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Author
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Topic: New screw and barrel made to old design having problems with the new screw and barrel
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Pmac
Member Posts: 1
From:Australia
Registered: Jul 2005
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posted July 13, 2005 09:26 AM
   
One of customers has a single screw extruder compounding LLDPE base masterbatch with 50 MFI,He has been using one extruder which is 63.5mm dia screw 30:1 L/D ratio.The barrel is vented and the screw consist of around 700mm feed section then tapers over 250mm to the first compression zone of 3.2:1 comp ratio then decompresses for 216mm for venting and tapers for 170mm to the second compression zone which is 2.7:1 compression ratio over 258mm then has two rows of mixing pins then into the maddock head.They have had a new screw and barrel made to the same as this design which had compounded for them for the past 15 years,since installing the new screw and barrel which are made to the same specs although being 65mm in dia, they are having promblems with material coming out of the vent some of which is still in pallet form and the extruded strand of not being compounded enough?There has been suggestion of the feed section being to long before the first compression zone which a compression type ring was put on the screw which had made it even have more non melted pallets,the temperature zones have been checked and altered because of the larger through put, also ceramic heaters required for the first two zones as they could not reach the required temperature as there was to much temp draw down and all are the rest of the zones are working fine.What we do not understand that although we did not manufacture the screw it has been made to the same design and ratio as the old screw which has never had a vent issue and nor a compounding issue since new to when it had been removed with quite a bit of wear yet it still in this condition give better results but not the output.We can supply drawings if required,however we are open to any suggestions and we also awhere of better design screws for this application however this is what has been requested and ordered by the client to the manufacturer who is out of ideas.Iam interested to listen to any suggestions that is given as there must be quite a large variable that has been over looked as we have only had a visual of the two screws and now have copies of the both drawings.Please let me know your thoughts as this has become quite urgent as although we have not supplied this to the client which does not matter as they are still our client in need of help and that is what we do supply is support in anyway possible as we supply New and Used Plastic processing equipment and as well as you people responding are doing is giving your free advise and passing on some of your knowledge because someone needs it.I appreciate any prompt reply to our compounding problems IP: Logged |
Tom C
Moderator Posts: 554
From:Brodheadsville, PA USA
Registered: Jun 2001
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posted July 13, 2005 03:15 PM
Pmac,The primary issue is the low viscosity resin. With a tight screw and barrel it will pump very fast. With just a little wear output will drop significantly and eventually a balance between output and melting will be acheived. That said, the screw you described is primative in design. Much better alternatives are available. My services are available professionally. ------------------
Best Regards, Tom Cunningham Extrusion Technical Services
www.ExtrusionTechnicalServices.com [This message has been edited by Tom C (edited July 13, 2005).] IP: Logged |
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