Abstract:
A method for strengthening an end member for a container comprises the steps of providing an end member shell and reforming the end member shell. The finished the end member has a central panel wall with a product side and a public side. The public side has a means for opening a frangible panel segment. The end member shell has a central panel extending radially outwardly from a central axis, a panel radius along a peripheral edge of the central panel, a countersink integral with the panel radius, a chuckwall extending upwardly from the countersink having a bend with a radius of curvature and angled axially outwardly, and a seaming curl defining the outer perimeter of the end member shell and integral with the chuckwall. The chuckwall of the end member shell is reformed to decrease the radius of curvature of the bend.

Description:
TECHNICAL FIELD 
     The present invention relates to end closures for two-piece beer and beverage metal containers having a non-detachable operating panel. More specifically, the present invention relates to improved reforming techniques to produce a lightweight end closure. 
     BACKGROUND OF THE INVENTION 
     Common end closures for beer and beverage containers have a central panel that has a frangible panel (sometimes called a “tear panel,” “opening panel,” or “pour panel”) defined by a score formed on the outer surface, the “consumer side,” of the end closure. Popular “ecology” can ends are designed to provide a way of opening the end by fracturing the scored metal of the panel, while not allowing separation of any parts of the end. For example, the most common such beverage container end has a tear panel that is retained to the end by a non-scored hinge region joining the tear panel to the reminder of the end, with a rivet to attach a leverage tab provided for opening the tear panel. This type of container end, typically called a “stay-on-tab” (“SOT”) end has a tear panel that is defined by an incomplete circular-shaped score, with the non-scored segment serving as the retaining fragment of metal at the hinge-line of the displacement of the tear panel. 
     The container is typically a drawn and ironed metal can, usually constructed from a thin plate of aluminum. End closures for such containers are also typically constructed from a cut-edge of thin plate of aluminum or steel, formed into a blank end, and manufactured into a finished end by a process often referred to as end conversion. These ends are formed in the process of first forming a cut-edge of thin metal, forming a blank end from the cut-edge, and converting the blank into an end closure which may be seamed onto a container. Although not presently a popular alternative, such containers and/or ends may be constructed of plastic material, with similar construction of non-detachable parts provided for openability. 
     These types of “stay-on-tab” ecology container ends have been used for many years, with a retained tab and a tear panel of various different shapes and sizes. Throughout the use of such ends, manufacturers have sought to save the expense of the metal by down-gauging the metal of the ends and the tabs. However, because ends are used for containers with pressurized contents and are sometimes subject to pasteurization, there are conditions causing great stresses to the components of the end during pasteurization, transit and during opening by a user. These conditions limit the available gauge reduction of the end metal, and make it difficult to alter design characteristics of the end, such as by reducing metal gauge or the thickness of the metal residual in the score defining the tear panel. 
     The pressurized contents of the container often causes risk for the end to buckle. The pressurized contents may also result in a condition in which the tab is forced upwardly. There is a maximum allowable distance that the tab can be displaced without the tab extending upwardly above the remainder of the container. This is called tab-over-chime. Tab-over-chime leads to ship abuse problems wherein the frangible panel prematurely fractures during distribution of filled beverage containers. 
     As manufacturers reduce the thickness of the metal used to make the ends, buckle and tab-over-chime become more and more of a problem. Therefore, a need for can end with improved ability to withstand buckle and tab-over-chime is needed. 
     SUMMARY OF THE INVENTION 
     It is an object to provide a method for strengthening an end member for a container. The end member has a central panel wall with a product side and a public side. The public side has a means for opening a frangible panel segment. The method comprises the steps of providing an end member shell and reforming a portion of the end member shell. 
     The end member shell comprises a central panel which extends radially outwardly from a central axis. A panel radius is located along a peripheral edge of the central panel. A countersink is integral with the panel radius, and a chuckwall extends upwardly from the countersink and has a bend with a radius of curvature which angles the chuckwall axially outwardly. A seaming curl defines the outer perimeter of the end member shell and is integral with the chuckwall. 
     The reforming step is provided to reform the bend of the chuckwall to decrease the radius of curvature. 
     Another object of the present invention is to provide an end member for a container. The end member comprises a central panel, a first panel radius, a countersink, a chuckwall, and a seaming curl. 
     The central panel extends radially outwardly from a central axis. The panel radius is located along a peripheral edge of the central panel and includes a radius of curvature joining the central panel with the countersink. The countersink is integral with the first panel radius and joins the first panel radius with the chuckwall through an annular concave segment. The chuckwall extends upwardly from the countersink to a seaming curl located at an outer perimeter of the end member. 
     The end member further comprises an approach point. The approach point is defined by a lower outer position of an axially stacked second end member. This lower outer position is generally the lower extent of the countersink. A bend located on the chuckwall having an outwardly directed angle with a radius of curvature adapted to position the chuckwall radially outwardly of the approach point. 
     Other features and advantages of the invention will be apparent from the following specification taken in conjunction with the following drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of the can end of FIG. 1 with a tab staked thereto; 
     FIG. 2 is a partial cross-sectional view of end member shell prior to reforming; 
     FIG. 3 is a partial cross-sectional view of a reformed end member; and 
     FIG. 4 is a partial cross-sectional view of the two axially stacked reformed end members. 
    
    
     DETAILED DESCRIPTION 
     While this invention is susceptible of embodiment in many different forms, there are shown in the drawings and will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated. 
     The container end of the present invention is a stay-on-tab end member  10  with improved physical properties including strength. Essentially, the present invention provides a lightweight end member  10  which embodies the physical characteristics and properties required in the beverage container market, as explained below. 
     Referring to FIG. 1, the end member  10  for a container (not shown) has a central panel wall  12  having a seaming curl  14  for joining the wall to the container. The container is typically a drawn and ironed metal can, usually constructed from a thin plate of aluminum or steel, such as the common beer and beverage containers. End closures for such containers are also typically constructed from a cut edge of thin plate of aluminum or steel, formed into blank end, and manufactured into a finished end by a process often referred to as end conversion. In the embodiment shown in the Figures, the central panel  12  is joined to a container by a seaming curl  14  which is joined to a mating curl of the container. The seaming curl  14  of the end closure  10  is interconnected to the central panel  12  by a chuckwall  15  and a countersink area  16  which is joined to the center panel  12  outer peripheral edge  18  of the central panel  12 . This type of means for joining the central panel  12  to a container is presently the typical means for joining used in the industry, and the structure described above is formed in the process of forming the blank end from a cut edge of metal plate, prior to the end conversion process. However, other means for joining the central panel  12  to a container may be employed with the present invention. 
     The outer peripheral edge  18  of the central panel  12  is typically coined to add strength to can end  10 . Coining is the work hardening of metal between tools. The metal is typically compressed between a pair of tools, generally an upper and lower tool. 
     The central panel wall  12  has a displaceable tear panel  20  defined by a curvilinear frangible score  22  with an adjacent anti-fracture score  24  on the tear panel  20 , and a non-frangible hinge segment  26 . The hinge segment  26  is defined by a generally straight line between a first end  28  and a second end  30  of the frangible score  22 . The tear panel  20  of the central panel  12  may be opened, that is the frangible score  22  may be severed and the tear panel  20  displaced at an angular orientation relative to the remaining portion of the central panel  12 , while the tear panel  20  remains hingedly connected to the central panel  12  through the hinge segment  26 . In this opening operation, the tear panel  20  is displaced at an angular deflection, as it is opened by being displaced away from the plane of the panel  12 . 
     The frangible score  22  and the second groove or anti-fracture score  24  are formed using conventional-type of scoring operation during the can end forming process, using tools including an upper (public side) die with a score knife and a lower (product side) die with an anvil surface. 
     The end member  10  also has a tab  44  secured to the center panel  12  by a rivet  46 . The tab  44  has a lift end  48 , a central region  50 , and a nose portion  52 . The lift end  48  and the nose portion  52  are generally aligned along a central longitudinal axis passing through the rivet  46 . The rivet  46  is formed in the typical manner. 
     The user initiates opening of the end member  10  by lifting the lift end  48  of the tab  44 . This lifts the rivet  46  which causes the score groove  22  to fracture in a vent region  60  which is located at least partially within the bounds of the coined region surrounding the rivet  46 . As the nose portion  52  presses against the tear panel  20 , the fracture of the score  22  propagates around the tear panel  20 , preferably in progression from the first end  28  of the score  22  toward the second end  30  of the score  22 . 
     The frangible score  22  includes a length defined by a thickened portion of the residual. This length is often referred to as a check slot region  62 . The check slot  62  causes the propagation of the fracture of the frangible score  22  to slow naturally as the fracture reaches the check slot region  62 . This allows the container to vent safely before the fracture of the frangible score  22  continues. 
     A deboss panel  69  is formed in the public side  34  of the central panel  12 . The deboss panel  69  is formed in the central panel  12  using conventional die-forming techniques. The deboss panel  69  has a substantially gibbous-shaped deboss profile  70  which is, in turn, defined by an inner radius line  72  and an outer radius line  74 . The deboss panel  69  may have bilateral symmetry with respect to a plane defined by axes X—X and Y—Y. 
     The deboss profile  70  includes first and second opposing end portions  76 ,  78  joined by a pair of sidewalls  80   a ,  80   b . The first end portion  76  includes an apex  82 . The apex  82  is joined to the sidewalls  80   a ,  80   b  by first and second arcuate portions  84   a ,  84   b . The apex  82  lies between the transition region  34  of the frangible score  22  and the outer peripheral edge  18  of the center panel  12 . 
     According to another aspect of the invention, a method for reforming a can end shell to produce the end member  10  described herein is disclosed. The method is used to produce a lightweight end member  10 , for example from an 0.0080 inch thick aluminum stock for attachment to a container necked to a  202  (2.125 inches) open end. End members  10  of the present invention are generally manufactured using a multi-stage reforming method. 
     Referring to FIG. 2, an end member shell  89  from a shell press and prior to reforming in a conversion press is illustrated. The shell center panel diameter is a distance designated D SCP  from a central axis which is located at the intersection of the Y—Y and X—X axes (see FIG.  1 ). The countersink  16  of the end member shell  89  includes an inner wall  90 , a curved segment  92 , and an outer wall  94  and is a distance D SCS  from the central axis. The curved segment  92  has a radius of curvature R SCS  and includes an annular base  100  positioned along a horizontal plane containing a baseline  101 . The center panel  12  is a height H SCP  above the baseline, generally about 0.058 inches. The inner wall  90  is joined to a shell panel radius  102  along the outer peripheral edge portion  18  of the central panel  12 . The shell panel radius  102  is located at a distance D SPR  from the central axis and has a radius of curvature R SPR . The outer wall  94  of the countersink  16  is joined to the chuckwall  15 . 
     The chuckwall  15  includes a crease or bend portion  108  creating an angle φ of approximately 24°-28°, more preferably between 25°-26°, and most preferably about 25° 58′, or any range or combination of ranges therein. The angle φ is directed outwardly of the central panel  12 . The crease  108  has a radius of curvature R SCW1  between 0.100 and 0.200 inches, preferably between 0.130 to 0.170 inches, more preferably about 0.150 inches, or any range or combination of ranges therein. The chuckwall  15  includes a second crease or bend having a radius of curvature R SCW2  of about 0.070 inches. 
     The seaming curl  14  is located at an outer perimeter of the end member shell  89  at a height H EMS  above the baseline  101  and has a shell seaming curl height H SSC  which is measured from a lower extent of the seaming curl  14  to an upper extent of the seaming curl  14 . 
     The end member shell  89  undergoes a reforming operation during which the center panel  12 , the shell panel radius  102 , the countersink  16 , and the chuckwall  15  are reformed. FIG. 3 illustrates the shell member after reforming in a conversion press. 
     The reformed end member  112  includes a stepped profile along the outer peripheral portion  18  of the center panel  12 . The stepped profile includes a first panel radius  114  interconnected to a second panel radius  116 . A portion of the first panel radius  114  is coined. The first panel radius  114  is joined to the inner wall  90  of the countersink  16  and has a height H RS1  which is approximately 0.070 inches above the baseline  101  and a radius of curvature R RS1 . The second panel radius  116  is joined to outer peripheral portion  18  of the center panel  12  and has a radius of curvature R RS2  and a height H RS2  which is approximately 0.088 inches above the baseline  101 . 
     The dimensions of the first panel radius  114 , the second panel radius  116 , and the crease portion  108  are selected to optimize resistance to buckle. Buckle is the loss or degradation of ability of the pour panel  20  to withstand internal pressure. 
     Further to the reforming operation, the chuckwall  15  is reformed. In particular, prior to reforming, the crease  108  radius of curvature R SCW1  is approximately 0.150 inches. Subsequent to reforming, the reformed end member  111  has a crease  108  radius of curvature R RCW1  of 0.010-0.080 inches, more preferably between 0.015-0.025 inches, and most preferably 0.020 inches, or any range or combination of ranges therein. The reforming also increases the distance L CW  between first and second radii of curvature R RCW1  and R RCW2  from approximately 0.108 to 0.125. The second radius of curvature RRCW 2  is substantially unchanged during the reforming operation. This reforming of the chuckwall  15  increases the chuckwall angle φ creating a new chuckwall angle δ of about 24°-28°, more preferably between 25°-26°, and most preferably 26°, or any range or combination of ranges therein. 
     The reforming also creates a compound radius structure in the countersink  16 . Prior to reforming, the countersink  16  includes the annular base  100  having a radius of curvature R SCS . Subsequent to the reforming operation, the countersink  16  has an inner radius of curvature R RCS1  and an outer radius of curvature R RCS2  which is generally less than the inner radius if curvature R RCS1 . 
     Other dimensions of the end member shell  89  in relation to the reformed end member  111  include the diameter D SCP  of the shell center panel  12  which is generally greater than a diameter D RCP  of the reformed center panel  12 . The diameter D SPR  of the shell panel radius is substantially equal to the diameter D RPR1  of the reformed end member&#39;s first panel radius. The diameter D SCS  of the shell  89  countersink  16  is generally less than the diameter of a diameter D RCS  of the reformed countersink  16 . The height H EMS  of the end member shell  89  is generally greater than a height H EMR  of the reformed end member  111 . 
     The height H EMR  of the reformed end member  111  is preferably about 0.235 inches. This allows the radius of curvature R RCW1  of the reformed bend to be decreased to improve strength of the reformed end member  111 . In order to reform the countersink  16  of the end member shell  89 , the end member shell  89  must wrap around the tooling in the conversion press. Thus, the end member shell  89  must have a deeper countersink  16  (H EMS  being about 0.0242 inches) and a shallower panel than the reformed end member  111 . 
     However, the deeper countersink  16  of the end member shell  89  causes interference when the end member shells  89  are nested or stacked. The interference occurs at the point where the bend  108  on the chuckwall  15  meets a lower portion of the countersink  16  of an upper stacked end member shell  89 . To eliminate the interference, the radius of curvature R SCW1  is increased. 
     In the conversion press, the end member shell  89  is reformed so that the center panel  12  is forced upwardly. The center panel  12  depth is increased from H SCP  to H RS1 . In a subsequent operation, the center panel depth is increased to H RS2 . The countersink  16  depth is decreased from H EMS  to H EMR . Thus, the countersink  16  has a shorter length in the reformed end member  111  as compared to the end member shell  89 . This process allows the radius of curvature R SCW1  of the bend  108  of end member shell  89  to be reformed (decreased) to the radius of curvature R RCW1  of the bend  108  of the reformed end member  111  to achieve a better buckle strength. 
     Another advantage of the present method is illustrated in FIG.  4 . Namely, the reforming of the first radius of curvature R RCW1  displaces the chuckwall  15  outwardly relative to the central axis. This controls axial stacking of a first reformed end member  130  and second reformed end member  132 . Proper stacking is important for transportation of the finished end members and subsequent feeding of the end members for attachment onto a filled can body. 
     During stacking of the reformed end members  130 ,  132 , an approach point  134  defined by the lower outer position of the axially stacked second end member  132 , generally the outermost portion of the countersink  16  of the upper stacked end  132 , is located radially inwardly of the chuckwall  15 . The approach point  134  as illustrated in FIG. 4 is actually located on an annular radial approach segment, which is spaced from the chuckwall  15  of the lower stacked end  130  along its entire annular length. 
     The method of reforming the chuckwall  15  according to the present invention is adapted to move the chuckwall  15  away from the approach point  134 . Stated another way, the reformed radius of curvature R RCW1  is adapted to position the chuckwall  15  radially outwardly of the approach point  134 . Thus, the end members  130 ,  132  contact each other along the seaming curl area  14 , and there is no interference generated by the remaining portions of the end members  130 ,  132 , and especially no contact of the chuckwall  15  with the outermost lower portions of an axially stacked end member. 
     The approach point  134  is located on a horizontal plane having a height HAP above the baseline  101 . The approach point  134  height H AP  is generally above the height H RB  of a horizontal plane containing at least a portion of the reformed crease or bend  108 . 
     The end members  130 ,  132  are stacked such that the seaming curl  14  of the second end member  132  rests upon the seaming curl  130  of the first end member  130 . Again, the interference from the chuckwall  15  or other portions of the end members  130 ,  132  is eliminated during the reforming operation. 
     While the invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the broader aspects of the invention. Also, it is intended that broad claims not specifying details of the particular embodiments disclosed herein as the best mode contemplated for carrying out the invention should not be limited to such details.