Trommel screen is one of the most commonly used screening equipment in solid waste treatment. The solid waste is classified according to different particle sizes by the trommel screen. Under the action of gravity, too small solid waste (fine material) through the screen into the bottom of the hopper, too large solid waste (coarse material) by the drum screen tail discharge port.
1. The material motion states of the common trommel screen can be divided into three types.
1) The State Of Sink Down
In this state, the rotation speed of the machine is very low. Due to circular motion, the material tumbles above the upward-moving particles. In this case, the material mixing is inadequate, which makes it difficult for the in-between fine material to tumble and move towards the screen cloth, leading to extremely low screening efficiency.
2) The State Of Throw Down
When the rotating speed of the drum screen is high enough but below the critical speed, the material will overcome gravity and move up to the highest point of the rotating drum. In this case, gravity exceeds centrifugal force and the material falls in a parabolic trajectory and returns to the bottom of the rotating drum. What's more, the particle tumble is the most severe and the material accumulation rarely occurs, so the screening efficiency is the best.
3) Centrifugal State
When the rotary speed of the trommel screen is increased to the critical speed, the material will be attached to the cylinder wall so that the screening efficiency is very low.
2. The trommel screen of municipal solid waste has been improved on the basis of common equipment, and sorting or cleaning structures have been added to make the machine more suitable for the screening of municipal solid waste. The movement of municipal solid waste in machines is divided into two types.
1) The Motion Along The Axis Direction Of Screen Body
The inclined installation of the screen body produces linear motion along the axial direction, and its speed is the speed of waste through the screen body.
2) Planar Motion Perpendicular To Axial Plane Of Screen Body
This planar motion is closely related to the rotational speed of the screen body. When the screen body rotates at a speed below the critical speed, the waste material moves to a certain height and falls in a parabolic shape, which is conducive to screening. The speed is generally 30% to 60% of the critical speed.
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