Any pointers on silver soldering steel to steel and brass to steel?

HMF

HMF

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Hi Folks,

I want to obtain a smooth capillary-action type joint when silver soldering small parts together made of steel to steel and steel to steel.

Any pointers on techniques to obtain smooth, complete welds with silver solder on these materials?


Thanks,


Nelson
 
I seem to be on a roll today with your postings Nelson.

I have done quite a bit of silver soldering or what is sometimes called silver brazing.

Important points.

1. The parts must be clean and a smooyh surface is good.
2. Parts should fit fairly close together.
3. Flux all the surfaces of the parts to be joints before assembly.
4. The parts should be heated slight glow appears.
5. Do not over heat or the flux will burn and the solder will not flow and will likely need to be cleaned again.

I have a refractory brick that I often place small parts on and heat them with a propane torch. Propane is sometimes not hot enough for parts other than quite small ones. If you use Acetylene, keep the torch well back and heat the parts evenly. As you bring the parts up to temperature, touch the hard solder to the part and a small ball of solder will come off of the solder stick and sit on the parts. Gradually continue heating until the solder flows. Move the heat around and watch the solder follow the heat.

Charlie W.
 
I find that the surface needs to have a little "tooth", that is, not dead smooth like a mirror for example. The surfaces should be flat. I scarify the surface with some 80 grit paper in the area to be joined. If this would present objectionable appearance outside the joint, just hit the middle of the surfaces, not touching the areas that will be exposed.

Cleanliness is absolutely essential. Ether (starting fluid) is a good cleaner in preparation.

Silver alloys (and there are a few) like small gaps, on the order of 0.0020 or so. Too much and the joint strength falls away quickly. Thin is good. When the temp is right, capillary action will draw the solder into the joint. The solder will have a very low surface tension and viscosity at the proper temperature. It will "wet" the fluxed surfaces. Don't get flux where you don't want the solder.

After a short cooldown, while the assembly is still quite warm, water will remove the slag/excess flux. If you do this when the assembly is warm enough, the water will boil and the resultant steam will aid in removing the flux residue.

Adjust the torch for a slightly reducing flame. It is a little cooler and this makes the temperature of the assembly to be controlled better. And there will be little oxygen added to the work.
 
My secret is you have to have some kind of small gap for the silver solder. Use the chocolate brown solder flux. And the best thing for heat I have ever found is a map gas hand held bottle torch. Acetylene torch get too hot to fast for good control.
 
The recommendation of small 'gap' is quite right but I question the need for any other more exotic flux for mild steel and or brass/copper.
Again, mapp gas efforts are OK for puny joining jobs but you need something a bit more substantial like propane or oxy/acetylene to get the whole lot sufficiently hot.

Here, I have to criticise the abject refusal to read up 'What the Brits did'
Three books immediately spring to mind. One is Alan Robinson's The Repair of Vehicle Bodies which was my standard text book and written for students- and manure students like me. I used 'oxy' and my father used 'oxy' in his shop in the 1930's when I could barely see over his anvil.
The second is the book on model boilers by the redoubtable Alex Farmer. He is the guy that is quoted by British boiler testers- and I would agree.
The final book is by the Guru of them All, George Thomas and the Model Engineers Workshop Manual and Workshop Techniques.

There is an adage by welders of the old school. They boast that they can even stick the tail back on a donkey- given the right flux.
Borax will do, mix it with water with a drop of detergent and heat it till it gets glassy.

Remember silver soldering is not a New Topic- it is thousands of years old. It's a bit like re-inventing the wheel. I would say 'Why?'
 
CharlieW said:
I seem to be on a roll today with your postings Nelson.

I have done quite a bit of silver soldering or what is sometimes called silver brazing.

Important points.

1. The parts must be clean and a smooyh surface is good.
2. Parts should fit fairly close together.
3. Flux all the surfaces of the parts to be joints before assembly.
4. The parts should be heated slight glow appears.
5. Do not over heat or the flux will burn and the solder will not flow and will likely need to be cleaned again.

I have a refractory brick that I often place small parts on and heat them with a propane torch. Propane is sometimes not hot enough for parts other than quite small ones. If you use Acetylene, keep the torch well back and heat the parts evenly. As you bring the parts up to temperature, touch the hard solder to the part and a small ball of solder will come off of the solder stick and sit on the parts. Gradually continue heating until the solder flows. Move the heat around and watch the solder follow the heat.

Charlie W.
Click to expand...

i use stay bright low temp silver solder and a heat gun instead of a torch. I also use a brass rod with a fine edge ground on it to clean up any stray solder when done it works great and will not scratch the steel surface. If using high temp I use a torch and heat the pieces before placing a small precut piece of solder on the joint surface while while continuing to heat until it flows. I clean the same way. I use a qtip to apply flux. Hope this helps.
 
I'm only good at putting bandsaw blades back together. Once the pieces are aligned, I put a drop of flux on the joint along with a tiny piece of the solder. I use a little pick to hold the piece in place and I hit the joint with mapp gas from underneath. It bubbles for second, the solder melts and flows into the joint. -Done!


Ray
 
i'm old school, i either use the air/acetylene torch or oxy/acetylene. My father is a retired plummer.
i learned a lot about soldering from a master.
i can't claim the recipe, it was learned.
if interested take a look...

clean and scuff up the parts to be soldered (emery cloth works well, stainless steel brushes also are great )
apply the correct flux for the materials to be soldered.
heat the part to be soldered,not the solder.
i was taught to use bar or coil solder.
i was taught to give a little touch now and again with the solder as you're heating.
when you get hot enough it will start to melt then flow. don't overheat just keep the solder flowing.
resist the urge to quench the joint after soldering , let it cool slow as possible.

i hope the lesson helps someone...

mike:))
 
real old school..brush with sulfuric acid, torch/solder
 
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