cleaning brass after soldering

fabricated cylinder and slide out of brass and soldered

what do you use to clean before painting is there a chemical to clean off flux

many thanks Geoff

Hi Geoff,

If soft solder I use warm soap water and a brush. For silver (hard) solder I use citric acid and then fine emery or steel wool.

Thor

It all depends, Geoff, on what sort of solder and what sort of flux.

If you used hard solder (such as silver solder, braze, etc - fairly high temperature (almost red-hot)) the flux is likely to include borax, and it will form hard glassy (but brown) blobs. This might be soluble in water (depending on the recipe used) so try the effect of an overnight soak - perhaps starting with very hot water. If this doesn't help, there are acids which will work. Citric acid is popular, fairly safe and easy to handle. It generally comes as a powder, so mix a couple of teaspoonsful in a tumbler of water*. This will have very little effect on the brass. Alternatively, sulphuric acid is the traditional silversmith's method. Battery acid from a proper old-fashioned garage will do - add acid to about the same amount of water, and keep it in a polythene or glass container - not metal or enamel. But do be careful, as this acid, even when diluted, will attack all sorts of household things. Cotton jeans, for example, will crumble to dust where you have spilt acid. And while citric acid can be tipped down the sink - its only like strong lemon juice - sulphuric needs looking after carefully, or diluting with lots of water before you tip it away. Mop up any spillages with a cloth soaked in washing soda (sodium Carbonate solution) which will neutralise it.

If you have used soft solder (with lead or tin or both as the major constituent, and melting at around 200 C) the flux is usually a resin (which looks rather like borax residue but can be crumbled with a fingernail) or an acid such as 'killed spirit'. Other inorganic chemicals are also used. To remove resin residues, use a solvent such as alcohol (ethyl or methyl) or acetone. Or even petrol (gasoline) as long as you do it outside and carefully. The acid products are generally water-soluble, so a good soak in hot water should serve well. Again, some washing soda in the water will help with neutralising and will do no harm to the brass.

And I do hope you used hard solder on your live steam parts, as otherwise the running temperature might cause failure. Steam under pressure can be much hotter than 100C.

* Please note these units - my attempt to avoid conversion factors which can cause pages and pages of responses for and against different systems ...

Regards, Tim

For silver soldered joint I have moved away from citric acid as it takes quite a while and won't shift some of the fluxes such as HT5. I now use brick cleaner available from your local builders merchant or large DIY shed. Takes about 1/2hr to remove flux and discolouration for example

From this gunmetal & bronze fabrication

To this in 1/2hr

Fumes can be a bit corrosive so use it outside. Also just the job for removing the black scale from hot rolled steel.

Brick cleaner usually contains hydrochloric acid. It would work pretty well.

Regards

Richard.

> sulphuric needs looking after carefully, or diluting with lots of water before you tip it away

For avoidance of doubt, always add acid to water, not the other way around, less likely to be nasty fizzing and popping and any splashes are mostly water, not acid.

Neil

Just as a comment on Tim's advice above (with regards to cleaning flux off after soft soldering) & mainly because it's still fresh in my mind!

I was reading an article about painting (and lining) in old issue of MRJ (No 76) this morning and the Author (Alan Brackenborough) - a professional model loco painter - strongly recommended not using "paste" flux at all when soft soldering brass kits. He stated it was extremely difficult to completely remove paste flux and that he'd had problems with it causing paint blisters to "bubble-up" months after painting. Although he was referring to his work on 7mm finescale locomotives, it seemed useful advice where brass parts are being soft soldered and painted afterwards. He advised the use of a liquid flux instead.

Regards,

IanT

Can we please not make a silly situation worse? There are already concerns about 'never adding water to acid' - but this advice applies to only one acid, which we have here - sulphuric acid. BUT - and it is an important BUT - the advice applies to CONCENTRATED SULPHURIC ACID. ONLY.

If we follow the advice offered by Neil, we would never be able to top up an overcharged battery - because that is adding water to acid.

My advice, as stated above, is to start with 'Battery Acid'. This is nothing like concentrated acid, and concentrated acid is NOT available from your local (or any other) garage.

And for the benefit of others, it is not because we are talking about acid that is the problem. The particular property of Conc Sulphuric is that it reacts violently with water. It gets very hot, and the mixture boils. Not because it is acid, and the problem does not occur with other concentrated acids.

And I am obliged to IanT for his advice about paste and liquid flux. I do wish I could be sure which of these is resin-based and which includes zinc chloride or other corrosive chemicals. I'm not saying he is wrong, it is just that the advice regarding resin and killed spirit followed by advice to use liquid and not paste will not make sense to everyone.

There. I feel better now.

Regards, Tim

Oneshot drain cleaner is 91% pure sulphuric acid and is available in most hardware stores!

Edited By vintagengineer on 10/07/2017 01:08:51

Can we please not make a silly situation worse? There are already concerns about 'never adding water to acid' - but this advice applies to only one acid, which we have here - sulphuric acid. BUT - and it is an important BUT - the advice applies to CONCENTRATED SULPHURIC ACID. ONLY.

Based on my experiences with concentrated hydrochloric acid with a pH of -1 I would remove the word Sulphuric from the above advice, i.e. any concentrated acid should be added to water and not vica versa.

Hi Tim,

I'm afraid I'm not an expert on the chemistry of these things. Apart from resin-cored solders used for electrical work in the past, I've used Fry's 'Fluxite' paste when required for soft soldering my modelling work. However, I generally prefer to silver solder (non-ferrous) and Sifbronze/braze (ferrous) parts whenever possible, mainly for strength quite apart from any issues of heat. So my soft soldering experience has not been really that extensive, although I do find solder 'chucks' quite useful in some circumstances.

I am currently trying to get back into electronics (which will involve some SMD work) as well as having some etched parts to assemble (which I've been putting off and putting off for some reason) - and it seems I will need to start using some form of liquid (acid?) flux in both of these areas.

Regards,

IanT

Tim , I've often wondered how you wash an acid container after emptying if you don't add water to acid

Roy

I've just been reading a safety fact sheet on Sodium Hydroxide and the advice is

"Never add water to a corrosive. Always add corrosives slowly to COLD water."

so it's safest to assume it applies to all, acids and alkalis.

John

A few comments:

If you are soldering wiring for electrical contact, you can normally rely on resin-cored (soft) solder. The resin, once cold, has no effect on the metal, so you do not need to remove it. Except, of course, for appearance. This is not so effective if you are re-using old wire as this tends to be brown (or even green) from age.

It is true that there are a few other chemicals which have a strong affinity for water. Solid caustic soda (Sodium Hydroxide) is one of these. My comment was about acids, and caustic soda is not an acid.

Anyone worried that they have some sulphuric acid but they don't know if it is concentrated? The real dangerous stuff, in this context, is thick (viscous), rather like thin honey, and noticeably heavier than water.

And as regards advice never to add water to corrosives, like much of the advice offered in these oh so careful times, it is much too broad. One of the most corrosive substances is ordinary everyday 'common' salt. And every day it rains into the sea quite harmlessly. I am not saying that corrosives can be treated carelessly, they can cause serious problems. The context I was dealing with is regarding battery acid, which, as I said, will eat away even the trousers you are wearing.

Finally, I am seriously concerned about some advice regarding DIY products such as brick cleaner and drain cleaner. Unless you know what is in them, in scientific terms, it is not safe to say what else they can be used for. If it doesn't say what's in it, leave it in the shop. This advice is based on the fact that some drain cleaners are mainly caustic soda, some contain strong bleach, and others, according to Vintageengineer, are strong acid. And if it isn't clear why this is a problem, leave well alone.

Regards, Tim

Don't use liquid flux fro soldering SMD components, or any electronic components for that matter. A fine flux cored solder will do the job but best for smd is to use solder paste under the pads, place the SMDs, and then reflow on a hotplate or in an oven. Leaded components can be added after.

Russell.

Or rather than leave it on the shop shelf look up whats in it on the makers site.

This is the one I use

I think the last time the acid/water debate came up this got posted, have to wait until abouy 9.30 in to get a reaction and I think you would get teh same reaction at the end by addin clod water to boiling water as you would cold water to boiling acid

many many yeas ago I diluted some Oleum to refill an empty car battery

that something you don't do in a rush

https://www.youtube.com/watch?v=nHiVyesJ04U

the reaction of sulfuric acid and suger is a classic  I remember from school

 https://youtu.be/xK4z_YhtTBM

  John

to correct link

Edited By john swift 1 on 10/07/2017 13:12:19

That acid to water video is misleading. That bad things happen when you add water to acid is not a myth and there should be no debate about it.

Concentrated Sulphuric has a strong affinity for water. When water and acid are mixed rather a lot of heat is evolved. If a small quantity of water is dropped into the acid, it is possible for the water to flash to steam. When this happens the mixture spits, which is not nice when it hits flesh.

Whether or not you get a spit depends mostly on the way the two liquids happen to make contact. It doesn't always do it. The safest way to dilute Sulphuric Acid is to add small quantities of acid to a large quantity of water whilst stirring. The most dangerous way to do it it is to fling a small dollop of water into a large quantity of acid. In a lab a few drops of water into a test-tube of acid might spit dangerously. Even more fun can be had in Industry where concentrated Sulphuric Acid is used by the ton. Back in the good old days before H&S went mad, there were many accidents due to haphazard mixing. Don't forget that even small chemical burns are nasty.

Quite an interesting statistic to think of when watching internet videos. Nine times out of ten it is possible to stir Nitroglycerin with a red-hot poker without causing an explosion. (We know this because Alfred Nobel did a lot research into ways of using Nitroglycerin safely, including how best to reliably set it off ). If you insist on trying it, you've got a good chance of surviving. But I sincerely hope no-one is daft enough to think it's OK to have at explosives with a red-hot poker.

Dave

Edited By SillyOldDuffer on 10/07/2017 13:13:25

MauriceIf you have soft soldered your fabrication, and there are blobs of solder where you don't want them, a glass fibre stick, as used to clean commutators, will remove the solder and not the brass. It's a slow process, but you know you are not damaging the underlying metal.