A screw conveyor or auger conveyor is a mechanism that uses a rotating helical screw blade, called a "flighting", usually within a tube, to move liquid or granular materials. They are used in many bulk handling industries. Screw conveyors in modern industry are often used horizontally or at a slight incline as an efficient way to move semi-solid materials, including food waste, wood chips, aggregates, cereal grains, animal feed, boiler ash, meat and bone meal, municipal solid waste, and many others. The first type of screw conveyor was the Archimedes' screw, used since ancient times to pump irrigation water.
They usually consist of a trough or tube containing either a spiral blade coiled around a shaft, driven at one end and held at the other, or a "shaftless spiral", driven at one end and free at the other. The rate of volume transfer is proportional to the rotation rate of the shaft. In industrial control applications the device is often used as a variable rate feeder by varying the rotation rate of the shaft to deliver a measured rate or quantity of material into a process.
Screw conveyors can be operated with the flow of material inclined upward. When space allows, this is a very economical method of elevating and conveying. As the angle of inclination increases, the capacity of a given unit rapidly decreases.
The rotating part of the conveyor is sometimes called simply an auger.
arious other applications of the screw or auger conveyor include its use in snowblowers, to move snow towards an impeller, where it is thrown into the discharge chute. Combine harvesters use both enclosed and open augers to move the unthreshed crop into the threshing mechanism and to move the grain into and out of the machine's hopper. Ice resurfacers use augers to remove loose ice particles from the surface of the ice. An auger is also a central component of an injection molding machine. An auger is used in some rubbish compactors to push the rubbish into a lowered plate at one end for compaction.
Augers are also present in food processing. They are a tool of choice in powder processing, when it comes to convey or dose precisely bulk solids (powders, pellets...). In a conventional meat grinder, chunks of meat are led by the auger through a spinning blade and a holed plate. This method emulsifies the fat in beef to soften hamburger patties, and is also used to produce a wide variety of sausages and loaves. Augers are also used to force food products through dies to produce pellets. These are then processed further to produce products such as bran flakes.
Augers are also used in oil fields as a method of transporting rock cuttings away from the shakers to skips. Augers are also used in some types of pellet stoves and barbecue grills, to move fuel from a storage hopper into the firebox in a controlled manner. Augers are often used in machining, wherein the machine tools may include an auger to direct the swarf (scrap metal or plastic) away from the work piece.
Screw conveyors can also be found in waste water treatment plants to evacuate solid waste from the treatment process.