Page 33 - Curriculum Visions Dynamic Book

extrusion: forming a shape by pushing it through a die. For example, toothpaste is extruded through the cap (die) of the toothpaste tube.
Contrasts in canning
A “tin can” is made from steel that has
been coated with tin and sealed by soldering. The tin coating can be scratched away, allowing the steel to rust. Aluminium
cans are lighter, do not rust, and can be extruded, thus removing the need for soldered seals. It is also easier to paint
a decoration directly onto aluminium,
so no more costly paper wrappers are
used on steel cans.
Aluminium and acid containers
Aluminium has the advantage of being resistant to attack by a variety of chemicals. Although it is readily corroded by most alkalis (which attack the surface oxide film) aluminium does not react with ammonia and so it can be used to store and transport it.
Aluminium is far more resistant to neutral
or acid solutions, in particular, acetic acid and concentrated nitric acid. For this reason many transport and storage containers for these chemicals are made from aluminium.
H Aluminium can be made thin enough so that it can be torn. The special shapes on the top of many cans are designed to fail and produce a clean pouring opening. The lever-arrangement on the can is to save
the can pulls from being discarded and polluting the environment.
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