Abstract:
High strength beverage end shells formed in high speed, commercial production of an aluminum alloy having a specific range of constituents, especially magnesium within a specific range.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This claims the benefit of U.S. Patent Application Ser. No. 61/496,624 filed Jun. 14, 2011, the disclosure of which is hereby incorporated by reference as if set forth in its entirety herein. 
     
    
       [0002]    This application relates to metal packaging, and more particular to aluminum beverage can ends and seamed cans. 
       BACKGROUND 
       [0003]    There are at least three types of light weight or high strength beverage can ends that have been produced in commercial quantities since the 1990&#39;s. Each of these high strength end type has, among other things, the attribute of a smaller diameter center panel as a percentage of the seam diameter. 
         [0004]    Crown Cork &amp; Seal first developed its SuperEnd high strength can end, such as that disclosed in U.S. Pat. No. 6,065,634. Later, Metal Container Corporation developed its Lid Of The Future end, such as disclosed in U.S. Pat. No. 7,100,789 and Container Development Corporation Ltd. developed its CDL end, such as disclosed in  FIG. 13  of U.S. Pat. No. 7,819,275. 
         [0005]    Crown Cork &amp; Seal also identified improvements to the SuperEnd shell provide disclosed in the U.S. Pat. No. 6,065,634 patent. U.S. Pat. No. 7,370,774 in  FIG. 4B  and U.S. Pat. No. 7,591,392 in  FIGS. 6 and 7  illustrate, among other things, improved end that includes a weakening feature or a weakened configuration to improve leaking performance of failed ends. 
         [0006]    Most conventional high strength ends are formed of a 5182 alloy having the following maximum limits of constituents: 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Other 
                   
               
             
          
           
               
                   
                 Si 
                 Fe 
                 Cu 
                 Mn 
                 Mg 
                 Cr 
                 Zn 
                 Ti 
                 Each 
                 Total 
                 AL 
               
               
                   
                   
               
             
          
           
               
                 5182 
                 0.2 
                 0.35 
                 0.15 
                 0.20-0.50 
                 4.0-5.0 
                 0.10 
                 0.25 
                 0.10 
                 0.05 
                 0.15 
                 Rest 
               
               
                   
               
             
          
         
       
     
         [0007]    The source for alloy specifications is the Aluminum Association of Arlington, Va. 
         [0008]    5182 aluminum is produced in massive quantities to produce the many billions of high strength beverage can ends manufactured and seamed each year throughout the world. Many commercial high strength can ends are made from 0.0082 inch 5182 alloy. 
         [0009]    Several dozen billion beverage can ends are manufactured per year in the United States, and several dozen beverage can ends are manufactured per year in the rest of the world. These vast quantities require vast quantities of aluminum. 
         [0010]    The beverage can industry has specification for various parameters, such as a burst strength requirement of an average of 90 psi and a minimum of 85 psi. 
       SUMMARY 
       [0011]    High strength beverage end shells formed in high speed, commercial production of an aluminum alloy having a specific range of constituents, especially magnesium within a specific range, are disclosed. 
         [0012]    A method of forming a high strength can end in commercial quantities comprises the steps of (i) providing from a coil a sheet of an aluminum alloy having between 3.0% and 4.5% magnesium; (ii) forming high strength beverage end shells from the aluminum alloy coil in a shell press operating at least at 180 strokes per minute to produce 4140 shells per minute; (iii) whereby, when the seamed can ends are fully aged, the aged ends satisfy a burst pressure specification of a minimum of at least 80 psi and an average of at least 90 psi. High strength ends include modern, commercially available ends and their variants. Preferably, the aluminum alloy has between 3.5% and 4.5% magnesium. 
         [0013]    The ends may be configured such that the aged seamed ends satisfy a burst pressure specification of a minimum of at least 85 psi, especially wherein the burst pressure specification requires substantially all the aged seams end to satisfy the minimum burst pressure requirement and/or satisfaction of the burst pressure specification requires commercial acceptance by a beverage company. 
         [0014]    Preferably, the structure of the shell includes a center panel, a cover hook, and an inclined wall located between the center panel and a peripheral curl, the inclined wall is inclined at an inclined wall angle of at least 20 degrees from vertical. Also, the structure of the shell preferably includes a countersink bead extending between the center panel and the inclined wall. The inclined wall is a multipart wall that extends between the countersink bead and the peripheral curl. 
         [0015]    The inclined wall preferably includes an upper portion and a lower portion that are joined at a juncture, the upper portion is defined between a first point at an innermost point of the peripheral curl and the juncture, and the lower portion is defined between the juncture and a second point that is defined by an intersection of a horizontal projection from the plane of the center panel with the inclined wall or outer wall of the countersink bead. 
         [0016]    The inclined wall angle may be measured between the first point and the second point, such that a lower wall angle measured between the second point and the juncture is at least 28 degrees, preferably the inclined wall angle is between approximately 23 degrees and approximately 60 degrees and the lower wall angle is between approximately 32 degrees and approximately 55 degrees, and more preferably the inclined wall angle is between approximately 25 degrees and approximately 60 degrees and the lower wall angle is between approximately 34 degrees and approximately 53 degrees. 
         [0017]    The lower wall angle measured between the second point and the juncture preferably is at least 33 degrees. This inclined wall angle preferably is between approximately 23 degrees and approximately 60 degrees and the lower wall angle is between approximately 34 degrees and approximately 53 degrees. 
         [0018]    The present invention encompasses a system for manufacturing beverage end shells in commercial quantities from a coil of aluminum alloy sheet, comprising (i) a shell press operating at least at 180 strokes per minute producing at least 4140 beverage end shells per minute; (ii) each shell: including a center panel, a cover hook, and an inclined wall located between the center panel and a peripheral curl, the inclined wall is inclined at an inclined wall angle of at least 20 degrees from vertical; and is formed of an aluminum alloy having between 3.0% and 4.5% magnesium; (iii) whereby, when the seamed can ends are fully aged, the aged ends satisfy a burst pressure specification of a minimum of at least 80 psi and an average of at least 90 psi. Preferably, the aluminum alloy has between 3.5% and 4.5% magnesium. 
         [0019]    The structure preferably includes a countersink bead extending between the center panel and the inclined wall. And the inclined wall may be a multipart wall that extends between the countersink bead and the peripheral curl. Thus, the inclined wall includes an upper portion and a lower portion that are joined at a juncture, the upper portion is defined between a first point at an innermost point of the peripheral curl and the juncture, and the lower portion is defined between the juncture and a second point that is defined by an intersection of a horizontal projection from the plane of the center panel with the inclined wall or outer wall of the countersink bead. 
         [0020]    The inclined wall angle may be measured between the first point and the second point such that it is at least 28 degrees. Preferably, the inclined wall angle is between approximately 23 degrees and approximately 60 degrees and the lower wall angle is between approximately 32 degrees and approximately 55 degrees. More preferably, the inclined wall angle is between approximately 25 degrees and approximately 60 degrees and the lower wall angle is between approximately 34 degrees and approximately 53 degrees. 
         [0021]    The lower wall angle measured between the second point and the juncture such preferably is at least 33 degrees. Using this measurement, the inclined wall angle is between approximately 23 degrees and approximately 60 degrees and the lower wall angle is between approximately 34 degrees and approximately 53 degrees. 
         [0022]    The present invention also encompasses plural beverage can end shells formed in a commercial shell press operating at least at 180 strokes per minute and at least 4140 shells per minute. Each one of the plural shells comprises (i) a center panel, a cover hook, and an inclined wall located between the center panel and a peripheral curl, the inclined wall is inclined at an inclined wall angle of at least 20 degrees from vertical; (ii) the shell formed of an aluminum alloy having between 3.0% and 4.5% magnesium; (iii) whereby, when the seamed can ends are fully aged, the aged ends satisfy a burst pressure specification of a minimum of at least 80 psi and an average of at least 90 psi. Preferably, the aluminum alloy has between 3.5% and 4.5% magnesium. The structure of the end shells preferably includes a countersink bead extending between the center panel and the inclined wall. 
         [0023]    The inclined wall may be a multipart wall that extends between the countersink bead and the peripheral curl. The inclined wall thus includes an upper portion and a lower portion that are joined at a juncture, the upper portion is defined between a first point at an innermost point of the peripheral curl and the juncture, and the lower portion is defined between the juncture and a second point that is defined by an intersection of a horizontal projection from the plane of the center panel with the inclined wall or outer wall of the countersink bead. 
         [0024]    The inclined wall angle may be measured between the first point and the second point. A lower wall angle may be measured between the second point and the juncture such that it is at least 28 degrees. Preferably the inclined wall angle is between approximately 23 degrees and approximately 60 degrees and the lower wall angle is between approximately 32 degrees and approximately 55 degrees. More preferably the inclined wall angle is between approximately 25 degrees and approximately 60 degrees and the lower wall angle is between approximately 34 degrees and approximately 53 degrees. 
         [0025]    The lower wall angle measured between the second point and the juncture may be at least 33 degrees. Thus, the inclined wall angle preferably is between approximately 23 degrees and approximately 60 degrees and the lower wall angle is between approximately 34 degrees and approximately 53 degrees. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0026]      FIG. 1  is a flow chart showing the shell making processes; and 
           [0027]      FIG. 2  is a cross sectional diagram of an example high strength end shell. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    In addition to 5182 aluminum, 5042 aluminum alloy is also widely manufactured. 5042 aluminum has the following constituents: 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Other 
                   
               
             
          
           
               
                   
                 Si 
                 Fe 
                 Cu 
                 Mn 
                 Mg 
                 Cr 
                 Zn 
                 Ti 
                 Each 
                 Total 
                 AL 
               
               
                   
                   
               
             
          
           
               
                 5042 
                 0.2 
                 0.35 
                 0.15 
                 0.20-0.50 
                 3.0-4.0 
                 0.10 
                 0.25 
                 0.10 
                 0.05 
                 0.15 
                 Rest 
               
               
                   
               
             
          
         
       
     
         [0029]    The inventor has demonstrated that SuperEnd end shells can be made from 5042 alloy, even though the end shells would like end shells made from 0.0082 inch thick 5042 alloy have an average buckle pressure of only about 85 psi when aging is simulated by heating the seamed ends at 90 degrees C. for 30 minutes. Buckle strength was determined by seaming aged ends onto cans, then pressurizing the can incrementally. A gauge records the pressure at the point of failure. 
         [0030]    The inventor surmises that for commercial SuperEnd ends and other high strength ends, an alloy having a range of constituents that overlaps some of the ranges of 5042 alloy and 5182 alloy constituents would be preferred. 
         [0031]    Even just a few years ago, it would not have been feasible to customize aluminum alloy between industry standard 5182 and 5042 in sufficient quantities because of high cost and inconsistent properties, but the capability of mills to produce consistent product of a customized chemistry at high capacity has improved. 
         [0032]    The perceived lack of uniformity in any material other than 5182 or like standardized, mass produced material created a disincentive to switching to new materials for commercial high strength beverage can ends because essentially all ends must meet minimum specifications for carbonated soft drink, beer, or other beverage uses. If a minimum buckle strength would be specified, as is typically required by commercial specifications of beverage companies, then the aluminum sheet must be sufficiently thick such that the worst or weakest coils of aluminum satisfy the buckle strength requirement. Accordingly, even up to several years ago, many believed that the lack of uniformity in customized aluminum alloy made its use infeasible for beverage can ends. 
         [0033]    Further, many believed that switching from 5182 to a weaker material was unwise because 5182 alloy had the best combination of strength and ductility. 5182 alloy has proven to be sufficiently brittle such that the score about the tear panel would consistently propagate all the way around the tear panel. In other words, brittle material was a benefit to the opening process. Sufficiently brittleness to enhance opening has become even more important as the beverage industry has converged on large opening, oval ends, which inherently are more difficult to open compared with smaller, round opening ends. 
         [0034]    An aluminum alloy that the inventor surmises provides an optimum combination of ductility (that is, brittleness) for good score propagation, strength for burst pressure resistance, and cost by reducing the amount of magnesium and other elements that promote strength is provided by an aluminum alloy provided below: 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Other 
                   
               
             
          
           
               
                 Si 
                 Fe 
                 Cu 
                 Mn 
                 Mg 
                 Cr 
                 Zn 
                 Ti 
                 Each 
                 Total 
                 AL 
               
               
                   
               
               
                 0.2 
                 0.35 
                 0.15 
                 0.20-0.50 
                 3.0-4.5 
                 0.10 
                 0.25 
                 0.1 
                 0.05 
                 0.15 
                 Rest 
               
               
                   
               
             
          
         
       
     
         [0035]    Preferably, the magnesium content would be approximately 4.0 percent. 
         [0036]    A system  110  includes a conventional shell press  120  that includes multiple (conventional) tools for forming multiple shells  140  per stroke. Most commercial shell press machines operate at least at 180 strokes per minute and have a minimum of 23 or 24 tools such that each stroke produces shells at a rate of at least 4140 shells per minute. Shell press  120  may be any commercial press, such as produced by Stolle Machinery, Inc. 
         [0037]    A coil  101  of an aluminum alloy sheet having between 3.0% and 4.5% magnesium, and preferably having the chemistry provided above, is fed into shell press  120  to produce high strength end shells at a commercial rate. 
         [0038]    Shells  140  are conveyed to a conventional conversion press, such as produced by Minter Machine Company, where a tab is applied. 
         [0039]    A high strength can end formed by system  110  of an aluminum alloy having between 3.0% and 4.5% magnesium, more preferably having between 3.5% and 4.5% magnesium preferably having the chemistry provided above, are provided. A first example of a high strength can end is a SuperEnd can end shell  10   a,  as provided by Crown Cork &amp; Seal Company and shown in  FIG. 2 . End shell  10   a,  a center panel  12   a,  a countersink bead  14   a,  an inclined wall  16   a,  and a peripheral curl  18   a.  Center panel  12   a  merges into inner wall  30   a  of the countersink bead  14   a  at a transition  30   a.  An arcuate bottom  34   a  extends downwardly from a lower portion of inner wall  30   a.  An outer wall  36   a  of bead  14  a extends upwardly from an outermost portion of bottom  34   a.    
         [0040]    Wall  16   a  includes a lower wall  42   a  and an upper wall  44   a.  As shown in the figure, lower wall  42   a  extends from an uppermost portion of bead outer wall  34   a  and joins upper wall  44   a  at a juncture  46   a.    
         [0041]    Peripheral curl  18   a  includes a seaming panel  60   a  and a cover hook  62   a.  A first point  48   a  is defined at the junction of the uppermost end of upper wall  44   a  with the innermost end of seaming panel  60   a  or peripheral curl  18   a.  A second point  50   a  is defined where a horizontal line L is extended from the plane of center panel  12   a  to intersect with wall  16   a.  For measuring other high strength end shells, the first point, juncture (if any), and second point may be defined as described above.