This invention relates generally to attaching ends to can bodies and more particularly to a process and apparatus for pressing can ends onto can bodies and forming a tight, hermetic, curled double seam.
In manufacturing cans, high-speed automatic machinery is utilized for high-production rates. Once a can body is formed, one end is then attached prior to attaching a second end and filling. End closures can be attached to can bodies in a number of different ways but most require bending of the can material into a mechanical joint such as by curling an edge of the end closure into the opening between a flanged edge of the can body and the can body itself, using a side pressure. Oftentimes a suitable sealing compound is inserted within the joint or seam to form a hermetically sealed end. When one end is attached to a can body or if a can body is a single piece body, it can then be filled with suitable product and finally closed for packaging and shipment.
The most common method of forming hermetic double-end seams is by "roll" seaming, using a side pressure. Roll seaming requires that the can be made to revolve by being driven with a chuck after which "seaming rolls" are caused to advance toward the curl of the can end and roll the curl end to the can body so as to form a mechanical lock. Another alternative often used is to hold the can in a stationary position, again using a seaming chuck, and to cause the seaming rolls to revolve about the can end, after which the seaming rolls are caused to advance and to roll in the curl flange of the can end, using a side pressure. Similarly, this method also forms a mechanical lock with the can body. Using these end-attachment methods, either the can itself or the seaming rolls which iron the curl end to the can body are caused to revolve at high speeds. With either of these methods, there is a limitation as to the number of cans which may be closed (or seamed). This limit is imposed for a number of reasons. In the case where the can is caused to revolve, the cans must be automatically fed into the closing machine and caused to be accelerated radially at high speeds. Also, when a base plate, the bottom portion of the tooling which picks the can body up and raises it to the seaming position, is rotating rapidly and when a body is fed onto a base plate, they "chatter" and become unstable. When cans with thick side seams are rotating at high speeds, they often cause the seaming rolls to skip while forming the end seam. Another problem is that the side pressure from the seaming rolls used to iron the end seam down is oftentimes excessive, causing bearings to wear out rapidly.
Others have considered the aforenoted problems with roll seaming and two examples of press forming of the seams may be seen by referring to U.S. Pat. No. 3,385,249--Czarnecki, and U.S. Pat. No. 3,908,572--Johnson et al. The Czarnecki patent discloses an end seaming process and apparatus for forming a mechanical joint having a gap within the seam. By providing the annular gap, it is apparent that no side or vertical compressive forces are applied to form a flat, tight joint. The joint formed by Czarnecki does not result in a tight, well-sealed joint and would not withstand particularly high internal pressures. The Johnson et al disclosure (see particularly FIGS. 10 and 11) shows an end closing process and apparatus where radially moving fingers press the edge of a can end in against the can body; however, the edge is not curled upwardly into a flange portion on the can body. Johnson et al does disclose an overall end closing method and apparatus with certain elements being adaptable for use with the present invention. For example, the tooling comprising the machine portion of the present invention could be individually mounted on a typical rotating turret used in high-speed can closing operations. A plurality of individual closing devices are commonly mounted about the circumference of the typical turret and are functionally operable through cams rolling on circular, suitably contoured cam rings.
Accordingly, from the foregoing, one object of the present invention is to provide a can end closing method and apparatus that is operable at high speeds without the aforementioned typical problems with roll seaming.
Another object of the invention is to form a pressed hermetic double-end seam that is tight and firmly locked.
Still a further object of this invention is to provide a closing apparatus that is adaptable for use with currently available machine systems.
These and other objects will become more apparent upon reading the specification to follow in conjunction with the attached drawings.