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Melting down 925 with some investment still present?

Hey there everyone!!

Just wondering what my options were for reusing 925 metal from a previous crappy cast with investment still stuck in some of the hollow areas which I can’t remove? I have already tried the pickle and ultrasonic.

Can I melt it down in my graphite crucible(preferably an old one just for this purpose) with my melting furnace and expect the investment to float or sink in the molten metal, perhaps be able to remove it some way?

I know everyone is going to naturally suggest for me to send it off to refining, which I usually do, but that’s about 600km away and I don’t really have the time for shipping it right now.

Any thoughts would be much appreciated!!

Cheers

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I haven’t yet had a problem with remelting and casting in this situation. I do however add about 25% new metal to the melt.

sure, you can melt it, and then pour off the metal, or hammer the piece

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I routinely recycle my clean (no solder) scrap—sterling, bronze, yellow, rose & white golds—and I often don’t add any new metal. I understand that this goes against conventional wisdom (and practice) but that’s how I’ve been working for many years.

I would try to get off as much investment as possible and be sure that all pickle is rinsed off.

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I have a similar issue. I spilled a melt directly on the fire brick and a small amount of brick came up when I lifted the cooled metal off the brick. I have done three melts and graphite stirs subsequently. Do I dare forge and roll an ingot of this material? Can I ship it off as scrap to the refinery?

Don Meixner

I guess my age shows when I reply to these. I also first pickle , then melt old silver for new castings. I try to remove solder if possible. When I melt I use borax powder to help settle any contamination. I either pour (for making shot) or let it cool in the crucible for a few moments till I can pry it out in one piece. I do not add fresh metal unless there was tons of solder. Those will be sent to a refiner. I was taught that adding fresh metal was for gold. That it had to do with the proper alloying.to get to the proper karat

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Don
Just send the whole “spilled” items to your refinery. I’d let them separate it out themselves!

I’d telephone them ahead of time letting them know exactly what’s coming via “secured” mail.
Regards!
gerrysdiamondsettingessays.blogspot.com

Gerry, on my iPhone

I was consulting for a small manufacturer. I was appalled the first time I watched him cast.
He used an induction melter and was feeding entire trees w/sprue buttons and investment where the sprues came off the tree. I watched the melt, and all of the investment floated to the surface and with a graphite rod and some borax and was then he cast. His castings were surprisingly good!

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Sandblasting is a good option.

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Thanks Tony for the info.

Thanks for the info. This is exactly what I wanted to know. It sounds risky, but I guess I won’t know until I give it a try myself.

Thanks for the info. Would try it, but the investment is in a lot of 3mm curved tubing. I don’t think anything can get it out.

At this point it sounds like you don’t have much to lose. I’m guessing that you’re torch melting? The silver should melt off the investment and go to the bottom of the crucible.

It sounds like it’s not a lot of metal. It might be easier to throw it in with your refining.

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That sounds difficult and time consuming.
I would probably soak it overnight or longer and use a small bit and rotary tool, broken saw blade (spiral would be best), strong wire, dental pick or a wax spoon to loosen the investment and flush it out with high pressure water or steam. The pic attached is a selection of tools they sell for ear wax, similar are sold for jewelers wax. They also make pipe cleaners with steel bristles. If you could cut the casting in pieces it may make it easier. Of course this is easier if you have a short length to drive out.
Melting it as is will most likely bring it to the investment to the surface or bottom of the crucible but my guess is at least some of the investment will mix in the metal and make your metal porous and unsuitable. If you choose melting use lots of Borax and a graphite or quartz rod as stated in the other posts to remove as much as possible.

I have a faint memory of rolling out a recycled ingot and exposing a clump of investment.

Good luck with that.

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If you recast these tubes - There is a product made to fill hollow areas, like your 3mm tubes. It is often used to reduce the metal weight of casting and is more water soluble. I have never used it and I don’t know what it is called but Rio Grande casting department should be able to tell you and advise you as to what will work for your casting. Call and ask for their Casting specialist.
Another option MAY be to fill the tubes with a solution of weak investment (to much water?) to make the investment more porous and easier to remove.

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I spent nearly twenty years teaching ceramic shell investment casting, and as a result had a lot of sterling (and occasionally fine) silver for re-use. Anywhere between a kilo and five kilos per week.

Ceramic shell is very different from plaster investment so I’m not expecting my experiences to be directly relevant. However I would say that if any of this investment got into an ingot intended for rolling into strip, then not only would you be able to guarantee cracking of the strip, but you would also be able to spot the particles of molochite investment in the cracks under modest magnification.

Embedded molochite was not usually a problem for cast items which merely needed finishing, but could be such a pain in rolled strip that I would often take such batches of scrap sterling to Blundell’s of Wardour Street (London) to be reimbursed in cash over the counter. Those were the days…

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Just to let you all know that I managed to melt the material down in my furnace at 1035c and surprisingly the investment simply floated to the top and I just removed it with a graphite rod. I used borax and shortly after a pinch of Argoflux for the process then poured into a cold bucket of water. I may repeat the melt and pour again before using the metal, but to me it looks great. Saved time and money not having to send it off to the refinery. I will definitely use a mix of fresh metal with it in my future cast just in case.

Thank you all for you input!

I nearly had 1kg in my melting furnace. I managed to pull it off. The investment just floated to the top. Really easy to remove. Thanks

I’m glad that it worked out for you. I thought that you probably had a trees worth pendants with tubes full of investment. That was a lot of metal!