Casting of aluminium
About two-thirds of all aluminium castings are used in the automotive industry, e.g. in cars, buses, lorries, trains and aircraft. The need to reduce vehicle fuel consumption and weight has increased the interest in aluminium. The total mass of aluminium in a European car roughly doubled between 1990 and 2000. This growing use of aluminium in its major user sector clearly has an effect on the overall number of castings produced. Aluminium is mainly cast into permanent moulds. The relative shares of applied casting techniques for Al are given in Table 1:
Table 1: Relative shares of applied casting techniques for Al [143, Inasmet and CTIF, 2002], [225, TWG, 2003]
Many different types of melting furnaces are used in aluminium foundries the choice depending on individual requirements. Directly and indirectly heated furnaces, using fuel and electricity, are applied. The fossil fuels currently used are natural gas, liquid petroleum gas (LPG) and oil. Natural gas is favoured by most foundries on convenience grounds. Electrical heating may be provided by either resistance elements or by induction. Capacity is one of the most important parameters for melting and holding furnaces. Today induction furnaces are normally used when a high melting capacity, e.g. above 10 tonnes/hour, is needed. Shaft melting and holding furnaces, as well as crucible furnaces, are often used when the melting capacity is less than five tonnes/hour. Small and medium crucible furnaces are often used when it might be necessary to be able to change the alloy easily or if the production rate is low.
For holding, electric furnaces have the advantage of not producing burner off-gases and being able to sustain a homogeneous temperature over the whole molten volume, at a relatively low energy expense.
Aluminium melting in foundries generally uses alloyed ingots as a starting material, although in some cases the metal is delivered already as a liquid. The secondary melting of aluminium scrap is usually not performed in foundries and falls outside the scope of this document. It is discussed in the BAT reference document for the non-ferrous metals industries. [48, ETSU, 1994] [148, Eurofine, 2002], [155, European IPPC Bureau, 2001]
Source: European Commission, Reference Document on Best Available Techniques in the Smitheries and Foundries Industry, May 2005, p. 19