This type of moulding uses a machine that is also used in injection stretch blow moulding and horizontal injection blow moulding. Extrusion blow moulding machines are also very similar but they are fitted with a nozzle to force a particular shape of plastic out of the end of the machine.
Injection moulding is the most commonly used process for moulding plastics because it gives a good surface finish and can be used for very complicated mouldings. Injection moulding cost a lot to set up but once that is done, it becomes very cheap because the machines can mass produce and give a very low unit production cost. Injection moulded plastics are invariably thermoplastics because thermosetting plastics assume their final shape through heat and so can not be moulded with this process.
The plastics that are used in injection moulding include: polythene, low density polyethylene (LDPE), high density polyethylene (HDPE), polystyrene (PS), polypropylene (PP) and acrylonitrilebutadienestyrene (ABS) (GOSH THAT'S A MOUTHFUL).
It's easy, particles of plastic are fed into the hopper. The screw thread (yellow in the diagram) is turned round by a motor, the plastic passes near the heaters (red) and melted, the screw thread is then pushed forwards by the hydraulic system (blue) and the plastic is pushed into the mould. he new piece is cooled and ejected.
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