The circular vibrating screen is named because the motion track of the sieve box is round or oval, and because the vibrator has only one axis, it is also called the single axis vibrating screen. The circular vibrating screen is usually divided into a general circular vibrating screen and a self fixed center vibrating screen. The cross section of the sieves is shown in Figure 1.
（a）general circular vibrating screen （b）Self fixed center vibrating screen.
Figure1. circular vibrating screen
1.Shaft; 2. bearing; 3. sieve box; 4. hanger spring; 5. disc; 6. eccentric block; 7. pulley; 8. sieve.
working principle of circular vibrating screen
As shown in Figure 1, the sieve box with sieve 8 is suspended by spring 4 (hanging type) or supported (seat type), which can be freely vibrated by exciting force. The bearing 2 of the spindle 1 is mounted on the sieve box 3, and the main shaft is driven by the belt wheel 7. The disc 5 with eccentric weight is mounted on the spindle and rotates with it. The centrifugal inertia force is produced when the eccentric weight is rotated, which drives the vibration of the circular trajectory of the sieve box.
Main parts of circular vibrating screen
The main components of the circular vibrating screen include the vibrator, the screen box, the transmission device and the isolation device.
The circular vibrating screen has a pure vibrator, a bearing eccentric and a belt wheel eccentric self fixed center vibrator. The latter has been widely used in practice because of its simplification, easy manufacture and long service life. Figure 2 is a self fixed center vibrator structure diagram.
Figure2. elf fixed center vibrator
1. eccentric block; 2. pulley; 3. bearing end cover; 4. roller bearing; 5. bearing seat; 6. cylinder; 7. spindle; 8. disc.
The roller bearing seat 5 of the spindle of the vibrator is fixed with a bolt on the side wall of the screen frame. The two ends of the main shaft 7 are equipped with a belt wheel and a disc with an eccentric block 1. The central part of the main shaft also has an eccentric block that protruded to one side. The joint force of both kinds of eccentric blocks produces exciting force, and the amplitude of the sieve box can only be adjusted by increasing or decreasing the eccentric block on the pulley and the disc. The vibrating screen of the spindle center and bearing center on the same line, as the center of the shaft hole and the belt wheel disc relative to the circumference of a eccentricity, its value is equal to the amplitude of the body, so the center of gravity between belt wheel center is still located in the center of the bearing and the eccentric block, the space is not moving, can be avoided when a belt is damaged .
The screen box is composed of screen frame, screen mesh and its fastening device.
The screen mesh is the basic working part of the screening equipment. The size and shape of the hole are evenly distributed on the screen, which is called the sieve hole. When the material is sieved on the screen, the material that passes through the sieve hole is sifting, and the material on the screen is the sifting product. General use of the screen mesh with low carbon steel, high carbon steel, manganese steel, spring steel, stainless steel and other materials quality effort is made mainly by metal screen mesh; rubber, nylon, polyurethane and other non-metallic materials screen also increased in the development. According to the grain size of the material and the requirements of the screening process, the screen mesh can be divided into the following several kinds:
2.1.1.Bar screen mesh
The bar screen mesh is composed of a group of parallel - arranged steel bars with a certain section shape. The shape of the section bar of the common bar is shown in Figure 3. The rod is arranged in parallel, and the interval between bars is the size of the sieve. The bar screen mesh is suitable for sieving the coarse-grained material above 50mm.
Figure 3. Bar screen mesh cross section
2.1.2. Punching screen mesh
The punching screen mesh is usually made of round, square or rectangular screen holes in the thick 5-12mm steel plate. The arrangement of sieve holes on the punching screen mesh is shown in Figure 4. The circular sieve holes are usually arranged on the equilateral triangle, and the square sieve holes can be arranged in parallel or diagonally arranged in the right angle isosceles triangle. The rectangular sieve holes are arranged at a certain angle with the longitudinal axis of the mesh, and can also be arranged in other ways. There should be a certain distance between the sieve holes to wear and ensure the necessary strength of the mesh.
Figure 4. Punching screen mesh
2.1.3. Weave screen mesh
The weave screen mesh is made of steel wire for warp and weft, and the shape of the sieve is square or rectangular (Figure 5). In order to ensure uniform distribution of wire mesh size to avoid dislocation in mesh at the intersection of alternately arranged. The effective area of the weave screen mesh is large (up to 75%), the quality is light, and it is easy to make. The weave screen mesh is usually suitable for screening of medium and fine sized materials.
Figure 5.weave screen mesh
2.1.4. Wavy screen mesh
The sieve bar is pressed laterally into a wave form, and the two is combined to form a sieve hole, which is a wavy screen mesh(Figure 6). The sieve bar can also be pressed along the longitudinal direction to be wavy, and the screen surface composed of the wavy screen is also called the string screen. The wavelength depends on the size of the sieve hole. Usually, the sieve holes are square. The sieves are made of flexible manganese steel to produce secondary vibration of small amplitude, thus reducing the bonding and blocking of viscous materials or micro fines.
Figure 6. Wavy screen mesh
2.1.5. Slit screen mesh
The slit screen mesh is made of stainless steel as a sieve, and there are three types of structure, which are piercing, welding and weaving (Figure 7). The shape of the screen section of the seam screen is round or as shown in Figure 8. The width of the seams can be 0.25mm, 0.5mm, 0.75mm, 1mm and 2mm. The slit screen mesh is suitable for dehydration and dewatering of medium fine particles.
Figure 7. Slit screen mesh
Figure 8.section shape of Slit screen mesh
2.2. Fastening device for screen mesh
If the screen mesh is installed on the sieve box, it can be tightened evenly and firmly, and it has a great influence on the sieving efficiency and the service life of the screen. Usually, punching sieve surface and slot sieve surface fixed with wedge; twine diameter smaller woven screen surface and a thickness of less than 6mm with a fixed hook punching sieve surface; mesh diameter greater than 9.5mm braided sieve surface and a thickness greater than 8mm punching sieve surface of the strip and screw fixation. Figure 9 is a more advanced screen tensioning device.
Figure 9. Fastening device for screen mesh
1.damping rubber strip; 2. sieve bracket; 3.side plate; 4. tightening bolts; 5. guiding angle steel bolts; 6. double hole backing plate: 7. guide angle steel 8. tension plate; 9. screen mesh; 10. intermediate pressed flat steel.
2.3. Screen frame
The vibrating screen frame is composed of the side plate and the cross beam. The side plate is made of steel plate thickness of 6-16mm, and the crossbeam is made of steel pipe, channel steel or I-beam. It can be joined by three ways: riveting, welding or high strength bolts. When the riveting structure is used, the manufacturing process is complex, but it has good adaptability to the vibration load. The welding structure has the advantages of simple process, but the weld complex, large internal stress, under severe vibration effect of weld cracking, even cause fracture of the component, the thermal annealing treatment to eliminate internal stress, under normal circumstances, the welding structure applicable to small vibrating screen, high strength bolts and ring groove rivet structure for large vibrating screen.
3. Transmission device
The vibrating screen usually adopts the V belt drive device. It is simple in structure and can choose the speed of the vibrator arbitrarily. Some vibrating screens use the coupling to drive the vibrating screen directly, which can keep the vibrator steady and prolong the use life, and can not adjust the speed of the vibrator.
4. Vibration damping device
Spiral springs, plate springs and rubber springs are commonly used in vibration screening. The spiral spring is compact in structure and small in shape, with small stiffness, good vibration elimination, no fastener and reliable work. The advantage of the plate spring is that the transverse stiffness is large and the transverse vibration can be eliminated. The advantages of rubber springs are small shape size, but large stiffness and good vibration isolation performance. Because of the larger amplitude of the vibrating screen, a cylindrical spiral spring is generally used as a damping device.
Specification of Circular vibrating screen
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The motor makes the exciter rotating speedily through the V-belt. Besides, the great centrifugal force produced by rotating eccentric block makes the sieve box do circular motion of some amplitude, together with the impulse transmitted through sieve box on the slope surface, which makes the materials on the screen surface successively tossed forward. Thus the classification is achieved in the process of thrown-up as materials with smaller size than the mesh is falling through.