The bearing industry is governed by specific testing standards (JB/T3573-93). Bearing manufacturing plants are equipped with specialised testing instruments to measure the radial clearance of bearings. For self-aligning bearings, the radial clearance is typically measured using a feeler gauge. The following describes the method for measuring the radial clearance of self-aligning roller bearings using a feeler gauge: inspection equipment, assembly equipment, customised equipment, bearing inspection, component inspection, bore measurement, bore measurement, outer diameter measurement, bore diameter, outer diameter, dimensional measurement, measuring instruments, automatic measurement, automatic inspection, vision inspection, image inspection, runout inspection, automated equipment, automatic inspection instruments, inspection equipment development, bore measurement instruments, electric vehicle equipment

A. Stand the bearing upright and close it. Key points: The inner and outer ring end faces of the bearing must be parallel; there must be no tilt. Press the inner ring with your thumb and wiggle it 2–3 times, then press down firmly to ensure the inner ring and rolling elements are correctly seated. Position the rollers so that there is one roller on each side of the top of the inner ring raceway. Push the two top rollers inwards to ensure they maintain proper contact with the inner ring raceway.

B. Select the appropriate feeler gauges according to the clearance standards. Key point: Look up the corresponding clearance values in the clearance standards based on the bearing’s inner bore diameter, and determine the corresponding maximum and minimum feeler gauge sheets based on their maximum and minimum values.

C. Select the point of maximum radial clearance for measurement. Key point: After the bearing is positioned vertically, the gap between the outer ring raceway at the top of the housing and the rollers is the point of maximum radial clearance.

D. Measure the bearing’s radial clearance using feeler gauges. Key point: Rotate the ring and roller cage assembly through one full revolution; the thickness of the feeler gauge that fits between three consecutive rollers but not between the remaining rollers is the maximum radial clearance measurement; the thickness of the feeler gauge that does not fit between three consecutive rollers but fits between the remaining rollers is the minimum radial clearance measurement. Take the arithmetic mean of the maximum and minimum radial clearance measurements as the bearing’s radial clearance value. Once the radial clearance in each column is found to be within specification, take the arithmetic mean of the clearances in the two columns as the bearing’s radial clearance. For single-row angular contact ball bearings, tapered roller bearings and thrust bearings, the final step in installation is to adjust the bearing’s axial clearance. The bearing’s axial clearance must be precisely adjusted according to the mounting configuration, load, operating temperature and bearing performance. The following describes the methods for measuring axial clearance and how to adjust it. Method for measuring the axial clearance of automotive wheel hub bearings using a dial gauge: Securely mount the support with the dial gauge on the machine body or housing; place the dial gauge tip on a smooth surface of the shaft; push the shaft in both directions; the limit deviation indicated by the dial needle is the axial clearance value.

I. Original Clearance

The clearance when the bearing is in a free state prior to installation. The original clearance is determined by the manufacturer’s machining and assembly processes. II. Installation Clearance

Also known as fitting clearance, this is the clearance between the bearing, shaft and bearing housing after installation but before operation. Due to interference fit—achieved by enlarging the inner ring, reducing the outer ring, or a combination of both—the installation clearance is smaller than the original clearance.

III. Operating Clearance

This is the clearance of the bearing whilst in operation. During operation, the inner ring experiences the greatest temperature rise and thermal expansion, causing the bearing clearance to decrease; simultaneously, under the influence of the load, elastic deformation occurs at the contact points between the rolling elements and the raceways, causing the bearing clearance to increase. Whether the operating clearance of the bearing is greater or smaller than the installation clearance depends on the combined effect of these two factors.

Some rolling bearings cannot have their clearance adjusted, nor can they be disassembled; these bearings comprise six types, namely types 0000 to 5000; Some rolling bearings allow clearance adjustment but cannot be disassembled; these include Type 6000 (angular contact bearings) and Types 1000, 2000 and 3000 with tapered inner rings. For these types of rolling bearings, the mounting clearance will be smaller than the original clearance after adjustment; Furthermore, some bearings can be disassembled and their clearance adjusted. These include three types: Type 7000 (tapered roller bearings), Type 8000 (thrust ball bearings) and Type 9000 (thrust roller bearings). These three types of bearings do not have an original clearance; For 6000- and 7000-series rolling bearings, reducing the radial clearance also reduces the axial clearance, and vice versa; whereas for 8000- and 9000-series rolling bearings, only the axial clearance is of practical significance. Appropriate installation clearance is essential for the bearing to function correctly. If the clearance is too small, the rolling bearing will overheat, fail to operate normally and eventually seize; if the clearance is too large, the equipment will vibrate excessively and the rolling bearing will generate significant noise.

The methods for checking radial clearance are as follows:

I. Manual inspection

1. Turn the bearing by hand; it should rotate smoothly and freely without any sticking.

2. Shake the outer ring of the bearing by hand; even if the radial clearance is only 0.01 mm, the axial displacement at the top of the bearing will be 0.10–0.15 mm. This method is specifically