Ngk Spark Plug Company, Limited

Niterra Co., Ltd.

Junji Kimura

Keiji Ozeki

A spark plug includes a ceramic insulator, and the insulator includes a melted portion formed by melting a surface of a base material. In a cross section of the insulator, the value obtained by dividing a length of an interface between the base material and the melted portion by the length of a line segment connecting two ends of the interface is 1.1 or more and 1.5 or less.

Spark plug

A spark plug including an insulator and a metallic member such as a metallic shell. In the spark plug, a mark such as a two-dimensional code is provided on the surface of at least one of the insulator and the metallic member. Also, a protective layer covers the mark. The protective layer is optically transparent and contains a fluorescent substance.

Spark plug and method for manufacturing spark plug

A spark plug includes a tip extending in a first direction and an electrode base metal having an extending portion extending in the first direction and connected to the tip through a fusion zone. In a section taken along the first direction and containing a center axis of the tip, in a case where two ends of the interface between the extending portion and the fusion zone are located at the same position with respect to the first direction, the linear distance between the ends is denoted by A, or, in a case where one end is located forward of the other end, the distance from the one end to an intersection between a straight line passing the one end and extending perpendicularly to the center axis and the outline of the fusion zone is denoted by A. The interface length B satisfies a relational expression B/A&#x2265;1.2.

A method for manufacturing a spark plug comprising the steps of: placing an assembly of the center electrode, an insulator, and a metal shell in a pressure resistant vessel and determining whether or not the insulator has a defect by applying a voltage to the center electrode, and bending the ground electrode toward the center electrode after the defect inspection step, the defect inspection step being performed while a pressure in the pressure resistant vessel is changed to a plurality of different pressures.

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Nagoya, Japan

Junji Kimura