Manufacturing - Blow Moulding

Blow Moulding is a thermoplastic moulding process that is used to form large hollow cavity plastic parts such as bottles. The process uses air to expand heated plastic much like a balloon and fill the space within a mould cavity. It's origins are from traditional glass blowing methods.

As with Injection Moulding, pellets of thermoplastic are mixed with coloured dye and fed into a hopper. They are then heated along an Archimedes screw to a molton state towards the extruder. The plastic is then extruded into a hollow tube called a 'parison'. Air is then blown into the heated parison causing it to expand and fill the shape of the mould block. Once cooled the plastic part is cut from the extrusion and ejected from the mould block by ejector pins allowing the process to be repeated.


The advantages of Blow Moulding are;

  • Incredibly low cost manufacturing process once setup
  • Completely automated and can run continuously 
  • Forms complex geometry easily with uniform wall thickness
  • Thin wall thickness to maximise material usage
  • Suitable for a range of thermoplatsics (PVC, PP, PET, HDPE, LDPE)
  • High production rate with minimal material wastage

The dis-advantages of Blow Moulding are;

  • High setup cost, precision enginnering/design for mould block
  • Wall thickness difficult to control and thickness limited
  • Can not mould internal geometry only part cavity
  • Larger moulding create thinner wall thickness
  • Limited size part that can be moulded (32m³)
  • Poor surface finish on moulded parts

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