Balancing Family Molds…

A common blog reader asked this question regarding family molds…

What is the best way of balancing a family mold?
My Response
When balancing family molds, it is best to approach it in two steps.
Step 1 – Balance the runner system – When possible, try to balance the runner system so that each gate starts filling the mold cavities at the same time. Keep in mind, different rates of fill will affect this balancing.
Step 2 – Balance the gates – After you have determined that all the mold cavities have begun filling at the same time, then adjust the gate dimensions to balance the filling of the mold cavities.
In the best case scenario, you could… 1) short shot the runner system and see all the mold cavities begin to fill at the same time, and 2) end filling with a short shot on each mold cavity, so that all the cavities can complete filling and begin packing under pressure control.
Additional Thoughts
Most people only adjust the thickness of a gate to restrict or promote flow, yet this has a significant impact on the shear thinning of the polymer. Adjustments to the length, width or number of gates can often promote or restrict flow, yet have less impact on the shear heating and thinning of the polymer.

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