The invention relates to a method of manufacturing a tin filled with food, the tin having a generally cylindrical circumferential outer surface and being provided with a bead, i.e. a deepened wall portion, extending around its circumference.
A method of this kind is known from US-A-3 117 873. This prior art reference relates to a method, in which the tin, after filling and closing, is compressed axially so long that the contents, particular granular or powdery products, such as coffee, provide the wall with an essential additional support. Clearly the strength and stability of this prior art tin is to a substantial degree obtained by a mechanical interaction of forces, i.e. the combination of the tin, the lid and the contents of the closed tin.
It is a purpose of the invention to provide a method of manufacturing a tin, the strength and stability of which is inherent only to the tin itself.
In view thereof, the method according to the invention is characterized in that prior to the closing of the tin by means of a lid, the edges of the bead are pressed substantially one against the other.
Also, the invention relates to a tin having a generally cylindrical circumferential outer surface and being provided with a bead, i.e. a deepened wall portion, extending around its circumference, the tin being manufactured with the method according to the invention.
The invention will now be explained with reference to the drawing showing an arbitrary embodiment.
Figure 1 shows a cylindrical preserving tin 1 having a cylindrical wall 3 provided with a bead 2 around its circumference.
Figure 2 shows the bead 2 on an enlarged scale. The arrows 4 indicate the distance between the edges of the bead 2.
Figure 3 shows the same tin 1. However, in the condition shown in Figure 3 the edges of the bead 2 are pressed towards one another. In order to indicate the difference with Figure 1 the bead 2 is designated by reference numeral 2'. The pressing of the edges towards each other has taken place by exerting an axial force on the tin prior to the closing of the tin by means of a lid.
Figure 4 shows the bead 2' on an enlarged scale. The distance 4' between the edges is appreciably smaller than the distance designated by 4 in Figure 2, as will be apparent from a comparison between the Figures 2 and 4. When stacking a plurality of tins, the edges can be pressed against one another, so that the axial resistance becomes equal to that of a tin which is not provided with a bead 2. The presence of a bead, however, is of vital importance to improve the tin's resistance to collapse, that is to say to exhibit indentations in the body resulting from e.g. the sub-atmospheric pressure occurring in the tin after filling products in the hot state, closing the tin and cooling the tin down. The bead, in that case, serves as a reinforcing element. The resulting reduction of the axial stability is according to the invention avoided by pressing the edges of the bead substantially one against the other. This explains the reason why the axial resistance in this case becomes equal to that of a tin not provided with a bead.
It is noted that the distance 4' may even be zero. For obtaining a satisfactory stackability, it is, however, sufficient for the edges to be relatively near one another, so that when a stack is formed, the edges are pressed against one another.
The invention is not limited to a preserving tin with only one recess of the kind described. Other numers of recesses may be used. Other bead-shapes provide the same result. Therefore, the invention is not limited to the shape shown in the drawing.