Foundry processes

Moulding in expendable moulds can be carried out using a non-expendable mould, as in the case of sand casting where the mould is made of refractory material (foundry sand) and is broken at the end of the process so that the part can be extracted, or by using an expendable mould, as with lost wax casting, which is used especially for artistic castings.
With regard to non-expendable mould casting, the mould, called a shell, is made in steel or cast iron and is not broken when the product is removed. The advantage of this method is that the same mould can be used in multiple production cycles, it can give a better surface finish and the process can be automated.

Non-expendable mould casting processes can be divided further into different categories depending on whether the casting of the metal into the mould is dynamic or static. In the case of dynamic casting, we have centrifugal casting, in which the mould moves, pressurised casting or die-casting, in which the liquid metal moves, and continuous casting, in which both move. On the other hand, as regards static casting, we have gravity casting, in which the molten metal is poured into the shell from above, and flows into the mould due to the force of gravity. The die-casting process, in which molten metal is injected into the mould at high pressures, is highly automated, with very short cycle times and thus very high productivity. The surface finish of the end product is further improved by the high casting pressure, which makes the material stick to the mould better.

Aluminium alloys

An alloy of which the main constituent is aluminium and whose density is no greater than 3 kg/dm³ is called a ‘light alloy’.

The mechanical characteristics are certainly among the most important properties of aluminium alloys. For some alloys, the yield point and ultimate tensile strength values approach those of some steels; the low coefficient of elasticity is a further advantage, given the considerable deformability that it allows. A density of around one third that of steel, is, however, the most important characteristic, since it reduces the weight of structures by up to 50% compared to similar steel constructions. In addition, the high general corrosion resistance boosts the life of buildings, which, amongst other things, don’t need painting because of the material’s attractive appearance.

The use of aluminium alloys in industry has grown exponentially over the years.

The main fields of application are:

• Aeronautics: light alloys are widely used because of the importance of structural weight in this sector.
• Automotive applications: light alloys are used mainly for the warm parts of the engine, the temperature of which must not exceed 250°C.
• Railway field.
• Bicycle frames: Light alloys allow the building of more rigid and lighter frames.
• Pressurised tanks and pipes: high ductility, even at low temperatures, and the good corrosion resistance of aluminium alloys make them ideal.
• Kitchen accessories.
• Windows and doors and other domestic applications: windows in anodised aluminium or in painted aluminium are widely used.