WO1999007605A1

WO1999007605A1 - Can body with internal radiused profile

Info

Publication number: WO1999007605A1
Application number: PCT/US1998/016350
Authority: WO
Original assignee: Reynolds Metals Company
Priority date: 1997-08-07
Filing date: 1998-08-05
Publication date: 1999-02-18
Also published as: AU8693998A

Abstract

An aluminum can body (20) formed by a drawn and ironed process comprising a bottom wall (22) of input gage thickness, a cylindrical sidewall (26) extending away from the bottom wall and having an open end, the sidewall having a thinwall section of a thickness which is less than gage thickness. A nose transition area (50) joins the bottom wall to the thinwall section and has a curved surface extending between the bottom wall (22) and the thinwall section with the curved surface being tangent to the thinwall section (26) and the bottom wall. The sidewall includes a thickwall section at its open end (30) and a thickwall transition area joining the thinwall section to the thickwall section. The thickwall transition area (326) has an internal radiused surface extending between the thinwall section and the thickwall section. The radiused surfaces in the transition areas (50, 326) reduce the metal content of the can body without sacrifycing the structural integrity of the can.

Description

CAN BODY WITH INTERNAL RADIUSED PROFILE

BACKGROUND OF THE INVENTION

This invention relates generally to aluminum beverage cans and more particularly to an aluminum can of novel design in which the amount of metal in the can is reduced without sacrificing the structural integrity of the can.

The most common commercial 12-ounce aluminum can is constructed in two pieces, an open ended integral can body including a bottom and a generally cylindrical sidewall formed by a drawn and ironed (D & I) process and a separate lid or end double seamed over the open end after the can is filled with product. A general description of the history of the two-piece can and its method of manufacture is set forth in an article entitled "The Aluminum Beverage Can " which appeared in the September, 1994 issue of Scientific American. As pointed out in that article there is a continuing effort to reduce the amount of metal in the can while maintaining necessary strength of the can to withstand column loads of about 250 pounds for an empty can body and internal pressure of about 90-100 psi for a filled container.

Historically, most downgaging or reduction of metal in the can has come at the expense of can wall thickness but current can wall thickness is nearing minimum acceptable customer limits. If downgaging is to continue, metal will have to be removed from other areas of the can without sacrificing strength.

A common conventional can body is currently manufactured from an aluminum blank 5.465 inches diameter with an input gage thickness of 0.01 12 inches. The blank is first drawn into a cup of about 3.5 inches diameter, and then redrawn and ironed into a can body including a domed bottom having a peripheral nose section joining a substantially cylindrical vertical thinwall having a thickness of 0.0039 inches, an outer diameter of about 2.6 inches, and a height of about 4 3/4 inches after trim. The domed bottom is of input gage thickness (0.01 12 inches) and the peripheral nose section includes a transitional area in which the wall thickness decreases from 0.01 12 inches to thinwall thickness of 0.0039 inches along a straight taper forming an upwardly diverging cone on the inside surface of the can body. Because of the straight taper, this nose transitional area contains a significant amount of metal .

The upper end of the D & I can body includes a thickwall section from which a reduced diameter neck is subsequently formed, and the thinwall is joined to the thickwall section by a neck or thickwall transition area having a straight taper forming an upwardly converging cone on the inside surface of the can body. This neck transition area also contains a significant amount of metal .

In the prior conventional can the significant amount of metal in the nose and neck transition areas was required to provide sufficient strength to those areas of the can. However, in analyzing the construction and profile of the conventional D & I can, we recognized that if the amount of metal in those transition areas could be reduced while maintaining the strength and stability of the can, significant savings in the cost of the can would result. SUMMARY OF THE INVENTION

Accordingly, the primary object of this invention is to provide an aluminum can of novel design in which the amount of metal contained in the can is reduced without sacrificing the structural integrity of the can.

Another object of the invention is to provide a novel aluminum can in which the amount of metal in the nose transition area and the thickwall transition area is reduced. This is accomplished by replacing the straight tapered conical sections in those areas by full tangency three-dimensional curved sections which have shorter run lengths along the can. thereby increasing the run length or height of the thinwall area of the can. This allows downgaging (decrease in thickness) of the input metal, an increase in thinwall thickness, or longer trim at the top edge of the can body which may be recycled. Economically, downgaging provides the greatest benefit.

Still another object of the invention is to provide the above novel aluminum can in which the three-dimensional curved section at the thickwall transition area coacts with a corresponding curved surface on the can forming punch to facilitate removal of the can body from the punch.

A further object of the invention is to provide a novel radiused punch by which the novel can of the invention may be formed, utilizing apparatus such as that shown in U.S. Patent No. 4,996,865.

Other objects and advantages of the invention will become apparent from reading the following detailed description of the invention wherein reference is made to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a fragmentary sectional view generally illustrating a can body formed by a D & I process;

Fig. 2 is a fragmentary view of the can body of Fig. 1 after it has been subjected to a necking operation;

Fig. 3 is a fragmentary view of a conventional can body illustrating the straight tapered nose and thickwall transition areas on the inside surface of the can body;

Fig. 4 is a view similar to Fig. 3 but illustrating the novel can body of the invention wherein the nose and thickwall transition areas have full tangency three-dimensional curved inside surfaces;

Fig. 5 is an enlarged fragmentary view of the nose transition area of the conventional can body of Fig. 3;

Fig. 6 is an enlarged fragmentary view of the radiused nose transition area of the can body of the invention shown in Fig. 4;

Fig. 7 is an enlarged fragmentary view of the thickwall transition area of the conventional can body of Fig. 3;

Fig. 8 is an enlarged fragmentary view of the radiused thickwall transition area of the can body of the invention shown in Fig. 4;

Fig. 9 is a fragmentary schematic view illustrating the line contact which occurs between the tapered thickwall transition area of the conventional can body of Fig. 3 and its corresponding forming surface on a conventional D & I punch as the body is stripped from the punch;

Fig. 10 is a view similar to Fig. 9 but illustrating the point contact which occurs between the radiused thickwall transition area of the can body of the invention shown in Fig. 4 and its corresponding forming surface on a radiused D & I punch as the body is stripped from the punch;

Fig. 1 1 is a fragmentary section view of a novel radius punch by which the can body of Fig. 4 may be formed. DETAILED DESCRIPTION OF THE INVENTION

Referring to Fig. 1 , typically a one-piece can body 20 produced by a known D & I process includes a domed bottom 22 having a peripheral nose section 24, a generally cylindrical sidewall including a thinwall 26. and a nose transition area 28 joining nose section 24 to thinwall 26. The upper open end of the sidewall includes a thickwall section 30 and a thickwall transition area 32 joining thinwall 26 to thickwall 30.

The D & I can body 20 of Fig. 1 is then subjected to a necking operation to form a reduced diameter neck 34 (Fig. 2) and after the can is filled a lid is seamed on the top flange of neck 34.

Figs. 3, 5 and 7 illustrate the profile of a conventional can body 20a. Bottom 22a and its peripheral nose 24a are of input gage thickness, e.g. 0.01 12 inches. Thinwall 26a may be 0.0039 inches and thickwall 30 may be 0.0065 inches. The interior surface 40 of the nose transition area 28a extends along a straight taper from a point P I on nose 24a where it intersects with nose radius R„ to a point P2 where it merges with thinwall 26a, the tapered surface 40 forming a diverging cone from PI to P2 within the interior of can body 20a. The slope angle A, of surface 40 is determined by the " rise" i.e. the radial distance between PI and P2, over the "run" i .e. the longitudial distance between PI and P2.

Similarly, the interior surface 42 of the thickwall transition area 32a extends along a straight taper from point P3 of intersection with thinwall 26a to point P4 of intersection with thickwall 30, the tapered surface 42 forming a converging cone from P3 to P4 within the interior of can body 20a. The slope angle A₂ of surface 42 again is determined by the rise over run.

The tapered cone surface 40 joins nose radius Rn at P I and thinwall 20a at P2 at sharp angles, and similarly tapered cone surface 42 joins thinwall 26a at P3 and thickwall 30 at P4 at sharp angles, thus creating undesirable stress concentrations on those areas. Traditionally, the standard taper/conical punch is hand polished at those sharp edges corresponding to points PI , P2, P3 and P4 to break the edges and to try to blend those areas on the can body. However the hand blending is not uniform and does not eliminate the stress concentrations. In addition breaking those sharp edges adds metal to can body 20a. Moreover the run length of tapered surfaces 40 and 42 has to be long enough to provide sufficient metal in the transition areas 28a and 32a to withstand the required column loads. In the conventional can for the nose transition area 28a, the rise was 0.0078 inches and the run was 0.5736 inches making the rise/run ratio 0.0136. For the thickwall transition area 32a. the rise was 0.0026 inches and the run was 0.2921 inches, with the rise/run being 0.0089.

In a slightly different conventional can, instead of the transition areas having a single taper, two tapers on different angles are used, but this design suffers from the same problems as the single taper.

Referring now to Figs. 2, 6 and 8 which illustrate a can body 20b constructed according to the invention we have discovered by replacing the tapered conical surfaces 40 and 42 in the conventional can body with smooth radiused curved surfaces 50 and 52, the can is stronger in a column load condition with less metal in the transition areas 28b and 32b. This is due to the three dimensional curvature of surfaces 50 and 52 and the fact that surface 50 is tangent to nose radius Rn at P5 and thinwall 26b at P6 and surface 52 is tangent to thinwall 26b at P7 and thickwall 30b at P8. Consequently stress concentrations are eliminated in those areas.

As shown in Figs. 4 and 6, surface 50 is formed on a single radius R, which is within the range of 9 to 50 inches. A radius R, smaller than 9 inches reduces column strength and one larger than 50 inches increases run length and adds metal .

For a radius R, of 22.7650 inches, surface 50 extends through a rise of 0.0066 inches and a run of 0.5481 inches, thus producing a rise/run ratio of 0.0120.

Comparing the transition area 28b of the invention with the conventional transition area 26a, even though the rise/run ratios (0.0120 vs. 0.0136) are roughly equal, the rise 0.0066 inches for surface 50 is much smaller than the rise 0.0078 inches for tapered surface 40. and the run 0.548 inches for surface 50 is appreciably shorter than the run 0.5736 inches for tapered surface 40. Thus, less metal is present in transition area 28b than in area 28a.

As shown in Figs. 4 and 8, contoured surface 52 includes an inwardly curved section of radius R₂ tangent to thinwall 26b at P7 and an outwardly curved section of radius R, tangent to thickwall 30b at P8, with radii R₂ and R, tangent to each other at their point of intersection P9. An angle B perpendicular to a line drawn through the center points of radii R2 and R3 represents how steep surface 52 is. The radiused profile allows this angle to be much steeper than the angle A₂ formed by the taper 42 on body 20a.

For a radius R₂ = 1 .200 inches and radius R, = 4.250 inches, surface 52 extends through a rise of 0.0019 inches and a run of 0. 1458 inches, with the rise/run ratio being 0.0130. The higher the rise/run ratio the steeper the angle B, and the less metal in area 32b.

Comparing the thickwall transition area 32b of the invention with the conventional area 32a the rise/run ratio of 0.0130 for area 32b is substantially greater than the 0.0089 ratio for area 32a and the run 0. 1458 inches for area 32b is about half the run 0.2921 inches for area 32a. Again, less metal is present in area 32b than in area 32a, yet area 32b has greater strength .

Because of the increased strength of area 32b, the thickness of thickwall 30b is reduced by 0.0007 inches. Also since the run lengths of areas 28b and 32b are shorter than areas 28a and 32a, thinwall 26b in can body 20b is longer. This allows downgaging of the input metal, increased thickness of thinwall 26b, or longer trim from the top edge of thickwall 30b after the D & I forming. Economically, downgaging provides the greatest benefit. The radiused profile of can body 20b permits downgaging of 0.0006 inches from the current input metal thickness of 0.01 12 inches which is estimated to produce a savings of about $ 18 million/year based on production of about 16 billion cans per year. This is accomplished while at the same time increasing the overall strength of the can.

Another advantage afforded by radiused surface 52 is that it facilitates removal or stripping of can body 20b from the radiused punch on which the body is formed. Fig. 9 illustrates how tapered surface 42 of a conventional body 20a has full line contact with a mating tapered forming surface on a conventional punch 60a as the body is being stripped from the punch in the direction of arrow 62. Because of this full line contact, the thickwall rise/run ratio on tapered surface 42 and conventional punch 60a can not exceed 0.009. If it does, stripping of the can body 20a will be difficult and damage to the body may result.

In contrast as shown in Fig. 10, radiused surface 52 of can body 20b has point contact with a mating radiused forming surface 70 on a radiused punch 60b as the body is being stripped from the punch. The radius design allows rise/run ratios as high as 0.01 .

Fig. 1 1 illustrates a generally cylindrical radiused D & I punch 60b by which the radiused can body 20b is formed . Punch 60b has an outer surface profile which forms the interior profile of body 20b for a subsequent smooth die necking process. Punch 60b includes a nose piece 61 having a curved dusrve 62 which forms bottom22b, a front radiused section 64 which forms contoured surface 50 of transition area 28b, an outer surface 66 which forms thinwall 26b, a reduced diameter surface 68 which forms thickwall 30b, and a radiused transition section 70 which forms contoured surface 52 of transition area 32b. Outer surface 66 tapers and enlarges ( .0001 to .0002 inches) from the nd of surface 64 to the beginning of section 70, thus providing thinwall 26b with three- dimensional curvature. The D &I forming operation may be performed by apparatus such as that described in U.S. Pat. 4,996,865, with the radiused punch 60b being substituted for the punch 18' illustrated in that patent. The profile of can body may be varied in some respects. For example, instead of forming surface 50 on a single radius, it may be formed with a multi- radius profile, with each successive radius from P5 to P6 being larger than and tangent to the preceding radius. Theoretically, an infinite number of radii will provide the best performance.

Similarly, instead of the single radius sections R² and R , each may include a plurality of radii with each successive radius in each section increasing as thickwall 32b is approached.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1 . A one-piece metal can body formed by a drawn and ironed process comprising a bottom wall of input gage thickness, a generally cylindrical sidewall extending away from said bottom wall and having an open end, said sidewall having a thinwall section of a thickness which is substantially less than said input gage thickness, a nose transition area joining said bottom wall to said thinwall section and having an internal curved surface extending between said bottom wall and said thinwall section.

2. The can body of claim 1 , wherein said curved surface is substantially tangent to said thinwall section and said bottom wall .

3. The can body of claim 2, wherein said curved surface is formed on a single radius.

4. The can body of claim 3. wherein said radius is greater than nine inches and less than fifty inches.

5. The can body of claim 2, wherein said curved surface is formed with a multi-radius profile with each successive radius from said bottom wall to said thinwall section being larger than and tangent to the preceding radius.

6. The can body of claim 1 . comprising a thickwall section at the open end of said sidewall, a thickwall transition area joining said thinwall section to said thickwall section, said thickwall transition area having an internal radiused surface extending between said thinwall section and said thickwall section.

7. The can body of claim 6, said radiused surface including a first inwardly curved section formed on a first radius which is tangent to said thinwall section and a second outwardly curved section formed on a second radius which is tangent to said thickwall section, said first and second radii being tangent to each other at their point of intersection.

8. A one-piece metal can body formed by a drawn and ironed technique comprising a bottom wall of input gage thickness, a generally cylindrical sidewall extending away from said bottom wall and having an open end, said sidewall having a thinwall section of a thickness which is substantially less than said input gage thickness, a thickwall section at the open end of said sidewall, a thickwall transition area joining said thinwall section to said thickwall section, said thickwall transition area having an internal radiused surface extending between said thinwall section and said thickwall section.

9. The can body of claim 8, said radiused surface including a first inwardly curved section formed on a first radius which is tangent to said thinwall section and a second outwardly curved section formed on a second radius which is tangent to said thickwall section, said first and second radii being tangent to each other at their point of intersection.

a nose transition area joining said bottom wall to said thinwall section and having an internal curved surface extending between said bottom wall and said thinwall section.

10. In a one-piece metal can body formed by a drawn and ironed process comprising a bottom wall of input gage thickness, a generally cylindrical sidewall extending away from said bottom wall and having an open end, said sidewall having a thinwall section of a thickness which is substantially less than said input gage thickness, a nose transition area joining said bottom wall to said thinwall section and having an internal surface extending between said bottom wall and said thinwall section, a thickwall section at the open

of said sidewall. a thickwall transition area joining said thinwall section to said thickwall section and having an internal surface extending between said thinwall section and said thickwall section; the improvement wherein said nose transition area internal surface

(a) is concave,

(b) is continuously curved,

(c) is substantially tangent to both said thinwall section and said bottom wall, and

(d) has one or more radii greater than nine inches and less than fifty inches.

1 1. The can body of claim 10, wherein said nose transition area internal surface has a single radius.

12. The can body of claim 10, wherein said nose transition area has multiple radii, all of which are greater than nine inches and less than fifty inches, with each successive radius from said bottom wall to said thinwall section being larger than and tangent to the preceding radius.

13. In a one-piece metal can body formed by a drawn and ironed process comprising a bottom wall of input gage thickness, a generally cylindrical sidewall extending away from said bottom wall and having an open end, said sidewall having a thinwall section of a thickness which is substantially less than said input gage thickness, a nose transition area joining said bottom wall to said thinwall section and having an internal surface extending between said bottom wall and said thinwall section, a thickwall section at the open end of said sidewall, a thickwall transition area joining said thinwall section to said thickwall section and having an internal surface extending between said thinwall section and said thickwall section; the improvement wherein saad thickwall transition area internal surface, as viewed in cross-section, is an ogee curve whose ends are substantially tangent to both said thinwall section and said thickwall section.

14. A punch for use in producing a one-piece metal can body by a drawn and ironed process, the can body having a bottom wall, a generally cylindrical sidewall extending away from the bottom wall and having an open end, and a nose transition area joining the bottom wall to said sidewall and having an internal curved surface extending between said bottom wall and said sidewall, said punch comprising a generally cylindrical outer surface for forming said sidewall, a nose piece at one end thereof for forming said bottom, and a curved surface extending between said nose piece and said outer surface for forming the internal curved surface in the nose transition area of the can body.

15. The punch of claim 14, wherein said curved surface is substantially tangent to said outer surface and said nose piece.

16. The punch of claim 15, wherein said curved surface is formed on a single radius.

17. The punch of claim 16, wherein said radius is greater than nine inches and less than fifty inches.

18. The can body of claim 15. wherein said curved surface is formed with a multi-radius profile with each successive radius from said nose piece to said outer surface being larger than and tangent to the preceding radius.

19. The punch of claim 14, comprising a reduced diameter surface at the other end thereof for forming a thickwall section adjacent the open end of said sidewall, a second curved surface extending between said outer surface and said reduced diameter surface for forming an internal radiused surface extending between a thinwall section and thickwall section of the sidewall of the can body.

20. The punch of claim 19, said second curved surface including a first outwardly curved section formed on a first radius which is tangent to said outer surface and a second inwardly curved section formed on a second radius which is tangent to said reduced diameter surface, said first and second radii being tangent to each other at their point of intersection.

21 . A punch for use in producing a one-piece metal can body by a drawn and ironed process, the can body having a bottom wall, a generally cylindrical sidewall having a thinwall section extending away from the bottom wall and a thickwall section at its upper open end, said punch comprising a generally cylindrical outer surface for forming said thinwall section, a nose piece at one end thereof for forming said bottom, a reduced diameter surface at its other end for forming the thickwall section at the open end of the sidewall, and a curved surface extending between said outer surface and aid reduced diameter surface for forming an internal radiused surface extending between the thinwall section and thickwall section of the sidewall of the can body.

22. The punch of claim 21 , said curved surface including a first outwardly curved section formed on the first radius which is tangent to said outer surface and a second inwardly curved section formed on a second radius which is tangent to said reduced diameter surface, said first and second radii being tangent to each other at their point of intersection.