Silver soldering stainless steel

[ettingtonliam]

I apologise for asking this question, I know its been covered before, but I can't trace it.
I need to silver solder a 3/8" dia collar onto a 1/8" dia spindle, both parts stainless steel, described as 'free cutting stainless steel' by the well known supplier.
I intend to use 38% silver solder and HT5 flux, both from Cupalloy. I'd use a higher silver content solder, but I don't have any at the moment.

Any special points I need to be aware of, or do I just flux it well, and put a silver solder ring at the ends of the collar.

Will this affect the machinability at all, as the collar will need some work after soldering. It can't be done before.

Richard

[92220]

Hi Richard.

I've never had any problems silversoldering stainless, though I haven't used modern siulversolders. I used the good old Easyflo No.2 and sometimes Argoflo, with Thesco or Easyflo flux, whichever was available from the stores. In those days, the stainless specs I used were EN56 and EN58.

Bob.

[Deleted]

Hi Richard

As with Bob, I've used normal flux for silver soldering stainless, having said that, if it was a part where stress is involved I'd probably go with a flux designed for the job in hand, although normal flux worked fine when making my tender handbrake which has some force on it..

Cheers

Pete

[uuu]

I think previous advice has been that HT5 is the right stuff. Don't use grit or wire brush to clean the parts.

Wilf

[Roger]

Dazza (oily rag) is the man to ask, he does it for a living. I seem to recall that he mechanically cleans the joint immediately prior to silver soldering because an oxide forms if you leave it and you won't get a strong joint, even if it looks right.

[jasonb]

The HT5 flux contains what is needed to remove the chromium oxide you get with stainless so OK to just use that. I've just come in from soldered a couple of 5/8" dia 416 discs onto 1/4" 303 rod to make a couple of valve for an IC engine. The flux may end up a bit green as that is the colour of the removed oxide.

[Oily Rag]

Jun 28, 2019 16:56:32 GMT Roger said:

Dazza (oily rag) is the man to ask, he does it for a living. I seem to recall that he mechanically cleans the joint immediately prior to silver soldering because an oxide forms if you leave it and you won't get a strong joint, even if it looks right.

Yes. For best results, chew it away by mechanical means, sharp new grit paper or cloth or abrasive bands and blow the dust off. Relying on the flux can lead to tears. In my daily caper of professional expression a joint letting go can do serious harm to the rider. I have never seen it recommended by the manufacturers of braze materials to never rely on the flux to clean any joint for you, be it stainless or ferrous or non ferrous. It may still wet out but it is not necessarily the best inter molecular interaction. The braze filer material actually does interact/dissolve into the parent materials.

www.sciencedirect.com/topics/chemistry/brazing

[Roger]

Jun 28, 2019 22:39:36 GMT Oily Rag said:

Jun 28, 2019 16:56:32 GMT Roger said:

Dazza (oily rag) is the man to ask, he does it for a living. I seem to recall that he mechanically cleans the joint immediately prior to silver soldering because an oxide forms if you leave it and you won't get a strong joint, even if it looks right.

Yes. For best results, chew it away by mechanical means, sharp new grit paper or cloth or abrasive bands and blow the dust off. Relying on the flux can lead to tears. In my daily caper of professional expression a joint letting go can do serious harm to the rider. I have never seen it recommended by the manufacturers of braze materials to never rely on the flux to clean any joint for you, be it stainless or ferrous or non ferrous. It may still wet out but it is not necessarily the best inter molecular interaction. The braze filer material actually does interact/dissolve into the parent materials.

www.sciencedirect.com/topics/chemistry/brazing

Thanks for that Dazza. Before you explained how it was done, I didn't think it was possible. I've mentioned before on another thread where we had what appeared to be a beautiful joint between two pieces, with a lovely fillet and wetting out to a thin edge. However, that snapped right off, leaving the wafer thin edge of the fillet perfectly intact.

So you may well get a great looking joint using flux alone, only to find it shears off with very little force.

[cupalloys]

For all silver soldering operations to be successful, the surfaces have to be oxide free. Chromium forms an oxide layer naturally. It CANNOT be removed mechanically. On a good day, grit can really screw things up by further contaminating the surfaces.
Oxide removal is not your job. It is what the flux does and it does it more efficiently than you can.

Use HT5.

It's been like that ever since I entered this business in 1967. Thinking about it,it was probably the same before that!

If a joint can be simply pulled apart, the joint was not sound to begin with. Alloy only running around the edges? Sounds like a flux or heating problem. Either way, the problem lies behind the torch- not in front of it!

Keith

For more information read the book available from CuP Alloys or why not just ring them?

You will also find that they have whatever material you might need ex stock. See the website and you don't have to walk any further than your phone!

[ettingtonliam]

Thanks for the tips, chaps. I've done one, using 38% silver content and HT5 flux. It seems OK so far, but we will see. When I've finished one, with all its post soldering machining, slotting, threading etc, I'll post a photo. If the joint stands that lot, I think I can assume that its OK for service as a valve spindle.

[ettingtonliam]

Heres a photo of the spindle and collar before soldering, and the nearly finished product, just needing a bit more cleaning up, and the central slot finishing to size with a rectangular drift ground from 1/4" x 1/4" HSS.




Its all held together so far.

[Oily Rag]

Jun 29, 2019 7:20:19 GMT cupalloys said:

For all silver soldering operations to be successful, the surfaces have to be oxide free. Chromium forms an oxide layer naturally. It CANNOT be removed mechanically. On a good day, grit can really screw things up by further contaminating the surfaces.
Oxide removal is not your job. It is what the flux does and it does it more efficiently than you can.

Use HT5.

It's been like that ever since I entered this business in 1967. Thinking about it,it was probably the same before that!

If a joint can be simply pulled apart, the joint was not sound to begin with. Alloy only running around the edges? Sounds like a flux or heating problem. Either way, the problem lies behind the torch- not in front of it!

Keith

For more information read the book available from CuP Alloys or why not just ring them?

You will also find that they have whatever material you might need ex stock. See the website and you don't have to walk any further than your phone!

Well some of that goes contrary to Harris and 50 years of technical advice from other industry players with the use of stainless on the "workshop floor". Investment castings are sand blasted and centre less ground tubing has contamination so there is a bit more to it than that. Good luck with relying on any flux to lift 316 and 304 oxides on a previously sand blasted casting or from Columbus XCr stainless tubing of 0.45mm wall, good luck. I will leave it at that.

[Oily Rag]

Stainless steel investment castings and stainless XCr tubing or Niobium doped or Nivocrom double butted wall tubing.

[jasonb]

I think that in a case of castings and to a lesser extent tube that may have been stored for several months or more will require some form of cleaning, the castings will still have a heavy oxide layer from being cast and not easy to clean in other ways. Where as freshly machined parts will only have formed a minute oxide layer before they come to be soldered so the active ingredient in the flux is enough to remove that and anything that tries to form as the work is heated.

Really horses for courses, I certainly would not want to blast or take heavy abrasive to a stainless spindle or valve shaft preferring a light rub Scotchbrite so the surface remains smooth, on your lugs and tube that will subsequently get painted or polished that's a different matter.

J

Nice lugwork by the way, my uncle was also a frame builder - T J Quick. I still have one of his frames though smooth fillet brazed.