Abstract:
The invention relates to a method for forming a sheet metal lid. At least one projection is formed twice. First, the projection is shaped from a panel of the sheet metal lid, the pre-form being located near an attaching portion of a tab, but at a distance from the mounting place. Second, at least a front edge of the pre-form of the at least one projection is re-formed. No score line is provided in the panel, neither during shaping, nor during re-forming. An improved blocking for an outer edge portion of the attaching portion is thus obtained, the outer edge portion being associated with the front edge.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The invention relates to a further improvement or further provision of a positional fixing of a tab on a sheet metal lid according to the simultaneously filed (co-pending) PCT application No. PCT/DE2002/004283, originating from the same inventors and the same legal successors, the disclosure of said application being incorporated by reference herein. The corresponding U.S. application is Ser. No. 10/541,845, published as US 2007/0062950. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a method of shaping a portion of a sheet metal lid of a beverage can, the lid including a panel having an openable area defined by a score line in the panel, and a mounting place for attaching a tab for breaking into the openable area. 
   2. Description of Background and Relevant Information 
   When the tab is in an attached condition to the sheet metal lid, it is known by the expect as a SOT (Stay on Tab), which is provided for opening an openable area in the surface of a lid (usually designated as a “panel”). For this purpose, the tab is taken at a grip end and raised with a vertical tilting motion for breaking open an openable area along a line of weakness (usually called a “score line”) with its opening end. 
   Particularly when large opening ends (LOE) are used for the openable area, difficulties are encountered in the related art to when fixing the positions of the tab in an attached condition to the sheet metal lid. Suggestions on this topic have already been made, for example, in U.S. Pat. No. 5,799,816 (Schubert). In this document, an opening of an attaching portion of the tab is proposed, which attaching portion is usually designated as a “rivet island”. The attaching portion is secured to the panel of the sheet metal lid through a shaped rivet and overlaps a round to elongated reformed bead with an opening provided in the attaching portion. The bead may also be formed after attaching the tab, compare column 3, lines 63-67, column 5, lines 37-44, claim 3 of Schubert and the associated graphical illustration in FIGS. 2 and 4 thereof. 
   SUMMARY OF THE INVENTION 
   The invention addresses the technical problem of achieving the aforementioned effect, but with an improved manufacture and reliability of the anti-rotation block and with an improved positional alignment of the tab in the attached condition. For this purpose, a method is proposed. 
   Advantageously, an already present peripheral edge on a usual tab is used, the edge not having to be specifically formed additionally for obtaining the rotation barrier after the attachment of the tab to the panel (commonly referred to as “staking”). The only manipulation is effected on the sheet metal lid itself, which is provided with a shape or molding, as the rivet is in a preliminary phase, which shape or molding may preferably also be pre-formed in parallel together with the formation of the rivet and subsequently be modified in shape, or more precisely “reformed”, in a further processing step of the sheet metal lid being manufactured. The projection can thus be formed integrally with the sheet metal lid, as is the securing point is formed by one-piece manufacturing for the attaching portion of the tab. 
   The projection does not protrude through an opening of the attaching portion, and the attaching portion is not provided with an opening beforehand, but the attaching portion remains entire and a blocking means that acts on the attaching portion from an outside is provided, as disclosed in the aforementioned PCT application and the aforementioned US 2007/0062950. 
   Forming at least one projection to have an asymmetrical cross section is particularly advantageous, such projection having a steeper side facing the attaching portion than the side facing away from the attaching portion. Such a shape may also be selected for punctiform or oval projections. 
   In a subsequent reshaping, reforming, or post-forming, the thickness of a top side of the (strip-shaped) projection is reduced. Thereby, a solidification of the portion and the projection as a whole is achieved. This also applies to the method. The score line can be introduced not simultaneously with the reforming, in temporally shifted or offset processing steps. The same is valid for the pre-forming of the bead, which is not shaped at the same time, as the score line is introduced. 
   In order to obtain the blocking effect, which can also be a limiting effect, which is to be understood to range from a complete prevention of a rotating movement up to a substantial limitation of the rotating movement, an outer edge of the flat attaching portion (i.e., the rivet island) is stopped by abutting against the projection that is shaped to protrude out of the sheet metal lid. 
   The projection can have a strip shape (i.e., a line shape) and be preferably oriented one of transversely and in parallel to a longitudinal extension of the tab (longitudinal axis or longitudinal plane), the projection engaging at a correspondingly oriented peripheral edge of the attaching portion for its blocking effect or being provided very closely adjacent thereto. In a longitudinal extension, the projection can extend over more than 30%, preferably over more than 50% to more than 80% of the width of the attaching portion. 
   Several projections can be provided, not all projections having to be associated with the same outer edge portion of the attaching portion. The projections can also be differently shaped, i.e., strip-shaped, round to oval, or a combination thereof. If a straight-lined outer edge portion of the attaching portion is provided, a straight-lined (strip-shaped) embodiment of the projections can be advantageous. The straight-lined or linear strip embodiment can also be achieved by arranging at least two punctiform projections in a line, which then form a group that is associated with the same outer edge portion of the attaching portion. 
   When several projections are provided in the aforementioned sense, they do not have to engage the same edge line of the attaching portion when starting a rotating movement, but instead they can be assigned to different outer edges. 
   When providing a strip-shaped projection, it can be designed to have a length longer than the diameter of the finished rivet head. 
   The attaching portion being formed from a piece of the central portion of the tab, only minor gaps are visible between the attaching portion, which is displaced downwards to a lower plane by a double buckling line, and the somewhat higher, parallel plane of the remaining tab. Accordingly, the mounting of the projections on at least one of the free peripheral edges facing outward from the attaching portion is barely or only hardly visible from the outside, so that the rotation blocking is virtually invisible to the observer. A colored tab is not changed further in its colored appearance. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments explain and supplement the following detailed description of the invention, wherein further reference is made to the content of the disclosure of the aforementioned PCT application and US publication. The invention is further described in the detailed description, in which like reference numerals represent similar parts throughout the views of the drawings, and wherein: 
       FIGS. 1 ,  2 , and  3  show three stages in a manufacturing process of a sheet metal lid, comprising a station for inserting a score line or a weakening line  16 , a station for introducing a finger depression  13  and additional beads  18   a  in the openable area inside the score/weakening line, and a first station at which a pre-form  19  of a bead  20  is shaped, achieving a blockage of the rotational behavior of a tab  30 ; 
       FIGS. 4 and 5  show a further, subsequent manufacturing station, at which a tab  30  is mounted over a rivet  11  integrally formed on the sheet metal lid, via an attaching portion  31 , which as a flat attachment tongue (rivet island) serves for mounting (“staking”); 
       FIG. 6  is a sectional view, taken along line  6 - 6  of  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The sheet metal lid obtained according to a method as shown in  FIGS. 1 to 3  has a visible edge portion  12  as a seamable edge that is suitable for seaming to a body of a beverage can. The sheet metal lid itself is produced from thin sheet metal, typically less than 0.24 mm, and has already passed through preceding workstations before reaching the stage shown in  FIG. 1 . The lid comprises an inner surface portion (panel)  10  surrounded by a seamable edge  12 . Within the panel  10 , a weakening line  16  is to be introduced around an openable area, the openable area being surrounded by a substantially U-shaped bead  18 . Within the bead, which opens in the center portion of the panel, a substantially oval weakening line  16  is to be designed as a score line having a transitional section that is not scored and thus serves as a connecting portion to the rest of panel  10  when the openable area  17  is broken in along the score line  16  by the effect of a tab, which is explained below. This is illustrated in  FIG. 2 . 
     FIG. 5  shows a mounting place  11  provided approximately in the middle of the panel  10 . An attaching portion  31  as a sheet metal tongue is schematically associated therewith, the attaching portion  31  being part of the tab according to  FIG. 4 , on which it is formed integrally via an articulation line as a buckling line  38 . The tab  30  comprises a grip portion  32 , provided here with a circular opening, at which the tab is operated by the user for breaking open the score line  16  according to  FIG. 2 . The tab  30  also comprises an opening nose portion  33  before the attaching portion  31 , the opening portion being located as a break-in nose above the openable area  17 , for which purpose an additional, eyeball-shaped bead  18   a  as shown in  FIG. 3  is provided in a separate working step, the bead reinforcing the transverse LOE openable area, for being able to apply the opening forces to the break-open starting portion (loop-shaped end of the score line  16 ). The mounted tab  30  is substantially parallel to the panel  10 , which itself does not have to be designed exactly in one plane, but may be slightly bulged, though the area around the mounting place  11  is substantially planar, or flat, allowing a substantially parallel arrangement of the attaching tongue  31  of the tab  30 . 
   As shown in the figures, at least one of the three strip-shaped projections  20 ,  21   a,    21   b  (see  FIGS. 5 ,  6 ) is re-formed around the area for the mounting place  11  as upwardly protruding beads (i.e., towards the outside of the sheet metal lid). The bead  20 , extending transversely to a midplane  100 , is longer than the two neighboring beads  21   a,    21   b,  which extend parallel to the midplane  100 . 
   At one manufacturing station, the re-forming of the three beads  20  (or also  21   a,    21   b ) is improved or designed more exactly. The “re-forming” results in a formation of the beads (projections) as used later for the positional fixing, according to  FIG. 3  and as shown in various ones of the drawing figures of the aforementioned US 2007/0062950. At the station, the at least one projection receives its correct profile geometry, after having been re-formed integrally from the sheet metal lid (the panel) according to  FIG. 1 . As mentioned in the Summary above, forming at least one projection to have an asymmetrical cross section is particularly advantageous, such projection having a steeper side  21   a  &#39; and  21   b  &#39; facing the attaching portion  31  than the side (such as  21   b ”) facing away from the attaching portion. Such a shape may also be selected for punctiform or oval projections. 
   As more particularly described in the aforementioned US 2007/0062950, reference being made below to drawings and reference numerals thereof, a re-forming step comprises a shaping of the pre-form  19  with a coining operation (i.e., an embossing operation) for further flattening the top surface  20   c.  In the re-forming process, the tool is applied likewise from the top and from the bottom for the re-forming. The slight bend according to FIG. 8 a  of the aforementioned US 2007/0062950 that is detectable on the left in the rising side of the pre-form  19  can be recognized in the final form illustrated in FIG. 8 a  of the aforementioned US 2007/0062950, the way in which the sharp front edge  20 ″ is introduced in the initially gently rising left incline of the shaped pre-form  19  also being visible. To the right of the transverse plane  101 , the second incline of the pre-form is shaped from bottom to top, for forming a flat top side  20   c  starting approximately at the instep of the pre-form  19 , the top side, in a portion  20   b,  leading gently over to the rest of the sheet metal panel  10 . 
   Additionally, in the final form, the attaching portion  31 , which is mounted at the rivet  11 , and also the tab  30  are already attached according to  FIG. 4 , also in a sectional view. The tab is arranged with its intermediate web between the left opening and the grip opening  32   b,  substantially above the transversely extending projection  20 . The two openings of the tab are shown in  FIG. 4 , one opening resulting from the formation of the attaching portion  31 , which is further connected to the tab  30  via an articulation line  38 , whereas the opening for inserting a finger is designed particularly. The opening  32   b  forms part of the grip portion  32 , the web  32   a  between the two openings being shown slightly bulged in FIG. 8 a  of the aforementioned US 2007/0062950, having a front edge  32   c  that was related to the free edge  31   c  of the attaching portion  31  during manufacture. A major part of the projection  20  is thus located below the web and is barely visible from outside. 
   In this context, a modified sequence of the two-stage re-forming can be performed besides the processing sequence according to  FIGS. 1 to 3  herein or in the aforementioned US 2007/0062950, for example an initial introduction of the at least one pre-form, as illustrated by the pre-form  19  in the top picture of FIG. 8 a  of US 2007/0062950, in a first working step, still without the introduction of score lines (as weakening lines), of which weakening line  16  is an example. For a projection  20  with a related pre-form  19 , this is illustrated by the sequence of  FIGS. 1 ,  2 , and  3 ; the subsequent assembly can be identical to that illustrated in  FIG. 4 . 
   If multiple projections are used for blocking rotating movements of the tab—all pre-forms  19  are shaped according to  FIG. 1 . In the figure, only one projection is illustrated. The first score line is introduced only later, in a separate working step, e.g., after re-forming (further shaping) of the pre-shaped projection  19 . Here, the one projection receives its correct, assigned profile, as is shown in the bottom illustration of FIG. 8 a  of US 2007/0062950. In this way, it can be realized that a scoring operation, subjecting the sheet metal to severe stresses, is not performed at the same time as the shaping of the pre-form takes place in the first working step, the shaping considerably stressing the sheet metal lid. The score line can be introduced prior to or after the re-forming operation which also stresses the sheet metal. During re-forming—as shown in FIG. 8 a —the wall thickness on the top side of the projection is reduced by about 10% to 15%, with a simultaneously occurring compression and solidification of the portion, which is achieved by the embossing operation (coining) uniformly from the top and from the bottom.