Influencing factors of vibration of vibrating screen rolling bearing


1.1 Eccentric vibration
At present, the vibrator used by the vibrating screen is mostly eccentric shaft vibrator and box type vibrator. Eccentric shaft vibrator is easy to install and adjust, but the cost is high, and the eccentric distance can not be adjusted; The box type shaker adopts the fan-shaped eccentric block with adjustable relative position, which can realize the adjustment of the excitation force and achieve the purpose of adjustable amplitude.
When the vibrator works, the centrifugal force generated by the eccentric mass makes the eccentric shaft bend, resulting in the relative deflection of the bearing inside and outside the ring. Because of the eccentricity, the vibration caused by the rotating frequency and each order harmonic frequency will be produced, so the inertia force and inertia force couple generated in the operation will cause the dynamic reaction and vibration of the bearing, destroying the smooth working state of the bearing and other parts, producing high frequency vibration. The analysis of vibration spectrum shows that when the vibration frequency of the shaker bearing is the same as the natural frequency of the elastic vibration of the screen box, the strong vibration of the elastomer of the screen box will be caused.
The vibration system composed of bearing and eccentric system can be regarded as a single degree of freedom system. There is a resonance frequency of a certain value in both the driving shaft and the driven shaft system of the bearing. If a certain exciting frequency is close to the resonance frequency, resonance occurs. In addition, due to the presence of centrifugal inertia forces in the eccentricity, bending vibration will occur, and bending resonance will occur if the speed is close to the critical value.
1.2 Bearing geometric accuracy
Vibration screen excitation force is large, resulting in a great deal of radial force bearing, resulting in strong vibration. The higher the bearing accuracy, the smaller the vibration. Raceway, especially rolling surface corrugability, has the greatest influence on bearing vibration. The clearance between rolling body and cage and the rolling surface of inner and outer rings and their relative motion will cause bearing vibration, which is due to the high spin frequency of rolling body and the contact between working surface and inner and outer raceway at the same time. The vibration size generated by rolling body, ring and cage is roughly 4:3:1. Therefore, reducing bearing vibration should first improve the surface machining accuracy of rolling body. Because corrugability is a kind of shape error between roughness and roundness, which is generated in the grinding process of rolling body, it is difficult to control the generation of corrugability, so we should seek other methods to control the vibration of rolling body.
1.3 Radial clearance of bearing
If the radial clearance is too large or too small, the bearing system will have great vibration. Too small radial clearance causes high frequency vibration and too large low frequency vibration. The test results of the large shaker bearing 3E3626 show that the radial natural frequency of the bearing elastic system is reduced because of the large radial clearance, which is easy to generate resonance and produce large low-frequency vibration. This is because large acceleration will be generated at the impact points of the rolling body and the ferrule. At the initial stage of impact, high frequency compression waves unrelated to mechanical mass and object shape are generated and transmitted inside the metal. At the later stage of the impact, mechanical force will produce a mechanical vibration with a frequency lower than that of the impact compression wave. Therefore, the larger radial clearance will aggravate the vibration of the bearing on the pass band.
The test analysis shows that too much radial clearance of the bearing will cause greater impact vibration of the bearing system. If the radial clearance is too small, the bearing will be burned at high temperature because the radial force is large and the friction temperature rises quickly. In addition, with the increase of radial clearance, the cage will also produce large radial runout, and then produce large vibration.
1.4 Coordination
The fit of the outer ring and the supporting hole will affect the transmission of vibration, and the tight fit will force the raceway deformation, increase the shape error, and lead to the increase of vibration. Loose fit can make the oil film in the gap produce damping effect. The material properties of the outer ring and the supporting hole (bearing seat) are quite different, especially the rubber damping ring placed in the middle can inhibit the transmission of vibration.
1.5 Friction and lubrication
Bearing is the vibrating screen more difficult to control the main vibration source, because the vibrating screen is by a lot of exciting force to maintain the work, so the radial force of the bearing is very big, vibrating screen in the process of work, a lot of exciting force will cause the elastic vibration of the bearing system. If the lubrication is poor, there will be greater friction to make the bearing temperature rise is too high, the thermal expansion is too large, so that the radial clearance is significantly reduced, which intensifies the friction and further increases the temperature rise. For this reason, many vibrating screens generally use large clearance bearings such as 3E3626, 3G36240, however, because the radial clearance is too large, reduces the radial natural frequency of the bearing system, but also increases the possibility of radial pulsation after the rolling body is disturbed and the energy of the impact ring in the pulsation, thus increasing the vibration value of the high frequency part, producing strong high frequency vibration.

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