Patent Publication Number: US-2006016815-A1

Title: Anti rotation bead

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention relates to the provision of a positional fixing of a tab on a sheet metal lid for attaching to a body of a beverage can.  
      2. Discussion of Background Information  
      Tabs which are also called Stay on Tabs, e.g., SOT, are attached to sheet metal lids and are known devices for opening beverage cans, so a consumer can gain access to a liquid within the beverage can. When the tab is in an attached condition to the sheet metal lid of the beverage can the tab provides for a consumer to open an openable area in the surface of a lid (usually designated as “panel”). For example, the tab is taken at a grip end of the tab and raised with a vertical tilting motion, so as to break open the openable area of the lid along a line of weakness (usually called score line).  
      Particularly when large opening ends (LOEs) are used for the openable area, difficulties are encountered in the related art when arranging the positioning of the tab along the line of weakness (or score line), when the tab is in an attached condition to the sheet metal lid. U.S. Pat. No. 5,799,816 (Schubert) attempts to deal with the above problem, by arranging an attaching portion (or “rivet island”) of the tab to be secured to the panel of the sheet metal lid through a shaped rivet. The shaped rivet provides for an anti-rotation feature which maintains proper alignment of the tab and particularly its nose portion, so as to minimize failed openings. See FIGS. 2 and 4 and Col. 3, lines 63-67 and Col. 5, lines 37-44 of Schubert.  
      The instant invention addresses the technical problems related to the positional alignment of the tab in the attached condition, as well as the manufacture and reliability of the anti-rotation block.  
     SUMMARY OF THE INVENTION  
      The present invention improves the positional alignment of a tab in an attached condition arranged on a panel, as well as improve the manufacture and reliability of the anti-rotation block.  
      According to one feature of the invention, a sheet metal lid can be used for closing a can body. The lid may include a panel portion and a seamable edge that surrounds the panel, so the edge can be adapted for attaching to the can body. An openable area defined on the panel includes a weakening line, wherein a tab can be disposed on a mounting place outside of the openable area. The tab embodied according to the invention may include a grip portion, an opening portion, and an attaching portion. The attaching portion can be provided for attaching the tab substantially parallel with respect to the panel, such that the tab as attached is disposed with its opening portion above the openable area. Further, near the at least one edge of the attaching portion, at least on strip-shaped projection can be shaped to protrude out of the panel for a limiting pivoting movement (α) of the tab around the mounting place.  
      According to another feature of the invention, the projection need not protrude through an opening in the attaching portion, and the attaching portion does not need to be provided with an opening for the above purpose. Instead, the attaching portion can be kept whole, and a blocking element is provided to act on the attaching portion from an outside arrangement.  
      In order to obtain the blocking effect, which may also be a limiting effect, —or to completely prevent a rotating movement of the tab up to a substantial limit of the rotating movement, an outer edge of the flat attaching portion (rivet island) abuts against the projection that is shaped to protrude out of the sheet metal lid. Since the projection has positional stability on the panel in all operating positions, even when starting to break open the openable area, and since the attaching portion is substantially coplanar with the panel of the lid, tightly surrounding the central rivet as a mounting place, none of the above elements provided for preventing rotation operationally moves apart with an opening movement of the tab. Since the opening movement is a vertical tilting motion, anti-rotation is unaffected due to an outer edge of the attaching portion abutting on the panel projection.  
      Advantageously, a peripheral edge on a known tab within the art may also be used, since the edge does not have to be specifically arranged for obtaining the rotation barrier effect after the attachment of the tab to the panel (“staking”). The only manipulation is effected on the sheet metal lid itself, which is provided with a shape, as is the rivet in a preliminary phase, which shape may preferably also be pre-formed together with the formation of the rivet and modified in shape, or more precisely “reformed” subsequently, in a further processing step of the sheet metal lid being manufactured. The projection may thus be formed integrally with the sheet metal lid, as is the mounting place by one-piece manufacturing for the attaching portion of the tab.  
      The projection may have a strip shape (or line shape) aligned transversely and/or parallel to a longitudinal extension of the tab (e.g., longitudinal axis or longitudinal plane), engaging at a correspondingly aligned peripheral edge of the attaching portion for its blocking effect. In a longitudinal extension, the projection may extend over more than 30%, 50%, or possibly to more than 80% of the width of the attaching portion.  
      If the projections extend parallel to the longitudinal extension of the tab, or perpendicular to the transverse direction mentioned above, than the longitudinal extension may be shorter than the longitudinal extension of the attaching portion (rivet island) of the tab. Further, the projection may be at a position as distant as possible from the mounting place, such that at least one portion of the two peripheral lines mentioned above, abuts and prevents rotation on the at least one projection when starting a rotating movement.  
      Arranging the attachment portion as distant as possible from the mounting place allows the greatest possible force to be exerted, which provides a blocking effect to prevent rotation of the tab by a user. In particular, the projections oriented parallel to the longitudinal extension of the tab allows for a great force to be applied for the locking effect. All three of the above structural arrangements may be used either singularly or used in a combination.  
      The height or vertical extension of the at least one projection, may be at least equal to or possibly greater than the thickness of the sheet metal of the attaching portion, in order to obtain a reliable fixing position. Further, the above arrangement does not impair the operating or raising the grip portion, since the attaching portion is reliably situated on the other side of the mounting place and coplanar with the panel section surrounding the rivet (button coin area).  
      Several projections may be provided, but not all projections have to be assigned to the same outer edge portion of the attaching portion. The projections may also be differently embodied, i.e. strip-shaped, round to oval, or a combination thereof. If a line-shaped outer edge portion of the attaching portion is provided, a line-shaped (strip-shaped) embodiment of the projections may be advantageous. The line-shaped strip design may also be achieved by arranging at least two punctiform projections in line, which then form a group that is assigned to the same outer edge portion of the attaching portion.  
      The attaching portion in the form of a mounting tongue can be connected to the rest of the tab via a buckling portion in the form of an articulation line, i.e. integrally. It is thus provided between the opening portion (the rupture nose) and the grip portion which can be provided with a hole.  
      If the attaching portion is substantially rectangular, the substantially rectangular, flat, attaching portion can be formed by using the articulation line and three edge lines. Particularly, the flat or surface portion can be square in shape, and the rivet head positioned closer to the articulation line, so as not to be centrally arranged after mounting. The distance of the outwardly directing peripheral edge can therefore be larger than half the longitudinal extension of the attaching portion, so that a correspondingly improved force effect is achieved when a projection on the panel can be assigned to the peripheral edge farthest from the mounting place.  
      Further, it is possible for at least one of the projections to have an asymmetrical cross section, so as to have a steeper flank facing the attaching portion than the flank facing away from the attaching portion. The above configuration may also be selected for example, for the punctiform or oval projections.  
      According to another feature of the invention, a subsequent reshaping, reforming, or post-forming may include the reduction of the thickness of a top side of the (strip-shaped) projection, thus, achieving the solidification of the portion together with the projection as a whole. The score line may also be applied simultaneously with the reforming as mentioned above.  
      The result of reforming can be visually apparent in a flattened top side. Thus, the projection mentioned above can have a larger width than its total height. Further, the respective longitudinal extension of a projection can be considerably larger than the width of the projection. This can apply to elongated strip-shaped or line-shaped projections. When a steeper flank portion is formed it can be more pronounced than the preform. Further, a peripheral edge may be obtained having (at least) one portion extending at an angle substantially 90° relative to the plane of the panel. This applies to the edge opposing the assigned peripheral edge portion of the attaching portion. An embossing process also helps to give a stronger or steeper shape to the flank, the embossing provides for the reinforcement of the reformed sheet metal on the top side.  
      Further, if several projections are provided they do not have to engage the same edge line of the attaching portion at the start of a rotating movement, but instead may be assigned to different outer edges.  
      A still unfinished sheet metal lid is prepared to receive a tab includes the formation of the projection that is sufficiently positioned to be distant from the intended mounting place (from the re-formed rivet or its preform). Further, at such a distance the outer edge in the form of an edge of the attaching surface (rivet island) facing away from the future rivet can be located very close to the projection, thereby achieving the rotation stopping effect. Furthermore, since the location is in the outer edge portion of a rivet head zone or the “rivet base”, it can extend visibly around the formation of the rivet center remaining from the rivet perform.  
      The projection arranged as a line or strip can be positioned at least partially outside the weakened rivet base portion, in which the sheet metal may be thin due to the shaping of the mounting place. The above arrangement can address a peripheral portion of the rivet base zone which may be more than 40% of an assumed surface of a strip-shaped projection lying outside the rivet base zone.  
      The rivet base zone can be arranged to visibly change the surface remaining on the inside of the sheet metal lid after the rivet has been formed and the tab has been mounted. Since the projection is placed in the outer portion, i.e. as distant as possible from the weakened sheet metal or the thin sheet metal, the re-formed portion may be considerably higher before the sheet metal is damaged. Further, the re-forming may achieve heights that can be above a sheet metal thickness of the attaching portion of the tab.  
      The projection may be provided with a strip shape, as well as be designed to have a length longer than the diameter of the finished rivet head.  
      The attaching portion can be formed from a piece of the central portion of the tab, in which only minor gaps are visible between the attaching portion, which is displaced downwards to a lower plane by a double buckling line, and the parallel plane of the rest of the tab, which may be somewhat higher. Accordingly, the mounting of the projections on at least one of the free peripheral edges facing outward from the attaching portion may be barely visible from the outside, so that the rotation blocking is virtually invisible to the observer. A colored tab does not necessarily have to change in a colored shape. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention is further described in the detailed description which follows, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:  
       FIG. 1  shows the first stage of three stages in a manufacturing process of a sheet metal lid, which introduces, in part, a score line or weakening line, U-shaped bead and mounting place;  
       FIG. 2  shows the second stage of three stages in a manufacturing process of a sheet metal lid, which introduces, in part, beads along the tab, finger depression and an eyeball shaped bead;  
       FIG. 3  shows the third stage of three stages in a manufacturing process of a sheet metal lid, which introduces, in part, an attaching tongue, tab, buckling line and open position;  
       FIG. 4  is an enlarged section from  FIG. 3 , particularly showing the attaching portion  31  and the rivet  11  as mounting place;  
       FIG. 4   a  is a cross section along line C-C in  FIG. 4 ;  
       FIG. 5  is an alternative configuration for the positional fixing of attaching portion  31  and thus of the entire tab  30 ;  
       FIG. 5   a  is a sectional view through the center plane of  FIG. 5 , alternatively through the vertical longitudinal plane  100  of  FIG. 3 ;  
       FIG. 6  is an alternative arrangement of projections for blocking rotation of the tab;  
       FIG. 7  is another alternative arrangement to  FIG. 6 ;  
       FIG. 8  is a cross section along a longitudinal plane  100 , to illustrate a sharp front edge  20   a  of a strip-shaped or line-shaped projection  20 ;  
       FIG. 8   a  is a cross section of an embodiment of the invention corresponding to the illustration in  FIG. 8 ;  
       FIG. 9   a  is a schematic explanation of the effective torques in a projection extending parallel to the center plane  100 ;  
       FIG. 9   b  is a comparable explanation of the effective torques in a projection  20  located transversely to the center plane  100 ; and  
       FIG. 10  is an illustration of a portion  11   a  around a rivet  11 , the portion being visible from the inside of the lid, a projection  20  being visible as an outwardly vaulted cavity. This figure identifies only a section around a rivet  11  as a mounting place. 
    
    
     DETAILED DESCRIPTION OF THE PRESENT INVENTION  
      FIGS.  1  to  3  show a sheet metal lid having a visible edge portion  12  suitable for seaming to a body of a beverage can. The sheet metal lid can be produced from thin sheet metal, typically less than 0.24 mm, which may have already passed through previous workstations before reaching the stage shown in  FIG. 1 . Further, the lid may include an inner surface portion or panel  10  that can be surrounded by a seamable edge  12 . Further, within the panel  10 , a weakening line  16  can be provided around an openable area, wherein the openable area may be surrounded by a substantially U-shaped bead  18 . The bead opens towards the center portion of the panel, wherein the substantially O-shaped weakening line  16  is designed as a score line. A transitional section that is not scored serves as a connecting portion to the rest of panel  10 , when the openable area  17  is broken in and along the score line  16  by the effect of a tab.  
      A mounting place  11  is positioned approximately in the middle of the panel. An attaching portion  31  or a sheet metal tongue can be part of the tab ( FIG. 3 ), which can be integrally formed via an articulation line or a buckling line  38 . The tab  30  can include a grip portion  32  that may be arranged with a circular opening, so the tab  30  can be operated by the user for breaking open the score line  16 . See  FIG. 1 . The tab  30  may also include an opening portion  33  arranged before the attaching portion  31 , wherein the opening portion may be located as a rupture nose above the openable area  17 . Further, an additional eyeball-shaped bead  18   a  ( FIG. 2 ) can be provided to reinforce the transverse LOE (large opening ends) openable area, resulting in an arrangement in which the applied forces from the opening forces are able to rupture the starting portion or arcuate end of the score line  16 . The mounted tab  30  may be substantially parallel to the panel, so as to be slightly bulged or not exactly arranged in one place, through an area around the mounting place  11 . Further, the mounting place  11  can be substantially planar so as to allow for a substantially parallel arrangement of the attaching tongue of the tab  30 .  
       FIGS. 1, 3  and  5  show the longitudinal midplane  100  extending in a direction to the longitudinal extension of the tab  30 , as well as a transverse plane  101  ( FIG. 5 ) extending perpendicularly thereto.  
      The grip portion  32  (of an attached or staked end) of the tab  30  overlaps a finger depression  13 , which is provided in the panel  10 , at approximately the same distance as the inner reinforcing bead  18   a  on the other side of mounting place  11 . The tab  30  may only be attached ( FIG. 3 ) during the manufacture of the finished sheet metal lid. Prior to the completion of manufacture of finished sheet metal lid, the mounting place  11  may initially be formed as a bubble to permit the attaching portion  31  of the tab  30  to be attached to the panel  10 .  FIG. 1  shows three strip-shaped projections  20 ,  21  re-formed as upwardly protruding beads (i.e. towards the outside of the sheet metal lid) around said mounting place  11 . The bead  20  can extend transversely to the midplane  100  which may be longer than the two neighboring beads that can extend parallel to the midplane  100 .  FIG. 4  shows detailed view via  21   a ,  21   b  of a possible arrangement of the longer bead  20  with respect to the attaching tongue  31 .  
       FIG. 1  shows the attachment tongue  31  and the distances of the beads  20 ,  21  from the mounting place  11 . At a particular manufacturing station, the re-forming of the three beads  20 ,  21   a ,  21   b  results in a formation of the beads (or projections). See  FIG. 3 . At the above manufacturing station, the projections are re-formed integrally from the sheet metal lid or panel  10  so as to extend in a vertical direction at least to a height h that is equal to the sheet metal thickness of the attaching portion  31  of the tab  30 . Further, the projections are then provided with correct profile geometries.  
       FIG. 3  shows the rivet head in a forming process with a larger diameter than is shown in  FIGS. 1 and 2 , wherein the tab  30  is placed over the rivet shaft. While the rivet head is forming, the tab  30  is attached to the panel  10  via the attaching portion  31 , wherein the attaching portion  31  can be connected to the rest of the tab  30  through a buckling line  38 . The opening section  33  can be located above the openable area  17  inside the score line  16 , close to an additional stiffening bead  18   a.    
      In order to ensure the rupture force and the accuracy in the breaking-open process, the tab  30  rotational movement direction is designated by α in  FIG. 4 .  
      To open the opening area  17 , the front nose end of the opening portion  33  is moved away from an exact position to provide a rupture force, resulting in continued tearing until the subsequent complete opening of the opening area  17 . It is obvious that the front nose end of the opening portion  33  would be moved away from the exact position that is provided to ensure the rupture force, the continued tearing and the subsequent complete opening of the opening area  17 .— FIG. 4  shows the tab rotational movement α being as minimal as possible, or possibly restricting all rotational movement.  FIGS. 4-6  show the three strip-shaped projections  21   a ,  21   b  and  20  being assigned to the three free peripheral edges  31   a ,  31   b ,  31   c  of the attaching portion  31  of the grip portion  30 . A small gap  21 ′,  21 ″ and  20 ′ may be left between each outwardly facing edge and the respective inner edge of the each projection, for example,  31   c  from 20″ at the projection  20 . However, the gap may also be reduced to zero on at least one of the outwardly facing edges of said attaching portion  31 .  
       FIG. 4  shows the width of the attaching portion  31  being marked with “b”, and the two projections  21   b ,  21   a  (or beads) positioned parallel to the longitudinal midplane  100  and at a distance from the attaching portion  31  via inside edges  21   b ′ and  21   a ′. The longitudinal extension of the attaching portion  31  in the plane  100  extends over the rivet head as the mounting place  11 . The length of the two beads  21   a ,  21   b  can be shorter than half the longitudinal extension of the attaching portion  31 . Further, beads may be positioned as far as possible to the rear area of the attaching portion in order to apply the greatest possible force for the locking effect or positional fixing with an assumed rotation movement α.  
      The above arrangmement of the locking effect (or positional fixing) with the assumed rotation movement α, may further be effected with the greatest possible distance of the projection  20  disposed in the transverse plane  101 , which is transverse to the longitudinal mid-plane  100 . Further, the projection  20  may be longer than two projections  21   b ,  21   a  (or beads) positioned parallel to the longitudinal midplane  100 . It is possible for the projection  20  to extend over more than half or even more than 80% of the width b of the attaching portion  31 .  
      According to another feature of the invention, it is also possible for one or more of the three strip-shaped projections or beads described above to be omitted from the attaching portion  31 .  
      According to another embodiment of the invention, the attaching portion  31  may be arranged with one projection  20 , as viewed in  FIG. 5 . Further, the outwardly facing edge  31   c  is positioned farthest from the rivet or mounting place  11  and approximate the strip-shaped projection (or geometry)  20 , so as to minimize or even prevent the rotational movement α of the tab  30 . It is possible to limit the rotational movement α of the tab  30  with the positioning of the projection  20  to such an extent that the opening behavior of the tab is not affected when the tab  30  is tilted upwards at the grip portion  32 . The rotating movement α can be predetermined by at least two limit values, which are defined by the abutment in an assumed rotation α (in both directions about the axis of the rivet  11 ), resulting in limited or even possibly no rotating movement α. Further, the rotational or pivoting movement α is substantially in the plane in which the panel is disposed in an area surrounding the rivet head  11 , such that the plane is kept parallel by the plane of the attaching portion  31  (which may have a planar or surface extension). The attaching portion  31  may be embodied as a rectangle or square, having two parallel peripheral edges or edges  31   b ,  31   a  and one peripheral edge  31   c  at a distance from the articulation line  38  and extending parallel thereto. Another embodiment may include the attaching portion  31  having an arcuate form similar to a triangular shape, or a more distant shape which may not have a straight extending peripheral edge  31   c.    
      The cross-section shown in  FIG. 4   a  relates to the corresponding sectional line of  FIG. 4 . According thereto, an asymmetrical design of the strip-shaped projections  21   a ,  21   b  is provided, a steeper flank  21   b ′ being located closer to a peripheral edge  31   b  than the less steep flank  21   b ″ of strip-shaped projection  21   b . The same is valid for the parallel projection  21   a  and its associated peripheral edge  31   a.    
      In  FIG. 4   a , the sheet metal lid in the panel  10  and the attaching portion  31  are parallel, with the rivet  11  (not shown). An assumed rotation movement causes the peripheral edge  31   a  to abut on the steeper flank of the projection  21   a , or the peripheral edge  31   b  to abut on the steeper flank  21   b ′ of the projection  21   b . A narrower association of the steeper flanks, due to their almost vertically extending ridges or steps, permits any minor (residual) rotating movement in the plane of the sheet metal lid of the panel  10  in the rivet zone  11  to be almost completely prevented.  
       FIG. 5   a  shows a cross section relating to  FIG. 5  and arranged through the longitudinal plane  100 .  FIG. 5   a  shows one projection  20  cooperating with the peripheral edge  31   c  of the attaching portion  31  to prevent function-affecting rotational movements α. Further, the rivet head designed as a mounting place  11  is visible through an opening in the attaching portion  31 . Also visible is the allocation of the free peripheral edge  31   c  to the projection  20  re-formed from the metal sheet lid, which projection  20  (see  FIG. 4   a ) indicates that other projections  21   b ,  21   a  may also have an asymmetrical shape.  
       FIG. 8  shows the asymmetry in a transverse direction to the longitudinal extension of the projection  20  (in the longitudinal plane  100  of the lid or the tab). Further, the projection  20  can be associated to the peripheral edge  31   c  of the attaching portion  31 . By a double forming process, a first pre-forming according to  FIG. 1  and a second re-forming according to  FIG. 2 , resulting in a very steep front edge  20 ″ or  20   a  can be obtained, having a very large height h (relative to the thickness of the sheet metal). Furthermore, the projection  20  is arranged as distant as possible from the sensitive area of the rivet base  11   a , in case the sheet lid is damaged which would resulting in damage to the projection  20 . The steep front edge  20   a  (or  20 ″ according to  FIG. 4 ), together with a less steeply extending second flank  20   b , which provides no blocking effect with the attaching portion  31 , allows higher forces to be applied. Further, the attaching portion  31  is less likely to be deformed upwards (perpendicularly to the plane of panel  10 ) on a more flatly extending peripheral edge and to thereby lose the blocking effect.  
       FIG. 8   a  shows the cross section extending in a longitudinal direction, as determined by the longitudinal midplane  100  for  FIG. 4, 5 ,  8  as viewed in the bottom section. Further, the top illustration shows a preform  20 *, in a two-stage manufacturing process prior to the second step (post-forming or re-forming). In a first shaping step, for example according to  FIG. 1 , a pre-form  20 *, which may have a rampart (or ridge-shaped structure), can be shaped to protrude out of a panel  10  with two flat inclines and a middle portion extremely rounded. In a second re-forming step, (see  FIG. 2 ), a much steeper front edge  20 ″ (see  FIG. 4 ) or  20   a  (see  FIG. 8 ) is obtained, while the sheet metal lid nevertheless remains undamaged. The second re-forming and the result after attaching the grip portion are shown in the lower illustration of  FIG. 8   a . It is understood that in both the upper and the lower illustrations, the strip-shaped projection  20  can extend perpendicularly to the paper plane, in a transverse plane  101  extending perpendicularly to the longitudinal midplane  100 . The transverse plane  101  is a relative indication referring to the position of the pre-form  20 *, in which there is a symmetry of the pre-form initially shaped from the sheet metal lid relative to the plane  101 , that is abandoned during re-forming, as is illustrated by the finished projection  20  in the bottom representation, in which it is no longer symmetrical to the transverse plane  101 .  
      The following embodiments refer to the bottom illustration of  FIG. 8   a . The rivet  11  used for attaching portion  31  to the sheet metal lid  10  can be located to the left (not shown). A rear end  31   c  of an attaching portion  31  is the peripheral edge that is assigned to a front edge  20 ″ of a projection  20 , possibly leaving a narrow gap  20 ′ (see  FIG. 4 ). The projection  20  is characterized by an asymmetry, with a steep front edge  20 ″ (or  20   a ) and a less steeply extending peripheral edge  20   b  facing outwards. As a result of re-forming, the projection may also have a plateau-shaped top side  20   c , providing for the projection  20  to reach a very large height h relative to the thickness of the sheet metal, despite the relatively flat appearance of its shape. However, the width of the projection is arranged to have an increased strength with the width being larger than its height h, particularly about twice as wide as it is high, so that the essential portion of the projection  20  can be situated to the right of the transverse plane  101 .  
      The re-forming step includes shaping the pre-form  20 * with a coining (or an embossing operation) for flattening the top surface  20   c . In the re-forming process, a tool is applied from the top and from the bottom for re-forming. The slight bend that is detectable on the left in the rising flank of the pre-form  20 ′ may be recognized in the bottom final form via the sharp front edge  20 ″ being introduced in the initially gently rising front incline of the shaped rampart  20 *. To the right of the transverse plane  101 , the second incline of the rampart is formed from bottom to top, for forming a flat shape  20   c , starting approximately at the instep of said rampart  20 * and leading gently over to the rest of the sheet metal panel  10  in portion  20   b.    
      Additionally, in the final form, the attaching portion  31  and the tab  30  are already attached according to  FIG. 3 . The tab can be 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 figure  3 , 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  is a part of the grip portion  32 , the web  32   a  between said two openings being shown slightly bulged in  FIG. 8   a , 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 said web and is barely visible from outside.  
      In this context, a modified sequence of the two-stage re-forming may be performed besides the processing sequence according to FIGS.  1  to  3 . For example, the initial introduction of the pre-forms, as illustrated by the pre-form  20 * in the top picture of  FIG. 8   a , in a first working step, shown without the introduction of score lines (as weakening lines 16). In this case multiple projections can be used to block rotating movements which may include all the pre-forms being shaped. The first score line introduced can be jointly in a single working step, in which the re-forming (further shaping) of the pre-formed projections takes place. In this step, the projections receive their correct, assigned profile, as is shown in the bottom illustration of  FIG. 8   a . For example, this profile is capable of being transferred not only to the transversely extending projection  20 , but also to the other projections, provided that they have been shaped as pre-forms in the previous operation. In this way, a scoring operation, which subjects the sheet metal to severe stress, is not performed at the same time as the shaping of the pre-form takes place in the first operation, since the shaping process causes considerable stress to the sheet metal lid. The score line may be introduced simultaneously with the re-forming operation. During re-forming (see  FIG. 8   a ), the wall thickness on the top side of the projection is reduced by about 10% to 15%, with simultaneous compression and solidification of the same portion, thus achieving uniformity from top to bottom by the embossing operation (or coining).  
       FIG. 6  shows an attachment of two substantially punctiform projections  23   a ,  23   b  to the longitudinal sides  31   a ,  31   b  of the attaching portion  31 . Additionally, a projection  22  may be provided on transverse edge  31   c  of the attaching portion  31 , wherein the projection  22  may be elongated (such as oval shape) and or substantially circular shape.  
       FIG. 7  shows a group of projections arranged to a single outer edge (outwardly facing peripheral line) of the attaching portion  31 . The group  24  may include three individual, substantially punctiform projections assigned to the peripheral edge  31   c , but may as well be assigned to the two other peripheral edges  31   a  and  31   b . Also, only two punctiform projections can be used in  FIG. 7 . In the same way, the asymmetrical shape of the projections formed to protrude in upward direction in accordance with  FIG. 4   a , or also  FIG. 5   a  or  8   a , may also be applied to the above mentioned embodiments.  
      For example, one projection may be used with a peripheral edge  31   c  extending transversely to the longitudinal plane  100  of the tab  30 , wherein the rotational movement in both directions can be prevented if the projection extends at least on both sides of the midplane. On the other hand, if a projection is arranged on a peripheral edge extending parallel to the longitudinal plane  100 , then at least two projections should be provided on the two correspondingly available edges as “stop edges”, for symmetrically limiting rotational movements of the tab  30 .  
      All the projections described may be arranged outside the attaching portion  30 , in order to be able to cooperate in a blocking manner with at least one of its respective outer peripheral edges (edge).  
       FIGS. 9   a  and  9   b  show a top view of the attaching portion  31  disposed on the panel  10  over a mounting place  11  (or rivet head). A lateral projection  21   a  extends parallel to the midplane  100  of the tab  30 , upon which a force is exerted on the projection due to an assumed rotation movement in a direction α. An assumed length I of the attaching portion  31  to the mounting place  11  can be located closer to the articulation line  38  than to the rear end  31   c  of the attaching portion  31 , so that an effective power arm I 1  is larger than half of the length I of the attaching portion  31 . Because of the positioning of the line or strip-shaped projection  21   a  that is close to the rear edge line  31   c , a force via a large lever arm can apply a large torque for blocking (blocking moment) an undesired rotation.  
      Similarly, the exertion of torques may be explained in a projection  20  that extends perpendicularly to a midplane  100 , wherein the projection can substantially occupy the entire width b of the attaching portion  31  near to a rear edge line  31   c  thereof. In this case, the (maximum) power arm is designated b 1 , and in a first approximation, the lever arm is approximately (but not exactly) equal to half of the width b, marked as lever arm b 1  in an assumed (hypothetical) rotational movement in a direction α as illustrated. The corresponding force via the lever arm b 1  is applied by the projection  20 , or the front edge  20   a  thereof (edge  20 ″ in  FIG. 4 ). The corner of the attaching portion  31  being slightly rounded, the entire half of the width is not available for use as a lever arm, but instead between 70% and 100% of b/2, substantially in the range of between 80% and 90%.  
       FIG. 10  shows a thinned zone of the sheet metal lid around a rivet head  11  said zone being visible from the inside. Said rivet base zone  11   a  is a zone that remains on an outer side after the second re-forming of the rivet head  11 , usually visibly by circular lines surrounding the center of the rivet as mounting place  11 .  
      The “button coin area” most likely cannot withstand strong stresses, since the sheet metal is reduced in thickness due to the rivet being shaped to protrude in an outward direction. Projection  20  occupies a surface area f 20  that is line or strip-shaped mounted in the outer edge zone  11   b  of the rivet base, or rather displaced far outside of the thin sheet metal zone susceptible to possible damage. The attaching portion  31  is marked by a dashed line showing the relative position of the “coin area”. Alternatively or cumulatively, the projection  20  can be shown as located at the rear edge  31   c , where the two lateral projections  21   a ,  21   b  may also be provided. Which can result in the projections being positioned close to the peripheral zone of the rivet base and not displaced to the thinned out portion near the rivet head, which portion is susceptible to damages.  
      For example, a more precise dimensioning of the surface areas may show the strip-shaped projection  20  situated at least partly outside the rivet base zone (or coin area) and outside the outer peripheral portion  11   b  thereof. The outward displacement can be equal to at least 40% of the surface portion f 20 , which is no longer in the periphery  11   b  of the rivet base  11   a , but outside thereof. This position and the position and extension of the coin area can easily be visible from the inside of the sheet metal lid.