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| Author | Topic: 4.5" Extruder Surging |
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jkrue Member Posts: 3 |
posted December 16, 2004 10:39 PM
   
We are running a 250hp, 4.5" 40:1 profile extruder using a blend of recycled HDPE/HMW/HDPE with EVOH. The existing 'worn' screw (as much as 0.125" in places) runs this well, though mixing suffers in profile. The screw is nearly 18" short of the screen changer. We have installed a nearly identical screw, but added length to the screw within 1/2" of screen changer. Here's the problem: While the 'worn' screw runs well, the new screw immediately will surge badly, sending motor amps from 60 to 200, with all other variables constant. We pulled the screw and noticed 'sticking' to the root, so the screw was chrome plated. We set it back in the machine, and same problem exists. Any thoughts? Suggestions? Anyone want to buy a used machine? LOL Suggestions are welcome. Thanks IP: Logged |
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jkrue Member Posts: 3 |
posted December 16, 2004 10:41 PM
Added info: screw is barrier design, starting earlier than normal, and has a 4 in / 4 out spiral mixer. IP: Logged |
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Elvis Member Posts: 3 |
posted December 16, 2004 11:08 PM
Let me get this straight Baby... I think I got your answer... But, let me get it straight before I perform. Your old screw runs fine... Right? ------------------ IP: Logged |
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Tom C Moderator Posts: 415 |
posted December 17, 2004 07:12 AM
Sounds like a feeding problem. Start with the first zone cold. See how it runs. Gradually warm up zone one and watch the amps. Record where the amps are maximum even if still surging, looking for the highest minimum amps. Using the best temperature in Zone 1 run the screw slowly. See if the amps hold over the course of time, at least 2 hours. Let us know how things are going when you reach this point. Tom C IP: Logged |
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Steve H Moderator Posts: 332 |
posted December 17, 2004 06:06 PM
J, welcome to the Single Screw Forum. I'd guess that the surging problem is present with the old screw, the 18" of "space" between screw tip and screen has been acting as a melt accumulator and suppressing the effects. Your new screw has filled this gap in and made the problem more apparent. Tom's advice sounds good to me, give it a try while you wait for Elvis to bolt down another burger ------------------ If at first you don't succeed, skydiving is not for you. IP: Logged |
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louis33 Senior Member Posts: 95 |
posted December 20, 2004 08:20 AM
Somehow I'm guessing that the new srew also puts out more pounds per hour than the old screw. Maybe quite a bit more. Is that right? IP: Logged |
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griffex Senior Member Posts: 24 |
posted December 21, 2004 10:06 AM
Numbers, numbers, numbers. Can't tell a screw without the numbers. Channel depths are critical. 40 to 1 is very long. Are both screws barrier? What kind? Is there a vent? Plugged? Can you cool the screw with water? How far down? Where's the wear? Where's the sticking to root? Without all this information we're flying in a fog (sailing in NZ) and can't really tell what the screw can or should do. But there is still a problem, so -- 1. Agree with suggestion to adjust rear barrel, starting low. Don't be afraid to run it up high, even 500 F if needed to get sticking to wall which is needed for inpush. 2. Early barrier implies not ready for melt extraction yet. Try preheating a gaylord, if no preheater put out in AZ sun with black cover. 3. Take hopper off and hand feed for as long as needed to see if makes a difference. HDPE is slippery, usually doesn't cause feed problem UNLESS it's scrap chopped sheet, film, etc. If that is the problem there are lots of feeding machines available. 4. Last not least, consider using the old screw with static mixer elements filling the last 18" space. Sulzer type will do more in that distance than Kenics. Season's greetings. It was 15 F outside last night. Allan Griff algriff@griffex.com IP: Logged |
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louis33 Senior Member Posts: 95 |
posted December 21, 2004 10:32 AM
That's what I was thinking - melting rate! The new screw sounds like it may have the barrier section kicking in too early. Preheating the resin or raising the rear zone or slowing the RPM's (thus output) may help, but the solution is to get the "right" design not one that just "works." Of course in manufacturing, we all to often use a bandaid to keep production running. IP: Logged |
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jkrue Member Posts: 3 |
posted December 21, 2004 10:47 AM
Okay... I suspect I have a serious heating problem in zones 1-4, so the plant (which is in SC) is going to check all of this for: 1. Barrel heaters of same wattage (3500 per half, 7000 per zone), ohm equally, and perform. Also will check to make sure no air gap between heater and barrel The plant has since placed the old screw back in to get production out the door. Not a lot of time to experiment. However, the screw is: 203" long There originally was a vent on this extruder, but it has been plugged for years. There is no screw root cooling. Now that screw has been chromed, there is some sticking in the mixer and tip, but otherwise clean. Also, blend includes HDPE w/EVOH. All material is 100% regrind, sized less than 3/8". A similar shorter screw, 34:1, runs well in Phoenix where the extruder had been completely rebuilt. Screw builder suggest if all is in good working order, feed section might need to be cut a little deeper. Any new suggestions or thoughts? This screw has provided more challenges than any before in 15 years of extrusion. Then again, I'm trying to help plant from a distance, like you all. I appreciate any additional comments. The missing 18" on the old screw acting as an accumulator certianly shed new light on why the old one works. Thanks, and you all have a Merry Christmas (I'm not politically correct, that's my excuse, and I'm sticking to it). IP: Logged |
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