Types of Blow Molding Process

Extrusion Blow Molding (EBM)

•          Begins with a parison/ pre-form and is then placed into an enclosed cooled metal mold

•          Then air is blown into this mold to shape the material to the desired shape

•          Once it is cooled the part is ejected from the mold

•          Can be made continuously or intermittently

The production cycle consists of the following steps:

•          The parison is extruded vertically in downward direction between two mold halves.

•          When the parison reaches the required length the two mold halves close resulting in pinching the top of parison end and sealing the blow pin in the bottom of the parison end.

•          Parison is inflated by air blown through the blow pin, taking a shape conforming that of the mold cavity. The parison is then cut on the top.

•          The mold cools down, its halves open, and the final part is removed.

Injection Blow Molding

•       Polymer melt is supplied to mold halves from injection molding machine

•       Pre-form injection molded over a mandrel and transferred to the blowing die

•       Air is injected under pressure through the mandrel blowing the polymer against the mold walls where it cools and freezes as with extrusion blow molding

•       In Injection Blow Molding method a parison is produced by injecting a polymer into a hot injection mold around a blow tube or core rod.

•       Then the blow tube together with the parison is removed from the injection mold and transferred to a blow mold.

•       Following operations are similar to those in the extrusion blowing molding.

•       Injection Blow Molding is more accurate and controllable process as compared to the Extrusion Blow Molding.

•       It allows producing more complicated products from a wider range of polymer materials.

•       However production rate of Injection Blow Molding method is lower than that of Extrusion Blow Molding.

Stretch Blow Molding

•          Injection molded preformed top

•          Heaters raise the pre-form above the glass transition temperature

•          Core rod stretches polymer to the bottom of the mold

•          High pressure air expands the polymer to the walls of the mold

•          Stretch Blow Molding is similar to Injection Blow Molding.

•          Stretch Blow Molding involves injection molding of a parison, which is then stretched in the downward direction by means of the blow tube.

•          The extended parison is then inflated in a blow mold.

•          In this method biaxial molecular orientation is produced. The specific molecular orientation provides higher mechanical strength, rigidity and transparency of the material.

•          Material, commonly used in this method is Polyethylene Terephtalate (PET).

•          Stretch Blow Molding is used for manufacturing containers for carbonated beverages.