Silver Solder Versus Silver Braze

Silver Solder Versus Silver Braze

I just got another call from somebody that had a lot of problems with brazing.

Once we got into it, it became apparent that the problem was that he was trying to use silver braze alloy with a silver solder flux.  He wasn’t clear on the difference between silver soldering and silver brazing. He went to a welding supply store where the clerk wasn’t clear on the difference either and the clerk sold him soldering flux for a brazing application.

Flux does a lot of things but primarily it is an oxygen interceptor. It is designed to keep the materials from oxidizing during brazing. If you get an oxide layer formed the braze alloy and the two parts being brazed will not join together.

Silver solder is a solder which has typically 1% to 3% silver in it and melts around a couple hundred degrees Fahrenheit. Silver braze or silver braze alloy may have 30% and 60% silver and it melts above 1100°F. These are approximations but they serve to illustrate the difference.

Typically brazing takes place above 800°F and soldering takes place below 800° Fahrenheit.

Silver solder flux and silver brazing flux are two very different compounds. Silver solder flux is designed to become active at very low temperatures and to work at very low temperatures. Silver brazing flux becomes active around maybe 500°F or so and stays active up to maybe 1500°F.

If you use silver solder flux for silver brazing then the silver solder flux will be all used up before the metals get anywhere near hot enough.  If you use silver brazing flux for silver soldering the metals will be heavily oxidized before the flux even begins to become active.

The term silver soldering is often used to cover all joining using silver of any the amount and thus covers silver brazing as well. I am as guilty of doing this as anyone.

I think it would be for the general good of the industry overall, and certainly the new people, if more care was taken in differentiating between soldering and brazing.

The latest guy to call was a nice young guy and he had messed up $50 worth of parts which was a lot of money to him. I kind of hate to see that happen to anyone.

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