Sweating/Brazing Stainless?

Discussion in 'Technologies and Hardware' started by nomuse, Dec 3, 2010.

  1. nomuse
    nomuse New Member
    I need to make a high-strength connection to a different element. I am caught between either printing a stud on the stainless and threading that (cutting threads on this material is apparently possible but not fun), or inserting a mild steel rod that is easier to cut threads on -- and sweating the connection with silver solder and MAPP gas.

    Because of the mixed metal sintered makeup of the stainless, I don't know how it will behave at high temperatures. Will it warp? Will it explode?

    I don't think a cold solder joint will work here. It is possible "metal weld" epoxy might, though.
  2. GlenG
    GlenG New Member
    Hi temp silver soldering works wonderfully well on this material and on mild steel or pure stainless steel as well. However, it does take a fair amount of practice to master. Welding supply companies will have what you need. "Harris" manufactures a line of silver solders as "Safety-Silv". These are cadmium free alloys. A minimum of 45% silver content is recommended for the SW stainless. You must use a hi temp flux! This is referred to as "black flux" and is also made by Harris. On small parts a MAPP torch should work just fine. Slow even heating is very important. The flux will begin to melt and change in color. When it goes from brownish to clear the solder will flow into the tiniest crevice. Done properly, the joint will be almost as strong as the parent metal and certainly the strongest bond possible.
  3. nomuse
    nomuse New Member
    Thanks, Glen, and I can now confirm. I did several connections to a stainless print using an "all in one" kit of 56% silver solder wire and flux, and heating the parts with a can of MAPP gas. The higher silver content wires really slip into the finest cracks (such as a threaded brass rod I drilled out for and inserted into the print).
  4. GlenG
    GlenG New Member
    Hi Mike,
    glad it worked out for you. Nice to see a member who is not afraid to get his hands dirty, or singed on occasion.

    Here is a soldering tip: In cases where you do not want solder to flow into an adjacent area you can selectively brush on a solder retardant. Traditionally, yellow iron oxide (yellow ochre) was mixed into a thin paste and used as a solder barrier. Something that is easier to find and works even better is correcting fluid, also known as "white out". Any office supply store will have this. So, if you don't want solder to flow into threads or tight slots you just paint on a bit of this stuff first. Works like magic. Good to add to your "kit'.

  5. nomuse
    nomuse New Member
    Good tip.

    It's been fun getting into gas. I learned on stick, and switched to wire when they started to become common. Only gas I'd used in the past was a brief bit of cutting with oxy-acetylene, and hot-bending mild steel with MAPP gas.

    I do have to say, I prefer my old Benzomatic trigger-start torch over the Worthington oxy/MAPP kit I just picked up. Takes five minutes of fiddling just to get the torch started and you've only got twenty minutes of gas to work with.

    The biggest problem I'm having now is finding ag-56 in a local store. All they seem to have is the 4% stuff...flux-core, too...the stuff designed for copper pipe.

    For anyone that hasn't had their hands on a stainless steel printing, believe me, you can bang the heck out of those things without it breaking. I've drilled, carved away with Dremel, leaned in on files, heated it red-hot and glowing, pounded a brass rod through with a ball-peen hammer, and haven't noticed anything cracking.

    Last edited: Jan 11, 2011