Screw conveyor Working and Applications:
Screw Conveyor applications are required in Food, Pharmaceuticals, Chemical industries, Packaging industries, salt, cement, coal, biomass, agriculture, gypsum and other industries where there is a need for industrial duty equipment to convey free-flowing bulk materials. Screw Conveyors are used in a wide variety of applications to efficiently convey dry, free-flowing, semi-fluid and sticky bulk materials. These conveyors are employed for handling a great variety of materials which have relatively good flowability. Sticky and stingy materials are unsuitable for screw conveying.
Screw conveyors have a few favourable points to its credit for recommending its application in different industries. Simplicity of design, easy construction and maintenance, are the few points which are often mentioned in favour of its application. But material characteristics often dictate the choice of its selection.
Dusty, hot materials or materials having foul odour are often conveyed by this type of conveyor systems, because it can be easily made dust-proof by jacketing the trough.
Typical applications include grain storage plants, feed mills, cereal processing plants, chemical plants, and sand preparation shop of a foundry for delivery of clay to the mixing machines.
Screw conveyors are very suitable for being adopted as a device to control the volume of materials flow from the bottom of bins, hoppers, storage silos etc. when screw-conveyors are used for this purpose they are termed as screw feeders. Screw feeders have wide applications for the operation of processing units like driers, hammer mills, oil expellers and other innumerable mills.
History of the Screw Conveyor
Archimedes designed the first screw-conveyor in the third century B.C. It was used for removing water from ships and for irrigating farmland. The device consisted of a hollow cylinder with a center shaft and a spiral fixed to the inner wall of the cylinder and center shaft. As the assembly rotated, water was conveyed and lifted from one location to another. The spiral design is based on the theory of the inclined plane.
The screw-conveyor began to evolve in the late 1800s and was used as a means of increasing feed and grain production to serve the needs of the rapidly growing American population. The first feed mills utilized screw-conveyors throughout the process. Even the most modern feed mills today depend on screw-conveyors for many of their material handling requirements. The screw-conveyor has evolved to modern times. It is now used in almost every major industry.
Screw Conveyor Operation
The flexible screw-conveyor operation begins with product entering the sealed tube as the auger rotates. The shape, design style, size, and length of the auger are factors selected for each application. The screw-conveyor is typically mounted to a hopper for easy loading of material. A single motor drives the auger rotation allowing the material to be pulled through the enclosed tube. The helicoid design of the auger effectively conveys a wide range of materials from powder, to granular, to larger particles.
Screw-conveyors may be used to convey materials which can be subjected to thermal operation during transit. The conveyor trough is provided with jacket through which the heating or cooling medium may be circulated to effect the thermal operation.
Screw-conveyors may be operated horizontally, on an incline, or vertically. Often inclined conveyors can solve a transportation problem effectively, but otherwise a combination of horizontal and vertical units should be installed. The angle of inclination of inclined conveyors is usually 10° to 20°. Vertical conveyors are usually complex in design and should be run at faster speed.
Screw-conveyors do not always get favourable consideration due to high friction of the material against screw and trough, probability of material degradation due to crushing of material and due to higher power consumption resulting from higher friction. Therefore screw-conveyors have limitation in capacity and distance of conveying. They are suitable for low and medium capacities for short distance. Capacity may be as high as 100m3/hr and distance of conveying is of the order of 30 to 40m typically.
Screw conveyor Applications:
Screw conveyors are bulk material transporting devices capable of handling great variety of materials which have relatively good flow ability. This characteristic is important in screw-conveyor operation as the screw helix mounted on a central pipe or shaft, rotates within a fix trough or tube, pushes the material along the bottom and sides, sharing the material in the radial clearance between the helix and trough and causing the material to tumble upon itself as the moving face of the helical flight tends to lift the material.
Screw Conveyor Applications Gallery:
Screw Conveyor Advantages:
The screw-conveyor has many advantages over other types of bulk material handling equipment. Some of the advantages are:
- Screw-conveyors are capable of handling a great variety of bulk materials from sluggish to free-flowing.
- Screw-conveyors can have multiple inlets and discharge points. Bulk materials can be conveyed and distributed to various locations as required. Slide gates or valves can be added to control the flow into and out of a screw conveyor.
- When a screw conveyor is used as a metering device, it is considered a screw feeder. Screw feeders are used to initiate a material process by metering product from a bin or hopper.
- Screw-conveyors are very compact and adaptable to congested locations. Screw conveyors do not have a return similar to a belt or drag conveyor.
- Screw conveyors are totally enclosed to contain the product and prevent spillage. Screw conveyors can be utilized in the horizontal, vertical or any inclined position depending upon the characteristics of the product being conveyed.
- Screw conveyors can be used for mixing various products together and for breaking up large lumps.
- Screw conveyors can be designed without a center pipe. This type of conveyor is called a shaftless screw conveyor and is designed for conveying wet, sticky, sluggish products such as industrial sludges and biosolids.
- Screw conveyors can be used to cool, heat or dry products in transit. Depending on the heat transfer requirements, a screw conveyor can be jacketed, or a hollow-flight design utilized to provide the necessary heat transfer for the application.
- Screw conveyors can be designed to be vapor-tight or hold an internal pressure. This is very important when conveying toxic or hazardous products such as those in the chemical industry.
- Screw conveyors can provide an airlock between upstream and downstream equipment.