Fig. 7 shows an injection moulding machine used to produce polymer components in large quantities. The polymer has been chosen for its specific properties i...

(a) The part labelled A is the hopper. [1] The hopper is a funnel-shaped container mounted at one end of the injection moulding machine. Its purpose is to hold and feed the raw polymer granules (or pellets) into the heated barrel by gravity. Without the hopper, there would be no controlled supply of material entering the system.

(b) The heated barrel and Archimedean screw perform two essential functions in injection moulding:

• The heated barrel surrounds the polymer granules with heat as they travel along its length, melting them from a solid granular form into a viscous molten state. [1] The barrel contains heating elements (electric band heaters) that raise the temperature sufficiently to soften the specific thermoplastic being processed.
• The Archimedean screw (also called the reciprocating screw) rotates inside the barrel, pushing the molten polymer forward along the barrel and forcing it under high pressure into the mould cavity. [1] The screw action also contributes to mixing and even heating of the polymer, ensuring a uniform melt before injection.

(c) Two advantages of injection moulding for manufacturing polymer products in large quantities:

1. High production rate with fast cycle times, making it economical for mass production. [1] Each cycle (injection, cooling, ejection) can take only seconds to minutes, so thousands of identical components can be produced per day.
2. Very consistent and identical products with high dimensional accuracy and good surface finish. [1] Because the same precision-machined mould is used repeatedly, every part produced is virtually identical, reducing quality-control costs and rejection rates.