Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
  • B21D22/20—Deep-drawing
  • B21D22/201—Work-pieces; preparation of the work-pieces, e.g. lubricating, coating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
  • B21D22/20—Deep-drawing
  • B21D22/28—Deep-drawing of cylindrical articles using consecutive dies

Definitions

• This invention relates to forming one-piece steel
• the cups may then be
• 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.
• tin wipe 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.
• 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.
• an improved tin-free steel container stock 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 (ZnSO 4 .H 2 O).
• 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.
• 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.
• 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.
• FIG. 9 is a schematic view of a finished drawn and ironed can in accordance with the present invention.
• 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.
• 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.
• 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 conciseally 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.
• 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.
• 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 (ZnSO 4 .H 2 O) has been added to give the desired zinc concentration.
• a running length of sheet steel 16 typically blackplate having a T-4 temper
• 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.
• 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.
• 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 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.
• 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.
• 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.
• the can body 32 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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 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.
• 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.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Shaping Metal By Deep-Drawing, Or The Like (AREA)
• Containers Having Bodies Formed In One Piece (AREA)
• Electroplating Methods And Accessories (AREA)

Applications Claiming Priority (4)

Publications (2)

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• 1982
  • 1982-02-10 ES ES509475A patent/ES509475A0/es active Granted
  • 1982-02-11 WO PCT/US1982/000178 patent/WO1982002683A1/en not_active Application Discontinuation
  • 1982-02-11 IT IT47770/82A patent/IT1189222B/it active
  • 1982-02-11 GB GB08228760A patent/GB2108416B/en not_active Expired
  • 1982-02-11 BR BR8206158A patent/BR8206158A/pt unknown
  • 1982-02-11 NL NL8220068A patent/NL8220068A/nl unknown
  • 1982-02-11 EP EP19820900896 patent/EP0076803A4/en not_active Withdrawn
  • 1982-02-11 JP JP57500910A patent/JPS57502252A/ja active Pending

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