| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a stepped square pipe of good appearance at low cost as a square pipe for building that is used in such a manner as ends are connected together, by a simple facility and a simple manufacturing step. <P>SOLUTION: Four surfaces at an end of a square pipe whose cross section is square are provided with a V-groove which is parallel to the length direction of a processed square pipe, to form bellows. Then each of surfaces provided with the V-groove is pressurized by a flat outer die whose surface is flat, so that the end of the square pipe is reduced in diameter. When forming the V-grooves at four surfaces of the end, an inner die in which a V-shaped concave surface is formed is inserted into a diameter-reduced place of the square pipe, and a V-shaped outer die having, on its surface, a V-shaped projection at a position corresponding to the concave surface is arranged outside the square pipe. The V-shaped outer die is pressurized against each surface of the square pipe. <P>COPYRIGHT: (C)2013,JPO&INPIT |
