Extruded Aluminium Block

This stunning metal block is a billet of extruded aluminium. Extrusion is the familiar everyday process of pushing material through a hole: whenever we squeeze toothpaste from a tube we are doing extrusion. In the industrial version, plastics, foodstuffs or metals like aluminium can be made into very long objects with a fixed profile such as square rods, round bars and the I-beams that hold up many of our buildings. This is done by pushing material through a die of the chosen cross-sectional shape. 

Extrusion is done in the solid state (the metal is not molten), but the aluminium is heated to around 300-600°C to keep it soft and avoid work hardening the metal. Extreme pressures are needed to push soft, solid aluminium through a die, and that’s probably why you can see black streaks on the outside of the block if you look closely; this is likely from graphite which is used as a solid lubricant. The process for extruding metals was first patented by Joseph Bramah, an inventor and locksmith from Yorkshire, in 1797. It was later paired with a hydraulic press, also of Bramah’s invention.

Although aluminium is the third most abundant element in the earth’s crust, its existence wasn’t established until 1808, and even after that it took many years of research to ‘unlock’ the metal from one of its ores, bauxite. As a result, aluminium is a relatively young metal in comparison to gold, copper and even steel. It was made for the first time in 1825 in Copenhagen by H. C. Oersted but since its commercial production was reliant on the development of electrolysis, it was only produced in significant quantities from the 1880s onwards. 

Because of its extraordinarily light weight and strength, aluminium has become a very popular metal and is used in volumes second only to steel in all areas of modern life from car bodies to drinks cans. It also transmits conducted heat and reflects radiant heat, making it a favourite material for cooking utensils, kitchen foil and building insulation. 

Although efforts have been made to make production processes more efficient over the years, aluminium requires a huge amount of energy to extract it from its ore by electrolysis, and only melts at 2000ºC. However, its environmental credentials are helped by the fact that it is, in theory, 100% recyclable and that recycled aluminium uses about 5% of the energy needed for virgin aluminium. The energy required for its initial production can also be offset over time by the energy saved in use, for example, through fuel savings gained by using lightweight aluminium in a car body instead of heavier steel.