Stainless To Copper Joint

[herefishy]

I am having difficulty brazing stainless steel gas flex connector to copper fitting. I have successfully made the joint with a fluxed bronze brazing rod, but I am only able to get it done because I am so damn good. not really

Anyone have a better suggestion? The stainless is rather thin, and if I overheat the steel, I get a POP!, and whala! Look at that hole! good grief~!

Thanks in advance

[herefishy]

Well, DUH! I did a websearch myself and found:

http://hbd.org/hbd/archive/3389.html#3389-15


I guess I need to find some BAg-5 rods.

Thank me very much!

[herefishy]

Well 'ought dern-it! That's just 45% silver brazing alloy! I had tried that... maybe I'd better try again!

[rbartlett]

i remember we made a flatbed display fridge which we braized copper pipe to the bottom ..

we used silver solder and when we turned it over the bed was all buckled and discoloured ..

if it's not critical use soft solder..

cheers

richard

[frank]

Hi Fish

can't say that I've come across this before but this site has a recommendation http://www.jwharris.com/welref/faq/

Hope this helps - just scroll down till you find the s/s copper one


frank

[herefishy]

Hmmmm Aluminum Bronze A2... I'll check into it

Thanx.

[DaBit]

I tried brazing stainless steel to copper only once, but the 45% Ag rods with standard (sodiumtetraborate based) flux worked fine for me. Strange...

[herefishy]

Aluminum bronze A2 is for TIG.

I talked a bit with the welding supplier, and he suggested that I use the balck high heat flux. the stainless that I am welding is very thin. He suggested that my problem may be that I'm burning the flux off the steel.

I'll give it a go.

[DaBit]

If it is so thin, why don't you heat the copper alone (which will transfer heat to the stainless steel), and finally put just a little heat into the steel to ensure a good flow of the filler material?

Maybe a less hot flame (eventually from a normal propane/air torch?) will do the trick. The fact that you are melting the steel indicates a hot flame.

IMHO those 45% Ag rods should do the trick.

Just kicking in an open door:
when joining copper and steel, I try to keep the copper on the outside of the joint (copper fitting, steel pipe). Thermal expansion of copper is larger than thermal expansion of steel, so during cooling down the joint is compressed by the copper, which it stands well. When doing it the other way around (steel fitting, copper pipe), the joint might crack due to the copper pipe shrinking more than the steel.

[Gary]

The trick to soldering/brazing thick to thin is to tin the pieces first, then join them and heat the thick piece until the two melt together.

[Derek]

All depends on diameters but as an alternative to hot working

Vulcan Lockring Fitting (TUV approved)
Swagelok double furrel fitting

Disimilar metals always an issue but both have worked for me with Swagelok being No1.

[herefishy]

Thanks guys.

Hi Gary. I like the pre-tinning suggestion . I'll give it a go.

[dwarthstar]

Hi, i found that tinning the pipework beforhand works well, and as it seems you cant get the stainless to hot,, wot about soft solder,, works for me,,,,,..

[DaBit]

I don't like pre-tinning and then melting the two pieces together since it is very hard to prevent oxides or flux residues to become stuck between the two pieces, compromising the joint strength.

Is it really all that difficult?



A brass bolt (3mm / 0.12") with a thin stainless needle attached using normal 45% Ag brazing rods. The problem here was that my MAPP flame is larger than the complete assembly, so it is very easy to overheat the needle before the brass is hot. A small oxy/acetylene flame would have helped a lot.

BTW; I spoiled two needles before this one , but I don't have 15 years of experience.

[herefishy]

YOOOOHOOOOO! Hot diggity dawg!

I'll tell ya', if you don't have any high temp flux in your kit, you'd best get some. boyhowdy

I have concluded (as may have been suggested previously) that the problem with the steel to copper joint is that the copper dissipates the heat very rapidly, however the steel doesn't and the heat builds up overheating the steel at the joint (burning off the standard flux).

The high heat flux (the stay-silv stuff in the black bottle, not the blue) hung right in there, and with 45%, it was lickity-split. No Prob. the black flux looks like roof tar, almost.

BTW, the stainless that I was welding was (very) thin gas flex connect tubing.