Silver Soldering Steel.

[arch1947]

Hi Everyone, I have been silver soldering items for a long time, have built a boiler, made boiler fittings etc. but recently have had troble with silver soldering mild stell (black not bright) and I can't get the solder to flow very well. The solder I am using is cadmium free and I suspect that is the problem. I would appreciate any advice and ideas.
Cheers,
Arch

[digger]

Make sure the parts you are trying to silver solder are truly clean, use a high temperature Flux, Tenacity Number 6 is pretty good,
the parts to be joined need to be brought up to heat fairly quickley, the flux already applied should take on a glassy apperance, when sufficient heat is applied, the silver solder, should melt by the heat of the parts being joined, (and not in the flame) once the solder has flown into the joint, remove the heat, and let the parts cool naturally, pickle in a solution of citric acid and wire brush the flux off if necessary.

Digger

[Jim]

Just to add to Digger's comment I make sure the black mill scale is cleaned off on the linisher or with a flap disc to give a bright steel working surface.

Jim

[weary]

I do a fair amount of fabrication using '55' silver solder of black steel parts. In my experience preparation is as crucial as it is for copper - if not more so!

I always clean using hydrochloric acid (path cleaner)to remove scale, etc., degrease the areas to be joined using commercial engine cleaner ('gunk'), rinse in detergent/water and then 10 minutes in a sulphuric acid (battery acid) bath. I have found that the gap tolerance is quite important with '55' silver solder = about a 'thou'.

Long duration flux, and heat as quickly as possible. When possible I lay the silver solder rod along the joint to be 'brazed' before heating up, adding more if necessary. I try and construct the part support to ensure that heat is reflected back on the part to be joined as much as possible and heat input is retained.

Whilst (black) steel seems to need more heat input than copper I have found that 55 silver solder flows well under these conditions.

Regards, and best of luck,

Phil

[cupalloys]

Hi Arch,

Your difficulties have nothing to do with your solder being cadmium free.

If the alloy doesn't flow you have a flux problem. For whatever reason it is not working.

Perhaps the alloy has too high a melting point and it is taking too long to heat the joint sufficiently to melt the alloy. (Steel does require more heat)
Use a lower temp alloy eg 455, or use a longer life flux eg HT5 or fit a bigger burner to generate more heat.

If using oxy-propane make sure you heat the joint evenly and get the whole of the joint upto temperature. Remember you are brazing.

Do not adopt a welding technique of heating the joint locally and applying rod locally.
It is easier to exhaust a flux

Most amateurs find that this is easier to achieve with a propane torch.
Good advice from Phil.

Re cleaning. DO NOT USE A GRIT BASED PRODUCT. It can leave behind residues that the flux cannot remove = no joint.

For more information see "Introduction to Brazing" on www.cupalloys.co.uk

Keith

[peterseager]

Had the same problem. My solution has been to braze a steel assembly instead of silver soldering. From reading above, maybe it works better for me because I use a flux intended for brazing so it withstands the heat.

Peter

[arch1947]

Hi Peter, I was thinking the same thing, brazing is less costly and appearance is not a big issue where the parts need to. It has been a long time since I did any brazing so I probably should practice a bit.
Cheers,
Arch