The circular vibrating screen is named because the movement path of the screen box is circular or elliptical, and because the vibrator has only one axis, it is also called a single-axis vibrating screen.
The circular vibrating screen is usually divided into a common circular vibrating screen and a self-centering vibrating screen, and its cross-sectional schematic view is shown in Fig. 1. The screen box 3 equipped with the screen 8 is suspended (hanging) or supported (seat type) by the spring 4, and can be freely vibrated by the exciting force. The bearing 2 of the main shaft 1 is mounted on a screen box 3, and the main shaft is driven to rotate by the pulley 7. The eccentric disc 5 is mounted on the spindle and rotates therewith. The centrifugal inertia force is generated when the eccentric weight is rotated, and the screen box is driven to generate a circular trajectory vibration. In the figure, the amplitude is represented by A, and r is the excitation eccentricity, that is, the distance between the eccentric weight and the centerline of the bearing.
As can be seen from Fig. 1, the ordinary circular vibrating screen differs from the self-centering vibrating screen only in that the structure of the vibrator is slightly different. The bearing center of the former is on the same line as the center of the pulley. When the vibrating screen is running, the pulley vibrates with the screen box, thus causing the V-belt to repeatedly expand and contract to be easily damaged, and a smaller amplitude is required ( Generally less than 3mm). Due to these shortcomings, such vibrating screens have been seldom used. The center of the pulley of the self-centering vibrating screen is located between the center of the bearing and the center of gravity of the eccentric block, and the center line of the pulley is located on the centroid of the eccentric block and the vibrating body. Therefore, when the vibrating screen is working, the pulley does not follow The screen boxes vibrate together and only rotate, so that a larger amplitude can also be used to improve the screening efficiency. Therefore, the self-centering vibrating screen has developed rapidly and has been widely used. The circular vibrating screens currently used in industrial production generally belong to the type of self-centering vibrating screens.
Fig. 2 is a schematic structural view of a 1500 mm × 4000 mm hanging self-centering vibrating screen. The screen frame 1 is suspended from the floor or frame of the plant by four spring-loaded booms 4. The screen frame and the horizontal inclination angle are 15°-20°, and the screen 2 and the vibrator 3 are mounted thereon. The roller bearing housing 5 (see Fig. 3) of the vibrator main shaft is bolted to the side wall of the screen frame. Both ends of the main shaft 7 are provided with pulleys and discs with eccentric blocks 1. There is also an eccentric block protruding toward one side in the middle of the main shaft. The resultant force of the two eccentric blocks produces an exciting force, and the amplitude of the screen box can only be adjusted by increasing or decreasing the pulley and the eccentric mass on the disk. The center of the main shaft of the vibrating screen is on the same line as the center of the bearing. Since the center of the shaft hole of the pulley and the disc has an eccentricity with respect to the circumference thereof, the value is equal to the amplitude of the body, so the center of rotation of the pulley is still at the center and eccentricity of the bearing. Between the center of gravity of the block, the space is not moving, and the belt can be prevented from being damaged when the belt is relaxed. At the same time, the structure of the pulley eccentric vibrator has the advantages of simplified mechanical structure and easy manufacture, compared with the bearing eccentric type (Fig. la). At present, advanced circular vibrating screens basically adopt this mechanical structure, such as the YA-type circular vibrating screen produced by the introduction of technology in 1980.
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Figure 4 is a self-centering heavy-duty vibrating screen for screening coarse-grained, high-density materials. It also uses a wheeled eccentric vibrator, which is characterized by a self-moving eccentric weight vibration absorbing device (Fig. 5). . When the circular vibrating screen (especially heavy-duty) is started and stopped, the amplitude of the screen machine will increase rapidly due to the resonance zone, which will cause the spring to be seriously overloaded, shorten its service life, the transmission belt is easy to be damaged, and the building construction is also subject to severe vibration. Hazard. This vibration damping device is used to eliminate this resonance phenomenon. The eccentric block 6 of the self-propelled eccentric device is mounted on the pin 8 with a hinge and is spring-tensioned near the middle portion. When the rotational speed of the main shaft 5 is lower than twice the resonance rotational speed, the centrifugal force generated by the eccentric mass on the pin 8 is lower than the moment of the spring force against the pin 8, which is in the position shown. This position produces little excitation force to the screen box. Even if the vibrator main shaft has a certain speed, the amplitude of the screen box is still small. When the speed of the vibrator increases to about twice the resonance speed, the eccentric mass pops up, producing the exciting force and amplitude required for normal operation. When parking, the situation is reversed: when the vibrator speed drops to about twice the resonance speed, the eccentric block is pulled back by the spring, the vibrator is basically in equilibrium position, does not generate any exciting force, and the vibrator passes near the resonance speed. At the same time, the amplitude of the screen box does not increase sharply.
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The Other two methods to eliminate the above resonance phenomenon are: 1 The motor is reversely connected to the brake, that is, when the screen is stopped, the power supply is converted into two phases when the rotation speed is reduced to near the resonance speed. As the direction of the magnetic field of the stator of the motor changes, the rotor is suddenly slowed down to zero. At this time, the sieve moves rapidly across the resonance zone, making the resonance phenomenon difficult to occur, and a good vibration-absorbing effect can be obtained. 2 Elastic limit, that is, the rubber vibrating member fixed on the rigid bracket limits the vibrating screen in all directions so that it cannot be greatly beaten.
The sieve surface of the self-centering vibrating screen has a single layer and a double layer. Different types of sieve surfaces can be used depending on the application. For example, a strip-shaped sieve surface welded by steel bars is commonly used for screening ore, and a sieve mesh is commonly used for screening coal . The installation method is hanging type and seat type.
Self-centering heavy-duty vibrating screens are usually seated, single-layer and double-layer, and three-layer; the screen box is welded by steel plate and section steel, and the screen surface is made of cast steel rafters, and the structure is firm.
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