Patent ID: 6138481
Filing Date: 2000-10-31
Classification: C03B,Y10T

Abstract:
A heating furnace for elongating a glass rod, which holds at least one end of said glass rod with a holding portion and elongates said glass rod by softening said glass rod successively from the other end portion thereof being heating while applying a tensile force thereto,said heating furnace comprising:a tubular portion through which said glass rod to be elongated is inserted such as to be longitudinally movable;heating means, positioned within said tubular portion so as to circumferentially surround said glass rod, for heating said glass rod;a moving portion through which one end of said glass rod is inserted;an expandable member the ends of which are respectively secured to said moving portion and said tubular portion and which is longitudinally expandable and contractible and comprises a double cylinder surrounding part of said glass rod so as to block outside air from flowing into said heating furnace;an expandable muffle tube, disposed inside the innermost cylinder of said expandable member, which surrounds said glass rod and expands and contracts in synchronization with the expansion and contraction of said expandable member as said moving portion moves; andgas supply means for supplying and purging an inert gas into a space within said tubular portion and the inner cylinder of said expandable member as well as the space between inner and outer cylinders of said expandable member.