The rigidity of machine tool spindles is divided into two types: bearing rigidity and shaft rigidity. The rigidity of bearings is determined by the elastic deformation of the rolling element and raceway surface under the action of load, and usually pre tightening is required to improve rigidity.

Under the same load conditions, the rigidity of roller bearings is higher than that of ball bearings, but due to the sliding surface of roller bearings, it is not conducive to high-speed rotation.

The rigidity of the shaft increases with the increase of the shaft diameter, and due to the larger size of the installed bearing at this time, its dmn value (center diameter of the rolling element mm * n, speed min-1) also increases, which is not conducive to high-speed rotation.

Therefore, after fully considering the spindle stiffness, determine the bearing stiffness (bearing type and preload) and the shaft stiffness.

Bearing rigidity:

The rigidity of the bearing will affect the rigidity of the spindle on which it is installed. The rigidity of a bearing is determined by factors such as the type of rolling element, the size and number of rolling elements, the material of the rolling element, the contact angle of the bearing, and the preload of the bearing.

The contact between the rolling element and the raceway surface is line contact when using roller bearings, and point contact when using ball bearings. Therefore, the elastic deformation of roller bearings is smaller when the load is the same

The size and number of rolling elements used on bearings are determined by the purpose and performance of the bearings used. The larger the rolling element, the higher the rigidity of the bearing, but due to its susceptibility to gyro sliding and centrifugal force, its high-speed performance will be reduced. In addition, although the more rolling elements there are, the more favorable the rigidity of the bearing is. However, due to the increase in the heat source, there will be adverse effects on temperature rise.

Therefore, the higher the speed specification, the smaller the rolling element used.

Bearings using ceramic rolling elements have a higher stiffness due to the larger longitudinal elastic coefficient of silicon nitride compared to the coefficient of bearing steel.

For angular contact ball bearings, the smaller the contact angle of the bearing, the greater its radial stiffness. In addition, when used as a thrust bearing, in order to improve its axial stiffness, bearings with large contact angles are used

The greater the preload of the bearing, the greater its rigidity. However, if the preload of the bearing is too large, it may lead to bearing heating, sintering, premature peeling, etc. In order to improve axial stiffness, bearings can be arranged in 3 or 4 rows for assembly use.

The preloading of bearings is divided into two types: positioning preloading and fixed pressure preloading. Positioning and pre tightening the position of the opposite bearing helps to improve rigidity. Constant pressure preloading applies a load through spring deformation, and due to thermal and load effects during rotation, even if the position of the bearing changes, it can still maintain a stable preload.

Bearing preloading is a very important project, not only related to the rigidity of the bearing, but also directly related to the heating and wear of the bearing. If there is an opportunity later, I will carefully explain the relevant content of bearing preloading for you.