Ngk Spark Plug Company, Limited

Yoshito Uemura

Wataru Matsutani

Hiroaki Nasu

Makoto Sugimoto

Hirohito Ito

A method for manufacturing a spark plug, the spark plug includes: a cylindrical metal shell having a portion to be caulked and a tool-engaging portion that is to be attached on an engine; an insulator that is inserted into the metal shell and extends axially; and a caulking metallic mold, the method including caulking the portion to be caulked to be fixed to an outer circumferential face of the insulator with the caulking metallic mold, where in the caulking metallic mold includes a face, the face including a hard carbon film that includes an amorphous carbon phase, and the face is contact with or sliding to the portion to be caulked.

Method for manufacturing spark plug and caulking metallic mold

A metal member (with a zinc plating layer for prevention of corrosion) having a sliding expected surface that is expected to slide with the other member is immersed into a chromating bath containing a mixture of trivalent chromium salt and a complexing agent for trivalent chromium. And a chromate coat having a film thickness of 0.2 to 0.5 &mgr;m and composed of trivalent chromium at 95 mass % or more of chromium component contained is formed at least on the sliding expected surface. Thereinafter, its chromate coat is subjected to the heat treatment at temperatures from 85 to 255&deg; C., thereby enhancing the sliding property of the chromate coat As a result, the metal member with chromate coat can be easily slid with the other member.

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Kagoshima, Japan

Yoshito Uemura