Electrical contact tip refining

[nsjaqson]

I know this has been asked a million times...but I have a ton of these silver alloy contact tips from large electrical motor starters. I've read up on how to refine them, but I have two questions.

1. Are the bars the silver tips are mounted to worth anything? I plan to melt the tips off, but it seems like a waste to throw away the bars.

2. Are the burned/black tips still usable?

I've attached a photo of showing a few of the ones I want to refine.

 

[etack]

They are #2 Cu and you should heat from the back to remove them. Not melt them off.

Eric

 

[FrugalRefiner]

I agree with Eric, the large ones look like copper. Sometimes you might find copper plated steel.

The burned contacts can still be processed. They were heavily used and the arcing when they made and broke contact burned away some of the contact. The dark color is oxidized silver and/or other metals used in the alloy.

As Eric said, most are soldered/brazed to the buss bars and they can be heated from the back till the solder melts. They will either slide off the buss or you can give them a whack against a collection container to knock them loose. There are those that cannot be removed in this way. There are ways to deal with them if you run into them.

The most important thing is to be aware that there may be cadmium present, either as an alloy component of the contact, or as part of the solder/braze used to attach them to the buss. Cadmium volatilizes before the solder melts. You DO NOT want to breathe it. If you start to see any whispy, cobweb like reddish or brownish "smoke" coming off them when you heat them, STOP.

Dave

 

[nsjaqson]

Once the tips are removed, I had planned to process them in nitric acid, but due to the high cost of nitric acid I may end up paying more in materials than I'll actually get out of them. Does it make sense to remove the silver tips and sell them on ebay by weight, or would I better off going through with processing them and then selling the refined silver?

 

[jimdoc]

Once the tips are removed, I had planned to process them in nitric acid, but due to the high cost of nitric acid I may end up paying more in materials than I'll actually get out of them. Does it make sense to remove the silver tips and sell them on ebay by weight, or would I better off going through with processing them and then selling the refined silver?

Or you could just save them, and look for more, until you have enough to process.

Jim

 

[nsjaqson]

Once the tips are removed, I had planned to process them in nitric acid, but due to the high cost of nitric acid I may end up paying more in materials than I'll actually get out of them. Does it make sense to remove the silver tips and sell them on ebay by weight, or would I better off going through with processing them and then selling the refined silver?

Or you could just save them, and look for more, until you have enough to process.

Jim

I came up with about 60 lbs from an old warehouse (total weight including buss) with no chance of getting more. I'm going to take off the silver tips/pads and from there determine if it's worth the time to refine. Thanks for your help.

 

[ilikesilver]

keep half of the lot and sell the other half for the expenses

 

[solar_plasma]

The most important thing is to be aware that there may be cadmium present, either as an alloy component of the contact, or as part of the solder/braze used to attach them to the buss. Cadmium volatilizes before the solder melts. You DO NOT want to breathe it. If you start to see any whispy, cobweb like reddish or brownish "smoke" coming off them when you heat them, STOP.

And the copper bearings are often alloyed with beryllium, aren't they? As far as I could read incorporated beryllium is as evil as cadmium.

 

[goldsilverpro]

The purpose of the copper buss is to conduct electricity. Therefore, it is pure copper. No beryllium. Nothing else will do but pure copper. The silver plating on the copper buss is very thin and has no real value. The silver contacts are usually of coin silver - 90Ag/10Cu. When the contact is sweated off, the braze is included. After sweating, the average silver percentage of the point is about 83%. The braze usually contains cadmium.

The only hitch is the possibility of a tungsten/silver composite point. These are usually thin and have a waffle pattern on them. In the photo, I see no obvious tungsten points. They all appear to be coin silver points.

 

[solar_plasma]

The purpose of the copper buss is to conduct electricity. Therefore, it is pure copper. No beryllium. Nothing else will do but pure copper. The silver plating on the copper buss is very thin and has no real value. The silver contacts are usually of coin silver - 90Ag/10Cu. When the contact is sweated off, the braze is included. After sweating, the average silver percentage of the point is about 83%. The braze usually contains cadmium.

The only hitch is the possibility of a tungsten/silver composite point. These are usually thin and have a waffle pattern on them. In the photo, I see no obvious tungsten points. They all appear to be coin silver points.

Okay, I just thought that, because I've read this on wikipedia:

Verwendet wird Berylliumkupfer für hochbelastete........, Kontaktfedern in Relais, elektrischen Berührungskontakten, Oberleitungen von Straßen- und Eisenbahnen, für funkenfreie Werkzeuge und anderes. Pistons für Vorderladerwaffen werden ebenfalls aus Berylliumkupfer gefertigt, da sie hohen thermischen Belastungen ausgesetzt sind.

TRANSLATION:

Used in high duty......contact springs in relais, electrical contacts, tram and train wires......made of beryllium copper, because they are exposed to high thermal stresses.

and silver/cadmium:

http://books.google.de/books?id=-t...A#v=onepage&q=silber cadmium kontakte&f=false

Table 7.2-4 (cadmium in contactors)
Table 7.2-5 (cadmium in high currency contact points)

I believe you since I'm no electrician, professional refiner or electroengineer, nevertheless I would not eat or inhale them as a powder or as their chemical compounds, because I'm drilled to suppose the highest assumable danger.

 

[goldsilverpro]

I may have spoken too soon but, after a search on the uses of various copper alloys, I don't think so. For bus bars, all the references I found used 99.90% electrolytic copper, mainly C110. Beryllium (2% max) copper (more expensive) is very hard and is used for applications where strength, stiffness, or hardness are needed, like bushings or contacts. In this case, the silver point is the contact.

 

[nsjaqson]

I tried to heat up the back of the bar with a propane torch but I'm only able to get the small contacts hot enough to let the silver tips loose. The larger ones (like in the photo) don't even get red hot.

Any cost effective ideas on how to remove these tips?

 

[etack]

More heat. Use some insulation if you have to. I've removed them from the bigger bars with just propane but with the more expensive torch.

Eric