Truncated cone metal container and method for manufacturing the same

Abstract: A '3-piece' truncated cone shaped container (1) is described, which is made of welded sheet metal and has absolutely smooth internal surface, so that the container can be easily cleaned. The container is easy to stack, and has a ring shaped upper lip (6) that is concave (7) in the centre. A method for manufacturing above container is also described.

Description: Background to the Invention The invention consists of a '3-piece' truncated cone shaped container which is made of welded sheet metal and has absolutely smooth internal surface, so that the container can be easily cleaned and its contents completely removed. The container is easy to stack, and has ring shaped upper lip that is concave in the centre. A method for manufacturing the above container is also described. Previous Methods Metal containers, with lids, are often used to contain, pack, and transport a large number of very different products in a wide range of technical fields. Purely as an example, we mention here food products (ice-cream, confectionary, dressings, and sauces, etc.), agricultural products and their derivates (fruit, vegetables, juices, sauces, and concentrates, etc.), chemical products (all types of ink, putty, paints, dyes, and solvents, etc.), and so forth. Cylindrical or truncated cone shaped containers stiffened by grooves or reinforcing ribs on their side walls are both well known and widely used, however the reinforcing ribs can create serious problems both from an economic and ecological point of view. If containers can be completely cleaned, the product, often expensive, packed in them can be completely consumed, thus making the containers themselves easier to recover and recycle, and avoiding (or at least helping to avoid) containers with not inconsiderable quantities of the products packed in them (often hazardous and polluting) being dumped in the environment. In order to meet the aforementioned requirements, it would be advantageous to use, at least for more expensive and/or potentially polluting products, containers with totally smooth interiors, in other words without any grooves or ribbing in which hard to remove deposits of the material packed in them can form. The interior of completely smooth containers is easier to clean with brushes and/or jets of water or solvent, for example. The smooth containers (preferably truncated cone shaped ones) available on the market are made by drawing a normally pre-painted and/or pre-printed metal sheet and folding the edge into a lip in one or more rolling stages. The truncated cone shape makes the sheet metal drawing process easier and makes it possible to stack the containers, thus saving space; the external lip allows, amongst other things, to handle the containers easily, to attach the lid well, and to easily separate two containers that have been stacked one inside the other. There are however numerous disadvantages to these drawn containers (known as '2-piece' containers as they consist of a drawn body and of a lid), including the fact that: The thickness of the sides is not uniform, they are thickest at the base and progressively thinner towards the upper lip; The drawing process is slow and expensive, and requires several stages of stamping before the desired depth is gradually reached. Each of these stages requires the use of a machine, often very bulky, that is capable of developing the considerable power necessary for drawing, and the molds (mold and counter-mold) are costly because they must be made of special materials and are subject to considerable and rapid wear; It is difficult to print lettering and artwork on the side wall. It is in fact extremely difficult to lithograph the truncated cone shaped side wall of the finished product and achieve a satisfactory result. As an alternative, it is perfectly possible to lithograph onto the sheet metal whilst it is still flat, but lettering and artwork are inevitably distorted ( often of unacceptable amount) when the container is drawn; Containers are often required that have a special internal protective coating, which is difficult to apply to a truncated cone shaped finished product, and if the coating is applied to the flat sheet, it is inevitably damaged when the sheet is drawn, as cracks form, the coating is lifted from the support, etc. As an alternative to '2-piece' truncated cone shaped containers, '3-piece' (lid, side wall, and base) truncated cone shaped containers are also well known and widely available on the market, and do not suffer from the above mentioned disadvantages, as: The side wall is obtained by forming (in an 'coning' machine, well known to one skilled in the art) a cylindrical body obtained from a flat sheet by cutting, rolling, and welding. This production process is much faster and cheaper than drawing, and does not require the use of expensive and bulky special machinery and molds; The sheet metal used is far less thick than that required to produce a drawn container of the same size; Wall thicknesses are uniform over the entire side wall, and can be the same thickness as the base and lid, which are manufactured separately; The flat metal sheet can easily be lithographed and/or coated with a protective coating. The process by which the side wall is formed does not damage coatings or distort lithographed artwork. DE-A-2 819 490 refers to a container whose body is hollow-cylindrical in the mouth region and cone-shaped in the lower region: in the cylindrical mouth region an "open" edge rolling is provided, which is turned over outwardly, projects downwardly and comprises a hollow bead, a flat constriction and a support for a tool for lifting off the cover of the container; the lower end of the edge rolling is formed as a stacking support to allow the storage of two containers by stacking one container inside the other. The edge rolling is "open" as a gap is always provided between the mouth region of the container body and the stacking support. DE-A-3 041 001 refers to a production method and to a "coning" machine (comprising an elastic punch and a rigid external matrix) for realising (according to said production method) a cone-shaped container made of welded sheet metal by forming a metal cylindrical body: to form the cone-shaped container from the metal cylindrical body, the elastic punch is inserted into the metal cylindrical body and then pressed against the external matrix. We wish to specifically draw attention to the fact that in the present description, the term 'metal sheet' is used to signify any type of tinned or chromed strip, or even more generally, any type of thin metal sheet that is protected and is suitable for manufacturing the above described containers. Summary of the Invention The object of the present invention is a container made of welded sheet metal and including a truncated cone-shaped side wall with a smooth interior and a base attached to the side wall by a folded seam, said container being characterized in that the upper edge of the side wall is cone-shaped and folded to produce a closed, curvilinear ring-shaped lip which comprises a concave central area. A particularly advantageous method for manufacturing the above mentioned container is a further object of the present invention. List of Figures The invention is described with reference to a non-limiting embodiment, that is shown in the attached figures, wherein: Figure 1 shows a container according to the invention, without its cover and partly cross-sectioned; Figure 2 schematically shows the main steps of the method for producing a container according to the invention; Figure 3 shows a sequence of some steps of the working of the side wall according to the invention; Figure 4 shows an enlarged detail of the upper edge of the side wall; Figure 5 schematically shows the exterior side of a 'coning' machine modified according to the invention and with a narrowed area. Detailed Description Figure 1 is a partly cross-sectioned view of a container (1) according to the invention - in the attached figures, the lid is always omitted in order to make the drawings easier to understand. The truncated cone shaped smooth side wall (2) is visible in figure 1, to which the base (3) is attached by a folded seam. As can be seen, the lower part of the side wall (2) has a narrower area (4) deep enough for the folded seam area (5) attaching the base (3) to the side wall (2) to be within the truncated cone shape of the side wall (2). The upper edge of the side wall (2) is folded over, preferably by pressure-forming, to form a ring shaped lip (6) with a central concave area (7), as can be seen clearly from the cross-section on the left of figure 1 and the cross-section shown in figure 4. A simple and efficient method of producing a container according to the invention, including the ring-shaped lip (6) with the particular cross-section shown in figures 1 and 4, is described with reference to the other figures. The ring shaped edge (6) enables the lid to be attached and removed from the container more easily, and to separate two containers that have been stacked one inside the other to reduce storage space. In a preferred embodiment of the invention, the dimensions of the ring shaped lip (6) are such that the lower part of the ring shaped lip (6) of a container (1) makes contact with the upper part of the ring shaped lip (6) of a second container (1) that has been stacked inside the first. Figure 2 schematically shows the main steps of the production process that is an object of the present invention. The two edges of the side wall (2), obtained (step A) by rolling and then welding a piece of sheet metal, are worked, as will be fully described with reference to figure 3, to produce the fold area (10) and edge (13) (step B). The side wall is then formed using a machine known to one skilled in the art as a 'coning' machine so that it becomes truncated cone shaped (step C), and the container is then completed by folding the seam that attaches the base (3) to the side wall (2) (step D). Figure 3 shows a sequence of four steps of the process used to pass from step A to step B of figure 2. The folded seam area (10) of the lower edge (11) of the side wall (2) is shaped by a first die (16) and prepared for being attached to the base (3) by a folded seam, and the upper edge (12) of the side wall (2) is shaped by a second die (17) to form a lip (13) consisting of a closed circular shaped loop (14). In known production processes, this circular shaped looped lip is formed at the end of the production process and, in any case, once the container has assumed its final truncated cone shape: this enables the dimensions of the lip to be controlled with sufficient accuracy to ensure that the lid seals hermetically. A characterizing feature of the production process according to the invention is the fact that the circular shaped closed loop lip (14) is produced whilst the side wall (2) is still cylindrical in shape, and is then further shaped by pressure exerted by the second die (17) until it forms an elongated shaped closed loop lip (15). In a preferred embodiment of the invention, the two dies (16 and 17) consist of two suitably grooved discs that act simultaneoulsly at both edges (11 and 12) of the side wall (2) along the entire circumference of the side wall. Once the circular shaped loop (14) has been produced, the second die (17) effects a second stroke of a length comparable with the larger axis of the elongated shaped loop (15). A further characterizing feature of the production process according to the invention is the fact that the tensions that are created in the lip (13) when it is subjected to stretching during the 'coning' step, cause the permanent deforming of the central area of the lip (13) (which is less rigid than the external folded areas of the lip), and the concave area (7) is thus spontaneaously formed and does not require the use of molds, tools, or further production steps. Figure 5 is a cross-section of a detail of a 'coning' machine (18) modified according to the invention. The part of the 'coning machine' (18) with the narrowest diameter has a narrowed section (19) that is used during the 'coning' steps to create a narrower part (4) of the side wall (2) deep enough that once the seam folding stage following the 'coning' step has been completed, the folded seam (5) attaching the base (3) to the side wall (2) is within the truncated cone shape of the side wall (2). Within the scope of the invention as defined in the claims, a skilled man may make a number of improvements or modifications to the above described container and to its production method that arise through normal experience and the natural evolution of the relevant art.

Claims: Container made of welded sheet metal and including a truncated cone-shaped side wall (2) with a smooth interior and a base (3) attached to said side wall (2) by a folded seam (5), characterized in that the upper edge (12) of said side wall (2) is cone-shaped and folded to produce a closed, curvilinear ring-shaped lip (6) which comprises a concave central area (7). Method for the production of a container made of welded sheet metal and including a truncated cone shaped side wall with a smooth interior and a base attached to the side wall by a folded seam, this method including at least the following steps: realising a cylindrical side wall (2) by cutting a section of metal sheet, rolling this section of metal sheet, and then welding its ends together; forming a first edge (11) of said cylindrical side wall (2) so as to be suitable to be attached to said base (3) by a folded seam; forming said cylindrical side wall (2) by a 'coning' machine; forming the second edge (12) of said side wall (2) to obtain a lip (13) with a circular closed loop (14) cross-section; folding said folded seam to attach said base (3) to said formed first edge (11) of said cylindrical side wall (2); and characterized in that: said lip (13) with a circular closed loop (14) cross-section is produced before forming said cylindrical side wall (2) by said 'coning' machine (18); said lip (13) with a circular closed loop (14) cross-section is pressure formed until it forms an elongated closed loop shaped lip (15); said elongated closed loop shaped lip (15) is produced before forming said cylindrical side wall (2) by said 'coning' machine (18); when said side wall (2) is formed by said 'coning' machine (18), the central area of said elongated closed loop shaped lip (15) bends inwards forming said concave area (7). Method as in Claim 2, characterized in that said first and second edges (11 and 12) of said cylindrical side wall (2) are simultaneously formed by pressing dies, and in that said circular closed loop shaped lip (14) obtained by die pressure on the second edge (12) of said cylindrical side wall (2) becomes said elongated closed loop shaped lip (15) because of a further axial pressure of the corresponding die (17). Method as in Claim 3, characterized in that once said circular closed loop shaped lip (14) has been formed on said second edge (12) of said cylindrical side wall (2), said corresponding die (17) makes a further stroke whose length is equal to the length of the larger axis of said elongated closed loop shaped lip (15). Method as in Claim 2, characterized in that the narrow part of said 'coning' machine (18) has a narrower section (19) designed to create, during the 'coning' step, a narrower section (4) in the lower part of said side wall (2) of such a depth that said folded seam (5) attaching said base (3) to the side wall (2) is within the truncated cone shape of said side wall (2).

Inventors: CEREDA VINCENZO, CEREDA, VINCENZO
Applicants: S I L F A SOCIETA IMBALLAGGI L, S.I.L.F.A. SOCIETA' IMBALLAGGI LATTA FUSTI ACCIAIO S.R.L.
Application year: 1992
Main classification: B65D6
IPC codes: B21D51, B65D21