BACKGROUND OF THE INVENTION

A. Field ofthe Invention

This invention relates to the can manufacturing art, and more particularly to a novel construction and arrangement of the bottom portion of a drawn and ironed can body and method for making such a can body.

B . Description of Related Art

It is well known to draw and iron a sheet metal blank to make a thin-walled can body for packaging beverages, such as beer, fruit juice or carbonated beverages. In a typical manufacturing method for making a drawn and ironed can body, a circular disk or blank is cut from a sheet of light gauge metal (such as aluminum). The blank is then drawn into a shallow cup using a cup forming equipment. The cup is then transferred to a body maker where the can shape is formed. The body maker re-draws and irons the sidewall of the cup to approximately the desired height, and forms dome and other features on the bottom of the can. The dome and other feature on the bottom edge of the can are referred to herein as the "bottom profile" of a drawn and ironed can body. Can body manufacturing techniques are described in the patent literature. Representative patents include US Patents 6,305,210; 6,132,155; 6,079,244; 5,984,604, and 5,934,127, the contents of which are incorporated by reference herein. Domer assemblies for drawing and ironing machines are described in U.S. Patents 4,179,909; 4,620,434; 4,298,014, all assigned to National Can Corporation, the contents of which are incorporated by reference herein. hi current practice, after the can is formed in the body maker, the can is sent to a separate necking and flanging station, where the neck and flange features are formed on the upper regions of the can. The flange is used as an attachment feature for permitting the lid for the can, known as an "end" in the art, to be seamed to the can. The last station in the necker- flanger is a reformer station. This station includes a set of tools for reforming the bottom profile of the can in order to increase the strength of the bottom profile. U.S. Patents 5,222,385 and 5,697,242, both assigned to American National Can Co., describe a can body reforming apparatus and methods for reforming can bodies to increase the strength of the bottom profile. IhIy, U.S. Patent 5,934,127 also describes can bottom reforming apparatus. Other patents of interest include Gouillard, U.S. Patent 6,132,155 and Saunders et al., U.S. Patent 6,305,210. After necking, flanging and bottom reforming, the top edge of the can is trimmed. Long ago, when cans were made from a relatively heavy gauge aluminum, a bottom profile could be formed by the body maker that did not require a separate reforming operation in order to increase the strength of the bottom of the can. The separate reforming operation was not necessary due to the relatively thick aluminum gauge material providing the required strength. However, under current practice, aluminum stock used for drawn and ironed beverage cans is of a much thinner gauge than it used to be, in order to reduce the amount of material used to make a can. Consequently, it is much more difficult to provide a can bottom profile resulting from the shaping performed by the body maker that possesses the strength required to meet customer requirements for bottom performance. Thus, in accordance with the present practice of the assignee of this invention, after formation of the can by the body maker, the separate bottom reforming step is performed to further form or shape the bottom of the can in order to increase the strength of the bottom profile and allow it to meet customer requirements in terms of can bottom performance. The bottom performance of a drawn and ironed can body is typically characterized by three independent and distinct criteria: can growth, drop, and buckle. Can growth refers to a deformation of the can bottom due to the pressurized contents of the can causing the bottom of the can to extend further in the axial direction. The can is pressurized to 90 PSI, the pressure is removed, and the growth g is measured. The phenomenon is shown in Figure 1. The can bottom profile prior to pressurization is shown in dashed lines, the bottom profile after pressurization is shown in solid lines. The bottom profile 10 includes a nose portion 12 which defines a circumferential stand or base on which the can sits. The bottom profile 10' after growth shows the nose portion 12'. Growth occurs by an unrolling action of the nose 12, wherein the material forming the nose moves away from the region of the dome 14. Growth resistance is thus a measure of the stiffness of the bottom profile - - how much pressure can the can withstand before the nose 12 unrolls, and the amount g of can growth at a given pressure. As is known in the art, the tighter the radius of the nose 12 is, the more pressure required to "unroll" the nose and incur can growth. Hence, bottom profile reforming typically involves reforming the nose so as to decrease the nose radius to improve can growth characteristics. Drop refers to a measurement of the height at which a can, filled with water and pressurized with nitrogen to 60 pounds per square inch, is dropped and lands square on a steel platform, which results in a reversal (either whole or partial) of the dome in the bottom of the can, such that the can will no longer stand without tipping. The drop height starts at three inches and increases one inch until the failure criteria is reached. Typically, 10 or more cans are tested and the average and standard deviation are reported as results. During a drop test, the sudden dynamic load of the liquid increases the pressure on the dome. The result is shown in Figure 2. The figure shows the dome 14' (solid line) just prior to the dome reversal. The dome at 14' in the Figure is not the final shape of the dome at failure, as in the final configuration the dome completely reverses, as shown. The following results are observed, as shown in Figure 2: The nose is restrained from unrolling (as shown in Figure 1) by the steel platform; the inner leg or chime 16 rotates outwardly and results in a negative angle; a more shallow dome results; and the dynamic load of the liquid in the can causes a local collapse of the dome 14. The dome becoming shallower does not constitute a failure; the inability to stand a can without tipping is considered a failure. Buckle refers to the internal pressure limit (e.g., 100 PSI) at which point the dome in the bottom of the can reverses. Like the growth issue described previously, dome reversal involves a dynamic "rolling" at the nose of the can. See Figure 3. Dome reversal occurs when there is no more leg material available to the roll (nose), additionally the leg angle tilts inwardly by a considerable margin (positive angle). A design goals for increasing buckle is to provide a deeper dome depth, reforming to tilt the leg angle outward (provide a negative chime angle) and provide a larger nose radius and dome corner radius to provide more material for the dynamic rolling of the nose. As is known in the art, and as indicated by the above discussion, changing the parameters or values of the various features of the can bottom profile (dome radius of curvature, stand diameter, nose radius, chime angle, etc.) tend to effect the ability of the can to meet the above-referenced bottom performance criteria. However, a change in a particular value in the can bottom profile may result in a positive improvement in one criteria (such as minimize can growth), but at the same time negatively affect one or more of the other parameters (such as, for example, lower the buckle limit and lower the drop limit). Complicating the situation is the fact that can bodies are made from a very thin gauge of aluminum material, and as the material becomes thinner (currently 0.0108 inches), it becomes increasingly difficult to design the can body that meets all the bottom performance criteria. Further considerations of the design of the bottom of a can are reduction in bottom wrinkling and reduction in bottom thinning. These considerations, in addition to the previously described goals of increasing bottom performance in terms of buckle, drop and growth, typically oppose each other. In other words, the steps a designer may take to improve can bottom performance may actual work against reducing bottom wrinkling or bottom thinning. Accordingly, there has been a need in the art for a new and improved can body which optimizes the various can bottom design parameters such that it not only meets the bottom performance criteria required by the industry, using current gauge material for the can body, but allows the can body to be formed without requiring a separate reforming process to strengthen the bottom profile. This need is particularly strong in today's environment since the can body reforming process can represent the most consistent bottleneck in high-speed can manufacturing operations. It has been the experience of the inventors that the reforming tools require more frequent maintenance and are more prone to problems than the other equipment used in the process. Furthermore, to the extent that the bottom reformer can be completely eliminated, it represents a savings in capital expense, since the equipment does not have to be purchased, and savings of labor and energy consumption. An objective of the present invention is to provide a bottom profile design for a thin walled drawn and ironed can body made from 0.0108 inch gauge material or thinner which does not require a separate reforming step in order for the can body to meet customer (industry) strength requirements for bottom performance, passes a drop test of at least 5 1A inches, and has acceptable bottom wrinkling and bottom thinning characteristics. SUMMARY OF THE INVENTION We have described herein a beverage can having a can body made from aluminum having a gauge thickness of 0.0108 or thinner, the can body having a bottom profile, wherein the following two properties are observed by virtue of the selection of values for the bottom profile: (1) the forming of said can body is completed without performing a step of reforming of the bottom profile to increase the strength of the bottom profile to meet customer requirements for can growth, drop and buckle, and (2) the can passes a drop test of at least 5 1A inches. In one embodiment, the bottom profile comprises a dome corner radius R2 connecting a dome in the bottom profile to a chime in the bottom profile, and wherein R2 is greater than 0.080 inches, and in a particular embodiment is between 0.080 and 0.15 inches. In another embodiment, the bottom profile further comprises a nose portion having a radius R3, and wherein R3 is at least 0.048 inches. In another embodiment, the bottom profile comprises a dome and a dome corner radius R2. The dome tangentially intersects the dome corner radius R2 at a point R. The included angle α between lines Ll and L2 is between about 45 degrees and about 55 degrees, where line Ll extends from the center of curvature of the dome corner radius R2 in a direction perpendicular to a longitudinal axis of the can body, and line L2 extends from the center of curvature of the dome corner radius and intersects the point R. BRIEF DESCRIPTION OF THE DRAWINGS A presently preferred embodiment of the invention is described below in conjunction with the drawings, in which like reference numerals refer to like elements in the various views, and in which: Figure 1 illustrates the growth phenomenon in can bottom profiles; Figure 2 illustrates the drop deformation in can bottom profiles; Figure 3 illustrates the buckle phenomenon in can bottom profiles; Figure 4 is a cross-sectional view of a can body showing a bottom profile in accordance with the invention; Figure 5 is a detailed view of a portion of the bottom profile in the region of the dome corner radius and chime, illustrating the dome angle α defined between lines Ll and L2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

In a first aspect, an improved bottom profile for one-piece drawn and ironed beverage can body is provided. The can body is made from aluminum having a gauge thickness, in the preferred embodiment, of approximately 0.0108 inches, and meets all specified performance requirements for drop, growth and buckle, will be explained further below. The improved bottom profile provides for improvements in bottom performance, reduction in bottom wrinkling, and reduction in bottom thinning. The improved bottom profile can be formed by a domer assembly in a standard drawing and ironing machine, without requiring any subsequent bottom profile reforming operation or apparatus to increase the strength of the bottom profile. The presently preferred embodiments balance all the various bottom profile parameters with 0.0108 gauge aluminum material and meets can bottom performance criteria without requiring the use of separate bottom reforming. Furthermore, preliminary indications are that further downgauging of the aluminum below 0.0108 starting gauge (e.g., to 0.01075 inches) is possible without requiring reforming. Some modification may be needed to the bottom profile from the disclosed embodiments to meet drop requirements with lighter gauge materials, but from the present disclosure such modifications can be achieved without undue experimentation by persons skilled in the art. In a first aspect, and improved bottom profile for one-piece drawn and ironed beverage can body is provided. The can body is made from aluminum having a gauge thickness of 0.0108 inches or thinner. The bottom profile has a stand portion having an imier nose radius and an outer nose radius, a chime adjacent to the stand portion and having a chime length, a dome portion having two radii of curvature RIa and RIb, and a dome corner radius R2 joining the chime to the dome radius RIb and having a dome corner radius of curvature. The inner nose radius and outer nose radius, chime length, dome radius (radii) of curvature and dome corner radius are all selected relative to each other so as result in the can body meeting customer requirements for can bottom performance in terms of buckle, drop and growth. In a particular embodiment, the dome radius RIa is greater than 1.5 inches and radius RIb is between 0.2 and 1.0 inches, and radius R2 is between 0.060 and 0.120 inches. Furthermore, the can body including bottom profile are formed in a body former, without the use of a further bottom profile reforming process or apparatus to meet the objectives for can body performance. In a preferred embodiment, the dome tangentially intersects the dome corner radius at a point R (shown in the drawings), and wherein the included angle α ("dome angle" herein) between lines Ll and L2 (also shown in Figure 5) is between about 45 and 55 degrees and more preferably between 47 1A degrees and about 52 1A degrees, where line Ll extends from the center of curvature of the dome comer radius in a direction perpendicular to the longitudinal axis of the can body, and line L2 extends from the center of curvature of the dome corner radius and intersects the point R. The dome corner radius also tangentially intersects the adjacent portion of the bottom profile, i.e., the chime leg. In a second aspect, a method is provided of manufacturing a can body from an aluminum blank having a gauge thickness of 0.0108 inches or thinner, comprising the steps of forming a cup from said blank and drawing and ironing the cup in a body former to form a can body, wherein the can body includes a bottom profile. The body former has tooling to form the following features in the bottom profile: a stand portion having an inner nose radius and an outer nose radius, a chime adjacent to the stand portion and having a chime length, a dome portion having at least one dome radius of curvature, and a dome corner radius joining the chime to the dome and having a dome corner radius of curvature. The dimensions of the tooling forming the inner nose radius and outer nose radius, chime length, dome radius (radii) of curvature and dome corner radius are selected relative to each other so as result in the can body meeting customer requirements for can bottom performance in terms of buckle, drop and growth and wherein subsequent to the drawing and ironing step no further bottom profile reforming process or apparatus is applied to the can body to provide further strengthening of the bottom profile of the can body in order to meet the requirements for can bottom performance. The method continues with a step of necking the can body. hi a particular embodiment, a drawn and ironed can body is provided. The can body includes a generally cylindrical side wall, a bottom portion integral with the side wall and closing off one end of the can body, the bottom portion having a profile comprising a stand portion having an inner nose radius and an outer nose radius, a chime adjacent to the stand portion and having a chime length, a dome portion having at least one dome radius of curvature, and a dome corner radius joining the chime to the dome and having a dome corner radius of curvature. The dome intersects the dome corner radius at a point R, and wherein the included angle α between lines Ll and L2 is between about 47 1A degrees and about 52 1A degrees, where line Ll extends from the center of curvature of the dome corner radius in a direction perpendicular to the longitudinal axis of said can body, and line L2 extends from the center of curvature of the dome corner radius and intersects the point R. The dome corner radius is between 0.06 and 0.12 inches, and the chime length is between 0.060 and 0.080 inches, the inner and outer nose radii are between 0.050 and about 0.060 inches. The bottom profile in accordance with a preferred embodiment is shown in Figure 4 and now will be described in detail. Figure 4 is a cross-sectional view of a can bottom profile 10. The can body is symmetrical about a longitudinal axis 15. The dome portion 14 includes two portions with different radii of curvature, a central or inner portion 18 having a radius RIa, and a peripheral or outer portion 20 having a radius RIb. The outer portion 20 connects with the chime or leg 16 via a dome corner radius 22 having a radius R2. The dome corner radius 22 is tangential with both the peripheral dome portion 20 and the chime 16. The chime 16 is inclined at a positive angle αi, referred to herein as the chime angle. The chime or leg 16 leads to the nose or stand portion 12. The nose 12 may have one continuous radius for both the inner and outer portions 26 and 28 (see Figure 5), or, alternatively have separate radii, shown as the inner and outer nose radii R3i and R3o in Figure 5. The bottom profile 10 further includes an outer chime 30, arranged at an outer chime angle αo, a profile radius 32 having a radius of curvature R4, a profile portion 34 arranged at a profile angle β, a punch radius portion 36 having a radius R5, and a transition region 38 where the material is progressively thinned to form the thin sidewall of the can body. The transition region 38 is formed at a lower transition angle θ relative to the longitudinal axis 15.

To manufacture the can body and profile, a cup is made from a circular blank of aluminum in a cupper apparatus and the cup is sent to a draw and iron body maker. A punch is inserted in the cup and the cup is drawn and ironed in the body maker. Domer tooling at the base of the body maker forms the bottom profile shown in Figure 4. The manufacturing process is conventional and known in the art, and described in the patents cited previously. In the illustrated embodiment, the punch has a punch diameter A which fits closely inside the body of the cup during the re-drawing and ironing process. The domer tooling has a tooling clearance x relative to the punch nose tooling which sets the inner chime angle to a positive value to allow the can body to be stripped from the body maker. In order to meet customer requirements for can bottom performance (buckle, drop and growth) and meet targets for thinning and wrinkling, careful study of the performance elements, and the contributions of the various parameters to these elements, was performed using a finite element analysis modeling of the can body bottom profile. From this study, and subsequent experiments on actual cans made with the profile, we have determined that it is possible to make a can body from approximately 0.0108 gauge aluminum which meets customer requirements without using a subsequent bottom profile reforming process or apparatus. These standards for bottom performance are currently 0.050 maximum growth g (Figure 1), 90 PSI buckle strength, and a 5.5 inch can drop height. In the course of our study, we have found that fine tuning of following parameters relative to each other were particularly significant in meeting our objective: the nose radius (both inner nose radius and outer nose radius), chime length, dome radii of curvature, dome angle α, and dome corner radius. As to the dome radii, we have chosen a dome with two radii. The central portion with radius RIa can be made with a relatively large radius. The peripheral portion, with radius RIb, has a substantially less radius in order to place the stand or nose at the correct location. This permits us to use a relatively large dome corner radius R2, without significantly reducing the drop characteristics, contrary to conventional wisdom. In fact, increased buckle and drop values are observed at the same time with the preferred embodiment. We are able to use a larger dome corner radius R2 given our selection of relatively large central dome radius RIa, i.e., one with a radius of curvature greater than 1.5 inches, and the relatively small peripheral dome radius, i.e., one with a radius of curvature of between 0.2 and 1.0 inches. It may be possible to substitute a dome with three or more radii of curvature, or use a dome with a constantly varying radius of curvature, in less preferred embodiments. In a preferred embodiment, and as shown in Figure 5, the dome 14 (i.e., peripheral dome radius 20) tangentially intersects the dome corner radius 22 at a point R (shown in the Figure 5). The point R, and the included angle (dome angle α) between lines Ll and L2, are carefully chosen to optimize buckle, drop and growth characteristics. The included angle α between lines Ll and L2 (shown in Figure 5) is preferably selected to be between about 45 and 55 degrees, and more preferably between about 471^ degrees and about 52 1A degrees. Ll is defined as a line that extends from the center of curvature 24 of the dome corner radius 22 in a direction perpendicular to the longitudinal axis 15 of the can body (shown in Figure 4), and line L2 extends from the center of curvature 24 of the dome corner radius 22 and intersects the point R. Preferred ranges and a presently preferred value for a specific 12 oz. beverage can embodiment with the can bottom profile of Figures 4 and 5 are set forth in Table 1.

TABLE 1

Variable Typical Range (inches) Value (inches) A punch diameter 2.5980 -2.6030 2.600 D dome depth 0.420 - 0.435 0.433 RIa dome radius (central) 1.600 - 2 1.905 RIb dome radius (peπpheral) 0.200 - 1 0.400 R2 dome corner radius 0.060 - 0.15 0.120 R3i inner nose radius 0.040- 0.060 0.050 R3o outer nose radius 0.040 - 0.060 0.050 Ds stand diameter 1.864 - 1.904 1.864 Y profile height .360 - .380 0.378 L chime length 0.060 - 0.080 0.075 ai chime angle 2 - 5 degrees 2 degrees chime tooling clearance 0.010 - 0.015 0.015 R4 profile radius 0.089 - .100 0.100 R5 punch radius 0.180 - 0.200 0.200 ao outer chime angle 20 - 25 degrees 250 O' β profile angle 28 - 35 degrees 30° 0' θ lower transition angle 1 — 1.5 degrees 1.075° α dome angle 45-55 degrees 50 degrees Table 2 sets for the various design parameters, describes their function, and explains the

trends in variation of values for the parameters.

TABLE 2

Parameter Function Trend

DEFINES THE BODY AS DIAMETER INCREASES: DIAMETER OF THE CAN CAPACITY INCREASES

D PROVIDE BUCKLE RESISTANCE AS DOME DEPTH INCREASES: BUCKLE RESISTANCE INCREASES

RIa PROVIDE DOME CURVATURE AS RADIUS INCREASES: TO RESIST BUCKLE AND DROP DROP RESISTANCE FORCES DECREASES

RIb PROVIDE DOME CURVATURE AS RADIUS INCREASES: TO RESIST BUCKLE AND DROP DROP RESISTANCE FORCES (ADDED SPECIFICALLY DECREASES TO IMPROVE DROP)

R2 BLEND DOME PROFILE AS RADIUS INCREASES: INTO CHIME AREA BUCKLE RESISTANCE INCREASES, DROP DECREASES

R3i STRENGTHEN BOTTOM AND AS RADIUS INCREASES: BLEND IN WITH RIDING SURFACE BUCKLE RESISTANCE INCREASES, GROWTH VALUE INCREASES, THINNING DECREASES

R3o STRENGTHEN BOTTOM AND AS RADIUS INCREASES: BLEND IN WITH RIDING SURFACE GROWTH VALUE INCREASES, THINNING DECREASES

Ds TYPICALLY DETERMINES AS DIAMETER INCREASES: THE COMPATIBLE END SIZE FOR BUCKLE DECREASES, STACKING WRINKING DECREASES

profile EFFECTS STACKING, AS Y INCREASES: height (Y) BOTTOM PERFORMANCE AND PERFORMANCE FORMABILITY INCREASES, WRINKLING INCREASES

Chime L HAS A DIRECT INFLUENCE AS LEG INCREASES: ON BOTTOM PERFORMANCE BUCKLE INCREASES, DROP INCREASES, TYPICALLY THINNING INCREASES

at ADDS TO BUCKLE RESISTANCE AS ANGLE INCREASES: BUCKLE DECREASES, THINNING DECREASES

tooling SETS THE INNER CHIME ANGLE AS CLEARANCE INCREASES: clearance BUCKLE DECREASES, THINNING DECREASES

R4 MAKES THE PROFILE STACKABLE

R5 BLEND TRANSITION TO BOTTOM AS RADIUS INCREASES: BUCKLE RESISTANCE DECREASES, GROWTH VALUE INCREASES, WRINKLING DECREASES

αo LOCATE STACKING RADIUS ON OUTER PROFILE

PROVIDES BOTTOM STRENGTH AS ANGLE INCREASES: TO A PROFILE BUCKLE INCREASES, GROWTH VALUE DECREASES, WRINKLING INCREASES

PROVIDES A TRANSITION FOR AS ANGLE INCREASES: MATERIAL THICKNESS FROM CAN WEIGHT DECREASES, STARTING GAUGE TO MIDWALL AXIAL LOAD DECREASES, HEEL DENTS INCREASE Dome angle PROVIDES DROP PERFORMANCE AS ANGLE INCREASES: α DROP RESISTANCE DECREASES

Table 3 sets forth performance data for a can made in accordance with the present

invention. The results show that the can bottom profile meet the customer specifications

shown in the right hand column without requiring reforming.

TABLE 3

PERFORMANCE DATA - 0.0108" STARTING GAUGE

Minimum Maximum Average Standard Customer Deviation Specifications

Dome Growth 0.036 0.048 0.043 0.0039 0.050 max @ 75 (in.)

Bottom Buckle 95 99 97.7 1.6 90 min (psig)

Single Can drop 11 9.5 1.0 5.5 min (in.)

Axial Load 255 280 270.6 9.1 avg. - (3 X Std. Dev.) > 76

Further finite element analysis experiments' were conducted to determine the effect of

certain parameters in producing wrinkles and thickness reduction (thinning) in the bottom

profile. It was determined that increasing the Y dimension (Figure 4) produced a significant increase in the occurrence of wrinkles, and increasing the punch radius R5 had a significant effect on reducing wrinkling. Increasing the nose radius R3 had a relatively significant effect in lowering the thickness reduction.

Variations from the specifics of the preferred embodiment are contemplated without departure from the scope of the invention. We have demonstrated that it is possible to make acceptable cans without requiring subsequent bottom profile reforming from aluminum with a starting gauge of 0.0108 inches. The teachings are also adaptable for forming cans of thinner gauge without reforming, for example cans with gauge of 0.01075 inches.