The mining and mineral processing industry uses screening for a variety of processing applications. For example, after mining the minerals, the material is transported to a primary crusher. Before crushing large boulder are scalped on a shaker with 0.25 in (6.4 mm) thick shielding screening. Further downstream after crushing the material can pass through screens with openings or slots that continue to become smaller.
Finally, screening is used to make a final separation to produce saleable products based on a grade or a size range. Vibrating screen is most used in concentration plant, according to the difference of transmission mechanism, it can be divided into the following kinds: eccentric vibrating screen, inertial vibrating screen, ripple flow vibrating screen and resonance screen.
Screening machine can be divided into the following kinds according to its structure and working principle:
(1) Gravity flow screen
Working parts keep stationary, make material slide along working face to screen material. Static grizzly is more applied in concentration plant and used to pre-screen before coarse or medium crushing. It has a simple structure and is easy to manufacture. It can directly discharge mine ore on screening surface without consuming power. Its defect includes low productivity and low screening efficiency which is often 50—60%.
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(2) Roller screen
Working surface is composed of a lot of axises of roll arranged horizontally. There is a plate on the axis, fine material goes through the clearance between roller and plate. Material with big block is driven by roller, moves forward to one end and discharges from the end. Concentrate plant seldom uses this kind of screen.
(3) Cylinder screen
Working parts is in the shape of cylinder and the whole screen rotates along the axis of cylinder. Axis is installed with a certain dip angle in general case. Material enters from one end of cylinder, and material with fine classification goes through sieve pore of working surface, coarse material discharges front the other end of cylinder.
Rotation speed of cylinder is very low and has good dynamic balance and works in a steady state. But its sieve pore is easy to block, with low screening efficiency, small working area and low productivity. Concentrate plant seldom uses it as screening equipment.
(4) Plane motion screen
It swings or vibrates in a plane. According to its plane motion path, it can be divided into linear motion, circular motion, elliptical motion and complex motion. Shaking screen and vibrating screen belong to this kind.
Shaking screen regards crank and connecting rod mechanism as transmission part. Electric motor drives eccentric shaft rotate through belt and belt pulley, and depends on connecting rod to make machine do reciprocating motion along a certain direction. Motion direction of machine is vertical to pole support or center line of hanging stick. Because pendulum motion of machine makes material move forward to the exhaust end with a certain speed, material can be screened at the same time.
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