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Brazing Brass

Posted: Thu Aug 09, 2018 10:23 am
by ctwo
A friend dropped this off thinking I should try and duplicate it on my CNC from a block of steel. Lol... This bracket I believe is brass and is from a historic building in SF. The bracket attaches to the top of large doors with links so all doors open at the same time.

Clearly this looks like a brazing job to me. I've never brazed, but at least have a small oa set. Which rod would you use on this? I'll stop by the welding shop on my way home.

Also, should I even try this? It would seem easy. I'm good with soldering :lol: but suspect melting brass rod into cast brass will result in a big puddle of metal.

Re: Brazing Brass

Posted: Thu Aug 09, 2018 10:32 am
by NP317
Looks like a silver brazing job. 45% silver alloy will melt before the brass casting. Cleaning and preparation is important for success.
Brass rod brazing probably will result in a puddle, as you surmise.
~RN

Re: Brazing Brass

Posted: Thu Aug 09, 2018 10:50 am
by DavidF
I dont think they would make a hinge like that from brass.. seems more likely it would be a bronze. Aluminum bronze maybe? how hard is it??

Re: Brazing Brass

Posted: Thu Aug 09, 2018 10:51 am
by DavidF
I dont think they would make a hinge like that from brass.. seems more likely it would be a bronze. Aluminum bronze maybe? how hard is it??

Re: Brazing Brass

Posted: Thu Aug 09, 2018 11:11 am
by ctwo
I'm not that well versed on metallurgy so I'm not sure if it is bronze. I thought it might be, but it has bright and shiny screw marks. How could I determine this?

I thought of silver solder too, but since it broke I suspect it would readily break in the same spot.

Re: Brazing Brass

Posted: Thu Aug 09, 2018 11:20 am
by DavidF
Hard to tell sometimes. Some scrap metal yards can scan it and give you an idea of the composition. Im kind of thinking it may be aluminum bronze, hitting it with a file and comparing the hardness to some known 360 brass might help. Even just hitting it with a hammer and punch.
Aluminum bronze is very hard compared to brass. Also look at the break, did it bend much before failure or does it look like it just cracked??

Re: Brazing Brass

Posted: Thu Aug 09, 2018 11:44 am
by Bob D.
I would think hard silver braze would work well for this. Consider a 1/4" steel backing plate on the backside. Would need to inset the wood some it bolts to, but you wouldn't see it and would add some strength.

Bob D.

Re: Brazing Brass

Posted: Thu Aug 09, 2018 11:51 am
by warmstrong1955
I have some brazing filler rod, that I bought for repairing some bronze valves, until we could get new ones. Had a lower melting point than brass, and is supposed to work on brass, but I have never tried it on anything other than bronze & steels. It is flux coated, and a lot stronger than silver solder.
Not sure who made it....Hobart or Lincoln maybe. It's not in the original cardboard tube it came in.

Maybe you can do a little searching on the interweb.

Re: Brazing Brass

Posted: Thu Aug 09, 2018 12:34 pm
by ctwo
I believe there was some bending. I'll look at when I get home and may wait til Friday to stop at the welding shop. Maybe I'll contact them to see what's in stock, too.

Re: Brazing Brass

Posted: Thu Aug 09, 2018 12:41 pm
by liveaboard
Bob D. wrote:
Thu Aug 09, 2018 11:44 am
Consider a 1/4" steel backing plate on the backside.
Bob D.
That's a really good idea.

Re: Brazing Brass

Posted: Thu Aug 09, 2018 1:20 pm
by ctwo
Well, if we can sink in an angle bracket, I'd probably go with silver soldering it together and then tap a few holes to hole the bracket to the angle iron.

Re: Brazing Brass

Posted: Thu Aug 09, 2018 5:21 pm
by Harold_V
The dump door on the muller I'm working on had broken hinges, both made of a cast copper alloy. In breaking, they were badly distorted (the muller got tipped over), so I made a fixture from asbestos (I have a good quantity of the stuff) to hold the pieces in alignment, then I used TIG to weld them together, using silicon bronze rod as filler. I didn't prepare the joint for TIG, as that was a last second decision, as I had planned to use silver solder. Because of the lack of preparation, I didn't get 100 % penetration with TIG, but I welded three sides, leaving one side open. That was then fluxed well, and the resulting pocket filled with silver solder. The hinges turned out very nicely, and function as required. The fixture I made re-created the required offset, so the distorted break of the hinges wasn't a problem.

Using silicon bronze rod, I fully expect you could do the same thing with that hinge. Nice thing is, if you use TIG, you can manipulate the molten metal until it forms a nice, uniform surface.

Aluminum bronze is yellow in color, so if the picture posted is faithful, the hinge shown is not aluminum bronze.

One thing. If you silver solder, DO NOT use a steel backer. Not unless you want it to become part of the hinge. If you gas braze or TIG, it most likely won't be a problem, though.

H