Effect of Bearing Structure on Vibration and Noise
1. Raceway sound
The raceway sound is caused by the rolling of the rolling element in the raceway when the bearing rotates, which generates a steady and continuous noise. Only when the sound pressure level or tone of the raceway is very high can it attract people's attention. Actually, the sound energy generated by the raceway sound is limited. For example, under normal conditions, the raceway sound of 6203 bearing with high quality is 25-27 dB. This kind of noise is typical of single row deep groove ball bearings under radial load. It has the following characteristics:
A. Noise and vibration are random.
B. Vibration frequency is above 1 kHz.
C. No matter how the rotational speed changes, the main frequency of noise is almost unchanged while the sound pressure level increases with the increase of rotational speed.
D. When the radial clearance increases, the sound pressure level increases sharply.
E. When the rigidity of bearing seat increases, the total sound pressure level decreases, and even if the speed increases, the total sound pressure level increases slightly.
F. The higher the viscosity of lubricant, the lower the sound pressure level. But for grease lubrication, the viscosity and the shape and size of soap fibers can affect the noise value.
Raceway sound is generated by the inherent vibration of the raceway ring after being loaded. The elastic contact between the ring and the rolling body constitutes a non-linear vibration system. When the lubrication or processing accuracy is not high, the inherent vibration associated with this elastic characteristic will be stimulated, and the transmission into the air will become noise. It is well known that even if the most advanced manufacturing technology is used to process bearing parts, there will always be small geometric errors of varying degrees on the working surface, which will cause small fluctuations between the raceway and the rolling body to excite the inherent vibration of the vibration system. Although it is unavoidable, it can be used to process the working surface of parts with high precision, to select bearings correctly and to use bearings accurately to reduce noise and vibration.
2. Rolling sound of falling body
In general, the noise mostly occurs in large bearings with low rotating speed and radial load. When the bearing runs under the radial load, the inner load area and the non-load area of the bearing do not contact the inner raceway if the bearing has a certain radial clearance, but the rolling body in the non-load area may contact the outer raceway because of the centrifugal force. Therefore, at low speed, when the centrifugal force is less than the self-weight of the rolling body, the rolling body will fall and fall. Collision with inner raceway or cage and excitation of inherent vibration and noise of bearing have the following characteristics:
A. Grease lubrication is easy to produce, oil lubrication is not easy to produce. It is easier to produce when using inferior grease.
B. Winter often occurs.
C. When the radial load is applied only and the radial clearance is large, it is easy to produce.
D. Bearings of different sizes can also be produced in a certain range and their speed ranges are different.
E. It may be continuous or intermittent.
F. The forced vibration often excites the second-order and third-order bending natural vibration of the outer ring, thus generating the noise. By using preloading method, the noise can be effectively reduced, the radial clearance of the bearing after installation can be reduced, and the selection of good lubricants can also be improved. Some foreign enterprises adopt technical measures such as ceramic rollers or hollow rollers to prevent the noise.
It is a very violent scream caused by sliding friction between metals. Although the temperature rise of bearings is not high at this time, it has little effect on the life of bearings and grease, and does not affect rotation, but the unpleasant sound is disturbing, especially for large short cylindrical roller bearings subjected to radial loads. Its characteristics are as follows:
A. Bearings with large radial clearance are easy to produce.
B. Usually occurs in grease lubrication, but oil lubrication is rare.
C. It decreases with the increase of bearing size and often occurs in a certain speed range.
D. Winter often occurs.
E. Its appearance is irregular and unpredictable, and is related to the amount and performance of filling, installation and operation conditions. This kind of noise can be prevented by reducing the radial clearance of bearing and adopting shallow raceway structure of outer ring.
4. Cage sound
This noise is generated by the free vibration of the cage and its impact with the rolling element or ring during the rotation of the bearing. It may occur in all kinds of bearings, but its sound pressure level is not too high and its frequency is low. Its characteristics are:
A. Stamping cage and plastic cage can be produced.
B. Both light oil and grease lubrication will occur.
C. When the outer ring is subjected to bending moment, it is most likely to occur.
D. It is easy to appear when the radial clearance is large.
It is very difficult to eliminate cage noise completely because of the inevitable existence of cage pocket clearance and CAGE-RING clearance in finished bearing products. However, it can be improved by reducing assembly error, optimizing reasonable clearance and cage movement.
Another kind of special sound of cage is the noise caused by self-excited vibration of cage caused by friction between cage and other guide surfaces of bearing parts. The stamping cage of deep groove ball bearings is thin, the bending stiffness in the radial and axial planes is low, and the overall stability is poor. When the bearings rotate at high speed, they will produce self-excited vibration due to bending deformation, causing "buzzing sound".
When the bearing is subjected to radial load and the grease performance is poor, the noise of "click and click" will be heard in the initial stage of operation, which is mainly caused by the sudden acceleration of the rolling element after it leaves the load area and the collision between the rolling element and the cage. This kind of impact noise is inevitable but will disappear after a period of operation. Loss.
Measures to prevent cage noise are as follows:
A. In order to make the cage's rotation stable, we should try our best to adopt the ring guiding mode and pay attention to the full lubrication of the guide surface, improve the bearing structure under high speed conditions, change the L-type cage guided by rollers into Z-type cage guided by ring edge.
B. When the bearing rotates at high speed, the vibration amplitude of the cage of the bearing with large pocket clearance is much larger than that between pockets.