Modeling and analyzing the journal-thrust bearing system in rock-drilling bits under mixed-elastohydrodynamic lubrication

The increasingly high demands for compact design require modern machinery to work under severe operating conditions. Moreover, global competition requires industries to rapidly improve their product design. Numerical modeling and computer simulation can be utilized to help industries develop cutting edge products in a short design cycle. The research in this thesis aims at modeling journal bearing and journal-thrust bearing systems for rock-drilling bit design.; A steady-state mixed-thermo-elasto-hydrodynamic (TEHD) model for journal bearings has been developed first as the baseline information for the coupled journal-thrust bearing system, which considers the fluid flow in the gap formed by rough surfaces, asperity contact, surface thermoelastic, as well as heat transfer. The model is verified with experimentally measured temperature data. Numerical simulations of the operation of a typical journal bearing are conducted and the importance of several factors affecting the mixed lubrication mechanism is discussed.; Drilling bits, as well as many mechanisms, such as computer hard drives, gear trains, and machine tool spindle systems, operate under both axial and radial loads, which should be respectively supported by thrust and journal bearings. By utilizing the end face of the shaft of a journal bearing as a thrust bearing, a coupled journal-thrust bearing system can be formed. A mixed lubrication model is then developed to investigate the lubrication of this type of coupled bearing system. A conformal-mapping method is proposed in the model formulation to facilitate a universal flow description. In order to study the influence of boundary conditions on the performance of the bearing system, either the Reynolds boundary conditions or the JFO's mass conserving cavitation conditions are applied to the governing Reynolds equations. Two types of misalignment (axial and twisting) are considered. The performance of a typical coupled journal-thrust bearing system is numerically studied. Effects of elastic deformation, misalignment on the system performance are discussed.; The method developed for the coupled bearing systems is extended to a methodology of bearing module integration. Eight generic modules are created, which can be assembled to obtain multiple coupled bearing systems.