Shaping plastics
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.
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.
Press moulding is used to make electrical fittings, handles, and many other products. It can only be used with thermosetting plastics.
Blow moulding
A tube of softened plastic called a parison is extruded into a mould.
Blow moulding is used to shape plastics, mainly for making bottles, plastic buckets and similar shapes.
Vacuum forming
This process uses a wooden mould or form. A sheet of thermoplastic is heated, then shaped by creating a vacuum underneath it. Air pressure then forces the plastic over the mould.
Vacuum forming is used to for food and confectionary packaging, trays, shop fittings and baths.
Shaping by reforming
Reforming is a method of shaping materials which changes their overall appearance by first melting or softening them into a paste, then hardening them. Reforming methods include casting, extrusion and injection moulding.
Die casting
Die casting uses a metal mould that can be very detailed. The mould is made in two parts to allow the casting to be removed. Die casting is a very important industrial process used for many different types of products.
Extrusion
Extrusion moulding is used to produce long, but fairly thin products such as pipes or curtain tracks. Both plastics and metal can be extruded. The material is forced through a die, which contains a hole which is the same shape as the required product.
Injection moulding
A metal mould is used and softened or molten plastic is forced into the mould by pressure from a screw thread or pneumatic plunger. The mould is made in two parts to allow the moulding to be removed. Injection moulding is used extensively in industry.
