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| Author | Topic: CPET and chill roll temperature |
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Lovell Member Posts: 2 |
posted November 06, 2003 10:20 AM
   
My process is extrusion/thermoforming of CPET sheet. the sheet is approx .015" thick and 30" wide. We extrude the sheet and run it through the 2 chill rollers. as soon as the sheet leaves the chill rollers it is put on a rotary vacuum forming wheel. The problem I'm haveing is the sheet will stick to the top chill roller for a few seconds and then fall off. and then stick back to the top roller and then fall off. Its alomost like the sheet is breathing back and forth. We run our chill rollers @ top 95F and the bottom @ 75F. We have adjusted the temps up and down and nothing seems to help. We've check the gap, water supply, cleaned the rollers, wet wiped, barrel profile, die temps. Anyone have any ideas??? IP: Logged |
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Tom C Moderator Posts: 250 |
posted November 06, 2003 12:38 PM
Lovell, Please add your production rate, melt temperature and roll size-position relative to the layouts on this site: I will plug the numbers in and display the results. I'm not sure it will show anything or not, but it is worth a try. Tom Cunningham IP: Logged |
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Lovell Member Posts: 2 |
posted November 06, 2003 03:12 PM
Tom, Thanks for responding so quickly. I'm not sure what you mean about production rate. We can run about 1300 lbs/hr of material through the extruder, which is equal to about 65 FPM of sheet. The melt temp is 520F. The chill roller diameters are 12" and 4". Its kinda hard to describe the position and angle of the chill rollers ......think of a percent symbol % this will represent the 2 big rollers which turn at 54 FPM. Little or laydown roller turns at 55.6 FPM and is located about 2feet away from the big rollers and slightly below the big bottom roller in the downstream direction. I hope this description helps. if not give me your email address and I will sketch it and send it to you. IP: Logged |
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Tom C Moderator Posts: 250 |
posted November 06, 2003 07:48 PM
 The above image is the simulation result of the described problem. The film is sticking intermitently to the topmost roll. I can only guess as to what is going on, but the simulation shows only a very short contact time on the top roll. I think the material does not have enough time to cool and release so it is trying to stay on the roll. As the upper roll rotates a little the material does cool enough to release and is pulled off. It may not be a matter of roll temperature, but of contact time because of heat transfer limitations. If the upper roll could be moved towards the die closer than the lower roll, but still at the same height, this problem may be resolved. The upper roll would have more contact time. Tom Cunningham
[This message has been edited by Tom C (edited November 06, 2003).] IP: Logged |
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