GB2071546A

GB2071546A - Metallic containers

Info

Publication number: GB2071546A
Application number: GB8106112A
Authority: GB
Original assignee: SEXTON CAN CO Inc
Current assignee: SEXTON CAN CO Inc
Priority date: 1980-03-13
Filing date: 1981-02-26
Publication date: 1981-09-23
Also published as: IT8147885A0; BR8101390A; JPS56142146A; IT1170755B; DE3105538A1

Abstract

A flat metal blank is drawn into cup having a cylindrical side wall, with an open end surrounded by a radially extending external flange, and with an opposite end at least partially closed by an end wall. The side wall is then ironed without disturbing the as- drawn condition of the flange and the adjoining section of the side wall. A closure element is then applied to the open end of the side wall by deforming both the flange and the periphery of the closure element. <IMAGE>

Description

SPECIFICATION Metallic containers Conventionally, multiple-piece metallic containers are produced by first drawing a flat blank into a cup which is then progressively shaped to a finished size by a further series of drawing and/or ironing operations. The open end of the container is then trimmed, flanged and connected to a cover or like closure element by a double seaming operation.

Methods which include ironing operations are preferred because of the material savings which can be realized by increasing the container length through a reduction of its side wall thickness.

However, experience has indicated that ironing is accompanied by work hardening, and that this work hardening can materially decrease the ductility of the container side wall and the flange thereafter formed at its open end. During the double seaming operation subsequently employed to secure a closure element to the container's open end, this decrease in flange ductility can result in flange cracking which in turn can be the cause of leakage, particularly where the containers are destined for high pressure service.

A primary object of the present invention is the provision of a method of producing a metallic container by a combination of drawing land ironing operations, without adversely affecting the ductility of the flange or the side wall immediately adjoining the flange. By avoiding work hardening of the flange, flange cracking is either avoided or at least substantially minimized during the subsequent application of the cover or closure element, thereby reducing the percentage of finished containers rejected because of leakage.

It is another object of the present invention to provide a method which requires less material than the conventional methods of producing high pressure containers by successive drawing operations, and yet avoids undesirable work hardening of flanged areas. Still other objects and advantages of the invention will become apparent as the description proceeds in conjuction with the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side elevation of a finished high pressure container in accordance with the present invention, with top and bottom portions broken away.

Figure 2 is an enlarged sectional view of the container shown in Figure 1, illustrating details of the double seam connection between the bottom closure element and the flanged open end of the container side wall.

Figure 3A is an edge view of a circularflat blank at the beginning of the container forming operation.

Figure 3B is a sectional view of a shallow cup formed by a first drawing operation on the flat blank of Figure 3A.

Figure 3C is a sectional view of a deeper cup resulting from a second drawing operation on the cup of Figure 3B.

Figure 3D is a sectional view of a still deeper cup resulting from a third drawing operation on the cup of Figure 3C.

Figure 3E is a sectional view of the drawn cup of Figure 3D after the flange surrounding its open end has been trimmed and its closed end has undergone further shaping.

Figure 3F is a sectional view of the cup of Figure 3E after the completion of the ironing step, with the external flange and an adjoining section of the side wall delineated by an internal shoulder remaining in the "as drawn" condition.

Figure 3G is a sectional view of the ironed container wall after the closed end has been punched and rimmed, and immediately prior to the double seaming operation.

Figure 4A is a somewhat schematic horizontal sectional view of the ironing apparatus shown at the commencement of the ironing operation.

Figure 4B is a similar view of the ironing apparatus shown at the furthest extension of the ironing post.

Figure 4C is still another view of the ironing apparatus immediately after the ironed cup has been stripped from the ironing post.

Figure 5 is an enlarged sectional view showing an unironed wall section adjoining the end flange and delineated by an internal shoulder.

Figure 6 is an enlarged sectional view showing an unironed wall section adjoining the end flange and delineated by an external shoulder.

Figure 7 is a schematic drawing showing a modified ironing apparatus having components adapted to produce an external rather than internal shoulder.

As used herein, the term "drawing" refers to an operation wherein the peripheral margin of a circular flat metal blank is simultaneously turned upwardly and smoothed by means of a pressure pad, drawing punch and die to form a cup having a wrinkle free side wall whose thickness is substantially equal to the thickness of the original blank. Subsequent redrawing of the cup turns up more of the flat blank material into the cup side wall thereby elongating the side wall with an accompanying reduction in the cup diameter.

"Ironing" refers to an operation wherein the side wall of a cup is elongated by reducing its thickness with no appreciable reduction in the inside diameter of the cup. Ironing is generally accomplished by placing the cup on a closely fitting punch or post and forcing the cup and post through an ironing or reducing die whose diameter is slightly less than the outer diameter of the cup, thereby forcing excess metal back and producing a longer but thinner side wall.

Turning now to the drawings with initial reference to Figure 1, there is shown at 10 a twopiece high pressure container in accordance with the present invention. The container has a body consisting of a cylindrical side wall 12 with an integral top or end wall 14, the latter having a somewhat truncated conical shape with stepped circular ridges 16 and a central hole 18 appropriately rimmed as at 20. A bottom or closure element 22 is joined to the open end of the side wall 12 by means of a double seam connection generally indicated at 24.

The container body is formed by a drawing and ironing process, the steps of which are schematically depicted in Figures 3A-3F. The process begins with a circular flat metal blank B as shown in Figure 3A. Typically, for a container of the type destined for high pressure applications on the order of 300 p.s.i. and higher, the metal stock for the blank B will consist of electro tin plate having a thickness t of 0125 to 013 inches and a diameter of 7 to 8 inches.

The flat blank B is first subjected to a drawing operation, resulting in the production of a shallow cup C as shown in Figure 3B. This cup has a cylindrical side wall 12 open at one end as at 13 and closed at the opposite end by an integral end wall 14. At this stage, the cup C will have an internal diameter d, and the thicknesses of the side wall 12 and the end wall 14 will remain substantially equal to the thickness t of the original blank B.

The cup C of Figure 3B is then redrawn into the deeper cup C' shown in Figure 3C. Cup C' has a longer side wall 12 with an external flange 15 surrounding the open end 13. Cup C' retains the end wall 14 and has a somewhat reduced internal diameter d'.

Cup C' is then redrawn again into the still deeper cup C" shown in Figure 3D. The lengthening of the side wall 12 of Cup C" is accompanied by a further reduction in the internal diameter d' and a shaping of the end wall 14.

Flange 15 also has been enlarged.

Figure 3E shows another stage in the operation after the end wall 14 of the cup C" has undergone further shaping to produce the ridges 16, and the flange 15 surrounding the open end 13 has been trimmed. The internal cup diameter remains unchanged at d", and the thickness of the flange 15, side wall 12 and end wall 14 remains unchanged at t, which is the original thickness of the blank B.

It will be understood that the drawing, trimming and shaping operations thus far referred to are performed in a conventional manner on conventional equipment, and thus are well known to those skilled in the art. The number of these drawing operations can of course be varied to suit various production requirements.

The drawn cup C" of Figure 3E is next subjected to a special ironing operation to produce the container body shown in Figure 3F. This ironing operation is performed on an apparatus of the type generally indicated by the reference numeral 30 in Figures 4A-4C.

The ironing apparatus includes a stationary pair of opposed mutually spaced abutment walls 32, 34 interconnected by guide rods 36. A platen 38 is mounted on the guide rods 36 for reciprocal movement between the abutment walls 32, 34.

The rear side of the platen 38 is connected to the piston rod 40 of a hydraulic piston-cylinder unit 42 mounted on abutment wall 34. An ironing post 44 extends forwardly from platen 38. Ironing post 44 has a circular recess or groove 46 and a shaped nose 48.

An ironing die 50 is supported on the inner side of wall 32. A second piston-cylinder unit 52 is supported by means of legs 54 on the outer side of wall 32. Piston-cylinder unit 52 has a piston rod 56 which extends through an opening 58 in wall 32 and which carries a knock-out member 60. The knock-out member has a shaped cavity 62 facing the shaped nose 48 of ironing post 44.

An annular stripper 64 surrounds the ironing post 44. The stripper is supported on guide rods 66 which extend rearwardly through guide holes 68 in the platen 38. The rear ends of the guide rods 66 are threaded for connection by means of nuts 70 to a connecting plate 72 having a central opening 74 through which extends the piston rod 40 of piston cylinder unit 42. Coiled springs 76, 78 surround the guide rods 66 on opposite sides respectively of the platen 38.

The stripper 64 is further provided with rearwardly extending legs 80, and a sensor bar 82 axially aligned with an opening 84 in platen 38. A sensor 86 is supported by a bracket 88 attached to the rear surface of the platen 38.

During an ironing operation, the apparatus 30 performs as follows: the apparatus is shown in Figure 4A immediately prior to commencement of the actual ironing operation. The drawn cup C" has been inserted over the end of ironing post 44.

The ironing post 44 and knock-out member 62 have been axially adjusted to positively grip the contoured end wall 14 of the cup between the axially opposed surfaces of the shaped nose 48 and shaped cavity 62. The external diameter of the ironing post is sized in relation to the internal cup diameter d" to fit reasonably snugly within the cup. Actual ironing is commenced by operating piston-cylinder unit 42 to advance the platen 38 and ironing post 44 and thereby force the cup C" through the ironing die 50. The inner die diameter is sized in relation to the external post diameter to decrease the thickness of the cup side wall from its original dimension t of 0125 inches to a reduced thickness t (See Fig. 5) of approximately inches. The axial length of the cup side wall increases proportionately as material is forced back during the ironing operation. Advancement of piston rod 40 is accompanied by a corresponding retraction of piston rod 56, with the result that the closed container end 14 remains positively gripped between knock-out member 60 and the ironing post nose 48.

During ironing, the stripper 64 and post 44 move forward at the same rate until the stripper contacts the cup flange 15. It will be understood, however, that because of the lengthening of the cup side wall 12 during ironing, the ironed portion of the cup experiences a greater forward velocity than that of the flange 1 5. For this reason, after the stripper 64 abuts cup flange 15, the post 44 will move forward more rapidly that the stripper 64. The difference in velocities of the post 44 and stripper 64 cause the distance between the stripper and the platen 38 to decrease, with the result that the springs 66 are increasingly compressed. As this occurs, sensor bar 82 moves through the opening 84 in platen 38 towards sensor 86.

The movable platen 38, post 44, and sensor 86 move at the same rate as the ironed portion of the cup. Thus, the position of the sensor 86 is fixed relative to the location of the front or closed end wall 14 of the cup. In contrast, the positions of the stripper 64 and sensor bar 82 are fixed relative to the location of the flange 1 5 at the opposite open end of the cup. Thus, the overall length of the cup body resulting from the ironing operation can be measured and monitored as a function of the relative positions of the sensor 86 and the end of the sensor bar 82. Sensor 86 is triggered by the proximity of the end of sensor bar 82 and generates a signal used to stop both the advancement of piston rod 40 and the retraction of piston rod 56 when the cup body C" has grown to the desired length.At this stage, as shown by the location of the ironing die 50 in Figure 4B, the ironing operation has stopped short of the cup and flange 15, and the groove 46 of the ironing post 44 has been pushed beyond the flange 15 and into the cup. This allows an unironed wall section 89 adjoining flange 15 and delineated by an internal shoulder 90 to remain. As can be best seen in Figure 5, the wall section 89 and the external flange 15 both remain unironed or "as drawn" both having the thickness t of the original blank B, i.e., 0125 inches. The ironed wall portion has been reduced to a thickness t' of 008 inches.

The ironing cycle is completed by retracting the ironing post 44 and movable platen 38 while advancing the knock-out member 60 to the positions shown in Figure 4C. The knock-out member 60 pushes the cup C" back through the ironing die 50. As the platen is retracted, it compresses springs 78, which act on connecting plate 72, causing a corresponding retraction of guide rods 66 and a stripper 64 until the nuts 70 on the ends of the rods 66 contact the ends of stop bolts 92 on the abutment wall 34. Thereafter, as retraction of the ironing post 44 continues the stripper 64 provides a stop acting against the cup and flange 15. This allows the cup C" to be stripped from the ironing post 44.

With reference to Figure 3G, it will be seen that following the ironing operation, the closed end 14 of the can body is then conventionally punched at 18 and rimmed at 20. Fabrication of the can is then completed by applying a bottom or closure element 22 to the open end 13 of the can body.

The closure element has a concave central portion 92 with a peripheral flange 94 terminating in a lip 96. The closure element 22 is secured to the can body by a conventional double seaming operation which entails simultaneous deformation of the external flange 1 5 on the can body as well as the peripheral flange 94 and lip 96 of the closure element. The resulting seam is shown in Figure 2, which shows the addition of an elastic sealing compound 93 at the interface between flange 15 and flange 94 and lip 96, again in accordance with conventional double seaming techniques.

Deformation of the can body occurs only at the more ductile, unironed portions, specifically the flange 15 and adjoining wall portion 89 delineated by internal shoulder 90. No plastic deformation occurs at the more brittle ironed portion of the side wall 12. By limiting double seaming deformation to these more ductile areas of the can body, cracking problems are avoided or at least greatly minimized, thereby resulting in significantly fewer seal failures under high pressure applications. If production techniques preclude accurately controlling the overall length of the container body during the ironing operation, the flange 15 can be removed and the adjoining unironed wall portion then can be re-flanged to achieve a desired length before applying the closure element 22.

A slightly modified form of the invention is illustrated in Figure 6. Here, as in the previously described embodiment, the can body has an ironed side wall 12 and an "as drawn" unironed external flange 15 and adjoining side wall section 89 at its open end 13. However, unlike the previously described embodiment, the adjoining side wall section 89 is delineated by an external shoulder 90', rather than an internal shoulder. This embodiment is produced by an ironing apparatus of the type depicted in Figure 7, where the ironing post 44' is not grooved or recessed, and the post and die 50 are sized to produce the external shoulder 90'.

In light of the above, it will now be understood that the present invention provides a method of fabricating a can body by utilitizing both drawing and ironing operations, thereby realizing the increased material savings made possible by ironing. This advantage is achieved without an accompanying detrimental work hardening of flange and wall areas which must subsequently undergo extensive deformation during the double seaming operation employed to secure a closure element to the open end of the can body. The resulting seam is thus less prone to failure due to material cracking.

Claims

1. A method of producing a metallic container, comprising: drawing a flat metal blank into a cup with a cylindrical side wall which is open at a first end and at least partially closed at an opposite second end by an end wall; ironing said side wall from said second end towards said first end to increase the length of said side wall while simultaneously reducing the thickness thereof, with the said ironing being terminated at a location spaced from said first end to allow an unironed portion of said side wall adjacent to said first end to remain in the asdrawn condition: and applying a closure element to said first end by deforming both the periphery of said closure element and the unironed portion of said side wall.

2. The method of claim 1 wherein during ironing, said cup is pushed in one direction through an ironing die, and at the termination of the ironing operation, said cup is retracted in the opposite direction from the ironing die.

3. The method of claim 2 wherein ironing is terminated upon achievement of a predetermined cup length measured from said flange to said end wall.

4. The method in accordance with any of the preceding claims wherein following said ironing, the ductility of said unironed portion is greater than that of the ironed portion of said side wall.

5. The method of claim 1 wherein the drawing is accomplished in a plurality of stages, at least some of which are accompanied by a shaping of said end wall.

6. The method of claim 12 wherein the exterior of said side wall is smooth and continuous from said end wall to said flange, and wherein the interior of said side wall is interrupted by a shoulder at the location of termination of said ironing.

7. A metallic container having a cylindrical side wall surrounded at a first end by a radial flange and at least partially closed at an opposite second end by an end wall, said end wall and side wall and said flange consisting of a unitary structure drawn from a flat blank, said flange and an adjoining portion of said side wall being in the asdrawn condition with the remainder of said side wall having been ironed, and a closure element applied to the front end of said side wall, both said flange and the periphery of said closure element having been deformed to provide a fluid-tight seal therebetween.

8. The container of claim 7 wherein said flange and the adjoining portion of said side wall each have an equal thickness which is greater than the thickness of the ironed portion of said side wall.

9. The container of claim 8 wherein said flange and the adjoining portion of said side wall have a ductility greater than that of the ironed portion of said side wall.

10. The container of claim 8 wherein a shoulder is formed on said side wall at the juncture of said ironed portion with the unironed wall portion adjoining said flange.

11. The container of claim 10 wherein the exterior of said side wall is smooth and continuous from said end wall to said flange, and wherein said shoulder is located on the interior surface of said side wall.

12. The method of claim 1 wherein said unironed portion includes a radially outwardly extending flange surrounding said first end.

13. The method of claim 1 wherein said flange is deformed during the application of said closure element.

14. The method of claim 12 wherein said flange is produced during the drawing operation and said flange is trimmed to a desired size prior to said ironing.

1 5. The method of claim 1 wherein said unironed portion has a greater thickness and ductility than that of the ironed portion of said side wall.

16. A metallic container having a cylindrical side wall surrounded at a first end by a radial flange and at least partially closed at an opposite second end by an end wall, said end wall and side wall and said flange consisting of a unitary structure drawn from a flat blank, said flange and an adjoining portion of said side wall being in the as-drawn condition with the remainder of said side wall having been ironed.

17. A method of producing a metallic container.

the method comprising drawing a flat metal blank into a cup having a cylindrical side wall extending upwardly from a base, swaging a portion of the side wall from the base toward the open end of the cup, and applying a closure element to the remaining unswaged portion of the side wall at the said open end.

18. A method of producing a metallic container, substantially as herein described with reference to the accompanying drawings.