Correcting for Cavity Imbalance…

I received this inquiry the last week…

I have been using the intelligent moulder worksheets and have found poor fill balance in our hot runner tooling. I have had variations from 14 to 22%. How do you get to 6% or

note: The Dynamic Cavity Imbalance Test measures the imbalance by comparing the part weights from each cavity using three different injection speeds. 

My Response
You should first look for inconsistencies such as blocked or damaged vents and gates.

You should review your hot runner system and determine if any gates can be adjusted. Often an adjustment can be made, or a him can be placed behind the gate drop to reduce flow in the mold cavities which are not filling well.

If the runner system has sharp turns, you can first try rounding the corners to reduce the stresses.

Additional Thoughts
Each mold can pose it’s own unique circumstances. For branched runner systems, the ‘Melt Flipper’ can often be used, even with hot runner molds. This technology, licensed by Beaumont Technologies Incorporated, uses strategically placed inserts at runner branches. The inserts rotate the polymer melt to help manage the uneven stresses resulting from runner turns. I have seen this become very helpful in many different applications.


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