Introduction: Clearance adjustment is the key technology for bearing installation and adjustment, which is related to the operating status of the bearing and even the entire equipment. Today, let's talk about the little knowledge about bearing clearance!

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.

Why adjust the bearing clearance 

For example, too much or too little water when cooking rice will affect the taste of rice. Similarly, if the bearing clearance is too large or too small, the working life of the bearing and the stability of the entire equipment operation will be reduced.

Bearing types suitable for different adjustment methods 

The method of clearance adjustment is determined by the type of bearing, which can generally be divided into non-adjustable bearings and adjustable bearings. 

Clearance non-adjustable bearing means that after the bearing leaves the factory, the clearance of the bearing is determined. The deep groove ball bearings, self-aligning bearings and cylindrical bearings we are familiar with all belong to this category.

  The adjustable clearance bearing refers to the relative axial position of the moving bearing raceway to obtain the required clearance. This type includes tapered bearings, angular contact ball bearings and some thrust bearings.

Classification of bearing clearance adjustment

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 matching amount of the corresponding inner and outer rings is determined, and the clearance after installation cannot be changed. Since the matching amount is a range in the design stage, the final clearance also has a range, which is not applicable to applications that require clearance accuracy.

The adjustable bearing solves 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 we move the position of the inner ring, we can roughly get positive and negative clearances.

Factors Affecting Bearing Clearance

The choice of the best working clearance is determined by the application conditions (load, speed, design parameters) and the desired 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 clearance value after installation based on the analysis and experience of the application.

Adjustment method of tapered roller bearing clearance

The post-installation clearance of non-adjustable bearings is mainly affected by the fit, so the following mainly introduces the clearance adjustment method of adjustable bearings, taking tapered roller bearings with a wide range of speeds that can withstand 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 elements can be measured. Apply a force to the shaft or bearing seat in one direction, set the dial indicator to zero as a reference after pushing it to the end, and then apply a force in the opposite direction, and the amount of rotation of the pointer on the dial indicator after pushing it to the end is the clearance value. When measuring, it is necessary to shake and rotate the roller slowly to ensure that the roller is correctly positioned on the large rib of the inner ring.

2.Acro-SetTM method

The theoretical basis of Acro-Set is Hooke's law, the deformation of an elastically deformed object is proportional to the external force it receives. Under a certain installation force, measure the gasket or spacer clearance to obtain the correct clearance. Follow a chart created during prior testing to directly read off the correct gasket or spacer size required. 

This method works for positive clearance and preload and operators need to be trained to create the diagrams.

3.Torque-SetTM method

The principle of Torque-Set is that under preload, the rotational torque of the bearing increases as a function of the bearing preload. The experimental results show that for a group of new bearings of the same type, under the condition of a given preload, the variation of the bearing's rotational torque is very small. Therefore, the rotational torque can be used to estimate the preload.

The principle of this method is to establish a conversion relationship between the rotational torque of the bearing and the preload, which needs to be obtained through testing. Then during actual installation, 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 gasket or spacer that cannot be measured directly to a place where it is easy to measure. This is achieved using a special gauge sleeve and spacer. When the inner and outer rings of the bearing are tight fit conditions, the removal and adjustment of the bearing can be difficult and time-consuming, at which point Projecta-Set shows its advantages.Projecta-Set is to project or transform the thickness of gasket or spacer that cannot be measured directly to a place where it is easy to measure. This is achieved using a special gauge sleeve and spacer. When the inner and outer rings of the bearing are tight fit conditions, the removal and adjustment of the bearing can be difficult and time-consuming, at which point Projecta-Set shows its advantages.

This method requires separate gauges for different series of bearings, which is relatively expensive. But when installed in large quantities, the average cost per time is very cost-effective. Especially in the field of automation, it has proved to be a very effective method.

5.Set-RightTM method

Set-Right uses a probabilistic approach and controls the dimensional tolerances of related parts to ensure that 99.73% of all assemblies have bearing clearances within acceptable limits. This is the mathematical prediction of a combination of a set of random variables, namely bearing tolerances and tolerances of mounted components such as shafts and housings.

This method does not require installation and adjustment, and the application components can be simply assembled and clamped, so mass installation is very convenient. But in the end, a clearance range (about 0.25mm) will be obtained. Whether Set-Right can be used in some applications needs to be determined at the design stage. The Set-Right method has been used successfully for many years in both industrial and automotive fields.

Timken has developed a variety of bearing clearance adjustment technologies. Whether it is a small batch of large equipment, or a large batch of small equipment, we aim to reduce bearing installation time, reduce assembly costs, and increase the consistency and reliability of bearing clearance. We hope that the clearance selection and adjustment techniques introduced above can help your equipment run stably and for a long time.