JP6024475B2 - Optical fiber drawing furnace seal structure, optical fiber drawing method - Google Patents

Description

  The present invention relates to a sealing structure for an optical fiber drawing furnace for closing a gap between an upper end opening of an optical fiber drawing furnace and an optical fiber glass preform, and an optical fiber drawing method.

  An optical fiber is made by lowering a glass base material for optical fiber (hereinafter referred to as a glass base material) mainly composed of quartz from an upper end opening of an optical fiber drawing furnace (hereinafter referred to as a drawing furnace) into a furnace core tube. The tip is heated and melted, and the tip of the glass base material is reduced in diameter and drawn from the lower end opening. Since the temperature in the drawing furnace at this time is as high as about 2000 ° C., carbon having excellent heat resistance is used for the parts in the drawing furnace.

  This carbon has the property of being oxidized and consumed in a high-temperature oxygen-containing atmosphere. For this reason, it is necessary to keep the inside of a drawing furnace in the atmosphere of noble gases, such as argon gas and helium gas, and nitrogen gas (henceforth inert gas etc.).

  In this case, the inside of the drawing furnace is set to a positive pressure to prevent outside air (oxygen) from entering the drawing furnace. However, the gap between the upper end opening of the drawing furnace and the glass base material is well sealed. Otherwise (if not sealed), the outside air will be drawn into the drawing furnace, which will affect the life of the drawing furnace, and the amount of inert gas used will increase, making it impossible to reduce the manufacturing cost of the optical fiber. . Therefore, a sealing mechanism for closing the gap between the upper end opening of the drawing furnace and the glass base material is required.

  For example, Patent Document 1 discloses a seal structure including upper and lower two-stage blade members that are in contact with a side surface of a glass base material at an upper end opening of a drawing furnace. Specifically, the upper blade member and the lower blade member are alternately arranged in the vertical direction, and each blade member has a base material contact surface parallel to the side surface of the glass base material. .

JP 2012-106915 A

  By the way, in recent years, in order to further reduce the manufacturing cost of optical fibers, the glass base material has been made longer and larger in diameter, and the glass base material has been reduced in the number of steps. The variation in material diameter is also increasing. When the base metal diameter fluctuates more than about ± 10 mm, for example, the gap between the upper end opening of the drawing furnace and the glass base material also fluctuates greatly. Don't be.

  In Patent Document 1, sealing is performed by bringing a plurality of blade members into contact with a glass base material, but the base material contact surface of each blade member has a substantially rectangular cross-sectional shape with a curved surface close to the base material radius. Since it has a predetermined thickness in the vertical direction and is formed parallel to the side surface of the glass base material, the outer diameter of the glass base material varies greatly, and the base material contact surface of each blade member and the side surface of the glass base material Is not parallel, there is a gap between the base material contact surface of the blade member and the side surface of the glass base material, and this gap communicates between the upper and lower blade members and the outside air is drawn into the drawing furnace. There is.

  More specifically, as shown in FIG. 12A, when the base material diameter of the glass base material 5 is increased toward the upper part, the upper blade member 104 is more glass than the lower blade member 105. The base material contact surface 104a of the upper blade member 104 is in contact with the side surface of the glass base material 5, and moves to the side farther from the drawing furnace central axis Z when viewed in the radial direction of the base material 5. The part is separated from the side surface of the glass base material 5. For this reason, in the upper blade member 104, a gap is formed between the lower end portion of the base material contact surface 104a and the side surface of the glass base material 5, and further, in the circumferential direction of the glass base material 5 along with the movement. Since a gap is also formed between the adjacent upper blade members 104, the inside of the drawing furnace communicates with the outside through the gap formed between the lower blade members 105 that are also adjacent in the circumferential direction. May be caught in the drawing furnace.

  On the other hand, as shown in FIG. 12B, when the glass base material diameter of the glass base material 5 decreases toward the upper part, the lower blade member 105 is larger in diameter than the upper blade member 104. The base metal contact surface 105a of the lower blade member 105 is in contact with the side surface of the glass base material 5 and the upper end portion thereof is the glass base. Separate from the side of the material 5. Therefore, in the lower blade member 105, a gap is formed between the upper end portion of the base material contact surface 105a and the side surface of the glass base material 5, and further, a gap is also formed between adjacent lower blade members 105. Therefore, the drawing furnace communicates with the outside through a gap formed between the adjacent upper blade members 104. Therefore, in this case as well, as in the case where the base material diameter increases, there is a possibility that outside air may be caught in the drawing furnace.

  The present invention has been made in view of the above circumstances, and is an optical fiber drawing furnace capable of avoiding the entrainment of outside air into the drawing furnace and reducing the amount of inert gas used. An object is to provide a sealing structure and a method for drawing an optical fiber.

An optical fiber drawing furnace seal structure according to the present invention is for an optical fiber for closing a gap between an upper end opening of an optical fiber drawing furnace and an optical fiber glass preform inserted from the upper end opening. The drawing furnace has a sealing structure, and is provided with a plurality of blade members that are alternately arranged in two upper and lower stages and have tip portions that come into contact with the side surfaces of the optical fiber glass preform. The tip portions are upper and lower blade members. Are formed in such a shape that the upper and lower blade members are in line contact with the side surface of the optical fiber glass preform.

  Further, the tip of the upper blade member is inclined linearly so that the lower part approaches the center axis of the upper end opening, and the tip of the lower blade member approaches the center axis of the upper end opening as the upper part. You may incline linearly. The tip of the upper blade member is curved and inclined so that the lower part approaches the center axis of the upper end opening, and the upper part of the lower blade member approaches the center axis of the upper end opening as the upper part. It may be curved and inclined.

An optical fiber drawing method according to the present invention includes an optical fiber drawing furnace for closing a gap between an upper end opening of an optical fiber drawing furnace and an optical fiber glass preform inserted from the upper end opening. An optical fiber drawing method for drawing an optical fiber by using the sealing structure of the above, and a plurality of blades having tip portions that are alternately arranged in two stages and are in contact with the side surface of the optical fiber glass preform The upper and lower blade members are in line contact with the side surfaces of the optical fiber glass preform at the position where the upper and lower blade members overlap, and the optical fiber is drawn.

  According to the optical fiber drawing furnace sealing structure of the present invention, the optical fiber drawing method, the tip of each blade member is in line contact with the side surface of the glass base material at the position where the upper and lower blade members overlap, Even if the gap between the upper end opening and the glass base material fluctuates greatly, the lower end portion of the upper end and the side of the glass base contact, and the upper end of the lower end and the side of the glass base Contact is maintained. Therefore, the gap between the upper end opening and the glass base material can be closed, and the outside air can be prevented from being caught in the drawing furnace.

It is a figure explaining the outline of the drawing furnace for optical fibers of this invention. It is a perspective view showing the outline of a 1st embodiment of the seal structure by the present invention. It is a figure explaining an example and operation | movement of a blade member in the seal structure of FIG. It is a fragmentary sectional view of the blade member of FIG. It is a fragmentary sectional view of other examples of a blade member. It is sectional drawing which shows the outline of 2nd Embodiment of the seal structure by this invention. It is a top view which shows the principal part of the seal structure of FIG. It is a figure which shows the AA cross section of the seal structure of FIG. It is a figure which shows an example of the cylindrical slit spring in the seal structure of FIG. It is sectional drawing which shows the outline of 3rd Embodiment of the seal structure by this invention. It is a figure explaining the open / close state of the blade member in the seal structure of FIG. It is a figure explaining operation | movement of the blade member in the conventional seal structure.

  An outline of a drawing furnace to which the present invention is applied will be described with reference to FIG. 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. The drawing furnace 1 includes a furnace casing 2, a furnace core tube 3, a heating source (heater) 4, and a seal mechanism 8. 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 at the center of the furnace housing 2 and communicates with the upper end opening 2a. The core tube 3 is made of carbon, and the glass base material 5 is inserted into the core tube 3 after being sealed by the seal mechanism 8 from the upper end opening 2a.

  In the furnace casing 2, the heater 4 is disposed so as to surround the furnace core tube 3, and the heat insulating material 7 is accommodated so as to cover the outside of the heater 4. The heater 4 heats and melts the glass base material 5 inserted into the core tube 3, and melts and droops the optical fiber 5b melted and reduced in diameter from its lower end portion 5a. The glass base material 5 can be moved in a drawing direction (downward direction) by a separately provided moving mechanism, and the glass base material 5 is suspended and supported on the upper side of the glass base material 5. The support rod 6 for connecting is connected. The drawing furnace 1 is provided with an inert gas supply mechanism (not shown) to supply an inert gas or the like into the furnace core tube 3 or around the heater 4 to prevent oxidation or deterioration. ing.

  Although FIG. 1 shows an example in which the upper end portion of the inner wall of the core tube 3 forms the upper end opening 2a as it is, the present invention is not limited to this. For example, an upper lid that is 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. It becomes a gap generated between the two. In addition, the cross-sectional shape of the glass base material 5 is basically generated to aim at a perfect circle, but some non-circles may exist regardless of the accuracy, and the glass base material 5 may have an elliptical shape. May be. The upper end opening 2a may have a circular cross section, but this accuracy does not matter.

  The present invention is directed to the sealing mechanism 8 for closing the gap S between the upper end opening 2a of the drawing furnace 1 and the outer periphery of the glass base material 5 inserted from the upper end opening 2a. The glass base material 5 in the furnace is heated by the heater 4 while the outside air outside the furnace is not caught by the seal mechanism 8 provided in the upper end opening 2a. In addition, the cover body 9 arranged on the upper part of the glass base material 5 is made to correspond to the seal near the end of the drawing process, which will be described later.

[First embodiment]
Hereinafter, the seal structure according to the first embodiment of the seal mechanism will be described with reference to FIG. FIG. 2 is a perspective view schematically showing the seal structure 10.
The seal structure 10 has a plurality of blade members 14 and 15 having heat resistance, a cylinder 11 that is a part of a support mechanism that supports the blade members 14 and 15, and an action of pressing the blade members 14 and 15 inward. And a mechanism (hereinafter referred to as a pressing mechanism). Hereinafter, in order to distinguish from the outer cylinder 12 described later, the cylinder 11 is referred to as an inner cylinder. The outer cylinder 12 also forms part of a support mechanism that supports the blade members 14 and 15.

  The inner cylinder 11 includes a plurality of guide holes 13 a and 13 b for sliding the plurality of blade members 14 and 15 on the circumference of the inner cylinder 11, for example, in two steps. The guide holes 13a and 13b are provided radially with respect to the central axis of the inner cylinder 11, and the blade members 14 and 15 are also installed so as to be radially movable linearly. The guide holes 13a and 13b are not provided directly in the inner cylinder 11, for example, but as shown in FIG. 3, the inner cylinder 11 is provided with a disk-shaped storage portion 13 for storing the blade members 14 and 15, Each guide hole 13 a, 13 b can be provided in the storage portion 13.

  For example, the blade members 14 and 15 have a substantially rectangular parallelepiped shape in which a cross-sectional shape in a plane perpendicular to the moving direction is a substantially rectangular shape. In addition, the thickness of the blade members 14 and 15 may be thin, for example, may be about 1 mm in thickness. The guide holes 13a and 13b described above are holes having a shape that matches the cross-sectional shape of the blade members 14 and 15.

  The tips of the blade members 14 and 15 are brought into contact with the side surfaces of the glass base material when pressed by a pressing mechanism, as will be described later. Accordingly, the tips of the blade members 14 and 15 are the maximum value assumed as the radius of the glass base material (the maximum diameter of the glass base material to be used) in order to make the gap with the glass base material as small as possible at the time of contact. It is preferable to use an arc shape having a curvature suitable for the above. FIG. 2 etc. show an example in which such an arc is adopted.

  The material of the blade members 14 and 15 is preferably carbon. Carbon is not only excellent in heat resistance but also a soft material that can be processed with a small coefficient of friction, so there is no fear of damaging the glass base material. In particular, it is preferable to employ soft carbon having a Shore hardness of 100 or less for the blade members 14 and 15 of this example. Carbon is also preferred in that it can be easily molded by press molding or machining.

As a material for the blade members 14 and 15, for example, glass (quartz), SiC-coated carbon, or the like can be employed in addition to carbon. Further, even when other hard materials are used, for example, the glass base material is not damaged by using soft carbon only at the tip portion.
The blade members 14 and 15 are required to be made of a material that does not melt with the heat of the drawing furnace, and preferably have a heat resistance of about 200 ° C. or higher. When the heat resistance of the blade members 14 and 15 is not sufficient, a mechanism for cooling the blade members 14 and 15 (for example, a water cooling method) may be provided.

In addition, when carbon is used as the blade members 14 and 15, in order to prevent oxidation and deterioration, an inert gas or the like is sprayed onto the blade members 14 and 15 to surround the blade members 14 and 15. Is preferably an atmosphere of inert gas or the like.
The inner diameter of the inner cylinder 11 and the length of the blade members 14 and 15 in the moving direction may be determined so as to fill a gap generated between the drawing furnace and the glass base material. In the example of FIG. 1, the width of the gap S generated between the core tube 3 and the glass base material 5 in the upper end opening 2 a is halved by subtracting the diameter φ of the glass base material 5 from the diameter d of the core tube 3. Value.

  However, in practice, since the outer diameter of the glass base material 5 varies, the inner diameter of the inner cylinder 11 and the blade members 14 and 15 are based on the distance assumed as the gap S (preferably the assumed maximum distance). What is necessary is just to determine the length of the moving direction. For example, when the diameter φ of the glass base material 5 is 90 mm and is formed with a diameter variation of ± 10 mm, the diameter d of the core tube 3 only needs to be about 120 mm, so the width of the gap S is about 10 to 20 mm. Become.

Further, the width (the length parallel to the tangential direction of the inner cylinder 11) and the number of blade members 14 and 15 may be appropriately selected according to the outer diameter, the outer diameter fluctuation amount, the bending amount, etc. of the glass base material to be used. Good.
Basically, the greater the number of blade members 14 and 15, the easier it is to seal.
And the said press action mechanism makes the front-end | tip of several blade member 14,15 contact | abut to the side surface of a glass base material in the state which inserted several blade member 14,15 in each of several guide hole 13a, 13b. As described above, the blade members 14 and 15 are individually pressed in the radial direction of the drawing furnace (more precisely, in the radial direction of the inner cylinder 11 and the storage portion 13). This pressing force is assumed to be weak enough not to inhibit the lowering of the glass base material.

  As described above, the inner cylinder 11 is provided with a plurality of guide holes 13a and 13b alternately on the circumference thereof, and the blade members 14 and 15 can move linearly in these guide holes. Inserted in the state. Therefore, a plurality of blade members 14 are provided at equal intervals on the circumference of the inner cylinder 11, and a plurality of blade members 15 are also provided at equal intervals on the circumference of the inner cylinder 11. As shown in FIGS. 2 and 3, the blade member 14 and the blade member 15 are not spaced apart in the vertical direction.

  Further, the blade members 14 and 15 fill the gap generated in the adjacent blade member 14 with the blade member 15 and fill the gap generated in the adjacent blade member 15 with the blade member 14. That is, the gaps between the adjacent blade members 14 and the gaps between the adjacent blade members 15 do not overlap each other. Thereby, it is possible to seal the gap S in FIG. 1 so that the inert gas or the like hardly leaks.

  Thus, in the present invention, it is preferable that the plurality of blade members 14 and 15 are alternately stacked in a two-layer structure. With such a structure, the gap generated in the upper end opening of the drawing furnace is closed by bringing the tips of the blade members 14 and 15 into contact with the glass base material. Each of the plurality of blade members 14 and 15 is installed to be slidable independently in the horizontal direction toward the center of the glass base material.

  For example, as shown in FIG. 2, the pressing mechanism includes a plurality of rod-like members 16 each having one end fixed to the rear ends of the blade members 14 and 15 and the other end held by the outer cylinder 12. A plurality of coil spring members 17 provided along each of the plurality of rod-like members 16 can be used. The outer cylinder 12 is not limited to a cylinder, and may be a polygonal cylindrical member as long as it can function as an outer wall. The coil spring member 17 may not have a coil shape as long as the coil spring member 17 extends and contracts in the axial direction.

  In this pressing mechanism, the plurality of rod-like members 16 are inserted into the loose insertion holes of the fixing member 18 fixed to the outer cylinder 12 and are movable in the radial direction. A plurality of coil spring members 17 are arranged along the rod-shaped member 16 and are respectively brought into contact with the plurality of blade members 14 and 15 and the fixing member 18. Thus, the pressing mechanism can press the blade members 14 and 15 individually to the glass base material side by the biasing force of the coil spring member 17.

  In addition, although the press action mechanism demonstrated in FIG. 2 was comprised by the rod-shaped member 16, the coil spring member 17, etc., you may be comprised by the air cylinder. Each air cylinder in this case is configured such that its length can be expanded and contracted with respect to the radial direction of the drawing furnace. The blade members can be individually pressed to the glass base material side.

FIG. 3 is a view for explaining an example of the blade member and its operation in the above-described seal structure 10.
In the above-described seal structure 10, for example, when the glass base material 5 having the assumed minimum diameter (diameter Da) is used, each blade member 14, 15 is formed of the blade member 14 as shown in FIG. What is necessary is just to design so that it may come out to the extent that the front-end | tips or the front-end | tips of the blade member 15 contact. On the other hand, when the glass base material 5 having the assumed maximum diameter (diameter Db) is used, the blade members 14 and 15 are designed to be substantially accommodated in the accommodating portion 13 as shown in FIG. Just keep it.

And each blade member 14 and 15 absorbs the diameter fluctuation | variation of the glass base material 5 by slidingly moving the range between the examples illustrated by FIG. 3 (A) and FIG. 3 (B) individually. Can do.
As described above, in the seal structure 10 of this example, the gap S between the core tube 3 and the glass base material 5 can be satisfactorily closed even if the diameter fluctuation of the glass base material 5 in FIG. 1 is large. As a result, the inflow of outside air into the furnace can be suppressed.

  Further, in the seal structure 10, the blade members 14, 15 move radially toward the outer cylinder 12 (outward) at locations where the glass base material is thick. On the other hand, in a thin portion, the blade members 14 and 15 can close the gap S with a simple structure in which they move radially toward the center of the inner cylinder 11 (inward). Diameter fluctuations can be automatically absorbed. Furthermore, since each of the plurality of blade members 14 and 15 has a structure that slides independently, it is necessary to cope with a case where the diameter of the glass base material is not constant on the same cross section, that is, a non-circular cross section. Can do.

By the way, the blade members 14 and 15 shown in FIGS. 2 and 3 have, for example, tip portions that overlap vertically in a state shifted by a half pitch, and these tip portions are made of the glass base material at the alignment position. It is formed in a shape that makes line contact with the side surface.
Specifically, as shown in FIG. 4 which is cut along the moving direction of the blade member, the tip portion 14a of the upper blade member 14 is a straight line so that the lower portion approaches the central axis of the upper end opening 2a in FIG. The lower end of the blade member 14 protrudes toward the glass base material from the upper end thereof. On the other hand, the tip portion 15a of the lower blade member 15 is inclined linearly so as to approach the central axis of the upper end opening 2a toward the upper portion, and the upper end of the blade member 15 is made of a glass base material rather than its lower end. Sticks out.

  Thereby, each front-end | tip part 14a, 15a can be in line contact with the side surface of a glass base material in the position where an upper and lower blade member overlaps. Even if the gap S in FIG. 1 fluctuates greatly and a gap is formed between adjacent blade members in the circumferential direction, the contact between the lower end portion of the upper end portion 14a and the side surface of the glass base material, and the lower step Contact between the upper end portion of the tip portion 15a and the side surface of the glass base material is maintained.

  More specifically, the upper blade member 14 is provided with a relief to the upper surface end side while leaving the lower surface end, and the lower blade member 15 is provided with a relief to the lower surface end side leaving the upper surface end. Yes. For this reason, a gap may be generated between the upper end portion of the upper end portion 14a and the glass base material and between the lower end portion of the lower end portion 15a and the glass base material. However, even when the base material diameter increases / decreases, there are gaps between the lower end portion of the upper end portion 14a and the glass base material and between the upper end portion of the lower end portion 15a and the glass base material. In addition, since the upper and lower blade members have overlapping portions, the gap between the upper end opening and the glass base material can be closed without the gap communicating in the vertical direction. As a result, it is possible to prevent gas leakage in the drawing furnace, avoid entrainment of outside air, and reduce the amount of inert gas used.

In addition, in said FIG. 4, although the blade members 14 and 15 inclined linearly were demonstrated, you may curve.
Specifically, the blade members 14 ′ and 15 ′ shown in FIG. 5 also have tip portions 14a ′ and 15a ′ formed in a shape in line contact with the side surfaces of the glass base material at the positions where the upper and lower blade members overlap. ing. The tip portion 14a ′ of the upper blade member 14 ′ is curved and inclined so as to approach the central axis of the upper end opening 2a in FIG. On the other hand, the tip 15a ′ of the lower blade member 15 ′ is curved and inclined so as to approach the central axis of the upper end opening 2a toward the upper part. In this way, if the tip portions 14a 'and 15a' are curved and inclined, the load on the tip portion can be reduced compared to the case where the tip portions are inclined linearly, and a long-life blade member can be provided. Become.

[Second Embodiment]
Next, a seal structure according to a second embodiment of the seal mechanism will be described with reference to FIGS. 6 is a cross-sectional view schematically showing the seal structure 20, FIG. 7 is a top view showing a main part of the seal structure of FIG. 6, and FIG. 8 is a view showing an example of a blade member storage portion in the seal structure 20. These are figures which show an example of the cylindrical slit spring used for the seal structure 20. FIG.
The seal structure 20 includes a plurality of blade members 24 and 25 having heat resistance, a storage portion 23 that is a part of a support mechanism that supports the blade members 24 and 25, and a cylindrical slit spring 26.

  The blade members 24 and 25 can have the same shape as the blade members 14 and 15 described in the first embodiment and the like, and have a substantially rectangular parallelepiped shape whose cross-sectional shape in a plane perpendicular to the moving direction is substantially rectangular. Shaped. The blade members 24 and 25 may be thin, for example, about 1 mm thick. Further, the guide hole of the storage portion 23 that supports the plurality of blade members 24 and 25 is a hole having a shape that matches the cross-sectional shape of the blade members 24 and 25.

  The tip portions 24a and 25a of the blade members 24 and 25 have the same shape as the tip portions 14a and 15a described in FIGS. 2 to 4 of the first embodiment and the tip portions 14a ′ and 15a ′ described in FIG. Can be used. In addition, when the tip portions 24a and 25a are pressed by the pressing action mechanism described later, the tip portions 24a and 25a are in contact with the side surfaces of the glass base material as much as possible. Similarly to the blade member described in (4), it is preferable to form an arc having a curvature that matches the maximum value assumed as the radius of the glass base material.

  Moreover, it is preferable that the material of the blade members 24 and 25 is carbon like the blade members of the first embodiment and the like. When carbon is used as the blade members 24 and 25, in order to prevent oxidation and deterioration, an inert gas or the like is sprayed onto the blade members 24 and 25 to surround the blade members 24 and 25. Is preferably an atmosphere of inert gas or the like.

  The storage unit 23 is a disk-shaped member, and is stored and fixed in the housing 27. FIG. 8 shows a state in which the storage portion 23 is viewed from the AA cross section in FIG. As shown in FIG. 8, the storage unit 23 includes a plurality of guide holes 23 a and 23 b for sliding the plurality of blade members 24 and 25 in two stages on the circumference of the storage unit 23. Yes. The guide holes 23a and 23b are provided radially with respect to the central axis of the storage portion 23, and the blade members 24 and 25 can also be moved radially linearly in the same manner as the blade member in the first embodiment. Installed. The inner diameter of the storage portion 23 and the length in the moving direction of the blade members 24 and 25 are determined so as to fill a gap generated between the drawing furnace and the glass base material. The width and the number of blade members 24 and 25 are selected according to the outer diameter of the glass base material to be used.

As shown in FIG. 6, the cylindrical slit spring 26 is provided around the blade members 24 and 25 and presses the blade members 24 and 25 in the central direction of the storage portion 23 (biasing force in the central direction). Functioning as an urging mechanism).
The cylindrical slit spring 26 is desirably formed of any one of heat resistant materials such as carbon, ceramics, carbon-ceramic composite materials, and metal materials, and preferably has heat resistance of 200 ° C. or higher.

  The cylindrical slit spring 26 of this example is formed by alternately forming slits in the cylindrical heat-resistant material from above and below. FIG. 9 illustrates a part of the cylindrical slit spring 26. The cylindrical slit spring 26 is formed by alternately forming slits 26a from above and slits 26b from below. In particular, when carbon is used as the material of the cylindrical slit spring 26, the process of providing the slits 26a and 26b is relatively easy.

The cylindrical slit spring 26 can be expanded and contracted in the circumferential direction by such slits 26a and 26b, and a force (shrinking force) for contracting in the cylindrical radial direction is generated by the elastic force in the circumferential direction. . The cylindrical slit spring 26 is provided so as to press the blade members 24 and 25 against the side surface of the glass base material by the contraction force in the cylindrical radial direction.
The installation form of the cylindrical slit spring 26 is as shown in the sectional view of FIG. 6 and the top view of FIG. In the case of the example of FIGS. 6 and 7, the sealing structure 20 individually accommodates a plurality of blade members 24 and 25 in the radial direction of the drawing furnace (more precisely, by the contraction force of the cylindrical slit spring 26 in the cylindrical radial direction). The tips of the blade members 24 and 25 are brought into contact with the side surface of the glass base material 5 by pressing in the radial direction of the portion 23. The pressing force can be adjusted to be weak enough not to inhibit the lowering of the glass base material 5 by adjusting the thickness and slit width of the cylindrical slit spring 26.

As a result, as shown in FIG. 6, the glass base material 5 descends as shown by the arrow as the drawing progresses, and the outer diameter of the glass base material 5 increases, for example, from φ ₁ to φ ₂ (> φ ₁ ). Even so, the cylindrical slit spring 26 extends outward as indicated by the arrow with the blade members 24 and 25 uniformly tightened in the circumferential direction, and conversely shrinks when the outer diameter of the glass base material 5 decreases. Can do. Therefore, the cylindrical slit spring 26 can automatically absorb the diameter variation of the glass base material 5.

Furthermore, since the seal structure 20 of this example has a structure in which each of the plurality of blade members 24 and 25 slides independently, when the diameter of the glass base material 5 is not constant on the same cross section, that is, a non-circular shape. It is possible to cope with the case of having a cross section.
As shown in FIG. 6, the casing 27 of the seal structure 20 is provided with a gas introduction port 27a through which an inert gas or the like is supplied by a supply mechanism (not shown). A mouth 23c is provided. When carbon is used as a member such as the blade members 24 and 25 and the cylindrical slit spring 26, an inert gas or the like reaches the inside of the casing 27 and the blade members 24 and 25 through the gas introduction port 27a and the gas vent port 23c. The oxidation and deterioration of the member can be prevented. In addition, the inert gas etc. here may be the same as the gas supplied into the furnace, or may be different types.

  As described above, also in the seal structure 20 of this example, the gap S can be satisfactorily closed even if the diameter variation of the glass base material 5 in FIG. It is possible to prevent leakage of gas in the furnace and prevent inflow of outside air. Moreover, since the sealing structure of this example uses the cylindrical slit spring 26 having a simple structure that expands and contracts in the radial direction as the pressing mechanism, the equipment can be simplified and the maintenance is facilitated.

[Third embodiment]
Next, with reference to FIGS. 10 and 11, a seal structure 30 according to a third embodiment of the seal mechanism will be described. 10 is a cross-sectional view schematically showing the seal structure 30, FIG. 11 shows a state in which the blade member in the seal structure in FIG. 10 is in an open / closed state, and FIG. 11 (A) is a state in which the blade member is in an open state. 11 (B) is a diagram showing a state in which the blade member is in a closed state (most closed state).

The seal structure 30 includes a plurality of blade members 34 and 35 having heat resistance, and a support mechanism including an inclined base 31 and a slide mechanism that support the blade members 34 and 35.
Further, the plurality of blade members 34 and 35 and the support mechanism are placed and stored in a housing 37 shown in FIG. In FIG. 10, the housing 37 is illustrated so as to cover the upper and lower surfaces and the side surfaces of the tilting table 31, but the present invention is not limited to this, for example, the bottom wall of the housing 37 is eliminated and the upper end portion of the drawing furnace Alternatively, the tilt table 31 may be placed directly. Moreover, the structure which does not have the housing | casing 37 may be sufficient.

  The inclined base 31 that supports the plurality of blade members 34 and 35 is inclined so as to be lowered toward the central axis direction of the upper end opening 2a of FIG. 1 and has an insertion port for inserting the glass base material 5 at the center. It is a stand with. That is, as shown in FIG. 10, the tilting table 31 has a right triangle with the bottom side parallel to the upper end of the drawing furnace and the height as the central axis direction of the upper end opening, and the center of the upper end opening. It is a disk-shaped member having a shape that is rotated around the upper end opening with the shaft as the center of rotation. Note that the right-angled triangle described above may actually have a trapezoidal shape even if it has another shape such as a trapezoid as shown in the figure. Moreover, although it is desirable that the diameter of the insertion port of the glass base material 5 in the inclined base 31 is the same as the diameter of the upper end opening, there may be some length.

  The above mechanism corresponds to the pressing mechanism in the first and second embodiments described above, and the plurality of blade members 34 and 35 are individually separated by the weight of the plurality of blade members 34 and 35. It is a mechanism that slides in the radial direction of the drawing furnace along the inclination. And by this slide mechanism, the front-end | tip of several blade members 34 and 35 can be made to contact | abut to the side surface of the glass base material 5 with the dead weight.

  Next, the slide mechanism will be described with a specific example. As shown in FIG. 11, a plurality of protrusions 32 for linearly sliding the plurality of blade members 34 radially with respect to the central axis of the tilt table 31 are provided on the circumference of the tilt table 31. Is provided. As shown in FIGS. 10 and 11, a plurality of blade members 35 are slidably linearly moved in the radial direction with respect to the central axis of the tilt table 31 on the circumference of the tilt table 31. A protrusion 33 is provided.

  The use of the plurality of protrusions 32 and 33 is an example of the above-described slide mechanism, and the protrusions 32 and the protrusions 33 are alternately provided along the circumferential direction of the inclined base 31. The auxiliary member 36 shown in FIG. 11 is disposed on the inclined base 31 so as to form a slide surface of the blade member 34, and the blade member 34 is at the height of the upper surface side of the blade member 35 and the blade member 34. A part of the lower surface of the blade can slide while contacting the upper surface of the blade member 35.

  The horizontal sections of the protrusions 32 and 33 are substantially rectangular, and guide slits (slide holes) 34 s and 35 s having widths matching the short sides are provided in the blade members 34 and 35, respectively. Since the plurality of projecting portions 32 and 33 having such a shape are provided radially on the inclined base 31, as shown in the example of transition from the state of FIG. 11A to the state of FIG. The members 34 and 35 can also be slid radially. The protrusions 32 and 33 may be provided on the blade members 34 and 35 side, and a slide groove for guiding the blade members 34 and 35 may be provided on the inclined surface side of the inclined base 31. Moreover, although the example which provided one protrusion part with respect to one blade member is given, you may make it slide by providing two guide pins.

  The blade members 34 and 35 can have the same shape as described in the first and second embodiments, and the cross-sectional shape in a plane perpendicular to the moving direction is substantially rectangular. The shape has an arc in the width direction. The thickness of the blade members 34 and 35 (the length of the short side in the case of a substantially rectangular shape, the width in the case of an arc shape) may be thin, for example, about 1 mm in thickness. Further, the length (slide distance) in the moving direction of the blade members 34 and 35 with respect to the inclined base 31 is determined by the length of the guide slits 34s and 35s described above, but occurs between the drawing furnace and the glass base material. Decide to close the gap.

The tip portions 34a and 35a of the blade members 34 and 35 are the same as the tip portions 14a and 15a described in FIGS. 2 to 4 of the first embodiment and the tip portions 14a ′ and 15a ′ described in FIG. Any shape can be used.
The tip portions 24a, 25a of the blade members 24, 25 are in contact with the side surfaces of the glass base material 5 as much as possible when the tip portions 34a, 35a are lowered along the inclination due to their own weight. As in the blade member described in the embodiments 2 and 2 and the like, it is preferable to form an arc having a curvature that matches the maximum value assumed as the radius of the glass base material 5.

10 and 11, the blade member 35 slides relative to the protrusion 33 while contacting the inclined surface of the inclined base 31. On the other hand, the blade member 34 slides relative to the protrusion 32 while contacting the upper surface of the auxiliary member 36.
The blade members 34 and 35 are configured so that the gap generated in the adjacent blade member 34 is filled with the blade member 35, and the gap generated in the adjacent blade member 35 is filled with the blade member 34, that is, the gap between the adjacent blade members 34 and It arrange | positions so that the clearance gap between the adjacent blade members 35 may not overlap.

  The material of the blade members 34 and 35 is preferably carbon as in the blade members of the first and second embodiments. When carbon is used as the blade members 34 and 35, in order to prevent oxidation and deterioration, an inert gas or the like is sprayed onto the blade members 34 and 35 to surround the blade members 34 and 35. Is preferably an atmosphere of inert gas or the like. In addition, it is preferable to employ | adopt the thing with high heat resistance also for the inclination base 31 and other components, and it is preferable to have heat resistance of 200 degreeC or more similarly to the blade members 34 and 35.

  As described above, the seal structure 30 is configured such that the blade members 34 and 35 are individually slid along the inclination of the inclined table 31 in the radial direction of the drawing furnace by the weight of the blade members 34 and 35. The tips of the blade members 34 and 35 are brought into contact with the side surface of the glass base material 5. Then, the angle of the inclined portion of the inclined base 31 and the weight of the blade members 34 and 35 may be designed so that the pressing force due to the own weight is weak enough not to inhibit the lowering of the glass base material. . The angle of the inclined portion is assumed to be about 20 ° to 45 ° with respect to the horizontal direction, but can be applied by adjusting the weight in the range of 5 ° to 85 °. For example, in order to retract the blade members 34 and 35 in the outer peripheral direction without damaging them when the glass base material 5 is inserted, it is desirable to reduce the angle of the inclined portion (for example, about 5 ° to 45 °).

Accordingly, in the example shown in FIG. 10, the glass base material 5 is lowered as indicated by an arrow during the optical fiber drawing, and the outer diameter of the glass base material 5 is, for example, φ ₁ to φ ₂ (> Even if it increases to φ ₁ ), the blade members 34 and 35 are moved from the state shown in FIG. 11B to the state shown in FIG. 11A while pushing the side surface of the glass base material 5 with a constant force. It can be slid outward and upward. Conversely, when the outer diameter of the glass base material 5 decreases, the blade members 34 and 35 can be slid inward and downward while pressing the side surface of the glass base material 5 with a constant force.

  As a result, the seal structure 30 can automatically absorb the diameter variation of the glass base material. Further, since each of the plurality of blade members 34 and 35 has a structure that slides independently, it is possible to cope with a case where the diameter of the glass base material 5 is not constant on the same cross section, that is, has a non-circular cross section. be able to.

  As shown in FIG. 10, the seal structure 30 is provided with a gas introduction port 37 a to which an inert gas or the like is supplied by a gas supply mechanism (not shown) in the housing 37. When carbon is used as a member such as the blade members 34 and 35 and the inclined base 31, the inert gas or the like reaches the inside of the casing 37 and the blade members 34 and 35 and the inclined base 31 through the gas introduction port 37a. It is possible to prevent oxidation and deterioration. In addition, the inert gas etc. here may be the same as the gas supplied into the furnace, or may be different types. Further, a gas vent (not shown) may be provided in the inclined base 31 so that an inert gas or the like flows from the back side of the blade members 34 and 35.

As described above, also in the seal structure 30 of the present example, the gap S can be satisfactorily closed even when the diameter variation of the glass base material is large, as in the first and second embodiments. While preventing leakage of internal gas, it is possible to prevent inflow of outside air.
In addition, since the seal structure of this example is a simple seal mechanism in which the blade members 34 and 35 arranged along the inclination are brought into contact with the side surface of the glass base material using its own weight, the equipment is simple. And easy maintenance.

  Next, returning to FIG. 1, the lid 9 disposed on the upper end of the glass base material 5 will be described. As shown in FIG. 1, in the configuration in which the support rod 6 is provided on the glass base material 5, the support rod 6 is lowered to the position of the core tube 3 by the progress of the drawing process, that is, the support rod 6 is drawn. There is a state located below the upper end of the furnace 1. In order to keep sealing the inside of the drawing furnace even in such a state, it is preferable to include a lid 9 in addition to the sealing mechanism 8.

The lid 9 is a lid that penetrates the support bar 6 and is placed on the upper side of the glass base material 5, and has a through hole 9 a and a shoulder 9 b for the support bar 6 as shown in the figure. Examples of the material of the lid body 9 include quartz and metal.
By providing the lid body 9, even if the drawing of the optical fiber 5 b progresses and the glass base material 5 and the support rod 6 are lowered, before the glass base material 5 is detached from the seal mechanism 8, The state where the end face is in contact with the seal mechanism 8 can be maintained and the sealed state can be maintained.

  In addition, although it demonstrated on the assumption that the cover body 9 has the shoulder part 9b, the cover body 9 may be a shape which just opened the through-hole 9a of the support bar 6 in the disk. Even in such a shape, transition between states as described above is possible as well.

DESCRIPTION OF SYMBOLS 1 ... Optical fiber drawing furnace, 2 ... Furnace housing, 2a ... Upper end opening part, 2b ... Lower end opening part, 3 ... Furnace core tube, 4 ... Heater, 5 ... Optical fiber glass preform, 5a ... Lower end part, 5b: optical fiber, 6: support rod, 7: heat insulating material, 8 ... sealing mechanism, 9 ... lid, 9a ... through hole, 9b ... shoulder, 10, 20, 30 ... sealing structure, 11 ... inner cylinder, 12 ... outer cylinder, 13, 23 ... storage part, 13a, 13b, 23a, 23b ... guide hole, 14, 15, 24, 25, 34, 35, 104, 105 ... blade member, 14a, 15a, 14a ', 15a' 24a, 25a, 34a, 35a ... tip, 16 ... rod-like member, 17 ... coil spring member, 18 ... fixing member, 23c ... gas vent, 26 ... cylindrical slit spring, 26a, 26b ... slit, 27, 37 ... housing Body, 27a, 37a ... Gas inlet 31 ... ramp, 32, 33 ... protruding portion, 34s, 35s ... guide slit, 36 ... auxiliary member.

Claims (4)

An optical fiber drawing furnace sealing structure for closing a gap between an upper end opening of an optical fiber drawing furnace and an optical fiber glass base material inserted from the upper end opening;
Are alternately arranged in two upper and lower stages, comprising a plurality of blade members having a tip that abuts on the side surface of the glass preform for the optical fiber, the tip is at a position where the upper and lower of the blade member overlap, vertical The optical fiber drawing furnace seal structure , wherein the blade member is formed in a shape in line contact with a side surface of the optical fiber glass preform. Tip of the blade member of the upper stage is inclined linearly so as to approach the center axis of the top opening as the lower, distal end of the blade member of the lower stage, closer to the central axis of the more upper the top opening The optical fiber drawing furnace seal structure according to claim 1, wherein the sealing structure is linearly inclined as described above. Tip of the blade member of the upper stage is inclined curved to approach the center axis of the top opening as the lower, distal end of the blade member of the lower stage, closer to the central axis of the more upper the top opening The sealing structure of the drawing furnace for an optical fiber according to claim 1, wherein the sealing structure is curved and inclined. The optical fiber is drawn using the sealing structure of the optical fiber drawing furnace for closing the gap between the upper end opening of the optical fiber drawing furnace and the glass preform for the optical fiber inserted from the upper end opening. An optical fiber drawing method,
Are alternately arranged in two upper and lower stages, comprising a plurality of blade members having a tip that abuts on the side surface of the glass preform for the optical fiber, the tip is at a position where the upper and lower of the blade member overlap, vertical An optical fiber drawing method , wherein the blade member is brought into line contact with a side surface of the optical fiber glass preform to draw the optical fiber.

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