METHOD FOR EXPANDING A CYLINDRICAL METALLIC PRECURSOR IN THE MANUFACTURE OF A THREE-PIECE CAN AND SHAPING MANDREL FOR EXPANDING A CYLINDRICAL METALLIC PRECURSOR

Abstract

A method is described for expanding a cylindrical metallic precursor in the manufacture of a three-piece can. The method comprises the steps of: arranging the precursor, having an initial diameter, around a shaping mandrel, the shaping mandrel having a plurality of longitudinally extending segments disposed radially about a longitudinal axis of the shaping mandrel, the segments having arcuate surfaces for engaging an inner surface of the precursor wall; actuating, in a first step, a first subgroup of the plurality of segments to expand outwards to engage with the inner surface of the precursor wall and expand at least a portion of it to a first diameter that is larger than the initial diameter of the precursor; and actuating, in a second step, a second subgroup of the plurality of segments to expand outwards and also engage with the inner surface of the precursor wall whereby the second subgroup expands at least a portion of the precursor to a second diameter that is larger than the first diameter. The method allows a greater degree of expansion of the wall of a cylindrical metallic container, whereby greater variations in diameter can be achieved between recessed portions and the remainder of the wall.

Claims

1. Method for expanding a cylindrical metallic precursor in the manufacture of a three-piece can, the method comprising the steps of: arranging the precursor having an initial diameter, around a shaping mandrel, the shaping mandrel having a plurality of longitudinally extending segments disposed radially about a longitudinal axis of the shaping mandrel, the segments having arcuate surfaces for engaging an inner surface of the precursor, actuating, in a first step, a first subgroup of the plurality of segments to expand outwards to engage with the inner surface of the precursor and expand at least a portion of it to a first diameter that is larger than the initial diameter of the precursor, actuating, in a second step, a second subgroup of the plurality of segments to expand outwards and also engage with the inner surface of the precursor whereby the second subgroup expands at least a portion of the precursor to a second diameter that is larger than the first diameter.

2. Method according to claim 1, wherein the first subgroup consists of alternate segments about the longitudinal axis of the shaping mandrel and the second subgroup consists of all remaining segments.

3. Method according to claim 1 or claim 2, wherein during the first step, the segments of the second subgroup are actuated to expand outwards at a velocity that is greater than a velocity at which the segments of the first subgroup expand outwards.

4. Method according to any one of the preceding claims, wherein during the second step, the first subgroup expands from the first diameter to the second diameter.

5. Method according to any one of the preceding claims, wherein during the second step, all the segments are actuated to expand outwards at the same velocity.

6. Method according to any one of the preceding claims, wherein the second step comprises an initial stage where the arcuate surfaces of the second subgroup are engaged with the inner surface of the precursor and radially inwards of the arcuate surfaces of the first subgroup.

7. Method according to any one of the preceding claims, wherein the second step comprises an intermediate stage where the arcuate surfaces of the second subgroup are radially aligned with the arcuate surfaces of the first subgroup and edges of the arcuate surfaces of adjacent segments are initially engaging.

8. Method according to any one of the preceding claims, wherein the second step comprises a final stage where the arcuate surfaces of the second subgroup are radially outwards of the arcuate surfaces of the first subgroup.

9. Method according to any one of the preceding claims, wherein the first diameter is between 10% and 20% greater than the initial diameter of the precursor.

10. Method according to any one of the preceding claims, wherein, after the second step, a circumferential gap is formed between edges of the arcuate surfaces of adjacent segments and a width of the gap does not exceed 5 mm, preferably does not exceed 2 mm, more preferably does not exceed 1.5 mm.

11. Method according to any one of the preceding claims, wherein the second diameter is between 20% and 30% greater than the initial diameter of the precursor.

12. Method according to any one of the preceding claims, wherein the first and second steps are performed without rotation of the precursor with respect to the mandrel.

13. Method according to any one of the preceding claims, wherein the arcuate surface of one or more of the plurality of segments is profiled in the longitudinal direction such that after the second step, the expanded precursor body has a profiled outer surface.

14. Method according to claim 13, wherein the profile comprises, at an end portion of all of the segments, a curve towards the longitudinal axis of the shaping mandrel.

15. Method according to any one of the preceding claims wherein, after the second step, the expanded precursor body has a profiled outer surface with portions of the outer surface having the second diameter and other portions of the outer surface being recessed with respect to the second diameter by at least 10%, 12% or 15% and preferably at least 20%.

16. Method for manufacturing a three-piece can comprising the steps of: expanding a metallic cylindrical precursor by a method according to any of claims 1-15; attaching a base to one of two open end portions of the expanded precursor body; attaching a rim to the other of the two open end portions, preferably without trimming the open end portions.

17. A three-piece can manufactured according to the method of any one of claims 1-16.

18. A three-piece can having 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% and preferably by at least 20% with respect to a second portion of the outer surface having the outer diameter.

19. The three-piece can of claim 18, wherein the first portion and the second portion are at a same longitudinal position of the outer surface.

20. A shaping mandrel for expanding a cylindrical metallic precursor in the manufacture of a three-piece can, the mandrel comprising: an actuator arm; and a plurality of longitudinally extending segments, arranged about the actuator arm, each of the segments having an inner cam surface and an arcuate outer surface for engaging an inner surface of a precursor positioned over the mandrel, the segments comprising a first subgroup of segments and a second subgroup of segments, wherein the actuator arm is longitudinally movable relative to the segments and has a plurality of wedge surfaces, arranged to contact the cam surfaces of the respective segments and move the first subgroup and the second subgroup radially outwards at respective different speeds in a series of steps to expand the mandrel from a first state to a final state.

21. The shaping mandrel according to claim 20, wherein the first subgroup consists of an even number of segments equal to or greater than 6, preferably equal to or greater than 12, and the second subgroup consists of an identical number of segments.

22. The shaping mandrel according to any one of claim 20 or 21, wherein the plurality of wedge surfaces comprises a first set of wedge surfaces radially aligned with segments of the first subgroup and a second set of wedge surfaces radially aligned with segments of the second subgroup.

23. The shaping mandrel according to claim 22, wherein a 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 and subsequently equal to the wedge angle of the first set of wedge surfaces.

24. The shaping mandrel according to any one of claims 20 to 23, wherein the first subgroup of segments are undercut, whereby the second subgroup of segments can be recessed behind the arcuate outer surfaces of the first subgroup in the first state of the mandrel.

25. The mandrel according to any one of claims 20 to 24, wherein the arcuate surfaces of the first subgroup and the second subgroup are equal in size.

26. The mandrel according to any one of claims 20 to 25, wherein, in the final state, a major part of the arcuate surfaces of all the segments has a diameter corresponding to a maximum outer diameter of the can and a minor part is recessed by at least 10%, preferably 15% and more preferably 20%, with respect to the outer diameter.

27. A three-piece can having an outer diameter and a profiled outer surface, wherein a first portion of the outer surface is recessed by at least 10% with respect to a second portion of the outer surface having the outer diameter and the first portion and the second portion are at a same longitudinal position of the outer surface but at different circumferential positions and a longitudinal profile length at all circumferential positions around the can is equal.

28. The can of claim 27, wherein the profiled outer surface comprises a recessed groove that surrounds the can.

29. The can of claim 28, wherein a longitudinal position, shape and/or orientation of the groove varies around the circumference.

30. The can of any one of claims 27 to 29, wherein the outer surface has a profile that is rotationally asymmetric around the circumference but has reflectional symmetry about a plane through a longitudinal axis of the can.

31. A three-piece can having a can body with a profiled outer surface comprising a groove extending around a circumference of the body and wherein a longitudinal position, cross-sectional shape and/or orientation of the groove varies around the circumference, subject to each longitudinal section around the circumference of the can body having an identical profile length.

32. The can of claim 31, comprising a single continuous groove.

33. A shaping mandrel for expanding a cylindrical metallic precursor in the manufacture of a three-piece can, the mandrel comprising: an actuator arm; and a plurality of longitudinally extending segments, arranged about the actuator arm, each of the segments having an inner cam surface and an arcuate outer surface for engaging an inner surface of a precursor positioned over the mandrel, the outer surfaces each having a longitudinal profile wherein, at least a first segment has a different longitudinal profile from a second segment, while all segments have the same longitudinal profile length.

34. The mandrel of claim 33, wherein all segments have different longitudinal profiles but the same overall longitudinal profile length.

35. The mandrel of claim 33 or claim 34, wherein each segment has a generally flat profile with a recessed channel and the longitudinal position, cross-sectional shape and/or orientation of the recessed channel varies from segment to segment around the circumference.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Embodiments of the present invention will be described by way of example, with reference to the attached drawings, in which:

[0043] FIG. 1A shows a flowchart representing a sequence of steps for manufacture of a three-piece can from a metallic blank and comprising an expansion step,

[0044] FIG. 1B shows an illustration of a top and a side wall of a cylindrical metallic precursor expanded according to methods known in the art,

[0045] FIG. 2A shows a cross-sectional view of an expansion apparatus, for expanding a cylindrical metallic precursor, the apparatus shown in a contracted state before expansion, with the precursor positioned around the apparatus,

[0046] FIG. 2B shows a cross-sectional view of the expansion apparatus of FIG. 2A, after completion of expansion,

[0047] FIG. 3 shows a cross-section through the mandrel of FIG. 2A at position III-III,

[0048] FIGS. 4A to 4C show a longitudinal-section taken at position IV-IV in FIG. 3 taken at different stages during expansion of the mandrel;

[0049] FIG. 5A shows a cross-sectional view of two adjacent segments in the mandrel of FIG. 3 prior to a first expansion step,

[0050] FIG. 5B shows a cross-sectional view of two adjacent segments in the mandrel of FIG. 3 at the start of a second expansion step,

[0051] FIG. 5C shows a cross-sectional view of two adjacent segments in the mandrel of FIG. 3 at a further stage of expansion,

[0052] FIG. 5D shows a cross-sectional view of two adjacent segments in the mandrel of FIG. 3 at a final stage of expansion,

[0053] FIG. 5E shows a cross-sectional view of two adjacent segments in the mandrel of FIG. 3 at an alternative final stage of expansion, and

[0054] FIG. 6-8 show three exemplary container bodies expanded according to the method of the invention.

DESCRIPTION OF EMBODIMENTS

[0055] FIG. 1A shows a sequence 100 of steps 110-160 for manufacture of a three-piece can from a metallic blank 1. This sequence comprises in particular an expansion step 140. Other steps will be known to the person skilled in the art and only briefly described. In step 110, a metallic sheet is cut into a flat blank 1. In step 120, the blank may be coated and cured. After this optional step, the flat blank 1 is welded into a generally cylindrical precursor 2 in step 130. The precursor 2 has a metallic body with two open ends and a vertical seam (not shown) present where the sidewall has been joined to itself to form a cylinder. The metallic body of the cylindrical precursor 2 is generally a steel body, prepared from a steel blank. In step 140 a portion of the wall of the cylindrical metallic precursor 2 is expanded outward. The resulting expanded container 3 has a shape that is contoured and deviates from the original cylindrical shape. This step may be performed according to the method of the invention, described later. In step 150 the expanded container 3 may be subject to any of flanging (F, as shown) and/or other processes known in the art comprising for instance any of printing or beading (not shown). In step 160 the expanded container 3 may be provided with closures 4, 5 attached at each of the two open ends with or without sealing and/or pre-filling. This terminates the manufacturing cycle of the three-piece can. It is noted that this sequence is serving merely as an example and the expansion step of the invention may also be part of other sequences known in the art for manufacturing a three-piece can. It will however be noted that in the illustrated embodiment, there is no requirement for trimming of the container ends prior to closure step 160.

[0056] FIG. 1B shows an illustration of a top and a side view of a cylindrical precursor 2 of diameter d before and after expansion into an expanded body 3 according to expansion methods known in the art. The illustration of the expanded body exaggerates the shape of the precursor in order to illustrate the problem of expansion methods known in the art. Instead of a round body of diameter D the surface of the resulting body 3 has a number of vertical split lines(S). These correspond with locations of high stretching of the metal wall during expansion. The vertical split lines have formed between adjacent segments of an expansion mandrel (not shown) and do not follow the curvature of the mandrel. In this illustration, it would correspond to the locally flat section between each two of six segments.

[0057] FIG. 2A shows a cross-sectional view of a conventional expansion apparatus 10, which is shown to explain the underlying principle for expanding a metallic cylindrical precursor 2. The apparatus is shown in a retracted state, i.e. before expansion. The expansion apparatus 10 comprises a housing 11 and a shaping mandrel 13 extending from the housing 11. The shaping mandrel 13 comprises a plurality of similar segments 14 spaced about an expander arm 12. Each segment 14 has an arcuate contacting surface A for contacting or engaging an inner surface I of a cylindrical precursor 2 placed around the segments 14. Each segment 14 further has a cam surface 18 at its inner side, facing towards the expander arm 12. In the retracted state the contacting surfaces A of the segments 14 are spaced radially inward from the inner surface I of the container body 2. A proximal end 12A of the expander arm 12 and ends 20 of the segments 14 are received within the housing 11. A distal end 13B of the mandrel 13, has a reduced diameter.

[0058] The expander arm 12 is movable axially within the housing (along axis Z) to cause expansion of the segments 14. The segments 14 extend longitudinally along the expander arm 12. A pair of wedges 16 are positioned about the expander arm 12 in tandem. The expander arm 12 and the wedges 16 form the actuator of the shaping 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 arm 12 together with the wedges 16, causes the wedge surfaces 17 to ride along the cam surfaces 18 to expand the segments 14 outwards to contact the precursor 2 inner surface I.

[0059] FIG. 2B shows a cross-sectional view of the same expansion apparatus 10 of FIG. 2A, shown in a finally expanded state. This view shows how the expander arm 12 has been moved proximally in the direction of the housing 11 (Z-direction). This axial movement has caused the wedge surfaces 17 to cooperate with corresponding cam surfaces 18 of the segments 14 to force the segments 14 radially outwards into engagement with the inner surface I of the precursor 2. The inner surface I of the precursor 2 is deformed accordingly to adopt the shape of the expanded mandrel 13. The distal end 13B of the mandrel defines the smallest internal diameter of the expanded precursor 2.

[0060] When the expansion is completed, the expander arm 12 is moved axially away from the housing 11 and the segments 14 may be brought back into a collapsed or retracted position. The precursor 2 may then be removed from the shaping mandrel 13. It will be understood that the mandrel 13 must collapse sufficiently such that the largest outer diameter can pass through the smallest diameter portion of the precursor 2. In conventional expansion devices such as the apparatus 10 of FIG. 2, around 6 or 8 segments 14 may be provided, all of which are substantially identical.

[0061] FIG. 3 shows a cross-sectional view in the plane (XY), of a shaping mandrel 12 of an expansion apparatus 10 according to the invention. Like numerals will be used for like components as in the case of the conventional apparatus of FIG. 2. The mandrel 13 is shown in its initial state, prior to any expansion, with an outer diameter of d1.

[0062] The shaping mandrel 13 comprises twelve segments 14, which surround the expander arm 12. In this case the segments 14 are divided into two subgroups, namely first subgroup segments 14A and second subgroup segments 14B. The first subgroup segments 14A are spaced outwardly of the second subgroup segments 14B at the initial outer diameter d1. It will also be noted that the segments 14A have undercut flanks 19. This allows the second subgroup segments 14B to be recessed behind the arcuate contacting surfaces A of the first subgroup segments 14A in this initial state of the mandrel 13.

[0063] The first subgroup segments 14A have first cam surfaces 18A at their inner side, while the second subgroup segments have second cam surfaces 14B at their inner side. Due to the presence of the undercut flanks 19, the second cam surfaces 18B are slightly narrower than the first cam surfaces 18A even though the respective arcuate contacting surfaces A of all the segments 14 are identical in size.

[0064] The expander arm 12 carries a wedge 16, with wedge surfaces 17, which are also divided into first wedge surfaces 17A and second wedge surfaces 17B. These engage respectively with the first and second cam surfaces 18A, 18B of the segments 14.

[0065] FIG. 4A shows schematically the wedges 16 illustrating the profiles of the wedge surfaces 17 and cam surfaces 18 of the shaping mandrel 13 of FIG. 3 in a longitudinal section at position III-III. First wedge surfaces 17A, actuating the first subgroup segments 14A are shown in the top half of the figure, while second wedge surfaces 17B actuating the second subgroup segments 14B are shown in the bottom half of the figure. Also shown in this view is a channel 40 formed in the arcuate surfaces A of the mandrel 13. The channel 40 has a depth that is almost equal to the overall expansion of the mandrel 13. It also corresponds to a diameter of a distal portion 13B of the mandrel 13. The channel 40 extends around the complete circumference of the mandrel 13 but varies in its longitudinal position from segment to segment. Nevertheless, the width and depth of the channel 40 is for each segment 14 arranged such that the profile length of each segment 14 following the arcuate surface A in the longitudinal is identical.

[0066] Dealing first with the first wedge surfaces 17A and the mating first cam surfaces 18A, these have a constant angle 1 that generally corresponds to that of the conventional apparatus 10 of FIG. 2. In the case of the second wedge surfaces 17B, these have a two-step surface. A first part of the surface denoted 17Bi has an angle 2, that is greater than the angle 1 of the first wedge surfaces 17A. A second part 17Bii of the surface, has an angle 1 that again corresponds to that of the first wedge surface 17A. In the illustrated embodiment, the first and second parts 17Bi and 17Bii are of approximately equal length. Similarly, the second cam surfaces 18B are also in two parts, with a first part 18Bi having an angle 2 and a second part having an angle 1.

[0067] FIG. 4B shows the shaping mandrel 13 of FIG. 4A, with the expander arm 12 and wedges 16 partially withdrawn in the proximal direction with respect to the segments 14. The first wedge surface 17A has progressed along the respective first cam surface 18A, causing the first subgroup segments 14A to move radially outward. The second wedge surface 17B has also progressed along the respective second cam surface 18B. As depicted, during this part of the movement, the first part 17Bi of the second wedge surface and the first part 18Bi of the second cam surface are in sliding engagement and dictate the expansion of the segment 14B at the angle 2. Since the angle 2 is greater than the angle 1, the second subgroup segment 14B has moved radially outward by a distance that is greater than that of the first subgroup segment 14A.

[0068] FIG. 4C shows the shaping mandrel 13 of FIG. 4A, with the expander arm 12 and wedges 16 almost fully withdrawn in the proximal direction with respect to the segments 14. The first wedge surface 17A has continued along the respective first cam surface 18A, causing the first subgroup segments 14A to continue to move radially outward at the same rate, as dictated by the angle 1. The second wedge surface 17B has progressed further along the respective second cam surface 18B such that now, the second first part 17Bii of the second wedge surface 17B and the second part 18Bii of the second cam surface 18B first enter into sliding engagement. From this point of the trajectory, further proximal movement of the expander arm 12 causes expansion of the second subgroup segment 14B to be dictated by the slope of these parts. This will occur at the angle 1 at the same speed as that of the first subgroup segment 14A.

[0069] FIG. 5A shows an enlarged view of two adjacent segments 14A, 14B of FIG. 3 at the beginning of a first step of expansion. The arcuate surface A of the first subgroup segment 14A contacts the inner surface I of the precursor 2 and causes the curvature of the inner surface I to conform to its curvature. The arcuate surface A of the second subgroup segment 14B is spaced radially inwards from the inner surface I by a distance Rx. Also visible are the undercut flanks 19 of the first subgroup segment 14A and a pair of transition ears 30 behind which the second subgroup segment 14B is recessed. During this stage of expansion, all stretching of the precursor is caused by the first subgroup segments 14A, in contact with just about half of the inner surface I.

[0070] FIG. 5B shows an enlarged view of the segments 14A and 14B at the point at which the second subgroup segment 14B first enters into contact with the inner surface I of the precursor 2. At this point, the second subgroup segment 14B is still radially inwards of the first subgroup segment 14A. Although from this point, some of the stretching of the precursor 2 will take place by engagement of the second subgroup segment 14B, nevertheless, the lateral edges of the first subgroup segments 14A at the position of the transition ears 30 are a critical location P, where stretch marks may be created in the precursor 2. With reference to FIG. 4B, this figure still corresponds to the period of expansion depicted where the first part 17Bi of the second wedge surface and the first part 18Bi of the second cam surface are in sliding engagement and dictate the expansion of the segment 14B at the angle 2.

[0071] FIG. 5C shows an enlarged view of the segments 14A and 14B during a second stage of the expansion step at the point at which the arcuate surfaces A of all of the segments 14 first align. In the illustrated embodiment, this also corresponds to the point where the lateral edges of adjacent segments 14 just touch and there is thus no gap between adjacent segments 14. It will be understood that this is a chosen position and it is not necessary for the mandrel 13 to pass through this no-gap configuration. This corresponds to the position depicted in FIG. 4C, where first part 17Bi of the second wedge surface and the first part 18Bi of the second cam surface first enter into sliding engagement. From this point forwards, all segments will expand at the same rate and the arcuate surfaces A of all of the segments 14 will remain radially aligned.

[0072] FIG. 5D shows an enlarged view of the segments 14A and 14B during a final stage of the expansion step. The arcuate surfaces A of all of the segments 14 are still aligned but have now expanded to a second diameter d2 that is larger than the initial diameter d1. During the expansion from the position depicted in FIG. 5C, the segments 14A, 14B have moved apart, creating a circumferential gap 32 between adjacent segments 14A, 14B. It will be understood that the circumferential gap 32 also extends in a longitudinal direction of the mandrel 13.

[0073] FIG. 5E shows an enlarged view of the segments 14A and 14B at an alternative final stage of expansion. In this situation, the second subgroup segment 14B has expanded to a diameter that is slightly larger than the second diameter d2. This can be used to stretch the precursor 2, slightly away from the edges of the first subgroup segment 14A at the position of the transition ears 30. This may be used to provide a slight over-stretch at the critical location P, to remove previously created stretch marks. This alternative final stage could be achieved by a further part of the second cam surface 18B, following the second part 18Bii.

[0074] FIG. 6 shows the completed can 3 after finishing the expansion step and after providing top and bottom closures 4, 5. A profile 42 is provided around the outer surface, corresponding to the channel 40 in the mandrel 13. FIGS. 7 and 8 depict alternative cans 3, all of which have contoured outer surfaces. As a result of the improved expansion achievable with the disclosed mandrel, variations in diameter of up to 30% are achievable, while ensuring an otherwise smooth, flaw-free surface of the can 3.

[0075] The invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art. In particular, different numbers of segments and different wedge angles and profiles can be used to create cans of different designs. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention