Hello Ganoksin!
After browsing the forum for about a month or more I finally decided to make an account to hopefully solve some of the problems I’m dealing with.
I’m currently trying to produce Sterling silver wire from my own cast Ingot. I’m making my own Sterling using copper and fine silver. I’ve been able to cast what appear to be good ingots but I have problems when I start to mill, mainly cracking on the edges of the ingot when it starts going from square to round/octagonal. I’ve filed these cracks out and everything looks good until I start running the wire through my draw plate. After the first or second pass I start to get flaking on the wire. It almost looks like fish scales where these flakes are only attached at one point.
I haven’t tried forging the Ingot first as I don’t have a good work surface yet. My process is as follows.
Cast silver in a carved out charcoal block (could never get steel mold hot enough to pour fluidly), let cool, pickle, and file smooth.
Run Ingot through draw plate until metal starts to feel harder or curl. At this point it is less than a 30 percent reduction.
Anneal and repeat drawing/annealing until I get within 1-2mm of my final wire diameter.
Draw wire through draw plate annealing every 3 passes.
The “flakes” seem to persist even after filing them out between steps. Perhaps I’m not annealing correctly? I’ve tried annealing less and more but don’t seem to notice any improvement. It should be noted I’m never able to reach the 30-50 percent reduction that is suggested between annealing as I always see cracking and curling before this point.
Any suggestions or thoughts would be greatly appreciated!
The best explanation that anyone has ever told me about ingots cracking is to think of a wave on the surface of the ocean. The wave on the ocean surface moves at a different rate than at the bottom of the ocean. A similar thing is happening with ingots and a rolling mill. The surface is moving at a different rate than the inside of the ingot. That leads to cracking. The other issue is that cast metal is (an artist explanation, not a scientific one) is kind of like super annealed metal, meaning that it’s brittle until it builds up a work hardened surface. Where all this is going, I’ve never successfully done what you’re trying to do without doing at least 5 courses of hammer, anneal, pickle before ever touching the rolling mill. You can make an adequate and relatively inexpensive forging surface with a steel bench block turned vertical in a vise. I’m sure folks will have other tips as this is a popular forum topic.
Hope that helps!!
Jeff
This is a regular topic on ganoksin and you should be able to find some good discussions doing a search. Search on recycling sterling silver. You mention that you make your own sterling with copper and fine silver. The sterling that you purchase may have some other metals in it than just fine silver and copper. Argentium is an example. It still has 92.5% fine silver and can be thought of as sterling silver in how it behaves, plus, it is tarnish proof to some extent. Depending on the source of your fine silver and copper, there may be other metals in the mix. Use a reducing to neutral flame helps keeping atmospheric oxygen from getting into the mixture. The charcoal environment also helps in this regard. Using an electric furnace is another way to reduce the introduction of atmospheric oxygen. Heating the mold and coating it in some way with carbon is also important. This can be done by passing a candle flame over it or just the gas flame from your torch. You can also coat the mold with a finely refined oil and burn it off. There is some discussion that this may introduce dirt into the melt. Once you complete your casting and the ingot is cooled, you should sand or ground off any flashing or sharp points that might get rolled over into the ingot when it is rolled. Otherwise they will show up later as little feathers or sharp spots. The ingot needs to be forged prior to rolling. I think that Jeff covers this in his reply. It is important to forge all sides in the same direction using a dull chisel type hammer or the ball of a ballpeen hammer. Annealing often is real important. I also will always roll the ingot in the same direction relative to the mill until it gets annealed again. If you don’t have an anvil to work on, you can buy a fairly inexpensive steel bench block from the usual sources. You might also visit a machine shop and see if you can buy a piece of scrap steel with at least one finished surface to work on. Welcome to ganoksin. Good luck and keep us posted…Rob
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