Injection blow molding is a two stage process since the parison is produced in a separate operation. In the first process molten plastic is injected into a heated preform mold around a hollow mandrel blow tube or core rod. This is similar to insert injection molding. The workpiece for the second, blow molding, process is the preform-mandrel assembly. The preformed parison is placed in a larger mold cavity for blow molding. Between the preform production and blow blow molding processes a heated preform may be held in a temperature conditioning stage or a cooled preform re-heated. After blow molding part is stripped from the core rod at an ejection station.

  • Injection Blow Molding General Processing Guidelines

Process Steps

Step 1. 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.

Step 2. 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.

Step 3. 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.

Raw Materials

  • Polyethylene (Low Density) LDPE, LLDPE
  • Polypropylene PP
  • Polyethylene – Terephthalate PET
  • Polyvinyl chloride PVC
  • Polyethylene (High Density) HDPE

These factors are critical to this process:

  • Shear & temperature dependent viscosity
  • Temperature-dependent tensile strength on the pin
  • Tensile elongation during inflation
  • Crystallization kinetics on the core pin
  • Crystallization kinetics during blowing and cooling

Examples of Application

  • Bottles
  • Jars
  • Roll-on containers