Plastic extrusion is a continuous process. Plastic granules are fed into a hopper. Underneath the hopper is a rotating screw inside a heated cylinder. As the plastic becomes semi - molten it is forced out of the end of the machine through a die which determines the shape of the end product. The diagram shows pipe being made. This process can be used for waste pipes, drain pipes, window frames and any other shape which is exactly the same along its length.

There are only plastic ones of me left.

Injection Moulding

Injection Moulding
Look at the telephone, the TV case, the microwave case, the Lego bricks and many other household items. These are complicated plastic shapes which can only be formed by injection moulding. Injection moulding is used for large scale production. The expense of this type of moulding is in the making of the mould. Once this has been produced large quantities of one item can be made very quickly. The mould is made in two parts which usually are cooled by means of holes being drilled in them and either air or water being pumped through the holes. The plastic is fed into a hopper, heated as it passes through a revolving screw and forced into the mould under pressure. At this stage, when the mould is full, the mould is cooled causing the plastic to shrink a little making it easier to remove from the mould (and also making the plastic go solid of course), the mould is then split and the component removed. 

Dip Coating
This is a method of covering intricate and complicated pieces of metal with a thin coating of plastic. Small particles of plastic are blown into airspace within a closed box. The work piece which has been previously heated to the correct temperature is plunged into the particles and the heat from the work makes the particles stick and melt to the job, coating it completely. This process is often used for covering steel to prevent it from rusting, as with radiator drying racks used in the home.

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