Technical field

The present invention relates to a method and apparatus for making cans for storing e.g. foodstuff, such as cookies. More particular, the invention relates to production of cans by fastening a can body to a bottom part.

Background of the Invention

A large number of different methods and apparatuses for making cans made of three pieces, a body part, a bottom part and a lid, are known. These cans are made by fastening the bottom part to the body part by folding their respective edge together in order to provide a seamed connection between these.

Fig. 1 shows a prior art method of fastening a can body 1 to a bottom part 2. The can body comprises a curl end portion 3, and the bottom part 2 comprises a flange 4 having a curl end portion 5. The body 1 is attached to the bottom part 2 by moving the seaming tool 6 radially into contact with the flange while rotating the can body in relation to the tool until the two end portions 3, 5 are seamed together, as shown in the right illustration of fig. 1.

Fig. 2 shows another prior art method of fastening a can body 1 to a bottom part 2. The can body 1 comprises a lower end portion 3, and the bottom part 2 comprises a flange 4. The body 1 is attached to the bottom part 2 by moving the seaming tool 6 upwards into contact with the flange and portion 3,4 until these are seamed together as shown in the right illustration in fig. 2.

Both of these methods provides a seaming which can be seen from outside the container and which provides a kind of base on which the container stands. This base takes up space when stacking the containers on top of each other.

Further, as the seam is provided outside the container, the diameter of the pre-punched bottom part has to be larger for the same diameter of container than if the seam was provided inside the container. Thus, a substantial amount of material need to be used for making this can. Description of the Invention

It is an object of the present invention to provide a method and apparatus for fastening a can body to a bottom part, wherein the material consumption for making the can is reduced in order to provide a more cost efficient production of cans.

It is a further object of the present invention to provide a method and apparatus for fastening a can body to a bottom part, wherein the stacking volume of the produced can is reduced.

It is a further object of the present invention to provide a method and apparatus for fastening a can body to a bottom part, wherein the final container has a smoother outer look.

The present invention overcomes the above-described disadvantages by providing a method for fastening a can body to a bottom part, the method comprising the steps of:

providing a bottom part having a bottom wall and a sidewall extending upwards from said bottom wall and terminating in an outwardly curled rim portion, a radial opening being defined between said sidewall and the curled rim portion, ■ providing a can body having first and second opposite ends, positioning said can body and bottom part in relation to each other in a curling or folding tool having a first tool path for said first end, ■ pressing on said second end whereby the first end curls by following said first tool path and enters into said opening and engages with an internal side of said curled rim portion, so as to fasten the can body to the bottom part.

Preferably, the tool comprises

■ a base portion for supporting said bottom wall, • a wall portion extending upwards in relation to the base portion for supporting the can body, the transition from the wall portion to the base portion being defined by:

said first tool path for the first end of the can body, and a second tool path provided adjacent to and circumvented by the first tool path for supporting an edge of the bottom part defined between said bottom wall and said sidewall. The bottom part is placed in the base portion of the tool such that the bottom wall is supported on said base portion and such that said edge of the bottom part is positioned and supported by the second tool path. The can body, which is preferably a cylinder, is then positioned over the bottom part, such that the body surrounds the bottom part and such that the first end of it is in engagement (not necessarily) with the first tool path. By pressing on the opposite second end of the can body, the first end will be pressed against the first tool path and curls according to the radius of curvature of the first tool path, while entering into the opening between the sidewall and curl portion of the bottom part.

The method provides a can where the seam between the bottom part and the can body is provided on an inner side in relation to the can body, and thus the can has a more smooth outer surface without any visible seams or curled portions.

Furthermore, as the seam is provided inside the can body, the bottom part can be pre- punched with a smaller diameter (or circumference if its not circular) than a bottom part for the prior art methods mentioned earlier, and thus a huge reduction of material consumption is achieved for a produced can having the same volume.

Preferably, the radius of curvature of the second tool path is substantially equal to the radius of curvature of the edge of the bottom part.

This method may be carried out in a press, wherein said tool may be positioned below a plunger.

As the bottom part preferably comprises a sidewall having a given height, the first tool path is provided higher than the second path in relation to the base portion, such that a sidewall of the tool between the first and second path supports the sidewall of the bottom part.

However, it may be that the bottom part is pre-punched without (or with a minimal) sidewall, such that the bottom wall of the bottom part almost terminates in a curled rim portion. This method may of course also be used to such bottom parts, and in that case, the first and second tool path will be positioned closer to each other or even at the same level in the tool.

In order to ensure that the first end of the can body follows the first tool path properly, said first end is preferably pre-curled prior to be positioned in relation to the bottom part in the tool. The bottom part is preferably pre-formed in a conventional manner, such as deep drawing the part from a sheet blank.

The method may further comprise the step of inwardly curling the second end of the can body after the can body has been fastened to the bottom part, so that the upper edge is rounded in order ease the mounting of a lid on the can.

The method according to the invention further has the advantage that it allows the entire circumference of the first end to be curled and fastened to the bottom part in one single step of pressing, as the tool supports the first end of the can body along its entire extension.

The present invention also relates to an apparatus for fastening a can body to a bottom part having a bottom wall and a sidewall extending upwards from said bottom wall and terminating in an outwardly curled rim portion, a radial opening being defined between said sidewall and the curled rim portion, the can body having first and second opposite ends, the apparatus comprising;

a curling or folding tool wherein said can body and bottom part is to be positioned in relation to each other, the tool defining a first tool path for said first end, and

■ means for pressing on said second end so as to press the first end towards said first path and into said opening for engaging with an internal side of said curled rim portion, so as to fasten the can body to the bottom part.

Preferably, the tool comprises

a base portion for supporting said bottom wall a wall portion extending upwards in relation to the base portion for supporting the can body, the transition from the wall portion to the base portion being defined by:

said first tool path for the first end of the can body, and ■ a second tool path positioned adjacent to and circumvented by first tool path, said second path supporting an edge of the bottom part defined between said bottom wall and said sidewall.

The radius of curvature of the second tool path is preferably substantially equal to the radius of curvature of said edge of the bottom part. The means for pressing may comprise a press having a plunger for pressing on said second end, the tool being adapted to be positioned in said press.

The apparatus may further comprise a support member to be positioned inside the bottom part for supporting the bottom wall and sidewall on their opposite sides in relation to the support provided by the base portion of the tool.

The tool may of course be provided with different types of tool path geometry, such as circular, oval, quadrangular or polygonal, and thus it is possible to produce cans having a circular, oval or polygonal cross-section. Thus, the bottom part and can body may be circular or oval or polygonal, and the can body may be cylindrical or conical.

The can body and bottom part are preferably made of conventional sheet metal, such as tinplate, aluminium or aluminium alloys, e.g. having a thickness of 0.12 mm to 0.2 mm.

Description of the figures

A preferred embodiment of invention will now be described in details with reference to the accompanying figures 3-6.

Figs. 1-2 shows prior art methods of attaching a can body to a bottom part, as described above.

Referring to fig. 3, a preferred tool 7 is shown from above having a base portion 8 and a wall portion 9.

Fig. 4 shows the tool in cross-section A-A of fig. 3, and as shown the tool 7 comprises a base portion 8, a wall portion 9 and first and second tool paths 10, 11 defining the transition between the base portion and wall portion (best shown in fig. 5).

Fig. 5 shows section B of fig. 4, where the first path 10 extends along the entire circumference of the tool 7 and has a predetermined radius of curvature for a first end of the can body (not shown), when pressing the can towards said path. The second path is provided lower than the first path and has a radius of curvature being almost equal to the radius of curvature of an edge of the bottom part defined between its bottom wall and sidewall (see fig. 6).

Fig. 6 shows the tool 7 wherein the can body 1 and bottom part 2 are positioned in relation to each other. The can body 1 has a first end 3 that has been pre-curled before being inserted into the tool 7. The tool 7 comprises a first tool path 10 having a predetermined radius of curvature for the first end of the can body 2. When pressing on a second end 4 of the can body, the first end 3 will follow the first tool path 10 and be curled into the curl portion 12 of the bottom part - shown with dashed lines (3a).

The tool 7 has a second tool path 11 having a radius of curvature being equal to the radius of the edge 13 of the bottom part, and thus provides a support therefore when pressing the can body into the curl portion 12.

The final result of this method is an attachment/fastening as shown in fig. 7, wherein the seam is provided inside the can and thus provides a much smoother outer surface. Depending on the height of the sidewall of the bottom part 2, the base on which the can stand may be varied.

As the seam between the can body and bottom part is provided inside the can, the diameter of the bottom part can be reduced for the same diameter of the produced can in relation to prior art methods. Tests have shown that a reduction of 12% is achievable in relation to the above-mentioned prior art methods for a can of the same diameter. The diameter of the punched bottom part can e.g. be reduced from app. 211 mm to 198 mm for a can having a diameter of 200 mm. Thus, the method and apparatus provides a more cost efficient production of cans.