Noise of Bearing
Rolling sound
Raceway noise is a kind of steady and continuous noise which is excited by rolling element rolling in raceway when bearing rotates. It can only be noticed when its sound pressure level or tone is very high. In fact, the acoustic energy excited by the raceway sound is limited. Under normal conditions, the raceway sound of 6203 bearing is 25 ~ 27db. The single row deep groove ball bearing with radial load is the most typical one.
The sound source of raceway is the natural vibration of inner and outer rings after loading. Due to the elastic contact between the inner and outer rings and the rolling element, a nonlinear vibration system is formed. When the lubrication or machining accuracy is not high, the natural vibration related to the elastic characteristics will be excited, and it will become noise when transmitted to the air. As we all know, even if the bearing parts are processed by the most advanced manufacturing technology, there will always be small geometric errors in different degrees on the working surface of the bearing parts, which will cause small fluctuations between the raceway and the rolling body to excite the natural vibration of the vibration system. Although it is inevitable, high-precision machining of the working surface of the parts can be adopted, the correct selection of bearings and the accurate use of bearings can reduce noise and reduce vibration.
characteristic:
1) Noise and vibration are random;
2) The vibration frequency is above 1kHz;
3) No matter how the rotating speed changes, the main frequency of noise almost remains unchanged, while the sound pressure level increases with the increase of rotating speed;
4) When the radial clearance increases, the sound pressure level increases sharply;
5) The higher the stiffness of the bearing pedestal, the lower the total sound pressure level (SPL);
6) The higher the viscosity of lubricant is, the lower the sound pressure level is. However, for grease lubrication, the viscosity and the shape of soap fiber can affect the noise level.
Falling body rolling sound
The noise usually occurs in large bearings with low speed and radial load. When the bearing operates under the radial load, it is divided into the inner load area and the non load area. If the bearing has a certain radial clearance, the roller in the non load area does not contact with the inner raceway, but may contact with the outer ring due to the centrifugal force. Therefore, at low speed, when the centrifugal force is less than the self weight of the rolling element, the rolling body will fall down and collide with the inner raceway or cage, and the natural vibration and noise of the bearing will be excited.
characteristic:
1) It is easy to produce when lubricated by grease, but not by oil lubrication. It is easier to produce when using inferior grease;
2) It often occurs in winter;
3) When only radial load is applied and the radial clearance is large, it is easy to produce;
4) It also occurs in a certain range, and the speed range of bearings with different sizes is also different;
5) It may be continuous or intermittent;
6) The forced vibration often excites the second-order and third-order bending natural vibration of the outer ring, thus generating the noise. The noise can be effectively reduced by using preloading method, the radial clearance of bearing after installation can be reduced, and the selection of good lubricants can also be improved. Some foreign enterprises adopt light rolling elements, such as ceramic rollers or hollow rollers, to prevent the noise.
Squealing
It comes from the screeching sound generated by sliding friction between metals. Although the temperature rise of bearing is not high at this time, it has little effect on bearing life and grease life, and does not affect rotation, but the sound is sharp and disturbing. This noise is often found in large cylindrical roller bearings with radial load. This kind of noise can be prevented by reducing bearing radial clearance and adopting shallow outer ring raceway structure.
characteristic:
1) When the bearing radial clearance is large, it is easy to produce;
2) It usually occurs in grease lubrication, but oil lubrication is rare;
3) It decreases with the increase of bearing size and often appears in a certain speed range;
4) It often appears in winter;
5) Its appearance is irregular and unpredictable, and is related to the amount and performance of grease filling, installation and operation conditions.
Cage sound
In the process of bearing rotation, the free vibration of cage and its impact with rolling element or ring will produce this noise. It may appear in all kinds of bearings, but its sound pressure level is not too high and its frequency is low.
It is difficult to eliminate cage noise completely because cage pocket clearance and cage ring clearance are inevitable in bearing products. However, it can be improved by reducing assembly error and optimizing reasonable clearance and cage movement.
Another special noise of cage is the noise caused by self-excited vibration of cage caused by friction between cage and guide surface of other bearing parts. The stamping cage of deep groove ball bearing is thin, the bending stiffness in radial and axial plane is low, and the overall stability is poor. When the bearing rotates at high speed, it will produce self-excited vibration due to bending deformation and cause “beep”.
When the bearing is under the radial load and the grease performance is poor, the noise of “click, click” will be heard at the initial stage of operation. This is mainly due to the noise generated by the roller suddenly accelerating and colliding with the cage after leaving the load area. This kind of impact noise can not be avoided, but will disappear after running for a period of time.
characteristic:
1) Stamping cage and plastic cage can be produced;
2) Both thin oil and grease lubrication will appear;
3) When the outer ring bears the bending moment, it is easy to occur;
4) It is easy to appear when the radial clearance is large.
Measures to prevent cage noise are as follows:
1) In order to make the cage stable in revolution, we should try our best to adopt the guide way of ring and pay attention to the full lubrication of the guide surface. The structure of tapered roller bearing under high speed condition is improved. The L-type cage guided by roller is replaced by Z-type cage guided by ring rib;
2) Bearing with large pocket clearance when bearing rotates at high speed
