Patent Application
20050194388
A. Field of the 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 U.S. Pat. Nos. 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. Pat. Nos. 4,179,909; 4,620,434; 4,298,014, all assigned to National Can Corporation, the contents of which are incorporated by reference herein.
In 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. Pat. Nos. 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. Ihly, U.S. Pat. No. 5,934,127 also describes can bottom reforming apparatus. Other patents of interest include Gouillard, U.S. Pat. No. 6,132,155 and Saunders et al., U.S. Pat. No. 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
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
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
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, 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 0.01075 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 5½ inches, and has acceptable bottom wrinkling and bottom thinning characteristics.
We have described herein a beverage can having a can body made from aluminum having a gauge thickness of 0.01075 inches or less, 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:
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 L1 and L2 is between about 45 degrees and about 55 degrees, where line L1 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.
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:
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 starting gauge thickness, in the preferred embodiment, of approximately 0.01075 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 0.01075 inche gauge aluminum material and meets can bottom performance criteria without requiring the use of separate bottom reforming. Furthermore, testing has indicated that that further downgauging of the aluminum below 0.01075 inches, and to 0.01060 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 one specific embodiment, 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 0.01075 inches or less. The bottom profile has 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 two radii of curvature R1a and R1b, and a dome corner radius R2 joining the chime to the dome radius R1b 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 R1a is greater than 1.5 inches and radius R1b 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 L1 and L2 (also shown in
In a second aspect, a method is provided of manufacturing a can body from an aluminum blank having a gauge thickness of 0.01075 inches or less, 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.
In 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 L1 and L2 is between about 47½ degrees and about 52½ degrees, where line L1 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
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
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 0.01075 inch 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 (
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 R1a can be made with a relatively large radius. The peripheral portion, with radius R1b, 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 R1a, 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
Preferred ranges and a presently preferred value for a specific 12 oz. beverage can embodiment with the can bottom profile of
Table 2 sets for the various design parameters, describes their function, and explains the trends in variation of values for the parameters.
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 (
While the invention has been tested and found to work with starting gauges of 0.01075 inches, further testing has shown satisfactory results for growth, buckle and drop, without reforming of the bottom profile at a starting gauge of 0.01060 inches. It is predicted that satisfactory results can be obtained for gauges as thin as 0.01040 inches by persons skilled in the art without undue experimentation, although some variation of the parameters from the presently preferred embodiment and testing can be expected. Further down gauging of the metal is possible below 0.01040 inches, although good results without bottom reforming may require a material change and use of a more advanced aluminum alloy than those commonly used for beverage cans today.
Variations from the specifics of the preferred embodiment are contemplated without departure from the scope of the invention.
