Background of the Invention There are known cans presenting a cylindrical tubular body obtained by conventional operations of cutting the metallic sheet, calendering the sheet to the cylindrical tubular shape and longitudinally welding the sheet for laterally closing the body.

Aiming at increasing the structural resistance of the lateral wall of the can body, the latter is often submitted to an operation, usually in a milling machine, in order to provide the lateral wall with a certain number of circumferentially reinforcing ribs, which are axially spaced from each other and slightly projecting inwardly the can body.

Said ribs are obtained by deforming the cylindrical lateral wall of the can body, allowing to increase its structural resistance in the radial direction, and consequently the use of a thinner metallic sheet for manufacturing the can, thus relevantly reducing the cost of the final product.

Nevertheless, the above mentioned constructive solution is only economically and industrially viable when applied to cylindrical cans, in which the ribs are circumferentially developed, with no interruption and without causing a structural weakening of the can in the axial direction. In the cylindrical cans, the provision of the continuous circumferential ribs does not reduce the resistance of the can against axial

compression forces to levels sufficient to impair the normal operation of the can, being therefore possible to compensate the thickness reduction of the metallic sheet by providing the reinforcing ribs.

However, in the case of the cans with a polygonal cross-section, more specifically the cans with a square section and rounded longitudinal edges, the provision of said continuous circumferential reinforcing ribs to increase the resistance of the walls against radial forces and to allow a corresponding thickness reduction in the metallic sheet, has not proven to be convenient because such ribs weaken in an unacceptable manner the longitudinal edges of the can, which suffer a great reduction in their resistance against axial compression forces, impairing the operation of the can. The attempts to compensate for the thickness reduction in the metallic sheet of cans with a square section, by providing continuous circumferential ribs, have not reached a satisfactory result, due to the degree of weakness produced in the longitudinal edges of the can.

The interruption of the circumferential ribs in the region of the longitudinal edges of the can requires such rib extensions to be produced only on the lateral wall portions, by rather complex operations which lead to the production of undesirable wrinkles in the end regions of each circumferential rib extension. These inconveniences have prevented the cans with a polygonal, usually square cross-section, from having the thickness reduction of the metallic sheet compensated by the provision of circumferential reinforcing ribs.

In patent application PI 9801887-6 of the same applicant, there is proposed a technical solution to provide the desired circumferential rib extensions

only on the lateral wall portions in the tubular body of the can, said solution comprising the initial step of manufacturing a cylindrical tubular body from a metallic sheet with a longitudinal seam, providing said cylindrical tubular body with continuous circumferential ribs. Then, the cylindrical tubular body is expanded to the desired polygonal cross- section, whereby the circumferential ribs are eliminated in the region of the rounded edges of the expanded polygonal tubular body.

Although allowing to obtain an economically viable can with a polygonal contour, with a structure that is much more resistant than those cans without ribs, this prior solution of the same applicant presents an aspect that may be improved, resulting from the fact that the metallic sheet regions, which in the initial step are circumferentially ribbed and located in the edges of the cans, are posteriorly deformed, in order to eliminate the ribs in these regions, when the circumferentially ribbed cylindrical tubular body is expanded to the desired polygonal contour. This deformation of the metallic sheet in opposite directions in the region of the edges causes a certain material fatigue, which, joined to the fact that the deformation of the metallic sheet back to the original condition is not complete, prevents the structural resistance of the can, particularly against compression axial forces, from reaching greater values.

Aiming at minimizing the undesirable effects of double deformation of the metallic sheet in the region of the longitudinal edges of the can, the same applicant has proposed the provision of longitudinal rib extensions in said can edges. Although providing new elements with axial structural reinforcement, these

longitudinal rib extensions in the can edges did not eliminate the effects of double deformation of the metallic sheet, as above mentioned, maintaining the limitation as to obtaining a substantial increase in the structural resistance of the can.

Disclosure of the Invention Thus, it is an object of the present invention to provide a process for manufacturing a can with a polygonal, usually square cross-section, which allows, by means of simple operations, to provide said can with circumferential and longitudinal reinforcing rib extensions, without provoking weakness in the longitudinal edges of the can and allowing to reduce the thickness of the metallic sheet which forms the lateral walls of the can.

A further object of the invention is to provide a can with a polygonal cross-section, whose tubular body is provided with longitudinal and circumferential rib extensions with a substantially increased structural resistance.

The process for manufacturing a can with a polygonal cross-section comprises the initial step of forming, from a metallic sheet, a tubular body having a cylindrical lateral wall with a longitudinal seam.

According to the invention, the manufacturing process further comprises the steps of: -expanding the tubular body of the can to a desired polygonal cross-section, by deforming its cylindrical lateral wall, in order to define rounded longitudinal edges matching with flattened lateral wall portions; -deforming the flattened lateral wall portions of the tubular body, in order to provide each of them with a plurality of circumferential rib extensions, which are axially spaced from each other, and with at least one longitudinal rib extension, said rib extensions being

defined by a certain degree of radial plastic deformation in the respective region of the flattened lateral wall portion of the tubular body; and -double-seaming a bottom and an upper wall of the can to the tubular body of polygonal cross-section.

According to the new process, the steps of forming the can body are simple, do not require complex proceedings and are the same as those generally used, until the point of obtaining the lateral closing of the tubular body of the can.

However, from this point on, the steps of forming the cans with a polygonal cross-section are distinct from those already known. The tubular body is then expanded from the original cylindrical shape to the desired polygonal tubular shape, without the provision of any longitudinal and circumferential rib extensions thereon.

Only after completing the step of expanding to the polygonal tubular shape it is possible for the can body to have its lateral wall portions deformed, in order to define the longitudinal and circumferential rib extensions.

This solution allows providing the can with said rib extensions, by submitting the metallic sheet to one deformation only (not reverted) in these regions, increasing the resistance of the lateral wall portions and allowing a substantial reduction in the thickness of the metallic sheet without structurally weakening the can.

Brief Description of the Drawings The invention will be described below, with reference to the attached. drawings, in which: Figure 1 illustrates a perspective view of the tubular body having a cylindrical lateral wall with a longitudinally double seam, obtained by a known

initial step of forming the can from a metallic sheet; Figure 2 is a perspective view of the tubular body of the can illustrated in figure 1, but after said body has been expanded to a polygonal cross-section shape, which in the example, is square; Figure 3 illustrates a partially cut perspective view of the can with a square section of figure 2, but already provided with circumferential and longitudinal rib extensions according to the present invention; Figure 4 is a magnified cross-sectional view of the can of figure 1, taken along a lateral wall portion of the can, illustrating the relative disposition of the rib extensions; and Figure 5 illustrates a magnified and partial longitudinal sectional view of a lateral wall portion of the can of figure 1.

Detailed Description of the Invention As illustrated in figure 1, the invention is applied for manufacturing cans with a polygonal cross-section.

The present process requires the known steps of producing a tubular body, such as that of cutting a metallic sheet of a predetermined thickness and presenting dimensions that are calculated in order to form, after being calendered, a cylindrical tubular body 10, with a perimeter which is substantially equal to the perimeter of the polygonal cross-section of the can to be produced. The lateral closing of the tubular body 10 is usually obtained by mutually longitudinally welding the end edges of the calendered metallic sheet, forming a longitudinal seam 11.

According to the process proposed herein, the tubular body 10, still in the calendered cylindrical form, is expanded, in a machine (not illustrated) of any adequate known construction, so that the cylindrical lateral wall thereof is radially deformed, as

illustrated in figure 2, to the desired shape with a polygonal cross-section. In this step of expanding the tubular body 10, radial forces are applied thereon, to form the rounded longitudinal edges 12 matching with the flattened lateral wall portions 13.

After completing the expansion of the tubular body 10 to a polygonal cross-section shape, the deformation of the flattened lateral wall portions 13 takes place, in order to provide each of them with a plurality of circumferential rib extensions 20 and with at least one longitudinal rib extension 40.

The circumferential rib extensions 20 are disposed in a plurality of planes transversal to the axis of the can and which are axially and mutually spaced, each circumferential rib extension 20 having a length which is at maximum equal to the width of the respective lateral wall portion 13 on which it is formed preferably by radially deforming the metallic sheet inwardly the can.

The longitudinal rib extensions 40 are preferably dimensioned to practically occupy the whole height of the tubular body 10 of the can and disposed in order to intercept the circumferential rib extensions 20 provided in the same flattened lateral wall portion 13.

In the illustrated preferred embodiment, each flattened lateral wall portion 13 is provided with a pair of longitudinal rib extensions 40, the extremes of the same side of the plurality of circumferential rib extensions 20 of the same flattened lateral wall portion 13 ending in a respective longitudinal rib extension 40.

The degree of deformation of the lateral wall portions 13 of the tubular body 10, that is, the dimensioning of the circumferential and longitudinal rib extensions

20 and 40 is determined as a function of the desired increase in the structural resistance of these lateral wall portions, allowing a substantial reduction in the thickness of the metallic sheet.

With the new process, it is possible to obtain a can with a polygonal cross-section, with a reduced thickness of the metallic sheet and which is structurally reinforced by circumferential and longitudinal rib extensions 20 and 40 in the flattened lateral wall portions of the can, without submitting the metallic sheet to reverse double folds.

In the illustrated embodiment, the circumferential and longitudinal rib extensions 20 and 40 have a rounded V shaped section. However, it should be understood that this basic shape may suffer certain modifications, without neglecting the desired reinforcing function.