Framebuilders - What's the difference between silver brazing and soldering?

What's the difference between silver brazing and soldering?

What's the difference between silver brazing and soldering?
The temperature at which the filler material melts.

Soldering is characterized by a melting point of the filler metal below 400 °C (752 °F).

Brazing is done with filler metals which melt above temperatures of 450 °C (840 °F) and which are distributed between two or more close-fitting parts by capillary action.

Solder does the same thing - filling gaps through capillary action. That's what's done when a plumber "sweats" copper pipe (though these days the most plumbers use tin solder I believe).

But I'm talking specifically about silver soldering - if you are using silver either way, how do they manipulate the melting point?

Ahh....just found the answer. Shoulda Googled it in the first place. Solder has a silver content of less than 40%, braze rod more. Giving the temps that Scooper mentions. Also more strength I would guess. I suppose they alloy the silver with tin?

I can sweat a pipe pretty well, I reckon I could braze a frame decently with some practice. The mitering, aligning, etc. now that's a different story. In plumbing work you just cut it off square (ish - doesn't matter) stick it in the "lug" with some flux. Hit it with the torch and a quick touch with the solder wire. I suppose the brazing part is the same - just a bit more heat - the cutting vastly different!

To steer the conversation in another direction - why is 953 so difficult to braze? (at least that's what "they" say).

Thanks,

Chris

There's a lot of ambiguous jargon going on.

Much of the time, when people talk about "Silver Soldering" they really mean "Silver Brazing".

There are a variety of silver-containing joining compounds, ranging from epoxy with particulate silver to solder that has a few percent silver for strength, to brazing metals that are mostly silver that require lots of heat to join.

There are a lot of metalurgical issues to be considered. If you take two sets of copper pipe and solder one and braze the other, the brazed pipe will burst first because of the larger heat effected zone.

The idea is that the hotter silver brazing materials will form a very very very tough joint because the silver partially diffuses into the joined metal and otherwise snuggles very close in ways that a lower temperature wouldn't let you do.

The manipulation comes from what other metals are included or aren't. Lead and cadmium and tin and copper lower the melting point. Pure silver takes a lot of heat. You should be able to look up the metalurgical analysis of various soldering and brazing alloys.

I've never brazed 953, but apparently any stainless is much easier to overheat, and then there are problems. I guess I wouldn't try it first.

Brazing is much like sweating copper, at least for me. Just as with copper, you only need as much heat as it takes, more heat doesn't help

To steer the conversation in another direction - why is 953 so difficult to braze? (at least that's what "they" say).
Chris, as unterhausen says, the only significant problem with silver brazing lugged 953 is that while it behaves the same as regular steel during the heat-up phase, once it's up to temperature it can overheat instantly if you're not careful. It's all about how you use the torch to regulate the heat.

Bob Brown builds lugged 953 frames, and discusses the differences in brazing steel alloys like chromoly and mangaloy, and stainless in his blog HERE (http://bobbrowncycles.blogspot.com/2006/10/more-953.html).

Mitering is a piece of cake, it used to be regarded as a skilled profession, but the existence of tube mitering programs takes all the guesswork out, or the use of machine tools. The fact that bike tubing is so thinwalled means it is relatively easy and fast to shape with simple hand tools.

Brazing lugs is very similar to plumbing work as far as the principles being similar, clean, flux, heat, and draw the filler to the source of heat. But there are many differences. The torch needs to be used skillfully because the relative heat is extreme, the torch can easily melt the metal, and certainly destroy it. Also the lug is a lot more complicated in shape, and can have considerable heat sink built into it. One is making a joint that is required to bear structural loads, and using the bare minimum of materials to get to that end. There is also no easy test, like a pressure test with plumbing, to prove the efficacy of the result. I'm sure that virtually anyone can learn to braze, but it does take some skill to do to the level required in a fine frame.