Three-piece can and forming mandrel for expanding metal precursor in manufacture of three-piece can

Abstract

A three-piece can having an outer diameter and an outer surface in a band configuration is disclosed, wherein a first portion of the outer surface is recessed by at least 10%, 12%, or 15% relative to a second portion of the outer surface having the outer diameter. Also disclosed is a forming mandrel for expanding a cylindrical metal precursor in the manufacture of a three-piece can, comprising: an actuator arm; a plurality of longitudinally extending sections arranged around the actuator arm, each section having an inner cam surface and an arcuate outer surface for engaging an inner surface of a precursor positioned above the mandrel, the sections comprising a first subset of sections and a second subset of sections, the actuator arm being longitudinally movable relative to the sections, the first sub-group and the second sub-group are coupled to each other and have a plurality of wedge surfaces arranged to contact the cam surfaces of the respective sections and move the first sub-group and the second sub-group radially outward at respective different speeds to expand the mandrel from a first state to a final state.

Description

Technical Field

[0001] The present disclosure relates to a method of forming a cylindrical metal precursor for use in the manufacture of cans, and to cans so manufactured, in particular cans for packaging powdered products such as infant nutrition and formula. The disclosure also relates to an apparatus suitable for carrying out such a method. Background Art

[0002] Metal cans have been used for years to package powdered materials because they can be sealed for long-term storage and are relatively easy and inexpensive to produce. The aesthetics of such cans play a huge role in the customer experience. The shape of the can can be both eye-catching and provide practical functionality, such as a handle. Various can constructions are known, including what are commonly referred to as two-piece cans and three-piece cans. In the case of a two-piece can, the base and sidewalls are produced in a single step from a single piece of metal, typically by a combination of deep drawing and necking. A three-piece can typically comprises a cylindrical sidewall with a longitudinal seam and two end portions connected to the sidewall by a single or double folded seam.

[0003] While two-piece and three-piece cans share many similarities, fundamental differences in their production lead to significant differences. Two-piece cans typically lack longitudinal seams and may be subject to significantly higher twisting forces and pressures during manufacturing. In three-piece cans, the longitudinal seam will always be an asymmetrical point, which will distort differently from other areas of the circumference. Expansion of the can may be limited by the strength of this seam. Due to the significant deformation common in two-piece can production, this is generally only suitable for aluminum or softer alloys. Three-piece cans are typically made of steel. Another important difference is the need to trim the upper end of a two-piece can before applying the closure. Due to the longitudinal stretching during the deep drawing process, the upper edge of the can body may no longer be level. To achieve the required tolerances for a proper seam, the upper end of this can body is often trimmed, requiring an additional step. This cutting process introduces metal particles into the production environment and may not be preferred for certain sensitive products. Three-piece cans do not require longitudinal stretching, so the end seam can be kept within acceptable tolerances.

[0004] To create a specific body shape for a three-piece can, an expansion forming process can be used, in which a cylindrical mandrel is expanded, stretching a portion of a cylindrical precursor from an initial diameter to a larger diameter. Such a mandrel typically includes a plurality of longitudinally extending segments radially arranged about the longitudinal axis of the mandrel. When the mandrel is expanded by the action of a wedge or cam surface, the segments have arcuate surfaces that engage the inner surface of the precursor. It will be understood that the depth of any configuration, relief, or contour in the final can will depend on the amount the can is stretched.

[0005] In existing procedures that attempt to achieve a high degree of stretch, it has been found that the final body shape exhibits vertical parting lines at the gaps between the segments of the mandrel. These parting lines may exist in various locations around the entire circumference of the body. The parting lines can be seen with the naked eye and are detrimental to the aesthetics of the final can, especially on an otherwise smooth or distinctive surface. The parting lines are formed due to localized stretching of the metal sidewall at the edge of the segment. This is exacerbated as the segments move further apart, and the unsupported sidewall between the segments forms a flat strip that no longer follows the same curvature as the arcuate surface. Typically, a softer, more ductile steel grade needs to be used to avoid the problem of cracking at the location of these parting lines. This has the consequence of making the final package weaker and more susceptible to dents.

[0006] Patent publication DE102011100506A1 describes a method for expanding cylindrical tubes, particularly for producing tin cans with a circular cross-section. In a first expansion step, forming lamellae are expanded outward by actuator arms equipped with wedge surfaces, expanding the tube to the desired shape. The forming lamellae are then moved back again, so that they are no longer in contact with the inner wall of the tube. The forming lamellae are then rotated relative to the tube about their longitudinal axis. In a second expansion step, the forming lamellae are again moved radially outward to the same extent as in the first expansion step. In this second expansion step, the forming lamellae shape the areas of the cylinder that were not in direct contact with the forming lamellae at the end of the first expansion step.

[0007] These existing two-stage expansion methods are cumbersome because they require a rotation step, which requires additional time and tooling. Even so, this method may not be able to achieve high expansion without the aforementioned cracking issues that occur at the end of the second stage. Furthermore, the rotation of the mandrel is not suitable for producing certain surface features because it may disrupt the intended position of the features. Generally speaking, only rotationally symmetric shapes can be produced using this process.

[0008] It would be desirable to provide an alternative method for expanding cylindrical metal precursors, particularly cylindrical metal precursors suitable for making three-piece cans of both symmetrical and asymmetrical designs. Utility Model Content

[0009] According to a first aspect of the present invention, a method for expanding a cylindrical metal precursor in the manufacture of a three-piece can is provided, the method comprising the steps of: placing a precursor having an initial diameter around a forming mandrel, the forming mandrel having a plurality of longitudinally extending segments radially arranged about a longitudinal axis of the forming mandrel, the segments having arcuate surfaces for engaging an inner surface of a wall of the precursor; in a first step, actuating a first subset of the plurality of segments to expand outwardly so as to engage the inner surface of the wall of the precursor and expand at least a portion thereof to a first diameter, the first diameter being greater than the initial diameter of the precursor; and in a second step actuating a second subset of the plurality of segments to expand outwardly and also engage the inner surface of the wall of the precursor, whereby the second subset expands at least a portion of the precursor to a second diameter greater than the first diameter. The method allows for a greater degree of expansion of the wall of a cylindrical metal container, wherein a greater diameter change can be achieved between a concave portion of the wall and a remaining portion thereof.

[0010] Hereinafter, reference to recessed sections will refer to areas of the container wall that have been intentionally expanded less than other areas of the wall in order to create a profiled outer surface. These recessed sections may still be in a position corresponding to the original diameter, or they may have been expanded, but by less than the rest of the wall. The method is particularly suitable for welded steel containers made from high-grade steel. In the past, to avoid cracking, high expansion levels could only be achieved by selecting more ductile steels. The ability to use this stronger steel allows for better performance in terms of top load, side load, and dent resistance in the final packaging. This allows for lower can wall thicknesses. Because the individual sections expand outward in different steps, a better distribution of tensile forces in the metal is created. As a result, the final can can be up to 25% thinner than existing cans: where conventional cans are made with a wall thickness of 0.24 to 0.25 mm, a thickness of 0.18 to 0.20 mm can be used. Furthermore, the precursor can expand up to 30% of its original diameter without cracking.

[0011] The segments can be divided into any suitable subgroups that allow the desired expansion sequence to be performed in a single stroke of the tool. There can be more than two subgroups, and not all subgroups need to be equal in number. However, in a preferred embodiment, the first subgroup consists of alternating segments around the longitudinal axis of the forming mandrel, while the second subgroup consists of all the remaining segments. In this case, the number of segments in each subgroup will be the same. First expanding the body with only half of the segments at a time and then with all of the segments subsequently allows for better distribution of the tensile forces during the critical final stage of expansion.

[0012] Depending on the initial position of the segment groups and the stage at which overall expansion is reached, the segment groups can be actuated to expand at different rates. Those skilled in the art will be familiar with the actuators and wedges required for such expansion. The absolute rate of expansion of the precursor wall can be greater during the initial stage of expansion than during the final stage of expansion. The relative speeds of the different subgroups will also be different. In one embodiment, during the first step, the segments of the second subgroup can be actuated to expand outward at a rate that is at least slightly greater than the rate at which the segments of the first subgroup expand outward. This is because they will typically be initially retracted further than the segments of the first subgroup and therefore need to catch up before participating in the expansion of the wall in the second step. In this case, reference to the first step is intended to refer to the portion of expansion in which only the segments of the first subgroup engage the inner surface. Reference to the second step is intended to refer to the portion of expansion in which both subgroups are in contact with the inner surface. Thus, in the first step, contact with the wall is limited to one subgroup of segments, while the second subgroup remains free of contact with the wall. However, it should be understood that although two steps are mentioned, these steps are merely temporary stages in the operation and the process may otherwise be continuous without the need to remove or readjust the mandrel between steps.

[0013] In a second step, the first subset is also expanded from the first diameter to the second diameter. In this way, all longitudinal portions of the precursor of the contact segment are enlarged into a cylinder whose entire circumference is at the second, larger diameter. Thus, this method allows for the expansion of most or all of the precursor into a cylinder having the larger, i.e., second, diameter.

[0014] Once the segments of the second subset have caught up to the segments of the first subset, all of the segments can be actuated to expand outward at the same speed during a second step. The two subsets of segments can alternately expand at different speeds. However, the skilled person will understand that the precise expansion speed will depend on the design of the cam surfaces or wedge surfaces used and the relationship between the groups of segments.

[0015] For the purposes of this description, the second step can be considered to begin when the second subset contacts the precursor wall. However, it will be understood that the actuation and movement of the subsets can be continuous. In one embodiment, the second step can include an initial phase in which the arcuate surface of the second subset engages the inner surface of the precursor, but remains radially inward of the arcuate surface of the first subset. During this phase, only a portion of the arcuate surface of the second subset contacts the precursor wall.

[0016] In one embodiment, the second step may include an intermediate stage in which the arcuate surfaces of the second subset are radially aligned with the arcuate surfaces of the first subset. This intermediate stage may begin at the point where the edges of the arcuate surfaces of adjacent segments initially engage, i.e., the arcuate surfaces form an almost complete circumference with no gaps. It will be understood that although the circumference may be complete, it may not be a perfect circle because at this expansion point, the individual segments may have a curvature that is slightly larger in diameter than the precursor. After the initial stage of the second step in which the central portion of the second subset of segments has engaged the precursor, a point will be reached at which the complete surfaces of all segments will engage the precursor wall. Thereafter, all segments may expand to a final and almost uniform curvature corresponding to the arcuate surfaces of the second subset. During this intermediate stage (which may also be the final stage), the segments will move slightly apart, leaving gaps between adjacent segments.

[0017] In one embodiment, the second step may include a final stage after the intermediate stage in which the arcuate surfaces of the second subset are moved radially outward beyond the arcuate surfaces of the first subset. This final step may provide a slight overstretching of the precursor to remove any remaining marks caused by the edges of the segments of the first subset during the first step.

[0018] The precursor can be expanded in a first step to a first diameter that is preferably 10% to 20% larger than the initial diameter of the precursor, although other diameters are contemplated. A first step of expansion to a first diameter within this range can generally be achieved without creating unacceptable stress levels in the precursor wall at the edges of the segments, particularly when working with high-grade steel.

[0019] After the second step, a circumferential gap may exist between the edges of the arcuate surfaces of adjacent segments. The manner in which the expansion is achieved and the number of segments allow for limiting the width of this gap. In one embodiment, the gap may not exceed 5 mm, preferably not exceed 2 mm, and more preferably not exceed 1.5 mm. This prevents or avoids the visibility of vertical dividing lines in the final form.

[0020] In one embodiment, the second diameter is preferably 20% to 30% greater than the initial diameter of the precursor. The method and associated apparatus provide for greater expansion of the precursor than is typically possible with high-grade steel. This provides greater scope for enhancing the aesthetics of cans made from durable materials. Expanding only a portion of the container surface in the first step, while carefully providing an ideal force distribution across the material in the second step, ensures optimal expansion without creating unwanted parting lines or other distortions. This results in an optimally expanded container body with a smooth outer surface and no defects.

[0021] In one embodiment, the first and second steps can be performed without rotating the precursor relative to the mandrel. The method of the present disclosure avoids the need to rotate the precursor at any time during the process. This is more time-efficient and reduces potential errors in realigning the precursor for further expansion. In addition, expansion can be obtained with a relatively simple and single device. However, it is not excluded that a slight rotation can be provided to further avoid the presence of a parting line or to enhance a specific expected contour or configuration.

[0022] The method can utilize arcuate segment surfaces that have the same curvature at a given longitudinal position along the longitudinal axis and / or a constant curvature at all positions along its longitudinal extent. However, designs with differently shaped surfaces are also contemplated. The arcuate surface of one or more of the multiple segments can be contoured in the longitudinal direction so that, after the second step, the expanded precursor body has a contoured outer surface. Thus, the method can provide the expanded cylindrical body with gripping features and / or any pattern that satisfies the customer. To avoid variations in the upper and lower edges of the precursor body, each segment can have the same longitudinal contour length, despite variations in the actual contour. In this manner, trimming of the ends of the expanded precursor body can be avoided. In this case, the longitudinal contour length is the path length along the surface of the segment (or precursor body) from a first reference position to a second reference position corresponding to the top and bottom of the can. Generally, it is desirable that the upper and lower ends of the expanded precursor body deviate from a flat plane perpendicular to the longitudinal axis of the body by no more than 0.5 mm, preferably less than 0.25 mm or less than 0.1 mm.

[0023] In one embodiment, at least the first segment can have a different longitudinal configuration than the second segment, or all segments can have different longitudinal configurations while all segments have the same longitudinal configuration length. A skilled artisan will recognize that a variety of attractive tank designs can be created while respecting the geometric requirement that each longitudinal section of the wall should have equal length. In particular, designs can be created that are not rotationally symmetric about the tank's longitudinal axis.

[0024] At the end portions of all segments, the longitudinal configuration may include a curve toward the longitudinal axis of the forming mandrel. This configuration of the segments allows the bottom or top portion of the can to remain at or close to the initial diameter, or at least to remain at a diameter that is significantly smaller than the second diameter. This can be used to ensure a smaller base for stacking purposes or to reduce the presence of sharp corners at the base. This curvature at the base is advantageous for approaching, for example, a spoon with a corresponding curved shape. At the upper end of the can, the smaller diameter can facilitate connection with the lid assembly, allowing the outer circumference of the lid assembly to remain within the outer circumference of the can.

[0025] The overall design of the expanded precursor at the end of the second step will generally depend on the combined outer surface of all segments and the extent to which they have been expanded. The expanded precursor body may have a profiled outer surface, wherein a portion of the outer surface has a second diameter and the other portion of the outer surface is recessed relative to the second diameter by at least 10%, 12% or 15%, preferably at least 20%. The recessed portion may form a design or pattern in relief relative to an otherwise uniform outer surface. In this case, uniform is intended to mean a cylindrical surface of constant diameter, i.e. 2D curved. However, it is not excluded that external tools may also be provided for engaging the outer surface of the precursor, in particular for applying a force to recess a portion of the outer surface inwardly, for example into the contour of the arched surface of part or all of the segments.

[0026] Can be made by the method described above that makes the metal cylindrical precursor expand, and then the base is attached to one of the two open end parts of the expanded precursor body. In this case, the manufacture of the three-piece can is not intended to require that the three parts must be combined together, but only refers to the technology for forming the side wall without end. In an embodiment, only the base can be attached in the manufacturing step, and the upper open end can be folded or otherwise provided with an edge and closed with a separate closure. However, in a preferred embodiment, the method can further include attaching a separate edge to another of the two open end parts to form a three-piece can. Thus, a closed container with sufficient volume and attractive shape can be formed for storing products, particularly infant nutrition products.

[0027] Attachment of the base and / or rim is preferably performed without first trimming the end portions of the expanded precursor body. As discussed above, the expanded precursor preferably has a constant and accurate length around its circumference that is within the tolerance of the seam, thereby eliminating the need for trimming. It will be appreciated that avoiding trimming is desirable because any such procedure may generate metal fragments. In the past, length changes and the need for trimming may also be avoided by holding or clamping the ends of the can during expansion. However, this may lead to other disadvantages, such as wrinkling and / or cracking, and impose further limitations on equipment and design. The present solution also avoids the need to clamp the ends of the can during expansion.

[0028] The present invention also includes a three-piece tank as described above and below. The tank body may have an outer diameter and a profiled outer surface, wherein a first portion of the outer surface is recessed by at least 10%, 12% or 15%, preferably by at least 20%, relative to a second portion of the outer surface having the outer diameter. The method allows a large number of design options with a high expansion threshold, preferably up to 30% of the initial diameter, even when using thin high-strength steels as discussed above. In a preferred embodiment, a highly anisotropic steel with a small directionality may be used, such as tin-plated steel (TPS) TS275 according to the EU packaging steel standard EN10202, which preferably has a strength of 225 and 325 N / mm 2 Yield / 0.2% proof strength (Rp) between.

[0029] In one specific embodiment, the components of the first and second sections can be located at the same longitudinal position on the exterior surface, i.e., at the same height on the tank wall. The exterior tank design can be rotationally asymmetric about the longitudinal axis. Conversely, reflectional symmetry about selected faces of the tank can be achieved, which is highly desirable for branding purposes. This is particularly achievable if each longitudinal section of the tank body has the same longitudinal configuration length.

[0030] In one desirable embodiment, the configuration includes a groove recessed around the circumference of the tank, wherein the longitudinal position of the groove varies around the circumference. The groove may have a constant shape, i.e., a cross-sectional shape, around the circumference, or may vary in shape (e.g., depth and width) around the circumference. However, such variation should remain within the overall requirement that each longitudinal portion of the tank body have the same longitudinal configuration length.

[0031] In certain embodiments, the first concave portion may be a small or minor portion of the can's outer surface, while the second portion having the outer diameter may be a major portion of the outer surface. The major portion may be greater than 50%, greater than 60%, greater than 70%, or greater than 80% of the can's outer surface. The major portion may be generally flat, i.e., having a constant curvature corresponding to the maximum outer diameter.

[0032] According to another aspect of the present invention, a forming mandrel for expanding a cylindrical metal precursor in the manufacture of a three-piece can is provided. The mandrel may include an actuating arm and a plurality of longitudinally extending segments arranged around the actuating arm, each segment having an inner cam surface and an arcuate outer surface for engaging an inner surface of a precursor positioned above the mandrel. The segments each have a longitudinal configuration, and in one embodiment, at least a first segment may have a different longitudinal configuration than a second segment, while all segments have the same longitudinal configuration length.

[0033] In certain embodiments, all segments can have different longitudinal configurations, but the same overall longitudinal configuration length. For example, each segment can have a generally flat configuration with a recessed channel, and the longitudinal position, cross-sectional shape, and / or orientation of the recessed channel can vary from segment to segment around the circumference. In this way, a groove or contour can be created around the body of a can formed on a mandrel without causing a change in the overall length of the can around its circumference.

[0034] Additionally or alternatively, the segments include a first subset of segments and a second subset of segments, wherein the actuating arm is movable longitudinally relative to the segments and has a plurality of wedge surfaces arranged to contact cam surfaces of the respective segments and radially move the first subset and the second subset at respective different speeds in a series of steps to expand the mandrel from the first state to the final state. The forming mandrel of the present invention allows a cylindrical body made of high-grade steel to be expanded in a single process, which provides better control of the tensile force on the material.

[0035] The first subgroup may be composed of an even number of segments, equal to or greater than 6, preferably equal to or greater than 8, or even 12 or more. The second subgroup may be composed of the same number of segments. By increasing the number of segments, better force distribution can be achieved, and for a given expansion, the overall gap between adjacent segments at the completion of the operation can be reduced. Thus, there may be up to 24 segments in total.

[0036] The plurality of wedge surfaces may include a first set of wedge surfaces radially aligned with the segments of the first subset and a second set of wedge surfaces radially aligned with the segments of the second subset. By having each segment have an associated wedge surface, control over the expansion of each segment can be achieved. As a result, each step of the expansion method of the present disclosure can be accurately performed. The wedge surfaces can be separate surfaces on a single wedge body, or can be formed by multiple wedge bodies assembled together. It will also be understood that the wedge surfaces can be arranged in series or one after the other in the longitudinal direction to provide a balanced expansion force for each segment at two points along the longitudinal axis.

[0037] Each of the plurality of wedge surfaces can be defined by a wedge angle relative to the longitudinal axis of the forming mandrel. The wedge angle of the first set of wedges can be constant over the longitudinal movement of the actuator arm, and the wedge angle of the second set of wedges can also be constant but higher than the wedge angle of the first set of wedges. In one embodiment, the wedge angle can initially be higher than and subsequently equal to the wedge angle of the first set of wedges. By controlling the wedge angle of the second set of wedges to be different from and greater than the angle of the first set, the second subset of segments can catch up with the first subset of upper segments.

[0038] In one embodiment, the first subset of segments can be undercut so that, during the first step, the second subset of segments can be recessed behind the arcuate outer surface of the first subset. Thus, the overall initial diameter of the mandrel can be reduced for insertion into the precursor. Furthermore, at the end of the expansion process, the mandrel can be retracted for removal, even if some areas of the precursor are still at or near the initial diameter.

[0039] The arcuate surfaces of the segments of the first and second subsets can have different sizes. In particular, the segments of the first subset can be larger than those of the second subset. In a preferred embodiment, the arcuate surfaces of the first and second subsets can be equal in size. This ensures that during the final critical expansion step, the inner surface of the precursor undergoes balanced expansion and that any gaps between the segments are equally spaced.

[0040] It will be appreciated that the ability to provide significant expansion provides considerable scope for forming tanks having different aesthetic, functional and ergonomic forms, while still allowing the mandrel to be extracted after the expansion step is completed. In certain designs, it may be desirable to fully expand only a minor area of ​​the tank's outer surface to the maximum extent possible, while leaving the primary area with less expansion. Typically, in the final state, the major portion of the arcuate surface of all segments may have a diameter corresponding to the maximum outer diameter of the tank, and the minor portion may be recessed relative to the outer diameter by at least 10%, preferably 15%, more preferably 20%. For the purposes of definition, when referring to the diameter of the tank, this will therefore refer to the maximum outer diameter. The major portion may be more than 50% or more than 60% or more than 70% or more than 80% of the tank's outer surface. The major portion may be substantially flat, i.e. having a constant curvature corresponding to the maximum outer diameter.

[0041] An additional advantage of this high expansion is that for the same volume of can, less material is required. The material reduction may be at least 2.5%, or 5%, or even 7.5% of the total weight of the tin.

[0042] In general, the present invention discloses the following technical solutions:

[0043] 1. A three-piece can having an outer diameter and a contoured outer surface, wherein a first portion of the outer surface is concave by at least 10%, 12% or 15%, and preferably at least 20%, relative to a second portion of the outer surface having the outer diameter.

[0044] 2. A three-piece can according to the aforementioned scheme 1, characterized in that it includes an expanded metal precursor body, wherein the precursor body has a base at the first end of the body and an edge at the second end of the body, wherein the outer surface with the configuration is arranged on the precursor body.

[0045] 3. The three-piece tank according to the aforementioned solution 1 or 2, characterized in that the first part and the second part are located at the same longitudinal position of the outer surface.

[0046] 4. A forming mandrel for expanding a cylindrical metal precursor in the manufacture of a three-piece can, characterized in that the mandrel comprises:

[0047] an actuator arm; and

[0048] a plurality of longitudinally extending segments arranged about the actuator arm, each segment having an inner cam surface and an arcuate outer surface for engaging an inner surface of a precursor positioned above the mandrel, the segments comprising a first subset of segments and a second subset of segments,

[0049] The actuator arm is capable of longitudinally moving relative to the segments and has a plurality of wedge surfaces arranged to contact cam surfaces of the corresponding segments and cause the first and second subgroups to move radially outward at respective different speeds to expand the spindle from a first state to a final state.

[0050] 5. The forming mandrel according to the aforementioned solution 4 is characterized in that the first subset consists of an even number of segments equal to or greater than 6, preferably equal to or greater than 12, and the second subset consists of the same number of segments.

[0051] 6. The forming mandrel according to any one of the aforementioned options 4 or 5, characterized in that the multiple wedge surfaces include a first group of wedge surfaces radially aligned with the segments of the first subset and a second group of wedge surfaces radially aligned with the segments of the second subset.

[0052] 7. A forming spindle according to the aforementioned scheme 6, characterized in that the wedge angle of the first group of wedge surfaces is constant during the longitudinal movement of the actuator arm, and the wedge angle of the second group of wedge surfaces is initially higher than the wedge angle of the first group of wedge surfaces and then equal to the wedge angle of the first group of wedge surfaces.

[0053] 8. A forming mandrel according to any one of the preceding solutions 4 to 7, wherein a first subset of segments is undercut, whereby a second subset of segments can be recessed behind the arcuate outer surface of the first subset in the first state of the mandrel.

[0054] 9. The spindle according to any one of the preceding schemes 4 to 8, wherein the arcuate surfaces of the first and second subsets are of equal size.

[0055] 10. A spindle according to any one of the preceding schemes 4 to 9, characterized in that, in the final state, the main part of the arcuate surface of all segments has a diameter corresponding to the maximum outer diameter of the tank, and the secondary part is concave relative to the outer diameter by at least 10%, preferably 15%, more preferably 20%.

[0056] 11. A three-piece tank having an outer diameter and a contoured outer surface, wherein a first portion of the outer surface is recessed by at least 10% relative to a second portion of the outer surface having the outer diameter, and wherein the first portion and the second portion are at the same longitudinal position of the outer surface but at different circumferential positions, and wherein the longitudinal contour lengths at all circumferential positions around the tank are equal.

[0057] 12. The tank according to the above-mentioned embodiment 11 is characterized in that the outer surface of the belt configuration includes a concave groove around the tank.

[0058] 13. A can according to the preceding embodiment 12, characterized in that the longitudinal position, shape and / or orientation of the groove varies around the circumference.

[0059] 14. A tank according to any one of the preceding schemes 11 to 13, characterized in that the outer surface has a configuration that is not rotationally symmetrical around a circle but has reflection symmetry about a plane passing through the longitudinal axis of the tank.

[0060] 15. A three-piece tank, characterized in that it has a tank body with a configured outer surface, the tank body including a groove extending around the circumference of the body, and wherein the longitudinal position, cross-sectional shape and / or orientation of the groove varies around the circumference so that each longitudinal section around the circumference of the tank body has the same configured length.

[0061] 16. The can according to the above embodiment 15, characterized in that it comprises a single continuous groove.

[0062] 17. A forming mandrel for expanding a cylindrical metal precursor in the manufacture of a three-piece can, said mandrel comprising:

[0063] an actuator arm; and

[0064] A plurality of longitudinally extending segments are arranged around the actuator arm, each segment having an inner cam surface and an arcuate outer surface for engaging an inner surface of a precursor positioned above the spindle, the outer surfaces each having a longitudinal configuration, wherein at least a first segment has a different longitudinal configuration than a second segment and all segments have the same longitudinal configuration length.

[0065] 18. The mandrel of claim 17, wherein all segments have different longitudinal configurations but the same overall longitudinal configuration length.

[0066] 19. The spindle of claim 17 or 18, wherein each segment has a generally flat configuration with a recessed channel, and wherein the longitudinal position, cross-sectional shape and / or orientation of the recessed channel varies between segments around the circumference.

[0067] 20. A three-piece tank substantially as herein described and as illustrated in the accompanying drawings.

[0068] 21. A forming mandrel substantially as herein described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Embodiments of the present disclosure will be described by way of example with reference to the accompanying drawings, in which:

[0070] Figure 1A A flow chart showing a sequence of steps for manufacturing a three-piece can from a metal blank is shown, and includes an expansion step,

[0071] Figure 1B shows an example of the top and sidewalls of a cylindrical metal precursor expanded according to methods known in the art,

[0072] Figure 2A shows a cross-sectional view of an expansion device for expanding a cylindrical metal precursor, the device being in a retracted state before expansion, wherein the precursor is positioned around the device,

[0073] Figure 2B Shown Figure 2A Cross-sectional view of the expansion device after expansion is completed,

[0074] Figure 3 Shown through Figure 2A The cross section of the mandrel at position III-III,

[0075] Figures 4A to 4C Shows the different stages during mandrel expansion Figure 3 Longitudinal section taken at position IV-IV;

[0076] Figure 5A Shown Figure 3 A cross-sectional view of two adjacent segments of a mandrel before a first expansion step,

[0077] Figure 5B Shown Figure 3 A cross-sectional view of two adjacent segments of a mandrel at the beginning of a second expansion step,

[0078] Figure 5C Shown Figure 3 A cross-sectional view of two adjacent segments of a mandrel in a further expansion stage,

[0079] Figure 5D Shown Figure 3 A cross-sectional view of two adjacent segments of a mandrel in a final expansion stage,

[0080] Figure 5E Shown Figure 3 a cross-sectional view of two adjacent segments of a mandrel in an alternative final stage of expansion, and

[0081] Figures 6 to 8 Three exemplary container bodies are shown expanded according to the methods of the present disclosure. DETAILED DESCRIPTION

[0082] Figure 1A A sequence 100 of steps 110-160 for manufacturing a three-piece can from a metal blank 1 is shown. In particular, the sequence includes an expansion step 140. The other steps are known to those skilled in the art and are only briefly described. In step 110, a metal sheet is cut into a slab 1. In step 120, the blank may be coated and cured. Following this optional step, the slab 1 is welded into a generally cylindrical precursor 2 in step 130. The precursor 2 has a metal body with two open ends and a vertical seam (not shown) at which the side walls have been joined to form the cylinder. The metal body of the cylindrical precursor 2 is typically a steel body prepared from a steel blank. In step 140, a portion of the wall of the cylindrical metal precursor 2 is expanded outwardly. The resulting expanded container 3 has a contoured shape and deviates from the original cylindrical shape. This step can be performed according to the method of the present disclosure described later. In step 150, the expansion container 3 may be subjected to any flanging (F, as shown) and / or other processes known in the art, including, for example, any printing or curling (not shown). In step 160, the expansion container 3 may be provided with closures 4, 5 attached to each of the two open ends, with or without sealing and / or pre-filling. This concludes the manufacturing cycle of the three-piece can. It should be noted that this sequence is merely an example and that the expansion steps of the present disclosure may also be part of other sequences known in the art for manufacturing three-piece cans. However, it will be noted that in the illustrated embodiment, it is not necessary to trim the container ends prior to the closing step 160.

[0083] Figure 1BA top view and a side view are shown of a cylindrical precursor 2 of diameter d before and after expansion into an expanded body 3 according to an expansion method known in the art. The illustration of the expanded body exaggerates the shape of the precursor in order to illustrate the problems of the expansion method known in the art. The surface of the resulting body 3 does not have a circular body of diameter D, but has a plurality of vertical dividing lines (S). These vertical dividing lines correspond to locations of high stretching of the metal wall during expansion. The vertical dividing lines have been formed between adjacent segments of the expansion mandrel (not shown) and do not follow the curvature of the mandrel. In this illustration, it will correspond to a locally flat section between every two of the six segments.

[0084] Figure 2A A cross-sectional view of a conventional expansion device 10 is shown, which is used to explain the basic principle of expanding a metal cylindrical precursor 2. The device is shown in a retracted state, i.e., prior to expansion. The expansion device 10 includes a housing 11 and a forming mandrel 13 extending from the housing 11. The forming mandrel 13 includes a plurality of similar segments 14 spaced apart around expander arms 12. Each segment 14 has an arcuate contact surface A for contacting or engaging the inner surface I of the cylindrical precursor 2 positioned around the segment 14. Each segment 14 also has a cam surface 18 on its inner side, which faces the expander arm 12. In the retracted state, the contact surface A of the segment 14 is spaced radially inward from the inner surface I of the container body 2. The proximal ends 12A of the expander arms 12 and the ends 20 of the segments 14 are received within the housing 11. The distal end 13B of the mandrel 13 has a reduced diameter.

[0085] The expander arms 12 are axially movable (along the axis Z) within the housing to cause expansion of the segments 14. The segments 14 extend longitudinally along the expander arms 12. A pair of wedges 16 are positioned one behind the other around the expander arms 12. The expander arms 12 and the wedges 16 form an actuator for the forming mandrel 13. Each wedge 16 has a plurality of wedge surfaces 17, each of which contacts a mating cam surface 18 of the segments 14. Axial movement of the expander arms 12 together with the wedges 16 causes the wedge surfaces 17 to travel along the cam surfaces 18, causing the segments 14 to expand outwardly to contact the inner surface I of the precursor 2.

[0086] Figure 2B Shown Figure 2A FIG2 is a cross-sectional view of the same expansion device 10 in FIG2 , showing the final expanded state. This view shows how the expander arms 12 have moved proximally in the direction of the housing 11 (the Z direction). This axial movement has caused the wedge surfaces 17 to cooperate with the corresponding cam surfaces 18 of the segments 14 to force the segments 14 radially outward into engagement with the inner surface 1 of the precursor 2. The inner surface 1 of the precursor 2 is correspondingly deformed to adopt the shape of the expansion mandrel 13. The distal end 13B of the mandrel defines the minimum inner diameter of the expanded precursor 2.

[0087] When expansion is complete, the expander arms 12 are moved axially away from the housing 11, and the segments 14 can be returned to their retracted or retracted positions. The precursor 2 can then be removed from the forming mandrel 13. It will be appreciated that the mandrel 13 must be sufficiently retracted so that the largest outer diameter can pass through the smallest diameter portion of the precursor 2. In conventional expansion devices, such as the device 10 of FIG. 2 , approximately six or eight segments 14 may be provided, all of which are substantially identical.

[0088] Figure 3 A cross-sectional view in plane (XY) of a forming mandrel 12 of an expansion device 10 according to the present invention is shown. Like numbers will be used for like parts as in the case of the conventional device of FIG2 . Mandrel 13 is shown in its initial state before any expansion, with an outer diameter d1 .

[0089] The forming mandrel 13 includes twelve segments 14 that surround the expander arms 12. In this case, the segments 14 are divided into two subgroups, namely a first subgroup segment 14A and a second subgroup segment 14B. The first subgroup segment 14A is spaced outwardly from the second subgroup segment 14B at an initial outer diameter d1. It will also be noted that the segment 14A has an undercut side 19. This allows the second subgroup segment 14B to be recessed behind the arcuate contact surface A of the first subgroup segment 14A in the initial state of the mandrel 13.

[0090] The first sub-group segment 14A has a first cam surface 18A on its inner side, while the second sub-group segment has a second cam surface 14B on its inner side. Due to the presence of the undercut side 19, the second cam surface 18B is slightly narrower than the first cam surface 18A, even though the corresponding arcuate contact surfaces A of all segments 14 are the same size.

[0091] The expander arm 12 carries a wedge 16 having a wedge surface 17 which is also divided into a first wedge surface 17A and a second wedge surface 17B which engage with a first cam surface 18A and a second cam surface 18B of the segment 14 respectively.

[0092] Figure 4A The wedge 16 is shown schematically, illustrating Figure 3Figure 1 shows the profile of the wedge surface 17 and the cam surface 18 of the forming spindle 13 in the longitudinal section at position III-III. The first wedge surface 17A that actuates the first sub-group segment 14A is shown in the upper half of the figure, while the second wedge surface 17B that actuates the second sub-group segment 14B is shown in the lower half of the figure. Also shown in this view is the channel 40 formed in the arcuate surface A of the spindle 13. The depth of the channel 40 is almost equal to the overall expansion of the spindle 13. It also corresponds to the diameter of the distal portion 13B of the spindle 13. The channel 40 extends around the entire circumference of the spindle 13, but its longitudinal position varies between the segments. However, for each segment 14, the width and depth of the channel 40 are arranged so that the length of the profile of each segment 14 following the arcuate surface A in the longitudinal direction is the same.

[0093] First, the first wedge surface 17A and the mating first cam surface 18A are processed, which have a constant angle α1, which generally corresponds to the angle of the conventional device 10 of Figure 2. In the case of the second wedge surface 17B, these wedge surfaces have two-level surfaces. The first part of the surface, represented by 17Bi, has an angle α2, which is greater than the angle α1 of the first wedge surface 17A. The second part 17Bii of the surface has an angle α1, which again corresponds to the angle of the first wedge surface 17A. In the illustrated embodiment, the first part 17Bi and the second part 17Bii have approximately equal lengths. Similarly, the second cam surface 18B is also divided into two parts, wherein the first part 18Bi has an angle α2 and the second part has an angle α1.

[0094] Figure 4B Shown Figure 4A 1 , wherein the expander arms 12 and wedges 16 are partially withdrawn in the proximal direction relative to the segments 14. The first wedge surfaces 17A have advanced along the corresponding first cam surfaces 18A, causing the first subset segments 14A to move radially outward. The second wedge surfaces 17B have also advanced along the corresponding second cam surfaces 18B. As depicted, during this portion of the motion, the first portions 17Bi of the second wedge surfaces and the first portions 18Bi of the second cam surfaces slide into engagement and direct the segments 14B to expand at an angle α2. Because the angle α2 is greater than the angle α1, the second subset segments 14B move radially outward a greater distance than the first subset segments 14A.

[0095] Figure 4C Shown Figure 4AFigure 1 shows forming mandrel 13 in the figure, with expander arms 12 and wedges 16 almost completely withdrawn in the proximal direction relative to segments 14. First wedge surface 17A continues along corresponding first cam surface 18A, causing first subset segment 14A to continue moving radially outward at the same rate, as indicated by angle α1. Second wedge surface 17B has advanced further along corresponding second cam surface 18B, such that second portion 17Bii of second wedge surface 17B and second portion 18Bii of second cam surface 18B are now brought into sliding engagement for the first time. From this point in the trajectory, further proximal movement of expander arms 12 results in expansion of second subset segment 14B as determined by the slope of these portions. This will occur at the same rate as the speed of first subset segment 14A at angle α1.

[0096] Figure 5A Shown Figure 3 FIG2 shows an enlarged view of two adjacent segments 14A and 14B at the beginning of a first expansion step. The arcuate surface A of the first subassembly segment 14A contacts the inner surface I of the precursor 2 and causes the curvature of the inner surface I to conform to that of the arcuate surface. The arcuate surface A of the second subassembly segment 14B is spaced radially inward from the inner surface I by a distance Rx. Also visible are the undercut side surfaces 19 of the first subassembly segment 14A and a pair of transition ears 30 behind which the second subassembly segment 14B is recessed. During this expansion phase, all stretching of the precursor is caused by the first subassembly segment 14A, which is in contact with approximately half of the inner surface I.

[0097] Figure 5B An enlarged view of segments 14A and 14B is shown at the point where the second subassembly segment 14B first comes into contact with the inner surface 1 of the precursor 2. At this point, the second subassembly segment 14B is still radially inward of the first subassembly segment 14A. Although some stretching of the precursor 2 will occur from this point on through the engagement of the second subassembly segment 14B, the lateral edge of the first subassembly segment 14 at the location of the transition ear 30 is a critical point P at which stretch marks can be generated in the precursor 2. Figure 4B , which still corresponds to the depicted expansion cycle, wherein the first portion 17Bi of the second wedge surface and the first portion 18Bi of the second cam surface are in sliding engagement and indicate that the segment 14B is expanding at an angle α2.

[0098] Figure 5C An enlarged view of segments 14A and 14B is shown at the point where the arcuate surfaces A of all segments 14 are first aligned during the second stage of the expansion step. In the illustrated embodiment, this also corresponds to the point where the lateral edges of adjacent segments 14 just touch and therefore there is no gap between adjacent segments 14. It should be understood that this is a selected position and the mandrel 13 does not have to pass through this gapless configuration. This corresponds to Figure 4C , wherein the first portion 17Bi of the second wedge surface and the first portion 18Bi of the second cam surface first enter into sliding engagement. From this point onwards, all segments will expand at the same rate, and the arcuate surfaces A of all segments 14 will remain radially aligned.

[0099] Figure 5D An enlarged view of segments 14A and 14B is shown during the final stage of the expansion step. The arcuate surfaces A of all segments 14 are still aligned, but have now expanded to a second diameter d2 that is larger than the initial diameter d1. Figure 5C During expansion in the depicted position, the segments 14A, 14B have separated, thereby forming a circumferential gap 32 between adjacent segments 14A, 14B. It will be appreciated that the circumferential gap 32 also extends in the longitudinal direction of the mandrel 13.

[0100] Figure 5E An enlarged view of segments 14A and 14B is shown in an alternative final stage of expansion. In this case, second subassembly segment 14B has expanded to a diameter slightly larger than second diameter d2. This can be used to stretch precursor 2 slightly away from the edge of first subassembly segment 14A at the location of transition ear 30. This can be used to provide a slight overstretch at critical location P to remove previously created stretch marks. This alternative final stage can be achieved by another portion of second cam surface 18B following second portion 18Bii.

[0101] Figure 6 The finished can 3 is shown after completion of the expansion step and after provision of the top closure 4 and the bottom closure 5. Formations 42 are provided around the outer surface, corresponding to the channels 40 in the mandrel 13. Figure 7 and Figure 8 Alternative cans 3 are depicted, all having a contoured outer surface. Due to the improved expansion achievable using the disclosed mandrel, diameter changes of up to 30% can be achieved while ensuring an otherwise smooth, defect-free surface for the can 3.

[0102] The present disclosure has been described with reference to certain embodiments described above. It will be appreciated that these embodiments are susceptible to various modifications and alternatives well known to those skilled in the art. In particular, different numbers of segments, different wedge angles, and configurations can be used to create tanks of varying designs. Therefore, while specific embodiments have been described, these are merely examples and are not intended to limit the scope of the present invention.

Claims

1. A three-piece tank having an outer diameter and a contoured outer surface, characterized in that: The first portion of the outer surface is recessed by at least 10%, 12% or 15% relative to a second portion of the outer surface having the outer diameter, and wherein the three-piece can comprises an expanded metal precursor body having a base at a first end of the body and an edge at a second end of the body, and the contoured outer surface is disposed on the precursor body.

2. The three-piece tank according to claim 1, characterized in that The first portion and the second portion are located at the same longitudinal position of the outer surface.

3. The three-piece tank according to claim 1, characterized in that The first portion of the outer surface is concave by at least 20% relative to a second portion of the outer surface having the outer diameter.

4. A forming mandrel for expanding a metal precursor in the manufacture of a three-piece can, characterized in that The forming mandrel comprises: an actuator arm; and a plurality of longitudinally extending segments arranged about the actuator arm, each segment having an inner cam surface and an arcuate outer surface for engaging an inner surface of a precursor positioned over a forming mandrel, the segments comprising a first subset of segments and a second subset of segments, The actuator arm is capable of moving longitudinally relative to the segments and has a plurality of wedge surfaces, which are arranged to contact the cam surfaces of the corresponding segments and cause the first subgroup and the second subgroup to move radially outward at corresponding different speeds to expand the forming mandrel from a first state to a final state.

5. The forming mandrel according to claim 4, characterized in that The first subset consists of an even number of segments equal to or greater than 6, and the second subset consists of the same number of segments.

6. The forming mandrel according to claim 4 or 5, characterized in that The plurality of wedge surfaces include a first set of wedge surfaces radially aligned with the first subset of segments and a second set of wedge surfaces radially aligned with the second subset of segments.

7. The forming mandrel according to claim 6, characterized in that The wedge angle of the first set of wedge surfaces is constant over the longitudinal movement of the actuator arm, and the wedge angle of the second set of wedge surfaces is initially higher than the wedge angle of the first set of wedge surfaces and subsequently equal to the wedge angle of the first set of wedge surfaces.

8. The forming mandrel according to claim 4 or 5, characterized in that A first subset of segments is undercut, whereby a second subset of segments can be recessed behind the arcuate outer surface of the first subset in the first state of the forming mandrel.

9. The forming mandrel according to claim 4 or 5, characterized in that The arcuate surfaces of the first and second subsets are of equal size.

10. The forming mandrel according to claim 4 or 5, characterized in that In the final state, the major portion of the arcuate surface of all segments has a diameter corresponding to the maximum outer diameter of the three-piece tank, and the minor portion is concave at least 10% relative to the outer diameter.

11. The forming mandrel according to claim 4, characterized in that The first subset consists of an even number of segments equal to or greater than 12, and the second subset consists of the same number of segments.

12. The forming mandrel according to claim 4 or 5, characterized in that In the final state, the major portion of the arcuate surface of all segments has a diameter corresponding to the maximum outer diameter of the three-piece tank, and the minor portion is concave 15% relative to the outer diameter.

13. The forming mandrel according to claim 4 or 5, characterized in that In the final state, the major portion of the arcuate surface of all segments has a diameter corresponding to the maximum outer diameter of the three-piece tank, and the minor portion is concave by 20% relative to the outer diameter.

14. A three-piece tank having an outer diameter and a contoured outer surface, characterized in that: A first portion of the outer surface is recessed by at least 10% relative to a second portion of the outer surface having the outer diameter, and the first portion and the second portion are at the same longitudinal position of the outer surface but at different circumferential positions, and the longitudinal configuration length at all circumferential positions around the three-piece tank is equal.

15. The three-piece tank according to claim 14, characterized in that The contoured outer surface includes a concave groove surrounding the three-piece can.

16. The three-piece tank according to claim 15, characterized in that The longitudinal position, shape and / or orientation of the grooves vary around the circumference.

17. A three-piece tank according to any one of claims 14 to 16, characterised in that The outer surface has a configuration that is not rotationally symmetric about a circumference but has reflectional symmetry about a plane passing through the longitudinal axis of the three-piece can.

18. A three-piece tank, characterized in that: It has a tank body with a configured outer surface, the tank body including a groove extending around the circumference of the body, and wherein the longitudinal position, cross-sectional shape and / or orientation of the groove varies around the circumference so that each longitudinal section around the circumference of the tank body has the same configured length.

19. The three-piece tank according to claim 18, characterized in that Consists of a single continuous groove.

20. A forming mandrel for expanding a metal precursor in three-piece can manufacturing, characterized in that The forming mandrel comprises: an actuator arm; and A plurality of longitudinally extending segments are arranged around the actuator arm, each segment having an inner cam surface and an arcuate outer surface for engaging an inner surface of a precursor positioned above a forming spindle, the outer surfaces each having a longitudinal configuration, wherein at least a first segment has a longitudinal configuration different from a second segment, and all segments have the same longitudinal configuration length.

21. The forming mandrel according to claim 20, characterized in that All segments have different longitudinal configurations, but have the same overall longitudinal configuration length.

22. A forming mandrel according to claim 20 or 21, characterised in that Each segment has a generally flat configuration with a recessed channel, and the longitudinal position, cross-sectional shape, and / or orientation of the recessed channel varies between segments around the circumference.

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