Mechanical screening should be considered in terms of overall plant economy. For example, better screening can significantly reduce unnecessary crushing, thus decreasing your power usage for crushers and conveyors, and reducing wear and downtime.
There are dozens of factors that can impact upon screening performance – from the type of material to be sorted, to the moisture content, particle size distribution, screening area, screening media, the means of moving the material, and the goals of the screening process. Later in this series, we’ll discuss the impact of these factors in more detail, but before that, it’s important to having a firm grip of the basics.
Firstly, motion is important. If you put a load of material onto a flat, static screen, hoping to isolate fractions of a certain size, you will be disappointed. Without some kind of motion, most of the material will stay in place. When the screen moves, it starts to allow smaller particles to fall to the bottom of the material bed, and pass through the screen underneath. As you continue to shake, the smaller fractions will continue to move to the bottom, albeit at a diminishing rate. The time duration for the shaking to allow the smallest particles to reach the bottom will be roughly proportional to the amount of material on the deck.
This video shows how movement prompts stratification and allows separation to take place.