PROBLEM TO BE SOLVED: To increase the strength of a joint part between a binding tube/a binding bar and a side plate at a low manufacturing cost.;SOLUTION: A unit plate material 8 is constituted of a plate part 8a for constituting the side plate in the center and two strip plate parts 8b and 8b extending in parallel with both side parts at the upper end of the plate part 8a for constituting the side plate, from the side parts, as strip plate parts 8b and 8b for constituting a binding bar or a binding tube on both sides of the plate part 8a. Next, a region 8a5 for constituting a reinforcing side on the upper side of a region 8a4 for constituting an upper end reinforcing surface and a main body part 8a1 of the plate part 8a for constituting the side plate on the lower side and a region 8a6 for constituting a connection reinforcing side, are bent at a right angle and in the mutually same direction at a border with the region 8a4 for constituting the upper end reinforcing surface respectively. At the same time, the strip plate parts 8b and 8b are processed into a U shape by bending both their sides in the same direction and later, subjected to a cupping process for rounding off the parts 8b and 8b into a cylindrical shape from the U shape.;COPYRIGHT: (C)2005,JPO&NCIPI
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