Introduction to bearing clearance and measurement methods

May 27, 2024

Bearings are an indispensable part of mechanical equipment. They are responsible for supporting rotating parts, reducing friction and wear, and ensuring the normal operation of mechanical equipment. Clearance is an important parameter in bearing design and selection. The size of bearing clearance affects the performance and life of the bearing as well as the operational stability and reliability of the entire mechanical equipment.

1. What is bearing clearance?

Bearing clearance is the space between the inner and outer rings. It has two types: radial and axial. The radial is perpendicular to the axis, while the axial is in the same direction as the axis. The existence of clearance is to ensure that the bearing can rotate flexibly during operation and to avoid friction and wear caused by direct contact between the inner and outer rings. At the same time, the clearance can also compensate for bearing size changes caused by temperature changes, load changes and other factors.

2. Types of bearing clearance

Bearing clearance can be divided into the following types according to different measurement methods and purposes:

Initial clearance: The measured clearance before the bearing is installed on the mechanical equipment is called the initial clearance. The initial clearance is one of the key parameters controlled during the bearing design and manufacturing process. It directly affects the performance and service life of the bearing.

Working clearance: During the operation of mechanical equipment, the bearing clearance will change due to changes in temperature, load, and other factors. The clearance measured at this time is called the working clearance. The size of the working clearance directly affects the operational stability and reliability of mechanical equipment.

Ultimate clearance: The maximum clearance that a bearing can withstand under extreme working conditions (such as maximum load, maximum temperature, etc.) is called the ultimate clearance. Ultimate clearance is one of the important parameters that need to be considered in the bearing design and selection process. It determines the bearing capacity and application range.

3. Factors affecting bearing clearance

The size of bearing clearance is affected by many factors, including the following aspects:

Bearing type and structure: Different types of bearings have different clearance characteristics. For example, roller bearings typically have greater clearance than ball bearings to accommodate greater loads and deformations. At the same time, the structural design of the bearing will also affect the size and distribution of clearance.

Bearing material: The elastic modulus, thermal expansion coefficient and other physical properties of the bearing material will affect the size of the clearance. For example, materials with a large thermal expansion coefficient will produce large dimensional changes when the temperature changes, thus affecting the size of the clearance.

Temperature changes: Bearings will generate heat during operation, causing the temperature of the inner and outer rings to rise. Changes in temperature can cause the inner and outer rings of a machine to expand or contract differently due to their varying thermal expansion coefficients. As a result, the size of the clearance between the two rings may be affected.

Load change: The bearing will deform when it is loaded, causing the gap between the inner and outer rings to change. The greater the load, the more obvious the deformation will be, and the clearance will increase accordingly.

Installation error: There may be errors during the installation process of the bearing, such as the inner and outer rings are not parallel, the axis being misaligned, etc. These errors will cause additional stress and deformation of the bearing during operation, thereby affecting the size and distribution of clearance.

4. Measurement and adjustment methods of bearing clearance

Measurement method: Bearing clearance is usually measured by using measuring tools such as micrometers, vernier calipers and other tools. When measuring, the bearing needs to be removed from the mechanical equipment first and then operated according to the prescribed measurement method. Common measurement methods include radial clearance measurement and axial clearance measurement.

Adjustment method: Adjustment of bearing clearance is usually achieved by changing the relative position of the inner and outer rings of the bearing. 

Specific adjustment methods include:

Adjust the height and position of the bearing seat to change the relative position of the inner and outer rings of the bearing;

Add or remove gaskets between the inner and outer rings of the bearing to change the size of the clearance;

Use specialized adjustment tools to fine-tune the bearings to achieve the desired amount of clearance.

When adjusting bearing clearance, the appropriate clearance size needs to be tested based on the actual operating conditions and requirements of the mechanical equipment. At the same time, attention must be paid to keeping the bearings clean and lubricated to ensure normal operation and extend the service life of the bearings.

Bearing clearance is one of the important parameters to consider during bearing design and selection. Its size directly affects the performance and life of the bearing as well as the operational stability and reliability of the entire mechanical equipment. It is crucial to strictly control bearing clearance size and distribution during design, manufacturing, installation, and use. It ensures the normal operation of mechanical equipment and extends its service life.