Patent Publication Number: US-2015082749-A1

Title: Metal can for a food product

Description:
FIELD OF THE INVENTION 
     The present invention relates to a metal can, for preserving a food product sterilised by heat treatment after the closing of the can. 
     PRIOR ART 
     Traditionally, as shown in  FIG. 1 , the cans were formed by a rectangular sheet metal portion  10  folded and welded in such a manner to form a body, with a bottom  11  and a lid  12  formed of sheet metal plates assembled at both ends of this body. Such a can is called a “three-part” can, because it involves three separate elements welded or seamed together. 
     More recently, as shown in  FIG. 2 , cans have been produced by drawing a sheet metal, called a flank, so as to form into a single integral body  20  the bottom and the side wall of the can body. A lid  23  formed of a sheet metal plate then permits to close this can. Such cans, whose bottom and side wall form a single part, are called “two-part” cans. 
     As shown in  FIG. 3 , which is a sectional view of the can of  FIG. 2 , such can has a variable thickness, according to the height in the can, within a range of +25% to −25% of the initial thickness of the flank. 
     Another drawing technology, commonly called DWI (“Drawn and Wall Ironing”) technology, has been developed, which makes it possible to form “two-part” cans whose side walls are ironed.  FIG. 4  is a sectional view of such a can  30 . The thickness “e” of the centre of the bottom  31  of this can is substantially equal to the thickness of the flank that has been drawn. The thickness of the bottom is between +0% and −15% of this thickness “e”, as the shaping thereof is liable to locally cause a slight thinning. On the other hand, the thickness “e′” of the wall  33  is reduced down to 20% of the thickness “e” of the centre of the bottom. The lid  32  has the thickness “e″” of the sheet metal in which it has been formed. 
     This DWI technology makes it possible to produce cans, hereinafter called “ironed-wall cans”, lighter in weight than the other types of can. Their characteristics make them advantageous for being used as beverage-can, but they remain not very appropriate for being used as cans for food products. Indeed, the latter must be submitted, after the closing thereof, to a sterilisation by heat treatment that induce positive and negative variations of the internal pressure in the can. 
     The most often used ironed-wall cans, and in particular the beverage-cans, are not adapted to such pressure variations. The use of such cans for containing food products is consequently of little interest, and thus remains rare. 
     Objects of the Invention 
     One object of the present invention is to overcome these prior art drawbacks. 
     In particular, one object of the invention is to provide metal cans for preserving a food product sterilised by heat treatment after the closing of the can, using an optimized quantity of material. 
     Another object of the invention is to provide such cans, whose sterilisation by heat treatment, after the closing thereof, is facilitated and consumes a minimum quantity of energy. 
     The invention has also for object to make it possible to manufacture and easily implement such cans, using at most material and elements that are identical or similar to those used for the prior art cans. 
     Disclosure of the Invention 
     These objects, as well as others, which will become more clearly apparent hereinafter, are reached by a metal can, for preserving a food product sterilised by heat treatment after the closing of the can, made up of an integral body forming the bottom and the side wall of the can, and of a lid assembled to this body so as to close the latter, the minimum thickness of the side wall being between 20% and 60% of the thickness of the centre of the bottom, the height of the can being, according to the invention, between 1.5 and 3.5 times the width thereof, and preferably between 1.7 and 3 times, and the bottom and/or the lid of the can having a central wall with an outwardly convex shape, connected to the side wall by a peripheral groove opening up outwards. 
     Such a can may be manufactured with an optimized quantity of material, and may be subjected to a sterilisation heat treatment without any damage and consuming less energy than the prior art cans. 
     Preferentially, the internal pressure of the can is higher than the atmospheric pressure. 
     This characteristic, in combination with the other characteristics of the can according to the invention, contributes to the rigidity of the can. 
     Advantageously, said peripheral groove has a first wall connected to the convex central wall, a second wall connected to a peripheral area of connexion to the side wall of the can, and a bottom forming a rounded shape, and:
         the first wall forms an angle between 2° and 45° with the axis of the can,   the connexion between the first wall and the central wall forms a rounded shape with a radius greater than 0.5 mm,   the depth of the groove is between 1 mm and 7 mm, and   the rounded shape of the bottom of the groove has a radius smaller than 5 mm.       

     A bottom or a lid with such characteristics provides the can with a good resistance to internal pressure. 
     According to an advantageous embodiment, the lid is made up of a disk of steel-based material, the can capacity is 212 ml, 425 ml or 850 ml, and to these capacities are associated lids of diameter 52 mm, 65 mm and 83 mm, respectively. 
     According to an advantageous embodiment, the lid is made up of an aluminium disk, the can capacity is 212 ml, 425 ml or 850 ml, and to these capacities are associated lids of diameter 52 mm, 63.7 mm and 81.5 mm, respectively. 
     These combinations of lid sizes and standard can volumes make it possible to implement the invention, respecting the food packer needs and using the existing lids and seaming equipment. 
     According to an advantageous embodiment, beads are formed on the side wall of the can so as to increase the resistance thereof to the external pressure. 
     The present invention also relates to an integral body of a metal can, for preserving a food product sterilised by heat treatment after closing of the can, the body comprising a bottom and a side wall, the minimum thickness of the side wall being between 20% and 60% of the thickness of the centre of the bottom, the height of the body being, according to the invention, between 1.5 times and 3.5 times the width thereof, and preferably between 1.7 and 3 times, and the bottom having a central wall with an outwardly convex shape, connected to the side wall by a peripheral groove opening up outwards. 
     This body makes it possible to manufacture a can such as described above. 
     Preferentially, the peripheral groove of this body has a first wall connected to the convex central wall, a second wall connected to a peripheral area of connexion to the side wall of the can, and a bottom forming a rounded shape, and:
         the first wall forms an angle between 2° and 45° with the axis of the can,   the connexion between the first wall and the central wall forms a rounded shape with a radius greater than 0.5 mm,   the depth of the groove is between 1 mm and 7 mm, and   the rounded shape of the bottom of the groove has a radius smaller than 5 mm.       

     According to an advantageous embodiment, beads are formed on the side wall of the body so as to increase the resistance thereof to the external pressure. 
    
    
     
       LIST OF FIGURES 
       Other purposes, advantages and characteristics of the invention will become more clearly apparent from the following description of a preferred embodiment, non-limitating of the object and scope of the present patent application, in connection with the appended drawings, in which: 
         FIG. 1  is a schematic view of the elements constituting a can of the “three-part” type according to the prior art; 
         FIG. 2  is a schematic view of the elements constituting a can of the “two-part” type according to the prior art; 
         FIG. 3  is a sectional view of the can of  FIG. 2 ; 
         FIG. 4  is a sectional view of the ironed-wall can of the prior art; 
         FIG. 5  is a sectional view of a can according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION 
     The “three-part” cans and the “two-part” cans produced by a conventional drawing process have a thickness that varies between +25% and −25% of the thickness of the flank used. To optimise the quantity of metal implemented to manufacture such a can of a given capacity, the diameter “D” of the can is close to the height “h” thereof. 
     Therefore, standard sizes have been defined by the profession for the cans intended to contain food products, in particular by the standards EN 13 025 to 13 029, implementing for example lids forming disks with the following diameter:
         99 mm for the cans of 850 ml capacity;   83 mm for the cans of 425 ml capacity;   65 mm for the cans of 212 ml capacity.       

     These sizes, which are conventionally used, make it possible to obtain cans with a diameter that does not differ by more than 20% from the height thereof, with an optimised quantity of material. 
     Due to its low thickness, the side wall of the body of an ironed-wall can does not have naturally a satisfying rigidity with respect to the external stresses. 
     A conventional technique to reinforce this rigidity consists in forming beads on the body of the can to improve the resistance thereof to the side external pressure. However, these beads do not favour the resistance of the can to a vertical effort. 
       FIG. 5  is a schematic sectional view of a cylindrical can  40  according to a preferential embodiment of the invention. The side wall  43  of this can has been ironed with the “DWI” technology. Hence, the lowest thickness “e′” thereof is between 20% and 60%, and preferably between 30% and 50%, of the thickness “e” of the middle of the bottom  41 . 
     To reinforce the rigidity of this can, a substance is added to the content of the latter, before the closing thereof, which, when vaporizing, produces an overpressure inside the can. This substance, which may be for example liquid nitrogen, has for effect to rigidify the pressurized can and to improve the resistance thereof both to the side external pressure and to the vertical effort. 
     The cans for food products must, unlike the beverage-cans, be submitted to a sterilisation by heat treatment after the closing thereof. Such sterilisation, which involves to heat the content of the can to a temperature of about 110° C. to 150° C. (preferably between 110 and 135°), generates a pressure increase inside the can up to about 3 bars. Such increase is more important for the pressurized cans, in which the pressure may reach 5 bars. 
     Generally, the side wall of the can undergoes a very small deformation under the effect of this pressure. Only the bottom and the lid get out of shape, and allow the expansion of the can, thus limiting the increase of the internal pressure during the sterilisation process. For a can with a given volume, the greater the size of the bottom and the lid, the greater the possible expansion thereof. 
     The one skilled in the art was thus convinced up to now that, to undergo a heat treatment after the closing thereof, the ironed-wall cans had to have a bottom and a lid with a great enough size with respect to the height thereof. In practice, these cans have the common proportions of the cans containing food, whose diameter is close to the height. 
     As determined by the inventors, to optimise the quantity of metal implemented to manufacture a pressurized ironed-wall can of a given capacity, the height “h” of the can must be greater than the diameter “D” thereof. This height has thus to be between 1.5 and 3.5 times, and preferably between 1.7 and 3 times, the diameter D. 
     Consequently, the conventional proportions of the cans intended to contain food products did not make it possible, up to now, to optimize the quantity of material of the ironed-wall cans. The one skilled in the art was led to think that the use of ironed-wall cans was of little interest for the food products. 
     The can  40  shown in  FIG. 5  has a height “h” that is between 1.7 and 3 times the diameter “D” thereof, which makes it possible to optimize the quantity of metal implemented for the manufacture thereof. 
     To permit the heat treatment of this can  40  without generating an excessive internal pressure, the lid  42  and the bottom  41  have a particular shape with a central wall,  421  and  411 , respectively, having an outwardly convex shape, connected to the side wall of the can by a peripheral groove,  420  and  410 , respectively, opening up outwards. This particular shape facilitates the elastic deformation of the bottom and the lid in case of internal overpressure. Bottoms and lids of this type are well known in themselves and are notably described in the document EP 1 813 540. 
     The lid  42  thus has:
         a central wall  421 ,   a peripheral area  422  for the seaming thereof with the side wall  43  of the can,   a peripheral groove  420 , having a first wall  423  connected to the central wall  421 , a second wall  424  connected to the peripheral area  422 , and a bottom  425  forming a rounded shape.       

     In this lid  42 , the first wall  423  forms an angle of about 45°, and in any case between 2° and 45°, with the axis of the can; the connexion between the first wall  423  and the central wall forms a rounded shape with a radius greater than 0.5 mm; the depth of the groove  422  is between 1 mm and 7 mm; and the rounded shape of the bottom  425  of the groove has a radius smaller than 5 mm. 
     Likewise, the bottom  41  has:
         a central wall  411 ,   a peripheral area  412  of connection with the side wall  43  of the can,   a peripheral groove  410 , having a first wall  413  connected to the central wall  411 , a second wall  414  connected to the peripheral area  412 , and a bottom  415  forming a rounded shape.       

     In this bottom, the first wall  413  forms an angle of about 5°, and in any case between 2° and 45°, with the axis of the can; the connection between the first wall  413  and the central wall  411  forms a rounded shape with a radius greater than 0.5; the depth of the groove  410  is between 1 mm and 7 mm; and the rounded shape of the bottom  415  of the groove has a radius smaller than 5 mm. 
     The grooves  410  and  420  having these characteristics facilitate the deformation of the bottom and the lid, respectively, of the can  40 . Therefore, when the can  40  is heated during the heat treatment thereof, the increase of its internal pressure causes the temporary and reversible deformation of the bottom  41  and the lid  42 , which increases the internal volume of the can. This volume increase makes it possible to limit the effective pressure in the can  40  to values that do not risk damaging it. 
     The lid  42  and the bottom  41  providing a better resistance to the internal pressure, it is therefore possible to manufacture a pressurized ironed-wall can that can be sterilised by heat treatment, and whose height to diameter ratio can be chosen in such a way to optimize the quantity of material used. 
     In other possible embodiments of the invention, it is possible that only the lid, or only the bottom, is designed so as to exhibit a good resistance to the internal pressure. 
     It is also to be noted that the invention is not limited to the shown bottom and lid profiles. Other profiles allowing the can to support high pressures can be implemented, as for example those described in the document EP 1 813 540. 
     The volumes of the cans are standardised, in particular by the standards EN 13 025 to 13 029. The modifications of the can proportions in order to optimize them have thus to be made, preferably, with keeping identical volumes. 
     Moreover, the sizes of the can lids are also standardised. For the can manufacturers, it is important to respect these standards because the application of the lids for the closing of the cans is not performed by the can manufacturer but by the food packer that fills the can. The lids used have thus to be adapted to the seaming machines used by the food packers. 
     To modify the can proportions of the cans without having to use lids of non-standardized diameters, it has been imagined by the inventors to size the cans, for each standard capacity, in such a way that they can be closed by the standard lids commonly used to close cans of lower capacity. 
     Therefore, it is advantageous, for the cans closed with lids formed in disks of steel-based material, to use:
         lids of 52 mm diameter for cans of 212 ml capacity,   lids of 65 mm diameter for cans of 425 ml capacity,   lids of 83 mm diameter for cans of 850 ml capacity.       

     For the cans closed by lids formed in disks of aluminium-based material, it is advantageous to use:
         lids of 52 mm diameter for cans of 212 ml capacity,   lids of 63.7 mm diameter for cans of 425 ml capacity,   lids of 81.5 mm diameter for cans of 850 ml capacity.       

     These combinations make it possible to easily manufacture cans having proportions close to the optimized proportions. 
     The cans having the characteristics of the invention can be heat sterilised more rapidly and using less energy than the prior art cans. Indeed, the proportions of these cans allow them to have a greater surface of thermal exchange with the outside, which facilitates the heating thereof. Moreover, the thickness of food to be heated in the can is smaller, due to the small width of the latter. The side walls being thinner, they better transmit the heat. Finally, the total quantity of metal material that is heated during the sterilisation of a can is smaller, which consumes less energy. 
     The cans having the characteristics of the invention may also have sizes that make them adapted for a more efficient and more compact storage. Therefore, by way of example, a type of pallet that is used has a length of 1200 mm, a width of 800 mm, and the height thereof has to be between 1000 and 1030 mm. 
     On such a pallet, it is possible to store 1860 conventional cans of 425 ml, having a diameter of 73 mm for a height of 101.54 mm. These cans are stored into 10 layers of 186 cans. On the other hand, it is possible to store 1960 cans of the same volume according to the invention, having a diameter of 65 mm for a height of 128.08 mm. These cans are then stored into 8 layers of 245 cans. The invention thus makes it possible to place 100 more cans on each pallet than in the prior art, i.e. 2400 more cans in a truck transporting 24 pallets. Consequently, it provides substantial saving on the transportation costs. 
     It is to be noted that the lid size is not necessarily equal to the width of the can side wall. It is indeed possible to provide a necking-in at the top of this side wall, for the seaming of a lid having a size that is smaller than the width of the wall. It is also possible, in some cases, to seam a lid having a size that is greater than the width of the can. 
     The present invention may be implemented for cans closed by lids with a size between 20 mm and 153 mm. However, it is preferably implemented for cans closed by lids having a size between 52 mm and 99 mm. 
     In a particular embodiment of the invention, it is possible to shape the side walls of the can in such a way to form therein beads for improving the resistance of the latter to the external pressure. 
     The present invention mainly applies to the cylindrical cans, the quasi-cylindrical cans, the cans with a polygonal (hexagonal, octagonal . . . ) cross-section, the cans whose side walls are slightly “barrel-shape” bulged, or the cans of different shapes liable to have the same proportions. 
     The body of the cans, forming the bottom and side walls of the latter, is also within the scope of the present application, independently of the lid thereof, in particular if it has the characteristics allowing it to form a can according to the invention when associated with a common lid that is not shaped so as to be deformable.