AN IMPROVED BOTTOM PROFILE FOR A CAN

Abstract: A thin metal pressure-resistant can comprising a can body having a deep-drawn and wall-ironed cylindrical side wall, the can body comprising an outwardly convexed bottom integrally with said body and an inwardly projecting dome.

Description: AN IMPROVED BOTTOM PROFILE FOR A CAN The invention relates to a thin metal pressure-resistant can comprising a can body having a deep-drawn and wall-ironed cylindrical side wall, such as for instance a beverage can. Further the invention relates to a metal can body comprising such an improved bottom profile. Partly for environmental reasons too, there is a continuing aim for manufacturing beverage cans of the type mentioned in the preamble, which cans are manufactured in very large numbers, ever more lighter in weight by starting with a thinner basic material. With a reduction of the material thickness of beverage cans, for instance from a thickness of the basic steel material of 0.26 mm to less than 0.22 mm, it appeared that the resistance against an internal a pressure of over 100 psi in particular of existing bottoms of standard beverage cans are not in all cases sufficient, causing the occurrence of unacceptable deformation of the beverage cans. A further existing requirement in respect of the resistance of the bottom, regardless of the material thickness, is that the standing rim of a beverage can should not deviate more than 0.4 mm in an axial direction with a test pressure up to 100 psi as to allow a good stability of a standing beverage can. Cans having a bottom profile comprising an outwardly convexed bottom integrally with said body, are known from The Canmaker, November 1996, pp. 43 - 44, "Light years ahead", and European Patent Application EP-A-040014. A bottom profile according to said article comprises a flat bottom, which has at its centre an inward flat projection. An object of the present invention is to provide a can with an alternative bottom and bottom profile, which has a higher resistance so as to allow thinner basic materials to be used. The can in accordance with the invention is characterized in that the can body comprises an outwardly convexed bottom integrally with said body and an inwardly projecting dome. By this combination of features it is achieved that the bottom of the beverage can is more resistant against internal pressure and meets the requirements set out above using thinner materials. The dome, which is relatively small compared to the diameter of the can, can expand into convex shape as an indication of an unexpectedly pressure increase in a closed beverage can. A thin-walled can with an outwardly convex bottom integrally with said body has the required pressure resistance and is easy to manufacture. A preferred embodiment of the can in accordance with the invention is characterized in that the dome has a diameter in the range of 18 - 30 mm for a can with a diameter of more than 55 mm, and more preferably by the dome has a diameter in the range of 20 - 25 mm. By this it is achieved that the dome will expand from a concave shape into convex shape at a pressure rise in a closed beverage can of about 7 bar or more. In a preferred embodiment of the can in accordance with the invention, the can has a plurality of seating dimples which allows the can to stand more stable on a flat surface. Preferably the can in accordance with the invention is from a basic steel material thickness of less than 0.22 mm, and more preferably of less than 0.20 mm. By this it is achieved that the can itself weights 20 grams, while it is able to withstand the required pressure of 100 psi. The can according to the invention is made of a packaging steel and typically has a side wall thickness of said body after wall-ironing equal to or less than 0.10 mm, even equal to or less than 0.06 mm. The seating dimples extend below the lowest part of the convex bottom and the setting area is offset within practical limits towards the periphery consistent with the requirements of adequate strength. The number of seating dimples can be chosen freely. The height of the seating dimples relative to the convex bottom depends significantly on the requirement whether the can should be stackable or not. When it is not required that the can is stackable with other cans of a similar type, the height of the seating dimples can be kept as low as possible, preferably in the range of up to 4 mm. This allows for a stable positioning of the can on a flat surface. Relatively short seating dimples are easy to produce in the convex shaped bottom of a can. The seating dimples can be attached to the bottom of the can in various manners, such as welding or adhesion. In a preferred embodiment the dimples are integrally with said can body. When it is also required that the can should be stackable with similar type of cans, the height of the seating dimples should be in a range of 4 to 6 mm when using a standard stay-on-tab lid. Modifications of such a standard lid might lead to a reduction of the height of the seating dimples, which is preferred in respect to the ease of manufacture. The invention will now be explained by reference to the drawings in which Fig. 1 gives schematically a standard 60 - 65 mm diameter can body part in accordance with the state of the art; Fig. 2 gives schematically a part of a can body part in accordance with the invention; Fig. 3 gives schematically a part of a can body part in accordance with the invention, with a plurality of seating dimples; Fig. 4 gives schematically a can body part as function of the height of the seating dimples. Fig. 1 shows a part of the bottom of an axi-symmetrical can comprising a standing rim (1) and a hollow part towards the inside, also called dome (2). Fig. 2 shows a part of the bottom of the can in accordance with the invention comprising an outwardly convexed bottom and a small inwardly projecting dome at the centre of the bottom, which dome can flop out as an indication of an unexpectedly pressure increase in a closed beverage can. The dimensions of the dome are set so that the dome will deform significantly at a pressure of 7 bar or more. Fig. 3 shows a part of the bottom of the can in accordance with the invention which also includes a plurality of seating dimples. These seating dimples allow the can to stand more stable on a flat surface. Fig 4A shows a part of an axi-symmetrical can body with an outwardly convexed bottom with the dome in accordance with the invention. Fig. 4B shows a part of a can body as shown in Fig. 4A, but also including seating dimples which allow the can for a stable positioning on a flat surface. Fig. 4C shows a part of a can body as shown in Fig. 4B, but with higher seating dimples, which makes the can stackable to a can with for example an at least partly outwardly projecting stay-on-tab lid.

Claims: CLAIMS 1. A thin metal pressure-resistant can comprising a can body having a deep-drawn and wall-ironed cylindrical side wall, the can body comprising an outwardly convexed bottom integrally with said body and an inwardly projecting dome. 2. The can according to claim 1, characterized in that the dome has a diameter in the range of 18 - 30 mm. 3. The can according to claim 1 or 2, characterized in that the dome has a diameter in the range of 20 - 25 mm. 4. The can according to claim 1, characterized in that the outwardly convexed bottom has a plurality of outwardly projecting seating dimples. 5. The can according to any one of claims 1 - 4, characterized in that the metal is a packaging steel. 6. The can according to claim 5, characterized in that the bottom has a material thickness of not more than 0.22 mm. 7. A can body for use in a can according to any one of claims 1 - 6.

Inventors: KAMPERMAN STEPHANUS MARIA, TAMIS PAULUS JOZEF, KAMPERMAN, STEPHANUS, MARIA, TAMIS, PAULUS, JOZEF
Applicants: HOOGOVENS STAAL BV, KAMPERMAN STEPHANUS MARIA, TAMIS PAULUS JOZEF, HOOGOVENS STAAL B.V., KAMPERMAN, STEPHANUS, MARIA, TAMIS, PAULUS, JOZEF
Application year: 1997
Main classification: B65D1
IPC codes: B65D1