There are dozens of rolling bearings in cars, including almost all common bearing types, large and small. The crash and damage of rolling bearings are also common. Since rolling bearings are generally installed inside the mechanism, it is inconvenient to conduct visual inspection. Only a brief judgment can be made according to the fault phenomenon, and then disassembled for inspection.
The correct use of rolling bearing is a reliable guarantee to reduce bearing failure and prolong bearing life, including correct installation and reasonable lubrication.
The following describes the use requirements, common faults and damages of rolling bearings.
The bearing shall be cleaned before installation. During installation, the auxiliary bearing shall be pressed straight and evenly with special tools. Do not knock with a hand hammer. In particular, it is forbidden to knock directly on the bearing.
When the fit between the bearing race and the seat hole is loose, the seat hole shall be repaired or the bearing shall be replaced. Do not reluctantly use the method of pitting or padding copper skin on the bearing mating surface. When disassembling the bearing, use a suitable puller to pull out the bearing, and do not knock the bearing with a chisel, hammer, etc.
There are two kinds of lubricants commonly used in rolling bearings: lubricating oil and grease. When the circumferential speed of the shaft is less than 4-5m / s, or the parts on the vehicle that cannot be lubricated with lubricating oil, grease shall be used for lubrication. The advantage of grease lubrication is that the sealing structure is simple, the grease is not easy to lose, and it is not affected by temperature. Adding grease once can be used for a long time.
Two problems should be paid attention to when using grease. One is to select the appropriate brand of grease according to the requirements of the automobile manual. For example, nano base grease should not be selected for automobile water pump bearing because of its poor water resistance.
Second, the amount of lubricating grease added to the bearing should be appropriate. Generally, it is appropriate to fill only 1 / 2-L / 3 of the bearing cavity. Too much is not only useless, but also increases the running resistance of the bearing and heats it up.
Special attention should be paid to the automobile hub bearing. It is necessary to advocate “empty hub lubrication”, that is, only apply an appropriate layer of grease on the bearing. Otherwise, it will not only waste and poor heat dissipation, but also cause the grease to overflow due to heating, which may affect the braking performance.
The advantages of lubricating oil lubrication are low friction resistance and heat dissipation. It is mainly used for bearings with high speed and high working environment temperature. The brand of lubricating oil shall be selected according to the requirements of the vehicle manual, and shall be replaced in time after the vehicle maintenance cycle.
After discharging the old oil, the mechanism shall be cleaned before adding new oil. The oil shall be added to the specified marking line or flush with the oil filler (depending on the specific structure and requirements of the vehicle), and no more oil shall be added.
There are generally two kinds of fault phenomena of rolling bearing: one is that the temperature of the bearing installation part is too high, and the other is that there is noise during bearing operation.
During the operation of the mechanism, the part where the bearing is installed is allowed to have a certain temperature. When touching the mechanism shell by hand, it should be normal not to feel hot. Otherwise, it indicates that the bearing temperature is too high.
The reasons for high bearing temperature are: the quality of lubricating oil does not meet the requirements or deteriorates, and the viscosity of lubricating oil is too high; The mechanism assembly is too tight (insufficient clearance); The bearing assembly is too tight; The bearing race rotates on the shaft or in the shell; Excessive load; Broken bearing cage or rolling element, etc.
The rolling bearing is allowed to make slight running noise during operation. If the noise is too loud or there is abnormal noise or impact sound, it indicates that the bearing is faulty.
The causes of rolling bearing noise are complex. One is the wear of the mating surfaces of the inner and outer rings of the bearing. Due to this wear, the matching relationship between the bearing and the shell, the bearing and the shaft is damaged, resulting in the axis deviation from the correct position and abnormal noise when the shaft moves at high speed.
When the bearing is tired, the metal on its surface will peel off, which will also increase the radial clearance of the bearing and produce abnormal noise. In addition, insufficient bearing lubrication, dry friction and bearing breakage will produce abnormal sound. After the bearing is worn and loose, the cage is loose and damaged, which will also produce abnormal noise.
During the disassembly and inspection of rolling bearing, the fault and damage cause of bearing can be judged according to the damage of bearing.
The bearing rolling element and the inner and outer ring raceways are subjected to periodic fluctuating load, resulting in periodic contact stress. When the number of stress cycles reaches a certain value, fatigue spalling will occur on the working surface of rolling element or inner and outer race raceway. If the load of the bearing is too large, this fatigue will be exacerbated. In addition, improper bearing installation and shaft bending will also produce raceway peeling.
The fatigue spalling of bearing raceway will reduce the running accuracy of shaft and cause vibration and noise of mechanism.
There is a return fire color on the raceway and rolling element of the burned bearing. The causes of burns are generally insufficient lubrication, unqualified or deteriorated lubricating oil quality, and too tight bearing assembly.
Uneven pits appear on the contact surface between the raceway and the roller of the bearing, indicating that the bearing has plastic deformation. The reason is that under the action of large static load or impact load, the local stress on the working surface exceeds the yield limit of the material, which usually occurs on the bearing rotating at low speed.
The causes of bearing race cracks may be too tight bearing fit, loose bearing or inner ring, deformation of bearing containment parts, poor surface processing of installed bearing, etc.
The reasons are insufficient lubrication, broken rolling element, seat ring skew, etc.
The possible cause is that the rolling element is stuck in the cage or the lubrication is insufficient.
It may be that foreign matters fall into the seat ring, insufficient lubricating oil or inappropriate lubricating oil brand.