MX2012011886A

MX2012011886A - Can manufacture.

Info

Publication number: MX2012011886A
Application number: MX2012011886A
Authority: MX
Inventors: Stuart Monro
Original assignee: Crown Packaging Technology Inc
Priority date: 2010-04-13
Filing date: 2011-04-13
Publication date: 2012-11-30
Also published as: BR112012026177A2; JP5952804B2; WO2011128385A1; RU2567077C2; CN102834195A; US20130098926A1; US20130037555A1; US20150283597A1; NZ603524A; RU2012148040A; CO6630100A2; AU2011239981B2; UA112058C2; EP2558229A1; AU2011239981A1; CA2794120A1; CA2794120C; JP2013523460A; ZA201208514B

Abstract

A method and apparatus are disclosed which are suitable for use in the manufacture of two-piece metal containers. In particular, a press is disclosed which makes cup sections from metal sheet using a combination of drawing and stretching operations. The cups resulting from the press have the advantage of having a base thickness that is thinner relative to the ingoing gauge of the metal sheet.

Description

MANUFACTURE OF CANS TECHNICAL FIELD This invention relates to the production of metal cups and in particular (but not limited to) metal cups suitable for the production of "two-piece" metal containers.

BACKGROUND OF THE INVENTION US 4095544 (NATIONAL STEEL CORPORATION) 06/20/1978 details the conventional Draw & Wall Ironing (DWI, embossing, and ironing walls) and Draw & Re-Draw (DRD, re-embossing) to manufacture cup sections for use to make two-piece metal containers. [Note that in the United States of America, on the other hand, DWI is normally referred to as D &I. The term "two pieces" refers to i) the cup section and ii) the closure which would subsequently be attached to the open end of the cup section to form the container.

In a DWI process (D &I) (as illustrated in Figures 6 to 10 of US Pat. No. 4,095,544), a flat (usually) circular (usually) blank stamped from a roll of sheet metal is embossed by an embossing matrix, under the action of a punch, to form a shallow first phase cup. This initial drawing phase does not result in any intentional thinning of the blank. Next, the cup, which is normally mounted on the end face of an adjusted punch or rod, is pushed through one or more annular wall ironing dies in order to effect a reduction in the thickness of the side wall of the cup that results, in that way, an elongation of the side wall of the cup. By itself, the ironing procedure will not result in any change in the nominal diameter of the first stage cup.

Figure 1 shows the distribution of metal in a container body resulting from a conventional DWI (D &I) process. Figure 1 is illustrative only, and is not intended to be precisely to scale. Three zones are indicated in figure 1: • zone 1 represents the material of the non-ironed base. This retains approximately the same thickness as the initial caliper of the blank, ie it is not affected by the independent manufacturing operations of a conventional DWI process.

• Zone 2 represents the ironed half section of the side wall. Its thickness (and thus the amount of ironing required) is determined by the required performance of the container body.

• Zone 3 represents the ironed upper section of the side wall. Normally in the manufacture of cans, this ironed upper section is approximately 50 to 75% of the thickness of the initial gauge.

In a DRD process (as illustrated in Figures 1 to 5 of US Pat. No. 4,095,544), the same embossing technique is used to form the first phase cup. However, instead of employing an ironing process, the first stage cup is then subjected to one or more re-turning operations which act to progressively reduce the diameter of the cup and thereby elongate the side wall of the cup. By themselves, most of the conventional re-shaping operations are not intended to result in any change in the thickness of the cup material. However, taking the example of container bodies made from a typical DRD process, in practice there is usually some thicknessing in the upper part of the finished container body (of the order of 10% or more). This thickening is a natural effect of the re-shaping process and is explained by the compression effect on the material when it is re-drawn from a large diameter cup to a smaller diameter cup.

Note that there are known alternative DRD methods that achieve a reduction in thickness in the side wall of the cup through the use of small radius or compound slitting dies to thin the side wall by stretching in the drawing and re-shaking phases.

Alternatively, a combination of ironing and re-embedding can be used in the first stage cup, which thereby reduces both the diameter of the cup and the thickness of the side wall. For example, in the field of the manufacture of two-piece metal containers (cans), the container body is normally made by drawing a blank to form a first-phase cup and the cup is subjected to several operations of re-embedding until reaching a container body of the desired nominal diameter, followed by subsequent ironing of the side wall to provide the desired thickness and side wall height.

However, the DWI (D & I) and DRD procedures used on a large commercial scale have a serious limitation because they do not act to reduce the thickness (and therefore the weight) of the material at the base of the cup. In particular, the embossing does not result in a reduction in the thickness of the object being drawn, and the ironing only acts on the side walls of the cup. Essentially, for the DWI (D & I) and DRD procedures known for the manufacture of cups for two-piece containers, the thickness of the base does not change substantially with respect to that of the initial caliper of the blank. The result is that the base thickness of this can is greater than what is required for the desired performance.

The metal packaging industry is very competitive, with weight reduction being a main objective because it reduces transport and raw material costs. By way of example, approximately 65% of the manufacturing costs of a typical two-piece metal food container is derived from raw material costs.

Therefore, there is a need for improved lightening of metal cup sections in a cost effective manner. Note that in this document, the terms "cup section" and "cup" are used interchangeably.

SUMMARY OF THE INVENTION Accordingly, in a first aspect of the invention (defined in claim 1) there is provided a method for manufacturing a metal cup from a sheet of metal, the method comprising the following operations: i. an embossing operation comprising pressing the metal sheet to form a cup having a side wall and a solid base; ii. a stretching operation carried out on the cup, the operation comprising holding an annular zone at the base of the cup to define an enclosed part, and deforming and stretching at least part of the base that is inside the enclosed part for thereby increasing the surface area and reducing the thickness of the base, the annular holder being adapted to restrain or prevent the flow of metal from the area subject to the enclosed part during this stretching operation; performing the operations of drawing and drawing in a common press.

In a second aspect of the invention (defined in claim 5) there is provided a press for the manufacture of a metal cup from a sheet of metal, the press comprising - i. means for drawing the metal sheet to form a cup having a side wall and a solid base; ii. a fastening element for holding the pressed cup during a stretching operation, the fastening element being adapted to hold an annular area at the base of the embossed cup to define an enclosed part; iii. a stretching tool adapted to deform and stretch at least part of the base that is inside the part enclosed in the stretching operation to thereby increase the surface area and reduce the thickness of the base, the fastening element being adapted in addition to restrict or prevent the flow of metal from the area subject to the enclosed part during the drawing operation.

The method and apparatus of the different aspects of the invention have the advantage (with respect to the known methods / apparatuses) of achieving the manufacture of a cup having a base that is thinner than the initial caliper of the metal sheet, without requiring loss or waste of metal. This is achieved by the use of a single press, thereby simplifying the manufacturing process. When applied to the manufacture of two-piece containers, the invention makes it possible to obtain cost savings in the order of several dollars per 1,000 containers in relation to the existing manufacturing techniques.

To ensure that the enclosed part (and hence the base of the cup) is stretched and thinned during the stretching operation, the base of the drawn cup is sufficiently restrained to restrict or prevent the flow of metal from the area subject to the part. enclosed during the stretching operation. If the clamping loads are insufficient, the material of the subject area (or outside of the subject area) would simply be withdrawn into the enclosed part, instead of experiencing thinning the enclosed part (and the base of the cup). It has been found that stretching and thinning of the can still occur when a limited amount of material flow is allowed from the subject area (or from outside the subject area) to the enclosed part, i.e. when it is restricted the metal flow instead of completely avoiding it.

The method and apparatus of the invention are particularly suitable for use in the manufacture of metal containers, the final resulting cup being used for the container body. The final resulting cup can be shaped to give a closed container by fastening a closure to the open end of the cup. For example, one end of a metal can can be welded to the open end of the final resulting cup. However, normally the cup resulting from the method of the invention would be subject to any one or a combination of a re-firing operation and an ironing operation. The re-shaping operation may comprise one or more phases, each phase having the effect of inducing a successive reduction in the diameter of the cup. The ironing operation would have the benefit of increasing the height of the side wall of the cup produced by the method and apparatus of the invention. Preferably, the drawing operation comprises deforming and stretching at least part of the base within the enclosed part to form a domed profile. In the field of metal containers for carbonated beverages, it is usual for the base of the container body to be bulged inward to resist the pressure generated by the product. The "bulging" provided by the method and apparatus of the invention can serve as the bulged area inwards of a beverage container body. However, it is likely that the cup undergoes a subsequent reshaping operation to provide the domed base of the cup with a desired final profile necessary to withstand the internal pressure of the can.

The method of the invention is suitable for use in cups that are both round and non-round in plan. However, it works best in round glasses.

Another way to minimize the amount of material in the base of cup sections produced using conventional DWI and DRD procedures would be to use thinner gauge starting material. However, the cost of tinplate per ton increases the lower its caliber. This increase is explained by the additional costs of laminating, cleaning and tinning the thinner steel. When taking into account also the use of material during the manufacture of a two-piece container, the variation in the overall net cost of manufacturing the container versus the initial caliber of the material resembles the graph shown in Figure 2. This graph demonstrates that from a cost perspective, the choice of thinner gauge material does not necessarily reduce costs. Basically, there is a cheaper material gauge for any container of a given side wall thickness. The graph also shows the effect of reducing the thickness of the upper and middle sections of the container to lower the cost curve. Figure 3 shows the same graph based on actual data for tinplate supplied in the United Kingdom of the type normally used in can making. For the material illustrated in Figure 3, 0.285 ram represents the optimum thickness in terms of cost, increasing, the use of thinner gauge material, the overall net costs of can production. The graph of Figure 3 shows the increase in percentage of the overall cost per 1,000 cans when a deviation from the optimum initial gauge thickness of 0.285 mm occurs.

The final resulting cup of the invention has the benefits of a thinner (and therefore lighter) base.

The "metal sheet" can includes a blank cut from a large sheet metal extension.

By "annular fastening" or fastening an "annular zone" it is meant that the base of the embossed cup is held either continuously or at annularly spaced intervals.

The fastening element may be in the form of a continuous annular sleeve; alternatively, it can be a set of individual fastening elements annularly distributed to act against the metal sheet.

The method and apparatus of the invention are not limited to a particular metal. They are particularly suitable for use with any metal that is commonly used in the DWI (D & I) and DRD procedures. Also, there is no limitation on the final use of the cup resulting from the method and apparatus of the invention. Without limitation, the cups can be used in the manufacture of any type of container, be it for food, drink or anything else.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a side elevational view of a prior art container body resulting from a conventional DWI process. It shows the distribution of material in the base and in the side wall areas of the container body.

Figure 2 is a graph showing in general terms how the net overall manufacturing cost of a typical two-piece metal container varies with the initial sheet metal caliper. The graph shows how reducing the thickness of the side wall area (for example, by ironing) has the effect of lowering the net overall cost.

Figure 3 is a graph corresponding to Figure 2, but based on actual tinplate price data supplied in the United Kingdom.

Embodiments of the invention are illustrated in the following drawings, with reference to the accompanying description: Figure 4 is a cross-section through a press of the invention showing a sheet metal blank prior to the drawing and drawing operations.

Figure 5 is a cross section through the press of Figure 4, but after the drawing operation to embed the sheet metal blank to form a cup having a side wall and a solid base.

Figure 6 is a cross section through the press of Figures 4 and 5, but after the drawing operation to deform and stretch the base of the embossed cup.

MODE (S) OF CARRYING OUT THE INVENTION OPERATION OF EMBUTITION Figure 4 shows a combined drawing and drawing press 10. A blank piece 5 of sheet metal is "slidably held" in position between the opposite surfaces of a drawing bearing 11 and an end face of a drawing die 12. An embossing punch 13 is located above the upper surface of the sheet metal blank 5. Within the bore defined by the embossing die 12 is a drawing punch 14 which is radially inward of and surrounded by the annular clamping element 15.

Once the blank 5 is "slidably held" between the stuffing bushing 11 and the stamping die 12, the stamping punch 13 moves axially downward (along the axis 16) until the area The peripheral ring 17 of the end face of the punch comes into contact with a corresponding area in the blank 5 (see FIG. 5). The embossing punch 13 is pushed down through the hole in the drawing die 12 to progressively embed the initially flat blank 5 to form a cup 30 having a side wall 31 and a solid base 32.

By "sliding clamping" is meant that the clamping load during the drawing is selected to allow the metal sheet 5 to slide, in relation to the clamping means that are used (in this case a "drawing bearing 11"). "), in response to the deformation action of the embossing punch 13 / die 12 in the metal sheet. An intention of this fastening in a sliding manner is to avoid or restrict the wrinkling of the material during the drawing.

STRETCHING OPERATION Once the embossing punch 13 reaches the end of its stroke, the annular clamping element 15 moves axially upwards until an annular region 33 in the base 32 of the embossed cup is clamped between the annular clamping element and the clamping cup. peripheral annular zone 17 of the end face of the embossing punch 13 (see FIG. 5). The material of the base of the cup waxed by this annular holder is called "part 34 enclosed".

The drawing punch 14 then moves axially upwards (along the axis 16) to contact the enclosed part 34 (see FIG. 6). The drawing punch 14 is pushed up into the hollow 18 defined within the end face of the embossing punch 13 to progressively deform and stretch the material of the enclosed portion 34 of the cup 30 to form a domed profile 35 (see Figure 6). The clamping load applied between the annular clamping element 15 and the peripheral annular region 17 of the end face of the embossing punch 13 is sufficient to restrict or prevent the flow of metal from the annular area 33 held towards the enclosed part 34 during this stretching operation. To improve the gripping effect, the end face of the annular clamping element 15 may have a texture (not shown in the figures) to thereby allow the use of a reduced clamping load compared to the use of a clamping element. ring holder having a smooth polished end face.

As shown in Figure 6, the cup resulting from the stretching operation carried out in the press 10 has a reduced thickness in its base in relation to the initial caliber of the sheet metal blank 5. As indicated above in the general description of the invention, this cup can be used as a container body, but would generally be subject to any one or a combination of re-refilling and ironing operations to optimize the diameter and thickness of the side wall of the container. Cup. As also indicated in the general description of the invention, the bulged zone 35 can be particularly beneficial for the containers provided for pressurized products, such as carbonated drinks.

Claims

NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following is claimed as a priority: CLAIMS i. Method for manufacturing a metal cup from a sheet of metal, the method comprising the following operations:

1. an embossing operation comprising pressing the metal sheet to form a cup having a side wall and a solid base; ii. a stretching operation carried out on the cup, the operation comprising holding an annular zone at the base of the cup to define an enclosed part, and deforming and stretching at least part of the base that is inside the enclosed part for thereby increasing the surface area and reducing the thickness of the base, the annular holder being adapted to restrain or prevent the flow of metal from the area subject to the enclosed part during this stretching operation; performing the operations of drawing and drawing in a common press.

2. The method according to claim 1, wherein the drawing operation comprises locating the metal sheet between a drawing punch and a drawing die, and moving any one or both of the drawing punch and the drawing die towards the other of such so that the embossing punch extends through the embossing die to thereby embed the metal foil to form the cup, the annular fastener comprising during the drawing operation holding the annular area at the base of the cup between the punching die and a holding element disposed on the opposite side of the cup to the drawing punch.

3. Method according to claim 2, wherein the drawing operation comprises using a drawing punch disposed on the opposite side of the cup to the drawing punch and moving either or both of the drawing punch and the cup held towards the other to deform and stretch at least part of the base that is inside the enclosed part.

4. Method according to any preceding claim, wherein the drawing operation comprises deforming and stretching at least part of the base that is inside the enclosed part to form a domed profile.

5. A press for the manufacture of a metal cup from a sheet of metal, the press comprising: i. means for drawing the metal sheet to form a cup having a side wall and a solid base; ii. a fastening element for holding the pressed cup during a stretching operation, the fastening element being adapted to hold an annular area at the base of the embossed cup to define an enclosed part; iii. a stretching tool adapted to deform and stretch at least part of the base that is inside the part enclosed in the stretching operation to thereby increase the surface area and reduce the thickness of the base, the fastening element being adapted in addition to restrict or prevent the flow of metal from the area subject to the enclosed part during the drawing operation.

6. Press according to claim 5, wherein the means for drawing the metal sheet comprises a drawing punch and a drawing die, one or both of the drawing punch and the drawing die being able to move towards the other in such a way that The embossing punch can extend through the embossing die to embed the metal sheet to form the cup, the fastening element being disposed on the opposite side of the cup to the embossing punch in such a manner that in use during the operation of stretching the clamping element holds the annular area of the base between the clamping element and the drawing punch.

7. Press according to claim 6, wherein the drawing tool comprises a drawing punch disposed on the opposite side of the cup to the drawing punch, any one or both of the drawing punch and the combination of embossing punch and element being able to move. of clamping towards the other in such a way that in use the drawing punch deforms and stretches at least part of the base that is inside the enclosed part.

8. Press according to any of claims 6 or 7, wherein the embossing punch is provided with a recess or hole to allow the drawing tool to extend fully or partially into the recess u. hole during the stretching operation.

9. Method or press as described herein, with reference to the accompanying drawings.