1. Raceway sound
Raceway noise is a smooth and continuous noise generated by the rolling elements rolling in the raceway when the bearing rotates. It only attracts people's attention when the 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 high-quality 6203 bearing raceway sound is 25-27dB. This type of noise is most typical for single row deep groove ball bearings bearing radial loads, which have the following characteristics:
a. Noise and vibration are random;
b. The vibration frequency is above 1kHz;
c. No matter how the speed changes, the main frequency of the noise is almost unchanged and the sound pressure level increases with the increase of the 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 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 noise is the natural vibration of the ring after being loaded. Due to the elastic contact between the ring and the rolling element, a nonlinear vibration system is formed. When the lubrication or machining accuracy is not high, the inherent vibration related to this elastic feature will be excited, and it will become noise when it is transmitted to the air. As we all know, even if the bearing parts are processed with the most advanced manufacturing technology, 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 elements to excite the natural vibration of the vibration system. Although it is unavoidable, high-precision machining of the working surface of the part, correct selection of bearings and precise use of bearings can reduce noise and vibration.
2. Falling body rolling sound
Under normal circumstances, this noise mostly occurs in large bearings that are subjected to radial loads at low speeds. When the bearing operates under radial load, if the bearing has a certain radial clearance between the inner load area and the non-load area, the rolling elements in the non-load area do not contact the inner raceway, but due to the centrifugal force, they may contact the outer raceway. For this reason, at low speed, when the centrifugal force is less than the weight of the rolling body, the rolling body falls and collides with the inner raceway or cage and excites the inherent vibration and noise of the bearing, and has the following characteristics:
a. It is easy to generate when grease is lubricated, but not easy to generate when oil is lubricated. It is more likely to occur when inferior grease is used.
b. Occurs frequently in winter.
c. It is also easy to occur when only radial load is applied and the radial clearance is large.
d. It will also be produced in a certain range and the speed range of bearings of different sizes is also different.
e. It may be a continuous sound or an intermittent sound.
f. The forced vibration often excites the second-order and third-order bending natural vibrations of the outer ring, thereby emitting the noise. The noise can be effectively reduced by adopting the preload method, and the radial clearance of the bearing after installation can be reduced. The selection of a good lubricant can also improve it. Some foreign companies use light rolling elements, such as ceramic rollers or hollow rollers, and other technical measures to prevent this noise.
3. Screaming
It is a fairly violent squeaking sound produced by sliding friction between metals. Although the temperature rise of the bearing is not high at this time, it has little effect on bearing life and grease life, and does not affect rotation, but the unpleasant sound is disturbing, especially Large short cylindrical roller bearings subjected to radial load often have this noise, which is characterized by:
a. It is easy to produce when the radial clearance of the bearing is large.
b. Usually occurs in grease lubrication, but rare in oil lubrication.
c. Decreases as the bearing size increases, and often occurs within a certain speed range.
d. It often appears in winter.
e. Its appearance is irregular and unpredictable, and it is related to the amount of grease filling, performance, and installation and operating conditions. This noise can be prevented by reducing the radial clearance of the bearing and adopting a shallow outer ring raceway structure.
4. Cage sound
This noise is produced by the free vibration of the cage during the rotation of the bearing and its impact with the rolling elements or rings. It can appear in all kinds of bearings, but its sound pressure level is not too high and it is low frequency. Its characteristics are:
a. Stamping cage and plastic cage can be produced.
b. Whether it is thin oil or grease lubrication, it will appear.
c. It is most likely to occur when the outer ring is subjected to a bending moment.
d. 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 ring inevitably exists in the finished bearing, it is very difficult to completely eliminate the noise of the cage, but it can be improved by reducing the assembly error and optimizing the reasonable gap and cage movement. .
Another special sound of the cage is the noise caused by the self-excited vibration of the cage caused by the friction between the cage and the guide surface of other bearing parts. The stamping cage of the deep groove ball bearing is thin, the bending stiffness in the radial and axial planes is low, and the overall stability is poor. When the bearing rotates at high speed, it will generate self-excited vibration due to bending deformation, causing "buzzing" .
When the bearing is under the action of radial load and the performance of the grease is poor, the noise of "click, click" will be heard at the beginning of operation, which is mainly due to the sudden acceleration of the rolling element after leaving the load zone and the contact with the cage. The noise caused by the collision is inevitable but will disappear after a period of operation.
The measures to prevent cage noise are as follows:
a. In order to stabilize the revolution movement of the cage, the ferrule guiding method should be adopted as much as possible and the guide surface should be fully lubricated. The bearing structure under high-speed working conditions should be improved, and the roller-guided L-shaped cage should be changed to a ferrule. Rib-guided Z-shaped cage.
b. When the bearing rotates at high speed, the vibration amplitude of the cage of the bearing with a large pocket clearance is much larger than that of the cage with a small pocket clearance, so the value of the pocket clearance is particularly important.
c. Pay attention to minimize the radial clearance.
d. Improve the manufacturing accuracy of the cage as much as possible, improve the surface quality of the cage, and help reduce the noise generated by the collision or friction between the rolling body 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.
5. The rolling element vibrates
When the bearing operates under the action of radial load, only a few rolling elements inside bear the load. Due to the "spring" support formed by the elastic contact with the ferrule, the rolling elements produce periodic vibration when passing through the radial load line, while The center of the rotating shaft will therefore move vertically up and down or move horizontally, causing noise at the same time. This type of vibration is called rolling element passing 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 it will only cause damage when the amplitude is large. For this reason, it is often reduced by reducing the radial clearance or applying an appropriate preload.
Effect of Operating Temperature on Bearing Life
During the operation of the bearing, its size will change due to the change of the material structure. This transition is affected by temperature, time and stress.
In order to avoid impermissible dimensional changes due to structural changes in the material during work, the bearing material must undergo special heat treatment.
Depending on the type of bearing, standard bearings are made of through-hardened and induction-hardened heat-treated steel, and the recommended maximum operating temperature is between 120 and 200 degrees. The maximum working temperature that can be achieved is directly related to the heat treatment process. If the normal operating temperature of an application is higher than the maximum recommended temperature, a bearing with a higher stability rating should be selected. If the bearing is required to operate continuously at high temperature, the dynamic load capacity of the bearing may need to be adjusted.
