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| Author | Topic: Melt pump |
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john green Senior Member Posts: 17 |
posted April 17, 2006 11:32 PM
   
Does anyone have knowledge of converting an existing screw to incorporate a melt pump we run a cast extrusion line using ldpe 130mm screw ratio ld 28/1 with 90 to 140kw motors .I have been trying to run pp material on dies up to 2.5 mtrs wide the problem I have been getting is surging on the output causing an ununiform thickness across the web any info or contacts in the UK would of great help John help IP: Logged |
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Tom C Moderator Posts: 695 |
posted April 18, 2006 03:34 PM
A better screw design would be much cheaper. Dr. Peter Prentice of Polytech Consultants in the UK would be a good place to start. Tom C IP: Logged |
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Stephen J. Derezinski Senior Member Posts: 35 |
posted April 18, 2006 09:06 PM
Hello John-- Yes, the screw was ok for LDPE, but is likely not suited to PP. But, before a new screw is designed, some trial and error with barrel zone temps could give clues to the source of the instability. So, try changing the solids conveying zone up and down slightly to see if you get any improvement. Next try the zone over the transition section. Do one zone at a time, and give it 1/2 day to come to thermal equilibrium. With luck, you may be able to solve the problem with barrel zone temps and not need to change screws. For some information on the effect of your delivery system on stability, see http://www.extrudertech.com/antec971.pdf steve@extrudertech.com ------------------ IP: Logged |
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john green Senior Member Posts: 17 |
posted April 19, 2006 10:58 AM
Dear Sirs Thankyou for your input I tried varying temps on the barrel and die improved considerably running from 240 to 280 degrees on the die but I could only run at 15mpm as opposed to 45mpm with pe I have taken your suggestion of the screw and am looking into this Regards John IP: Logged |
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Stephen J. Derezinski Senior Member Posts: 35 |
posted April 19, 2006 02:16 PM
John-- For a truly good analysis all of the machine and material data are needed. Barrel temperaturte profile, hp, rpm, rate, and pressure. For the material, viscosity,(or at least m.i.) as a function of temperature and shear, friction factors, bulk density, and melt density. Details of the screw geometry also. If you some assistance, e-mail steve@extrudertech.com ------------------ IP: Logged |
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Cor Member Posts: 1 |
posted May 04, 2006 07:17 AM
Meltpumps are normally used to make the downstream extrusion independent of the extruder stability. We run all our installations with meltpumps and it works very good. We run PE, PP and PET. What I noticed in the previous post is that meltpumps can enable you to increase capacity, however at a higher price than a new screw. Regarding extruding PP; PP is less stable than for example PE or PET (if properly dried). Therefore, the temperature of the PP shouldn't be too high if you're performing extrusion coating or casting. You can do that when you're using meltpumps. I hope this information helps a little. IP: Logged |
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