Maintenance of bearings

1. Regular inspection

In order to give full play to the bearing and maintain its due performance for a long time, regular maintenance (regular inspection) must be carried out. It is very important to improve productivity and economy to find faults early and prevent accidents before they happen through proper regular inspection.

1.1 Cleaning

When disassembling the bearing for inspection, take photos and other methods to make appearance records. In addition, confirm the amount of remaining lubricant and sample the lubricant before cleaning the bearing.

A. The cleaning of bearings is divided into rough cleaning and fine cleaning, and a metal grid can be placed at the bottom of the used container.

b. During rough cleaning, use a brush to remove the grease or adhesive in the oil. If the bearing is rotated in oil at this time, be careful that the rolling surface will be damaged due to foreign matters.

c. During fine cleaning, rotate the bearing slowly in oil and carefully.

The commonly used cleaning agent is neutral and water free diesel oil or kerosene, and warm alkali liquor is sometimes used as required. No matter what kind of cleaning agent is used, always filter it to keep it clean.

After cleaning, immediately coat the bearing with antirust oil or grease.

1.2 Inspection and judgment

1.2.1 Fault identification method of bearing

It is very important to improve productivity and economy that bearing faults in operation can be identified or predicted without disassembly inspection. The main identification methods are as follows:

a. Recognition by voice

Sound recognition requires extensive experience. Must be trained to recognize bearing and non bearing sounds. To this end, we should try to assign special personnel to carry out this work. The sound of the bearing can be clearly heard by sticking the sound detector or sound stick on the housing.

b. Identification by operating temperature

This method belongs to comparative identification method, and is only used in situations where the operating state does not change too much. For this reason, continuous temperature recording must be carried out. When a fault occurs, not only the temperature increases, but also irregular changes occur.

c. Identification by the state of the lubricant

The lubricant shall be sampled and analyzed to determine whether it is contaminated with foreign matters or metal powder. This method is particularly effective for bearings that cannot be observed close to or large bearings.

1.2.2 Bearing inspection

Check the bearings removed during regular maintenance, operation inspection and replacement of peripheral parts of the equipment to determine whether they can be used again or whether the use is good or bad. Carefully investigate and record the removed bearing and its appearance. In order to find out and investigate the residual amount of lubricant, the bearing shall be well cleaned after sampling.

Secondly, check the condition of the raceway surface, rolling surface and mating surface, as well as the wear condition of the cage for damage and abnormality.

To judge whether the bearing can be used again, it shall be determined after considering the degree of bearing damage, machine performance, importance, operating conditions, inspection cycle, etc. Check the results. If the bearing is found to be damaged or abnormal, find out the cause of the damage and formulate countermeasures. In addition, if the following defects are found, the bearing can no longer be used and needs to be replaced.

a. Any one of the inner and outer rings, rolling elements and cages has cracks or fragments.

b. Any one of the inner and outer rings and rolling elements is stripped.

c. The raceway surface, rib and rolling body are obviously jammed.

d. The cage is seriously worn or the rivets are loose.

e. Raceway surface and rolling body are rusted and scarred.

F. There are obvious indentations and scratches on rolling surfaces and rolling elements.

g. Creep is found on the inner diameter of the inner ring or the outer diameter of the outer ring.

h. Overheating causes severe discoloration.

i. The sealing ring and dust cover of the grease sealed bearing are seriously damaged.

2. Shutdown inspection

It is important to check the bearing seal regularly to keep the bearing in the best condition. The most favorable inspection time is arranged in the period of regular shutdown inspection. The prior planning and knowing of the bearing model and the spare parts of the bearing are usually based on the inspection work.

2.1 It is important to keep the bearings and lubrication clean.

Clean the machine surface before inspection, and then remove the parts around the bearing. The oil seal is a very fragile part, so it is necessary to remove it carefully without exerting excessive force, and then carefully check the oil seal and its surrounding parts. If the oil seal has shown bad symptoms, it must be replaced. Poor oil seals will lead to bearing damage and severe equipment shutdown.

2.2 Check lubricant

Rub the two fingers with a little lubricant. If there are pollutants, they can be felt, or apply a thin layer of lubricant on the back of the hand, and then conduct light sealing inspection.

2.3 Replace lubricant

After draining the old oil from the oil lubricated bearing, if possible, fill it with fresh oil and let the machine rotate at low speed for several minutes. Make the engine oil collect residual pollutants as much as possible, and then drain the engine oil. It is better to filter the engine oil before use.

When replacing grease for grease lubricated bearings, the arbor remover with cotton joint angle to any part of the bearing shall be avoided, because these residual fibers may wedge between rolling elements and cause damage, especially for the application of small bearings.

2.4 Cover exposed bearings

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

If the uncovered bearing can be cleaned without disassembly and inspection, the brush used for coating shall be dipped with white spirit for cleaning, and then a piece of lint free cloth shall be used for wiping or compressed air shall be used for drying (be careful not to let the bearing assembly start rotating).

Check the track surface, retainer and beads of the bearing with a small mirror and a probe similar to that used by dentists. If the bearing is not damaged, re lubrication should be carried out according to the recommendations of the lubrication instructions provided by the original manufacturer of the machine.

Do not clean the sealed cover or dust-proof bearing; Just wipe the external surface. If the bearing is damaged, replace it. It is much more economical to replace bearings during regular shutdown maintenance than to choose sudden shutdown due to damage of array bearings.

3. Inspection and troubleshooting during operation

The inspection items during operation include rolling sound, vibration, temperature and lubrication status of the bearing. The rolling sound, vibration and temperature of the bearing are as described above. Lubrication is described here as follows:

3.1 Function of bearing lubrication

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

a. An oil film is formed between the two rolling surfaces or sliding surfaces in contact with each other to separate the two surfaces and reduce friction and wear of the contact surfaces.

b. When oil lubrication is used, especially when circulating oil lubrication, oil mist lubrication and oil spray lubrication are used, the lubricating oil can take away most of the friction heat inside the bearing and play an effective role in heat dissipation.

c. When grease lubrication is used, it can prevent foreign matters such as external dust from entering the bearing and play a sealing role.

d. Lubricants can prevent metal corrosion.

e. Prolong the fatigue life of the bearing.

3.2 Grease lubrication

Grease is a lubricant composed of base oil, thickener and additives. When selecting, lubricating grease that is very suitable for the service conditions of the bearing shall be selected. Due to different trademarks, there will be great differences in performance, so attention must be paid to the selection. The common lubricating grease for bearings includes calcium base grease, sodium base grease, calcium sodium base grease, lithium base grease, aluminum base grease, molybdenum disulfide grease, etc. The amount of grease filled in the bearing should be 1/2-1/3 of the bearing internal space. It shall be reduced to 1/3 at high speed. Excessive grease increases the temperature.

3.3 Selection of lubricating grease

When selecting lubricating grease according to the working temperature, the main indicators should be the drop point, oxidation stability and low temperature performance. The drop point can generally be used to evaluate the high temperature performance. The actual working temperature of the bearing should be 10-20 ℃ lower than the drop point. The use temperature of synthetic grease shall be 20-30 ℃ lower than the dropping point. When selecting the grease according to the bearing load, the grease with small penetration shall be selected for the heavy load. When working under high pressure, in addition to low penetration, it also has high oil film strength and extreme pressure performance. When selecting grease according to environmental conditions, calcium based grease is insoluble in water and suitable for dry and low moisture environments.

3.4 Supplement and replacement of lubricant

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

3.5 Bearing damage and countermeasures

It is impossible to directly observe the bearing during operation, but the abnormal condition of the bearing can be found out through noise, vibration, temperature, lubricant, etc.