Feeding Screw

Brief Introduction to Feeding Screw

A feed screw, feeding screw, or screw feeder is a component of certain types of industrial machinery that is designed to feed, or move, materials through a tube. Generally speaking, a feeding screw is a metal cylinder with an incline plane wound around its outside, resembling a long screw or auger. The feeding screw is then placed in a tube wherein myriad materials flow from a chute or hopper. As the material from the hopper flows into the tube, the feeding screw rotates, pushing the material along the length of the tube to where it will be utilized. 

Feeding screws are commonly employed in food and the plastics production industries to move, mix and extrude product. Further applications are probable by varying the length and geometry of the screw. Based on the principle of a screw, the product is conveyed through rotation in an axial direction. The designs vary to fit the application and bulk material. Slow-running mechanisms are frequently utilized to supply and break up the material and we would recommend their use with bridging materials in particular as well. There are two basic designs:

● Single-shaft feeding screws: have an unimportant barrier impact. They are not suited to bulk materials in which can become fluid, but are perfect for powder.

● Twin-shaft feeding screws: provide a good barrier impact, making them suited to bulk materials in which can become fluid and products that are clingy and sticky.
 

Feeding Screw Applications

Feeding screws are the hearts of the extruders utilized in blow molding, injection molding, sheet extrusion and profile extrusion in the plastics industry. In these cases, the tube that circles the screw is heated to the point that it will melt the plastic resin. While the screw moves the material down the tube (a barrel), the material is melted and mixed together. At some point along the screw, the pitch of the threads alters, enabling less space for the material to flow and causing the material to amass pressure. Once the material reaches the end of the screw, it is extruded either through a die, forming the melted plastic resin into the ideal shape or profile, or into a mold where it is cooled down into the ideal shape.

Feeding screws are utilized fundamentally the same as above in the food industry. The chief difference is that instead of melting the material, the food is cooked as it goes through along the feed screw and formed into the ideal shape at the end. Some types of food processing equipment use the feed screw to increase pressure instead of applying direct heat, which generates the heat required to cook the food product.

Feeding screws are not only helpful in extruding products. They are also utilized all the time in many industries to mix different raw materials into a final product. In this type of application, a number of feed screws will be piled up into an array wherein each screw feeds a separate ingredient into a hopper, bin or other container. As each screw feeds material into the container at a certain rate, very precise and different amounts of material can be distributed as desired. For instance, if three equal-size screws are arrayed and one screw turns at 5 revolutions per minute (rpm), the next at 20 rpm and the final screw at 25 rpm, the final compound will comprise 10 percent of the first material, 40 percent of the second and 50 percent of the third.
 

Screw Feeder Versus Screw Conveyor

The prime difference is in how the system is being loaded, in order to accurately design the right conveyor to meet your needs.

Screw Feeder
Screw feeders are utilized to operate the product flow of the system. It is often mounted at the bottom of a hopper or a bin, and serves as a controlling conveyor. As a matter of fact, it can manage the capacity for the whole system, and is accessible in a single screw, twin, or multi-screw format. As a result, the pitch, diameter, torque, and trough design are indispensable to a screw feeder.

Screw Conveyor
A screw conveyor or auger conveyor is a mechanism that employs a rotating helical screw, called "flighting", that is placed within a tube or trough, to carry liquid or granular materials. They are employed in many bulk-handling industries. Screw conveyors are often used horizontally in modern industry as an efficient means of carrying semi-solid materials, such as wood chips, food waste, municipal solid waste and so on. The Archimedes’ screw was the prototype of screw conveyor, which was used since the early days to pump irrigation water.

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