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Correct use and common faults of rolling bearings

by:JNSN     2021-12-26
There are dozens of types of bearings in automobiles that are rolling bearings, including almost all common bearing types. The collision and damage of rolling bearings are also more common. Because rolling bearings are generally installed inside the mechanism, it is inconvenient to inspect visually. You can only make a rough judgment based on the failure phenomenon, and then disassemble and inspect. The correct use of rolling bearings is a reliable guarantee for reducing bearing failures and extending bearing life. Its contents include correct installation and reasonable lubrication. The following describes the requirements for the use of rolling bearings and common failures and damages. 1. Correct use of rolling bearings 1. Disassembly and assembly of bearings. The bearings should be cleaned before installation. When installing, use special tools to press in the auxiliary bearing straight and evenly. Do not hit with a hammer. In particular, it is forbidden to hit directly on the bearing. When the bearing race is loose with the seat hole, the seat hole should be repaired or the bearing should be replaced. Do not use pitting or pad copper on the bearing mating surface. When disassembling the bearing, use a suitable puller to pull the bearing out, and do not hit the bearing with a chisel, hand hammer, etc. 2. Lubrication of bearings Commonly used lubricants for rolling bearings are lubricating oil and grease. When the peripheral speed of the shaft is less than 4-5m/s, or the parts on the car that cannot be lubricated with lubricating oil, grease lubrication is used. The advantages of grease lubrication are that the sealing structure is simple, the grease is not easy to lose, and it is not affected by temperature. It can be used for a longer time with one grease. There are two problems to pay attention to when using lubricating grease. One is to select the appropriate brand of lubricating grease according to the requirements of the car manual. For example, it is not appropriate to use nano-based grease for automotive water pump bearings because of its poor water resistance. The second is to add an appropriate amount of grease to the bearing. Generally, it is only suitable to fill 1/2-l/3 of the bearing cavity. Too much is not only useless, but also increases the running resistance of the bearing, causing it to heat up and heat up. It should be noted that for automobile wheel bearings, 'empty hub lubrication' should be promoted, that is, only an appropriate layer of grease should be applied to the bearing. Otherwise, it will not only waste and poor heat dissipation, but will also cause the grease to be heated and overflow, which may affect the system. Dynamic performance. The advantages of lubricating oil are low frictional resistance and heat dissipation. It is mainly used for bearings with high speed and high working temperature. The brand of lubricating oil should be selected according to the requirements of the car manual, and replaced in time after the car maintenance cycle. After the old oil is discharged, the mechanism should be cleaned before adding new oil. The fuel should be added to the specified line or flush with the fuel filler. (It depends on the specific structure and requirements of the car), no more. 2. Common Faults of Rolling Bearings Generally, there are two types of fault phenomena of rolling bearings. One is that the temperature of the bearing installation part is too high, and the other is that there is noise during the operation of the bearing. 1. The bearing temperature is too high. When the mechanism is running, the part where the bearing is installed is allowed to have a certain temperature. When touching the housing of the mechanism with your hand, it should be normal that you do not feel hot, otherwise it indicates that the bearing temperature is too high. The reasons for the excessively high bearing temperature are: the quality of the lubricant does not meet the requirements or deterioration, the viscosity of the lubricant 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 housing; Large; the bearing cage or rolling elements are broken, etc. 2. Bearing noise Rolling bearings are allowed to have a slight running noise during operation. If the noise is too loud or there is abnormal noise or impact, it indicates that the bearing is faulty. The causes of noise produced by rolling bearings are more complicated. One is the wear of the mating surfaces of the inner and outer rings of the bearing. Due to this kind of wear, the matching relationship between the bearing and the housing, and the bearing and the shaft is destroyed, causing the axis to deviate from the correct position, and abnormal noise occurs when the shaft is moving at a high speed. When the bearing is fatigued, 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, formation of dry friction, and bearing breakage will all produce abnormal noise. After the bearing is worn and loosened, the cage is loose and damaged, and abnormal noise will also be produced. Third, the damage of the rolling bearing When the rolling bearing is disassembled and inspected, the fault and the cause of the damage can be judged according to the damage of the bearing. 1. The metal peeling off the surface of the raceway. The rolling elements of the bearing and the inner and outer ring raceways are subjected to periodic pulsating loads, resulting in cyclical contact stress. When the number of stress cycles reaches a certain value, fatigue spalling occurs on the working surfaces of the rolling elements or inner and outer ring raceways. If the bearing load is too large, this fatigue will be aggravated. In addition, if the bearing is installed incorrectly and the shaft is bent, the raceway may peel off. Fatigue spalling of the bearing raceway will reduce the running accuracy of the shaft and cause vibration and noise to the mechanism. 2. Bearing burns Burned bearings have tempered colors on raceways and rolling elements. The causes of burns are generally insufficient lubrication, the quality of the lubricating oil does not meet the requirements or deterioration, and the bearing assembly is too tight. 3. Uneven dents appear on the contact surface between the raceway and the roller of the plastic deformation bearing, indicating that the bearing is plastically deformed. The reason is that the local stress on the working surface of the bearing exceeds the yield limit of the material under the action of a large static load or impact load. This situation generally occurs on a bearing that rotates at a low speed. 4. Cracks in the bearing races The causes of cracks in the bearing races may be that the bearing is too tightly fitted, the outer part of the bearing or the inner ring is loose, the bearing housing is deformed, and the surface on which the bearing is installed is poorly processed. 5. The reason for cage cracking is insufficient lubrication, broken rolling elements, skewed seat ring and so on. 6. The possible reason that the metal of the cage adheres to the rolling elements is that the rolling elements are stuck in the cage or insufficient lubrication. 7. Severe wear of the raceway of the seat ring may be caused by foreign matter falling into the seat ring, insufficient lubricating oil or improper lubricating oil grade.
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