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What is clearance and how is the clearance of rolling bearings measured?

by:JNSN     2022-03-16
The so-called rolling bearing clearance is the maximum amount of movement of one ferrule in the radial or axial direction when one ferrule is fixed and the other ferrule is fixed. The maximum movement along the radial direction is called radial clearance, and the maximum movement along the axial direction 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: 1. 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. 2. Installation clearance Also called matching clearance, it is the clearance when the bearing, the shaft and the bearing seat are installed but not working. Due to the interference installation, either the inner ring is enlarged, the outer ring is reduced, or both, the installation clearance is smaller than the original clearance. 3. Working clearance The clearance of the bearing in the working state, the temperature rise of the inner ring is the largest and the thermal expansion is the largest during operation, which reduces the bearing clearance; Increase 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 be adjusted for clearance, let alone disassembled. These bearings have six types, namely type 0000 to type 5000; some rolling bearings can adjust the clearance but cannot be disassembled. 1000 type, 2000 type and 3000 type rolling bearings, 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 7000 type (tapered roller bearings) ), 8000 type (thrust ball bearing) and 9000 type (thrust roller bearing), these three types of bearings do not have original clearance; 6000 type and 7000 type rolling bearings, the radial clearance is reduced, the axial clearance It also becomes smaller, and vice versa, while for 8000 and 9000 rolling bearings, only the axial clearance has practical significance. Appropriate installation clearance is helpful for 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, and the rolling element will be stuck; if the clearance is too large, the equipment will vibrate greatly, and the rolling bearing will be noisy. The inspection methods for radial clearance are as follows: 1. Feeling method 1. If the bearing is rotated by hand, the bearing should 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 uppermost point of the bearing is 0.10~0.15mm. This method is dedicated to single row radial ball bearings. 2. Measurement method 1. Check with a feeler gauge to confirm the maximum load part of the rolling bearing, insert a feeler gauge between the rolling element and the outer (inner) ring that is 180 degrees, and the thickness of the feeler gauge with appropriate elasticity is the radial clearance of the bearing . This method is widely used in spherical bearings and cylindrical roller bearings. 2. Check with a dial gauge, first set the dial gauge to zero, and then jack up the outer ring of the rolling bearing. The reading of the dial gauge is the radial clearance of the bearing. Axial clearance inspection methods are as follows: 1. Feeling method Use fingers to check the axial clearance of rolling bearings. This method is applied to occasions where the shaft end is exposed. When the shaft end is closed or cannot be checked with fingers for other reasons, it can be checked whether the shaft rotates freely. 2. Measurement method (1) Check with a feeler gauge. The operation method is the same as that of checking radial clearance with a feeler gauge, but the axial clearance should be cu003dλ/(2sinβ) where c is axial clearance, mm ; λ feeler gauge thickness, mm; β bearing taper angle, (). (2) Check with a dial gauge. When the shaft is moved with a crowbar to make the shaft in two extreme positions, the difference between the dial gauge readings is the axial clearance of the bearing. However, the force applied to the crowbar should not be too large, otherwise the casing will be elastically deformed, and even if the deformation is small, it will affect the accuracy of the measured axial clearance.
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