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Chris B
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Hey guys. I'm doing research on composite materials in the US, and I've scoured the internet looking for an answer to this question, so I'm asking you guys for help. First, pictures of my set up: http://i.imgur.com/VAfDkGV.jpghttp://i.imgur.com/zqhy5a2.jpgThe hose leading to the right goes to my resin jar, and the one on the left goes to my catch jar. Some background: the resin/hardener system I'm using is EPON 862/Agent W. I've never worked with it before, and it has 5 cure cycles at 2 different temperatures: 250 F and 350 F (121 C and 177 C). This led to issues with the PVC tubing as it melted when I placed it in the furnace. I noted it and got silicone rubber tubing from another supplier as it can withstand the higher temperatures. My issue arises when I attempt to create a vacuum seal in the bag. The sealant tape doesn't stick to the silicone tubing and thus can't hold a vacuum. I'm searching for a solution to this problem. I noticed Easycomposites sells silicone tubing for high temperature use, so I figured this community might have a solution to the problem. Things I've tried so far: - My most successful solution was to take a small piece of brass tubing and put the sealant tape on that, then attach the silicone tubing to the brass tubing. It (strangely) holds a decent vacuum, but tiny amounts of air still leaks in.
- I've tried using sandpaper to rough it up a bit. Doesn't work.
- I've rubbed acetone on the outside of the tube. Doesn't work.
- I've tried black sealant tape, which is slightly tackier than the yellow stuff. It doesn't really work either, plus the black tape doesn't go up to the temperature I need it to.
- I've tried wrapping paper around the tube before placing it on the gum tape. Shouldn't be surprising that doesn't work.
Any tips?
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Matthieu Libeert
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Chris B
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I could do that, but I would still need to run the hose through the vacuum seal in order to get the resin in. Or are you suggesting switching to vacuum bagging? The epoxy system is made for VARTM and I'd prefer to use resin infusion to work with this. Also, the hosing doesn't have to be silicone rubber. If there's another material that will work, I'd be fine with working with that as well.
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carboncactus
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Silicone releases naturally, so you'll have trouble sticking anything to it, even though it makes a good seal under pressure. Have you tried a jubilee clip or a thick cable tie to make full contact between the hose and the tape? The other option is a steel airline fitting with 1/4 bsp thread going into a nut, with another airline fitting on the other side of the nut. Sealant tape on either sides of the nut as a double barrier, PTFE in the thread. I can't see how that wouldn't seal. The only problem I see is the yellow tape going cheesy at 170C, although it should be good for 250.
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Matthieu Libeert
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Thats how I do it for vacuum infusion skip to 5:54 min |
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Chris B
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carboncactus: I thought of using a zip tie to wrap around the tubing and then adhering that to the gum tape, but I wasn't sure if the mechanical contact between the zip tie and the tube would hold a vacuum. The tubing is only 1/4" (6.35 mm) in diameter. Same idea goes for a jubilee clip; I'm not entirely convinced it would hold a vacuum. I'll see what I have lying around the lab and try it out. Matt: I did see that video from easycomposites, and I liked that vacuum connector. It seems a lot cleaner than what I'm doing. The only issue is that you still have gum tape wrapped around the seal between the silicone connector and the tubing, which leads back to the original problem of that I can't get the gum tape to adhere to the silicone tubing. Maybe if there was a way to connect the resin hose, do the infusion, then take the resin hose out without breaking the vacuum before throwing the part into the furnace.
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carboncactus
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The problem is the resin which cures at a high temperature. Standard resin infusion is out the window since you can't use pvc tubing and vacuum connectors. At those temperatures, you have to use a silicone hose.
You could try a couple of these:
^ ^ ^ ^ ^
tape tape hose tape tape
Don't push the hose all the way in so there's space for the tape.
I will ask this: Are you sure that it cures at those temperatures or is that a post-cure cycle?
The other option is to wet lay then vac bag it as if it were a prepreg layup (using steel valves and connectors and silicone hose), but that defeats the point of VARTM.
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Chris B
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carboncactus (13/06/2013)
The problem is the resin which cures at a high temperature. Standard resin infusion is out the window since you can't use pvc tubing and vacuum connectors. At those temperatures, you have to use a silicone hose.
Interesting. I never realized how much of a pain working at 350 F is (I mean, I can bake a cake at that temperature). The barbed fittings are a good idea. I may try that. I could probably get some mold release agent inside of it so that I can reuse them (assuming that the metal can withstand the chemical reaction).
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Matthieu Libeert
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Chris B
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matthieutje65 (13/06/2013)
you could also just drill them out, if resin hardened in the metal part  Genius. I never thought of that. Thank you.
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