基于等温弹流润滑理论的滚珠丝杠副摩擦机理研究

Study on the Friction Mechanism of the Ball Screws Based on the Isothermal Elastohydrodynamic Lubrication Theory

针对滚珠丝杠副在低转速状态存在混合润滑导致丝杠滚道加速磨损的问题,基于等温弹流润滑理论建立了滚珠丝杠副弹流润滑接触模型研究滚珠与滚道间的摩擦机理和磨损形式.首先基于Frenet-Serret坐标转换方法建立丝杠与螺母的滚道曲面几何模型.其次基于Reynolds方程建立了滚珠丝杠副弹流润滑接触模型,求解了润滑油膜接触压力分布、油膜厚度分布和微凸体接触压力分布.最后从微观角度阐明了滚珠丝杠副的摩擦机理,其摩擦因数由微凸体接触摩擦因数和油膜润滑摩擦因数组成.实验结果表明:在低转速阶段丝杠滚道的磨损方式为黏着磨损和磨粒磨损,且模拟的摩擦因数曲线趋势和经典的Stribeck摩擦曲线趋势吻合较好,根据实测摩擦力矩准确识别了不同转速下滚珠丝杠副的摩擦因数和润滑状态.

In terms of the accelerated wear of the screw raceway due to mixed lubrication in the low-speed operating ball screws,an elastohydrodynamic lubrication(EHL)contact model of ball screws based on the isothermal EHL theory was proposed to study the friction mechanism and wear form between the ball and raceway.First,the raceway surface geometric model based on the Frenet-Serret coordinate transformation method was established.Subsequently,the EHL contact model of ball screws based on the Reynolds equation was proposed,and the distributions of the film contact stress,film thickness,and asperity contract stress were determined.Finally,the friction mechanism of ball screws was clearly elucidated from a microcosmic perspective,which was composed of the asperity contact friction coefficient and the oil film lubrication friction coefficient.Results show that the wear forms of screw raceway are adhesive wear and abrasive wear,and the simulated friction coefficient curve trend agrees well with the classical Stribeck friction curve trend,which accurately identifies the friction coefficient and lubrication status of ball screws under different screw speeds based on the measured friction torques.