A screw conveyor is a device that uses an inclined, spiraling plane to move material. The spiral of the screw conveyor is stretched out over the distance to be traversed and is either positioned in a trough or fully enclosed in a cylinder. One end of the conveyor screw is put into contact with a liquid, semi-solid, or granulated substance. When the spiral is rotated, it forces the substance to move along the trough or cylinder. Other names for the device include auger conveyor, spiral conveyor, and helix conveyor.
Screw conveyors may be a frequent site in agricultural applications, where they can be used to move grain or other bulk substances. The conveyor screw, or auger, may be easily identified in this application, as it commonly requires only a trough, leaving the upper half of the screw visible. Examples of this kind of application may be seen feeding grain into or out of a silo or filling a bin on the back of farm machinery.
Agriculture and industry may also employ flexible screw conveyors, which require a complete enclosure, usually a flexible tube. Aside from the most obvious feature — flexibility — the flexible screw conveyor may differ from other types of conveyors in that the screw does not typically make contact with the enclosure walls. It also is commonly without a cylindrical core, and the screw resembles a spring with flattened coils. Flexible screw conveyors allow for substances to be moved between locations where a straight pipe will not work, whether around simple obstructions or through floors and walls, as well as in virtually any direction or at any angle. This also allows the screw conveyor system to be moved between extraction or delivery sites, much like a hose.
The screw conveyor may also be known as an Archimedes's screw, as the discovery of the principle behind it is sometimes attributed to the Greek mathematician Archimedes. Regardless the true innovator, the device has been used since at least 235 BCE in Egypt to move water for irrigation. The screw in this application is usually wrapped around a cylindrical core and may be placed in a trough or cylinder. The device is typically positioned at a slight angle in order to raise water from one level of irrigation ditch to another. This use of screw conveyors may also be seen in such diverse applications as pumps at waste-water treatment plants and hemopumps, medical devices used to maintain blood circulation during heart surgery.