Screw conveyors are used to handle finely divided powders, damp, sticky, heavy viscous materials, hot substances that may be chemically active, and granular materials of all types. Because of simplicity, freedom from sharp recesses, cracks, and crevices, dust-tightness, and ease in disassembly, screw conveyors are used for moving food products such as powdered milk and peanut butter. Screw conveyors are used for batch or continuous mixing, for feeding where a fairly accurate rate is required, and for conventional conveying and elevating jobs particularly where the run is short. Flights are made of stainless steel, copper, brass, aluminum, cast iron, etc., for hot, corrosive, or mildly abrasive materials, and are hard surfaced with stellite or similar material to resist highly abrasive materials.