Most motors use rolling bearings, and the friction between the bearing rolling elements and the inner and outer rings is rolling friction, with very little friction between the two contact surfaces. The fit between bearings and shafts, as well as between bearings and end caps, is generally interference fit, with a few cases being transitional fit. The mutual squeezing force between each other is relatively large, resulting in static friction. The bearings and shafts, as well as the bearings and end caps, remain relatively stationary, while mechanical energy is transmitted through the rotation between the rolling elements and the inner (or outer) ring.

If the fit between the bearing and the shaft or bearing chamber is a clearance fit, the torque will break the relative static state and cause sliding, resulting in the so-called "running circle". The sliding between the bearing inner ring and the shaft is called running inner ring, and the sliding between the bearing outer ring and the bearing chamber is called running outer ring.

The appearance and harm of bearing running circle

If the bearing runs out of turn, the temperature of the bearing area will be higher and the vibration will be greater. Disassembly and inspection will reveal slip marks on the surface of the shaft (bearing chamber), and even grooves on the surface of the shaft or bearing chamber. From this situation, it can be concluded that the bearing is running in circles.

The negative impact of bearing outer race on equipment is very significant, which can exacerbate the wear and tear of matching parts, even lead to scrapping, and even affect the accuracy of matching equipment; In addition, due to increased friction, a large amount of energy is converted into thermal energy and noise, greatly reducing the efficiency of the motor.

The reason for bearing runout

(1) Fit tolerance: There are strict requirements for the fit tolerance between bearings and shafts (or bearing chambers), and different specifications, accuracies, stress conditions, and operating conditions have different requirements for fit tolerance.

Once there is a problem with tolerance fit, the problem of motor bearing runout will be a batch quality issue.

(2) Processing and installation accuracy: refers to technical parameters such as machining tolerances, surface roughness, and assembly accuracy of shafts, bearings, and bearing chambers. Once the requirements are not met, it will affect the fitting tolerance and cause the bearing to run.

(3) The material of the shaft and bearings is crucial. Different types of bearings should be made of suitable bearing steel, with high strength and stiffness, good wear resistance, and a low friction coefficient of the bearing alloy, in order to ensure the normal use of the bearing and reduce the possibility of running.

Common repair measures for bearing running circle

At present, the common methods for repairing bearing runout in China are bushing, marking, welding, brushing, thermal spraying, laser cladding, etc.

Welding overlay: Welding overlay is a welding process that deposits a layer of wear-resistant, corrosion-resistant, heat-resistant and other performance metal layer on the surface or edge of the workpiece.

Thermal spraying: Thermal spraying is a metal surface processing method that atomizes and sprays molten spraying materials onto the surface of parts through high-speed airflow, forming a spraying layer.

Brush plating: Brush plating is the process of obtaining a coating on the surface of a workpiece using electrolytic methods.

Laser cladding: Laser cladding, also known as laser coating or laser deposition, is a new surface modification technology.