| 摘要 |
PURPOSE:To improve the mass productionability by setting the communication hole of bulb into an oval having the short diameter in the axial direction of glass tube and the long diameter same with the outer diameter of the glass tube thereby suppressing formation of lump in the axial direction of glass tube thus reducing fracture of bulb. CONSTITUTION:A burner 21 is inserted through the open ends 11a, 12a of the juxtaposed glass tubes 11, 12 to weld them 11, 12 and to form a communication hole 14 by means of the flame of burner 21 and the wind pressure. Then the vecinity of the open ends 11a, 12a including the jointing section 13 is heated and encapsulated and prior to choking of the communicating hole 14, metal die 22 splitted into two having the short diameter X in the axial direction B-B of the glass tube and the long diameter same with the outer diameter D of the tubes 11, 12 is mounted while enlarging the hole 14 then the air is blown from the other ends 11b, 12b of the tubes 11, 12 to fit the tubes 11, 12 with the metal die 22 thus to form a U-shaped glass bulb 1. Because the short diameter is in the axial direction B-B, turning up of glass at the circumferential edge of said hole 14 due to the flame of burner 21 is reduced to suppress lumping resulting in reduction of rejection rate of bulb due to fracture. |
