GB2068887A - Two-piece metal can and a method of forming it - Google Patents

Abstract

A two-piece metal can, designed to be interchangeable with a traditional three-piece can, includes an outwardly-directed bead 12a formed in the side wall, an annular relief 17, a flat ring-shaped section 16, an inner annular wall 15a and a recessed centre panel 15b. The bead and relief co-operate, in a stack of similar cans, with seamed end 18 of a subjacent can. The can is formed by drawing and re-drawing a tubular body having a recessed bottom, and then rotating the body and a male die inserted therein whereby the body is rolled against an eccentrically-movable female die to produce the bead. <IMAGE>

Description

SPECIFICATION Two-piece metal can and method of forming same This invention relates to can ends and more particularly to the bottom end of a two-piece drawn steel food container which is designed to be packed and then processed at high temperature and pressure in a retort. More particularly, in a can where the contents are to be heated above their boiling point and then cooled, the bottom end is subjected to internal pressure and then external pressure.

Each sealed container must be retorted to prevent bacterial growth and spoilage which will generate metabolic products such as organic acids and carbon dioxide; the latter tending to inflate the sealed container causing it to bulge or become unseamed. In order to have commercial sterility (safety) the food must be heated to a state which renders it free of viable forms of micro-organisms which are there or which would reproduce in the future under normal storage conditions. A certain group of high acid foods need not be retort processed, but these acidic foods are hot packed. That is to say that, they are heated to near the boiling point and then packed in the container. Even hot packing places considerable stress on the container.

The combination of the hot fill and the acid is equivalent to retort sterilization of low acid level foods. Foods with pH level of 4.6 or higher must be retored in order to achieve commercial sterility.

In the past it has been the practice to use heavy gauge high stength metal to resist processing stresses in a double seamed on bottom end for a three-piece container, e.g.

85 Ibs per base box plate. In general, the three-piece container is less satisfactory because it costs more, it may require soldering, it produces a needlessly heavy container, it is subject to side seam and double seam leaks and it is wasteful of energy and resources.

More process steps are necessary during the fabrication of a three-piece container. More particularly, such containers include on their ends a deep chuck countersink for strength and chuck clearance, and such a countersink is subject to buckling during processing. A two-piece can with an integral bottom does not require a bottom end chuck countersink for double seaming, but a bottom recess is necessary in order to manufacture a two-piece can with the same height and capacity as a conventional three-piece can so that either may be interchangeably used in the same packing and processing line. Profiling has been used to apply ribs, creases and the like to add rigidity to the bottom of a two-piece can. The weakest area of a drawn two-piece can is the bottom and consequently, the material thickness of the steel is a function of the bottom strength required (buckle resistance).

With only moderate profiling, the pressurized two-piece can bottom may tend to distend and exceed the elastic limit of the metal.

When that happens the can is unacceptable as it will rock about its distended bottom and appear to contain tainted-or spoiled contents.

Consequently, a bottom recess can improve the performance of thin-two-piece cans if such a recess is designed to include work hardened areas of metal which increase the elastic limit of the bottom metal particularly in areas of high stress. The highly worked bottom is more rigid. Spoiled contents will tend to force outward the top end and simplify the process of checking the packed cans.

The large capital investments in equipment for handling three-piece cans in the packing plant cannot be merely written off. A twopiece container which will physically resemble the three-piece container is essential in order to permit continued use of the existing threepiece equipment, e.g., labelling, runways, retort, etc. The 100% interchangeability is recognized in the patent art, see, for example, United States Patent No. 3,912,109 which discloses an approach and several methods of making same. Similarly, see United States Patent No. 3,272,383 which discloses an extruded aluminum can with a recessed bottom profile. Such prior art is typical in its emphasis on duplicating the shape of the three-piece can but fails to teach of a container which is of adequate strength and will protect food without corrosion and move through customer's equipment.For economy and high-speed production a drawn two-piece can made of coil coated metal or subsequently coating a drawn and beaded container should be designed so that the interior coating remains intact even though the bottom is deeply recessed and formed to include a chime-like bead to provide rolling in the track-work and through the labeller and other food packing and processing equipment. The prior art teachings show chime-shaped beads at the bottom of the can. It is very difficult to form a chime-shaped bead without damaging the inside coating surface. More particularly, the use of internal tools to form a chime-shaped bead is detrimental to the coating. In the present invention the forming of a simple bead of prescribed shape is moderate by comparison and prevents undue loading by the inside tools necessary to form a chimeshaped bead.Consequently, the danger of scuffing and sharp bends in reforming which would crack the inside coating is completely eliminated because there is sufficient space inside the bottom can corner to operate a beading tool.

Since drawn two-piece containers offer numerous advantages particularly in the elimination of the side seam and one end seam, it is commerically important that the bottom profile formed in accordance with the preferred method and shape also be able to withstand a retort temperature of 260 F. for thirty minutes or more, and yet be interchangeable in all respects with the three-piece container which from time to time may have to be used on the same package and processing line.

It is, therefore, an object of the present invention to provide a two-piece can bottom profile which is resistant to ultimate stress by improving the elastic limit of the can material particularly in the bottom.

The present invention is a two-piece metal can having a seamless container body of circular cross-section formed of a thin material into an integral side and bottom wall, a circular closure adapted to be joined to said side wall by an annular double seam having interfolded adjacent layers of metal, and a profile of the area of the corner of the side and bottom wall and the bottom wall includes an outwardly extending lower side wall bead which extends the diameter of the can body so that the most distal extent of bead is above the bottom plane of the can an amount equal to about three-quarters the length of a double seam chime, a substantially flat circular ring section extending generally normal to the plane of said side wall and in-line with the outwardmost plane of the container bottom, an inner annular side wall extending into the container from the outardmost plane of said bottom and joining the inside edge of said ring-shaped section to a recessed and domed central panel of said bottom, and an annular relief disposed intermediate said chime-like bead and said outside edge of said ringshaped section.

The present invention is also a method of forming a two-piece metal can having a seamless container body of circular cross-section formed of a thin material into an integral side and bottorn wall with an outwardly extending lower side wall bead above the juncture of said side and the bottom wall and a recessed domed central panel in said bottom wall connected to said bead by a flat circular ringshaped section and an annular relief, the method including the following steps, drawing an elongated cup-shaped container having an integral side and bottom, redrawing and profiling said container and bottom to include an annular wall extending to a domed central recess from a flat rim ring section said wall being tipped inwardly at its upper end toward the axis of said can, and applying a bead in the form of a lateral convolution into said lower side wall of the container body, said bead being disposed above the bottom corner of said side wall for forming a relief beneath the distal portion of said bead and the outer circumference of said ring section.

The profile design concept which permits the objects to be realized is found in a press forming process where the profiling is accomplished in the final drawn die at the bottom of the stroke, in a draw/redraw press. At that stage the bottom profile has all the essentials of the final desired profile including a central recess. The drawn can bearing the preferred profile shape has a flat outer circumferential portion extending from the corner inwardly to an annular wall concentrically located relative to the axis of the can. The annular wall tips slightly toward the axis and extends inwardly from the circumferential portion forming the boundary of the central recess. The central recess is essentially parallel to the bottom plane defined by the circumferential portion and is formed by doming inwardly along the axis.The resulting bottom profile maximizes the work hardening by increasing the elastic limit of the bottom metal in the areas likely to buckle whereby the strength (buckle resistance) is improved. Similarly, the domed central recess acts in cooperation with the annular wall whereby internal pressure causes the wall to flex away from the axis, and in a spring-like fashion resist the tendency of the dome to pop outward.

The profile as described is applied during a draw/redraw of the precoated steel and forms the bottom of an essentially straight sidewall container. Such a container is then sent to the beading machine where the sidewall and bottom (or stacking) beads are applied to the can sidewall. The bottom stacking bead is placed on the sidewall slightly above the plane of the bottom panel (usually commencing about .035 inch above the plane of the can bottom).

A beading mandrel may be placed inside the can and operates to form the outwardly disposed stacking bead without scuffing or scraping off the bottom interior coatings and making the container vulnerable to corrosion. The position of the annular wall allows ample room for beading at a very low level along the sidewall. It is important that the bead be located just above where the centre of a regular lower chime would be on a 3-piece can; this is because the tracks that guide and, carry cans through a continuous retort will develop wear grooves at the places across which the chimes ride. A simulated chimeshaped bead, while having the dimensions of a chime, will not necessarily follow the groove as accurately as the low level bead herein described. That is to say that, it is easier for a smaller bead to follow the larger groove than a chime-shaped bead to follow a chime worn groove. Similarly, the position of the bead relative to the sidewall is important. A bead which is located more nearly at the level where the top of a chime might be, is likely to interfere with the chime worn groove whereas a low level bead is sure to fit more centrally within the chime worn groove.

The metal working of the bottom panel which provides the central recess is done in such a manner that the amount of material in the blank need not be increased. More particularly, the central recess is formed substantially from stretching the metal from the bottom panel and as such has little or no bearing on the sidewall length or remaining flange of the drawn container. This is beneficial from the standpoint of economical material usage and is important from the standpoint of work hardening only the bottom to improve the elastic limit of the bottom panel. The formed central recess may have Luder's lines which indicate that a level of stress 1 to 2%, i.e., metal working has taken place such that the overall strength is increased.

The completed can has identical height and capacity (volume) when compared to a conventional three-piece can. Consequently, the same height label as used on a three-piece can is usable and similarly this two-piece can configuration will roll smoothly through any labeller and processing equipment or trackwork designed for three-piece containers due to the same rolling diameter at both ends.

For purposes of high-speed production and the dilnint.-tion oF subsequent post spray treatment it is pi-t;-red that the metal for this twopiece can woody be drawn from a precoated stock. More particusarly, steels such as TFS-CT or E7GL", the latter having from 10 to 135 pounds per base box of electrolytically deposited tin work well. The tinplate would be continuously cast, continuously annealed alu minus, (or silicon) killed or rimmed and stabilized ingot eat steel.Steel thickness from 55 pounds per base box up to 85 pounds per base box with a ,:mper of T-1 to T-6 single reduced plate or double reduced plate of DR-7 a DR-9 can be used. The preferred emboa'irnant is a T-4 steel of the TFS-CT type. Ouch 3 material is precoated with an epoxy phsnolio exterior surface (of can body) to prevent corrosion and an organosol interior surface (of can body) to protect the metal from the foole's which will ultimately be packed and processed in the container.The precoated mete is Fed into a press in which it is blanked, supped, drawn and redrawn into a can-like cylindrical shape having a side and integral bottom ''all, the side length being almost t.sics the diameter of the can body. It has been found that the work hardening of the bottom during profiling will raise the hardness of the T-4 steel approaching the level of DR-9 double reduced steel.Consequently, the containe. has the requisite strength across the bosom and in the lower bead, but is formed from he easier to work with 75 pound T-4 see If the metal used for drawing cans eC dw pound DR-9 plate even with a reduced ccjuntsi-sinkt depth buckle strength would remain the same. Some penalty in extra power would be required to form each can.

An embodimen. of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partial elevational view o [ - the prior art three-piece container having double seamed top and bottom ends; Figure 2 is a partial fragmentary enlarged sectional view of the lower corner of the container of the present invention showing the beading tool entering the container wherein the axis and the container and the tool are in line with one another; Fig. 3 is similar to the view of Fig. 2 and shows the beading operation wherein the container is run over by means of a female die to the beading tool by moving the axis of the container with respect to the axis of the beading tool;; Figure 4 is like the view of Fig. 3, but shows the opposite side of the container and beading tool and particularly the clearance between bead die and the centre recess; Figure 5 is a partial cross-sectional view of the entire bottom profile; and Figure 6 is a partial cross-sectional view showing the stack relationship between the double seam below and the preferred bottom wall profile of the present invention.

Fig. 1 is a side partial cross-sectional view of a prior art 3-piece container 10 used to pack comestibles. Such containers are formed of a body rolled into a tube and seamed along a longitudinal side and two ends which are double seamed to the tubular hollow body. It is desirable that the side seam be eliminated and the weight and labour penalties of the additional double seamed end be removed.

Therefore, considerable effort has gone into the development of a drawn hollow 2-piece container to which an end may be double seamed. This is referred to as a 2-piece sani tary can, and such containers are usable for packing comestibles. They are more compact, in terms of material usage and cleaner in terms of number of seams per container.

Efforts to make such containers which are totally interchangeable with the prior art 3piece container have met with many difficult ties, the most important of which, relative to this invention, is the ability to form a lower chime-like bead which will act to replace the lower chime in a prior art 3-piece container.

Such a bead has to perform a number of functions. More particularly, the bead has io have the same diameter as the upper chime of a double seamed container whereby the complete 2-piece container will roll without cocking in the trackwork and processing equipment. Similarly, the lower bead has to provide a space for the labelling. That is to say that, the distance along the side wall between the top part of the lower bead and the bottom part of the upper chime has to be equal to that between the two double seam chimes of a 3-piece container. In addition, the lower bead has to function similarly to a chime in that it must provide increased strength for abuse resistance and aid in rolling and stacking processed containers.

The improvement herein is twofold, being the particular lower bead which substitutes for the chime and the overall can profile (bottom and lower side wall) which permits an appropriate bead to be formed without destroying the inside surface of the container or the overall buckle strength of the bottom. The container is formed of a precoated stock which is blanked and drawn and redrawn into the finished container. Just before all of the drawing is complete, a bottom profile is added which gives the necessary bottom recess and imparts the requisite bottom strength. The recess provides the same internal volume in a 2-piece container as that of a 3-piece container. Profiling is also required to improve the overall bottom strength by work hardening metal.Sanitary cans for comestibles must resist internal and external pressures to which they are subject during processing. The bottom recess configuration is specifically selected to do that. Buckle pressures up to 44 psi are realized. Previous recessed integral ends achieved less than 33 psi buckle pressure, a 38% increases in buckle resistance.

Turning now to Fig. 2, a beading tool 11 is shown entering the container to the depth at which the bead is to be produced. Tool 11 has a bead nose 11 a which is shaped in the preferred configuration and acts to form the container with a lower chime-like bead. The tool 11 enters the can concentrically with respect to the conicainer. That is to say that, the tool 11 is cylindrical and has its central axis in line with the central axis of the container 1 2 upon the entry of the tool into the container 12, same being as formed in the draw/redraw operation. The container 12 is carried in a beading machine which includes an eccentrically movable female beading die 13 positioned outside of the container 1 2 and moved in the direction A, shown by the arrow 3 in Figs. 3 and 4.Female beading die 1 3 includes a complimentary beading surface 1 3a which cooperates with the surface 11 a of the tool 11. In operation the beading die 13 is eccentrically moved toward the container 12 left to right in Fig. 3, whereby the container 12 and the tool 11 which are rotating will be caused to roll against the female die 13. In a manner well known in the industry, the bead 1 2a is thus formed by rolling into the lower side wall of the container 12, see Fig. 4. While the technique for rolling beads is well known, the particular bead 1 2a and its location of the present invention are not. The reason for this is that heretofore, it has been difficult to provide a bead 1 2a of the desired configuration and location in a container 12 having the requisite bottom recess without damaging the internal surface of a container.

More particularly, space for the beading tool 11 is necessary so that there is clearance between the bottom inside of container 12 and the tool 11. In Fig. 4, clearance between the tool 11 and the bottom recess is shown during the beading operation shown in Fig. 3.

Such clearance is a function of the bottom profile shape. If the container 12 were to have a shaped bead which was chime shape for interchangeability, and the container has a recess bottom for strength and volume, the beading tool would not be able to enter the space provided without damaging the inside surface of the container or destroying the tool.

A thin tool wall would be needed and same would be fragile. Consequently, a combination of bead shape and recessed configuration are necessary to permit the formation of a lower bead 1 2a which is chime-like but not chimeshaped. In addition, the bead 1 2a must be of a depth which will make the lower can wall the same diameter as the double seamed chime. The lower bed 1 2a of the present design has been found to give increased overall can strength and more particularly, the work hardening of the bead 1 2a during the forming raises the vertical crush strength of the finished and packed can, a measurable percentage being 10% greater than a similar can with a chime-shaped bead. Similar, the abuse resistance of the bottom corner of the can is also increased by 30% over a more chime-shaped bead located near the can bottom.

As shown in Fig. 5, the overall lower wall and bottom profile 14 includes recessed centre section generally designated 15. The centre section includes an annular inner wall 1 spa, which is substantially straight but tipped inwardly at its upper end toward the central axis B of the container 12. The wall 1 5a is connected across its top by a shallow dome shaped portion 1 5b which is of even curvature to a flat rim shaped ring 16 which faces outwardly with respect to the container bottom. Ring 16 is planar and represents the outwardmost portion of container 12 bottom,, i.e., the part upon which the container rests when standing in an upright position. Between the rim ring 16 and the bead 1 2a is a relief section 17 which is formed by the beading die 1 3a during the beading operation.

Relief 17, as shown in Fig. 6, is designed to cooperate in stacking relationship with upper double seamed end 18 of a similar container. Consequently, any containers having the same overall outside diameter are stackable relative to one another by means of the top portion of a double seamed end 18 fitting within the relief 17 when the central axes C of the two containers are in alignment with one another, see the side line 19 in Fig. 6.

In a preferred embodiment, the container 12 is 3 3/16" in diameter and the centre of the bead 1 2a is .1" above the plane of the bottom rim ring 16 and the overall bead height is .18" above the plane of the bottom ring 16 whereby were the can to be labelled the bottom edge of the label would rest between the area at which the bead starts, which is .18" above the bottom, and the lower end of the upper double seam 18. The bead extends approximately .04" outwardly from the wall of the container 12. This is an amount which will increase its diameter to approximately the diameter of the upper double seam. The combination of the height of the bead centre and the distance to which it extends will place the bead 1 2a squarely within any chime worn grooves in the trackwork or processing equipment.The radius of the beading tool nose at 11 a is approximately .04" and the external radius formed by die 13a at the point .18" above the bottom where the container wall 12 bends outwardly to form the bead is approximately .030".

In Fig. 5, the annular wall 1 5a is connected to the dome-shaped centre section 1 5b by a section with a radius of .070". Similarly, the ring shaped section 16 joins the annular wall 1 5a with a radius of .07". The overall radius of curvature for the domed centre portion 1 5b is 3" and the height at the centre of the container 12 of the recess domed centre portion 1 5b is .390" above the bottom plane of the container as established by the flat rim ring 16. The annular wall 1 5a tips inwardly at an angle of about 10 with respect to the vertical.

It has been found that a container 12 of the preferred diameter will take the processing temperature incurred during retort sterilization of a sealed container. That is to say that, such a container with the described bottom profile will withstand up to 44 pounds per square inch of internal pressure without the bottom buckling outwardly. More particularly, the centre recess portion 15 will maintain its configuration and the growth during sterilization will be at the flat ring 16 which tends to bow outwardly near the annular wall 1 5a by pivoting somewhat relative to the point at which it joins the relief section 1 7.

For purposes of stacking, the relief section 17 has a radius of curvature of .03" whereby the upper portion of the double seam 1 8 will rest relative to the relief 17 if the containers are of similar diameter and are vertically and axially aligned relative to one another.

Claims (14)

1. A two-piece metal can having a seamless container body of circular cross-section formed of a thin material into an integral side and bottom wall, a circular closure adapted to be joined to said side wall by an annular double seam having interfolded adjacent layers of metal, and a profile of the area of the corner of the side and bottom wall and the bottom wall includes an outwardly extending lower side wall bead which extends the diameter of the can body so that the most distal extend to bead is above the bottom plane of the can an amount equal to about threequarters the length of a double seam chime, a substantially flat circular ring section extending generally normal to the plane of said side wall and in-line with the outwardmost plane of the container bottom, an inner annular side wall extending into the container from the outwardmost plane of said bottom and joining the inside edge of said ring-shaped section to a recessed and domed central panel of said bottom, and an annular relief disposed intermediate said chime-like bead and said outside edge of said ring-shaped section.

2. A can as claimed in claim 1, wherein the thin seamless container body is formed by a multiple drawing operation, then beading, or a precoated metallic sheet, the coating being an organosol and the metal being a tin free steel of the chromium treated type.

3. A can as claimed in claim 1, wherein the seamless container body is formed of electrolytically desposited tin plate by a multiple drawing operation then beading and thereafter coated.

4. A can as claimed in any preceding claim, wherein said annular relief is adapted to cooperate with a double seamed end in mating engagement when the central axes of cans are aligned in head-to-bottom relation as during stacking.

5. A can as claimed in claim 4, wherein said circular ring section extends axially outwardly to a greater extent at its inside edge than the part thereof nearest said side wall bottom periphery during when the can is subjected to pressures resulting from packing, hot filling or processing.

6. A can as claimed in claim 1, wherein said lower side wall bead and said circular ring-shaped section form a relatively inwardly open can profile adapted to receive a beading tool arranged to clear said domed recess to protect the interior surface from all but the forming portion of the beading tool.

7. A can as claimed in claim 1, wherein said most distal extent of said lower side wall bead is identical to the most distal extent of said annular double seam on a hermetically sealed container body.

8. A can as claimed in claim 7, wherein the longitudinal distance along said side wall between said lower side wall bead and said double seam is of a predetermined amount essentially equal to the space between double seams on a similar size three-piece container.

9. A can as claimed in claim 1, wherein said recessed central panel is displaced axially inwardly to the extent required to establish the ultimate internal volume of the sealed container at an amount equal to that of a similarly exteriorly sized three-piece container and the metal of the bottom is stretched sufficiently to raise its elastic limit.

10. A method of forming a two-piece metal can having a seamless container body of circular cross-section formed of a thin material into an integral side and bottom wall with an outwardly extending lower side wali bead above the juncture of said side and the bottom wall and a recessed domed central panel in said bottom wall connected to said bead by a flat circular ring-shaped section and an annular relief, the method including the following steps, drawing an elongated cupshaped container having an integral side and bottom, redrawing and profiling said container and bottom to include an annular wall extending to a domed central recess from a flat rim ring section said wall being tipped inwardly at its upper end toward the axis of said can, and applying a bead in the form of a lateral convolution into said lower side wall of the container body, said bead being disposed above the bottom corner of said side wall for forming a relief beneath the distal portion of said bead and the outer circumference of said ring section.

11. A method as claimed in claim 10, wherein said relief includes an annular convolution disposed substantially in the centre thereof and limited to a radial extent equal to the diameter of a double seamed end of a similarly sized container.

12. A method as claimed in claim 11, wherein said container is packed and hermetically sealed with a circular closure adapted to be joined to said side wall by an annular double seam having interfolded adjacent layers of metal and subjected to internal pressure causing said flat ring section to bulge outward axially to a greater extent at said inner annular side wall than at said bottom corner near said relief.

13. A two-piece metal can substantaliy as hereinbefore described with reference to, ånd as shown in, Figs. 2 to 6 of the accsmpany- ing drawings.

14. A method of forming a two-piece metal can substantially as hereinbefule described with reference to Figs. 2 to 6 of the accompanying drawings.