Mig weld aluminium sheet?


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Old 03-02-21, 05:07 PM
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Mig weld aluminium sheet?

I'm trying to make a submersible stove for a wood hot tub (spring project).
I've seen that mig is not great at welding thin aluminum sheet. However, I'm a beginner welder and mig is the easiest of the options.
Do you think it'll work for a 16 guage sheet?
or better still... Flux

I guess the alternative is propane and a stick? Kind of long though.
 
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Old 03-03-21, 04:51 AM
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It is possible to weld aluminum using a mig welder with Argon as a shielding gas.
It does take a bit of skill and is more difficult on thin material.
TIG is easier to control but I am not sure its worth investing in for a single project.
Aluminum solder would be too difficult to use and would likely not stand up.

If you visit a scrap yard there is a good chance you could find an aluminum or SS tank or box that would only need to be modified.
 
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Old 03-03-21, 05:48 AM
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What about propane and aluminum flux rods or is this what you meant by solder?
 
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Old 03-03-21, 06:36 AM
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Aluminum is horrible for a firebox. There is a reason you never see aluminum wood stoves or anything aluminum in a wood fire. The heat is WAY too much for aluminum. You can experiment yourself by having a bonfire and put in an empty aluminum can. By the end of the evening there will only be a blob where the can used to be.

No, you can not solder a firebox. The fire's temperature is high enough to melt the solder. It might be OK in the under water portions but you've still got the solder joints above the waterline that can melt. You really need to weld and make it out of steel.
 
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Old 03-03-21, 06:55 AM
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Pilot - The aluminium is under water. It doesn't even get hot - all the heat is transferred to the water of the tub. Has to be something that doesn't rust.
if you look up snorkel stove you'll see they're common for wood fired tubs inside the tub. Agreed the top might get hot but they seem to work.
I could make an external stove but the heat transfer is longer.

Steel with paint? Chlorine water will make it flake off eventually
 
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Old 03-03-21, 08:09 AM
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I am very familiar with wood fired hot tubes. The problem is not all the stove is under water. The top of the stove and flue must be above water. I had a friend make one out of aluminum. They had too big a fire and warped the snot out of the above water aluminum. It's especially going to be an issue using thin aluminum like you're considering. If you use thick enough aluminum and follow the factory designs so the fire is contained will below the water line so the exhaust gasses cool enough before they get above the water it works. You'll notice many designs have heat exchanger tubes below the waterline and below the flue. It helps heat the water faster but more importantly it cools the exhaust gasses before they go above water.
 
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Old 03-03-21, 08:11 AM
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Steel would rust I guess.
So stainless steel is my only option?
galvanized not possible as it gives off toxic fumes
Sounds like the external heater would be easier, just use steel and copper pipe for the water
 

Last edited by qwertyjjj; 03-03-21 at 08:59 AM.
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Old 03-03-21, 08:54 AM
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SS will be similar to mild steel for welding than aluminum but you still need to change wire and gas for either.

I know guys that aluminum weld with 75% argon but it's crappy weld!
 
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Old 03-03-21, 10:38 AM
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Think seriously about how much this will actually get used? I've built a couple in water stoves out of steel. One was not much more than a barrel then a second more like you see available online. It's such a long process to fill the tub, start the fire and wait for the water to warm that it's not the sort of thing we used very often. Fun for the occasional party though. I don't think I used the thing a half dozen times when I scrapped it. I was the only one doing all the work required to make it, fill it, light it, clean it, put it away when done...

To preserve the heater I stored it in the shed when not in use. If you want to protect it you can paint it with high temperature exhaust header paint. The underwater portions will be protected and only the areas above water seeing the highest heat will discolor or burn off the paint. But, mine still had only minor surface rust in a few areas when I chunked it.

If you want to try it and see if you like the idea of a wood fired hot tub. I would make a heater out of scrap using almost any type of steel box, tube or sphere. Then if you like it you can go to the trouble of totally fabricating one from scratch out of sheet metal. You can use a barrel, steel mooring buoy, steel tubing, storage tank... any sort of steel container that holds water can be the main body. To be really basic you can start with just an open topped barrel. If you like using the hot tub then add a top with loading door and a smokestack.
 
 

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