WO2021193567A1 - Optical fiber wiredrawing furnace and method for producing optical fiber - Google Patents

Optical fiber wiredrawing furnace and method for producing optical fiber Download PDF

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Publication number
WO2021193567A1
WO2021193567A1 PCT/JP2021/011793 JP2021011793W WO2021193567A1 WO 2021193567 A1 WO2021193567 A1 WO 2021193567A1 JP 2021011793 W JP2021011793 W JP 2021011793W WO 2021193567 A1 WO2021193567 A1 WO 2021193567A1
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Prior art keywords
optical fiber
gas
drawing furnace
lower chamber
protective tube
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PCT/JP2021/011793
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French (fr)
Japanese (ja)
Inventor
巌 岡崎
惣太郎 井田
仁広 森本
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住友電気工業株式会社
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Application filed by 住友電気工業株式会社 filed Critical 住友電気工業株式会社
Priority to JP2022510503A priority Critical patent/JPWO2021193567A1/ja
Priority to CN202180023039.3A priority patent/CN115335337A/en
Publication of WO2021193567A1 publication Critical patent/WO2021193567A1/en

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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01—Manufacture of glass fibres or filaments
    • C03B37/02—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor
    • C03B37/025—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor from reheated softened tubes, rods, fibres or filaments, e.g. drawing fibres from preforms
    • C03B37/029—Furnaces therefor

Definitions

  • the present disclosure relates to an optical fiber drawing furnace and an optical fiber manufacturing method.
  • This application claims priority based on Japanese Patent Application No. 2020-051898 filed on March 23, 2020, and incorporates all the contents described in the above application.
  • Patent Document 1 discloses an optical fiber manufacturing apparatus in which helium gas is supplied into a drawing furnace to draw an optical fiber, and the drawn optical fiber is cooled in argon gas in a cooling pipe connected to the drawing furnace. Has been done.
  • the optical fiber wire drawing furnace houses a core tube into which a glass base material for optical fiber is inserted, a heater for heating the glass base material for optical fiber from the outside, and the core tube inside.
  • the furnace body the lower chamber arranged below the core tube, the protective tube arranged below the lower chamber, and the in-core gas introduction in which the inert gas flows into the core tube from above to below.
  • An optical fiber wire drawing furnace provided with a portion, which has a gas introduction port for introducing a predetermined gas into the protective tube, and has a radial cross-sectional area of an internal space on the upper side of the gas introduction port. It has a smaller constriction than the lower chamber.
  • optical fiber manufacturing method is a method of manufacturing an optical fiber using the above-mentioned optical fiber drawing furnace.
  • FIG. 1 is a schematic view of an optical fiber drawing furnace according to an embodiment of the present disclosure.
  • FIG. 2A is a diagram showing another example of the gas inlet of the protective tube.
  • FIG. 2B is a diagram showing still another example of the gas inlet of the protective tube.
  • FIG. 3A is a schematic view of an optical fiber drawing furnace according to another embodiment of the present disclosure.
  • FIG. 3B is a cross-sectional view taken along the line 3B-3B of FIG. 3A.
  • the drawing furnace is provided with a lower chamber (lower chimney) and a protective tube below the lower chamber, and inside the lower chamber and the protective tube so that the glass diameter of the optical fiber (glass fiber portion) is stable.
  • the optical fiber is protected by.
  • SiO 2 gas or the like since SiO 2 gas or the like is generated from the high temperature glass base material, the SiO 2 gas or the like cools in the lower chamber and silica (SiO 2 ) powder is generated.
  • Silica powder floats in the inert gas flowing into the drawing furnace, accumulates in the drawing furnace, is discharged to the outside of the furnace from the lower chamber of the drawing furnace or the outlet of the protective pipe, or comes into contact with the optical fiber. Or collide.
  • the strength of the optical fiber decreases.
  • the frequency of disconnection of the optical fiber increases in the fiber screening test (proof test) performed after the drawing is completed, and the productivity may decrease.
  • the temperature of the drawing furnace In order to reduce the amount of silica powder generated from the glass base material, there is a method of lowering the temperature of the drawing furnace.
  • it is difficult to simply lower the drawing furnace temperature because the drawing furnace temperature affects the desired glass tension during drawing and also depends on the size of the base metal and the like.
  • the optical fiber drawing furnace houses (1) a core tube into which a glass base material for optical fiber is inserted, a heater for heating the glass base material for optical fiber from the outside, and the core tube inside.
  • the furnace body the lower chamber arranged below the core tube, the protective tube arranged below the lower chamber, and the in-core gas introduction in which the inert gas flows into the core tube from above to below.
  • An optical fiber wire drawing furnace provided with a portion, which has a gas introduction port for introducing a predetermined gas into the protective tube, and has a radial cross-sectional area of an internal space on the upper side of the gas introduction port.
  • the concentration of silica powder per gas flow rate in the protective tube can be reduced, so that the probability that the silica powder comes into contact with or collides with the optical fiber is reduced, and the occurrence of a decrease in the strength of the optical fiber can be suppressed.
  • the protective tube may be connected below the lower chamber. As a result, the optical fiber is not exposed to the outside air between the lower chamber and the protective tube, and the glass diameter is stabilized.
  • the gas inlet is provided from the center to the upper side of the protective pipe.
  • the concentration of silica powder per gas flow rate can be reduced in most of the inside of the protective tube, so that the probability that the silica powder comes into contact with or collides with the optical fiber is reduced, and the occurrence of a decrease in the strength of the optical fiber is suppressed. Can be done.
  • the lower part of the lower chamber may have a gas vent hole for discharging the inert gas in the lower chamber to the outside.
  • Gas may be forcibly exhausted from the gas vent hole. As a result, the probability that the silica powder comes into contact with or collides with the optical fiber is further reduced, and the occurrence of a decrease in the strength of the optical fiber can be suppressed.
  • the gas introduction port is provided at the upper end of the protective pipe.
  • the concentration of the silica powder can be rapidly reduced in the protective tube over almost the entire length of the protective tube, and the probability of the silica powder coming into contact with or colliding with the optical fiber is further reduced.
  • the predetermined gas may be argon, nitrogen, or air.
  • the gas introduction ports may be provided at equal intervals in the circumferential direction of the protective pipe. As a result, the gas evenly hits around the optical fiber, so that the optical fiber can be prevented from shaking in the protective tube, which affects the fluctuation of the optical fiber diameter and the bending of the fiber due to the non-uniformity of temperature (fiber curl). Can be suppressed.
  • the gas introduction port may be provided downward so as to introduce the predetermined gas downward into the inside of the protective pipe. As a result, turbulence of the gas flow in the protective tube can be suppressed.
  • the gas introduction port may be obliquely downward and may face in a direction along the wall surface of the protective pipe so as to introduce the predetermined gas into the protective pipe in a spiral shape. This makes it easier to separate the silica powder from the periphery of the fiber. Moreover, the turbulence of the gas flow around the fiber can be reduced.
  • the optical fiber manufacturing method is (11) a method of manufacturing an optical fiber using the above-mentioned optical fiber drawing furnace.
  • the concentration of silica powder per gas flow rate in the protective tube can be reduced, so that the probability that the silica powder comes into contact with or collides with the optical fiber is reduced, and the occurrence of a decrease in the strength of the optical fiber can be suppressed.
  • FIG. 1 is a schematic view of an optical fiber drawing furnace according to one aspect of the present disclosure.
  • the optical fiber wire drawing furnace (hereinafter referred to as “line drawing furnace”) 10 has a furnace main body 11, an upper chamber 12 provided above the furnace main body 11, and a lower chamber 13 provided below the furnace main body 11. ..
  • the upper chamber 12 and the lower chamber 13 have a hollow tube shape.
  • a heater 15 for heating and melting the glass base material 1 is arranged inside the furnace body 11, and a cylindrical core tube 14 is arranged so as to be surrounded by the heater 15.
  • a heat insulating material 16 is provided between the heater 15 and the furnace body 11 so as to surround the heater 15 so that the heat from the heater 15 is not dissipated to the outside.
  • the heater may be one using induction heating.
  • a protective tube 20, which will be described in detail later, is arranged below the lower chamber 13, a protective tube 20, which will be described in detail later, is arranged.
  • the protective tube 20 is preferably in close contact with and connected to the lower chamber 13, but there may be a gap between the protective tube 20 and the lower chamber 13 to some extent. Further, in the present embodiment, the lower chamber 13 and the protective tube 20 are described one by one, but each of them may be divided into a plurality of parts or may be integrated with each other.
  • the glass base material 1 is suspended in the core tube 14 by a base material suspension mechanism (not shown), the lower part of the glass base material 1 is heated by the heater 15, and the lower end portion of the molten glass base material 1 is drawn.
  • This is a step of melting and hanging the optical fiber (glass fiber portion) 2 from the glass fiber (glass fiber portion) 2 so that the optical fiber 2 taken out from below the drawing furnace 10 has a predetermined outer diameter.
  • Nitrogen introduced from the in-core gas introduction unit 17 or an inert gas such as helium or argon is supplied into the core tube 14 from above to below. Since the inside of the core tube 14 is under an inert gas atmosphere, it is possible to prevent oxidation of the core tube 14 and the like, which are carbon components, and to keep the inside clean.
  • the inert gas introduced into the core tube 14 is heated to about 2000 ° C. or higher in the core tube 14. Then, a part of the heated inert gas is discharged to the outside together with the optical fiber 2 through the space inside the core tube 14 through the lower chamber 13 and the protective tube 20 by the downflow.
  • the lower chamber 13 and the protective tube 20 are connected to each other, and the narrowed portion 13a and the protective tube 20 of the lower chamber 13 whose internal space cross-sectional area is smaller than that of the lower chamber 13 are narrowed at the connecting portion, respectively.
  • the portion 20a is formed.
  • a gas introduction port 21 is provided directly below the narrowed portion 20a of the protective tube 20.
  • the gas introduction ports 21 are provided at equal intervals, for example, at four locations in the circumferential direction of the protective tube 20.
  • the narrowed portion 13a and the narrowed portion 20a make the pressure inside the core tube 14 and the lower chamber 13 above the narrowed portions 13a and 20a more positive than the pressure inside the protective tube 20 below the narrowed portions 13a and 20a. It is for keeping pressure.
  • the constriction portion is not limited to being provided at the connecting portion between the lower chamber 13 and the protective pipe 20, but is provided only at one of the lower chamber 13 and the protective pipe 20. You may.
  • the gas introduction port 21 is preferably provided at the upper end portion of the protective pipe 20 (including not only the upper end but also the vicinity of the upper end), but the gas introduction port 21 may be provided from the center in the longitudinal direction to the upper side of the protective pipe 20.
  • a clean gas such as argon, nitrogen, or air, which is cheaper than helium, is introduced into the gas introduction port 21 from the outside.
  • the concentration of silica powder suspended in the inert gas in the drawing furnace 10 per unit gas flow rate is lowered in the protective tube 20 having the gas introduction port 21, so that the optical fiber 2 being drawn is drawn. Reduces the chance that the gas will come into contact with or collide with the silica powder.
  • the concentration of the silica powder in the protective tube 20 per gas flow rate is N / Q3, and the concentration of the silica powder suspended in the inert gas in the drawing furnace 10 per unit gas flow rate is set to the gas introduction port 21. It can be lowered in the protective tube 20 having the.
  • the pressure inside the lower chamber 13 is higher than the pressure inside the protective tube 20 below the narrowed portions 13a and 20a. Can be kept. As a result, the gas introduced from the gas introduction port 21 is suppressed from flowing to the lower chamber 13 side.
  • the probability that the silica powder comes into contact with or collides with the optical fiber 2 in the protective tube 20 can be reduced.
  • the silica powder contained in the gas flowing in the core tube 14 is quickly discharged to the outside from the inside of the protection tube 20 by the gas introduced from the gas introduction port 21 of the protection tube 20.
  • the optical fiber 2 moves through the core tube 14, the lower chamber 13, and the protective tube 20 at a constant speed, but the concentration of silica powder per unit gas flow rate when passing through the protective tube 20 does not introduce gas. Since it is lower than that of the above, the probability of contact or collision of silica powder can be reduced as a whole, and the occurrence of a decrease in the strength of the optical fiber can be suppressed.
  • the silica powder concentration in the protective tube 20 below the gas introduction port 21 can be quickly reduced. Therefore, it is desirable to reduce the silica powder concentration in the entire length of the protective tube 20 by providing the gas introduction port 21 near the upper end of the protective tube 20. Further, it is desirable that the gas introduced into the protective tube 20 flows evenly from the circumferential direction of the optical fiber 2 so as not to shake the optical fiber 2.
  • FIG. 2A is a view showing another example of the gas inlet of the protective tube, and is a cross-sectional view in the length direction.
  • the plurality of gas introduction ports 21'provided in the protection pipe 20 are provided so as to be inclined obliquely downward toward the protection pipe 20. Therefore, the gas introduced into the protective pipe 20 from the gas introduction port 21'is introduced into the protective pipe 20 at a downward angle.
  • the gas introduced into the protective tube 20 flows smoothly in the traveling direction of the optical fiber 2, so that the turbulence of the gas flow is suppressed, and the influence on the diameter fluctuation of the optical fiber 2 and the influence on the fiber curl are affected. It is suppressed. Also in this embodiment, it is desirable that the gas introduced into the protective tube 20 flows evenly from the circumferential direction of the optical fiber 2.
  • FIG. 2B is a diagram showing still another example of the gas inlet of the protective tube, and is a cross-sectional view in the radial direction.
  • the plurality of gas introduction ports 21 "provided in the protection pipe 20 are provided so as to introduce the gas in the direction along the wall surface, not in the direction toward the center of the protection pipe 20, but diagonally downward.
  • the gas introduced into the protective tube 20 swirls along the inner wall of the protective tube 20, that is, flows in a spiral shape in the circumferential direction, and easily separates the silica powder from the periphery of the optical fiber 2.
  • the gas to be introduced into the protection pipe 20 may be flown from one gas introduction port or may be uniformly flown from a plurality of gas introduction ports 21 ”.
  • FIG. 3A is a schematic view of an optical fiber drawing furnace according to another aspect of the present disclosure.
  • FIG. 3B is a cross-sectional view taken along the line 3B-3B of FIG. 3A.
  • the present embodiment is different from the first to third embodiments in that a gas vent hole 13b that opens to the outside is provided below the lower chamber 13, but the other configurations are the same, so that they overlap. The description of the configuration to be performed will be omitted.
  • a plurality of degassing holes 13b are provided at equal intervals around the narrowed portion 13a provided below the lower chamber 13. From the gas vent hole 13b, a part of the inert gas flowing through the core tube 14 and the lower chamber 13 is discharged to the outside together with the silica powder.
  • the degassing hole 13b is configured to discharge the inert gas below the lower chamber 13, but is provided on the lower side surface of the lower chamber so as to discharge the inert gas to the side of the lower chamber. You may.
  • the core tube 14 contains N silica powders per liter of Q1 when the inert gas having a flow rate of Q1slm is flowing downward.
  • the concentration of silica powder per gas flow rate in the lower chamber 13 is N / Q1.
  • the inert gas of Q4slm is discharged to the outside from the gas vent hole 13b, the gas of (Q1-Q4) slm is introduced into the protective tube 20 from the lower chamber 13.
  • the concentration of silica powder per gas flow rate contained in the inert gas introduced into the protective tube 20 is the same as N / Q1, but the amount of silica powder entering the protective tube 20 per minute is N. It becomes ⁇ (1-Q4 / Q1).
  • Q4 + Q2) It becomes slm. Therefore, the concentration of silica powder in the protective tube 20 per gas flow rate is ⁇ N ⁇ (1-Q4 / Q1) ⁇ / Q5. Therefore, the concentration of the silica powder suspended in the inert gas in the protective tube 20 per unit gas flow rate can be lowered as compared with the first embodiment.
  • the gas introduced into the protective tube 20 can be introduced into the protective tube 20 at a downward angle, or the protective tube 20 can be introduced. It is desirable to introduce it so that it flows in a spiral direction in the circumferential direction along the inner wall of the. Further, in order to make the flow rate of the inert gas discharged to the outside from the gas vent hole 13b larger than the flow rate of the inert gas toward the protection tube 20, the inert gas in the lower chamber 13 is sucked from the gas vent hole 13b. However, it may be forcibly exhausted. By discharging the inert gas from the gas vent hole 13b to the outside in this way, it is possible to control the ratio of the gas flow rate towed by the optical fiber to the gas flow rate discharged from the gas vent hole.

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Abstract

A wiredrawing furnace comprising: a furnace core pipe into which a glass base material for optical fiber is to be inserted; a furnace body which houses therein a heater for heating said glass base material for optical fiber from the outside; a lower chamber disposed below the furnace core pipe; and a protective pipe disposed below the lower chamber, wherein an inert gas is streamed from top to bottom within the furnace core pipe. Further, the wiredrawing furnace has: a gas introduction port through which a prescribed gas is introduced into the protective pipe; and a narrowed area which is disposed on the upstream side of the gas introduction port and which is provided with an interior space that has a radially-oriented cross-sectional area smaller than that of the lower chamber.

Description

光ファイバ線引炉および光ファイバ製造方法Optical fiber wire drawing furnace and optical fiber manufacturing method
　本開示は、光ファイバ線引炉および光ファイバ製造方法に関する。
　本出願は、２０２０年３月２３日出願の日本国特許出願２０２０－０５１８９８号に基づく優先権を主張し、前記出願に記載された全ての記載内容を援用するものである。 The present disclosure relates to an optical fiber drawing furnace and an optical fiber manufacturing method.
This application claims priority based on Japanese Patent Application No. 2020-051898 filed on March 23, 2020, and incorporates all the contents described in the above application.
　特許文献１では、線引炉内にヘリウムガスを供給して光ファイバを線引きし、線引きした光ファイバを線引炉に連結された冷却管内のアルゴンガス中で冷却する光ファイバの製造装置が開示されている。 Patent Document 1 discloses an optical fiber manufacturing apparatus in which helium gas is supplied into a drawing furnace to draw an optical fiber, and the drawn optical fiber is cooled in argon gas in a cooling pipe connected to the drawing furnace. Has been done.
日本国特開２０００－１２８５６６号公報Japanese Patent Application Laid-Open No. 2000-128566
　本開示の一態様に係る光ファイバ線引炉は、光ファイバ用ガラス母材が挿入される炉心管と、前記光ファイバ用ガラス母材を外側から加熱するヒータ、および前記炉心管を内部に収納する炉本体と、前記炉心管の下方に配された下部チャンバと、前記下部チャンバの下方に配された保護管と、前記炉心管内に不活性ガスを上方から下方に向けて流す炉内ガス導入部と、を備えた光ファイバ線引炉であって、前記保護管内に所定のガスを導入するガス導入口を有するとともに、前記ガス導入口より上部側に、内部空間の径方向断面積が前記下部チャンバよりも小さい狭窄部を有する。 The optical fiber wire drawing furnace according to one aspect of the present disclosure houses a core tube into which a glass base material for optical fiber is inserted, a heater for heating the glass base material for optical fiber from the outside, and the core tube inside. The furnace body, the lower chamber arranged below the core tube, the protective tube arranged below the lower chamber, and the in-core gas introduction in which the inert gas flows into the core tube from above to below. An optical fiber wire drawing furnace provided with a portion, which has a gas introduction port for introducing a predetermined gas into the protective tube, and has a radial cross-sectional area of an internal space on the upper side of the gas introduction port. It has a smaller constriction than the lower chamber.
　また、本開示の一態様に係る光ファイバ製造方法は、上記の光ファイバ線引炉を用いて光ファイバを製造する方法である。 Further, the optical fiber manufacturing method according to one aspect of the present disclosure is a method of manufacturing an optical fiber using the above-mentioned optical fiber drawing furnace.
図１は、本開示の一実施形態に係る光ファイバ線引炉の概略図である。FIG. 1 is a schematic view of an optical fiber drawing furnace according to an embodiment of the present disclosure. 図２Ａは、保護管のガス導入口の他の例を示す図である。FIG. 2A is a diagram showing another example of the gas inlet of the protective tube. 図２Ｂは、保護管のガス導入口のさらに他の例を示す図である。FIG. 2B is a diagram showing still another example of the gas inlet of the protective tube. 図３Ａは、本開示の他の実施形態に係る光ファイバ線引炉の概略図である。FIG. 3A is a schematic view of an optical fiber drawing furnace according to another embodiment of the present disclosure. 図３Ｂは、図３Ａの３Ｂ－３Ｂ矢視断面図である。FIG. 3B is a cross-sectional view taken along the line 3B-3B of FIG. 3A.
［本開示が解決しようとする課題］
　線引炉には、下部チャンバ（下煙突）と、下部チャンバの下方に保護管とが設けられており、光ファイバ（ガラスファイバ部）のガラス径が安定するように下部チャンバや保護管の中で光ファイバが保護されている。一方、高温になったガラス母材からＳｉＯ２ガス等が発生するため、下部チャンバの中では、ＳｉＯ２ガス等が冷えてシリカ（ＳｉＯ２）粉が発生する。シリカ粉は線引炉内に吹き流している不活性ガス中に浮遊し、線引炉内に堆積したり、線引炉の下部チャンバや保護管出口から炉外へ排出されたり、光ファイバに接触または衝突したりする。線引中のガラスファイバ部が線引炉内ガスに浮遊したシリカ粉と接触または衝突すると、光ファイバの強度が低下する。光ファイバの強度が低下すると、線引終了後に実施するファイバスクリーニング試験（プルーフ試験）において、光ファイバが断線する頻度が上昇し、生産性が低下する場合があった。
　ガラス母材からのシリカ粉の発生量を低減させるためには、線引炉温度を下げる方法がある。しかし、線引炉温度は所望する線引中のガラス張力に影響を与えるほか、母材の大きさなどにも依存するため、単純に線引炉温度を下げることは難しい。また、線引炉内ガスに浮遊したシリカ粉の単位ガス流量当たりの濃度を下げるために線引炉内のガス流量を増やすことも考えられるが、製造コストが増加する場合があった。 [Issues to be solved by this disclosure]
The drawing furnace is provided with a lower chamber (lower chimney) and a protective tube below the lower chamber, and inside the lower chamber and the protective tube so that the glass diameter of the optical fiber (glass fiber portion) is stable. The optical fiber is protected by. On the other hand, since SiO 2 gas or the like is generated from the high temperature glass base material, the SiO 2 gas or the like cools in the lower chamber and silica (SiO 2 ) powder is generated. Silica powder floats in the inert gas flowing into the drawing furnace, accumulates in the drawing furnace, is discharged to the outside of the furnace from the lower chamber of the drawing furnace or the outlet of the protective pipe, or comes into contact with the optical fiber. Or collide. When the glass fiber portion during drawing comes into contact with or collides with the silica powder suspended in the gas in the drawing furnace, the strength of the optical fiber decreases. When the strength of the optical fiber decreases, the frequency of disconnection of the optical fiber increases in the fiber screening test (proof test) performed after the drawing is completed, and the productivity may decrease.
In order to reduce the amount of silica powder generated from the glass base material, there is a method of lowering the temperature of the drawing furnace. However, it is difficult to simply lower the drawing furnace temperature because the drawing furnace temperature affects the desired glass tension during drawing and also depends on the size of the base metal and the like. It is also conceivable to increase the gas flow rate in the drawing furnace in order to reduce the concentration of silica powder suspended in the drawing furnace gas per unit gas flow rate, but the manufacturing cost may increase.
［本開示の実施形態の説明］
　最初に本開示の実施形態を列記して説明する。
本開示に係る光ファイバ線引炉は、（１）光ファイバ用ガラス母材が挿入される炉心管と、前記光ファイバ用ガラス母材を外側から加熱するヒータ、および前記炉心管を内部に収納する炉本体と、前記炉心管の下方に配された下部チャンバと、前記下部チャンバの下方に配された保護管と、前記炉心管内に不活性ガスを上方から下方に向けて流す炉内ガス導入部と、を備えた光ファイバ線引炉であって、前記保護管内に所定のガスを導入するガス導入口を有するとともに、前記ガス導入口より上部側に、内部空間の径方向断面積が前記下部チャンバよりも小さい狭窄部を有する。
　これにより、保護管内のガス流量当たりのシリカ粉の濃度を下げることができるため、光ファイバにシリカ粉が接触または衝突する確率が低くなり、光ファイバの強度低下の発生を抑制することができる。 [Explanation of Embodiments of the present disclosure]
First, the embodiments of the present disclosure will be listed and described.
The optical fiber drawing furnace according to the present disclosure houses (1) a core tube into which a glass base material for optical fiber is inserted, a heater for heating the glass base material for optical fiber from the outside, and the core tube inside. The furnace body, the lower chamber arranged below the core tube, the protective tube arranged below the lower chamber, and the in-core gas introduction in which the inert gas flows into the core tube from above to below. An optical fiber wire drawing furnace provided with a portion, which has a gas introduction port for introducing a predetermined gas into the protective tube, and has a radial cross-sectional area of an internal space on the upper side of the gas introduction port. It has a smaller constriction than the lower chamber.
As a result, the concentration of silica powder per gas flow rate in the protective tube can be reduced, so that the probability that the silica powder comes into contact with or collides with the optical fiber is reduced, and the occurrence of a decrease in the strength of the optical fiber can be suppressed.
　（２）前記保護管は、前記下部チャンバの下方に連結されていてもよい。
　これにより、下部チャンバと保護管の間で光ファイバが外気に曝されることが無くなり、ガラス径が安定する。 (2) The protective tube may be connected below the lower chamber.
As a result, the optical fiber is not exposed to the outside air between the lower chamber and the protective tube, and the glass diameter is stabilized.
　（３）前記ガス導入口は、前記保護管の中央から上部側に設けられていることが望ましい。
　これにより、保護管内の大半部分においてガス流量当たりのシリカ粉の濃度を下げることができるため、光ファイバにシリカ粉が接触または衝突する確率が低くなり、光ファイバの強度低下の発生を抑制することができる。 (3) It is desirable that the gas inlet is provided from the center to the upper side of the protective pipe.
As a result, the concentration of silica powder per gas flow rate can be reduced in most of the inside of the protective tube, so that the probability that the silica powder comes into contact with or collides with the optical fiber is reduced, and the occurrence of a decrease in the strength of the optical fiber is suppressed. Can be done.
　（４）前記下部チャンバの下部に、前記下部チャンバ内の前記不活性ガスを外部に排出するガス抜き穴を有していてもよい。
　これにより、光ファイバにシリカ粉が接触または衝突する確率がさらに低くなり、光ファイバの強度低下の発生を抑制することができる。 (4) The lower part of the lower chamber may have a gas vent hole for discharging the inert gas in the lower chamber to the outside.
As a result, the probability that the silica powder comes into contact with or collides with the optical fiber is further reduced, and the occurrence of a decrease in the strength of the optical fiber can be suppressed.
　（５）前記ガス抜き穴から強制的にガスを排気してもよい。
　これにより、光ファイバにシリカ粉が接触または衝突する確率がさらに低くなり、光ファイバの強度低下の発生を抑制することができる。 (5) Gas may be forcibly exhausted from the gas vent hole.
As a result, the probability that the silica powder comes into contact with or collides with the optical fiber is further reduced, and the occurrence of a decrease in the strength of the optical fiber can be suppressed.
　（６）前記ガス導入口が、前記保護管の上端部に設けられていることが望ましい。
　これにより、保護管内のほぼ全長において、シリカ粉の濃度を保護管内で速やかに下げることができ、光ファイバにシリカ粉が接触または衝突する確率がさらに低くなる。 (6) It is desirable that the gas introduction port is provided at the upper end of the protective pipe.
As a result, the concentration of the silica powder can be rapidly reduced in the protective tube over almost the entire length of the protective tube, and the probability of the silica powder coming into contact with or colliding with the optical fiber is further reduced.
　（７）前記所定のガスが、アルゴン、窒素、または、エアであってもよい。
　これにより、安価なガスを使用することによって、製造コストを抑えつつ、光ファイバの強度低下の発生を抑制することができる。 (7) The predetermined gas may be argon, nitrogen, or air.
As a result, by using an inexpensive gas, it is possible to suppress the occurrence of a decrease in the strength of the optical fiber while suppressing the manufacturing cost.
　（８）前記ガス導入口が、前記保護管の周方向に等間隔で設けられていてもよい。
　これにより、光ファイバの周りにガスが均等に当たるため、光ファイバが保護管内で揺れることを防止でき、光ファイバ径変動への影響や、温度の不均一性に起因するファイバの曲がり（ファイバカール）を抑制できる。 (8) The gas introduction ports may be provided at equal intervals in the circumferential direction of the protective pipe.
As a result, the gas evenly hits around the optical fiber, so that the optical fiber can be prevented from shaking in the protective tube, which affects the fluctuation of the optical fiber diameter and the bending of the fiber due to the non-uniformity of temperature (fiber curl). Can be suppressed.
　（９）前記ガス導入口が、前記所定のガスを前記保護管の内部に下向きに導入するよう、下向きに設けられていてもよい。
　これにより、保護管内のガス流の乱れを抑制できる。 (9) The gas introduction port may be provided downward so as to introduce the predetermined gas downward into the inside of the protective pipe.
As a result, turbulence of the gas flow in the protective tube can be suppressed.
　（１０）前記ガス導入口が、前記所定のガスを前記保護管の内部にスパイラル状に導入するよう、斜め下向きであり、保護管壁面に沿った方向に向いていてもよい。
　これにより、シリカ粉をファイバ周囲から引き離しやすくなる。また、ファイバの周囲のガス流の乱れを低減することができる。 (10) The gas introduction port may be obliquely downward and may face in a direction along the wall surface of the protective pipe so as to introduce the predetermined gas into the protective pipe in a spiral shape.
This makes it easier to separate the silica powder from the periphery of the fiber. Moreover, the turbulence of the gas flow around the fiber can be reduced.
　本開示の一態様に係る光ファイバ製造方法は、（１１）上記の光ファイバ線引炉を用いて光ファイバを製造する方法である。
　これにより、保護管内のガス流量当たりのシリカ粉の濃度を下げることができるため、光ファイバにシリカ粉が接触または衝突する確率が低くなり、光ファイバの強度低下の発生を抑制することができる。 The optical fiber manufacturing method according to one aspect of the present disclosure is (11) a method of manufacturing an optical fiber using the above-mentioned optical fiber drawing furnace.
As a result, the concentration of silica powder per gas flow rate in the protective tube can be reduced, so that the probability that the silica powder comes into contact with or collides with the optical fiber is reduced, and the occurrence of a decrease in the strength of the optical fiber can be suppressed.
[本開示の実施形態の詳細]
　以下、図面を参照しながら、本開示に係る光ファイバ線引炉および光ファイバ製造方法の好適な実施形態について説明する。以下の説明において、異なる図面においても同じ符号を付した構成部材は同様のものであるとして、その説明を省略する場合がある。なお、本開示はこれらの実施形態での例示に限定されるものではなく、請求の範囲に記載された事項の範囲内および均等の範囲内におけるすべての変更を含む。また、複数の実施形態について組み合わせが可能である限り、本開示は任意の実施形態を組み合わせたものを含む。 [Details of Embodiments of the present disclosure]
Hereinafter, preferred embodiments of the optical fiber drawing furnace and the optical fiber manufacturing method according to the present disclosure will be described with reference to the drawings. In the following description, the components having the same reference numerals may be omitted because they are the same in different drawings. It should be noted that the present disclosure is not limited to the examples in these embodiments, and includes all modifications within the scope of the matters stated in the claims and within the scope of equality. Further, as long as a combination of a plurality of embodiments is possible, the present disclosure includes a combination of any of the embodiments.
（第１の実施形態）
　図１は、本開示の一態様に係る光ファイバ線引炉の概略図である。光ファイバ線引炉(以下、「線引炉」という。)１０は、炉本体１１と、炉本体１１の上方に設けた上部チャンバ１２と、下方に設けた下部チャンバ１３とを有している。上部チャンバ１２及び下部チャンバ１３は、中空の管形状である。炉本体１１の内部にはガラス母材１を加熱溶融するヒータ１５が配されており、ヒータ１５に囲われるようにして、円筒状の炉心管１４が配置されている。ヒータ１５と炉本体１１との間には、ヒータ１５からの熱が外部に放散されないようにするために、ヒータ１５を取り囲むように断熱材１６が設けられている。なお、ヒータは、誘導加熱を用いたものであっても良い。
　下部チャンバ１３の下方には、後で詳述する保護管２０が配されている。保護管２０は、下部チャンバ１３に密着し、連結されていることが好ましいが、多少であれば、保護管２０と下部チャンバ１３との間に隙間があっても良い。また、本実施形態では、下部チャンバ１３と保護管２０とが一つずつある構成で説明しているが、各々が複数個に分割されていても良いし、一体となっていても良い。 (First Embodiment)
FIG. 1 is a schematic view of an optical fiber drawing furnace according to one aspect of the present disclosure. The optical fiber wire drawing furnace (hereinafter referred to as “line drawing furnace”) 10 has a furnace main body 11, an upper chamber 12 provided above the furnace main body 11, and a lower chamber 13 provided below the furnace main body 11. .. The upper chamber 12 and the lower chamber 13 have a hollow tube shape. A heater 15 for heating and melting the glass base material 1 is arranged inside the furnace body 11, and a cylindrical core tube 14 is arranged so as to be surrounded by the heater 15. A heat insulating material 16 is provided between the heater 15 and the furnace body 11 so as to surround the heater 15 so that the heat from the heater 15 is not dissipated to the outside. The heater may be one using induction heating.
Below the lower chamber 13, a protective tube 20, which will be described in detail later, is arranged. The protective tube 20 is preferably in close contact with and connected to the lower chamber 13, but there may be a gap between the protective tube 20 and the lower chamber 13 to some extent. Further, in the present embodiment, the lower chamber 13 and the protective tube 20 are described one by one, but each of them may be divided into a plurality of parts or may be integrated with each other.
　光ファイバ２の線引きは、図示しない母材吊り機構によってガラス母材１を炉心管１４内に吊り下げ、ガラス母材１の下部をヒータ１５で加熱し、溶融されたガラス母材１の下端部から光ファイバ（ガラスファイバ部）２を溶融垂下させる工程であって、線引炉１０の下方から取り出される光ファイバ２が所定の外径となるように行われる。炉心管１４内には炉内ガス導入部１７から導入された窒素、または、ヘリウム、アルゴン等の不活性ガスが上方から下方にわたって供給されている。炉心管１４内は不活性ガス雰囲気下であるため、カーボン部品である炉心管１４等の酸化を防ぐととともに内部を清浄に保つことができる。 To draw the optical fiber 2, the glass base material 1 is suspended in the core tube 14 by a base material suspension mechanism (not shown), the lower part of the glass base material 1 is heated by the heater 15, and the lower end portion of the molten glass base material 1 is drawn. This is a step of melting and hanging the optical fiber (glass fiber portion) 2 from the glass fiber (glass fiber portion) 2 so that the optical fiber 2 taken out from below the drawing furnace 10 has a predetermined outer diameter. Nitrogen introduced from the in-core gas introduction unit 17 or an inert gas such as helium or argon is supplied into the core tube 14 from above to below. Since the inside of the core tube 14 is under an inert gas atmosphere, it is possible to prevent oxidation of the core tube 14 and the like, which are carbon components, and to keep the inside clean.
　炉心管１４内に導入された不活性ガスは、炉心管１４内でおよそ２０００℃以上に加熱される。そして、加熱された不活性ガスの一部は、ダウンフローにより、炉心管１４の内側の空間を通り、下部チャンバ１３と、保護管２０とを経て光ファイバ２とともに外部へ放出される。 The inert gas introduced into the core tube 14 is heated to about 2000 ° C. or higher in the core tube 14. Then, a part of the heated inert gas is discharged to the outside together with the optical fiber 2 through the space inside the core tube 14 through the lower chamber 13 and the protective tube 20 by the downflow.
　本実施形態では、下部チャンバ１３と保護管２０とが連結されており、連結部には、それぞれ内部空間の断面積が下部チャンバ１３よりも小さい下部チャンバ１３の狭窄部１３ａおよび保護管２０の狭窄部２０ａが形成されている。また、保護管２０の狭窄部２０ａの直下には、ガス導入口２１が設けられている。ガス導入口２１は、保護管２０の周方向に例えば４箇所、等間隔で設けられている。狭窄部１３ａおよび狭窄部２０ａは、これらの狭窄部１３ａ、２０ａより上部の炉心管１４および下部チャンバ１３の内部の圧力を、狭窄部１３ａ、２０ａより下部の保護管２０の内部の圧力よりも陽圧に保つためのものである。 In the present embodiment, the lower chamber 13 and the protective tube 20 are connected to each other, and the narrowed portion 13a and the protective tube 20 of the lower chamber 13 whose internal space cross-sectional area is smaller than that of the lower chamber 13 are narrowed at the connecting portion, respectively. The portion 20a is formed. Further, a gas introduction port 21 is provided directly below the narrowed portion 20a of the protective tube 20. The gas introduction ports 21 are provided at equal intervals, for example, at four locations in the circumferential direction of the protective tube 20. The narrowed portion 13a and the narrowed portion 20a make the pressure inside the core tube 14 and the lower chamber 13 above the narrowed portions 13a and 20a more positive than the pressure inside the protective tube 20 below the narrowed portions 13a and 20a. It is for keeping pressure.
　狭窄部は、ガス導入口２１の上部側にあれば、下部チャンバ１３と保護管２０との連結部に設けることには限定されず、下部チャンバ１３と保護管２０のいずれか一方だけに設けられてもよい。また、ガス導入口２１は、保護管２０の上端部（上端だけでなく、上端近傍も含む）に設けられることが望ましいが、保護管２０の長手方向中央から上部側に設けられればよい。なお、下部チャンバ１３と保護管２０とが一体となっている場合は、ガス導入口２１を、その中央部付近に設けることが望ましい。そして、ガス導入口２１には、外部から、クリーンな状態の、アルゴン、窒素、または、エア等のような、ヘリウムよりも安価なガスが導入される。 If the constricted portion is on the upper side of the gas inlet 21, the constriction portion is not limited to being provided at the connecting portion between the lower chamber 13 and the protective pipe 20, but is provided only at one of the lower chamber 13 and the protective pipe 20. You may. Further, the gas introduction port 21 is preferably provided at the upper end portion of the protective pipe 20 (including not only the upper end but also the vicinity of the upper end), but the gas introduction port 21 may be provided from the center in the longitudinal direction to the upper side of the protective pipe 20. When the lower chamber 13 and the protective tube 20 are integrated, it is desirable to provide the gas introduction port 21 near the central portion thereof. Then, a clean gas such as argon, nitrogen, or air, which is cheaper than helium, is introduced into the gas introduction port 21 from the outside.
　本実施形態では、線引炉１０内の不活性ガスに浮遊したシリカ粉の単位ガス流量当たりの濃度を、ガス導入口２１を有する保護管２０内で下げることで、線引中の光ファイバ２がシリカ粉と接触または衝突する確率が低減する。 In the present embodiment, the concentration of silica powder suspended in the inert gas in the drawing furnace 10 per unit gas flow rate is lowered in the protective tube 20 having the gas introduction port 21, so that the optical fiber 2 being drawn is drawn. Reduces the chance that the gas will come into contact with or collide with the silica powder.
　例えば、炉心管１４内に、下向きにＱ１slm（標準状態に換算してＱ１リットル／分）の流量の不活性ガスを流している際に、Ｑ１リットル当たりＮ個のシリカ粉が含まれていると仮定した場合、下部チャンバ１３内におけるシリカ粉のガス流量当たりの濃度は、Ｎ／Ｑ１となる。そして、保護管２０のガス導入口２１からＱ２slmのガスを保護管２０内に導入すると、保護管２０を上方から下方に流れるガス流量は、Ｑ３（＝Ｑ１＋Ｑ２）slmとなる。このため、保護管２０内におけるシリカ粉のガス流量当たりの濃度は、Ｎ／Ｑ３となり、線引炉１０内の不活性ガスに浮遊したシリカ粉の単位ガス流量当たりの濃度を、ガス導入口２１を有する保護管２０内で下げることができる。なお、下部チャンバ１３の狭窄部１３ａと、保護管２０の狭窄部２０ａとを設けることで、下部チャンバ１３内の圧力を、狭窄部１３ａ，２０ａより下部の保護管２０の内部の圧力よりも高く保つことができる。これにより、ガス導入口２１から導入されたガスが下部チャンバ１３側に流れることが抑制される。 For example, when an inert gas having a flow rate of Q1slm (Q1 liter / min in the standard state) is flowing downward in the core tube 14, N silica powders are contained per liter of Q1 liter. Assuming, the concentration of silica powder in the lower chamber 13 per gas flow rate is N / Q1. Then, when the gas of Q2slm is introduced into the protection tube 20 from the gas introduction port 21 of the protection tube 20, the gas flow rate flowing through the protection tube 20 from above to below becomes Q3 (= Q1 + Q2) slm. Therefore, the concentration of the silica powder in the protective tube 20 per gas flow rate is N / Q3, and the concentration of the silica powder suspended in the inert gas in the drawing furnace 10 per unit gas flow rate is set to the gas introduction port 21. It can be lowered in the protective tube 20 having the. By providing the narrowed portion 13a of the lower chamber 13 and the narrowed portion 20a of the protective tube 20, the pressure inside the lower chamber 13 is higher than the pressure inside the protective tube 20 below the narrowed portions 13a and 20a. Can be kept. As a result, the gas introduced from the gas introduction port 21 is suppressed from flowing to the lower chamber 13 side.
　これにより、保護管２０内で光ファイバ２にシリカ粉が接触または衝突する確率を低くすることができる。また、保護管２０のガス導入口２１から導入されたガスによって、炉心管１４内を流れるガスに含まれるシリカ粉が保護管２０内から早く外部に排出される。光ファイバ２は、炉心管１４、下部チャンバ１３、および、保護管２０を等速で移動するが、保護管２０を通過する際のシリカ粉の単位ガス流量当たりの濃度が、ガスを導入しない場合に比べて低くなっているため、シリカ粉が接触または衝突する確率を全体として低くすることができ、光ファイバの強度低下の発生を抑制することができる。 Thereby, the probability that the silica powder comes into contact with or collides with the optical fiber 2 in the protective tube 20 can be reduced. Further, the silica powder contained in the gas flowing in the core tube 14 is quickly discharged to the outside from the inside of the protection tube 20 by the gas introduced from the gas introduction port 21 of the protection tube 20. The optical fiber 2 moves through the core tube 14, the lower chamber 13, and the protective tube 20 at a constant speed, but the concentration of silica powder per unit gas flow rate when passing through the protective tube 20 does not introduce gas. Since it is lower than that of the above, the probability of contact or collision of silica powder can be reduced as a whole, and the occurrence of a decrease in the strength of the optical fiber can be suppressed.
　また、保護管２０内に導入するガスは、保護管２０の最上部近傍から導入することによって、ガス導入口２１より下方の保護管２０におけるシリカ粉濃度を速やかに低減することができる。このため、ガス導入口２１が保護管２０の上端部近傍に設けられることで、保護管２０内の全長において、シリカ粉濃度を低減することが望ましい。また、保護管２０に導入するガスは、光ファイバ２を揺らさないように、光ファイバ２の周方向から均等に流すことが望ましい。 Further, by introducing the gas introduced into the protective tube 20 from the vicinity of the uppermost portion of the protective tube 20, the silica powder concentration in the protective tube 20 below the gas introduction port 21 can be quickly reduced. Therefore, it is desirable to reduce the silica powder concentration in the entire length of the protective tube 20 by providing the gas introduction port 21 near the upper end of the protective tube 20. Further, it is desirable that the gas introduced into the protective tube 20 flows evenly from the circumferential direction of the optical fiber 2 so as not to shake the optical fiber 2.
（第２の実施形態）
　次に、保護管２０に設けたガス導入口２１の他の例について説明する。図２Ａは、保護管のガス導入口の他の例を示す図であり、長さ方向の断面図である。本実施形態では、保護管２０に設けた複数のガス導入口２１’が、保護管２０に向かって斜め下方に傾斜するように設けられている。このため、ガス導入口２１’から保護管２０内に導入されるガスは、保護管２０の内部に下向きの角度で導入される。これにより、保護管２０内に導入されたガスは、光ファイバ２の走行方向にスムーズに流れるため、ガス流れの乱れが抑制され、光ファイバ２の径変動への影響やファイバカールへの影響が抑制される。なお、本実施形態においても、保護管２０に導入するガスは、光ファイバ２の周方向から均等に流すことが望ましい。 (Second Embodiment)
Next, another example of the gas introduction port 21 provided in the protection pipe 20 will be described. FIG. 2A is a view showing another example of the gas inlet of the protective tube, and is a cross-sectional view in the length direction. In the present embodiment, the plurality of gas introduction ports 21'provided in the protection pipe 20 are provided so as to be inclined obliquely downward toward the protection pipe 20. Therefore, the gas introduced into the protective pipe 20 from the gas introduction port 21'is introduced into the protective pipe 20 at a downward angle. As a result, the gas introduced into the protective tube 20 flows smoothly in the traveling direction of the optical fiber 2, so that the turbulence of the gas flow is suppressed, and the influence on the diameter fluctuation of the optical fiber 2 and the influence on the fiber curl are affected. It is suppressed. Also in this embodiment, it is desirable that the gas introduced into the protective tube 20 flows evenly from the circumferential direction of the optical fiber 2.
（第３の実施形態）
　次に、保護管２０に設けたガス導入口２１のさらに他の例について説明する。図２Ｂは、保護管のガス導入口のさらに他の例を示す図であり、径方向の断面図である。本実施形態では、保護管２０に設けた複数のガス導入口２１”が、保護管２０の中心に向かう方向ではなく、斜め下向きで、壁面に沿った方向にガスを導入するように設けられている。これにより、保護管２０内に導入されたガスは、保護管２０の内壁に沿って旋回、すなわち周方向にスパイラル状に流れ、シリカ粉を光ファイバ２の周囲から引き離しやすくなる。なお、保護管２０に導入するガスは、一つのガス導入口から流してもよいし、複数のガス導入口２１”から均等に流してもよい。 (Third Embodiment)
Next, still another example of the gas introduction port 21 provided in the protection pipe 20 will be described. FIG. 2B is a diagram showing still another example of the gas inlet of the protective tube, and is a cross-sectional view in the radial direction. In the present embodiment, the plurality of gas introduction ports 21 "provided in the protection pipe 20 are provided so as to introduce the gas in the direction along the wall surface, not in the direction toward the center of the protection pipe 20, but diagonally downward. As a result, the gas introduced into the protective tube 20 swirls along the inner wall of the protective tube 20, that is, flows in a spiral shape in the circumferential direction, and easily separates the silica powder from the periphery of the optical fiber 2. The gas to be introduced into the protection pipe 20 may be flown from one gas introduction port or may be uniformly flown from a plurality of gas introduction ports 21 ”.
（第４の実施形態）
　図３Ａは、本開示の他の一態様に係る光ファイバ線引炉の概略図である。図３Ｂは、図３Ａの３Ｂ－３Ｂ矢視断面図である。本実施形態では、下部チャンバ１３の下方に外部に開口するガス抜き穴１３ｂが設けられている点で、第１から第３の実施形態と異なるが、他の構成については同様であるので、重複する構成についてはその説明を省略する。 (Fourth Embodiment)
FIG. 3A is a schematic view of an optical fiber drawing furnace according to another aspect of the present disclosure. FIG. 3B is a cross-sectional view taken along the line 3B-3B of FIG. 3A. The present embodiment is different from the first to third embodiments in that a gas vent hole 13b that opens to the outside is provided below the lower chamber 13, but the other configurations are the same, so that they overlap. The description of the configuration to be performed will be omitted.
　本実施形態では、図３Ｂに示すように、下部チャンバ１３の下方に設けた狭窄部１３ａの周囲に、均等な間隔で複数のガス抜き穴１３ｂを設けている。このガス抜き穴１３ｂからは、炉心管１４および下部チャンバ１３を流れてきた不活性ガスの一部が、シリカ粉とともに外部に排出される。
　ガス抜き穴１３ｂは、不活性ガスを下部チャンバ１３の下方に排出するように構成されているが、不活性ガスを下部チャンバの側方に排出するように下部チャンバの下部の側面に設けられていても良い。 In the present embodiment, as shown in FIG. 3B, a plurality of degassing holes 13b are provided at equal intervals around the narrowed portion 13a provided below the lower chamber 13. From the gas vent hole 13b, a part of the inert gas flowing through the core tube 14 and the lower chamber 13 is discharged to the outside together with the silica powder.
The degassing hole 13b is configured to discharge the inert gas below the lower chamber 13, but is provided on the lower side surface of the lower chamber so as to discharge the inert gas to the side of the lower chamber. You may.
　例えば、第１の実施形態と同様に、炉心管１４内に、下向きにＱ１slmの流量の不活性ガスを流している際に、Ｑ１リットル当たりＮ個のシリカ粉が含まれていると仮定した場合、下部チャンバ１３内におけるシリカ粉のガス流量当たりの濃度は、Ｎ／Ｑ１となる。そして、本実施形態の場合は、Ｑ４slmの不活性ガスがガス抜き穴１３ｂから外部に放出されるとすると、（Ｑ１－Ｑ４）slmのガスが下部チャンバ１３から保護管２０内に導入される。なお、保護管２０に導入される不活性ガスに含まれるガス流量当たりのシリカ粉の濃度は、Ｎ／Ｑ１と変わらないが、１分間あたりに保護管２０に入ってくるシリカ粉の量はＮ×（１－Ｑ４／Ｑ１）となる。 For example, as in the first embodiment, when it is assumed that the core tube 14 contains N silica powders per liter of Q1 when the inert gas having a flow rate of Q1slm is flowing downward. The concentration of silica powder per gas flow rate in the lower chamber 13 is N / Q1. Then, in the case of the present embodiment, assuming that the inert gas of Q4slm is discharged to the outside from the gas vent hole 13b, the gas of (Q1-Q4) slm is introduced into the protective tube 20 from the lower chamber 13. The concentration of silica powder per gas flow rate contained in the inert gas introduced into the protective tube 20 is the same as N / Q1, but the amount of silica powder entering the protective tube 20 per minute is N. It becomes × (1-Q4 / Q1).
　そして、第１の実施形態と同様に、保護管２０のガス導入口２１からＱ２slmのガスを保護管２０内に導入すると、保護管２０を上方から下方に流れるガス流量は、Ｑ５（＝Ｑ１－Ｑ４＋Ｑ２）slmとなる。このため、保護管２０内におけるシリカ粉のガス流量当たりの濃度は、｛Ｎ×（１－Ｑ４／Ｑ１）｝／Ｑ５となる。よって、保護管２０内の不活性ガスに浮遊したシリカ粉の単位ガス流量当たりの濃度を、第１の実施形態よりも下げることができる。 Then, as in the first embodiment, when the gas of Q2slm is introduced into the protection tube 20 from the gas introduction port 21 of the protection tube 20, the gas flow rate flowing through the protection tube 20 from above to below is Q5 (= Q1-). Q4 + Q2) It becomes slm. Therefore, the concentration of silica powder in the protective tube 20 per gas flow rate is {N × (1-Q4 / Q1)} / Q5. Therefore, the concentration of the silica powder suspended in the inert gas in the protective tube 20 per unit gas flow rate can be lowered as compared with the first embodiment.
(実施例)
　連結箇所に狭窄部を設けず、ガスも導入しなかった場合、スクリーニング試験における光ファイバの断線頻度（＝１Ｍｍ(＝１０００ｋｍ)当たりの断線回数）は、２回/Ｍｍであった。一方、狭窄部を設け、ガスを導入した場合、断線頻度は、１．５回/Ｍｍまで低減した。さらに、下部チャンバの下部にガス抜き穴を設けてガスを導入した場合、断線頻度は、１回/Ｍｍまで低減した。 (Example)
When no constriction was provided at the connecting portion and no gas was introduced, the frequency of disconnection of the optical fiber in the screening test (the number of disconnections per 1 Mm (= 1000 km)) was 2 times / Mm. On the other hand, when a narrowed portion was provided and gas was introduced, the frequency of disconnection was reduced to 1.5 times / Mm. Further, when the gas was introduced by providing a gas vent hole in the lower part of the lower chamber, the frequency of disconnection was reduced to 1 time / Mm.
　なお、第４の実施形態においても、第２、第３の実施形態と同様に、保護管２０内に導入されるガスを、保護管２０の内部に下向きの角度で導入したり、保護管２０の内壁に沿って周方向にスパイラル状に流れるように導入したりすることが望ましい。さらに、ガス抜き穴１３ｂから外部に放出される不活性ガスの流量を保護管２０に向かう不活性ガスの流量よりも大きくするために、ガス抜き穴１３ｂから下部チャンバ１３内の不活性ガスを吸引し、強制的に排気してもよい。このように、ガス抜き穴１３ｂから不活性ガスを外部に放出させることによって、光ファイバがけん引するガス流量と、ガス抜き穴から排出されるガス流量との割合を制御することが可能となる。 In the fourth embodiment as well, as in the second and third embodiments, the gas introduced into the protective tube 20 can be introduced into the protective tube 20 at a downward angle, or the protective tube 20 can be introduced. It is desirable to introduce it so that it flows in a spiral direction in the circumferential direction along the inner wall of the. Further, in order to make the flow rate of the inert gas discharged to the outside from the gas vent hole 13b larger than the flow rate of the inert gas toward the protection tube 20, the inert gas in the lower chamber 13 is sucked from the gas vent hole 13b. However, it may be forcibly exhausted. By discharging the inert gas from the gas vent hole 13b to the outside in this way, it is possible to control the ratio of the gas flow rate towed by the optical fiber to the gas flow rate discharged from the gas vent hole.
１…ガラス母材、２…光ファイバ、１０…線引炉、１１…炉本体、１２…上部チャンバ、１３…下部チャンバ、１３ａ…狭窄部、１３ｂ…ガス抜き穴、１４…炉心管、１５…ヒータ、１６…断熱材、１７…炉内ガス導入部、２０…保護管、２０ａ…狭窄部、２１，２１’，２１”…ガス導入口。 1 ... glass base material, 2 ... optical fiber, 10 ... wire drawing furnace, 11 ... furnace body, 12 ... upper chamber, 13 ... lower chamber, 13a ... constriction, 13b ... degassing hole, 14 ... core tube, 15 ... Heater, 16 ... Insulation material, 17 ... Gas inlet in the furnace, 20 ... Protective pipe, 20a ... Constriction, 21,21', 21 "... Gas inlet.

Claims (11)

  1. 　光ファイバ用ガラス母材が挿入される炉心管と、
    　前記光ファイバ用ガラス母材を外側から加熱するヒータ、および前記炉心管を内部に収納する炉本体と、
    　前記炉心管の下方に配された下部チャンバと、
    　前記下部チャンバの下方に配された保護管と、
    　前記炉心管内に不活性ガスを上方から下方に向けて流す炉内ガス導入部と、
    を備えた光ファイバ線引炉であって、
    　前記保護管内に所定のガスを導入するガス導入口を有するとともに、前記ガス導入口より上部側に、内部空間の径方向断面積が前記下部チャンバよりも小さい狭窄部を有する、光ファイバ線引炉。     The core tube into which the glass base material for optical fiber is inserted, and
    A heater that heats the glass base material for optical fiber from the outside, and a furnace body that houses the core tube inside.
    The lower chamber located below the core tube and
    A protective tube arranged below the lower chamber and
    An in-core gas introduction unit that allows an inert gas to flow from above to below into the core tube,
    It is an optical fiber wire drawing furnace equipped with
    An optical fiber drawing furnace having a gas introduction port for introducing a predetermined gas into the protective tube and a constricted portion having a constriction portion having a radial cross-sectional area of an internal space smaller than that of the lower chamber on the upper side of the gas introduction port. ..
  2. 　前記保護管は、前記下部チャンバの下方に連結されている、請求項１に記載の光ファイバ線引炉。 The optical fiber drawing furnace according to claim 1, wherein the protective tube is connected below the lower chamber.
  3. 　前記ガス導入口は、前記保護管の中央から上部側に設けられている、請求項１又は請求項２に記載の光ファイバ線引炉。 The optical fiber wire drawing furnace according to claim 1 or 2, wherein the gas introduction port is provided on the upper side from the center of the protective tube.
  4. 　前記下部チャンバの下部に、前記下部チャンバ内の前記不活性ガスを外部に排出するガス抜き穴を有する、請求項１から請求項３のいずれか１項に記載の光ファイバ線引炉。 The optical fiber drawing furnace according to any one of claims 1 to 3, further comprising a gas vent hole for discharging the inert gas in the lower chamber to the outside in the lower part of the lower chamber.
  5. 　前記ガス抜き穴から強制的にガスを排気する、請求項４に記載の光ファイバ線引炉。 The optical fiber wire drawing furnace according to claim 4, wherein the gas is forcibly exhausted from the degassing hole.
  6. 　前記ガス導入口が、前記保護管の上端部に設けられている、請求項１から請求項５のいずれか１項に記載の光ファイバ線引炉。 The optical fiber drawing furnace according to any one of claims 1 to 5, wherein the gas introduction port is provided at the upper end of the protective tube.
  7. 　前記所定のガスが、アルゴン、窒素、または、エアである、請求項１から請求項６のいずれか１項に記載の光ファイバ線引炉。 The optical fiber drawing furnace according to any one of claims 1 to 6, wherein the predetermined gas is argon, nitrogen, or air.
  8. 　前記ガス導入口が、前記保護管の周方向に等間隔で設けられている、請求項１から請求項７のいずれか１項に記載の光ファイバ線引炉。 The optical fiber wire drawing furnace according to any one of claims 1 to 7, wherein the gas introduction ports are provided at equal intervals in the circumferential direction of the protective tube.
  9. 　前記ガス導入口が、前記所定のガスを前記保護管の内部に下向きに導入するよう、下向きに設けられている、請求項１から請求項８のいずれか１項に記載の光ファイバ線引炉。 The optical fiber wire drawing furnace according to any one of claims 1 to 8, wherein the gas introduction port is provided downward so as to introduce the predetermined gas downward into the inside of the protective tube. ..
  10. 　前記ガス導入口が、前記所定のガスを前記保護管の内部にスパイラル状に導入するよう、斜め下向きであり、保護管壁面に沿った方向に向いている、請求項１から請求項８のいずれか１項に記載の光ファイバ線引炉。 Any of claims 1 to 8, wherein the gas introduction port is obliquely downward and faces in a direction along the wall surface of the protective pipe so as to introduce the predetermined gas into the inside of the protective pipe in a spiral shape. The optical fiber wire drawing furnace according to item 1.
  11. 　請求項１から請求項１０のいずれか１項に記載の光ファイバ線引炉を用いて、光ファイバを製造する光ファイバ製造方法。 An optical fiber manufacturing method for manufacturing an optical fiber using the optical fiber drawing furnace according to any one of claims 1 to 10.
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