Screw conveyors with variable pitch
If the screw conveyor is manufactured with increasing pitches, the material gets more and more space and is conveyed at an increasingly faster pace. This way, material buildup is avoided..
On the other hand, if the screw conveyor is manufactured with decreasing pitches, the material is gradually pressed together. This effect is used in some screw presses for e.g. dewatering solids.
On the 3th picture, is a screw press with thermal coating of tungsten carbides.