Flash at the nozzle

[finerdetail]

I'm somewhat new to the injection mold process, but I'm learning quickly. I run a BOY 55A hot runner I.M. with a dual cavity puck mold for quality purposes (plastic recycling). I'm having issues with flashing or, for lack of a better term, nipple (?) at the nozzle. It varies anywhere from 1 - 7 millimeters in length. The shorter ones aren't a problem, but the longer ones sure are. Any help here would be great!

[finerdetail]

I've attached a photo (a poor one) of a 6mm nozzle flash per my previous post.
13

[rickbatey]

I think what you have is referred to as drool. It is due to the molten resin in the nozzle not separating from the cooled resin in the cavity.
Root causes are: nozzle temp too high or low; too short or long of a suck back (decompression) stroke or incorrect speed; screw recovery is finished too early before the cooling timer runs down and the mold opening; too slow mold break away speed; wrong nozzle type or orifice used for the mold. Also your resin could be wet.
Rick.

[finerdetail]

Thanks so much for the advice. Alot to consider for what seems to be such a small problem. Decompression is available, but we don't use it. I'll start there.

[moldingppm]

I'm going to say because you're not using decompression and/or too high of temperature.

[Pilot]

Which material is it?

Pilot

[rickbatey]

Any changes? What's different now?
Rick.

[finerdetail]

It's recycled PET. Very dirty stuff, compaired to what most of you are using (I'm guessing).

[finerdetail]

I'm going to say because you're not using decompression and/or too high of temperature.

The decompression helped some. Too much and I got black streaks (we make clear pucks to test for color and contaminants). I took the temps down and the pucks got cloudy. A fine line I'm walking here. I think I'll increase my mold separation speed next........

[Pilot]

Try to reduce back pressure.... with decompression.
Pilot

[rickbatey]

PET should be dry or the moisture will cause drool and bubbles in parts. A slow decompression speed should let you use more stroke without causing color shift or other issues;but there will always be limits. How long from charge completion to mold open starts? More than five seconds, you'll have increased drooling. If the press press has a high torque setting for the screw run, turn it on. Also what is the barrel heat settings? It could be your too high for the amount of shots in the barrel or even degrading the resin with shear heat from screw rotation or nozzle tip style/orifice.
Rick.

[finerdetail]

I have the temps as low as possible without my pucks getting cloudy. Decompression (dc) is starting to cause blistering and what I call "hyper-drool"! Drool that is approx. 5 - 8 mm in length. When the dc is set to zero the blisters and the hyper-drool go away. Increase in mold separation speed helped some. It's hard for me to know how each change is going to affect the other.........

[finerdetail]

PET should be dry or the moisture will cause drool and bubbles in parts. A slow decompression speed should let you use more stroke without causing color shift or other issues;but there will always be limits. How long from charge completion to mold open starts? More than five seconds, you'll have increased drooling. If the press press has a high torque setting for the screw run, turn it on. Also what is the barrel heat settings? It could be your too high for the amount of shots in the barrel or even degrading the resin with shear heat from screw rotation or nozzle tip style/orifice.
Rick.

Sorry Rick, I didn't see your post before my other post. We dry the PET for 3 hours (320 C/-49Dewpoint). Maybe it's not long enough? Charge completion.....define. The actual injection or when the screw stops turning? Barrel temps 475/485/500/tip=510. Block temp=510. Nozzles=620.

[finerdetail]

By the way, this site is an amazing source of knowledge for I.M. I can't get my supervisor/manager to let me take ANY classes or seminars on this.

[rickbatey]

I think the nozzle temps are way too hot. They should be an extension of the barrel zones. I think you need to start dropping that temp.
Now what I'm talking about is after injection and hold is finished; the screw starts to rotate and charge/recover shot for the next shot. What I'm wondering is how long between the screw stopping after charge and decompression, until the mold opens. Your looking for about five seconds: more and you'll drool, less and you'll drool.
Now that we have a better picture of your process, Do you have any melt filter? It could be they are filling up or since you don't have them, there is something in the nozzle tip or injection unit.
Rick.

[Pilot]

If I am reading this thread, I am thinking, that as a first aid you can use recovery delay with decompression, which must be balanced between flash and blistering.
What about your setting sheet, could be available for us?

[finerdetail]

If I am reading this thread, I am thinking, that as a first aid you can use recovery delay with decompression, which must be balanced between flash and blistering.
What about your setting sheet, could be available for us?

Sorry for the long delay.....no melt filter. We actually want the contaminants to flow through so we have an idea how clean/dirty our chip is. We don't have any kind of print-out or electronic copy of a setting sheet. The I.M. we use is fairly new but runs off of FLOPPY DISKS!!!!! Can you believe it?!! I can get you the info you need to help me.

Rick, it's about 10 seconds from charge completion to mold open. I found the delay setting for this and I'm working on it.

[rickbatey]

It's an Engel press? Great machine if so. Can you guys do a moisture check to make sure resin is dry? The resin doesn't sit in the hopper too long does it? It could pick up moisture from the plant all though that is a long shot at this time of the year. I've seen cracks in the feed throat areas of machines that allow some water from that cooling circuit to get on the pellets.
I still think your nozzle temps are too high. Have you tried dropping them slowly over several hours?
Rick

[Davidflakejr]

Use some decompression after recovery

[Davidflakejr]

I just retrofitted all of our Engel presses with floppy to USB adapters. Love them so far.