Moulding of plastics

Vacuum forming

Thermoplastics such as polyethene, perspex and polypropene are suitable for such moulding procedures. The plastic comes in a sheet which is heated and then set into the mould by suction. Air is pumped from the mould forcing the plastic sheet to take shape over the mould.

 

 Plastic cups are formed by vacuum forming. The plastic beads are mixed and coloured as shown on the left.

 

 The hot plastic is then extruded into a plastic sheet a few millimetres thick.

 

 The mould for the cups is made of metal.

 

 

The plastic sheet is heated and pulled over the mould. It is then sucked into the mould and quickly cooled to the solid state.

The process is fully automated, as shown on the left.

 

 

Vacuum forming is used in many school technology classes.

A mould is first prepared.

 

 

 The plastic sheet is placed over the top.

 

 The plastic is heated before been sucked onto the mould.
Click to see a video of vacuum forming a toy car. Notice how the hot plastic is sucked over the mould. Air is then blown through the plastic to release it from the mould.

 

 

What type of plastic is used in vacuum forming?

What actually forces the soft plastic over the mould?
Extrusion moulding