Is it possible? Preferably using an iron rather than a torch. What flux and solder work best. This is for small repair work on cast-off medical equipment being salvaged for third world countries. All help appreciated. Ray
It's certainly possible. You need a good flux, and aggressive cleaning. Most of my experience is with torch, not iron, and there's some benefit since the torch (with a long carburizing flame) can provide some protection against further oxidation. OTOH I guess you could set up a nitrogen glove box if you were doing a lot of work, and that would help. But an adequate coating of flux will work without that level of fuss.
Either an olde-fashioned zinc dichloride flux or something specific to stainless like Eutetic Castolin 157 (if my memory is not shot, and they still sell the same stuff decades later). Anything that works for flux on stainless will need to be cleaned off carefully after use, as it has to be fairly aggressive to work at all.
95-5 tin-antimony is a good choice for solder, lead free, food safe, not as wimpy as the typical lead free plumbing solders mostly are.You can probably solder some small stainless steel parts with a soldering iron, Ray, if you can get enough heat to transfer into the workpiece(s).
Harris Stay-Brite #8 silver bearing solder is a low temp (melt 430/flow
530F) solder that can be used on stainless. The #8 formula is lead-free, tin plus 5-6% silver by weight (about $53/lb last year, 1/16" dia) Harris Stay-Clean liquid flux (zinc chloride/hydrochloric acid) will work on most metals, including stainless, except it's not recommended for aluminum (or electrical/electronic applications).You probably realize that typically, stainless alloys don't conduct heat very well, and soft solders generally aren't exceptionally strong. I suppose that there would be some strength information on the Harris website.
Staybrite is considerably stronger than ordinary lead-tin solder, and it wets stainless like magic. There is Staybrite and Staybrite 8. Regular Staybrite is very fluid while Staybrite 8 has a "mushy" zone and can build up a bit of filet.
Strength is about 14000 PSI tensile, 10000 PSI shear, or about 5x the strength of ordinary lead-tin soft solder.
Way back when I serviced restaurant equipment, I used Staybright on stainless. It was strong enough, and food safe.
Steve R.
Thanks for including the relative strength comparison, Don. That puts the strength of the StayBrite products into better perspective.
I had checked Harris's specifications for #8, but didn't follow up by checking any strength specs for typical 60/40 alloys.
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