| 摘要 |
PROBLEM TO BE SOLVED: To prevent generation of cracks even when a light emission part is hot by fusing between Vycor glass parts welded at both ends of a quartz tube and partly at a tungsten electrode with two intermediate glasses having their prescribed expansion coefficients. SOLUTION: A first intermediate glass part 6 with its expansion coefficient in which welding limit coefficient is within 8 is welded at a Vycor glass part 5 welded at a quarts tube of a quartz bulb 1, and an air exhaust tube 4 is mounted. The tip of the glass part 6 is flare-shaped so as to be easily trimmed during sealing. Preferably, the expansion cofficient of the glass part 6 is 10×10<7> to 18×17<7> . On the other hand, a pulley-shaped second intermediate glass 8 having a taper along an outer periphery of a Vycor glass 7 thermally spayed at a sealing part 2a of a tungsten electrode 2 is welded, and this expansion coefficient is the same as that of the glass part 6. The electrode 2 is inserted into the quartz tube, injected and rotated by a heating Ar gas, welded after preheating between the glass parts 6 and 8 by a processing hand burner 9, and annealed after trimming.
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