Soldering bronze - What flux do you recommend?

J

jones78

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Nov 27, 2022
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I'm trying to solder bronze bolsters to brass liners on a slipjoint. The silver solder I'm using works great for steel on steel and brass, but the solder just rolls off the bronze. I'm wondering if anyone can recommend a flux that works for bronze?
Just so we are clear when I say solder I mean low temp like 400 degrees, not brazing which takes a lot more heat. Thanks.
 
What type of bronze do you have? Aluminum bronze doesn't solder well.
 
jones78 said:
I

I'm not sure. It is some bronze scrap from a machine shop I use to work at.
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That may be important. Silicon bronze is best for our type of stuff, as it solders, brazes, machines, and patinates well enough. That said, for what you are trying, I would say "try" a simple flux intended for copper alloys. I.E., consider the flux you'd use for sweating copper pipe. That should hold to low-temp silver-bearing solder temps, but may take some experimenting. Your next bet would be a good old white flux, but that's mostly higher temps.
Once you know your alloys, google becomes your friend. Unfortunately, you'll have to experiment a bit based on what other stuff folks here have to say. Someone may well come up with exactly the right answer on how to deal with mystery bronze.
Stacy E. Apelt - Bladesmith Stacy E. Apelt - Bladesmith knows a lot more than me about this stuff. He's a goldsmith/jeweler by profession.
Good luck!
 
fitzo said:
That may be important. Silicon bronze is best for our type of stuff, as it solders, brazes, machines, and patinates well enough. That said, for what you are trying, I would say "try" a simple flux intended for copper alloys. I.E., consider the flux you'd use for sweating copper pipe. That should hold to low-temp silver-bearing solder temps, but may take some experimenting. Your next bet would be a good old white flux, but that's mostly higher temps.
Once you know your alloys, google becomes your friend. Unfortunately, you'll have to experiment a bit based on what other stuff folks here have to say. Someone may well come up with exactly the right answer on how to deal with mystery bronze.
Stacy E. Apelt - Bladesmith Stacy E. Apelt - Bladesmith knows a lot more than me about this stuff. He's a goldsmith/jeweler by profession.
Good luck!I
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I have some brass that I may try instead. It just takes a while to shape it, I hate to start over again. 😐
 
jones78 said:
I have some brass that I may try instead. It just takes a while to shape it, I hate to start over again. 😐
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Don't we all! LOL That said, wisdom comes from having to start over. Sounds corny, but it's true. We learn a bit from our successes, but far more from our "start-overs".
The lesson this time, of course, is "know thy alloys."
Good luck with your project! :thumbsup:
 
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Hengelo_77 said:
I've soldered bronce with stainless flux
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I tried looking on McMaster Carr but everything they sell is large amounts and expensive. I figured I would stick to the knife supply companies, but all the information on the different fluxes usually only mention brass, stainless, titanium.
 
REPLY CHANGED - i JUST SAW HE IS DOING SOFT SOLDERING, NOT SILVER SOLDERING.

As Fitzo said, bronze is a word like steel - it can be many different alloys.

Try Stay-Clean Flux.

The bronze will suck heat away from the joint faster that the steel heats. Slowly heat the whole joint making sure a;; surfaces are at the liquidous point for the solder. In all types of soldering this is the ke0y to a good flowing joint. If the solder beads up and does not flow, it is a 95% chance that one half of the joint isn't hot enough.

In soldering, the surface oxides will stop the flow. When the joint is at the right temp to melt and flow the solder, give it a quick and light fluxing and re-apply the heat. The solder should flow immediately. Always apply the flame from the back side of a joint .... never directly on the surface to be soldered or directly on the solder. The flame should also be just hot enough to provide the needed heat. Using too much heat or too big a flame will not make the solder flow easier. It will make more oxides and stop the flow.
 
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Stay clean flux. You need to file/sand the material to bright metal immediately before applying flux.
 
Yeah, I've used the stayclean flux for soldering bronze to steel. I've always found preparation and heat more important than the exact flux, check that you're getting the bronze hot enough
 
I sanded the liners and the bolsters with 220 grit before I applied the flux. I don't think heat is an issue. I heated from the bottom of the bolsters and watched the solder melt as soon as the heat was right.
 
You should able to soft solder the parts easily.
I have never had a problem with any copper alloy.
 
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