Solder Paste

[robcas631]

Has anyone used solder paste on a project? I ask because I've just finished a project in which the tolerances are less than .003", and I'm concerned that capillary action won't spread the soldier via traditional means.

 

[Sshire]

Rob
Most silver solders and pastes, except for the "hard" varieties, will flow into a joint with .001-.002 clearance by capillary action.
Here's a good reference

http://www.pollymodelengineering.co.uk/global/technical-notes/basic-silver-soldering.asp

 

[crueby]

The pastes also have a shelf life, so dont buy more than you need for a project...

 

[goldstar31]

Can I step in, please?
I've used solder paste both in the silver based and lead based varieties. However might I advise you to say once it has been used, I have used it to 'tin' the part before using the other solder and appropriate flux to actually make the joint.

Contrary to this confusion or misunderstanding about boilers nearly blowing up. Ye Gods, protect me from so called experts who have yet to qualify. The books by the British boiler people suggest a change of melting point as the silver within the solder actually alloys with the part(s) to be joined- and therefore the future melting point of the boiler which some predict is likely to go into space at some exiting moment in the future. Somehow, I believe the Brits.

I know the editor of perhaps the best two books on model engineering. He qualified as a silver solderer- 51 or 52 years ago. Nothing like lasting the test of time, is there?

So bash on with the silver soldering and remember that cleanliness is next to Godliness- and the washroom.

Regards

Norman

 

[BaronJ]

The pastes also have a shelf life, so dont buy more than you need for a project...

I agree they do have a limited shelf life, however it will keep much longer if you keep it at around freezing point. I've used paste that has been kept this way over a year later without problems, but you do need to let it come to room temperature first.

 

[robcas631]

Norman,

I agree and will tin the surfaces before putting them together. I don't see the need to use silver solder,
it's unnecessary and too problematic IMHO. This is after all a pneumatically powered machine. Thanks!

 

[robcas631]

Thanks for all the input.

 

[goldstar31]

Rob,
Thanks for your comments. The nice thing about solder paste is actually twofold.

The first is the high silver content( well, mine had) and the cleansing by the flux in the paste.

I was having a natter with her Ladyship who is or was a senior consultant in orthodontics. So I am a wirebender's spouse! So from interesting discussions on silver amalgum and casting with 'gold' fillings from extracted teeth and centrifugal worly gigs, she said 'I simply used plain, common or garden borax and Easyflow solder to do stainless steel bridges'

All done with a mouth blow pipe and meths( wood alcohol). She drinks the better sort LOL!

And Rob, my score is even funnier. An old tosser and I were doing his Simplex boiler. I was instructing with the oxy'acetylene going. Nice rings of solder on the tubes and all that.
Then he had a mild heart attack- with me shutting off and playing silly buggers with nitro glycerine and getting him to A&E!

Some of us have other interests than sticking boiler tubes in!

Cheers

Norman

 

[robcas631]

Norman now that is funny! Also, no more C3H5N3O9 for you! ha ha

 

[Entropy455]

Here is another example where someone asks a question about soldering, and the lines between soldering and brazing are immediately blurred.

What is the material makeup of your parts (i.e. the base material of each part)? What is the maximum operating temperature the joint must endure? Would you describe the joint as heavily loaded, or lightly loaded? What is your intended heat-source for making the joint - oxy-fuel torch, fuel-air torch, electric iron, etc? The answers to these questions will impact your solder selection (60/40 lead-tin alloy, or a higher temperature lead-free tin alloy) - whereas an elevated joint operating temperature and/or higher stressed joint might warrant using a stronger sliver "brazing" alloy.

For soldering In NY, you’ll have a choice between rosin soldering flux, or acid soldering flux. A rosin flux is typically used within electronic applications, where a strong flux is not required to obtain proper wetting action – and also because acid fluxes can damage electronic components. For general joining of metals however, you’ll probably want to use a good acid-flux – like the type intended for soldering copper pipes (assuming your parts are made of brass or bronze).


Based on what I’ve read thus-far of your intended application, I would recommend using lead-free tin solder, with acid pipe-soldering flux, and a fuel-air soldering torch.

 

[crueby]

I agree they do have a limited shelf life, however it will keep much longer if you keep it at around freezing point. I've used paste that has been kept this way over a year later without problems, but you do need to let it come to room temperature first.

Nice tip - thanks!