Abstract:
Over the years there have been numerous attempts to improve the can lid oftentimes found on aluminum beverage can lids. The aims have traditionally been to reduce costs and improve performance. These aims have been accomplished through a variety of means, such as creating different formations within the can lid to reduce the amount of metal used while maintaining performance levels. Here, step portions are utilized between the annular countersink and the center panel of the can lid that cause a curvature of the center panel or to simply provide an angled inside wall. These formations, thus, reduce the amount of metal used while maintaining quality and yielding the desired performace.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation-in-part of U.S. patent application Ser. No. 10/752,928 entitled “CAN LID CLOSURE AND METHOD OF JOINING A CAN LID CLOSURE TO A CAN BODY,” filed on Jan. 7, 2004 which is a continuation of U.S. patent application Ser. No. 10/153,364, now U.S. Pat. No. 6,702,142, entitled “CAN LID CLOSURE AND METHOD OF JOINING A CAN LID CLOSURE TO A CAN BODY,” filed on May 22, 2002 which was a continuation of U.S. patent application Ser. No. 09/456,345, now U.S. Pat. No. 6,499,622, entitled “CAN LID CLOSURE AND METHOD OF JOINING A CAN LID CLOSURE TO A CAN BODY,” filed on Dec. 8, 1999 for inventor/applicant Christopher G. Neiner, wherein each related application is incorporated by reference herein for all purposes. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates generally to containers, particularly to metallic beverage cans, and more particularly to metallic beverage can end closures adapted for interconnection to metallic beverage cans.  
       BACKGROUND OF THE INVENTION  
       [0003]     Aluminum cans are used primarily as containers for retail sale of beverages, typically in individual portions. Annual sales of such cans are in the billions and consequently, over the years, their design has been refined to reduce cost and improve performance. Typically, the can is formed from a single piece of metal, which is drawn and ironed, and has an open end. The can is filled with a beverage by means of the open end, and a can lid is then positioned over the open end and sealed to the can to contain the beverage therein and prevent contamination of the beverage. In some arrangements, the can has two open ends to which can lids are sealed.  
         [0004]     Cost reductions in can production may be realized in material savings, scrap reduction and improved production rates. Performance improvements may be functional in nature, such as better sealing and higher ultimate pressure capacity. Such improvements can allow the use of thinner sheet metal, which leads directly to material cost reductions. Performance improvements may also be ergonomic in nature, such as a can end configured to allow for easier pull tab access or better pouring characteristics.  
         [0005]     Beverage cans and ends, which are typically made from relatively thin sheet metal, must be capable of withstanding internal pressures approaching 100 psi (with 90 psi being an industry recognized requirement) without the can failing, such as by leaking or bulging. Additionally, these components must meet other specifications and requirements. For instance, the upper surface of the can lids must be configured to nest with the lower surface of the can bottoms so that the cans can be easily stacked one on top of the other. It is also desirable to have the can lids themselves nest with each other in a stacked arrangement for handling and shipping purposes prior to attaching the can lid to the can body. The ability to satisfy these functional requirements with the use of ever less material continues to be a goal for can manufacturers.  
         [0006]     There have been various beverage can lids developed having various unique geometric configurations in an effort to reduce material costs while still making can lids that meet the various industry requirements. For example, U.S. Pat. No. 6,065,634 describes a can lid design for reduced metal usage having a peripheral curl portion, an outwardly concave annular reinforcing bead, a frustoconical chuckwall inclined at an angle of between 40° and 60° with respect to an axis perpendicular to the center panel connecting the peripheral curl and the reinforcing bead, and a center panel connected to the interior portion of the annual reinforcing bead. It has been found that the can lid of U.S. Pat. No. 6,065,634 is susceptible to increased metal deformation during seaming and resulting failure at lower pressures.  
         [0007]     Other patents disclose can lids having modifications of the chuckwall and/or annular countersink that are designed to improve the strength of the can lids while saving material costs. Examples of these include U.S. Pat. Nos. 6,499,622, 6,561,004, and 6,702,142 to Neiner which are incorporated herein in their entirety by reference. Another pending application which attempts to make further improvements to the can lid by means of improving the countersink region is U.S. Patent Application Publication No. 20030173367 to Nguyen, et. al.  
         [0008]     There have also been a variety of other applications that have employed structures between the annular countersink and the center panel. Examples of such designs include U.S. Pat. Nos. 5,149,2358, 4,832,223, 4,796,772, 4,991,735, and 4,577,774, Reissue Pat. No. RE33,217, European Patent Application No. EP0103074, German Patent No. DE29906170, and Japanese Patent Application No. 2002-178072.  
         [0009]     One example of a prior art can lid configuration that employs a structure between the annular countersink and the center panel is depicted in  FIG. 1 . Referring to  FIG. 1  of the drawings, the reference numeral  100  generally designates a can lid having a step portion between the annular countersink and the center panel. The can lid  100  comprises a peripheral curl portion  108 , a chuckwall  114 , an annular countersink  112 , a center panel  110 , a first step portion  116 , a transitional portion  118 , a second step portion  120 , and a third step portion  122 . It should also be noted that the term “negative concavity” is relative to concavity in the “downward” direction toward the bottom of the can lid, and “positive concavity” is relative to concavity in the “upward” direction.  
         [0010]     Can lid  100  is generally circular in shape having the center panel  110 , also with a generally circular shape, at the center. Along the outer circumferential edge of the can lid  100  is the peripheral curl  108  portion, which is employed to form a double seam with a can body (not shown). Immediately adjacent to the peripheral curl portion  108  is the chuckwall  114  that extends radially inward toward the center of the can lid  100  and transitions downward to a lower depth than the peripheral curl portion  108 . Annular countersink  112  is then formed adjacent to the chuckwall  114  having a radius of curvature r a1  with positive concavity, where the lowest depth of the can lid  100  is located at the apex of the annular countersink  112 .  
         [0011]     As the annular countersink  112  transitions from the apex upward, as well as radially inward, a transitional portion  118  is employed. First step portion  116  with a radius of curvature r a2  with a negative concavity is formed between the annular countersink  112  and the step portion  118 . Second step portion  120 , having a radius of curvature r a3  and positive concavity, and third step portion  122 , having a radius of curvature r a4  and negative concavity are utilized to smoothly transition between the depth of the step portion  118  and the center panel  110 .  
         [0012]     Another example of a prior art can lid configuration that employs a structure between the annular countersink and the center panel is depicted in  FIG. 2 . Referring to  FIG. 2  of the drawings, the reference numeral  200  generally designates a can lid having a transitional portion and a raised bead between the annular countersink and the center panel. The can lid  200  comprises a peripheral curl portion  108 , a chuckwall  114 , an annular countersink  112 , a center panel  110 , a first step portion  216 , a transitional portion  214 , a second step portion  220 , a raised bead  222 , and a third step portion  224 .  
         [0013]     Can lid  200  is generally circular in shape having the center panel  110 , also with a generally circular shape, at the center. Along the outer circumferential edge of the can lid  200  is the peripheral curl  108  portion, which is employed to form a double seam with a can body (not shown). Immediately adjacent to the peripheral curl portion  108  is the chuckwall  114  that extends radially inward toward the center of the can lid  200  and transitions to a lower depth than the peripheral curl portion  108 . Annular countersink  112  is then formed adjacent to the chuckwall  114  having a relatively flat bottom parallel to the center panel  110 , where the lowest depth of the can lid  200  is located at the at the bottom portion of the annular countersink  112 .  
         [0014]     As the annular countersink  112  transitions from the apex upward, as well as radially inward, a transitional portion  214  is employed. First step portion  216  with a radius of curvature r b1  with a negative concavity is formed between the annular countersink  112  and the transitional portion  214 . Transitional portion  214  is at a depth that is approximately equal to center panel  110 . Second step portion  220 , having a radius of curvature r b2  and positive concavity, is located between the transitional portion  214  and the raised bead  222 , which has a radius of curvature r b3  with negative concavity and a height greater than the center panel  110 . Third step portion  224 , having a radius of curvature r b4  and positive concavity, is utilized to smoothly transition from the raised bead  222  to the center panel  110 .  
         [0015]     Yet another example of a prior art can lid configuration that employs a structure between the annular countersink and the center panel is depicted in  FIG. 3 . Referring to  FIG. 3  of the drawings, the reference numeral  300  generally designates a can lid having a step portion with a bevel between the annular countersink and the center panel. The can lid  300  comprises a peripheral curl portion  108 , a chuckwall  114 , an annular countersink  112 , a center panel  110 , and a step portion  316 .  
         [0016]     Can lid  300  is generally circular in shape having the center panel  110 , also with a generally circular shape, at the center. Along the outer circumferential edge of the can lid  300  is the peripheral curl  108  portion, which is employed to form a double seam with a can body (not shown). Immediately adjacent to the peripheral curl portion  108  is the chuckwall  114  that extends radially inward toward the center of the can lid  300  and transitions to a lower depth than the peripheral curl portion  108 . Annular countersink  112  is then formed adjacent to the chuckwall  114  having a radius of curvature r c1  with positive concavity relative to the top of the can lid  100 , where the lowest depth of the can lid  300  is located at the apex of the annular countersink  112 .  
         [0017]     As the annular countersink  112  transitions from the apex upward, as well as radially inward, step portion  316  with a radius of curvature r c2  with a negative concavity is formed between the annular countersink  112  and the center panel  110 . Additionally, on the outer surface of the step portion  316 , a beveled edge  318  is utilized.  
         [0018]     A last example of a prior art can lid configuration that employs a structure between the annular countersink and the center panel is depicted in  FIG. 4 . Referring to  FIG. 4  of the drawings, the reference numeral  400  generally designates a can lid having a raised bead between the annular countersink and the center panel. The can lid  400  comprises a peripheral curl portion  108 , a chuckwall  114 , an annular countersink  112 , a center panel  110 , a raised bead  416 , and a step portion  418 .  
         [0019]     Can lid  400  is generally circular in shape having the center panel  110 , also with a generally circular shape, at the center. Along the outer circumferential edge of the can lid  400  is the peripheral curl  108  portion, which is employed to form a double seam with a can body (not shown). Immediately adjacent to the peripheral curl portion  108  is the chuckwall  114  that extends radially inward toward the center of the can lid  400  and transitions to a lower depth than the peripheral curl portion  108 . Annular countersink  112  is then formed adjacent to the chuckwall  114  having a radius of curvature r d1  with positive concavity relative to the top of the can lid  400 , where the lowest depth of the can lid  400  is located at the apex of the annular countersink  112 .  
         [0020]     As the annular countersink  112  transitions from the apex upward, as well as radially inward, raised bead  416  is employed. Raised bead  416  has a radius of curvature r d2  with a negative concavity where the apex of the raised bead  416  is at a height greater than the center panel  110 . Transitional portion  418 , having a radius of curvature r d3  and positive concavity, couples the raised bead  416  to the center panel  110 .  
         [0021]     Each of these varying designs poses a particular subset of problems, such as difficulty in manufacturing, inability to withstand internal pressures, cost, and so forth. Therefore, there is a need for a method and/or apparatus that at least addresses some of the problems associated with conventional or prior art can lids and that provides better can lids that can save material costs while still withstanding internal pressures.  
       SUMMARY OF THE INVENTION  
       [0022]     The present invention provides a lid for a can body. Specifically, the lid comprises a center panel having a central axis that is perpendicular to a diameter of an outer rim of the lid, where the center panel has a height that varies as a function of radial distance relative from the central axis. Extending radially outward from the center panel is a first step portion having negative concavity and having a radius of curvature less than about 0.015 inches. A second step portion, then, extends radially outward from the first step portion having a positive concavity and having a radius of curvature less than about 0.015 inches. From there, an angled inner wall extends radially outward from the second step portion having an angle from a line extending through each end of the angled inner wall relative to the central axis of less than about 50°. Additionally, an annular countersink portion extends radially outward from the center panel, and a chuckwall extends from the annular countersink. Finally, a peripheral curl portion extends radially outward from the chuckwall.  
         [0023]     In another embodiment of the present invention, the chuckwall further comprises a number of other features. In particular, an arcuate portion extends radially outward from the annular countersink and is characterized by a radius of less than about 0.5 inches with a center point below the surface of the lid, wherein a line passing through the ends of the arcuate portion is at an angle with respect to the central axis of the center panel of from about 20° to about 80°. Additionally, a third step portion extending radially outward from the arcuate portion and characterized by a radius of at least 0.010 inches, with a center point above the surface of the lid is formed. A first transitional portion also extends radially outward from the step portion and being generally frustoconical and inclined at an angle with respect to the central axis of at least about 15° and less than about 25°. A second transitional portion extends radially outward from the first transitional portion and is characterized by a radius of at least 0.020 inches with a center point below the surface of the lid.  
         [0024]     In yet another some other embodiment of the present invention, a line passing through the ends of the angled inner wall is at an angle with respect to the central axis of the center panel is from about 25° to about 35° in one embodiment and is about 30° in another embodiment.  
         [0025]     In another embodiment of the present invention, the first step portion has a radius of curvature that is about 0.010 inches.  
         [0026]     In another embodiment of the present invention, the second step portion has a radius of curvature that is about 0.010 inches.  
         [0027]     In yet another embodiment of the present invention, the center panel is substantially domed or arcuate.  
         [0028]     In another embodiment, the diameter of the center panel is from about 1.4 to about 2.0 inches, and there is an annular countersink height of from about 0.030 to about 0.115 inches.  
         [0029]     The present invention also provides a method of forming a double seam joining a can body to a can lid, the can lid having a center panel having a central axis that is perpendicular to a diameter of an outer rim of the lid, wherein the center panel has a variable height relative to a radial distance relative to the central axis, a first step portion extending radially outward from the center panel, a second step portion extending radially outward from the first step portion, an angled inner wall extend radially outward from the second step portion having an angle from a line extending through each end of the angled inner wall relative to the central axis of less than about 50°, an annular countersink portion extending radially outward from the center panel, a chuckwall having an arcuate step portion and a transitional portion, wherein the chuckwall extends radially outward from the annular countersink, a peripheral curl portion extending radially outward from the chuckwall, and the can body having a can body flange. The method includes or comprises supporting the can body on a base plate and positioning the can lid on the can body with the transitional portion resting on the can body flange. Once positioned, a chuck is provided to engaging the can lid with the chuck so as to contact the annular countersink while leaving the arcuate step portion undeformed. The can and lid assembly are then rotated using the chuck to roll the peripheral curl and can body flange together to form an intermediate peripheral seam and to compress the intermediate peripheral seam against the chuck to form a double seam.  
         [0030]     In alternative embodiment of the present invention, another lid for a can body is provided. With this lid, there is a center panel having a central axis that is perpendicular to a diameter of an outer rim of said lid. Extending radially outward from said center panel portion is an an angled inner wall having an angle from a line extending through each end of said angled inner wall relative to said central axis of less than about 50°. Then, extending radially outward from said angled inner wall is an annular countersink portion. A chuckwall is also formed, which extends radially outward from said annular countersink. Extending radially outward therefrom is a peripheral curl portion.  
         [0031]     Some other additional embodiments of the present invention are also provided, namely, step portions at each end and a first step portion extending radially outward from said center panel having negative concavity and having a radius of curvature less than about 0.015 inches with a second step portion extending radially outward from said angled inner wall having a negative concavity and having a radius of curvature less than about 0.015 inches.  
         [0032]     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]     The accompanying drawings are incorporated into and form a part of the specification to assist in explaining the present invention. The drawings are intended for illustrative purposes only and are not intended as exact representations of the embodiments of the present invention. The drawings further illustrate preferred examples of how the invention can be made and used and are not to be construed as limiting the invention to only those examples illustrated and described. The various advantages and features of the present invention will be apparent from a consideration of the drawings in which:  
         [0034]      FIG. 1  depicts an elevational cross-sectional view of a portion of a conventional or prior art can lid having a step portion between the annular countersink and the center panel;  
         [0035]      FIG. 2  depicts an elevational cross-sectional view of a portion of a conventional or prior art can lid having a step portion and a raised bead between the annular countersink and the center panel;  
         [0036]      FIG. 3  depicts an elevational cross-sectional view of a portion of a conventional or prior art can lid having a beveled edge in the step portion between the annular countersink and the center panel;  
         [0037]      FIG. 4  depicts an elevational cross-sectional view of a portion of a conventional or prior art can lid having a raised bead between the annular countersink and the center panel;  
         [0038]      FIGS. 5A and 5B  depict elevational cross-sectional views of a portion of a can lid constructed in accordance with the invention;  
         [0039]      FIG. 6  depicts an elevational cross-sectional view of a portion of a can lid according to  FIG. 5  on a can body before forming of a double seam;  
         [0040]      FIG. 7  depicts an elevational cross-sectional view of the manner of stacking can lids of  FIG. 5  prior to seaming constructed in accordance with the invention;  
         [0041]      FIG. 8  depicts an elevational cross-sectional view of the manner of stacking filled cans according to  FIG. 5  of the present invention; and  
         [0042]      FIG. 9  depicts an elevational cross-sectional view of the chuck used to seam the can lid of  FIG. 5  to the can body;  
         [0043]      FIG. 10  depicts an elevational cross-sectional view of a second embodiment of the can lid  FIG. 5 . 
     
    
     DETAILED DESCRIPTION  
       [0044]     The present invention is described in the following text by reference to drawings of examples of how the invention can be made and used. The drawings are for illustrative purposes only and are not necessarily exact scale representations of the embodiments of the present invention. In these drawings, the same reference characters are used throughout the views to indicate like or corresponding parts. The embodiments shown and described herein are exemplary. Many details are well known in the art, and as such are neither shown nor described. It is not claimed that all of the details, parts, elements, or steps described and shown were invented herein. Even though numerous characteristics and advantages of the present invention have been described in the drawings and accompanying text, the description is illustrative only, and changes may be made, especially in matters of arrangement, shape and size of the parts, within the principles of the invention to the full extent indicated by the broad general meaning of the terms used in the claims. The dimensions provided in the description of the lids are tooling dimensions and the actual dimensions of can lids manufactured in accordance with the present invention may be slightly different from the tooling dimensions. The words “extend radially outward,” “extend radially inward,” “extend radially downward,” and “extend radially upward” as used in this document mean that a part or portion extends in the noted direction from another part referred to. It does not, however, necessarily mean that the parts are joined or connected to each other; there could be other parts or portions between the two described portions that are neither shown nor described. When the words “joined” or “connected” are used in this document, they have their normal meanings. The word “up”, as used in this document, is used in reference to a can lid as it would be appear when placed on a flat surface with the tab on the face away from the top of the flat surface, such as a can lid would appear when looking down onto the top of a beverage can. Moreover, the term “negative concavity” is relative to concavity in the “downward” direction of the bottom of the can lid, and “positive concavity” is relative to concavity in the “upward” direction.  
         [0045]      FIGS. 5A and 5B  are a cross-sectional view of a portion of a can lid  510 , illustrative of the currently preferred embodiment of the present invention. Can lid  510  comprises a center panel  512 , a step portion,  552 , a step portion  516 , an angled inside wall  518 , an annular countersink  522 , an arcuate portion or arcuate chuckwall  532 , a step portion  534 , a transitional portion  536 , a step portion  537 , and a peripheral curl portion  538 . Additionally, annular countersink  522  comprises an exterior wall  528 , a curved bottom portion  524 , and an interior wall  520 .  
         [0046]     Can lid  510  is preferably made from sheet metal, although other materials can also be used. Typically, an aluminum alloy is used, such as aluminum alloy 5182. The sheet metal typically has a thickness from about 0.007 to about 0.010 inches. The sheet metal may be coated with a coating (not shown) on at least one side. This coating is usually provided on that side of the sheet metal that will form the interior of the can. Those skilled in the art will be well acquainted with the methods of forming can lids as described herein.  
         [0047]     The can lid  510  has a center panel  512 . The center panel  512  is generally circular in shape but may be intentionally noncircular. The center panel  512  may have a diameter d, of from about 1.3 to about 2.0 inches. Although the center panel  512  is shown as being generally peaked or domed, it may also have a generally flat configuration as well, and is not necessarily limited to the peaked or domed configuration shown. The center panel  512  has a central axis  514  that is perpendicular to a diameter d 2  of the outer rim, or peripheral curl portion  538 , of can lid  510 . Diameter d 2  is from about 2.25 to 2.50 inches, with a preferred diameter of 2.34 inches. The diameter d 1  of center panel  512  is preferably less than 80% of the diameter d 2  of the outer rim.  
         [0048]     Around the outside diameter d 1  of the center panel  512  is a step  552  having a radius of curvature r 1 , with a negative concavity that allows transition to a lower depth, that is from about 0.0060 to about 0.015 inches. Step portion  516 , then, is adjacent to step portion  552 , having a radius of curvature r 2 , with a positive concavity that allows transition to a lower depth, that is from about 0.010 to about 0.015 inches.  
         [0049]     Descending from the bottom of the step portions  516  and  522  is an angled inside wall  518 . Specifically, one end of step portion  516  is attached to a step portion  556  of angled inside wall  518 , having a radius of curvature r 3  with negative concavity, and interior wall  520  of annular countersink  522  is attached to a step portion  554  of angled inside wall  518 , having a radius of curvature r 4  with negative concavity. Angled interior wall  518  is preferably a straight or flat angled interior wall  518 ; however, it is possible to have arcuate wall with a negative or positive concavity. In either case, however, a straight line can drawn between the step portion  556  and the step portion  554  that forms an acute angle a 1  with respect to central axis  514  of the center panel  512  of about 15° to about 50°.  
         [0050]     Specifically, in one configuration, the step portion  554  extends radially inward from interior wall  520  toward the remainder of the angled inside wall  518 , where the radius of curvature r 3  that is from about 0.006 to about 0.03 inches. Additionally, the step portion  554  extends radially inward from the angled inside wall  518 , where the radius of curvature r 4  that is from about 0.006 to about 0.03 inches. Thus, the angled interior wall  518  can be formed of a surface that includes a pair of curved junctures or step portions with the remainder of the angled interior wall  518  extending linearly and tangentially therebetween; however, it is also possible in an alternative configuration to have a completely arcuate angled inside wall  518  forming a uniform curve or substantially uniform curve.  
         [0051]     The annular countersink  522  is formed from the interior wall  520  and an exterior wall  528 , which are spaced apart and extend radially outward from a curved bottom portion  524 . The inner wall  520  and the outer wall  528  are generally flat and may be parallel to one another and to the central axis  514  but either or both may diverge by an angle of about as much as 15°. Bottom portion  524  preferably has a radius of curvature r 4  with positive concavity. Radius of curvature r 4  is from about 0.009 to about 0.030 inches. The center panel  512  has a depth h 1  of from about 0.05 to about 0.15 inches. The bottom portion  524  of annular countersink  522  may also be formed with different inner and outer radii extending radially outward from a flat portion.  
         [0052]     This particular configuration that includes the formation of the angled inside wall  518 , step portion  516 , and step portion  552  allows for easier bowing or doming of the center panel  512 . As can be seen in  FIG. 1 , conventional or prior art can lids typically utilize a center panel, such as center panel  110  of  FIG. 1 , that employs a uniform depth h 1  of the center panel  512 . With center panel  518  as shown according to the present invention, the depth h 2  is variable as a function of the radial distance from the center axis  514 , having a generally negative concave shape. This configuration allows for the reduction in the amount of metal used in the lid without having some existing problems. Specifically, the use of a negatively concaved center panel  512  increase the internal volume of a can, which in turn reduces internal pressure, so tension can be decreased so as to reduce the probability of premature or unexpected failure of seams within the can lid  510 . Additionally, it is also possible, but not preferable, for the center panel  514  to have a positive concave shape.  
         [0053]     In addition to the particular structures employed between the annular countersink  522  and the center panel  512 , the outer wall  528  contains a second chuck contacting portion  550  that is one of two points at which the chuck  544  comes in contact with the interior of the can lid  510  during the seaming operation, the other point being the transitional portion  536 . An arcuate portion  532  extends radially outward and upward from the outer wall  528 . The arcuate portion  532  is shown as having a radius of curvature r 5  with negative concavity that is from about 0.100 to about 0.300 inches. The preferred design parameter for radius of curvature r 5  is 0.0185 inches. The arcuate portion  532  is configured such that a line passing through the innermost end of arcuate portion  532 , near the terminus of curved juncture  530 , and the outermost end of the arcuate portion  532 , near the beginning of step portion  534 , forms an acute angle with respect to central axis  514  of the center panel  512 . This acute angle is from about 20° to about 80°. The preferred lid design uses an angle of about 50°.  
         [0054]     The step portion  534  extends radially outward from the arcuate portion  532 . Step portion  534  is preferably curved with a radius of curvature r 6  with positive concavity from about 0.02 to about 0.06 inches. The current lid design parameter for radius of curvature r 6  is 0.0446 inches.  
         [0055]     First transitional portion  536  extends radially upward and slightly outward from step portion  534 . First transitional portion  536  forms an angle a 2  with respect to central axis  514  of the center panel  512 . This angle is from about 15° to about 25°. As shown in  FIG. 6 , angle a 2  is intended to be larger than angle a 3 , which is measured relative to central axis  514 . Angle a 3  is preferably at least about 2° to aid in removing the can from the chuck  544  after the seaming operation and preferably less than about 8°. The current design parameter for angle a 3  is about 4°.  
         [0056]      FIG. 6  shows can lid  510  resting on can body  540 , and particularly resting on flange  542  of can body  540 . The radius r 6  of the can flange  542  is slightly smaller than the step portion  537  radius (not shown). Because the flange radius r 6  and second transitional portion radius are very similar, the lid easily centralizes on the can for seaming. The can body has an inside neck diameter d 3  from about 2.051 to about 2.065 inches, with a target diameter of about 2.058 inches.  
         [0057]     The functional purpose of the chuck  544  in conjunction with can lid  510  is to create a double seam between the can flange  542  and the peripheral curl  538 . This is accomplished through the rotation of the chuck  544  so that the peripheral curl  538  can be rolled under the can flange  542  and compressed against the can body  540 . Thus, a double seam  554   b , as shown in  FIG. 8 , can be formed.  
         [0058]      FIG. 7  shows the manner in which a plurality of can lids  510   a  and  510   b  stack for handling, packaging, and feeding a seaming machine. Underside of peripheral curl  538   a  bears against upper portion of peripheral curl  538   b  of adjacent can lid  510   b . Can lid  510   a  is supported and separated from can lid  510   b  by a height h 3  sufficient to accommodate the thickness of a pull-tab (not shown). In this manner, can lids  510  are compactly and efficiently handled and are more readily positioned for magazine feeding in a mechanized seaming operation.  
         [0059]      FIG. 8  shows the manner of stacking filled can  564   a , closed and sealed according to the present invention on a like filled can  564   b . Stand bead  566   a  rests upon double seam  554   b.    
         [0060]      FIG. 9  shows those portions of the chuck  544  shown in  FIG. 6 , and described above, and also provides a more detailed view of the upper frustoconical portion  546 , lower curved portion  580 , and the transitional portion  582 . Specifically, the upper frustoconical portion  546  and the lower curved portion  580  provide a contact portions for the transitional portion  563  and step portion  534  while the peripheral curl  538  is rolled under the can flange  542  and compressed against the can body  540 . Additionally, the transitional portion  582  is designed such that it should not contact the chuckwall  532  during a seaming operation.  
         [0061]     Additionally, there are other configurations that can include an angled inner wall, such as the angled inner wall  518 . Referring to  FIG. 10  of the drawings, a second embodiment of the present invention of a can lid  510  employing an angled inner wall  518  is depicted. This particular embodiment differs from that of  FIG. 5  in that there are not multiple structures interposed between angled inner wall  518  and center panel  512 .  
         [0062]     As with  FIG. 5 , the center panel  512  is generally circular in shape but may be intentionally noncircular. The center panel  512  may have a diameter d 1  of from about 1.3 to about 2.0 inches. Additionally, the central axis  514 , which is substantially located at the center of can lid  510 , is perpendicular to the diameter d 1  of the outer rim of the can lid  510 . However, in contrast to  FIG. 5 , the center panel  512  is shown as having substantially flat shape with a relatively uniform depth h 1 ; however, it is possible to have a domed or arcuate shape.  
         [0063]     Around the outside diameter d, of the center panel  512  is step portion  556  having radius of curvature r 4 , with a negative concavity that allows transition to a lower depth, which is from about 0.0060 to about 0.015 inches. Step portion  556 , then, is adjacent to angled inside wall  518 . Descending from the bottom of the step portion  556  is angled inside wall  518 . Angled interior wall  518  is preferably a straight or flat; however, it is possible to have arcuate wall with a negative or positive concavity. At the end of angled inside wall  518  is step portion  554 . Step portion  554  is located between angled inside wall  518  and countersink  522 , having a radius of curvature r 4  with negative concavity that is from about 0.0060 to about 0.015 inches. A straight line can, thus, be drawn between the step portion  556  and the step portion  554  that forms an acute angle a 1  with respect to central axis  514  of the center panel  512  of about 15′ to about 50°.  
         [0064]     With this configuration, there are a variety of advantages over conventional can lids. Specifically, this particular configuration, thus, would allow for a substantial reduction in the amount of metal used in the production of can lid  510  resulting in a lower cost of production. Additionally, the use of the angled inner wall  518  would help to decrease tension within the center panel  512 , which increase the structural integrity of the can lid  510  and which reduces the potential for failure.  
         [0065]     The restrictive description and drawings of the specific examples above do not point out what an infringement of this patent would be, but are to provide at least one explanation of how to use and make the invention. The limits of the invention and the bounds of the patent protection are measured by and defined in the following claims.  
         [0066]     Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.