Injection Blow Moulding

Injection blow molding

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 the part is stripped from the core rod at an ejection station.

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

Injection blow molding

The process of Injection Blow Molding (IBM) is used for the production of hollow glass and plasticbottles. The process is divided into three steps: injection, blowing and ejection. objects in large quantities. In the IBM process, the polymer is injection molded onto a core pin; then the core pin is rotated to a blow molding station to be inflated and cooled. This is the least-used of the three blow molding processes, and is typically used to make small medical and single serve

The injection blow molding 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 mold. The preform mold 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.

The preform mold opens and the core rod is rotated and clamped into the hollow, chilled blow mold. The core rod opens and allows compressed air into the preform, which inflates it to the finished article shape.

After a cooling period the blow mold 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 mold 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 molding and ejection.

Another application of injection blow molding is in the production of soft elastic gelatin capsule for pharmaceutical applications. Two strips of gelatin are pressed together in a rotary die which cuts out the desired shape of capsule while the fill liquid is injected. Afterwards, they are cooled and dried to yield a firm, strong capsule.