1. Field of the Invention
The invention relates generally to presses and, more particularly, to shell presses and associated methods for forming container closures or ends, commonly referred to as shells. The invention also relates to die assemblies for shell presses.
2. Background Information
The forming of can ends or shells for can bodies, namely aluminum or steel cans, is generally well-known in the art.
There is an ongoing desire in the can-making industry to manufacture shells as rapidly and efficiently as possible. Among the ways companies have attempted to achieve these objectives are: (1) to increase the number of pockets in the die set, within which shells can be formed; and (2) to increase the speed (e.g., strokes per minute (spm)) at which the shell press operates. In general, with each stroke of the shell press ram, one shell is formed in each tooling pocket of the die assembly. Thus, a 24-out die assembly, for example, which has 24 tooling pockets, is capable of forming 24 shells, per stroke. U.S. Pat. No. 5,491,995, which is hereby incorporated herein by reference, discloses an example of a relatively high capacity (e.g., without limitation, operating speed of up to 400 spm, or more) end shell manufacturing system having a 24-out die assembly.
However, forming shells at relative high speeds generates heat. The heat, which is caused by the friction associated with drawing the metal over forming surfaces of the die assembly and/or clamping the metal between various pressure pads and drawing it through reduced tooling clearances to provide a desired shape, can be excessive, resulting in thermal expansion of the die shoes. Among other disadvantages, such thermal expansion undesirably shifts tooling and/or reduces critical clearances between cutting and/or forming tools. Consequently, tooling wear or damage can result and/or certain features of the end shells are manufactured out-of-specification. For example, thinned spots can be created in the material from which the end shell is manufactured, leading to a loss in buckle pressure performance in the final product.
The foregoing difficulties have been exacerbated by the development of new shell designs having aggressive material thicknesses and shapes. For example, some shells require reduced material thickness and/or have a relatively complex geometry. Such shapes often necessitate additional pressure pads and increased forming pressures in order to properly manufacture the end shells.
Prior proposals that attempted to address thermal expansion of the die assembly tooling (e.g., without limitation, upper and lower die shoes) involved aligning the upper tooling with respect to the lower tooling in the die assembly in a manner intended to compensate for the thermal expansion. Other proposals require coolant (e.g., chilled water) to be pumped throughout the die assembly, for example, to reduce the rate and amount of thermal expansion of the die shoes. However, estimating and establishing the proper aligning of the upper tooling with respect to the lower tooling is a time-consuming process, and it can be difficult to maintain the desired alignment. Similarly, systems that add coolant or other suitable additional cooling or heating mechanisms to the die assembly to compensate for thermal expansion, are costly to install and maintain.
There is, therefore, room for improvement in shell presses, and in die assemblies and associated methods therefor.