Blow Molding, Injection Molding, and Extrusion

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  • Topic: Plastic, Polystyrene, Plastics industry
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  • Published : March 2, 2011
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Blow Moulding, Injection Moulding and Extrusion

Blow moulding:
Using blow moulding, there is a mould, and the plastic is injected into the middle of the mould and, heated until soft, then air is blasted in between the plastic so it is pressed to the outside of the mould making the shape, because they then use cold air, it cools down and forms that shape quickly.

Things made using blow moulding:
Plastic bottles.
Hollow tubs.

Injection moulding:
With injection moulding, thermoplastic granules are fed into the machine through the hopper, which is like a funnel into the rotor/screws; the motor rotates the screw rotor through a gear box, then the rotating screws force the plastic through the machine. As it goes through the machine, it slowly gets heated up to make it soft, then when the plastic is ready the hydraulic ram pushes the rotor forward, then injects the plastic into the mould, then it cools down, and the mould is ejected.

Things made using injection moulding:
Parts for a computer e.g. keyboard, mouse..
Plastic model kits.


The machine used to extrude materials is very similar to an injection moulding machine. A motor turns a screw which feeds granules of plastic through a heater. The granules melt into a liquid which is forced through a die, which is something that cuts, or folds the plastic; it is often personalized to the item being made. Forming a long tube like shape. The shape of the die determines the shape of the tube. The extrusion is then cooled and forms a solid shape. The tube may be printed upon, and cut at equal intervals. The pieces can be rolled or stacked for storage.

Things made using extrusion:
Plastic piping.
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