How to unbraze silver buttons from copper switchgear contacts

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Something is very strange here, Harold. Practically every source says that coin silver is the predominant material for silver electrical contacts. There is even an ASTM specification for it -- ASTM B617 - 98(2010) Standard Specification for Coin Silver Electrical Contact Alloy.
Reply to
Ed Huntress
Any tips for separating the silver from the sludge in photographic silver reclamation systems that use steel wool? The silver dust ends up mixed with iron and iron oxides and who knows what from the used fixer.
Reply to
Cydrome Leader
heh.
I though it would be fun to try to forge a brass bar once. The thing collapsed like a piece of solder then grew large cubic crystals where it fell apart. That was amusing.
Reply to
Cydrome Leader
I have gotten a couple of brass surprises myself, trying to silver-braze it with some old braze metal of unknown composition. It worked a couple of times, and then I watched it turn into a bag of oxide-covered molten brass a couple of other times.
I imaging it's disconcerting to discover that property when you're trying to forge it.
Reply to
Ed Huntress
The O/A method will work fine. Have someone poke the silver with a screwdriver and it will fall off when you hit the proper temp. I used to do it with all my contactor tips but with the price of gas it just wasn't worth it anymore.
Reply to
jeff
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I have a 1948 Metals Handbook. Two pages of Coin Silver alloys, with specific info on contact material, physical characteristics, and how the metal is worked for contact applications. Two more pages of Silver alloys for electrical contacts. Silver-Tungsten, Silver-Molybdenum, Silver-Nickel, Silver-Graphite, Silver-Cadmium, Silver-CdO, Silver-Lead. The latter seem to be powder metallurgy, sintering and heat treatments. With paragraphs on specific applications. Eg. Silver-CdO used in WW2 warplane gunnery switchgear. Charts of how electrical properties vary with alloy content, etc. Some info on how some contact pairs used different materials on each side to reduce arcing. Eg Silver-Nickel in one contact and Silver-Graphite in the other. Seems like 1948 era materials engineering was more sophisticated than the casual reader would have guessed.
Reply to
bw
Huh. That's interesting. My 1979 edition doesn't have near that much about it. It just lists coin silver as the primary alloy for electrical contacts.
Yes indeed.
Reply to
Ed Huntress
Silver and iron won't alloy, so you can melt the sludge with soda ash and borax. Pour to a cone mold to separate the resulting silver from the slag. If there's sulfates present, a couple pieces of scrap iron (lengths of rebar work fine) inserted will ensure that the sulfur liberates any silver that's combined. In such a case, you'll get three layers in the cone mold, the top one being slag, the second a sulfide layer, hopefully sulfur and iron, and the bottom silver. The silver should be of good quality, but can be parted in a silver cell to ensure purity.
Harold
Reply to
Harold & Susan Vordos
Even heavy duty contacts? That's predominantly what I refined. From switching gear, for instance, not small appliances. Traces of copper report in the solution, but nowhere near enough to account for the color you'd expect from coin silver. In fact, the small amount could easily be determined to be from the solder used to mount the contact.
I have almost no experience with small contacts, so that makes me wonder if, perhaps, that's the type that may be made of coin silver (90% silver, 10% copper).
Some silver contacts are alloyed with cadmium. I did encounter a small lot of those. Amazing how little silver they contained.
Harold
Reply to
Harold & Susan Vordos
I suspected that was it, because you certainly know your precious metals. Coin silver apparently is used for the ordinary types of contacts, both for consumer and industrial applications, but a variety of other alloys are used for very high-current or high-voltage applications.
Some low-voltage applications that require the lowest resistance use fine silver, too.
Reply to
Ed Huntress
Awesome tip. I've looked on photo forums and found nothing of value. The dissolve the silver in acid and precipite it methods don't seem applicable as iron will dissolve in those acids, and buying huge tanks of nitric acid doesn't seem worth the effort considering the extra hazards.
I've been sending the used fixer to a lab with an electrolytic cell, so they keep the silver, but it's more of a hassle for them once you factor in transporting the stuff and returning the containers.
How much soda ash and borax should be used?
I did notice a hydrogen sulfide smell when steel wool is thrown into the fixer tank. I'm not really clear on when it's ok to stop adding steel wool as nobody has any idea how much silver is in the spent fix to start with. One guide mentioned upto an ouce of silver per gallon. I suspect I need to get some silver test strips to make sure the leftover liquids are safe enough to dump. One doc says there can be upto an ounce of silver per gallon of used fix, but until the silver is removed, I have no way to see how accurate this is.
Reply to
Cydrome Leader
I know this is a very old thread, but all I did to remove my silver was take a sharp chisel, a hammer, and a vise and the contacts just popped right off. I had a wide variety of contacts, so some removed easier than others, but all of them came off without too much trouble. Just make sure you use a chisel that you don't care about.
Reply to
hep2it
Be careful, some of the older contacts had cadmium as part of the alloy. Most of the refiners I talked to would not deal with them.I have several pounds of contacts still attached to a small portion of brass. I would like to find some one to buy them.
Reply to
Brown

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