Blow Molding

Start
PET Resin
Preform molding
Preform design
Preform Animation
Blow Molding
Bottle Design
Reheat stretch blow machinery
Single stage machinery
One stage vs. two stage machinery

For both one-stage and two-stage blow molding processes, a hot preform is clamped in a blow mold. A stretch rod is usually used to stretch the preform to the base of the mold, while low pressure compressed air is used to “pre-blow” the preform into a bubble. Then high pressure air is applied to push the PET bubble into all the details of the blow mold, and to cool the newly-made bottle. Time is allotted in the cycle to depressurize the mold before opening it and removing the bottle.

The little graphic above is a reasonable but not exact representation of how the preform inflates.

Important factors to make high-quality bottles at good production rates include:

• The right preform and bottle designs
• The right grade of PET resin
• Good injection molding practices, to make high-quality preforms
• The correct temperature profile of the preform before blow molding
• The correct timing for stretch, pre-blow and blow
• Equipment and molds in good operating condition
• Adequate auxiliary services such as compressed air and chilled water