How are Aluminium conductors made?
Aluminium is an element, which means that it is not 'made' - albeit it doesn't exist as the shiny metal we all think of it as. It has to be processed from its rawest form.
Though aluminium is a very common element on earth, making up 8.23% of the earth’s crust by mass, it’s very rare to find pure aluminium in the ground. Aluminium has a strong affinity for oxygen, meaning that it usually is found as an oxide or a silicate.
The most common source of aluminium is within a sedimentary rock called bauxite. It's extracted from the ground, consisting mainly of aluminium oxide and other minerals. Bauxite is currently the main source for aluminium, with some of the major reserves being present in countries like Australia, Brazil, China, Guinea, and India. Bauxite can come in various consistencies and colours - white, yellow, green, and tan - but it's mostly associated with being a reddish rock, from dull scarlet to a flaming red due to the increased iron oxides (goethite and haematite).
Some of our mining case studies involve bauxite plants.
Extraction – The Bayer Process
Once the bauxite has been mined it has to be refined to create pure aluminium, processing the raw material into aluminium oxide (aka alumina). This is achieved with a method called the Bayer process: by heating and pressurising the bauxite, and adding sodium hydroxide, the process separates out the aluminium oxide from the wider bauxite.
The aluminium oxide is then smelted; heating with a reducing agent, typically a fossil fuel, or other source of carbon in order to remove the oxygen from the ore, leaving pure aluminium. At this point, the pure aluminium (which is generally around 99.8% pure) is moulded into ingots, and sold onto companies to use in manufacturing.
To turn that aluminium ingot into a wire for use in cables, a process called wire drawing is used. Drawing involves pulling the metal through a die which incrementally reduces the diameter of the metal, while also increasing its length. By drawing the metal through increasingly small dies, the aluminium can eventually be drawn into a thin, flexible wire – which can then be used as the aluminium conductors in electrical cables.
Beyond conductors, aluminium has other uses in cables: providing mechanical protection for cables in the form of aluminium wire armour (AWA). It is used specifically on single core cables to prevent induced current in the armour - a current which reach a level that could in itself be fatal.
Aluminium cables are lighter than their copper counterparts, but as the metal is less conductive, it must be around one-third larger in cross-sectional area size to achieve parity in current carrying capacity. They are commonly used for overhead lines and also in installations where copper theft may be a risk, such as the rail industry.
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