Sealing Problem On Pe
Q: I am working on a plastic solar collector. In this collector I am looking a way to seal a gab between a LDPE (Low Density Poly Ethylene) and an Aluminum Annodisised construction. The function of tis construction is to transfer heat from the Aluminum to the PE. Therefore I have to avoid air gabs between the materials. So I need a material to fill the air gaps between the PE and the Aluminum. Water is the best material but it will not sty permanently. I have done some test with cyanoacrilates adhesive without increasing the surface energy from the PE. It was to stiff. When the construction moved (bended) the glue was cracking. Now I am testing silicones also without increasing the surface energy from the PE. The sealing function looks ok. The adhesion on the PE is poor but if there are no external forces I image it will be ok. But I don't know the result over time in outdoors conditions. What is the resistance to UV light? What is the resistance to frost? Is there an easier way to make material contact from PE to Aluminum?
A: The best way is going to be mechanical, but due to the diferences in expansion between aluminum and PE nothing is going to work well without allowing the materials to slide against one another. If you don't allow for expansion your panels will buckle and warp even if you achieve a good bond. The best suggestion I can make is to extrude your PE with a bead along the edge which fits into a mating slot in the aluminum, but you will loose some surface contact. Also trying to conduct heat into PE is very inefficent, plastics in general are very poor conductors. I don't know if this is possible but I use a clamping method to seal PE against alum. I use through bolts with a reinforcing bar on top of the PE. This makes a sandwich that can be pulled tight. I use RTV applied to the surface of the alum for a surface seal. The process I use is to clean the alum. Apply the RTV to both of the alum pieces and allow to dry/cure. Place the PE sheet on the bottom part made from alum and then place the clamp on top. Run the bolts (be sure to use large washers!) from the bottom part, up through the PE and through top clamp. Tighten the blots 1 turn past finger tight. If you don't space the bolts too far apart, this should give you an air tight box. I suggest a fillet of fibered asphalt roof patch beneath and alongside of the tubing. This stuff sticks to almost anything, including you, the work and the applicator. Bed the tubing well into the stuff, more area transverse to heat flow is better (goop it up!). It's cheap enough that you can afford to use plenty of it, and has enough body to stay put while it dries (which ranges from hours at 1/8" to months at 1"). So you might want to do a tack-down bead, let dry, and build up in a couple of thin stages. I'm looking to design (and build) a solar collector for my pool in Florida. Commercial options have a number of negative characteristics, all of which I'm trying to avoid...... Design goals include: 1. Being able to remove the collector(s) when storms threaten. Specifically, hurricanes. Storm risk makes roof-mounted collectors problematic at best; if they tear off they could conceivably cause the entire roof to fail, or become missles doing significant damage to the house. Dismounting roof-mounted collectors is a problem no matter how you slice it, and as such I'd prefer not to do that. 2. I have a Lanai that encircles the pool. It would seem that a single-gang, long-linear run collector would work IF I can get enough surface area. 3. I'm not trying to COMPLETELY replace gas heat (which I have). I'm fully prepared to use the gas in the "winter" here (where night temps dip to near freezing, but daytime ones are still in the 60s and 70s a good part of the time.) What I AM trying to do is avoid running the gas all the time, including the summer when we have a few cooler-than-usual days.
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