POROUS PREFORM VITRIFICATION APPARATUS

摘要

PROBLEM TO BE SOLVED: To provide a porous preform vitrification apparatus for producing high-quality optical fiber preforms at a high yield. SOLUTION: This apparatus is provided with a furnace core tube for housing the porous preform 1 and a means for forcibly supplying nitrogen, and the like, from the furnace core tube to a discharge gas tube 4 in order to balance the pressure between the furnace core tube and a heating furnace casing enclosing the same and to minimize the pressure fluctuation in the furnace core tube as far as possible and is provided with a mechanism for controlling the gas supply rate and discharge rate to and from the inside of the furnace core tube and the heating furnace casing and for controlling the nitrogen supply rate from the furnace core tube to the discharge gas tube in accordance with a differential pressure signal between the pressure in the furnace core tube and the pressure in the heating furnace.