Such can lids with which the invention is concerned, comprise a cover ring, which is produced by deep-drawing and stamping from a coated sheet metal blank, made e.g. of tinplate, chromed plate or aluminium. Provided on the outer edge of the cover ring is an external rim for later formation of a double seam, and the inner edge of the cover ring has an annular flange formed by a flat-pressed rolling, which surrounds a lid opening. A tear-off portion closing the lid opening is attached by heat-sealing to the annular flange. In such can lids, the opening extends over the entire surface surrounded by the relatively narrow cover ring. In this way, after the tear-off portion, usually formed by an aluminium foil, is peeled off, similarly to a full tear-off lid, a relatively large container opening is provided, so that the contents of the can are easily accessible. The rolling of the inner edge of the cover ring is intended to remove the risk of injury and also to contribute to increased rigidity of the can lid. Due to the external rim, such can lids can be extremely reliably connected to the can body by a double seam, and the tear-off foil ensures simple opening of the lid by peeling off the tear-off portion which is connected to the cover ring by heat-sealing. Such an easily-opened can lid and a method for its manufacture are described in DE 28 38 505.
In this known method of manufacturing an easily-opened can lid from a lacquered sheet metal blank, firstly a groove, corresponding to the ring contour of the cover ring, and comprising a groove base and two groove walls, is shaped by a first deep-drawing process in the blank, an outer rim on the one hand being formed at the edge of the blank for later formation of a double seam, and on the other hand a flat indentation being formed, surrounded by the outer rim. This flat indentation consists of a wall portion, i.e. the inner groove wall and a base portion surrounded thereby. The wall portion extends substantially vertically to the base portion. An opening is then stamped in this base portion in such a way that the cut edge by means of which this opening is formed extends at a certain spacing from the wall portion or the inner groove wall. In this way it is intended to form an annular leg forming a collar from the groove wall, and which extends from the groove wall to the cut edge. Stamping of the opening gives rise to a circular sheet metal disc as waste. The annular leg is then aligned straight, i.e. is bent upwards into the plane of the inner groove wall, and a groove-like shaping is introduced thereon in the groove base by deep-drawing, then the portion formed from the inner groove wall and the annular leg is bent upwards and outwards by further widening as far as the groove base, and pressed on to the groove base. This forms, inside the cover ring, an inner opening surrounded by a hollow lateral bead, whose diameter roughly corresponds to that of the previously-formed inner wall. The round sheet metal disc resulting during stamping of the original opening from the base portion has a diameter which is still substantially smaller than that of the final opening. As, in previously-known can lids, this cannot be further used, the stamped-out discs can only be re-used as scrap. As the area of the stamped-out disc as a rule comes to more than half of the area of the original sheet metal blank, the loss of material is extremely high. In addition, in order to close the final lid opening, a separate aluminium foil is required, which must be coated with a layer which is capable of heat-sealing. In order to save material, this foil is frequently extremely thin, so that there is a risk that said foil may be accidentally pierced.
The object of the invention is therefore to indicate a method of manufacturing an easily-opened can lid from a sheet metal blank, which enables re-use of the sheet metal part resulting when the opening is stamped, and thus reducing loss of material to a minimum. The further object of the invention is to provide an easily-opened can lid of the type already mentioned, likewise with the aid of enabling re-use of the stamped-out sheet metal part and reducing loss of material.