CONTAINERS

Abstract: In a process for forming a double seam between the flange (2) of a can body (3) and a peripheral curl (5) of a can end, the assembly of can body and end are supported between a chuck (6) and a lifter (7). Relative rolling motion between the can end and first and second rolls (12, 15) progressively forms first and second operation seams. During first and second operations the lifter is raised to encourage engagement of the flange and curl. A preferred form of first operation seaming profile permits formation of small seams made of thin starting materials e.g. 0.14 mm.

Description: "CONTAINERS" This invention relates to a method and apparatus for making a double seam between an end wall and the body of a container, and more particularly but not exclusively to a double seam joining thin body and end wall materials. GB 2047144 describes the problem of wrinkling which arises as the periphery of a can end is reduced as it is turned under the flange of a can body. It is claimed that wrinkling may be minimised by limiting the quotient of diameter of the can end and lid hook length, and also controlling the overlap quotient in the double seam so that a lesser diameter of thinner, stiffer metals is folded into the double seam without wrinkling which could spoil the hermetic seal provided by the double seam. US 5320 458 describes a process for producing a double seam between stiff materials, such as DR8 or DR9 tinplate as thin as 0.16mm. The success of these small seams, called microseams is attributed to use of smaller can end blanks and redesigned tooling for first and second operation rolls used to form the double seam against a supporting chuck without changing the volumetric capacity of the can. Our study of seams, made by this prior art method, have shown examples of inward deformation of the top of the seam, a lack of seam tightness arising from a generally rounded shape which gives rise to a risk of leakage, and some deformation of the sidewall of the can body adjacent the double seam. Voids in these double seams indicate a risk of wrinkles in the cover hooks. In order to overcome these problems this invention provides improved control of a first seaming operation to correctly position the can body flange to a lining compound on the can end. In a first aspect this invention provides a method of forming a double seam between a flange of a container body and an end wall having a peripheral curl, said method comprising the steps of:- supporting the end wall on a chuck, moving a lifter to lift the flange of the body into the peripheral curl of the end wall, applying a first operation tool to the periphery of the end wall to progressively make a first operation seam, and then applying a second operation tool to flatten the first operation seam to form the complete double seam, wherein pressure is applied to the body throughout at least the first operation to encourage the body flange to become a body hook in the double seam, characterised in that, the first operation is carried out by a tool having a concave seaming profile including an arcuate entry surface of radius R ]( an intermediate arcuate surface of radius R : ,, and a further arcuate surface of radius R-., wherein the centre of at least radii Rj and Ri are within the seaming profile so that in the first operation seam the free edge of the cover hook is not in contact with the sidewall of the container body and outboard of an arcuate surface of the cover hook. In one embodiment of the method the first operation tool is a roll having an externally concave profile. However the profile may be formed in the interior surface of an anular tool or rail. Typically the profile will comprise radius R 3 at about 1.09mm, radius R at about 1.21mιτι, radius Ri at about 0.3mm, an axial height of 1mm and a depth of 1.16mm. The second operation roll may have a seam forming profile of axial extent between 1.70mm and 1.95mm to be suitable for completing small seams. Typically the lifter is moved a distance between 0.1mm and 0.8mm during the first operation and between 0.1mm and 0. βrtvrn during the second operation. The pressure may be applied to the can body by moving on a lifter along to rising cam surface or use of fluid pressure on the underside of a lifter. In a second aspect this invention provides apparatus for forming a double seam between a flange of a container body and an end wall having a peripheral curl, said apparatus comprising:- a chuck to support the end wall; a lifter to lift the flange of the body into the peripheral curl; a first operation tool movable towards and away from the periphery of the end wall to form a first operation seam; a second operation tool movable towards and away from the periphery of the end wall to complete the double seam, and lifting means to apply a compressive pressure in an axial direction to the body during at least the first operation of seaming, characterised in that the first operation tool has a concave seam-forming profile which includes an arcuate entry surface of radius R), an intermediate surface radius R and a further arcuate surface of radius R 3 , the centre of each radius Ri and R 3 being within the concave seam forming profile. The first operation tool may be a roll having an externally concave groove, or a ring having a groove in its interior surface or a curved rail. Typical values for the radii of curvature of the first operation profile are R, = 1.09mm, R 2 = 1.21; R- = 0.3mm, an axial length of 1.0mm and a depth of 1.16mm. The height of the profile in the second operation tool is preferably between 1.70mm and 1.95mm to permit completion of small seams. Preferably the lifting means is capable of moving the lifter a distance of 0.1mm to 0.8mm during the first operation and an additional distance between 0.1 to 0.8mm in the second operation. In one embodiment the lifting means is a cam. In a further aspect of this invention provides an end wall for a container, said end wall comprising a peripheral curl, a chuck wall dependent from the interior of the curl and a centre panel spanning the chuck wall wherein the peripheral curl includes a peripheral cover hook, a radial panel portion extending inwards from the cover hook, and a panel radius supporting the dependent chuck wall characterised in that the cover hook has a curl length measured after straightening at between 3/7mm and 4.lmm and has between 20 and 30mg of lining compound located in the cover hook. Various embodiments will now be described by way of example and with reference to the accompanying embodiments in which:- Figs la to Id are diagrammatic side views seam forming apparatus at various stages in the formation of a double seam. Figs 2a to 2d are fragmentary sections through a can end and can body at stages corresponding to Figs la to Id; Fig 3a is a plan view of a can end according to this invention; Fig 3b is a sectioned side view on a diameter of the can end shown in Fig 3a; Fig 4 is a detailed cross-section of a first operation seaming profile, to permit comparisons of old and new profiles; and Fig 5 is a detailed cross-section of second operation seaming profiles, to permit comparison of old and new profiles. Fig 1 shows apparatus for forming a double seam 1 between a flange 2 of a container body 3 and an end wall 4 having a peripheral curl 5. This apparatus has a chuck to support the end wall 4, a movable lifter 7 axially aligned with the chuck to lift the flange 2 of the can body into the peripheral curl 5 of the end wall 4. Although seaming apparatus is known on which the can does not rotate, in this particular example the chuck is driven to rotate in a turret 10 and the lifter 7 is freely mounted for rotation on a spring 8 in a follower 9 mounted in the turret 10. If desired, the lifter may be driven to rotate at the same speed as the chuck. The follower 9 is urged to rise and fall by a cam 11 as the turret rotates from positions (a) to (d) in Fig 1. A first operation seaming roll 12 is supported for free rotation on a pivotable arm 13 which holds a first operation seaming profile 14 of the roll at a level to receive the peripheral curl 5 of the can end as the first operation roll is swung in to progressively generate the first operation seam of Figs lb and Fig 2b from the assembled body and can end as shown in Fig 2a. As shown in Fig la the follower has moved from a low portion of the cam 11 at which the can end and body are assembled between the chuck and lifter, to a higher position at which the can end is firmly clamped onto the body flange 2. The lifting force on the follower 9 is delivered through spring 8 to the lifter 7 so that the can and end assembly is resiliently clamped under a known pressure imposed by the cam in the axial direction. As the turret moves from the position shown in Fig lb the cam 11 causes the follower 9 to rise further so increasing pressure on the spring 8 which causes the lifter to rise to lift the can body so feeding flange material into the curl to generate the first operation seam shown in Fig 2b. Comparing Fig 2a with Fig 2b it will be seen that the profile of the first operation roll has progressively turned in the end curl 5 to turn in between the turned down body flange and the body wall. The free edge of the flange is bedded in a lining compound without scraping it off the can end curl. This ideal configuration is achieved by controlled placement of the lining compound in curl of the can end, controlled lifter pressure, and in the case of so called "small seams" a modified first operation profile. Fig lc shows the apparatus at commencement of a second operation to complete a double seam. The cam 11 has raised the follower 11 from the position shown in Fig lb to continue to apply a compressive pressure on the body and end. A second operation seaming roll 15 is supported for free rotation on a pivotable arm 16 which holds a second operation seam forming profile at a level to receive the first operation seam as the arm is swung-in to progressively flatten the first operation seam to complete a double as shown in Figs 2(d) and 1(d) . After completion of the double seam the cam 11 lowers the lifter to release the seamed can for removal. Fig 2a shows a peripheral portion of a can end 4 resting on the flange 2 of a can body 3 at commencement of a first operation of double seaming. The can end 4 comprises a centre panel 20, a chuck wall 22 joined to the centre panel by a chuck wall radius 2, a seaming panel 24 joined to the chuck wall by a seaming panel radius 23, and a peripheral curl 5. An annulus 25 of lining compound extends around the inside of the curl 5. The can body 3 comprises a side wall portion 28, and the flange 2 joined to the side wall by a flange radius 26. In Fig 2a a chuck 6 supports the chuck wall 22 while the first operation seaming roll 12 is moved laterally towards the chuck 6 so that the profile 14 of the first operation roll turns the seaming panel downwards and the curl 5 inwards and upwards to extend between the sidewall portion 25 and the turned down flange or body hook 2A as shown in Fig 2b. Fig 2b shows a preferred form of first operation seam in which the turned down flange or body hook 2A is bedded in the annulus of lining compound 25 and the free edge of the end curl or cover hook 5 reaches well up into the gap between the sidewall portion 26. This configuration of first operation seam reforms well in the second operation of seaming to achieve adequate overlaps of body flange and cover hook, and seam tightness in the finished seam. However Fig 2b illustrates a problem of excess metal on the first operation seam. In Fig 2b the seaming panel radius 23 has been bent to a tighter radius 23A standing proud of the bent down flange radius 27A. Excess metal in the first operation seam may give rise to a short end hook, excessive seam length or pleating (corrugation) during the second operation. The "slack" metal of panel radius may even be pushed inwards and disturbs the chuckwall fit in the side wall. Fig 2c shows a first operation seam made according to this invention. The pressure applied by cam 11 has been passed through the side wall portion 26 to feed side wall metal into the first operation seams so tightening the body flange radius 27A to fit the seaming panel radius 23A. Also the radii of curvature of the can end seaming panel and curl have been tightened using a modified first operation roll to be described later. Using lifter pressure in conjunction with this modified first operation profile has enabled us to make small seams from components made of sheet metals less than 0.25mm (about 0.010 inches) thick for aluminium or its alloys and 0.19mm (0.008") for steel base sheet because the curl 5 has been turned up and in towards the down- turned body flange leaving a clearance between the curl material and sidewall. It will be noticed that the curl presents an arcuate surface 28 to the side wall 26. It is essential that the free edge 29 of the cover hook in the first operation seam is not in contact with the side wall 26 and must be outboard of the arcuate surface 28. Fig 2d shows the completed double seam 1 after the second operation roll 17 has cooperated with the chuck 6 so progressively to flatten the arcuate surface so reducing any wrinkles and generate the double seam by crushing the first operation seam of Fig 2c. Double seams are usually assessed by reference to the dimensions as indicated in Fig 2d and tabulated on table 1. TABLE 1 MICRO SEAMS: MAKERS END: DOUBLE SEAM DIMENSIONS PARAMETERS MEAN FOR 6 CANS CONVENTIONAL TESTED (nan/Inches) mm/ Inches Countersink Depth (D) 2.69mm (0.1058") 3.35mm (0.132") Seam Length (L) 1.8mm (0.0707") 2.68mm (0.094") Seam Thickness t, 0.86mm (0.0343") 0.86mm (0.035") Bodyhook Length (H) 1.35mm (0.0532") 1.83mm (0.072") Endhook Length (E) 1.36mrn (0.0538") 1.65mm (0.065) Actual Overlap (0) 1.09mm (0.0428") 1.27mm min 1.0mm Percentage Bodyhook 91.3*. 90* Butting 70 a to 95* 70* to 95* Percentage Tightness 5 @ 100* 100* Rating 1(. 90* 75* to 100- Freespace 0.13mm (0.0051") 0.13mm (0.005) Bodyplate t ! 0.14mm (0.0055") 0.14mm (0.0055) Endplate t 2 0.14mm (0.0055") 0.16mm (0.0063) We have observed that during the seaming process described with reference to Figs 1 and 2 the countersink depth of a can end increases indicating a decrease in can volume related to the distance the lifter is raised. Figs 3a and 3b show a can end particularly adapted for formation of small seams from thin metal such as tinplate, electrochrome coated steels or aluminium or aluminium alloy. The can end comprises a centre panel 20 surrounded by an expansion bead 31 which is surrounded by a stiffening bead 32. A chuck wall 12 rises from the periphery of the stiffening bead 32 to a lateral seaming panel 34 terminating in a peripheral curl 35. Typical dimensions for this can end are tabulated in Table 2:- TABLE 2 Dimension as shown on Fig 3b Conven t onal Modified End End Overall height of can end (1) 2.88mm 2.71mm Stiffening bead radius (2) 0.95mm 0.99mm Chuck wall height (3) 0.67mm 0.75mm Seaming panel width (4) 1.15 mm Curl edge to chuckwall 3.26mm 2.07mm distance (5) Overall curl to chuck wall 4.20mm 2.82mm (6) Curl height (7) 1.96mm 1.41 mm Curl + panel lengths * (8) 5. 1mm 3.96mm * measured when straightened; chuckwall height subtracted. Table 2 shows that the amount of metal in the curled flange of this preferred can end is smaller than was used previously. When this can end is used in conjunction with a small flange to make a small seam the dimensions of the first operation seam must be carefully controlled. According to this invention this control is achieved by means of controlled lifter pressure in combination with lateral pressure provided by the modified first operation profile. Fig 4 shows a conventional first operation profile 40 drawn on the same scale as a profile 41 modified according to the invention. Both old and new concave seam forming profiles comprise an entry slope 42, a first arcuate surface 43 of radius Ri, an intermediate arcuate surface 44 of radius R 2 and a further arcuate surface 45 of radius R 3 . In contrast to the conventional profile, the Radii R], and R 3 are centred within the concavity of the profile. R } is smaller than R. ? which is greater than R.i so that as the can end curl enters the profile it is directed downwardly against the arcuate surfaces until it abuts a lower annular surface 46 of the profile as the curl is tightened in curvature to extend under the body flange. This modified tool makes a tighter and smaller first operation seam with the free edge 29 of the can end curl clear of the sidewall and the leading edge progressed to be of greater diameter than the arcuate surface 28, as shown in 2c. Typical dimensions for each profile shown in Fig. are in Table 3: TABLE 3 A result of the tighter curvature of the modified profile is that not only the can end curl but also the body flange are turned into the seam to ensure required overlap in the final seam as the arcuate portion is straightened. Lifter pressure also assists the body flange to conform to the end curl shape. Fig 5 shows a conventional second operational profile 50 and a modified second operation profile drawn on the same scale. The purpose of both profiles is to flatten a first operation seam into the form of a tight double seam. The modified profile 51 is for practical purposes a scaled down version of the conventional profile 50 to cope with smaller seams. Typical dimensions for the second operation profiles shown in Fig.5 are tabulated in Table 4. Using the method and apparatus described we have found it possible to make seams from components made from common sheet metals as thin as 0.14mm. A small reduction in contained volume arises as the chuck wall lengthens and body sideward to feed into the double seam but this is acceptable as a reduction in ullage. TABLE 4 CONVENTIONAL NEW 2ND OP ROLL 2nd OP. ROLL ENTRY SLOPE (52) 2.5° 2.5° FIRST RADIUS (53) (0.013") (0.013") SECOND RADIUS (54) (0.328") (0.328") THIRD RADIUS (55) (0.1665") (0.100") FOURTH RADIUS (56) -0.030" -0.005" PROFILE HEIGHT H 2.75mm 1.95mm (0.108") (0.077") PROFILE DEPTH D 0.508mm 0.431mm (0.020") (0.016")

Claims: CLAIMS : 1. A method of forming a double seam between a flange of a container body and an end wall having a peripheral curl, said method comprising the steps of:- supporting the end wall on a chuck, moving a lifter to lift the flange of the body into the peripheral curl of the end wall, applying a first operation tool to the periphery of the end wall progressively to make a first operation seam, and then applying a second operation tool to flatten the first operation seam to form the complete double seam, wherein pressure is applied to the body throughout at least the first operation to encourage the body flange to become a body hook in the double seam, characterised in that, the first operation is carried out by a tool having a concave seaming profile including an arcuate entry surface of radius R|, an intermediate arcuate surface of radius R , and a further arcuate surface of radius R 3 , wherein the centre of at least radii R] and R 3 are within the seaming profile so that in the first operation seam the free edge 29 of the cover hook in the first operation seam is not in contact with the side wall 26 and outboard of the arcuate surface 28. 2. A method according to claim 1 wherein the first operation tool is a roll having an externally concave profile in which Ri is 1.09mm, R- is 1.21mm, R 3 is 0.3mm, the axial length is 1.00mm and the depth is 1.16mm. 3. A method according to claim 1 and claim 2 wherein the second operation roll has seaming profile axial extent between 1.70mm and 1.95mm. 4. A method according to claim 1 characterised in that the lifter is moved a distance between 0.1mm and 0.8mm during the first operation. 5. A method according to claim 4 characterised in that the lifter is moved an additional distance between 0.1mm and O.Bmm in the second operation. 6. A method according to any preceding claim characterised in that the lifter is moved by engagement of a follower with a rising cam surface. 7 Apparatus for forming a double seam between a flange of a container body and an end wall having a peripheral curl, said apparatus comprising:- a chuck to support the end wall; a lifter to lift the flange of the body into the peripheral curl; a first operation tool movable towards and away from the periphery of the end wall to form a first operation seam; a second operation tool movable towards and away from the periphery of the end wall to complete the double seam, and lifting means to apply a compressive pressure in an axial direction to the body during at least the first operation of seaming, characterised in that the first operation tool has a concave seam-forming profile which includes an arcuate entry surface of radius Ri, an intermediate surface radius R : and a further arcuate surface of radius R 3 , the centre of at least radius R,and Ri being within the concave seaming profile. 8. Apparatus according to claim 7 wherein the first operation tool is a roll having an externally concave profile. 9. Apparatus according to claim 8 or claim 7 in which the seaming profile has Ri = 1.09mm, R 2 = 1.21mm R 3 = 0.3mm, an axial length of 1.0mm and a depth of 1.16m . 10. Apparatus according to any one of claims 7 to claim 9 wherein a profile of the second operation tool has an axial extent between 1.70 and 1.95mm. 11. Apparatus according to claim 9 wherein the means to apply a lifting pressure moves the lifter a distance between 0.1mm and 0.8mm during at least the first operation. 12. Apparatus according to any preceding claim wherein the means to apply a lifting pressure is the rising surface of a cam. 13. An end wall for a container, said end wall comprising a peripheral curl, a chuck wall dependent from the interior of the curl and a centre panel spanning the chuck wall wherein the peripheral curl includes a peripheral cover hook, a radial panel portion extending inward from the cover hook, and a panel radius supporting the dependent chuck wall characterised in that the cover hook has an curl length, measured after straightening to be between 3.7mm and 4.1mm and between 20 and 30mg of lining compound as located in the cover hook. 14. A method substantially as herein before described with reference to Figs.lb and lc; Figs. 2c and 2d and Figs. 4 of the accompanying drawings. 15. Apparatus substantially as herein before described with reference the accompanying drawings. 16. A can end substantially as herein before described with reference to 3a and 3b of the accompanying drawings .

Inventors: AHERNE PATRICK THOMAS, CULVERWELL JOHN WILLIAM, WOODFORD ROY CHARLES, AHERNE, PATRICK, THOMAS, CULVERWELL, JOHN, WILLIAM, WOODFORD, ROY, CHARLES
Applicants: AHERNE PATRICK THOMAS, CARNAUDMETALBOX HOLDINGS USA, CARNAUDMETALBOX NV, CARNAUDMETALBOX SA, CULVERWELL JOHN WILLIAM, METAL BOX PLC, WOODFORD ROY CHARLES, AHERNE, PATRICK, THOMAS, CARNAUDMETALBOX (HOLDINGS) USA INC., CARNAUDMETALBOX N.V., CARNAUDMETALBOX PLC, CARNAUDMETALBOX S.A., CULVERWELL, JOHN, WILLIAM, WOODFORD, ROY, CHARLES
Application year: 1996
Main classification: B21D51
IPC codes: B21D51