| 摘要 |
PURPOSE:To make it possible to change a porous glass base material having a large diameter into a transparent glass base material, by reducing the dimension of the porous glass base material prepared by the VAD method under preheating, and subjecting the material to a treatment for obtaining the treansparent glass base material. CONSTITUTION:A heating furnace preparing transparent glass is constituted of a preheating furnace (5a) for carrying out only the reduction in the dimension of a porous glass base material and a high-temperature heating furnace (5b) for carrying out the final transparentizing (clarifying) having a smaller capacity than the furnace (5a). Fine particles of core and cladding fine glass particles are deposited on a starting base material 3 by synthetic torches 1 and 2 respectively to grow a porous glass base material 4 having a diameter of 100mm.. The diameter of the resultant base material 4 is then reduced to about 60mm. during the passage of the furance (5a) at about 1,300 deg.C. The temporarily sintered material 4' is completely deaerated during the passage of the furnace (5b) at about 1,550 deg.C to give a transparent base material 6 having a diameter of about 50mm.. The temperature control of the furnaces (5a) and (5b) provides the stable conditions (maintenance) of furnace core tubes 8a and 8b of large and small diameters without deformation, damage and consumption even in operation for a long time. |
