| 摘要 |
PROBLEM TO BE SOLVED: To prevent the generation of breakdown and loose-out of an electrode material, and while to prevent the generation of welding fault by integrally forming an arc electrode with an electrode supporting part with melting of the high-conductive metal, and specifying the diameter of the fire resistant metal grains forming the electrode. SOLUTION: An upper and a lower opening parts of an insulating cylindrical body 35 are provided with end plates 38a, 38b so as to form a vacuum container. A fixed electrode 30a and a movable electrode 30b provided in this vacuum container have arc electrodes 31a, 31b made of the alloy, which includes fire resistant metal grains, high-conductive metal and low-melting point metal, and electrode supporting parts 32a, 32b made of the high-conductive metal and for supporting the arc electrodes 31a, 31b. These arc electrodes 31a, 31b and the electrode supporting parts 32a, 32b are integrally formed with each other by melting of the high-conductive metal. The fire resistant metal grains at 140μm or more of grain diameter are included at 5% or less by weight in relation to the all fire resistant metal, the grains at 70-140μm of grain diameter are included at 45-90% by weight, and the grains at 40-70μm of grain diameter are included at 7-35% by weight, and the grains at a diameter less than 40μm are included at 0.5-15% by weight.
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