Chapter 3-Blow Moulding Flashcards
What is blow molding used for?
The process of blow molding is used for the production of hollow glass and plastic objects in large quantities.
What is the process of injection molding?
The polymer is injection melded onto a core pin. The core pin is rotated to a blow molding station to be inflated and cooled. This method is used to make small medical and single serve bottles.
What are the three steps?
Injection,blowing and ejection.
What happens during the blow molding process?
The blow molding machine melts the polymer. The molten polymer is then put into a hot runner where it is injected through nozzles into a heated cavity and core pin. The cavity mold forms the external shape and is clamped around a rod which forms the internal shape of the preform. The preform mold then opens and the rod is rotated and clamped into the hollow blow mold. The end of the core rod opens and allows air into the preform inflating it to the finished article shape.
What happens during the cooling process?
The blow mold opens and the core rod rotates to the ejection position. The finished article is taken off the core rod and is often leak tested prior to packing.
What are the advantages and disadvantages?
The advantage is that it produces an injection mould neck for accuracy.
On the down side, it only suits small capacity bottles and it is difficult to control the base centre during blowing. Handles cannot be incorporated.
What type of plastic is used in blow moulding?
The plastics normally used are polythene, PVC and polypropylene.
