US3293895A - Method of forming a coated metal container - Google Patents

Description

De@ 27, -1966 R. Kol-IAN ETAL 3,293,895

METHOD OF FORMING A COATED METAL CONTAINER Filed Oct. 23, 1962 5 Sheets-Sheet l O M ff wz y 7@ if /ff Dec 27, 1966 L. R. KOHAN ETAL 3,293,895

METHOD OF FORMING A COATED METAL CONTAINER Filed Oct. 25, 1962 y 5 Sheets-5h88?. 2

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METHOD OF FORMING A COATED METAL CONTAINER Filed Oct. 23, 1962 3 Sheecs-Sheerl 3 fm @fw/.M

United States Patent O 3,293,895 METHD @iF FHNG A CUATED METAL CUNTAINER Leonard Raymond Kohan, Hyattsville, Md., and John Anthony Storace, Barrington, ill., assignors to American Can Company, New York, NPY., a corporation of New Jersey Filed ct. 23, 1962, Ser. No. 232,559 Claims. (Cl. '72-46) This invention relates to lthe manufacture of coated seamless aluminum containers produced by drawing and ironing an aluminum oxide coated blank, without exfoliation of the oxide coating.

Many devices and processes are presently being used for forming seamless aluminum containers from fiat blanks. One of these procedures involves first drawing the blank into cup form by forcing the blank through a drawing die by means of a punch mounted upon a press. After drawing, the cup is passed through an ironing die, whose inside diameter is slightly smaller than the outside diameter of the cup.

As drawn, the cup usually has bottom and side wall thicknesses substantially equal to the thickness of the blank. The ironing die thins the side wall of the drawn cup and forces the metal back, thereby also increasing the height of the container. Additional ironing steps may be added to achieve a desired body wall thickness and container height.

As used herein, the term drawing may be defined as the forming of recessed parts by forcing the plastic flow of metal in dies, and refers to the operation wherein a peripheral margin of a flat blank is turned inwardly and simultaneously smoothed by means of a 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 merely turns up more of the end materia-l into the side wall, thereby elongating the side wall, but resulting in a substantial reduction in the diameter of the cup.

Ironing may be dened as thinning the walls of a deep-drawn article by reducing the clearance between punch and die. In the ironing operation the side wall of a cup is elongated by reducing its thickness with no reduction in the inside diameter of the cup. It is generally accomplished by placing the cup` on a closely fitting punch or mandrel and forcing the cup and mandrel through an ironing or reducing die, whose diameter is slightly less than the outer diameter of the cup, thereby forcing the excess metal back and producing a longer but thinner side wall.

Ironing has sometimes been compared to extrusion of metals, since there is an actual squeezing out of the metal. However, the punch pushes the part downwards resulting in a pulling of lthe material in the ironing process. In extrusion, the metal is pushed through a die in the same direction with the punch. Both processes do, however, squeeze the metal.

Prior to the advent of these seamless containers, both interior and exterior decoration of metal cans, e.g. tin cans, had usually been done upon the flat sheet prior to forming the cylinder. This was especially true of the outside coating. But, prior to this invention, seamless aluminum containers required the application of exterior coatings after forming the can. This necessitated the use of complex equipment to insure proper coverage and also exact indexing when designs or lettering were utilized in the coating.

In addition, aluminum, which is used for many of these seamless containers, often requires a primer coat ice for adherence of subsequent organic coatings. Even then, on occasion, considerable deterioration of adhesion between the coating and the aluminum occurs on the interior of containers used to package many potable products. This results in attack upon the container side wall by the product and eventual spoilage of the contents ofthe container.

It is well known that aluminum is frequently anodized in order to form an aluminum oxide on the surface to promote organic coating adhesion and resistance to corrosion. This oxide coating may also be colored for aesthetic purposes. The aluminum oxide formed in the anodizing process is generally porous and has a lower density than conventional A1203 which is used as an abrasive.

Accordingly, an object of the present invention is to provide a method of forming a thin-walled aluminum cup-shaped container having a coating of aluminum oxide.

Another object is to provide a method of forming a coated, thin-walled, cup-shaped, aluminum container directly from a coated sheet blank.

An additional object is to form an anodized aluminum sheet into a thin-walled, cup-shaped container having an oxide coating thereon.

A further object is to thin the side wall of an oxidecoated, aluminum container without exfoliation of the oxide coating thereon.

A still further object is to provide a method for forming an aluminum oxide-coated, cup-shaped container having an end thickness equal to and a side wall thickness substantially less than the thickness of the original blank.

Yet a further object is to form a color impregnated, anodically-coated aluminum sheet into a thin-walled, cupshaped container having a colored aluminum oxide coating thereon.

Numerous other objects and advantages of the invention will be apparent as it is better understood from the following description, which, taken in connection with the accompanying drawings, discloses a preferred embodiment thereof.

rIlhe above objects are accomplished by electrolytica-lly anodizing aluminum sheet in a suitable electrolyte, thereby forming a thin, porous aluminum oxide upon the surface of the sheet. Thereafter the sheet may be immersed in a dye to impregnate the oxide coating with an aesthetic color. Subsequently, a circular disc is cut from the coated sheet and the disc is placed in a press over drawing and ironing dies and having a mandrel positioned over the blank and in mating relationship with the dies. The mandrel then forces the blank through lche drawing die, thereby forming a shallow cup, and then the drawn cup is forced through a plurality of ironing dies, each of the ironing die faces having a diameter slightly less than the preceding one. Thus, as the cup moves through the ironing dies, its side wa-ll is elongated and thinned while the aluminum oxide coating remains visibly adherent to the side wall.

Referring to the drawings:

FIG. l is a fragmentary, enlarged, cross-sectional View ofthe anodized aluminum sheet;

FIG. 2 is a sectional view of the drawing and ironing die gang and the mandrel used to force the aluminum through the gang.

FIGS. 3 through 5 are fragmentary views, similar to FIG. 2, showing a blank being formed to a desired container configuration.

FIG. 6 is a perspective view of the container with parts broken away and partly in section; and

FIG. 7 is an enlarged macro photograph of the exterior side wall of the container after drawing and ironmg.

As a preferred or exemplary embodiment of the instant invention, a sheet of aluminum alloy 3003H- is cleaned in a suitable manner and made the anode in an electrolytic cell having an aqueous solution of sulphuric acid as the electrolyte. The concentration of the acid will generally vary from 10 to 25 percent, with a bath temperature of about 70 F. A current density of approximately 14 amperes per square foot is impressed upon the anode, and the action of the electrolyte upon the aluminum is allowed to continue for about 5 minutes. It should be understood that this anodizing treatment is well known in the art and is included principally for purposes of clarity, as other electrolytes and anodizing conditions may be used without departing from the scope of the invention.

Once the anodic coating is formed to a suitable thickness it is removed from the electrolytic cell, rinsed, and immersed in a dye solution. During immersion, pores in the oxide, which have formed during the anodizing process, adsorb the dye, thereby imparting a desired color to the coated metal. This dying step may be eliminated if an aluminum color is desired, since the aluminum oxide itself is colorless.

The next step in the process is to seal the pores in the coating. Although this is not essential to insure adherence of the oxide coating during the container-forming operation, it may be desirable. Immersion of the anodized aluminum in water at a temperature greater than 190 F. for a period of to 15 minutes is generally adequate to form the hydrated aluminum oxide which seals the pores. The sealing time may vary depending upon the temperature of the water and the thickness of the aluminum oxide coating. FIG. 1 shows a cross-section of the coated aluminum 6 with the aluminum oxide 7 covering the surface.

After the anodized sheet is dried, a circular blank 8 is cut therefrom by a suitable means such as a punch press.

FIG. 2 shows a gang of dies, generally designated 10, within a die carrier 12. Both the gang 10 and the carrier 12 are mounted in a suitable hydraulic press. An annular die 14 having a die aperture 16 is suitably mounted in the die carrier 12. The die aperture 16 has a rounded drawing face 18 adjacent the upper surface of the die 14.

Reciprocably mounted above the die 14 in axial alignment with the die aperture 16 is a cylindrical forming punch 20 having a lower end surface 22. The shape of the end surface 22 determines the end shape of the article to be formed and may be flat, conical, spheroidal or a combination of these shapes. In the preferred embodiment shown in the drawings, a at end surface 22 is used for producing flat-ended containers.

The flat circular blank 8 is inserted between the die 14 and an annular blank holder 24 disposed above the die. The blank holder 24 has an inner diameter slightly greater than the diameter of the punch 20 and a spaced series of guide holes 26 extending through the blank holder, adjacent the outer edge. Studs 28, having Shanks 29 and heads 30, are threadably engaged to the die carrier 12 with the shank portions extending upwardly through the holes 26 in the blank holder 24 to prevent the blank holder from moving transversely relative to the die 14, while permitting it to move upwardly along the longitudinal axis of the die.

Within the lower surface of the blank holder 24 is a circular recess 32 of substantially the same diameter as that of the blank 8 and having a depth which is slightly less than the thickness of the blank, the recess 32 serving to position the blank 8 in axial alignment with the die aperture 16. As thus positioned, the marginal edge 34 of the blank 8 is gripped between the die 14 and the blank holder 24 with a substantial predetermined force due to the action of the compressed springs 36, disposed about the stud Shanks 29 between the blank holder and the stud heads 30.

The upper end of the punch 20 is attached to a piston rod 38 which in turn is actuated by a suitable power source such as a hydraulic cylinder, which is not shown. Upon actuation, the punch 20 moves downward bringing the lower surface 22 of the punch into contact with the blank 8.

Continuing its movement downward, the punch 20 progressively pulls the marginal edge 34 of the blank 8 from beneath the blank holder 24 and forces it into contact with the drawing face 18 of the die 14. The edge 34 is thus drawn across the drawing face 18 and is stretched and shaped into a tubular configuration to form a side wall 40 of a cup-shaped article having an end 42 (FIG. 3). At this point both the side wall 40 and the end 42 of the drawn article have thicknesses substantially equal to the thickness of the blank 8.

During the drawing operation the force with which the marginal edge 34 of the blank 8 is gripped between the blank holder 24 and the die 14 is maintained at a level sufficient to insure that the blank 8 is plastically stretched, rather than being wrinkled or folded, as the marginal edge is withdrawn from beneath the blank holder, but is not so great as to result in tearing or cracking of the metal.

Thus the metal is simultaneously subjected to two types of loading in the drawing operation, i.e. a compressive loading on the marginal edge 34 of the blank 8 due to the holding force, and a tension or stretching load on the metal adjacent the drawing face 18 as the metal is drawn from the at to the tubular form. This is true for both the aluminum metal 6 and the aluminum oxide coating 7. In fact, the tension force is probably greater upon the oxide 7 than the aluminum itself.

Generally the holding force used will be determined by the particular forming operation. For example, in the drawing and ironing of a 4.625 diameter x 0.023" thick oxide-coated aluminum blank into a 2.062 diameter cup having a 0.008" side wall thickness, a holding force equivalent to approximately 30-40 p.s.i. on the marginal edge of the blank is preferred.

While still being engaged by the drawing face 18, the cup-shaped article enters an annular ironing die 44 mounted in the die holder 12, below the die 14 (FIG. 4). The ironing die 44 has an ironing face 45 which is smaller than and axially aligned with the drawing face 18 of the die 14. A spacer plate 46 is disposed between the die 14 and the die 44 to produce a predetermined spacing between the respective dies. The downward movement of the punch 20 forces the aluminum-oxide coated side Wall of the cup-shaped article past the ironing face 45, thereby reducing the thickness of and also elongating the side wall 40.

A second ironing die 48 having an ironing face 49 is similary mounted in the die holder 12 below the ironing die 44. A spacer 50 disposed between the ironing dies 44 and 48 produces a predetermined spacing between the respective ironing faces 45 and 49 thereof. As the punch 20 continues downwardly, it carries the cup-shaped article into the ironing face 49 while the side wall is still engaged by the ironing face 45 of the first ironing die 44. Depending upon the spacings between the respective ironing faces, the side wall may also still be engaged by the drawing face 18 of the drawing die 14 when it initially enters the ironing face 49 of the second ironing die 48. As it is moved downwardly, the side is then disengaged from the drawing face 18 while still engaged by the ironing faces 45 and 49 of the ironing dies 46 and 48 respectively (FIG. 5).

Further ironing of the side wall is done by the ironing face 49 in order to reduce the side walls thickness and increase its length. The drawn and ironed container 52,

finally formed, has the end 42 of substantially the same thickness as that of the blank 8 and a side wall 54 whose thickness is substantially less than that of the blank 8. It is to be understood that, while the drawings show only two ironing dies, additional ironing dies may be used to produce any desired side wall.

Although the formation of the coated container from the at circular blank has been shown as a one-step operation, it is possible to rst draw the blank into a shallow seamless cup, and then transfer the cup to another machine, containing the ironing dies, where the cup is then forced through the ironing dies in order to thin and also elongate the side wall.

After passing through the second ironing die 48, the continuous downward movement of the punch carries the formed container 52 through a conventional stripper, generally designated 56. The stripper S5 consists of a segmented flat annular ring 58 having a series of segments 60 adapted to slide radially within a recess 62 in the lower surface of the die holder 12. The segments 50 are urged radially inwardly by springs 64 and are retained within the recess 62 by an annular flat retaining ring 66, secured to the die holder 12 by screws 68. At the extreme inwardly position of the segments 60, the segmented ring 58 has a substantially cylindrical inner surface 70 whose diameter is slightly less than the diameter of the punch 20, with a smoothly rounded upper edge 72 and a sharp lower edge 74.

As the formed container 52 (FIG. 6) is conveyed toward the stripper 56 by the punch 20, it contacts the rounded upper edge 72 of the segmented ring 53 forcing the segments 60 outwardly to allow the punch and container to pass through the ring. After the container 52 has passed through the ring 58, the springs 64 move the segments 60 inwardly against the punch 20. By suitable means (not shown), the punch 20 is then moved upwardly. During the upward movement of the punch 20, the upper rim 76 of the formed container S2 engages the sharp lower edge 74 of the segmented ring 58. This prevents any further upward movement of the container, thereby stripping it from the punch 20.

It is apparent from the foregoing description of the process that the aluminum oxide coatings on the interior and exterior side wall surfaces of the drawn and ironed container are subjected to different mechanical actions. The internal side wall surface is forced to undergo a 90 tensional bend around a curved drawing die and a tensional force during ironing, whereas the exterior side wall surface undergoes a 90 compressive bend in the drawing and is then exposed to an extrusion or squeezing action when passing through the ironing dies. On the other hand, the bottom end of the container has not been deformed.

Since the aluminum oxide coating produced by anodizing aluminum metal is generally considered quite brittle and barely amenable to even slight bending, without fracturing, it is quite unexpected that this coating could withstand extreme bending or an extrusion type deformation without exfoliating from the aluminum metal. Although the oxide 7a on the aluminum metal side wall does indeed remain adherent during the drawing and ironing process, it nevertheless does not form a continuous, intact coating as found in undeformed anodized alluminum. However, the anodic coating 7 on the bottom end of the container, which has not undergone deformation, remains intact in the as-anodized condition.

Although the exterior side wall oxide coated surface appears as a shiny continuous coating, metallographic examination reveals that the oxide has been fractured during drawing and ironing and microscopic particles of aluminum oxide appear as islands adhering to the aluminum. FIG. 7 shows the darker dyed oxide formation in relation to the exposed lighter colored aluminum. Even though the dull surface appearance of the anodized metal has been converted to a shiny surface, somewhat lighter in shade than the as-anodized and dyed color, the oxide is microscopically rough and discontinuous. This ironed surface not only resists linger-printing, which is a serious problem in handling uncoated alluminum, but in addition exhibits a remarkable resistance to atmospheric corrosion.

On the other hand, the oxide coating on the interior side wall of the container has not been ironed and therefore does not exhibit the bright surface characteristic of an ironed anodically coated aluminum. As mentioned, the interior side wall coating has only been forced to undergo a tensional bend in the drawing operation and then elongation during ironing. However, its microscopic appearance is quite similar to the exterior surface of the container. It is possible that the separation of the oxide on the interior side wall may be due to metal stretching rather than squeezing as in the exterior side wall.

It should be noted, however, that both the interior and exterior surfaces of the bottom end of the container, which had been neither drawn nor ironed, retain the asanodized alluminum oxide coating, without the fractures found in the anodic coating on the side wall of the container.

Even though the interior oxide coating on the container side wall is not intact, it has been found that this surface provides more adherent bonding for the subsequent application of organic coatings than the plain aluminum surface. This is especially true when the container is used for holding an alcoholic potable liquid.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the steps of the method described and their order of accomplishment Without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred embodiment thereof.

We claim:

1. A method of forming an anodized porous aluminum oxide coated aluminum blank into a cup-shaped article and then elongating the side wall thereof without complete separation of the aluminum oxide from the basic aluminum metal which provides an improved surface for the subsequent adherence of an organic coating, the steps comprising:

drawing said blank into a shallow cup without thinning the end and side wall of said cup while said oxide coating remains adhered to the aluminum surface; and thereafter simultaneously subjecting the internal side wall of said cup and its oxide coating to an elongational force and the external side wall of said cup and its oxide coating to a compressive force by forcing the side wall through a reducing die thus stretching the internal coating While extruding the external coating to thereby fracture said coatings into microscopic discontinuous particles which adhere to said basic metal, although the aluminum oxide coatings appear continuous to the naked eye.

2. The method of claim 1l wherein said reducing die is an ironing die.

3. The method of claim 1 wherein said drawing and ironing is accomplished in a continuous operation.

4. The method of claim 1 wherein said porous alluminum oxide is impregnated with a dye.

5. The method of claim 4 wherein said dyed porous aluminum oxide coating is sealed.

References Cited by the Examiner UNITED STATES PATENTS 2,116,954 5/1938 Singer 72-46 2,412,813 12/1946 Keller 113-120 2,538,317 1/1951 Mason et al 204-35.1 2,914,213 11/ 1959 Muehling et al 220-64 2,994,454 8/ 1961 Crowe 220-64 3,045,618 7/1962 Adams 113-51 3,056,367 10/1962 Lyon 113-51 3,203,218 8/1965 Bolt et al 72-349 CHARLES W. LANHAM, Primary Examiner.

EARLE DRUMMOND, R. T. HERBST, I. M.

CASKIE, Assistant Examiners.

Claims (1)

1. A METHOD OF FORMING AN ANODIZED POROUS ALUMINUM OXIDE COATED ALUMINUM BLANK INTO A CUP-SHAPED ARTICLE AND THEN ELONGATING THE SIDE WALL THEREOF WITHOUT COMPLETE SEPARATION OF THE ALUMINUM OXIDE FROM THE BASIC ALUMINUM METAL WHICH PROVIDES AN IMPROVED SURFACE FOR THE SUBSEQUENT ADHERENCE OF AN ORGANIC COATING, THE STEPS COMPRISING: DRAWING SAID BLANK INTO A SHALLOW CUP WITHOUT THINNING THE END AND SIDE WALL OF SAID CUP WHILE SAID OXIDE COATING REMAINS ADHERENT TO THE ALUMINUM SURFACE; AND THEREAFTER SIMULTANEOUSLY SUBJECTING THE INTERNAL SIDE WALL OF SAID CUP AND ITS OXIDE COATING TO AN ELONGATIONAL FORCE AND THE EXTERNAL SIDE WALL OF SAID CUP AND ITS OXIDE COATING TO A COMPRESSIVE FORCE BY FORCING THE SIDE WALL THROUGH A REDUCING DIE THUS STRETCHING THE INTERNAL COATING WHILE EXTRUDING THE EXTERNAL COATING TO THEREBY FRACTURE SAID COATINGS INTO MOCROSCOPIC DISCONTINUOUS PARTICLES WHICH ADHERE TO SAID BASIC METAL, ALTHROUGH THE ALUMINUM OXIDE COATINGS APPEAR CONTINUOUS TO THE NAKED EYE.

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