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Jomar Product Troubleshooting – Rocker Bottoms


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

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.

  • 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.


Rocker bottoms show up as bulges in the bottom of the bottle or as “warped” bottoms in ovals. The bottoms are usually still hot and soft in either case.

Common causes of rocker bottoms are:

a. Not enough exhaust time.

b. Poor blow mold venting.

c. Insufficient cooling of blow mold bottom.

d. Melt temperature too hot.

e. Cycle too fast for mold or bottle.

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 rocker bottoms persist, contact Jomar’s Process and Tooling department at

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Egg Harbor Township, NJ
08234 USA

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