Metal container suitable to accommodate a heating or cooling component method and for manufacturing it

Abstract

A method of producing a metal container from a low carbon steel strip or sheet coated on at least one of its surfaces with a coherent laminated coating of a thermoplastic polymer material includes one or more redrawing stages which reduce the thickness of the side walls by a drawing/stretching operation, and a partial reverse redrawing stage to produce an initial internal chamber whose depth is produced by a reduction of its height. The initial internal chamber is then redrawn to produce two chambers of differing diameter and depth, the diameter of the initial chamber being decreased by the redraw operation and inserting by base reforming the final chamber with a new internal diameter and depth produced by a reduction in the container height.

Description

[0001] The invention relates to a metal container and its manufacture. The metal container comprises a plurality of internal chambers of various depths and diameters, the design of which can be varied dependent on the respective application. The internal chamber or chambers may be filled with appropriate substances and used to heat or cool via a chemical reaction the contents of another chamber. The container according to the invention can thus be used to accommodate a heating or cooling component to heat or cool the contents, although it could also be used for alternative applications, e.g. where food products need to be kept separate.

[0002] This invention also relates to a method of manufacturing such a metal container, incorporating a combination of internal chambers, suitable to accommodate a heating or cooling component, used for heating or cooling its contents.

[0003] The method of manufacture used in producing the metal container may involve a combination or a series of the following processes, cupping, draw redraw (DRD) and/or draw stretch redraw (DSRD), reverse (partial) redraw, redraw of the reverse chamber and base reform depending on application and container size. Examples of such methods are disclosed in U.S. Pat. No. 5,088,870 and WO 99/61326.

[0004] For a typical design the process developed is as follows: The original cup is redrawn in sequential stages until a container of correct diameter is produced. The container is then subjected to a reverse (partial) redraw in order to insert an internal chamber. The next stage involves redraw of the internal chamber, hence producing two internal chambers of different diameter and depth. The final chamber is produced by means of base reform which produces a container of correct external diameter and height and, hence, a finished container of correct internal chamber diameters and depths.

[0005] For this invention, the configuration of internal chambers of the metal container consists of three internal chambers, with the following typical dimensions: 61.6 mm diameter at 4 mm deep, 53.7 mm diameter at 15 mm deep and 45 mm diameter at 73 mm deep. The starting material is conventionally a double reduced product of high strength high ductility low carbon steel with a proof strength of 480-720 N/mm.sup.2, and coated with a polymer coated film on one or each surface. The use of DR products for the metal container is not exclusive to the design, as it is possible that a range of SR tin mill products can be used for the application.

[0006] This invention concerns a method of producing a typical metal container used to accommodate a heating or cooling component, used in the heating or cooling of the contents of the metal container.

[0007] The feed stock for the method of manufacture for the metal containers to be produced in accordance with the invention is a double reduced high strength high ductility low carbon steel with a proof strength of 480-720 N/mm.sup.2. The maximum carbon level for the steel is typically 0.05% by weight. A typical specification for this steel is by weight %: C 0.01-0.04; S 0.02 max.; P 0.015 max.; Mn 0.15-0.30; Ni 0.04 max.; Cu 0.06 max.; Sn 0.02 max.; As 0.01 max.; Mo 0.01 max.; Cr 0.06 max.; A 0.02-0.09 and N 0.003 max. The steel is reduced by hot or cold rolling to a gauge typically of between 0.12 mm and 0.30 mm and is processed by known appropriate heating cycles and continuous annealing. The steel has a minimum earing quality.

[0008] As an example, the feed stock used is DR 580 CA 0.24 mm, coated with a PET laminate coating of 0.025 mm (white) on one side and a PET laminate coating of 0.020 mm (clear) on the other.

[0009] The specification for this steel is by weight %: C 0.012-0.04; S 0.02 max.; P 0.015 max.; Mn 0.15-0.30; Al 0.025-0.055 and N 0.003 max., plus trace elements: Ni 0.04 max.; Cu 0.06 max.; Sn 0.02 max.; As 0.01 max.; Mo 0.01 max.; Cr 0.06 max.

[0010] Strip produced from the feed stock is subjected to an electrolytic coating process. In this process, the steel strip is cleaned and pickled before being passed through a plating bath in which it is coated with a thin layer of chromium metal, typically of 0.010 mm thickness followed by a thin layer of chromium oxide, again typically of 0.010 mm thickness. Alternatively, tinplate or other suitable substrate could be employed.

[0011] The strip is then coated with a polymer material. In this process a layer of PET (polyethylene terephthalate) and/or PP (polypropylene) is bonded to the surface of the metallic coated steel strip or sheet using heat and pressure.

[0012] The films are co-extruded so that the bonding layer of 0.002 mm first makes contact with the steel and forms a strong bond. After the bond is formed with the substrate the polymer films are melted and held above the recrystallisation temperatures for a few seconds before being rapidly quenched to below their softening temperatures.

[0013] This produces an amorphous structure in the PET and a minimal crystalline structure in the PP. The method of coating the strip can be a direct extrusion or laminating process. Typically the thickness of the external polymer is in the order of 0.025 mm thickness and the internal polymer is between 0.015 and 0.030 mm. Laminating processes and polymer films of a different structure and composition other than those discussed may be employed.

Cupping

[0014] The strip, either in sheet or coil form is fed to a cupper in a pre-waxed condition or is passed through a waxer on entry to the cupping system. The wax may be edible and petroleum based with film weights in the range 5-20 mg/ft.sup.2. Discs are stamped from the sheet or strip. The cup is drawn in one operation using a die with a diameter typically in the range 150 mm to 300 mm.

[0015] This diameter is dependent (with gauge) upon the required can size and type of application. The draw ratio (i.e. ratio of the diameter of the disc to that of the cup) is typically in the range 1.0-2.0:1. The geometry of the tooling is designed in combination with the correct blank holding load to give a reduction in wall thickness at the cupping stage of up to 20%, however this can be produced with a smaller or greater reduction depending on application.

[0016] This is accomplished with a die radius typically between 0.5 mm and 6.5 mm and a parallel land length of up to 10 mm. The blank holding load is achieved by use of a boosted air pressure of up to 200 psi fed into a series (typically three) of internal multiplying pistons. The punch/die gap is important and is controlled by the feed stock gauge and coating and gaps of 1.20-2.50 times the starting total laminate thickness are typically used.

[0017] The punch nose radius is carefully controlled to achieve the required draw/stretch whilst minimising subsequent can wall marking which could lead to laminate rupture. Punch nose radii in the range of 0.5 mm to 10 mm are generally required.

First Redraw Processing

[0018] The cupper cup is passed into the draw/stretch redraw press which contains tooling for both first and second redraw operations. The diameter of the cup is reduced in the first redraw operation with a draw ratio in the range 1.0-1.7:1, and with a wall thickness reduction typically 25% of the in going cup wall thickness, however this can be produced with a smaller or greater reduction (in the range of 10-60%) depending on application.

[0019] The wall thickness reduction is achieved by a stretching technique. The wall thickness reduction is balanced with the draw ratio and is achieved by use of pressure sleeve and die geometry in combination with controlled blank holding loads.

[0020] The tooling geometry typically is as follows: pressure sleeve diameter up to 0.66 mm smaller than the cupper cup internal diameter; pressure sleeve radius up to 2.0 mm; die radius up to 2 mm with a parallel land length up to 5 mm.

[0021] The blank holding load is achieved by use of air pressure of up to 100 psi fed into a stack of two or more internal multiplying pistons.

[0022] Location of the cup on the die is effected by means of a nest recess with a diameter matched to the cupper cup, allowing for the thickness of the actual laminate. The radius of the nest diameter with the die at the base of the nest is in the range 0.10-2.00 mm.

[0023] The punch is parallel along its length and the gap between the punch diameter and die (per side) is generally controlled to between 1.20 and 1.50 times the starting laminate thickness. The punch radius is important to achieve the required stretch whilst minimising subsequent en wall marking which could lead to laminate rupture. Punch nose radii in the range 1 mm to 3 mm are typically used.

Second Redraw Processing

[0024] The first redraw cup is passed back into the stretch redraw press a station containing the second redraw tooling. The cup diameter is reduced in this operation to the final metal container diameter, typically 211, however, may vary depending on application. The draw ratio is generally in the range 1.0-1.7:1, and with a wall thickness reduction typically 25% of the ingoing cup wall thickness, however this can be produced with a smaller or greater reduction (in the range 10-60%) depending on application.

[0025] The wall thickness reduction is again achieved by a stretching technique using a combination of pressure sleeve and die geometry with controlled blank holding loads. The correct choice of diameter reduction ratio to achieve the finished can is also important in enabling the stretch process to be successful. The tooling geometry used typically is as follows: pressure sleeve diameter up to 0.30 mm smaller than the first redraw cup internal diameter; pressure sleeve radius up to 2.0 mm; die radius up to 2 mm with a parallel land length up to 5 mm.

[0026] The blank holding load is achieved by use of air pressure of up to 100 psi fed into a stack of two or more internal multiplying pistons. Location of the cup on the die is effected by means of a nest recess with a diameter matched to the cupper cup, allowing for the thickness of the actual laminate. The radius of the nest diameter with the die at the base of the nest is in the range 0.10-2.00 mm.

[0027] The punch is parallel along its length and the gap between the punch diameter and die (per side) is generally controlled to between 1.00 and 1.20 times the starting laminate thickness. The punch radius is important to achieve the required stretch whilst minimising subsequent can wall marling which could lead to laminate rupture. Punch nose radii in the range 1 mm to 3 mm are typically used.

[0028] Gap control or arrested draw is employed at the redraw stages to eliminate high spot clip off or the generation of laminate "whiskers". When gap control is used, gaps of 0.10 to 0.15 mm between the pressure sleeve and die face are generally used depending upon the laminate feed stock used. The overall metal container wall thinning employed is 5-40% dependent upon the end use of the container.

[0029] The second redraw container (i.e. final container diameter) is transferred to a different redraw press, which can accommodate tooling for the reverse draw for the internal chamber, redraw of the reverse chamber and base reform operations.

Reverse Draw Operation

[0030] The container undergoes a reverse draw operation, in order to produce an initial internal chamber. The draw ratio for the initial internal chamber is generally in the range 1.0-1.7:1, with no (or limited) wall thickness reduction instead the internal depth is achieved by a reduction of the in going second redraw container height. To prevent wall thickness reduction correct choice of die radius, punch radius and controlled blank holding pressure are required. The tooling geometry typically is as follows: die external diameter up to 0.60 mm smaller than the second redraw can internal diameter; die external radius up to 2.0 mm; die radius up to 5 mm with a parallel land length up to 5 mm.

[0031] The blank holding load is achieved by use of air pressure of up to 100 psi fed into a stack of two or more flexible pressure chambers. Location of the container on the pressure sleeve is effected by means of a nest recess with a diameter matched to the second redraw can, allowing for the thickness of the actual laminate. The radius of the nest diameter with the die at the base of the nest is in the range 0.10-2.00 mm.

[0032] The punch is parallel along its length and the gap between the punch diameter and die (per side) is generally controlled to between 1.10 and 1.40 times the starting laminate thickness. The punch radius is important to prevent 1 limit wall thickness reduction, instead it is used to draw the container wall to produce the internal chamber. The punch nose radius in the range 2 mm to 7.5 mm is typically used, Depth of the reverse draw is controlled out by the means of a mechanical stop. The depth of the reverse draw is dependent on the application, typically between 10-100 mm.

Redraw of the Reverse Chamber

[0033] The reverse redraw container is transferred to the next operation station, where redraw of the reverse chamber is performed. The container's internal chamber is redrawn to a smaller diameter for a portion of it's depth, i.e. two different chamber diameters and depths. The draw ratio used in the reduction of the internal chamber is generally in the range 1.0-1.7:1. The increase in height of the internal chambers is caused by a reduction of the reverse redrawn can base diameter and base thickness reduction.

[0034] Base thickness reduction is again achieved by a stretching technique using a combination of pressure sleeve, punch and die geometry with controlled blank holding loads. The correct choice of internal diameter reduction ratio to achieve the required internal parameters is important in enabling the process to be successful.

[0035] The tooling geometry used typically is as follows: die external diameter up to 0.60 mm smaller than the second redraw can internal diameter; die radius up to 5 mm with a parallel land length up to 5 mm.

[0036] The blank holding load is achieved by use of air pressure of up to 100 psi fed into a stack of two or more flexible pressure chambers. Location of the container on the pressure sleeve is controlled by means of the internal chamber from the reverse redraw operation with a diameter 0.60 mm smaller than the internal chamber for can location, allowing for the thickness of the laminate to be taken into account.

[0037] The punch is parallel along its length and the gap between the punch diameter and die (per side) is generally controlled to between 1.10 and 1.40 times the starting laminate thickness. The punch radius is important to achieve the required stretch. The punch nose radii in the range 2 mm to 7.5 mm is typically used.

[0038] Depth of the redraw is controlled by the means of a mechanical stop. The depth of the redraw operation is dependent on the application, typically between 10-100 mm.

Base Reform

[0039] The redraw container is transferred to the final operation station for this application, where base reform is performed. The final internal chamber is reformed to the largest diameter chamber for a specified depth (i.e. three different chamber diameters and depths). The draw ratio used in the reduction of the internal chamber is generally in the range of 1.0-1.4:1; with no wall thickness reduction, instead the internal depth for this final chamber is achieved by a reduction from the ingoing second redraw container height.

[0040] To prevent wall thickness reduction, a correct choice of die and punch radius is required. The tooling geometry typically is as follows: punch external diameter up to 0.60 mm smaller than the second redraw can internal diameter; punch external radius up to 2.0 mm; punch internal radius up to 2.0 mm; die radius up to 2.0 mm with a parallel land length up to application requirement;

[0041] The base reform load is applied by the reaction between the punch and die that is used to apply the base design.

[0042] Location of the container on the die is effected by means of a nest recess with a diameter matched to the second redraw container, allowing for the thickness of the actual laminate. The radius of the nest diameter with the die at the base of the nest is perpendicular.

[0043] Depth of the redraw is controlled by the means of a mechanical stop. The punch bottoms out on the die face at the specified depth for the application requirements.

[0044] After the final operation the container is trimmed (this can occur after the second redraw operation) and passed through an oven. This oven is typically held at 200-230' C and the pass time is typically between 1 and 3 minutes. This facilitates the removal of petroleum wax lubricant to such a level so that it does not interfere with the lay down of printing inks used to decorate the can. It also raises the surface energy of the PET coating to at least 38 dynes/cm, which increases the wettability of the PET surface to printing inks. The temperature cycle in the oven is chosen to minimise recrystallisation of the PET by rapid temperature rise and cooling cycles.

[0045] Printing is currently carried out using conventional machinery, which applies thermally curing inks onto the external surface of the can. Again, recrystallisation of the PET is minimised as above. Alternatively, a shrink wrap sleeve may be applied at lower temperatures.

[0046] The invention will now be further described with reference to the accompanying diagrammatic drawings, in which:

[0047] FIG. 1 illustrates five stages of a cupping operation of the method of the present invention;

[0048] FIG. 2 illustrates five stages of a first draw 1 stretch redraw operation of the method of the present invention;

[0049] FIG. 3 illustrates five stages of a second draw/stretch redraw operation of the method of the present invention;

[0050] FIG. 4 illustrates six stages of a reverse redraw operation of the method of the present invention;

[0051] FIG. 5 illustrates six stages of a redraw operation of the method of the present invention;

[0052] FIG. 6 illustrates five stages of a base reform operation of the method of the present invention;

[0053] FIG. 1 shows five stages of a cupping operation of the method of the present invention. The five stages are labelled A to E. Stage 1A shows a feed stock strip 1 of laminated steel strip held between a draw pad 2 and a blank and draw die 3. A disc of the required diameter is cut from the strip, by downward movement of a cutter 5 (see FIG. 1B). A punch 6 (FIGS. 1C and 1D) is then moved downwardly with the disc edges trapped between the opposed surfaces of the draw pad 2 and draw die 3. A cup 7 is thereby formed which is removed from the die by air pressure (see FIG. 1E).

[0054] As will be seen from FIG. 2, the cup is then placed on a die for first redraw purposes. This stage is illustrated in FIG. 2A. The die is formed with a shaped lip 9 and has a curved annular projection 10 protruding inwardly from its upper surface. As seen in FIG. 2B, a pressure sleeve 11 and punch move downwardly and within the side wall of the cup 7. The outer rim of the cup base seats between the opposed surfaces of the pressure sleeve 11 and the die 8. The gap between these members is sufficient only to restrict movement of the cup 7, not to impose a force sufficient to deform or iron the cup. As the punch is moved downwardly, so the cup wall is stretched to increase the cup height.

[0055] This stretching process can be seen more clearly from FIG. 5. It will be seen that the cup wall between the projection 10 and the punch lower face is not in contact with either the die 8 or the side wall of the punch 12. Movement of the cup between the pressure sleeve 11 and the die 8 and over the curvilinear projection 10 is restricted to cause stretching of the cup wall. After stretching, the cup is ejected by air pressure (see FIG. 2E).

[0056] Turning to FIG. 3, the second redraw operation uses the same or similar pressure sleeve and die as those used in the first redraw operation. These have been accordingly been given the same numerical reference. In FIG. 3, the cup 7 is again shown in positioned on the die 8, see FIG. 3A. The pressure sleeve 11 is moved downwardly as shown in FIG. 3B to position the sleeve within the cup 7. Again, the spacing between the sleeve 11 and the die 8 is to restrict movement of the cup, not to preclude such movement. A punch 14 is moved downwardly into engagement with the cup base to once again stretch the cup side wall and effect elongation thereof. This stretching operation being as described above in relation to FIG. 2. This stretching operation is shown in FIGS. 3C and 3D. The fully stretched and formed cup is ejected by air pressure (see FIG. 3E).

[0057] FIG. 4 concerning the reverse redraw operation illustrates how the initial internal chamber is applied. Cup 7 is placed on the pressure sleeve 15 for the reverse redraw for the initial internal chamber. This stage is illustrated in FIG. 4A. As seen in FIG. 4B, the die 14 moves downwardly and locates in the cup 7. The die 14 continues its downward movement and clamps the cup 7 between itself and the pressure sleeve 15, see FIG. 4C. The die 14 continues the downward motion, and in doing so, forces the pressure sleeve 15 to move in the same direction, hence, causing the cup 7 to be drawn over the fixed punch 16, resulting a reduction in the height of the second redraw cup (i.e. material is not thinned, but moved to new position, due to minimal blank holding pressure to be applied). The depth of the internal chamber is controlled by a mechanic stop at a described displacement. This operation applies the initial internal chamber, see FIG. 4D. The die 14 begins its upward motion as illustrated in FIG. 4E. After the reverse redraw operation the cup 7 is ejected by air pressure, see FIG. 4F.

[0058] In FIG. 5, the redraw of the initial internal chamber is illustrated, which produces two internal chambers of different diameters and depths. Cup 7 is placed on the pressure sleeve 18 for the redraw of the initial internal chamber. This stage is illustrated in FIG. 5A. As seen in FIG. 5B, the die 17 moves downwardly and locates in the cup 7. The die 17 continues it downward movement and clamps the cup 7 between itself and the pressure sleeve 18, see FIG. 5C. The die 17 continues the downward motion, and in doing so, forces the pressure sleeve 17 to move in the same direction, hence, causing the cup 7 to be drawn over the fixed punch 19. As the die 17 moves downwardly the cup base is reduced in diameter, producing two internal chambers of different diameters and depths, see FIG. 5D. The depth of the internal chamber is controlled by a mechanic stop at a described displacement. The die 17 begins its upward motion as illustrated in FIG. 5E. After the reverse redraw operation the cup 7 is ejected by air pressure, see FIG. 5F.

[0059] FIG. 6, describes the process of base reform, this is whereby the final internal chamber (for this application) is applied to the can. In FIG. 6, the cup is located in the die 21 for the base reform operation to occur see FIG. 6A. As seen in FIG. 6B, the punch 20 moves downwardly and locates in the cup 7. The punch 20 continues it downward movement into engagement between the cup 7, itself and the die 21. With the third recess applied, due to a reduction, once again, from the ingoing cup height, as explained in relation to FIG. 4. This base reform operation is shown in FIGS. 6C and 6D. The punch 20 begins its upward motion, and the fully formed cup 7 is ejected by air pressure, see FIG. 6E.

[0060] It will be appreciated that the foregoing is merely exemplary of methods and apparatus in accordance with this invention and that modifications can readily be made thereto without departing from the true scope of the invention.

[0061] The advantage of such a two piece can over the three piece version is that there is no seaming of the heat exchange unit to the welded cylinder, which removes the problem of corrosion encountered at the seaming of the cylinder to the heat exchange unit.

Claims

1. Method of producing a metal container from a low carbon steel strip or sheet coated on at least one of its surfaces with a coherent laminated coating of a thermoplastics polymer material in which a blank produced from the coated steel strip of sheet to a drawing operation to produce a cup, the method being comprised of the following steps: (i) subjecting the cup to at least one drawing and stretching operation to reduce the thickness of the cup wall and to increase the cup height without ironing of the wall surface; (ii) subjecting the stretched cup to at least on partial reverse redrawing operation to produce within the stretched cup a first internal chamber whose depth is produced by a reduction of its height without any reduction in wall thickness; (iii) subjecting the first internal chamber to a reverse redrawing operation to produce a second internal chamber whose diameter and depth differs from those of the first internal chamber; and (iv) subjecting the cup base to a reforming operation to produce a third internal chamber whose diameter and depth differ from those of the first and second chamber and whose depth is produced by a reduction in the cup height.

2. Method according to claim 1 wherein the thermoplastic polymer has good formability and comprises an internal coating which prevents corrosion of the container by its contents and an external coating which prevents corrosion of the container by its heating/cooling solution, the laminate coating being applied to the metal surface by means of direct extrusion or lamination.

3. Metal container produced by a method as claimed in claim 1 having a combination of internal chambers of differing depths and diameters.

4. Metal container as claimed in claim 3 produced from a double reduced high strength high ductility low carbon steel having a proof strength in the range 490 to 720 N/mm.

5. Metal container as claimed in claim 3 wherein the maximum carbon level for the steel is 0.050% by weight.

6. Metal container as claimed in claim 4 wherein the steel comprises by weight %: C 0.01-0.10; S 0.02 max.; P 0.015 max.; Mn 0.15-0.30; Ni 0.04 max.; Cu 0.06 max.; Sn 0.02 max.; As 0.01 max.; Mo 0.01 max.; Cr 0.06 max.; Al 0.02-0.09 and N 0.003 max.

7. Metal container as claimed in claim 4 wherein the steel is reduced by hot or cold rolling to a gauge of between 0.12' mm and 0.3 mm.