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.

The confusion between silver solder and silver braze came up because of lead free solder. The alloys used in lead free soldering contain silver - thus the confusion. Prior to that, silver soldering and silver brazing meant the same thing. At least that is how I learned.

Tom,
Very informative and well written. That sums it up pretty good. I just tell people silver soldering is a misnomer. It's called silver bearing solder and it's just that. Solder!

Good summary. I think the brazing/solder issue goes way back before lead free solder. Kester has sold high strength silver solder (low temp) for years and I know confusion has always existed to some degree. Whenever I hear the word solder, I think low temp. Brazing=high temp. What I really wish existed was something in between the two, with in between strength as well. Sometimes I don't want to heat a part to full brazing temp, but a solder isn't really strong enough.

Tektronix used to use silver deposited on ceramic rods for soldering their electronic components to in their instruments. In the back of the chassis was a little reel of silver bearing solder which you should use for repairs. If you tried to use ordinary soft solder, the deposited silver would "dissolve" into the soft solder and disappear from the ceramics, leaving the components soldered to each other but not supported on the ceramic.
Frank

Tom,

I agree with everything you've said, but unfortunately a switcheroo has been pulled by someone in the marketing dept.

The stuff you are calling solder is typically sold as "Silver Bearing Solder" an name which is easily confused with what is sold as "Silver Solder" which you are more accurately calling silver-brazing alloy. I have both products in my shop and that's how they're labeled.

Jeweler who would not dream of using the low temperature stuff call what they do 'soldering'. Carbide tipped tooling is soldered with silver-solder according to most sources. That's the high temperature stuff as well. Silver solder used to only mean silver-brazing, it's the 'silver-bearing' label that's produced the problem.

I blame the Stay-Brite folks for this confusion personally. I doubt it will get fixed anytime soon, but at least we can complain on the internet.

I am joining carbide pads to crs plate or a carbide ball to a post with a torch, white paste flux, and "Safety Silv silver brazing compound" (made by Harris). It's about a .02 diameter wire. I've always thought I was silver soldering. From this it sounds like I'm silver brazing. Think I can get a raise?

The term silver braze in an oxymoron.

Brazing is soldering with a spelter based on copper and zinc. Silver soldering is soldering with a spelter based on silver. Soft soldering is soldering with a spelter based on lead, tin, bismuth or other low temperature alloys. Bronze welding is just that.

These opinions are worth exactly what you paid for them, even though they're correct.

Borax type flux will actually dissolve existing oxidation on a part. So if you
burn a piece badly, you can re-flux and recover to some degree.

Once the flux gets loaded up with oxides it is tough to remove however.

There is basically no distinction in industry betweeen the following terms which
are used interchangeably:

Silver soldering
Silver brazing
Brazing
Hard soldering

And the salient points are: two similar or dis-similar metals being joined by a third
metal with a melting point over about 800F.

Soft soldering or just plain soldering are the same, except the material has
a melting point less than about 800F.

There's a lot of confusion about this and that accounts for the person in
question getting a SOFT SOLDER FLUX when he really needed a HARD SOLDER FLUX.

I recall this topic being discussed in welding class in engineering school around 1959. I started learning to silver solder broken gun parts with a Bernzomatic torch and silver solder and flux bought at Sears while I was still in high school. Then I learned in college that I was really doing silver brazing. Then I began watch and jewelry repairing and found the professional supply catalogs sold gold solder and silver solder (brazing alloys) along with real (low temperature) solder. Around 1966 or so I bought some low temperature solder composed of 95% tin and 5% silver. I found it could dissolve sterling silver when trying to do a repair that did not lend itself to the high temperature of silver braze.

Point is, the distinction and confusion has been around a long time. I know the difference, but I don't assume others know. So I try to be clear when discussing a repair.

Larry

Interesting to note about the 95/5 solder dissolving sterling.

I learned the hard way, that gold forms a very low melting point eutectic
with lead/tin solder. If you want to solder gold wire for an electronic
application, use indium instead!

Very interesting and informative read as this applys to myself. I have a few types of soldering materials and use both the low and high temp products. Next time I go to the welding supply house Im going to make sure I pick up the right flux for my silver brazing rods.
Anyone ever soldered aluminum? I bought some special wire and flux just for that a few years back. I only used it for that one job.

Long time ago, I bought solder and flux at Sears that said it was for aluminum. I never got it to work, though it is decades ago that I last tried it.

About 20 years ago I bought some rods that need no flux after seeing a guy at a flea market repairing aluminum with a propane torch. I had a friend run a lab test on it and was told it was pure tin. I have used it ever since with perfect results. The funny name on the package was "Mad Dog Weld." Tin melts at 450 degrees F, so I guess this a solder, not a braze.

Larry

I bought some aluminum "solder" about 30 years ago. Probably still have some.

I DID use it to "solder" aluminum, and found that even though I was using a propane torch, apparently I was actually welding, since the aluminum melted quite nicely, making the join. I don't know what the "solder" was, but probably not tin. Didn't look like tin at all, and didn't seem heavy enough.

Now I am curious and I'll have to look for it.

I got done what I wanted to do, although it was pretty ugly.

Eutectec makes some interesting solder / brazes, but they are pricey and the last time I tried to buy some, they had large minimums. As I recall, the aluminum solder also will fail from the difference in the electromotive potentials between it and the aluminum in a couple of years.

While on the subject, what removes the black oxide that forms on stainless steel when it it's overheated?

Bill

If you really want to learn a lot about silver brazing you can find a lot of info on the hand built bicycle boards. There are many artists there that work with various forms and brands of silver braze. Maybe also google Freddy Parr, probably one of the best authorities on the subject.

Some truly excellent points.

Thank you all.

We have more information on brazing at the following address:
Brazing carbide, carbide brazing overview, brazing tungsten carbide, advanced carbide brazing

It is specific for brazing carbide because that's what we do. The pictures of failure analysis of been very helpful to many.

RJT,
That wire is probably a 50% silver, cadmium free braze alloy. We sell it in small quantities of pretty good prices. We also sell a 49% silver braze alloy with manganese that is much stronger.

We prefer white flux when you want to see the work. We far and away prefer black flux because it seems to be much more reliable and much more forgiving.

Yes, I think you should get a raise now that you're brazing instead of soldering.

Jim Rozen
I agree with you about borax-based fluxes removing oxides. However, when I lecture or teach, I usually include this fact that add that it is a fairly weak effect and is much better to have the parts clean before you start. Based on other things you have posted I am well aware of your considerable expertise in this matter and just wanted to clarify.

Thank you for adding the part about refluxing and recovering. That technique has been important to me many times over the years and I don't think it is nearly as widely known as it should be. We have also found that if you don't use enough flux in the first place, you can reflux, reheat and have a good join. If you burn up or use up all the flux so that you have the glasslike condition when it cools, you can add more flux, reheat and then it should be much easier to remove.

You are absolutely correct about the four terms and the American Welding Society definition of brazing.

Most parts are usually clean enough from machining, I've found that small amounts
of oil simply vaporize off during the fluxing stage. When I've burned stuff up, it's
usually because I did not put enough flux on to start, or missed a spot in the back,
or dug in with the torch too far in one spot.

The eutectic white flux I've gotten recently is far and above better than the
inexpensive white flux they used to have in the stockroom. The old stuff was
just water-based and tended to blow off very easily. The eutectic stuff is
somehow more 'slimy' for lack of a better word, I wonder if there is a bit of an
organic binder in it. But it sticks great.

I suggest to folks that you cannot put on too much flux - most burned up parts
are because of too little. I heat, apply flux, heat more, apply flux, heat more,
etc, until I feel like the coating is getting clear and is all over the part. This is
where patience really counts.

I also like to dip the solder wire in the flux and get it cooked off near the flame
that's heating the part, before applying the wire to the joint.

9100 said:

While on the subject, what removes the black oxide that forms on stainless steel when it it's overheated?

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I believe you are referring to "sugaring", which happens when you weld stainless without sufficient/proper shielding gas. If so, about the only thing you can do is use a wire-wheel or some form of abrasive to remove the oxides and check carefully for porosity, especially on the backside of welded parts.

The other problem with you see with overheated stainless is a dull gray surface due to carbide precipitation. Quite common with Tig welding if your travel speed is to slow or your amps too high.

Eutectec makes some interesting solder / brazes, but they are pricey and the last time I tried to buy some

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I was wondering if anyone else has used them. I have some that my dad bought years ago when the Eutectic rep used to stop by from time to time. I have some that are pink, and some blue. I dont know the difference between the two but I have to say that they are tried and true STRONG brazing rods. I only have a few left and save them for when I need to make a strong braze weld on something. I would actually like to find out if they still market them.