String mold on plant machine only

[kev1lev]

I have a stringing gate issue. It run’s fine on the trial machine, but when taken to the plant. The mold has strings. The mold is a non-valve gated. Material is TPO. Has one gate, which is a film gate. Single cavity. The string are about 3 to 10 inches long. I could not make it string on the trial machine, but the mold is not going to run on the trial machine.

Things I have changed:
Cooling - 5, 10, 20, 30. Stringing at all time.
Decompression – 0 to 30mm (Nothing)
Mold Runner heats 50F above and below melt temp
Back pressure same as trial.
Purge temps same as trial
Plant runs Pneumatic shut-off nozzle, trial plant is hydraulic
Mold Cooling is to design.
Runner system taken out check material types, tolerances, watts, heat-up temps times, etc.


The nozzle does not leak when close during purge. Cannot figure it out. Plant says it not there machine, but other tools they have their string as well.

[Suhas]

Hi,
When you say back pressure same as trial - have to tried to lower it on the production machine? Remember that the back pressure is also subjected to the intensification factor on hydraulic machines.
I suggest that you make a table of the machine specifications between the trial and the production, look at the difference and you may get a hint. Also why do you have a shut off valve? (May be OK, just trying to understand) How do you know it is working correctly?
Suhas

[kev1lev]

When I talk about shut-off, I'm referring to the barrel shut-off nozzle. I figure that this is where my problem is, but I'm not finding anything to back up my hunch. My cycle time varies less that a second, on a cycle time over 40sec. My cushion varies less than 1mm on a shot over 400mm. My fill time is right on everytime. Shot size is also very consistance as well.

Other tools have been made for this machine over the years, but this tool I has a problem. But what is different is that this mold does not have a valve gate for the nozzle.

When I compare machines, and process set points. I always go off actuals. The actual back pressure is around 1500 psi. Max injection pressure is 16000 psi, while transfer pressure is just a little less than max injection pressure.

[Suhas]

How much cushion do you have? 1 mm = 0.040" and that is 'OK' not great. What is the screw diameter?
Suhas

[rickbatey]

I think it's the nozzle control on the machines. One opens the nozzle during all suck back strokes; the other doesn't. Watch the nozzle open output and see when it shuts off. There is some delay timers, more than likely on the press or you can adjust the control parameters if its an Engel.
Rick.

[Ashley]

I have found nozzle shutoffs are more likely inches behind the actual nozzle opening. Make sure you are using the same style nozzle as the trial machine.

Reverse Taper(nylon),Full taper (abs, etc), General Purpose.?