Study On The Structure And Performance Of Self Adjustment Of Spindle Bearing Preload

For the high speed machine tool,it is necessary to have a larger bearing preload to improve the stiffness of the spindle at low speed,and a smaller bearing preload to decrease the temperature rise of spindle at high speed.there are some shortages in the two kinds of preload methods,including position preload and constant preload: when position preload is applied,the temperature rise of the bearing is too high at high speed;when constant preload is applied,bearing stiffness is not enough at low speed.Therefore,this paper hopes to take into account the advantages of position preload and constant preload to focus the following contents:The self-adjusting preload structure that the bearing preload changes with rotation speed is designed.By computing the key parameters of the structure componts such as elastic ring and the special sleeve,the relationship between the preload and the rotation speed of the bearing is simulated and analyzed,the influence of different key parameters on the preload is also analyzed.Based on Hertz contact theory and quasi statics model,the change rules of contact angle,rigidity and friction moment of the hybrid ceramic ball bearing under the preload system are analyzed,which provides the theoretical basis for the following temperature field analysis.And the modified quasi-Newton iteration method is used to solve the quasi-static nonlinear equations of high speed angular contact ball bearings in Matlab.Under the preload structure,the steady temperature field of the bearing at the highest speed is analyzed,and furtherly compares with the bearing temperature rise during the constant preload.Taking the bearing temperature upper limit given by the bearing company as the evaluating indicator,adjust the preload of the bearing or change the cooling condition.The results show that in the preload system,the bearing preload decreases with the parabolic trend with the increase of rotation speed.The smaller the cone angle,the greater the width of the end,the higher the end height,the smaller the root thickness of the elastic ring,the smaller the preload.The radial stiffness of the bearing decreases with the increase of speed,and increases 16.6% than that of the constant preload at low speed;the bearing temperature increases with the increase of speed,and decreases 7.2% than that of the constant preload the temperature rise at the highest speed.The results show that the selfadjusting preload can better meet the requirement of the new generation high speed machine tool that realizes high torque at low speed,high power at high speed.