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| Author | Topic: Gel filtering |
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poly Senior Member Posts: 18 |
posted September 04, 2005 05:43 AM
   
We are curently using a 10 µm screen to filter our melted polymer. I would like to know if a single 10 µm filter is enough to stop gels or if I should put a couple together. What works best for you? Thank you IP: Logged |
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Tom C Moderator Posts: 590 |
posted September 04, 2005 08:15 PM
It is fairly well known that a filter with "depth" is required to stop gels. Of course this is assuming you are delaing with true gels, a somewhat uncommon issue these days with most polymers. The gels paper on this page may help; http://www.extrusiontechnicalservices.com/downloads.php ------------------
Tom Cunningham
Extrusion Technical Services [This message has been edited by Tom C (edited September 04, 2005).] IP: Logged |
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poly Senior Member Posts: 18 |
posted September 05, 2005 02:31 AM
Reading your article, I understand that a stack of five 325 mesh filters should do the trick. So, I guess I will have to add extra 10 µm filters to increase depth. Why are you assuming I'm dealing with true gels? Won't this work with other types of gels like unmelted or crosslinked? Thank you IP: Logged |
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Tom C Moderator Posts: 590 |
posted September 05, 2005 08:15 AM
I assumed you were talking about true gels to simplify my answer. I understand that some extrusion processes, especially film, classify many melt contaminates as gels. In my opinion different sources of contaminates require different solutions. For example if you are dealing with cross linked and carbonized materials because of a poor screw design, you would likely want a screen pack that progresses to a tighter mesh like Flow-> 20-40-100-250-20. This screen pack will build up pressure much more slowly than a 325 x 5 stack, requiring less screen changes and consequential line disruption. Unmelted pellets would be a problem I would suggest solving first by slowing the extruder down, then by installing a screw design more appropriate to the resin. Sometimes unemlted pellets can be solved by building a high pressure loss screen pack which changes the dynamics of pumping and melting in the screw. This method can work, but I'm not a big fan of this technique as a lot of energy is wasted heating up the resin, and melting is not assured.
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Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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poly Senior Member Posts: 18 |
posted September 05, 2005 01:55 PM
Our process requires we filter particules smaller than 20 µm. That's why we use a screen pack consisting of 40 mesh - 10 µm - 40 mesh - 20 mesh. I'm wondering though if this should have been enough to capture gels or if we need a couple more 10 µm filters. I'm afraid though that back pressure will increase way to rapidely. Perhaps I could gradually decrease mesh size down to my last 10 µm filter (for example: 40-80-100-250-325- 10 µm - 40-20). What do you think? Thanks [This message has been edited by poly (edited September 05, 2005).] [This message has been edited by poly (edited September 05, 2005).] IP: Logged |
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Tom C Moderator Posts: 590 |
posted September 05, 2005 08:00 PM
I think you have not given me enough information to properly engineer a solution. You should look at this issue in whole, from material, screw design, process conditions, process objective, and contaminates analysis. From that point I would think you could attack the problem from a number of directions, with the last resort being the filtering that is used. Filtering can only handle very small amounts of contaminates. The contaminates should be engineered out first. ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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poly Senior Member Posts: 18 |
posted September 05, 2005 09:33 PM
I absolutely agree with you. Unfortunately, I work with a very stuck up bunch of individuals. They are not interested in finding the cause. So, in an effort to save my job, I'm trying to find a simple and fast solution for them. I know there has to be a cause but nobody seems to care. Can you please tell me what you need to know in order to find a solution? Thank you IP: Logged |
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Tom C Moderator Posts: 590 |
posted September 05, 2005 11:10 PM
Formulation Extruder type and screw design Adaptor and Die design Process conditions Microscopic examination of filter packs Microscopic examination of product defects Some of these items might not be related to the problems but I can't tell from here. This would be a good start, however I would check with the management before publishing this data. You may want to contact me via email. ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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poly Senior Member Posts: 18 |
posted September 06, 2005 02:45 PM
I will try to get some information but it might not be easy. The microscopic examinations will surely not be available. As for the rest, I'll see what I can do. I might not have the right to give you the formulation. Thank you IP: Logged |
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Tom C Moderator Posts: 590 |
posted September 06, 2005 03:09 PM
I have a microscope and have done the examinations as a matter of course on many problem solving missions. Send a sample of screen pack and product and I'll look them over. HCR #1 Box 635 ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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