Posts: 9
From:Istanbul, Marmara, Turkey
Registered: Feb 2005

posted December 08, 2009 09:40 AM            

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I have a surface problem in extusion process of rigid PVC. There is an "arrow-shaped" (I dont know how to make a better description) traces on the bottom part of the profile. I am sure it is neither from material nor from screws. Because tryed to change both of them and it didnt effect anything. And only one profile making this among lots of them. Tryed to make adjustment from extruder temperatures (raised them, lowered them) but didnt change. Can there be something wrong with the die-design, in fact it is not a brand new tool and worked about 3 weeks ago without this problem but couldnt solve it since 10 days.
Serdar

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Posts: 177
From:Allentown, PA - USA
Registered: Jun 2001

posted December 10, 2009 04:35 PM            

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From what you describe, it sounds like "material flow" marks or melt fracture, but that is just a guess.

Can you post a link to a photo?

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Posts: 1
From:Newport gwent UK
Registered: Feb 2010

posted February 09, 2010 12:27 PM            

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Hi
It’s important to establish if the marks you are seeing are coming from the extruder or from the calibration. Typically the melt may be flowing too heavy to this wall and its struggling to enter the calibrator. Check the wall dimension. If it’s too heavy this is a good indicator it’s the cause. You then need to find out why it’s too thick- Die has been incorrectly rebuilt or started too cold so the plates have shifted, temperature of die too hot ( thermocouple not seated correctly not giving full temperater is normal cause)or the melt is too hot due to screw speed too high/temperature settings too high.
If the extruder looks correct the calibration may be too hot due to blocked water flow/general low flow/trapped air. Die to calibrator gap may be too short-try increasing.

Hope this helps

stevet

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