The present invention relates to improvements in the method and apparatus for forming flanged can ends with curled edges. The improvements are intended for stamping circular or noncircular can ends, the latter being square, oval or the traditional triangular ham can ends being curled along the outer edges whereby they may be secured to a flanged can body by double seaming. Double seaming metal end closures to flanged can bodies, for example, those used for packing comestibles and the like requires an end with a prescribed configuration. More particular standards have been established defining the countersink radius the countersink wall length extending from the countersink to the end closure cover hook and the radial extension and curl configuration of the cover hook. Consequently, a conventional method of double seaming an end closure to an open ended container body includes interfolding the flange of the marginal end portion of the can body during double seaming the body flange with the closure cover hook by rolling or tucking the closure edges under the body flange to form five metallic layers. The pressing or ironing of the five layers tightly together against the upper side body wall of the container hermetically seals the open body end.
Closure ends are generally formed with a countersink groove and wall extending outwardly of the can to a radially disposed cover hook flange. The cover hook flange extends outwardly to the cover hook whereat it curls downwardly and inwardly relative to the can body outer side wall when the closure and can body are in their normal relationships as, for example, prior to double seaming. The cover hook is curled such that the outermost extreme edge of the cover hook has a smaller radius of curvature than the middle of the cover hook. Thus, the extreme edge of the cover hook is folded inwardly toward the center of the closure which causes the closure to be doubled back to some degree upon itself. This makes the process of forming the end closure in a single operation impossible.
In the past, techniques for producing round and nonround end closures having the required cover hook had been disclosed, see for example, U.S. patent to Douglas U.S. Pat. No. 1,890,936, which discloses an apparatus and a method for forming the complete end closure in two steps in different dies. The first step preforms the end such that the extreme edge of the cover hook extends generally downward but not inward (relative to its position in a container open upwardly). The second operation in a second die forms the cover hook extremity inwardly thus, the complete end closure is formed in two operations in two different dies. The problem with this technique is that in a high-speed operation it becomes very difficult to transfer the preformed end into the second die for final forming. That is to say that, in order to handle the preformed end same must be lifted out of the first die and transferred laterally to a second die whereat centering and depositing of the end in that die has to occur. In a process taking place at several hundred per minute the mechanism for carrying transversely and precisely positioning the preformed end into the final forming die is a problem. This is even a greater problem in connection with nonround ends wherein mere centering is not enough. Register with respect to the corners must be perfect in order to avoid jamming and misforming.
Attempts at overcoming this handling problem have been tried. One technique uses the concept of leaving a portion of the first die for preforming open or making same openable whereby the end can be slid laterally sideward from that die to the second die for final forming. Similarly, the second die also includes an open side or moveable die section designed to receive the sliding and preformed end closure. Such an arrangement is difficult and complicated to make and presents problems with respect to uniformly and completely forming a continuously made cover hook adequate for providing a proper hermetic double seam.
Another prior art approach for making an end closure with a curved cover hook included a first operation which formed the end and the second operation of roll forming to curl the edge. In order to keep up with the high speed of the preforming operation a number of curlers are required to tip the edge inward.