Method of necking and impact extruded metal container

Abstract

A method of forming an elongated narrowed neck on an impact extruded metal container, in which a larger portion is trimmed from the open end of the container than is necessary merely to produce a straight unwrinkled edge. The trimmed part is sufficiently long that the metal at the new edge formed by trimming comprises substantially more formable metal than the metal which would have been present at the edge produced by normal trimming. The increased formability occurs because excess impurities which migrate to the open edge of the container are largely removed by the deep trim. It is then possible to process the open end through a series of forming dies to produce a long narrowed neck with a much lower reject rate than previously. The method is further assisted by trimming the end of the neck again part way through the series of forming dies, and by maintaining very small clearances in the dies, and by using compressed air in the first few dies to aid in ejecting the containers from the dies.

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