| 摘要 |
<p>A manufacturing process of a spark plug is provided, which includes providing a cut body (220) having a thread forming portion (152), which serves as an original form for a metal shell (50). Processing faces (301,311) of thread rolling cylindrical dies (300,310) are pressed against cut body to thereby form a thread ridge (521) by a thread rolling process. A gasket (5) having an inner diameter A larger than an outer diameter (blank diameter) D of the thread forming portion (152) is slide over the thread forming portion 152 before threading. In the thread rolling process, the gasket (5) is pressed by end faces (305,315) of the thread rolling cylindrical dies (300,310) and disposed in a locating portion (59). The maximum outer diameter B of the thread ridge (521) is larger after the thread rolling step than the inner diameter A of the gasket (5) so as to prevent the gasket (5) from falling out.</p> |
