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| Author | Topic: Polypro Surface Defects |
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Justin7 Member Posts: 3 |
posted March 05, 2005 03:31 PM
  
I've been helping to develop a santoprene-polypro coextrusion. Our facility is new to polypro and have been finding it difficult to process. The extrudate looks good, but after it comes out of a wet sizer we find air bubles on it. Does this material gas on cooling, could we be boiling the water in the sizer??? Any ideas would be appreciated. IP: Logged |
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Tom C Moderator Posts: 502 |
posted March 07, 2005 08:21 AM
Justin, PP does not gas on cooling. Check the inside of the extrudate to see if it is foamed. If so, then you are experiencing degradation in the extruder. I have seen cases where the cooling water boils and casues surface defects. Try increasing the volume of water to keep it from boiling. ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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louis33 Senior Member Posts: 115 |
posted March 07, 2005 04:28 PM
Water cooling tank? Are you vacumm sizing this extrusion? Are the bubbles on the surface of the tube causing little pock marks or depressions in the tube surface. A little more detail would help us to help you.
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Justin7 Member Posts: 3 |
posted March 07, 2005 08:02 PM
Yes, the part goes into a water cooling tank immediately after the sizer. The bubbles do cause the small pot marks and are predominently on the bottom surface which is flat. It doesn't seem to matter what combination of water flow into the sizer we use. We only seem to change the size and frequency of the pot marks, we don't seem to eliminate them. Thanks. IP: Logged |
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Tom C Moderator Posts: 502 |
posted March 07, 2005 10:19 PM
Justin, If you send me the part and downstream details I can put it into the cooling simulator and see what comes out. I only ask that you will allow the results of the cooling simultion to be posted here. ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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Justin7 Member Posts: 3 |
posted March 09, 2005 09:01 PM
To be clear, you need a drawing, linespeed, extrudate temps, draw down, and tank dimensions and temps. I'll have to run it by the higher ups before giving out this kind of info. Thanks for the help. IP: Logged |
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Tom C Moderator Posts: 502 |
posted March 09, 2005 09:22 PM
Justin, That would do it. Details like dimensions don't need to be published. Just a graphic representation of the process is shown. ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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louis33 Senior Member Posts: 115 |
posted March 10, 2005 07:41 AM
If they are only on the bottom, and you can move them around, then you can eliminate them. You might try low pressure water jets along with some thin pieces of brass shaped to fit the underside of the profile that would disturb them as the profile ran over the brass. Perhaps a series of water jets aimed across the flow of the product to "blow" them off. Hope that helps. IP: Logged |
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alanv Senior Member Posts: 7 |
posted April 24, 2005 03:29 PM
Hi Justin7, I too have had a similar problem running HDPE tube. The build up of bubbles becomes visible on the brass sizing die then when they leave they stick to the extrudate then cause the indent. I have moved the water circulating baths closer to the extruder (almost gravity fed) and have one length of flexi tube (approx 4m) feeding to through a glass venturi jar then to the sizing die. As of two days ago I ran for 11 hours without any air bubbles on the sizing die or marks on the tube. Got some good advice from the guys here also. My original posting is listed in the index. Good luck and hope the common problem is eradicated. Alan V IP: Logged |
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