Hot Runner-Nozzle Heater

[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.

[Sammy101]

Dear Rick,

Yes. That is actually what is happening. We are also looking for the possibility of suggesting to change the setting to increase the barrel temp instead of the runner heaters.
Yes. The temperature is in Celsius. The setting of coolant for the core and cavity is set at around 25~28 deg.C (chilled water). As for the heat transfer paste, I am not sure if they are using such but I am glad you mentioned it. I will take a sneak peak on their PM process to see if they do.The last time I checked the condition, we have seen no leaking water in anywhere that may close to the heater but we are looking for the possibility of moist (from air) that may develop as heat and very cold medium interacts. Do you think this is reasonable to consider?

Thank you very much!

Sammy

[Jendalf]

First rise temperatures on barrell to 235-240 °C.
Second the temperatures on HR are too high. Set them +5-10°C higher than barell temperatures.

What is the closing/opening mechanism on HR nozzles? are they self closing, pneumatic or hydraulic controled?

[rickbatey]

Sammy the extreme high heat is shortening the life of the heaters but there is another method that really reduces heater life span, not using soft start when the mold heats are turned on!! Check and most likely you'll find out the cold start or evaporation mode is disabled to start the mold sooner. When cold, some moisture will be in a heater and if the amount of current is too high, that moisture when released can short the heater internally. I'm sure the thermal shock hurts the heater elements as well; room temp one moment and red hot the next. Also I think that the mold might suffer from setting it in the press without pre-heating the hot runner.
The reason I asked about the water is there may be too much surface contact between the cold section of the mold and the hot runner. That's another reason why the heats are so high as the manifold is losing so much heat to the mold steel. I worked on an early manifold system that used the gas inside to transfer the heat around the entire system. We had an issue with too much heat transfer so we made insulating crush rings out of alternating pieces of brass and stainless steel. No more issues. Last possibility: when pulling the mold for change over, depending on mold design and water fittings it could be easy to not drain and blow out the water lines, disconnect tyem while under pressure and the cold water spray, run, drip, or soak onto the hot runner.
Rick.

[Sammy101]

Jendalf,

Sorry but I dot quote understand your second instruction, are your saying that I should increase the HR temp than of the barrel with +5/-10 deg. C variance?
I appreciate if you make it clearer.

I am not sure of the system for closing and opening. I will get back to you on this.

Thank you so much!

Sammy