WO2012033158A1

WO2012033158A1 - Seal structure for optical fiber drawing furnace

Info

Publication number: WO2012033158A1
Application number: PCT/JP2011/070469
Authority: WO
Inventors: 正敏早川; 利巳幅崎; 榎本　正; 山崎　卓; 巌岡崎
Original assignee: 住友電気工業株式会社
Priority date: 2010-09-10
Filing date: 2011-09-08
Publication date: 2012-03-15

Abstract

Provided is a seal structure for an optical fiber drawing furnace, which, even when a glass preform with large variations in outer diameter is used, can sufficiently seal a gap created between an upper end opening of the drawing furnace and the glass preform by a simple structure. A seal structure (8) for an optical fiber drawing furnace is used to seal a gap between an upper end opening (2a) of an optical fiber drawing furnace (1) and an optical fiber glass preform (5) inserted from the upper end opening, is provided with a heat-resistant and flexible ring-shaped seal member disposed so as to surround the outer peripheral surface of the optical fiber glass preform (5), and a pressing mechanism for pressing the seal member inward, and seals the gap by pressing the seal member to the outer peripheral surface of the optical fiber glass preform. The seal member is formed from carbon felt or ceramic felt.

Description

Seal structure of draw furnace for optical fiber

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

The optical fiber is heated and melted while lowering the optical fiber glass base material (hereinafter referred to as glass base material) cited in the optical fiber line from the upper end opening of the drawing furnace into the core tube, and the front end of the glass base material is It is manufactured by reducing the diameter and drawing. 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 is oxidized and consumed in a high-temperature oxygen-containing atmosphere. In order to prevent this, the interior of the drawing furnace needs to be maintained in an atmosphere of an inert gas such as argon gas or helium gas or nitrogen gas.

In addition, the positive pressure inside the furnace prevents outside air (oxygen) outside the drawing furnace from entering the furnace, but the gap between the optical fiber preform inlet at the upper end of the drawing furnace. In other words, if the air gap is not well removed (not sealed) in the gap between the upper end opening of the drawing furnace and the optical fiber preform, outside air outside the drawing furnace is entrained. Therefore, a sealing mechanism that seals the gap at the upper end of the drawing furnace is necessary so that outside air is not caught in the furnace. If this portion can be well sealed, the amount of inert gas used can be reduced, which can lead to cost reduction.

For example, Patent Document 1 discloses a drawing furnace that seals the upper end opening of a drawing furnace and a glass base material. With reference to FIG. 11, a drawing furnace according to Patent Document 1 will be described. The drawing furnace 101 has a ring-shaped diaphragm plate 102, and the diaphragm plate 102 is slidably installed on the upper surface 104 a of the furnace body 104 in a state where the diaphragm plate 102 is loosely fitted to the glass base material 103. The diaphragm plate 102 seals between the upper end opening 105 and the glass base material 103 by ejecting high-pressure gas from the inner periphery 102a.

Further, Patent Document 2 discloses an XY table provided with an insertion port through which a glass base material is passed, an inner diameter variable seal mechanism disposed on the inner periphery of the insertion port, and an XY table directly above the XY table. And an outer diameter measuring means for measuring the outer diameter of the optical fiber preform, and a deviation amount measuring means for measuring the deviation amount of the optical fiber preform with respect to the X-direction center of the XY table and the deviation amount with respect to the Y-direction center. I have. Then, based on the measurement data of the deviation amount measuring means, the movement control of the XY table is performed so that the center position of the XY table coincides with the center of the optical fiber preform, and the measurement data of the outer diameter measuring means is obtained. Originally, there is provided control means for performing contraction control so that the inner diameter of the seal mechanism is always kept constant with respect to the outer diameter of the optical fiber preform.

Patent Document 3 includes an upper seal ring that is installed at the upper end of the drawing furnace body so as to surround the glass base material, and a telescopic mechanism that applies a force to the outer periphery of the upper seal ring in the center direction of the upper seal ring. A seal structure is disclosed that seals the gap at the upper end of the drawing furnace body so that the upper seal ring is always in close contact with the optical fiber preform. Here, the upper seal ring is an inner seal ring configured by connecting a plurality of inner seal ring pieces, and an outer seal ring configured by connecting a plurality of outer seal ring pieces arranged on the outer periphery thereof,
Further, the connecting portion of the inner seal ring piece and the connecting portion of the outer seal ring piece are arranged so as not to overlap each other.

JP-A-62-176938 Japanese Patent Laid-Open No. 10-167751 JP 2006-342030 A

In recent years, in order to reduce the manufacturing cost of optical fibers, the length of the glass base material is increased and the outer diameter is increased to reduce the number of glass base material setup changes. However, when the outer diameter of the glass preform increases, the outer diameter fluctuation of the glass preform in the longitudinal direction becomes larger than that of the smaller outer diameter of the glass preform. The gap between the upper end opening and the glass base material may change greatly.

In this case, the sealing structure by jetting high pressure gas disclosed in Patent Document 1 cannot sufficiently seal, and oxygen such as outside air enters the drawing furnace, and carbon such as a furnace core tube in a high temperature state. There was a possibility that the manufactured member was eroded by oxidation.
Further, the seal structure that reduces the inner diameter of the seal mechanism disclosed in

Patent Documents

2 and 3 has a structure that is difficult to deal with a glass base material having a large circumferential diameter variation, that is, a non-circular glass base material. .

The present invention has been made in view of the above-described actual situation, and even if a glass base material having a large outer diameter variation is used, a gap formed between the upper end opening of the drawing furnace and the glass base material has a simple structure. It is an object of the present invention to provide a drawing furnace sealing structure for an optical fiber that can be sufficiently sealed.

An optical fiber drawing furnace sealing structure for sealing 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, A heat-resistant and flexible ring-shaped seal member disposed so as to surround the outer peripheral surface of the base material, and a pressing mechanism for pressing the seal member inward, and the outer periphery of the optical fiber glass base material A sealing member is urged on the surface to seal the gap.
The seal member is preferably made of carbon felt or ceramic felt.

A gas pressure using a seal gas can be used as a pressing mechanism for the seal member. In this case, it is preferable that the seal gas is an inert gas or a nitrogen gas, the seal member has air permeability, and a seal gas layer is formed in the gap.
The seal member pressing mechanism includes an annular housing having a communication hole portion in the center portion that communicates with the upper end opening and a glass base material, and an internal space that communicates with a gas supply path into which seal gas flows. It is preferable to have a structure in which a seal member is arranged so as to close the communication hole and the opening communicating with the internal space. The seal member preferably has a drum shape in which the diameter of the central portion is smaller than the diameter of the end portion, and both ends are fixed along the edge of the opening.
The seal member pressing mechanism includes an annular housing in which a plurality of annular members whose positions are fixed and a plurality of annular seat packings that are movable in the radial direction are alternately stacked, and the annular seat packing is provided between the annular seat packings. It can also be set as the structure where each sealing member is arranged.

As a pressing mechanism for other seal members, a force obtained by converting gravity into a horizontal direction can be used. The pressing mechanism for the seal member in this case includes a plurality of pressing devices that press the sealing member independently from each of a plurality of equally divided directions. The pressing device includes an arc-shaped contact plate provided so as to contact the seal member, an L-shaped member provided with a concave portion to which a weight is engaged and pivotably mounted, a contact plate, An intermediate member that connects the L-shaped member, a weight that is engaged with the concave portion of the L-shaped member, and a support member that supports the L-shaped member, and the weight by the L-shaped member and the intermediate member Is converted into horizontal pressing force. The pressing force may be adjusted by changing the position where the weight is placed.

According to the seal structure of the present invention, even if the gap between the upper end opening of the drawing furnace and the glass base material fluctuates greatly, the seal member is deformed according to the change in the outer diameter of the glass base material, and the glass is pressed by the pressing mechanism. A sealing member is urged to the outer peripheral surface of the base material to seal the gap. For this reason, even when drawing the glass base material with the diameter fluctuation | variation of the circumferential direction, it can seal reliably.

It is a figure explaining the outline of the drawing furnace of this invention. It is a figure explaining 1st Embodiment of the seal structure by this invention. FIG. 3 is a diagram showing a cross section aa of FIG. 2 and a seal member. It is a figure explaining 2nd Embodiment of the seal structure by this invention. It is a figure which shows the sealing member and sheet packing of FIG. It is a figure which shows the annular member which comprises the housing of FIG. It is a figure explaining 3rd Embodiment of the seal structure by this invention. It is a top view which shows the seal structure of FIG. It is a figure explaining the other example of 3rd Embodiment of the seal structure by this invention. It is a figure explaining other examples of a 3rd embodiment of a seal structure concerning the present invention. It is a figure explaining an example of the conventional drawing furnace.

FIG. 1 illustrates an outline of a drawing furnace to which the present invention is applied. The drawing furnace 1 includes a furnace casing 2, a furnace core tube 3, a heating source (heater) 4, and a sealing device 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. A cylindrical furnace core tube 3 is disposed at the center of the furnace casing 2 and communicates with the upper end opening 2 a of the furnace casing 2. The furnace core tube 3 is made of carbon, and a glass base material 5 is inserted into the furnace core tube 3 by being sealed from the upper end opening 2 a of the furnace housing 2 by a sealing device 8.

In the furnace housing 2, a heater 4 is disposed so as to surround the furnace core tube 3, and a 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 the optical fiber 5 b is melted and drooped from the melted and reduced lower end portion 5 a. 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.

In addition, in FIG. 1, although the upper end part of the inner wall of the core tube 3 forms the upper end opening part 2a in the upper end part of the drawing furnace 1 as it is, the example is not restricted 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, and in this case, the gap to be sealed is the narrow upper end opening and the glass base material 5. 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 arranged at the upper end portion of the furnace casing 2 and provides a gap between the upper end opening 2a of the furnace casing 2 and the outer periphery of the glass base material 5 inserted from the upper end opening 2a of the furnace casing 2. This is intended for a sealing device 8 for sealing. In particular, the lower portion of the glass base material 5 in the furnace is heated in the furnace core tube 3 while preventing outside air from being exposed outside the furnace by the sealing device 8 provided at the upper end. 4 is heated. 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]
2 and 3, the seal structure 10 according to the first embodiment will be described as a seal device. FIG. 2 is a cross-sectional view of the seal structure, and FIG. FIG. 3B is a view showing the shape of the seal member according to the present embodiment.
The seal structure 10 of this example includes a housing 11 and an annular seal member 12. The housing 11 has a substantially cylindrical shape in which a communication hole portion 14 is formed at the center thereof. The housing 11 is provided with a gas supply path 13 a that forms a pressing mechanism for the seal member 12, a gas ejection path 13 b, a seal member fixing portion 15, and an internal space 16. An opening 16 a that communicates with the internal space 16 is formed on the peripheral surface that forms the communication hole portion 14.

The communication hole portion 14 has substantially the same diameter as the upper end opening 2a of the furnace casing 2 and is a hole communicating with the upper end opening 2a. Further, the communication hole portion 14 surrounds the outer periphery of the glass base material 5 with a certain gap when the glass base material 5 is inserted.
The gas supply path 13a is a flow path into which seal gas is injected, and is formed, for example, at four locations on concentric circles. The seal gas is, for example, an inert gas such as argon or helium, or a gas such as nitrogen, and is supplied to the gas supply path 13 a through the valve 18.

The internal space 16 is a substantially ring-shaped space formed between the gas supply path 13a and the communication hole 14, communicates with the gas supply path 13a through the gas ejection path 13b, and communicates through the opening 16a. It communicates with the hole 14.
A seal member fixing portion 15 for fixing the seal member 12 is formed at an edge of the housing 10 constituting the internal space 16 where the opening 16a is formed.

As shown in FIG. 3B, the annular seal member 12 has a drum shape in which the diameter of the central portion 12a is smaller than the diameter of the end portion 12b, and has heat resistance (200 ° C. or higher) and flexibility. It has breathability. The seal member 12 is made of, for example, carbon felt or ceramic felt. Here, it is desirable that the carbon felt and ceramic felt used as the sealing member 12 have a density in the range of 0.05 to 0.4 g / cm 3.
The end 12 b of the seal member 12 is held by the seal member fixing portion 15 of the housing 10. At this time, the small-diameter central portion 12a of the seal member 12 protrudes from the opening 16a toward the communication hole portion 14, and when the glass base material 5 is inserted into the communication hole portion 14, the glass base material 5 Contact the outer periphery.

When the opening 16a is closed by the seal member 12, the internal space 16 constitutes a space where the seal gas is accumulated, and the seal gas is poured from the gas ejection path 13b and accumulated. When seal gas accumulates in the internal space 16, the seal member 12 generates pressure that acts so as to protrude from the opening 16 a toward the communication hole 14. At this time, when the glass base material 5 is inserted into the communication hole portion 14, the central portion 12 a of the seal member 12 is biased toward the outer periphery of the glass base material 5. And when the outer diameter variation occurs in the glass base material 5 (when the outer diameter becomes smaller as shown by the two-dot chain line in FIG. 2), the central portion 12a of the sealing member 12 is caused by the pressure of the sealing gas, The glass base material 5 protrudes further to the outer peripheral side and comes into contact with the outer periphery of the glass base material 5.

The seal member 12 has air permeability as described above, and is biased toward the outer periphery of the glass base material 5 while leaking the seal gas. As shown in FIG. 2, the seal gas leaked from the seal member 12 leaks from above and below the contact portion between the outer peripheral surface of the glass base material 5 and the seal member 12, and between the seal member 12 and the outer periphery of the glass base material 5. A seal gas layer is formed in the gap. This sealing gas layer seals the gap between the upper end opening 2a and the glass base material 5 more strongly.

In addition, for example, when the seal member 12 is formed of carbon felt, the seal gas layer prevents the carbon felt from being oxidized by touching the outside air containing oxygen. Note that when the seal member 12 is formed of ceramic felt, there is no risk of oxidation, and therefore the air permeability of the seal member 12 may not be present.

According to the drawing furnace provided with the seal structure 10 according to the first embodiment described above, even if the gap between the upper end opening 2a of the drawing furnace and the glass base material 5 varies greatly, the sealing member 12 The sealing gas leaked from the sealing member 12 forms a sealing gas layer while being urged to the outer periphery of the glass base material 5 following the change in the outer diameter of the glass base material 5. As a result, even when a drawing furnace with a large outside diameter variation of the glass base material 5 is used for drawing, it can be sealed well, and oxygen-containing outside air enters the drawing furnace and is in a high temperature state. It is possible to suppress oxidation of the carbon member such as the furnace core tube.

Further, the drawing furnace provided with the seal structure 10 according to the first embodiment is configured to mainly seal the seal member 12 against the outer periphery of the glass base material 5. For this reason, the usage-amount of sealing gas can be restrained compared with the prior art (FIG. 11) which ejects high pressure gas and seals.

[Second Embodiment]
A seal structure 20 according to the second embodiment will be described as a seal device with reference to FIGS. FIG. 4 shows a cross-sectional view of the seal structure, FIG. 5 (A) shows a seal member, and FIG. 5 (B) shows a sheet packing. 6 is a view showing the components of the annular member constituting the housing, FIG. 6 (A) shows the lid member, FIG. 6 (B) shows the main body member, and FIG. 6 (C) is the base member. Is shown.

The seal structure 20 of this example includes a housing 21, an annular seal member 22, and a seat packing 23. The housing 21 has a substantially cylindrical shape in which a communication hole 24 is formed at the center thereof. In the housing 21, a gas supply path 25 a that forms a pressing mechanism for the seal member 22, a gas ejection path 25 b, and an internal space 26 are formed. An opening 26 a that communicates with the internal space 26 is formed on the peripheral surface that forms the communication hole portion 24.

First, prior to the description of the housing 21, the seal member 22 and the seat packing 23 will be described. The seal member 22 has an annular shape as shown in FIG. 5A, and has an inner peripheral surface 22a and an outer peripheral surface 22b. The seal member 22 has heat resistance, flexibility, and air permeability, and can expand and contract in the radial direction. The seal member 22 can be formed of carbon felt, ceramic felt, or the like, for example, as in the example of FIG. 3B, and the density of carbon felt and ceramic felt is 0.05 to 0.4 g / cm 3. It is desirable to be in the range.

As shown in FIG. 5 (B), the sheet packing 23 has a perforated disk shape in which an insertion portion 23a through which the glass base material 5 is inserted is formed at the center, and has heat resistance. The sheet packing 23 is formed, for example, by compression molding carbon felt. The insertion part 23a is fitted or loosely fitted to the outer periphery of the glass base material 5, and is formed according to the outer diameter of the glass base material 5 to be used. And when the insertion part 23a is fitted and used for the outer periphery of the glass base material 5, it is preferable to form the notch 23b in order to permit the fluctuation | variation of the diameter of the glass base material 5. FIG.

As shown in FIG. 6, the housing 21 is formed by laminating a plurality of divided annular members. That is, the housing 21 includes, for example, a base member 27, three main body members 28, and a lid member 29. For the base member 27, the main body member 28, and the lid member 29, for example, stainless steel is used.
The base member 27 has a disc shape with a hole in which an insertion hole 27a is formed in the center, and a sheet packing mounting portion (lamination surface) which is a recessed portion on which the sheet packing 23 can be slidably mounted. 27b is formed. The base member 27 is fixed to the upper end of the drawing furnace.

The insertion hole 27a is a hole through which the glass base material 5 is inserted, and communicates with the upper end opening 2a when the base member 27 is placed on the upper end of the drawing furnace. The insertion hole 27a becomes the above-described communication hole portion 24 in a state assembled as the housing 21, and has substantially the same diameter as the outer diameter of the upper end opening 2a. The sheet packing placement portion 27b has an outer diameter of the recessed portion larger than an outer diameter of the sheet packing 23, a depth of the recessed portion is substantially the same as the thickness of the sheet packing 23, and the sheet packing 23 is slid in the radial direction. It can be placed movably.

The main body member 28 has a substantially cylindrical shape with an outer diameter equal to that of the base member 27, has a hollow portion 28 a at the center, and can slide the sheet packing 23 on the upper surface in the same manner as the base member 27. A sheet packing placement portion 28b, which is a dent portion that can be placed, is formed. The main body member 28 is fixed to the upper surface of the base member 27.

The hollow portion 28 a communicates with the insertion hole 27 a of the base member 27 when the main body member 28 is fixed to the base member 27. The inner diameter of the cavity 28 a is larger than the inner diameter of the insertion hole 27 a of the base member 27 and larger than the outer diameter of the seal member 22. The cavity 28 a has a larger inner diameter than the outer diameter of the seal member 22, so that a gap (cavity) can be provided between the cavity 28 a and the seal member 22.

A gas supply path 25a and a gas ejection path 25b are formed inside the main body member 28. The gas supply path 25 a is a flow path through which a seal gas is supplied, and is formed at, for example, four locations at equal intervals in the circumferential direction of the main body member 28. The gas ejection path 25b communicates with the gas supply path and the cavity 28a, and serves as a flow path for flowing the seal gas that has flowed into the gas supply path 25a into the cavity 28a. Such a main body member may have only one layer, or may have a structure in which a plurality of layers are stacked in a similar structure (three in the example in the figure are stacked).

The lid member 29 has a holed disk shape in which an insertion hole 29a is formed at the center and four gas supply ports 29b are formed at equal intervals outward in the radial direction. The lid member 29 has the same outer diameter as the main body member 28 and is fixed on the main body member 28.
The insertion hole 29 a allows the glass base material to be inserted. When the lid member 29 is fixed on the main body member 28, the insertion hole 29 a communicates with the hollow portion 28 a of the main body member 28. The diameter of the insertion hole 29 a of the lid member 29 is smaller than the diameter of the hollow portion 28 a of the main body member 28, and is substantially the same as the diameter of the insertion hole 27 a of the base member 27. Further, the insertion hole 29a becomes the communication hole portion 24 in a state assembled as the housing 21, and has substantially the same diameter as the outer diameter of the upper end opening 2a. The gas supply port 29 b is a port through which a seal gas is poured through the valve 18, and communicates with the gas supply path 25 a when the lid member 29 is fixed on the main body member 28.

4 to 6, the seal structure 20 described above has the sheet packing 23 slidably mounted on the sheet packing mounting portion 27b of the base member 27, and the main body member 28 is mounted on the base member. 27 is fixed on top.
Then, the sealing member 22 is disposed in the hollow portion 28 a of the main body member 28 so that the outer peripheral surface 22 b faces the ejection hole of the gas ejection path 25 b of the main body member 28. At this time, the lower side of the seal member 22 is supported by the sheet packing 23 placed on the base member 27, and when the sheet packing 23 is placed on the sheet packing placement portion 28 b of the main body member 28, the sheet packing 23 The upper side is supported and disposed in the cavity 28a. Here, as described above, the outer diameter of the seal member 22 is smaller than the inner diameter of the cavity portion 28a, and the diameter can be expanded and contracted.

As described above, a space (internal space) 26 is formed by the two sheet packings 23, the inner peripheral surface of the hollow portion 28 a, and the outer peripheral surface 22 b of the seal member 22 in the hollow portion 28 a of the main body member 28. That is, the seal member 22 is disposed so as to close the opening 26 a formed between the two sheet packings 23. Seal gas is poured into the internal space 26 from the ejection port of the gas ejection path 25b. The seal member 22 is reduced in diameter by receiving the pressure of the seal gas when the internal space 26 is filled with the seal gas.

In the present embodiment, there are further two main body members 28, and three seal members 22 are supported by four sheet packings 23 as shown in the figure. A lid member 29 is fixed to the main body member 28 at a predetermined position. A valve 18 is attached to the gas supply port 29 b of the lid member 29, and seal gas is flowed through the valve 18.
The seal structure 20 configured as described above has a communication hole portion 24 communicating with the upper end opening 2a of the furnace casing 2 at the center thereof, and the glass base material 5 is inserted therethrough. The main body member 28 is not limited to a configuration in which three main body members 28 are stacked, and can be appropriately changed.

When the glass base material 5 is inserted into the communication hole portion 24, the glass base material 5 is passed through the insertion portion 23 a of each sheet packing 23 and the inside of the seal member 22. At this time, the insertion portion 23 a of each sheet packing 23 is fitted to the outer periphery of the glass base material 5.
In the seal structure 20, when a seal gas is flowed through the valve 18, the seal gas flows through the gas supply path 25 a of each main body member 28 and flows into the internal space 26 from the jet outlet of the gas jet path 25 b.

When the sealing member 22 is filled with the sealing gas flowing into the internal space 26, the outer peripheral surface 22 b of the sealing member 22 is pushed by the pressure of the sealing gas, the diameter is reduced, and the inner peripheral surface 22 a of the glass base material 5 is compressed. It is biased to the outer peripheral surface.
In addition, when the outer diameter of the glass base material 5 is changed during drawing (when the outer diameter is reduced as shown by a two-dot chain line in FIG. 4), the sealing member 22 Due to the pressure, the diameter is further reduced and the inner peripheral surface 22 a comes into contact with the outer periphery of the glass base material 5 to seal the gap between the upper end opening 2 a and the glass base material 5.

Moreover, the sealing member 22 has air permeability as described above, and is biased toward the outer periphery of the glass base material 5 while leaking the sealing gas. The seal gas leaked from the seal member 22 forms a seal layer of the seal gas in the gap between the communication hole 24 a of the seal structure 20 and the outer peripheral surface of the glass base material 5. As a result, the gap between the upper end opening 2a of the furnace body 2 and the glass base material 5 is sealed more strongly, and oxidation of the seal member 22 is prevented.

Further, as described above, each sheet packing 23 is slidably mounted by the sheet

packing mounting portion

27b or 28b. Accordingly, when the glass base material 5 being drawn is eccentric, each sheet packing 23 can move so as to allow the eccentricity by sliding the sheet

packing mounting portions

27b and 28b. In addition, although the sheet packing 23 was demonstrated in the aspect by which the insertion part 23a was fitted by the outer periphery of the glass base material 5, it should just be able to guide the sealing member 22, and it is not limited to this. For example, the diameter of the insertion portion 23a may be larger than the outer diameter of the glass base material 5 to provide play.

According to the drawing furnace provided with the seal structure 20 according to the second embodiment described above, the diameter of the seal member 22 is increased even if the gap between the upper end opening 2a of the drawing furnace and the glass base material 5 varies greatly. Expands and contracts in response to a change in the outer diameter of the glass base material 5, and the inner peripheral surface 22 a biases the outer periphery of the glass base material 5. Thereby, even if the glass base material 5 having a large outer diameter variation is used, the gap between the upper end opening 2a of the drawing furnace and the glass member 5 can be sealed.

Moreover, since the drawing furnace provided with the seal structure 20 according to the present embodiment is configured to mainly seal the seal member 22 against the outer periphery of the glass base material 5, the high pressure gas is ejected. Compared with the prior art for sealing, the amount of seal gas used can be reduced.

[Third embodiment]
A seal structure 30 according to the third embodiment will be described as a seal mechanism with reference to FIGS. 7A and 7B are cross-sectional views of the seal structure, and FIG. 8 is a view illustrating the top surface of the seal structure of FIG.
The seal structure 30 of this example includes a disk-shaped base 31, an annular seal member 32, and a plurality of pressing devices 33. The plurality of pressing devices 33 form a pressing mechanism for the seal member 32, and are arranged evenly around the seal member 32.

The seal member 32 has heat resistance (200 ° C. or higher) and flexibility. The seal member 32 can be formed of the same carbon felt, ceramic felt, or the like as used in the first and second embodiments. In particular, the carbon felt is preferable because it not only has excellent heat resistance but also has a small friction coefficient, so that there is no fear of damaging the glass base material 5.
Further, the seal member 32 is provided so as to contact the side surface of the glass base material 5, and preferably provided in an annular shape so as to surround the glass base material 5.

Each pressing device 33 is a device that presses the seal member 32 in the radial direction independently from each of the directions in which the periphery of the glass base material 5 to be inserted is equally divided into n pieces in the circumferential direction. Here, the division number n may be appropriately selected according to the outer diameter, the outer diameter fluctuation amount, the bending amount, and the like of the glass base material 5 to be used. Basically, the more n, the easier the airtightness.

Furthermore, each pressing device 33 according to the present invention is a mechanism that obtains a pressing force to the seal member 32 by converting gravity into a horizontal force using, for example, a lever principle. That is, these pressing mechanisms apply a radial pressing force converted from gravity by the lever principle (seesaw structure) from the outside of the seal member 32. Since the pressure is applied by converting the gravity, the load can be easily changed (adjusted). This adjustment may be performed by monitoring the detection result of the internal pressure of the drawing furnace and changing the load so as to ensure a positive pressure. As will be described later, the load can be changed by changing the weight of the weight or changing the position of the weight (changing the power point).

The pressing device 33 shown in FIG. 7 and FIG. 8 is an arc shape provided so as to contact the seal member 32 on the base 31 and the support mechanism by the two support members 37 standing on the base 31. A contact plate 34, an L-shaped member 35, an intermediate member 36 connected to the contact plate 34 and the L-shaped member 35, and a connecting portion thereof being rotatable, and a weight 39. . The support mechanism is a mechanism that rotatably supports the L-shaped member 35. Further, the L-shaped member 35 is illustrated as being composed of a shorter member 35a and a longer member 35b.

In addition, each member constituting the pressing device 33 described above preferably has a heat resistance of 200 ° C. or higher, like the seal member 32. For example, carbon (especially, what is called high purity carbon is preferable), ceramics, carbon-ceramic composite material, or metal material is preferable. In addition, when employ | adopting what does not have high heat resistance as each member, what is necessary is just to devise, such as providing the mechanism (for example, water cooling system) which cools them.

The base 31 is a disk-shaped member on which the seal member 32 is placed. If the seal structure 30 has a housing, the base 31 is a member corresponding to the bottom of the housing. The intermediate member 36 may be a rod-shaped or plate-shaped member. The two support members 37 serving as a support mechanism are set up vertically with respect to the base 31, but may be set up obliquely.

The abutment plate 34 is shaped so as to abut on the side surface of the glass base material 5 with as much area as possible by pressing obtained from gravity. Therefore, the contact plate 34 has a shape obtained by dividing the cylindrical plate into n parts (in this example, four parts), and the maximum value assumed as the radius of the glass base material 5 (that is, the maximum diameter of the glass base material 5 to be used). It is preferable to make the shape of an arc (that is, a shield shape) having a curvature suitable for the above. In addition, since the both ends of the adjacent contact plate 34 contact when the glass base material 5 becomes small if only the cylindrical plate is divided into n when the maximum diameter is applied, the cylindrical plate is divided into n when the minimum diameter is applied. Just make it into shape. An example of the contact plate 34 adopting such a shape is shown in FIG.

Further, the L-shaped member 35 is connected so that one end (the member 35a side) is connected so as to rotate with respect to the intermediate member 36, and the corner 35c (the boundary between the member 35a and the member 35b) serves as a fulcrum. The member 37 is rotatably attached to and supported by the member 37.
Further, although not shown in detail, the contact plate 34 shown in FIG. 7 is slidable on the base 31, and a connection point with the intermediate member 36 is also rotatably attached. Thereby, the pressing force transmitted from the L-shaped member 35 can be transmitted horizontally to the seal member 32.

Furthermore, the L-shaped member 35 has a recess 38 for attaching the weight 39 to the other end side (the member 35b side). The concave portion 38 may be a concave portion that hooks a wire attached to the weight 39 or a concave portion that mounts and attaches the weight 39 itself. In this example, the example which has the recessed part 38 for hooking the weight 39 with a wire in the several position of the other end side is given.

The position of the power point is adjusted according to the position of the recess 38 to which the weight 39 is attached. Here, although the example which provided the three recessed parts was given, the recessed part may be one and it is preferable that it is two or more in the point which can adjust pressing force. Also, in the case of one or more than two, the weight 38 is appropriately selected from a plurality of weights having a weight that allows the internal pressure of the drawing furnace to be positive (can be sealed). Good. If the pressing force pressing the glass base material 5 with the sealing member 32 is too strong, the glass base material 5 may be damaged, and the glass base material 5 is prevented from descending when the diameter of the glass base material 5 increases. Therefore, it is preferable that the weight 39 having an appropriate weight can be selected and used.

The selection of the weight 39 and the movement of the power point may be performed by an operator, and in that case, it is necessary to devise such as lengthening the member 35b so that the operation at room temperature can be performed. Prolonging the member 35b is advantageous not only in that the work can be performed at normal temperature, but also in that the adjustment range of the position of the power point is expanded and the adjustment range of the pressing force is expanded. On the other hand, the weight 39 can be selected and the power point moved mechanically by an operator by remote control or by automatic control based on a positive pressure check result.

Further, the inner diameter of the base 31 and the degree of bending of the seal member 32 may be appropriately determined so that the gap between the glass base material 5 and the upper end opening 2a can be filled. However, since the diameter of the glass base material 5 actually varies, the inner diameter of the base 31 and the deflection of the seal member 32 (that is, how much the width is shortened) based on the maximum distance assumed as the gap. Or). The width of the gap in the example of FIG. 1 is a value obtained by subtracting the outer diameter φ of the glass base material 5 from the inner diameter d of the core tube 2 and halving it. For example, when the outer diameter φ of the glass base material 5 is 90 mm and formed with a diameter variation of ± 10 mm, the inner diameter d of the core tube 3 only needs to be about 120 mm. d−φ) / 2 is about 10 to 20 mm.

An example of how to determine these conditions will be given on the assumption that only one weight 39 is used. As shown in FIG. 7 (A), when the assumed maximum diameter (outer diameter φa) is reached, the seal member 32 having the width L moves to the outermost side, as shown in FIG. 7 (B). When the assumed minimum diameter (outer diameter φb) is reached, the seal member 32 having the width L moves to the innermost side. Each parameter is determined so that sealing can be performed without any problems even in these states. Parameters include the inner diameter of the base 31, the flexibility (density, etc.) of the seal member 32, the weight and position of the weight 39, the position and movable range of the contact plate 34, and the like. As a result, the four contact plates 34 slide individually within the ranges illustrated in FIGS. 7A and 7B.

In this way, the pressing device 33 converts the gravity of the weight 39 by using the lever principle to obtain a pressing force to the seal member 32. As shown in FIG. The sealing member 32 is individually pressed in the direction of the glass base material 5 by the contact plates 34 provided in each of the directions in which the periphery of the glass base material 5 to be inserted is equally divided into four in the circumferential direction.

Thereby, even if the glass base material 5 descend | falls by progress of drawing and the outer diameter (phi) of the glass base material 5 increases from (phi) b to (phi) a (> (phi) b), for example, the sealing structure 30 WHEREIN: It is possible to automatically absorb the diameter variation.
As described above, in this example, even if the outer diameter φ of the glass base material 5 changes, the sealing member 32 can be kept in contact with the glass base material 5 as much as possible by the pressing force converted into the horizontal direction. That is, even if the glass base material has a large variation in diameter, the gap formed between the upper end opening 2a and the glass base material 5 in the optical fiber drawing furnace can be reliably sealed, and Inflow of outside air from the section can be prevented. As a result, it is possible to prevent the deterioration of the in-furnace parts and to draw without increasing the diameter variation of the formed optical fiber.

Further, the seal structure 30 according to the present embodiment has a structure in which a plurality of contact plates 34 are installed so as to be movable radially, and each of the contact plates 34 slides independently. It is possible to seal the contact plate 34 with a simple structure in which the contact plate 34 moves radially toward the outer side when the thickness 5 is thick and moves radially toward the center at the narrow location. Therefore, the seal structure 30 can cope with the case where the diameter of the glass base material 5 is not constant on the same cross section, that is, when the glass base material 5 has a non-circular cross section. Here, although the example divided into four is given, it becomes possible to more appropriately cope with the glass base material 5 having a non-circular cross section by increasing the number of divisions.

Actually, the glass preform 5 having an outer diameter of 150 mm was drawn with n = 4 and the furnace gas was drawn as Ar to produce a 125 μm optical fiber. As a result, the width of the diameter variation of the manufactured optical fiber was 0.10 μm within 3 times the standard deviation (3σ), and there was no deterioration of the carbon parts in the furnace. It was confirmed that it had.

FIG. 9 illustrates another example seal structure 40 according to the third embodiment. The seal structure 40 of this example is obtained by dividing the seal member 32 into two upper and lower layers in the seal structure described with reference to FIGS. In addition, although demonstrated in the example divided into two layers, you may divide into three or more layers.

In the contact plate 34, a partition plate 34a is provided on the glass base material 5 side in a direction perpendicular to the contact plate 34 (that is, in the horizontal direction). Then, an upper seal member 32a is disposed on the partition plate 34a, and a lower seal member 32b is disposed on the base 31 below the partition plate 32a. Of course, also in this case, the inner diameters of the

seal members

32 a and 32 b are located inside the inner diameter of the base 31. Further, in this example, in order to make the contact plate 34 be a side wall without being separated from the

seal members

32a and 32b, an adhesion or hooking portion is provided so that the contact plate 34 and the

seal members

32a and 32b are not separated from each other. May be provided.

The contact plate 34 is provided with a purge gas inlet 34b for supplying an inert gas or the like as a purge gas by a supply mechanism (not shown) at a part of the partition plate 34a or below the partition plate 34a. The purge gas supplied from the purge gas introduction port 34b reaches the inside of the contact plate 34 serving as a side wall, and can prevent oxidation and deterioration of the contact plate 34 itself and the seal member 32. The purge gas here may be the same as the inert gas supplied into the furnace, or may be a different type of gas.

FIG. 10 illustrates another example seal structure 41 according to the third embodiment. The seal structure 41 of this example is provided with a casing 42 (enclosure) in the seal structure described with reference to FIGS. The housing 42 includes a side wall 43 that surrounds the outside of the contact plate 34 and an upper wall 44 that covers the top of the seal member 32. The side wall 43 is provided with a purge gas inlet 45 for supplying an inert gas or the like as a purge gas by a gas supply mechanism (not shown). The purge gas supplied from the purge gas introduction port 45 reaches the inside of the housing 42, and can prevent oxidation and deterioration of internal members including the inner wall of the housing. The purge gas here may be the same as the inert gas supplied into the furnace, or may be a different type of gas.

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 device 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 is advanced and the glass base material 5 and the support bar 6 are lowered, the glass base material 5 is removed from the sealing member of the sealing device 8 before the glass base material 5 is detached. The state where the lower end surface of the body 9 is in contact with the sealing device 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 ... Drawing furnace, 2 ... Furnace housing, 2a ... Upper end opening part, 2b ... Lower end opening part, 3 ... Core tube, 4 ... Heat source (heater), 5 ... Optical fiber glass base material (glass base material), DESCRIPTION OF SYMBOLS 6 ... Support rod, 7 ... Heat insulating material, 8 ... Sealing device, 9 ... Lid body, 10, 20, 30, 40, 41 ... Seal structure, 11, 21 ... Housing, 12, 22, 32 ... Seal member, 23 ... Seat packing, 13a, 25a ... gas supply passage, 13b, 25b ... gas ejection passage, 14, 24 ... communication hole portion, 15 ... sealing member fixing portion, 16, 26 ... internal space, 16a, 26a ... opening, 18 ... valve 27 ... Base member, 28 ... Main body member, 29 ... Lid member, 31 ... Base, 33 ... Pressing device, 34 ... Contact plate, 35 ... L-shaped member, 36 ... Intermediate member, 37 ... Support member, 38 ... concave part, 39 ... weight, 42 ... housing, 43 ... side wall, 44 ... upper wall, 45 ... Purge gas inlet.

Claims

An optical fiber drawing furnace sealing structure for sealing 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,
A heat-resistant and flexible annular seal member disposed so as to surround an outer peripheral surface of the optical fiber glass preform; and a pressing mechanism that presses the seal member inward, and the optical fiber. A sealing structure for an optical fiber drawing furnace, wherein the sealing member is urged to an outer peripheral surface of a glass base material to seal the gap.
The sealing structure for an optical fiber drawing furnace according to claim 1, wherein the seal member is formed of carbon felt or ceramic felt.
3. The optical fiber drawing furnace sealing structure according to claim 1 or 2, wherein the sealing member pressing mechanism uses a gas pressure using a sealing gas.
The drawing furnace for an optical fiber according to claim 3, wherein the seal gas is an inert gas or a nitrogen gas, the seal member has air permeability, and forms a seal gas layer in the gap. Seal structure.
The seal member pressing mechanism has an annular shape having a communication hole portion that communicates with the upper end opening at the center thereof and a gas supply passage through which the seal gas is poured. The optical fiber drawing furnace sealing structure according to claim 3, wherein the sealing member is disposed so as to close an opening communicating with the communication hole portion and the internal space.
6. The optical fiber according to claim 5, wherein the seal member has a drum shape in which a diameter of a central portion is smaller than a diameter of an end portion, and both end portions are fixed along an edge of the opening. Drawing furnace seal structure.
The pressing mechanism of the seal member includes an annular housing in which a plurality of annular members whose positions are fixed and a plurality of annular seat packings that are movable in the radial direction are alternately stacked, and the annular seat packing is interposed between the annular seat packings. The seal structure for an optical fiber drawing furnace according to claim 5, wherein the seal members are respectively arranged.
3. The optical fiber drawing furnace sealing structure according to claim 1 or 2, wherein the pressing mechanism of the sealing member uses a force obtained by converting gravity into a horizontal direction.
The pressing mechanism of the sealing member includes a plurality of pressing devices that press the sealing member independently from each of a plurality of equally divided directions,
The pressing device includes an arc-shaped contact plate provided so as to contact the seal member, an L-shaped member provided with a concave portion to which a weight is engaged and pivotably mounted, and the contact An intermediate member for connecting the plate and the L-shaped member, a weight engaged with the concave portion of the L-shaped member, and a support member for supporting the L-shaped member. 9. The sealing structure for an optical fiber drawing furnace according to claim 8, wherein the weight of the weight is converted into a horizontal pressing force by the cylindrical member and the intermediate member.
The sealing structure for an optical fiber drawing furnace according to claim 9, wherein the pressing force is adjusted by changing a position where the weight is placed.