SOFT SOLDERING OF STAINLESS STEEL

[CHAS LIPSCOMBEParticipant @chaslipscombe64795]

Does anyone on the forum have practical experience of soft-soldering stainless steel parts together? I make stainless steel reproduction parts for vintage motorcycles from stainless steel. Current project is petrol filler caps. the design I want to reproduce would use a stainless peg projecting downwards from the stainless cap, into the air space below the cap. I need to join the peg to the cap so it cant drop into the tank. The stainless (304) is just too hard to rivet the peg to the top of the cap (the originals were brass so the manufacturers could use tin/lead solder, no problems).

I could use a product like Loctite 680 but I’m not confident that this would work because it is being exposed to petrol/ petrol vapour on a long term basis.

I read that tin/lead solder can be used to join stainless steel for low-strength joints like this and I wonder if anyone has practical experience of this and what flux they used. The obvious answer would be to use silver solder but as well as difficulties with heat source etc I can’t see how this would lend itself to a pre-tinning sequence.

Chas

[HopperParticipant @hopper]

Never tried it. But the guys at CupAlloys would probably know. https://cupalloys.co.uk/

They are forum members and usually very helpful with any kind of soldering/brazing info.

[Michael GilliganParticipant @michaelgilligan61133]

It is, of course, a matter of Trust and for you to decide … but I would have more confidence in Loctite 680 than in any soft solder.

 

Here [from the first source that I happened to locate this morning] is the technical data-sheet:

https://www.aimsindustrial.com.au/assets/tds/A0049918.pdf

What’s not to like ??

MichaelG.

[Speedy Builder5Participant @speedybuilder5]

Use Phosphoric acid – this acid is used in some rust remover products, it used to be in Jenolite, but I haven’t seen it around lately.

Bob

[Michael GilliganParticipant @michaelgilligan61133]

[ footnote to my post ]

Information about the standard form of test seems to be getting more difficult to find without substantial cost … so this is worth referencing:

https://staging-6ade-infinitalab.wpcomstaging.com/material-testing-service/adhesives-shear-strength-using-pin-and-collar-specimen-astm-d4562/#

Note: … the US and European tests have always been very similar, except for using different units-of-measure … harmonisation seems to be creeping-in now.

MichaelG.

[JasonBModerator @jasonb]

You don’t tin the surfaces with silver solder so no need to worry if it does not lend itself to the job. I you do now decide to silver solder then HT5 flux as that contains something to remove the chrome oxide that forms on stainless.

The Harris Stay-clean that CuP do is for stainless, if you can find it locally it will be cheaper as the hazardous postage puts the cost up.

[Robert Atkinson 2Participant @robertatkinson2]

If the original had a peened part on the outside of the cap could you replicate this with a threaded fastener?
I’m thinking a SS screw with it’s head reduced to a flatish dome, femalr thread in peg and permanent loctite (other threadlocking products are available e.g. permabond). The thread lock is no linger in simple tension shear.

Robert.

[CHAS LIPSCOMBEParticipant @chaslipscombe64795]

Michael Gilligan: Thanks once again for your help in answering my queries. As you say it is a matter of trust in Loctite but the SD Sheet seems quite clear that Loctite 680 would be satisfactory. Interesting that this material goes on improving in petrol resistance for such a long time.

Robert Atkinson: This is much the same as what I had in mind. Use a 4mm cap screw done up tightly in conjunction with Loctite 680 then cut the socket head off. The original was simply riveted in place (brass peg) but a trial hammering over of a stainless capscrew shows the capscrew is just too tough for this to work. As Michael says, its all a matter of trust and I can see that a mechanical fixing e.g. riveting, would not allow the peg to fall into the tank. I can’t see such a fail-safe situation with an adhesive and I have seen some quite spectacular failures of adhesives when I was still working.

When making reproduction parts, the original appearance is almost everything so I will indeed shape the threaded end of the capscrew to look like a rivet. Thanks for your input.

I am still interested in the practicability of soft soldering stainless steel as it might come up again in future. I do have a copy of Keith Hales ( of CUP) excellent book but he does not cover the use of soft solder for stainless.

Chas

[JasonBModerator @jasonb]

See Keith’s reply in this thread, the flux cored solder is cheaper to post

[noel shelleyParticipant @noelshelley55608]

For the threaded method a socket button head looks neat. Stainless chip shop friers are soft soldered, if using silver solder then try to avoid overheating as the chrome oxide is difficult to remove, use a high temp flux, as Jason says HT 5. Noel.

[Howard LewisParticipant @howardlewis46836]

Ordinary household bleach will remove oxide film from stainless steel saucepans, teapots etc, so may be efeective in cleaning up after soft, or silver, soldering.

The effectiveness may vary accoriding to the grade of stailnless steel, but has to be worth a trial.

Howard

[Speedy Builder5Participant @speedybuilder5]

CHAS, Its so simple – Phosphoric Acid.

[JAParticipant @ja]

I did quite a bit of stainless steel soft soldering using phosphoric acid at university making very small pitot tubes. Easy, no problems other than the size.

Phosphoric Acid for soldering is readily available. Taking a quick look on the internet there are quite a few companies selling it.

JA

[Clive SteerParticipant @clivesteer55943]

As already mentioned Phosphoric acid, sold as something like Stay-clean by Harris, I have found works well. However for a more secure joint you may consider silver solder with a borax flux which also works on stainless. Unfortunately it requires higher temps but in the range of a normal Butane blowtorch.

The metal loaded Loctite adhesives are very strong for shear and tension loads but not as good for peel loading. I’m not sure how they will be affected by the alcohol that is added to Mogas these days.

CS

[Martin KyteParticipant @martinkyte99762]

Google flux for stainless steel. We have a tub of flux at work which I have used successfully to solder M1 screws to the top of earthing studs for patch clamps. (Fly brain neuron sensors) don’t ask!

regards Martin

[shaun meakin 1Participant @shaunmeakin1]

Jason is right here, please see his link to Keith’s thread. the key to soldering or brazing stainless steel is using the right flux.

Shaun@cupalloys.co.uk

[Trevor Drabble 1Participant @trevordrabble1]

For soft soldering of stainless steel I would suggest you contact Solders and Fluxes on 01291 624400 or sales@soldersandfluxes.co.uk . I have no connection with the company other than a satisfied customer after purchasing some of their products from the Midlands Exhibition.

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