RU2567077C2 - Production of cans - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: claimed set of inventions relates to metal forming, particularly, to production of two-piece metal vessels. Metal sheet is dawn to bowl with side wall and stretch-wrap forming with pressing of ring area at one press. Then, redrawing of bowl is performed along with its necking for stepwise bowl diameter increase and/or bowl sidewall height increase, respectively. Said press comprises drawing means, pressing element, stretch-wrap forming means, redrawing and/or necking means.

EFFECT: decreased base depth compared with inlet depth of sheet metal.

8 cl, 6 dwg

Description

FIELD OF THE INVENTION

The present 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

US Pat. No. 4,095,544 (NATIONAL STEEL CORPORATION) of 06/20/1978 describes in detail conventional methods for producing cup parts — wall thinning (DWI) and deep drawing (DRD) used in the manufacture of two-piece metal containers. (It should be noted that DWI is commonly referred to as D&I in the United States of America.) The term “two-part” refers to i) a cup portion and ii) a closure that will subsequently be attached to the open end of the cup portion to form a container.

In the DWI (D&I) method (as shown in FIGS. 6-10 of US Pat. No. 4,095,544), a flat (usually) round billet stamped from a sheet metal roll is pulled through an exhaust die under the action of a punch to form a first stage hollow cup. This initial stretching step does not significantly thin the workpiece. After that, the cup, which is usually mounted on the end surface of a tightly fitting punch or press rod, is pushed through one or more ring thinning dies to reduce the thickness of the side wall of the cup, which leads to an extension of the side wall of the cup. The thinning method itself will not lead to any changes in the nominal diameter of the cup in the first stage.

In FIG. 1 shows the distribution of metal in a container body as a result of a conventional DWI (D&I) method. FIG. 1 is provided for illustrative purposes only and is therefore not to scale. In FIG. 1 shows three areas:

Region 1 is an unshaded base material. It remains approximately the same thickness as the original workpiece thickness, i.e. independent of the individual manufacturing operations of the conventional DWI method.

Region 2 is the thinned middle part of the side wall. Its thickness (and, accordingly, the amount of required thinning) is determined by the characteristics necessary for the tank body.

Region 3 represents the thinned upper part of the side wall. As a rule, in can production, the thinned upper part is about 50-75% of the original thickness.

In the DRD method (as shown in FIGS. 1-5 of US Pat. No. 4,095,544), the same drawing technique is used to form the cup in a first step. However, instead of using the thinning method in the first stage, the cup is subjected to one or more re-drawing operations, which serve to gradually reduce the diameter of the cup and, thereby, lengthen the side wall of the cup. By themselves, most common re-stretching operations are not designed to change the thickness of the cup material. However, taking as an example the container bodies made in the usual DRD method, it is seen that in practice there is usually some thickening in the upper part of the finished container body (about 10% or more). This thickening is a natural effect of the re-drawing method and is explained by the compression effect on the material when re-drawing from a large-diameter cup to a smaller-diameter cup.

It should be noted that there are alternative known DRD methods that can achieve a decrease in the thickness of the side wall of the cup due to the use of exhaust dies of small or complex radii to thin the side wall by tightening at the stages of drawing and re-drawing.

As an alternative, a combination of thinning and re-drawing can be used in the first step in the manufacture of the cup, thereby reducing both the diameter of the cup and the thickness of the side wall. For example, in the production of two-piece metal containers (cans), the container body is usually produced by drawing the blank at the first stage of cup production, and then the cup is subjected to several repeated drawing operations until the container body of the required diameter is obtained, followed by thinning of the side wall to provide the required thickness and height of the side wall.

However, DWI (D&I) and DRD methods used on a large industrial scale have a serious limitation in that they are not aimed at reducing the thickness (and therefore weight) of the material at the base of the cup. In particular, the hood does not reduce the thickness of the object being drawn, and thinning affects only the side walls of the cup. In fact, with the known DWI (D&I) and DRD methods of manufacturing cups for two-piece containers, the thickness of the base remains essentially unchanged relative to the original thickness of the workpiece. This can give the base a thickness that will be significantly greater than is necessary to fulfill work objectives.

In the production of metal packaging, there is fierce competition, while weight reduction is a primary goal, as this reduces the cost of transportation and raw materials. For example, about 65% of the cost of producing a conventional two-piece metal food container is derived from the cost of raw materials.

In view of this, there is a need to reduce the weight of metal cup parts in a cost-effective manner. It should be noted that in this document the terms “cup” and “cup” are used interchangeably.

SUMMARY OF THE INVENTION

Accordingly, according to the first object of the invention (defined in paragraph 1), a method for the production of a metal cup from sheet metal, comprising the following operations:

i. an operation of drawing, including drawing sheet metal into a cup with a side wall and made in one piece base,

ii. the tightening operation performed on the cup, including the pressing operation of the annular region to the base of the cup to form a closed section, and deformation and tightening of at least a portion of the base lying in the closed section, thereby thereby increasing the surface area and reducing the thickness of the base, and the ring clamp is made with the possibility of limiting or preventing the flow of metal from the clamped region to a closed area during this tightening operation,

while the operation of drawing and tightening is performed in a common press.

According to the second object of the invention (defined in paragraph 5), a press for the production of a metal cup from sheet metal, comprising:

i. means for drawing sheet metal into a cup with a side wall and made in one piece base,

ii. a clamping element for clamping the elongated cup during the tightening operation, wherein the clamping element is adapted to clamp the annular region to the base of the elongated cup to form a closed portion,

iii. a tightening tool configured to deform and tighten at least a portion of the base lying in a closed area during the tightening operation to thereby increase the surface area and reduce the thickness of the base, while the clamping element is further configured to limit or prevent metal flow from the pressed region in a closed area during tightening operation.

The method and device according to various objects of the invention have an advantage (over known methods and devices) in that they produce a cup whose base is thinner than the original thickness of the sheet metal without loss and waste of metal. This is achieved through the use of a single press, which simplifies the production method. Being used in the production of two-component containers, the invention provides a reduction in future costs of several dollars per 1000 containers in comparison with existing production technologies.

To ensure tightening and thinning of the closed portion (and therefore the base of the cup) during the tightening operation, the base of the elongated cup is pressed firmly enough to limit or prevent the metal from flowing from the pressed region to the closed portion during the tightening operation. If the pressing forces were insufficient, the material from the pressed region (or from outside the pressed region) would simply be pulled into a closed section, and the closed section (the base of the cup) would not undergo any thinning. It was found that tightening and thinning can still occur with limited fluidity of the material from the pressed region (or from outside the pressed region) to a closed section, i.e. when the fluidity of the metal is limited and not completely prevented.

The method and device according to the invention is particularly applicable for use in the manufacture of metal containers, while the finished cup can be obtained in the form of a closed container by attaching a closure to the open end of the cup.

For example, the end of a metal can may be welded to the open end of the finished cup. However, as a rule, a cup obtained by the method according to the invention will undergo one of the operations or a combination of re-drawing and thinning operations. The re-drawing operation may include one or more steps, with the result of each step being a phased reduction in the diameter of the cup. The result of the thinning operation will preferably be an increase in the height of the side wall of the cup produced according to the method and device of the invention. The tightening operation preferably includes deforming and tightening at least a portion of the base lying in a closed area in a dome-shaped profile. In the area of metal containers for carbonated drinks, the base of the container body usually has an inwardly domed shape to withstand the pressure created by the product. The “dome” provided by the method and device according to the invention can serve as a domed inwardly directed region of the body of the beverage container. However, it is likely that the cup will undergo a reforming operation in the future to give the domed base of the cup the required final profile necessary to resist internal pressure.

The method of the present invention is suitable for use on both round and non-circular cups. However, it is best used on round cups.

Another way to reduce the amount of material at the base of the cup portion produced using conventional DWI and DRD methods would be to use a sheet with a lower initial thickness. However, as the thickness decreases, the cost of a ton of tinplate increases. This increase is due to additional costs for rolling, cleaning and tinning of thinner steel. Also, taking into account the use of materials in the manufacture of a two-component vessel, a change in the net total cost of production of the vessel depending on the initial thickness of the material is presented in the form of a diagram in FIG. 2. This diagram shows that from a cost point of view, a decrease in the initial thickness of the material does not necessarily lead to a reduction in costs. In fact, there is the cheapest material thickness for any tank with a given side wall thickness. The diagram also shows the effect of reducing the thickness of the upper and middle sections of the vessel wall in reducing the cost curve. In FIG. Figure 3 shows the same chart based on actual data from the UK-supplied tinplate of the type commonly used in can production. For the material shown in FIG. 3, 0.285 mm represents the optimum thickness in terms of cost, using a thinner material that increases the net total cost of can production. The diagram in FIG. 3 shows the percentage increase in the total cost by 1000 cans, with a deviation of 0.285 mm of the optimal initial sheet thickness.

As a result, the finished cup according to the invention preferably has a thinner (and therefore lighter) base.

“Sheet metal” may include a blank carved from a larger sheet metal.

An “annular clip” or a clamping “annular region” means that the base of the elongated cup is attached either in a continuous manner or at regular intervals in an annular manner.

The clamping element can be made in the form of a continuous annular sleeve, as an alternative, it can be a set of individual fasteners distributed in an annular manner to act on the sheet metal.

The method and device according to the invention is not limited to a particular metal. They are especially applicable for use with any metals commonly used in DWI (D&I) and DRD methods. In addition, there are no restrictions on the end use of the cup produced by the method and device according to the invention. Cups can be used without restriction in the manufacture of any type of container, whether for food, drinks or anything else.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a prior art container body obtained by a conventional DWI method. It shows the distribution of material in the base and areas of the side wall of the container body.

FIG. 2 is a diagram showing, in general terms, how the net total cost of manufacturing a typical two-piece metal container varies with the initial sheet metal. The diagram shows how a decrease in the thickness of the side wall region (for example, by thinning) leads to a decrease in the net total cost.

FIG. 3 is a diagram corresponding to FIG. 2, but based on actual pricing for tinplate supplied to the UK.

Embodiments of the invention are illustrated by the following drawings, with reference to the accompanying description:

FIG. 4 is a sectional view of a press according to the invention, showing a sheet metal blank before drawing and tightening operations.

FIG. 5 is a sectional view of the press shown in FIG. 4, but after the operation of drawing, which serves to draw the billet from sheet metal into a cup with a side wall and made in one piece base.

FIG. 6 is a sectional view of the press shown in FIG. 4 and 5, but after the tightening operation, which serves to deform and tighten the base of the drawn cup.

OPTION (S) FOR CARRYING OUT THE INVENTION

HOOD OPERATION

In FIG. 4 shows a combined fume-tightening press 10. A blank of sheet metal 5 is “movably pressed” in a position between opposite surfaces of the pressure ring 11 and the end surface of the exhaust die 12. Above the upper surface of the sheet metal 5 is an exhaust punch 13. In the hole formed exhaust stamp 12, there is a tightening punch 14, which is directed radially inward and is surrounded by an annular clamping element 15.

After the workpiece 5 is “movably pressed” between the pressure ring 11 and the exhaust stamp 12, the exhaust punch 13 moves axially downward (along axis 16), until the peripheral annular region 17 of the end surface of the punch touches the corresponding region of the workpiece 5 (see Fig. 5). The exhaust punch 13 is fed down through the opening of the exhaust stamp 12 for the gradual drawing of the initially flat billet 5 into the cup 30 with the side wall 31 and the base 32 made in one piece.

By "movable clamp" is meant that the clamping force during drawing is selected so as to ensure that the sheet metal 5 is sliding relative to any clamping means used (in this case, "clamping ring 11"), in response to the deforming effect of the drawing punch 13 / drawing stamp 12 on sheet metal. The purpose of this movable clip is to prevent or limit wrinkling of the material during drawing.

COVER OPERATION

After the exhaust punch 13 reaches the end of its stroke, the annular pressure member 15 moves axially upward until the annular region 33 on the base 32 of the elongated cup is sandwiched between the annular pressure element and the peripheral annular region 17 of the end surface of the exhaust punch 13 (see FIG. 5). The base material of the cup, closed inside this annular clip, is called the "closed section" 34.

The tightening punch 14 then moves axially upward (along axis 16) to come into contact with the closed portion 34 (see FIG. 6). The tightening punch 14 is fed upward into a recess 18 formed in the end surface of the exhausting punch 13 for gradually deforming and tightening the material of the closed portion 34 of the cup 30 into a dome-shaped profile 35 (see Fig. 6). The pressing force applied between the annular pressing element 15 and the peripheral annular region 17 of the end surface of the exhaust punch 13 is sufficient to limit or prevent the metal from flowing from the pressed annular region 33 into the closed portion 34 during this tightening operation. To enhance the gripping effect, the end surface of the annular clamping element 15 can be textured (not shown in the drawings), which allows the use of less clamping force than using the annular clamping element with a smooth polished end surface.

As shown in FIG. 6, the cup obtained as a result of the tightening operation in the press 10 has a reduced thickness in its basis relative to the initial thickness of the sheet metal blank 5. As indicated above in the description of the invention, this cup can be used as a container body, but, as a rule, is exposed one of the operations or a combination of drawing and thinning operations to optimize the diameter of the cup and the thickness of the side wall. In addition, as indicated in the description of the invention, the domed region 35 may be particularly preferred for containers intended for pressure products, such as carbonated drinks.

Claims (8)

1. A method of manufacturing a metal cup from sheet metal, comprising the following operations:
i. an operation of drawing, including drawing sheet metal into a cup with a side wall and made in one piece base,
ii. the tightening operation performed on the cup, while the drawing and tightening operations are performed in a common press,
characterized in that the tightening operation includes clamping the annular region to the base of the cup to form a closed area,
carry out the deformation and tightening of at least a portion of the base lying in a closed section to increase the surface area and reduce the thickness of the base, and the annular clamp is configured to limit or prevent the metal from flowing from the pressed region to the closed section during this tightening operation,
and
subsequent one of the operations or a combination of re-drawing and thinning the cup to gradually reduce the diameter of the cup and / or increase the height of the side wall of the cup, respectively. 2. The method according to p. 1, characterized in that the operation of drawing includes placing sheet metal between the exhaust punch and the exhaust stamp and moving one or both of the exhaust punch and the exhaust stamp to each other, while the exhaust punch passes through the exhaust stamp and, thus Thus, it draws the sheet metal into the cup, while the ring clamp during the tightening operation includes the clamp of the annular region on the base of the cup between the exhaust punch and the clamping element located on the side of the cup opposite to the exhaust puff anson. 3. The method according to p. 2, characterized in that the tightening operation involves the use of a tightening punch located on the side of the cup opposite to the exhausting punch, and moving one or both of the tightening punch and the clamped cup to each other to deform and tighten at least part base lying in a closed area. 4. The method according to any one of paragraphs. 1-3, characterized in that the tightening operation includes deformation and tightening of at least a portion of the base lying in a closed area in a dome-shaped profile. 5. Press for the production of metal cups of sheet metal, containing:
i. means for drawing sheet metal into a cup with a side wall and made in one piece base,
ii. a clamping element for clamping the elongated cup during the tightening operation, wherein the clamping element is adapted to clamp the annular region to the base of the elongated cup to form a closed portion,
iii. a tightening tool configured to deform and tighten at least a portion of the base lying in a closed area during the tightening operation to increase the surface area and reduce the thickness of the base, while the clamping element is further configured to limit or prevent the metal from flowing from the pressed region to the closed plot during tightening operation,
and
re-drawing and / or thinning means for optimizing the cup diameter and side wall thickness. 6. The press according to claim 5, in which the sheet metal drawing means comprise an exhaust punch and an exhaust stamp, wherein one or both of the exhaust punch and the exhaust stamp are movable to each other so that the exhaust punch can pass through the exhaust stamp for drawing sheet metal into a cup, the pressing member being located on the side of the cup opposite the drawing punch, so that when using the fitting operation, the pressing member presses the annular base region between the pressing member th and extract the punch. 7. The press according to claim 6, in which the tightening tool comprises a tightening punch located on the side of the cup opposite to the exhausting punch, wherein one or both of the tightening punch and the combination of the exhausting punch and the pressing member move to each other, and when using the tightening punch the punch deforms and tightens at least a portion of the base lying in a closed area. 8. The press according to claim 6 or 7, in which the exhaust punch is made with a recess or hole to ensure the passage of the tightening tool fully or partially into the recess or hole during the tightening operation.

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