Patent Publication Number: US-2012043340-A1

Title: Container with seamed closure and method and apparatus for its manufacture

Description:
TECHNICAL FIELD 
     This invention relates to a container in the form of a metal can body having an access opening closed with a flexible diaphragm, the container provided with an improved means of securing the diaphragm to the can body. In particular, the invention relates to a method and apparatus suitable for manufacturing such a container. 
     BACKGROUND ART 
     In the field of packaging, metal containers are known having a container body with an access opening sealed by a flexible diaphragm clamped between opposing surfaces of a bead provided in the sidewall of the container body. The use of clamping to secure the diaphragm in place offers an alternative to the use of a peelable diaphragm (such as that disclosed in GB 2237259 A (CMB FOODCAN PLC) May 1, 1991). GB 2237259 discloses a diaphragm in the form of peelable foil lidding, the diaphragm peelably bonded to a surface of an intermediate ring component, which is then seamed to the sidewall of a can body. The problem with such peelable lidding is that any positive pressure within the container acts to cause the diaphragm to progressively peel itself away from the surface to which it is bonded. This progressive peeling initiates and propagates from inside the container and is therefore invisible to the can manufacturer, the filler and end-consumer. In the case of containers for food products requiring sterilisation, this positive pressure can arise during processing in a retort. 
     Closing and sealing a container by clamp-securing the diaphragm overcomes the above described problems resulting from the use of peelable lidding. Various examples of such containers are known. For example, US 2003/0113416 A (WYCLIFFE ET AL) Jun. 19, 2003 discloses a metal container body for use as a can for carbonated beverages (which generate a positive internal pressure), where a peripheral annular portion of a diaphragm formed from a disk of aluminium alloy sheet is clamped between the opposing surfaces of an outwardly directed bead. Similarly, GB 350359 (HUGH WAGSTAFF; READS LIMITED) Jun. 11, 1931 discloses a container body formed with an inwardly extending bead, a diaphragm of thin sheet metal positioned on the upper exterior surface of the bead and the upstanding free edge of the container body being folded over to clamp a peripheral annular portion of the diaphragm against the upper exterior surface of the inwardly extending bead. GB 1361415 (THE METAL BOX COMPANY LIMITED) Jul. 24, 1974 discloses a container along similar lines to that of GB 350359. 
     However, the manufacturing process for such known containers having “clamp-secured” lidding is complex. There is therefore a need for a more efficient means of producing such a container. 
     DISCLOSURE OF INVENTION 
     According to a first aspect of the invention, there is provided a method of forming a container, the method comprising the following steps: 
     i. radially expanding the sidewall of a tubular can body at an end of the can body to define a circumferential radially-expanded region in the sidewall adjacent the end of the can body;
 
ii. applying a first axial load to the can body whilst using means adapted to limit radial growth of the end of the can body so that all or part of the circumferential radially-expanded region partially axially collapses to form an outwardly-directed open annular bead;
 
iii. locating a diaphragm relative to the can body so that a peripheral annular portion of the diaphragm locates between opposing surfaces of the open annular bead; and
 
iv. applying a second axial load to the can body to fully axially collapse the bead to thereby clamp the peripheral annular portion of the diaphragm between the opposing surfaces of the bead and close the end of the can body.
 
     By “axial load” is meant a load applied generally parallel to the longitudinal axis of the can body. 
     The invention takes advantage of the fact that on application of a sufficient (first) axial load to the can body, the sidewall of the can body will buckle (or collapse). Formation of the circumferential radially-expanded region in the sidewall provides a region that is highly susceptible to buckling or collapse on application of sufficient axial load. Therefore, the radially-expanded region serves the function of preferentially controlling where buckling or collapse of the sidewall will occur. In contrast to US 2003/0113416A1, which uses a complex sequence of forming operations to clamp its diaphragm in place (see  FIGS. 8   a - c  of US 2003/0113416A1), the present invention provides a manufacturing route having fewer process steps and therefore enables higher manufacturing speeds to be achieved. 
     The use of the metal of the can body—via the opposing surfaces of the collapsed annular bead—to secure the diaphragm overcomes the tendency of peelable lidding (for example, that of GB 2237259 A) to progressively peel away from its sealing surface when subjected to positive pressures. The clamping mechanism used by the invention to secure the diaphragm to the can body ensures that the diaphragm can sustain both negative and positive pressures in a better manner than conventional peelable lidding. Therefore, considering the case of containers for food products requiring sterilisation, the container resulting from the method of the invention may be processed within a larger range of retorts with a reduced need for pressure balancing. 
     The use of clamping to secure the diaphragm also avoids the use of adhesive, heat sealing or other sealing compounds, and therefore simplifies the manufacturing route for the container of the invention compared to containers provided with conventional peelable lidding. However, whilst the invention can deliver good seal integrity without the use of sealing compound, improved sealability is provided when using a sealing compound at the interface between the diaphragm and the opposing surfaces of the collapsed bead. 
     Additionally, the invention does not require the use of the intermediate ring component commonly used in the manufacture of containers closed with peelable lidding (see GB 2237259 A), and therefore results in material cost savings and a simplified manufacturing route. 
     The can body is conveniently made of aluminium or steel; however, other metals may also be used. Steel tinplate has been found to be a particularly suitable material, with trials performed using tinplate of 0.13 mm, 0.15 mm and 0.17 mm wall thickness. However, there is no reason to suggest that the invention would not work with other thicknesses or metals. The diaphragm is conveniently made from foil sheet metal, thereby providing flexibility and reduced weight relative to conventional generally rigid sheet metal can ends that are seamed onto can bodies. The diaphragm may also include one or more polymer coatings/films on either or both faces of a metal substrate. The use of such polymer coatings/films may provide a suitable surface for printing of text/graphics and protect the metal substrate from corrosion. Further, the polymer coating/film material would act like a gasket when clamped between the opposing surfaces of the collapsed bead, with its resilience enabling it to deform and adapt to the profile of the opposing bead surfaces, thereby helping to develop and maintain a hermetic seal between the diaphragm and the can body. The diaphragm may also be made from:
         A barrier plastic material. This is where the diaphragm is made wholly from plastics. It includes either a single homogeneous layer or a laminate composed of different plastics layers; or   A composite. For example, good seal integrity has been achieved using a composite of cardboard, metal foil, and polymer coatings (such as the material used on Tetra Pak® cartons).       

     Trials have been performed using diaphragms of 40-90 microns total thickness. By way of example, a diaphragm has been used of 20 microns polypropylene coated onto a 20 micron aluminium substrate. 
     Although paragraph 5 outlines the method of the invention in its broadest form, the method may be refined in various ways as detailed in the following paragraphs . . . . 
     Preferably, steps i &amp; ii are performed substantially simultaneously. For example, the invention may be enabled by steps i and ii comprising inserting a flared die within the end of the can body to apply both radial and axial loads to the can body. In a further example, the flared die preferably terminates in a generally radially-extending end face, a limit ring situated adjacent the end face, the limit ring having a generally axially-extending wall to thereby limit radial growth of the end of the can body. Most preferably, the limit ring is formed integral with the flared die to thereby minimise the number of moving parts. By “radially-extending” is meant having a component which extends radially—it is not limited to being purely perpendicular to the longitudinal axis of the can body. For example, the radially-extending end face may be curved in profile, progressively deviating radially-outwardly from the longitudinal axis of the can body. Similarly, by “axially-extending” is meant having a component which extends axially. 
     Without intending to limit the scope of the invention, it is anticipated that one such preferred example of the invention would work as follows:
         A tubular straight walled can body is used as a starting point.   Either or both of the flared die and the can body would be driven towards each other so that the flared die enters an end of the can body.   As the flared die enters the end of the can body, the flared walls of the die would act against the sidewall of the can body to thereby simultaneously apply both radial and axial loads to the can body sidewall, and progressively radially expand the sidewall.   When the die has sufficiently entered the can body, the free edge of the end of the can body would contact the radially-extending end face of the die, with further insertion of the die then leading to radial growth of the free edge of the can body along the die&#39;s radially-extending end face until contacting the axially-extending wall of the limit ring.   The limit ring acts as a constraint to additional radial growth of the free edge of the can body. Consequently, additional axial movement of the flared die within the end of the can body would result in the partial axial collapse (or buckling) of the sidewall in the radially-expanded region, resulting in formation of the outwardly-directed open annular bead.   The die would then be removed and the diaphragm inserted.   Once the diaphragm has been inserted, a flat plate (or equivalent conventional mechanical means) may be used to apply the second axial load to the can body to thereby fully collapse the bead and securely clamp the diaphragm in position between the opposing surfaces of the collapsed bead.       

     To provide increased rigidity and cut-edge protection, the end of the can body is preferably formed with a curl. The curl may be formed either before the radial expansion step which forms the circumferential radially-expanded region or subsequently to this step. Preferably however, the curl is formed in consequence of steps i and ii comprising inserting a flared die within the end of the can body to apply both radial and axial loads to the can body, the flared die and/or the limit defining an outwardly-curled end face, such that insertion of the flared die into the can body causes the free edge at the end of the can body to propagate along the surface of the outwardly-curled end face to form the curl, formation of the curl limiting further propagation of the free edge such that further insertion of the flared die induces the partial axial collapse of all or part of the circumferential radially-expanded region to form the outwardly-directed open annular bead. 
     Regardless of how and when the curl is formed on the end of the can body, conveniently during or subsequent to step iv the curl is flattened against the external surface of the collapsed bead to define a double thickness of metal above and adjacent the external surface of the collapsed bead. This flattening (or crushing) of the curl has the benefit of reducing the likelihood of corrosion of the raw edge of metal on the free edge of the can body. 
     As an alternative to the formation of a curl at the end of the can body, the method is conveniently adapted during step ii to leave a portion of the sidewall of the can body extending between the partly collapsed outwardly-directed open annular bead and the free edge at the end of the can body, wherein simultaneously with or subsequent to step iv the portion is deformed to lie adjacent the exterior surface of the collapsed bead such that the free edge is outwardly-directed. To minimise the risk of cuts to a consumer, it is preferred that the deformed portion does not extend radially-outward of the collapsed bead. 
     The flattening described above may be achieved by using a flat plate as referred to above (or other conventional mechanical means). 
     In a further variation to the method of the invention which would enhance protection against cuts to an individual, the method may be adapted during step ii to leave a portion of the sidewall of the can body extending between the partly collapsed outwardly-directed open annular bead and the free edge at the end of the can body, wherein simultaneously with or subsequent to step iv the portion is wrapped around the periphery of the exterior surface of the collapsed bead so that the free edge is directed inwardly towards the can body sidewall. 
     In a still further variation to the method of the invention which would again enhance protection against cuts to an individual, the method may be adapted during step ii to leave a portion of the sidewall of the can body extending between the partly collapsed outwardly-directed open annular bead and the free edge at the end of the can body, the portion comprising an inner region and an outer region, the inner region extending between the bead and the outer region, the outer region terminating at the free edge, wherein simultaneously with or subsequent to step iv the outer region is folded over the inner region, the combination of inner and outer regions then deformed such that the outer region is sandwiched between the inner region and the exterior surface of the collapsed bead to form a double thickness of metal above and adjacent the external surface of the collapsed bead. 
     To further increase container rigidity, the portion may be folded back and forth in a succession of folds (for example, in a concertina-like manner), these folds then substantially flattened. 
     To provide an improved clamped seal between the diaphragm and the opposing surfaces of the fully collapsed bead, preferably the method of the invention further comprises applying an upwards load to the underside of the fully collapsed bead to compress and tighten the clamped seal. Preferably, to avoid the end of the can body simply deforming radially inwardly in response to this upwards load, the sidewall of the can body is radially supported at the end of the can body during application of the upwards load to the underside of the fully collapsed bead. 
     Whilst the diaphragm used in the method of the invention is typically planar, improved sealability may be obtained by the peripheral annular portion of the diaphragm as located between the opposing surfaces of the open annular bead during step iii comprising an upturned peripheral annular region, with the application of the second axial load during step iv acting to fold over the upturned peripheral annular region to thereby clamp a double thickness of diaphragm material between the opposing surfaces of the collapsed bead. Where the diaphragm includes such an upturned peripheral annular region, it is possible to form the diaphragm profile by starting from a planar metal blank and inclining the periphery of the diaphragm to form the upturned peripheral annular region. However, this can lead to wrinkling of the upturned peripheral annular region and, ultimately, poor seal quality. To overcome this wrinkling, it is preferable to use a diaphragm formed of plastics material because plastics can be moulded into the desired profile and thereby avoid the problem of wrinkling of the periphery of the diaphragm to provide good sealability. 
     According to a second aspect of the invention, there is provided an apparatus for forming a container, the apparatus having: 
     i. a radial load member for radially expanding the sidewall at an end of a tubular metal can body to define a circumferential radially-expanded region in the sidewall adjacent the end of the can body;
 
ii. a first axial load member for applying a first axial load to the can body, plus a limit ring adapted to limit radial growth of the end of the can body such that during application of the first axial load the circumferential radially-expanded region partially axially collapses to form an outwardly-directed open annular bead;
 
iii. means for locating a peripheral annular portion of a diaphragm between opposing surfaces of the open annular bead;
 
iv. a second axial load member for applying a second axial load to the can body to fully axially collapse the bead to thereby clamp the peripheral annular portion of the diaphragm between the opposing surfaces of the bead and close the end of the can body.
 
     Preferably, the function of the radial load member and the first axial load member is performed by a flared die terminating in a generally radially-extending end face. Use of a flared die has the advantage of enabling the radial expansion of the sidewall and application of the first axial load to be performed virtually simultaneously. More preferably, the limit ring is situated adjacent the radially-extending end face, the limit ring having a generally axially-extending wall to thereby limit radial growth of the end of the can body. The flared die and limit ring may be separate components; however, it has been found preferable to combine the flared die and the limit ring into an integrally formed single component. 
     An alternative form of the invention to that described in the paragraph above is for the apparatus to comprise a flared die, the flared die acting as both the radial load member and first axial load member (in common with the paragraph above). However, in this alternative form of the invention the flared die and/or the limit ring define an outwardly-curled end face, such that insertion of the flared die into the can body causes the free edge at the end of the can body to propagate along the surface of the outwardly-curled end face of the die to form a curl. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS 
       The method and apparatus of the invention are described below and illustrated in the following drawings: 
         FIG. 1  relates to a first embodiment of the invention and shows a cross-section through a tubular can body of uniform diameter and a flared die before any deformation of the can body. 
         FIG. 2  is a detail view of part of  FIG. 1 , more clearly showing the profile of the flared die. 
         FIG. 3  shows a cross-section through the can body and the flared die after the die has been driven within an end of the can body to define an outwardly-directed open annular bead. 
         FIG. 4  is a detail view of part of  FIG. 3 , more clearly showing the profile of the outwardly-directed open annular bead. 
         FIG. 5  is a detail view of the can body prior to full collapse of the annular bead by an axial load member, with a diaphragm located in position between the opposing surfaces of the open annular bead. 
         FIG. 6  shows a cross-section through the can body in its final form, with the bead in its fully collapsed state to clamp the diaphragm in position between opposing surfaces of the bead. 
         FIG. 7  shows a perspective view of the can body after the process steps shown in the earlier figures. 
         FIG. 8  relates to a second embodiment of the invention and corresponds to  FIG. 6 , but adapted to provide enhanced rigidity and protection against cuts from the free edge at the end of the can body. 
         FIG. 9  relates to a further embodiment of the invention, showing an alternative design of flared die/limit ring capable of forming a curl on the end of the can body during the method of the invention. 
         FIG. 10  shows the curled can body that results use of the alternative design of flared die/limit ring of  FIG. 9 . 
         FIG. 11  shows the diaphragm located between the opposing surfaces of the open annular bead of the can body of  FIG. 10 , but before inducing full collapse of the bead. 
         FIGS. 13 to 15  show the use of a seaming chuck, seaming roll and table to assist in inducing full collapse of the open annular bead and subsequent tightening of the clamped seal that holds the diaphragm in place. 
     
    
    
     MODE(S) FOR CARRYING OUT THE INVENTION 
     As shown in  FIGS. 1 &amp; 2 , a tubular metal can body  1  of uniform diameter is initially located with one end co-axial with a flared die  2  and limit ring  3 . The flared die  2  terminates in a generally radially-extending end face  21  (see  FIG. 2 ) which is curved in profile and progressively deviates radially-outwardly from the longitudinal axis  11  of the can body  1 . In the embodiment shown in the figures, the flared die  2  locates within a recess provided in the limit ring  3 , the recess defined by a generally axially-extending wall  31  extending upwardly from the base  32  of the limit ring (see  FIGS. 1 &amp; 2 ). The periphery of the radially-extending end face  21  has a diameter corresponding in size to that of the axially-extending wall  31 , so that the limit ring  3  is situated adjacent the end face (see  FIG. 2 ). Therefore, there is little or no gap between the periphery of the radially-extending end face  21  and the axially-extending wall  31 . In an alternative embodiment not shown in the figures, the flared die and the limit ring would be integrally formed. 
     In the embodiment shown in  FIG. 1 , the flared die  2  and can body  1  are driven towards each other along the longitudinal axis  11  of the can body (indicated by arrows A), so that the die enters one end of the can body. However, it is within the scope of the invention for either or both of the die  2  and the can body  1  to be driven towards each other; for example, in an alternative embodiment to that shown in the drawings, only one of the die  2  and the can body  1  are moved, the other entity remaining stationary. In the embodiment shown in the figures, a forming operation is performed on the opposite end of the can body  1  (by means not shown), to provide a flare  12  (as indicated in  FIG. 3 ). The flare  12  enables a conventional sheet metal can end to be seamed to that opposite end of the can body  1 . 
     As will be understood from  FIGS. 1 ,  2 ,  3  &amp;  4 , as the flared die  2  gradually enters the end of the can body  1 , the flared walls  22  (see  FIG. 2 ) of the die act against the sidewall  13  of the can body, thereby progressively radially-expanding the sidewall adjacent the end of the can body to define a circumferential radially-expanded region  14  in the sidewall. By the nature of its flared profile  22 , the die  2  is able to simultaneously apply both axial and radial loads to the can body  1 . When the die  2  has sufficiently entered the end of the can body  1 , the free edge  15  of the can body contacts the radially-extending end face  21  of the die (see  FIGS. 2 &amp; 4 ), with further insertion of the die leading to radial growth of the free edge until constrained by the axially-extending wall  31  of the limit ring  3 . The constraint provided by the axially-extending wall  31  of the limit ring  3  means that further insertion of the die  2  causes the circumferential radially-expanded region  14  of the sidewall  13  to partially axially collapse (or buckle), resulting in formation of an outwardly-directed open annular bead  16   a . A portion  17  of the sidewall  13  extends generally axially between the partly collapsed outwardly-directed open annular bead  16   a  and the free edge  15 . The can body after formation of the outwardly-directed open annular bead  16   a  is shown in  FIGS. 3 &amp; 4 . 
     At this point, the flared die  2  is removed to allow insertion of a diaphragm  40  between the opposing surfaces of the outwardly-directed open annular bead  16   a  (see  FIG. 5 ). The diaphragm  40  is formed from a 20 micron thick aluminium sheet metal substrate coated with a 20 micron thick layer of polypropylene. However, as indicated in the general description of the invention, other materials and thicknesses may be used for the diaphragm  40 . 
     Once the diaphragm  40  is located in position, a second axial load is applied to the end of the can body  1  by an axial load member in the form of a flat plate  50  (indicated in  FIG. 5 ). In the embodiment shown, the plate  50  and the can body  1  are moved towards each other (indicated by arrows B in  FIG. 5 ). However, in alternative embodiments just one of the plate  50  and can body  1  is moved. Sufficient axial load is applied via the plate  50  to fully axially collapse (or buckle) the outwardly-directed open annular bead  16   a . The bead in its fully collapsed state  16   b  is shown in  FIG. 6 . In this state, an annular peripheral portion of the diaphragm  40  is clamped between the opposing surfaces of the fully collapsed bead  16   b  to seal the end of the can body  1 . The force exerted by the plate  50  also results in the portion  17  of the sidewall being flattened  18  to lie adjacent the exterior surface of the collapsed bead  16   b  (see  FIG. 6 ). The flattened portion  17 ,  18  does not extend radially-outward of the collapsed bead  16   b , thereby reducing the risk of individuals cutting their fingers on the free edge  15 . The flattening of the portion  17  against the exterior surface of the collapsed bead  16   b  also results in the clamped diaphragm  40  being recessed a distance ‘h’ beneath the uppermost plane of the can body (see  FIG. 6 ). This recessing of the diaphragm provides some protection against impact damage to the diaphragm of the resulting container. Furthermore, the flattening also results in a triple thickness of can body sidewall material at that end of the can body  1 , with consequent benefits to container rigidity. 
     The container that results from the above process steps is shown in  FIG. 7 , showing the can body  1  with the diaphragm  40  clamped in position to close one end of the can body. As can be seen from  FIG. 7 , the diaphragm is formed with a score line  41  to define a prearranged opening area for dispensing of the container&#39;s contents, with a tab  42  for opening of the prearranged opening area by severing of the score line. The tab shown in  FIG. 7  is adhered to the diaphragm by an adhesive. However, in an alternative embodiment, the tab may be riveted to the diaphragm. 
     In an alternative embodiment shown in  FIG. 8 , the portion  17  is greater in length than that of the embodiment of  FIGS. 1 to 7 . This additional length is necessary to enable the portion  17  to be wrapped around and under  19  the periphery of the exterior surface of the collapsed bead  16   b  (as shown in  FIG. 8 ), so that the free edge  15  is directed inwardly towards the can body sidewall, thereby providing enhanced rigidity and protection to an individual against cuts from the free edge. 
     In an alternative embodiment, the design of the flared die  2  and limit ring  3  is adapted to together define an outwardly curled end face  23  (see  FIG. 9 ). In common with the embodiment shown in  FIGS. 1 to 7 , the flared die  2  is driven into the end of the can body  1  to apply both radial and axial loads to the can body to first define the circumferential radially-expanded region  14 . Further insertion of the die  2  into the can body  1  causes the free edge  15  at the end of the can body to propagate along the surface of the outwardly-curled end face  23  to form curl  50  (see  FIG. 10 ). Ultimately, the curl  50  forms to such an extent that the free edge  15  opposes and contacts the outside of the sidewall  13 , which thereby inhibits further movement of the free edge. As a result, further insertion of the flared die  2  induces the partial axial collapse of all or part of the circumferential radially-expanded region  14  to form the outwardly-directed open annular bead  16   a .  FIG. 10  shows the curl  50  and outwardly-directed open annular bead  16   a  that results from use of the flared die  2  and limit ring  3  of  FIG. 9 . 
       FIG. 11  shows the diaphragm  40  located between the opposing surfaces of the outwardly-directed open annular bead  16   a  before full collapse of the bead. 
     In a subsequent operation, the can body  1  is then rotatably mounted on a seaming chuck  60  (see  FIGS. 12 &amp; 13 ). The seaming chuck  60  includes a circumferential axial wall section  61  and a circumferential tapered wall section  62 . In use, the axial wall section  61  of the chuck is inserted into the end of the can body  1  to radially support the sidewall  13 , with the tapered wall section  62  nestling against the top of the curl  50 . The opposite end of the can body  1  is supported on a table  63  (see  FIG. 12 ). In use, the table  63  is driven upwards (indicated by arrows C on  FIGS. 12 &amp; 13 ) to urge the end of the can body  1  against the tapered wall section  62  of the chuck  60 . This induces full collapse of the open annular bead  16   a . The resulting can body  1  with the fully collapsed bead  16   b  is shown in  FIGS. 12 &amp; 13 . After formation of the fully collapsed bead  16   b , seaming roll  64  having a tapered surface  65  is then brought into contact with the underside of the collapsed bead  16   b  whilst the can body  1  is rotated about longitudinal axis  11  (see  FIGS. 14 &amp; 15 ). The direction of rotation of the can body  1  and seaming roll  64  is indicated by arrows in  FIGS. 14 &amp; 15 . Urging of the tapered surface  65  of the seaming roll  64  against the underside of the collapsed bead  16   b  inclines the bead upwardly until the bead is sandwiched between the curl  50  and the tapered surface of the seaming roll (see  FIG. 15 ). This has the effect of further tightening the clamped seal that holds the diaphragm  40  in place. 
     Regardless of how and when the curl is formed on the end of the can body, the curl  50  may be flattened against the external surface of the collapsed bead  16   b  to define a double thickness of metal above and adjacent the external surface of the collapsed bead. In the embodiment of the invention shown in  FIGS. 14 &amp; 15 , this flattening (or crushing) of the curl would be achieved through the table  63  being urged further upwards to deform the curl  50  between the opposing surfaces of the tapered wall section  62  of the chuck  60  and the tapered surface  65  of the seaming roll  64 .