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 Extrusion, Single Screw
 Voids - Single Screw Extrusion - Rubber
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equate0404 Member Posts: 3 |
posted August 23, 2006 10:16 AM
  
Hello We make closed cell foam rubber (EPDM, SBR, Neoprene, etc. with blowing agent). Our main defect is what we term "air traps" in our pressed buns. We have tried a variety of experiments to get rid of this problem - largely to no avail. We believe that our extruder may be the culprit. It is a 10" single screw extruder with a 150 hp motor. We currently achieve an output of about 4800lbs/hour. The extruder is not vented (which may be a problem in and of itself). Our air trap problem comes and goes - which is to say that sometimes we will go a month without seeing one, and then we will see them in every bun. Our process is such that we remix some of our material and send it through 2 large mills and then on to the extruder. Other facts about our extruder... NRM Corp We currently have no measuring devices for pressure on the extruder. IP: Logged |
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Tom C Moderator Posts: 840 |
posted August 23, 2006 03:41 PM
If the problem occurs a lot in the summer and not in the winter, moisture from the air may be the problem. Can you heat the rubber more in the mills prior to extrusion to drive off moisture. Does some of the rubber sit in inventory and "get wet". Any possibility that the blowing agent is not well dispersed at times and a concentration of the blowing agent is the trouble? Do you have a method of increasing the back pressure in the extruder to help squeeze out trapped moisture or air? Any chance that the problem originates with your material supplier?, or rework? IP: Logged |
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equate0404 Member Posts: 3 |
posted August 23, 2006 05:18 PM
We do experience a downturn in quality over the summer months. In a recent correlation study comparing quality to relative humidity with regard to extrusion, there was a moderate negative correlation. However, our current problem appears to be occuring with only one of our stocks, while another similar stock is showing near 100% quality. IP: Logged |
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alanv Senior Member Posts: 21 |
posted March 01, 2007 12:59 PM
Do you run your compound through an anti-tac solution to prevent sticking? If so do you control the concentration of the anti-tac? Is there sufficient recirculation (or too much, the circulated emulsion will also heat up. Have seen similar problems where anti-tac causing surface defects on rubber. There are also "dry" anti-tac compounds that are less problematic to the surface, but the main drawback with these are airborne particles. Rgds IP: Logged |
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equate0404 Member Posts: 3 |
posted May 09, 2007 10:15 AM
Thank you. We do use a wet antitack solution. We are currently in the process of performing experiments using dry antitack. IP: Logged |
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