| 摘要 |
PROBLEM TO BE SOLVED: To obtain an inexpensive backing material with which welding for assembling a diaphram is surely executed and weld defects such as hot-water leakage is not generated by forming a radius part corresponding to the inner peripheral surfaces in the corner parts of a steel pole on the outer peripheral surface in the tubular corner parts of the backing material. SOLUTION: A male die 12 and female die 16 of a bending jig 11 are attached to a bending machine and the corner part of the welding backing-material 3 is set between the male die 12 and the female die 16. By pressing the male die 12 with the bending machine and pressurizing the inner peripheral surface 14 of the corner part of tubular structure of the backing material 3 for welding with the projection 13 for radius parts of the male die 13, the radius part 15 is formed on the outer peripheral surface in the corner part of the welding backing-material 3. Pressurization is furthermore continued and recessed parts are formed on the outer peripheral surfaces on both sides of the corner part with the projections 17 having a circular-arcuate cross section provided on the female die 16. The radius part 15 does not become a small radius by only pressurizing with the projection 13, so it is necessary to form the recessed parts with the projections 17. Since the depth of the recessed parts is small, the recessed parts do not cause defective welding at the time of welding.
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