Plastic extrusion melts plastic beads, which are mixed with dyes and UV inhibitors, and molds them into a continuous profile. The process is used to make a variety of items, including piping and plastic sheeting. The plastic is heated to around 400°F (200°C) and moves through a mold before being cooled and cut to size. Other materials, including aluminum and rubber, can also be extruded.
Plastic extrusion is a manufacturing process by which plastic is melted, molded into a continuous profile and cut to size. This process is used in the production of a wide variety of items including piping, cable insulation, and plastic sheeting. Masking tape and window frames also include extrusion as part of their manufacturing processes.
In this process, raw plastic is fed into a heated extruder cavity or barrel. Typically, the raw plastic is in the form of beads and can be mixed with dyes before the extrusion process begins, and in some methods, ultraviolet (UV) inhibitors can also be added to the raw plastic beads. Once inside the machine, the plastic beads and any accompanying material move through an opening in the extruder cavity towards a screw mechanism. The screw rotates, forcing the plastic material to advance through the cavity.
Inside the cavity, the temperature is very high, often reaching around 400°F (200°C), which melts the plastic. Many extruders use three different heaters that are set to gradually build up the heat within the cavity. This reduces the risk of overheating.
The friction and pressure within the cavity serve to produce extra heat which is independent of the heaters. Sometimes, the pressure and friction within the cavity produce so much heat that the heaters can be turned off. When this happens, the desired temperature is maintained by friction and pressure. The cooling fans are also employed frequently, helping to keep the machine at the desired temperature.
As the molten plastic reaches the front of the barrel, it moves away from the screw and passes through a special screen designed to filter out contaminants. The molten plastic then moves into a mold, which is responsible for giving the molten plastic its profile. The plastic must then be cooled, often with a sealed water bath; care must be taken to avoid collapse of the newly formed product in the still molten state. Plastic sheets and some other products are cooled by special chill rolls instead of water baths.
After cooling, the product is wrapped, rolled or cut to size. In addition to plastics, a variety of other materials can be extruded, including aluminum and rubber. Even clay and some types of food can be made this way. However, the process used may differ from that used to extrude the plastic.
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