The Impact of Bearing Maintenance on Service Life

Bearing service life refers to the number of revolutions or hours a bearing undergoes under a certain load before pitting occurs. Within this service life, initial fatigue damage should occur on any of its bearing rings or rolling elements.

However, in our daily practical use, it is clearly observed that bearings with identical appearances under the same working conditions have significantly different actual service lives. Many factors affect bearing service life. Today, we will briefly introduce the impact of bearing maintenance and rust prevention on bearing service life.

Bearing Maintenance Cycle

How often should bearings be maintained? Theoretically, bearings can be used for 20,000-80,000 hours, but the specific lifespan depends on wear during use, workload, and subsequent maintenance, etc.

How to Maintain Bearings

To ensure that bearings fully utilize and maintain their intended performance for a long period, regular maintenance (regular inspection) must be performed effectively. Proper regular inspections allow for early detection of faults and prevention of accidents, which is crucial for improving productivity and economy. Storage: Bearings are coated with an appropriate amount of rust-preventive oil and packaged with rust-proof paper at the factory. As long as this packaging is not damaged, the quality of the bearing will be guaranteed. However, for long-term storage, it is advisable to store them on a shelf 30cm above the ground under conditions of humidity below 65% and temperature around 20℃. Additionally, the storage location should avoid direct sunlight or contact with cold walls. Cleaning: When disassembling and inspecting the bearing, first record its appearance using methods such as photography. Also, confirm the amount of remaining lubricant and take a sample of the lubricant before cleaning the bearing.

Bearing Maintenance Steps:

1. Bearings should be replaced regularly, with the replacement cycle set reasonably according to the bearing's operating conditions.

2. New bearings must be inspected before use. The inspection should include checking the packaging (preferably with an instruction manual and certificate of conformity) for integrity; ensuring the markings (manufacturer's name, model number) are clear; and checking the appearance (rust, damage) for any issues.

3. New bearings that pass inspection do not require cleaning under normal operating conditions (for motors with 2 poles or higher); new sealed bearings do not require cleaning.

4. Before changing the oil, the bearing cap and bearing itself must be cleaned. Cleaning is divided into rough cleaning and fine cleaning. For rough cleaning, use clean diesel or kerosene; for fine cleaning, use clean gasoline.

6. After cleaning, the bearing should rotate freely by hand. Radial and axial shaking can be used to initially determine if it is loose or has excessive clearance. Check the clearance if necessary. Replace any bearings with severely worn, rusted, or with flaking metal, such as those with balls or rollers.

7. After cleaning and inspection, wipe the cleaning agent dry with a white cloth (or let it air dry), and add qualified grease. Do not add different types of grease to the same bearing.

8. The surrounding environment must be dusty when adding grease. Use clean hands to add grease. Slowly rotate the entire bearing with one hand, and use your middle and index fingers to press the grease into the bearing cavity with the other. Add grease to one side before moving to the other. Remove excess grease according to the number of poles of the motor.

9. Bearing and Bearing Cap Oil Volume: The bearing cap oil volume should be 1/2 to 2/3 of the bearing cap capacity (upper limit for higher motor pole numbers); the bearing oil volume should be 1/2 to 2/3 of the bearing's inner and outer ring cavity volume (upper limit for higher motor pole numbers).

10. Motor end caps with oil filler and drain holes must also be cleaned during oil changes to ensure unobstructed passage. The oil filler hole must be filled completely with oil during oiling.

11. Motors with oil filler holes must be replenished with oil regularly. The replenishment cycle is determined based on the motor's operating requirements and conditions (generally 500 hours for a 24-hour operating two-pole motor).

12. When replenishing oil, the oil filler port must be clean. The amount of oil replenished should be limited to a bearing temperature increase of only 2°C (for a 2-pole motor, quickly inject oil twice with an oil gun, observe for 10 minutes, and decide whether to continue adding oil based on the situation).

13. When disassembling and assembling bearings, ensure the correct stress points (inner ring on the shaft, inner and outer rings of the end cap) and even stress distribution. The best methods are press-fit (for small motors) and heat-shrink fitting (for large motors with large interference fit).

14. When installing bearings, apply a small amount of grease evenly to the contact surfaces. After installation, check the clearance between the bearing inner ring and the shaft shoulder (ideally, there should be no clearance).

15. For the heat-shrink fitting method, control the heating temperature between 80 and 100℃, and the time should be controlled within 10 minutes. For oil heating, ensure the use of non-corrosive mineral oil with good thermal stability (preferably transformer oil). Both the oil and the container should be clean. Place a metal mesh 50 to 70 mm from the bottom of the oil tank, and place the bearing on the mesh. Larger bearings should be suspended with hooks.

16. Regularly inspect the motor and record its operating status (motor vibration, motor and bearing temperature, motor operating current). Generally, two-pole motors above 75KW should be inspected once a day. When abnormal operating conditions occur, increase the frequency of inspections and notify the relevant parties.

17. All bearing maintenance work must be recorded, serving as the basis for setting bearing replacement cycles and judging bearing quality.

Bearing Cleanliness

Bearing cleanliness has a significant impact on bearing life. Higher cleanliness results in longer lifespan. Different cleanliness levels of lubricating oil greatly affect the lifespan of ball bearings. Therefore, improving lubricating oil cleanliness can extend bearing life. Furthermore, if the contaminant particles in the lubricating oil are controlled below 10µm, bearing life can increase several times over.

(1) Impact on Vibration: Cleanliness significantly affects bearing vibration levels, especially in the high-frequency band. Bearings with high cleanliness have lower vibration velocity values, particularly in the high-frequency band.

(2) Impact on Noise: Experiments have been conducted on the impact of dust in bearing grease on noise, demonstrating that more dust results in greater noise.

(3) Impact on Lubrication Performance: Decreased bearing cleanliness not only affects the formation of the lubricating oil film but also causes grease deterioration and accelerates its aging, thus reducing the lubrication performance of the grease.