Study On Lubrication Performance Of High-speed Motorized Spindle Conical Hybrid Bearing With Thermal Effect

The lubrication performance of bearing oil film directly affects the reliability and service life of spindle system when the sliding bearing is used as supporting part of high-speed precision motorized spindles.As the high-speed motorized spindle is working,the friction power consumption causes the temperature of the lubricant to rise sharply,and the viscosity decreases accordingly,then the temperature field and viscosity of the non-uniform distribution of bearing oil film will affect the lubrication performance,and even cause the oil film rupture and the instability of the rotor system.Therefore,the temperature rise of high-speed motorized spindle has become the main factor restricting its performance.this paper takes the conical hybrid bearing with a deep and shallow pocket on the inner motorized spindle as the research object,and discusses the influence of thermal effect on bearing oil film characteristics and rotor system stability parameters.The main research contents and results are as follows:Firstly based on the laminar flow lubrication theory,the Reynolds equation,energy equation,temperature viscosity equation and corresponding boundary conditions is established,which control the pressure distribution and temperature distribution.On the basis of this,the finite element method and finite difference method are used to discrete the control equations,the pressure distribution,temperature distribution and static/dynamic characteristic parameters of the high-speed conical hybrid bearing under different conditions are calculated,the minimum thickness of oil film to ensure that oil film of lubricant is not broken when thermal effect is taken into account is analyzed.The comparison between the calculated results and the isothermal model results shows that: the higher the spindle speed is,the greater the oil film temperature rise;the thermal effect makes the bearing capacity of bearing oil film decrease,the end discharge increase,and the angle of displacement increase;the minimum oil film thickness decreases.Secondly on the basis of static equilibrium calculation,the motorized spindle is simplified as a single mass rigid symmetric bearing-rotor system,and the system dynamics equation is established which takes into account the thermal effect.The Routh-Hurwitz criterion is used to derive and obtain the stability parameters of the system,such as the boundary vortex ratio and the instable speed etc.,which are compared with the isothermal state.The results show that,after the thermal effect is taken into account,the main stiffness and the main damping of conical bearing decrease,and the higher the speed is,the greater the reduction is;the critical mass decreases and when the eccentricity rate is 0.6,the decrease of the instability speed is as high as 50.5%;the thermal effect reduces the system stability.The thermal effect has a significant effect on the performance of high-speed precision motorized spindle,this paper provides a reference for high-speed motorized spindle.