Abstract:
For years, can bottoms have been formed to provide structural integrity for cans, which include many different configurations. A novel profile for a container bottom is shown herein. The bottom structure includes a multi-radial domed central panel extending from its outside edge to a downwardly projecting substantially cylindrical inner leg portion. The inner leg portion extends to a generally semi-toroidal nose portion. The outside of the nose portion extends to an upwardly and outwardly inclined outer leg portion. The outer leg portion is connected to an outwardly inclined peripheral portion. The peripheral portion is connected to the lower end of the generally cylindrical sidewall portion.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 60/680,782, entitled “CONTAINER BOTTOM AND METHOD OF MANUFACTURE,” filed on behalf of Mahesh Rajagopalan, Charles E. Brossia, Carl J. Szwargulski, and Michael Jansma, which is hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates generally to the design and manufacture of drawn and ironed beverage containers (cans), and in particular to an improved design for the can bottom structure and the method of manufacturing the improved can design. 
       BACKGROUND OF THE INVENTION 
       [0003]    Two-piece aluminum containers are used extensively for packaging beverages such as beer, carbonated soft drinks, and tea. The two-piece containers (cans) are comprised of a can body, which is typically made from lightweight materials, such as aluminum or aluminum alloys, and a can lid, which forms the top of the container. After the beverage has been introduced into the internal cavity formed by the can body, the can lid is placed on the open end at the top of the can body, and the can body and can lid are joined together to form a sealed container for the beverage contained therein. 
         [0004]    The can body is manufactured by a method called drawing and ironing. The process begins with a plurality of generally circular pieces or blanks being punched from a flat sheet of material, which is typically packaged in large rolls. Each blank is then drawn to produce relatively shallow cup-shaped pieces. Next, in a sequence of ironing operations, the cup is placed over a punch and forced through a set of dies to stretch and thin the sidewalls until the cup is of approximately the desired can height. After the sidewalls have been drawn, the bottom portion of the can is still flat, unworked and of about the same thickness as the original sheet metal. 
         [0005]    The bottom profile of a can body is typically formed as the last step, in a pressing process that draws material to the required shape and dimensions. The most common bottom profile for a can is a dome bottom, wherein a large portion of the can bottom is formed into a spherical inwardly concave dome, with a convex annular portion, or foot, formed around the outer diameter of the can bottom on which the can stands when it is upright on a horizontal surface. This configuration has been found to resist deformation of the can bottom under internal pressure, and provide sufficient strength to hold the formed can and its contents in an upright position, and resist ruptures and bulging. The can bottom dome is formed when a punch, sometimes referred to as punch nose tooling, which is positioned in the interior of the can body is forced against an end-forming die (sometimes called a dome plug) located on the outside of the can body, to form the generally upwardly extending dome configuration that becomes the bottom of the can. One known method of improving the strength of a can bottom profile is to reform either the outside or inside area around the nose. After the can body has been formed, the open top of the can is trimmed to provide a smooth continuous flat top edge to ensure a continuous seal with the can lid. 
         [0006]    The need for a strong can bottom has required substantial thickness be retained in the bottom to achieve required performance. If the can bottom is not sufficiently strong, the central dome area may reverse shape, becoming convex if the filled can is subject to high pressure. The resistance of a can bottom to reversing is one criteria which is used to measure the strength of a particular can bottom profile. This pressure is referred to as the “dome reversal pressure” or DRP. Design changes that increase the dome reversal pressure make the can more robust in higher pressure situations, such as in pasteurizing equipment. 
         [0007]    Another criteria for measuring the strength of a particular bottom profile is drop resistance, which is the capability of a container bottom to resist a downward bulge when dropped from a height. 
         [0008]    The pressure at which the can dome reverses or can bottom otherwise bulges or fails in response to dropping may be dependent upon can bottom design, gauge thickness, and the internal pressure of the can, which in turn is directly related to a variety of factors, such as the formula of the beverage in the can, carbonation of the beverage in the can, and ambient temperature conditions. 
         [0009]    In some circumstances, the standard cans previously used in the industry, such as those disclosed in U.S. Pat. No. 6,182,852, can fail, especially in areas with temperature or pressure extremes, or when beverages that exert greater internal pressure are placed in the cans. Thus, there remains a need for improved container bottom profiles that show an increased resistance to failures. 
       SUMMARY OF THE INVENTION 
       [0010]    In accordance with the design of the present invention, many of the disadvantages, shortcomings, and problems associated with previous container designs have been substantially reduced or eliminated. 
         [0011]    One advantage of the present invention is that it increases the drop resistance of the can to downward bulges, which are considered unacceptable failures of the cans. Additionally, this particular design has been found to work very well when it is subsequently reformed. Other advantages of the present disclosure will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein, by way of illustration and example, embodiments of the present invention are disclosed. 
         [0012]    While there are a variety of cans having domed central panels, the embodiment of the present invention is an improvement over the cans of the prior art for one or more reasons, as explained below. 
         [0013]    For example, U.S. Pat. No. 3,693,828 to Kneusel et al. discloses a unibody can having a domed central panel. However, the can of Kneusel only provides for a single section in the outer leg between the nose and can sidewall. Similarly, U.S. Pat. No. 4,685,582 to Pulciani discloses a unibody can bottom having a domed central panel and a single section in the outer leg separated from the can sidewall by a single, inwardly directed transitional radii. Similarly, U.S. Pat. No. 4,919,294 to Kawamoto et al. discloses a unibody can having a domed central panel that has two arrangements. One arrangement, like the arrangement in the Kneusel patent, has only a single straight, outwardly angled outer leg; the other arrangement has an outer leg that has a single section that is inwardly convex in shape. In contrast, the can of the present invention provides for two leg portions separated by a transitional radii, which provides for greater strength, stability and versatility over the prior art can. 
         [0014]    In a preferred embodiment of the present invention, a container is disclosed, having a sidewall portion, an open top to which a can lid is sealed after the can has been filled, and a bottom structure of a unique configuration. The bottom structure has a domed central panel. The outer edge of the domed central panel is connected to the upper edge of a substantially cylindrical vertical inner leg portion by a transitional radii. The lower edge of the inner leg portion is connected to the inside edge of a generally semi-circular or semi-toroidal nose portion by an inner bottom nose radius. The outside edge of the nose portion is connected to the lower edge of an upwardly and outwardly inclined outer leg portion by an outer bottom nose radius. The upper edge of the outer leg portion is connected to the lower edge of an outwardly inclined peripheral portion by an inwardly directed transitional radii. The upper edge of the peripheral portion is connected to the lower end of the generally cylindrical vertical sidewall portion that extends axially about the centerline of the container by an outwardly directed transitional radii. 
         [0015]    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 embodiment 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 
         [0016]    For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
           [0017]      FIG. 1  is a cross-sectional side view of a standard beverage can in which the preferred embodiment may be used; and 
           [0018]      FIG. 2  is an enlarged cross-sectional side view of the bottom of the container, showing the details of a preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    In the discussion of the FIGURES the same reference numerals will be used throughout to refer to the same or similar components. In the interest of conciseness, various other components known to the art, such as can drawing and ironing equipment, punch nose tooling and the like, have not been shown or discussed. 
         [0020]    In the following discussion, numerous specific details are set forth to provide a thorough understanding of the present invention. However, various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, deviations from the described invention can be made and still achieve the desired outcome of the present invention. Therefore, for measurements made herein, assume a tolerance of ±0.015 inches, and for angles, assume a tolerance of ±2°, unless otherwise specified. 
         [0021]    To facilitate understanding of the disclosure herein presented, clarification of certain of the terms used herein is provided. The terms “container” and “can” are used interchangeably. “Container stand plane” means an imaginary horizontal plane perpendicular to a longitudinal central axis of the container, and upon which the container bottom would rest when placed in an upright position on a horizontal surface. As related especially to elements of the container, “downwardly” means a direction towards the container stand plane, and “upwardly” means a direction away from the container stand plane, unless otherwise noted. Likewise, “outwardly” means a direction away from the longitudinal central axis of the container, and “inwardly” means a direction towards the longitudinal central axis of the container, unless otherwise noted. 
         [0022]      FIG. 1  is a cross-sectional side view of a typical container  10 . Container  10  has a mouth or open portion  20  at its uppermost end. Mouth portion  20  is integrally connected to generally circumferential or generally cylindrical sidewall portion  40 . Sidewall portion  40  is connected at its lowermost end to bottom structure  100 , thus forming an open-ended vessel. Container  10  has a longitudinal central axis  60 , perpendicular to a container stand plane  80 . The design of bottom structure  100  is further detailed in  FIG. 2 . 
         [0023]      FIG. 2  is an enlarged cross-sectional side view of bottom structure  100  of container  10  in  FIG. 1 . As can be seen in this view, a central panel  110  forms the center of bottom structure  100 . The central panel  110  is formed of a plurality of generally concentric domes (which are referred to as bi-radial or multi-radial domes). As depicted, the central panel  110  has two domes. The first, innermost dome has a first, or major, radius of curvature R 1  that is approximately 1.75 inches at a point that is approximately 0.630 inches from central axis  60 . The outermost dome has a second, or minor, radius of curvature R 2  that is approximately 0.55 inches at a point that is approximately 0.848 inches from central axis  60 . 
         [0024]    Without any spring back or deflection from pressure or contents, the top of the central panel  110  has a height H 1 . Typically, H 1  is preferably from about 0.42 to about 0.48 inches above the container stand plane  80 , but most preferably, H 1  is about 0.453 inches. Prior art cans typically have a domed central panel that has a height above the stand plane of about 0.425 inches. 
         [0025]    The outer edge of the central panel  110  is connected to the upper edge of an inner leg portion  130  by a transitional inner radius  120 . Preferably, transitional inner radius  120  is from about 0.05 to about 0.120 inches. The inner leg portion  130  extends generally axially downwardly from the central panel  110 , and is inclined inwardly toward longitudinal central axis  60  of container  10  at angle α. Angle α is typically less than 3°, and preferably about 2°30′. 
         [0026]    The lower edge of inner leg portion  130  is connected to generally semi-toroidal nose portion  140  by an inner bottom nose radius  136 . The preferred value of inner bottom nose radius  136  is about 0.0598 inches. Prior art cans have an inner bottom nose radius of about 0.025 inches. The lowest point of the nose  140  is generally tangential to container stand plane  80 . Nose portion  140  forms a “ring” or a portion of a “ring” upon which container  10  may rest upright on the container stand plane  80 , or other horizontal surfaces. The nose diameter, or rim stand diameter, D 1 , of a can of the present invention (the distance from the center of the nose portion  140  on one side of the can to the center of the nose portion directly across the can) is preferably 1.850 inches, ±0.010 inches. This nose radius  136 , which is larger than prior art cans, provides better stability, such that when the cans are being moved along a conveyor and conveyor transfer plates, there are fewer tipped-over cans that can cause conveyor jams, especially when the cans are empty. Fewer tipped over cans mean increased production efficiency. However, the nose radius  136  is still of a size that the beverage container can be stacked on top of another beverage container and to rest on the lid of the lower container. 
         [0027]    The outside edge of nose portion  140  is connected to the lower edge of an upwardly and outwardly inclined frustoconical outer leg portion  160  by an inwardly directed outer bottom nose radius  150 . The preferred value of outer bottom nose radius  150  is about 0.0745 inches. The outer leg portion  160  extends generally axially upward, and is inclined outward at angle β. Although not critical, angle β is between about 27° and about 33°, and preferably about 29°40′. The upper edge of the outer leg portion  160  is connected to the lower edge of an outwardly and upwardly inclined frustoconical peripheral portion  180  by an inwardly directed transitional outer leg radius  170 . The preferred value of transitional outer leg radius  170  is about 0.080 inches. The inclined peripheral portion  180  extends generally axially upward, and is inclined outward at angle δ. Preferably, angle δ is between about 25° and about 33°, and preferably about 29°20′. 
         [0028]    The upper edge of the inclined peripheral portion  180 , connected to the lower end of the generally cylindrical sidewall portion  40 , extends axially about the centerline of the container by an outwardly directed transitional radius  190 . The preferred value of transitional outer radius  190  is about 0.1608 inches. A line drawn between the bottom of the nose portion  140  and the bottom of the outwardly directed transitional radius  190  forms an angle Δ upward from the stand plane  80 . Preferably, angle Δ is between about 35° and about 45°, and preferably about 40°31′. 
         [0029]    While this can bottom structure works well with a variety of cans, it has been found that a can bottom of this structure works particularly well with thinner gauge metals. Test results for cans formed using this can bottom from a metal of 0.0108 gauge were surprisingly robust; much better than would be expected from a metal of this thin a gauge. These test results are discussed in more detail below. Additionally, this particular can bottom structure, which works well as originally formed, has also been found to work well as the basis for a can that can be inside reformed, although such reforming is not necessary. 
         [0030]    While various can bottom shapes and thicknesses can be designed, the products must be able to perform in use. For example, they must hold beverages without leaking, reversing, bulging, or experiencing other failures, while maintaining the food or beverage within in a consumable state that is satisfactory to the ultimate consumer. The cans must also be able to withstand the pressure applied to the inside of the can by the carbonated beverage contained therein. Additionally, the can design must function to enable stacking of cans of similar construction in more than one layer, while maintaining a stability of the stacked structure. Therefore, the can bottom must sit stably on, or nest in, a can lid attached to the top of a can below it in the stack. This can be achieved by having two or more points of contact between the can bottom and adjacent can lid and/or can neck. 
         [0031]    The performance of a can will vary, even in a specific type of can, depending on a variety of factors, such as the formula of the beverage in the can, carbonation of the beverage in the can, and ambient temperature conditions. Two similarly filled cans in different environments could bulge or reverse at different pressures. For example, as the temperature of the beverage in a can increases, the beverage exerts more pressure against the inside of the can than a similar can of beverage at a lower temperature. Additionally, carbonated beverages in a can apply more outward pressure against the can than non- or low-carbonated beverages. In both these situations, the drop and reversal resistance of the can bottom is related in part to the internal pressure of the can. Similarly, the outside, or atmospheric pressure, can also impact the pressure at which the dome reverses or can bulges. 
         [0032]    Testing is performed on cans to ensure they meet various requirements for use. There are a variety of tests used to determine the qualities of cans. In addition to meeting certain specified standards, it is desirable to anticipate how cans will perform in the consumer environment (i.e. stores, homes, etc.). As previously stated, it should be appreciated that test results can vary based on location and other atmospheric factors. 
         [0033]    One standard test for can bottoms is the “buckle test” which determines the pressure, in pounds per square inch (psi), applied to the inside bottom of a can before the can bottom buckles from the pressure. Another standard test is the drop resistance test, in which a filled, pressurized can is dropped from sequentially higher distances to a fiat surface until a partial reversal (downward bulge) of the can bottom is achieved. The can is then dropped from greater heights until the bottom dome experiences a full reversal such that it is lower than the nose portion  140 , so that the can “rocks” when placed on a flat surface. 
         [0034]    As previously disclosed in U.S. patent application Ser. No. 10/983,841, assigned to the same entity as the present application, several additional new tests have been developed to help predict the performance of cans in actual use more accurately. These new tests include dropping a can to an angled, rather than flat surface, and dropping a 12-pack of cans to both flat and angled surfaces from a specific height, and checking the number of cans in the 12-pack that suffer reversals. 
         [0035]    Tests were performed using a sample set of prior art cans having a single domed radius and a metal thickness of 0.0110 inches, and a sample set of cans made in accordance with the present invention having a metal thickness of 0.0108 inches and a bi-radial dome. 
         [0036]    In particular, the single can and 12-pack angled drop tests show an unexpected improvement over prior art cans, which is even more surprising given the thinner gauge of the cans of the present invention. These test results are indicators of the improved performance in actual use of the can of the present invention. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                   
                 Test 
                 Prior Art 
                 MC12 Can 
               
               
                 Test Name 
                 Measurement 
                 Can Results 
                 Results 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Buckle Test 
                 Mean 
                 100.6 
                 psi 
                 98.6 
                 psi 
               
               
                   
                 Standard 
                 1.1 
                 psi 
                 1.3 
                 psi 
               
               
                   
                 Deviation 
               
               
                 Flat Drop Resistance Test, Single 
                 Mean 
                 9.3 
                 in. 
                 9.1 
                 in. 
               
               
                 Can pressurized to 60 psi - First 
                 Standard 
                 0.6 
                 in. 
                 0.9 
                 in. 
               
               
                 Reversal Height 
                 Deviation 
               
               
                 Flat Drop Resistance Test, Single 
                 Mean 
                 10 
                 in. 
                 12 
                 in. 
               
               
                 Can pressurized to 60 psi - Rocking 
                 Standard 
                 0.9 
                 in. 
                 1.0 
                 in. 
               
               
                 Bottom Height 
                 Deviation 
               
               
                 Angled Drop Resistance Test, 
                 Mean 
                 6.9 
                 in. 
                 10.2 
                 in. 
               
               
                 Single Can pressurized to 60 psi - 
                 Standard 
                 0.3 
                 in. 
                 0.7 
                 in. 
               
               
                 First Reversal Height 
                 Deviation 
               
               
                 Angled Drop Resistance Test, 
                 Mean 
                 7.7 
                 in. 
                 11.9 
                 in. 
               
               
                 Single Can pressurized to 60 psi - 
                 Standard 
                 017 
                 in. 
                 1.3 
                 in. 
               
               
                 Rocking Bottom 
                 Deviation 
               
             
          
           
               
                 12-pack Flat Drop Test at 8 in., cans 
                 Mean 
                 2.3 
                 cans 
                 1.3 
               
             
          
           
               
                 pressurized to 80 psi - number of 
                 Standard 
                 1.1 
                 0.7 
               
               
                 cans showing first reversal 
                 Deviation 
               
             
          
           
               
                 12-pack Angled Drop Test at 8 in., 
                 Mean 
                 2.9 
                 cans 
                 4.4 
               
             
          
           
               
                 cans pressurized to 80 psi - number 
                 Standard 
                 1.6 
                 1.1 
               
               
                 of cans showing first reversal 
                 Deviation 
               
               
                   
               
             
          
         
       
     
         [0037]    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.