Under pressure the billet is crushed against the die, becoming shorter and wider until it has full contact with the container walls.
While the aluminium is pushed through the die, liquid nitrogen flows around some sections of the die to cool it.
This increases the life of the die and creates an inert atmosphere which keeps oxides from forming on the shape being extruded. In some cases, nitrogen gas is used in place of liquid nitrogen. Nitrogen gas does not cool the die but does create an inert atmosphere.
Because of the pressure added to the billet, the soft but solid metal begins to squeeze through the die opening.
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