Tooling arrangement for end closure scoring
SUMMARY OF THE INVENTION 
     The present invention relates generally to an easy-opening metal can and, more particularly to the formation of the opening score line. 
     Currently, metal cans for packaging of foodstuffs, soft drinks, beer and the like are produced with an enamel coating covering the interior surfaces of the container. This coating protects the metal can walls from possibly corrosive effect of the container contents. However, current scoring methods frequently result in enamel loss and, hence, necessitate coating repair before the end panel may be attached to the can body. 
     It is, therefore, the primary object of the present invention to provide a means of forming the opening score line without loss of the enamel protective coating on the reverse side of the end panel. This is accomplished by controlling the angular relationship of the score punch and anvil, while simultaneously confining the flow of metal displaced by the score line formation. 
     It is a further object to provide an improved means of score line formation which is inexpensive and compatible with existing production equipment. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The various features and advantages of the improved score line tooling arrangement of this invention will be more apparent from the following detailed description when considered in connection with the accompanying drawing wherein: 
     FIG. 1 is a cross-sectional view of the punch and anvil used to create the score. 
     FIG. 2 is a side perspective view of the tooling shown in FIG. 1. 
     FIG. 3 is an enlarged, fragmental sectional view similar to FIG. 1. 
     FIG. 4 is an enlarged fragmental sectional view similar to FIG. 3, illustrating the formation of the score line. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The improved tooling arrangement of the present invention comprises a punch 1 and an anvil 2 between which a sheet metal blank 3 may be positioned to have a score line 10 formed therein. The punch 1 has a flat, substantially horizontal bottom face 4 and a lateral outer face 5 which meet at a relatively sharp corner 6 in order that a similar sharp corner will be formed in the score line 10. 
     The anvil 2 has a flat, substantially horizontal top face 7, a lateral inner face 8 extending downwardly from the top face 7 and a substantially vertical side face also extending downwardly therefrom. The top face 7 meets both the inner face 8 and the side face 9 at relatively sharp corners 11 and 12 respectively. 
     The lateral faces 5 and 8 overlap each other in a horizontal direction as indicated by the X dimension in FIG. 3. 
     As the punch 1 and the anvil 2 are moved together against the blank 3, metal is displaced by tool surfaces 4, 5, 7 and 8. Although the mechanism is not fully understood, it has been observed that retention of the enamel coat 3a requires that metal displacement be along laminar streamlines parallel to the metal/enamel interface 3b and that stretching of this interface 3b be minimized. It has further been observed that these requirements can be met by controlling the angular relationship of the punch 1 and the anvil 2 while simultaneously confining the displaced metal. Specifically, punch angles A of 90°-110° and anvil angles B of 25°-35° have been found to be effective, with a punch angle A of 90° and an anvil angle B of 30° being optimum. 
     The metal confinement may be achieved by simultaneously forming an anti-fracture score line 14 when the opening score line 10 is being formed. The anti-fracture score line 14 is preferably formed concentric with, and radially inward of, the opening score line 10 by conventional tool member 13 held within a recess 15 in the center of the punch 1. 
     Experiments with 0.0130-0.0135 inch thick aluminum blanks indicate that an overlap (X) of 0.0020 inches and an anvil depth (H) of 0.0180 inches will yield an opening score line 10 with a 0.0023 inch residual thickness wherein the enamel coat 3a on the reverse side of the blank remains substantially in place with only a slight reduction in thickness. The experiments further reveal that the depth of the anti-fracture score line 14 and the distance between the opening score line 10 and the anti-fracture score line 14 are not critical variables but, rather, may be chosen with a wide degree of latitude.