balanced runners 1

[meh70us]

I have an 8 cavity plastic injection mold with hot manifold into cold runner.
The outside cavities short shot about 25% less of the inner cavities. What is the best way to balance the outside cavities for uniform mold fill?

 

[bradphillips]

Hopefully your design started as a "double H" or "double X" layout of the runner system.
If not , choke off the inner runner or widen the outer runner.
Avoid multiple gate sizes if your cavities are identically machined.

 

[formula1]

iF YOU WANT TO UNDERSTAND WHY THE INNER IS FILLING BEFORE THE OUTSIDE, THEN GOTO

http://www.meltflipper.com

 

[smokehouse]

I'll just add one more thing besides making the outermost runners a little larger and that is to vent the runners.

 

[patprimmer]

I agree with the meltflipper comments, but also advise the check where the waterways run. Are the outside runners only, passing close to a waterway. Regards
pat

 

[dhuffy]

As for the cooling effects on balance, there have been studies done where the inside cavities are cooled and no cooling on the outside cavities to try and reduce imbalance since it was once thought that a thermal imbalance existed in the molds and that created the imbalance. It sounded good and we have all used that explanation before. But the results of the test mentioned showed little to no change in imbalance when varying individual inside and outside cavity/core temps 100F or more.

This is supported by a few points in the study. For one, you will see imbalances on the first shots and not only once the tool heats up and it thermally stable, or if you short shoot with no cooling - simply put the mold in and do a short shot. Also cooling has little impact on short shot filling. Cooling has more of an impact on cosmetics, packing, etc...as the above tests indicate.

Take care and have fun,

Dave