Abstract:
The invention relates to a cover for opening and closing cans, in particular beverage cans, having a top circular cover component and a bottom cover component. By moving the two cover components relative to one another, at least one through-hole can be opened and re-closed by both cover components. A highly effective seal is obtained by precise coordination of the form of the top and bottom cover components, which can be increased even further by the additional use of sealing materials such as varnish, rubber, plastic or welded connections.

Description:
RELATED APPLICATION 
     The present application is a Divisional Application of U.S. application Ser. No. 13/497,547, filed Mar. 22, 2012, which application is a 371 International Application of PCT/EP2010/000906, filed Feb. 11, 2010. 
    
    
     FIELD OF THE INVENTION 
     The invention refers to a cover for opening and closing cans, especially beverage cans. 
     BACKGROUND 
     There are many drawing can covers with opening systems known from the state of the art. Generally, the beverage cans used nowadays have a stay-on tab with a rivet-fastened, ring-shaped metallic cover plate that is pressed towards the interior of the can, following the slitting line marked on the oval area of the cover. This opening system for drinking has the disadvantage that it cannot be closed once again after it has been opened. 
     A possibility of attaching a re-closable cover would be to join it to the top edge of the can. Such an embodiment has been described in DE 69809567T2, for example. However, the top edge of the can is attached during the filling process, leading to the following problems: The product spills out while the cover is being attached, the spilled-out liquid must be removed, a second cover must be immediately attached so filling speed is not affected and costs increase. In addition, attachment to the top edge of the can is difficult because the tolerance values are not sufficiently low and there can be up to 0.3 mm difference between two covers. An attachment to the top edge of the can would also lead to changed packaging modifications and transportation capability owing to the different piling height. This would lead to higher planning modification expenses for fewer products per volume. 
     SUMMARY 
     An objective of this invention is the further improvement of known opening systems for beverage cans. Additional objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     The main objective of this invention is to consider, as far as possible, all current production standards and criteria. In particular, high cost effectiveness is pursued, followed by marked production delimitation. The fewer modifications that are needed in current standards, the larger the possible savings. To accomplish this objective, it is essential to implement all changes in one spot of the production line (either in production or in the filling station). In this case, the improved approach centers on the production step, as it is carried out less often and can be better implemented owing to existing technical resources. 
     Therefore, the filling step is completely ruled out as possible means of improvement in this invention. An exception to this rule would be an “add-on” design feature not functionally essential and merely optional for the customer. 
     According to an initial aspect of the invention, the task of improving current opening systems for drinking cans is solved by a cover for the opening and closing of cans, especially beverage cans, that features a top circular cover component and a bottom cover component. By moving the cover components relative to one another, at least a through-hole can be achieved, re-closable by moving the cover components relative to one another. This makes it not only possible to open a can that was once opened, but to securely close it again. 
     It is especially advantageous for the top cover component to be attached to the inner area of the bottom cover component. Attaching the drinking closure system on the interior surface of the bottom cover component instead of on its outer edge has the advantage that the cover can be entirely produced in an upstream step and then be merely attached to the body of the can in one step after filling. 
     The bottom cover component can have at least one opening, which can already be there or made only after moving the cover components towards one another. In this way, an opening for allowing the liquid to flow out and another one for ventilation purposes can be provided. 
     The opening and closing movement of the cover components relative to one another can be achieved by pivoting the top cover component on the bottom cover component. However, a lateral displacement is also conceivable. 
     It is especially advantageous to create a joint on the bottom cover component and to use it for attaching the top cover component. In a rotatable mounting, the bottom cover component can have a circular movement groove on its surface. In this case, the radius of the groove is smaller than the radius of the bottom cover component and the top cover component has a spring that snaps and/or clicks in place into the fastening groove. 
     Here, the invention falls back on folding mechanisms for can covers known from the state of the art. A possibility for bending such a joint is described in WO 01/897 37 A1. It describes how a safety fold can be bent in several steps in a can cover. Other ways for bending such a joint can also be employed. Another method is described in the published U.S. application Ser. No. 09/578,044, which also describes how a can cover can be bent to a safety fold in several steps. Other methods known to the expert can also be used for folding the joint. 
     At the same time, there are other possibilities from the state of the art, as well as turning flanging and edge rolling that can be utilized to create the fastening joint on the bottom cover. Placing this fastening joint inside the bottom cover makes it possible to separate the critical features of the filling design from the production of the cover. The additional manufacture of the fastening joint also facilitates the attachment to the top cover by a hook, thus creating an optimal functional design and not depending on the edge flange results. 
     Thanks to the positioning on the bottom cover component, the top cover component is protected from possible dropping damage by the top external edge of the can. The top cover component is located below the edge of the can, and is thereby no longer exposed. In addition, less material is needed for the top cover component by attaching it to the bottom cover component in a fastening joint with a radius within the outer edge of the can. Weight-wise, this feature makes this invention comparable to stay-on tab versions. 
     In addition to the material and cost savings, further improvements are possible owing to system compatibility. Current production speeds make it possible to classify the covers mechanically and join them with the bottom cover component. This can be done by employing the identical technology and method as is already being used in standard stay-on tab technology for attaching the loop or ring. The current design of the elevations on the bottom cover is similar to the anti-rotation tip used for classifying the stay-on tab for the ring. The top cover component would be attached in the same step in which the ring or loop is placed in the stay-on tab system. 
     The standard folding technology used for the loop or ring can also be employed for shaping the bends of the top cover component. These bends also serve as cover strengthening, as compensation for the material that is missing on the sides and at the same time as mechanism for opening the closure. 
     Additionally, the folded structure of the top cover component has the following advantages with regard to the spilled-over liquid: The folded shape makes it easier to reach the surface of the bottom cover component and also easier to clean spilled-over liquid at the filling station. Also, condensation of the liquid after pasteurization can dry up quite well. 
     It is advantageous for the bottom cover component to have an elevation that acts together with the corresponding design of the top cover component. It can be shaped in any way—for example, cylindrical or pyramidal. The top cover component can have either a respective elevation or a recess that corresponds to the shape for mounting the cover components. In addition, the element can also maintain the cover components separate. 
     The top cover component can be made of aluminum, but the use of tinplate or plastic is also conceivable. 
     In the plastic version, it is possible to remove the top component slightly so the plastic can be recycled. Since the bottom cover component is larger than the top cover component made of plastic, the product keeps flowing across the bottom cover, keeping the liquid cold and separated from the top cover. Furthermore, in case a plastic version is used, the feeling of drinking from a “cold can” does not get lost, as the edge of the can still touches the mouth. 
     It is additionally possible to use tinplate because no open metal ending touches the product on the top cover component, thereby preventing rust and contamination. With the stay-on tab tinplate system, it is customary to re-paint pressure-formed parts as additional protection. This can also be done for the opening of the bottom cover component, if necessary. Owing to its price and general application advantages in the market, tinplate is a particularly suitable material. In this case, the smallest material thickness used as standard (0.16 mm) is sufficient. Due to the smaller radius of the top cover component, this is innately stiffer, making an even thinner tinplate diameter of 0.12 mm possible. 
     According to a further aspect of the invention, the top cover component can have a recess so less material is used for it. At the same time, the recess can serve as an opening in the top cover component. The top cover component, in particular, can have a recess shaped like a circular segment—even two recesses shaped like a circular segment and arranged opposite one another are conceivable. 
     The opening inner edge can be angled. This applies both to an opening in the bottom cover component and to an opening in the top cover component. As a result of the angle, a sealing can take place when the top cover component interlocks with the bottom one. 
     Alternatively or cumulatively, a sealing can also be arranged between the cover components. In this regard, a sealing is understood to be any medium suitable for attaching the two cover components. Thus, a coat of paint is conceivable as a form of sealing, but rubber, plastic or suitable liquid media such as adhesives and even welding are possible. In this context, the sealing can be designed so it fits tightly in place in the opening of the bottom cover component. Finally, it can also interlock with the top cover component. 
     The sealing must be able to resist numerous stresses, like vibrations during transportation, pressure changes, and changes in the contact area caused by thermal expansions during temperature changes. The manufacture of a sealing ring is therefore very costly, both during development and production. Since this can lead to a considerable production slowdown and make the sealing considerably more expensive to manufacture, the aim should be to accomplish the sealing with other media. 
     Another aspect of the invention foresees the top and bottom cover components to be made from a hybrid coating material with a plastic layer. It is advantageous for the plastic layer of the bottom cover component to be placed on that of the top cover component, between the two of them. 
     The utilization of such a hybrid layered composite material consisting of one-half plastic and one-half tinplate or aluminum, for example, makes it possible to combine the advantages of the various materials in different areas so they have a favorable effect on the general performance features. 
     If the plastic side is processed while on top on the bottom cover, and on the bottom on the top cover, then the two plastic sides will have direct contact. The conical opening in the bottom cover component forms a good sealing surface contact with the conical projection of the top cover component. This contact area is subsequently joined with heat or high-frequency welding. In this case, the welding focuses on the surroundings of this area and is utilized only for an instant after the second cover is assembled. Later, the user breaks through this welded part by pressing inward the hood-shaped structure on the top cover component, destroying the welded sealing in the process. The top cover component can now be turned. This can also be accomplished by an instantaneous loss of pressure that evens out the two cover surfaces, facilitating the slight turning of the top cover component. 
     In a plastic version, the seal would be designed as part of the top cover component. A projection on the top cover component would then have the identical negative shape of the top part of the opening of the bottom cover component. This arching on the top cover component is joined snugly with the hole on the bottom cover component with which it will be later welded to by pressing into a tear line on the inner side. The seal-less plastic version is opened in the same way as the version with a seal. 
     With regard to the opening and closing possibilities, it is conceivable to integrate a snap closure in the top cover of the metallic version. To achieve this, it is conceivable to provide an arching in the middle of the top cover so that the side of the top cover that is folded upward snaps downward, thereby closing—but not sealing—the can. In order to seal the can, the folded lateral components are then pressed inward in this closed position and the cover locks in place in a sealed position. When the cover is re-opened, the arching snaps out and locks in place in the open position. 
     Another aspect of the invention refers to a method for manufacturing a cover. Here, the top cover and the bottom cover are manufactured separately and subsequently joined in a downstream step. 
     A final aspect of the invention refers to a method for joining a cover with a bottom cover component. In this case, the pre-manufactured cover is joined to the can in a downstream step. Thus, the filling section of the production line is left unchanged and the current filling speed is maintained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be discussed in greater detail with the help of numerous embodiments depicted in the drawings, which show: 
         FIG. 1  is a three-dimensional view of the cover made of aluminum. 
         FIG. 2  is a three-dimensional view of the cover made of plastic. 
         FIG. 3  is a section view through a cover made of aluminum. 
         FIG. 4  is a section view through the bottom cover component with marked fastening joint, 
         FIG. 5  is a section view through a bottom cover component with marked elevations. 
         FIG. 6  is a section view through a bottom cover component with marked opening area. 
         FIG. 7  is a section view through a bottom cover component with marked cutting edge on the opening. 
         FIG. 8  is a section view through a cover with a top cover component made of plastic. 
         FIG. 9  is a view of the hook of a top cover component made of aluminum. 
         FIG. 10  is a view of the hook of a top cover component made of plastic. 
         FIG. 11  is a view of the target expansion points of a top cover component of an aluminum cover. 
         FIG. 12  is a view of the target expansion points of a top cover component of a plastic cover. 
         FIG. 13  is a view of the middle area of an aluminum cover. 
         FIG. 14  is a view of the middle area of a plastic cover. 
         FIG. 15  is a section view through an aluminum cover with marked opening area. 
         FIG. 16  is a section view through a plastic cover with marked opening area, 
         FIG. 17  is a three-dimensional view of a bottom cover component. 
         FIG. 18  is a three-dimensional view of the cover with a top cover component made of plastic in an unopened state. 
         FIG. 19  is a three-dimensional view of the cover with a top cover component made of plastic in an unsealed, but unopened state. 
         FIG. 20  is a three-dimensional view of the cover with a top cover component made of plastic in an opened state. 
         FIG. 21  is a three-dimensional view of the cover with a top cover component made of plastic, in a state opened for recycling. 
         FIG. 22  is a three-dimensional view of a top cover component made of aluminum. 
         FIG. 23  is a three-dimensional view of a can with an “add-on” design feature with a two-part top plastic cover component. 
         FIG. 24  is a three-dimensional view of the outer edge section of the plastic cover component. 
         FIG. 25  is a three-dimensional view of the inner edge section of the plastic cover component. 
         FIG. 26  is a three-dimensional view of a small seal. 
         FIG. 27  is a three-dimensional view of a large seal. 
         FIG. 28  is a three-dimensional view of the bottom cover component of the can with opened seals. 
         FIG. 29  is a section view through a bottom cover component made of aluminum with a seal. 
         FIG. 30  is a section view through a bottom cover component made of aluminum with a seal. 
         FIGS. 31 a  through 31 h    are views of possible designs of the connecting point between top cover component and bottom cover component. 
         FIGS. 32 a  through 32 s    are views of possible designs of the sealing mechanism in the opening for drinking between top cover component and bottom cover component. 
         FIGS. 33 a  through 33 i    are views of possible designs of the guide from the top cover component to the bottom cover component. 
         FIGS. 34 a  through 34 o    are views of the various closure variants both in the open and closed position. 
     
    
    
     DESCRIPTION 
     Reference will now be made to embodiments of the invention, one or more examples of which are shown in the drawings. Each embodiment is provided by way of explanation of the invention, and not as a limitation of the invention. For example features illustrated or described as part of one embodiment can be combined with another embodiment to yield still another embodiment. It is intended that the present invention include these and other modifications and variations to the embodiments described herein. 
     The cover  1  made of aluminum shown in  FIG. 1  consists of a bottom cover component  2  and a top cover component  3 . 
       FIG. 2  shows a cover  21  partly made of plastic with a bottom cover component  22  made of aluminum and a top cover component  23  made of plastic. 
       FIG. 3  shows a section through the cover  1  made of aluminum of  FIG. 1  with the bottom cover component  2  and the top cover component  3 . The top cover component  3  engages in a fastening joint  4  located in the bottom cover component  2 . Here, a seal  6  closes the opening  5 , but it can be broken through by exerting pressure on the elevation  7 . The top cover component  3  is pivoted on the elevation  8  in the bottom cover component  2 . 
       FIG. 4  shows the bottom cover component  2  with the fastening joint  4  marked. 
     The utilization of the so-called “safety fold-end” technology or of another folding technique known by the expert makes it possible to displace the fastening joint  4  for the top cover component (not shown) from the outer edge of the can towards the interior. This has the advantage of making an intervention in the filling process unnecessary because the second cover component (not shown here) can already be mounted in the production step. The mounting of the second cover component is similar to the steps necessary for joining the ring with the cover in stay-on tab closures. 
       FIG. 5  emphasizes the elevation  8  for mounting located in the bottom cover component. 
     The elevation  8  pointing upward allows a better alignment of the covers. It could also be used as an ordering aid for the bottom cover  2  if the latter must be aligned. 
     In  FIG. 6 , the opening area towards the opening  5  in the bottom cover is marked. An angled wing  9  located there allows a larger sealing surface on a more restricted space by taking advantage of the vertical length. This design allows a possible minimization of pressure loss caused by the thermal expansion of the material when aluminum or plastic is used, for example. An angled surface also makes more sealing surface available and serves as an inner ring for increasing sealing effectiveness. 
     In the bottom cover component  2  shown in  FIG. 7 , the cutting edge  10  in the opening  5  is marked. A flattened cut on this cutting edge  10  allows keeping the seal in place because the cut offers resistance when the seal is pressed, thereby preventing the seal to slide downward. The flattened cut  10  also allows a precise size adjustment necessary for the good fit of the seal. 
       FIG. 8  shows a cross section through a can cover  21  with a bottom cover component  22  made of aluminum and a top cover component  23  made of plastic. Here, the top cover component  23  also engages in a fastening joint  24 . A seal  26  has been arranged in the opening for drinking  25 . Here, too, mounting is achieved by the elevation  28  in the bottom cover component, but an opening of the seal takes place here by pressing the T-shaped engagement component  27  inward. After use, the top cover component  23  can be easily removed when the T-shaped engagement component  27  is cut off from the fastening joint  29  and then pushed out of the lead  30 . Then it is possible to press the top cover component  23  together to unhook and remove it. 
     Both in the design of the top cover component  3  made of aluminum shown in  FIG. 9  and in the design of the top cover component  23  made of plastic shown in  FIG. 10 , it is in each case possible to manufacture the hook  11  and  31  according to function because the mounting possibilities no longer have to be adapted to the shape of the edge rim of the edge of the can after attaching the cover. This is especially important when the surface of the hook  11  and  31 , respectively, is reduced as this invention suggests. 
     It is also possible to manufacture the top cover component with a double hook for strengthening the mounting of the second cover component. In this case, a second fastening groove could be attached on the top side of the bottom cover component for this second hook. Even a triple spring in the top cover component is conceivable for further strengthening the mounting of the second cover component.  FIG. 31  shows this structural variant and others in detail below. 
     The top cover component  3  or  23  made of aluminum in  FIG. 11  and made of plastic in  FIG. 12  can have cuts  12  or areas  32  with fewer materials in certain spots in order to eliminate excessive stiffness that can prevent the top cover component  3  or  32  from fitting successfully together with the bottom cover. Here, the cuts  12  or areas  32  with fewer materials can be arranged in such a way that the stress relief acts only in one direction for preventing the unhooking of the top cover component  3 ,  23 . 
     The top cover component  3  or  23  made of aluminum ( FIG. 13 ) or plastic ( FIG. 14 ) has a rounded section in the marked middle area  13  or  33  that allows the top cover component  3 ,  23  to easily slide above the elevation  8  (cf.  FIG. 5 ). 
     The top cover component  3  shown in  FIG. 15 —with cuts  14  on the elevation  7 —is the aluminum version. These cuts create a tong shape that will later engage in a grooved tab on the seal. As a result of this, it would be joined with the top cover component  3  while the cover is being put together during production. So that the user can open it later, the hood  7  is pressed inward, leading to the opening of the seal along a predetermined tear line. 
       FIG. 16  shows a variant of the cover  23  made of plastic. It is equipped with a similar mechanism so it engages with the seal, with the exception of the projection that the seal of the metallic version has. This allows the direct placement of the cover on the seal when the former is attached in the production line. In this case, the top plastic cover  23  is mounted with the open snapper  27  (shown closed here), thus making it possible to bend the cover and facilitating the mounting in the production line. If the end user engages the snapper  27  to open the can (as shown here), the cover will jump upward during the engaging process and weaken the seal so it can be torn open. If this does not tear it open, then it can surely be accomplished by turning the top cover component  23 . 
     The bottom cover component  2  shown in  FIG. 17  can be utilized both for the aluminum version of the cover  1  and for the plastic version of the cover  21  (cf.  FIGS. 1 and 2 ). It has the fastening joint  4  (or  24 ), the opening for drinking  5  as well as two elevations  8  and  8 ″ for mounting the top cover component. 
     In  FIG. 18 , a top cover component  23  made of plastic has been placed on the bottom cover component  22  so that both of them together build the cover  21 . If the cover  21  should be opened, the engagement component  27  is pressed into the guide  30  to tear open the seal. Now the top cover component  23  can be turned on the bottom cover component  22  and the opening  25  is exposed, as shown in  FIG. 20 . After the can is used, the engagement component  27  can be removed by separating the tab  29  so the top cover component  23  can be completely detached from the bottom cover component  22 . 
     Likewise, the top cover component  3  made of aluminum shown in  FIG. 22  can be placed on top of the bottom cover component  2  shown in  FIG. 17 . Even this one can afterwards be turned on the bottom cover component  3  after the seal has been broken through. The wings  15  and  15 ′ provide a gripping surface for this purpose. 
       FIG. 23  shows a complete can  40  consisting of a can body  41  with a two-part top plastic cover  42 —an “add-on” design feature that also makes changes in the filling step necessary. In the course of this, an outer plastic ring  43  (see also  FIG. 24  for a detailed image) is mounted onto the top can edge  44  (see  FIG. 28 ). An inner cover component  45  (see also  FIG. 25  for a detailed image) that covers the top can cover from above can then be pressed inward in the plastic ring  43  around the can edge  44 . The inner plastic part  45  engages in the inner side of the outer can edge. At the same time, possible seals  46 ,  47  (cf.  FIGS. 26 and 27 ) engage in the cover component  45  and are permanently joined to it. Also simultaneously, the seals are broken through around the opening of the cover  48  by a sharp edge. To accomplish this, the seals  46 ,  47  are designed with a predetermined breaking spot to facilitate the process. Now the can  40  can be used. If it is turned by 90°, it opens, if it is turned back, it closes again. This cover design allows rivets and a clear visual indicator as soon as the cover was opened once. 
     Based on the same engagement principle, the top cover component can be designed as one single component. The top cover component would be engaged in the seal in the filling station and fixed in place there until turning tears it open. This would also serve as a tamper-proof mechanism. This version can be used with both plastic and aluminum materials. 
     In a further execution—the “break-open design”—the functional spot is located directly above the spot that should be opened. Here, the functional spot of the cover that has been mounted above the seal is a component separated by the cover. This component is small compared to the opening&#39;s proportions. The form is pressed inward for breaking the seal, which engages in the component, and the latter engages in a lower recess in the cover. 
     A further embodiment has an arching above the opening. Here, the material is so thin that the thumb can press the arching inward, thereby connecting the seal with insertion openings in the arching. The pushing-in of the arching opens the seal and at the same time serves as tamper proof. This design variant can also be utilized with both materials (plastic and aluminum). 
     The bottom cover component  2  of  FIGS. 29 and 30  has in each case a seal (shown here in the different variants  6  and  6 ′). 
     The can cover  51  in  FIG. 31 a    consists of a bottom cover component  52  and a top cover component  53 . Here, the bottom cover component  52  corresponds to a standard can cover with a fastening joint  54  that engages in a hook  55  of the top cover component  53 . The hook  55  of the top cover component  53  has been folded for increased stability. This also improves the turning of the hook  55  in the joint  54 . In  FIG. 31 b   , the same cover  51  is once again shown three-dimensionally. 
     The can cover  61  in  FIG. 31 c    consists once again of a bottom cover component  62  that corresponds to the normal can cover and of a top cover component  63 . This time, however, a second hook  65  on the top cover component  63  has been provided beside the first hook  64  in order to improve the mounting of the top cover component  63 . The bending on the outer edge  66  allows a more flexible movement in this area. This can be helpful because this area is stiffer owing to the proximity to further structures on the top cover component  63 . 
     In the structural variant of a can cover  71  shown in  FIG. 31 d   , the top cover component  73  has beside the hook  74  a lateral indentation  75 , which is in contact with the fastening joint  76  of the bottom cover component  72  in order to prevent a lateral slipping out of position of the top cover component  73 . Additionally, the top cover component  73  has a groove  77  that creates another fastening connection point. The former plus an additional groove  78  act together on the bottom cover component  72 . The grooves  77  and  78  serve as guiding rail for mounting and lifting the top cover component  73  if they are not continuously mounted on the entire circumference. 
     In  FIG. 31 e   , the bottom cover component  82  of the cover  81  has a fastening joint  83  oriented inward that acts like a hook. The edge of the top cover component  84  is flat and has a roll edge  85  for making frictionless turning possible. Furthermore, it has a V-shaped opening  86  that acts as a spring. If the V-shaped opening  86  is pressed together with the index finger and thumb, the radius of the top cover component  84  becomes smaller, making an easy turning possible. With the smaller radius of the top cover component  84 , it moves upward along the fastening joint  83 . 
     In the structural variant shown in  FIG. 31 f   , the bottom cover component of the can cover  91  has—as fastening joint  94 —a flange  93  pointing inward with a groove  95  that serves as guide for the top cover component  96 . The groove  97  on the top cover component  96  increases stiffness and creates a constant separation between the cover components in order to prevent a blockage when the top cover component  96  is turned. 
     In the cover component  101  of  FIG. 31 g   , the bottom cover component  102  has a fluted form  103  on which two inner plastic cover components  104  represent the functional elements and engage in the bottom cover component  102 . The toothed form  103  of the bottom cover component  102  prevents the slipping out of position of the cover on the connecting surface. The toothing arrangement as far as possible below the top cover component  105  allows mounting without previous orientation because there is always only a small gap to the next engaging position. The two inner cover components have been provided with a snap-on device  106  that can be executed in various ways depending on the shape and needs. If it extends along the radius, it can also serve as guiding rail with varying height for accomplishing a lifting of the inner top cover component  104 . In addition to the mounting of the two inner cover components, the engagement device can serve as safety seal that is broken through when the cover is turned. The second top cover component  107  merely serves to make a better gripping surface available for turning. However, it is not essential for functioning, as all functional components are located on both inner cover components. 
     In the structural variant of a can cover  111  shown in  FIG. 31 h   , the bottom cover component  112  is closed by a plastic shape  113  that engages in the opening of the bottom cover component  112 . The seal  113  has some toothed tabs  114  that engage in a hook  11  (likewise toothed) on the inner cover component  116 . The inner top cover component  116  engages on the top cover  116  in the top position. If it is oriented with the opening of the bottom cover component  112 , the inner top cover component  116  is pressed inward to a second (lower) position and engages in the recess  117 . In this case, the seal engages in the inner top cover component and is torn or cut in by the cutting device  118 . 
     In the variant of a can cover  141  shown in  FIG. 32 a   , the bottom cover component  142  has an opening  143  whose edges  144  are folded inward. With the cone  145  on the top cover component, these rounded edges  144  create a close contact to achieve a sealing. The sealing is interrupted when the top cover component  146  is turned. Until opening by the user, the edge on top of the cone creates a complete sealing. 
     In the structural variant of a can cover  151  shown in  FIG. 32 b   , the bottom cover component  152  has an opening  153  with an edge  154  folded upward. This can be advantageous for preventing the liquid in the can to make contact with the open cutting edge of the metal. Together with the tight fit of the cone  155  on the top cover component  156 , a gastight sealing is achieved until the break occurs. 
     In the structural variant of a can cover  161  shown in  FIG. 32 c   , the bottom cover component  162  has a fold  163  for enhancing the stiffness of this area and at the same time for increasing the sealing surface. A sealing can be achieved by using a remaining plastic layer composite, which is attached in the contact area by thermal or high-frequency welding. 
     A double fold  173  on the bottom cover component  172  creates an expansion of the sealing surface in the top cover component  175  with a double cone  174  (cf.  FIG. 32 d   ). 
     If the fold  183  is attached below the surface of the bottom cover, a larger free space while turning and lifting the top cover component  184  is ensured (see  FIG. 32 e   ). 
     In the variant  191  shown in  FIG. 32 f   , the bottom cover component  192  has an opening  193  with a groove  194  in which a seal  195  can be arranged. An additional reinforcement  196  prevents the seal  195  from slipping or sliding. 
     If the bottom can cover  202  and the top can cover  203  are separated by an elevation in the middle (not shown) in the can cover  201  shown in  FIG. 32 g   , then the distance of the cover components  202  and  203  to each other towards the exterior decreases with the radius. Additionally, the pressure on the closed cover decreases when it is closed, starting with the radius from the middle (i.e. the pressure in the middle is higher than on the sides). The asymmetrical form of the cone  204  and the fold  205  account for the compensation. 
     In the structural variant of a can cover  211  shown in  FIG. 32 h   , the bottom cover component  212  remains covered with the original cover surface. It has been partly—but not fully—cut, so that material remains standing to serve as hinge for the material that has been broken through. The breaking point can be either a tear line  213  or a cut  214  protected by a seal, in which case the seal breaks as soon as it is opened for the first time. 
     The cover  211  is opened by turning the top cover component  215  above the elevation  216 . Here, the rounded edge  217  located on the top cover component is pushed on and above the elevation  216 , as a result of which it is pressed inward and the seal is broken. 
     As soon as the connecting piece is broken through by turning the top cover component  215  in the closed position, the piece swings even further back because the second elevation  218  acts together with the lateral surface of the cone  219  of the top cover component  215  (cf. the position of the cover  211  in  FIG. 32 i   ). 
     In the structural variant of a can cover  221  shown in closed and open position in  FIGS. 31 j  and 32 k   , the bottom cover component  222  has a series of perforations  223 ,  224  and  225  covered by a soft seal  226 . Owing to the small diameter of the openings, the pressure exerted on the seal is sufficiently reduced so that it remains in place without additional fastening. In addition, the cover that will later close the can serves as an additional support for the seal. 
     The can cover  221  is opened by a few cones with punched holes  227 ,  228  and  229  (cf.  FIG. 32 k   ). They have a cutting edge that meets the exposed rubber seal. As soon as these cones  227 ,  228  and  229  are brought into alignment with the openings  223 ,  224  and  225 , they engage and the cut takes place. Liquid can now flow into the openings created in this fashion. The severed plastic remains hanging on the main seal  226  and is now pushed aside only by the cones  227 ,  228  and  229 . This design prevents insects from reaching the can&#39;s interior owing to the small size of the openings. 
     The  FIGS. 32 l  and 32 m    show how the seal  234  is used:  FIG. 32 l    shows the original form of the seal before it is incorporated into the cover  231 . The seal  234  has been shaped in such a way that it can easily fit into the opening  235  located in the bottom cover component  232  so it can be firmly welded later on this spot for achieving the sealing. The seal  234  has a predetermined breaking point that will slide open when the elevation  237  on the top cover component  233  is pressed inward. This pressure is transferred to the seal  234  via the projection  238 , opening the former in the process. The top cover component  233  has openings  239  that engage in the tongue-shaped tabs  240  of the seal. 
     The can cover  241  shown in  FIG. 32 o    consists once again of a bottom cover component  242  and a top cover component  243 . The seal  244  has been integrated into the top cover component. The top cover component  243  developed from plastic is shown separately in  FIG. 32 n   . The original shape of the seal that can be seen in  FIG. 32 n    allows a slight adjustment of the sealing component  245  to the shape of the opening  246  in the bottom cover component  242 . The seal will be later welded to the bottom cover component  242  to achieve a secure sealing. When the can cover  241  is opened, the part of the seal  245  connected to the bottom cover component  242  remains on this spot, whereas the remaining part separates along the tear line  247  and stays part of the top cover component  243  with the remaining seal part. 
     In the can cover  251  of  FIG. 32 p   , the plastic seal  253  is surrounded by a rib-shaped structure  254  that engages in a fixed position when it is pressed inward. By pressing the seal inward, the bottom part of the seal  255  breaks off. For closing the can again, the upper part of the seal acts together with the bottom part of the seal. 
     In this context, the seal  253  engages in three positions: On the top cover component  256 , on the bottom cover component  252  and finally against itself, when the seal was broken (cf.  FIG. 32 q   ). 
     In the structural variant shown in  FIG. 32 r   , a seal  264  engages in the opening of the bottom cover component  262 . The seal has a tear line  265  and a rod shape  266  and when the seal  264  is pressed inward, the bottom plastic part  267  engages in a rib-shaped structure  268  located on the top cover component  263 . It engages farther down in a position that allows a connection of the seal with the plastic part owing to the rod-shaped structure  265 . As a result of this movement, the cutting tip  269  of the plastic part breaks through the seal  264 . As can be seen in  FIG. 32 r   , the conical cutting tip  269  simultaneously protects the cutting area of the seal  264  and also the seal  264  from the cover surface. 
     As shown in  FIG. 33 , there are various structural variants for guiding the top cover component on the bottom one. In this connection,  FIG. 33 a    shows a three-dimensional view of the bottom cover component  272  and the top cover component  273  (both of them seen in cross section in  FIG. 33 b    put together as cover  271 ). The bottom cover component  272  has one single ramp  274  projecting upward, located in the middle of the bottom cover component  272 . When the top cover component  273  is turned, the ramp  274  presses against the corner  275  of the top cover component  273  and lifts it. A 180° turn brings the cover components  273  and  272  back to their original position. 
     In the structural variant shown in  FIGS. 33 c  and 33 d   , the bottom cover component  282  has at least one ramp  283  pointing upward, attached on the outer perimeter of the cover. The top cover component  284 , on the other hand, has a ramp  285  that points downward. When the top cover component  284  is turned on the bottom cover component, the two elevations located between them come into contact and the covers are separated from each other. The fold  286  of the top cover component  284  prevents permanent damage through lifting and facilitates the lifting in this area. 
     In the structural variant  291  shown in  FIGS. 33 e  and 33 f   , the bottom component  292  has once again two ramps  293  and  294 . This time, however, the upper component  295  has a different design with openings  296  and  297  in the corresponding spots of the ramps. When the top cover component  295  is twisted in such a way that the openings no longer come to rest above the ramps, the two cover components are separated from one another. 
     The structural variant  301  shown in  FIGS. 33 g  and 33 h    has two ramps  303  and  304  in the bottom cover component  302 . These ramps press against the open side  306  of the top cover component  305  when the latter is turned and separate both cover components in this fashion by lifting. 
     The bottom cover component  312  of the structural variant shown in  FIG. 33 i    has a three-sided elevation  313 . The top cover component  317  has a smaller opening  314 , a larger opening  315  and a closed lid  316  as well as an elevation  318 . With the help of the three-sided elevations  313 ,  318 , every one of these functional elements can be lined up by turning the top cover component  317  with the opening  319  located in the bottom cover component  312 . 
     In the structural variant  321  of  FIG. 34 a    (left after opening, right before), a hard plastic seal  324  has been attached on the opening  325  of the bottom cover component  322 . The seal  324  has a tear line  328 . The top cover component  323  has an elevation  329  that has holes  327  with tongues, which act together with the toothed tabs  330  when the elevation  329  is pressed inward. As a result of this, the seal is extended in such a way that it tears along the predetermined tear line  328 . The torn seal remains attached to the top component  323  and serves as closure so the can be closed once again after opening. 
     In the structural variant  331  of  FIG. 34 b    (right after opening, left before), the top cover component  334  has a middle section that acts together with the elevation  333  in the bottom cover component  332 . If the top cover component is turned above the lifting ramps  335 , the elevation  336  will jump from convex to concave. When that happens, the two flaps  337  and  337 ″ will fold slightly outward and hold the top cover component  334  upward. In this upper position, the can may only be closed, but not sealed. In order to seal the can, the two flaps  337  and  337 ″ are pressed together to their original position, whereupon the top cover component  334  engages. 
     In the structural variant  341  shown in  FIG. 34 c   , the cone  347  of the top cover component  343  has an asymmetrical form with an elevation  344 . The cone  347  is welded to the wall  345  by welding a plastic layer of a hybrid coating material made of plastic and metal. If the asymmetrical elevation  344  is pressed from concave to convex, the welded sealing opens and allows gas to escape. This causes the top cover component  343  and the bottom cover component  342  to separate sufficiently, thus facilitating the turning of the top cover component  343 . 
     In the structural variant  351  (shown in an open position in  FIG. 34 d    and in a closed position in  FIG. 34 e   ), a plastic seal  354  is attached on the bottom cover component  352 . The former has an engagement device  355  that will subsequently act together with the top cover component  353 . The top cover component  353  has an engagement device  356  connected to the top cover component  353  with a tab  357 . When the engagement component  356  is pressed into the guide  358 , the top cover component  353  is lifted, thereby breaking through the seal  354  on the bottom cover component  352  (cf.  FIG. 34 e   ). 
     In the structural variant of  FIGS. 34 f  and 34 g   , the bottom cover component  362  has an opening  363  strongly bent outward for securing the seal  364 . The connection between the cone  365  of the top cover component  366  and the seal  364  is interrupted when the elevation  367  is pressed, going from the concave position in  FIG. 34 f    to the convex position shown in  FIG. 34   g.    
     In the structural variant of a can cover  371  shown in  FIGS. 34 h  and 34 i   , the bottom cover component  372  remains covered with the original cover surface. The area lying underneath the lateral wall has a tear line  373  or is partly cut  374 , but not fully separated. Thus, there remains material that can serve as hinge for the broken-through material. The cover  371  is opened by turning the top cover component  375  above the elevation  376 , in which case the edge  377  in the upper cover component is pushed on and above the elevation  376 . 
     In the closed position (cf.  FIG. 34 i   ), the cover piece that was broken inward swings even farther back because the second elevation  378  acts together with the lateral surface of the cone  379  of the top cover component  375 . 
     The inner ring  384  of the top cover component  383  exerts sufficient pressure on the seal  385  to keep the can cover  381  shown in  FIGS. 34 j  and 34 k    tightly closed. In addition, the inner ring  384  protects the elastic seal from expanding under extreme pressures after all. Once the cover  381  has been opened, the opened wall of the cones  385 ,  386 ,  387  presses so tightly on the seal  385 , that no liquid can reach between them. 
     In the variant shown in  FIGS. 34 l  and 34 m   , the locking position of the top component  394  of the seal  395  exerts, when pressed, a lateral pressure on the wall  396  of the opening edge, thereby creating a sealing. At the same time, the top section  394  of the seal also severs the actual seal along the predetermined tear line  398 . The broken off section  397  of the seal integrates itself into the top component  394 . 
     In the structural variant of a cover  401  (cf.  FIGS. 34 n  and 34 o   ), the bottom cover component  402  has an edge  403  bent inwards. The top cover component  403 , in turn, has an inverse cone  404  that is somewhat bigger than the inner edge of the opening  405 . Owing to the larger circumference, the top cover component  403  engages and the can is tightly closed. The utilization of a plastic-metal coating material can prevent the two metallic cover components from touching. The can is opened by pressing the elevation  406  inward from its concave ( FIG. 34 n   ) to a convex form ( FIG. 34 o   ). 
     Modifications and variations can be made to the embodiments illustrated or described herein without departing from the scope and spirit of the invention as set forth in the appended claims.