Electric Wall Heater Repair

[jakeru]

I did a quick welding repair job today on an old electric wall heater that had a damaged heat exchanger, which was obsolete (no longer available.) The ~50 year old heat exchanger became bent (not shown) due to excessive heating (from previously replaced components in the heater, such as the fan motor) and customer had cold straightened, leaving some cracks in the aluminum alloy I quickly and partially TIG welded (crack repair not shown.)

Curiously, the heat exchanger mounting brackets were also about 1/4" too tight, so I repositioned one of them by cutting it off from the rest of the sheetmetal frame (4.5" angle grinder w/ cut-off wheel) and re-welded the bracket back on to the frame in a new position. Resulting in the heat exchanger able to be installed without stress.

As the bracket / frame was pretty thin sheet steel (I didn't measure but would guess perhaps .050" or so), I used some aggressive pulse settings (minimum pulse background current, and minimum pulse duty cycle, and minimum pulse frequency) to minimize heat input and oxidation, while welding it up in one quick pass. I used 1/16" 309L stainless filler rod, a #6 gas lens with ~13 cfh argon, and a really sharp 1/16" tungsten electrode.

[sportbike]

How did you manage to get the torch down in between the fins to do the crack repair?

I've looked around throughout your posts. I definitely need to make one (or two) of those third hand doo dads.

John

[jakeru]

How did you manage to get the torch down in between the fins to do the crack repair?

I've looked around throughout your posts. I definitely need to make one (or two) of those third hand doo dads.

John

I didn't manage to do it successfully. I tried extending the tungsten way out to reach in between the fins, but atmosphere must have been drafting past the cup into the area between the fin, because I encountered some oxidation. So I just welded about 1/2" or so of the crack on both sides of the heat exchanger, and called it a day. I didn't spend much time or do any veeing out the groove for deep penetration or anything either.

Sometimes its OK to just do a quick and dirty repair when its called for.

But anyhow, I was thinking later, if I could try and weld down in between those fins again, for fun what I'd try is probably setting up the back purge hose line with some tape around the hose, covering the opposite side of the heat exchanger at the other end of the groove between the fins. That might have made all the difference I was thinking in creating an inert atmosphere between the fins and maybe kept atmospheric air from drafting past the shielding cup.

I forgot to mention previously that I did make an electrical resistance check on the heating element after the repair. It came back with the expected resistance value for the 2kw 240V heating element, with no continuity (infinite resistance) between heating element and aluminum housing.

I do use my third hand (AKA welder's finger) quite a bit. I added on some silicon bronze on the tip, as well as on the sides where my ground clamp makes contact. I find I haven't had to file off the steel oxidation to get a better ground yet since doing that. The silicon bronze has a high copper content, conducting electricity very well, and also seems to resist nonconductive oxide buildup quite well. Just a small enhancement.

[presure2]

good stuff man, like the tip for the 3rd hand as well!