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Subject: Re: Fisheyes on PP

Date: 07/05/00 at 7:14 AM
Posted by: Carl Howarth
E-mail: howarthc@mindspring.com
Message Posted:

In Reply to: Fisheyes on PP posted by Angel Urbina on 07/05/00 at 4:04 AM:


I will try to answer your question on specks, but I don't know about 'fisheyes'.

Black specks in your material is not uncommon; it can be from a variety of sources. First, check the pellets before they are molded. Often material suppliers will accidently ship material with specs in it. The source is generally in their extruder. They may have been running another color, and did not sufficiently clean their extruder. Another possibility is the machine that you are using to mold. If you haven't 'purged' it enough, colored materials from previous moldings will hang up in the barrel and check ring. As you mold the PP, they work their way out and appear as black specs. This problem is exagerrated by the fact that PP is a relatively low temperature material, and if a higher temperature material was run in that press (like nylon), it will not melt in the PP. The result is that you will get a continuous supply of 'black specs' from the check ring and nozzle.

I would try purging the press thoroughly with a clear material (typically styrene), and mold again.

You might also want to try drying the mateiral (most people do not dry PP, but it can improve surface appearance).

If neither of these helps, I suggest you contact your material supplier to begin troubleshooting the materia on their end.

I hope that this helps.


Carl Howarth

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