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Design & Technology

Production techniques

Shaping by deforming: plastics

Bending

Thermoplastics cannot be bent when cold. They are bent using a strip heater or line bender which will heat the plastic in a straight line, so it can be bent by hand.

Plastic bends where the heat is applied

Press or compression moulding

A mould is made in two halves. Sheet plastic is placed between the two halves, which are then heated and pressure applied, enabling the plastics to assume the new shape.

Piece of plastic is moulded by being pressed between 2 shaped moulds

Press moulding is used to make electrical fittings, handles, and many other products. It can only be used with thermosetting plastics [Thermosetting plastics: A type of plastic that can only be shaped once. ].

Blow moulding

A tube of softened plastic called a parison is extruded [extruded: Shaped by being forced through an opening. ] into a mould.

Blow moulding

step 1 - parison is inserted into mould. step 2 - parison based pinched by mould, sealing it. step 3 - air is blown in and plastic expands. step 4 - finished product, a plastic bottle
  1. Parison inserted into mould.
  2. Base of parison squeezed by mould.
  3. Air blown in to parison, parison expands to fill mould.
  4. Finished product.

Blow moulding is used to shape plastics, mainly for making bottles, plastic buckets and similar shapes.

Vacuum forming

This process uses a wooden mould [mould: A shape or hollow form used to shape a material that has been softened or melted. The material hardens and the mould is then removed to produce a product of the desired shape. ] or form [form: The three-dimensional shape of a solid object. ]. A sheet of thermoplastic is heated, then shaped by creating a vacuumvacuum: A volume that contains no matter - space is almost a vacuum. underneath it. Air pressure then forces the plastic over the mould.

Vacuum moulding

Step 1 - plastic is above a mould and below a heater. step 2 - plastic is heated and melts. step 3 - air is removed, sucking the melted plastic into the shape of the mould.
  1. Plastic placed over mould.
  2. Plastic heated.
  3. Air in mould removed.

Vacuum forming is used to for food and confectionary packaging, trays, shop fittings and baths.

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