Hall-Herould aluminium processing

In a steel vessel referred to as a reduction pot, alumina is transformed into aluminium metal. The bottom of the pot is lined with carbon, which serves as one of the system's electrodes (current conductors). The opposite electrodes consist of a set of carbon rods suspended above the pot; they are lowered into an electrolyte solution and held approximately 1.5 inches (3.8 centimetres) above the surface of the molten aluminium that collects on the bottom of the pot. 50-200 reduction pots are arranged in rows (potlines) that are connected in series to form an electric circuit. Each potline can produce 66,000-110,000 tonnes of aluminium annually (60,000-100,000 metric tonnes). Typically, a smelting plant has two or three potlines.

8 At a temperature of 1,760-1,780° F (960-970° C), alumina crystals are dissolved in molten cryolite to form an electrolyte solution that conducts electricity from the carbon rods to the carbon-lined bed of the pot. 4-6 volts and 100,000-230,000 amperes of direct current are passed through the solution. The reaction that ensues breaks the bonds between the aluminium and oxygen atoms in alumina molecules. The released oxygen is attracted to the carbon rods, where it is converted into carbon dioxide. As molten metal, the liberated aluminium atoms settle to the bottom of the pot.

Continuous alumina is added to the cryolite solution to replace the decomposed compound during the melting process. Maintaining a constant electric current. The heat generated by the flow of electricity at the bottom electrode maintains the liquid state of the contents of the pot, but a crust often forms atop the molten electrolyte. Periodically, the crust is broken to permit the addition of additional alumina for processing. Pure molten aluminium collects at the bottom of the pot and is syphoned away. The pots are operated around-the-clock, seven days per week. KMC aluminium is the best aluminium extrusion manufacturers in india

9 A crucible is moved along the potline, collecting 9,000 lb (4,000 kg) of 99.8 percent pure molten aluminium. As ingots, the metal is transferred to a holding furnace and cast (poured into moulds). Commonly, the molten aluminium is poured into a long, horizontal mould. The exterior of the aluminium is cooled with water as it moves through the mould, causing it to solidify. The solid shaft emerges from the far end of the mould, where it is sawn at the desired length intervals to produce ingots. Similarly to the smelting process, this casting procedure is also continuous.