Interaction Between Bearings, Shafts and End Covers

Most motors adopt rolling bearings, where the friction between rolling elements and inner/outer races belongs to rolling friction with minimal contact friction. The fit between bearing and shaft, as well as bearing and end cover, is generally an interference fit, with a small number of transitional fits. The large mutual extrusion force generates static friction, keeping the bearing stationary relative to the shaft and end cover. Mechanical energy is transmitted through the rotation between rolling elements and the inner or outer race.

If the bearing is clearance-fitted to the shaft or bearing housing, torque will break the static relative position and cause sliding, which is known as bearing creep. Sliding between the bearing inner race and the shaft is defined as inner ring creep, while sliding between the bearing outer race and the bearing housing is outer ring creep.

Phenomena and Hazards of Motor Bearing Creep

When bearing creep occurs, abnormal high temperature and severe vibration will appear at the bearing position. Disassembly inspection will reveal sliding scratches on the surface of the shaft or bearing housing, and even grooves worn on these surfaces, which can confirm the occurrence of bearing creep.

Bearing creep exerts severe adverse impacts on equipment. It accelerates wear of mating components and may lead to component scrapping, impairing the precision of supporting equipment. In addition, increased friction converts massive energy into heat and noise, greatly reducing motor operating efficiency.

Root Causes of Motor Bearing Creep

1. Fit Tolerance

Strict tolerance requirements are specified for the fit between bearings and shafts (or bearing housings). Fit tolerances vary according to bearing specifications, precision grades, load conditions and actual operating environments.

2. Machining and Installation Precision

This covers technical parameters including machining tolerance, surface roughness and assembly precision of shafts, bearings and bearing housings. Failure to meet these standards will alter the designed fit tolerance and trigger bearing creep.

3. Material Performance of Shafts and Bearings

Material selection is critical. Bearings of different types shall be manufactured from matched bearing steel featuring high strength, high rigidity and excellent wear resistance. Bearing alloys are required to have a low friction coefficient to guarantee normal bearing operation and lower the risk of creep failure.

Common Repair Solutions for Motor Bearing Creep

Common domestic repair processes for bearing creep include bushing installation, stippling, surfacing welding, brush plating, thermal spraying and laser cladding.

1. Surfacing Welding:

A welding process that deposits a wear-resistant, corrosion-resistant or heat-resistant metal layer onto the surface or edge of workpieces.

2. Thermal Spraying:

A metal surface treatment technology that atomizes molten coating materials via high-speed airflow and sprays them onto component surfaces to form protective coatings.

3. Brush Plating:

An electrolytic process used to form metal coatings on workpiece surfaces.

Laser Cladding: Also known as laser coating, it is an innovative surface modification technology.