Increase in contact strength of heavy-loaded rolling bearings for gear drives and transmissions

Abstract

Special rolling bearings are applied in layouts of various types of machine. The serviceability of these bearings greatly affects the main performance characteristics of power gears and gear drives. A special class of gear contains parts which are subjected to different advanced hardening treatment. The reason for the failure for such bearings is progressive contact fractures. Trouble spots for these fractures originate in sub-surface layers of the structurally non-homogeneous material obtained as a result of hardening treatment. In this relation, the study of kinetics and ways of generation of sub-surface (depth) contract failures is vital for the purpose of developing a method for analysis and an increase in the load-carrying capacity of the part under cyclic and dynamic loads. Trends of surface layer generation for heavy-loaded bearing parts of planetary turnover mechanisms (PTM) for mobile machines have been studied. The features of contact loading are revealed for parts of power gears with a surface hardened layer obtained through the use of various hardening treatments. Methods for depth contact stress analysis are proposed, design relations are obtained which allow for determining, in each specific case, the position of a risky zone where the trouble spots of fatigue depth fractures can appear. A method for analysis is proposed which permits determining the values of the hardened layer parameters necessary to provide high resistibility to contact fractures. Examples of the analysis of depth contact strength are given for the bearing parts of PTM for the mobile machine.