Silver soldering stainless

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stragenmitsuko

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I guess I learned something new today .

I''m quite familiar with silver soldering , mostly brass fittings on red copper , or red copper to red copper .
Never had any problems with it . If the copper is clean enough I can even do it without flux .

So I'm retrofitting an airco to a vintage toyota MR2 Mk1 .
and I needed to solder ss parts to 1/2 copper , and to 1/2 stainless .
And to my surprise that didn't work as I expected .
So first thouht , I had the wrong kind of flux . I bought new one , specificly asked for stainless , and the result
was even worse . The solder wouldn't flow , wouldn't bind to the stainless .
Made such a mess I was ashamed of myself .

So what went wrong ?

To much heat , to fast .
Red copper is a very good heat conductor , so it's easy to heat it evenly and then apply the solder .
Basicly just blaze that oxy /acetetylene torch until it's hot enough and solder .
Only takes a couple of seconds really on thin walled 1/2 pipe .

Ss is a bad conductor , so what happend is with that acetylene torch I overheated the flux while
the metal wasn't up to temperature yet . I got local red hot spots on the stainless , while the opposite side
was still relatively cold . The flux turned into a black scale that had to be sand blasted to remove it .
Impossible to silver solder that .

So I turned down the heat on the torch , made a longer flame with less oxygen , and
allowed the stainless to reach the brazing temperature slowly .
Carefully watching the flux colour also helped .
As soon as it turnes kind of transparent it's hot enough , and then you just keep gently heating the ss
until the solder starts to flow .

Once I knew what I was doing wrong , it all worked out as I expected .

So as the saying goes , never to old to learn something new :)
 

Lloyd-ss

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Glad you stuck with it and got it to work. Do you know what flux and silver solder you were using to bond to both the SS and Cu?

Along those same lines, a connector sales rep, who had probably been around since Mil style connectors were invented, related his thoughts to me about crimp style connectors vs solder style.
"Crimping is a science, Soldering is an art."
Nice art work on your project. :cool:
 

stragenmitsuko

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Here's a picture of a failed joint .
Altough the copper pipe in the background is fully soldered , the stainless isn't .
There's a black spot inside , and that is the burned flux .

I had to machine it out to get rid of it and resolder .





solder.jpg



About connectors , crimping is for mechanical strength , soldering is for good electrical contact .
At least that's what I'v been told , and that's the way I've away's done it .
Crimped only connectors will work just fine , but give it a few years in the harsh conditions
under the hood of a car and they'll start corroding and eventually fail .

Cheers

Pat
 

Dubi

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Here's a picture of a failed joint .
Altough the copper pipe in the background is fully soldered , the stainless isn't .
There's a black spot inside , and that is the burned flux .

I had to machine it out to get rid of it and resolder .





View attachment 137379


About connectors , crimping is for mechanical strength , soldering is for good electrical contact .
At least that's what I'v been told , and that's the way I've away's done it .
Crimped only connectors will work just fine , but give it a few years in the harsh conditions
under the hood of a car and they'll start corroding and eventually fail .

Cheers

Pat
Which is why I always solder electrical connections where possible.
 

Lloyd-ss

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I understand the controversy over crimp-vs-solder. I worked in an environment of making marine navigation systems for navies around the world. Lots of wiring and wire harnesses. In all of this, probably 99% of the electrical connections were crimped. But, despite that, I too, solder most of my electronic connections at home, and do not really trust my at-home-crimp connections.

And here is why.
The crimping of the military electrical connections is very much a science. All wire was stranded silver plated copper to various mil-specs. All of the wire terminals were mill-spec for the specific wire size and connector or terminal board. All crimping was done with the proper mil-spec die and mil-spec crimper handle. Whenever a project was started, crimped wire samples were submitted for inspection under a microscope and for a pull test to be sure the crimp was secure. All inspections and tests were documented on paperwork. A lot of care, skill, inspection, etc, was done to make sure the crimping and materials were correct.

So with all this info about crimping, why do I still solder most of my connections? Because I don't have access (or money) for access to all the resources necessary to make 100% reliable crimped connections. Using no-name plain copper wire, doing crimping with a pair of pliers or "universal" crimper instead of a proper crimper, no reliable method to do a pull test or inspect 100% of the joints. etc. All of this leads to failures in the future. But done correctly, crimping is fast, reliable, and only requires attention to detail, not a super specialized skill.

I specifically remember one project from years ago where we were manufacturing the large slip-ring that went between the hull and turret of the M1 tank. One of the sliprings in the unit had 4 circuits that each carried 200 amps. I think plain copper 4 gauge stranded wire was used to make the internal runs. There was a voltage drop test that was done to each unit at final test. Some of the units, that had previously passed at an earlier test, were failing the voltage drop test. We found that just wiggling the 6 gauge wire at a set-screw type of termination fixed the voltage drop problem. The plain copper wire had developed tarnish,which is not very conductive, at some of the connections. The simple fix was changing from plain copper stranded wire to silver plated copper wire. Unlike copper tarnish, silver tarnish IS conductive. Problem eliminated, but everything had to be done correctly.

Moral of the story: Use either crimp or solder, whichever you have most confidence in, but no matter what, do it correctly.
I think I overspent my 2 cents, LOL.

And sorry for hijacking your thread.
Lloyd
 

davidyat

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I had the same problem with the Meyers Rider Ericsson Hot Air Engine. Specs called for Silver Soldering a SS round to an Iron tube. What I had acted like your first try. Wouldn't flow. Went to the welding shop with my blueprints. What solder were you using, they asked? Showed them. No, that won't work, use this. I was using silver solder with a silver content something like 3, 6 or 9%, too low. They showed me 3 sticks of 51% silver solder, orange covered flux about 20 inches long. $10 a stick, $30 for the tube of 3. Did it work? Absolutely. I will pay for something, IF IT WORKS!!
 
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I worked in TV maintenance for about 30 years. Our transmitters used various combinations of voltage and current 36KV at 1.5A and 40V at 400 A. Gas-tight, mechanically strong joints were very important. The correct crimp tool was, as you said, very important too.
The joints which had the most failures were the RF (radio frequency) connections on the microwave trucks, out in the elements. For those, a good crimp or soldered connector followed by a sealant was required.
I had an argument once with one of the older guys when he saw me soldering a spade lug after I crimped it. He said the solder made the wires brittle at the joint. My point was, in all of the connections I repaired, none had broken due to brittleness, but plenty had pulled out of the connector! I still solder after I crimp.
 

davidyat

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I have an oxy/acetylene set up. I slowly heated the material until I touched the rod to the work and it started flowing. Then I lightly heated the work all around and watched the solder flow nicely around the material until done. Try to slowly bring up the temperature of the metal until the solder starts to flow.
 
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