Rolling bearings have their own unique sound depending on size and speed of operation. If you can clearly understand the reasons for the following sounds, it is very helpful to judge the bearing damage in advance.
First, the rolling channel
The rolling sound is caused by the rolling of the rolling elements in the raceway when the bearing rotates to excite a smooth and continuous noise, which only attracts people's attention when its sound pressure level or tone is extremely large. In fact, the sound energy stimulated by the rolling track is limited. For example, under normal conditions, the quality of the 6203 bearing raceway is 25 to 27 dB. This type of noise is the most typical of single row deep groove ball bearings that can withstand radial loads. It has the following characteristics:
· Noise and vibration are random;
· The vibration frequency is above 1kHz;
· Regardless of the change in the rotational speed, the main frequency of the noise is almost constant and the sound pressure level increases as the rotational speed increases;
· When the radial clearance increases, the sound pressure level increases sharply;
· The rigidity of the bearing housing increases, and the lower the total sound pressure level, the total sound pressure level increases little even if the rotation speed increases;
· The higher the viscosity of the lubricant, the lower the sound pressure level, but for grease lubrication, the viscosity and shape of the soap fiber can affect the noise value.
The source of the rolling sound is caused by the natural vibration of the ferrule after the load. Due to the elastic contact of the ferrule and the rolling body, a nonlinear vibration system is formed. When the lubrication or machining accuracy is not high, the natural vibration associated with this elastic characteristic is excited, and when it is transmitted to the air, it becomes noise.
It is well known that even with the most advanced manufacturing techniques used to process bearing parts, there are always small geometric errors in the working surface, which causes small fluctuations between the raceway and the rolling elements to excite the natural vibration of the vibration system. Although it is unavoidable, it is possible to use high-precision machining of the working surface of the part, the correct selection of the bearing and the precise use of the bearing to reduce noise and vibration.
Second, the body rolling sound
This noise is generally found in large bearings that are subjected to low radial loads and subjected to radial loads. When the bearing is running under radial load, the bearing load zone and the non-load zone are in the bearing. If the bearing has a certain radial clearance, the rolling element in the non-load zone does not contact the inner raceway, but it may be external due to the centrifugal force. Circle contact, for this reason, at low speed, when the centrifugal force is less than the weight of the rolling element, the rolling element will fall and collide with the inner race or cage and stimulate the natural vibration and noise of the bearing, and has the following characteristics:
· It is easy to produce during grease lubrication and is not easy to produce when oil is lubricated. It is more likely to be produced when using inferior grease.
· Winter often happens.
· It is easy to produce when only radial load is applied and the radial clearance is large.
· Bearings that are also produced in a certain range and have different sizes have different speed ranges.
· It may be continuous or intermittent.
· The forced vibration often excites the second-order and third-order bending natural vibrations of the outer ring to emit the noise.
By using the preload method, the noise can be effectively reduced, and the radial clearance of the bearing after installation can be reduced. The use of a good lubricant can also be improved. Some foreign companies use light rolling elements such as ceramic rollers or hollow rollers. To prevent this noise from being generated.
Third, the sound
It is a squeaking of the metal between the sliding friction, although the temperature rise of the bearing is not high, it has little effect on the bearing life and grease life, and does not affect the rotation, but the unpleasant sound is disturbing, especially Large short cylindrical roller bearings with radial loads often have this noise and are characterized by:
· The bearing radial clearance is easy to produce.
· Usually occurs in grease lubrication, oil lubrication is rare.
· Decreases as the bearing size increases, and often occurs within a certain speed range.
· It often appears in winter.
· Its appearance is irregular, unpredictable, and related to the amount of grease and performance, installation and operation conditions.
This noise can be prevented by reducing the radial play of the bearing and using a shallow outer ring raceway structure.
Fourth, the cage sound
This noise is generated by the free vibration of the cage during the rotation of the bearing and its impact with the rolling elements or ferrules. It can occur in all types of bearings, but its sound pressure level is not too high and is low frequency. Its characteristics are:
· Both stamped cages and plastic cages can be produced.
· Both thin oil and grease lubrication will appear.
· It is most likely to occur when the outer ring is subjected to bending moments.
· It is easy to appear when the radial clearance is large.
Since the gap between the cage pocket and the gap between the cage and the ferrule are inevitable in the finished bearing, it is very difficult to completely eliminate the cage sound, but it can be improved by reducing assembly errors, preferably reasonable clearance and cage turbulence. .
Another type of cage special sound is the click of the cage due to the friction between the cage and the guiding surfaces of other bearing components. The deep groove ball bearing has a thin stamping cage, low bending rigidity in the radial and axial planes, and poor overall stability. When the bearing rotates at high speed, it will generate self-excited vibration due to bending deformation, causing "beep". .
When the bearing is under radial load and the grease performance is poor, the noise of “咔嚓, 咔嚓” will be heard at the beginning of the operation. This is mainly because the rolling element suddenly accelerates and stays with the cage after leaving the load zone. The noise emitted by the collision is inevitable but will disappear after a period of operation.
The measures to prevent cage noise are as follows:
· In order to make the cage revolving motion stable, the ferrule guiding method should be used as much as possible and the guiding surface should be fully lubricated. The tapered roller bearing structure under high speed conditions should be improved, and the roller-guided L-shaped cage should be changed to Z-shaped cage guided by ferrule ribs.
· When the bearing rotates at high speed, the bearing vibration amplitude of the bearing with large pocket clearance is much larger than the vibration amplitude of the cage with small pocket clearance. Therefore, the value of the pocket clearance is particularly important.
· Be careful to minimize radial play.
· Try to improve the manufacturing accuracy of the maintenance price and improve the surface quality of the cage, which is beneficial to reduce the noise generated by the collision or friction between the rolling element and the cage.
· Actively adopt advanced cleaning technology to effectively and thoroughly clean the spare parts and the finished products to improve the cleanliness of the bearings.
Five, the rolling body through the vibration
When the bearing is operated under radial load, only a few rolling elements are subjected to the load inside, and the "spring" support formed by the elastic contact with the ferrule causes the rolling element to periodically vibrate through the radial load line. The center of the shaft therefore moves up and down vertically or horizontally, causing noise. This type of vibration is called a rolling element that vibrates through vibration, especially at low speeds.
The amplitude is related to the bearing type, radial load, radial clearance and the number of rolling elements. Usually the amplitude is small, and if the amplitude is large, a hazard is formed, which is often reduced by reducing the radial play or applying an appropriate preload.