balanced runners 2

[meh70us]

originaly i said this was a maifold into cold runner.
this is a 3 plate mold 8 cavity "H" style runner on both sides of cender line of mold. the outside parts are short shot when backing off mold pressure. is there a trick orcalculation for ballanceing the runner from the differance in volume of the short shot part to the full part?

 

[Ricar]

Hello! I am doing a research in ways to eliminate the subjectivity of the molder while tuning an injection molding machine. Any sugestions?

 

[ornerynorsk]

MEH70US, vent, vent, vent !!! This cannot be overstressed. Most molds are not constructed with enough venting. The further out from the sprue that you get, the heavier the venting required (melt flow is cooling rapidly as it travels).

 

[PrentP]

MEH70US,

See my webpage at

http://www.polytechconsultants.com/balancing.htm

and adapt the analysis for an H shaped cavity system.

Regards,

Peter P

 

[ornerynorsk]

Proportional gating will only be useful if there exists proper venting.

 

[dhuffy]

Simply visit

http://www.meltflipper.com

for an indepth explanation on why you see filling imbalances on geometrically balanced runners. Basically it is shear creating different material properties that flow to certain cavities in multi-cavity molds (which is not always the inside cavities - it depends on material, runner layout, and process conditions). Venting does play a role but is not a major factor at all for the type of filling imbalances you are talking about.

If you have any further questions or would like to know how to solve the root cause of the problem, just ask. Thanks and good luck.

Dave

 

[dhuffy]

In addition to my previous post (because I could not figure out how to edit it, hehe), simply changing runner sizes will create a pressure balance at best that MAY work for one given process and material lot. If the pressure in the system changes for any reason (different injection rate, material lot, temperature settings, etc...) that balance will no longer work. This is why we need to address the problem at the root cause.

Putting band-aids on problems like this is why we are loosing our manufacturing edge. We need to mold smarter and not be afraid of new technologies or explanations on how we can improve. When business is down is when we need to look at what we have on our plate and make it better to increase existing profits. Ok, that's enough for now. Have a great day everyone.

Dave