What is a Power Screw?

A feed screw can look like an auger.

A feed screw is a component of certain types of industrial machinery designed to move or feed materials through a tube. Typically, a feed screw is a metal cylinder with an inclined plane wound around its outside, similar to a long screw or auger. The feed screw is then placed in a tube into which various materials flow from a hopper or chute. As material from the hopper flows into the tube, the feed screw rotates, pushing material along the length of the tube where it will be used. Feed screws are commonly used in the plastics and food production industries to move, mix and extrude products.

In the plastics industry, feed screws are the heart of extruders used in blow molding, injection molding, sheet extrusion and profile extrusion. In these cases, the tube surrounding the screw is heated to the point of melting the plastic resin. As the screw moves material through the tube, called a barrel, the material is melted and mixed. At some point along the screw, the pitch of the threads changes, allowing less space for material to flow and causing the material to build up pressure. Once the material reaches the end of the screw, it is extruded through a die, forming the molten plastic resin into the desired shape or profile, or into a mold where it is cooled into the desired shape.

In the food industry, feed screws are used in essentially the same way as in the plastics industry. The main difference is that instead of melting the material, the food is cooked as it passes through the feed screw and is given the desired shape at the end. Instead of applying direct heat, some types of food processing equipment use the feed screw to increase pressure, which generates the heat needed to cook the food product.

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Feed screws are not just useful for extruding products. They are also frequently used in many industries to blend various raw materials into a final product. In this type of application, a series of feed screws will be collected in a die where each screw feeds a separate ingredient into a hopper, box or other container. As each screw feeds material into the container at a specific rate, very precise and different amounts of material can be dispensed as desired. For example, if three screws of equal size are arranged and one screw rotates at 5 revolutions per minute (rpm), the next at 20 rpm, and the final screw at 25 rpm, the final composite will consist of 10% of the first material, 40% of the second and 50% of the third.

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