Anyone ever gas weld without flame arrestors?

[etpm]

So on another note, I ran into one of the machinists from the shop around the corner today at the hardware store. Actually the first dude I showed it to asking for advice a couple weeks ago when I started analyzing what the heck I'm gonna do about this.

Told him I was thinking of brazing it with bronze instead of stick welding it with nickel cuz I'm worried 5/8" thick of weld bead by 8" long would generate way too much heat and warp the thing. He said it's the other way around, because for the bronze to flow and stick well the whole vicinity of the patch has to be heated red hot if not orange.

Sooo, what's correct? Conventional wisdom is that brazing doesn't require heating the base metal as much as welding. I think my machinist friend's viewpoint is incorrect cuz we all know that under that welding stick the metal is white hot. And, for what it's worth, when I stick welded a stabilizer foot that had broken in half the other day it twisted and warped all over the place. That didn't bother me cuz the foot isn't a precision piece. But the hub is.

I think my machinist buddy is like an "on the job training" kinda guy who specializes more in cutting metal with lathes and mills rather than weird types of welding. I know he's a wizard in other aspects so don't want to discard what he says but I'm hoping he's wrong here.

What do y'alls think?

Well, your buddy is kinda right. If you were stick welding you would end up putting in less total heat to the parts than if brazing. And if it was mild steel you were joining then stick welding would be a good choice.
Cast iron though is not as near as ductile as mild steel. It will get very hot in the heat affected zone when welded. And the heat affected zone is small, just as the machinist said. So the cast iron gets real hot in a small area which causes it to expand. Then when it cools it shrinks. But since it is not very ductile the cast iron cannot move. So it cracks.
The remedy to the cracking problem is heating a large area, in your case the whole part. Then upon cooling the shrinking happens over a large area and so there is less relative movement and the part doesn't crack. There are welding rods for stick welding cast iron that tend to cause less cracking. Castweld 55, made by Stoody, is one rod. But for a piece as thick as yours I guarantee your part will crack unless pre-heated if stick welded with Castweld 55. But you are gonna be gas welding anyway.
Since it seems like you are getting the hang of brazing and you can obviously get a good braze then I wouldn't be concerned. However, you need to practice on a hot part the same approximate thickness as your broken part before you attempt to braze the real thing.
And your machinist friend needs to read up on weld and braze repairing cast iron.
Good Luck,
Eric

 

[Sebculb]

Prepping the patch, sorta tried drilling with a big bit but that was a total no-go. Poked holes with the torch and cleaned them out a bit with the bit. Even that was abusive work.

 

[etpm]

Prepping the patch, sorta tried drilling with a big bit but that was a total no-go. Poked holes with the torch and cleaned them out a bit with the bit. Even that was abusive work.

Looks good so far. I'm sure you know but for other folks looking at this to learn they should know that the torch cut surface must be ground down to clean bare metal. All the metal to be brazed needs to start off as clean bare metal. No oxides, no oil, no dirt.
Eric

 

[Sebculb]

Sooo here is the "finished" product. Bolted the hub and patch to the outer housing and heated it up in the kitchen oven for close to an hour. Put down one bead of 1/8 nickel rod with a stick welder on the backside. Sorta like a heavy duty version of tacking it in place. That nickel rod is very poorly behaved, cursing and spitting all over the place. Maybe it's actually the cast iron that's the poorly behaved part but it's always impossible for me to put down a pretty looking bead. Minimal slag inclusions at least. Wasn't worried about one bead overheating the thing. A half dozen or more beads on top of each other, yes.

Once the first nickel bead on the backside was done I unbolted the hub from the outer cover and threw it back in the oven for a bit while I got the torch and workbench ready. Then I filled in the big bevel on the front side with bronze.

I wouldn't say it went badly, but definitely not as nicely as I would have hoped. Used a cutting torch to do it cuz I found it heats a larger area than the pointy welding tips, based on my minimal miniscule inconsequential amount of experience with the acetylene torch.

Anyways the small cutting torch didn't heat the thick metal as effectively as I wanted and the bronze wasn't flowing as freely as would've been optimal. But I muddled through it and hopefully it stuck to the cast iron sides. Afterwards I threw it back in the hot oven and ten minutes later turned off the oven and let it cool down in there overnight.

I'm using the logic that if the hot bronze wasn't beading up into annoying little balls and rolling away from the work area, then it was flattening out and sticking to something. I hope it stuck. When I ground it down it looked pretty well fused, for what it's worth.

Took it to my machinist buddy around the corner and they machined the inner face for me. That way there won't be any stressors on the repair when it's bolted up tightly against the outer hub housing.

Tomorrow is reassembly day for the hub!

 

[Sebculb]

Looks good so far. I'm sure you know but for other folks looking at this to learn they should know that the torch cut surface must be ground down to clean bare metal. All the metal to be brazed needs to start off as clean bare metal. No oxides, no oil, no dirt.
Eric

Actually i didn't know that, if I had done that maybe cutting the patch out would have been less "spectacular". Was a bit of a fireworks display.

Thanks again Eric, and everyone else, for all your advice through this process. It really helped me get what I think is a solid repair for what was an ugly break. I really appreciate it!

Sebastian