Removing Flux

[Paul LousickParticipant @paullousick59116]

What is good for removing flux on copper, bronze or brass after silver soldering ?

Paul

[Paul LousickParticipant @paullousick59116]

[Thor 🇳🇴Participant @thor]

Hi Paul,

Diluted sulphuric acid is often used for pickling, but must be handled carefully. I now use citric acid in warm water.

Thor

[mechman48Participant @mechman48]

I have used citric acid, from the home brew counter in a well known discount store, vinegar also works well.

George.

[Former MemberParticipant @formermember19781]

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[Simon CollierParticipant @simoncollier74340]

Is this a trick question Paul? The obvious answer is sulphuric acid. A friend recently found 1 litre bottles of concentrated H2SO4 in a cleaning supply shop. Cheap too. The plastic bottles are weirdly heavy too, reflecting the concentration of relatively heavy sulphate ions. I use it at 2 molar (roughly 1:10) but that is overkill.

[Paul LousickParticipant @paullousick59116]

No trick Simon. I have done a lot of welding and brazing but have not pickled the metal to clean. (My search of previous posts did not come up with anything). Will give the citric acid a go first to see if it works.

I have used typist's correcting fluid to mask the metal where I did not want the solder to flow. This worked but is there a better method ?

Cheers, Paul.

 

Edited By Paul Lousick on 02/05/2019 12:13:13

[Simon Williams 3Participant @simonwilliams3]

Hi Paul, this comes up every so often, and the perceived wisdom seems to be brick cleaner from your local builders merchant. I've tried it and it works a treat. Buy the one that actually says it contains citric acid, other formulations exist.

Good luck Simon

[Nick Clarke 3Participant @nickclarke3]

Most acid based brick cleaners appear to be based upon 10%-18% Hydrochloric Acid (sometimes otherwise described as Hydrogen Chloride)

Citric Acid is often cheaper when bought from a shop selling homebrew ingredients.

[BWParticipant @bw]

Baking section at Tescos, Sainsburys, Woolworths, Foodland, Safeway etc etc will usually have citric acid in powder form. Quite cheap.

[SamsarandaParticipant @samsaranda]

Cheaper source of Citric Acid is the internet, food grade available at very reasonable cost, much less than supermarket prices. Citric Acid works well for me and I wouldn’t contemplate using Sulphuric or Hydrochloric, way too dangerous, Citric takes longer to achieve the same results but we are not working in industry tied to production schedules so a bit extra time doesn’t matter.

Dave W

[Former MemberParticipant @formermember19781]

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