Random Splay on a part using Celcon M90

[joeprocess]

Ran into this issue of random splay on a part we have been molding here in the same press many times before. The mold is a 4 cavity tool and when the splay shows up it shows up on all 4 parts. When the splay does not show up all 4 parts are good. The shot size is on the high side of barrel capacity. The machine will run 1 to 3 shots of perfect parts than 1 to 3 shots of splay. I've been through all of the normal troubleshooting melt temp., dry material, machine consistency, check ring test, visually checked raw material for contamination, water leak in mold, etc.

I still suspect the material is contaminated. But if it is I'm thinking it is contaminated with a homo-poly acetal. That being said I don't know if mixing co-poly and homo-poly acetal would cause this type of reaction.

I am going to bring in a new lot of material and test it, and also test the suspect material in a different press, but any feedback to my question would be appreciated. This one has me stumped.

[brentb]

Test your mixed/contamination theory by mixing some and observing
Could you have a barrel zone overheating

KOM

brent

[JayDub]

The shot size is on the high side of barrel capacity. The machine will run 1 to 3 shots of perfect parts than 1 to 3 shots of splay.

I had this problem once with a large PC part. The problem was too much shear from the screw on recovery. You can check this by slowing down the screw RPM - add more cycle time as necessary (we increased ours by 30 seconds). If the splay goes away you know you need a bigger barrel.

[chrisprocess]

Mold temp and cycle time?
First thought was to verify sufficient flow in all waterlines, come up in mold temp to help with cosmetics. (worked yesterday with hostaform copolymer)

Or if residence time is too little (large barrel capacity) and if there's not enough back pressure your melt may not be homogenized.. So your pellets may not be melting all the way through
And of course a good purge to gt rid of whatever was running in the barrel previously

Let us know what you find

[MNDesign81]

I had this problem running a 4 cavity family mold in my 75 ton, 4 oz & 150 ton, 8 oz presses.
It happened using real Celcon as well as Iupital & another Korean POM [unfilled, black].
We pre dry the material & run a little higher back pressure. We also use a reverse injection profile going from low to high [500 & 1000 PSI hydraulic]
Been running like that more than 5 years now.

[rickbatey]

What are the actual barrel settings? Screw rpm and back pressure? How about recovery time versus cooling time? Maybe it’s from heats cycling on and off on barrel? Can you trace the splay from the spruce all the way into the parts? What is nozzle orifice and bushing diameter? What type of nozzle tip?
Rick.