Periodic inspection of bearings

Check the regular maintenance of the equipment, operation inspection and the removed bearing during the replacement of the peripheral parts, so as to judge whether it can be used again or whether the use condition is better than bad. Carefully investigate and record the removed bearings and their appearance. In order to understand and investigate the remaining amount of lubricant, clean the bearings well after sampling.

Secondly, check the rolling surface, rolling surface and matching surface and the wear state of the holder.

To judge whether the bearing can be used again, it should be decided after considering the degree of bearing damage, machine performance, importance, operating conditions, inspection cycle, etc. Inspection results, if the bearing is found to be damaged and abnormal conditions, the content of the injury section to find out the cause, formulate countermeasures. In addition, the inspection result, if there are the following defects, the bearing can not be used again, the need to replace the new bearing.

A. The inner and outer rings, rolling bodies, and holders with cracks and fragments.

B. Any of the inner and outer circles and rolling bodies has stripped.

C. Rolling way surface, edge blocking and rolling body have significant card damage.

The d. The holder is badly worn or the rivets are severely loose.

E. Rolling road surface, rolling body is rusty and scarred.

F. Significant indentation and marking on the rolling surface and rolling body.

G. Creep on the inner ring inner diameter surface or the outer diameter of the outer ring.

H. Overheat and discoloration badly.

I. The seal ring and dust cover of the grease seal bearing are severely damaged.

1. Check and troubleshooting during operation

The inspection items in operation include the rolling sound, vibration, temperature and lubrication status of bearings. The specific conditions are as follows:

1.1 Rolling sound of bearings

The sound detector is used to check the size and sound quality of the rolling sound of the running bearing. Even if there is slight damage to the bearing, the bearing will emit abnormal and irregular sounds, which can be distinguished by the sound detector.

1.2 Vibration of the bearing

Bearing vibration is very sensitive to the damage of bearings, such as peeling, indentation, rust, crack, wear and etc. will be reflected in the bearing vibration measurement. Therefore, the size of vibration can be measured by using special bearing vibration tester (frequency analyzer, etc.), and the specific abnormal situation can not be inferred through the frequency points. The measured value varies according to the use conditions of the bearing or the installation position of the sensor, so it is necessary to analyze and compare the measured value of each machine and determine the judgment criteria in advance.

1.3 Temperature of the bearing

The temperature of the bearing, generally the temperature outside the bearing room can be inferred, if the oil hole can directly measure the temperature of the bearing outer ring, it is more appropriate. Usually, the temperature of the bearing rises slowly with the start of the operation and reaches a steady state after 1-2 hours. The normal temperature of the bearing varies with the heat capacity, heat dissipation, rotation speed and load of the machine. If the lubrication and installation parts are appropriate, the bearing temperature will rise sharply, and there will be abnormal high temperature, at this time, we must stop running and take necessary preventive measures. Based on extensive test data, Table 4-1 lists the average of the outer ring temperature of bearings in various machines for reference. Because the temperature is affected by lubrication, rotation speed, load and environment, the value in the table only indicates the approximate temperature range. The working temperature of the bearing can be monitored at any time, and the automatic alarm or stop to prevent the ignition shaft accident when the temperature exceeds the specified value.

1.4 Lubrication

1.4.1 The role of bearing lubrication

Lubrication has an important influence on the fatigue life, friction, wear, temperature rise, vibration, etc. Without normal lubrication, the bearing cannot work. Analysis of the causes of the bearing damage shows that about 40% of the bearing damage is related to poor lubrication. Therefore, good lubrication of bearings is an effective measure to reduce bearing friction and wear.

In addition, bearing lubrication also has heat dissipation, rust prevention, sealing, impact relief and other functions. The role of bearing lubrication can be briefly explained as follows:

A. Form an oil film between the two rolling surfaces or the sliding surfaces to reduce friction and wear on the contact surfaces.

B. When oil lubrication is used, especially when circulating oil lubrication, oil fog lubrication and oil injection lubrication, the lubricating oil can take away most of the friction heat inside the bearing and play an effective heat dissipation role.

C. When using grease lubrication, it can prevent the external dust and other foreign bodies from entering the bearing and play a sealing role.

D. Lubricants can prevent metal rust.

E. Extend the fatigue life of the bearings.

1.4.2 Comparison of grease lubrication and oil lubrication The lubrication methods of bearings can be roughly divided into grease lubrication and oil lubrication. In order to give full play to the function of bearings, it is important to use the lubrication method according to the adjustment and purpose of use. Table 4-2 shows the advantages and disadvantages of grease lubrication and oil lubrication.

1.4.3 Fat grease Grease is a lubricant composed of base oil, thickener and additives. When choosing, should choose very suitable for the use conditions of bearing oil, because the trademark is different, there will be a great difference in performance, so in the choice, we must pay attention to. The grease commonly used in bearings are calcium-based grease, sodium-based grease, calcium-sodium-based grease, lithium-based grease, aluminum-based grease and molybdenum disulfide grease. The quantity of filling grease in the bearing is 1 / 2-1 / 3 of the interior space of the bearing. High speed should be reduced to 1 / 3. Excessive grease increases the temperature.

1.4.4 Selection of Grease When the grease is selected according to the working temperature, the main index should be the drop point, oxidation stability and low temperature performance. The drop point can generally be used to evaluate the high temperature performance, and the actual working temperature of the bearing should be 10-20℃ lower than the drop point. The use temperature of synthetic grease should be 20-30℃ lower than the drop point. When selecting the grease according to the bearing load, the grease with small needle intake should be selected for the heavy load. Under high pressure, in addition to small needle penetration, but also high oil film strength and extreme pressure performance. When selecting grease according to environmental conditions, calcium-based grease is not easily soluble in water and is suitable for dry and less water environment.

1.5 Oil lubrication

Under the condition of high speed and high temperature, oil lubrication can be used when the grease lubrication is not suitable. Through the circulation of lubricating oil, it can take away a lot of heat. Viscosity is an important characteristic of lubricating oil. The size of viscosity directly affects the fluidity of lubricating oil and the thickness of the oil film formed between the friction surfaces. The viscosity of lubricating oil at the working temperature of the bearing is generally 12-15 cst. The higher the speed should be the lower viscosity, and the higher the load should choose the higher viscosity. Commonly used lubricating oil is mechanical oil, high-speed mechanical oil, steam turbine oil, compressor oil, transformer oil, cylinder oil and so on.

Oil lubrication methods include:

a. oil bath lubrication

Oil bath lubrication is the most common lubrication method, suitable for the lubrication of low and medium speed bearings, part of the bearing is immersed in the groove, the lubricating oil is carried by the rotating bearing parts, and then flows back to the oil surface should be slightly lower than the center of the lowest rolling body.

b. drip lubrication

Oil drop lubrication is suitable for the bearing parts that require quantitative supply of lubricating oil, the oil drop is generally appropriate every 3-8 seconds, too much oil will cause the bearing temperature to increase.

C. Cyclic oil lubrication

Use an oil pump to deliver the filtered oil to the bearing parts and cool it through the lubricating oil after the bearing. Because the circulating oil can take away a certain amount of heat to cool the bearing, this method is applicable to the bearing parts with high speed.

d. fog lubrication

Dry compressed air is mixed with lubricating oil to form oil mist. In the injection bearing, the air flow can effectively cool the bearing and prevent the invasion of impurities. This method is suitable for the lubrication of high-speed and high-temperature bearing components.

e. splash lubrication

Use an oil pump to inject the high-pressure oil into the bearing through the nozzle, and the oil injected into the bearing flows into the oil tank through the other end of the bearing. When the bearing rotates at a high speed, the rolling body and the holder also make the surrounding air flow at a very high rotation speed. It is difficult to send the lubricating oil to the bearing with the general lubrication method. At this time, the lubricating oil must be sprayed into the bearing by the high pressure injection method, and the position of the nozzle should be placed between the inner ring and the center of the holder.

1.6 Solid lubrication

Under some special use conditions, a small amount of solid lubricant into the grease, such as adding 3~5% 1 molybdenum disulfide can reduce wear, improve the heat resistance, for high temperature, high temperature, high vacuum, corrosion resistance, radiation resistance, and extremely low temperature, the solid lubricant into engineering plastics or powder metallurgy materials, can be made into bearing parts with self-lubricating performance, such as the roller, holder and rolling body, form lubricating film, has a certain effect on reducing friction and wear.

1.7 Rebrication and replacement of lubricant

A. Interval time of the grease supplementation

Due to the mechanical action, aging and increased pollution, the lubrication base filled in the bearing configuration will gradually lose its lubrication performance. Therefore, the lubrication rank should be constantly supplemented and updated. The interval time of lubricant supplement will vary according to the formation, size and speed of bearings, and the approximate interval time of grease supplement needs according to the operation time. In addition, when the bearing temperature exceeds 70℃, the replenishment interval of the lubricating grease is reduced by half for every 15℃ increase. Double-sided closed bearings have been loaded with fat when manufacturing, "HRB" in these products use standard grease, the total operating temperature range and other performance are suitable for the specified occasions, and the amount of fat filling is corresponding to the size of the bearing, the service life of the fat can generally exceed the bearing life, except for special occasions, no grease is needed.

B. Replacement cycle of the lubricating oil

The replacement cycle of lubricating oil is different due to the use conditions and oil quantity. Generally, when used in a good environment with the operating temperature below 50℃ and less dust, it should be replaced once a year. When the oil temperature reaches 100℃, it should be replaced once in 3 months or less time.

2. Downtime inspection

It is important to check the bearing seal regularly to keep the bearing in optimal condition. The most favorable inspection time is to be arranged in the regular shutdown inspection period, etc. Prior planning and knowing of the bearing letter xuan and the equipped bearing drawings are usually helpful to the inspection work.

The Importance of a clean shaft:

A. It is very important to keep the bearings and the lubrication clean.

B. Clean the surface of the machine before the inspection, and then remove the parts around the bearing. Oil seal is a very fragile part, so it is necessary to carefully remove, do not apply excessive force, and then carefully check the oil seal and its surrounding parts, if it has shown bad symptoms, be sure to replace, bad oil seal will lead to the damage of the bearing and strict equipment shutdown.

And c. Check the lubricant

Touch a little lubricant friction between the fingers, if there are pollutants, can feel out, or apply a thin layer of lubricant on the back of the hand, and then seal the light inspection.

D. Replace the lubricant

The oil lubricated bearing removes old oil and, if possible, fills fresh oil and rotates the machine for a few minutes at low speed. As far as possible, the oil collects the residual contaminants, and then remove the oil, which is best filtered before use. The remover used in the grease bearings should be avoided from any part of the bearing, as these residual fibers may be wedged between the rolling parts and cause damage, especially in the application of small bearings.

F. Cover with the exposed bearing

When checking the bearing, never keep the bearing exposed to pollutants or moisture. If the work is interrupted, the machine shall be covered with oil paper plastic sheet or similar material.

If the bearing may be cleaned without disassembly, clean the coated brush with petroleum solvent (white spirit), then dry with a piece of cloth or blow dry with compressed air (be careful not to rotate the bearing assembly).

Check the bearing track, retainer and beads with a small mirror and probes similar to the dentist. If the bearing is not damaged, re-lubrication shall be performed according to the lubrication instructions provided by the original manufacturer or the recommendations on pages 204 to 247 of this book.

Do not clean with sealing cover or dustproof bearings; only wipe the external surface. If the bearing is damaged, it should be replaced. Replacement of bearings during regular shutdown and maintenance periods is far more economical than the loss of sudden shutdown selected due to array damage.

3. Lubrication of the bearings

3.1 Function of bearing lubrication

Lubrication has an important impact on the fatigue life, friction, wear, temperature, vibration, etc. Without normal lubrication, the bearing cannot work. Analysis of the causes of the bearing damage shows that about 40% of the bearing damage is related to poor lubrication. Therefore, good lubrication of bearings is an effective measure to reduce bearing friction and wear. In addition, bearing lubrication also has heat dissipation, rust prevention, sealing, impact relief and other functions. The role of bearing lubrication can be briefly explained as follows:

A. Form an oil film between the two rolling surfaces or the sliding surfaces to reduce friction and wear on the contact surfaces.

B. When oil lubrication is used, especially when circulating oil lubrication, oil fog lubrication and oil injection lubrication, the lubricating oil can take away most of the friction heat inside the bearing and play an effective heat dissipation role.

C. When using grease lubrication, it can prevent the external dust and other foreign bodies from entering the bearing and play a sealing role.

D. Lubricants can prevent metal rust.

E. Extend the fatigue life of the bearings.

3.2 Comparison of grease lubrication and oil lubrication The lubrication methods of bearings can be roughly divided into grease lubrication and oil lubrication. In order to give full play to the function of bearings, it is important to use the lubrication method according to the adjustment and purpose of use. Table 4-2 shows the advantages and disadvantages of grease lubrication and oil lubrication.

3.3 Lipid lubrication

Grease is a lubricant composed of base oil, thickener and additives. When choosing, should choose very suitable for the use conditions of bearing oil, because the trademark is different, there will be a great difference in performance, so in the choice, we must pay attention to. The grease commonly used in bearings are calcium-based grease, sodium-based grease, calcium-sodium-based grease, lithium-based grease, aluminum-based grease and molybdenum disulfide grease.

The quantity of filling grease in the bearing is 1 / 2-1 / 3 of the interior space of the bearing. High speed should be reduced to 1 / 3. Too much grease will increase the temperature rise.

3.4 Selection of lubricating grease

When selecting grease according to the working temperature, the main index should be the drop point, oxidation stability and low temperature performance. The drop point can generally be used to evaluate the high temperature performance, and the actual working temperature of the bearing should be 10-20℃ lower than the drop point. The use temperature of synthetic grease should be 20-30℃ lower than the drop point.

When selecting the grease according to the bearing load, the grease with small needle intake should be selected for the heavy load. Under high pressure, in addition to small needle penetration, but also high oil film strength and extreme pressure performance.

When selecting grease according to environmental conditions, calcium-based grease is not easily soluble in water and is suitable for dry and less water environment.

3.5 Oil lubrication

Under the condition of high speed and high temperature, oil lubrication can be used when the grease lubrication is not suitable. Through the circulation of lubricating oil, it can take away a lot of heat. Viscosity is an important characteristic of lubricating oil. The size of viscosity directly affects the fluidity of lubricating oil and the thickness of the oil film formed between the friction surfaces. The viscosity of lubricating oil at the working temperature of the bearing is generally 12-15 cst. The higher the speed should be the lower viscosity, and the higher the load should choose the higher viscosity. Commonly used lubricating oil is mechanical oil, high-speed mechanical oil, steam turbine oil, compressor oil, transformer oil, cylinder oil and so on.

Oil lubrication methods include:

a. oil bath lubrication

Oil bath lubrication is the most common lubrication method, suitable for the lubrication of low and medium speed bearings, part of the bearing is immersed in the groove, the lubricating oil is carried by the rotating bearing parts, and then flows back to the oil surface should be slightly lower than the center of the lowest rolling body.

b. drip lubrication

Oil drop lubrication is suitable for the bearing parts that require quantitative supply of lubricating oil, the oil drop is generally appropriate every 3-8 seconds, too much oil will cause the bearing temperature to increase.

C. Cyclic oil lubrication

Use an oil pump to deliver the filtered oil to the bearing parts and cool it through the lubricating oil after the bearing. Because the circulating oil can take away a certain amount of heat to cool the bearing, this method is applicable to the bearing parts with high speed.

d. fog lubrication

Dry compressed air is mixed with lubricating oil to form oil mist. In the injection bearing, the air flow can effectively cool the bearing and prevent the invasion of impurities. This method is suitable for the lubrication of the high-speed and high-temperature bearing components.

e. splash lubrication

Use an oil pump to inject the high-pressure oil into the bearing through the nozzle, and the oil injected into the bearing flows into the oil tank through the other end of the bearing. When the bearing rotates at a high speed, the rolling body and the holder also form the surrounding air flow at a very high rotation speed. It is difficult to send the lubricating oil to the bearing with the general lubrication method. At this time, the lubricating oil must be sprayed into the bearing by the high pressure injection method, and the position of the nozzle should be placed between the inner ring and the center of the holder.

3.6 Solid lubrication

Under some special use conditions, a small amount of solid lubricant into the grease, such as adding 3~5% 1 molybdenum disulfide can reduce wear, improve the heat resistance, for high temperature, high temperature, high vacuum, corrosion resistance, radiation resistance, and extremely low temperature, the solid lubricant into engineering plastics or powder metallurgy materials, can be made into bearing parts with self-lubricating performance, such as the roller, holder and rolling body, form lubricating film, has a certain effect on reducing friction and wear.