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

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