Research On Convexity Design Of Ceramic Roller Bearings

"Edge effect" occurs in the practical application of straight roller bearings.This thesis is based on the finite line contact thermal elasto-hydrodynamic theory and the research method of convexity of steel roller bearings to study the convexity design of silicon nitride ceramic roller bearings.The study includes both convex shape and convexity measurement aspects,and further explores the influence of load,speed,and surface morphology parameters on the lubrication performance of rollers.Using FORTRAN programming language,the study first discusses the influence of convex shapes on the lubrication performance of silicon nitride ceramic roller bearings,including pressure,film thickness,and temperature field distribution.The research indicates that the influence of convex shapes on the lubrication performance of ceramic rollers is similar to that of steel rollers: the distribution of the elasto-hydrodynamic solution of the intersecting arc-shaped roller and the tangent arc-shaped roller is similar,and the starting position of the shaping results in an increase in pressure and temperature.However,the former is more conducive to the establishment of lubricating oil films.A fully convex roller exhibits the characteristic of point contact lubrication,and the pressure is concentrated towards the axial center,thus exhibiting the worst bearing performance.The logarithmic roller exhibits the best lubrication performance,but even in lubrication conditions,Lundberg’s logarithmic roller that can eliminate the "edge effect" in its static elastic state still exhibits a certain "edge effect".Therefore,convexity design research,especially convexity measurement,should be conducted for ceramic rollers.In various convex shapes,the distribution of temperature and pressure fields is similar.Therefore,the convexity design can simultaneously optimize the distribution of temperature fields.Next,the thermal elasto-hydrodynamic performance of intersecting and tangent arc-shaped ceramic rollers was analyzed separately,and the influence of shaping parameters,such as shaping radius and shaping length,and working conditions,such as load and speed,on their lubrication performance were discussed.The study indicates that the influence of shaping parameters and working condition parameters on the lubrication performance of intersecting and tangent arc-shaped rollers is similar,and the lubrication performance first improves and then worsens as the shaping radius increases and the shaping length decreases.The shaping parameters of arc-shaped rollers should be frictionally designed from the perspective of ensuring the axial uniformity of pressure film thickness distribution and lubrication reliable angles,and an optimization interval exists for the shaping parameters.Under heavy load and low speed working conditions,the shaping radius should be appropriately reduced or the shaping length should be appropriately increased.The appropriate increase of roll suction speed is beneficial to film formation,but excessive speed can cause excessive temperature rise and is not conducive to the life of the contact pair.Next,the lubrication performance and convexity design of fully convex ceramic roller bearings were studied,and the influence of the mother curvature radius was discussed.The study indicates that as the mother curvature radius increases,the concentration of pressure in the center weakens,but if the mother curvature radius is too large,the thickness of the film will fall and the lubrication will fail at the end of the roller.Therefore,there is an optimized range of mother curvature radius.When discussing the influence of the mother curvature radius,it was found that the fully convex roller,which was thought not to have an "edge effect",can still exhibit an "edge effect" under certain conditions,and the conditions and reasons for its occurrence were discussed.The results indicate that when the curvature radius of the roller is too large,the load is too large,or the length of the roller is too short,the pressure-bearing area reaches the edge of the roller in the axial direction,causing an increase in pressure at the end and a drop in film thickness,resulting in the "edge effect".In the convexity design of fully convex rollers,such situations should be avoided.Finally,by introducing convexity measurement coefficients to change the convexity measurement of the rollers,and introducing design criteria from the perspective of comprehensively considering the distribution of pressure and film thickness,the convexity measurement design of ceramic logarithmic rollers and the influence of surface morphology on the lubrication performance of ceramic logarithmic rollers were studied.The research indicates that under lubrication conditions,the convexity measurement of ceramic logarithmic rollers should be greater than that of Lundberg’s logarithmic profile.Under the same load and Hertz pressure,the optimal convexity measurement of ceramic logarithmic rollers is smaller than that of steel logarithmic rollers.Surface morphology can cause pressure and film thickness to oscillate with the same frequency as the roughness peaks,worsening the lubrication state and making it difficult to form a full film lubrication.The greater the amplitude or the shorter the wavelength of the roughness peaks,the more detrimental it is to the formation of the lubricating film and the pressure distribution.