The Friction of radially loaded hybrid spindle bearings under high speeds

Friction losses are an important parameter for evaluating the operational behaviour of high-speed rolling bearings. Especially in machine tool applications, the bearings are subjected to high radial loads, which lead to increased forces in the rolling contact and thus to increased bearing friction. At high speeds, hybrid spindle bearings are typically used, consisting of ceramic balls and steel raceways, which are characterised by better frictional behaviour compared to steel bearings. A precise knowledge of the friction characteristics, especially at high speeds, makes it possible to improve friction models and to extrapolate them to spindle bearings of other types and sizes, geometries and other operational conditions. In the following article, a new straight forward method to measure the frictional torque in spindle bearings is presented. A rigidly arranged hybrid spindle bearing pair of the type 7008 was tested over varying speeds and radial loads evaluated in a characteristic diagram. The influence of oil air and grease lubrication was investigated. Based on the test parameters, a current friction calculation method was presented and validated. The influence of outer race control and minimized power dissipation is discussed.

摩擦损耗是评估高速滚动轴承运行性能的关键参数。尤其在机床应用场景中，轴承需承受较大径向载荷，这会增大滚动接触区域的作用力，进而提升轴承摩擦损耗。高速工况下通常采用混合主轴轴承（hybrid spindle bearings），其由陶瓷球与钢制滚道组成，相较于全钢制轴承，该类轴承的摩擦性能更优。精准掌握摩擦特性，尤其是高速工况下的摩擦特性，有助于优化摩擦模型，并将模型外推至其他类型、尺寸、几何参数及运行工况的主轴轴承中。
本文提出了一种全新的简易方法，用于测量主轴轴承的摩擦转矩。对刚性安装的7008型混合主轴轴承副开展了变转速、变径向载荷的测试，并将测试结果整理至特性曲线图表中。研究了油气润滑与脂润滑的影响。结合测试参数，提出并验证了一种现行的摩擦计算方法。本文还探讨了外圈控制策略与功率损耗最小化的相关影响。