Silver copper electrical contacts

[Long Shot]

Of course Harold, duh on my part!

 

[Alegiance]

hehe What you meam Toxic fumes at Low Temp ?

if i keep my silver contact in a metalic bowl ?

is there a risk of Toxic fume by 20 or 30 celcius degree ?

:roll:

 

[bswartzwelder]

Many years ago when I worked for a major electrical equipment manufacturer, we made circuit breakers for use by the electrical power industry. These circuit breakers ranged from a couple of thousand volts up to more than a half million volts. Current ranges were from a couple hundred amps up to about 6000 amps if my memory serves me correctly. Depending on the model of breaker many of them had contacts which had a tip brazed onto the copper. One day, I picked one of the tips out of the scrap and gave it to a friend who thought it might contain massive amounts of silver.

He told me that upon heating, the silver in something of this nature would migrate towards the heat. Never did say why, but I suspect he just plain didn't know since he was not scientifically minded. He heated up the tip with an oxy-acetylene torch. Sure enough, there was a small (very small) button which showed up and he claimed was silver. Out of a tip which may have weighed a pound or two, he got maybe a fourth of an ounce. He then hit the tip with all the heat his torch could put out. Nothing happened except maybe it started to glow red due to the heat.

Since there wasn't enough silver to make extracting it profitable, we gave up. I'll bet the braze used to hold the tip onto the conductor had more silver than the massive contact tip since the braze was approximately 50% silver. Always wondered what the base metal in that contact tip was. I suspect it might have been tungsten because of the tremendous heat generated when the contacts opened. The quenching medium in the circuit breakers was either oil (which kind of exploded) when the breaker opened, thus blowing out the arc or sulfur hexafluoride gas. The gas breakers eventually became more popular because of oil shortages in the 1970's and the fact that the gas was a much better insulator (electrically) than the oil.

 

[kurtak]

One day, I picked one of the tips out of the scrap and gave it to a friend who thought it might contain massive amounts of silver.

He told me that upon heating, the silver in something of this nature would migrate towards the heat.

Out of a tip which may have weighed a pound or two, he got maybe a fourth of an ounce.

Since there wasn't enough silver to make extracting it profitable, we gave up.

Always wondered what the base metal in that contact tip was. I suspect it might have been tungsten

Sorry for the delay in responding to this but my computer was down for a couple days

Anyway yes those contacts were most likely tungsten/silver (considering the application) & should run between 30 - 40% silver - so at a pound or two should have had 4.35 - 5.8 ozt silver per pound

The problem was that trying to heat them the way he did he only got a small amount of the silver (near the surface) to migrate out

The only real way to get the silver out of them is to leach it out by boiling them in nitric acid for an extended period of time (which can be done in a SS pot/kettle)

Being that large you would most likely need to pull them out of the nitric leach a few times & chip the tungsten away (about every 4 - 6 hours) & it would likely take at least 2 or 3 days

As a note - this is done with a low simmer type boil

Kurt

 

[bswartzwelder]

Thanks, Kurt.

I am no longer in a position where I can get hold of these little gems. Sounds like putting them into a Crock Pot on low heat for a while might have worked, except I don't think Crock Pots were on the market yet.

The engineers at that place said that in oil filled circuit breakers, as the contacts started to separate, oil rushed in and the intense heat of the arc caused a small explosion which blew out the oil and the arc. Some of these circuit breakers required 3 or 4 railroad flat cars to ship them out to the customer. Most of the higher amperage unit had 2 or 3 sets of contacts per pole. Upon initiating an open sequence, the main current carrying contacts would open first and then several milliseconds later, the arcing contacts would open. By doing it this way, the silver plating on the main current carrying contacts would be mostly undamaged and the arcing contacts took the beating if being destroyed in the process. However, these large breakers seldom operated once in service, unless there was a fault on the line somewhere.