brazing aluminum tubing

Real aluminum brazing is fairly difficult, I hear.

Stainless brush, brush the molten flux and/or molten brazing material to tin it, other finicky things you need to do.

maybe it'd be easier to put a slightly smaller tube inside and bolt the thing?

Dave

Well

HF has this

If you can get the part out and on the bench, you can probably find a local welder to fix it for less than that. Try a lawnmower repair shop.

Other options would be epoxy (like JB weld) if the tube is light duty or fabricating a new part out of steel tubing. or making a steel collar and epoxying to splint the broken section.

According to PipeDown :

You know the guys who show up at trade shows with chamois clothes?

Well, there's another variety, far less common, that sells brazing rods for aluminum that can be done with a propane torch. It's really soldering.

The stuff _does_ work (albeit a bit tricky). A guy in a metal shop brought a few pieces in to try.

But finding some in small quantities is pretty hard unless you luck into one of the salesmen. I personally have never seen one.

Or find a piece of pipe (aluminum or steel) that you can epoxy inside the tube as a splice. Properly cleaned, epoxy works well on aluminum.

Home Depot sells aluminum brazing rods made by Bernzomatic.

I couldn't get them to work, nor have I heard anyone else report success.

It is an inherently difficult operation.

Did you try them with propane or something hotter?

I've seen aluminum brazing rods used, and they do work. The time I saw them it was with an oxy-acetylene torch, but I think a MAPP would have worked just as well, and be less likely to oxidize the surfaces before you manage to get it soldered.

The problem isn't heat, it is the evenness of the heat and the oxidation.

The brazing temperature is near the melting point of the aluminum, so you have a problem getting the brazed area hot enough without melting the item being brazed. There is very little temperature range in between, and given the thermal conductivity of aluminum, the geometry of the part, and the limitations of the fuel and flame you have at hand, it is quite possible that no amount of skill will bring together a simultaneous three-way collision of bare elemental aluminum, proper temperature, and braze.

Getting through oxidation is a tough game without a shielding gas, because freshly exposed elemental aluminum oxidizes instantaneously in air at any temperature, just deeper and "more instantaneous" at higher temps. It is not a matter of more or "less likely" to oxidize; it will oxidize. Before heating, you clean what you can with a stainless wire brush, apply heat, and try to scratch through the new oxide with the brazing rod to get it wetted. I couldn't get brazing to work very well, although I've had some success MIG welding aluminum. I suppose it also has to do with the mass, shape and the alloy of what's being brazed.

It is possible to do it, but things like A/C evaporators are done inside inert gas blankets, that aren't available to the small shop or do-it- yourselfer.

I've brazed aluminum with oxy-acetylene. The trouble most people have is with burning away material because they can't judge the temperature of the metal. Steel lest you know by glowing red before it melts. Aluminum doesn't gice any visual clues so it's easy to have a bad result. No matter what, it takes more skill and practice than brazing thin sheet steel. Here's a tip though... With a pure acetylene flame, cover the seam with soot. Then readjust your flame to begin working. The acetylene soot will burn off at 900 degrees F, while aluminum melts at around 1100 degress. So when you see the soot vaporising, the aluminum is just a hair away from melting.

"Well, there's another variety, far less common, that sells brazing rods for aluminum that can be done with a propane torch. It's really soldering. "

Alumalloy, that's the name of the stuff I remember being advertised about a year ago. Looked easy to use, but y9ou had to spend about $50 just to get some...

Dave

Many years ago Sears sold aluminum solder in a wire form. I used it successfully. No longer there.

Don't know if this will work for you, but this outfit has aluminum solder paste. Never tried it. It might work for applying a patch.

Just take it to your local weld shop and have it heli-arc'd.