What is the Process of Plastic Extrusion?

EXTRUSION plays a prominent part on the plastics industry. Extrusion, unlike moulding, is a continuous process, and can be adapted to produce a wide variety of finished or semi-finished products, including profile, sheet, film, covered wire and pipe.

The process of plastic extrusion begins with the placement of raw resin into the extruder’s hopper. If the resin lacks additives necessary for the particular application (such as anti- oxidants, colorants, or UV inhibitors), then they are then added to the hopper. The resin is typically gravity-fed through the feed throat of the hopper down into the extruder’s barrel, once in place. A long, rotating screw within the barrel that feeds the resin forward in the barrel towards the die.

The resin is subjected to extremely high temperatures as it moves along within the barrel, until it starts to melt. Temperatures can range between 400 and 530 degrees Fahrenheit depending on the type of thermoplastic.  Most extruder’s have a barrel that gradually increases in heat from the loading end to the feed pipe to enable gradual melting and minimize the possibility of plastic degradation.

Once the end of the barrel is reached by the molten plastic, it is forced through a screen pack and fed into the feed pipe that leads to the die. This screen removes contaminants that may be present in molton plastic. The porosity of the screen, number of screens, and other factors can be manipulated until uniform melting occurs as a result of the right amount of back pressure.

Once in the feed pipe, the molten metal is fed into the die cavity, where it cools and hardens. To expedite the cooling process, the newly formed plastic receives a sealed water bath. In the case of plastic sheeting extrusions, cooling rolls replace the water bath.

Plastics material can be classified in two groups. Thermoplastics and Thermosetting plastics:

  • Thermoplastics when heated to a sufficient high temperature will softer and flow under pressure. On cooling they will harden. Repetition of this process number of times is possible till the degradation of the material takes place.
  • Thermosetting plastics can be heated only once. On heating the material will soften and flow under pressure. The chemical reactions in this process causes the material to harden and set. Once set material will not soften again by applying heat and pressure.

Our expert team at Harkness will consistently exceed all of our customers’ expectations in supplying molded parts from a wide variety of engineering grade resins and cast urethanes. Our entire team strives to take care of our most valuable asset — our customers.

Our manufacturing flexibility in urethane casting, injection molding, and thermoplastic extrusion enables us to provide a cost-effective process for any application or quantity. Contact us at for more information at info@harknessindustries.com.


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