black or white flux?

[Builder01]

Black flux and cadmium silver solder if you can get it. I always do my soldering right on the floor of my garage. I also use refractory bricks so I'm not directly on the floor. I also use the bricks to surround the part of the object I may be working on that will become a heat sink and pull too much heat away from the area I am working on . Use the bricks to keep the heat in. Don't use fire bricks for fireplaces or stoves, The correct bricks are thermal insulating fire bricks and are very light weight and a bit fragile.

As far as fumes I have never had a problem as I always leave the door of my garage open. Also, the shade provided in the garage lets you see how hot things are getting.Color is important, at least when doing copper. The direct sun does not help. I recently finished a copper boiler with a 5" barrel for a 4-3/4" gauge loco this way. Just passed hydro 3 weeks ago.

David

[Bill Shields]

both will work if you are careful with the heat.

like most here, my opinion is that the black is more forgiving (easier to work with)

CCV gives good suggestions but I shudder at the cost of SILVER WIRE for large(r) projects.

[JohnHudak]

Thanks for all the help, is the black flux better on all metals, or just steel? I have some soldering to do on brass and I'd like to try it there too..?
John

[Builder01]

My entire boiler was done with black flux, as I mentioned, it is all copper. It works just as well with brass. I have made up many fittings by silver soldering brass, bronze and phosphor bronze. Also works fine on stainless steel. I have even able to get a bit of aluminum bronze to co-operate, but, it was a real pain to get to flow. I don't recommend that. Just be careful not to melt the brass!

David

[Fender]

I think that another factor is the fuel being used. Most of my silver soldering is done with a large air/propane torch. There is much less likelihood of overheating the flux, because the flame temperature is lower. The white flux becomes transparent when melted, so it is easy to see the solder flow into the joint.

[Bruce_Mowbray]

John,
Are you sure your 1018 is not 12L14? Leaded steel is a tough one to silver solder.

[JohnHudak]

John,
Are you sure your 1018 is not 12L14? Leaded steel is a tough one to silver solder.

No, I'm not 100% sure.. It was ordered as 1018 from McMaster Carr...?
John

[Harold_V]

John,
Are you sure your 1018 is not 12L14? Leaded steel is a tough one to silver solder.

No, I'm not 100% sure.. It was ordered as 1018 from McMaster Carr...?
John

A cut on a lathe will quickly disclose if it is leaded, or not. Leaded does not tear, and machines with a nice, smooth surface, regardless of feed rate or depth of cut. Unleaded will tear, leaving a lousy surface under normal conditions.

Harold

[BClemens]

John,
Are you sure your 1018 is not 12L14? Leaded steel is a tough one to silver solder.

No, I'm not 100% sure.. It was ordered as 1018 from McMaster Carr...?
John

That's an excellent point. Tried borax/brass brazing a piece of 1018 from McMaster Carr to cast iron. The iron would tin but the "1018" would not. We suspected too that we had a piece of 12L14 or something leaded. So even a grand source can easily make that identity mistake.

BClem

[Fender]

I've been trying to Silver Solder some 1/8" 1018 CRS together, and am not having much success.. Once it gets hot enough, it seems as if all the white flux has burned away, leaving the steel unprotected, and allowing the impurities to contaminate the steel.. Needless to say, that the solder didn't flow at all.. I'm using a Sievert torch, and I'm sure I got the steel hot enough.. Will the black flux possibly work better?
Thanks; John

Another possibility is how the surface is prepared. If there is any oil or oxidation on the metal, you won't have success. I usually file the joint to bare metal, and then wash with detergent and rinse with hot water before soldering. The white flux, when heated, will bubble up and then become transparent and smooth out. When it reaches a dull red, the solder will melt and suck into the joint.
As far as the leaded steel, I have only seen that in round or hex bars, not flat sheet.