Listen to the sound to determine the bearing abnormal
- 2020/3/16 16:49:27
Listen to the sound to determine the bearing abnormal
According to the size and running speed, the rolling bearing has its own unique sound. If the cause of the following sounds can be clearly identified, it will be of great help to determine the bearing damage in advance.
Raceway sound
The rolling track sound is a kind of smooth and continuous noise that is caused by the rolling elements rolling in the rolling track when the bearing rotates. It only attracts people's attention when its sound pressure level or tone is extremely large. 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 of single-row deep groove ball bearings that support radial loads. It has the following characteristics:
1) Noise and vibration are random;
2) The vibration frequency is above 1kHz;
3) No matter how the speed changes, the main frequency of the noise is almost unchanged and the sound pressure level increases as the speed increases;
4) When the radial clearance increases, the sound pressure level increases sharply;
5) The rigidity of the bearing seat increases, and the lower the total sound pressure level, even if the speed increases, the total sound pressure level does not increase much;
6) The higher the viscosity of the lubricant, the lower the sound pressure level, but for grease lubrication, its viscosity and the shape of the soap fiber can affect the noise value. The origin of the raceway sound is caused by the natural vibration of the ferrule after receiving the load. The non-linear vibration system is formed by the elastic contact between the ferrule and the rolling element. When the lubrication or machining accuracy is not high, the natural vibration related to this elastic characteristic is excited, and it is transmitted to the air to become noise.
As we all know, even if the bearing parts are processed using the most advanced manufacturing technology, there will always be slight geometric errors of varying degrees on the working surface, so that small fluctuations between the raceway and rolling elements will excite the inherent vibration of the vibration system. Although it is unavoidable, it is possible to adopt high-precision machining of the working surface of the part, the correct selection of bearings and the accurate use of bearings to reduce noise and vibration.
Falling rolling sound
In general, this noise mostly occurs in large bearings at low speeds and bearing radial loads. When the bearing is running under radial load, the bearing's internal load area and non-load area, if the bearing has a certain radial clearance, the rolling body in the non-load area does not contact the inner raceway, but due to the effect of centrifugal force, For this reason, at low speeds, when the centrifugal force is less than the weight of the rolling element, the rolling element will fall and collide with the inner raceway or cage and excite the inherent vibration and noise of the bearing. It has the following characteristics:
1) It is easy to produce when grease lubricated, but it is not easy to produce when oil lubricated. It is easier to produce when using inferior grease.
2) Winter often occurs.
3) It is also easy to occur when only radial load is applied and the radial clearance is large.
4) The speed range of bearings with different sizes will also be generated in a certain range.
5) It may be continuous or intermittent.
6) The forced vibration often excites the second- and third-order bending natural vibrations of the outer ring, thereby emitting the noise. This noise can be effectively reduced by using the preload method, and the radial working clearance of the bearing after installation can be reduced. It can also be improved by using a good lubricant. Some foreign companies use light rolling elements such as ceramic rollers or hollow rollers To prevent this kind of noise.
Squeal
It is a very screaming noise caused 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. This noise is often found in large short cylindrical roller bearings that are subjected to radial loads
Its characteristics are:
1) It is easy to produce when the bearing radial clearance is large.
2) It usually occurs in grease lubrication, but oil lubrication is rare.
3) It decreases as the size of the bearing increases, and it often appears in a certain speed range.
4) It often appears in winter. Its appearance is irregular and unpredictable, and it is related to the amount of grease filling and performance, 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.
Cage sound
This noise is emitted by the free vibration of the cage during the rotation of the bearing and when it collides with the rolling element or the ferrule. It may appear in all types of bearings, but its sound pressure level is not too high and is low frequency.
Its characteristics are:
1) Both stamped cages and plastic cages can be produced.
2) Either thin oil or grease lubrication will occur.
3) It is most likely to occur when the outer ring is subjected to a bending moment.
4) It is easy to appear when the radial clearance is large.
Because the cage pocket gap and the cage and ferrule gap inevitably exist in the finished bearing product, it is very difficult to completely eliminate the cage sound, but it can be improved by reducing assembly errors, and optimizing reasonable clearance 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. Deep groove ball bearings have thin stamping cages, 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 "buzzing" .
When the bearing is under radial load and the grease performance is poor, "clicking and clicking" noise will be heard at the beginning of the operation. This is mainly because the rolling body suddenly accelerates after it leaves the load area and is in contact with the cage. The noise produced 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 of the cage, the ferrule guidance method should be adopted as far as possible, and the guide surface should be fully lubricated. The tapered roller bearing structure under high-speed conditions should be improved. The roller-guided L-type cage should be modified. Z-type cage guide for ferrule flanges.
b. When the bearing rotates at a high speed, the vibration amplitude of the cage of a bearing with a large pocket gap is much larger than the vibration amplitude of a cage with a small pocket gap, so the value of the pocket gap is particularly important. Care should be taken to minimize radial clearance. Try to improve the manufacturing accuracy of the cage and improve the surface quality of the cage, which will help reduce the noise caused by the collision or friction between the rolling elements and the cage.
c. Actively adopt advanced cleaning technology to effectively and thoroughly clean parts and assembled products to improve the cleanliness of bearings.
d. When the bearing is operating under radial load, only a few rolling elements bear the load inside. Due to the "spring" support formed by the elastic contact with the ferrule, the rolling element generates periodic vibration through the radial load line The center of the shaft will therefore move vertically or horizontally, and cause noise.
This type of vibration is called rolling body vibration, especially when it is running at low speed. The amplitude is related to the bearing type, radial load, radial clearance and number of rolling elements. Usually, the amplitude is small. If the amplitude is large, a hazard will be formed. To this end, it is often reduced by reducing the radial clearance or applying an appropriate preload.
What you feel is not necessarily understandable, only what you understand can be felt more deeply. The use of "five senses" for point inspections is an activity that combines the existing "five senses" function with existing knowledge and experience on the basis of fully mobilizing the "five senses" of the human body. The key is to choose the appropriate part of the device, and to gain more experience and accumulate knowledge and experience in order to compare the slight changes in the status and characteristics of the device during normal operation.