| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug having a significantly increased life, since cracks at a welded joint is prevented, and to provide its manufacturing method. SOLUTION: This spark plug includes a rivet-shaped or a spherical iridium alloy tip portion. The tip portion is coated with platinum, annealed, and then resistance welded to the nickel based electrode of the spark plug. The platinum coating helps to prevent cracks from being caused at the welded joint part. Otherwise, the cracks are considered to be caused by a difference in coefficients of thermal expansion between the nickel based alloy electrode and the iridium based alloy tip portion. In addition, the iridium alloy tip portion is not susceptible to attack by lead or combustion gas. Thereby, the life of the spark plug is significantly increased. COPYRIGHT: (C)2005,JPO&NCIPI
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