3: Moulding

Question 1

Blow Moulding (4)

Answer 1

1. Plastic resin is fed into an extruder, where it is melted and formed into a parison (a tube-like piece of plastic with a hole in one end).
2. The parison is then clamped into a mould.
3. A blow pin introduces compressed air into the parison, inflating it so that the plastic expands to fill the mould cavity.
4. After cooling, the mould opens, and the part is ejected.

Question 2

Injection Moulding (4)

Answer 2

1. Plastic pellets are poured into a hopper and then fed into a barrel, where they are heated and melted.
2. A rotating screw transports the molten plastic forward and then injects it through a sprue into the mould cavity via runners and gates.
3. Once inside the mould cavity, the plastic cools and solidifies into the desired shape.
4. Ejector pins then push the finished part out of the mould.

Question 3

Vacuum Forming (4)

Answer 3

1. A plastic sheet is clamped into a clamp frame and heated by a heater until it becomes pliable.
2. The softened sheet is then placed over a mould (or buck).
3. A vacuum removes air from beneath the sheet, pulling it down to conform to the shape of the mould.
4. After cooling, the formed plastic is removed from the mould and trimmed to remove any excess material.

Question 4

Extrusion (3)

Answer 4

1. Plastic pellets are fed from a hopper into an extruder barrel, where they are melted by heating elements.
2. A rotating screw pushes the molten plastic through a die, which shapes the material into the desired cross-sectional profile.
3. The extruded plastic is then cooled in a cooling chamber and drawn away from the die by a puller.

Question 5

Rotational Moulding (4)

Answer 5

1. A charge of plastic powder is placed into a mould, which is mounted on an arm that rotates bi-axially.
2. The mould is then heated in a curing oven, melting the plastic powder, which coats the interior surfaces of the mould.
3. After the plastic has melted uniformly, the mould is moved to a cooling chamber, where it solidifies.
4. Finally, the mould is opened, and the finished part is removed (demoulding).