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Nachi bearing noise judgment and control

wallpapers Low Carbon 2021-05-11
Nachi bearing noise judgment and control
 
(1) Fault phenomenon:
 
The noise of Nachi bearing of crankshaft is heavier and stuffy than that of connecting rod Nachi bearing, and it becomes bigger with the increase of engine speed. The transition noise from medium speed to high speed is the most obvious, and it intensifies with the increase of engine load.
 
(2) Troubleshooting:
 
When the engine speed is increased and the throttle is increased, the noise increases with the increase of the speed. When the speed is changed, the sound of the sound is led by a screwdriver at the bearing part of Nachi. The noise is larger, and there is a heavy "whistle at the mouth" noise, and the engine still vibrates.
 
The engine speed is changed repeatedly, and the spark plug of two adjacent cylinders will be broken simultaneously. If the noise is obviously reduced, it indicates that the Nachi bearing is loose.
 
When the Nachi bearing clearance is too large, checking the lubricant pressure will decrease significantly.
 
When the engine is started, the oil film a degree between Nachi bearing and shaft neck is larger, so the noise is smaller. With the increase of temperature, the oil film turnover decreases and the noise will increase.
 
Once the crankshaft Nachi bearing is confirmed to ring, it is not allowed to continue driving, and it should be repaired immediately, otherwise there will be a big fault.
 
Bearings can be divided into two categories: sliding bearing and rolling bearing. Sliding pumping movement is stable, vibration is small, and voice is low. It is designed by itself according to specific structure. The common confusing bearing may be in the start-up, not enough oil to form a thousand friction detection, produce a large voice and make the bearing scratch, so, in the general machine tool important transmission shaft do not need to clear the bearing. The following mainly introduces the voice control of rolling bearing:
 
Rolling bearing is usually composed of two inner rings, a rolling body and a retainer. The control methods of rolling bearing voice and voice can be summarized as follows:
 
(1) The voice and control caused by the vibration of the structure. There is a rolling body in the bearing. It is rolled on the raceway between the inner and outer ferrules. The inner and outer rings are deformed after being stressed. In the high speed rotation, the internal and external deformation may produce radial and axial vibration, among which the axial vibration is strong, which is called elastic vibration. When the rolling body passes through the force area, the elastic deformation of the rolling body aggravates the elastic vibration of the inner and outer rings, which adds the vibration of the bearing axial and radial bearing pedestal. When the distance between the inner and outer rings is large, the vibration resonates with the bending or torsional vibration of the transmission shaft and gear, or other rotating bodies; It radiates a strong sound absorption. The effective method of the noise caused by the vibration of the control side is to lift the stiffness of the pump and reduce the deformation, that is, to adjust the direction and axial aging, and increase the preload load, the vibration and noise of the bearing can be reduced.
 
(2) The noise of bearing is related to its structure. Different types of bearings, whose voice is different, are generally classified according to their rolling shape and bearing form. The rolling body of ball bearing is spherical. The point contact between ball bearing and rolling pass is: roller bearing rolling body is cylindrical in the picture. The rolling body and raceway are linear contact two rolling bodies, in addition to spherical and eye column shape. There are also inverted or circular simple shapes. In the bearing form, the bearing can be divided into I-core bearing and centripetal thrust bearing, the former can only bear radial force, The latter can bear both radial force and internal axial force. The rolling body is the main component of rolling friction in rolling bearing. The rolling body has different shape and different relative motion condition with the inside and outside, which causes different types of bearings to have different lifting sound. A unit has tested the f7520, 1) 7518 round roller bearing, 220, 218 centripetal ball bearing and 4620, 46218 centripetal thrust ball bearing, and Bian axle Bu installed in C6150 lathe as the front and rear bearings, and conducted experiments at 1250r/min speed. It is found that the throat of I-1 and thrust ball is 9dB (a) lower than that of cone bearing. Therefore, considering the square meat to reduce the bearing noise, the ball bearing is better than other kinds of bearings.
 
(3) The influence of bearing accuracy and geometry error on the voice. The results show that the rolling body, inner and outer ring of bearing have higher precision and the bearing voice will be reduced. The data listed in table 12-1 are combined with "7520 and 9751. single row roller bearings, which are combined according to different precision of inner and outer rings and rollers, and installed in the condition of bearing the whole shaft of the machine tool () 6150, and the spindle speed is 1250r / min.
 
It can be seen from the table that the bearing noise can be reduced by 7-10db (a) as long as the roller tip degree is increased. Roller precision is the main factor affecting the bearing sound.
 
The smaller the diameter difference of the rolling body, the more uniform the contact between the roller and the inner and outer raceway, the better the contact stiffness of the bearing.
 
Besides controlling the geometry and fine skin of rolling rest, the waviness of inner and outer rings should be controlled to improve the surface roughness. The rolling failure surface shall be strictly controlled for breaking and stabbing. In this way, the bearing noise and vibration factors can be reduced comprehensively,
 
(4) The influence of bearing assembly on voice. The assembly quality of bearing is 1t, tit and vertical connection affect the noise of bearing. When assembling bearings, the alignment is guaranteed first, and the geometric accuracy of the bearing will be damaged by the misalignment. The vibration of the cherry leaves the rolling path; Secondly, it is necessary to have proper assembly clearance and pre tightening force. At the same time, the bearing and bearing pedestal should be removed from resonance. Resonance will produce a loud voice.
 
Figure 12-13 shows the resonance between the bearing and the bearing seat. Because the motor has thin joint parts at both ends, the axial bending stiffness of bearing pedestal is smaller because the cover is free of reinforcement. When the motor is running, abnormal sound is generated in the right end. According to the continent test and the potential searching analysis, it is found that the natural child rate of the axial vibration of the outer ring of the ball bearing is 2700h, and the inherent pre rate of the axial bending vibration of the motor bearing seat is 263ohc, because the inherent level ratio of the two is close. The above-mentioned abnormal sound is the result of resonance between the axial vibration of the outer ring and the bending vibration of the bearing seat, The effective method of eliminating the resonance of the tip is to change the wall thickness and shape of the bearing bearing. The preload force and axial clearance are applied to the bearing with two - shaped spring zannes. The bearing installation shall be carried out according to the correct method mentioned above. Before the installation, the bearing shall be completely removed from impurities and ash, and then it clean bath oil shall be added to clean the bearing. The sound of low voice of the array shall be better than that of the sub ton.
 
In order to reduce the vibration of bearing passing through the box, some elastic vibration isolation materials, such as rubber and other synthetic materials, are installed between the outer ring and the bearing seat hole to achieve the purpose of vibration reduction and noise reduction.
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Tag: Nachi   Bearing