silver soldering advice needed

[Paul Saffold]

Need help with silver soldering. I want to try silver soldering for shop projects. Possibly split nuts, for joining metal for tool making, jigs, and whatchamacallits. I other words I'm not working on anything specific right now, but want to learn how.

I have soldered lots and lots of copper pipe so know the general process. I have propane, MAPP, and a little micro butane torch. Do I need any other equipment?

I'm not interested in silver soldering for electronics or jewelry making.

I'm looking for advice on what solder and flux to use. Would either the Lincoln Electric's Safety-Silv 45 2-Piece Brazing Kit (solder and flux) or the Safety-Silv 56 kit be good? What is the difference? Home Depot carries them so they will be easy for me to pickup. Or do you have other recommendations?

Any other general advice and cautions?

Thanks,Paul

[David Keller NC]

It would appear that the difference is the melting point of the braze wire - the 56 is a low-melting point alloy that would presumably allow a homeowner to more effectively braze joints with a propane torch. Since you've a MAPP gas torch, that's unlikely to be an issue (MAPP gas burns hotter than propane, and a MAPP-Oxygen torch burns way hotter than both of them).

But - you titled your thread "silver soldering". As I understand it, the distinction between brazing and silver soldering is the metallic compound used to join the two metals, and typically, the geometry of what you're trying to join.

Specifically, if you're trying to join 2 pieces of flat metal on their faces (silver soldering a steel sole onto a brass plane is a typical example), one uses a very thin sheet of a silver-cadmium-copper alloy, clamps this between the two metallic sheets, and heats the whole sandwich with a brazing torch.

Here's a chart from the McMaster-Carr catalogue that shows a list of different silver solders for different applications:

http://www.mcmaster.com/#silver-solder/=cbcvqd

[Dave Beauchesne]

Need help with silver soldering. I want to try silver soldering for shop projects. Possibly split nuts, for joining metal for tool making, jigs, and whatchamacallits. I other words I'm not working on anything specific right now, but want to learn how.

I have soldered lots and lots of copper pipe so know the general process. I have propane, MAPP, and a little micro butane torch. Do I need any other equipment?

I'm not interested in silver soldering for electronics or jewelry making.

I'm looking for advice on what solder and flux to use. Would either the Lincoln Electric's Safety-Silv 45 2-Piece Brazing Kit (solder and flux) or the Safety-Silv 56 kit be good? What is the difference? Home Depot carries them so they will be easy for me to pickup. Or do you have other recommendations?

Any other general advice and cautions?

Thanks,Paul

Paul:

So much to answer in a thread!

My trade (refrigeration mechanic ) dictates I silver solder a fair amount.

1) Clean, clean clean !! the surfaces to be joined must be clean, as well as the surrounding metal. Oxides, contaminants and grunge will migrate from adjacent areas to ruin your day. My old instructor used to say -'' If you have 10 minutes to do a joint, 9 will be spent cleaning it up ''. I also clean the alloy - unroll about as much as you think you need and pull it through a piece of sand cloth a few times to be sure. I use green or maroon scotch pads or sand cloth - oil is your enemy - the abrasive has to be squeaky clean as well or you are just transferring contaminants.

2) Silver solder ( it is more like silver braze due to the temps. involved - around 1250*F or so depending on the alloy ) can joint Stainless steel, brass, copper, steel or any combination thereof - no aluminum! Clearance is critical also - a few thousandths of an inch - I don't have the critical tolerances in front of me, but with
proper heat control, a 1/16th inch gap is fillable.

3) The paste is critical, and usually is water soluble - I add water till it is a bit thicker than thick cream - has some ' cling ' to it - after the joint is heated, it is almost glass like, and will shatter when tapped - I slather it on liberally, but caution is required if too much is used.

4) The number in the part number of the solder is usually the percentage of silver - 45% is a general purpose alloy, the 56 is likely 56% silver - I have a 1 pound roll of 75% here, but it is tricky to use. Stay with 45% for most things.

5) HEAT - - - Critical you have enough, critical you don't overheat - if you overheat the joint, you scorch the flux and the alloy WILL NOT stick to it. The only way to salvage the joint is to dis-assemble and clean it THOROUGHLY and start over - not a pleasant task. If you get the metals to even dull red you have overheated. When doing stainless or steel, a pinpoint flame will turn the metal red hot real easy - practice is important. I can't comment on what you need, but a straight propane torch to join a couple pieces of 1/4 '' steel butted together would not cut it. Dis-similar metals are tricky; steel to brass especially - the steel heats up really quickly and brass dissipates the heat better - so you can scorch the steel part of the joint easily. Same goes for joining different thickness pieces. If you scorch the joint, the flux will be black when you are done - another thing you can ' read '.

6) READ THE FLUX - Here is how I teach people - ( I presently have an apprentice, and teach the Instrument Mechanics at the Mill I work at how to silver solder if they ask ) - assuming the joint is prepped, fluxed and in a vice - - -

aa) WEAR SAFETY GLASSES and be in a well ventilated area !!
a) Play the torch around the entire item being soldered to heat it up somewhat evenly. Don't get the alloy close till step ( d )
b) The flux will begin to bubble, even violently - keep up with the even heating thing
c) The bubbling will subside, and the flux ' dries out ' - starts to look chalky - keep up the even heating thing
d) Then, the flux starts to look like thick, clear syrup - you are real close - did I mention the even heating thing again?
e) Concentrate somewhat on one area, and get the alloy in at the joint - don't heat the alloy directly, but you may get a
' ball ' drop off onto the joint - play the torch on that area, and when you hit the critical temperature, it should flow and look cream like and
fluid in the joint
f) Don't get mesmerized with your success!! Keep heating the rest of the joint - leading the alloy with the flame I like to say - keep adding
alloy as it ' wicks ' around the joint, it should form a small radius-ed shoulder - too much alloy is very possible, especially if clearances are excessive
e) Let it cool - the alloy will quickly set, but let it cool for a couple minutes before moving. You can quench it, but that can cause other troubles

There is a Coles Notes version - others can chime in if I missed anything - PRACTICE LOTS BEFORE you try it on something valuable !!

Good Luck

Dave Beauchesne

[Paul Saffold]

Thanks David. I said silver solder but brazing may be the more accurate term for what I'm attempting. Also, I thought the process was one of capillary action to fill the gap. Is this also brazing?

[Dave Beauchesne]

Thanks David. I said silver solder but brazing may be the more accurate term for what I'm attempting. Also, I thought the process was one of capillary action to fill the gap. Is this also brazing?

Capillary action is the process by which the clearance between two pieces of metal is filled with a filler alloy. No melting of the metal takes place, only the alloy.

Soldering vs brazing is the same concept, except the range of temperatures involved - soldering is cooler than brazing.

Welding is where the filler metal actually melts with the two metals being joined.

Correct me if I am wrong - I can weld somewhat; the vast experience I have is in the soldering / brazing area.

Dave Beauchesne

[Shawn Pixley]

Paul,

I think David gave you good advice on silver soldering (AKA brazing). There is no one size fits all approach to this. Depending upon your application, sizes, stresses, and materials, there are better or wose methods of joining materials. For instance if I were joing steel at a 90 degree angle, i would use a fillet braze (brass or broze) rather than silver solder. For that application there is minmal capillary action involved unlike the process David describe so well.

The real secret is practice, practice, practice for the application that is needed. There is no single method than works in all aplications. I use acetylene / air for silver solder. For alloying steel, I forge weld damasquene style with borax.

As to cautions, uv protected goggles, welders chaps, gloves, fire protection, and a bucket of water. When some hot steel or solder goes down your boot, you will learn a new dance. DAMHIKT

[Chris Fournier]

There is a significant range of heat input required for the various silver solder alloys available to us.

I choose the solder/braze/fusion welding processes used on a job based on the materials and application parameters of the job.

I like to silver solder and it can require less heat than brazing with bronze in many applications but silver solder is EXPENSIVE so the application has to merit the $$$. I use both raw solder and flux paste as well as the flux covered rods. For fixing fine instruments, like where I don't want to see evidence of a repair I reach for the silver solder.

As has been pointed out: clean all parts including the solder, flux all, learn to get the heat just right for the solder alloy that you are using - this inlolves practice!

If you are using a MAPP gas set up be realistic about how much metal you can heat up to a dull red temperature. You need to heat up the entire fitment, not just the face that you can see. For smaller work the MAPP set up is great but it doesn't take alot of material before you really do need the BTUs of a good O/A rig.

Bronze brazing rod is so much less expensive and for many repairs (cast iron) and tool building jobs where aesthetics aren't critical (later painted etc.) I would go for this option right away.

Regardless don't let anyone try to tell you that brazing isn't good enough for situations requiring great strength and push you toward fusion welding - this simply isn't true. Brazing is a great process to have in your back pocket. Make up different test and trial coupons (test pieces) and develop your technique before you go for the real project. Flux is cheap, try different brands to see what works best when.

If you can find an experienced friend to show you the process I would be asking what his favorite Scotch/beer is before his/her offer was finished being offered. Priceless help.

[Johnny Kleso]

Heat the back side if you can.. This will draw the solder toward the heat and not burn your flux..

[Paul Saffold]

Thanks for all the good advice, tips and safety precautions. Looks like I need to practice. Paul

[David Nelson1]

Capillary action is the process by which the clearance between two pieces of metal is filled with a filler alloy. No melting of the metal takes place, only the alloy.

Soldering vs brazing is the same concept, except the range of temperatures involved - soldering is cooler than brazing.

Welding is where the filler metal actually melts with the two metals being joined.

Correct me if I am wrong - I can weld somewhat; the vast experience I have is in the soldering / brazing area.

Dave Beauchesne

You exactly correct, its all about temperture ranges and equipment.

[john brenton]

I brazed quite a bit as a pipefitter, doing everything from small refrigeration lines to medium sized medical gas lines in hospitals, all the way to larger underground supply lines. Paste flux isn't necessary when silver soldering, as the rods have a fluxing agent already in them...there may be some that don't (I've never seen one), but most rods will have a flux core. It doesn't even help, except for maybe wiping the joint off so it looks nice and pretty. There's one more thing to read up on for the OP I guess.


Thanks for all the good advice, tips and safety precautions. Looks like I need to practice. Paul

[Johnny Kleso]

John, The SS I used in a machine shop is a lot different than thats used on refrigeration lines...
The machine stuff needs an oxy/acc torch where the refer. stuff you can use Mapp gas...

Stuff I have in my tool box has a heavy blue flux coating but I still would use white paste flux when I use it..
When the flux turns clear and liquid is a good clue as to the temp of you parts for me..
If it drys and turns to white clauk you know you got it too hot..

[john brenton]

I don't think I ever used mapp gas for silver solder...except maybe in a pinch on some 1/2" stuff underground, and even then it took forever. Refrigeration and HVAC guys use oxy/acc, and their stuff is tiny. I did mainly 3/4" to 2" copper and I used Oxy/Acc torches too...accompanied by a loud "poof" and black soot everywhere until you got the mix right.

I'm sure at one point I used flux, maybe when it seemed like the solder wasn't flowing like it should...I just know that most of the time it got sucked right in there just by evenly and adequately heating was being brazed.


John, The SS I used in a machine shop is a lot different than thats used on refrigeration lines...
The machine stuff needs an oxy/acc torch where the refer. stuff you can use Mapp gas...

Stuff I have in my tool box has a heavy blue flux coating but I still would use white paste flux when I use it..
When the flux turns clear and liquid is a good clue as to the temp of you parts for me..
If it drys and turns to white clauk you know you got it too hot..

[Johnny Kleso]

John,
Open the oxy a crack before you light the torch and then you'll have no black soot..
The nutural mix is about 3-1 acc to oxy

I learned quick at my first job to crack oxy.. I would mostly be using a torch during my lunch break... The old guys would all moan and complain when I made black soot and tell me it was all over there sandwiches hehehe

[john brenton]

I don't plumb anymore (thank God). I knew how to do it but silver soldering is a pretty infrequent thing for a plumber, but when you do it you're doing a lot of it. After a few times I'd remember how it was supposed to be done. I worked with old jpurneyman who would eat a sandwich without washing their hands after cracking open a very used waste line....black soot wouldve been the least of their worries!


John,
Open the oxy a crack before you light the torch and then you'll have no black soot..
The nutural mix is about 3-1 acc to oxy

I learned quick at my first job to crack oxy.. I would mostly be using a torch during my lunch break... The old guys would all moan and complain when I made black soot and tell me it was all over there sandwiches hehehe