Cup mould

A widely used process for thermoplastics, though it can also used for rubbers, thermosets and composites, is injection moulding. With this process, the polymer raw material is pushed into a cylinder by a screw or plunger, heated and then pushed, i.e. injected, into the cold metal mould. The pressure on the material in the mould is maintained while it cools and sets. The mould is then opened and the component extracted, and then the entire process repeats itself. High production rates can be achieved and complex shapes with inserts, threads, holes, etc. produced; sizes range from about 10 g to 25 kg in weight. Typical products are beer or milk bottle crates, toys,

control knobs for electronic equipment, tool handles, pipe fittings.

Reaction injection moulding

Reaction injection moulding involves the reactants being Cup mould combined in the mould to react and produce the polymer. The choice of materials that are processed in this way is determined by the reaction time, this must be short, e.g. 30 seconds, so that cycle times are short. It is mainly used with polyurethanes, polyamides and polypropylene oxide and composites incorporating glass fibres. The preheated reactants are injected at high speed into a closed mould where they fill the mould and

combine to produce the finished product. This method is used for large automotive parts such as spoilers, bumpers and front and rear fascia.

Compression moulding

Compression moulding is widely used for thermosets. The powdered polymer is compressed between the two parts of the mould and heated under pressure to initiate the polymerisation reaction. The process is limited to relatively simple shapes from a 2-3 g to 15 kg in weight. Typical products are dishes, handles and electrical fittings.

Transfer moulding

Transfer moulding differs from compression moulding in that the powdered polymer is heated in a chamber before being transferred by a plunger into the heated mould.

Plastic Forming processes

Forming processes involve the flow of a polymer through a die to form the required shape.

Plastic Extrusion forming

A very wide variety of plastic products are made from extruded sections, e.g. curtain rails, household guttering, window frames, polythene bags and film. Extrusion involves the forcing of the molten thermoplastic polymer through a die. The polymer is fed into a screw mechanism which takes the polymer through the heated zone and forces it out through the die. In the case of an extruded product such as curtain rail, the extruded material is just cooled.