| 摘要 |
PROBLEM TO BE SOLVED: To improve a productive efficiency of a relief valve by forming an opening of one end of the cylinder as a flow inlet of a fluid, opening a flow outlet of the fluid to a side surface of the cylinder, forming a contract part on an intermediate part of the cylinder as a valve casing by drawing, and slidably housing a bottomed cylindrical valve element in the valve casing. SOLUTION: A pipe raw material 12 formed by cutting a pipe by a prescribed length, is externally fitted around a main shaft 20 of a molder. A positioning pin of a tip end part of a driven shaft 30 is fitted to a positioning hole 22 of a tip end part of the main shaft 20, and a groove mold is formed by the main shaft 20 and the driven shaft 30. The pipe raw material 12 is positioned by attaching an end surface of the pipe raw material 12 to a reference surface of a driving jig 24, and a work tap bolt is fastened so as to fix the pipe raw material 12. In a condition in which push-press disk rolls 45 are rotated, a hydraulic cylinder 41 is extended, a diameter of the pipe raw material 12 is contracted at a groove mold part between the main shaft 20 and the driven shaft 30 so as to form a constriction part 51. After that, it is removed from the main shaft 52, and a valve casing 52 is completed.
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