Brief description of bearing clearance

2024-12-13

The so-called clearance of rolling bearings refers to the maximum radial or axial movement of one ring while the other ring is fixed. The maximum radial movement is called radial clearance, and the maximum axial movement is called axial clearance.

Generally speaking, the larger the radial clearance, the larger the axial clearance, and vice versa. According to the state of the bearing, the clearance can be divided into the following three types:

Original clearance: the clearance in the free state before the bearing is installed. The original clearance is determined by the manufacturer's processing and assembly.

Installation clearance: also called fit clearance, which is the clearance when the bearing, shaft and bearing seat are installed but not yet working. Due to interference installation, the inner ring is enlarged, the outer ring is reduced, or both, which makes the installation clearance smaller than the original clearance.

Working clearance: the clearance of the bearing in the working state. When working, the inner ring has the largest temperature rise and thermal expansion, which reduces the bearing clearance; at the same time, due to the effect of load, the rolling element and the raceway contact point produce elastic deformation, which increases the bearing clearance. Whether the bearing working clearance is larger or smaller than the installation clearance depends on the combined effect of these two factors.

Some rolling bearings cannot adjust the clearance, let alone disassemble. These bearings have six models, namely 0000 to 5000; some rolling bearings can adjust the clearance, but cannot be disassembled, including 6000 (deep groove ball bearings) and 1000, 2000 and 3000 rolling bearings with tapered inner rings. The installation clearance of these types of rolling bearings will be smaller than the original clearance after adjustment; in addition, some bearings can be disassembled and the clearance can be adjusted. There are three types: 7000 (angular contact ball bearings), 8000 (thrust ball bearings) and 9000 (thrust tapered roller bearings). These three types of bearings do not have original clearance; for 6000 and 7000 rolling bearings, the radial clearance is reduced, and the axial clearance also becomes smaller, and vice versa, while for 8000 and 9000 rolling bearings, only the axial clearance is of practical significance.

Appropriate installation clearance helps the normal operation of rolling bearings. If the clearance is too small, the temperature of the rolling bearing will rise, and it will not work properly, so that the rolling element will get stuck; if the clearance is too large, the equipment will vibrate greatly and the rolling bearing will make a lot of noise.

Checking the bearing clearance The radial clearance check method is as follows:

Turn the bearing by hand, and the bearings Feeling method:

1. Hould be stable and flexible without jamming.

2. Shake the outer ring of the bearing by hand. Even if the radial clearance is only 0.01mm, the axial movement of the top point of the bearing is 0.10~0.15mm. This method is dedicated to single-row radial ball bearings.

Measurement method:

1. Check with a feeler gauge to confirm the maximum load part of the rolling bearing. Insert the feeler gauge between the rolling element and the outer (inner) ring at 180°. The thickness of the feeler gauge with appropriate tightness is the radial clearance of the bearing. This method is widely used in self-aligning bearings and cylindrical roller bearings.

2. Check with a micrometer. First adjust the micrometer to zero, then lift the outer ring of the rolling bearing. The reading of the micrometer is the radial clearance of the bearing.

The inspection methods for axial clearance are as follows:

1. Feeling method: Use fingers to check the axial clearance of rolling bearings. This method is used in situations where the shaft end is exposed. When the shaft end is closed or cannot be checked with fingers for other reasons, check whether the shaft rotates flexibly.

2. Measurement method

(1) Check with a feeler gauge. The operation method is the same as the method of checking radial clearance with a plug, but the axial clearance should be c=λ/(2sinβ), where c is the axial clearance, mm; λ is the thickness of the feeler gauge, mm; β is the bearing taper angle.

(2) Check with a micrometer. When the shaft is moved with a pry bar so that the shaft is at two extreme positions, the difference in the micrometer reading is the axial clearance of the bearing. However, the force applied to the pry bar should not be too large, otherwise the shell will undergo elastic deformation. Even if the deformation is very small, it will affect the accuracy of the measured axial clearance.