Brazing rod materials

Education
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Hi all,

I was hoping to get some clarity on the different types of brazing rod/metals. I watched quite a few of YouTube videos and read through the forums but I’m still a bit confused.

Is there a difference between Brass and Bronze brazing? I just brought some brass rod (messing in German), I can’t find bronze rods here in Switzerland. Or are the builders just using these interchangeable?

In Paul Brodies video on fillet brazing he tins the joint first with silver nickel. Is this silver rod (Ag-Cu alloy)? Or is this a silver nickel rod (Cu-Ni-Zn)what I’d call in German Neusilver? Which actually has no silver in it.

Silver rod is used for brazing bottle cage bosses and lugged joints. Right?

Thanks for your help

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Yes, I like to call it brass because its principal elements are copper and zinc, the dictionary definition of brass. But the welding/brazing industry (in the US and Britain anyway, not sure of elsewhere) calls it bronze for some reason. Brazing bronze does have a little tin, as does “dictionary” bronze, though the tin is a small portion of the brazing bronze.

Correct, there is no silver in it. Another poor naming choice that became the standard industry jargon for some reason.

Yes among other things. High silver content rod like 56% should only be used on tight fitups with substantial wetted area. Lower silver content like 40 or less can be used to build a fillet, but it’s inferior to brass for that, unless you’re joining stainless, which brass doesn’t wet out on or bond to properly. Nickel-silver (with zero silver) does work on stainless and it’s very strong, but its liquidus is higher, so there are trade-offs.

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What Mark says, I’ll add that Nickle/Silver rods (50N) I’ve used are rather harder to file. Not a nice feature for a newbie:) Andy.

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I’ve only tried nickel silver on stainless, but I found it really frustrating to work with. It has a narrower working temperature window than the other fillers that I use because it melts near the maximum temperature of the recommended flux. So I wouldn’t start with this unless you need to.

I’ve wondered why Paul Brodie uses nickel-silver and then fillets with bronze on top. I wonder if it is to avoid remelting the tinning pass?

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Thanks Mark for the help, really appreciate insights.

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I’ve used Silver-Nickel once at work (I work in the HVAC industry) and didn’t like it. I found it really hard to get it to flow, but maybe I was using the wrong flux or something. Silver is a lot easier to use and I’m using it to make my first custom rack, I hope it holds….

My first thought about tinning with silver, was that it’s flows a bit easier than other material and it penetrates the tight joint clearance. But Paul is using Silver-Nickel, so I don’t know :person_shrugging:.

I’m going to stay away from silver-nickel at the moment and just use brass to tin and fillet.

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Yes that is sensible. I think Brodie is misguided to use NS for a first pass and brass over that. He’s a smart guy, so maybe there’s a benefit I’m not seeing. But then he makes fairly gigantic brass fillets, so the strength gained from using NS as the first pass is completely moot, as far as I can tell.

NS is a little annoying to use, as you noticed, so it’s only worth it when you need the extra strength it brings. Like making a frame with minimal, almost zero fillet size — do-able, but customers don’t like that look.

NS is great for machinery repairs, example a spur gear in a lathe that crashed, breaking one or two teeth. Build that area back up with NS and hand-file* it into shape, and that gear will last a good long while (as long as you don’t crash it again). NS is as strong as some steels, maybe stronger than whatever that old lathe gear was made of.

*or machine the teeth if you’re set up for that, but we weren’t, didn’t have a milling machine only that one lathe.

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Preach! The 3rd frame I ever made for myself (1977), for some stupid reason I decided to use NS to make a lugless. I had been an apprentice for over a year, and lugless was all we made (Santana, the tandem people) so I had a ton of experience with brass fillets, but the frame I made with NS was definitely hard to file.

I think the older journeyman FBs in the shop might have tried to warn me, but I was “young dumb and full of…” you know the rest. The bike came out pretty nice for all that, but I made a lot more work for myself, with little to no benefit to show for it. Frame would have been 100% as strong with brass, probably even a little stronger since the brazing temperature was higher. It didn’t break though, so strength was moot.

For the benefit of any newbs reading this who don’t know: the strength of the fillet is not the bottleneck, it’s not the limiting factor in the strength of the frame (unless your fillets are way inadequate, but most people make them too large). It’s the strength of the steel adjacent to the fillet that you need to worry about. Most often, a smaller fillet will make a stronger frame due to less heat input, and just less mass. More mass causes slow cooling, which leaves the steel softer and the heat-affected zone larger.

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I think Paul is doing the first pass with Nickel Silver because when it’s at flowing temp, it penetrates and creates an internal fillet very well, and has a higher tensile strength than Brass (80000psi vs 65000 psi). I wonder if he does this mostly as a remnant from teaching newbies in his framebuilding course, just to kind of guarantee good bonding under the brass fillet.

I’ve used Gasflux Nickel Silver for a few projects, usually where I don’t need to file fillets or for joining stainless. I did use it on all joints on my first frame, but only that one. I like using it for a root pass on stems in particular, just for the piece of mind of having a strong internal fillet. It seems to have a slightly higher liquidus flow temp than brass rods & likes a hot/fast flame in my experience. Trying to use low/slow flame or a stop/start stacking fillet doesn’t work as well and ends up with a lot of cooked blackened flux, or lumpy erratic stacks. I generally use a #1 tip & ~3.5mm long neutral flame, try to get in & out in one pass as fast as possible, paying attention to the flowing the filler right into the joint more than building up a fillet

That all being said, I don’t think a root pass with Nickel Silver is that necessary for regular framebuilding . Just a preference/application thing, perhaps a placebo effect lol

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Before the Internet, Americans called the brass rods an the British called them bronze.

No difference.

Since the internet, bronze has become popular as the “correct” term.

Low fuming bronze is recommended for bronze / brass brazing of bicycles.

Nickel-silver rods have no silver, but are silver in color.

Nickel-silver is 9 to 10 percent nickel.

If built up too thickly, such as thick fillets, nickel-silver can become brittle and prone to cracking.

Nickel-silver is for use when brazed joints are exposed to abrasive wear and really have no application in bicycle brazing and it is difficult to to polish.

In America there is low fuming bronze with 2 percent nickel available and is meant for brazing high carbon iron.

It has limited availability in Europe, as the European industry considers regular bronze to be suitable for brazing high carbon iron.

Some frame builders like the 2 percent nickel low fuming bronze as it wets out well and it does not become brittle like 9-10% nickel-silver can.

For bronze brazing of bikes, it is recommended to stick with low fuming bronze.

“Naval brass / bronze” is not low fuming and it not as strong as low fuming bronze, though it is softer and easier to polish.

It was common in old mild steel city bikes in Europe, years ago.

Low fuming bronze is easier to polish than nickel-silver, as nickel-silver is made to resist abrasion.

When chrome moly steel tubing gets “too hot” the copper in bronze brazing can get into the grain of the chrome moly steel tubing and cause it to crack later, when cold.

Nickel-silver has an even higher melting temperature than low fuming bronze.

I’m retired and in America now, but I built frames in Italy from 1987 to 2015.

The air hardening tubing calls for bronze brazing and not silver brazing, as the high temperature of bronze brazing hardens the steel.

The best method to not overheat chrome moly steel tubing is to use a hot torch and heat quickly, but it takes practice.

Thicker tubing is easier to braze than thinner tubing, so it is easiest to learn with thicker tubes.

To me, “brass” and “bronze” brazing rods are the same thing.

When I first started brazing in school in the 1970’s, I only heard it called brass.

If you get low fuming bronze or low fuming brass, you’ve got the right stuff.

The thinner rods are easiest to use.

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@BikePlumber thanks for the very informative reply!

As a quick side question: I’m just starting to build bike frames. I’ve made a bike rack from 10x2mm S235 steel and am planning to make a walking bike for my son from this steel also. Again with a 2mm wall thickness. Maybe it’s overkill, but I figure it is strong enough and easier for me to practice my brazing.

Do youknow what wall thickness the old mold steel bikes used? Is 2mm too much?

I’ve read here about the CrMo tubing, but haven’t found much about mild steels.

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I’m not sure how thick the old city bike frames were.

I used to see cheaper road bike frames that were labelled “high tensile steel”, which some people claimed was something less than chrome moly steel.

Chrome moly tubes can be found in thicker butted seamed tubing and in straight gauge tubing that isn’t butted.

These may be cheap enough to start and thick enough to braze easily.

Do you know the grade of brass brazing rod you found?

The lowest grade is not low fuming, and may produce a lot of fumes or smoke.

It is softer and weaker than low fuming, but might be strong enough.

Low fuming bronze / brass is very common and it may be low fuming.

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I’m sorry, I did not see that you already have 2.0mm tubing.

That may be fine.

It will take a lot to heat it to brazing temperature.

If it doesn’t have any moly in it, it won’t respond to the heat as much and may not get copper into its grain when heated.

Steel with moly responds to heat more than mild steel and not always in a good way.

With that thickness, it should be strong enough to not matter much either way.

I

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The international numbers for low fuming bronze / brass are,

The EN number is CU303 and the ISO number is Cu670, these are both the same brazing rod alloy.

I believe these numbers are correct.

brazing alloy brochure

“Argentel No.1” is pure brass.

“Argentel 302” is pure bronze

“Argentel 303” is low fuming bronze

“Argentel” is nickel silver (no silver)

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In my experience, 50N is much softer than what we typically call Nickel-Silver (which doesn’t have silver). 50N is a silver with a tiny bit of Nickel for added strength and behaves similar to 38%/Fillet Pro. I use this with stainless dropouts and other places where I want a good fillet.

Safety-Silv® 50N

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Most reasonable quality road/MTB/Gravel bikes will use tubing with wall thickness between .6mm-1.2mm. Tube diameter factors into this as well but 2mm is very thick. I’m ‘husky’ and have a road bike with .6/.4/.6mm downtube for many thousands of miles. 2mm walled tubing will be quite heavy, stiff and more expensive than you need - especially in a 4130 alloy!

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A correction, in Europe low fuming bronze is CU304 or Cu471.

Double check this if possible though.

Nickel silver is CU305 / Cu773

2 percent nickel low fuming bronze is CU306 / Cu680 (Not easy to find in Europe, but possible.

CU302 / Cu470 is the softest and the weakest, but easiest to file, sometimes used for braze-ons as it is easier to polish.

Low fuming bronze has 45 Mpa tensile strength.

Nickel silver has 54 Mpa tensile strength.

CU302 has 40 Mpa tensile strength.

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