Removing soft solder from brass before silver soldering

I have a small brass part that has been soft soldered to a piece of steel in order to machine it.

I now need to silver solder another piece to it but I believe that the remaining traces of soft solder will blow pits into the brass unless the soft solder is completely removed.

Many years ago at work we had a similar problem and used a chemical to remove any traces of soft solder. The problem is that I cannot remember what we used!

Does anyone know what will do the trick?

Brian

Hello Brian,

It might be easier altogether to make a new brass part and braze to that, this time using other holding methods for the machining.

Regards

Brian

Filing it off works for me.

Terence Holland wrote in ME about scraping off soft-solder from sweated stay holes in his loco firebox and re-soldering new stays with silver-solder a little while ago in his Barclay articles. It worked for him, too...

So just file it all off and go for it is my advice.

[This posting has been removed]

FWIW Jason and br suggestions get my vote

Howard

I think filing is now your most likely route forward Brian - but I've been using alternatives (to leaded soft solder) for a while now, namely Super Glue and Shellac. Both are useful but I tend to use Shellac more often, mainly because it's always to hand and I'm afraid my tubes of Super Glue don't seem to have a great shelf-life once opened (I'm probably using the wrong kind?).

However, I have it in mind to experiment with lead-free solder which (I think I've read somewhere) doesn't cause the same problem with Silver brazing as leaded soft solders do. I haven't tried it yet though - although I'm sure a job will come along where I'll want to do so.

If anyone here has already tried lead-free solder for this purpose (and followed it up by silver brazing without further filing or machining) it would be useful to hear.

Regards,

IanT

The pickle that br mentions is useful, as it will highlight any tiny areas of solder missed originally.

I usually heat the part and while the solder is molten I wipe with wire wool to remove as much as possible.

I would only trust mechanical removal myself.

An online search reveals " Dissolution is usually accomplished after hours of using nitric and fluoroboric acids. " - I am really sure I would want to avoid that!

Neil

I followed the advice of using mechanical methods and used some silver solder with a slightly lower melting range than normal. Everything worked OK..

I still cannot remember what was used at work but was likely something highly toxic; it would be nice to know though.

We used Woods Metal in a mould to hold jet engine turbine blades in a set position so that a weld repair could be machined back to drawing. So maybe not relevant to brass.

Brian

Hi Brian.

Check my personal profile. Relevant?

Then see personal message.

Regards Keith

IanT 01/01/21 " and I'm afraid my tubes of Super Glue don't seem to have a great shelf-life once opened (I'm probably using the wrong kind?). "

Hi Ian. I find that keeping the super glue in the fridge door behind the wifes pickle pots seem to make it last a very long time. Just allow it to warm up a bit before use then straight back in the fridge.

regards

Thank you - I'll try that.

Although I may have to find a cunning way to hide it. My wife has a thing about "non-food" being kept in her fridge - probably dating back to when my son's maggots escaped from their bait-box over-night. It looked and sounded like a scene from a Hammer Horror film when she opened the door (and the screaming started).

He wasn't quickly forgiven and (being his Father) nor was I.

Regards,

IanT

Do be sure that the soft solder is ALL removed, if the part is to be subject to significant loads - especially alternating loads. Or anything where a failure will release eg hot steam. For that reason, I concur with the 'start again' suggestion.

Cheers, Tim

Hi all

What soft solder is the subject? Lead is poison to the body and silver solder joints.

Lead free solders....?

Another story......?

Regards

Keith

Hi Everybody,

Liquid Mercury will shift lead deposits very quickly. In the old days when gun ownership was possible I used it with great effect to remove lead deposits from barrels and it was standard process with shooters. With sensible precautions it was quite safe. Not sure if if would be possible to do in today's PC world.

Len

Can you still buy liquid mercury ?

regards

Late replying IanT sorry. I am very lucky that my wife is a mechanical engineer and is into steam engines & tractors and fully understands my sometimes strange habits. Like putting a bearing in the freezer or a part in the oven.

regards

Hi Oldiron,

Yes apparently you can still buy liquid Mercury. It's illegal in the USA but in the UK it's available from a couple of laboratory supply companies. Not cheap at £25 for 100 grams. My small stock has been built up over the years from scrap thermometers, tilt switches etc. Needs careful thought before it's used but looking back, as kids in the 50's we used to roll it about in our hands in amazement, and that was in school labs! As I said, shifts lead deposits a treat.

Len