1.1 Eccentric vibration At present, the vibration exciters used in vibrating screens are mostly eccentric shaft exciters and box exciters. The eccentric shaft exciter is easy to install and adjust, but the cost is high, and the eccentricity is not adjustable. The box exciter adopts a fan-shaped eccentric block with adjustable relative position, which can adjust the excitation force to achieve amplitude adjustable. purpose. Ball Mill Ball,Grinding Mining Balls For Mill,Grinding Ball For Cement Mill,Grinding Ball For Ball Mill Jinan Zhongwei Casting And Forging Grinding Ball Co.,Ltd , https://www.cngrindingballs.com
The centrifugal force generated by the eccentric mass of the vibration exciter bends the eccentric shaft, resulting in the relative deflection of the outer ring of the bearing. Since the eccentricity generates vibration caused by the frequency conversion and its various harmonics, the inertial force generated during the operation and The inertial force couple will cause the dynamic reaction force and vibration of the bearing, destroy the smooth working state of the bearing and other components, and generate high-frequency vibration. The vibration spectrum analysis of the vibrating screen shows that when the vibration frequency of the vibrator bearing is the same as the natural frequency of a certain order of the elastic vibration of the screen box, it will cause strong vibration of the screen box elastic body.
A vibration system consisting of a bearing and an eccentric system can be considered as a single degree of freedom system. Both the bearing drive shaft and the driven shaft system have a certain resonant frequency. If an excitation frequency is close to the resonant frequency, resonance occurs. Further, since the eccentricity has a centrifugal inertial force, bending vibration occurs, and if the rotational speed approaches a critical value, bending resonance occurs.
1.2 Bearing geometric accuracy The vibrating screen has a large excitation force, which causes the bearing to bear a large radial force, resulting in strong vibration. The higher the bearing accuracy, the smaller the vibration. The raceway, especially the waviness of the surface of the rolling element, has the greatest influence on the vibration of the bearing. The clearance between the rolling element and the cage and the rolling surface of the inner and outer rings and their relative motion can cause the vibration of the bearing, which is due to the higher spin frequency of the rolling element. The working surface is in contact with the inner and outer raceways at the same time, and the vibration generated by the rolling elements, the ferrules and the cage is approximately 4:3:1. Therefore, reducing the bearing vibration should first improve the surface machining accuracy of the rolling elements. Since the waviness is a shape error between roughness and roundness, which is generated during the grinding process of the rolling element, it is difficult to control it. For this reason, other methods should be sought to control the vibration of the rolling element.
1.3 Bearing Radial Clearance If the radial clearance is too large or too small, the bearing system will generate large vibration. If the radial clearance is too small, it will cause high-frequency vibration, and if it is too large, it will cause low-frequency vibration. The test results of the large-size bearing 3E3626 show that the radial clearance is too large, which reduces the radial natural frequency of the elastic system of the bearing, which is easy to generate resonance and generate large low-frequency vibration. This is because a large acceleration is generated at the impact point of the rolling elements and the ferrule. In the early impact generated regardless of the shape of the object and the mechanical quality of a high frequency compressional wave, and metal internal successor; in the late impact, will have a low compression ratio of the vibration frequency of the mechanical shock wave by a mechanical force. Therefore, a large radial clearance will increase the vibration of the bearing in the passband.
The test analysis shows that the bearing radial clearance is too large, so that the bearing system has large impact vibration. If the radial clearance is too small, the radial temperature is very high, and the friction temperature rises quickly, which will cause the bearing to burn at a high temperature. In addition, the cage will also have a large radial runout as the radial clearance increases, resulting in greater vibration.
1.4 Coordination The cooperation of the outer ring and the support hole will affect the transmission of vibration. The tighter fit will force the deformation of the raceway and increase the shape error, resulting in increased vibration. A looser fit can cause damping of the oil film in the gap. The material properties of the outer ring and the bearing housing are quite different, especially the rubber damping ring is placed between them to suppress the transmission of vibration.
1.5 Friction and lubrication The bearing is the main vibration source that is difficult to control. Because the vibrating screen is maintained by a large excitation force, the radial force of the bearing is very large. The vibrating screen is in the working process. Large excitation forces will cause elastic vibration of the bearing system. If the lubrication is poor, a large friction will occur to make the bearing temperature rise too high, and the thermal expansion is too large, so that the radial clearance is significantly reduced, thereby intensifying the friction and further increasing the temperature rise. For this reason, many vibrating screens generally use large clearance bearings such as 3E3626 and 3G36240. However, due to the excessive radial clearance, the radial natural frequency of the bearing system is reduced, and the possibility of radial runout after the rolling element is disturbed is also increased. Sex and its impact on the energy of the ferrule during the jump, thereby increasing the vibration value of the high frequency part, resulting in strong high frequency vibration.
Factors Affecting Vibration of Vibrating Screen Rolling Bearings