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| Author | Topic: Plastic Extrusion Calculator |
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nick p Member Posts: 1 |
posted October 02, 2009 02:10 AM
  
I have tried to calculate our extruder rate through your calculator for a rough evaluation of our BOPP line main extrusion. The extusion is a cascade one with a seperate melt and metering extruder. Metering extruder rpm are set manually and melt extruder is "slave" through a pressure controller set to 40bar between melt and metering. I used the data from the metering extruder rpm:41, 10inch, 22 L  , and for homo-PP (PP-H)I got back a flow of 1268kg/h. I know there is something wrong with the calculation (probably the melt density because of the pressure built up and the tuning factor) because we have an output of 1700 kg/h in our final product, without adding the regrind output that is fed to the extruder without being able to measure. (somewhere about 250kg/h) What values should I use for a better calculation? IP: Logged |
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Tom C Moderator Posts: 964 |
posted October 02, 2009 08:56 AM
The calulator predicts typical output. The calculation is related to melting ability which is a function of exposed barrel area. If you are significantly off the calculated value, instability and poor product quality could occur. A couple of things could be causing the dfference: Is there filler in the PP causing and increase in melt density? If you change the tuning factor to 1.00, you get 1691 kg/hr which is very close to your result. PP has a history of producing only 70-75% of predicted output. Some screw designs overcome the output limitation of PP which is caused by poor feeding and slipping on the barrel. The output on those screws is equivelent of other polymers which have a 1.00 tuning factor. You may have such a screw. Becasue fo your tandem extruder setup the first extruder has less responsibility for generating pressure and therefore potentially more of the length can be devoted to melting rather than pumping increasing it's output rate potential. In a typical extruder a portion of the L:D is devoted to pumping and not melting. This is compensated for in the calculator. The tuning factor can be used to adjust for this situation. The calculator is a predictor of approximate extrusion output rates over a wide range of materials and extruder designs and can be used as a benchmark. Your results seem to fall within "normal" with a small concern that you are potentially not getting enough melting and mixing in the first extruder. A more in depth analysis can be done using a screw simulation program. I have such programs available produced by SPR and Compuplast. ------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
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