Re-heat & Blow (RHB or 2-step)

  • 2 separate and distinct process – intermittent injection molding + then a re-heating of the injection molded preform prior to blowing it into a final geometry.
  • Bottles: water bottles, carbonated soft drink bottles, clear or highly transluscent personal care.
  • Typical Resins: PET, some oriented polypropylene (oPP)
  • Standard Machinery:
    • injection molding machines: Husky, Milacron
    • blow molders: Sidel, Sipa, Krones
  • Typically single layer, but there is a growing multi-layer market segment
  • Preforms are allowed to cool or “cure” between injection and blow molding processes.
  • It is best to allow the preforms to come down to ambient plant temperatures prior to re-heating & blowing – this is best achieved by practicing stringent FIFO (First- in, First-out) procedures with preforms, as well as enforcing rules that the preforms must be in the plant for at least 12 hours (more for very thick preforms or large gaylords) prior to blow molding.
  • Focus on purging the injection molder per standard injection molder procedures
  • Use a purging compound approved for high cavitation hot runners as preforms are often molded in very high cavitation (96+ cavity) molds.
  • Use a purging compound that is easily displaced by PET after purging to maintain optimal part clarity.
  • Closely monitor preform inclusions like carbon, because once it starts, you make a lot of bad parts in a short period of time.
  • Make sure that manifold drops are on as many separate heating zones as possible to insure consistent heating of inboard and outboard drops.
  • Seal the injection unit with a sealing grade commercial purging compound during extended downtime events.
  • Purging compounds are not used to directly clean the blow molding unit (Sidel, Krones, Sipa, etc.). The key here is that good preforms = good bottles. Keep contamination out of the injection process for the best results in the blowing process.
  • Monitor air temperatures in the blow molding plant. I have observed good machines making bad bottles after a bay door was briefly opened during the winter.