Smelting Brass 1

[esinc]

My question is this...
I have a small foundry at home powered by propane. I know for a fact that it can melt copper, zinc, lead, tin, bismuth, and anything else within a 2500 degree range. I have been trying to make brass, but i have yet to get a nice "nugget" of brass from the furnace. I put a measured amount of copper into the crucible, heat it up to about 2300 degrees, then add the zinc. when i do this it produces a cloud, (I'm guessing of zinc, or zinc oxides) and sparks a little. when all is said and done, i end up with a piece of mostly copper, some zinc, and very little specks of brass. even more frustrating yet, for some reason, I cannot remelt the nugget because it simply wont melt no matter how high i turn the temperature! I have also tried to use map gas, (which supposedly burns about 800 degrees hotter,) and still get nothing. so, i guess my question is...what exactly is the smelting process for brass? what goes in first, copper or zinc, and at what temperature does brass melt? I would really like to know because I want to try my hand and making brass coins. The crucible I'm using is made of some sort of steel alloy, but doesn't melt, under the intense heat. The crucible is surrounded by a ceramic "cup" of sorts, to insulate it. and all of this is inside a big steel wok to protect the work surface beneath. The torch is basically turned on, and aimed directly into the crucible. the metals are then added, then they melt. What am I doing wrong? do I need a more professional setup?

 

[redpicker]

Your biggest problem is that the boiling point of zinc is 1664F and the melting point of copper is 1981F. If you have the copper melted, the zinc will boil away when you add it.

Why not just buy some brass at the composition you want and melt that?

rp

 

[btrueblood]

Direct flame heating of the puddle from above is going to accelerate the evaporation of zinc from the melt, and yes, possibly pull oxygen into the mix to even more rapidly deplete zinc. Suggest heating from below. Also suggest starting with an ingot of a known alloy composition, so that the melting will take place at a more-or-less uniform temperature.

 

[arunmrao]

Heat the copper until it is just liquid and begins to melt. Cover the surface of the melt always with charcoal. Just when it begins to be liquid add the zinc metal and some borax. Cover them again with fresh charcoal powder. Add a little zinc more than what is necessary to compensate for the losses. Once the zinc is dissolved,slowly then raise the melt temperature.

Hope it helps,it is more from memory rather than any reference.

_____________________________________
"The richer we have become materially, the poorer we have become morally and spiritually." Martin Luther King Jr

 

[swall]

Arunmrao--just curious--what function does the charcoal serve? I can understand the borax as a fluxing agent. Does the charcoal act as a deoxidizer?

 

[Hercules28]

I had trouble keeping Zinc inside the melt in Aluminum castings. It wants to evaporate. What I did in Al to put it inside the melt is wrap it in Al foil and then Plug it in the melt and hold it down. There is some violence there.
Very tough to dissolve.

Also tried some salts... hazardous for health though.

I think that you are creating Oxides and these are the ones that have very high melting points.

 

[moltenmetal]

I too have a propane fired home foundry, hence the handle. Mine is a side-fired box made of stacked insulating firebricks with a bottom "hearth" of a 2.5" hard refractory firebrick tile, wrapped with a batt of Roxul Flexibatt mineral fibre (house wall cavity) insulation.

Yes, starting with a brass or bronze is best, and #1 copper scrap is so valuable these days that you can trade it 2 to 3 for one with brass scrap- especially if you don't mind a little lead, tin and antimony in the mix.

But if you insist on doing your own alloying, here's another thought: start with zinc, cover with charcoal or borax or both (to flux the oxides and to keep away oxygen). Melt the zinc, then add the required quantity of solid copper and slowly raise the temperature, keeping covered with the molten borax the whole time. The borax forms a skin which, if left unbroken, reduces the oxidation and volatilization of the zinc. All the copper-zinc sub-alloys are going to be lower melting than pure copper if I remember the diagram correctly, so you should be able to slowly dissolve the copper into the zinc to form a puddle of the desired composition. Cast an ingot, then mechanically remove the borax and charcoal from the surface prior to re-melting.

Any time you melt brasses you're going to need borax there to reduce oxidation (at my scale that's certainly true, so I suspect it'll be true at yours as well). It's tough to keep the molten borax out of your castings. By the way, the molten borax is hard on the refractories as well- it fluxes their oxides too over time.

Popping zinc into molten copper is a recipie for rapid zinc loss by fire, with the nasty toxic fume to be concerned with. I wouldn't recommend it.

From experience, the dissolution of solid copper into a brass puddle below the melting point of pure copper is relatively slow, so this will take some time.

 

[unclesyd]

The Charcoal is the anti-oxidizing agent while the Borax is the flux not very scientific a wetting agent.
Posts concerning the boil of Zinc is quite common and is used in several metallurgical processes, like recovery of Zinc from galvanizing dross where the Zinc is vaporized and condensed and the recovery of Silver from Lead.
Be real careful when working around molten Zinc as the fumes are very detrimental to one's health. It call zinc fume poisoning and can make one feel very bad.
I concur with getting the proper scrap or ingot metal for you project.

 

[unclesyd]

If there is a metal supplier near you I would check with them abouts their drops. The same if a machine shop handles brass/bronze products.

The first link is to a lot of metal suppliers. The second is to a hobbyist with a lot links to others.

http://www.ask.com/web?l=sem&ifr=1&..._uid=6f427459eebcdae5ca33e150f177600081fefcfd

http://www.backyardmetalcasting.com/links.html

 

[metengr]

A very wise warning by unclesyd.

 

[blacksmith37]

A difficult way to make brass;As most have said , just start with brass, will be cheaper than Cu.
Typical flux has soda ash , silica ,and borax. Avoid fluorspar, it can make "spinels".
The brass will melt a few hundred degrees lower than Cu, your temps should be well below Zn boiling (if you start with brass).
Brass founders ague,= zinc chills, = oxide shakes; not all that terrible; Avoid FRESH ZnO, no problem after it is a few hours old.