silver reclaimers

[Anonymous]

Thanks Harold, as usual, right on. I now have purchased an acetylene/oxy torch from a local welding shop and have practiced in small batches in a small crucible. I have attempted to pour molten silver into a small graphite mold and below are the results.. I still need some practice with the pouring to keep the silver molten but lots of fun none the less. Thanks for all the input and I am learning about the amounts of borax for the flux at the end of the melting prior to pouring, lots of lessons, but still great fun for me.

Here are the photos, Adam

P.S. would be really spectacular if it was gold. On to more lessons.

 

[Lou]

Looks to me that your silver is impure or oxidised (go easy on the oxygen!) or both.

Here's what I do when melting silver (if you want shiny ingots of nice clean metal).

Assuming you start with 999 fine or better silver:

Take a silica crucible, tall form. Wet your finger lightly and smear the inside of the crucible with water, and the rim too. Dry your hands and now dust on borax. It will stick to the water.

Place your crucible upside down on a flat piece of graphite that is situated on a noncombustible surface (granite is very nice, so is asbestos board, Kaowool also works). Light your torch, and heat up the crucible to an orange colour, spinning the crucible around with tongs. The borax will melt and coat the inside in a nice glassy non-stick surface. Flip the crucible over (it will stick a little bit to the graphite, but not enough to damage anything). Let it cool down to the point where you can no longer see it glow, the graphite block helps it cool. Now put in your metal, cover with a half teaspoon of charcoal powder and a 1/4 teaspoon of borax (per 5 ounce of metal). Cover the crucible with another block of graphite, or something refractory. Then heat the crucible til orange-yellow, giving it about 2 min with the torch, remove the lid, and check to see that it is molten. The charcoal powder keeps the silver from oxidizing, as does the crucible cover. You can remove all of it with a stainless spoon that has been carbonised with a sooty acetylene flame.

Quickly cast your silver into your prewarmed, pregreased ingot mold and quick richen your oxy-acetlyene flame (lower the oxygen input). Play this reducing flame over your silver ingot. Once it has cooled to red heat, take up the mold into your tongs, flip it over and let the ingot fall into cool water.

Should be nice and shiny, and pretty darn pure!


Keep in mind that this is how I do it, and it's by no means the best way to do it.

Lou

 

[Anonymous]

Lou wrote: Looks to me that your silver is impure or oxidised (go easy on the oxygen!) or both.

Thanks for the great post.Quick question? What is the best to use to pregrease the graphite mold? Remember I am a true newbee, but quick learner. Thanks. Adam

 

[Lou]

I have used mineral oil on a cast iron ingot mold many a time and it has worked fine. Just preheat your mold to a couple hundred degrees--this removes any water.

If you don't want the stink of oil, sooting up the mold with a sooty acetylene flame will give it a nonstick surface. A graphite product called Plumbago also does the same thing. You can also heat up the mold to a good red heat with graphite, this gives a better finish to your ingot.

Lou

 

[Harold_V]

Pure silver is prone to absorbing a huge amount of oxygen (nine times its volume), which it liberates as it solidifies. You can often see evidence of the exiting oxygen by tiny spikes that form on the surface of pure silver as it solidifies after casting. Silver does not readily combine with oxygen, so oxidation isn't a concern, assuming you have pure silver.

The spikes of which I speak can be limited or eliminated by providing substances that consume oxygen. Charcoal on the surface of molten silver as it is melted serves well, although it can influence the surface finish of an ingot. Skimming the charcoal prior to pouring can serve to eliminate the problem, with a smoky torch taking the place of the charcoal after the ingot has been poured. Alloyed silver (sterling, for example) does not suffer the oxygen absorption in the same way, although it is subject to oxidation of the base metal (copper).

A smoky acetylene torch, which would be used to blacken the mold, can be played on the surface of an ingot as it cools in the mold, performing two functions. One is to control oxygen, the other being to permit the ingot to cool uniformly, bottom to top, to minimize shrinkage in the center of the ingot. That is one of the more difficult things to control when you're trying to cast ingots that have a pleasing appearance.

Typically, an ingot will have considerable shrinkage in the center, assuming it is allowed to cool without intervention.

GSP may have some tips regards pouring silver. He processed far more than I did.

Harold

 

[ebola]

Hey guys , well i am new to this forum i started reading about this after yesterday i came across some vids on youtube that blew me away. I never knew that one can recycle PM at home and mainly from plated components from computers and other electronics. I've read that you have used acety torches to melt your silver ... now my question is ... what would be the outcome if you would use a HHO torch instead ? ... it has a higher burning temperature, would this affect the silver or gold while smelting ? (sry for typos and bad english)

 

[goldsilverpro]

GSP may have some tips regards pouring silver. He processed far more than I did.

I always used graphite book molds to pour 10 oz and 100 oz silver bars. The 10 oz mold had 5 depressions. The oxygen exited through the sprue hole and, since the sprue is sawed off and remelted, there is always a good surface on the bars. Also, any traces of slag will be on the top of the sprue, so that is never a problem. I found that by smoking the mold with acetylene, which isn't commonly done, I got an even better finish. I weighed the bar and stamped the weight to 1/100 of an ounce below the actual weight. Rarely, if the temp of the silver or the mold wasn't right, there could be an air hole on the bar. These were remelted. Also, if one poured too slow or, if the mold was too cold, there could be layering of the bar - also remelted. Out of 100 bars, I might have to re-melt 3 or 4. Book molds make it very easy to do. All you have to do is pour steady through that 1/2" x 1" sprue hole.

 

[qst42know]

Hello GSP.

Were these book molds made to your specifications or can they be bought off the shelf?

Chris

 

[goldsilverpro]

Bought off the shelf but I have no idea where I bought them. If you search well, I'm sure you can still get them. The graphite 10 oz mold had 5, 10 oz depressions with a sprue hole at the end of each depresssion, going to the edge. A flat 5/8" plate of graphite covered the depressions and the 2 parts were held gently together with 2 C-clamps. This was preheated and placed with the sprue holes up. You poured steadily, and not too slow, into each sprue hole until the sprue hole was filled with silver. I used either a #6 or #8 dedicated crucible in a gas crucible furnace. Easy money! The sprues were cut off with a band saw (catch the dust!) and the bars were weighed and then stamped with sets of number and letter stamps. I would stamp about 50-100 at a time (the part I hated - took an hour or two). I laid them all on a cardboard covered 1/2" steel table and did a mass production thing. I made and sold a jillion of them, using only one silver cell (500 oz every day).

 

[Irons]

do I need to add borax to the furnace or is the iron enough?

Borax is very much a part of the process. You might find you can roast the lot with the iron submerged, then add borax towards the end, to limit the time it has to destroy your crucible, but not using any would not be in your best interest. It is, more or less, the soap that cleans the molten material, for lack of better definition. Depending on what you're melting, you might even want to include soda ash, or even fluorspar, both of which are all the more hard on the crucible, but serve a good purpose, when needed.



Harold

A very useful tip to make the crucibles and furnace lining last longer. Thanks Harold