They are designed for horizontal, inclined or vertical movement, loose , small-sized or pulverized product.
It looks like a closed chute (pipe) inside which a shaft with blades on the helix rotates (Archimedes screw).
While rotation of a propeller blades push product along a trough.
Advantages: high performance, simple structure, easy operation and maintenance, leaks, small dimensions. Such conveyors can be used as mixers, feeders and bulk dispensers.
Limitations: a relatively rapid wear, grinding of a product, increased energy consumption.
Spiral conveyor (flexible) consists of a trough and a spiral situated in it; provides high performance comparing to a screw conveyor.