| With the application of journal bearing in high speed and super-high speed conditions, wall slip can occur when shear stress exceeds the critical shear stress at the solid-liquid interface, the oil film is easy to crack and becomes cavitation. The presence of wall slip and cavitation has a great effect on the lubrication characteristics of journal bearing, and possibly leads to the lubrication failure. Therefore, the wall slip and cavitation characteristics of journal bearing have been investigated, which has an important significance for the development of high speed journal bearings.Firstly, the two-dimensional slip model is established based on critical shear stress model, in which the circumferential and axial wall slip of sleeve surface and axial surface is considered. The shear stress angle is used to compute the circumferential and axial shear stress component in slip model. Considering the slip states in the sleeve surface and axial surface comprehensively, the four slip states are studied, the slip velocity profiles of four slip states are given, and the theoretical model of four slip states are established.In full film region, the related items with lubricant bulk modulus are analyzed, the cavitation model is established based on modified Elrod cavitation model, which is benefit for the calculation process of oil film pressure. The generalized equation that integrates the full film region and cavitation region based on JFO boundary condition is derived, which makes the JFO boundary condition more precisely to be applied in the computation of cavitation theory.The theoretical model of four slip states and the formulas of finite differential method are established considering cavitation mechanism based on the two-dimensional slip model and modified Elrod cavitation model. The model not only considers the four slip states but also optimizes the solution of generalized Reynolds equation in full film region compared with Elrod method, which is consistent with the actual work condition and increases the computation efficiency.Secondly, the wall slip is studied experimentally by the method of target speed tracking method. The material of spiral oil wedge journal bearing is synthetic glass in experiment, the coloured dyestuff is added into the lubricant from the inlet holes, the fluid flow of lubricant is taken using the high speed camera, the average speed is computed, and the circumferential and axial wall slip is found by the difference of theoretical results and experimental results. According to the figures of minimum circumferential slip velocity with the rotating speed and supply pressure in experiment, the critical shear stresses of sleeve surface and axis surface are obtained for high viscosity lubricant and low viscosity lubricant. It is found by experiment that the slip velocity increases with the increase of input pressure.Using the critical shear stresses of sleeve surface and axis surface that are obtained in experiment, the influence of critical shear stress and wall slip on the characteristics of spiral oil wedge journal bearing is studied. The influence of the bearing structure, eccentricity, spiral angle, rotating speed and critical shear stress on slip degree is studied. The results show that wall slip occurs first in the large shear stress, the small clearance of oil film and the envelop zone. Wall slip can cause the decrease of oil film pressure, carrying capacity, friction drag and temperature rise, but produces the increase of end leakage rate. The slip position and area influence each other in the sleeve surface and axial surface.In order to improve the carrying capacity and reduce the temperature rise in journal bearing, a combined surface radial sleeve bearing using the interfacial slip technique is discussed. An extended Reynolds equation is derived based on the modified slip length model considering wall slip. Comparing with the general journal bearing, the pressure, load capacity and end leakage rate of the combined surface sleeve bearing can be increased greatly, but the attitude angle, friction drag, temperature rise of the combined bearing can be decreased.Thirdly, the influence of lubricant viscosity on the cavitation characteristics and end leakage rate is studied by theory and experiment. The pictures of spiral oil wedge journal bearings under different rotating speeds and supply pressures for high viscosity lubricant and low viscosity lubricant are taken, the end leakage rate of the journal bearing is measured, and the cavitation shape, oil film rupture location, oil film reformation location, rupture area of oil film and end leakage rate are studied by theory and experiment. The relations of oil film reformation location with the rotating speed and supply pressure are obtained for high viscosity lubricant and low viscosity lubricant in experiment. The cavitaiton area decreases and end leakage rate increases for low viscosity lubricant compared with high viscosity lubricant. The modified Elrod calculation results are in general consistent with the experimental results.The dynamic characteristic model is established based on JFO boundary condition considering cavitation effect and wall slip. The influence of wall slip and cavitation effect on pressure, carrying capacity, friction drag, end leakage rate, temperature rise, stiffness and damping coefficients for different eccentricities, spiral angles, input pressures and rotating speeds is studied. The oil film pressure, carrying capacity, friction drag, end leakage rate, stiffness and damping coefficients are larger, temperature rise is lower and the oil film rupture delays using JFO boundary condition compared with Reynolds boundary condition when the wall slip is considered.Finally, the temperature rise and the bush inner surface temperature are measured by thermocouple and infrared thermometer, separately. The results show that the temperature rise decreases for low viscosity lubricant compared with high viscosity lubricant, so the application of low viscosity lubrication can solve the temperature rise in high speed machine tools.
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