Aluminium encyclopaedia

Foil

By the 1880s, aluminium leaf beaten by hand and only a few thousandths of a millimetre thick had displaced silver leaf for decorative purposes in Germany. In Switzerland in 1905, Alfred Gautschi managed to produce aluminium foil that was almost as thin by rolling and this quickly replaced the tinfoil commonly used at the time for food packaging; for example aluminium foil was used for wrapping chocolate from 1911 onwards. The expression "tinfoil" is still used colloquially today to describe foil used for food wrapping even when this is made from aluminium.

Production

"Aluminium foil" is the term used to describe rolled aluminium products less than 0.2 millimetres thick. Today it is made mainly from unalloyed aluminium by cold rolling in several steps (passes) and is thus really a semi-finished product. The starting material is foil stock with a thickness of 0.6-1.5 millimetres. Computer control of the rolling process coupled with automatic thickness measurement enables rolling speeds of up 2500 metres a minute to be achieved. In order to produce even thinner foil - down to four thousandths of a millimetre - two layers are placed one on top of the other and rolled simultaneously (so-called "double rolling"); the outsides of the finished foil have a very smooth, shiny surface from the working rolls, while the inner surfaces rub together a little and are thus matt.

 As a result of the large amount of deformation during rolling, the aluminium undergoes so-called "cold working" and the foil becomes hard and brittle. One can make the foil soft and flexible again by means of a heat treatment called "annealing". This fact coupled with the impermeability of the foil to gases and light, means the foil is very well suited to meeting the demands of packaging for foodstuffs and medication. Depending on the application, aluminium foil is supplied either in a "hard" or a "soft" condition. 54 square metres of aluminium foil seven thousandths of a millimetre thick weigh just one kilogram. The scrap that accumulates during production (fabrication scrap) is recycled and melted down again.

Processing

After the removal of rolling oil (mainly by annealing), some aluminium foil is used plain, for example as household foil, and some is processed in a similar manner to strip using one of the following treatments:

  • printing with colour patterns and images using various printing processes
  • colouring and lacquering in painting or lacquering machines
  • lamination with paper, cardboard, plastic film or cellulose film for flexible laminates
  • embossing with engraved or etched steel embossing rolls
  • deep drawing, used for semi-rigid aluminium containers, for example for pet food or ready meals.

 

Applications

The most important applications of aluminium foil are:

  • in electronics and electrical engineering as capacitor foil, up to a mere four thousandths of a millimetre thick
  • in the home as kitchen foil, usually 11 thousandths of a millimetre thick, or as thicker foil in the form of barbecue trays
  • as packaging for food and medication, mostly as a composite with paper and/or plastic
  • In building construction and air conditioning technology as a vapour barrier and for thermal insulation.