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| Author | Topic: TRI - SCREW EXTRUDER |
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BedHead Member Posts: 2 |
posted July 16, 2003 09:06 PM
  
Has anyone ever heard of a tri screw extruder? Any suggestions for a feeder handling material the consistency of wood chips?? What's easier temperature controllers with reall time auto tunning or a PLC? IP: Logged |
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zabielski Senior Member Posts: 233 |
posted July 17, 2003 06:31 AM
Wow, sound like a unusual design you have. I've heard of planetary geared extruders (10 scerws) used in the early days of the PVC compounding industry, and four screw extruders, but never a tri-screw (rotating) extruder. I'd always select a PID looped single heat/cooling unit for each zone over a PLC only because if the PLC goes down - your completely down. The single PID looped temperature controllers can be individually slid out and relaced on the run if need be. I have though heard of a twin ram feed extruder system though, and it somewhat resembles a solid "Y" type appearing design, giving one the impression that it is a tree screw extruder. However, it really is a two ram type, discharging and feeding (ramming) two materials into a single rotating screw. Very ineffiecient though. It's far from easy to improve upon the simple rotating screw extrusion system so common now. So in essence, screw extrusion systems went through many evolutionary changes in this last two centuries yielding to the more effiecient single or twin extruders used today, but perhaps now more advanced by an additional bolt on gear pump at discharge. IP: Logged |
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zabielski Senior Member Posts: 233 |
posted July 17, 2003 06:35 AM
By the way, there are many feeder systems that can handle the chips you describe, but you'll have to be more specific on the bulk density of the material, the angle of repose, and especially the design of the extrusion screw. IP: Logged |
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Tom C Moderator Posts: 212 |
posted July 17, 2003 09:34 AM
I don't like auto-tune controllers because they tune too tightly based on the current condition. An extruder barrel can require heat, or cooling, or be adiabatic when tuned. The controller only knows that condition, and does poorly when it encounters changes in condition. The continuously auto-tune controllers make the situation even worse, in my opinion. With a PLC you can typically develop utility screens to help in tuning. Usually tuning settings and temperature historical performance can be shown together. Using these tools it is easy to see the effects of various tuning combinations. Barrel cooling is particularly hard to tune. PLC tools can make the job easier. Tuning can be a personal preference. I tune for long term stability rather than quick recovery. I feel that quick temperature correction act to destabilize the extruder and make it even more difficult for the controllers to maintain temperature. In extrusion I think slow and steady wins the race. Tom C [This message has been edited by Tom C (edited July 17, 2003).] IP: Logged |
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2beeps Moderator Posts: 55 |
posted July 17, 2003 11:34 PM
I've seen the ads for the 3 screw extruder from the firm (can't recall name) in Michigan.What are the screw diameters and configurations?? Years ago, Krauss Maffei had a 3 screw extruder, with a central 220mm screw and 2 110mm planetary screws---in effect,both 1/2 diams. (110mm) of the larger screw and the 110mm planetarys functioned like two 110mm parallel twins side by side. PVC pipe output rates could reach over 2000lbs./hr. They had visions of a 330mm x 3 110's,and even a 440 x 4 110's, for estimated outputs over 3000 and 4000 lbs./hr. I think costs of screw and barrel machining and replacements hampered sucessful introductions, although the concept was sound. Skip IP: Logged |
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BedHead Member Posts: 2 |
posted October 08, 2003 07:50 PM
Gentlemen, Thank you for your replies. I do appreciate it. Being new in the extrusion industry makes things hard but I am learning. PS it is an old Kraus Maffei 220mm with two 110mm planetary screws. It is a museum piece to say the least. Thanks IP: Logged |
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