| 简介 |
PROBLEM TO BE SOLVED : To restrain a rare-metal chip from being peeled off caused by a difference of thermal stresses, and as a result, to aim at elongation of life of a spark plug.
SOLUTION : The spark plug 1 is provided with a ground electrode 27, to a tip part of which 27, a rare-metal chip 32 is joined. The ground electrode 27 and the rare-metal chip 32 are joined by a melting part 34 formed by melting a metal material and a rare-metal material. The melting part 34 is provided with a base-end-side melting part A formed at a base end side of the ground electrode 27 and a front-end-side melting part B formed at a front end side of the ground electrode 27. As the melting part 34 is viewed at a cross section including a center axis Y of the rare-metal chip 32 along a longitudinal direction of the ground electrode 27, a sum of a cross-sectional area of the base-end-side melting part A and a cross-sectional area of the front-end-side melting part B is to be 4.0 mm2 or more, and a cross-sectional area of the front-end-side melting part B is 1.1 to 1.3 times greater than that of the base-end-side meting part A.
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