The impact of bearing maintenance on service life

2023-03-18 13:49
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The service life of a bearing refers to the number of revolutions or hours that the bearing undergoes before pitting occurs under a certain load. Bearings within this lifespan should experience initial fatigue damage on any of their bearing rings or rolling elements.

However, in our daily practical use, it can be clearly observed that bearings with consistent appearance under the same working conditions have significantly different actual lifespans. There are many factors that affect the service life of bearings. Today, the editor will briefly introduce the impact of bearing maintenance and rust prevention on the service life of bearings?

Bearing maintenance interval

How often do bearings need to be maintained? In theory, bearings can be used for 20000 to 80000 hours, but the specific lifespan depends on wear and tear during use, working strength, and later maintenance.

How to maintain bearings

In order to fully utilize and maintain the expected performance of bearings for a long time, it is necessary to effectively carry out regular maintenance (regular inspections). It is important to detect faults early and prevent accidents from happening before they occur through appropriate regular inspections, in order to improve productivity and economy. The storage bearings are coated with an appropriate amount of anti rust oil and packaged with anti rust paper when leaving the factory. As long as the packaging is not damaged, the quality of the bearings will be guaranteed. However, for long-term storage, it is advisable to store it on a shelf 30cm above the ground at a humidity below 65% and a temperature of around 20 ℃. In addition, the storage location should avoid direct sunlight or contact with cold walls. When cleaning and disassembling the bearings for inspection, first use photography and other methods to make appearance records. In addition, it is necessary to confirm the amount of remaining lubricant and sample the lubricant before cleaning the bearings.

Steps for bearing maintenance

1. Regular replacement of bearings should be strictly implemented, and the replacement cycle should be reasonably set according to the operating conditions of the bearings;

2. New bearings must be inspected before use. The inspection content includes whether the packaging (preferably accompanied by a user manual or certificate of conformity) is intact; Is the identification (factory name, model) clear; Whether the appearance (rust, damage) is good;

3. New bearings that have passed the inspection may not be cleaned under general usage conditions (motors with 2 poles or more); The new sealed bearing is not cleaned.

4. The bearing cover and bearings must be cleaned before changing the oil. Cleaning is divided into coarse washing and fine washing. The oil used for coarse washing is clean diesel or kerosene, while the oil used for fine washing is clean gasoline.

5. After the cleaning of the bearing is completed, it should be flexibly rotated by hand and shaken radially and axially to preliminarily determine whether there is looseness or excessive clearance. Check the gap if necessary. If severe wear, corrosion, and metal peeling are found on the ball or roller frame, it should be replaced.

6. After the cleaning and inspection of the bearings, dry the cleaning agent (or air dry) with a white cloth and add qualified lubricating grease. It is not allowed to add different types of lubricating grease into the same bearing.

7. When refueling, it is prohibited to have dust in the surrounding environment; Use clean hands to refuel, slowly rotate the entire bearing with one hand, and use the middle and index fingers to inject oil pressure into the bearing cavity with the other hand. Add one side before proceeding to the other side. Remove excess grease according to the number of motor poles.

8. Oil filling amount for bearings and bearing covers: The oil filling amount for bearing covers is 1/2 to 2/3 of the bearing cover capacity (the upper limit of the motor pole number is taken); The oil content of the bearing is 1/2-2/3 of the inner and outer ring cavities of the bearing (the upper limit of the motor pole number is taken).

9. The motor end cover with oil replenishment and drainage holes must also be cleaned during oil change to maintain unobstructed passages. When refueling, the oil filling hole must be filled with oil.

10. Motors with oil filling holes must be regularly oiled. The oil replenishment period is determined based on the operating requirements and conditions of the motor (usually running a two pole motor for 500 hours within 24 hours).

11. When refueling, the refueling port must be clean. The amount of oil to be replenished is limited to a bearing temperature increase of only 2 ℃ (for a 2-pole motor, use an oil gun to quickly inject oil twice and observe for 10 minutes, and decide whether to continue adding according to the situation).

12. When disassembling bearings, it is necessary to ensure that the force points are correct (the inner ring on the shaft is subjected to force, and the inner and outer rings of the end cover are subjected to force), and the force is evenly distributed. It is best to use the pressing method (for small motors) and the hot sleeve method (for large and large motors with large interference).

13. When installing the bearing, evenly apply a small amount of grease to the contact surface. After the installation of the bearing, the clearance between the inner ring of the bearing and the shaft shoulder must be checked (preferably without clearance).

14. The temperature control of the bearing hot sleeve heating method is between 80 and 100 ℃, and the time control is within 10 minutes between 80 and 100 ℃. Ensure the use of non corrosive mineral oil with good thermal stability for oil heating (preferably transformer oil), and the oil and container should be clean. Install a metal mesh at a distance of 50 to 70mm from the bottom of the oil tank, and place the bearings on the mesh. Large bearings also need to be lifted with hooks.

15. Regularly inspect the motor and record its operating status (motor vibration, motor and bearing temperature, motor operating current). Generally, a two pole motor with a power output of 75KW or above is used once a day. Strengthen inspections and inform relevant parties when abnormal operating conditions occur.

16. All maintenance work of bearings must be recorded as a basis for setting the regular replacement cycle of bearings and determining the quality of bearings.

Bearing cleanliness

The cleanliness of bearings has a significant impact on their lifespan. The higher the cleanliness of bearings, the longer their lifespan. Lubricants with different cleanliness levels have a significant impact on the lifespan of ball bearings. Therefore, improving the cleanliness of lubricating oil can extend the lifespan of bearings. In addition, if the lubricating oil contains dirt particles below 10um, the lifespan of bearings will also increase exponentially.

(1) Impact on vibration: Cleanliness seriously affects the vibration level of bearings, especially in high-frequency bands. Bearings with high cleanliness have low vibration speed values, especially in high-frequency bands.

(2) Impact on noise: Tests have been conducted on the impact of dust in bearing lubricating grease on noise, proving that the more dust, the greater the noise.

(3) The impact on lubrication performance: The decrease in bearing cleanliness not only affects the formation of lubricating oil film, but also causes the deterioration of lubricating grease and accelerates its aging, thereby affecting the lubrication performance of lubricating grease.

Methods for rust prevention of bearings

1. Surface cleaning: The cleaning method must be selected according to the properties of the surface of the rust inhibitor and the current conditions. The commonly used methods include solvent cleaning, chemical treatment cleaning, and mechanical cleaning.

2. After the surface is dry and cleaned, it can be blown dry with filtered dry compressed air, or dried with a dryer at 120-170 ℃, or wiped dry with clean gauze.

3. Soaking method: Some small items are soaked in rust resistant grease, and cross tapered roller bearings are used to adhere a layer of rust resistant grease to their surface. The thickness of the oil film can be achieved by controlling the temperature or viscosity of the rust resistant grease.

4. Brushing method: used for outdoor building equipment or special shaped products that are not suitable for soaking or spraying. When brushing, attention should be paid to not only avoiding accumulation, but also to preventing leakage.

5. Spray method: some large antirust materials cannot be oiled by immersion method. Generally, the turret bearing is sprayed with filtered compressed air with a pressure of about 0.7Mpa in the air clean place. The spray method is applicable to solvent diluted antirust oil or thin antirust oil, but perfect fire prevention and labor protection measures must be taken.

It should be noted that the following types of acids cannot be used for bearing rust removal: sulfuric acid, hydrochloric acid, dilute sulfuric acid, and dilute hydrochloric acid. Because these acids can damage the good metal parts, these types of liquids must not be used! In daily life, there are several liquids that can remove rust without damaging good metal parts, but the effects vary. Firstly, dilute oxalic acid has a ratio of 3:1 to water, dilute oxalic acid 3, and water 1. This speed is slow, but the effect is very good, and it is sold everywhere. The second type is gun oil, also known as mechanical rust removal oil, which is not very easy to buy. This oil can quickly remove rust and has very good results.