plastic bruning

well Thank folks for all the help we had the new screw install and still had the problem change out the nozzle and it's ext. way to long and that's what we think it was the nozzle ext. was way to long and the lands were way out as well.. have not seen it in the past month doing good.. fingers crossed

Rendy.

Is this mold a hot runner or cold runner? I don't remember if that was mentioned. Several of our customers have complained about certain HR systems that cause PC and co-polyester (Tritan) to burn. If this is a cold runner then the screw &/or barrel is probably at fault.

Bill Baskind

yes problem went away but has come back just came back other day. we are getting a new screw built just for PC. found the old screw was not meant for PC only ABS.

well it still there only on one machine still comes and go's

Bill if it was the dryer it would show up in other press's we do run this matl. in other press with the same dryer. pretty sure that's not it but thanks.

not sure Brent i was thinking the same thing. but changed out T/C on nozzle yesterday and have not seen it for about 12 hrs. now, had clamp style now back to OEM type that goes into the nozzle body. may be the fix,trying to set up test in the AM to check each T/C out to see if there is any difference in the two you would think so. will see and again thanks everyone for your comments.

mold on !!!

Have you checked the dryer for contaminant resin? Many times I have found that to be the case as there are many nooks for contaminant to hide. Usually this is the last place for anyone to check.

Hope this helps.

Bill Baskind

Is this a new lot of resin?

Keep on Molding!

brent

right now it looks like one press and it is PC and has been running there for some years now with no issue's. no shut off nozzle. Bill is there a easy way of doing residence time. not sure my numbers were right. yes bill lowered all barrel temps. and screw rpms and back pressure seems to help a little. screw and barrel were pulled and checked looks ok at this time.

Hi,
some questions that might help:
- Do you have an HR? Is it properly designed to avoid stagnation of PC or excessive residence time?
- what was the resin you have ran before?
- do you have a shutoff nozzle on your machine?
- Are the check rings working correctly?
- Are the machines you are using with a correct size for your mold or are they too big?

Regards,
Pedro
http://www.linkedin.com/profile/view?id=23488898&trk=tab_pro

Here's the last possible point, what was the MFI, and what is it now? I wonder if something changed with the resin, since this problem went from press to press. Are you using the same drier and loader?
Rick.

Since this doesn't appear to be related to any specific machine, this is probably caused by the process. Look at your melt temps compared to the injection speed. Is the fill time consistent? With an electric machine you can pull up a record of fill times. If fill is pressure driven and not time/speed driven your problem is probably a slow fill shearing the material.

My two cents

we lowered all the barrel temps to see if that helps but it is not, nozzle tip and body are a nissie and is GP we have been running this matl. for a long time it just started happening. reg grade PC not UV or FR.

This usually happens when running the wrong nozzle body and tip, or when there is a dead spot for melt to sit in and cook (end cap)before being injected into the mold. What type of nozzle and tip are you using?
Also, is it FR or UV stable? That can be caused by too high barrel settings or shear.
Rick.