Hall-Herould aluminium processing

Alumina is smelted into metallic aluminium in a steel vat known as a reduction pot. The bottom of the pot is lined with carbon, which serves as one of the system's electrodes (conductors of electric current). The opposite electrodes are made up of a series of carbon rods suspended above the pot, which are lowered into an electrolyte solution and held 1.5 in (3.8 cm) above the surface of the molten aluminium that accumulates on the pot's floor. Reduction pots are arranged in rows (potlines) of 50-200 pots connected in series to form an electric circuit. Each potline can produce 66,000-110,000 tonnes of aluminium (60,000-100,000 metric tonnes) per year. Two or three potlines are typical of a smelting plant.

8 Alumina crystals are dissolved in molten cryolite within the reduction pot at a temperature of 1,760-1,780° F (960-970° C) to form an electrolyte solution that will conduct electricity from the carbon rods to the carbon-lined bed of the pot. The solution is passed through with a direct current (4-6 volts and 100,000-230,000 amperes). The reaction that follows breaks the bonds between the aluminium and oxygen atoms in the alumina molecules. The released oxygen is drawn to the carbon rods, where it forms carbon dioxide. Aluminum atoms that have been liberated settle to the bottom of the pot as molten metal.

The smelting process is ongoing, with additional alumina added to the cryolite solution to replace the decomposed compound. The electric current is kept constant. The heat produced by the flow of electricity at the bottom electrode keeps the contents of the pot liquid, but a crust forms on top of the molten electrolyte. The crust is broken on a regular basis to allow more alumina to be added for processing. The pure molten aluminium collects at the pot's bottom and is syphoned off. The pots are operational around the clock, seven days a week. KMC aluminium is the best aluminium extrusion manufacturers in india

9 A crucible is moved down the potline, collecting 9,000 lb (4,000 kg) of 99.8 percent pure molten aluminium. The metal is moved to a holding furnace before being cast (poured into moulds) as ingots. Pouring molten aluminium into a long, horizontal mould is a common technique. The exterior of the mould is cooled with water as the metal moves through it, causing the aluminium to solidify. The solid shaft exits the mould at the far end and is sawed at appropriate intervals to form ingots of the desired length. This casting process, like the smelting process, is continuous.