Axial clearance of the bearing

 

The so-called bearing clearance refers to the amount of movement when the bearing is not installed in the shaft or bearing housing, fixing one side of the inner ring or outer ring, and then making the unfixed side move radially or axially. According to the direction of movement, it can be divided into radial clearance and axial clearance.

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

When measuring the clearance of a bearing, it is the so-called bearing clearance, which refers to the amount of movement when the bearing is not installed in the shaft or bearing housing, fixing one side of the inner ring or outer ring, and then making the unfixed side move radially or axially. According to the direction of movement, it can be divided into radial clearance and axial clearance.

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

When measuring the clearance of a bearing, a specified measuring load is generally applied to the bearing in order to obtain a stable measured value.

As a result, the measured value is larger than the true clearance (known as the theoretical clearance), i.e. the amount of elastic deformation due to the measured load is increased.

However, in the case of roller bearings, this elastic deformation is negligible due to its small amount.

The internal clearance of the bearing before installation is generally expressed in terms of theoretical clearance.

The choice of clearance

The clearance after subtracting the amount of expansion or contraction of the ring due to interference fit when the bearing is mounted on the shaft or in the housing from the theoretical clearance is called the "mounting clearance".

 

The clearance after adding or subtracting the dimensional variation due to the temperature difference inside the bearing is called the "effective clearance".

The bearing is installed with a clearance when it is placed under a certain load mechanically, that is, the effective clearance is added to the elastic deformation caused by the bearing load, so that it is called "working clearance".　

 

When the working clearance is slightly negative, the fatigue life of the bearing is the longest, but with the increase of negative clearance, the fatigue life decreases significantly. Therefore, when selecting the clearance of the bearing, it is generally advisable to make the working clearance zero or slightly positive.

In addition, when it is necessary to improve the rigidity of the bearing or reduce the noise, the working clearance should be further negative, and when the temperature rise of the bearing is severe, the working clearance should be further positive, etc., and specific analysis must be made according to the use conditions.

 

The concept of clearance in rolling bearings

1. Primitive clearance

Clearance in the free state before bearing mounting. The original clearance is determined by the processing and assembly of the manufacturing plant.

 

2.The installation of clearance

It is also called the mating clearance, which is the clearance when the bearing, shaft and bearing seat are installed but have not yet worked. Due to interference installation, either the inner ring is enlarged, the outer ring is reduced, or both, the installation clearance is smaller than the original clearance.

 

3.The work clearance

When the bearing is in the working state, the temperature rise of the inner ring is the largest, and the thermal expansion is the largest, so that the bearing clearance is reduced; At the same time, due to the load, the elastic deformation occurs at the contact between the rolling element and the raceway, which increases the bearing clearance. Whether the operating clearance of the bearing is larger or smaller than the installation clearance depends on the combined effect of these two factors.