Abstract:
Disclosed are a top shell ( 1 ) or bottom shell ( 2 ) made from a deep-drawn molded plastic part as well as a receptacle which is composed of the two joined shells. The invention further relates to a method and a device for producing a top shell or a bottom shell ( 1, 2 ). The aim of the invention is to create a first and second shell ( 1, 2 ) which can be produced inexpensively as a disposable item while allowing the same to be locked together in a fixed but easily removable manner by joining the two shells together so as to create a largely tight receptacle. Said aim is achieved, among other things, by embodying a reducing collar ( 5 ) between the holding edge ( 4 ) and the pot-type central part ( 3 ) on the top shell ( 1 ) while disposing at least two identically pitched threads ( 7   a,    7   b,    7   c,    7   d,    7   e,    7   f ) on the inner face ( 6 ) of the holding edge ( 4 ). The reducing collar ( 5 ) delimits the at least two threads ( 7   a,    7   b,    7   c,    7   d,    7   e,    7   f ) on one side while said at least two threads ( 7   a,    7   b,    7   c,    7   d,    7   e,    7   f ) are provided with an open thread inlet ( 48 ).

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a top shell and a bottom shell made from a deep-drawn molded plastic part as well as a receptacle, which is composed of the two joined shells. The invention also comprises a method and a device for producing a top shell or a bottom shell.  
         [0003]     2. Description of Related Art  
         [0004]     A combination of a first shell, for example a top shell, with a second shell, for example a bottom shell, results in a receptacle, in which in the joined state the first shell engages the second shell from the outside, with the second shell being embodied with a circular opening edge, and with the first shell protruding from the second shell with its holding edge. Such receptacles serve to store and transport small parts of all sorts, in particular food, such as for example cream cheese, yogurt, and the like, and with the latter also comprising salad compositions provided with dressing or to which dressing remains to be added. A receptacle of a different type produced therein by injection molding is disclosed in U.S. Pat. No. 5,638,976. The injection molding process offers the advantage that the containers can be produced in a greater number of varieties with regard to their geometry. The disadvantage of this production process lies in its relatively high production costs per item.  
         [0005]     Due to the fact that the containers usually are to be disposed of after the consumption of their content, only containers with a particularly cost-effective production are considered for this use, which can be produced from a thermoplastic material using the deep-drawing method.  
         [0006]     A receptacle produced from a deep-drawn plastic material with two halves that can be screwed to each other is described in U.S. Pat. No. 3,322,262. The first half is provided with an exterior thread and the second half with an interior thread for a screwed connection. However, this structural design with two complementary adjusted threads requires an expensive production process. Furthermore, the seal of the receptacle screwed together is solely implemented by the connected threads, which leads to considerable leaks due to the unavoidable irregularities resulting from the deep-drawing method. This is particularly unacceptable for packaging food.  
         [0007]     Conventional resealable receptacles, for example for yogurt, using a closing or sealing means as simple and cheap as possible, comprise a bottom shell with a corresponding top shell, with the top shell in the area of the opening edge comprise a so-called lid apron with snapping elements, which engage below the edge of the shell. When opening the receptacle the lid aprons are pulled over the opening edge. For this purpose, the lid apron must be engaged from below and the snapping connection must be loosened, in order to lift the lid. This is not only awkward, but it also presents the risk that the fingers come into contact with the content of the receptacle.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     Therefore, the invention is based on the object to provide a first and a second shell, which can be produced cost-effectively as disposable units, on the one hand, and on the other hand, allow a largely tightly sealed container by connecting a tight but easily separable lock.  
         [0009]     Additional partial objects comprise the development of a method and a device for producing the first shells.  
         [0010]     The object is attained according to the invention in a first shell, for example a lid shell, with a mounting means being arranged for creating a threaded connection, with the mounting means comprising a reducing collar embodied between the holding edge and the pot-type central part and at least two threads arranged on the inside of the holding edge having the same incline, with the reducing collar limiting at least two threads on one side and the at least two threads each having an open thread inlet.  
         [0011]     Each thread is limited by the reducing collar like a flange, so that in the transitional area from the thread to the reducing collar a conically merging wedge is formed, in which elements of a second shell cooperating complementary to the thread are fixed by a clamping action. For this purpose the reducing collar is embodied circularly with a constant width. Such a clamping fastening is particularly advantageous for molded plastic parts produced by a deep drawing process.  
         [0012]     Advantageously, the threads are each arranged diametrically. This results, by also diametrically arranged complementary elements of the second shell, such as for example holding wings, in a clamping effect evenly distributed over the opening edge, connected with an evenly distributed pressure of the top shell to the bottom shell. This in turn increases the seal even over an extended period of use.  
         [0013]     Preferably, the threads are provided with an incline ranging from 5° to 30°. Although generally all inclines of threads can be realized, in the above-mentioned range a relatively low construction height of the holding edge is achieved with a simultaneously low displacement distance for loosening the first shell from the second one.  
         [0014]     Also, it has proven advantageous for the first shell to be provided with a seal. The seal may for example be embodied as a concentrically encircling sealing edge on the bottom of the first shell between the pot-type central part and the reducing collar. When the first and the second shell are connected the sealing cone is supported on the second shell at its transitional area from the opening edge to the interior wall and thus creates a sealing effect. Instead of the encircling sealing cone this may also be waived and a sealing sheeting may be welded to the opening edge.  
         [0015]     The second shell is provided with a cup wall, which is embodied at its upper section with a circular opening edge and in its lower section it is permanently closed by a bottom plate. According to the invention, a fastening means for creating a threaded connection is arranged at the second shell, with the fastening means comprising at least two radially protruding stiff holding wings at the circular opening edge. The term stiff used here is defined as a stiffness allowing a functionally appropriate opening and closing of the second shell without any reversible or irreversible deformation of the holding wings.  
         [0016]     The holding wings of the second shell cooperate with the threads of the first shell such that the holding wings in the connected state protrude into the threads and the first and second shells are mutually guided during the rotary motion. The essential advantage in reference to the known threaded connection lies the fact that a complex thread, complementary to the thread of the first shell, can be waived on the second shell, which considerably reduces the expense during production.  
         [0017]     The holding wings shall be arranged diametrically around the opening edge. This, together with the holding wings also being distributed evenly over the circumferential direction, achieves a surface pressure evenly distributed over the circumferential direction between the first and the second shell. This contributes to a good seal and prevents an unintended separation of the top shell from the bottom shell.  
         [0018]     With regard to the geometries of the holding wings a number of embodiments are possible. In a preferred embodiment the holding wings are provided with a front and rear edge extending radially in reference to the second shell, which are connected to each other via exterior edges arced concentrically in reference to the second shell.  
         [0019]     Alternatively to the above-described embodiment the holding wings may also provide a front edge extending radially in reference to the second shell and a convexly arced rear edge.  
         [0020]     It has also proven advantageous for the holding wings to be formed from a holding surface protruding rectangularly or squarely from the opening edge.  
         [0021]     In another advantageous embodiment the holding wings may also be formed as holding cams.  
         [0022]     The further partial object is attained in a resealable receptacle comprising a first shell and a second shell that can be mounted thereto with a reducing collar being embodied between the holding edge and the pot-type central part, and by which the first and the second shell can be screwed together via a threaded connection, with the thread connection at the first shell, on the inside of the holding edge having at least two threads of identical incline, limited on one side by the reducing collar, and having an open thread inlet each, and at the second shell comprising at least two holding wings protruding radially from the circular opening edge.  
         [0023]     Combining the first shell with a second shell creates a largely sealed receptacle. Being a complementary component to the above-described at least two threads they are engaged by radially protruding holding wings arranged at the second shell.  
         [0024]     Preferably the number of holding wings is smaller or equal to the number of threads. This facilitates the connection of the first to the second shell without holding wings blocking the corresponding thread and causing a blockage during threading.  
         [0025]     Advantageously, at least two threads are provided with a width larger than the holding wings in the circumferential direction of the holding edge. This allows a secure introduction of the holding wings into the respective threads particularly in the inlet area of the threads.  
         [0026]     The first shell can be provided with a nominal diameter slightly larger than the full-circle diameter of the holding wings in the area of the holding edge and between the opposite threads.  
         [0027]     Additionally, it may be advantageous for the first shell to be provided with an interior diameter slightly larger than the exterior diameter of the opening edge in an area between the thread cams of the threads.  
         [0028]     By the larger interior diameter of the holding edge in reference to the opening edge the first shell is allowed to grab over the second shell. When having an almost identical wall thickness it is visible to the outside in the area of the threads only. This widening of the interior diameter is adjusted to the sizing of the holding wings such that the holding wings are guided in the thread over the entire length of the thread. The interior diameter in the area of the threads should only be selected slightly larger than the full-circle diameter of the holding wings so that an overlapping as much as possible develops between the flank of the respective thread and the holding wing guided therein.  
         [0029]     The partial object is attained in a deep-drawing process, using a form tool with a torque-proof arranged holding sheath and a threaded sheath pivotal in the circumferential direction in reference to the holding sheath, in which first in an original position of the holding sheath and the threaded sheath a sheeting is moved over the form tool, the sheeting is entered into the form tool in order to form a first shell, clamped, and formed, the threaded sheath is brought into the end position by spindling, and the shell is removed from the holding sheath.  
         [0030]     The method according to the invention relates exclusively to the forming process for producing a shell comprising a thread, for example a top shell. After positioning the sheeting over the form tool the sheeting is preferably impinged on its upper side with pressurized air and molds to the form tool. In this processing step the shell is formed with threads. In order to separate the shell from the form tool, in particular from the contours of the threads, the threaded sheath is spindled off. This is a process similar to a nut and bolt, with the nut representing the first shell and the bolt being the threaded sheath. By screwing the bolt out of the nut and/or the threaded sheath out of the first shell the threaded sheath loses its contact to the first shell and thus releases it so that the first shell can be lifted upwards off the form tool.  
         [0031]     In a preferred embodiment of the method the shell is held by the holding sheath and/or the sheeting during the spindling off. In general, it is possible for the first shell to be fixed exclusively via the sheeting during the spindling off, in order to prevent that the shell rotates together with the threaded sheath. However, this is particularly problematic in soft or thin materials, because the sheeting cannot compensate the forces occurring during spindling off and deformations develop at the first shell. For this reason it is advantageous for the first shell also to be held at least additionally by the holding sheath.  
         [0032]     In the above-described method the shell can be removed off the holding sheath together with the sheeting. In another step the sheeting molded into the first shell is fed to another conventional punching machine and the shells are separated from the sheeting.  
         [0033]     By transporting the sheeting to a punching machine locally separated an additional cooling of the sheeting and the first shells molded therein occurs so that a separation cannot occur concentrically around the desired form of the first shell but off-set therefrom. This disadvantage is particularly dominant in materials with a high material-related shrinkage, for example in polypropylene (PP). The material PP has an irregular shrinkage of approximately 2% when cooling. Less critical is the time-delayed separation for polystyrene (PS), which shrinks as calculated by no more than 0.5%.  
         [0034]     For severely shrinking materials it is therefore advantageous when the first shell is punched immediately on the form tool after the threaded sheath has been spindled off the sheeting. This considerably reduces the rejects, because now an exact alignment of the shell to the punching machine is possible and an intermediate transportation from the form tool to the punching machine is omitted.  
         [0035]     A concentric molding even more precisely in quality can be achieved when the shell is already punched on the form tool prior to spindling the threaded sheath off the sheeting. Here, the first shell may be fixed against rotating with the threaded sheath exclusively by the holding sheath, because prior to spindling off it has already been separated from the sheeting. Here, the holding sheath is provided with a geometric structure, which is formed complementary in the first shell after the molding process and allows a form-fitting transfer of force.  
         [0036]     When the first shell is completely separated from the sheeting this relates to a blanking method.  
         [0037]     However, alternatively it has proven advantageous for the first shell to be punched off the sheeting only partially and to leave residual bars between the sheeting and the shell. This process relates to hoop-steel cutting. Here, at least partially, forces are still compensated by the sheeting during the spindling off and still very precisely concentrated parts are produced. The residual bars are broken in the subsequent stacking process. The lower production costs in reference to blanking are an essential advantage. A disadvantage in reference to blanking lies in the potentially remaining bars not completely broken off having dangerous cutting edges.  
         [0038]     The third partial object is attained in a form tool for producing a first shell with a fixed holding sheath and a threaded sheath pivotal in reference to the holding sheath in the circumferential direction out of the original position into an end position, with contours being embodied in the threaded sheath for forming at least two threads.  
         [0039]     Advantageously, an interior die is arranged centered inside the holding sheath. The interior die serves to form the interior pot-type central part and can be displaceable in the axial direction in a particular embodiment alone or together with the holding sheath. Based on the ability for displacement it is possible to lift and remove the first shell off the form tool after the threaded sheath has been spindled off.  
         [0040]     Advantageously the threaded sheath is arranged concentrically around the holding sheath so that the threaded sheath rotates symmetrically around the holding sheath during spindling off. Here, the holding sheath should be located at the inside and the threaded sheath at the outside.  
         [0041]     In a beneficial embodiment the holding sheath is provided with an inclined wall section in which holding ribs are arranged. Here, depending on the angle of the inclined wall section, the holding ribs can be aligned in the axial or radial direction of the holding sheath. In and case, the holding ribs shall be aligned perpendicular, if possible, to the rotational direction of the threaded sheath, so that a torque resulting from the pivotal motion of the threaded sheath unto the shell is compensated by the holding ribs.  
         [0042]     It is sufficient for the pure forming processing when a holding device is arranged around the threaded sheath, by which the sheeting can be clamped outside the form tool and thus can be fixed. The holding device may comprise, for example, a fixed punching thrust bearing and a holding plate that can be lowered.  
         [0043]     In case the blanking or hoop-steel cutting is performed by the form tool, instead of a holding device, a holding and punching device may be arranged around the threaded sheath.  
         [0044]     The blanking can be preformed particularly advantageous using a holding and punching device, which comprises a separating plate, a cutting plate that can be lowered, and a fixed knife sheath concentrically surrounding the threaded sheath, with the separating plate and the knife plate being displaceable in the vertical direction. Preferably the knife sheath is arranged between the threaded sheath and the separation plate.  
         [0045]     Using the knife plate that can be lowered the sheeting is clamped between the knife plate after it has been moved over the form tool. Subsequently to the forming process and after the threaded sheath has been spindled off said sheath is moved upwards and thus cuts the sheeting with the knife plate.  
         [0046]     It is particularly advantageous when the knife sheath slightly protrudes in reference to the separation plate during the movement of the sheeting, so that a step develops in the sheeting at the transfer to the separating plate, which serves to seal during the forming process.  
         [0047]     When the forming process shall be complemented with hoop-steel cutting, the holding and punching device may comprise a punching thrust bearing, a holding plate that can be lowered, and a hoop-steel knife that can be lowered to the punching thrust bearing. The hoop-steel knife comprises a unilaterally or bilaterally sharpened steel band, which is circularly closed in the circumferential direction and embodied with recesses for accepting residual bars on its sharpened bottom. The holding plate for holding the sheeting and the steel band knife are here two separate structural parts so that each worn steel band knife can easily and individually be exchanged. Here, particularly advantageous production costs are possible.  
         [0048]     It is particularly advantageous when ventilation bores are arranged in the holding sheath. During deep-drawing the form tool is usually impinged from above with pressurized air so that the sheeting molds to the form tool and accepts a cup shape. This molding is supported by the ventilation bores. It is also possible to connect a vacuum line to the ventilation bores and to suction the sheeting to the form tool.  
         [0049]     In a particularly beneficial embodiment during deformation the threaded sheath travels distance from 10% to 25% of its circumference between the original and the end position. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)  
       [0050]     The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. The invention is subsequently explained using 14 figures of the drawings. Here, they show:  
         [0051]      FIG. 1 a  perspective exterior view of a first shell being a top shell with an encircling sealing cone;  
         [0052]      FIG. 2 a  side view of the first shell according to  FIG. 1 ;  
         [0053]      FIG. 3 a  cross-section of the first shell according to  FIG. 1 ;  
         [0054]      FIG. 4 a  partially enlarged cross-section of the holding edge, reducing collar, sealing cone, and pot-type central part of the first shell embodied as a top shell;  
         [0055]      FIG. 5 a  perspective exterior view of a first shell embodied as a top shell without a sealing cone;  
         [0056]      FIG. 6 a  perspective exterior view of a first shell embodied as a top shell with an exclusively interior ruffled structure;  
         [0057]      FIG. 7 a  perspective exterior view of a second shell embodied as a bottom shell with symmetrically formed holding wings;  
         [0058]      FIG. 8 a  top view to a second shell according to  FIG. 7 ;  
         [0059]      FIG. 9 a  side view to a second shell according to  FIG. 7 ;  
         [0060]      FIG. 10 a  top view of a second shell embodied as a bottom shell with asymmetrically formed holding wings;  
         [0061]      FIGS. 11   a - c : a partial cross-section through a form tool in various functional positions;  
         [0062]      FIGS. 12   a - c : a partial cross-section through a form tool in various functional positions for blanking;  
         [0063]      FIG. 13 : a partial top view of the form tool according to  FIGS. 12   a - c;    
         [0064]      FIGS. 14   a - d : a partial cross-section through a form tool in various functional positions for hoop-steel cutting. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0065]      FIG. 1  shows a first shell in the form of a top shell  1 . The top shell  1  has a convex pot-type central part  3  arced outward, with its circumferential wall  29  transferring into a holding edge  4 . A step like reducing collar  5  is located between the pot-type central part  3  and the holding edge  4 . The circumferential wall  29  is provided with a ruffled structure  30  also protruding on the interior  29   a  (see  FIG. 4 ).  
         [0066]     The holding edge  4  is provided with mounting means  47  in the form of a total of four threads  7   a,    7   b,    7   c,    7   d,  their contours being embodied both on the inside  6   a  (see  FIG. 3 ) as well as on the outside  6   b  of the holding edge  4 . Using the threads  7   a,    7   b,    7   c,    7   d  a second shell (see  FIG. 7 ) embodied as a bottom shell  2 , for example, can be fastened to the top shell  1 .  
         [0067]     The holding edge  4  is also surrounded at the outside by an encircling punched edge  49 . Said edge has a larger diameter than the top shell  1 , because it has been separated from a sheeting  23  during the production, for example using a holding and punching device  43  described in greater detail in  FIG. 12 , with the holding and punching device  43  surrounding the top shell  1  in a sheath-like manner.  
         [0068]     In a side view of  FIG. 2 , the progression of the threads  7   a,    7   b,    7   d  is discernible in particular. The thread  7   c  is not visible in this view because it is located at the back of the top shell  1 . The four threads  7   a,    7   b,    7   c,    7   d  protrude towards the outside and are separated from each other by thread teeth  17   a,    17   b,    17   c,    17   d.  The thread teeth  17   a,    17   b,    17   c,    17   d  protrude on the inside  6   a  (see  FIG. 3 ) of the holding edge  4  towards the inside and form a tread for complementarily embodied elements of the bottom shell  2 . The elements can be embodied as holding wings  11   a,    11   b,    11   c,    11   d  according to  FIG. 5 , for example.  
         [0069]     On the inlet side  31  of each thread  7   a,    7   b,    7   c,    7   d  there is one thread inlet  48  each, which widens funnel-shaped in the direction of the inlet side  31  in order to allow an easier acceptance of a holding wing  11   a,    11   b,    11   c,    11   d,  for example. Furthermore, thread teeth  17   a,    17   b,    17   c,    17   d  located in the rotational direction are respectively rounded on the inlet side  31 .  
         [0070]     All threads  7   a,    7   b,    7   c,    7   d  feather out in reference to the reducing collar  5  at an acute angle of less than 45°. This area represents a clamping area  32 , in which for example holding wings  11   a,    11   b,    11   c,    11   d  are fixed with their front edge  12  (see  FIGS. 7 through 10 ) in the mounted state of the top and the bottom shells  1 ,  2 .  
         [0071]      FIG. 3  shows a cross-section extending through the center of the round top shell  1  and the sizing of the threads  7   a,    7   b,    7   d  as well as the arrangement of the seal  8  embodied as a sealing cone  8   a.    
         [0072]     The interior diameter  18  of the holding edge  4  is defined by the clear distance between two opposite thread teeth  17   a,    17   b,    17   c,    17   d.  In  FIG. 3 , the interior diameter  18  is defined by the distance between the thread teeth  17   b,    17   d.  The clear diameter inside two opposite threads  7   a,    7   b,    7   c,    7   d  is called the nominal diameter  15  of the holding edge  4 . In  FIG. 3 , the nominal diameter  15  is discernible, for example, between the threads  7   b,    7   d.  The nominal diameter  15  is always larger than the interior diameter  18 .  
         [0073]     Sealing cones  8   a  protruding in the direction of the bottom  9  are visible between the reducing collar  5  and the circumferential wall  29  of the pot-type central part  3 , extending closed around the pot-type central part  3 . In the connected state of the top shell  1  and the bottom shell  2  the sealing cone  8   a  contacts an opening edge  10  ( FIGS. 7, 9 ) from the inside and/or the upper section  34   a  ( FIG. 9 ) of the cup wall  33  of the bottom shell  2  and thus develops a seal.  
         [0074]     In an enlarged representation  FIG. 4  shows the area around the holding edge  4  according to the sectional level in  FIG. 3 . The thread  7   a  shown in this illustration is provided with a largely rectangular profile, open towards the inside  6   a.    
         [0075]     The reducing collar  5  extends horizontally and is thus essentially perpendicular to the upper section  34   a  of the cup wall  33  (see  FIG. 9 ). Between the reducing collar  5  and the circumferential wall  29  there is a sealing cone  8   a,  in the shown embodiment protruding the clamping area  32  downwards.  
         [0076]     In  FIG. 5 a  top shell  1  is shown without any surrounding sealing cone  8   a.  This embodiment is used for bottom shells  2 , whose opening edge  10  shall be sealed with a sealing foil. A sealing cone  8   a  in the mounted state of top shell  1  and the bottom shell  2  engaging below the opening edge  10  of the bottom shell  2  (see  FIG. 7 ) would pierce a sealing foil stretched over the opening edge  10  and is therefore unsuitable for such an embodiment.  
         [0077]     Furthermore, the embodiment of the top shell  1  shown in  FIG. 5  is provided with a total of six threads  7   a,    7   b,    7   c,    7   d,    7   e,    7   f,  which are evenly distributed over the interior  6   a  (see  FIG. 3 ). Such a top shell  1  can be screwed onto a bottom shell  2  (not shown) having six holding wings  11   a,    11   b,    11   c,    11   d.    
         [0078]      FIG. 6  shows another embodiment of the top shell  1  with a cylindrical circumferential wall  29  vertically positioned on the reducing collar  5 . For reasons of better visibility the pot-type central part  3  is shown without a central cover. On the interior  29   a  of the circumferential wall  29  a toothing is arranged as a ruffled structure  30 . The ruffled structure  30  does not extend through the circumferential wall  29 . The exterior  29   b  of the circumferential wall  29  is rather provided with a smooth surface. Due to the ruffled structure  30  aligned in the axial direction of the top shell  1  it is possible to compensate torque acting in the circumferential direction on the top shell  1  and a complementary embodied form tool  20  during the production process.  
         [0079]      FIG. 7  shows a bottom shell  2  as the second shell, with a slightly conical opening but essentially a cylindrical cup wall  33 , transferring in its upper section  34   a  into an opening edge  10 . The lower section  34   b  of the cup wall  33  transfers into an even more conically merging base section  35 . On the bottom, the bottom shell  2  is unilaterally closed by a bottom plate  36 .  
         [0080]     The opening edge  10  of the second shell has mounting means  47  in the form of a total of four holding wings  11   a,    11   b,    11   c,    11   d  evenly protruding towards the outside. These holding wings  11   a,    11   b,    11   c,    11   d  can engage correspondingly embodied threads  7   a,    7   b,    7   c,    7   d,    7   e,    7   f,  as shown in  FIGS. 1 through 6 , and be fixed by a rotary motion of the top shell  1  in reference to the bottom shell  2  in the treads  7   a,    7   b,    7   c,    7   d,    7   e,    7   f.  The fastening occurs by the holding wings  11   a,    11   b,    11   c,    11   d,  having commonly used clockwise threads at their frontal edge  12 .  
         [0081]     The holding wings  11   a,    11   b,    11   c,    11   d  are in a common level in reference to each other and end at the top plainly with the opening edge  10 .  
         [0082]     The distance from the exterior edge  14  of a holding wing  11   b  to the exterior edge  14  of the opposite holding edge  11   d  is called full-circle diameter. The full-circle diameter  16  is selected slightly smaller than the nominal diameter  15  of the top shell  1 . The exterior diameter  19  of the opening edge  10  is measured at the exterior of the holding wings  11   a,    11   b,    11   c,    11   d.  In order for the top shell  1  to engage around the bottom shell  2  the exterior diameter  19  is selected slightly smaller than the interior diameter  18  of the holder edge  4  (cf.  FIG. 3 ).  
         [0083]     The symmetrical distribution of the holding wings  11   a,    11   b,    11   c,    11   d  is also discernible in the top view according to  FIG. 8 . In this view the symmetrical embodiment of each holding wing  11   a,    11   b,    11   c,    11   d  is discernible. Originating from a rounded exterior edge  14 , adjusted to the curve of the opening edge  10 , the front edge  12  and the rear edge  13  of each holding wing  11   a,    11   b,    11   c,    11   d  extend at the same angle in the direction of the opening edge  10 .  
         [0084]      FIG. 9  shows the bottom shell  2  in a side view. First, a conically opening base area  35  engages the bottom plate  36 , transferring into an essentially cylindrical, only slightly conically opening cup wall  33 . In the upper section  34   a  of the cup wall  33  said wall transfers into a counter-conical wall, which in turn ends in the opening edge  10  and/or the holding wings  11   a,    11   b,    11   c,    11   d  arranged thereto. The holding wings  11   a,    11   b,    11   c,    11   d  are provided with the same material thickness as the opening edge  10 . Furthermore, it is discernible that the holding wings  11   a,    11   b,    11   c,    11   d  are also located in a horizontal level with the opening edge  10 . However, it is also possible to form the holding wings  11   a,    11   b,    11   c,    11   d  with a greater material thickness in reference to the opening edge  10 . The holding wings  11   a,    11   b,    11   c,    11   d  may then also be provided at their bottom with a ramp-like incline similar to the incline of the thread.  
         [0085]     In a top view  FIG. 10  shows a bottom shell  2  with four holding wings  11   a,    11   b,    11   c,    11   d  radially extending from the opening edge  10 . However, the holding wings  11   a,    11   b,    11   c,    11   d  have an asymmetrical shape compared to the embodiment shown in  FIGS. 8 and 9 . Here, the front edge  12  steeply inclines in the radial direction. The angle amounts to approx. 45 to 60 degrees. An evenly convexly arced common exterior and rear edge  13 ,  14  abuts to the front edge  12 , immediately transferring into the subsequently front edge  12 .  
         [0086]     In the following  FIGS. 11 through 14  the production of a first shell using the deep-drawing method is described with a thread as well as different embodiments of the forming tool  20  according to the invention. In the present case the shell is the top shell  1 .  
         [0087]     Sectionally, the cross-sections in  FIGS. 11   a  through  11   c  show a form tool  20  in three different functional positions with a sheeting  23  already formed to a top shell  1 .  
         [0088]     In  FIG. 11   a  an interior die  39 , a holding sheath  21 , and a threaded sheath  22  are located in an original position in reference to each other. Here, the threaded sheath  22  surrounds the holding sheath  21  and the interior die at the outside, both of which being arranged torque-proof in the form tool  20 . The threaded sheath  22  is supported pivotally around the holding sheath  21 . A contour  25  is formed inside the threaded sheath  22  for creating a thread  7   a,    7   b,    7   c,    7   d,    7   e,    7   f,  so that a heated sheeting  23  is adjusted according to the shape of the form tool  20  and, in particular, the contours  25  of the threaded sheath  22 .  
         [0089]     Using a multi-part form tool  20 , comprising a holding sheath  21  and a threaded sheath  22 , it is possible to first form in a first processing step according to  FIG. 11   a  at least two threads  7   a,    7   b,    7   c,    7   d,    7   e,    7   f  and subsequently to release the top shell  1  from the form tool  20 . This occurs according to  FIG. 11   b  by spindling off the threaded sheath  22  in reference to the fixed holding sheath  21  in the direction of motion  37 . After spindling off, the threaded sheath  22  is lowered below the level of the punching thrust bearing  41  and no longer engages the thread  7   a.    
         [0090]     During the forming process shown in  FIG. 11   a  and during spindling according to  FIG. 11   b  the sheeting  23  is fixed over a holding device  40  concentrically arranged around the form tool  20 . For this purpose, the holding device  40  comprises a locally fixed punching thrust counter bearing  41  and a holding plate  42  that can be lowered in the direction of the punching thrust bearing  41 . In order to fix the sheeting  23  it is clamped between the punching thrust bearing  41  and the holding plate  42 .  
         [0091]     A distortion of the top shell  1  formed in the sheeting  23 , in addition to the holding device  40 , is prevented by the holding sheath  21 . For this purpose the holding sheath  21  is provided with holding ribs  26  at its wall section  28 , particularly well discernible in  FIG. 13 . The holding ribs  26  are formed in the circumferential wall  29  of the top shell  1  as a ruffled structure  30  and allow a form-fitting force transmission.  
         [0092]     In the last processing step, shown in  FIG. 11   c,  the holding sheath  21  is moved back in the axial direction together with the interior die  39  and the holding plate  42  that can be lowered is raised so that the sheeting  23  with the top shell  1  embodied there is released from the form tool  20  and can be removed. In another processing step known to one trained in the art the top shell  1  can be separated from the sheeting  23 .  
         [0093]     Different functional positions of a form tool  20  for blanking are also shown in  FIG. 12  in a partial cross-section. Here, the construction comprises, to a large extent identical to the form tool  20  shown in  FIG. 11 , the centrally arranged interior die  39 , the holding sheath  21 , and the threaded sheath pivotal around it.  
         [0094]     However, the form tool  20  is concentrically surrounded by a holding and punching device  43 , by which the top shell  1  can be immediately minted from the sheeting on the form tool  20 .  
         [0095]     The holding and minting device  43  comprises the knife sheath  24 , immediately adjacent to the threaded sheath  22 , the separating plate  44  arranged around the knife sheath  24 , and the knife plate  45  located above the separating plate  44 . Both the separating plate  44  as well as the knife plate  45  can be moved vertically.  
         [0096]     The forming of the top shell  1  in the sheeting  23  occurs according to the position of the form tool  20  in  FIG. 12   a.  Here, the sheeting is fixed in a clamping fashion by the knife plate  45  lowered in the direction of the separating plate  44 . After fixation, the separating and knife plate  44 ,  45  are lowered together so that a step forms in the sheeting  23  at the transfer from the separating plate  44  to the knife sheath  24 .  
         [0097]     In  FIG. 12   b,  the threaded sheath is spindled off in the direction of motion  37  and a thread  7   a  is discernible in the top shell  1 . Prior to the spindling the knife sheath  24  was moved upwards, causing the sheeting  23  to be cut off over its entire exterior circumference at the knife plate  45 . In this embodiment the torque transferred to the sheeting loosely supported on the from tool  20  during the spindling process is compensated only by the ruffled structure  30  formed at the circumferential wall  21  and the holding ribs  26  complementary formed in the holding sheath  21 , and thus any complementary rotation of the top shell  1  already released from the sheeting  23  is avoided during spindling off.  
         [0098]     Finally, as shown in  FIG. 12   c,  the interior die  39  is axially pushed forward in reference to the fixed holding sheath  21  and the holding and punching device  43  is opened. The top shell  1  can easily be removed from the form tool  20  by the interior die  39  being pushed forward. The knife sheath  24  is returned to a lowered position.  
         [0099]      FIG. 13  shows in a partial top view, the form tool  20 , holding ribs  26  arranged in the holding sheath  21 , which allow the fastening of the top shell  1  already separated completely from the sheeting  23 , or a fastening of the top shell  1  still connected to the sheeting  23 . For this purpose, the holding ribs  26  are aligned in their axial direction perpendicular to the direction of motion  37  of the threaded sheath  22 . The holding ribs  26  are located in an inclined wall section  28  of the holding sheath  21 . After the production process, the holding ribs  26  are again found as the ruffled structure  30  of the finished formed top shell  1 .  
         [0100]     The holding sheath  21  is provided with several ventilation bores  27 , through which air located between the sheeting  23  and the form tool  20  can exit or be suctioned off.  
         [0101]      FIG. 14  shows another alternative concerning the holding and support device  43  arranged around the form tool  20  in a partially cross-sectioned view for performing hoop-steel cutting.  
         [0102]     The central component of the form tool  20  also comprises an interior die  39 , the holding sheath  21 , and the threaded sheath  22 . The form tool  20  is surrounded by the holding and supporting device  43  comprising a fixed punching thrust bearing  41 , a holding plate  42  that can be lowered, and a hoop-steel knife  46  guided at the holding plate  42 .  
         [0103]     According to  FIG. 14   a,  in a first processing step the sheeting  23  is moved over the mold  20  and fixed circularly around the form tool  20 , in which the holding plate  24  is lowered and thus the sheeting  23  is clamped, supported on the minting counter bearing  41 .  
         [0104]     Subsequently, as discernible in  FIG. 14   b,  the threaded sheath  22  is spindled off in the direction of motion  37 . Using this process, the sheeting  23  is held by both the holding sheath  21  and the sheeting compound.  
         [0105]     Another processing step shown in  FIG. 14   c  comprises the lowering of the hoop-steel knife  46  to the sheeting  23 , thus separating the top shell  1  circumferentially from the sheeting  23 . However, the hoop-steel knife  46  is embodied at its bottom with recesses at discrete distances, so that the top shell  1  remains connected to the sheeting  23  via residual bars  38 . These residual bars  38  are broken in a controlled manner in the subsequent stacking process.  
         [0106]     After the punching of the top shell  1  from the sheeting  23  the holding plate  42  is raised and the interior die  39  is moved together with the holding sheath  21  downwards to the same level as the punching thrust bearing  41  and the lowered threaded sheath  22  ( FIG. 14   d ). In this position the sheeting  23  can be removed in a simple manner horizontally out of the form tool  20  together with the top shell  1  and the holding and punching device  43 .  
         [0107]     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.  
       LIST OF REFERENCE CHARACTERS  
       [0108]      1  top shell  
         [0109]      2  bottom shell  
         [0110]      3  pot-type central part  
         [0111]      4  holding edge  
         [0112]      5  reducing collar  
         [0113]      6   a  interior side of the holding edge  
         [0114]      6   b  exterior side of the holding edge  
         [0115]    
       7 
       a,  
       7 
       b,  
       7 
       c,  
     
         [0116]      7   d,    7   e,    7   f  threads  
         [0117]      8  seal  
         [0118]      8   a  sealing cone  
         [0119]      9  bottom of the first shell  
         [0120]      10  opening edge of the second shell  
         [0121]    
       11 
       a,  
       11 
       b,  
       11 
       c,  
     
         [0122]      11   d  holding wing of the second shell  
         [0123]      12  front edge of the holding wing  
         [0124]      13  rear edge of the holding wing  
         [0125]      14  exterior edge of the holding wing  
         [0126]      15  nominal diameter of the holding edge  
         [0127]      16  full-circle diameter of the holding wings  
         [0128]    
       17 
       a,  
       17 
       b,  
       17 
       c,  
     
         [0129]      17   d  thread tooth  
         [0130]      18  interior diameter of the holding edge  
         [0131]      19  exterior diameter of the opening edge  
         [0132]      20  form tool  
         [0133]      21  holding sheath  
         [0134]      22  pivotal threaded sheath  
         [0135]      23  sheeting  
         [0136]      24  knife sheath  
         [0137]      25  contour thread  
         [0138]      26  holding ribs  
         [0139]      27  ventilation bores  
         [0140]      28  wall section holding sheath  
         [0141]      29  circumferential pot-type central part  
         [0142]      29   a  interior side of the circumferential wall  
         [0143]      29   b  exterior side of the circumferential wall  
         [0144]      30  ruffled structure of the circumferential wall  
         [0145]      31  inlet side thread  
         [0146]      32  clamping area thread  
         [0147]      33  cup wall of the bottom shell  
         [0148]      34   a  upper section of the cup wall  
         [0149]      34   b  lower section of the cup wall  
         [0150]      35  base section of the cup wall  
         [0151]      36  bottom plate  
         [0152]      37  direction of motion of the threaded sheath  
         [0153]      38  residual bars  
         [0154]      39  interior die  
         [0155]      40  holding device  
         [0156]      41  punching thrust bearing  
         [0157]      42  holding plate that can be lowered  
         [0158]      43  holding and punching device  
         [0159]      44  separating plate  
         [0160]      45  knife plate  
         [0161]      46  hoop-steel knife  
         [0162]      47  mounting means  
         [0163]      48  open thread inlet  
         [0164]      49  punching edge