JP6816670B2 - Seal structure of optical fiber drawing furnace, optical fiber manufacturing method - Google Patents

Description

The present invention relates to a seal structure of an optical fiber drawing furnace and a method for manufacturing an optical fiber. In detail, the present invention relates to an optical fiber drawing furnace and a glass for an optical fiber inserted into a core tube from the upper end opening. The present invention relates to a seal structure of an optical fiber drawing furnace for closing a gap between a base material and an optical fiber, and a method for manufacturing an optical fiber.

In the optical fiber, a glass base material for an optical fiber containing quartz as a main component (hereinafter referred to as a glass base material) is inserted into the core tube from the upper end opening of a drawing furnace for an optical fiber (hereinafter referred to as a drawing furnace). The tip of the glass base material is heated and melted to reduce the diameter, so that the glass base material is drawn from below the drawing furnace and manufactured. Since the temperature inside the drawing furnace at this time is extremely high, about 2000 ° C., carbon parts having excellent heat resistance are often used for the parts inside the drawing furnace.

In order to prevent thermal deterioration of carbon parts, generally, the inside of the drawing furnace is made positive pressure to prevent outside air (oxygen) from entering the drawing furnace, but the upper end opening of the drawing furnace and the glass If the gap between the base metal and the base metal is not properly airtight (unsealed), the outside air may be caught in the wire drawing furnace. In order to prevent this, for example, Patent Document 1 discloses a technique of a seal structure for closing the gap between the upper end opening of the drawing furnace and the glass base material.

Japanese Unexamined Patent Publication No. 2014-152803

However, in the case of the structure of Patent Document 1, the blade member (seal member) is housed in the housing, and a part (storage part) of the housing is exposed in the furnace space. The temperature of the space inside the furnace (upper part) may reach about 1000 ° C during drawing, and if the housing is made of metal, it will be thermally deteriorated. Therefore, a part of the housing, for example, water, etc. May be cooled with. However, when the housing facing the furnace space is cooled in this way, there is a place where the temperature changes locally in the furnace space, and gas flow (also called natural convection) near this housing. And this turbulence in the gas flow may affect the quality of the optical fiber.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a seal structure for an optical fiber drawing furnace that suppresses turbulence of gas flow in the drawing furnace, and a method for manufacturing an optical fiber. To do.

The seal structure of the optical fiber drawing furnace according to one aspect of the present invention includes an upper end opening of the optical fiber drawing furnace and a glass mother for optical fiber inserted into the core tube of the drawing furnace from the upper end opening. A seal structure for an optical fiber drawing furnace for closing a gap between materials, facing a space inside the furnace communicating with the core tube, and being cooled from the outside, and the core of the member. It is provided with a heat insulating member that insulates a portion facing the space inside the furnace that communicates with the pipe.

According to the above, the gas flow in the drawing furnace is less likely to be disturbed, and an increase in the glass diameter fluctuation of the optical fiber can be suppressed.

It is a figure explaining the outline of the optical fiber drawing furnace according to one Embodiment of this invention. It is a figure which shows an example of a seal structure. It is a figure explaining the operation of the blade member in the seal structure of FIG. It is a figure which shows another example of a seal structure.

[Explanation of Embodiments of the Present Invention]
First, the contents of the embodiments of the present invention will be listed and described.
The seal structure of the optical fiber drawing furnace according to one aspect of the present invention is as follows: (1) An optical fiber inserted into the core tube of the drawing furnace from the upper end opening of the optical fiber drawing furnace and the upper end opening. A seal structure for an optical fiber drawing furnace for closing a gap between a glass base material for glass, a member that faces the space inside the furnace communicating with the core tube and is cooled from the outside, and a member of the member. A heat insulating member for insulating a portion facing the space inside the furnace communicating with the core tube is provided. Since the portion of the member cooled from the outside facing the space inside the furnace is insulated, the temperature difference in the vicinity thereof becomes small. Therefore, the gas flow in the drawing furnace is less likely to be disturbed, and an increase in the glass diameter fluctuation of the optical fiber can be suppressed.

(2) The member includes a blade member provided so as to abut on the circumferential side surface of the glass base material for an optical fiber, and a housing for accommodating the blade member and a guide member for supporting the blade member. Is the housing. Since the part of the housing that is cooled from the outside facing the space inside the furnace is insulated, the temperature difference in the vicinity is small. Therefore, the gas flow in the drawing furnace is less likely to be disturbed, and an increase in the glass diameter fluctuation of the optical fiber can be suppressed.
(3) A carbon sheet member or a carbon felt member provided so as to abut on the circumferential side surface of the glass base material for an optical fiber, and a housing for supporting the carbon sheet member or the carbon felt member. The member is the housing. Since the part of the housing that is cooled from the outside facing the space inside the furnace is insulated, the temperature difference in the vicinity is small. Therefore, the gas flow in the drawing furnace is less likely to be disturbed, and an increase in the glass diameter fluctuation of the optical fiber can be suppressed.

(4) A space is provided between the heat insulating member and the member. If a space is provided between the heat insulating member, the heat of the cooled member is less likely to be transferred to the space inside the furnace, and the heat insulating effect can be further enhanced.
(5) In the method for manufacturing an optical fiber according to one aspect of the present invention, the optical fiber is drawn by using the seal structure of any of the above-mentioned optical fiber drawing furnaces. Since the above-mentioned seal structure is used, it is possible to prevent the gas flow in the drawing furnace from being disturbed, and it is possible to suppress an increase in the fluctuation of the glass diameter of the optical fiber.

[Details of Embodiments of the present invention]
Hereinafter, a preferred embodiment of the seal structure of the optical fiber drawing furnace and the method for manufacturing an optical fiber according to the present invention will be described with reference to the accompanying drawings. In the following, a resistance furnace in which the core tube is heated by a heater will be described as an example, but the present invention can also be applied to an induction furnace in which a high frequency power source is applied to the coil to induce and heat the core tube. Further, the structure of the core tube and the heat insulating material is also described below as an example, and is not limited to this.

FIG. 1 is a diagram illustrating an outline of an optical fiber drawing furnace according to an embodiment of the present invention. The wire drawing furnace 1 includes a furnace housing 2, a core tube 3, a heating source (heater) 4, and a seal structure 10. The furnace housing 2 has an upper end opening 2a and a lower end opening 2b, and is made of, for example, stainless steel. The core tube 3 is formed in a cylindrical shape in the central portion of the furnace housing 2, and communicates with, for example, the upper end opening 2a. The core tube 3 is made of carbon, for example, and the glass base material 5 is inserted into the core tube 3 in a state of being sealed by the seal structure 10 from the upper end opening 2a.

In the furnace housing 2, the heater 4 is arranged so as to surround the core tube 3, and the heat insulating material 7 is housed so as to cover the outside of the heater 4. The heater 4 heats and melts the glass base material 5 inserted inside the core tube 3, and causes the melt-reduced optical fiber 5b to hang down from the lower end portion 5a thereof. The glass base material 5 can be moved in the drawing direction (downward direction) by a separately provided moving mechanism, and the support rod 6 for suspending and supporting the glass base material 5 is above the glass base material 5. Are concatenated. Further, the drawing furnace 1 is provided with an in-core gas supply mechanism (not shown) using an inert gas or the like, and supplies the inert gas or the like in the core tube 3 or around the heater 4 to prevent oxidative deterioration. It is possible to do.

Note that FIG. 1 gives an example in which the upper end portion of the inner wall of the core tube 3 directly forms the upper end opening 2a, but the present invention is not limited to this. For example, an upper end opening narrower than the inner diameter d of the core tube 3 may be provided on the upper side of the core tube 3, and in this case, the gap to be sealed is between the narrow upper end opening and the glass base material 5. It becomes a gap that occurs. Further, the cross-sectional shape of the glass base material 5 is basically generated aiming at a perfect circle, but regardless of its accuracy, a non-circle may be present in a part thereof, or an ellipse or the like. You may. Further, the cross section of the upper end opening 2a may be circular, but the accuracy is not limited.

In one embodiment of the present invention, a seal structure 10 for closing a gap S between the upper end opening 2a of the drawing furnace 1 and the outer periphery of the glass base material 5 inserted into the core tube 3 from the upper end opening 2a is provided. This is a target, and in particular, the glass base material 5 in the drawing furnace is heated by the heater 4 while the seal structure 10 provided in the upper end opening 2a prevents the outside air from being entrained outside the furnace.

FIG. 2 is a diagram showing an example of the seal structure, and FIG. 3 is a diagram for explaining the operation of the blade member in the seal structure of FIG.
The seal structure 10 includes a plurality of heat-resistant blade members 14, 15 and guide members 16, 17 for accommodating the blade members 14, 15 and linearly sliding the blade members 14, 15. The housing 11 accommodating the blade members 14 and 15 and the guide members 16 and 17 and the blade members 14 and 15 have an action of pushing inward or pulling outward by using, for example, a pressure difference of gas. It is equipped with a mechanism that has been used.

As shown in FIG. 2, the housing 11 is a disk-shaped member having concentric through holes, and an opening for inserting the blade members 14 and 15 is provided on the inner peripheral surface of the housing 11. ing. The inner peripheral surface of the housing 11 is located in the furnace space I communicating with the core tube 3 described with reference to FIG. 1, and the temperature of the furnace space I in the vicinity of the housing is about 1000 ° C. during drawing. May reach.
The housing 11 is made of stainless steel, for example, and the blade members 14, 15 and the guide members 16, 17 are preferably 400 ° C. or lower (preferably 300 ° C. or lower when carbon is used as the material of each member). ) (For example, a water cooling system, not shown). As a result, it is possible to prevent the carbon and metal used for the blade members 14, 15 and the guide members 16, 17 and the housing 11 from deteriorating due to the radiant heat of the drawing furnace.

The blade members 14 and 15 extend radially with respect to the central axis of the housing 11, and are installed in the housing 11 in, for example, two upper and lower stages, and the blade members 14 are substantially along the inner peripheral surface of the housing 11. A plurality of blade members 15 are provided at equal intervals, and a plurality of blade members 15 are also provided below the blade member 14 at substantially equal intervals along the inner peripheral surface of the housing 11. The blade members 14 and 15 have, for example, a substantially rectangular parallelepiped shape having a substantially rectangular cross-sectional shape on a plane perpendicular to the moving direction, are arranged alternately in two upper and lower stages, and protrude from the housing 11 to be a side surface of the glass base material. To abut.

The material of the blade members 14 and 15 is preferably carbon, but in addition to carbon, for example, quartz glass, SiC coated carbon and the like can also be adopted.
The width and the number of the blade members 14 and 15 described above may be appropriately selected according to the outer diameter of the glass base material to be used, the amount of variation in the outer diameter, the amount of bending, and the like.

The guide members 16 and 17 are formed so that the blade members 14 and 15 can be inserted, for example, the guide member 16 is installed on the upper side of the blade member 14, and the guide member 17 is installed on the lower side of the blade member 15. The guide members 16 and 17 may be integrated.
The materials of the guide members 16 and 17 are preferably carbon, but metals such as boron nitride (BN), stainless steel, and molybdenum disulfide (MoS ₂ ) can also be used.

As shown in FIG. 3, the housing 11 is provided with a supply / discharge port 12 for supplying and discharging gas to the internal pressure applying space 40, and gas from the gas supply unit 51 is supplied through the supply / discharge port 12. It can be stored in the pressure applying space 40. Further, the gas accumulated in the pressure applying space 40 can be discharged (sucked out) from the gas discharge unit 52 via the supply / discharge port 12. The gas supply unit 51 and the gas discharge unit 52 are electrically connected to the controller 50.

By the way, the surface 11a on the furnace space side of the housing 11 shown in FIG. 2 is provided so as to be curved so as to surround the furnace space I at a position above the blade member 14. Similarly, the surface 11b is provided at a position below the blade member 15 in a curved manner so as to surround the furnace space I. As described above, since the housing 11 is cooled, a large temperature difference is generated between the housing 11 and the space I in the furnace at the locations near the surfaces 11a and 11b, which causes turbulence of the gas flow.

Therefore, in the present embodiment, the surfaces 11a and 11b of the housing 11 are covered with, for example, a tubular heat insulating member 20. Specifically, the heat insulating member 20 is composed of an upper heat insulating portion 21 arranged between the furnace space I and the surface 11a and a lower heat insulating portion 22 arranged between the furnace space I and the surface 11b. Become. The upper heat insulating portion 21 and the lower heat insulating portion 22 are formed in a cup shape, for example, and are arranged so that the cup-shaped opening is closed by the housing 11. The upper heat insulating portion 21 is curved so as to surround the furnace space I and covers the surface 11a, and the lower heat insulating portion 22 is curved so as to surround the furnace space I and covers the surface 11b.

In this way, the locally cooled portions such as the surfaces 11a and 11b of the housing 11 are covered with the heat insulating member 20, and the cooled member does not directly face the furnace space I. , The temperature difference from the furnace space I in the vicinity of the surfaces 11a and 11b can be reduced. Therefore, the gas flow in the drawing furnace is less likely to be disturbed, and an increase in the glass diameter fluctuation of the optical fiber can be suppressed. Specifically, the outer diameter variation (3σ) of the optical fiber was 0.6 to 1 μm when the housing 11 was not insulated by the heat insulating member 20, whereas when it was insulated, it was outside the optical fiber. The diameter variation (3σ) could be suppressed to 0.5 μm.

As the material of the heat insulating member 20, for example, quartz glass can be adopted. In this case, if it is made translucent instead of transparent, for example, the effect of heat insulating the housing 11 by the heat insulating member can be further enhanced. As the material other than quartz glass, for example, carbon may be adopted. Further, in order to prevent oxidative deterioration of the heat insulating member, SiC coated carbon or the like can be adopted.
Although FIG. 2 shows a configuration in which the upper heat insulating portion 21 and the lower heat insulating portion 22 are provided, even if only the upper heat insulating portion 21 or the lower heat insulating portion 22 is provided, the effect of suppressing an increase in the glass diameter fluctuation can be suppressed. is there.

As shown in FIGS. 2 and 3, spaces 31 and 32 are provided inside the upper heat insulating portion 21 and the lower heat insulating portion 22 of the heat insulating member 20. The spaces 31 and 32 are filled with a gas such as the gas supply unit 51 described with reference to FIG. 3, and it is preferable to use a gas having particularly high heat insulating properties and low thermal conductivity (for example, argon gas).

In this way, for example, if a gas layer made of argon gas having a low thermal conductivity is provided, the heat insulating effect of the housing 11 on the furnace space I can be further enhanced. The spaces 31 and 32 are not limited to a gas such as argon gas, and may be a solid as long as it is a member having high heat insulating properties. For example, quartz wool, carbon felt, or the like can be used.
According to the method for manufacturing an optical fiber using the seal structure described above, the gas flow in the drawing furnace can be made less likely to be disturbed, so that the glass diameter of the optical fiber is less likely to fluctuate.

In the above embodiment, the example of the seal structure including the blade member has been described, but the seal structure may be provided with the carbon sheet member and the carbon felt member. Further, the structure may be such that the blade member, the carbon sheet, the carbon felt and the like are not used, and the seal is sealed only with gas. Here, an example of a seal structure using a carbon felt member will be described in detail with reference to FIG.
The seal structure 10 shown in FIG. 4 has, for example, two carbon felt rings 14a and 15a having an inner diameter equal to or less than the outer diameter φ of the glass base material 5, and protrudes from the housing 11 to form the glass base material 5. Abut on the side of. Carbon felt is a felt made of carbon fiber and is used to ensure a certain degree of airtightness. As the carbon material, it is preferable to use what is called high-purity carbon from the viewpoint of mixing impurities.

A seat ring 64 is provided between the carbon felt rings 14a and 15a, a seat ring 63 is provided below the carbon felt ring 15a, and a seat ring 65 is provided above the carbon felt ring 14a. The seat rings 63, 64, 65 have a larger inner diameter than the carbon felt rings 14a, 15a. The material of the seat rings 63, 64, 65 is preferably high-purity carbon, but the material is not limited to this, and other heat-resistant materials such as quartz may be used.

The carbon felt rings 14a, 15a and the seat rings 63, 64, 65 are stacked in the order shown, for example, and supported by the housing 11, and the carbon felt rings 14a, 15a and the carbon sheet are placed on the upper side of the seat ring 65. A quartz ring 66 is provided so that the rings 63, 64, and 65 do not float and impair airtightness.
The housing 11 has a cooling mechanism (not shown) and is installed at the upper end 2c of the furnace housing 2. The surface of the housing 11 on the inner space side is curved so as to surround the inner space at the position below the seat ring 63. Therefore, the surface of the housing 11 on the furnace space side is covered with the heat insulating member 20. Therefore, also in the case of this example, the temperature difference from the furnace space in the vicinity of the surface of the housing 11 on the furnace space side can be reduced.

In the above embodiment, the member to be cooled from the outside is the housing 11 accommodating the blade members 14, 15 or the carbon felt rings 14a, 15a, and the housing 11 is heat-insulated. did. However, the present invention is not limited to this example, and can be applied as long as the member cooled from the outside faces the space inside the furnace. Specifically, the member of the present invention is a furnace housing 2 located below the seal structure 10 described with reference to FIG. 1, or an upper chamber (made of metal) arranged above the seal structure (not shown). It may be. Therefore, the surface of the member of the present invention also corresponds to the cylindrical inner surface portion of the upper lid (located near the upper end opening 2a) of the furnace housing 2, or the cylindrical inner surface portion of the lower end of the upper chamber.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is indicated by the scope of claims, not the above-mentioned meaning, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 ... Optical fiber drawing furnace, 2 ... Furnace housing, 2a ... Upper end opening, 2b ... Lower end opening, 2c ... Upper end, 3 ... Core tube, 4 ... Heater, 5 ... Glass base material for optical fiber, 5a ... Lower end, 5b ... Optical fiber, 6 ... Support rod, 7 ... Insulation material, 10 ... Seal structure, 11 ... Housing, 11a, 11b ... Surface, 12 ... Supply / discharge port, 14, 15 ... Blade member, 14a , 15a ... Carbon felt ring, 16,17 ... Guide member, 20 ... Insulation member, 21 ... Upper insulation part, 22 ... Lower insulation part, 31, 32 ... Space, 40 ... Pressure application space, 50 ... Controller, 51 ... Gas Supply unit, 52 ... gas discharge unit, 63, 64, 65 ... seat ring, 66 ... quartz ring.

Claims (5)

Seal of the optical fiber drawing furnace for closing the gap between the upper end opening of the optical fiber drawing furnace and the glass base material for optical fiber inserted into the core tube of the drawing furnace from the upper end opening. It's a structure
A member that faces the space inside the furnace that communicates with the core tube and is cooled from the outside,
A heat insulating member that insulates a portion of the member facing the space inside the furnace that communicates with the core tube.
The seal structure of the optical fiber drawing furnace. A blade member provided so as to abut on the circumferential side surface of the glass base material for an optical fiber, and
A housing for accommodating the blade member and a guide member for supporting the blade member is provided.
The seal structure of the optical fiber drawing furnace according to claim 1, wherein the member is the housing. A carbon sheet member or a carbon felt member provided so as to abut on the circumferential side surface of the glass base material for an optical fiber.
The carbon sheet member or the housing that supports the carbon felt member is provided.
The seal structure of the optical fiber drawing furnace according to claim 1, wherein the member is the housing. The seal structure for an optical fiber drawing furnace according to any one of claims 1 to 3, wherein a space is provided between the heat insulating member and the member. A method for manufacturing an optical fiber, wherein the optical fiber is drawn by using the seal structure of the optical fiber drawing furnace according to any one of claims 1 to 4.

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