properties resistant to weld formation in order to obviate the difficulty of assigning a representative value to the operating friction coefficient that is common to a number of proposed failure criteria.