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| Author | Topic: Loss of feed |
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hechaniz Member Posts: 2 |
posted December 15, 2005 07:18 PM
   
I am processing APET (60% pellets & 40% flake) with IV 0.82 on a 90mm 32 L/D extruder. The problem usually occurs within 30 minutes to an hour after start up. The extruder will be working fine, then the temperature in the first zone will drop by 30C and at that point material stops feeding through the extruder. Our quick fix has been to then purge the extruder with chunks. What might be the cure to this problem? IP: Logged |
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Tom C Moderator Posts: 675 |
posted December 15, 2005 07:58 PM
Are you pre-drying the PET? What temperature is the PET entering the extruder? What is the initial temperature in Zone 1, and what does it drop to? What is the throat temperature? The part of the extruder that takes an hour to equlibrate after startup is the screw temperature in the feed, so that would be my focus of investigation. I have a friction tester which has helped resolve some of these types of problems.
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Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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Steve H Moderator Posts: 378 |
posted December 16, 2005 12:46 AM
G'day Hector Welcome to the single screw forum. I assume the 40% flake content of your infeed is regrind from thermoformed sheet, was it coated with a silicon coating to aid denesting of the product being formed? Are you crystallizing the flake prior to drying and re-extruding? Steve IP: Logged |
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louis33 Senior Member Posts: 142 |
posted December 16, 2005 10:04 AM
Is it possible that the loss of feed due to the flake building up in the through section is causing the front zone temperature to drop? Loss of feed = loss of frictional heat, and much of that comes from the front half of the screw. Maybe the chunks just push the build up of flake through the throat section. Have you looked down into the through when the feed stops to see what is happening there? just thinking for a simple explanation . . . IP: Logged |
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john green Senior Member Posts: 13 |
posted December 19, 2005 07:58 AM
I have found if the temperature is too high on the throat then the flake wil melt before the granule and cause bridging which will in turn cause loss in feed. I do not run higher than 140 degrees increasing to 260 at the head. IP: Logged |
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hechaniz Member Posts: 2 |
posted December 19, 2005 05:50 PM
Thanks everyone for following up. In the following I have tried to answer your questions. The flake I run is from thermoformed parts, varying in thickness from 0.010” to 0.035”. It was coated with silicone for denesting purposes. I first cristalize the flake, then blend it with virgin, and then dry the blend for five hours at 175C, and therefore, it is entering the feedthroat at 175C. When I run 100% virgin, I have no feed problems whatsoever. The first section I run at 290C. When I start to have feeding problems it will drop to 270C. If it drops below that, I completely lose feed and have to stop the extruder. The feedthroat area I’m not sure what temperature it is at, but I normally keep it so it is slightly warm to the touch. The throat area has never had any build-up or bridging (that I could see). IP: Logged |
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Steve H Moderator Posts: 378 |
posted December 19, 2005 06:01 PM
I've had real problems with HIPS T'forming regrind that has been silicon coated. It behaved very like your discription, run for a while (until a coating of silicon builds up on the barrel) then it would stop conveying the material. If this were happening, I'd expect the temp in the feed zone to rise because the material flooding in from the hopper is the major source of cooling for this zone. Have you experimented with some other temps in the feed zone, is your screw bored for scrw cooling? Steve IP: Logged |
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Tom C Moderator Posts: 675 |
posted December 19, 2005 07:23 PM
Try setting the first zone to 320C, and turn that zone's cooling off. This temperature may induce and maintain early melting of the resin and overwhelm the silicone lubricating issues. IP: Logged |
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Stephen J. Derezinski Senior Member Posts: 7 |
posted January 03, 2006 10:34 PM
You may have stratification in the feed hopper that eventually results in only pellets reaching the screw. Excessive flakes are left in the feed hopper and tend to bridge. Try vibrating the feed hopper, manually for starters. S. Derezinski IP: Logged |
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Kevin Duggan Member Posts: 3 |
posted January 10, 2006 11:05 AM
Other areas to look; Although you are crystallizing your flake have you verifed the melt point? Have you backed off in regrind content at 10% increments to determine if it is a feedstock bulk density issue. Generally, when processing regrind the geometry of your feed throat is recommended to be rectangular with a 2D to 1 opening. Last, cooling on the throat and the feed- section of your screw is recommended. We have a considerable amount of APET sheet extrusion experience at Battenfeld, additionally we are right in your neighborhood.. give us a call (978)282-9387 IP: Logged |
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mademan5284 Senior Member Posts: 26 |
posted January 15, 2006 01:27 PM
It sounds like the regrind has a significant melt history. As stated before find its melt temp. Oh and the rectangular thoat pipe is a must to keep large amounts of flake moving. Also make sure your barrel fan isn't on its way out and or the heating element itself. ckeck to see that it is drawing the proper amount of amps consistently. IP: Logged |
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