PURPOSE: To prevent vanishing of heater and heat insulating material in a main body of furnace by arranging a heat insulating material at a lower gap part among gap parts between a furnace core pipe and a main body of furnace.
CONSTITUTION: A furnace core pipe 1 charged with optical fiber perform 9 is laid at the central part of a main body 4 of furnace equipped with a feed opening 5 of inert gas, a heater 2 and a heat insulating material 3 are arranged around the furnace core pipe 1 and a gas feed opening 6 to supply a dehydrating agent to the furnace core pipe 1 is set. A heat insulating material 12 made of a material different from that of the heat insulating material 3 is arranged in the vicinity of a lower gap part 42 among gap parts 41 and 42 between the furnace core pipe 1 and the main body 4 of furnace. The heat insulating material 12 is pressed by a tapered pressing plate 11 having a hole into which the furnace core pipe 1 can be inserted wherein the periphery of the hole is made into a tapered shape. The pressing plate 11 is located by a nut 14 screwed with a bolt 13 laid at the bottom of the main body 4 of furnace.
SHIOYA KEIICHIRO
HORIKOSHI MASAHIRO
SUZUKI RYOJI
