What you may not know about aluminium

Recently, aluminium is used on a mass scale thanks to its favourable characteristics:

• high heat conductivity
• high electric conductivity
• low weight
• corrosion and fire resistance
• excellent ductibility
• food compatibility
• excellent tensile strength when alloyed with other elements
• silvery gloss
• non-magnetic material
• recyclable

Basic physical values
melting point at 660°C
density 2 698 kg/m³

History

Earth's crust contents about 8% of aluminium, but it occurs in extremely stable oxygen compounds. That is why it took quite some time for scientists to figure out how to reduce it into pure metal. That process was first accomplished in 1824 in Denmark. Some small-scale „commercial“ production was achieved, but even five decades later aluminium remained more costly and coveted than gold. Breakthrough happened in 1886 when a process of electrolytic reduction was found while the main raw material was bauxit. Aluminium production still remains energy-intensive and a substantial cost reduction came later with supply of cheap electric energy. It opened door for worldwide expansion of aluminium.
Production of primary aluminium (from bauxit) consumes about 12 – 14 kWh/kg.
Production by means of recycling (re-melting) consumes just 5% of this energy, 0,6 – 0,7 kWh/kg.
Recycling of aluminium is of a key importance.

Worldwide aluminium production
1886 ... about 200 t
1950 ... 1 500 000 t
1998 ... 25 000 000 t

How aluminium foil is made

Aluminium foil is made in two possible ways:

• rolling sheet ingots cast from molten aluminium
• continuous casting and cold rolling (less energy-intensive)

Both production processes differ only at the very beginning, because, later, aluminium foil goes through many rolling stations every of which reduces thickness of the material. Technological problem is to maintain constant thickness of the material alongside the width of the foil. At the last rolling station where thickness of the foil undergoes 25µm it is not possible anymore to adjust rolls satisfactorily, therefore two layers of foils are lead at the same time through this station. The outer side of foil (which is in contact with the polished roll) is glossy, the inner one (which is in contact with the other foil layer) is matt. This method increases productivity and prevents tearing. Before going through every rolling station, the foil belt must be sprayed by lubricant similar to kerosene. In case of food-compatible foil production, the lubricant must be food-compatible, too.

Interesting links:
Aluminium alloy designation (http://en.wikipedia.org/wiki/Aluminium_alloy#Alloy_designations)
Education program on aluminium (http://www.eaa.net/eaa/education/TALAT/index.htm)
How aluminium foil is made (http://en.wikipedia.org/wiki/Aluminium_foil)