brazing flux residue

[Paul BarterParticipant @paulbarter66156]

Please can anyone advise me as to how best to remove the glass hard residue left after brazing?After brazing a handle back on a stainless steel sieve it seems to resist all attempts to remove it with steel wool,emery and solvol auto sol. The stainless steel of the sieve is soft and am at a loss as to how this stuff can be removed without further eroding the object of the exercise.Thanks for any suggestions.

Paul

[Paul BarterParticipant @paulbarter66156]

removal afterwards!

[John ReeseParticipant @johnreese12848]

I think most brazing fluxes are borax. Have you tried a long soak in hot water?

[Peter KroghParticipant @peterkrogh76576]

A good soak in boiling water will dissolve it. Takes 5-15 minutes depending on how much. Maybe a bit more.

Pete

[Paul BarterParticipant @paulbarter66156]

Thanks very much John and Pete for your advice.That seems a lot less hard work.

cheers Paul

[HevansccParticipant @hevanscc]

A tablespoon of citric acid in a kettle of boiling water will take off most fluxes. Silver braze flux comes off easier than brass braze flux so may need just hot water. Some borax fluxes are really glassy and hard to get off so the citric acid in boiling water is the way to go, then wire brush the residue off.

Hywel

[Paul BarterParticipant @paulbarter66156]

Thanks Hywel, I will be back to the chemistry set tomorrow! I use citric acid for derusting and HCl for the more serious cases.Maybe Hydrochloric acid will be the answer as it reacts with borax to form boric acid,salt NaCl and water, a mixture that should be more soluble in water than fused borax.Thanks for your advice . I am obliged.

/Paul

[julian atkinsParticipant @julianatkins58923]

Johnson Matthey recommend a hot solution of sodium hydroxide (wilko's sell it as drain cleaner in powder form very cheaply). it is also what keith hale advises in recent articles in EIM. i use boiling water added to it then leave the parts in for 10-15 mins

cheers,

julian

[HevansccParticipant @hevanscc]

As a chemistry lecturer I have used everything, including the most noxious substances. I wouldn't recommend using hot concentrated sodium hydroxide for safety reasons. Acids are safer but you have to watch out that you don't dissolve the metal if too concentrated. The most important factor in all this is the type of flux you use. SIF fluxes tend to form an extremely hard glassy residue which is almost impossible to remove, as do many of the borax fluxes. I use fluxes designed for brazing steel bicycle frames from a US company called Cycle Design USA http://cycledesignusa.com/wp/ which come off much easier. You can by them in the UK from CEEWAY and they are. not expensive http://www.framebuilding.com/Framesaver.htm

Hywel

[Tim StevensParticipant @timstevens64731]

A trick used for removing vitreous enamel (which is glassy like flux but not intended to be removed at all) is to heat the part and sprinkle with nitre / saltpetre / potassium nitrate (different names for the same stuff).

This will convert the glass into nitrates at least in part, and the silicates into potassium compounds, and the result is soluble in hot water.

I have used this process to repair enamel badges – which needs all the original to be removed first.

Regards, Tim

[IanTParticipant @iant]

Another vote here for citric acid and hot water. Simple, safe and affordable.

Regards,

IanT

[Neil WyattModerator @neilwyatt]

I use commercial food-grade limescale remover. It makes the flux brittle and easy to remove (I normally use easy-flo flux, but it works with straight borax too).

Neil

[julian atkinsParticipant @julianatkins58923]

can i perhaps suggest it rather what depends the type of silver soldering job being undertaken!

miniature loco copper silversoldered joints where prolonged heat is required necessitate the use of a more active flux and longer lasting than easyflo flux. the flux deposits that result are glass hard, and the only effect dunking in pickle has is the shock effect if the job is still hot. otherwise it remains glass hard with Tenacity 4a and Thessco F. J&M silverflo 55 used.

silver soldering steel components (which i do a lot) of is similar.

however smallish brass and bronze components with easyflo 2 and easyflo flux is a piece of cake removing the flux afterwards!

try silver soldering with J&M silverflo 24 with Thessco F and trying to remove the flux deposit afterwards using some of the methods advocated here!

cheers,

julian

[Paul BarterParticipant @paulbarter66156]

Thank you, to all of you who have taken the trouble to share your knowledge, I am obliged to you all.

Paul

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