The simplest way to explain how a screening machine works is to think about it as a large sieve. When you sieve flour you place it into a mesh container so that no clumps of flour can pass through to your mixing bowl. You might also shake your sieve to help the flour work it’s way through the mesh. 'Scalping' refers to removal of larger pieces of material from the mix, exactly like our sieve. Scalping screeners use vibrating meshes to output different sizes of material. The meshes, or 'screens' are stacked in tiers, and the material dumped on top. As the screens shake, smaller material falls through the holes in the mesh, leaving larger pieces on top. For fine screening applications (<6mm), the screens are usually on an incline, so any material that doesn't fall through each tier can tumble onto a conveyor to be carried away. For less fine screening, the throw of the decks will move the material on to the conveyors. The number of screens used is linked to the number of material grades output from a scalping screen. For example, if you want to turn a pile of mixed soil into 3 different sizes, you would pass the soil through two screens. These screens come in a range of different sizes and can be hot-swapped out of a machine. Changing screen size will change the size of materials that are being fed out of the machine. When the aim is a high volume of fine material the size of the bottom screen will be the limiting factor. A lot of screening machines will use a tapered design, where the decks get smaller towards the bottom. This restricts the flow of fine material at the bottom of the machine, and can cause a bottleneck. Screeners may also use water as part of the sorting process, but this can come with some challenges. For example, protecting the machine from water damage, or safe extraction and post-processing of water used during screening.