Causes Of Bearing Creep in Electric Motors

A batch of motors suffered bearing system failures, with distinct scuff marks visible on the bearing housing of the end shield, as well as prominent abrasion marks on the wave spring washers inside the bearing housing. Judging from the fault characteristics, this is a typical bearing creep failure.

Interaction Between Bearings, Shafts and End Shields

Most electric motors adopt rolling bearings. The friction between rolling elements and bearing inner/outer rings is rolling friction, featuring minimal contact friction. The fit between bearing and shaft, as well as bearing and end shield, is generally an interference fit, with a small number being transition fits. Large compressive contact force is generated between mating components, creating static friction that locks the bearing relative to the shaft and end shield. Mechanical energy is transmitted via rotation between rolling elements and the inner/outer rings.

If the fit between the bearing and shaft/bearing housing becomes a clearance fit, torque will break the static lock and trigger sliding motion, a phenomenon known as bearing creep. Sliding between the bearing inner ring and shaft is called inner ring creep; sliding between the bearing outer ring and bearing housing is outer ring creep.

When creep occurs, the bearing area will run hot and vibration levels will rise significantly. Disassembly inspection will reveal sliding scratches on the shaft or bearing housing surface, and even deep wear grooves. Such symptoms confirm bearing creep.

Outer ring creep inflicts severe adverse impacts on equipment: it accelerates wear of mating components and may render them irreparable, compromising the precision of coupled machinery. Additionally, the increased friction converts massive energy into heat and noise, drastically lowering motor operating efficiency.

Root Causes of Bearing Creep

Fit Tolerance Stringent fit tolerance requirements apply to the bearing-shaft and bearing-housing mating surfaces. Tolerance specifications vary by bearing size, precision grade, load condition and operating environment. Improper fit tolerance will result in mass bearing creep defects across production batches.

Machining & Assembly Precision This covers dimensional tolerances, surface roughness of shafts, bearings and bearing housings, as well as assembly accuracy. Failure to meet technical specifications will alter the designed fit clearance/interference and induce bearing creep.

Material Properties of Shafts & Bearings Material selection is critical. Bearings of different types must be manufactured from matching bearing steel with high strength, rigidity and wear resistance, while bearing alloys need a low friction coefficient. Proper material selection ensures reliable bearing operation and mitigates creep risks.

Common Remedial Solutions for Bearing Creep

Domestic mainstream repair techniques for creep damage include bushing insertion, stippling, surfacing welding, brush plating, thermal spraying and laser cladding.

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

Thermal Spraying: Molten spray feedstock is atomized by high-velocity airflow and propelled onto component surfaces to form a functional coating.

Brush Plating: An electrolytic process used to deposit metal coatings locally on workpiece surfaces.

Laser Cladding (Laser Overlay): An advanced surface modification technology.