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| Author | Topic: tape line extrusion |
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arasu Member Posts: 3 |
posted July 20, 2002 01:55 PM
   
Dear sir, we are facing problem in sheet extusion from the die which is used to form tapes used for woven sacks.Intermitently the film gets thin only at certain die zone which results in tape cutting at the hot plate stretching unit. kindly suggest all the parameter to be adjusted for polypropelene maetrial. thankyou. IP: Logged |
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Steve H Moderator Posts: 386 |
posted July 23, 2002 12:54 AM
Arasu What sort of die are you using, and are you casting the PP film onto a chill roll. From your discription of the problem, it appears that the gauge of your sheet is thinning in the same transverse location at intermitant intervals down the lenght of your sheet (MD)- If this is the case, it sounds like a faulty thermocouple,controller, die heater elements (in that zone)or the relay/contactor that supplies the elements in that zone. You could try swapping the T/C leads and heater leads with those of another zone. If the problem moves to the zone you exchanged the leads with, then you have a faulty (or out of calibration) controller or heater relay. If the thin zone stays in the same position- check the thermocouple, its connections and check the individual elements in that zone. Steve H IP: Logged |
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arasu Member Posts: 3 |
posted July 23, 2002 03:28 AM
Hello steve, Thank you for the reply,As asked by you we are using T die,the film is quenched in cold water and then slit to stretch on hot plate to get the required tape width and strength. Coming to the problem we have already checked the thermocouple ,heating elements and the controller and found all in good working condition.we also checked the die lip thickness and is in uniform thickness.we have a guess that chucker bar inside the die may be affecting to creat this problem,kindly respond with all the suggestion you would like us to ckeck. Looking forward to your valuable suggestion. Thanks & regards, Arasu. IP: Logged |
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Steve H Moderator Posts: 386 |
posted July 23, 2002 04:25 AM
Hi Arasu If your die is equiped with a choker bar check that it is true. If you have a variable depth melt thermocouple it could pay to check that the temperature of the melt entering the die is constant across the die inlet manifold. If the temperature varies across manifold, the viscosity of the melt will also change and this could result in more material flow in one part of the die and less in others. steve H IP: Logged |
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arasu Member Posts: 3 |
posted July 25, 2002 10:59 AM
Hello Steve, Thank you for your guidance on the choker bar.we have trued it and the film structure has significantly improved.I will keep you informed on the progress. We had one more question on mind,we reduced the die lip from 0.8 to 0.6mm thick.This has resulted in decrease in denier for any particular RPM of the screw as compared to earlier.can we increase the die lip ,what should be the optimum die lip opening for PP film and also the significance of die lip thickness. Looking forward to your kindly guidance. Thanks & Regards, Arasu. IP: Logged |
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Steve H Moderator Posts: 386 |
posted July 25, 2002 03:43 PM
Hi Arasu It's good to hear you have solved your gauge thinning problem. As far as the optimum die gap for your process- If you don't change other process parameters (screw RPM,screen packs etc), changing the die gap will alter the back pressure. Some back pressure is good as it helps with mixing/dispersing additives and/or blending resins. But by increasing back pressure, you cut down on the screws ability to pump material. Why did you reduce the die gap from .8mm to .6mm? What happened to the quality of your film and your output rates. How easy is it to change the lip on your die. These are questions I would ask before I made any more changes. Steve H IP: Logged |
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