CORNER PIECE-LESS DUCT, METHOD OF PRODUCING THE SAME, AND DUCT-FORMING MACHINE

摘要

A corner piece-less duct etc. with a rational construction, where, combined with effective use of portions that have been conventionally scrapped, the number of parts can be drastically reduced. A duct (10) having a tubular shape as a whole and a rectangular cross section is formed by joining each side end portions of board-like members using seam joints. The start portion and end portion of each of the board-like members are bent in a direction perpendicular to a length direction (Za) to integrally form flange-forming portions (3). Side ends of each of the flange-forming portions are extended in its width direction so as to integrally form corner-forming portions (4), and thus corner portions of the start portion and end portion of the duct are formed. In an extended shape of each of board-like members (1A, 1B), cuts (2) that extend in a width direction (Ya) of the each of the board-like members and have a depth substantially equals to an overlap allowance (W1) of each of the corner-forming portions (4) are formed at portions nearer to the central portion of the each of the board-like members than a start portion (1s) or end portion (1e) in a length direction (Za) of the each board-like member.