There are two types of axial preload for bearings, one is constant pressure preload and the other is positioning preload. Under constant pressure preload, the radial stiffness of the bearing increases slightly as the rotational speed increases, while the axial and angular stiffness decrease rapidly. Under positioning preload, the radial, axial and angular stiffness of the bearing increase rapidly with the increase of rotation speed, but the increase of axial and angular stiffness is relatively gentle. 1. Influence of preload As the preload load increases, the radial, axial and angular stiffness of the bearing increases slightly, but the effect is very small. Compared with positioning preload, this effect is more significant for constant pressure preload. This is because the increase in preload load increases the contact angle of the inner and outer rings, and also increases the contact load, thereby increasing the radial, axial and angular stiffness. However, the changes in contact load and contact angle caused by the preload load are small compared with the changes caused by the rotation speed and part displacement, so the impact on the bearing stiffness is limited. This is also the reason why the change under positioning preload is smaller than that under constant pressure preload. 2. Influence of channel curvature radius As the curvature radius of the inner and outer ring channels increases, the radial, axial and angular stiffness decreases, but this effect is very small. Only the change in stiffness under positioning preload is slightly more obvious. This is due to the channel curvature. The increase in radius increases the contact deformation. Therefore, its effect on stiffness can generally be ignored when selecting the channel curvature radius. 3. The influence of the number of balls Under positioning preload, the increase in the number of balls slightly increases the radial, axial and angular stiffness. The increase in the number of balls will increase the stiffness, but under the same preload load, the increase in the number of balls will reduce the contact load. Although their combined effect can increase the stiffness of the bearing, it is less. Under constant pressure preload, the increase in the number of balls will significantly increase the radial stiffness, while when the rotational speed increases to a certain value, the axial and angular stiffness will decrease, but the change is very small. This is because under constant pressure preload, the increase in the number of balls reduces the contact load of the inner ring, but also reduces the contact angle of the inner ring. Their combined effect significantly increases the radial stiffness of the bearing, while the axial and angular stiffness are slightly There is a decrease. Therefore, when the number of balls increases, the preload load should be increased accordingly. Only when the contact load is the same, increasing the number of balls can increase the bearing stiffness. 4. The influence of ball diameter Under positioning preload, the ball diameter increases, and the radial, axial and angular stiffness increases slightly. The increase in ball diameter increases the centrifugal force of the ball, decreases the contact angle of the outer ring, and increases the contact angle of the inner ring, but at the same time increases the contact load of the inner and outer rings. Their combined effect increases the bearing stiffness. Since changes in centrifugal force have little impact on contact load under positioning preload, changes in ball diameter have little impact on stiffness. Under constant pressure preloading, as the ball diameter increases, the radial stiffness increases, while the axial and angular stiffness decrease, but the impact is small. This is because as the ball diameter increases, the centrifugal force of the ball increases, the contact angle of the inner and outer rings decreases, and the contact load of the outer ring increases, while the contact load of the inner ring remains basically unchanged. Therefore, the radial stiffness increases, while the axial and angular stiffness decrease slightly. . Therefore, reducing the ball diameter not only improves speed performance, but does not reduce stiffness performance. This also proves theoretically that reducing the diameter of the ball is one of the current development trends of spindle bearings. 5. The influence of initial contact angle Under positioning preload, the initial contact angle increases, which significantly reduces the radial stiffness, and increases the axial and angular stiffness significantly. This is because the initial contact angle increases, the radial component of the contact stiffness decreases, and the axial component increases. At the same time, the contact load decreases under the same preload. Under constant pressure preload, the initial contact angle increases and the radial stiffness decreases significantly; at low speeds, the axial and angular stiffnesses increase, but at high speeds, there is basically no change. This is because under constant pressure preload, the inner and outer rings allow axial displacement. In order to maintain the balance of forces, the contact angle of the outer ring is almost close to 0. The initial contact angle has basically no effect on the contact angle of the outer ring. Similarly, the initial contact angle increases and the contact load decreases under the same preload. Therefore, increasing the initial contact angle of the bearing under positioning preload can improve the axial and angular stiffness, while increasing the initial contact angle under constant pressure preload not only fails to improve the axial and angular stiffness, but also reduces the radial stiffness.    

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