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 Extrusion, Twin Screw
 Counter rotating twin screw designers
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| Author | Topic: Counter rotating twin screw designers |
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Tom C Moderator Posts: 284 |
posted December 16, 2003 01:39 PM
   
Any independent fully intermeshing counter-rotating twin screw designers out there? If so, please contact. Tom Cunningham IP: Logged |
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2beeps Moderator Posts: 69 |
posted December 16, 2003 10:45 PM
Tom, You need to specify which type of counter-rotating,intermeshing twin screw extruders you mean----i.e "diverging" as seen from the top of the barrel, or"converging"?? The "diverging" counter-rotating twins(low shear) are the major Rigid PVC powderblend extruders for pipe,siding,profile,fencing, etc. Major producers include Milacron,American Maplan, Krauss Maffei,and several others. The "converging" counter-rotating twins (higher shear) are mainly used for compounding PVC and other polymers. Cheers, Skip IP: Logged |
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Tom C Moderator Posts: 284 |
posted December 16, 2003 11:03 PM
Skip, Thanks for the help. I'm not a PVC guy, yet, but I get a lot of requests for resources along these lines. How does your description relate to parallel vs. conical? Thanks, Tom IP: Logged |
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2beeps Moderator Posts: 69 |
posted December 17, 2003 11:22 AM
Tom, The same scenario applies whether conical or parallel twin screw.Again,PVC is normally run on diverging counter-rotating twins. I happen to be a fan of the conical approach for a variety of reasons, starting with a more robust, stronger gearbox due to the larger rear diameter. Downside is the higher production costs of screws and barrels vs. parallels--especially with the larger size extruders. Which is why many of the producers offer conicals in the smaller sizes--up to 90mm(front end) and stay with parallels for the larger (120-160+mm)sizes. Have a great holiday! IP: Logged |
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Tom C Moderator Posts: 284 |
posted December 17, 2003 04:36 PM
Skip, Is not a diverging twin from the top a converging twin from the bottom? Or am I missing the point? Tom IP: Logged |
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2beeps Moderator Posts: 69 |
posted December 17, 2003 11:02 PM
Hey Tom, You are correct--diverging at the top means converging at the bottom---which is why the screw/barrel wear normally occurs at the "10:00 O'clock/2:00 O'clock positions on the barrel--mainly in the compression zone and metering zone. The counter-rotation creates a vector force at those positions, due to accumulated material on the bottom of the barrel.With deep-cut flights on the screws, this is a LOW shear process which feeds and compresses PVC powder down the barrel, melting occuring via barrel heat zones,to the adapter and die, exiting at about 390deg.F. Skip IP: Logged |
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Tom C Moderator Posts: 284 |
posted December 18, 2003 08:58 AM
Thanks Skip. Have you implied that there are designers who specialize in diverging or converging screws? Most of my inquiries come from profile extruders with twin screws, who therefore must be using diverging screws. So I guess I'm seeking an independent with that expertise. Tom C IP: Logged |
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2beeps Moderator Posts: 69 |
posted December 24, 2003 01:12 AM
Hi Tom, I don't know of any "independant" twin screw designers---my impression over the years was that the basic extruder manufacturers had their own screw design people. I recall one firm, American Maplan,that did specialize in rebuilt screws for twins---they may be a good scource. My own background in this is more conceptual rather than engineering specific---i.e. knowing that deep-cut flights in the rear zones (1&2)to maximize powder intake,followed by compression prior to the vent to achieve a seal so vacuum won't pull powder,followed by a transition to the metering zones (3&4)with gradually decreasing flight volumes to furnish a smooth,nearly completly fused PVC melt to the adapter,head, and die----and the compression ratio in the die(with adequate heats)completes the PVC fusion process (meaning passing acetone &/or methylene chloride fusion tests, and impact tests). At least that's a polymer chemist's view of an engineering situation!!  Skip IP: Logged |
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malikengg Senior Member Posts: 13 |
posted February 03, 2004 12:22 PM
What is the application of the twin screw extruder? Also what material(s) you want to process? What is the screw diameter and L/D ratio required alongwith throughput in kgs/hr? Do you need the screws as repalacement on existing extruder? If so, we need to know the motor power and gear box centre distance in the first stage. As you might be aware, parallel twin screws usually have uniform depth throughout with varying pitches and specially profiled screws as well as several distributive/dispersive mixers build thereto, depending on the end use of extruder. The screw pitches and depths are decided on the basis of application and compression ratio required for the application. IP: Logged |
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