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Aluminium, a most wide-spread metal on the Earth, was discovered in 1825. In the air it acquires a specific thin white matt layer with strong anticorrosive qualities. Aluminium dissolves readily in caustic lyes and diluted hydrochloric and sulphuric acids. It does not normally react with aquafortis and organic acids. Its relative density is 2.7 and melting point is 660 C. Its crystal lattice is a face-centered cube. Aluminium possesses high thermal and electric conductivity.
Modern industrial aluminium production is based on electrolyzing of alumina, diluted in cryolith, a technique developed in 1886. To get 1t aluminium through electrolyzing 2t alumina, 0.6t applied as anodes carbon electrodes, 0.1t cryolith and from 17000 to 18000 kWh of electric power are used up.
Resulting liquid aluminium contains metallic impurities (iron, silicon, titan and natrium), dissolved gases, mainly hydrogen, and non-metallic inclusions - particles of alumina, carbon and cryolith.
Commercial aluminium varieties are obtained through liquid aluminium refining. You can get rid of non-metallic and gaseous impurities through metal recasting and blowing through with chlorine, of metallic impurities – applying electrolytic techniques. Unavoidable impurities resulting from aluminium production are iron and silicon. They impair product useful qualities.
Commercial aluminium of all types contains more than 99 % Al. A quantitative surpassing of this parameter in some hundredths or tenths percent is given in the name of a type after the initial A. For example, Type А85 contains 99.85 % Al. Types АЕ are the exception, as they contain the same amount of aluminium as Types А0 and А5, but the iron and silicon impurities ratio is different.
The letter Е in Type АЕ means, that aluminium of the type is meant to be used for electrical wire production. Aluminium of all types (high- and technically pure), meant for recasting, is casted as 5; 15 and 1000 kg billets. Their limiting values: the height - from 60 to 600 mm, the width - from 93 to 800 mm, and the length - from 415 to 1000 mm.
Aluminium, meant for plates and strands rolling (using a continuous or semi-continuous techniques), is casted in flat-shaped ingots of seventeen sizes. They are from 140 to 400 mm thick, from 560 to 2025 mm wide, and a 1m long ingot can weigh from 210 to 2190 kg. The ingot’s length is agreed upon with a customer.
To deoxidize steel during its smelting, to produce ferroalloys and in aluminothermy a hceaper type of less pure aluminium is applied, as in the Table (see above). Such aluminium can come in six types, in billets from 3 to 16.5 кг, and contain from 98.0 to 87.0 % Al, up to 2.5 % of iron, up to 5 % of silicon and copper. back |
