Aluminium

Aluminium is one of the metals that humans only recently started to use. Compared to iron and copper, which have been used for several millennia, it has only been known of for around 200 years. There are several reasons for this. Pure aluminium forms small crystals and is so rare in terms of quantity, that metallurgical exploitation of these deposits in not economical. Further, it is a very reactive metal and therefore virtually never occurs in its pure form.

minerals containing aluminiumWithout aluminium the most familiar precious stones would not exist. The metal bonds, for example, with beryllium, silicon and oxygen and forms crystals which – especially in their pure form – achieve top prices in the jewellery industry. Aluminium is contained in a large number of other minerals. But it is only in ore that it occurs in sufficient quantity to be suitable for industrial extraction. The ore in question is nondescript Bauxite.

The extraction process

BauxiteThe late discovery is probably because the aluminium is not identifiable, even if a lump of bauxite is examined more closely. Inside the ore, the metal appears nondescript and has no metallic shine. The metal in the ore is oxidised and therefore cannot be detected with the naked eye. Australia is one of the largest bauxite mining countries in the world. But the ore occurs virtually worldwide, however in highly different concentrations. Ores containing metal are usually crushed and melted after they have been mined.

The melting and the different melting points enable the individual metals to be separated out. This is not so easy in the case of bauxite. Bauxite is an ore that contains a large number of different metals and minerals.

CoinsSimple melting cannot release the chemical bonding. Apart from aluminium silicates, bauxite also contains iron, titanium and gallium compounds. As the aluminium cannot be melted out, the unwanted substances are separated out chemically using caustic soda. The silicate is then burned, forming aluminium oxide. As three oxygen atoms have bonded with each aluminium atom in aluminium oxide, a very large quantity of energy is required to extract pure aluminium electrolytically. Due to this high energy consumption, the production process is not environmentally friendly.

However, if the whole life cycle of the material is considered, the energy-intensive extraction of aluminium is balanced by the worthwhile recovery and reuse of the used metal. Recycling uses only approx. 5 % of the energy required to extract it from Bauxite.

A construction material at Rime

Aluminium has a low density and is therefore around 50 % lighter than iron. Its low weight makes this material very interesting for vehicle and aircraft constructions, which must not weigh much and nonetheless need to have a high degree of stability.

These sheets are not only lightweight, it is also a very soft metal, which makes it outstandingly easy to work and machine. Despite these properties, those sheets are very stiff and lend constructions a high degree of stability. Such sheets are worked regularly at Rime. We purchase our sheets from our dealers with a large selection of standard and special sizes. These are then worked in toll manufacturing to your specifications to produce products.

At the first glance, it should also be easy to cut with a laser, even if larger material thicknesses are involved. Although aluminium is softer than steel, precisely the opposite is true. Smooth aluminium surfaces have optical properties, which are similar to the degree of reflection (reflectance) of an old mirror. Depending on the degree of purity of the metal, the reflectance reaches around 75 – 85 %. In laser cutting the material is melted by the laser beam at the cutting joint and is blown out of the cutting gap (clearance) by a highly concentrated gas jet. In the case of aluminium this process requires far more energy, as the reflectance reduces the effect considerably. The outstanding thermal conductivity also reduces the performance of the laser.

The consequence of this is that part of the energy from the laser beam is discharged into the surrounding material. This circumstance and the fact that the power of the laser beam is limited, minimises the possible material thickness to 15 mm. Bending aluminium sheets is not a problem, provided several special features are noted. The bending can be carried out on the conventional press brake. It is only necessary to ensure that the bending radius does not fall below the value of twice the material thickness. Further, the aluminium sheet should be bent across the roll direction, as in this way the smallest bending radii are possible. The special material properties enable longer bending of thicker sheets or plates than is possible with steel.

Alongside steel and stainless steel, aluminium ranks 3rd among the materials most worked by Rime. Please note that we only machine sheets and plates and produce products to our customers’ specifications. For this reason we do not trade in metal sheets and plates.