| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a technique, by which a trunk of a central electrode of a spark plug can be formed at good accuracy. <P>SOLUTION: In a step for manufacturing a center electrode of a spark plug, a columnar electrode member is prepared as a material of the center electrode. From a tip side to a rear end side of the electrode member, an intermediate diameter part with a diameter larger than that of a small diameter part is formed by extrusion molding, and the small diameter part is formed on the tip side of the intermediate diameter part by extrusion molding. Then, an area of a cross section vertical to an axial line direction of the intermediate diameter part is designated as S1 and an area of a cross section vertical to an axial line direction of the small diameter part is designated as S2. When a value of ((S1-S2)/S1×100) is 30 or more, the intermediate diameter part is extrusion-molded, so as to form a trunk of the center electrode. <P>COPYRIGHT: (C)2012,JPO&INPIT |
