Short Shot Defects

A short shot defect occurs when the volume of plastic needed to fill the mold cavity is short by some amount. Because the plastic is injected from the bottom of the preform, the missing material is seen at the top of the preform, where the sealing surface is. In other words, the molten plastic injection is short and leaves the container incomplete and deficient, hence the name “short shot.”

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Plastic Material Types at Risk of Short Shots

Short shot defects are most common in High Density Polyethylene (HDPE) and Polyethylene Terephthalate (PET) plastic materials during blow molding processes where the injection step forms the finish in the preform, including IBM, 1-step PET (ISBM), or 2-step PET (RSBM).

Common Causes of Short Shots

There are several reasons why a short shot defect may occur, including:

  • Flow restriction due to narrow or blocked gates within the mold
  • Molten plastic is too viscous and may solidify before reaching all cavities
  • The mold is too cold to allow the molten plastic to completely fill the cavity before cooling
  • Inadequate venting technique resulting in air or gas pockets
  • Inadequate injection pressure 

General Troubleshooting

If a short shot is detected, adjust your blow molding machine and examine your blow molding process, which may include increasing injection speed, pressure, and temperature or redesigning your mold with wider channels and gates. Some short shots can be detected on ALPS leak testers by using tilted probes with harder seal durometers. 

ALPS Inspection is proud to be a market leader in manufacturing in-line leak inspection equipment for empty plastic containers of all sizes, shapes, and materials. Our team of experts provides thorough defect analysis and feasibility testing services, giving you the valuable insight needed to improve defect detection and ensure optimal leak detector performance.