1. What is bearing clearance?
In simple terms, bearing clearance is the clearance (or interference) within a single bearing or within a system of several bearings. Clearance can be divided into axial clearance and radial clearance, depending on the bearing type and measurement method.

 
2. Why adjust the bearing clearance?
 
For example, too much or too little water during cooking will affect the taste of the rice. In the same way, if the bearing clearance is too large or too small, the working life of the bearing and even the stability of the entire equipment operation will be reduced.

3.Bearing types suitable for different adjustment methods
 
The method of clearance adjustment is determined by the type of bearing, and can generally be divided into non-adjustable clearance bearings and adjustable bearings.
 
The non-adjustable clearance bearing means that the bearing clearance is determined after the bearing leaves the factory. The well-known deep groove ball bearings, self-aligning bearings and cylindrical bearings belong to this category.

 
Adjustable clearance bearing refers to the relative axial position of the bearing raceway can be obtained to obtain the required clearance, which belongs to this type of tapered bearings, angular contact ball bearings and some thrust bearings.

 
4. Bearing clearance adjustment classification
For the clearance of non-adjustable bearings, the industry has corresponding standard values ​​(CN, C3, C4, etc.), and specific clearance ranges can also be customized. When the dimensions of the shaft and bearing seat are known, the corresponding inner and outer ring fits are determined, and the clearance after installation cannot be changed. Since the fit amount is a range in the design stage, the final clearance also has a range, which is not suitable for applications that require clearance accuracy.

Adjustable bearings solve this problem very well. By changing the relative axial position of the raceway, we can get a certain clearance value. As shown in the figure below, when moving the position of the inner ring, we can roughly obtain two kinds of clearances, positive and negative.
 

5. Factors affecting bearing clearance
 
The selection of the optimal working clearance is determined by the application conditions (load, speed, design parameters) and the expected working conditions (maximum life, best stiffness, low heat generation, ease of maintenance, etc.). However, in most applications, we cannot directly adjust the working clearance, which requires us to calculate the corresponding post-installation clearance value based on the analysis and experience of the application.
 
6. Adjustment method of tapered roller bearing clearance
The clearance of non-adjustable bearings after installation is mainly affected by the fit, so the following will mainly introduce the method of adjusting the clearance of adjustable bearings.

Take tapered roller bearings with a wide speed range and can bear both axial and radial forces as an example. .
 
1) Push-pull method
 
The push-pull method is generally used for positive clearance, and the axial clearance between the bearing raceway and the rolling body can be measured. Apply a force to the shaft or bearing block in one direction, set the dial indicator to zero after pushing it to the end, and then apply a force in the opposite direction. After pushing it to the end, the amount of rotation of the pointer on the dial is the clearance value. During the measurement, the rotating roller should be shaken slowly to ensure that the roller is correctly positioned on the large rib of the inner ring.

2) Acro-SetTM method
 
Acro-Set's theory is based on Hooke's law. The deformation of an elastically deformed object is proportional to the external force. Under a certain installation force, measure the gap of the gasket or spacer to obtain the correct clearance. Directly read the correct gasket or spacer size required according to a chart created during prior testing.

 
This method is suitable for positive clearance and preloading, and operators need to be trained to create charts.
 
3) Torque-SetTM method
       
The principle of Torque-Set is that under preload, the rotation torque of the bearing increases as a function of bearing preload. The experimental results show that a set of new bearings of the same type has a small change in the rotating torque of the bearing under the condition of a given preload. Therefore, the pre-tightening amount can be estimated using the rotational torque.
 
The principle of this method is to establish a conversion relationship between the rotating torque of the bearing and the preload, which needs to be obtained through testing. Then when it is actually installed, the thickness of the gasket can be determined by measuring the rotational torque.

 4) Projecta-SetTM method
     
Projecta-Set is to project or transform the thickness of gaskets or spacers that cannot be directly measured to places that are easy to measure. This can be achieved using a special gage sleeve and spacer. When the inner and outer rings of the bearing are in tight fit, the removal and adjustment of the bearing will be difficult and time-consuming. At this time, Projecta-Set will show its advantages.
 
This method requires separate gauges for different series of bearings, and the relative cost is relatively high. But when installed in large quantities, the average cost per time is very cost-effective. Especially in the field of automation, it has proven very effective.

 
 5) Set-RightTM method
        
Set-Right uses a probabilistic method and controls the dimensional tolerances of related parts to ensure that 99.73% of the bearing clearance in all assembly assemblies falls within an acceptable range. This is a mathematical prediction of a set of random variables. The variables are the bearing tolerances and the tolerances of the mounting components such as the shaft and bearing housing.
 
This method does not require installation and adjustment, and simple assembly and clamping of the application components is sufficient, so mass installation is very convenient. However, in the end, a clearance range (about 0.25mm) will be obtained. In some applications, whether Set-Right can be adopted needs to be determined at the design stage. For many years, both in the industrial and automotive fields, Set-Right's method has been successfully used.