Blow Moulding

Blow moulding is a very high productivity method where cycle times are of great importance. It is a low-pressure method where strength and wear demands are very moderate but corrosion resistance and heat conductivity are important. Aluminum with inserts of MoldMAX are well suited for blow moulds.

General

Blow moulding is a process for shaping thermoplastic into a hollow product. A hot thermoplastic tube is stretched with air pressure and cooled against a mould surface.

A variety of blow moulding techniques exist for different applications:

  • Extrusion blow moulding
  • Injection blow moulding
  • Stretch blow moulding

In extrusion blow moulding, a hollow tube is extruded. The tube is then positioned in a mould and compressed air causes the tube to press against the cool walls and solidifies to the mould surface shape.

Extrusion moulding exists as continuous extrusion and intermittent extrusion. For PVC, the continuous process is normally used.

Injection blow moulding and stretch blow moulding involves first forming of a preform, by extrusion or injection moulding. This is later blown to the desired shape.

Mould material requirements

Mould material requirements are of course totally different if talking about the injection moulding or extrusion of preforms or if talking about the blow moulding itself.

Blow moulding is a low-pressure method where strength and wear demands are very moderate. Some parts of the mould, like shot off areas and/or neck ring, may require higher strength material. PVC is a common material for bottles and may cause corrosion problems.

Mould material properties

Important properties are:

  • Moderate strength demands
  • Corrosion resistance
  • Heat conductivity