Commercial processes

Since polymers have a relatively low melting point, they can be shaped easily once molten by either injection moulding or extrusion.

Injection moulding

Injection moulding is used in industry to produce most mass-produced polymer parts using the following process:

  1. granular plastic is held in a hopper
  2. it is moved via an Archimedean screw along a heated tube, called the heating chamber
  3. once the polymer has been melted, it is pushed into a mould with a hydraulic ram - the use of the hydraulic ram ensures just enough material is injected into the mould each time
  4. the mould is then cooled so that the moulded plastic can be removed
Step one in the injection moulding process, showing plastic pellets being fed into a hopper.

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Extrusion

Extrusion works in a very similar way to injection moulding:

  1. granular plastic is held in a hopper
  2. it is moved by Archimedean screw along a heated tube, called the heating chamber
  3. once the polymer has been melted it is pushed through a die mould, which will form the shape of the extrusion
  4. because there is no hydraulic ram in this process, molten plastic can be fed through the die continuously
The extrusion process, showing plastic pellets melted in a heater and pushed through a die and cooling chamber by an Archimedean screw to create a long and thin extruded part.

Common extruded polymer products are plastic pipes, tubes and guttering.