Hot Runner-Nozzle Heater

[Jendalf]

Both are possible, but heat influence on thermal behavior of the functional units of the hot runners is more probable.

note (out of theme):
I´v challenged simmilar effect. Problem here was the pneumatic controled needle malfunction due to the low temp of cooling water. The cooling water that cool down the base of the needle (that is connected to the manifold) caused the tightening of its diameter around the needle. The pneumatic wasnt able to moove with the needle (due to the friction) and that casued me short shots. Quite interesting

J

[Sammy101]

Rick and Jendalf,

Please correct me if my understanding is not inline with what you wanted to explain, but this tip expansion basically restrict flows, correct?
Does it really causes the nozzle heater got shorted easily? Does build up pressure inside the hot runner passage affects the heater itself?

Sammy

[Jendalf]

Sammy,
nothing is 100% sure here, but the heat influence is one of the most probable option. Especially because of the high temperatures set on HR.
Another thing is that if the nozzle is selfclose the function unit inside can be weared or broken or it can contain the forreign element inside (like metal).

J

[rickbatey]

Sammy, the tip growth from heat restricts melt flow. To compensate for the loss, the heat has to be cranked up really high to get the resin to start flowing again.
Obviously there's an issue with the hot runner and tooling due to the fact that you know which zones the failure occurs. Be that too much cooling or what have you. The hot runner is an extension of the barrel so it should be close to the same heat range. Then only slight differences should be required to balance the cavities. It could be that the gate inserts are wrong and that is driving the crazy high heats.
Rick.

[Jendalf]

Yesterday i´v talked with Incoe representatives on the Trade fair. Generally he agreed what was said here but maybe from lack of experience he didn´t know what will happen with hot runners at high temperatures exactly (he didn´t try it yet )

[Sammy101]

Rick.

I think the friction has less chance for the cause but for the excessive cooling, I think we have some issue here; but I will try to consider verifying both idea to see where the problem is.
I will post the result once we have the conclusion.

Sammy

[Sammy101]

Jendalf,

That is nice to here from the INCOE themselves.
We will try to consider of lowering the heater temp from 300 deg.c and see what will be the possible effect on the heater itself.

Sammy.

[rickbatey]

Sammy-I meant flow restriction not friction. The tip grows into the orifice and blocks the flow. Now I've seen tips that were so small they shear heated the resin to the point of thermal degradation before. Each time the mold was injected the temps would climb over 50*F!! But that didn't cause heater failure.
Rick.