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| Author | Topic: PE Foam Extrusion |
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Vic Senior Member Posts: 12 |
posted March 24, 2003 04:51 PM
  
Hi, Would anyone here have any good sources of information (ie websites etc) on PE foam extrusion using gas as a blowing agent via direct injection into the extruder barrel. I don't have any experience with this type of extrusion and any theory with regards to processing would be appreciated. Regards PS Our previous problem with regards to bridging in our throat has subsided somewhat but we still get agitation of the feed material in the throat. We have noticed too, that if we let the level of our feed climb too high in the throat we increase our chances of bridging. My opinion is that we have made it difficult for ourselves by having an all in one vacuum and feed throat system. Would it be simpler to have a vent port in the barrel to remove air bubbles etc on an SSE. IP: Logged |
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zabielski Senior Member Posts: 386 |
posted March 25, 2003 07:14 AM
Contact REEDY INTERNATIONAL for foaming help. Maintaining the hopper level is often an overlooked arena, as some fell that it is necessary to fill it full, and use the geometric shape that came with the system. Some are square at the top, most are round. You need to harness your vacuum pickup with a accurate sensor to alleviate your feeding to the feed post. Granual size and shape are other issues as well. Square cubes jam up easily, and round ones flow smoothly. However, granual sizes come in many shapes, so you should have a hopper that matches the "angle of repose" of the polymer beads, cubes or chips. You also may find that you can minimize throat jamming by adjusting your feed throat temperature. To cold, and you'll form condensation which eventually turns to steam once it dribbles in with your feed. To hot, and you'll pre-soften/melt the plastic. A rule of thumb is also not to turn it on full bore, as cooling won't occur. So, this rule of thumb is basically to throttle your feed thraot water to the point where you can comfortablly feel a warmness to the back of your hand without burning it - so be carefull. Some places will use an immersion thermometer on the outgoing water, as it leaves the throat. IP: Logged |
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Tom C Moderator Posts: 990 |
posted March 25, 2003 02:00 PM
Vic, I would like to add that screw design and process conditions can influence the amount of air entrainment, which will produce bubbles. For example if a pressure peak occurs in the screw prior to completely melting the polymer, the air around the unmelted resin will exit from the die rather than be forced towards the throat. Tom C IP: Logged |
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Vic Senior Member Posts: 12 |
posted March 25, 2003 06:29 PM
Zabielski, We have two extruders. The problem extruder has a separate vacuum cannister connected to the feed throat whereas the other does not. The feed throat configuration at the bottom of the feed throat is square for the problem extruder whereas the other extruder has rounded corners. Unfortunately we use both milled and granulated material and mixes of both. We only get bridging when using milled material and mixed material. Our vacuum pickup sensor is located level with our feed screw and tends to get blocked. Would we be better served if we repositioned it to another point? IP: Logged |
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zabielski Senior Member Posts: 386 |
posted March 26, 2003 07:02 AM
Yes and no. I'd first try to determine the Angle of Repose using the ASTM procedure, then contact a Hopper supplier, and asked for a gauranteed feed hopper, based on your findings. It's the milled and diced pellets that appear to be interlocking, so you should address this first. The angle of the hopper can be readily designed to overcome this unique issue. In general, it's been my experiance to try and maintain a 3/4 full hopper. You might have to install two sensors. I can assure you also that I spent a lot of time taming a few extrusion systems - using SPC - to show the cause and effect of gauge control on some very thin films. That maintenance of an ideal "level of fill" will get rid of more than 75% of gauge control. IP: Logged |
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louis33 Senior Member Posts: 177 |
posted March 26, 2003 08:09 AM
Just curious, but what is the feed configuration on the one that works best, straight over the center of the feed screw, off to the side . . . or is the problem the same on both designs? IP: Logged |
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Vic Senior Member Posts: 12 |
posted March 26, 2003 04:57 PM
louis33 The feed throat is directly on top of the extruder. The vacuum filters and hose sit directly on top of the feed throat hopper. The problem extruder has a separate vacuum cannister which is linked to the top of the feed hopper by a hose. IP: Logged |
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Stephen J. Derezinski Senior Member Posts: 88 |
posted April 03, 2003 12:21 AM
You can easlily put gas into PE with the proper two-stage screw design. It works the same as a two stage degasser, but in reverse. I have designed this type of screw for making foams. For help, contact me at 585 248 9343 IP: Logged |
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Steve H Moderator Posts: 428 |
posted April 03, 2003 04:22 AM
Hi Steve Thanks for joining us here  Steve H IP: Logged |
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ktgajjar Member Posts: 3 |
posted April 29, 2003 11:20 AM
dear sir , i hv read yr problem, so i suggest u , pl dont feed direct foaming agent with grannual in yr existing extruder, first u hv to make pallets from foaming agent with pe. then u can feed as require dosage with yr pe film.u can send me yr detailed problem on below address: kamlesh t. gajjar, c/o a n b plasware, gidc indl area, metoda,dist rajkot(india) ph no 91 2827 287461 IP: Logged |
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ktgajjar Member Posts: 3 |
posted August 09, 2010 09:09 AM
quote: IP: Logged |
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