Abstract: Rolling bearing is one of the most important components used in rotating machinery to support load and transmit the movement. The large size ball bearing is one kind of the rolling bearing. Due to the characteristic of large size and heavy duty, the large size ball bearing is widely used in the ram of heavy-duty machine tools. Based on the Hertz contact theory, the quasi static equations of the large size ball bearing are established, and the displacement and heat power under different operating condition is calculated. According to the criterion of Hirano for bearing skidding, the critical curve of skidding is given. A heavy duty machine tool is analyzed, and the force situation of the bearings in the ram is calculated with the help of force balance, moment balance and deformation compatibility equations. In addition, the ball bearing with the highest friction power is selected. In order to avoid the failure of this ball bearing, the critical skidding speed is calculated, which could be helpful in determining the rotating speed of the ram under different operating conditions.

Key words: heavy duty machine tool, large size ball bearing, skidding