Silver solder

[Stephen FollowsParticipant @stephenfollows82099]

Which is the best silver solder to use with a propane torch?

I have seen SSF 6 on a video but it only seems to be available in the USA.

[Stephen FollowsParticipant @stephenfollows82099]

[MWParticipant @mw27036]

Most will tell you silver solder containing 50% silver but in order to help you, you can't ignore the question of the flux as well, that will matter just as much as the solder itself and remember the golden rule, heat the joint, not the rod.

Check out CuP alloys on the net, they've got the most consistent advice going and I've found generic online traders to be good enough for my soldering needs, I just use silvaflo55 (Johnson mathey make) I think it's called? as a tub of white powder, mix with washing up liquid to form a solder paste before applying to a joint. 

Michael W

Edited By Michael-w on 05/03/2018 22:32:42

[Thor 🇳🇴Participant @thor]

Hi Stephen,

I use a silver brazing alloy with around 55% silver, similar to this from CuP Alloys, and a high temperature flux similar to this. This flux will work with long heating times. If you want to do step brazing you may want to start with an alloy with a higher melting temperature.

Thor

[Martin DowingParticipant @martindowing58466]

You are struggling for low melting point.

Alloys with 20-25% of silver, rest is brass are melting rather high and you will be able to work with only small items.

Alloys with 40-60% of silver, rest is brass are those which you are looking for.

Alloys containing 40-60% of silver, cadmium and brass as balance would be from engineering point of view the best (as they melt lowest, about 500-550 *C but not so nice for your health (cadmium). Best to work outside or under fumecupboard with these.

Fluxes – any borax based flux will do for general work.

Martin

[Brian HParticipant @brianh50089]

Quote; "but not so nice for your health (cadmium)". I beleive that cadmium has been banned by the EU for many years so will not be found in Johnson-Matthey products or others unless it is VERY old stock.

I used to work for a supplier to R-R Aero and their specifications call for flux to be mixed with surgical spirit with a spot of washing up liquid added to make a paste. This has the advantage that the spirit catches fire and bakes the flux onto the job.

If you mix the flux just with water, you will find that the water boils and the flux often just slides off the parts.

Brian

[Neil WyattModerator @neilwyatt]

Really you should be choosing a silver solder to suit the job in hand, then choose a torch capable of doing the job and some.

While it would be nice to have a seivert, you can buy economy torch sets (with regulators and three burners) in several size ranges for the cost of the solder for a decent sized project.

For larger (but not huge jobs) you can also add background heat with a gas blowtorch, adding insulation helps.

On smallish steel parts I have done 'real' brazing (with brass rod and borax as a flux) when I have found myself without any silver solder. Where there's a will there's a way, but I wouldn't recommend this over using silver solder as its so much easier to get a decent joint.

As mentioned above, silverflo55 is a good general purpose choice.

Neil

[shaun meakinParticipant @shaunmeakin78815]

For brazing and soldering technical advice please give us a call.

Shaun – CuP Alloys.

01909 547248.

[Tim StevensParticipant @timstevens64731]

If your torch is a bit on the small size, there are several ways to improve the heat retension in the job. Make sure that there are no drafts is fairly obvious, and ensure that the supports for the work are as non-conductive as possible. One way to help this is to use a bed of charcoal chunks – the flame will cause them to glow too, adding heat rather than taking it away. In this case, do be aware of carbon monoxide problems, and it is safest to douse the charcoal with water as soon as the job is done. Otherwise they can glow quietly for hours, including when the door is closed and you are away having your tea …

Hope this helps – Tim

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