Blow Moulding Flashcards
What is blow moulding?
Blow moulding a shape is a common industrial process. The plastics normally used in this process are; polythene, PVC and polypropylene.
Can you list the stages of blow moulding? (Summary)
- The plastic is fed in granular form into a ‘hopper’ that stores it.
- A large thread is turned by a motor which feeds the granules through a heated section.
- In this heated section the granules melt and become a liquid and the liquid is fed into a mould.
- Air is forced into the mould which forces the plastic to the sides, giving the shape of the bottle.
- The mould is then cooled and is removed.
Can you explain the three stages of blow moulding? (Longer)
Injection
The injection blow moulding machine is based on an extruder barrel and screw assembly which melts the polymer. The molten polymer is fed into a manifold where it is injected through nozzles into a hollow, heated preform mould. The preform mould forms the external shape and is clamped around a mandrel (the core rod) which forms the internal shape of the preform. The preform consists of a fully formed bottle/jar neck with a thick tube of polymer attached, which will form the body.
Blowing
The preform mould opens and the core rod is rotated and clamped into the hollow, chilled blow mould. The core rod opens and allows compressed air into the preform, which inflates it to the finished article shape.
Ejection
After a cooling period the blow mould opens and the core rod is rotated to the ejection position. The finished article is stripped off the core rod and leak-tested prior to packing. The preform and blow mould can have many cavities, typically three to sixteen depending on the article size and the required output. There are three sets of core rods, which allow concurrent preform injection, blow moulding and ejection.
Can you list the typical materials used?
Polyethylene (Low Density) LDPE, LLDPE Polypropylene PP Polyethylene - Terephthalate PET Polyvinyl chloride PVC Polyethylene (High Density)
