EP0076803A1

EP0076803A1 - Improved steel container stock, methods of forming drawn and ironed containers therefrom, and containers formed thereby

Info

Publication number: EP0076803A1
Application number: EP82900896A
Authority: EP
Inventors: William T. Saunders; Lowell W. Austin; John R. Smith; William D. Bingle
Original assignee: National Steel Corp
Current assignee: National Steel Corp
Priority date: 1981-02-11
Filing date: 1982-02-11
Publication date: 1983-04-20
Also published as: WO1982002683A1; GB2108416B; GB2108416A; EP0076803A4; ES8503982A1; JPS57502252A; ES509475A0; NL8220068A; IT8247770A0; BR8206158A; IT1189222B

Abstract

On forme des corps de boites (32) a partir d'une tole d'acier lamine a froid revetue d'une fine couche d'un alliage nickel-zinc formee par electro-deposition sur au moins un cote. La tole d'acier ainsi revetue est etiree sous la forme d'une coupelle (31) revetue de nickel-zinc au moins sur sa surface externe et on etire sur un mandrin (42) la paroi laterale de la coupelle afin de diminuer son epaisseur et d'accroitre sa longueur. L'etirage sur mandrin de l'acier revetu de l'alliage (11, 92) est ameliore grace a l'utilisation d'un ensemble (50) comprenant une pluralite de matrices annulaires d'etirage (44, 46, 48), chacune de ces matrices presentant une surface d'entree generalement conique dont l'angle par rapport a l'axe d'etirage est dans la gamme se situant entre 6 a 8,5 environ et une partie centrale sensiblement cylindrique (80) dont la longueur n'excede pas environ 0,063 centimetres. La longueur de la partie centrale (80) de la matrice finale (48) n'est pas superieure a celle de l'une quelconque des matrices precedentes et peut lui etre inferieure et se situe de preference dans la gamme de 0,0075 a 0,018 centimetres environ. Le diametre de la partie centrale des matrices successives decroit progressivement dans le sens du mouvement d'une boite a travers l'ensemble de matrices, le diametre de la matrice finale etant tel que la paroi laterale de la coupelle penetrant dans cette matrice soit reduite d'environ la moitie.Box bodies (32) are formed from a cold rolled steel sheet coated with a thin layer of a nickel-zinc alloy formed by electro-deposition on at least one side. The steel sheet thus coated is stretched in the form of a cup (31) coated with nickel-zinc at least on its external surface and the lateral wall of the cup is stretched on a mandrel (42) in order to reduce its thickness. and increase its length. The drawing on the mandrel of the steel coated with the alloy (11, 92) is improved thanks to the use of an assembly (50) comprising a plurality of annular drawing dies (44, 46, 48), each of these dies having a generally conical entry surface whose angle with respect to the drawing axis is in the range between approximately 6 to 8.5 and a substantially cylindrical central part (80) whose length does not exceed approximately 0.063 centimeters. The length of the central part (80) of the final matrix (48) is not greater than that of any of the preceding matrices and may be less than it and is preferably in the range of 0.0075 to 0.018 about centimeters. The diameter of the central part of the successive dies gradually decreases in the direction of movement of a box through the set of dies, the diameter of the final die being such that the side wall of the cup penetrating into this die is reduced by 'about half.

Description

IMPROVED STEEL CONTAINER STOCK, METHODS OF FORMING DRAWN AND IRONED CONTAINERS THEREFROM, AND CONTAINERS FORMED THEREBY

This invention relates to forming one-piece steel

can bodies and more particularly to forming one-piece steel

can bodies by a drawing and ironing process from cold rolled steel sheet having a thin coating of a nickel-zinc

alloy electroplated on at least one side.

It is well known to form containers, or cans, and

particularly cans for packaging foods and beverages, by a

drawing and ironing process wherein flat sheet metal fed from a coil is die-cut into circular blanks which are initially drawn into shallow cups having side and bottom walls

of substantially equal thickness. The cups may then be

redrawn to further reduce their diameter and increase their height before being ironed on a punch, or mandrel, having

an external diameter substantially equal to the internal

diameter of the cups. The mandrel forces the cups through

a plurality of ironing ring dies whose inside diameters are

each smaller than the outside diameter of the cup passing

therethrough so that pressure between the respective ironing

rings and the mandrel progressively reduces the thickness

of the sidewall and forces the metal along the mandrel to

increase the height of the can body. In the past, difficulty has been encountered in forming drawn and ironed can bodies from uncoated flat cold rolled steel. The substantial forces required by the ironing step frequently resulted in tearing of the thinned sidewall, or pushing the mandrel through the bottom. Thus, it has generally been found necessary to provide a coating of a softer metal such as tin on both sides of the steel base metal as a lubricating coating in order to successfully iron the sidewalls to the desired thickness. While tinplate can be drawn and ironed to produce commercially acceptable containers, a coating thickness of from about .38 up to about .76 microns on each side of the base steel has generally been considered necessary to provide the required lubricity for ironing.. This heavy tin coating not only greatly increases the cost of the completed cans, but there is a tendency for the tin to flow or be drawn from plateaus and deposited in valleys of the base steel surface during the ironing step, with the result that the thickness of the tin coating on the finished product varies widely. This movement of the coating tin on the surface is generally known as "tin wipe", and can produce an unacceptable appearance in a commercial product. However, a commercially acceptable substitute for tinplate which would provide proper corrosion protection and desired sidewall ironing properties for the manufacture of drawn and ironed can bodies has not been previously found although substantial effort has been made to do so. For example, nickel-coated cold rolled steel sheet has been used to produce drawn and ironed cans; however, ironing nickelcoated steel presents a number of problems not encountered in ironing tinplate and numerous factors must be controlled within extremely close limits in order to produce drawn and ironed can bodies on a commercial basis from such nickelplated steel.

In accordance with the present invention, an improved tin-free steel container stock is provided for the production of drawn and ironed cans. The container stock is a cold rolled steel sheet such as blackplate having a thin coating of a nickel-zinc (NiZn) alloy electroplated on at least one side. Drawn and ironed can bodies produced from the container stock on high-speed commercial presses incorporating an improved toolpack are of good commercial quality suitable for packaging foods and beverages Ironing ring wear is low, resulting in extended tool life.

The NiZn coating on the base steel substrate is preferably within the range of about 0.013 to about 0.13 microns, and preferably about 0.025 to about 0.075 microns in thickness. The coating is nickel-rich and may contain zinc within the range of about 2% to about 12% by weight and preferably within the range of about 5% to about 10%. The coating is applied by drawing a running length of the steel base material through a conventional nickel electro plating bath such as a Watts bath to which the desired amount of zinc has been added, preferably in the form of zinc sulfate (ZnSO₄.H₂O). The NiZn alloy coated steel is then chemicallly treated to facilitate coiling and increase storage life of the material and to enhance adhesion of organic coatings conventionally used in the production of containers.

The NiZn coated and chemically treated steel sheet is cut into circular blanks which are initially drawn into cups having side and bottom walls of substantially equal thickness and then ironed to produce low-cost containers suitable for use in packaging foods and beverages. It is to be understood that the drawn cups may be formed either by a single drawing operation or by drawing and redrawing. The drawn cups are supported on a cylindrical mandrel having an external diameter corresponding to the internal diameter of the finished can bodies, and passed through a toolpack consisting of a plurality of axially aligned, spaced ironing ring dies. The diameter of the opening in the successive ring dies is progressively smaller from the first to the final ring die, with each being slightly smaller than the external diameter of the sidewall of the container passing therethrough. Each ring die has a generally conical lead-in portion intersecting a substantially cylindrical land and an outwardly diverging generally conical exit portion. The conical lead-in portion of each ring die has a half-cone angle, i.e., the angle of the conical surface in relation to the draw axis of the toolpack, within the range of about 6° to about 8.5°, preferably about 7.5°, with the land having a length in the axial direction which does not exceed about 0.063 centimeters. The final ring die has a land which is shorter than 0.063 centimeters, preferably within the range of about 0.0075 to about 0.018 centimeters.

The invention will be described more fully hereinbelow with reference to the drawings, in which:

FIG. 1 is a fragmentary sectional view, on an enlarged scale, of a steel container stock embodying the invention;

FIG. 2 is a schematic illustration of a highspeed plating and treating line suitable for producing the container stock employed in the invention;

FIG. 3 is a sectional view schematically illustrating a toolpack and mandrel for use in drawing a cup from the container stock shown in FIG. 1 and for ironing the drawn cup into a can body;

FIG. 4 is an enlarged, fragmentary sectional view of one of the ironing dies illustrated in FIG. 3;

FIG. 5 is a fragmentary sectional view schematically showing a cup in the process of having its sidewall thickness reduced by an ironing ring die of the toolpack shown in FIG. 3; FIG. 6 is a view similar to FIG. 1 and showing an alternate embodiment of the container stock;

FIG. 7 is a view schematically illustrating a drawn cup formed from the container stock of FIG. 1 or FIG. 6;

FIG. 8 is a view similar to FIG. 7 and showing a can body blank drawn and ironed from the container stock; and

FIG. 9 is a schematic view of a finished drawn and ironed can in accordance with the present invention. Referring now to the drawings in detail, the present invention involves forming drawn and ironed containers, or cans, from steel container stock having a thickness and temper generally corresponding to that of tinplate used to form drawn and ironed cans. As shown in FIG. 1, one embodiment of the container stock 8 includes a base steel sheet 10 having a coating 12 of a NiZn alloy plated on both surfaces, and a protective coating 14 applied by a chemical treatment to increase the storage life of and enhance lacquer adhesion to the plated steel.

In the preferred embodiment, the chemical treatment is carried out non-electrolytically in a chromic acid solution which results in formation of a film of trivalent chromium oxide on both surfaces of the strip. The solution may contain about 40 grams of chromic acid per liter to provide the desired chromium oxide coating weight at com mercially acceptable processing rates for continuous steel strip. The chromium oxide film may also be applied from a cathodic dichromate treatment, and other suitable treatments may be used. However, it is important that the chemical treatment provide a corrosion protection film which will not interfere with the manufacture of the onepiece can body in a drawing and ironing fabrication process. Preferably, a chromium oxide film of about 2,000 to 3,200 micrograms per square meter of surface area is provided, with the chromium oxide being substantially free of elemental chromium.

The NiZn alloy coating is very thin and may be within the range of about 0.013 to about 0.13 microns, but preferably is within the range of about 0.025 to about 0.075 microns. The coating is nickel-rich in that the ratio of the percentage of nickel to zinc is relatively high. However, less than about 2% zinc, by weight, in the coating produces inferior results, and at least about 5% zinc is preferred to assure uniformly good results. While satisfactory results have been obtained in accordance with the present invention employing zinc percentages within the range of from about 2% to about 12% of the total weight of the alloy coating, the best results were obtained when the coating contained from about 5% to about 10% and preferably about 8% zinc. Zinc in excess of about 12% produced a less favorable appearance on the finished can body and resulted in greater difficulty in stripping the ironed can body blank from the mandrel.

The extremely thin NiZn coating described above may be applied on a high-speed nickel plating line as schematically illustrated in FIG. 2 wherein a running length of sheet steel 16, typically blackplate having a T-4 temper, is initially passed through an electrolytic tank 18, containing a quantity of nickel electrolyte solution 20, for example a modified Watts bath, into which the desired amount of zinc sulfate (ZnSO₄.H₂O) has been added to give the desired zinc concentration. The gage of the steel strip 16 will depend upon the type of product to be ultimately produced and may be about 65 to 90 pounds (29.5 to 40.8 kg) per base box for producing an ironed container of the type employed for packaging beverages and having sidewall thicknesses within the range of about 0.071 to about 0.102 millimeters while about 85 to 118 pounds (38.5 to 53.5 kg) per base box steel may be employed for food container wherein the ironed sidewall thickness may be within the range of about 0.114 to about 0.183 millimeters. Electric current is applied through electrodes 22 to produce the desired coating thickness and characteristics, depending on the line speed through the solution. When the NiZn coating is applied to only one side of the steel strip as shown in FIG. 6, current is supplied only to the electrodes adjacent that surface. From the nickel plating bath 20, the NiZn coated strip then may be passed through the chemical treatment bath 24 in tank 26 before being lubricated in an electrostatic oiler 28 and wound into a coil 30. As indicated above, the chemical treatment may be a cathodic dichromate or chromic acid treatment of the type known in the art.

Drawn and ironed can body 32 (FIG. 8) may be formed from the NiZn plated, chemically treated and oiled container stock by initially cutting the material into circular blanks and forcing the blanks through a circular drawing die by use of a cylindrical drawing punch to form shallow cups 33 as schematically illustrated in FIG. 7. As is known in the art, the cups may be removed from the drawing punch and redrawn before being ironed in a separate operation, or the drawing and ironing operations may be carried out in a continuous stroke of the drawing and ironing mandrel as schematically illustrated in FIG. 3. Thus, a can body blank 32 may be formed by initially drawing a flat blank 34 which has been clamped between the clamping plate 36 in cooperation with the face surface of a drawing die ring 38 to slip-hold the peripheral edge portion of the blank during drawing through the opening 40 of the drawing die 38 by the cylindrical mandrel, or punch, 42.

Continued downward movement of the mandrel 42 passes the cup 33 through a series of two or three ironing ring die assemblies 44, 46, 48 arranged in aligned, spaced relation to one another in a toolpack designated generally by the reference numeral 50. Annular spacer members 54, 56 and 58, respectively, are positioned between and accurately locate the drawing ring and the three ironing ring dies within a housing 52. At the exit end of the toolpack, stripper assembly 62 is in position to engage the top edge portion of the drawn and ironed can body 32 on the mandrel 42 at the end of the ironing stroke to strip the can body from the mandrel upon its return stroke. Upon completion of the ironing operation, the can body 32 has a bottom wall 64 having a thickness substantially equal the thickness of the blank 34, and a sidewall 66 which preferably is no more than about one half the thickness of bottom wall 64. As shown in. FIG. 5 the bottom end of mandrel 42 is shaped to cooperate with stop means (not shown) at the end of the ironing stroke to impart the desired concave contour to the bottom wall 64 in the conventional manner.

Referring now to FIGS. 4 and 5, the structure and function of the ironing ring die assemblies 44, 46 and 48 will be described more fully; however, since the three assemblies are substantially identical in construction except for the diameter and length of the cylindrical land portion of the respective ring dies, only die assembly 48 will be described in detail, it being understood that the description applies equally to assemblies 44 and 46. Also, it should be understood that only two ironing ring dies may be employed in the toolpack if desired.

Ironing ring die assembly 48 comprises a rigid annular support 68 having a generally conical, axial opening defined by the surface 70 extending upwardly from its bottom surface, i.e., the surface defining the exit side of the assembly. A counterbore is formed in the top, or entrance side of the support plate 68 and defines a cylindrical guide surface 72 terminating at a radial shoulder, or seat, 74. Guide surface 72 and radial shoulder 74 are accurately machined and cooperate to receive and position an annular ring die 76.

Ring die 76 has an axial opening formed therein defined by a conical entrance, or lead-in portion 78, a central cylindrical land portion 80, and a conical exit portion 82. The conical lead-in portion 78 has a semi-cone angle, i.e., the angle of the surface relative to the draw axis of the toolpack, within the range of about 6° to about 8.5°, preferably 7.5°. The inner or small diameter end of the lead-in portion intersects the cylindrical surface of land 80, and the cylindrical land 80, in turn, intersects the inner or small diameter end of conical exit portion 82. The semi-cone angle 86 of the conical exit surface 82 may be relatively small, typically about 2.5°. The maximum diameter of conical exit surface 72 is preferably slightly less than the minimum diameter of the conical surface 70, thereby providing a narrow overhang, or shoulder, 88 at the radial inner edge of the seat 74.

The drawn cups 33 (FIG. 7) formed as the flat blanks are passed through the drawing die 38 have sidewalls 92 and bottom walls 94 of substantially equal thickness. During the ironing process, reduction in thickness of the sidewall 92 to that of the sidewall 66 of can body 32 is accomplished by the tapering or conical lead-in surface 78; however, due to the compressive loads in the metal being ironed, and to the resiliency of this metal, substantial pressure is exerted on the cylindrical wall of the land. The land 80 is very short and should not exceed about 0..063 centimeters for all ironing ring dies except the final ring die which should be less than 0.063 centimeters. The land length of the final die may be as short as 0.0075 centimeters and preferably is within the range of about 0.0075 centimeters to about 0.018 centimeters.

In accordance with the present invention, the steel base metal having a NiZn alloy coating on both sides can be drawn and ironed to reduce the thickness of the sidewall portion of the drawn cup to less than one half of the original thickness of the coated steel blank to produce the thin sidewall 66 of the finished can. While reductions of this magnitude have previously been achieved in the production of steel cans, it generally has not been possible in a high-speed commercial operation utilizing tin-free steel, i.e., steel sheet not having a heavy lubricating coating of tin on its surfaces. The substantial sidewall reduction is achieved by utilizing the NiZn coated steel in combination with ironing ring die geometry such that at least about 50% of the total thickness reduction, i.e., at least about 25% of the original thickness of the blank 34, is accomplished in the final ring die, with a remainder of the reduction being accomplished in the preceding ring die or dies.

It has also been discovered that container stock similar to that described hereinabove but having the thin NiZn alloy coating electrodeposited on only one side can be successfully drawn and ironed on high-speed commercial drawing and ironing presses, provided the NiZn coating is on the outside of the container, i.e., the side engaging the ironing ring dies during the ironing operation. Thus, as shown in FIG. 6, an alternate embodiment of the container stock, designated generally by the reference numeral 96, may comprise the base steel sheet 98 similar to that described hereinabove, and have a thin layer of the NiZn alloy 100, electrodeposited on one surface only. The NiZn alloy coating is of the same thickness and composition as that described above, i.e., within the thickness range of about 0.013 to about 0.13 microns, preferably 0.025 to 0.075 microns, and with the alloy containing zinc in the amount of at least about 2% to about 12% by weight zinc with the remainder consisting essentially of nickel. Both sides of the base steel, i.e., the NiZn coated surface and the uncoated steel surface have the chromium oxide layer 102 applied thereto as described above.

Improved sidewall ironing is achieved utilizing the container stock with the NiZn alloy plated on either one or both sides and with the chemical treatment applied to both sides of the stock after electroplating with the NiZn alloy. Sidewall ironing without galling is consistently and reliably achieved at commercial production rates. Special ironing lubricants are not required but rather lubricants such as used in sidewall ironing of tinplate and which are readily removable on can production lines using conventional washing solutions can be used.

Uniformity of surface appearance of the ironed sidewall is a significant improvement available with the present invention. As is well known, the cylindrical land surface of the ironing ring dies used to iron tinplate on commercial machines are relatively long (up to 0.19 centimeters) and the friction produced during ironing can generate sufficient heat to reflow the tin. Wear of the ironing ring die surfaces frequently results in variation in surface appearance along the height of the can body, which differences in appearance are generally referred to in the art as "tin wipe". One approach in avoiding problems presented by tin wipe in ironing tinplate is the frequent change of ironing ring dies, especially the final ring die, and some can manufacturers regularly change the final ring die as frequently as every 15,000 can bodies.

In contrast to the problems in ironing tinplate, the thin NiZn plated container stock of the present invention provides a consistently uniform surface appearance when ironed with a toolpack in which the maximum length of the land in the ironing rings is not more than about 0.063 centimeters, and the length of the land of the final ironing ring die is less than 0.063 centimeters.. In excess of 140,000 can bodies have been ironed on such a toolpack without changing ring dies and without presenting surface appearance problems.

In a specific embodiment, a coil of 80 pounds (36.3 kg) per base box continuous cast steel was continuously annealed to T-4 temper. The coil was plated on a horizontal line of the halogen tinplating type where the tin anodes were removed and replaced with nickel anodes and the halogen tinplating solution was replaced with a Watts-type nickel plating bath to which zinc sulfate had been added to produce a plating solution containing about 103 ppm zinc. The strip was plated on one side only at 457 meters per minute to a thickness of 0.028 microns. The NiZn alloy coating contained 12% zinc by weight, with the remainder consisting essentially of nickel. After plating, the strip was chemically treated on both sides in a chromic acid treatment solution to apply a film of chromium oxide on each surface, with the film consisting of approximately 2,475 micrograms of chromium oxide per square meter of surface area. After the chemical treatment, the strip was dried and electrostatically oiled with ATBC at a level of 0.40 grams per base box, and recoiled.

The coated, chemically treated and oiled container stock just described was processed on a drawing and ironing can line by cutting the strip into blanks 14.242 centimeters in diameter and drawing the blanks into cups having a diameter of 9.111 centimeters with the NiZn plating on the exterior surface. The cups were then processed on a 45.7 centimeter bodymaker running at 200 cans per minute to redraw the cups to a diameter of 5.740 centimeters and iron the redrawn cup in a two-ironing-ring die toolpack. The first ironing ring die had a land length of 0.038 centimeters and a half-cone entry angle of 7.5°. The- second ironing ring die had a land length of 0.015 centimeters and a 7.5° half-cone entry angle. The diameter of the final ironing ring die produced a can having a sidewall thickness within the range of 0.0086 to 0.0089 centimeters.

The drawn and ironed can bodies were further processed in accordance with conventional procedure by trimming the top edge before cleaning and wash-coating with an organic primer. The can bodies were then spray-coated with a commercial water base epoxy spray coating and the open top end was necked-in as shown at 104 in FIG. 9 to form, a com pleted can 106. Tests conducted on the finished cans revealed that they were satisfactory for commercial use in the packaging of foods and beverages for human consumption. External appearance of the cans was of uniformly high quality.

In a second set of tests, container stock similar to that just described, but having a NiZn coating on both sides was prepared from 85 pound (38.5 kg) steel having a T-4 temper. The NiZn alloy coating contained 7% zinc with the coating thickness being approximately 0.075 microns. The container stock was initially cut into blanks and drawn into cups having a diameter of 9.088 centimeters and subsequently redrawn to a diameter of 6.635 centimeters before being ironed utilizing a toolpack having three ironing ring dies. The diameter of the final ironing ring die was such as to produce a can having a sidewall thickness within the range of 0.0087 to 0.0091 centimeters. 56,000 cans were ironed utilizing a first toolpack in which the three ironing ring dies each had a lead-in angle of 7.5°, with the first and second ring dies having a land length of 0.063 centimeters. The third ring die had a land length of only 0.0075 centimeters. The ring dies showed now measurable wear and still had a smooth surface after ironing 56,000 cans.

These tests were repeated using first and second ironing ring dies as described above, with the final ring die having the same diameter but with a land of 0.025 centi meters. Again, 56,000 cans were successfully ironed without measurable wear on the ring dies; however, it was necessary to stop and repolish the surface of the mandrel once before this number of cans could be ironed. The outer surface of the sidewall of the cans was good, displaying no scratching.

Attempts to repeat the test using ironing ring dies at any position having a land greater than about 0.063 centimeters were unsuccessful due to excessive can breakage. Difficulty was also encountered when using a 0.0063 centimeter land length in the third ring die due to the mandrel galling, and it was necessary to polish the mandrel after ironing 12,000 cans, after 16,000 cans, and again after 53,000 cans in order to iron 56,000 cans. No difficulty was encountered with short cans, breakage, or mandrel galling when utilizing a 0.00.75 centimeter land on the final ring die. Since the surface finish of the 0.0075 centimeter land die was smooth, and no measurable change in diameter resulted after 56,000 cans, the number of cans which could have been ironed using this toolpack is not known; however, it is apparent that a much larger number of cans could have been ironed before tool changing would be required.

While preferred embodiments of the invention havebeen described, it should be understood that it is not intended to be restricted solely thereto, but rather that t is intended to include all embodiments thereof which would be apparent to one skilled in the art and which come within the spirit and scope of the invention.

Claims

1. A process for forming a drawn and ironed container from flat sheet steel comprising, applying a nickel-zinc alloy coating of substantially uniform thickness to at least one side of a sheet or strip of flat rolled steel of a gage suitable for drawing and ironing, said coating containing zinc in the amount of about 2% to 12% with the remainder being nickel and impurities, drawing the nickel-zinc coated steel into a cup having sidewall and bottom wall thicknesses substantially equal to the thickness of the coated steel and having at least its external surface coated with the nickel-zinc alloy, and ironing the sidewalls of the drawn cup to reduce the sidewall thickness and increase the height to produce a drawn and ironed can body.

2. The process of claim 1 wherein the thickness of the nickel-zinc coating on the base metal is within the range of about 0.013 to about 0.125 microns.

3. The process of claim 1 wherein the thickness of the nickel-zinc coating on the base metal is within the range of about 0.025 to about 0.075 microns.

4. The process according to claims 2 or 3 wherein the step of coating the flat rolled steel comprises passing the steel through a composite nickel-zinc plating bath and electroplating thereon a coating of nickel-zinc alloy having a thickness within the stated range.

5. The process according to claim 4 further comprising the step of passing the nickel-zinc plated steel through a chemical bath consisting of a dichromate or chromic acid solution prior to the drawing step.

6. The process according to claims 1, 2, 3, 4, or 5 wherein the amount of zinc in said coating is whithin the range of about 5% to about 10% by weight.

7. The process of claims 1, 2, 3, 4 or 5 wherein the thickness of the nickel-zinc coating on both sides of the base metal is within the range of about 0.025 to about 0.075 microns.

8. The process according to any of the above claims wherein the step of ironing the sidewall of the drawn cup comprises supporting the drawn cup on a mandrel and passing the cup through an ironing ring toolpack including a final ironing ring die and at least one otherring die, the ring dies being aligned with one another and each having a conical lead-in portion, a cylindrical land portion and a conical exit portion, the final ring die having a land which is less than 0.063 centimeters in length and the length of the land of the other ring dies each being at least as great as the land of the final ring die.

9. The process as defined in claim 8 wherein the half-cone angle of the conical lead-in portion of each said ring die is within the range of about 6° to about 8.5°.

10. The process according to claims 8 or 9 wherein the length of the land of the final ring die is within the range of about 0.0075 to about 0.018 centimeters.

11. The process according to claim 10 wherein the toolpack includes three die rings and wherein the length of the land of the first ring die is no more than about 0.063 centimeters and wherein the length of the land of the second ring die is no greater than about 0.025 centimeters.

12. A nickel-zinc plated steel sheet- suitable for use- for forming can bodies and comprising, a flat rolled steel sheet .base metal having a thickness gage suitable for forming into drawn and ironed cans and having a substantially uniform nickel-zinc alloy coating electroplated on at least one side thereof, said nickel-zinc alloy coating having a thickness within the range of about 0.013 to about 0.125 microns and the amount of zinc in the coating being within the range of about 2% to about 12% by weight, and a chromium oxide coating applied to both surfaces of the nickel-zinc coated steel sheet.

13. The nickel-plated steel sheet according to claim 12 wherein the thickness of the nickel-zinc alloy coating on the steel sheet base metal is within the range of about 0.025 to about 0.075 microns.

14. The nickel-zinc plated steel according to claims 12 or 13 wherein the amount of zinc in said nickelzinc alloy coating is within the range of about 5% to about 10% by weight.

15. The nickel-zinc plated steel according to claims 12, 13 or 14 wherein the nickel-zinc alloy coating is electroplated onto both surfaces of the flat rolled steel sheet.

16. A nickel-zinc plated steel can comprising, a bottom wall and a seamless sidewall, said bottom and sidewalls being integrally formed by a drawing and. ironing process whereby the sidewall is ironed to a thickness substantially less than that of the bottom wall, said can being drawn and ironed from a flat rolled steel sheet having a nickel-zinc coating plated on at least the side thereof forming the external surface of the can, the nickel-zinc coating having a thickness within the range of .about 0.013 to about 0.125 microns before being drawn and ironed, and the amount of zinc in the coating being within the range of about 2% to about 12% by weight, said seamless sidewall being reduced during ironing to a thickness no greater than about one half the thickness of the nickel-zinc alloy coated steel sheet.

17. The can according to claim 16 wherein the amount of zinc in the nickel-zinc alloy coating is within the range of about 5% to about 10% by weight.

18. The can according to claim 17 further comprising a thin chromium oxide coating on both surfaces of the nickel-zinc alloy coated steel sheet, said chromium oxide coating being applied by immersing the nickel-zinc plated steel in a dichromate of chromic acid coating material solution before it is drawn and ironed.

19. The can according to claims 16, 17 or 18 wherein said nickel-zinc alloy coating is applied to both surfaces of the flat rolled steel sheet.