PURPOSE: To allow the welding in a short time by specifying the distance between an outer tube cullet section and an outer tube cullet receiver for the optimum softening contraction based on the inner diameter of an expected outer tube sealing section and the outer diameter of the flare outer periphery of a stem.
CONSTITUTION: In the method to weld an expected outer tube sealing section 109a and the flare outer periphery 2a of a stem 2 by softening and shrinking a lamp with a burner 108, the distance Xmm between an outer tube cullet section 110 and an outer tube cullet receiver 107 is set to -6.7X+90≤d/D≤-1.4X+90(%), 40<d/D(%), where D is the inner diameter of the expected outer tube sealing section 109a and (d) is the outer diameter of the flare outer periphery 21 of the stem 2. The softening contraction is thereby generated quickly, and the welding can be performed in a short time.
UCHIDA MINORU
SATO OSAMU
KIRYU MASAYUKI
