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Brazing Stainless to Brass with Less Heat

10/20/2007 3:00 PM

I am working on a small project where I had to braze a brass barb fitting to a stainless tank of sorts (non magnetic stainless). I used an oxy+Mapp gas torch to braze with special brazing rod that's meant for that kind of application. It was the only kind I could find in the area, it's Nickel-Silver (makes very attractive welds if done right, but it's hard to work with being as inexperienced as I am). I found it hard to work with and the end result was it didn't seal at all (lots of little holes), plus I ended up melting the brass fittings once because it's melting temperature was too close to the brazing rod.

My materials professor was talking about a special product that used an exothermic reaction to melt an alloy and bond stainless to other metals. I think he was pulling my leg, because he couldn't find anything about it, and I had no idea what he was talking about. Is there a product that that does that, and doesn't require a really hot torch to do so? The heat from my torch distorted the shape of my stainless tank, and made it almost unusable.

... Another question... is it required to use a #4 or #5 shade with an Oxy/Mapp gas torch? It says so in the manual, but is no where near as intense as Oxyacetylene, so I just used some quality dark sunglasses (which I thought was close to a #4 shade anyways).

Can anyone help with this?
Thanks,
Nick

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#1

Re: Brazing Stainless to Brass with Less Heat

10/20/2007 6:59 PM

Probably what he was referring to is the process called CadWeld, sold by Erico out of someplace in Ohio. I don't know if they still exist under that name; I haven't used the stuff for over twenty years. There may also be some restrictions on the sale of it these days.

If that's what you have it mind, it gets verrrry hot. I suspect it will be much harder to work with than your MAPP torch. And it is likely pretty expensive for a one-off application.

Can't you have a small boss welded on, tap it and screw the barbed fitting in? Any decent SS welder should be able to do that without a lot of distortion.

As for looking at your torch through sunglasses, how uv resistant are they? Are you thinking of having cataract surgery at an early age?

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#2
In reply to #1

Re: Brazing Stainless to Brass with Less Heat

10/20/2007 7:48 PM

Yes, that must have been what he was talking about. It does look like an expensive process, probably not worth the trouble, unless there actually is something else that's similar. So what is MAPP gas then, I was under the impression it was part Acetylene and something else, probably just propane. I guess I'll have to look for some local welders willing to do small projects.

And I was afraid that I was going to get a response like that about my sunglasses

I figured that since sunglasses are quote "100% UV resistant" (even cheap ones), I would be OK for the few minutes of exposure. Most of the plastic face shields are made of similar kinds of plastics (by look and feel), so I thought it was a "Good enough" kind of thing, especially with the metallic coating on my sunglasses

But you're probably right

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#3

Re: Brazing Stainless to Brass with Less Heat

10/20/2007 8:52 PM

Why not make a trip to the largest welding supply house in your vicinity. They have the materials and expertise to suggest solutions. They have the correct eye protection too.

A eutectic brazing alloy rod and appropriate flux are a must. Also an appropriate heat shield may be appropriate.

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#4

Re: Brazing Stainless to Brass with Less Heat

10/21/2007 5:02 AM

Hi Nickjd, Try using silver solder, a medium hard to hard one is good enough for brazing brass to stainless steel. You can use a hot propane gas brazing torch with this method, also you will need to use borax as a flux. All stainless steel surgical instruments are brazed by this method, and I have used this on many occasions. Spencer.

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#5

Re: Brazing Stainless to Brass with Less Heat

10/21/2007 7:18 AM

The best method is with 40% silver solder and as previously mentioned borax flux.

The most important thing is not to overheat the stainless steel and do not try to rush the weld, once the temperature is balaced around the weld the silver solder will flow around the joint perfectly.

It is a bit of an art and would suggest some experiment on test pieces first, allso use oxy and propane torch not Mapp this will give you cleaner and better control.

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#7
In reply to #5

Re: Brazing Stainless to Brass with Less Heat

10/21/2007 9:28 AM

Hi garth, As I said, "hard silver solder !" This is a silver solder of 40% silver! Spencer.

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#6

Re: Brazing Stainless to Brass with Less Heat

10/21/2007 8:47 AM

Your materials professor was likely thinking of a product made by RNT (http://www.rntfoil.com). It's neat stuff but probably not for your application. I suggest you get some wire or foil brazing alloy made to AWS A5.8 - BAg-1 specifications. It is available in any welding supply store. It is made by many companies and usually has the number 45 associated with it because its composition is 45% silver. Easy Flow 45 is made by Handy and is common. This alloy is available with and without Cadmium. The Cadmium version is slightly easier to work with but requires good ventilation. You will also need an appropriate flux (Borax types are okay). Propane, MAPP, or Oxy are all appropriate heat sources. The alloy is liquid at 1145 deg.F. Very little practice will make you a pro.

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#11
In reply to #6

Re: Brazing Stainless to Brass with Less Heat

12/07/2007 9:16 AM

Excellent info for a similar project. Thank you.

In case you are still monitoring this topic,

What process or alloy would you recommend if corrosion resistance not strength were the deciding factor? (the parts to be joined are also quite small)

Thanks in advance

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#8

Re: Brazing Stainless to Brass with Less Heat

10/21/2007 10:56 AM

Looks like the hard silver solder will be the best choice because of the ease of use requiring only propane. The stuff I was using (I noticed after I bought it) said the working temperature was 1680 degrees F, but was the only stuff that said it was made for stainless.

I found a real welding company a few miles from where I live, it would take them probably just a half hour to do what would take me 3 hours and lots of swearing . If they are cheap, I might just have them do it.

I'm going to try calling that "Reactive Nano Technologies" company and see if I could get some samples, that's an interesting product. It's amazing how many companies will give you samples for cheap or free if you make up a company you're from or just say that you're an engineering student (which I am).

Thanks for the advice everyone!

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#9
In reply to #8

Re: Brazing Stainless to Brass with Less Heat

10/22/2007 1:55 AM

I think you can use Silver Brazing Filler as Mr.Welderman advise (AWS A5.8 - BAg-1).

And don't worry about it was made for stainless or not, because of brazing is used for welding 2 different material.

Good luck and success

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#10

Re: Brazing Stainless to Brass with Less Heat

10/22/2007 7:20 AM

In addition to the above advice, consider replacing the brass part with stainless steel; it could then be welded instead.

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