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 Extrusion, Single Screw
 Best extrusion condition for blown film??
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T.K.Palanisami Senior Member Posts: 26 |
posted December 13, 2002 06:03 AM
   
I need some information about the blown filmextrusion. Each material has different MFI at different temperature. For example some grade of LLDPE MFI at 190°C is 2 gm/10 minutes at 210°C 2.7 gms/10 minutes and at 230°C 3,7 grams. How to select the best processing temperature to keep the stable blown film?? What is the maximum MFI temp that I can extrude??? can any one help me IP: Logged |
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zabielski Senior Member Posts: 386 |
posted December 13, 2002 06:34 AM
T.K.: You need to try either by trial and error with dirrerent temperatures (which requires a lot of climbing - and re-stringing the bubble - and by then - you start feeling like a monkey) or match the viscosities by way of capilary rheometry. With a rheometer, run your samples at three different temperatures and lay one over the other(s) and different shear rates. You need to match the viscosities first before making successful films of different MI's or MFR's. Both MI's and MFR's are normally taken at one point only - not good enough for the work your trying to accomplish. IP: Logged |
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T.K.Palanisami Senior Member Posts: 26 |
posted December 16, 2002 12:00 PM
I thank you very much for your information.. I am going to run some trials.. I planned to use the same screw speed. So I thought the same screw speed means same shear rate. Is it right?? That is why i mesaured MFI with different temperatures. To know the viscosity.. In our lab extruder when i increase the screw speed I also don't find much temperature increase ?? I feel bit difficult to interpert ´the data from capillary rehometer results to apply in the extrusion.. How to use the same shear rate from the rehometer in the extruder?? Can you give some tips.. Thanx in advance Regards T.K.Palanisami
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zabielski Senior Member Posts: 386 |
posted December 17, 2002 06:33 AM
T.K.: The same screw speeds will only give you the same shear rates if your using the same exact polymer. With other polymers, the molecular weight and molecular weight distributions enter into the scene, as well. You may not be seeing a temperature change only because your residence time has change (less when you speed up). Also, it could be the results of a wornscrew, barrel, or both. I'd suggest you try posting your questions on rheology on plastics.com On that web-site, you'll find many Consultant available to address specific questions. IP: Logged |
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Bob Cunningham Senior Member Posts: 115 |
posted December 18, 2002 06:27 AM
T.K.- Generally speaking, blown film is run as cool as possible to get the best bubble stability and rate. If you are trying to extrude a polymer that you haven't run before, I would start out by looking at the data sheet provided by the material manufacturer. Lets say for example that they recommend a melt temperature of X, I would start out with a temp profile that might look like this- Feedthroat - Room temp + 40 deg C Of course this depends on 1000 different factors, like screw design, material viscosity at different temps, etc. - but that's how I would start. I don't understand your question "What is the maximum MFI temp that I can extrude???" - are you asking about the highest melt temp? Also, there is a standard set of conditions for determining MFI in PE. Generally MI is only used as a rough indicator, better viscosity information is determined by other methods. Your material supplier can probably give you a viscosity curve. But why do you need to determine viscosity under different conditions? Are you trying to run a computer simulation of some sort? Are you trying to design a die or screw? You may be over-analyzing your situation. -Bob Cunningham IP: Logged |
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Steve H Moderator Posts: 386 |
posted December 19, 2002 01:24 AM
G'day Bob T.K is co-extruding film, thats why he's concerned about viscosity. Just looking at your sample temp profile- normally feed throat temps are 38-48c, I'd be worried about bridging running at an ambient of 20c+40. Steve H IP: Logged |
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Bob Cunningham Senior Member Posts: 115 |
posted December 20, 2002 09:48 PM
Okay, but speaking of feedthroats, are these grooved-feed or smooth-bore extruders? Also since this will is coex (would be easier to help with more information!), is this a concentric mandrel die or a stack/pancake die? I'm guessing it's a stack die, since the concerns with viscosity...? -Bob Cunningham IP: Logged |
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