The most suitable metals for the manufacture of rigid containers and closures are steel and aluminium based materials. The many and varied physical properties of these materials present the opportunity for metal packaging to be constructed in a number of different ways to satisfy both technical, economic and social requirements.
What is Steel?
Steel is an alloy of iron and carbon containing less than 2% carbon and 1% manganese and small amounts of silicon, phosphorus, sulphur and oxygen. Steel is the world’s most important engineering and construction material. It is used in every aspect of our lives; in cars and construction products, refrigerators and washing machines, cargo ships and of course, packaging.
How is Steel made?
Steel is produced via two main routes: the blast furnace-basic oxygen furnace (BF-BOF) route and electric arc furnace (EAF) route.
The key difference between the routes is the type of raw materials they consume. For the BF-BOF route these are predominantly iron ore, coal, and recycled steel, while the EAF route produces steel using mainly recycled steel and electricity.
About 75% of steel is produced using the BF-BOF route. First, iron ores are reduced to iron, also called hot metal or pig iron. Then the iron is converted to steel in the BOF. After casting and rolling, the steel is delivered as coil, plate, sections or bars.
Most steel products remain in use for decades before they can be recycled, this is after all one of the key benefits of the substrate. But equally, all of these production methods can use recycled steel scrap as an input and all material used in the metal packaging industry, contains recycled steel.
For more information on how steel is made, visit: https://www.worldsteel.org
What is Aluminium
Aluminium is remarkable for its low density and its ability to resist corrosion through the phenomenon of passivation. Aluminium is vital to the aerospace industry, transportation and building industries and in a wide range of packaging applications, from beverage cans to food containers, aerosols and tubes.
How is Aluminium made?
Aluminium production begins with bauxite, the “aluminium ore”. Most bauxite is mined in tropical areas, with around 50km2 of new land mined each year. At the same time, a matching area of land is restored to nature.
Pure aluminium oxide, called alumina, is extracted from bauxite via a process called refining. Molten aluminium is extracted from the alumina through an electrolytic process called smelting, which breaks the strong chemical bond of the aluminium and oxygen atoms using a powerful electric current. Once the liquid metal is collected it is transferred in the cast house, where it is purified, alloyed to specification and then cast into ingots.
The primary aluminium is cast into ingots and used in the production of aluminium alloys. Aluminium can be rolled into sheets from which aerosols and beverage cans are made. Using the forming process of extrusion, the aluminium is shaped in its required form and delivers almost unlimited possibilities in product design.
Aluminium which is supplied for end manufacture and for drawn or drawn/redrawn (DRD) can bodies has a passivation layer applied by the supplier which helps adhesion of organic coatings applied at the can maker. Aluminium which is supplied for drawn and wall ironed (DWI) can bodies is supplied unpassivated, passivation being applied by the can maker during his own process before the application of any organic coatings.
For more information on how aluminium is made, visit: www.european-aluminium.eu/about-aluminium/production-process/