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Jomar Product Troubleshooting – Flashing

Example of seal flash

Example of seal flash


When trying to solve processing problems, it cannot be emphasized enough to move slowly.

  • Make only minor changes and only one at a time.
  • It takes a while for a mold to stabilize after a temperature change.
  • Be patient! Go slowly and keep notes on what did and did not work so duplication of steps is avoided.

The following tips are suggestions only and may not solve your problem. If you have an issue that is impacting your production process, please contact Jomar and we’ll do our best to assist you.

Flashing in perform molds show as a ragged part lines in a blown bottle and as ragged edges on unblown preforms.  This is different than “pinching” in the blow mold, which is another common issue. The following are typical causes for preform flashing:

a.   Foreign material inside core rod bearing area in neck ring(s) or on mold surface, or on core rod. Visually inspect these areas and remove any debris.

b.   Melt temperature too high.

c.   Preform mold temperature(s) too high (Water temperature control unit).

d.   Injection pressure too high.

e.   Holding pressure too high.

f.    Clamping pressure insufficient for mold (mold too large for press or low hydraulic pressure in clamping system)

g.   Poor mold construction (parting surfaces not flat and level all the way across), or damaged mold.

h.   Nozzles not seated properly or are damaged, mold nozzle seats damaged.

i.   Mold and/or hose passages plugged.


If you’ve purchased a mold from Jomar, you should have received the optimized process parameters or “playbook” which indicates all the proper temperatures, pressures, settings, etc. for your particular mold. Compare your settings to those presented to you by Jomar and make sure your parameters match Jomar’s recommendations.

If your problems with bottle flashing persist, contact Jomar’s Process and Tooling department at

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Egg Harbor Township, NJ
08234 USA

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