Augers and Screw Conveyors
CFW produces standard and custom augers and screw conveyors, as well as fans and other equipment for pneumatic material handling. We undertake the design, manufacture and installation of industrial conveying systems, and continuously pursue our development of reliable and economical equipment, as we have for decades.
Devices with helical screw blades have been used since ancient times for moving materials and for drilling. Archimedes’ screw is an early example that was used to pump water for irrigation.
Modern devices come in many designs and can be used in a wide range of drilling and bulk material handling tasks, including extrusion, process feeding and transport. The screw blade (or “flighting”) is often designed with a particular application in mind and may be shaftless.
CFW provides screw conveyors for materials handling. A wide variety of granular bulk materials and powders can be conveyed. For alternative conveying solutions from CFW, see our pneumatic conveying equipment.
Screw conveyors (or auger conveyors) are the preferred solution for conveying many hazardous, abrasive, corrosive or sticky bulk solids. They are able to move materials as large as pellets or as fine as microscopic powders between storage bins, processing and packaging equipment, extrusion machines, and various other processing units.
They can also mix, blend or agitate materials if suitably modified, and can be used as a variable rate feeder, to measure the rate of material flows to a high degree of accuracy where flow control is of paramount importance.
Consisting of a helical screw blade (also known as a spiral blade or flighting) that is usually cased in a tube and may be coiled round a shaft, they are commonly used in conveying semi-solids such as wastes, cereals, animal feed and wood chips and in other bulk handling applications. While conveyors for semi-solid conveyance are usually horizontal or slightly inclined, they can also direct material flows upwards very economically. However, the capacity of the unit decreases with increasing angles of inclination. Some screw conveyors are shaftless or have flexible tubes. Sludges and other materials that can stick to the central shaft or flighting are usually handled with shaftless devices.
They are typically rated by screw diameter and capacity per hour.
Screw conveyors have many advantages:
- Versatile: Can convey a wide range of materials for many industries (mining, grain, paper…). The right screw conveyor can transport almost any kind of bulk material, even those that are not free-flowing.
- Compact: Occupy a relatively small space.
- Reliable: Simple and with few moving parts. This reduces maintenance costs.
- Diverse: Can be constructed from various metals and abrasion and corrosion resistant materials.
- Clean: Are generally completely enclosed to keep contamination low. Some designs are vapour and dust tight.
- Bespoke:Can be custom-made to fit particular needs (e.g. shaftless designs for sticky materials).
The flighting of screw conveyors is often encased, making for an especially versatile conveyor. They can operate at many speeds and angles of elevation, performing well when filled effectively. They are not generally used across long distances because intermediate bearings cannot be used. The exception is shaftless screw conveyors, which are sometimes employed for longer distances.
Both for performance and for practicality, a considerable clearance is needed between the flight and the casing. A section of the flight called the “choke” juts out beyond the casing and helps to take up the feed material into the conveyor. The end of the casing must reach the material for the conveyor to work.
How well the screw is filled with material, and the kind of motion the material exhibits when conveyed, influences the throughput of the material. The vortex motion of the material decreases as screw rotation speed increases up to a certain point. This improves volumetric efficiency and consequently throughput. Incomplete filling, however, reduces throughput. This occurs because gravity feed systems do not allow the feed rate to keep up with the potential capacity of the conveyor. This limitation can be overcome to some extent by using forced feed systems.
With most bulk materials, the bulk density increases up to a limit with greater consolidation pressures. The choice of bulk density is an important one to maximize throughput while avoiding blocking.
Alternatively, a trough arrangement can be used. They are common in industrial applications for long-distance conveying but are limited to low speeds, fill ratios and angles of elevation.
CFW augers are designed to function at a high capacity, be easy to use and have a long operating life. Bespoke solutions can be supplied. CFW also makes auger conveyors (see “screw conveyors”).
Grain augers are the most widely-used grain handling system on farms. They are typically used to convey grain to storage during the harvest season. Simple and easy to use and to maintain, they consist of a screw with flat flighting contained in a tube. Portable models are usually mounted on an undercarriage.
Augers should be designed with guards to prevent foreign material from being drawn into the machine and only permit the conveying of small grains. Augers without proper guards or that are not operated using the correct procedure can be dangerous.
Grain augers are available in various types, not all of which are mutually exclusive:
- Centreless augers consist of a flighting without a shaft.
- Drill fills are small augers used to fill seed drills.
- “Pencil auger” is a term used to refer to many augers with a small diameter.
- Utility augers have multiple uses and are mostly used in permanent or semi-permanent installations.
The performance of grain augers depends on operating conditions as well as design. At a given speed, their throughput capacity is higher at lower angles of inclination. Power requirements increase up to an angle of inclination of 45° and then decrease. Throughput also increases with increases in rotational speed, but only up to a certain point. Power requirements increase markedly when grain is wet for augers operating at low angles, and where moisture levels exceed 20%, throughput capacity also declines. A greater clearance between the flighting and the casing decreases capacity; however, closer clearances increase capital costs and may result in grain jamming the auger. The flight pitch is generally kept equal to the diameter of the flight; however, greater pitches can result in better capacity as long as the auger will only operate at low angles of elevation.
The design of the choke (i.e. the part of the screw outside the tube) and choke opening further influences performance. Many augers have adjustable choke openings. Larger choke openings are not as easy to handle because they must be completely covered by grain. However, they can also result in higher throughput.
A correctly sized motor is important for optimum performance. Friction losses and the possibility of overload must be taken into account, especially if the auger begins to operate with a full load. These factors can increase the required sizing of an electric motor by 30%.
Where feasible, the use of augers with greater diameters, at lower speeds, can extend the life of the machine and improve reliability.
Cape Town, South Africa (HQ)
3 Parin Road, Parow Industria, 7500, Western Cape
Johannesburg, South Africa
4 Chilworth Road, Founders View North, Modderfontein, Edenvale, 1645, Gauteng
Cape Town, South Africa (HQ)
T +27 (0)21 931 8331
F +27 (0)21 931 3165
Johannesburg, South Africa
T +27 (0)11 452 5830 / 5146
F +27 (0)11 452 5132