Buckle resistance for metal container closures

Abstract

The present invention relates to improvements in the strength of ends used on metal beverage containers. Such ends generally comprise a central panel portion of a substantially planer character, a surrounding U-shaped sidewall having inner and outer legs, a curved intermediate portion integrally joining the inner leg to the U-shaped sidewall, and a peripheral curl extending from the outer leg for double seaming the end onto a can body. In accordance with the present invention, the intermediate portion and adjacent central panel portion are firmly supported by a die while a clamping force is placed on an annular band of the upper surface of the end at the intermediate portion. The clamping force is increased until metal flows inwardly and outwardly from the contact point resulting in a free compression doming of the center panel and an outward deflection of the inner leg. An end of increased buckle resistance is thereby produced which end is approximately within standard dimensions such that customers can use the end on existing seaming equipment without alteration. An optional feature is provided to minimize the compression doming by clamping a peripheral band of the end with a hold-down pad while the metal flowing is accomplished. This reduces the dome depth and results in a strengthened end having a dome depth very close to standard specifications.