| 摘要 |
PROBLEM TO BE SOLVED: To suitably prevent the discoloration of combustion gas at an exhaust port by simple structure. SOLUTION: An annular upper cover 8 forming the exhaust port 23 for combustion gas is formed of a stainless steel plate, and electrolytic polishing treatment is applied to the surface thereof. Specifically, the upper cover 8 after formation is dipped in a container filled with electrolytic polishing solution, the upper cover 8 side is set to a positive pole, and a current is allowed to flow across the upper cover and the negative opposite pole for a specified time. By this, projected parts on the surface of the stainless steel are fused and smoothened, and passivation film with high chromium concentration is formed on the surface thereof to increase resistance against discoloration. COPYRIGHT: (C)2005,JPO&NCIPI
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