The second part in the series explaining the prominent methods of plastic manufacture.
The process of plastic injection moulding is very similar to plastic extraction except the parts produced are not long, continuous pieces but more compact items like toys.
With injection moulding, the thermoplastic is literally ‘injected’ into a mould at high pressure. The mould will be shaped like the part required and once the plastic within the mould has cooled and solidified, the part will be ejected from the mould.
The machine used for injection moulding comprises of a hopper, an injection barrel (with a reciprocating screw inside), a hydraulic motor and an injection cylinder.
In the same way as extraction, the process starts by plastic granules / resin being placed into a hopper either manually or by machine.
The injection moulding process continues by:
1. The resin entering the injection barrel via the hopper
2. The thermoplastic is dragged forward by the rotation of the reciprocating screw
3. The screw rotates by the power of the hydraulic motor
4. As the plastic is pushed forward, the frictional heat melts it
5. Heating bands add additional heat to the injection barrel
6. When the plastic is ready to be injected, the reciprocating screw pulls back to release the pressure in the barrel
7. The plastic is then pushed through an injection nozzle and into the mould
8. Once the plastic has cooled and solidified, it is cast out of the mould