| 摘要 |
PROBLEM TO BE SOLVED: To securely mount a neck portion to a stem and to prevent groove generation in an neck end in a sealing process, by raising the central part or the periphery of a stem to a neck end, and minimizing and uniformly sealing an air gap between the stem and the surface of the neck end that are mutually in contact. SOLUTION: For fixing a plurality of pins 22 arranged circularly, a stem mound 28 is formed every pin base, and the end of a neck portion 8 is surrounded with a erected portion of a circular rim 32 that bends toward the neck portion 8 in the periphery of a stem disk 26, and the rim 32 with a diameter larger than the outer diameter of the end. Therefore, when the neck portion 8 is connected to a stem 24, a cut surface 8a of the end of the neck portion 8 comes into contact with flat upper surface of the stem disk 26, the outer surface of the neck portion 8 comes into contact with the inner surface of the rim 32. After inter connection of the neck portion 8 and the stem 24, the periphery of the neck portion 8 is heated to melt the end of the neck portion 8 and the periphery of the stem 24, and thereby a micro groove is prevented from occurring between the end of the neck portion 8 and the stem 24.
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