Hot Runner-Nozzle Heater

[Sammy101]

Dear Everyone,

Good day!

First I would like to thank everyone especially this site to where I learned the way of scientific molding.
Now, for my concern, we have molds in our customer that reportedly experiencing frequent busted nozzle. At least two to three times of having this problem for a month of production.
When we asked them, they mentioned that it is due to type of heater used that is prone to problem. The existing nozzle heater is an INCOE cartridge heater. Now we are planning to reply the whole runner system to make the nozzle heater with cable heater (tubular type). The modification is costly and we need justification that the problem is really because of the type of heater.
Honestly, I am not familiar with the hot runner system cause for in seven years in the industry, I only handled cold-runner type.

Your insight on this concern is highly appreciated.

Thank you very much every one!

[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.