MXPA00001649A - Metal body for packaging purposes, for example a food can - Google Patents

Abstract

Metal body for packaging purposes comprising a closed metal shell extending around a longitudinal axis which is suitable for being provided on a side named here as the top with a lid running essentially perpendicular to the longitudinal axis, whereby the cross section through the shell on and closed to the top has a contour comprising 3=n=6 curved concavely inwards with a minimum radius of curvature R, and n essentially straight contour line pieces, as well as in that the shell comprises at least n essentially flat shell parts, which are separated from one another by a sharp fold running essentially parallel to the longitudinal axis, which fold has a maximum radius of curvature r, whereby r=0.4 R.

Description

METALLIC BODY FOR PACKING PURPOSES, FOR EXAMPLE A CAN OF FOOD DESCRIPTION OF THE INVENTION The invention relates to a metal body for packaging purposes comprising a closed metal cover extending around a longitudinal axis which is suitable to be provided on a side referred to herein as the top part with a cover running essentially perpendicular to the axis longitudinally, the cover comprises n essentially planar cover portions. Such a body is known, for example, as a component for a packaging container, for example a food can, see US 3,563,408. In US 3,563,408 a container with a central prismatic body portion which is attached to each end to a circular opening is described. In addition to its body, a three-piece packaging container comprises a base and a lid. With a packaging package of two pieces, the body and the base are in one piece. Furthermore, a conventional packaging container which is circular cylindrical is known, which is possibly provided with beds running essentially parallel to the face of the lid, or which are "blown" in a bulky form.

Also known is a packaging container of an essentially circular cylindrical shape which has finger-shaped panels curved inwardly convexly and extending to the height of the wall. The object of the invention is to create a lightweight packaging package which, while also moving away from the conventional circular cylindrical appearance and improving the rigidity, obtains advantages discussed below in greater detail. For this purpose, the body according to the invention has the features of claim 1. In this context, an essentially flat cover part will be fastened to comprise a cover part which is slightly convex or slightly concave and / or which comprises a or more overhanging terraces inwards and / or outwards. Here it is preferable that R = 15 mm and r = 5 mm. In a particular embodiment, the flat roof portions run essentially parallel to the parts of the straight contour line. The body has, for example, essentially flat deck portions and preferably 2n pronounced folds. The body then appears as illustrated in Figure 1. It is now not possible to work a method for heat treatment, for example sterilized from a full can comprising a body according to the invention, whereby a pressure pamb on the can and a pcan pressure prevails in the can, so? p = pcon - papüD and px < ? p < p2, characterized in that px < < < plref .. and p2 = p2"£. ,, where x ef .. Y P2rßf .. represent respectively the minimum and maximum p for a conventional reference can. It is found that when the can is in a state filled with a body according to the invention and heated treated in an autoclave, it needs to be handled much less critically in terms of pressure. The external pressure of the can can be set much higher and does not need to be reduced with precision when cooling. The invention also consists of a gas-tight can filled with a non-carbonated beverage or food, such as vegetables, fruits, pet food, fish, meat or soup, comprising a metal body according to the invention, preferably a can. of steel packaging, so the thickness of the steel packing material of which the body is manufactured is thinner than 0.16 mm. However, it is possible to use sterilizable cans according to the invention which are manufactured with a thickness of less than 0.15 mm, 0.14 mm, 0.13 mm or even less than 0.12 mm. The invention will now be illustrated with reference to the drawing, in which Figure 1 shows a tall and square can, according to the invention; Figure 2 shows a square short can according to the invention; Figure 3 shows a cross section of a can according to the invention at the closed end towards the upper part and at a slight distance thereof; Figure 4 shows the deformation of the can (filled) according to the invention as a consequence of the external pressure in different stages of filling the can; Figure 5 shows the flexibility of various forms of cans including the cans according to the invention; Figure 6 shows the relationship between the autoclave pressure and ρ p as defined; Figure 7 shows the relationship between the maximum autoclave pressure that can be supported by various forms of filled cans and the different filling degrees of the cans. Figure 1 shows a can according to the invention with a content and a height corresponding to the circular cylindrical food can of 73 mm in diameter and 110 mm in height. It can also be designed differently, for example, shorter as shown in Figure 2.

In Figure 3, R indicates the curvature of the radius of the curved contour line parts and the upper part of the can cover according to the invention, and r is the curvature of the radius which has the cover in a crease. The can according to the invention, for example, as shown in figures 1, 2 and 3, has the advantage that for the same content, it requires less space than a conventional circular cylindrical can, something which is of great importance on the sales shelves or in a distribution chain. The can according to the invention has, for example, a depth / width of approximately 66 mm and a height of 110 mm, while the height of a conventional can has a diameter of approximately 73 73 mm. Accordingly, for the same filler content, the can according to the invention requires approximately 20% less space when placed in rows than a known circular cylindrical can. In addition, the can according to the invention has less weight in the packaging material than a conventional can. For the dimensions mentioned, the conventional can weighs approximately 50 grams, while the can according to the invention weighs approximately or even less than 40 grams.

Because of this, with a difference? P between the pressure in the can pcan and the ambient pressure pamb, the can (filled) according to the invention can be deformed more than a conventional can, and the contents are capable of holding the can even under high external pressure (? p negative) without the can collapsing, which in practice offers great advantages as described below. Also in the case of a high internal pressure, the flexibility of the can according to the invention compensates for the differences in pressure. This has the effect that it satisfies conventional sterilization procedures. During the sterilization process, the pressure in the can changes as a result of temperature changes. This change in pressure in the can must be compensated by a change in pressure around the can in order to prevent the can from falling off or collapsing on itself. In general, during the sterilization process (autoclave pressure) it remains controlled. If the temperature and pressure of the can are not able to follow the drop in temperature and pressure in the environment fast enough, then the can can permanently deform or collapse outwards. Afterwards, the most common deformation is that of the lid projecting outwards.

A can is produced that collapses inward when the temperature and pressure in the can have decreased, while the pressure in the autoclave is still high. The known rounding, usually in food cans with flange then collapses inwards, in 3, 4, 5 or more sides. During the cooling process, the risk of a can deforming outward (discharging outward) changes the can deforming inwardly (collapsing inward). This means that during cooling the pressure in the environment of the known can must be allowed to gradually reduce. In practice it has been shown that it is difficult to control this ambient pressure. This is due to, based on local conditions, position and orientation, there are differences in the pressure in the cans due to differences in the heating / cooling speeds of the cans. Currently the collapsed is overcome by imposing high demands on the mechanical strength of the can. For example, the can for food known from? 73 x 110 mm must be able to withstand a pressure differential? P of px ref .. = 1.2 bar to p2 = 1.75 bar without deforming permanently. The working interval for? P extends from p? ref .. until p2 ref_ where? p <; p1 ref of the known can will collapse inward, where? p > p2ref .. where the can will explode. With the can according to the invention, the relationship between the pressure difference in the can and the expansion volume is much more flexible than with a can of conventional reference foods. This has many advantages. First, as long as the can is filled leaving an empty space of a certain maximum amount, there is no risk of the can collapsing inward. With the conventional cans there is a risk that the walls of the can collapse inwards in the case where? P > p-t. To avoid this, the wall of the known can has its bending stiffness increased by ridges that are placed around the circumference and a material of adequate thickness is used, for example greater than 0.16 mm for a food can of? 73 x 110 mm. With the flexible can, its potential to expand is such that the overpressure outside the can can be supported by the contents of the can and no longer by the side wall of the can. The can according to the invention can withstand a very high external pressure. For the can according to the invention, it is no longer necessary to place demands on the stiffness (thicknesses, flanges) of the can wall to prevent the wall of the can from collapsing inwardly. Consequently, the working range of this can is quite greater. In practice, this means that pressure control of the autoclave is much easier to obtain. With regard to the pressure in the autoclave which is greater than the pressure in the can nothing can malfunction. Figure 4 provides the results of several experiments, in which the cans according to the invention are filled to close them completely on top with water of 80 ° C on a pair of scales, and in order to create some empty space , 2.5%, 5% and 10% of water are respectively removed. The cans that are filled in this way until the filling extension of 90%, 95% and 97.5% are subsequently closed, and after cooling to room temperature in a pressure chamber, tests are performed to determine their behavior. Figure 4 represents vertically the deformation of the lateral wall of the can, and horizontally the external pressure in the bars, and in the rear the filling extension expressed in percent. During the test, the fact of exerting an overpressure that increases in stages of 0.5 bar (0.5 ... 3 bar) alternates with the atmospheric pressure (0 bar). It is clear that it is observed that with a higher extension of filling greater than 95%, the permanent deformation is practically less than with a smaller extension of filling. Therefore, with the can according to the invention, a large amount of the external load is supported by the content, so that less demanding requirements need to be imposed on the can itself. Because the can has its highest potential to expand, the empty space in the can can be reduced. This means that the can according to the invention can contain more food, and that the risk of the perishable condition as a consequence of the inclusion of oxygen is reduced. Third, it is no longer necessary to place horizontal flanges on the wall of the can, which increased the axial strength of the can. The axial resistance is necessary in order to avoid damage to the can during processing, for example when placed side by side and locked, and during transport. This also has the advantage that the product design, for example, a label or printing can be performed more easily and offers a more attractive appearance. Finally, it is now possible to use even thinner material for the wall of the can. In Figs. 5, 6 and 7, various properties of the different shapes of the cans have been illustrated in the diagrams. With dashed lines and points, further indicated with the reference number 1, the properties of conventional cans with a diameter of approximately 73 mm and a height of 110 mm have been illustrated. The solid lines, indicated with the reference number 2, are related to cans of similar height but with a square cross section, with a width and a depth of approximately 66 mm and with rounded corners with a curvature R as shown in the figure 3. Dashed lines, indicated by reference number 3, are related to cans of similar height but with a square cross section with a width and depth of approximately 66 mm and with flattened corners, as shown in the lower part of the Figure 3. Figure 5 illustrates the flexibility of these cans. Along the horizontal axis, the pressure change in bar exerted on the cans is shown, and along the vertical axis the relative change in volume in% is shown. All the cans were closed but empty. Apparently, the can with the flattened corners (3) combines a high flexibility with an increased performance before the implosion. Figure 6 illustrates the failure of the cans under different pressure conditions in an autoclave, indicated along the horizontal axis in absolute pressure in the autoclave, in bars. All the cans have been filled up to a top space free of 5% of the contents of the can. Along the vertical axis, the pressure difference? P (= Pean + Pamb) on the body of the can has been indicated. The horizontal lines with reference numbers la, 2a and 3a illustrate the strength of circular-cylindrical cans, square cans with rounded corners and square cans with flattened corners per se. The known 1 can of 73 x 110 mm shows an almost linear relationship of p with the absolute pressure of the autoclave. At the intersection x of lines 1 and 1, the can will fail and produce an implosion. Similarly at the intersections of lines 2 and 2a, respectively of lines 3 and 3a, square cans with rounded corners and square cans with flattened corners will become rigid and will undergo implosion. In the case of the circular-cylindrical can, the pressure of the autoclave is completely responsible for the high difference between the internal pressure of the can and the pressure of the autoclave. The pressure difference? P is completely supported by the wall of the can. Contrary to this, the relationship is strongly non-linear for non-circular filled cans. As a result of the volume change in the can, the pressure of the autoclave is partially supported by the rigidity of the can body and partially supported by the pressure increase in the free space. It can be concluded that the aforementioned tin with flat corners resists a higher autoclave pressure compared to existing circular and non-circular cans. This allows the use of a much thinner material for the body of the can. Figure 7 shows along the vertical axis the maximum autoclave pressure in bars that can be supported by the filled can for different free spaces, indicated in%. It is evident that for practical free spaces between 2 and 15%, the can with flat corners withstands extremely high autoclave pressures. It can be concluded that it is very unlikely that there will be an inclusion of the aforementioned can with flattened corners (line 3).

Claims (6)

1. A metal body for packaging purposes, comprising a closed metal cover extending around a longitudinal axis which is suitable to be provided on a side referred to herein as the upper part with a cover running essentially perpendicular to the longitudinal axis, the cover It comprises n essentially flat cover parts, the body is characterized in that 3 = n = 6, and wherein the cross section through the cover, in the upper part and near the upper part has a contour which alternatively comprises n pieces of contour lines which are concavely inwardly curved with a minimum radius of curvature R, and n substantially straight contour line pieces, as well as in the fact that the cover comprises at least 2n essentially flat cover portions which are separated from each other by a pronounced fold that runs essentially parallel to the longitudinal axis, fold which you has a maximum radius of curvature r = 0.4 R.

2. The body as described in claim 1, wherein R = 15 mm.

3. The body as described in claims 1 or 2, wherein r = 5 mm.

4. The body as described in one of the preceding claims, characterized in that the flat roof portions run essentially parallel to the straight contour line parts.

5. The gas-tight can filled with a non-carbonated beverage or food, such as vegetables, fruits, pet food, fish, meat or soup, comprising a metal body as described in one of claims 1 to 4.

6. The can as described in claim 5 for packaging steel, wherein the thickness of the packaging steel material from which the body is made is thinner than 0.16 mm.