A screw feeder is a device suitable for handling a wide range of materials with great flow-ability characteristics. It is commonly used in many industries on a daily basis, as it provides an accurate feed from one to another part of a process. In the structure, the screw feeder has no significant differences with the screw conveyor, as both working principles are based on the Archimedean screw. The screw feeder is responsible for delivering dense slurries and dry granular products with exceptional precision at various operational speeds. Also, it is able to maintain the high torque values, needed to feed all kinds of materials across its speed range.
The main advantage of this principle is the likelihood of having not one, but few openings, each able to load/unload the material. Although it is an old positive displacement method, the screw feeders today still use the Archimedean screw principle to transport materials. Simple, but highly efficient, this method of moving materials applies for both sand and water types of materials. As all machines based on this working principle, the screw feeder also has a helical screw mounted on a shaft and can be powered by various motors. The shaft rotates inside a fixed tube, with a feeder mechanism at one end. The material added in the screw feeder is transported from the one end to the other end, known as discharge end.
The most suitable materials for the screw feeders are some dense slurry and loose grained consistencies. These materials include suspended chemicals, pharmaceutical ingredients, cereal grains, molding thermoplastics and many others. To all these kinds of materials, the screw feeder can deliver its high torque levels at all operational speeds. Also, the screw feeder is known for operating at very slow speed, which is especially useful when feeding sensitive materials.
Most screw feeder drives are controlled by servo motors, which allow them more accurate turning the engine on-off and speed control. However, there are many screw feeder types, but the most common are volumetric and gravimetric screw feeder. Before the operation starts in a volumetric screw feeder, the amount of material to be transported is precisely calculated and controlled by adjusting the screw turning speed. In gravimetric screw feeder, on the other hand, the delivery rate is controlled by adjusting the rate at which the material enters the machine. The gravimetric screw feeder is much more precise, so is more commonly used in applications that require the highest levels of accuracy possible.