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The processes of plastic extraction and plastic injection moulding (Part 1)

An explanation of two prominent plastic manufacturing methods.

There are two main methods of manufacture when creating plastic parts – plastic extrusion and plastic injection moulding.  Part 1 in this series of articles explaining the production of plastic parts will concentrate on the plastic extrusion method.

Plastic extrusion is a technique used to produce plastic parts that are long and of the same size / shape cross section throughout.  This method is used to create items such as pipes and plastic edging.

The process of plastic extrusion involves a continuous practice where plastic is fed into an extruder and transformed into a molten material using heat and shearing force.  This molten liquid is shaped by being forced through a die opening.

A more in depth explanation of profile plastic extrusion follows:

  • Thermoplastic granules are fed into the feed barrel of the extruder
  • The material is transferred into the barrel from a hopper
  • The plastic within the feed barrel melts as it is pushed forward by a rotating screw
  • The friction from the thermoplastic being pushed / dragged causes it to heat up and melt
  • External heat is also applied via heater bands to further melt the material
  • To create long, constant shapes, the profile (plastic) is pushed through a die which is attached to the end of the barrel
  • The plastic is then extruded into a cooling tank
  • The tank is filled with water which cools the extruded plastic and allows it to solidify
  • Haul off units / pull rollers are utilised to pull the profile away from the die
  • Profiles are then cut to the required length by a machine

The next article in this series will explain the plastic injection moulding process.