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| Author | Topic: cleaning chill rolls |
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SamT878 Member Posts: 3 |
posted January 17, 2005 07:51 PM
   
I'm not sure if I'm in the right place or not. If not could someone please give me some direction. We are currently running a PVC sheet and having surface issues. The material is a customer compound that we cannot change. we run a 35rms Matte surface. The problem we have is that during the run we get a build up on the roll causing "blotches". Right now we dry wipe the roll every 10-15min w/ a dry rag but we still have to clean the roll with paint thinner every 10-12 hours. If there isn't anything to do about the build up can anyone recommend a better cleaner to use or just a better way of cleaning the roll altogether. The problem w/ the thinner is that we have to heat up the roll which is causing us to scrap and the whole process of heating and cooling the roll takes about an hour. Any help would be greatly appreciated. IP: Logged |
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Tom C Moderator Posts: 451 |
posted January 17, 2005 09:40 PM
Sam, Can you run the roll colder, or slow down the line to increase contact time? Tom C IP: Logged |
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SamT878 Member Posts: 3 |
posted January 18, 2005 11:29 AM
Running the roll colder increases the overall gloss of the sheet and puts it out of spec. Slowing the line down doesn't have any effect. I guess the main thing I'm looking for is an easier way to clean the rolls (a different solvent maybe?) during process so that we don't lose so much material. Just to give an idea a "roll clean" as we call it costs us approx. 1000 lbs. of material by the time we heat the roll up and cool it back down. if we don't heat up the roll the build up on the roll just smears and never really comes off the roll. In order to stay in spec as far as gloss we have to run the roll between 168 and 171 degrees. The optimal temp for cleaning seems to be at 225 degrees. At least using paint thinner. That's why I was looking for another type of solvent so that maybe we dint have to heat up and cool back down. IP: Logged |
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Tom C Moderator Posts: 451 |
posted January 18, 2005 03:44 PM
These are PVC solvents. I can't say whether they are safe to use or not in your application. You should check them out thoroughly before using for health, safety and enviromental concerns. Tetrahydrofuran Tom C IP: Logged |
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poly Senior Member Posts: 9 |
posted January 20, 2005 04:13 PM
I'm not sure what roll you are talking about, but where I work, we have a roll right under the die. The polymer coming out of the die coats a film running on this roll. The roll itself is made out of non sticking surface like ceramic. A glycol cooling runs through the roll. We used to have sticking problems before the use of this new surface. Now, it doesn't stick at all, even when the hot polymer runs on it without the film. IP: Logged |
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SamT878 Member Posts: 3 |
posted January 21, 2005 07:36 AM
Since I first posted this topic I have found out that the problem we are having is refferred to as "plate-out". I don't know if that helps. IP: Logged |
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poly Senior Member Posts: 9 |
posted January 21, 2005 09:29 AM
I'm not familiar with the term plate-out. IP: Logged |
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Tom C Moderator Posts: 451 |
posted January 21, 2005 11:35 AM
Plate-out is a term often used in injection molding. It refers to a build up of materials on the mold surface. Typically the buildup is due to the presence of a somewhat incompatible additive. In this case the roll is set to a high temperature to emboss the surface of the sheet with the matte pattern. The roll is set at the softening point of PVC in order to get the PVC to take the pattern. It is unlikely that the PVC resin is coming off the sheet and sticking to the roll, but rather an additive or plasticizer. Under these conditions some materials sticking to the roll will oxidize. This can change the chemical structure of the material on the roll, perhaps providing a surface for more material to build up onto. In injection molding, where there are similar problems, solutions include; modifying the melt and mold temperatures, solving melt overheating and degradation problems, lubricants, mold coatings, mold cleaning, and finally formulation change. By far the most effective is formulation change when degradation is not and issue. It would seem the solution to this problem would be to identify the material sticking to the roll and change the formulation. One thing to try would be to make sure the sheet was well cooled before the embossing roll. Then set the embossing roll temperature to whatever is required to get the pattern. This temperature may be much higher than currently being used, but because of the potential for less material being at the melt point, less plate-out may occur. Tom C www.ExtrusionTechnicalServices.com [This message has been edited by Tom C (edited January 30, 2005).] IP: Logged |
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