Metal containers and their manufacturing method and apparatus

In a method of manufacturing a metal container which includes the steps of fitting a tray-like end plate into an end of a cylindrical body so that a body flange formed by bending the edge of the body outwardly perpendicular to the body axis overlaps an end plate flange formed by bending the edge of the end plate outwardly so as to extend along and beyond the body flange, fitting a seaming chuck having a cylindrical forming face into the indented part of the end plate and abutting the cylindrical portions of the end plate and body from which said flanges extend against said seaming chuck, and sequentially pressing a seaming roll and a nip bending and press forming roll radially inwardly against said flanges, each roll having a circumferential forming groove opening toward the forming face of the seaming chuck, while rotating the forming face of the seaming chuck so that the forming grooves seam the body and end plate flanges into a triple seam, the improvement comprising the steps of:

• providing a nip bending recess in the corner of the cross-sectional profile of the forming groove in the nip bending and press forming roll which is toward the end of the container with said flanges therein at the start of the action of said nip bending and press forming roll;
• with a nip-bending recess,
• moving the nip bending and press forming roll radially inwardly in a first seam forming step and bringing said nip-bending recess toward the edge of the plate flange for contacting the bottom of the recess and the edge of the plate flange for nip-bending the radially outer edge of the end plate flange;
• stopping movement of the nip bending and press forming roll at a position where the nip-bent edge has a constant angle of from 90.degree. to 150.degree. and a predetermined length, and holding the nip bending and press forming roll at said position;
• then moving the seaming roll toward the nip-bent edge for seaming the body and end plate flanges together with the forming groove in the seaming roll to form a rolled seam;
• and then, after completion of the movement of said seaming roll;
• moving the seaming roll away from the thus rolled seam and simultaneously moving the nip bending and press forming roll further toward the seam for forcing the forming groove of said nip bending and press forming roll against the thus rolled seam for press forming the middle portion of the radially outer surface of the seam for forcing the top radially outer portion of the seam into said recess and pressing the parts of the flanges together and thereby simultaneously finishing the seam into a desired shape having, as a whole, a generally elongated rectangular shape when viewed in cross-section with at least the top portion of the radially outermost surface arching convexly outwardly and a middle portion thereof extending generally parallel to the axis of the container.