Influence of bearing preload mode and speed

There are two ways of axial preload of bearing, one is constant pressure preload, the other is positioning preload. Under constant pressure preloading, with the increase of rotating speed, the radial stiffness of the bearing increases slightly, 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 rotating speed, but the increase of axial and angular stiffness is relatively gentle.

Effect of preload

With the increase of preload, the radial, axial and angular stiffness of the bearing increase slightly, but the effect is very small. Compared with positioning preloading, this effect is more significant on constant pressure preloading. This is because the increase of preload increases the contact angle of inner and outer rings, and also increases the contact load, so as to increase the radial, axial and angular stiffness. However, the changes of contact load and contact angle caused by preload are smaller than those caused by speed and part displacement. Therefore, the influence on bearing stiffness is limited. This is also the reason why the change under positioning preload is less than that under constant pressure preload.

Influence of channel curvature radius

With the increase of the inner and outer ring channel curvature radius, the radial, axial and angular stiffness decrease, but this effect is very small. Only the change of stiffness under positioning preload is slightly obvious, which is due to the increase of channel curvature radius and the increase of contact deformation. Therefore, when choosing the radius of curvature of the channel, its influence on the stiffness can not be considered.

Influence of ball number

Under the positioning preload, the radial, axial and angular stiffness increase slightly with the increase of the number of balls. The increase of the number of balls will increase the stiffness, but under the same preload, the increase of the number of balls will reduce the contact load. Although they can increase the stiffness of the bearing, they are less.
Under constant pressure preloading, the increase of the number of balls significantly increases the radial stiffness, while when the speed increases to a certain value, the axial and angular stiffness decreases, but the change is very small. This is because under constant pressure preloading, the increase of the number of balls reduces the contact load of the inner ring, but also reduces the contact angle of the inner ring. Their joint action significantly increases the radial stiffness of the bearing, while the axial and angular stiffness decrease slightly.

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 bearing stiffness.

Shadow of ball diameter

Under positioning preload, the ball diameter increases, and the radial, axial and angular stiffness increase slightly. With the increase of ball diameter, the centrifugal force of the ball increases, the contact angle of the outer ring decreases, and the contact angle of the inner ring increases, but at the same time, the contact load of the inner and outer rings increases. Their combined action results in the increase of bearing stiffness. The change of centrifugal force has little effect on the contact load under positioning preload, so the change of ball diameter has little effect on the stiffness.
Under constant pressure preloading, the ball diameter increases, the radial stiffness increases, while the axial and angular stiffness decreases, but the effect is small. This is because the increase of the ball diameter increases the centrifugal force of the ball, the contact angle of the inner and outer rings decreases, the contact load of the outer ring increases, while the contact load of the inner ring basically remains unchanged. Therefore, the radial stiffness increases, while the axial and angular stiffness decreases slightly. Therefore, reducing the ball diameter not only improves the speed performance, but also does not reduce the stiffness performance. This also proves theoretically that the small diameter reducing ball is one of the development trends of the main shaft bearing at present.

Influence of initial contact angle

Under positioning preload, the increase of initial contact angle significantly reduces the radial stiffness and increases the axial and angular stiffness. This is because the initial contact angle increases, the radial component of contact stiffness decreases, the axial component increases, and the contact load decreases under the same preload.
Under constant pressure preloading, the radial stiffness decreases significantly with the increase of initial contact angle; At low speed, the axial and angular stiffness increase, and at high speed, it basically does not change. This is because the inner and outer rings allow axial displacement under constant pressure preloading. 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 has little 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 can not improve the axial and angular stiffness, but reduce the radial stiffness.