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Analysis of common failure causes of bearings

wallpapers Tech 2020-05-27
The early damage of the bearing may be caused by a variety of comprehensive factors. When there is a problem with the taking, you can refer to the possibilities mentioned in this article to investigate and find a solution according to the cause.
 
1. Improper installation (about 16%)
1) Improper cooperation
The base hole is used for the interaction between the bearing inner hole and the shaft, and the base shaft is used for the interaction between the bearing outer circle and the bearing seat hole. The shaft and bearing inner race of centrifugal pumps, centrifuges, reducers, motors, and centrifugal compressors that typically work under normal load conditions use j5, js5, js6, k5, k6, and m6 to cooperate. The outer seat ring adopts j6 and j7. Rotating seat ring (the inner seat ring of most bearings is a rotating seat ring, the outer seat ring is not a rotating seat ring, and a small part of the bearing is the opposite). Usually, an interference fit is used to avoid the seat ring in the shaft diameter under load. Rolling and sliding occur on the mating surface with the housing bore. However, sometimes due to the inaccurate measurement of the shaft diameter and the bearing seat hole size or the mating surface roughness does not meet the standard requirements, resulting in an excessive interference fit, the bearing seat ring is considerably squeezed, resulting in the radial clearance of the bearing itself The reduction will make the bearing challenging to rotate, generate heat, increase in wear or be stuck, and in severe cases will cause the inner and outer bearing rings to crack when installed. The non-rotating seat ring often adopts the clearance or the interference with little interference, so that the non-rotating seat ring may produce slight creep, and the contact surface of the seat ring and the rolling body is continuously replaced, and the raceway wears evenly. At the same time, the phenomenon of axial seizure of the rolling elements in the bearing due to thermal elongation can also be eliminated. However, the excessive clearance fit will cause the non-rotating seat ring to rotate with the rolling body, causing severe wear on the shaft (or bearing housing hole) and the inner seat ring (or outer seat ring), and friction will cause the bearing to generate heat and vibrate.
2) Improper assembly method
When the interference between the bearing and the shaft diameter or the bearing seat hole is small, the press-in method is often used for assembly. The easiest way is to use copper rods and hand hammers to strike the seat ring with the interference fit symmetrically in a particular order so that the bearing is smoothly pressed in. In addition, a soft metal casing can also be driven in with a hand hammer or pressed in with a press. The improper operation will cause the seat ring to be deformed and cracked, or the hand hammer will hit the non-interference fit seat ring, which will cause indentation of the raceway and rolling element or the bearing will be damaged indirectly.
3) Improper temperature control during assembly
When the rolling bearing is assembled, if its interference with the shaft diameter is significant, it is generally collected by hot welding. The bearing is put in an oil drum containing organic oil, and the outside of the oil drum is heated with warm water or flame. The process requires that the temperature of the heated oil is controlled at 80 ° C to 90 ° C, generally not exceeding 100 ° C, and at most not exceeding 120 ° C. After the bearing is heated, it is quickly taken out and put on the journal. If the heating temperature is too high due to improper temperature control, the bearing will be tempered, and the hardness will be reduced. During operation, the bearing will be easily worn, peeled, or even cracked.
4) Improper clearance adjustment during assembly
The clearance of rolling bearing is divided into radial clearance and axial clearance. Its function is to ensure the regular operation and lubrication of rolling elements and to compensate thermal elongation. For bearings with adjustable clearance, because there is a proportional relationship between the axial clearance and the radial clearance, the installation is to obtain the required radial clearance as long as the axial clearance is adjusted. Used in pairs (that is, installed at both ends or one end of the shaft), therefore, only need to change the axial clearance of one bearing. Generally, the axial gap is aligned with a gasket, and some can also be fixed with screws or thrust rings. For rolling bearings with non-adjustable clearance, the radial clearance has been determined according to the standard at the time of manufacture and cannot be adjusted. After such bearings are installed on the shaft diameter or in the housing bore, the actual radial clearance is called assembly Radial clearance, when assembling, the size of the radial clearance of the assembly can just cause the necessary working radial clearance during operation to ensure the flexible rotation of the bearing. During the process of this type of bearing, due to the thermal elongation of the shaft when the temperature rises, the inner ring of the bearing is relatively displaced, so that the radial clearance of the bearing is reduced, and even the rolling element is caught between the inner and outer rings. If one of the double-bearing rolling bearings (the other bearing is fixed on the shaft and the bearing housing) and the side cover leaves an axial gap, the above phenomenon can be avoided.
 
2. Inadequate lubrication (approximately 50%)
According to investigations, inadequate lubrication is one of the leading causes of premature bearing damage. The main reasons include: not filling lubricants or lubricants in time; oils or lubricants not filling in place; improper selection of oils or lubricants; incorrect lubrication methods, etc.
Suggestion: Choose the correct lubricant or lubricating oil and use the proper lubrication filling method.
 
3. Pollution (about 14%)
Pollution can also lead to premature bearing damage. Pollution means that sand, metal chips, etc. enter the bearing. The main reasons include: opening the bearing packaging prematurely before use, causing pollution; the working environment is not clean during installation, causing pollution; the working environment of the bearing is unclean, and the working medium is contaminated.
Recommendations: It is best not to unpack the bearings before use; keep the installation environment clean during installation, clean the bearings to be used; strengthen the sealing device of the bearings.
 
4. Fatigue (about 34%)
Fatigue damage is a common way of bearing the cost. The common causes of fatigue damage may be long-term overload operation of the bearing, failure to repair in time; improper maintenance; equipment aging, etc.
Suggestion: Choose the appropriate bearing type and replace the fatigue bearing in time.
The above are the most common causes of early damage to bearings. The objectives of early damage to bearings are many. The above are the primary considerations, and sometimes they may be comprehensive reasons. If the bearing selection is correct, the installation method is accurate, and the lubrication method and lubricant are selected correctly, the bearing can usually work for a long time.
Therefore, the early damage of the bearing may be caused by a variety of comprehensive factors. When there is a problem with the taking, we should check it according to the possibility of damage in this article, so as to solve it. Do not blindly investigate all the responsibilities of the supplier.

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