Melting brass and bronze for casting

I "know" that holding brass or bronze at high temp burns off the low melting zinc, tin, and lead and it is not recommended that brass or bronze scrap be melted into ingots per one site I checked out. None the less 1. Is it better (more consistant results) to bring the first batch of metal up from cold or to heat the crucible and furnace to near the final melt temp and add the metal at that time? 2. If it is desired to add tin to bronze or zinc to brass, how and when should this be done? Pellets or other bits of low melt metal to molten alloy? Cold mixing bits of both ingredients and heat mix? Lower temp metal melted and higher temp added? My basic stock at this point is surplus keys and what I am making is goblet stems to blow glass into and molds and tools. http://users.ticnet.com/mikefirth/castgobl.htm#CASTGOB

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[You have no idea what's in the scrap you're melting. You'll get ingots, sure, but of what? And what would you be breathing?]
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[Start with all the metal in the pot. Throwing cold metal into a hot pot can be dangerous.]
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[Melt the lowest-melting component first, with a reducing flame and under a flux coat, and add the higher-melting ingredient to that. Make sure it's heated enough to drive off any absorbed water before you do this. The copper will dissolve into the tin or zinc as it gets hot enough.]
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[If you're doing this for an actual use, and not just as an experiment, use metal of a known composition. Even if you had good results with your mixed keys (unlikely though that is), it would be hard to duplicate with the next batch. If you want to make your own alloy, start with pure tin or zinc (or silicon), and heavy-gauge bare copper wire. Wire is generally electrolytically pure copper. Keys can be any alloy of brass, bronze, aluminum, steel, or beryllium copper (which you don't want to mess with) - recycle them some other way. Here's a good article on alloying metal in the small shop: http://www.apecs.com.au/alloyinginsmal/alloying.htm . Here in the US, most art foundries prefer to work with silicon bronze, because it melts cleanly, doesn't fume, welds well, is strong and corrosion resistant. You can buy it in ingot form all ready to go...]
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[Hey, I've got a bin of broken glass - window glass, beer bottles, some pyrex and odd bits of stained glass - can I melt it all together and make beautiful art?]
Andrew Werby www.unitedartworks.com
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One thing you will get: consistency, since the batch of ingots (if you melted them all in the same crucible) will be homogenous.
The major loss is zinc, since you're above the boiling point (like leaving a soda out: the dissolved CO2 gas slowly bubbles out over time). Tin, lead and copper also oxidize, particularly if you don't use a cover flux (a combination of borax, silica, soda, lime and alumina (sourced from clay or etc.) to thicken it).
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What if it doesn't fit? Then you've got a problem...
It's called preheating, to prevent steam explosions.
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Ah, so once the zinc hits the boiling point, and boils off, what's left to dissolve with the copper?
When I'm making brass (or recouping lost zinc in general), I take a short chunk of zinc ingot, hold it over the melt with my stir stick until it starts dripping, then thrust it in. It quickly melts, boils and dissolves in the molten (copper, brass, bronze) with a minimum of splash and oxidation. Any oxides on the surface are soaked into the cover slag (zinc is a good flux for glass, as a matter of fact).
The ABSOLUTE *WORST* thing you can do when adding zinc, is going slowly. If you just drop it on the surface, it WILL slowly go up to and past the boiling point, popping and burning *on the surface* as it does so.
Before chipping it out, my furnace floor had a ring of dark red to black copper oxide soaked into the insulating refractory (a ring because the plinth shadowed it), testament to the dangers of zinc handled in this way. Obviously, I've learned better by now...
As long as the zinc is dry, you can thrust it in with little worry. Preheating (until melting) as I do makes sure of this, and dissolves it quicker.
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Not necessarily. If you've got a pile of keys and they're all mixed up good, each one isn't going to contribute much error to the overall alloy. Point being, a pot full of a particular mix of keys is going to be pretty close to another, for a large number of keys melted into each pot, gathered from a similarly large set. But that's generic probability theory.
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Also, pipe is similarly pure.
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Well, I'll hazard to say one 2% Be key in a pot of 100 keys making for 0.02% beryllium isn't going to be any worse than the lead poisoning or zinc fume fever you'd get if you *actually breathed the fumes from the furnace*.
I wouldn't know, but I doubt they'd be allowed to make keys from Be bronze anyways - aren't they usually made with a person nearby? Well, the copiers anyways...
Let's see, what goes into copper...
The worst thing in keys is probably going to be chromium, from plating. It is about 3% soluble in copper before it starts increasing the melting point. Likely it forms hard particles in the matrix, which may or may not be useful (either hardening or embrittling it). Or it might be something of a grain refiner.
Next to that would be aluminum, which makes a good and brittle alloy much above 15%. Fortunately, no alloys contain that much for that very reason. Around 10%, it can be heat treated similar to steel. In the 5% range and below it tends to strengthen without reducing ductility; most alloys in this range are rated for hot and cold working with no heat treating besides annealing (think strengthened copper).
I'm not sure how you'd tell if there's any aluminum content, but you could remove it by bubbling air or oxygen until the zinc starts burning out (I'm not sure how you'd tell that either..). Same goes for beryllium, which is even more reactive.
I don't know much about manganese, but I gather from there being alloys with as much as 25% of it (white manganese brass/bronze), it can't be too bad when diluted. It's kind of an intermediate thing between the aluminum bronze and normal bronze kind of alloys, being found in some of both classes; I can only presume that it wouldn't be too bad diluted with other keys.
Nickel, either as nickel content (nickel silver base metal) or nickel plating, only tends to strengthen the alloy; copper and nickel are fully soluble in each other and I'm not aware of a combination which isn't ductile. Most alloys that do contain nickel are usually in the 5 or 25% range.
The common bronze elements zinc, tin and lead and fully compatible alone in any combination I'm aware of. I've made plenty of bronze by tossing in solder and zinc at will. Tin is usually limited to 20%, much more is too brittle (the Liberty bell cracked from too high tin content; it was recast with less, but still cracked, as can be seen today). Tin and lead do not appear to be compatible with aluminum, but zinc does in small amounts (I've seen alloy specs for 5% Al, 5 to 10% Zn, and pretty much nothing else).
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Pff..
Hm, good inspiration Andy. I think I'll write a page on alloying. Then, since it's on the 'net, and everything on the net is true... I can quote it for reference on the most obscure newsgroups! :D
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resistant.
I personally have no need of this, but that's simply because I'm a cheapass and don't feel like paying $3/lb for it. Especially when I've had nothing but success with my mixtures. I'd probably like it, but go back when I use it up because it doesn't work any better for the price (free wire is so fun).
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Probably... maybe lay it out on a table of some sort (don't ask me what doesn't stick to glass!), fire it until it starts slumping together, cool slowly so it doesn't crack, and sell it for thousands to some yuppie... ;)
Anyways, Mike... the bottom line, long story short, melt some keys, pour a test bar and watch it cool, poke at it (if it remains "mushy" or "slushy" for a long while, it'll cast better) bend it, break it, file it, and everything else. If you like how it works and looks...then the alloy is a success. If it works, it works!
Tim
-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @ http://webpages.charter.net/dawill/tmoranwms