JP2014070010A - Optical fiber drawing furnace, and optical fiber drawing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber drawing furnace and an optical fiber drawing method, for reducing floating soot in a furnace core tube by capturing efficiently the floating soot in the furnace core tube by utilizing a gas flow in an upper flow.SOLUTION: An optical fiber drawing furnace used for producing an optical fiber, comprises: a furnace core tube 13 into which an optical fiber glass preform 11 is inserted; heating means 15 to heat the furnace core tube from the outside; and a lower-section extension tube 19 which is mounted below the furnace core tube. In the optical fiber drawing furnace and an optical fiber drawing method, an inert gas is made to flow into the furnace core tube from the upper side to the lower side thereof, and, from fiber drawing exit at the lower side of the furnace core tube 13, an optical fiber 12 is drawn outside and the inert gas is discharged outside, a soot capturing mechanism 18 is mounted in the lower-section extension tube for capturing and keeping soot inside the furnace. The soot capturing mechanism 18 is constituted of one or more circular mesh plates 21, and a surface 21b of the mesh plate is arranged to be perpendicular to an axial direction of the furnace core tube 13.

Description

  The present invention relates to an optical fiber drawing furnace and a drawing method for drawing an optical fiber by heating and melting a glass base material for an optical fiber.

  Drawing of an optical fiber by a drawing furnace is performed by heating and melting a glass preform for optical fiber (hereinafter referred to as a glass preform) with a heater. Since the temperature in the drawing furnace is as high as 2000 ° C. or higher, carbon is usually used as the material for the furnace core tube and the like surrounding the glass base material. This carbon is oxidized and consumed in a high-temperature oxygen-containing atmosphere. In order to prevent this, a rare gas such as argon gas or helium gas or nitrogen gas (hereinafter referred to as an inert gas) is sent into the furnace core tube.

It is also known that soot (SiC, C, SiO _2, etc.) adheres to the inner wall of the carbon furnace core tube or the like when the optical fiber is drawn. These soot are particles such as SiO ₂ which is the main component of the glass base material, carbon C, and SiC produced by the reaction of SiO ₂ and C, and these adhere to the inner wall surface of the core tube or the like. grow up. The soot before adhering to the inner wall of the furnace core tube, etc., moves inside the core tube by the inert gas sent into the reactor core tube, adheres to the glass base material and glass fiber, and changes in the glass diameter of the optical fiber and strength deterioration Will cause.
On the other hand, for example, Patent Document 1 discloses that the soot in the furnace is prevented from adhering to the glass base material by forcibly discharging the soot in the furnace.

  On the other hand, most of the inert gas or the like sent into the core tube flows from the top to the bottom of the core tube, along with the glass fiber drawn from the lower end of the optical fiber preform, and from the fiber outlet to the outside. Released. In this case, if the fiber outlet is wide open, outside air easily enters the core tube, leading to deterioration of carbon parts such as the core tube. For this reason, for example, Patent Document 2 discloses that a shutter is provided at the fiber outlet, and Patent Document 3 discloses that a cylindrical partition wall is provided at the lower end of the core tube and a shutter is provided at the lower end of the partition wall. Has been. By providing these shutters, airtightness can be maintained while suppressing the use of inert gas or the like.

JP-A-8-333130 Japanese Patent No. 2778783 JP-A-8-91862

  However, as disclosed in Patent Document 1, when the soot in the furnace tube is forcibly exhausted, the inside of the furnace is likely to be negative pressure, so that a large amount of inert gas or the like is introduced into the furnace so as not to entrain outside air. There is a problem that the manufacturing cost of the optical fiber becomes high. In addition, a method of recycling the gas exhausted together with the soot forcibly and cleaning it may be considered. However, it is necessary to construct a facility for this purpose, and the cost becomes high as described above.

  In addition, as disclosed in Patent Documents 2 and 3 above, as a method of suppressing the use of an inert gas or the like used in the drawing furnace, the outflow of gas is suppressed by narrowing the fiber outlet of the lower extension pipe. It is effective to do. However, with such a structure, the inert gas that flows downward becomes a gas flow (traction flow) accelerated by the linear velocity of the optical fiber, and a part of it flows out of the furnace together with the optical fiber. In many cases, the gas is reversed at the shutter exit portion to become a gas flow (upper flow) flowing upward along the inner wall of the lower extension pipe. The soot in the furnace core tube rises on the gas flow of the upper flow, and this collides with or adheres to the glass base material or glass fiber in a molten state, thereby causing a glass diameter variation or strength deterioration of the optical fiber.

  The present invention has been made in view of the above-described circumstances, and effectively captures the soot floating in the core tube using the gas flow of the upper flow and reduces the soot floating in the core tube. The purpose is to provide a draw furnace and drawing method.

  An optical fiber drawing furnace and a drawing method according to the present invention include a furnace core tube into which a glass preform for an optical fiber is inserted, a heating means for heating the furnace core tube from the outside, and a lower extension provided at a lower portion of the core tube. And an inert gas is allowed to flow from the top to the bottom of the core tube, and the drawn glass fiber is led out to the outside from the fiber outlet at the bottom of the core tube. In a drawing furnace and drawing method for an optical fiber that discharges gas to the outside, a soot trapping mechanism that traps and holds soot in the furnace is provided in the lower extension pipe.

  The soot capturing mechanism is composed of one or more annular mesh plates, and is arranged so that the surface of the mesh plate is orthogonal to the axial direction of the core tube. Further, a tubular body may be arranged between the inner diameter hole of the annular mesh plate and the traveling area of the glass fiber, and cooling means is provided on the outer peripheral wall of the lower extension pipe at the portion where the soot capturing mechanism is in contact. You may make it provide.

  According to the present invention, soot in the gas flow is captured by the annular mesh plate disposed in the gas flow region by the upper flow, and soot floating in the core tube can be reduced. As a result, it is possible to reduce soot from colliding with or adhering to the glass base material or the glass fiber, and to reduce the glass diameter variation or strength deterioration of the optical fiber.

It is a figure explaining an example of the drawing furnace for optical fibers by this invention. It is a figure explaining the other example of the drawing furnace for optical fibers by this invention. It is a figure explaining another example of the drawing furnace for optical fibers by this invention. It is a figure explaining another example of the drawing furnace for optical fibers by this invention.

The outline of the drawing furnace for optical fibers of the present invention will be described with reference to FIGS. In the following, a resistance furnace that heats the core tube with a heater will be described as an example. However, the present invention can also be applied to an induction furnace in which a high-frequency power source is applied to the coil to induction-heat the core tube.
In the figure, 10 is an optical fiber drawing furnace, 11 is a glass preform (glass preform) for optical fiber, 12 is a glass fiber, 13 is a furnace core tube, 14 is a furnace casing, 14a is a lower wall, 15 is a heater, 16 is a heat insulating material, 17 is a core tube receiving member, 18 is a soot capturing mechanism, 19 is a lower extension tube, 19a is a bottom wall, 19b is an inner wall surface, 20 is a shutter, 21 is a mesh plate, 21a is a central hole, and 21b is A mesh surface, 22 is a tubular body, 23 is a cooling means, and 24 is a fin.

  As shown in FIG. 1, the drawing of the optical fiber is performed such that the lower part of the glass base material 11 supported by suspension is heated, and the glass fiber 12 is melted and dripped from the melted lower end part so as to have a predetermined outer diameter. It is done by drawing. For this purpose, the optical fiber drawing furnace 10 is provided with a heater 15 so as to surround a furnace core tube 13 into which a glass base material 11 is inserted and supplied, and a heat insulating material is provided so that the heat of the heater 15 is not dissipated outside. 16, and the entire outside thereof is surrounded by a furnace casing 14.

  The glass base material 11 is suspended and supported by a base material suspension mechanism (not shown), and is sequentially controlled to move downward as the optical fiber is drawn. The furnace casing 14 is made of a metal having excellent corrosion resistance such as stainless steel, and a cylindrical furnace core tube 13 made of high-purity carbon is arranged at the center. The core tube 13 is supported by being placed on the lower wall 14 a of the furnace casing 14 via the core tube receiving member 17.

  A lower extension pipe 19 having an appropriate length is disposed at the lower part of the core tube 13 to alleviate the rapid cooling of the heated and softened glass fiber 12. The bottom wall 19 a of the lower extension pipe 19 is provided on the bottom wall 19 a. A shutter 20 is provided. In order to prevent oxidation and deterioration of the core tube 13, an inert gas such as argon gas or helium gas, or inert gas such as nitrogen gas is introduced into the core tube 13. The inert gas or the like passes through the gap between the glass base material 11 and the core tube 13, and most of the inert gas is released to the outside from below the core tube 13.

  In the drawing furnace having the above-described configuration, the present invention is provided with the soot capturing mechanism 18 that captures and holds the soot in the furnace so as to communicate with the core tube 13 from the lower wall 14a of the furnace casing 14. Features. The soot capturing mechanism 18 includes, for example, an annular mesh plate 21 provided inside the lower extension pipe 19.

  The mesh plate 21 disposed in the lower extension pipe 19 is formed of, for example, a corrosion-resistant, heat-resistant wire mesh of “32 count (wire diameter 0.274 mm) 25 mesh”, and has an annular shape having a central hole 21a. Is used. One or a plurality of mesh plates 21 (three are used in the illustrated example) are arranged such that the mesh surface 21 b is orthogonal to the axial direction of the core tube 13.

  In the optical fiber drawing furnace 10 described above, when an inert gas or the like is introduced into the core tube 13 from above, the gas passes between the glass base material 11 and the core tube 13 and enters the lower extension tube 19. Flowing. As shown in FIG. 1B, the gas flowing into the lower extension pipe 19 is pulled by the high-speed drawing of the glass fiber 12 to become a downflow gas flow Q1. A part of the downflow gas flow Q1 is discharged to the outside together with the glass fiber 12 from the shutter 20, but most of it is inverted and flows upward along the inner wall surface 19b of the lower extension pipe 19. It becomes flow Q2.

  The gas flow Q2 of the upper flow is directed upward along the inner wall surface 19b of the lower extension pipe 19 so as to pass through the mesh plate 21. When the gas flow Q2 of the upper flow passes through the mesh plate 21, a pressure loss occurs, and the flow rate of the gas flow is suppressed and the gas flow Q2 is stagnated. As a result, the soot in the gas flow is easily attached to the inner wall surface 19b of the lower extension pipe 19 and the mesh plate 21 and captured.

  One mesh plate 21 may be provided, but a plurality of pressure loss regions may be provided by arranging a plurality of mesh plates 21 in parallel. As a result, the soot that could not be captured at the first mesh plate is captured at the second, third,... Further, even when the first mesh plate is trapped and clogged and the gas flow cannot pass through the mesh plate, it is captured at the location of the next mesh plate. Further, by using a fine mesh plate, the pressure loss of one mesh plate may be increased to increase the soot capturing rate.

In the configuration shown in FIG. 1, three pieces of mesh plate 21 formed with a 32 mesh 25 mesh, an outer diameter of 90 mm and an inner diameter of 50 mm are arranged at intervals of 30 mm, and the amount of soot captured when the optical fiber is drawn 600 km is examined. It was.
As a result, the amount captured by the three mesh plates 21 was 0.0538 g / Mm, and the amount captured by the inner wall surface 19b of the lower extension pipe 19 was 0.267 g / Mm, which was 0.3208 g / Mm in total.

On the other hand, the amount of soot trapped when the optical fiber was similarly drawn by 600 km using only the lower extension pipe 19 having no mesh plate 21 was examined. The amount captured by the inner wall surface 19b of the lower extension pipe 19 at this time was 0.0414 g / Mm.
That is, it has been found that by using the mesh plate 21, soot that is 7.7 times as large as when the mesh plate 21 is not used can be captured.

  In addition, it is preferable that the soot capturing mechanism 18 is detachably attached to the inside of the lower extension pipe 19 from the outside. Thereby, even after the drawing is finished, even if the drawing furnace is not cooled to room temperature, the soot capturing mechanism 18 can be immediately removed and replaced or cleaned every time drawing is finished. As a result, it is possible to continuously capture the soot flowing in the furnace at the next drawing, and to facilitate the quality control of the optical fiber.

  2-4 is a figure explaining other embodiment. FIG. 2 is an example in which a tubular body 22 is arranged between the central hole 21a of the annular mesh plate 21 and the traveling region of the glass fiber 12 in the soot capturing mechanism of FIG. According to this example, only the downflow gas flow Q <b> 1 pulled by the high-speed drawing of the glass fiber 12 flows into the tubular body 22, and the upper flow gas flow Q <b> 2 passes through the mesh plate 21 outside the tubular body 22. In this way, the soot can be captured effectively. Moreover, according to this structure, it becomes possible to attach soot to the inner periphery and outer periphery of the tubular body 22 and capture them.

FIG. 3 is an example in which the cooling means 23 is arranged on the outer peripheral wall of the lower extension pipe 19 to cool the inner wall surface 19b by the soot capturing mechanism of FIG. In addition, the cooling means 23 can use the structure by water cooling or air cooling. According to this example, because of the thermophoresis effect, the soot moves toward the wall portion side of the lower extension pipe 19 where the temperature is lowered by cooling, so that it easily adheres to the inner wall surface 19b and enhances the capturing effect. Is possible.
In addition, it can be expected that the soot capturing effect is further enhanced by using the configuration using the cooling means of this example and the configuration using the tubular body of FIG. 2 together.

FIG. 4 shows the soot capturing mechanism of FIG. 1, and fins 24 (the figure shows eight pieces at regular intervals) between the annular mesh plates 21 and between the mesh plates 21 and the bottom wall 19 a of the lower extension pipe 19. Example). According to this example, by arranging the fins 24, it is possible to effectively increase the surface to which soot can be attached, and to increase the soot capturing effect.
In addition, it can be expected that the soot capturing effect is further enhanced by using the configuration using the fin of this example, the configuration using the tubular body of FIG. 2, and the configuration using the cooling means of FIG.

DESCRIPTION OF SYMBOLS 10 ... Optical fiber drawing furnace, 11 ... Glass base material (glass base material) for optical fibers, 12 ... Glass fiber, 13 ... Furnace core tube, 14 ... Furnace housing, 14a ... Lower wall, 15 ... Heater, 16 ... Heat insulation Material: 17 ... Core tube receiving member, 18 ... Soot capturing mechanism, 19 ... Lower extension pipe, 19a ... Bottom wall, 19b ... Inner wall surface, 20 ... Shutter, 21 ... Mesh plate, 21a ... Center hole, 21b ... Mesh surface, 22 ... tubular body, 23 ... cooling means, 24 ... fins.

Claims (5)

An optical fiber drawing furnace comprising: a furnace core tube into which an optical fiber glass base material is inserted; heating means for heating the furnace core tube from the outside; and a lower extension tube provided at a lower portion of the furnace core tube. There,
An optical fiber drawing furnace comprising a soot capturing mechanism for capturing and holding soot in the furnace in the lower extension pipe.   The said soot capturing mechanism is made of one or more annular mesh plates, and is arranged so that the surface of the mesh plate is orthogonal to the axial direction of the core tube. Drawing furnace for optical fiber.   The drawing furnace for an optical fiber according to claim 2, wherein a tubular body is disposed between a center hole of the annular mesh plate and a traveling area of the glass fiber.   The optical fiber drawing furnace according to any one of claims 1 to 3, wherein a cooling means is provided on an outer peripheral wall of the lower extension pipe at a portion where the soot capturing mechanism is in contact. Using a drawing furnace provided with a core tube into which a glass preform for an optical fiber is inserted, heating means for heating the core tube from the outside, and a lower extension tube provided at a lower portion of the core tube, An optical fiber line for flowing an inert gas into the core tube from the top to the bottom, leading the drawn glass fiber out from the fiber outlet at the bottom of the core tube, and discharging the inert gas to the outside A pulling method,
An optical fiber drawing method, wherein a soot trapping mechanism provided in the lower extension pipe is drawn while trapping and holding soot particles in a furnace.

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