Hot Runner-Nozzle Heater

[Suhas]

Hello Sammy,
Thanks for signing up here. In regards to your question, when you say nozzle, are you saying the one on the machine? Please give us a clearer pic and we can give you some suggestions. Yes, it is expensive. I have a feeling that you may just be Pressure limited.
Let us know.
Suhas

[Sammy101]

Suhas,

The nozzle I am referring is for the hot runner nozzle.
Does processing under pressure limited situation weighing

[Suhas]

If the process is using all the pressure the machine has then you are exerting all that pressure in the hot runner nozzle trying to fill the plastic in the last point to fill. Example, if you have a 20 inch long part with one gate on one end, by the time the plastic travels 20 inches not only has the plastic cooled down but because of fountain flow the flow channels is much smaller. Therefore you need a lot of pressure to fill the last say 1 inch. But now the plastic is still molten in the hot runner and so now you are putting all the machine pressure into the hot runner system and can damage it.
In my opinion, it is not the heater, it is the mold design, placement of gates and of course could be part design.
Here is what you do quick: Is the required injection pressure = the max machine pressure?? If yes, that is the problem.
Regards,
Suhas

[Jendalf]

Hi,
Suhas has right, we need usually more information. what type of materiál are you processing? what temperatures are set/get from the thermocouples for heaters (sometimes happend when you use wrong type of thermocouple you get different REAL temperatures even that required are shown at display). Also what is busted? freezed?

J.

[rickbatey]

Are the failures in the same location? If so that may be a combination of excessive injection pressure and the duration of time the manifold sees that pressure, poor mold or hot runner design, manifold supports. machining limitations, poor fit or expansion consideration of the hot runner when up to temperature. Are you using the correct temperature range in the manifold and barrel and not trying to push cold resin too far into the mold?
More info would help with a much more exact root cause.
Rick.

[Sammy101]

Dear Rick and Suhas,

The material is PP and the melt temp is set from 210 to 220 deg. C while the hot runner heater is set from Zone 1 to 7 with 366, 365, 351, 280, 327, 351 and 370 deg. C respectively.
The design of heater system was made by INCOE, so we have no further details of its effectiveness except in some of our molds, with INCOE hot runner also but we do not know if the design is similar, we barely experience the same problem.
For the max injection pressure, the max setting is set to 210 bar and actual is 160 bar so I think the process is not pressure limited.
The failure usually occured at zone 3, 5 and 6.
I just termed it 'busted' or broken (not working). I do not know if I used the term correctly for this problem.

In addition, I attached the picture of the drops layout.

The you so much guys.

[rickbatey]

So what you're saying is that you have to replace the heaters because they've stopped heating? Were those temps in C? If so perhaps you should increase the barrel heats so you run the mold heats lower. Also do you use heat transfer paste on the heaters you replace? Not anti-seize as it will short heaters out when it gets hot due to the conductivity of the metal flakes. Lastly what are your water temp settings? Does the mold have any internal water leaks that could be grounding the heaters out? I've seen some molds leak only when under tonnage but be perfect when checked in the shop. Also be careful of the wire routing when replacing heaters and tape them up with high temp fabric tape made for the job.
Rick.