Copper/Silver solder chemical question

I'm assembling some machined copper parts for my rocket project. I'm using silver solder. If I heat the parts hot enough to make the solder flow then
the parts get a scaly dark almost black coating.
On the exterior of the parts I can wire brish this away, but in the interior passages I have some very fine (0.010") passages I don't want to get clogged.
Does anyone know of a chemical method for cleaning this?
Does anyone know how to prevent it from forming?
I'm using a MAPP torch in normal air, I've Contemplated getting a sand blasting box and converting it to an argon purge box, then using and oxy acelelne torch to heat as the box has no Oxygen if it is a purge box. I could also maybe put it in a purge box and heat with a TIG torch.. Would the purge box help?
Am I better off just finding a furnace brazing shop?
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| I'm assembling some machined copper parts | for my rocket project. I'm using silver solder. | If I heat the parts hot enough to make the solder flow then | the parts get a scaly dark almost black coating. | | On the exterior of the parts I can wire brish this away, but in the | interior passages I have some very fine (0.010") passages I don't want | to get clogged. | | Does anyone know of a chemical method for cleaning this? | | Does anyone know how to prevent it from forming? | | I'm using a MAPP torch in normal air, I've | Contemplated getting a sand blasting box and converting it to an argon | purge box, then using and oxy acelelne torch to heat as the box has no | Oxygen if it is a purge box. I could also maybe put it in a purge box | and heat with a TIG torch.. | Would the purge box help? | | Am I better off just finding a furnace brazing shop? |
Dipping the heated copper in muriatic acid would remove the black oxidation out. It would turn the copper into a bright clean shinny metal. Afterwards you can do a second stage cleaning with an ultrasonic cleaner.
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thanks for the lighting quick response.
Sorry to be Dense, but It's unclear if you mean heat it and drop it in the acid, or after its been heated making the black scale drop it in the acid once its cooled.
If I should heat it to drop in the acid, how hot?
Paul
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| >Dipping the heated copper in muriatic acid would remove the black oxidation | >out. It would turn the copper into a bright clean shinny metal. | >Afterwards you can do a second stage cleaning with an ultrasonic cleaner. | | thanks for the lighting quick response. | | Sorry to be Dense, but It's unclear if you mean heat it and drop it in | the acid, or after its been heated making the black scale drop it in | the acid once its cooled. | | If I should heat it to drop in the acid, how hot? | | Paul
Immediately after you are done with your soldering/brazing. Around 500-600 degrees F would be fine. Immerse the heated part in the acid solution and rinse it in clean water afterwards.
You can keep on repeating the process if not satisfied with the results the first time.
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|| >Dipping the heated copper in muriatic acid would remove the black | oxidation || >out. It would turn the copper into a bright clean shinny metal. || >Afterwards you can do a second stage cleaning with an ultrasonic cleaner. || || thanks for the lighting quick response. || || Sorry to be Dense, but It's unclear if you mean heat it and drop it in || the acid, or after its been heated making the black scale drop it in || the acid once its cooled. || || If I should heat it to drop in the acid, how hot? || || Paul | | Immediately after you are done with your soldering/brazing. | Around 500-600 degrees F would be fine. | Immerse the heated part in the acid solution and rinse it in clean water | afterwards. | | You can keep on repeating the process if not satisfied with the results the | first time. |
There are other solutions that would work too. Search Google.com for "pickling solutions for copper".
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Sulfuric acid will dissolve copper oxide (the black stuff you mentioned) but won't touch pure copper. I don't recommend using HCL------it will dissolve copper.
Be real cautious about introducing a heated object to acid unless you're using lots of protection. The fumes could easily overwhelm you. If the part you're making isn't too large, you can use an old crock pot filled with sulfuric and water to clean the assembly after soldering. It need not be boiling, but hot solutions work faster than cold solutions.
When you mix sulfuric acid and water, there's considerable heat evolved. Be certain to introduce the acid to water, slowly, and stir. Do not add water to the acid.
The best scenario is to have it furnace soldered with a controlled atmosphere to eliminate any oxidization. I have a hunch that's not going to be cheap.
Harold
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says...

A relatively benign alternative to strong acids is Sparex or similar products. The description on this page is apparently not for Sparex's usual use as a scale-removing pickle. The Scalex stuff also sounds interesting for preventing the scale in the first place.
http://www.dickblick.com/zz306/03 /
Any jeweller's supply will have Sparex or an equivalent.
Ned Simmons
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A simple,safe, and cheap way, is to use pickling vinegar. It works best, if you heat the vinegar in a pyrex (or similar) container. I also use a cold solution, 1/2 pickling vinegar, 1/2 water to clean inkjet printer nozzles. It works like a charm, just let the printhead, or cartridge/printhead sit in a saucer of the solution over night. Rinse under the hot water tap, dry, and you are good to go!
Steve R.
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Avoid the mess altogether by running dry nitrogen through the copper parts while brazing.
LLoyd
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On May 19, 5:59 pm, snipped-for-privacy@Rasdoc.com wrote:

I had a nearly identical problem when MAPP silver soldering machined copper tubes together. However, they were cable swage fittings, so I was only concerned about the outside finish. I just bead-blasted the outsides and ignored the insides. The pickling technique seems logical and probably a good idea.
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I don't like using MAPP for soldering because the inner (oxidizing ) cone is too large and is impossible to see. If you are holding the torch any closer that about two inches from the part the you may be causing the oxidation that way. Try holding the torch further back from the part. I much prefer an acetyline/air torch for it's smaller, well defined, inner cone.
starbolin
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snipped-for-privacy@rasdoc.com wrote:

It looks like you have gotten some good advice for cleaning already.

There are several types of spray-on flux that will seal your work against oxygen and keep it from scaling up. Some you can make for yourself. Google up 'Prips flux'. It can be removed with boiling water. Rio Grande makes a nice blue spray on flux I like. Works great for soldering silver for me.

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I was just reading the OSHA sheet http://www.osha.gov/dts/chemicalsampling/data/CH_251200.html and it says that MAPP is incompatible with copper and copper alloys do to its oxidizing nature.
starbolin
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