Unmelted Nylon Plastic resin In final Molded part

[Monomer]

Hello all,

I am having an issue with a nylon 6,6 material. There is unmelted plastic pellets in the final product. We have tried melting the plastic by increasing the barrel temps as well as the fill speed and back pressure. We are still having problems with unmelted plastic pellets. We are using a General Purpose nozzle tip into a hot manifold system. Any suggestions on how to get the nylon melted??

[rickbatey]

How high are the heats? Mold and barrel? What is the residence time? How high did you go with back pressure? What's the recovery and cooling times? BTW, precolored or color at the press?
Now I HATE GP nozzle tips as they cause cold slugs. Try a full internal tape tip or even one of Sam Kern's Eliminator tips.
Rick.

[Airwinghma]

Greetings;

Not to Hijack but.. What is the attributes of a SAM Kern tip?

Is it worth it to start a Tip thread?

Scott

[Suhas]

Monomer,
What is the recommended melt temps and what is your actual melt temp (with a immersion probe)?
Suhas

Scott,
Worth the 'tip' - May be a new thread :)
Suhas

[Monomer]

How high are the heats? Mold and barrel? What is the residence time? How high did you go with back pressure? What's the recovery and cooling times? BTW, precolored or color at the press?
Now I HATE GP nozzle tips as they cause cold slugs. Try a full internal tape tip or even one of Sam Kern's Eliminator tips.
Rick.

We were running the barrel temps at around 535 F and up to 570 F. Our thermolators were set at 120 degrees F. The transfer pressure was around 1000. Recovery time is around 12.4 seconds. Fill time is around 3.5 secs. The resin was colored using a colorant. We tried shooting a couple of shots without the colorant and the unmelted plastic was still there.

Is it okay to use those nozzle types into a hot manifold system? The sprue heaters are set at 540 degrees.

[Ten Fingers]

Do you know what the compression ratio of the screw in the press is? A lower compression screw could have a difficult time melting 6,6 nylon pellets completely.

[rickbatey]

Great answers but you didn't tell me shot stroke versus max press stroke, cooling time, and Ten Fingers is dead on about the compression ratio. What's the actual melt temperature? Barrel settings may be off and if your residence time is low, your actual settings may be too cold. Can you watch the extruded psi? That can speak volumes as to what's actually happening in the barrel.

The Tip is indeed worth another post. I tried it and ran POM and ABS/PC cosmetic parts on the same Niigata w/o issue. It won't matter if the resin is shot into a manifold.
Rick.

[Monomer]

Great answers but you didn't tell me shot stroke versus max press stroke, cooling time, and Ten Fingers is dead on about the compression ratio. What's the actual melt temperature? Barrel settings may be off and if your residence time is low, your actual settings may be too cold. Can you watch the extruded psi? That can speak volumes as to what's actually happening in the barrel.

The Tip is indeed worth another post. I tried it and ran POM and ABS/PC cosmetic parts on the same Niigata w/o issue. It won't matter if the resin is shot into a manifold.
Rick.

The compression ratio of our screw is around 2:1. After talking with a resin supplier they suggested either getting a barrel with a higher compression ratio or doing a reverse temperature ramp and crank the temperatures higher then the recommended processing settings. We should be sampling tommorow and i am hoping these things will work.

[Ten Fingers]

I'd recommend using a different screw or different press with a higher compression screw in it. The extra high reverse profile will likely work when the press is running, but beware of the Rice Krispy bar like masses of partially melted pellets in your feed zone anytime the press sits down for even very short periods of time. They are frustrating to purge out.