WO1996035525A2 - Method of fabricating sheet metal can body - Google Patents

Abstract

Method and apparatus for combined-process fabricating of flat-rolled sheet metal precoated with an organic polymeric coating into an elongated cylindrical-configuration, one-piece can body precoated on interior and exterior surfaces. A circular configuration rigid flat-rolled sheet metal blank (70) precoated with organic polymeric coating is shaped into a unitary cup-shaped product (136) which is free of increased sheet metal thickness. In a single-stroke combined processing, the work product reshaped is passed through side wall ironing structure (154) to increase side wall height and to produce a substantially uniform thickness side wall free of damage to the precoated organic polymeric coating and ready for use.

Description

UNITARY SHEET METAL CAN BODY,

FABRICATING METHODS AND APPARATUS

This application is:

a continuation-in-part of copending and co-owned U.S. Patent Application Serial No. 08/303,660, filed September 9, 1994, which is a continuation-in-part of copending and co-owned U.S. Application Serial No. 08/269,687, filed July 1, 1994, which is a division of U.S. Application Serial No. 07/596,854, filed October 12, 1990, (now Patent #5,343,729);

a continuation-in-part of U.S. Patent Application Serial No. 08/198,222, filed February 17, 1994, which is a division of U.S. Patent Application Serial No. 07/926,055, filed August 6, 1992 (now U.S. Patent #5,296,127);

a continuation-in-part of copending and co-owned U.S. Application Serial No. 08/047,451, filed April 19, 1993; and a continuation-in-part of copending and co-owned U.S. Application Serial No. 07/866,661, filed April 8, 1992, which is a division of U.S. Application Serial No. 07/573,548, filed August 27, 1990 (now U.S. Patent #5,119,657).

This invention relates to a new combination of methods and apparatus for fabricating a new one-piece can body. More particularly, this invention is concerned with producing organic polymeric material precoated unitary can bodies of substantially uniform side wall thickness by a process which includes side wall ironing of polymeric precoated sheet metal.

Side wall ironing in the manufacture of one piece can bodies involves cold forging of metal. Cold forging has been limited to relatively soft metal, and commercial manufacture of drawn and ironed one-piece can bodies has required and been limited to fabricating bare metal into one-piece can bodies. Flat-rolled aluminum, as received, can be fabricated into drawn and ironed can bodies. However, flat-rolled steel has required coating with a softer metal, such as tin or a nickel-zinc alloy. In commercial production of drawn and ironed can bodies, bare metal fabrication has been the sole practice during recent decades of expanded use of drawn and ironed can bodies for carbonated beverages and comestibles.

However, that drawing and ironing commercial practice has required: (1) demanding post-fabrication washing procedures to remove metal fines and ironing lubricant, (2) handling in-line for drying procedures, and (3) post- washing coating procedures which require use of highly volatile solvents for separately coating individual parts of the fabricated can body with lacquer.

The present invention eliminates those post- fabrication removal of fines and coating requirements of the prior practice by enabling fabrication of rigid sheet metal substrate, which has been precoated with an organic polymeric coating material, into one-piece can bodies in which side walls of desired uniform thickness are produced by side wall ironing of organic polymeric precoated flat- rolled sheet metal.

Enabling side wall ironing of such precoated sheet metal in canmaking provides a significant practical contribution, that is, the unitary can body of the invention is ready for use as fabricated free of the above- mentioned post-fabrication requirements of the prior practice.

FIG. 1 is a general arrangement box diagram for describing production of one-piece drawn and ironed can bodies as commercially practiced prior to the present invention;

FIG. 2 is a general arrangement box diagram for describing one-piece organic polymeric precoated can body production, including side wall ironing, in accordance with the invention;

FIG. 3 is a side elevational view of a cut blank of organic polymeric precoated flat-rolled sheet metal of the invention;

FIG. 4 is an enlarged cross-sectional view for describing processing of such organic polymeric precoated sheet metal;

FIGS. 5-7 are partial cross-sectional views for describing shaping and reshaping of a rigid sheet metal cup-shaped work product utilizing regulated tension in accordance with the invention;

FIGS. 8-11 are cross-sectional partial views for describing achievement of dimensional and configurational tooling characteristics used in shaping and reshaping such rigid sheet metal as part of the invention;

FIG. 12 is a schematic cross-sectional partial view for describing work product reshaping and side wall ironing in a single-stroke embodiment of the invention;

FIG. 13 is an enlarged cross-sectional partial view for describing new configurational aspects of side wall ironing structure of the invention;

FIG. 14 is a cross-sectional partial view for describing one embodiment of a bottom wall configuration forming part of the present invention;

FIG. 15 is a cross-sectional partial view for describing an endwall preforming step in preparation for production of a dome-shaped carbonated beverage bottom wall configuration as part of the present invention;

FIGS. 16-18 are schematic cross-sectional views for describing sequential operations in forming such beverage can body dome-shaped bottom wall configuration as part of the invention;

FIG. 19 is a schematic cross-sectional partial view for describing results of necking-in and flange-forming operations, at the open end of a can body, performed after the ironing step of the invention; and

FIG. 20 is a schematic cross-sectional partial view for describing stacking features of the dome-shaped bottom endwall made available as part of the invention.

In the prior commercial practice of FIG. 1, flat- rolled aluminum, or flat-rolled steel with a coating of softer metal, from coil 20 is cut into circular blanks at station 22; draw lubricated at station 24; shaped into a drawn cup at station 26; and mounted for redraw at station 27. The cup is redrawn at an entrance portion 28 of a so- called "bodymaker" apparatus 30 in which the can body side wall is ironed.

In such prior commercial practice, the plunger-mounted drawn work product is forced through a plurality of ironing rings while awash in an ironing lubricant supplied from ironing lubricator 34. After removal of the drawn and ironed can body from the ironing plunger, its ragged edge open end is trimmed at station 35.

The ironing lubricant and metal fines from bare metal ironing must be thoroughly removed at station 37 before several post-fabrication coating steps can be initiated. A protective wash coating can be applied to the exterior of the can body at station 38. The can body is then dried (as represented by 39) while traveling toward further coating operations.

Lacquer in a volatile solvent is spray-coated on the interior of the can body at station 40. The exterior side wall is then coated at station 41. Volatile solvents must be removed and such post-fabrication coatings are cured at station 42.

The open end is necked-in and a flange formed at station 44. The dome-shaped bottom wall used for carbonated beverages has, in prior practice, required re- forming (as described in U.S. Patent #5,351,852 of October 4, 1994); such bottom wall re-forming steps are generally required to be carried out off-line but are schematically represented at station 46. The bottom wall was then separately coated at station 47; volatile solvents are removed and coating cured at station 47. The can body may then be filled and closed, e.g., at station 48.

In the present invention (FIG. 2), sheet metal is prepared and coated while in flat-rolled form. Both surfaces of rigid flat-rolled sheet metal of preselected nominal gage, from coil 50, are prepared for coating at 52 which can include surface passivation. An organic polymeric coating is then applied to each surface at 54. The steps carried out at stages 52 and 54 are described later in more detail in relation to FIGS. 3 and 4.

Circular cut blanks, as provided at station 55, are shaped into shallow-depth cups at station 56. During such shaping, tension regulation and tooling configuration teachings of the invention, as described in relation to FIGS. 5, 6, are used to prevent increase in sheet metal thickness of the cup endwall, side wall, or unitary curved surface joining the endwall and side wall.

The blanking and cupping operations can be carried out in a single press structure as described in copending and co-owned U.S. patent application Serial No. 08/303,660, filed September 9, 1992, which is incorporated by reference.

Shallow-depth cup 57 is directed for reshaping at station 58 using principles and tooling as described in relation to FIGS. 7-11. The reshaped work product 59 can be directed for endwall preforming at station 60, as described in more detail later herein, to form work product 61. Or, when producing a sanitary pack flexible-panel bottom wall embodiment of the invention, the work product can be transferred directly to apparatus 64.

A preferred embodiment of the invention combines a final reshaping of the work product and side wall ironing of the organic polymeric precoated work product in apparatus 62. Coolant during side wall ironing is supplied from station 63 and rinsed away, if required, at station 64. Also, the preselected bottom wall configuration is completed, in accordance with the invention, as part of operation of apparatus 62.

In apparatus 62, the work product is reshaped to the desired final container diameter using tooling as described in relation to FIGS. 7-11. The reshaping punch is sequentially used as the plunger for thinning the side wall by ironing as part of a single-stroke operation. In the preferred embodiment, a single ironing side wall structure is used in a single-stroke apparatus; and that stroke completes bottom wall formation of the can body shown schematically at 65.

The open end formed by such ironing elongation of the side wall has a ragged edge which is trimmed and a flange formed at stations 66-68. The can body is ready for use after rinsing away ironing coolant; the special washing procedures of the prior practice are not required, nor is an organic coating required, nor is repair of the applied polymeric coating required. The can body, as fabricated, can be sent directly to fill and closure station 69 or directed for shipment to point of use.

Circular configuration blank 70 of FIG. 3 has been cut from sheet metal of preselected nominal uniform gage. For example, flat-rolled steel is selected in the range of about thirty-five lb/bb (.01 mm) to about one hundred thirty-five lb/bb (0.38 mm); and the nominal gage for aluminum is in the range of about ten mils (.010"/0.25 mm) to about fifteen mils (.015"/0.38 mm). Nominal gauge allows for a plus or minus thickness variation of about point five percent to about six percent. The metal substrate is cleansed by mechanical scrubbing means and/or electrolytic or chemical washing to prepare for passivating and/or coating of each surface.

Surface passivation enhances adhesion of a polymeric finish coat, particularly for flat-rolled steel. Surface passivation can include (a) treatment in a chromate bath with a phosphorous solution or with silicates, (b) an electrolytically applied metallic coating, or (c) a polymeric primer coating electrolytically applied from an aqueous bath. Examples of surface passivation treatment are described in more detail in copending and co-owned U.S. patent application Serial No. 08/198,222, filed February 17, 1994, which is incorporated by reference.

Work hardening of the sheet metal substrate is preferred to avoid significant change in the mechanical properties of the sheet metal substrate during shaping and, also, to provide added strength for elongation under tension. In describing a specific embodiment schematically shown in FIG. 4, substrate 72 is preselected as flat-rolled steel which has been work hardened by double-reduction, without an intermediate anneal, to provide a longitudinal yield strength to enable elongation of the work product side wall under tension during reshaping. The embodiment is double cold reduced about 20% to about 40% without an intermediate anneal which increases hardness, tensile strength and longitudinal elongation yield strength. Each cleaned surface is electrolytically plated, in one specific embodiment, with a chromium-chromium oxide coating (referred to as a tin free steel [TFS] coating) indicated at 73, 74. Other surface passivation treatment than TFS can be selected to help provide long-range surface protection. TFS, with added organic polymeric coating, enables side wall ironing of flat-rolled steel (as set forth in later tabulated data) notwithstanding that a soft metal coating had previously been required for ironing flat- rolled steel. The present invention eliminates the soft surface metal mechanical properties which were necessary in prior practice drawn and ironed can body fabrication; other problems of bare metal ironing, such as producing fine metal particles, are also eliminated.

An outer organic polymeric coating is preferably applied as a solid film; the thickness of each coating 75, 76 can be readily selected for its respective surface. Preparations for required application of thermosetting polymeric materials such as epoxies, acrylics, vinyl polyesters, polyurethanes and selected thermoplastics such as polypropylene, polyethylene and polyethylene terephalate for canmaking are described in more detail in the above- mentioned copending and co-owned U.S. patent application and serial No. 08/198,222 which is incorporated by reference. Solid particulate polymeric applications and other types of organic polymeric application are made available by the flat-rolled sheet metal fabrication teachings of the invention.

In practice of the present invention, suitable organic polymeric coating materials are available through such coating manufacturers as: The Valspar Corporation, 2000 Westhall Street, Pittsburgh, PA 15233; The Dexter Corporation, East Water Street, Waukegan, IL 60805; solid film polymeric materials are available through ICI Films, Concord Plaza - Shipley Building, P.O. Box 15391, Wilmington, DE 19850.

In carrying out fabrication processing of the invention, shaping such precoated blank 70 and reshaping of work product 57, in preparation for side wall ironing of the organic polymeric precoated sheet metal, rely solely on planar clamping of the coated substrate. Planar clamping facilitates regulation of the tension in the substrate and substantially eliminates the opportunity for damage to the polymeric surface coating, or detriment to its adhesion. Regulated tension enables shaping and reshaping of the precoated rigid sheet metal substrate free of any increase in thickness; and, control of the tensile stress in the precoated substrate is facilitated by clamping solely between planar clamping surfaces.

In addition to planar clamping teachings, tooling surface geometry contributions of the invention facilitate the movement of the precoated metal (free of damage to the polymeric coating) during changes in configuration. That is, during changing from planar to cylindrical configuration during shaping; and from cylindrical to planar configuration, and vice versa, during reshaping. The principles applied to facilitate such movement of the precoated metal during shaping and reshaping operations are described in relation to FIGS. 5-7; and the curvilinear tooling surface geometry which helps to guide movement of coated substrate, during changes in configuration, free of detriment to coating or substrate, are described in relation to FIGS. 8-11.

Referring to FIGS. 5-7, blank 70 is shaped by moving punch 78 into cylindrical die cavity 79 as defined by the internal cylindrical wall of die 80. Punch 78 utilizes a large surface transition zone 82 between its endwall and side wall. Curved surface 82 is formed about a significantly larger radius than that used in the prior cupping practice of FIG. 1. A radius of about twenty to about forty times substrate thickness gage is used to form curved surface 82 for can body sizes used in popular food and beverage can sizes, such as for soup, vegetables, and beverages, which are set forth for three-piece cans in the Can Dimension Dictionary published by the Dewey and Almy Chemical Division of W.R. Grace & Co., 62 Wittemore Ave., Cambridge, MA 02140. A commerciallyy practical range of one-piece can bodies for such can sizes includes a can body height of from about 3" to about 5" which exceeds can body diameter selected in the range of from about 1.5" to about 3.5". Larger sized one-piece can bodies can be made using teachings of the invention.

Blank 70 is clamped between planar surface 84 of die 80 and planar surface 86 of clamping sleeve 88; direction of relative movement of the tooling is as indicated in FIG. 5 with clamping pressure of the planar surfaces being regulated to avoid any increase in thickness of the precoated substrate.

In shaping the shallow-depth cup-shaped work product 57, the precoated sheet metal is moved about cavity entrance transition zone 90 into the die cavity 79. The curvilinear surface of cavity entrance zone 90 is machined about multiple radii (as described later in relation to FIG. 11) to facilitate such movement of the precoated substrate and provide for the change from planar to cylindrical configuration to take place about a smaller effective radius surface than that indicated by the entire transition zone surface.

The shallow-depth work product 57 is reshaped at least once prior to side wall ironing. In a preferred embodiment of the invention, tooling providing for tension regulated reshaping is embodied in a single stroke combination of reshaping and side wall ironing processes, as described in relation FIG . 12 .

However, configurational and dimensional characteristics of reshaping tooling can be more readily visualized in relation to FIG. 7. The principles embodied in that reshaping tooling: (a) eliminate any increase in work product endwall, side wall or transition zone thickness, (b) enables side wall elongation during reshaping, and (c) avoids detriment to adhesion of the organic polymeric precoating so as to facilitate the combination of reshaping and sequential side wall ironing of the invention.

The cup-shaped work product endwall 57, positioned by arms 91, 92, presents a planar configuration endwall 94 (FIG. 7) in which relative movement is indicated for reading the tooling positions shown in FIG. 8, coated substrate endwall is clamped between the planar surfaces of sleeve-shaped die 96 and clamping ring 97 as punch 98 moves precoated substrate into the cavity defined by die 96.

Die 96 and clamping ring 97 each has a sleeve-like configuration with an inner and outer diameter and planar endwall surface. Planar clamping surface 99 of clamping ring 97 confronts planar clamping surface 100 of die 96. Curved surface transition zone 102 is located at the outer diameter of clamping ring 97. Curved surface 104 is at the inner diameter (cavity entrance) of die 96; and, curved surface 105 is at the outer diameter of die 96. Each of the curved surfaces 102, 104, 105 (FIGS. 7, 8) is machined about multiple radii in order to augment planar surface clamping and so as to provide for optimum movement of the precoated substrate from planar into cylindrical configuration, or movement from cylindrical into planar configuration. As a result, no measurable damage to the organic polymeric surface coating, to adhesion of that coating, or to the metal substrate can be observed.

The loading of the clamping sleeve and the effective clamping force can be more accurately controlled with solely planar surfaces so as to avoid increase of substrate thickness in the work product. Such improved control also enables desired side wall elongation, prior to side wall ironing, under controlled tension free of increase in side wall substrate thickness. The planar clamping principles embodied and being described in relation to FIGS. 7-11 are utilized in a final work product reshaping leading into side wall ironing as shown in FIG. 12.

With work product 57 positioned by arms 91, 92, the relative movement between die 96, clamping ring 97 and punch 98 takes place as indicated in FIG. 7. The large surface area transition zone 106, between endwall and side wall of work product 57, is shaped by smaller curved surface 102 of clamping ring 97 to initiate the reshaping which forms work product 59 (FIG. 2).

The steps for machining curved surface transition zone 102 about multiple radii are described with reference to FIG. 10. In place of machining a single radius surface between outer side wall 107 and planar endwall 108 of clamping ring 97, the curved surface transition zone is started from clamping ring endwall 108 by machining about radius "R"; and then, machining from clamping ring side wall 107 is started about radius "R." An intermediate portion of the transition zone, between those two "R" radii surfaces, is machined about a radius equal to 1/2 R, positioned as shown in FIG. 10. The latter surface (machined about 1/2 R) is tangential at the center of each surface formed about radius R.

The resulting curved surface 102, during movement into cup 57, reshapes the large radius transition zone 106 of cup 57 in a manner which provides for a more gradual change of configuration during movement of precoated substrate from the curvilinear side wall configuration into the planar clamping area between planar surfaces 99 and 100 of the clamping ring 97 and die 96, respectively.

Each of the multiple radii curved surfaces 102, 104 and 105 help to provide for more gradual movement from one configuration (planar or cylindrical) into the other. Also, as to curved surface 102, a single radius transition zone would have a value of .707 R; use of multiple radii incrementally increases the planar clamping surface area by the differential between R and .707 R.

After curved surface 106 of cup 57 has been reshaped, the reshaping tools are at the positions indicated by FIG. 8. Punch 98 is in position to move precoated planar endwall sheet metal into the cylindrical configuration die cavity 110. The precoated substrate is clamped between planar surfaces 99, 100 during movement from side wall cylindrical configuration through access 112 leading into the planar clamping area. The multiple radii clamping ring curved surface 102 (described in relation to FIG. 10) and curved surface 105, at the outer diameter of die 96, define entrance access 112 to the planar clamping area.

The curved surface 105 at the outer diameter of die 96 (FIGS. 7, 8) is machined around a pair of radii as shown in FIG. 9. Machining that portion of curved surface leading into the planar clamping area about large radius 116 provides for a more gradual transition into the planar configuration than would otherwise be possible using a single radius in the space available for the transition from outer cylindrical side wall surface 118 to the planar endwall surface 100. The radius 116 surface also incrementally increases planar clamping surface area. The smaller radius 120 (FIG. 9) completes the machined curved surface transition, avoiding damage to coated substrate, especially as the distal end of coated work product substrate rapidly approaches through access 112.

At the inner perimeter of die 96, the curved-surface cavity entrance zone 104 (FIG. 9) is machined about multiple radii using the steps depicted in FIG. 11. The extended length radius R_L, machined about center 124, provides a gradual transition surface 125 from the planar surface 100 toward the die cavity (110 of FIG. 7). Machining a surface using the same radius R_L about center 128 establishes more gradual transition surface 129 leading into the substantially cylindrical cavity side wall. Each such large radius surface also helps to make its respective configuration transition more gradual. Such surfaces 125, 129 are joined, tangentially, by surface 130 machined about smaller radius R_s, centrally of such surfaces.

The substantially cylindrical internal side wall 132 of the die cavity, extending from transition zone 129, can be formed with a slight taper of about thirty minutes to about one degree, as indicated at 134. Such taper allows a limited spring-back in the metal after moving into the cylindrical configuration as it is being elongated under regulated tension about the curved surface 130 defined by small radius (R_s).

The planar clamping, tension-regulated shaping and reshaping of the work product avoids any increase in substrate thickness of the work product bottom wall (which remains at starting thickness) and the side wall can be elongated under tension without any increase in thickness of substrate. As a result, adhesion of the polymeric finish coating to the substrate metal is not disturbed. An increase in side wall substrate thickness would disturb such adhesion because an increase in substrate thickness decreases the surface area for adhesion of the polymer

Maintaining coating integrity is facilitated by the control of tension made available with planar clamping. It has been found that clamping along curved surfaces leads to distortion and tension in the substrate cannot be adequately regulated. With planar clamping, the organic polymeric coating and its adhesion are not disturbed since side wall elongation is carried out with no increase in substrate thickness of the endwall, transition zone, or side wall of the work product.

In addition, the smaller effective surface 130, about which the coated substrate is elongated into the die cavity (110) decreases the clamping force required to achieve desired side wall elongation. That decrease diminishes the likelihood of damage to the organic polymeric coating, or its adhesion. The radius of a cavity entrance zone machined about a single radius would be about two times substrate metal thickness. Such a single radius cavity entrance is significantly decreased from prior practice where a large surface area (having a radius about ten to thirty times that used in metal gage) was used at the die cavity entrance.

In the invention, the die cavity entrance surface area is further selected to be as sharp-angled as practical without causing cutting of the sheet metal. Through use of the multiple-radii concept, the effective angle about which the coated substrate is elongated is diminished by about fifty percent while maintaining a graduated approach to and departure from that sharp-angled surface. For example, such central surface is machined about R_S having a value of less than about .007" while the R_L surfaces are machined about a radius which is significantly larger than R_S. The latter surfaces, machined about a larger radius, provide the previously mentioned advantages of gradually changing from the planar clamping configuration to the cylindrical configuration of the side wall, while decreasing the clamping force required for desired elongation.

The invention provides the option of elongation of the work product side wall, while controllably regulating tension in the coated substrate, being carried out in a plurality of tension regulated steps prior to the combination described in relation to FIG. 12; or, work product reshaping of a relatively shallow-depth cup can be completed in a single-stroke combination of a single reshaping step with sequential side wall ironing in a single ironing structure.

The capability of selecting from reshaping steps adds advantages to the combination precoating teachings of the invention. Tension regulated side wall elongation, during such reshaping preparation, can be readily selected to provide about 50% to about 90% of desired final can body height. The percentage of side wall elongation by ironing can thus be selectively diminished such that the side wall ironing can be selected to provide essentially its uniform thickness function and can be completed in a single ironing structure.

Referring to FIG. 12, work product 136 (which can represent a shallow cup such as 57, or a reshaped work product such as 59 or 61 of FIG. 2, is shown in interrupted lines. Work product 136 is positioned symmetrically with respect to central longitudinal axis 137 by sleeve holder 140. Punch/plunger 142 and clamping ring 144 are shown in interrupted lines at the initiation of work product reshaping as part of a single-stroke operation of FIG. 12. In combining reshaping and side wall ironing, work product 136 is first reshaped about the multiple radii die cavity entrance zone 148 of die 150. The final container diameter is formed as punch/plunger 142 moves the coated substrate of work product 136 into the cavity defined by die 150. The coated sheet metal is clamped between the planar clamping surfaces of clamping ring 144 and die 150 for reshaping the coated substrate moves about the multiple radii die entrance zone (in which the smaller central portion radius has, for example, a value from about .007" to about .015") into the die cavity 152.

The work product side wall is elongated by the reshaping tooling with movement of the plunger 142 into die cavity 152. And then, the plunger moves the reshaped work product into ironing structure 154. As shown in the embodiment of FIG. 12, ironing structure 154 is separated by tooling spacer 156, which is located in the direction of plunger travel.

The ironing structure 154 presents new working surfaces. As seen in cross section in FIG. 13, a conical configuration entrance surface 160 defines a small entrance angle 162, which is between about one degree and about two and a half degrees from the vertical (as represented by plunger side wall 164 of FIG. 13). Such conical surface 160 extends in the direction of movement of plunger 142, leading into the cylindrical ironing surface 166, of ironing structure 154. As conical surface 160 feeds into fixed-diameter ironing surface 166, the average thickness of the side wall is decreased and a desired substantially uniform side wall thickness is provided.

Ironing structure 154 is supported by press tooling support 168 (FIG. 12). The ironing surface 166 tapers radially outwardly (in cross-sectional view), as shown by surface 170 of FIG. 13, toward a rounded edge portion of tooling support member 168.

As the reshaping and ironing are being completed, the bottom wall 172 of the can body is shaped by bottom wall tooling to provide a flexible-panel bottom wall, as shown in FIG. 14; or is shaped to provide a bulge and implosion resistant bottom wall for pressure packs. Timing of the bottom wall shaping is selected so as to help release the ironed side wall can body 174 from plunger 142.

The can body bottom wall depicted in FIG. 14 is formed for so-called sanitary vacuum packs; and shaping of that configuration is capable of being carried out completely free of damage to coating substrate, during the plunger stroke, as side wall ironing is completed. Central panel 180, which covers a major portion of the bottom wall area, flexes outwardly under internal can pressure and inwardly when the can interior is under vacuum. Flexing capability for panel 180 is made available because of a hinge-like action of angled wall 182. As viewed in the enlarged cross section of FIG. 8, angled wall 182 is pulled radially inwardly toward centerline 183 as panel 180 flexes toward the interior of the can under vacuum; and angled wall 182 moves vertically outwardly as panel 180 flexes outwardly under internal pressure. That hinging action helps to eliminate implosion or bulging damage contiguous to the bottom wall area. Coacting matching surfaces of a punch endwall and bottom wall shaping tooling are shown and described in copending U.S. patent application Serial No. 07/866,661, filed April 8, 1992.

FIG. 15 is an enlarged cross-sectional view of a portion 185 (shown in FIG. 2) of work product 61. In prior commercial pressurized beverage can practice it was necessary to re-form a desired bottom wall configuration after the post-fabrication steps in FIG. 1. The need for those post-fabrication bottom wall re-forming requirements has been increasing as pour feature easy-open endwalls have decreased in diameter. Two-piece beverage cans originated with a diameter of two and 11/16 inches (211) for a twelve- ounce can. And a matching stacking configuration for each longitudinal end of the can was an early objective. Easy- open endwall diameters decreased in stages from two and 11/16 inches (211) to two and 2/16 inches (202). As a result, distortions in the bottom wall sheet metal and bottom wall configuration have been encountered and the need for post-fabrication bottom wall re-forming was increased in the prior art.

However, recessed bead 186 of FIG. 15 makes it possible to form a bottom wall with the so-called "dolphin nose" configuration as seen in cross section. Such protruding dolphin nose has a circular configuration in plan view with a concave dome shape within such circular configuration. While such carbonated beverage can bottom wall configuration has been the objective for many years, achieving its of fabrication has continued to face difficulties.

In fabricating the dolphin nose bottom wall, the recessed bead 186 of FIG. 15 enables a beverage can bottom wall to be shaped:

(a) without substantial change in endwall panel thickness and without significant thickness change to contiguous portions of the bottom wall configuration;

(b) without forming stress lines in the substrate;

(c) without requiring re-forming after dolphin nose can body fabrication; and

(d) without damage to the organic polymeric coating of the invention.

Thickness of a portion of the bottom configuration (which in radial cross section is tapered from the outer diameter of the dolphin nose toward the side wall) is determined by the tension regulated elongation from the reshaping operation(s) before side wall ironing. That taper portion has a thickness approaching starting thickness for the circular blank.

The bottom wall shaping steps are shown in FIGS. 15- 18; forming of the recessed bead 186 (FIG. 15) relies on use of matching configuration bottom wall shaping tooling, as shown and described in parent U.S. patent applications Serial No. 08/269,687 and Serial No. 08/303,660 which are incorporated by reference. As part of shaping recessed bead 186, coated side wall substrate of work product 61 is pulled into peripheral bead 190 of FIG. 15. Peripheral bead 190 projects toward the exterior of the can body, as shown in cross section; and, in plan view, extends around the circular periphery of the bottom wall.

The thickness of side wall 188 of the work product is dependent on the number of reshapings of the work product which have been carried out, as described earlier. The work product wall thickness can be approximately equal to, but not greater than bottom wall thickness of a shallow cup formed from a cut blank. Or, the side wall of a work product can have been elongated under regulated tension, as described previously, to achieve an average thickness which is about fifty to about ninety percent of the desired final can body side wall thickness.

In the embodiment of FIG. 15, the thickness of side wall 180 is less than the starting thickness shown in bottom wall panel 192. During formation of recessed bead 186, coated substrate of side wall 188 becomes part of peripheral bead 190 and extends toward recessed bead 186.

Referring to FIG. 16, plunger 200 presents protruding dolphin nose 202 and a centrally-located recessed portion 204 for defining a dome shape. During initiation of the reshaping of the bottom wall, as shown in FIG. 16, clamping ring 206 has clamped and reshaped bead 190 and reshaping of coated substrate of recessed bead 186 of FIG. 15 has started. Such unfolding of beads 190 and 186 is carried out without strain in the substrate metal. Coated substrate 208 is clamped between planar clamping surface 209 and planar clamping surface 210 of die 212; and, as stated, the peripheral bead 190 of FIG. 15 has been unfolded, and the recessed bead 186 of FIG. 15 has been partially unfolded, as indicated by FIG. 16.

Referring to FIG. 17, coated substrate 214, which has an axially tapered configuration, in cross section as shown, extends between outer diameter bottom wall planar panel 216 contiguous to ironed side wall portion 218. Side wall coated substrate 218 has been decreased in thickness by ironing through ironing tooling 224 as plunger 200 moves in the direction indicated.

In FIG. 18, as ironing of side wall 218 is completed, bottom wall shaping tooling 230 and 232 move axially in the direction indicated to complete the bottom wall configuration. Bottom wall sleeve 230 (which is angled radially outwardly and axially) moves to complete "fold- down" of substrate 214 about surface 234. And bottom wall central tooling 232 moves in the direction indicated to form the concave dome-shaped configuration within the diameter of the dolphin nose configuration of the bottom wall. These steps are carried out without strain to the sheet metal or damage to the organic polymeric surface coating; and with no need for subsequent re-forming of the bottom configuration after removal of the can body from the plunger 200. The central panel of the bottom configuration is not substantially changed in thickness from starting thickness for the circular blank.

The coated substrate side wall, which has been elongated under regulated tension, is free of any increase in thickness gauge; and has been decreased in thickness by such elongation. However, coated substrate located near the mid-side wall height can be thinned to a greater extent by such elongation under tension than the coated substrate is near each longitudinal end of the side wall.

Combining side wall ironing of coated substrate with such shaping and reshaping, as taught herein, produces a substantially uniform side wall thickness as set forth in the following tabulated data (TABLES I and II) in which measured thicknesses are set forth at quarter inch increment locations starting from the flanged open end of the can body and extending along side wall height.

And measurements in the bottom wall configuration are presented. The thickness of the centrally-located bottom wall panel is approximately equal to starting thickness. The protruding toroidal configuration dolphin nose has a thickness substantially equal to original thickness, and the portion of the bottom configuration which tapers toward the side wall has a thickness which is dependent on side wall elongation during tension regulated shaping/reshaping operations prior to side wall ironing.

FIG. 19 is a cross-sectional partial view of a coated substrate side wall ironed can body in which the open end has been tapered at 240, and a chime seam flange formed at 242. The chime seam is shown at 244 in FIG. 20. The protruding toroid (also referred to as a "dolphin nose" because of its cross-sectional configuration) and remaining portions of the bottom configuration are described in relation to FIGS. 16-18; protruding toroid fits within chime seam 244 for stacking purposes.

While specific values for dimensions, configurations and materials, and specific sequential steps have been set forth for purposes of describing the present invention, it should be recognized that other values and sequences are made available to those skilled in the art by the above teachings. Therefore, for purposes of evaluating the scope of the present invention, reference shall be had to the accompanying claims.

What is claimed is:

Claims

1. Process for fabricating flat-rolled sheet metal precoated with an organic polymeric coating into an elongated cylindrical-configuration one-piece can body precoated on interior and exterior surfaces with such organic polymeric coating by side wall ironing to produce a substantially uniform preselected thickness side wall free of damage to such coating and a side wall height which significantly exceeds its diametral dimension, comprising the steps of

(A) providing a circular configuration blank of rigid flat-rolled sheet metal substrate having a preselected nominal gauge, provided with an organic polymeric coating of preselected thickness on each surface; (B) shaping the circular configuration blank into a unitary shallow-depth cup,

such cup presenting:

(i) a substantially planar closed endwall, (ii) a central longitudinal axis which is perpendicularly transverse to the closed endwall at its geometric center,

(iii) a cylindrical-configuration side wall symmetrically disposed with relation to such central axis, and

(iv) a unitary transition zone extending between the planar closed endwall and unitary cylindrical-configuration side wall,

such transition zone presenting:

a curvilinear configuration in cross section as viewed in a radially-oriented plane which includes the central longitudinal axis of such cup, with

such endwall, side wall and transition zone being formed free of increase in coated substrate thickness;

(C) reshaping the shallow-depth cup into a work product of increased side wall height and decreased cylindrical diameter in relation to such shallow-depth cup, having

an endwall, side wall and a unitary curved- surface transition zone therebetween with each being formed free of increase in coated substrate thickness, such work product side wall presenting:

a predetermined internal diameter cylindrical configuration having a height produced by such shaping and reshaping steps which is in the range of about 50% to about 90% of the can body height being fabricated; and then

(D) providing side wall ironing structure presenting a predetermined diameter,

(E) passing such reshaped work product, while mounted on an elongated cylindrical-configuration plunger, having an exterior diameter corresponding to the interior diameter of such reshaped can body, through such side wall ironing structure,

such ironing structure presenting:

(i) a conical-configuration entrance surface leading into

(ii) such ironing surface,

such ironing surface having:

(a) a predetermined length in the direction of plunger travel, and presenting

(b) a uniform diameter throughout its ironing surface length, with

(c) such uniform diameter being selected to increase side wall height by producing a substantially uniform thickness side wall for such plunger-mounted work product;

(F) carrying out of such fabricating steps, including side wall ironing to increase side wall height, and uniformity of side wall thickness is taking place such that the can body with the organic polymeric coating is ready for use as fabricated, free of requirements for polymeric coating or repair of polymeric coating, and

so as to present a can body endwall thickness which is substantially equal to such preselected nominal gauge of such circular blank.

2. The process of Claim 1, including the step of selecting flat-rolled steel substrate of predetermined physical properties, having:

a nominal thickness gage between about 35 lb/bb and about 135 lb/bb.

3. The process of Claim 2, including the step of selecting double-reduced flat-rolled steel substrate, free of an intermediate anneal, to have a thickness gage selected in the range of about 35 lb/bb to about 90 lb/bb with a longitudinal yield strength in the range of about 75 ksi to about 85 ksi.

4. The process of Claim 1, in which

providing such organic polymeric coating to the rigid flat-rolled sheet metal substrate of such blank by application selected from the group consisting of:

(a) solid-film polymeric material,

(b) polymeric material in solvent solution,

(c) polymeric material in an aqueous carrier,

(d) powdered solid polymeric material, and

(e) combinations thereof; and

such fabricating steps are carried out such that thickness of the major centrally-located can body endwall is substantially equal to coated thickness of such nominal gauge substrate of the circular blank.

5. The process of Claim 4, including

selecting reshaping processing of the shallow-depth cup from the group consisting of:

(i) a single reshaping step carried out prior to side wall ironing, and

(ii) a plurality of reshaping steps are carried out prior to side wall ironing.

6. The process of Claim 5, including

selecting a single reshaping step, and

carrying out such single reshaping step and such side wall ironing are combined as part of a single stroke processing.

7. The process of Claim 5, including

selecting such reshaping to produce an average decrease in side wall thickness, prior to such side wall ironing, of about 50% to about 90% of desired final can body side wall thickness.

8. The process of Claim 5, including

selecting shaping of the shallow-depth cup and reshaping of such cup to produce an average decrease in work product side wall thickness, prior to side wall ironing, in the range of about 10% to about 30% of starting thickness of such preselected organic polymer coated nominal gauge substrate of such circular blank.

9. The process of Claim 8, including

carrying out such cup shaping, work product reshaping and side wall ironing free of lubricants which cannot be readily removed by water rinsing.

10. The process of Claim 9, including

selecting a side wall ironing coolant from the group consisting of:

(a) deionized water,

(b) filtered water, and

(c) combinations selected from (a) and/or (b) above with a water-based lubricant.

11. The process of Claim 1, including

assisting removal of the ironed side wall can body from the cylindrical-configuration ironing plunger by:

forming at least in part, upon completion of such side wall ironing, an axially recessed portion in the bottom wall of the can body while such ironed side wall can body is mounted on such plunger,

such bottom wall forming taking place by coaction between

(a) bottom wall forming tooling which is in coaxial relationship with such plunger coated and located exterior to such can body,

such exterior located bottom wall tooling having a protruding configuration confronting such ironed can body endwall, and

(b) a recessed configuration portion of the plunger located in its endwall, with such coaction including axially-directed relative movement of such exterior located bottom wall tooling and such plunger- mounted can body toward each other.

12. The process of Claim 11, including, prior to side wall ironing,

preforming a portion of the work product endwall prior to initiation of side wall ironing;

such endwall preforming including:

forming a ring-shaped bead in such work product endwall which is recessed axially toward the interior of such work product,

such recessed bead having a circular configuration diameter which is about 80% to about 95% of final can body diameter, and in which

such work product endwall preforming and such shaping of such bottom wall, after side wall ironing of the can body, are carried out without substantial change in thickness of a centrally-located major area portion of the bottom wall from the preselected thickness of the precoated substrate of such circular blank.

13. The process of Claim 11, further including the steps of:

preforming the closed endwall of the work product prior to plunger mounting for side wall ironing;

such preforming of the work product endwall comprising:

forming a circular-configuration bead which is axially recessed toward the interior of such work product,

such recessed bead having:

a circular configuration with a diameter which is preselected to be in the range of about 75% to about 95% of preselected final can body diameter, and

assisting stripping of the ironed side wall can body from the cylindrical-configuration ironing plunger by completing shaping of endwall substrate of the side wall ironed can body which is radially within such preformed bead, to have a concave dome shape as viewed in a vertically-oriented diametral plane through the central longitudinal axis of the can body.

14. The process of Claim 11, in which

forming such an axially-recessed portion in the bottom wall is substantially completely covered while such ironed side wall can body is mounted on such ironing plunger.

15. The process of Claim 14, subsequent to removal of such can body from the cylindrical-configuration plunger, further including

necking-in the open end of the can body, and

forming a flange at such open end for chime seam attachment of an end closure.

16. The process of Claim 15, in which

such can body open end is necked-in to establish a diameter for such a chime seam which corresponds to the preformed diameter at the closed endwall so as to enable coaxial stacking of corresponding cans having one-piece can bodies of like dimensional and configurational characteristics.

17. The process of Claim 8, including

selecting side wall ironing of the can body mounted on the cylindrical-configuration ironing plunger to produce a side wall precoated with such organic polymeric coating, having a substantially uniform thickness which is about one third less than selected thickness for such circular blank.

18. A one-piece cylindrical rigid flat-rolled sheet metal can precoated with an organic polymeric coating, and having a substantially uniform side wall thickness fabricated in accordance with the process of Claim 1.

19. A one-piece cylindrical rigid flat-rolled steel can body having, as formed,

organic polymeric coating on its interior and exterior surfaces, with

a substantially uniform side wall thickness fabricated, in accordance with the process of Claim 8, free of any requirement subsequent to fabrication for applying an organic polymeric coating or repairing such polymeric coating as applied before forming.

20. A one-piece cylindrical-configuration rigid flat- rolled steel can body precoated with organic polymeric coating on its interior and exterior surfaces, and having a bottom wall with a centrally located axially- recessed flexible panel portion of substantially uniform thickness fabricated in accordance with the process of Claim 11,

a side wall ironed to have a substantially uniform thickness, with

side wall thickness being about one-third of endwall thickness.

21. A one-piece cylindrical rigid flat-rolled sheet metal can body formed from such flat-rolled sheet which has been precoated on both surfaces with organic polymeric coating, and having

an ironed side wall of substantially uniform thickness, and

a dome-shaped concave bottom wall portion of greater thickness than such side wall, fabricated in accordance with the process of Claim 12.

22. A one-piece cylindrical-configuration rigid flat- rolled sheet metal can body fabricated from such sheet metal precoated with an organic polymeric coating, in accordance with the process of Claim 13.

23. A one-piece cylindrical-configuration can body, having

a closed bottom wall,

a cylindrical-configuration ironed side wall, and a unitary curved-surface unitary transition zone therebetween,

such can body being fabricated from rigid flat-rolled sheet metal of preselected thickness precoated on its exterior surfaces with organic polymeric coating, with

such side wall having a substantially uniform thickness and uniform diameter,

the diameter of such cylindrical side wall being in the range of about 50% to about 75% of the preselected height dimension for such can body side wall, and

such closed endwall having

a centrally-located recessed portion extending over an area representing about 75% to 95% of the cylindrical side wall diameter, with

such centrally-located recessed portion having a uniform thickness which is substantially equal to starting thickness of such sheet metal as precoated for use in fabricating the can body, and

such side wall having a substantially uniform thickness which is at least about one-third less than such central portion endwall thickness.

24. An elongated one-piece rigid sheet metal can body fabricated in symmetrical relationship to a central longitudinal axis using side wall ironing of work-hardened flat-rolled steel substrate precoated with an organic polymeric coating on both its substantially planar surfaces,

such can body, as fabricated, comprising:

a closed bottom wall,

a cylindrical-configuration side wall, extending in symmetrical relationship with a central longitudinal axis of the can body, to define an open end for such can body, and

a curvilinear transition surface extending between and in unitary relationship with such closed endwall and side wall, with

side wall ironing of such precoated substrate being utilized to complete side wall elongation of such fabricated can body, with

the organic polymeric coating on its interior surface enabling direct use of the can body in canning comestibles, free of any requirement for organic polymeric coating, or for repair of such organic polymeric coating, and in which the precoated endwall sheet metal substrate of such can body has a thickness substantially equal to starting thickness of the precoated flat-rolled sheet metal, with such can body side wall, prior to side wall ironing, being elongated under regulated tension, so as

to be free of detriment to adhesion of the precoated organic polymeric coating by eliminating increase in thickness of such precoated substrate side wall, with

side wall thickness of such can body being decreased by about 10% to about 25% by side wall elongation using regulated tension during shaping of the precoated flat- rolled sheet into a cup-shaped work product, followed by side wall ironing to establish a substantially uniform side wall thickness which is about 3-1/3% less than such starting thickness, and in which

such work product shaping and side wall ironing are carried out free of detriment to the precoated organic polymeric coating.

25. Canmaking apparatus for fabricating a one-piece cylindrical can body of preselected uniform side wall thickness and having side wall height exceeding diameter of such side wall, comprising

means for shaping substantially uniform starting thickness rigid flat-rolled sheet metal blank which has been precoated with a preselected uniform thickness organic polymeric coating on each planar surface into a unitary cup-shaped work product having a cylindrical side wall, an endwall, and a curved-surface transition zone therebetween, with such cup side wall, endwall and transition zone being formed free of any increase in precoated sheet metal thickness,

such work product shaping means establishing a desired can body internal diameter and achieving a side wall elongation within about 10% to about 80% of the desired can body side wall height, and

ironing means for receiving such cup-shaped work product and elongating its side wall height by side wall ironing without changing its internal diameter,

such ironed side wall being elongated to desired side wall height free of damage to such polymeric coating.