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Jomar Product Troubleshooting – Short Shots


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.

Short shots in the preform molds will manifest themselves as short necks or preform that are not fully filled.

Common causes of short shots are:

a.  Loss of heat in one or more zones in the preform mold. (Water temperature control unit)

b.  Loss of heat in one or more zones in the extruder or manifold.

c.  Loss of injection pressure, or injection pressure too low.

d.  Loss of holding pressure.

e.  Loss of screw RPM.

f.  Foreign material blocking the nozzle orifice(s).

g.  Nozzle “Frozen off” from low temperature in base or manifold being too cold.

h.  Nozzle orifices too small.

i.  Hopper out of material.

j.  Not enough low pressure preform time.

k.  Partially melted material blocking throat in hopper.

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 short shots in the preform persist, contact Jomar’s Process and Tooling department at

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Egg Harbor Township, NJ
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