Pink Flux-coated Silver Solder Rods

A friend of mine overseas who is 'in' to motorcycle restoration required to silver solder a 1/4" copper pipe into a steel housing. Silver soldering or brazing was a new thing for his restoration repertoire and he purchased some pink flux coated rods which, on the face of it, were quite expensive.

He didn't use any flux on the components themselves and perhaps unsurprisingly, the result looks awful!

Does anyone have any experience of these rods and if so, what flux can be used to protect the components from oxidation as they come up to temperature and before the rod, with its flux, is applied?

I would be intrested to learn for my own benefit and, of course, to pass on the knowledge.

I was given some a couple of years back the pink coating was the flux and I used them without any problems on brass and copper just wish I had more due to their easy use

H

I suppose it's practice makes perfect but expensive way to learn.

If he is not doing much chip a bit of flux off the rods, grind it into a powder, mix with a little water and apply.

I have used flux coated rods for silver soldering, but have always fluxed the joint surfaces first, the rods worked well although a bit more expensive.

Thor

Thank you for your responses as I had not seen them before. I note on some manufacturers products of this type that they claim that no pre-fluxing of the joint is required. Without flux, either from the rod or a 'standard' product, I can't see how oxidation is avoided unless the flux on the rod is very aggressive.

Anyhow, I'm going to encourage my friend to use a more conventional approach with products that I can relate to as the joints in the photos that I have seen are not acceptable.

Thanks again to the respondees.

It may help if you realise that the oxidation occurs outside the flame, while within it, the brass or copper is protected by the unburnt fuel. This can be seen clearly as black outside the flame but pink within, once the temperature gets high. So, if you heat with a big soft flame, and ensure that when the job is up to heat, the fluxed rod is applied within the protected area, all should (possibly) be OK.

The traditional flux for such work is borax, used in a solid form by jewellers, and ground down to a paste on a piece of slate with water.

Cheers, Tim

Thanks Tim, I agree.

Part of the problem in the case of my friend is that he has no prior experience and as the lump of steel into which the copper pipe is to be fitted is disproportionally large, he 'had at it' with a somewhat fierce Oxy/Acet flame. The fluxed rod ended up charred!

I used to braze with "Sif Bronze" pink coated rods, would these be the same thing ?

Is he perhaps not getting the work up to temperature, but melting the rod onto the work, He has to let the rod melt with the heat of the job.

Ian S C

Hi, I have to agree with others that they should be OK without additional flux. I used to use them quite often several years ago in a previous employment. However, if it is a large job, he may get on better with a normal rod and flux the job in the normal way. Whatever you use, it is still important to make sure the joint is clean in the first place.

Regards Nick.

Edited By Nicholas Farr on 17/12/2016 10:47:01

Page 7 of the Johnson Matthey product guide has a short but clear step by step to get people off to a good start.

I would welcome articles on silver soldering for MEW. Topics could be:

• Basic introduction for beginners
• More detailed technical explanation of how the process works
• Guide to different filler metals and their uses
• Equipment e.g. different types of gas torch, building a hearth
• Repairing small items
• Fabricating parts
• Step brazing
• Building a copper boiler (generic guide using a real world example) - probably a series.

Borax or any powdered flux mix with water to paste apply to area to be soldered only with brush or cocktail stick this should give good results

You say it was a large piece of steel he was joining the pipe to. These fluxed rods are often ained at the refridgeration & Air-con market where small dia copper pipe is being joined. This will get upto temp quite quickly unlike a big old lump of steel which will likely have oxidised before it is hot enough to melt the rod/lux.

Eutectic is the brand that is pink. The other clue is that They are expensive, sit down when pricing. Have a pound or 2 of stubs to use up.

I have no idea of the brand at this time as the friend (and this problem) is in Australia. I am awaiting better information from him but I agree with Jason that a lack of flux while the steel is heated is likely to have caused problems. I also happen to think that he did not get the steel component hot enough anyway.

I have used UNITOR AG60 pre-fluxed rods over many years at sea. I seem to remember UNITOR recommending that Easyflo flux was applied to the joint before starting to heat it. This is what I have always done and I've never had any problems.

Reg