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Stepside
10-29-2007, 09:14 AM
I need to silver braze some .500 diameter #304 stainless tubing. The wall thickness is .065. I am able to cut the "birdsmouth" so it fits really well. My question is " are there any tecniques with stainless that is different than copper or brass? This is not a fluid transfer application and there are no holes in the non-birdsmouth tube.As this is an architectural application it must be cleaned and given a light brushed finish. Are there any suggestions for cleaning afterwards?
Thanks
Pete

gbritnell
10-29-2007, 09:32 AM
Stainless tubing silver brazes quite well. As with any brazing the area needs to be cleaned well, fluxed and then brazed. One of the most important things is to get the material just hot enough for the braze to flow. You never want to overheat or burn the stock otherwise the filler material won't flow over that spot. As far as cleaning, it depends on the size of this structure. For small applications the flux can be boiled away in hot water but it can also be chipped off and then the area wire brushed.
gbritnell

agrip
10-29-2007, 10:01 AM
Adding information - -

If you lay an appropriately sized preform within a dollop of flux just inside the birds-mouth branch, you will get a barely visible and uniform filler line in the finished joint.
Within limits, more filler, forms more fillet.

Use a spring loaded jig to hold your joint in correct position.

Be patient while warming your joint and don't blow the flux away. What you want is the flux to fuse and flow out, and shortly thereafter the filler will flow.

If you don't apply uniform heating, (keep a torch moving) you are likely to over heat a spot. Takes practice.

Hth ag

mechanicalmagic
10-29-2007, 11:31 AM
Stainless needs a little more heat, I don't know why. Your typical white flux is VERY close to burning at the proper temperature. You should use black flux, it's rated 200 degrees hotter.

http://www.mcmaster.com/
search "brazing flux"

Definately use a preform.

darryl
10-29-2007, 12:38 PM
black flux- that's a new one on me. I'll have to look into that-

One other thing about silver soldering- there should be a small gap between parts for the solder to flow into. If the fit is too tight it won't happen. This is (from memory) 2 to 6 thou. There is a good article on silver soldering in HSM- what, about a year and a half ago-

hitnmiss
10-29-2007, 01:21 PM
I brazed up a r/c car chassis with .25" dia 304 stainless using safety silv 56 and a mapp torch. Worked extremely well. The silver solder has orange flux on the rod, which was all I need as far as flux went.

I bought a Smith little torch (oxy-aceytelene) but the mapp worked better. I was burning the flux with the concentrated heat of the oxy torch.

Scishopguy
10-29-2007, 03:31 PM
I always liked Aircosil Brazing flux the best for silversoldering. Clean the parts well, apply the paste where you want the solder to go, and carefully apply heat. THe flux will melt and then look wet. Once it starts to look a little dryer then apply solder. THe key is as was said before. Don't overheat. If you do the solder will ball up and fall off leaving a black nasty mess.

I had to make gas manifolds from stainless tubing for the science boys and this flux made it pretty easy. You can get it at any welding supply. It is a paste in a plastic squeeze bottle and is easy to work with. If it dries out just add a little water to the bottle and wait a while.

Good luck with the project,