Edge Bonding Aluminum Sheet

Weld it.

Al expands/contracts at 13x10^-6 in/in °F

So 350°F excursion will see considerable movement over 10 feet.

Depending where it's fastened down, you'll have lots of movement.

Will it be floating? Or bonded to another surface?

Silicone rubber is the only thing that comes to mind.

More details?

The aluminum is used as underlayment below my copper coils in my solar thermal collector. It floats on insulation and is not fixed on anything. The copper coils sit on the aluminum; all of which is then coated with a highly absorbent material. Welding is not my choice because of the cost, time and potential distortion involved. The aluminum is cut and then pulled into a cone shape and fits on the cone shape base. The copper is wound around this cone to complete the collector. By over lapping I create a void between the alumnum and copper at the point of overlap and for several inches there after. I want to avoid this. I will try to add a picture of the 'proof of concept' as further explanation. It works as well as I figured it would, and I am now incorporating improvements. Yes, I know it is too small to be effective except for two people who seldom shower and never wash dishes. I am working on two larger models at the moment.

I will have to investigate the silicone idea. An adhesive seems to be the only solution. I am having to use .025 aluminum and it is a bit springy and might pull away from the silicone. I would rather it be thinner. Problem is: although it is made, the minimun purchase is 2000 pounds. A bit more than I need at the moment. If anyone knows someone with about 4000 sq ft of .020 or thinner in a minumum width of 4 ft, I would appreciate the heads up.

Some sort of metal clips similar to how metal roofs are attached to homes maybe.

Some allow for the roof metal to expand and contract in a floating system. But the temp swing is not near as great as your expecting.

The size of your finished piece a supplier maybe able to get as a single sheet or cut from rolls. Otherwise like Bigg"s said you can get it welded.

There are a lot of High-Temperature Tapes on the market, many of Aluminum Foil that withstand up to 1000°F. You mention that overlap of the sheets is not an option. If that is because you have a thickness constraint, then this may or may not help you.

Good Luck

My apologies on above. The tapes that I viewed are rated for 400° continuous, and 1000° short term exposure. Still would work, though.

Do you have any more detailed information on the aluminum tape? What is it or what is it referred to as? Who has it?

Get 4x10 sheets here:MetalsDepot® - 3003, 5052, 6061 Aluminum Sheet

Metals Depot has .040 thickness at my last call they said they did not carry anything thinner. I can get .025 at metal by the inch in Charlotte. Sheets would be the best for the die cutter who will be doing my shaping for me.

GA to lyn. Unless the material is being sheared from a mile-long roll and don't want to waste the ends, it doesn't make sense not to use pre-cut lengths.

edge fold and press? 1/4 inch double fold, high pressure press.

You can roll the edges to half of thickness and than weld like below-

Ron.

AirCraftSpruce might just be the answer on the aluminum. Their prices are reasonable if they have it within a pickup range. shipping can be a deal killer on aluminum sheet. The damage can be very high. I just need to find out if the bare aluminum will 'take' the coating without it peeling later.

I think that by putting aluminum strips on the underside of the aluminum sheet where the copper does not go, I can rivet the pieces together and not have a ridge to deal with. The insulation should accept this additional thickness in stride. Shouldn't take more than 3 or 4 rivets to do the job. A simple jig would do nicely for this job.

If the idea of using aluminum tape is acceptable, you might consider thin aluminum strips that are spot or seam welded instead of tape. This construction will be both stronger and have better thermal properties than tape. You might also consider butt welding without the addition of strips or tape.

I don't know how tightly controlled is the placement of the coils, but following on welderman's idea of a strip, you could offset one edge by the thickness of the sheet or use the strip, but you could use pop rivets in between the lines of contact of the pipe and the cone.

I don't want to rain on your parade, but have you considered the galvanic corrosion potential you will have here?

Unless it is sealed against moisture, it won't be pretty.

Good point - but why not use aluminum tubing with the aluminum backing? I'm sure that 12 foot lengths won't be enough - but maybe longer can be ordered. Here's a link showing properties of 5052-0, which sounds right for this job: https://www.airpartsinc.com/shopexd.asp?id=200. Or go to 3003 alloy tubing, available in 50 foot lengths: https://www.aircraftspruce.com/catalog/mepages/3003versatube.php. This eliminates differential thermal expansion. Possible bonus in cost of aluminum tubing vs. copper, although copper is so much more common that it might not be the case.

"Bonding" of the tube to substrate could then be as direct as welding, locking the two parts into place with each other, simplifying coating [and eventual recycling?]. Welds need not be continuous - maybe just do two short stretches flanking where tube crosses joint in base material. Some of the processes are more akin to brazing or soldering than regular welding, which could make it easier for a home shop to handle. The natural "V" where tube and base join should be far easier to weld by these means than the edge-to-edge question originally posed.

I think aluminum tube is a good way to avoid galvanic corrosion. Check out thermally conductive adhesives and caulks.

For aluminum sheets, check print and litho shops. They dispose of the plates sometimes, good aluminum, about your size. All they get is scrap value. They also may be helpful on coating the aluminum for solar absorption.

Have you considered ultrasonic welding?

http://en.wikipedia.org/wiki/Ultrasonic_welding

For metal?

I understood that it was possible for thin metal sheets..... but I stand to be corrected

Ultrasonic welding is how aluminum wires have been attached to aluminized semiconductor surfaces for more than 50 years. Of course it works for metal. It was developed for metal in Germany in the early 1900s when a professor was attempting to refine the grain structure of aluminum spot welds using ultrasonic agitation. During a test, the resistance spot welder failed but the parts welded anyway. The rest is history.

Of course. I knew that, but my brain was too busy thinking that these metals are too thick. Guess my brain is too thnik.

If you have some extra length, you could bend a flange on each end of your cone blank before rolling and rivet/weld/screw the joint together on the inside. You may need to make clearance in your supporting insulation for the joint. There are other types of sheet metal joints that would put the overlap on the inside, away from your copper tube.

Any sheet metal fabricator will have the tool for the bend - an HVAC contractor or a siding installer would as well. Actually, an HVAC fabricator may be just the guy to make this for you, if it's in your budget, as they make conic transitions regularly in duct work.

Good thought. I have a friend in the HVAC business and it never crossed my mind. I will call him tomorrow to see what he can do.