The screw in the extruder rotates and develops sufficient pressure to force material to go through a die and produce products with desired geometry.
Components of an Extruder
There are five main components in an extruder: screw, extruder drive, barrel, feed hopper, and die. The heart of the extruder is a helical screw which facilitates transport, heating, melting, and mixing of plastic. An extruder drive is an electric motor which supplies power to rotate the screw. The stability and quality of products is highly dependent on the design of the screw. The screw is housed in the extruder barrel which provides heating and cooling capabilities. The raw material is supplied from the feed hopper which is connected to the barrel by a feed throat. The feed hopper is designed to hold plastic pellets and ensure a steady flow of the pellets into the barrel. The die is located at the outlet of the extruder and determines the shape of the product. There exist multiple types of dies, including tubing dies, flat film dies, and blown film dies. Note that the size and shape of the extruded products are not exactly the same as the size and shape of the die due to draw down, cooling, swelling, and relaxation of the extruded polymer.
In addition to an extruder, an extrusion process requires upstream and downstream equipment. Major equipment of an extrusion line is resin handling, drying system, extruder, post-shaping or calibrating device, cooling device, take-up device, and cutter or saw.