Figure 9-23 Structure of Rolling Bearing
(1) Common faults of rolling bearings
Due to the influence of its own quality and external conditions, the bearing capacity, rotary accuracy and wear resistance of rolling bearings will change during use. When the performance index of the bearing is lower than the use requirement and cannot work normally, the bearing will fail or even fail, and the machinery and equipment will stop running. Therefore, it is necessary to find out the reasons in a short time and take corresponding measures.
After long-term operation, rolling bearings will have the following faults:
① The clearance of rolling bearing is too large and the wear is serious.
② The cage is deformed or damaged.
(3) The rolling elements are worn and deformed, and they break in severe cases.
(4) The overheating of rolling bearings turns blue, which is mostly caused by long-term overheating of rolling bearings.
⑤ The inner ring, outer ring and rolling body of rolling bearing are worn, resulting in pits or rust.
(2) Failure causes of rolling bearings
Generally speaking, 1/3 is because the bearing has reached the fatigue spalling period, which belongs to normal failure; 1/3 is premature failure due to poor lubrication, and 1/3 is premature failure due to dirt entering the bearing or incorrect installation.
(1) Grease and lubricating oil are out of date or selected incorrectly.
② The grease in the bearing box is too full or the oil level is too high; Insufficient grease or low oil level.
③ The contact oil seal interferes too much or the spring is too tight; The contact oil seal is badly worn, which leads to the leakage of lubricating oil.
④ The diameter of the shaft is too large or too small.
⑤ Two or more bearings have poor coaxiality.
⑥ The shaft and bearing inner sleeve or outer sleeve are twisted.
⑦ Unreasonable shaft shoulder size leads to shaft bending.
⑧ The joint area of the shoulder in the bearing box is too small, which leads to the distortion of the bearing outer ring.
Pet-name ruby shoulder friction to the bearing seal cover, bearing seal cover twisted.
Attending the locking sleeve is not locked tightly enough or too tightly.
The locking snap ring contacts the bearing.
Excessive bearing clearance will lead to shaft vibration.
Bearing clearance is too small. Due to the expansion of the shaft, the bearing clearance becomes smaller, which leads to the serious expansion of the bearing inner ring and the reduction of the bearing clearance.
The inner hole of the bearing box is not round, the bearing box is twisted, the supporting surface is uneven, the inner diameter of the bearing box hole is too small, the bearing box hole is too large, and the force is unbalanced.
Because the material of the box hole is too soft, the aperture becomes larger after being stressed, which causes the outer ring to slide in the box hole.
Before installing the bearing, the debris and other sundries in the bearing box were not cleaned up.
Sundries, sand, toner, water, acid, paint and other contaminants enter the bearing housing.
Incorrect installation method, directly hit the bearing with a hammer.
Due to quick start, there are scratches on the rolling elements.
The rotating parts in the machine are in contact with the stationary parts.
(3) Detection of rolling bearing wear
Before disassembling lawn machinery, for small lawn machinery, you can shake the shaft extension by hand. If looseness is found, the clearance of the rolling bearing is worn and cannot be used again, as shown in Figure 9-24.
Figure 9-24 Shake the shaft extension end by hand (before the lawn seeder is disintegrated)
After the lawn machinery is disintegrated, the outer ring of the rolling bearing can be swung by hand. If the swing is too large, the rolling bearing will be worn, as shown in Figure 9-25.
Figure 9-25 Swing the outer ring of the rolling bearing by hand (after the lawn seeder is disintegrated)
After removing the rolling bearing, shake it radially by hand. If the rollers collide, the gap is too large. Shake the rolling bearing axially by hand. If the looseness between the inner ring and the outer ring is abnormal, it also means that the clearance of the rolling bearing is worn. As shown in figure 9-26.
Figure 9-26 Shake the rolling bearing by hand (after the rolling bearing is removed)
The thickness gauge can be used to check the wear of rolling bearings. When the wear of rolling bearings exceeds the wear limit, new rolling bearings should be replaced, and in principle, rolling bearings with the same specifications should be replaced. If there is no required rolling bearing model, it can be replaced by another type of rolling bearing if necessary, but the bearing capacity of the replaced rolling bearing should be suitable for the replaced rolling bearing. When the geometric dimensions of contemporary rolling bearings are slightly different from those of the original rolling bearings, thrust ring or inner and outer sleeves should be added.
See table 9- 1 for the allowable wear values of rolling bearings corresponding to different shaft diameters.
Table 9- 1 Allowable wear values of rolling bearings with different shaft diameters
(4) Cleaning of rolling bearing
The purpose of cleaning the removed old rolling bearing is to check the quality of the rolling bearing to determine whether it can be used continuously. It is recommended to clean with 805 detergent. Scrape the old oil in the rolling bearing with bamboo board first, then mix 805 cleaner with water (about 98%) and heat it to 60 ~ 70℃, and then clean it with a brush. Compared with gasoline or kerosene, using 805 cleaning agent to clean rolling bearings has the advantages of safety, non-toxicity, energy saving and low cost. Because the cleaning agent has temporary rust-proof ability (it can be stored for 7 days), there is no need to worry about the rust of the cleaned rolling bearing.
Of course, except for rolling bearings, rolling bearing covers, sealing rings, rotating fittings and end cover rolling bearing chambers can be cleaned with 805 cleaner, and then dried or coated with a thin layer of oil.
The cleaning method of rolling bearing is shown in Figure 9-27.
Figure 9-27 Cleaning method of rolling bearing
(5) Repair of rolling bearing
① If the wear of the rolling bearing exceeds the limit, the rolling bearing with the same specification should be replaced.
② After the rolling bearing is removed, it can be cleaned with gasoline or kerosene, and then checked. If the machined surface (especially raceway) has rust, it can be cleaned with No.00 emery cloth, and then cleaned with 805 cleaner; If there are deep cracks or the inner and outer rings are broken, the rolling bearing must be replaced.
(3) If the rolling bearing is damaged, several rolling bearings of the same model can be disassembled and their intact parts can be pieced together to form a rolling bearing. If the ball is lost or damaged, it can be used again.
④ Some rolling bearings used in high-speed motors can be used in low-speed motors if the wear is not serious.
⑤ If the outer cover of the rolling bearing presses the rolling bearing too tightly, it may be that the notch of the outer cover of the rolling bearing is too long, which can be corrected. If the inner hole of the rolling bearing cover rubs against the journal, it may be that the notch of the rolling bearing cover is loose or not concentric, and it should also be corrected.