Heating apparatus of induction furnace used for stretching large-diameter preformed rods of optical fibers
View Patent ↗A heating apparatus of an induction furnace used for stretching large-diameter preformed rods of optical fibers, said heating apparatus of the induction furnace comprising a furnace casing, a graphite exothermic sleeve, an insulating layer and an induction coil. At the upper end of the graphite exothermic sleeve is provided a floating seal gland, the inner bore thereof being adapted to the upper end of the graphite exothermic sleeve, and the outer periphery of the floating seal gland being adapted to the top cover plate furnace hole of the furnace casing. The use of the floating seal gland increases furnace stability and prolongs furnace life.
1. A heating apparatus of an induced fiber drawing furnace for large-diameter optical fiber preformed rods, comprising:
a cannular furnace casing defining a furnace cavity;
a graphite exothermic sleeve defining a bore, mounted in the furnace cavity;
a heat-insulation layer surrounding the graphite exothermic sleeve; and
an induction coil surrounding the heat-insulation layer,
wherein a diameter of the bore of the graphite exothermic sleeve is in a range of 150 to 240 mm, and an axial length of the graphite exothermic sleeve is in a range of 500 to 800 mm;
wherein a maximum power of the induction coil is in a range of 80 to 100 kilowatts;
wherein an upper end of the graphite exothermic sleeve is provided with a floating sealing gland, a bore of the floating sealing gland is matched with the upper end of the graphite exothermic sleeve, and a periphery of the floating sealing gland is matched with a furnace cavity aperture of a top cover plate of the furnace casing;
wherein an outlet of the furnace cavity at the lower end of the graphite exothermic sleeve is inward shrunk into a shape of a taper sleeve, an included angle between a conical surface of the taper sleeve and an end face of the large end of the taper sleeve is in a range of 70° to 85°, and an axial length of the taper sleeve is in a range of 80 to 400 mm;
wherein the lower end of the furnace casing is correspondingly inward shrunk into a shape of a frustum, and an included angle between a conical surface of the frustum and an end face of the large end of the frustum is in a range of 30° to 50°; and
wherein the furnace cavity aperture of the top cover plate is provided with two layers of seal rings, and the two layers of seal rings are matched with the periphery of the floating sealing gland.
2. The heating apparatus according to claim 1 , wherein the heat-insulation layer is formed by reeling in a rectangular soft long fiber graphite felt into a reeled cannula, the number of reeling layers is in a range of 3 to 10, and a single-sided thickness of the heat-insulation layer is in a range of 20 to 30 mm.
3. The heating apparatus according to claim 1 , wherein the middle of the floating sealing gland is provided with a through-hole corresponding to the bore of the graphite exothermic sleeve, the lower end face of the floating sealing gland is provided with an annular spigot, and the bore and the inner end face of the annular spigot are matched with the graphite exothermic sleeve.
4. The heating apparatus according to claim 1 , wherein the end face of the large end of the lower frustum in the furnace casing is provided with a glass support frame, and the glass support frame is engaged with the lower end of the heat-insulation layer.
5. The heating apparatus according to claim 4 , wherein the induction coil is mounted above the glass support frame in the furnace casing.