Stepper Motor Needle Roller Bearing Fault Analysis and Maintenance

As the connecting component between the stationary and rotating parts of a stepper motor, bearings directly affect the motor’s operation, service life and overall product quality. Therefore, daily operation and maintenance of bearings should be highly prioritized.

1. Common Fault Analysis of Needle Roller Bearings

Needle roller bearings feature low friction resistance, high mechanical efficiency, convenient lubrication and maintenance, and standardized specifications, making them widely applied in stepper motors. Their common faults are analyzed as follows:

1.1 Excessively High Bearing Temperature

During stepper motor operation, the temperature of the bearing end cover and seat is considered normal if it does not feel hot to the touch. Overheating indicates abnormal bearing temperature, which is mainly caused by the following factors:

(1) Substandard or deteriorated grease, excessive viscosity, or overfilled grease. The grease filling volume must be strictly controlled, generally accounting for 1/3 to 1/2 of the bearing seat capacity. More grease can be applied for bearings operating at low speed and light load, while less grease is required for high-speed and heavy-load bearings.

(2) Improper bearing assembly. Newly replaced or reprocessed shafts may lack relief grooves or have unqualified journal dimensions, resulting in incomplete bearing seating. Excessively small bearing clearance leads to severe shear friction loss of internal oil flow and insufficient heat dissipation, causing bearing overheating. In contrast, excessive clearance will alter the dynamic characteristics of the bearing and trigger unstable rotor operation. It is essential to select appropriate bearing clearance and optimize assembly processes according to different equipment and operating conditions. Re-machining on a lathe and reassembly are required for unqualified parts.

(3) Bearing creep. There are two types of creep: outer ring creep (relative displacement between the bearing outer ring and housing) and inner ring creep (relative displacement between the bearing inner ring and shaft journal). Creep causes bearing overheating accompanied by a squeaking sound, which can be mitigated with adhesives or resolved by disassembly, reprocessing and replacement.

(4) Insufficient lubrication. A normally operating motor produces a steady and uniform humming sound. A gurgling sound or intermittent howling noise indicates insufficient bearing grease. Grease can be refilled through the bearing oil filler hole during operation, while rear bearing lubrication must be performed after motor shutdown.

(5) Seven common types of needle roller bearing damage:

① Raceway surface spalling. The rolling elements and inner/outer raceways bear periodic pulsating contact stress during operation. Fatigue spalling occurs when the stress cycles reach a certain threshold. Excessive load, improper installation, shaft bending, and misalignment between the motor shaft and mechanical shaft will accelerate spalling. Raceway spalling reduces rotational accuracy and causes mechanical vibration and noise.

② Bearing burning

③ Plastic deformation

④ Bearing ring cracking

⑤ Cage fracture

⑥ Metal adhesion of the cage to rolling elements

⑦ Severe wear of raceway surfaces

1.2 Abnormal Bearing Noise

Slight operating noise of needle roller bearings is normal during operation. Loud, abnormal or impact noises indicate bearing faults. Different fault positions correspond to distinct noise characteristics:

A regular clicking sound superimposed on the normal humming noise means scratches, grooves or corrosion on rolling elements and raceways; irregular scraping noises indicate internal contamination by iron filings or fine particles; discontinuous stuttering noises may result from outer ring or cage fracture; periodic squeaking signifies outer ring creep; gurgling and intermittent howling noises are typical of insufficient lubrication.

Once abnormal noises occur, stop the motor for inspection. Verify smooth operation and no abnormal sound of front and rear bearings with professional testing. Visually check the cage, grooves, inner and outer rings for cracks, scratches and corrosion with a flashlight. Bearings with abnormal noise or jamming during rotation must be replaced promptly.

Bearings are core and vulnerable components of stepper motors, whose normal operation determines the stable performance of the whole motor. Bearing operation is affected by multiple internal and external factors, making fault diagnosis complex. Combined with practical maintenance experience, this paper analyzes common bearing faults and corresponding solutions, adopts a simple and practical touch-and-listen method to judge bearing operating status, and puts forward targeted preventive measures against bearing damage.