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Correct use and common faults of rolling bearings

by:JNSN     2022-03-13
There are dozens of bearings on automobiles that are rolling bearings, including almost all common bearing types, large and small, and the collision and damage of rolling bearings are also more common. Since rolling bearings are generally installed inside the mechanism, it is inconvenient to inspect visually, and only a rough judgment can be made based on the fault phenomenon, and then disassembled for inspection. The correct use of rolling bearings is a reliable guarantee for reducing bearing failures and extending bearing life, including correct installation and reasonable lubrication. The following introduces the use requirements, common faults and damages of rolling bearings. 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 the auxiliary bearing straight and evenly, do not hit it with a hammer, and it is especially forbidden to hit the bearing directly. When the bearing seat ring and the seat hole are loose, the seat hole should be repaired or the bearing should be replaced. Do not use the method of pockmarking or padding copper on the bearing surface. When the bearing is disassembled, 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 The 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, use grease lubrication. The advantages of grease lubrication are that the sealing structure is simple, the grease is not easy to lose, and is not affected by the temperature. It can be used for a long time after adding grease once. There are two problems to pay attention to when using lubricating grease. One is to choose a suitable grade of lubricating grease according to the requirements of the car manual. For example, nano-grease is not suitable 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, only 1/2-l/3 of the bearing cavity is suitable. Too much is not only useless, but also increases the running resistance of the bearing, causing it to heat up and generate heat. Special attention should be paid to the automobile wheel hub bearing. It is necessary to advocate 'empty hub lubricationraking performance. The advantages of lubricating oil are low friction resistance and heat dissipation, mainly used for bearings with high speed and high working environment temperature. The grade of lubricating oil should be selected according to the requirements of the car manual, and it should be replaced in time after the maintenance cycle of the car. After the old oil is released, the mechanism should be cleaned and then new oil should be added. The oil should be added to the specified marking line, or flush with the oil filler (depending on the specific structure and requirements of the car), no more. 2. Common faults of rolling bearings The fault phenomenon of rolling bearings is generally manifested in two types, one is that the temperature of the bearing installation part is too high, and the other is that there is noise in 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 stroking the mechanism shell with hands, it should be normal that it does not feel hot, otherwise it indicates that the bearing temperature is too high. The reasons for the high bearing temperature are: the quality of the lubricating oil does not meet the requirements or deteriorates, the viscosity of the 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; Large; the bearing cage or rolling element is 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 sound, it indicates that the bearing is faulty. The reasons for the noise of rolling bearings are more complicated, one of which 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 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 moves at 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 lubrication of the bearing, the formation of dry friction, and the crushing of the bearing will produce abnormal noise. After the bearing is worn and loose, the cage is loose and damaged, and abnormal noise will also occur. 3. Damage of the rolling bearing When the rolling bearing is disassembled and inspected, the fault and the cause of the damage of the bearing can be judged according to the damage of the bearing. 1. The metal peels off the raceway surface. The rolling elements of the bearing and the raceway surfaces of the inner and outer rings are subjected to periodic pulsating loads, resulting in cyclically changing contact stress. When the number of stress cycles reaches a certain value, fatigue spalling occurs on the rolling elements or the working surfaces of the inner and outer ring raceways. This fatigue is exacerbated if the bearing is overloaded. In addition, if the bearing is installed incorrectly and the shaft is bent, the phenomenon of raceway spalling will also occur. Fatigue spalling of the bearing raceway will reduce the running accuracy of the shaft, causing vibration and noise in the mechanism. 2. Bearings with burns and burns have tempered color on their raceways and rolling elements. The causes of burns are generally insufficient lubrication, unsatisfactory quality or deterioration of lubricating oil, and excessively tight bearing assembly. 3. Plastic deformation The 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 a large static load or impact load, the local stress of the working surface exceeds the yield limit of the material, which generally occurs on bearings rotating at low speeds.
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