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Author
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Topic: Mixing elements
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TheBeav
Member Posts: 3
From:St Paul, MN, U.S.
Registered: Jun 2003
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posted June 12, 2003 03:53 PM
   
I am a novice to compounding. I have seen set-ups using only kneading blocks for mixing and other set-ups using only reverse elements for mixing. What are the advantages and drawbacks of each method?IP: Logged |
zabielski
Senior Member Posts: 166
From:McHenry, IL USA
Registered: Nov 2002
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posted June 13, 2003 07:40 AM
Without knowing exactly what your actually compounding (specific ingrediants), it's anybodys guess at this point.Reverse blocks are just that - it diverts the polymer backwards - until the extrudate is well mixed, then conveys if forward. IP: Logged |
TheBeav
Member Posts: 3
From:St Paul, MN, U.S.
Registered: Jun 2003
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posted June 18, 2003 05:06 PM
quote:
Originally posted by zabielski:
Without knowing exactly what your actually compounding (specific ingrediants), it's anybodys guess at this point.Reverse blocks are just that - it diverts the polymer backwards - until the extrudate is well mixed, then conveys if forward.
IP: Logged |
TheBeav
Member Posts: 3
From:St Paul, MN, U.S.
Registered: Jun 2003
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posted June 18, 2003 05:16 PM
I understand how reverse elements work and how kneading blocks work but when would someone choose only reverse elements and not use keading blocks? Does it have to do with distributive mixing vs dispersive mixing? Does it relate to heat generation? Is one type of mixing better for low/high viscosity melts? Does it relate to dispersing solids into the melt? I am not asking about a specific application. When do you choose one type of mixing over the other? quote:
Originally posted by zabielski:
Without knowing exactly what your actually compounding (specific ingrediants), it's anybodys guess at this point.Reverse blocks are just that - it diverts the polymer backwards - until the extrudate is well mixed, then conveys if forward.
IP: Logged |
Tom C
Moderator Posts: 149
From:Wharton, NJ, USA
Registered: Jun 2001
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posted June 22, 2003 10:01 PM
The choice of reverse elements for melting and/or mixing is based more on the style of screw design an OEM extruder maker prefers. Only on some French made extruders do I see reverse elements used over kneading blocks these days. Kneading blocks are usually just short lengths of zero pitch screw sections staggered together to give more random mixing than screw elements. My choice is to use kneading elements for both mixing and melting because a lot more research has been done on kneading blocks in those applications. I can therefore more predictably design a process with kneading blocks over screw elements in those applications. This is not to say that using screw elements would be less effective than kneading blocks in mixing or melting. Everything depends on how they would be applied. Likely this does not answer your question, but the interaction between the material and the screw design is unique depending on a number of factors, so it is impossible to say which is best without all of the information. Tom C IP: Logged |
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