What Is a Screw Conveyor
What Is a Screw Conveyor
A screw conveyor or auger conveyor is a mechanism that uses a rotating screw, called "flighting", installed in a tube or trough to move liquid or granular materials. They are used in many bulk cargo handling industries. Screw conveyors are often used horizontally or slightly inclined in modern industry as an effective way to move semi-solid materials, including food waste, wood chips, aggregates, grains, animal feed, boiler ash, meat and bone meal, and municipal solid waste and many others. The first form of screw conveyor is Archimedes' screw, which has been used to pump irrigation water since ancient times.
They usually consist of a slot or tube containing a helical blade around a shaft, driven at one end, and called a solid shaft screw at the other end. Other types are open screw or shaftless screw drive at one end and free at the other end. The volume transfer rate is proportional to the speed of the shaft. In industrial control applications, the device is usually used as a variable rate feeder, changing the rotation rate of the shaft to feed the measured rate or amount of material into a process.
When space permits, the use of inclined screw conveyors is a very economical method of lifting and conveying materials. When the inclination angle increases, the capacity of a given unit decreases rapidly. The general rule of thumb is 45 degrees or less, otherwise the material will eventually fall backwards over the flight and not convey to reach the intended destination.
Some of its advantages are:
The screw conveyor can handle all kinds of bulk materials from slow to free flowing.
The screw conveyor can have multiple inlet and outlet points. Bulk materials can be transported and distributed to different locations as needed. Sliding gates or valves can be used to control the flow into and out of the screw conveyor.
When a screw conveyor is used as a metering device, it is considered a screw feeder. The screw feeder is used to start a material process to meter the product from the silo or hopper.
The screw conveyor is very compact and suitable for crowded locations. Screw conveyors have no return similar to belt or drag conveyors.
The screw conveyor is completely enclosed to contain the product and prevent spillage. Screw conveyor can be used in horizontal, vertical or any inclined position depending on the situation
Screw conveyors can be used to mix various products together and crush large pieces.
Screw conveyors can be used to cool, heat or dry products in transit. According to the heat transfer requirements, the screw conveyor can be jacketed or hollow flight design to provide the necessary heat transfer for the application.
Screw conveyors can be designed to be steam tight or to maintain internal pressure. This is very important when transporting toxic or dangerous products, such as those in the chemical industry.
Screw conveyors can provide an air lock between upstream and downstream equipment.
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