#1 Smelting Copper by Trewier Coshall 11.06.2013 18:36

avatar

There are 4 know methods of smelting copper: cold working, annealing, smelting, and the lost wax method.
As a side note: I won't go into annealing since I find it very hard to understand, even the wikipedia page was really hard to understand so I will leave annealing out of this post for now.


Cold working

Cold working was the first know way to man of making copper tools it was first used in Anatolia in 7500 BC
Copper was the first metal in common use for tools since it is one of the few metals available in non-oxidized form, not requiring the smelting of an ore. Copper is easily softened by heating and then cooling. In this annealed state it may then be hammered, stretched and otherwise formed, progressing toward the desired final shape, but becoming harder and less ductile as work progresses. If work continues beyond a certain hardness the metal will tend to fracture when worked and so it may be re-annealed periodically as the shape progresses. Annealing is stopped when the workpiece is near its final desired shape, and so the final product will have a desired stiffness and hardness.


Smelting

How the discovery of copper smelting came about is a matter of much debate. Campfires are about 200 °C short of the temperature needed for that, so it has been conjectured that the first smelting of copper may have been achieved in pottery kilns. (Basically what is said here is that we need to make a pottery oven and throw copper ore in it to achieve melting) The earliest current evidence of copper smelting, dating from between 5500 BC and 5000 BC, has been found in Pločnik and Belovode, Serbia.


Lost Wax method

Casts can be made of the wax model itself, the direct method; or of a wax copy of a model that need not be of wax, the indirect method. These are the steps for the indirect process:
Model-making.

Moldmaking. A mold is made of the original model or sculpture. The rigid outer molds contain the softer inner mold, which is the exact negative of the original model. Inner molds are usually made of a soft material like rubber or wax which is supported by the outer mold. The outer mold can be made from hardened clay, wax or other materials. Most molds are at least two pieces, and a shim with keys is placed between the two halves during construction so that the mold can be put back together accurately.

Chasing. Each hollow wax copy is then "chased": a heated metal tool is used to rub out the marks that show the parting line or flashing where the pieces of the mold came together. The wax is dressed to hide any imperfections. (Not needed per se; Stone age).

Spruing. The wax copy is sprued with a treelike structure of wax that will eventually provide paths for molten casting material to flow and air to escape. The carefully planned spruing usually begins at the top with a wax "cup," which is attached by wax cylinders to various points on the wax copy. This spruing doesn't have to be hollow, as it will be melted out later in the process.

Slurry. A sprued wax copy is dipped into a slurry of silica, then into a sand-like stucco, or dry crystalline silica of a controlled grain size. The slurry and grit combination is called ceramic shell mold material, although it is not literally made of ceramic. This shell is allowed to dry, and the process is repeated until at least a half-inch coating covers the entire piece. The bigger the piece, the thicker the shell needs to be. The ceramic shell-coated piece is placed cup-down in a kiln, whose heat hardens the silica coatings into a shell, and the wax melts and runs out. The melted wax can be recovered and reused, although often it is simply burned up. Now all that remains of the original artwork is the negative space, formerly occupied by the wax, inside the hardened ceramic shell. (We would probably need to use hardened clay or mud as a protective shell for our castings)

Testing. The ceramic shell is allowed to cool, then is tested to see if water will flow through the feeder and vent tubes as necessary. Cracks or leaks can be patched with thick refractory paste. To test the thickness, holes can be drilled into the shell, then patched.

Pouring. The shell is reheated in the kiln to harden the patches and remove all traces of moisture, then placed cup-upwards into a tub filled with sand. Metal is melted in a crucible in a furnace, then poured carefully into the shell. If the shell were not hot, the temperature difference would shatter it. The filled shells are allowed to cool.

Release. The shell is hammered or sand-blasted away, releasing the rough casting.

#2 RE: Smelting Copper by King Zultra I 11.06.2013 19:01

avatar

Yes, We'll set aside specific kilns to 'cook' any 'strange rocks' we will come across, if a pottery Kiln doesn't smelt it (since it isn't hot enough) it most likely isn't Copper (but could be Silver, Gold, Tin or some other soft metal which isn't suitable for tool use.

#3 RE: Smelting Copper by King Zultra I 11.06.2013 20:03

avatar

We will also experiment with various metalworking techniques till we hit the right ones.

Xobor Create your own Forum with Xobor