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I just did my first ever braze - brass to copper. 44% silver, paste flux with chlorides and fluorides, MAPP gas / air torch.

Holy crap you have to get things hot before it flows! I was looking a dull red and thinking Whiskey Tango Foxtrot? and then it got to liquidus temp and Kazango!

It's easier than soldering! I am lusting after an oxy torch now. That big MAPP gas flame is all over the place.

Anybody got any tips on a pickle (acid or sumpin') to strip the oxide off copper after brazing?

Yup, brazing is easier than soft soldering, which is quite a skill.

I soak the work in plain white vinegar. Works well, but can take 2-3 days to fully strip the crud off.

(BTW, soft tin based solders do not seem to like vinegar soaks, leaves a black coating on and around the joins. Only recommend it for cleaning up hard braze joints.)

If you don't want to buy pickling solution make up a mix of flour paste with salt and vinegar and brush it on the pipe, I leave it till it starts getting that dehydrated look and take it off with a copper scrubber. As Sir Hook said, keep it off the soft tin solder where possible.

Tip for hard solder brazing, flux the joints, taping off area not to be fluxed before hand for neatness if you care (I use anti flux, same difference). If it's a round joint, wrap a single strand of the appropriate gauge braze around the connection point so it sits tight to the fitting lip. Heat the connection in a circular motion starting about a and inch and half- 2 inches away from the joint with oxy-acet gradually moving upwards around the pipe. The heat with suddenly hit and POP you will have the neatest looking hard silver braze joint on the planet. I sometimes use this method on soft solder if appearances count, you can also look into adjustable dual head torch bodies for oxy-acet or oxy propane to get two side of the pipe at once - provides much more even heat, faster neater job. They can be hard to find/expensive . Found mine in a box lot at the auction.

Never water cool it, just let it cool off on it's own.

What vinegar does in three days can be done in 5 mins by using hydrochloric acid instead......I guess I'm impatient.

What Ugly says, but I just wrote this and here it is:
Untreated copper oxides are quite tough, acid will make them easier to scrub off. Hot water will get the flux off, acid will dissolve the flux along with the copper oxides and mostly leave the oxides there in some other chemical state. I've used sulphuric, hydrochloric, nitric and glacial acetic acids and they all work. About 7-10% acid in water is safe to play with, but avoid skin contact and use rubber gloves and eyeglasses.

Sulphuric acid (aka muriatic acid) is battery acid and hydrochloric (aka spirits of salts) is concrete cleaner, easily got at about 30% strength. Glacial acetic acid (aka vinegar) is dangerous stuff when pure - the fumes will dissolve flesh and it is flammable! Nitric acid will keep going and dissolve the copper so best leave it out. Dry swimming pool acid is supposed to be a good alternative because it is safer but I haven't tried it on copper.

The dilute acid can be painted or sprayed repeatably on big items and small items can be soaked in it. Scrubbing with a wire brush or stainless pot scrubber with lots of rinsing will get to clean copper again.

When I apply a neutralizer such as bi-carb soda I get a yellow compound and it is just as hard to scrub and rince off as the acid compounds.

Muriatic acid is hydrochloric acid.

One reason I prefer plain white vinegar is for safety. Doesn't matter much to me if it takes a day or three to do the job.

Anybody tried phosphoric acid for this application?

" "Anybody tried phosphoric acid for this application?"
Recommeded on stainless

Thanks guys.

The braze is 44% silver. It would have been impossible to keep the tolerances with solder. this is spraying phosphoric acid and then ScotchBrite and stainless steel brush results. It took three applications to cut through the oxide. I can't reach the inner areas, but they appear to have cleaned up pretty good.

I'm thinking of trying reverse electrolysis just because I want to (it's also supposed to be great for etching circuit boards without nasty ferric chloride.) the current issue of Make magazine has an article about it and how to deoxidize anything made of metal, but it doesn't talk about cleanup from braze or solder.





This is part of a coldfinger for a hybrid CM/VM head. I'll post the build log someplace when its done. It will require some explaining as to why I had to build it so funny looking. the target is to eat 1500W of vapor with it. it's approximately 1" x 6". According to the data I got from testing the other coldfingers, this ought to do it with headroom to spare -- IF I get a small enough deltaT over the funny looking slotted-cap thingys. I'm putting a backup condenser above it just in case it doesn't hit the target.

the goal of this particular exercise is VM with autoshutoff for the *heads* azeotrope. I dunno if it will work, but it's worth a shot.

Be careful. Reverse plating just might remove your solder joins.

I use it to strip gold plated items (pins, and jewelry). Solder 'might' drop off in the same manner, especially if it is silver (higher noble than copper).

The process I am talking about is 4.5 to 6v DC, 98% sulphuric acid with a touch of glycerin added. SS anode (or copper mesh bag anode for doing a batch of computer pins) trying to never to submerge the anode (just the gold plated item, but with copper bag, you have no choice), and poured lead cathode.

Not sure of the method you read about, but if it is the above listed (patented deplating) method, then beware, I think you might end up with problems.

H.

Wow, this is a great thread that I wish I would have read way sooner. This weekend I was trying to braise 2" SS ferrules to 2" copper with a Mapp/Oxygen torch and had the fight of my life. I ended up having to go over to a friends shop to use an acetylene torch to finish the job. I didn't think you could make this type of join with a tig. I might have to look into getting my hands on a tig...

x7

Husker I've had a similar experience with silver solder, left a piece of jewellery in the pickle (20% hot sulphuric acid) overnight and the solder was porous and crumbly. I think the zinc was eaten out.

Hookline, sulphuric acid = oil of vitriol....now I remember not that anyone uses that name nowdays.

Where is everyone buying all this exotic acid? I can get some types of acids via dairy supply etc, but not others. I'm in Canuckistan, pointers appreciated.

Phosphoric and muriatic are at most hardware stores. Phosphoric is used for rust removal and "pickling" metal before painting. The brand I get is Jasco Metal Prep (make that Jasco Metal Etch) - in the paint department. Muriatic acid is used for cleaning brick, concrete and tile. It's also used in swimming pools for adjusting the chlorine pH. sulfuric is battery acid. It can also be found in some hardware stores as super-duper drain cleaner. Dunno where you get glacial acetic acid. I used to get it from the pharmacy for removing warts. It's called glacial because it's sort of syrupy. I've had a quart of phosphoric around for years and it's still over half full. Doesn't take much.

acetic acid= white vinegar also used in photo developing