Silver solder.

[Michael CallaghanParticipant @michaelcallaghan68621]

Hi, I need to make some repairs to a copper boiler. Given the price of solder from U.K.  suppliers I had a look at other sites. However they are giving prices for 5 percent to 30 percent. I take it the lower value is low temp solder.

what do I need. Thanks

[JasonBModerator @jasonb]

No, a 30% solder will have a higher melting point than 55%

The 5% probably has about 1/3rd  zinc in it so not what you want for a boiler, again higher melting point than 55%

[Dave HalfordParticipant @davehalford22513]

Some strip silver solders are for jewellers, also the very fine wires.

The price of silver is the driver and that’s an international price on the metals market. If you see cheap 55% it is not real unless from a show in the UK.

[BazParticipant @baz89810]

For boiler work and any other model engineering related silver soldering you need something like Silverflo 55, the modern cadmium free equivalent to Easyflo No2. If you are going to the Midlands exhibition next week there will be a stand there where you will be able to buy what you require and get free expert advice, I would name them but don’t know if we are allowed to on this site, the chap you need to speak to will giving a talk on silver soldering.

[JasonBModerator @jasonb]

You don’t need 55 for all ME work, the lower silver content ones are fine for fabricated parts particularly if steel as there is no risk of it distorting due to the higher temps. Just needs a bit more heat.

But don’t take shortcuts with cheaper low silver content for boilers.

That 5% stuff is OK for refridgeration and HVAC work but not a model boiler.

[jon hill 3Participant @jonhill3]

I know I might get hated for this however its probably a good thing that cadmium baring solder is now discontinued.  My dad used a lot of it in boiler making and it could have been a contributory factor in his terminal cancer.

Out of interest could scrap 0.925 silver be used for copper soldering? For example cutting strips from scrap bought from a pawn broker / jeweller…

[bernard towersParticipant @bernardtowers37738]

Only about half of silver solder is silver it is a mix of other metals. Suggest you look at CUP alloys site, full of good info.

[Dave SParticipant @daves59043]

You can solder copper with .925, but you might be better off to weigh it in and buy actual solder.
I solder dial feet on with .999 wire – it doesn’t remelt at enamelling temps so the feet stay attached.

[jon hill 3]

On jon hill 3 Said:

 

Out of interest could scrap 0.925 silver be used for copper soldering? For example cutting strips from scrap bought from a pawn broker / jeweller…

If you’re happy to have to heat everything to around 900 degrees Celsius and maybe then use a hot caustic soda solution to clean off the high temperature flux you may have needed, you can use sterling silver as solder.

If you’re soldering copper to copper and it’s not a boiler, you’d be better off with a phosphorus-bearing alloy like Silbralloy. It’s cheap to buy and doesn’t need a flux for copper joining.

No jeweller worth their salt will use 55% silver solders for soldering Sterling, Britannia or Fine silvers, as 55% silver content does not make for a hallmarking grade of solder.

 

[Speedy Builder5Participant @speedybuilder5]

Adding to Bill Finn’s comment. Don’t use Silbralloy for steel. The bond strength is not there and joints may fail.

bob h

[Dave SParticipant @daves59043]

Plain old borax works fine as flux on copper with silver. Cleans off in hot water.

[JasonBModerator @jasonb]

That may be due to your small parts heating up to temp quite quickly. HT flux as well as taking the higher temperatures also has a much longer working life so does not get exhausted before you can get enough heat into a large part.

[Dave SParticipant @daves59043]

Quite possibly. Watch dials are somewhat lighter than even the smallest boiler

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