Petal Rod – a new method for optimum processing of preforms in stretch blow moulding


Polyethylene Terephthalate (PET) bottles for the carbonated soft drink (CSD) and water industries are responsible for 66% of the PET packaging market and play the most important role in the global consumption of PET.  Almost all PET bottles are manufactured by the injection stretch blow moulding process (ISBM) which begins with injection moulding of a preform. This is subsequently re-heated and formed into a hollow mould by a combination of axial stretching by a stretch rod and radial stretching by internal air pressure. The combination of stretch and blowing of the PET preform into a bottle is critical to the success of the stretch blow moulding process. Typically the stiffness of the material is increased by ~300% as a result of this process.  However the area in the base of the bottle which sticks to the stretch rod is not stretched during this process.  As a result the area in the centre of the base is the thickest part of the container and yet it is also the weakest. 

This project is developing a new type of stretch rod that will enable the material in the base region to be stretched, hence increasing the mechanical properties and offering the opportunity to reduce the thickness of the bottle in this region by at least 0.5g.  Even though this is a small saving per bottle, the huge volume of containers (billions per year) translate into significant savings in material, energy and money.

Patent Information:
  • Mechanical Engineering
  • For Information, Contact:
    Jason Wiggins
    The Queen's University of Belfast
  • Energy
  • Green Energy
  • Waste Reduction
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