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As the world's most widely used non-ferrous metal, it's remarkable how little the average person knows about aluminium. Important in so many areas including transportation, construction, packaging and everyday household items, being taught how and why it's so vital is something we feel could hugely benefit the engineers and metallurgists of the future. If you were lucky enough to get a basic understanding of Aluminium production at school, then great, but if not here's the process broken down into its 3 key steps:

Refining through the Bayer Process


Karl Josef Bayer's method for refining bauxite to produce alumina (aluminium oxide) has remained the principle, ergonomic process of the aluminium industry since its invention in 1887. The Austrian scientist realised that ore, when washed, crushed and dissolved in a hot caustic soda (NaOH) would dissolve the aluminium bearing minerals within the bauxite (aluminium ore). The alumina is then recovered from resulting 'pregnant' liquor by a process of crystallisation, seeded by an addition of alumina particles.

A series of flash tanks are then used to heat and subsequently cool the liquor, with the remaining caustic soda, reserved from earlier in the process, then recycled and added to the digestion process. The hydrated alumina is roasted at a heat of up to 1100°C, driving off free moisture and chemically-connected instances of water. This produces alumina solids, which is shipped to smelters.

The Hall-Héroult Smelting Process

In brief, the Hall-Héroult process of smelting involves passing a large, electric current through a molten mixture of cryolite (a halide mineral used elsewhere as an insecticide and pesticide), aluminium floride and the previously refined alumina to obtain liquid metal-35109_1280aluminium. The process takes place in a series of 'cells' known as a 'potline', with an electrolytic solution (known as a 'bath') containing the cryolite and aluminium floride maintained to a 960 – 980°C temperature. Alumina is then fed into the pot, normally into the 'bath' through a direct injection process.

An electric current of up to 600 Ka is passed through the bath. Ka, short for kiloampere, is a measure of flow rate of electric charge. For comparison's sake, a starter motor requires 80-160 A to power it, so the high significant amount of energy needed here is generated in power stations. Large carbon blocks are used to conduct electricity in the cell, reacting with the oxygen in aluminium oxide to produce liquid aluminium. Carbon is also used to form the negative electrode in this process by using it as lining for the pot, causing the liquid aluminium to be deposited at the bottom of the cell, where it can be 'tapped' when needed so it may be casted into solid, metal products.

Processes of Aluminium Semi-Fabrication


Once the process above has put aluminium in its most abundant and useful form, certain casting processes take it that final step into becoming the semi-finished industrial goods we know and appreciate everyday. Metal fabrication includes the assortment of cutting, bending and forming processes that take the product from its initial shape into something far more handy, and can include:

Ingot casting - The liquid aluminium is poured into moulds, which are then cooled, allowing the aluminium to solidify before being shipped out in its new, desirable shape. Casts can also be made with other metals, or sand, resin, plaster, graphite and even wax.

Rolling - Slabs of casted aluminium are heated to approximately 525°C, and are worked through a series of 'rollers' until they reach either their desired level of plate thickness, or they are thin enough (normally 3mm) for something called 'cold rolling'.

Extrusion - The cast aluminium is heated in billets and forced through a steel die. The aluminium is cooled as it is extruded, before it is cut to size in the processes we've more than covered before.

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