JPH05193694A - Body and lid of can and filling of the same - Google Patents

Abstract

(57) [Abstract] [Objective] A can having a thin side wall is supported so as not to be crushed, and it is possible to retain a desired shape. [Composition] This is a method of filling a product not containing saturated carbon dioxide into a can, and in order, A) a product whose top is open is filled so that a top space remains, and B) a top space is substantially filled. Permanent gas is blown into the top space to fill it with permanent gas and expel steam from it, C) splice the lid of the can to the can to close the can, and D) attach the lid of the can or the bottom of the can to the first stability Deformation from an abrupt shape to a second stable shape to reduce the volume of the top space and raise the pressure there to a level such that the internal pressure remains above 1 atm under expected conditions of processing, shipping and storage. Is included.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to filling cans, and more particularly to filling cans with food or saturated carbon dioxide free beverages.

[0002]

2. Description of the Related Art For packaging carbonated drinks, a lightweight material is squeezed and a wall is annealed (referred to as DWI processing).
It is common to use a can. Such cans consist of a one-piece can body having a bottom wall and a cylindrical side wall, and a top can lid that is spliced to the can body after filling. In this application field, the internal pressure generated by the carbon dioxide component of the product can be of the order of atmospheric pressure and above 2 bar at room temperature. This internal pressure imparts considerable strength to the extremely thin side walls of such cans by placing the walls of the cans under tension, protecting the cans from being dented and damaged during shipping, and Maximize the top load strength of the can. Such a can can accommodate an internal pressure above atmospheric pressure and above 7 bar, but is very easily damaged if the internal pressure falls below atmospheric pressure and within 0.4 bar.

Products that do not contain saturated carbon dioxide are often filled at high temperatures in cans, but when such cans are cooled, an internal vacuum is created which causes the walls of the can to collapse or become flat. It shows that it must be relatively thick in order to withstand the vacuum without getting tired.

[0004]

In order to illustrate this effect, consider the case where the can is filled with 300 ml of water at a temperature of 85 ° C. and then the can is closed with a total volume of 380 ml, joined to the lid. See.

When the lid is attached to this can, 50
The head space of ml shall be filled with a mixture of permanent gas and condensable vapor. The permanent gas should be primarily atmospheric oxygen and nitrogen and the condensable vapor should be primarily water vapor generated from the hot product. When the can is closed, the sum of the partial pressures of the components in the top space should be equal to the then atmospheric pressure, so to say 1.0 absolute bar, the temperature of the mixture being closed from the product at the side wall of the can. It should be close to the temperature of the product due to convective heat transfer to the components in the enclosed headspace.
At 85 ° C, water vapor should make up about 58% of the mixture and permanent gas should make up the remaining 42%. In other words, the partial pressure of water vapor is 0.58 absolute ba
should be r and the partial pressure of the permanent gas is 0.42 absolute b
Should be ar.

This state should exist as long as the can is kept at 85 ° C., but when the can is cooled to 5 ° C. like when it is placed in the refrigerator, the gas law is considered. As can be seen, both components in the top space should behave differently. Permanent gas follows Boyle-Charle's law, so its partial pressure is about 0.33 absolute bar
It is thought that it will decrease to. The water vapor in the top space is believed to condense into the liquid phase until its pressure there reaches the equilibrium saturated water vapor pressure at the reduced temperature. At 5 ° C., the saturated water vapor pressure is practically very small and can be ignored. The small additional volume of liquid produced by condensation can likewise be ignored. Therefore, at 5 ° C, the total pressure in the top space is believed to drop to 0.33 absolute bar. Since the ambient atmospheric pressure remains at 1.0 absolute bar, the can wall experiences a differential pressure of 0.67 bar. Therefore, the wall of the can must be relatively thick if collapse is to be avoided. This problem becomes more serious in practice. This is because the volume of the liquid component is substantially contracted as the temperature is lowered, and as a result, the pressure is further lowered.

It is ensured that the pressure in the top space of a can containing a product that does not contain saturated carbon dioxide remains well above atmospheric pressure throughout its shelf life, thereby DWI processing the lightweight material. Much effort has been devoted to methods intended to facilitate the use of P.

One such method, described in British Patent No. 2089191A, is to inject a small amount of liquid nitrogen into the top space of a can just prior to applying a lid and double seaming. Is included. This liquid nitrogen injection process has many drawbacks. The amount of liquid nitrogen to be injected into each can is small,
Its temperature is so low that it is difficult to handle and weigh accurately. Therefore, there is considerable variation in the amount injected into the can in succession. Liquid nitrogen, when poured into a hotter product, begins to boil, especially immediately if the liquid breaks down into small droplets,
Gas escapes from the can before the lid can be applied and formation of the double seam is complete. This results in significant unacceptable fluctuations in the final internal pressure between adjacent cans.

Alternative mechanical pressure processes are described, for example, in British Patent No. 1235060 and US Pat. No. 4836.
398. In these prior proposals, there is usually at least one deformable wall element,
It is provided at the upper or lower end of the can and is deformed after filling / seaming in order to reduce the internal volume of the can and thus increase the internal pressure.

This process of mechanical pressurization, when used with high temperature filled products, cannot prevent the generation of vacuum when the can is cooled to low temperatures and is still unsuccessful. It has not been seen to have been. It can be seen that the failure to prevent a vacuum from being generated is, in the present sense, due to the behavior of the water vapor in the top space when the can is mechanically deformed.

[0011]

According to a first aspect of the present invention, there is provided a method for filling a can with a product containing no saturated carbon dioxide gas, which comprises, in order, A) whether a top including a bottom wall and a side wall is open. B) filling the product into the body leaving a head space above it, and B) reducing the water vapor content of the head space by substantially filling the head space with a permanent gas. C) seaming the lid of the can to the can body to close the can; D) reducing the volume of the top space of the can to reduce the pressure in the top space to an internal pressure of 1 at the expected state of processing, transport and storage. A portion of the canister was moved from the first stable form to the second to raise it to a level such that it stays above atmospheric pressure.
To provide a stable form of the method.

According to this method, step D) deforms the bottom wall of the can body, or alternatively deforms the can lid that closes the upper side of the can body, or if desired. For example, it may include deforming both the bottom wall and the can lid.

For the purposes of explanation here again, product 3 at 85 ° C.
Consider the above case of a 380 ml canister containing 30 ml. 50m when the container is closed as above
The head space of 1 should contain a permanent gas with a partial pressure of 0.42 absolute bar and steam with a partial pressure of 0.58 absolute bar. If at this point one or both ends of the can are pushed in and deformed, its total internal volume is
If only reducing by ml, 330 ml of water should be reduced to 15 ml because the head space is practically incompressible. Therefore, it is considered that the partial pressure of the permanent gas component rises to 1.4 absolute bar according to Boyle's law. However, the water vapor has an equilibrium saturated water vapor pressure of 0.58 at 85 ° C because the excess water is condensed into water.
Absolutely considered to remain bar. Therefore, the total pressure in the top space is approximately 2 absolute bar at 85 ° C.
It is believed that

If this can is cooled to 5 ° C., the partial pressure of the permanent gas is considered to drop to 1.09 absolute bar, and the partial pressure of water vapor is considered to be negligible. Therefore, the total internal pressure is 1.09 absolute ba
r, ie only 0.09 bar above atmospheric pressure, D
It is believed that the pressure will drop to insufficient pressure to support the walls of the WI machined can.

The pressures mentioned in the examples above are theoretical pressures based on a simple consideration of the gas law. If actual experiments are performed, the observed pressure will deviate from the theoretically calculated value, and will tend to be lower than the theoretical prediction. This disengagement occurs because the volume of the can and the volume of the contents change differently with temperature, and the can expands elastically as the pressure increases.

In one embodiment of this method, the body of the can is provided with a bottom wall, the bottom wall being convex with an annulus enclosing an outwardly concave central panel. A bottom portion of the shape, in step D) a concave shape which bears the central panel inside the side wall by applying pressure to the central panel to make the convex portion the second stable shape. It is supposed to be transformed into.

In another embodiment of this method, the can lid includes a peripheral double seam portion, a chuck wall depending from a circumference inside the seam portion, and a radial inner portion of the chuck wall. In the step D), the center bead includes an annular bead extending in the direction of and an inner wall extending from the annular bead toward the level of the seam and leading to the bent annulus supporting the central panel. Deformation of the annular bead and the inner wall by exerting pressure on the central panel until the panel passes through the annular bead and the folded annulus reverses to form the second stable shape with the inner wall. I have decided.

The permanent gas is preferably nitrogen. Because it is easily obtained.

In a second aspect, the invention is a can lid suitable for transforming from a first stable shape to a second stable shape, said first stable shape comprising A double seam portion, a chuck wall depending from the inside of the seam portion wall, an annular bead extending radially inward from the chuck wall, and an annular bead extending toward the level of the seam portion, The second stable shape includes a peripheral seam portion, a chuck wall, the annular bead, and a deformable chuck that includes an inner wall leading up to a folded annulus supporting the central panel. A central panel, which is an extension of the wall and below the level of the seam, provides a lid for the can containing at least a portion of the interior wall depending therefrom.

If desired, the can lid is of an easily open type, including the open part limited by a weak line in which the central panel can be opened by a lever or tab attached to the can lid. May be

In a third aspect of the present invention, an end wall suitable for deforming from the first stable shape to the second stable shape and a side wall standing upright from the periphery of the end wall are provided. The first stable shape is an annular bead having an arc-shaped cross section for connecting the bottom wall to the side wall, and the annular bead and the side wall extend axially and inwardly. The second stable shape includes an elongated bead and an outwardly concave central panel that straddles the annulus, wherein the second stable shape is such that the annular bead and the tapered portion are deformed. A body of a can is provided which comprises an axially and radially inwardly extending portion with respect to the side wall and the central panel thus supported enclosed within the side wall.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments will be described below by way of example with reference to the accompanying drawings.

FIG. 8 contains 330 ml of product 1 in the form of a hot liquid at 85 ° C. with 50 ml of head space 2 of 5 ml.
It shows a stove containing 8% steam and 42% air. Since this can was sealed under atmospheric pressure,
The pressure in the top space is atmospheric pressure (1 absolute bar). FIG. 9 shows the same can after it has been cooled to 5 ° C. With the volume of liquid reduced by about 10 ml, the top space is increased to about 60 ml. The partial pressure of water vapor is small at this temperature, and the partial pressure of air is reduced due to the cooling it suffered and the volume of the top space increased by cooling the product. Therefore, the pressure in the top space of the can shown in FIG. 9 is approximately 0.4 absolute ba below atmospheric pressure.
r. Lightweight (DWI) cans will not withstand any external pressure and will collapse causing flattening of the sidewalls.

FIGS. 10 and 11 are similar to FIGS. 8 and 9, but relate to a can having a deformable bottom wall. If this can also be filled in the same way, but without gas blowing under the cover and before cooling to 5 ° C,
With the prior art treatment, by deforming the bottom of the can to reduce the volume by 35 ml, the pressure should still drop below 0.9 absolute bar. This is a low enough pressure to cause the wall of the can to collapse.

However, as is now known, if the top space of the can is flushed with nitrogen when the lid is applied, at the moment of closure the partial pressure of nitrogen in the top space is 1. Should be close to 0 bar,
The partial pressure of water vapor should be close to zero. After that the pressure of the water vapor regenerates very rapidly and 0.58 absolute bar
And the can should be pressurized to 1.58 absolute bar. If the volume was reduced by 35 ml by this deformation of the bottom and then allowed to cool to 5 ° C, the pressure should only drop to 1.5 absolute bar. This is a sufficiently high pressure to maintain the tension in the wall and thereby provide the necessary strength to avoid damage during shipping.

In practice, it is not possible to completely fill the top space 2 with nitrogen before closing the canister. Typical results achieved in practice show that about 80% of the top space gas is replaced when using modern undercover gas blown beverage seam forming machines. Is.

For experimentation, the Applicants have made a 65 mm × drawn and tinned walled tin plate.
I made a can body with a height of 115 mm. The body of these cans has a bottom wall thickness of 0.3 mm (0.012 ″),
With a side wall thickness of 0.13 mm (0.005 ″) and a total volume of typically 380 cl, for packing 330 cl of liquid product leaving a shortage or top space required for filling Was used.

FIG. 1 shows the body of the can over the tool forming the deformable portion of the bottom wall of the can. A standard can body is shown having a cylindrical side wall 5, a seam flange 6, and a bottom end wall 3 containing a dome-shaped central portion 7 and a stacking bead 8. The tool shown is an upper punch tool 10,
It includes a lower punch tool 11 and a die 12. When the upper punch tool 10 moves downwards, the dome-shaped central portion 7 of the end wall 3 is deformed by being bent at the die 12 into the substantially convex shape shown in phantom in FIG. The lower punch tool 11 has a first stable shape at the bottom, namely an annular bead with an arcuate cross section connecting the side wall to the bottom wall and extending inward axially from the annular bead. A portion of the portion 7 during this deformation that creates a first stable shape of the bottom, including a tapering annulus 13 supporting an outwardly concave central panel 7 .. FIG. 2 shows the closed can on the tool that deforms the bottom wall back to its original shape. This tool is used for the upper member 1 mounted on the lid 16 of the can.
5 and a lower punch tool 11 in die 12 as previously described. When the punch tool 11 is moved upwards, the bottom of the can is in a second stable form, i.e. the annular bead and the tapered portion are deformed to axially and radially with respect to the side wall. Also deformed to create a second stable shape that includes the inwardly extending portion and the central panel thus supported within the side walls. The inner volume of the can is reduced.

FIG. 3 shows the top of one can body with the can lid 16 resting thereon and held in position by the seam chuck 20. Punch 21
Located in the seam chuck to act on the central panel 22 of the can lid. 3 and 5, the can lid has a first stable shape, namely a peripheral seam portion 23, a chuck wall 24 depending from the inside of the seam portion, and a radial extension from the chuck wall. It is shown to be in a first stable configuration including an annular bead 25 that is open and an inner wall 26 that extends beyond the level of the seam from the bead 25 and supports the central panel 22.

FIG. 4 shows the arrangement of FIG. 3 after the can lid has been double seamed to the can body. The punch 21 is also moved downwards so that the can lid is in a second stable form, namely the peripheral seam, the chuck wall, the annular bead and at least part of the inner wall. Deformed to form an extension of the chuck wall and now with the central panel forming an outwardly concave surface. This reduces the inner volume of the can.

If desired, the central panel 22 of the can lid may be provided with a scored openable portion, such as may be opened by a lever (not shown in FIG. 5). One of many known notch and pull tab or lever combinations may be used.

Typically, the scored can lid is made of 0.18 mm (0.011 ") thick aluminum. However, the non-scored can lid is made of aluminum, tinned plate. , Or made of TFS.

Based on a number of subsequent actual tests,
Applicants have derived a mathematical model based on a quadratic polynomial that takes these variations into account and makes the theoretical values match the actual observations. As an example of comparison, the following Table 1
Is a 380 ml canister containing 330 ml of product,
It shows the absolute pressure that would occur when the volume was deformed to reduce to 345 ml. The effect of varying the filling temperature between 5 ° C and 100 ° C is shown in each vertical column, and the effect of subsequent temperature changes after the cans were closed was horizontally aligned along each row. It is shown.

[0034]

[Table 1] From the shaded quarter in the bottom left of the table, the prior art of simply reducing the volume of the can filled at high temperature and then storing at a lower temperature, the internal pressure is more likely to break the DWI processed can. Can't be prevented from dropping below the critical limit of 1.4 bar and cans filled above 75 ° C are likely to occur in household refrigerators and vending machines. It is clear that at refrigeration temperature the internal pressure should be vacuum. The shaded area in the upper right of Table 1 is cold filled and later heated to above 100 ° C. for sterilization to give an internal pressure above 8.2 absolute bar when the lid is permanently deformed. It shows the areas that may occur. This area is
It has little practical significance. This is because the cans to be sterilized are always filled at high temperature.

The Applicants have found the solution proposed here as a result of recognizing the inadequacy of the prior art. If the top space is flushed with a permanent gas such as nitrogen before the double seam is formed and the can lid is applied, the percentage of water vapor in the top space. Temporarily drops considerably. A suitable device for accomplishing this operation, known as under cover gas blowing, is described in British Patent No. 1263820, which blows oxygen out of the head space of a cold-filled beer can. Is widely used to replace carbon dioxide with carbon dioxide, thereby avoiding beer oxidation.

Returning to the above example, if
A can of full volume 380 ml is filled with liquid at 85 ° C. and the can is closed on a double seam forming machine equipped with an under-cover gas blowing facility as described above connected to a nitrogen source. Then, at the time of closing, the partial pressure of nitrogen in the top space is close to 1 bar, and the partial pressure of water vapor in the top space is temporarily suppressed to zero. Immediately after the can is closed, the partial pressure of water vapor in the top space is regenerated from the hot liquid and rises to the equilibrium saturated water vapor pressure at 85 ° C., ie 0.58 absolute bar. Therefore, within a few seconds after the formation of the double seam, the pressure in the kettle is 1b.
It rises from ar to 1.58 bar. This effect is further enhanced if the temperature of the injected nitrogen is lower.

By the way, if this can is deformed so that its volume is reduced to 345 ml as described above, the partial pressure of nitrogen is changed from 1 absolute bar to 3.3 absolute bar based on a simple theory. While expected to rise,
It is believed that the partial pressure of water vapor remains unchanged at 0.58 absolute bar and therefore the total pressure will be approximately 3.9 absolute bar. It is believed that when such a can is cooled to 5 ° C., the partial pressure of nitrogen drops to 2.56 absolute bar and that of water vapor drops to zero. In other words, the internal pressure is considered to be 1.56 bar above atmospheric pressure, which is necessary to support the wall of the lightweight DWI can.
Sufficiently above atmospheric pressure.

In practice, it is also known that the pressures observed are still lower than those inferred by theory. Moreover, achieving 100% efficiency of under cover gas blowing is not practical. Applicants have found that it is practical to achieve an in-coverage gassing efficiency of 80% using a modern beverage can seam forming machine and the pressures shown in Table 2 below. Was modeled and confirmed by an actual test.

[0039]

[Table 2] Table 2 shows that using the present invention, cans filled and mechanically compressed at temperatures up to 85 ° C maintain a pressure above 1.4 absolute bar even when cooled to 5 ° C. It shows that it is possible to ensure that a vacuum does not occur even if high filling temperatures are attempted. It should be noted that such under-cover gas injection does not seriously increase the pressure generated when the cold filled product is heated to the temperature of the retort after mechanical compression. Known from this table.

The present invention thus facilitates the use of lightweight DWI machined cans for all canning operations. These operations include: In order of increasing degree of change: A) cans that are aseptically filled, cans that are cold filled and stored at low temperature, and B) that are hot filled, such as acid products that have been pasteurized. Cans that are cooled, C) Cans that are filled while warm and then sterilized at temperatures above 100 ° C, such as low acid foods and beverages.

While the particular embodiments described above relate to a body of cans drawn from a single blank plate to a bottom plate and integral side walls, the present invention provides:
It will be appreciated that a body of a can having a side wall that is seamed and connected at a double seam to the bottom wall is equally well applicable, as the side wall can be made of thin metal sheet. ..

FIG. 6 shows another can lid embodiment in which the can lid 30 includes a peripheral cover hook 31 and the surface of the can lid from the inner periphery of the cover hook. A frusto-conical chuck wall 32 hung at an angle of about 5 ° with respect to a vertical line to the vertical line, and an annular reinforcing bead 33 extending inward in the radial direction from the chuck wall and having an arc-shaped cross section An inner wall 34 extending upwardly and inwardly from the inner periphery of the reinforcing bead and connecting the inner wall 34 to a central panel 36 which spans the inner wall just below the top of the cover hook. The bent annular portion 35 is included.

The slope of the inner wall need not be strict, as long as it extends up to 30 ° from the possible substantial vertical of the metal springback.

In FIG. 6, the can lid rests on the flange of the can body which is filled and gas blown under the cover, the can body having a double seam 38 at the other end of the side wall 37. It has a similar can lid 30A already installed. Since the central panel 36A is inside the outermost part of the double seam, the body of this can is
It has the advantage that it stands on the seam rather than on the central panel. That is, the central panel bulges during heat treatment,
They are easily damaged by shock and may not be able to stand upright again.

Eliminated by pushing this "flash top" center panel to change from its first stable shape (shown in FIG. 6) to its second stable shape (shown in FIG. 7). The volume available is not as great as the excluded volume achieved by the outwardly projecting panels of Figures 3 to 5, but this drawback is compensated by deforming both lids of the can if necessary. Depending on the temperature at which the contents of the can were charged and the efficiency of the gas injection under the cover, the deformation of only one lid may be sufficient.

In FIG. 7, after the upper double seam 39 is formed, only the upper can lid is in its second stable form, namely the double seam 39 and the chuck wall 32.
A reinforcing bead and a bent annular portion 35A inverted inward,
A substantially frustoconical unitary extension 40 of the wall, i.e. extending radially and axially inwardly of the body of the can and extending the central panel 36 to the side wall 37 of the can.
A second stable shape that includes an extension that resists internal pressure generated in the can inside the can.

The central panel may be flat as shown, or may be dome-shaped (not shown) to increase its rigidity. Furthermore, the upper lid of the can may be provided with a score line that limits the open part. The openable portion may, if desired, be provided with pull tabs or levers of known shape, which are attached to the lid of the can by integral rivets or adhesive bonding. If the can lid is a stamped sheet of a metal plate / polymer film such as PET / polypropylene / polymer film, and the tab is made of the same material, the can lid polymer film is Adhesive bonds are particularly convenient if they can be fused to a similar film of tabs or levers.

The advantage of distributing the deformation to the lids on both sides of the can body is that the individual can lids experience less deformation and the can lids used after the first can lid press and filling are filled. The stroke of the deformation press becomes shorter,
Therefore, the presses can be operated at a higher speed. As described above with respect to FIGS. 3 and 4, the can lid can be deformed in a double seam forming machine. Alternatively, in one or both can lids, the next machine, i.e., a machine with rotating turrets, provided with opposing pressure pads 41 which are operated in cooperation with the rotation of the turret, It can be deformed between mounted can profiles or between can profiles and support pads if only one lid is to be deformed. FIG. 7 shows the pressing pad 41 and the flat support pad 42 after the upper can is deformed by a chain line.

[Brief description of drawings]

FIG. 1 shows a tool for forming the bottom wall of a can body having a deformable portion.

FIG. 2 is a view showing a tool for deforming the bottom wall of the can body.

FIG. 3 shows a top of a can with a can lid thereon and a tool for deforming the can lid.

FIG. 4 is a view similar to FIG. 3, showing the tool after seam formation and deformation of the can lid.

5 is a perspective view showing a cross section of the can lid shown in FIGS. 3 and 4. FIG.

FIG. 6 is a side cross-sectional view of a filled can in which the can lid overlying the upper flange is of a different shape.

7 is a side cross-sectional view of the can of FIG. 6 after double seaming and deformation of the can lid.

FIG. 8 is a schematic view of a canister immediately after it has been conventionally filled with a hot saturated carbon dioxide free liquid product and the top space has been sealed with a can lid without being flushed with permanent gas.

9 is a schematic view of the can of FIG. 8 after cooling.

FIG. 10 is a schematic view of a deformable can immediately after being filled with hot saturated carbon dioxide free product and the top space flushed with permanent gas and sealed with a can lid.

11 is a schematic view of the can of FIG. 10 after cooling and after deformation of the can bottom.

[Explanation of symbols]

 1 Product 2 Top Space 3 Bottom End Wall 4 Can Body (Whole) 5 Side Wall 6 Seam Flange 7 Dome Center (Center Panel) 8 Stacking Bead 10 Upper Punch Tool 11 Lower Punch Tool 12 Die 13 Tapered annular portion 15 Upper member (of tool) 16 Can lid 20 Seam chuck 21 Punch 22 Central panel 23 Peripheral seam portion 24 Chuck wall 25 Annular bead 26 Inner side wall 30,30A Can lid 31 Cover hook 32 Chuck wall 33 Reinforcement bead 34 Inner side wall 35, 35A Bent annular part 36, 36A Center panel 37 Side wall 38 Double seam (lower side) 39 Double seam (upper side) 40 Extension 41 Pressure pad 42 Support pad

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Claims (9)

[Claims] 1. A method of filling a can with a product that does not contain saturated carbon dioxide, which comprises, in order: A) the product in a body of a can that has a bottom wall and side walls and an open top, with the top on top B) Filling leaving space, B) Blowing permanent gas into the top space to substantially reduce the water vapor content of the top space by filling the top space with permanent gas, C) Body of the can lid D) to reduce the top space volume of the can and increase the pressure in the top space to a level higher than 1 atmosphere, a portion of the can from the first stable form to the second stable form. A method comprising the steps of transforming into an infinite shape. 2. The method of claim 1 wherein step D) comprises deforming the bottom wall of the can body. 3. The bottom wall has a convex bottom portion including an annulus enclosing an outwardly concave central panel, wherein in step D) pressure is applied to the central panel. 3. The method of claim 2, wherein the convex portion is deformed into a concave shape that supports the central panel on the inside of the side wall as the second stable shape by applying. 4. The method according to claim 1, wherein step D) comprises transforming the can lid from a first stable form to a second stable form. 5. The can lid has a double seam portion around the can lid,
A chuck wall depending from the inner circumference of the seam portion, an annular bead extending radially inward from the chuck wall, and an annular bead extending toward the seam level from the annular bead to the central panel. Including the inner wall leading to the supporting bent annulus, in step D):
Deformation of the annular bead and the inner wall by exerting pressure on the central panel until the central panel passes through the annular bead and the folded annulus reverses to form the second stable shape with the inner wall. The method according to claim 4, wherein the method is performed. 6. The permanent gas according to claim 1, which is nitrogen.
The method according to any one of 1. 7. A can lid suitable for transforming from a first stable form to a second stable form, said first stable form comprising a perimeter double seam portion and its periphery. A chuck wall depending from the inside of the seam portion, an annular bead extending radially inward from the chuck wall, and an annular bead extending from the annular bead toward the level of the seam portion to support the central panel above. The second stable shape includes an inner wall leading to a bent annulus, wherein the second stable shape is an extension of the chuck wall deformed with the peripheral seam, the chuck wall, and the annular bead. A lid for a can, which includes at least a portion of the inner wall from which a central panel at a level below the seam portion depends. 8. The can lid of claim 7, wherein the central panel includes an openable portion bounded by a line of weaker force opened by a lever. 9. A body of a can having an end wall suitable for deforming from a first stable shape to a second stable shape, and a sidewall standing upright from the periphery of the end wall. The first stable shape is an annular bead having an arc-shaped cross section for connecting the bottom wall to the side wall, and a tapered annular portion extending axially and inward from the annular bead and the side wall. An outwardly concave central panel straddling its tapered annulus, wherein the second stable shape is the annular bead and the tapered portion deforms axially relative to the sidewalls. And a body of a car including a radially inwardly extending portion and said central panel supported therein surrounded by side walls.