Material of Machine Tool Spindle Bearings

With the continuous improvement of the speed requirements of the spindle bearing of the machine tool, on the one hand, the internal structure design of the bearing has been improved, and on the other hand, new bearing materials have been developed and utilized. At present, hybrid ceramic ball bearings made of silicon nitride ceramics as rolling elements have been widely used in the field of high-speed machine tools. Compared with bearing steel, the density of ceramic material is 40% of that of steel, and the coefficient of linear expansion is less than 1/4 of that of steel. Therefore, when the bearing rotates at high speed, the centrifugal force and rotational moment acting on the ball are small for the hybrid ceramic ball bearing, the bearing load caused by the thermal expansion difference between the ball and the ring is relatively moderate, the bearing friction heat is less, the wear is light, and the high-speed performance can be improved. In addition, since the longitudinal elastic modulus of the ceramic material is about 1.5 times that of the bearing steel, the rigidity of the ceramic ball bearing is larger than that of the steel bearing. The limit speed of the ceramic ball bearing is 20% to 30% higher than that of the steel bearing with the same structure. If the structure of the ceramic ball bearing is optimized according to the characteristics of the ceramic material, the limit speed can be higher. In this paper, the high-speed technology of high-speed machine tool spindle bearings is briefly summarized in terms of structure type, assembly method, preload, limit speed and material selection. Due to the limitation of space, the problems of rigidity and life of the bearing during high-speed rotation are not covered. In fact, the rigidity of the spindle bearing of the high-speed machine tool is also an important performance index, but it is very complicated to calculate and involves many physical quantities, and the precise calculation needs to be done with the help of a computer. The life of the high-speed machine tool spindle bearing usually refers to the accuracy life, and there is no unified and recognized method for its calculation. Generally, only 30% to 50% of the fatigue life is taken as the accuracy life value of the bearing. The demand for high speed in the machine tool industry is endless. As a method to achieve ultra-high speed, the spindle support form of magnetic bearing has appeared. However, from the perspective of operation and cost, the advantages of rolling bearings will continue to be maintained. , and the research and development work to challenge the higher speed limit needs to be further deepened.