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I've been attempting to practice torch brazing/soldering and am currently attempting to join a ring of stainless steel wire shut like a wrist sized 'o'.

Unfortunately the results have been pretty bad. The silver solder I'm using just does not want to stick, it keeps dripping off in globs. And when I heat the wire up it gets red hot pretty quick and then as soon as it cools down its coated in a layer of char which makes it not want to stick even further.

I've tried using this propane torch and this MAPP torch but neither seem to get the job done and seem to heat it to rapidly. I combat this by pulling it back a bunch and 'wafting' the heat over the target area which seems to help but things still go black. Furthermore I'm using this silver bearing solder and this flux paste which I suspect are more likely the issue. The solder is considerably thicker than the wire I'm trying to join and I'm not even 100% sure its the right kind for the job.

The wire I'm using is stainless steel (type 302/304), soft tempered and is 0.032" diameter.

I've come across a few tutorials on youtube but most seem to be for copper plumbing pipe work or a few seem to be jewellery (and using exotic metals). Can anyone suggest good tutorials to learn how to do this type of brazing/soldering?

Does anyone have any suggestions around where I'm going wrong?

Edit: In case it is somehow relevant, this is a high voltage electrical project and I'll be linking several of these 'o' rings in a sphere shape. Its not a simple matter to bolt them together and I must weld them.

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Are you welding or soldering? These are two very different things. –  DA01 Dec 12 '13 at 7:59
    
@DA01 It sounds like (according to Ecnerwal below) that I'm attactually attempting to do brazing... Which based on my understanding still seems like soldering (but neither of which are welding) –  NULLZ Dec 12 '13 at 12:06
    
As I stated in the answer that you are pointing to, what you linked to is a low-melting-temperature, soft solder. You are soldering, unless you change materials. –  Ecnerwal Dec 12 '13 at 15:19
    
-1 because this looks like it's OT (hobby project) to me. –  BMitch Dec 17 '13 at 12:03
    
If this is a "HV electrical project", why are you using stainless over, say, copper, which has better thermal and electrical conductivity, and can be soldered with minimal effort? –  Nick T May 25 at 20:14

2 Answers 2

up vote 3 down vote accepted

Successful soldering (you're not welding, and you have the wrong torch if you want to weld) requires that the work be physically clean (scrub it) and chemically clean (flux) - you need a very aggressive flux for stainless, because the reason it IS "stainless" is that it forms a strong oxide layer which protects it from most corrosion. Kester is not going to regard stainless as electrical work, for one thing, so don't bark up that tree too long.

With thin stainless, the other problem you almost certainly have (stainless conducts heat poorly, which makes it very easy to overheat) is overheating the work - once work has been overheated, you have to return to physically cleaning it and refluxing before you have a hope in heck of getting solder on it. You also need to stay out of the "oxidizing cone" of the torch flame - ideally, switch to an oxy-acetlyene torch, make the flame rich, and only use the feather - but you can get there with propane if you're careful. The thickness of the solder does not matter much - you heat the wires, and melt the solder on the wires - don't heat the solder.

You could also move up to brazing, which is a process similar to soldering but at higher temperatures, using different filler metals. When most folks refer to silver soldering, what they actually mean is silver brazing (the rod has some silver, but not a huge amount.) The solder you linked to is a low-temperature solder that has silver in it, from the "lead free" change in "soft solders."

What this is doing on a DIY home improvement site is another question. High voltage electrical projects are not exactly the bread and butter of DIY. Another approach in a lab setting would be to do the whole job in a glovebox full of nitrogen or argon. You could also TIG weld it, if you were good at TIG welding. Spot welding might be another approach, but that will also work better on stainless in an oxygen-free atmosphere (glovebox, etc.)

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Many thanks for your help, I can't afford a TIG rig at the moment, same goes for Nitrogen or argon gloveboxes. While indeed the project is a 'hobby' project, its more training for learning to weld in general (am also playing with Arc and MIG) to move onto DIY repairs of things around the house. I assume then that brazing at higher temperatures is therefore more suitable for high-temperature applications? –  NULLZ Dec 12 '13 at 4:17
    
It's more suitable for high temperature; it's also stronger. which is as often as not the reason it is used .vs. soldering. If you have a heavy-duty soldering iron (60W or better) you might want to try that - but clean the flux off the iron VERy carefully afterwards - stainless flux is nasty stuff, and it will eat your tip if you don't get it all removed. –  Ecnerwal Dec 12 '13 at 15:20

For electrical applications you should just bolt it, or use a surface that has been plated with copper or nickel so that electronically conductive flux can stick to it.

If this is strictly a mechanical application, you need a flux designed for stainless steel:

http://www.kester.com/kester-content/uploads/2013/06/Soldering_to_Stainless_Steel.pdf

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Sorry, I don't understand your first comment "for electrical applications; you don't"? –  NULLZ Dec 11 '13 at 23:07
    
It's in the paper I linked to, but I edited the post for you. –  virtualxtc Dec 11 '13 at 23:38
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Please include the relevant information from the PDF in the answer itself. That way if the link ever breaks your answer will still be useful. –  ChrisF Dec 11 '13 at 23:46
    
And your advice isn't great anyway. 'Kester does not recommend the use of acid fluxes for any electrical applications'. Okay, so what about non-acid-fluxes? Or any other alternatives? This is a short term application and I'm not terribly concerned about longevity at this stage. Additionally, I cannot plate the Stainless steel with copper or other materials as that would alter the project. –  NULLZ Dec 12 '13 at 1:04

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