Bearing Clearance Of Ball Bearings

Bearing clearance, also defined as internal clearance, refers to the maximum movable distance between the inner ring and outer ring of a ball bearing before it is assembled onto a shaft or bearing housing. According to different movement directions, bearing internal clearance can be classified into radial clearance and axial clearance.

It is essential to distinguish between the original internal clearance of a new bearing and the operating clearance after installation and temperature stabilization. The initial uninstalled clearance is generally larger than the running clearance. This variation mainly results from assembly fit interference, as well as inconsistent thermal expansion and contraction of bearing inner rings, outer rings and matching components during operation.

Bearing Internal Clearance and Standard Specified Values

The internal clearance of rolling bearings is a critical parameter that directly affects comprehensive bearing performance, including fatigue life, vibration level, noise generation and operating temperature rise. Therefore, reasonable selection of bearing internal clearance serves as a key consideration in bearing structural design and performance optimization.

In standard clearance testing, a specified preload is applied to the bearing to obtain stable and consistent measurement data. Consequently, the practically measured test clearance is slightly larger than the theoretical geometric radial clearance, due to additional elastic deformation produced by the test load. In industrial specifications, the uninstalled original clearance is defined as the standard theoretical internal clearance of bearings.

Selection Principles of Internal Clearance

To select the optimal internal clearance for different working conditions, the following influencing factors must be fully considered:

(1) Clearance variation caused by the fitting tolerance between the bearing, shaft and bearing housing;

(2) Clearance changes induced by temperature differences between the inner and outer rings during bearing operation;

(3) Thermal expansion coefficient differences of shaft and housing materials, which further affect the actual working clearance of bearings.

For conventional standard working conditions, bearings are prioritized to adopt standard basic-group radial clearance. For special operating scenarios such as high temperature, high speed, low noise and low friction requirements, auxiliary-group radial clearance is applicable. Precision bearings and machine tool spindle bearings usually adopt smaller radial clearance to guarantee machining accuracy and operational stability. Meanwhile, customized clearance schemes can be adopted to meet special customer application requirements.

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