Premature aging of rolling bearings can lead to equipment shutdown. Now, combined with the proprietary motor maintenance practices, we present the experience of preventing premature aging of rolling bearings. The causes of premature aging of rolling bearings are: excessive interference fit, poor lubrication, misalignment during installation, severe vibration, material fatigue, contamination and corrosion.

1.Excessive Interference Fit
When the inner ring of the bearing is forcibly pressed onto the shaft journal, the lighter raceway will cause severe wear on the roller path, while the heavier one will lead to cracks or spalling on the sliding surfaces of the inner and outer rings as well as the balls. The reason is that the clearance between the balls and the retainer is too small, resulting in increased torque, intensified friction, and excessively high operating temperature of the bearing, which exacerbates the wear and fatigue of the bearing and eventually leads to failure.
Preventive measures: Restore the radial clearance of the bearing and reduce the interference fit allowance.
There are two methods to check the bearing assembly quality:
Visual inspection method: After installing the bearing into the bearing chamber of the motor end cover, manually rotate the end cover. If the bearing rotates freely and flexibly without vibration or vertical wobbling, the assembly is deemed qualified.
Feeler gauge inspection method: Assemble the motor end cover with the bearing onto the bearing seat, and use a 0.03 mm thick feeler gauge to check the radial clearance around the bearing. If the maximum clearance is directly above the center (with the motor installed horizontally), the assembly is correct and reliable; otherwise, the installation is improper. The position of the end cover should be adjusted accordingly and reassembled until it is qualified.

2. Poor Lubrication
The cause is an acute lack of grease or grease dry-out. Due to the high frictional temperature generated by the high-speed operation of the motor, the bearing temperature becomes excessively high, resulting in oxidative discoloration, which is manifested as brown or blue stains on the bearing balls, cage, inner ring and shaft journal.

Preventive measures: The time for grease replenishment and replacement shall be determined by four factors: motor operating hours, ambient temperature, load conditions and grease quality. Under normal conditions, the motor shall be replenished with grease every 6000-10000 operating hours; grease shall be replaced every 10000-20000 operating hours. High-quality lithium-based lubricants (code ZL-2) shall be used.

3. Misaligned Installation
If the installation is not centered, the bearing raceway will show not only ball tracks but also signs of uneven ball wear, and misalignment will occur. When measuring the radial clearance on both sides of the bearing with a feeler gauge, there will be obvious differences. This may be caused by directly striking the bearing outer ring with a hammer; overtightening of the coupling (gear meshing); non-parallelism between the centerlines of the driving wheel and the driven wheels. When the deflection exceeds 1/1000, the bearing operating temperature will be too high, the raceways and balls will suffer severe wear, the shaft will bend, and the sealing surface of the end cover bolts will not be perpendicular to the bolt axis.
Correct installation method: Use a steel sleeve with a smooth end face and a thickness approximately equal to that of the bearing inner ring to press the bearing onto the clean shaft journal to the correct position. The pressing force should be uniform and not excessive. Then, according to the motor speed, check the allowable value of the shaft radial end runout.

4. Severe Vibration
Bearings will vibrate violently when the motor core malfunctions. The causes are: thermal deformation of the core; aging of motor bearings; excessive deflection of the rotating shaft; loosening of the end cover retaining bolts due to vibration; unstable foundation leading to bearing vibration.
Preventive measures: Reduce the core tightness, coat the silicon steel sheet surface with 1052 silicone organic paint to open up the clearance; replace with new bearings of the same type; remove the rotor core and straighten the bent part of the shaft; adopt the 180° symmetry installation method; reinforce the end cover fastening bolts and tighten the foundation anchor bolts.

5. Material Fatigue
Due to metal material fatigue, irregular debris will peel off from the bearing rollers and spherical surfaces. When mixed with lubricating grease, it will increase the operating noise, and the balls will be in a sliding state, leading to an increase in bearing radial clearance and shaft end runout tolerance, which can be 2-3 times the normal value. The determining factors of bearing fatigue are: motor load, rotational speed, air gap, end cover type, material viscosity, grease quality and grease filling amount.
Preventive measures: According to motor operation records, when the light-load operating current exceeds 60% of the rated value and the operating hours reach 20000-25000 hours; when the medium-load operating current is 60-80% of the rated value and the operating hours reach 15000-20000 hours; when the heavy-load operating current is 80-100% of the rated value and the operating hours reach 10000-15000 hours, the normal material fatigue of the bearing should be considered, and the bearing should be replaced with a new one of the same type.

6. Contamination and Corrosion
At this time, rusty red and brown spots of corrosion can be observed on the roller raceways and ball surfaces, and the operating noise is louder than that of new bearings.
The cause is the uncleanliness of the assembly site, such as the presence of moisture, acids, alkalis and toxic gases; contamination of tools and hands; use of inferior grease.
Preventive measures: The bearing assembly site, tools and instruments must be kept clean; the bearings must be thoroughly cleaned; replace with high-quality lithium-based lubricants.