What Are The Benefits Of Preloading Bearings?

The so-called bearing clearance refers to the amount of movement when the inner ring or outer ring of the bearing is fixed when it is not installed on the shaft or bearing box, and then the unfixed side moves radially or axially.

According to the direction of movement, it can be divided into radial clearance and axial clearance. Clearance is also very important for the use of bearings.

Six major matters regarding bearing clearance:

1. The size of the clearance during operation (called working clearance) has an impact on the rolling fatigue life, temperature rise, noise, vibration and other properties of the bearing.

2. When measuring the clearance of a bearing, in order to obtain a stable measurement value, a specified measurement load is generally applied to the bearing. Therefore, the measured value obtained is larger than the real clearance (called the theoretical clearance), that is, the amount of elastic deformation caused by the measured load is increased. For roller bearings, the elastic deformation is small and can be ignored.

3. The internal clearance of the bearing before installation is generally expressed as the theoretical clearance.

4. The clearance after subtracting the expansion or shrinkage of the ring due to interference fit when the bearing is installed on the shaft or in the housing is called "installation clearance" from the theoretical clearance. The clearance after adding and subtracting the dimensional change due to the temperature difference inside the bearing to the installation clearance is called "effective clearance".

5. The bearing is installed with a mechanical clearance when placed under a certain load, that is, the effective clearance plus the elastic deformation caused by the bearing load is called "working clearance".

6. When the working clearance is slightly negative, the fatigue life of the bearing is the longest, but as the negative clearance increases, the fatigue life decreases significantly.

Therefore, when selecting the bearing clearance, it is generally appropriate to make the working clearance zero or slightly positive. In addition, when the rigidity of the bearing needs to be improved or the noise needs to be reduced, the working clearance needs to be further negative, and when the bearing temperature rises drastically, the working clearance needs to be further positive, etc. Specific analysis must be done based on the use conditions. .

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What are the benefits of preloading on bearings?

What is bearing preload?

Generally, rolling bearings have a certain amount of clearance under working conditions.

However, in order to achieve a specific purpose, when configuring the bearing, a certain adjustment method is used to allow the bearing to obtain a certain internal load and be used in a negative clearance state. This method of use is called preload.

What are the benefits of preloading bearings?

For rolling bearings, appropriate preload can have the following benefits:

1. Improve rotation accuracy.
After the bearing is preloaded, the internal clearance is eliminated. Each rolling element bears a certain preload and supports the ring from all directions, which can improve the rotation accuracy, enable the shaft to be positioned correctly in the axial and radial directions, and improve the shaft Rotational accuracy, such as machine tool spindle bearings and measuring instruments.

2. Improve stiffness.
The contact between the rolling element and the raceway is elastic contact, and the rolling element can be regarded as a spring. Bearings with clearance are only supported by a few springs in the direction of force. The preloaded bearings are supported by springs in all directions and have a certain amount of preload. The number of rolling bearings under load is greater than when there is tension, so the stiffness can be improved. In ball bearings, the relationship between the contact deformation of the ball and the groove and the load is nonlinear. As the preload increases, the contact stiffness increases.

3. Improve the service life of bearings.
After preloading, the number of loaded rolling elements increases, and the load on each rolling element is reduced. At the same time, the load can be distributed evenly on each rolling element, so the life of the bearing can be increased.

4. Improve bearing damping and reduce noise.
Preloading establishes a stable oil film between rolling elements and raceways, improves the damping between rolling elements and raceways, and can improve the dynamic characteristics of the support structure and reduce noise.

5. Improve the dynamic performance of angular contact ball bearings.
In high-speed rotating angular contact ball bearings, proper preloading can prevent the steel ball from gyroscopic rotation, prevent or reduce the revolution slip of the steel ball, and also control the spin sliding of the steel ball.

6. Suppress vibration marks and friction and wear.
The outer spherical bearing is actually a variant of the deep groove ball bearing. Its characteristic is that the outer diameter surface of its outer ring is a spherical surface, which can be fitted into the corresponding concave spherical surface of the bearing seat to achieve alignment. Outer spherical bearings are mainly used to bear the combined radial and axial loads, which are mainly radial loads. Generally, they are not suitable to bear the axial load alone. It is used for vibration-free machining of low-roughness processing machine tools, or in mechanisms that need to control friction and wear during frequent starts and stops.

7. Control the slipping phenomenon of rolling element revolution and rotation.
This type of bearing also has a certain degree of alignment in design, is easy to install, has a dual-structure sealing device, and can work in harsh environments.

Bearing seats are generally cast.

Mounted bearings are high-precision component products composed of grease-sealed deep groove ball bearings and bearing seats of various shapes. The bearing assembly can be directly installed on the main body of the mechanical device through a few bolts. It has an aligning function and can replenish grease. It is a product that is very easy to install and use. Such as radial thrust ball bearings used in high-frequency motors and cylindrical roller bearings on jet engines.

8. Compensate for wear and tear during operation.
Bearings will increase clearance due to wear during operation. This situation can be compensated by preloading.

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