| 摘要 |
PROBLEM TO BE SOLVED: To overcome the conventional problem such that part of the molten metal, crushed and molten due to a high temperature, of a ring projection erupts into a pipe in the resistance welding of an upper cover and the pipe. SOLUTION: The upper cover 31 is formed with a flange part 32 having an opposed surface 32a opposed to the flange 2a of the pipe 2, the ring projection 33 protruding from the opposed surface 32a along the circumference concentric with the flange 32, and a circumference-shaped groove part 34 formed in such a manner as to be recessed in the opposed surface 32a inside the ring projection 33. The end of the molten metal of the ring projection 33 is housed in the groove part 34 and is not torn into dust to erupt into the pipe 2 differently from a conventional manner when the ring projection 33 is molten and crushed due to current-carrying and pressure treatment in the resistance welding of the flange part 32 and the pipe 2 to the flange 2a.
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