Keywords: Spindle bearing, FAG precision spindle bearings, angular contact ball bearing
Spindle bearing is an important part used on the spindle of machine tools and precision equipment. In the process of spindle transmission, it can play a role in supporting rotation and reducing friction. FAG precision spindle bearings are meant to be not only a good product but also a “higher RPM, higher accuracy, longer life, more cost-effective”.
Contact angles commonly used for FAG spindle bearings are 15°, 20° and 25°. Different contact angles have the different performance of bearings. If the contact Angle of the spindle bearing is 15°, the temperature difference between the shaft and the bearing seat is very sensitive when the rigidity is preloaded, especially when the bearing spacing is small, it will also produce radial force. And for spindle bearings with 20° or 25° contact Angle, if a large spacing bearing group is used, it is not so sensitive to temperature changes.
The contact Angle of the spindle bearing also affects the stiffness of the angular contact ball bearing system. The axial stiffness of a 15° contact Angle bearing is about 45% of that of a 25° contact Angle bearing, but the radial stiffness is only 10% higher. If the whole system of spindle bearing and cantilever is considered, the radial stiffness of 25° contact Angle bearing is better than that of 15° contact Angle bearing, because the support span arranged by 25° contact Angle bearing is larger than that of 15° contact Angle bearing. Bearings with a contact Angle of 20° can provide a good compromise. If the structure permits, it is recommended to select a bearing arrangement with appropriate spacing under rigid preload, then the radial and axial thermal expansion of the shaft can be compensated by preload. The optimal bearing spacing L is related to the contact angle of the bearing. For the spindle bearing with a 25° contact Angle, the optimal bearing spacing L is about 3 times of the shaft diameter D. For the spindle bearing with 20° contact Angle, the bearing spacing L is about 4 times the axle diameter D; For the spindle bearing with 15° contact Angle, the spacing L tends to be 5 times the axle diameter D, but the axial thermal expansion effect of the shaft is not obvious due to the long bearing spacing, so this design is relatively rare in practical application.
FAG spindle bearing contact Angle represents the axial bearing capacity of the bearing, the greater the contact Angle, the greater the corresponding axial bearing capacity. The direction of the general contact Angle is marked on the cylindrical surface of the bearing outer ring, and the opening end of the arrow is toward the outer ring with a retaining edge.
