Ngk Spark Plug Company, Limited

Katsunari Ninomiya

Wataru Matsutani

Hiroaki Nasu

Chiaki Kumada

In a glow plug and a spark plug, the surface of a main metal shell is coated with a chromate film in which the quantity of trivalent chrome is 95 wt % or more of the contained chrome components and which has a thickness of 0.2 &#x3bc;m to 0.5 &#x3bc;m.

Glow plug and spark plug, and manufacturing method therefor

In a glow plug and a spark plug, the surface of a main metal shell is coated with a chromate film in which the quantity of trivalent chrome is 95 wt % or more of the contained chrome components and which has a thickness of 0.2 &mgr;m to 0.5 &mgr;m.

A method of manufacturing a sheathed glow plug, the glow plug comprising: a cylindrical main metal shell; a heat resisting tube mounted to a leading end of a through hole of the main metal shell; a center electrode, that comprises a leading end axial shaft and a rear end axial shaft coaxially welded each other, disposed in a center portion of the through hole of the main metal shell; and an electric heat generator received in the heat resisting tube, the electric heat generator having one end electrically connected to the center electrode, which comprises a process of manufacturing the center electrode comprising the steps of: making a diameter of a connecting end of one of the axial shafts smaller than a diameter of a connecting end of the other axial shaft; disposing the leading end axial shaft and the rear end axial shaft on the same axis; bringing the connecting ends into contact; and connecting them by a resistance welding after bringing of the connecting ends.

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Tokai, Japan

Katsunari Ninomiya