Mucel causing zones in barrel to rise in temp far above set point.

Hi everybody. We are having a challenge with some of our machines when we use mucel. Mucel is nitrogen injected into the barrel and then into the part to create Hollow parts so to speak. Not sure if mucel is the proper word. Three zones In The barrel continuously rise in temperature around 300 degrees Celsius. The set points are around 240. We have to alter the set points to keep the machine running. We are all new to this type of molding, any suggestions? We are running poly pro with regrind in it. 10% regrind. Thank you in advance for any help you may offer.

Hi Joe,

what is the material type?
It seems like Your plastification profile isn´t well ballanced regarding to the Material used.
The overheating is caused by high friction of solid material in the late stage of barrel. Its typical for material with higher melting point, ABS, PC/ABS.
Rise the temp at zones before those that are overheated.
Also if possible reduce the backpreassure and pay attention to the screw rotation if it isn´t too high.

Let us know
J.

Thank you. I will find out exact material type today when I get to work. Will also ask the process techs about the ideas you gave. Will post results tonight or tomorrow morning.
Thanks again!

Yes. My point too. I too think the screw rpms are too high and/or the zones are set low on the temps.
Suhas

Regarding to the Mucell, there is also an influence of preassure gas. It can happend when screw plastification profile is not well balanced that this preassure works contra material direction flow caused by standard rotation.
When applied high backreassure even worse.

Its hard to say how high this influence is...so first check the standard conditions. Than play with mucell.

Sometimes its also possible to see this influence on Your own.
Ask colleague and prepare vacuum cleaner.
Drive injection unit out of tool.
Setup low plastifing length and Plastify with high (20-30bars) backpreassure (intention is to plastify and not reach the plastification length) due to the back preassure and at the same time to be sure that melted plastic is coming out from the inj. unit.
than stop and empty with vacuum cleaner material out of the hopper to be able to see the screw itself.
Ask colleague to go back with screw (setup slow speed; use protective glases when looking inside)
Take pictures or moovie with your colleagues comentary of length back.

You will probably not reach the position where the mucell inlet is, but You can see how the material lookslike, are they solid? semi melted? already melted? Gas traps, gas channels,...
All that will help You understand Your profile setup and what is actually going on there.

Sometimes this can´t be used for example if You have not enough plastification length available - than You are not able to moove the screw enough.

But sometimes its really interesting, what You can see.
J

Is this press a new one with the proper systems for MuCell or an afterthought retrofit? Without the exception I gut screw, counter pressure on the screw and proper non return valve; you will live this nightmare until project ends!!
I too think barrel is too cold and needs the proper heat profile plus slower screw rpm.
Rick

What is your recovery profile? I run Mucell on a daily basis for a load floor and do not see this issue. We have it on two machines. The screw and barrel should be set up for Mucell (and bought from Trexel). You say this doesn't happen when you are not running Mucell, correct? We run a slow recovery but a decent amount of back pressure due to mixing the gas into the melt. How long is your dose time? Whats your current recovery time? Send more information if you can and are still having this problem.