How to identify bearing failure by hearing the sound?
1. Rolling sound Raceway sound is a smooth and continuous noise caused by the rolling elements rolling in the raceway when the bearing rotates. It only attracts people’s attention when its sound pressure level or tone is extremely high. In fact, the sound energy excited by the raceway sound is limited. For example, under normal circumstances, the raceway sound of a high-quality 6203 bearing is 25 to 27dB. This kind of noise is most typical of single-row deep groove ball bearings that bear radial loads. It has the following characteristics: a. The noise and vibration are random; b. The vibration frequency is above 1kHz; c. No matter how the rotation speed changes, the main frequency of the noise It is almost unchanged but the sound pressure level increases with the increase of rotation speed; d. When the radial clearance increases, the sound pressure level increases sharply; e. The rigidity of the bearing seat increases, the lower the total sound pressure level, even if the rotation speed increases , the total sound pressure level does not increase much; f. The higher the viscosity of the lubricant, the lower the sound pressure level, but for grease lubrication, its viscosity and the shape and size of soap fibers can affect the noise value. The source of raceway sound is caused by the natural vibration of the ring after being loaded. Due to the elastic contact between the ferrule and the rolling element, a nonlinear vibration system is formed. When the lubrication or machining accuracy is not high, the natural vibration related to this elastic characteristic will be excited, and when transmitted to the air, it will become noise. As we all know, even if the bearing parts are processed using the most advanced manufacturing technology in the world, there will always be slight geometric errors of varying degrees on the working surface, which will cause small fluctuations between the raceways and rolling elements to excite the natural vibration of the vibration system. Although it is unavoidable, high-precision machining of the working surface of the parts, correct selection of bearings and precise use of bearings can reduce noise and vibration. 2. The sound of falling and rolling objects Generally, this noise occurs in large bearings that operate at low speeds and are subject to radial loads. When the bearing operates under a radial load, the inner load area and the non-load area of the bearing, if the bearing has a certain radial clearance, the rolling elements in the non-load area do not contact the inner raceway, but they may contact the outer raceway due to the action of centrifugal force. For this reason, at low speeds, when the centrifugal force is less than the self-weight of the rolling elements, the rolling elements will fall and collide with the inner raceway or cage and excite the inherent vibration and noise of the bearing, and have the following characteristics: a. It is easy to occur when grease is lubricated, but not easy to occur when oil is lubricated. It is more likely to occur when inferior grease is used b. Often occurs in winter c. It is also easy to occur when only radial load is applied and the radial clearance is large. d. It also occurs within a certain range and bearings of different sizes have different speed ranges. e. It may be a continuous sound or an intermittent sound. f. This forced vibration often excites the second-order and third-order bending natural vibration of the outer ring, thereby emitting the noise. The noise can be effectively reduced by using the preload method, and the radial clearance of the bearing after installation can be reduced. It can also be improved by selecting a good lubricant. Some foreign companies use technical measures such as lightweight rolling elements, such as ceramic rollers or hollow rollers. to prevent the generation of this noise. 3. scream It is a rather violent squeal produced by the sliding friction between metals. Although the bearing temperature rise is not high at this time, it has little impact on the bearing life and grease life, and does not affect the rotation. However, the unpleasant sound is disturbing, especially Large short cylindrical roller bearings that bear radial loads often have this noise. Its characteristics are: a. It is easy to occur when the bearing radial clearance is large. b. Usually occurs in grease lubrication, but is rarer in oil lubrication. c. Decreases as the bearing size increases, and often occurs within a certain speed range. d. Often appears in winter. e. Its appearance is irregular and unpredictable, and is related to the grease filling amount and performance, as well as installation and operating conditions. This kind of noise can be prevented by reducing the radial clearance of the bearing and using a shallow outer ring raceway structure. 4. Cage noise This noise is caused by the free vibration of the cage during bearing rotation and its impact with the rolling elements or rings. It may appear in all types of bearings, but its sound pressure level is not too high and it is low frequency. Its characteristics are: a. Both stamping cages and plastic cages can be produced. b. It will occur regardless of whether it is thin oil or grease lubrication. c. It is most likely to occur when the outer ring is subjected to bending moment. d. It is easy to occur when the radial clearance is large. Since the cage pocket gap and the gap between the cage and the ring inevitably exist in the finished bearing, it is very difficult to completely eliminate the cage sound, but it can be improved by reducing assembly errors and optimizing reasonable gaps and cage movement. . Another special cage sound is the noise caused by the self-excited vibration of the cage caused by the friction between the cage and the guide surfaces of other bearing parts. The stamped cage of deep groove ball bearings is thin, has low bending stiffness in the radial and axial planes, and has poor overall stability. When the bearing rotates at high speed, it will produce self-excited vibration due to bending deformation, causing a “buzzing sound” . When the bearing is under radial load and the grease performance is poor, a “clicking, clicking” noise will be heard in the early stages of operation. This is mainly due to the sudden acceleration of the rolling elements after leaving the load area and contacting the cage. The noise caused by the collision is inevitable but will disappear after a period of operation. Measures to prevent cage noise are as follows: a. In order to stabilize the revolution motion of the cage, the ring guide method should be used as much as possible and attention should be paid to sufficient lubrication of the guide surface. The structure of the tapered roller bearing under high-speed working conditions should be improved, and the roller-guided L-shaped cage should be modified. Z-shaped cage guided by the ferrule ribs. b. When the bearing rotates at high speed, the vibration amplitude of the cage of a bearing with a large pocket clearance is much greater than the vibration amplitude of a cage with a small pocket clearance, so the value of the pocket clearance is particularly important. c. Pay attention to reducing the radial clearance as much as possible. d. Try to improve the manufacturing accuracy of the retaining price and improve the surface quality of the cage, which will help reduce the noise caused by collision or friction between the rolling elements and the cage. e. Actively adopt advanced cleaning technology to effectively and thoroughly clean spare parts and assembled products to improve the cleanliness of bearings.
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