| 摘要 |
The spark plug manufacturing apparatus includes a holding plate formed with a plurality of mounting holes penetrating from a front surface to a rear surface thereof for holding therein hollow tubular insulators of spark plugs, each of which is fitted therein with a center electrode and a metal stem provided with a terminal part, and is charged with a powder resistance material between the center electrode and the stem, and an electric furnace for heating the insulators held in the mounting holes of the holding plate. The holding plate is made of a ceramic material containing not less than 50 wt % of silicon nitride.
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