JP5652328B2 - Seal structure of draw furnace for optical fiber - Google Patents

Description

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

  For example, the optical fiber is drawn by heating an optical fiber preform formed of quartz as a main component in a drawing furnace. Carbon is mainly used as the in-furnace part material of this drawing furnace, and in order to prevent oxidation of this carbon, rare gas such as helium and argon or nitrogen gas (hereinafter referred to as inert gas) is used in the furnace. It is filled inside.

Further, by making the pressure inside the furnace positive, air outside the furnace (oxygen) is prevented from entering the furnace, but the gap of the inlet of the optical fiber preform 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, air outside the furnace will be 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.

  Patent Document 1 discloses an optical fiber drawing device having a seal structure. This drawing device is located directly above the XY table, an XY table provided with an insertion port through which the optical fiber preform passes, an inner diameter variable seal mechanism disposed on the inner periphery of the insertion port, and the XY table. 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. ing. Here, a CCD camera is provided as the outer diameter measuring means and the deviation amount measuring means.

  Further, this drawing apparatus controls the movement of the XY table so that the center position of the XY table coincides with the center of the optical fiber preform based on the measurement data of the deviation amount measuring means, and the outer diameter. Based on the measurement data of the measuring means, there is provided control means for performing contraction control so that the inner diameter of the seal mechanism is always maintained at a constant clearance with respect to the outer diameter of the optical fiber preform.

  Patent Document 2 discloses a technique for providing a ring-shaped seal member around an optical fiber preform as a seal structure in an optical fiber drawing furnace. 6A and 6B are diagrams showing this seal structure, where FIG. 6A is a cross-sectional view of the seal structure, FIG. 6B is a top view of a carbon sheet without slits, and FIG. 6C is a top view of a carbon sheet with slits. FIG.

  The seal structure 50 shown in FIG. 6A is provided on the upper end surface (and the upper end surface of the core tube 12) of the furnace casing 11 of the optical fiber drawing furnace. In the seal structure 50, a purge gas introduction pipe 58 is provided in a cylinder 57 with an upper lid serving as an outer wall of the seal structure 50, and seal members 51, 52, and 53 are provided in multiple layers around the optical fiber preform 1. The seal members 52 and 53 are placed on the sheet support member 59. Among them, the seal member 51 is formed so that the non-slit carbon sheet 61 of FIG. 6B is placed on the upper end surface of the furnace casing 11 and then cut from the inner periphery as shown in FIG. 6C. The carbon sheet 63 provided with the inner peripheral slit 63a and the outer slit 63b formed so as to cut from the outer periphery is placed, and the non-slit carbon sheet 62 of FIG. 6B is placed thereon. Is formed. Finally, the upper part is pressed by the sheet presser 64.

  Patent Document 3 discloses a seal member different from the above-described seal members 51 to 53. FIG. 7 is a perspective view showing the seal member. The seal member 70 shown in FIG. 7 has a plurality of seal chips 71 arranged obliquely so that the seal chip surface and the rod axis (axis in the insertion direction of the insertion hole 72 of the optical fiber preform) are not orthogonal to each other. The tip of 71 is pressed against the optical fiber preform and sealed.

Japanese Patent Laid-Open No. 10-167751 JP 2010-173895 A JP 2010-189213 A

With regard to the drawing furnace seal structure described above, if the variation of the optical fiber preform diameter is small, the gap between the upper end opening of the drawing furnace body and the optical fiber preform should be simply blocked according to the preform diameter. A sufficient sealing effect can be obtained.
However, when the variation of the optical fiber preform diameter is as large as about ± 5 mm or more, for example, the gap interval fluctuates greatly. Therefore, a seal structure that can be sealed while taking into account the variation of the gap is required. .

  However, in the seal structure described in Patent Document 1, a shutter plate is provided as a variable-diameter seal mechanism that can uniformly deform the inner diameter. Based on the measurement result of the CCD camera, the shutter plate It is not only necessary to perform electronic control such as reducing the opening diameter, but also has a structure that is difficult to cope with an optical fiber preform having a large variation in diameter in the circumferential direction, that is, a non-circular optical fiber preform.

  In addition, the sealing structure described in Patent Document 2 is a structure in which a slit-added carbon sheet is provided around an optical fiber preform to seal a gap generated at the upper end opening. The variable width of the inner diameter of the carbon sheet is small only by the flexibility by the slits on the side and the outer peripheral side, and as a result, the diameter variation in the longitudinal direction of the optical fiber preform can be accommodated to about ± 2 mm.

  In addition, the seal structure described in Patent Document 3 is difficult to arrange and arrange in order to spread individual small seal chips, and some of the seal chips come off and fall into the furnace, The resulting optical fiber can cause spikes and breaks.

  The present invention has been made in view of the above-described actual situation, and an object thereof is to seal a gap generated between an upper end opening in an optical fiber drawing furnace and an optical fiber preform with a simple structure. It is possible to provide a sealing structure for a drawing furnace for an optical fiber capable of handling drawing of an optical fiber preform having a large diameter variation without causing spikes or disconnection. .

  The optical fiber drawing furnace sealing structure according to the present invention is a structure for sealing a gap between the upper end opening of the optical fiber drawing furnace and the optical fiber preform inserted from the upper end opening. . This seal structure holds a ring-shaped seal member having a plurality of slits cut on the inner peripheral side, and the seal member in a state where the inner peripheral side is inclined downward from the horizontal direction as compared to the outer peripheral side. And a holding portion, and the gap is sealed by abutting the inner peripheral end of the sealing member against the side surface of the optical fiber preform.

The seal member cuts out a part of the ring so as to be discontinuous, and overlaps the discontinuous ends to form a shape inclined downward, and is held by the holding part . Alternatively, one or more seal members having different inner diameters are stacked.
Further, it is preferable that two or more of the sealing members are stacked so as to be shifted so that the respective slits are not at the same position in the vertical direction .

  According to the sealing structure of the optical fiber drawing furnace according to the present invention, it is possible to seal the gap generated between the upper end opening and the optical fiber preform in the optical fiber drawing furnace with a simple structure, In addition, it is possible to handle drawing of an optical fiber preform having a large diameter variation without causing spikes or disconnection.

It is a figure for demonstrating the outline of the seal structure and optical fiber wire drawing furnace body which concern on this invention. It is a figure which shows an example of the seal structure which concerns on this invention, and is a figure which shows the detail of the seal structure in FIG. It is a figure which shows the detail of the sealing member and holding | maintenance part in the seal structure of FIG. It is the perspective view which looked at the principal part of the seal structure of FIG. 2 from diagonally downward. It is a figure which shows the other example of the seal structure which concerns on this invention, and is sectional drawing which shows the detail of the seal structure in FIG. It is sectional drawing which shows the seal structure by a prior art. It is a perspective view which shows the sealing member by a prior art.

FIG. 1 shows an example of a sealing structure according to the present invention and an optical fiber drawing furnace body, in which 1 is an optical fiber preform (glass preform for optical fiber) and 10 is a main body of the optical fiber draw furnace. (Hereinafter simply referred to as a drawing furnace body), 20 is a seal structure, and 30 is a lid.
As shown in FIG. 1, a draw furnace body 10 includes a furnace casing 11, a core tube 12 provided therein, a cylindrical heating source (heater) 13 provided on the outer periphery of the core tube 12, And a heat insulating material 14 provided on the outer periphery of the heater 13.

  The core tube 12 accommodates the optical fiber preform 1 inserted from the upper end opening. The heater 13 heats and melts the optical fiber preform 1 accommodated in the core tube 12. Further, the drawing furnace body 10 is provided with an inert gas supply mechanism (not shown) so as to supply inert gas or the like in the furnace core tube 12 or around the heater 13 to prevent oxidation or deterioration. It has become.

In the drawing furnace body 10, the optical fiber preform 1 can be moved in the drawing direction (downward direction) by a separately provided moving mechanism. The support rod 2 for suspending and supporting the optical fiber preform 1 from above is connected.
The support rod 2 may be formed integrally with the optical fiber preform 1 or may be separately manufactured and fused. Although the circular shape is mentioned as a cross-sectional shape of the support rod 2, it is not restricted to it. Further, in order to connect the support rod 2 and the optical fiber preform 1, a connection part (fitting part) may be provided separately.

  In addition, although the upper end part of the inner wall of the core tube 12 forms the upper end opening part in the upper end part 11a of the drawing furnace body 10 as it is in FIG. 1, the example is not restricted to this. For example, an upper lid that is a narrower upper end opening than the inner diameter d of the core tube 12 may be provided on the upper side of the core tube 12, and in this case, the gap to be sealed is the narrow upper end opening and the optical fiber preform 1. It becomes a gap generated between the two. In addition, the cross-sectional shape of the optical fiber preform 1 is basically generated with the aim of a perfect circle, but there may be some unevenness regardless of the accuracy, and it may be elliptical. May be. The upper end opening may have a circular cross section, but this accuracy does not matter.

  An optical fiber drawing process in the drawing furnace body 10 described above will be schematically described. In the drawing furnace body 10, the lower part of the optical fiber preform 1 in the furnace is heated by the heater 13 in the furnace core tube 12 while preventing outside air from being entrained by a seal structure 20 described later provided at the upper end portion 11 a. . In the draw furnace body 10, the optical fiber 3 is melted and drooped from the lower end of the optical fiber preform 1 which has been heated and melted to have a small diameter, and the discharge hole 16 provided in the lower end portion of the furnace casing 11 The optical fiber 3 is pulled out. Then, as the drawing progresses, the optical fiber preform 1 together with the support rod 2 is gradually lowered by the moving mechanism.

  The seal structure 20 according to the present invention includes a through hole (that is, an upper end opening) provided for penetrating (slowly inserting) the optical fiber preform 1 having a circular cross section at the upper end portion 11a of the drawing furnace body 10. It is a structure for sealing the clearance gap 15 produced between the optical fiber base materials 1 of the circular cross section inserted from 1st. And the seal structure 20 is installed in the upper end part 11a of the drawing furnace body 10. FIG.

  Hereinafter, the main features of the seal structure 20 according to the present invention will be described with reference to FIGS. Here, FIG. 2 is a diagram showing details of the seal structure 20, FIG. 2A is a partial cross-sectional view of the seal structure 20, and FIG. 2B is a seal structure 20 before the optical fiber preform 1 is passed through. It is a top view which shows the principal part. 3 is a diagram showing details of the seal member and the holding portion in the seal structure 20 of FIG. 2, FIG. 3 (A) is a top view showing the seal member before being attached to the tilting table, and FIG. 3 (B) is a seal. FIG. 3C is a cross-sectional view of the tilting table in the vertical direction. FIG. 4 is a perspective view of the main part of the seal structure 20 of FIG. 2 as viewed obliquely from below. The lid 30 will be described later.

  As shown in FIGS. 2A and 2B, the seal structure 20 according to the present invention includes a ring-shaped seal member 22 having a plurality of slits 22 b cut on the inner peripheral side, and the seal member 22. A holding portion that holds the inner peripheral side in a state inclined downward from the horizontal direction as compared to the outer peripheral side. About the said holding | maintenance part, the example comprised with the inclination base 21, the guide pin 23, and the pressing member 24 mentioned later is given. Since the seal member 22 is ring-shaped, it can be called a “seal ring”.

The seal structure 20 seals the gap 15 by bringing the tip on the inner peripheral side of the seal member 22 (tip portion 22a partitioned by the slit 22b) into contact with the side surface of the optical fiber preform 1. It is configured.
Specifically, as the configuration of the holding portion, a configuration is adopted in which the seal member 22 is held in a state where the seal member 22 can float downward while floating on the inner peripheral side. Of course, in order to contact the side surface of the optical fiber preform 1, holding portions (in this example, the tilting table 21 and the holding member 24) are arranged on the lower side and the upper side in the vertical direction of the inner circumferential side of the region to be bent. It is configured not to protrude.

In addition, the part to contact | abut is not necessarily the whole in which the slit 22b is cut, but becomes a part fundamentally. For example, only the most distal portion of the for the optical fiber preform 1 of the minimum diameter phi ₁ that is assumed abuts substantially at the tip portion 22a for the optical fiber preform 1 of the maximum diameter phi ₂ envisioned The whole is bent, and the tip side of the bent portion comes into contact.

  In addition, the seal structure 20 includes a housing 25, and the seal member 22 and the holding unit are stored in the housing 25 by fixing the inclined base 21 to the floor of the housing 25 of the seal structure 20. In FIG. 2, the housing 25 is illustrated so as to cover the upper and lower surfaces and the side surfaces of the tilting table 21. However, the present invention is not limited to this. It may be placed. A configuration without the casing 25 is also possible.

  The housing 25 is provided with a gas inlet 25a through which an inert gas or the like is supplied by a supply mechanism (not shown). When carbon is used as a member such as the seal member 22, an inert gas or the like spreads inside the housing 25 through the gas introduction port 25 a, and 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.

  Moreover, although the structure of the holding | maintenance part illustrated is mentioned later, the inclination base 21 and the pressing member 24 are provided so that the sealing member 22 may be pinched | interposed as shown to FIG. 2 (A). Therefore, a gas vent (not shown) may be provided in the tilt base 21 and / or the pressing member 24 so that an inert gas or the like flows from the lower side (back side) and / or the upper side of the seal member 22.

Next, details of the seal member 22 and the holding portion in the seal structure 20 according to the present invention will be described.
As shown in FIG. 2 (B), the distal end portion 22a of the seal member 22 has a cut (slit 22b) on the inner peripheral side as shown in FIG. Gives flexibility.

  The shape of the seal member 22 will be specifically described. The seal member 22 is attached to and held by the inclined base 21. Before mounting, as shown in FIG. 3 (A), a ring is formed from a single material, and a part of the ring is cut out to make it non-continuous, and a slit 22b is inserted on the inner peripheral side of the ring. Pin holes 22c are drilled at predetermined intervals around the periphery. The pin holes 22c are also provided at both ends that are discontinuous.

  Here, as illustrated in FIG. 3A, the slit 22 b is cut along the radial direction of the optical fiber preform 1 or a direction close thereto (oblique). It can be said that it is preferable because it is easy to bend in accordance with the downward movement. Note that it is preferable that all the slits 22b have the same length because the slits 22b can be uniformly bent, and such an example is given, but the present invention is not limited to this.

  The inclined table 21 is a table that is inclined so as to be lowered toward the central axis direction of the upper end opening and has an insertion port for inserting the optical fiber preform 1. That is, as shown in FIGS. 2 (A) and 3 (C), the tilting table 21 has a shape that is obtained by removing the inverted part of the truncated cone from the column. More specifically, the tilt base 21 has a right triangle whose base is the side parallel to the upper end 11a and whose height is the central axis direction of the upper end opening, and whose upper end is centered on the center axis of the upper end opening. It is a disk-shaped member having a shape rotated around the opening. In general, the tilt angle of the tilt base 21 can be assumed to be about 20 ° to 45 ° with respect to the horizontal direction, but the tilt angle can be applied within a range of 5 ° to 85 °.

  The right-angled triangle is actually a trapezoid as shown in the figure, but may be formed in a sloped portion even in other shapes. Further, the diameter of the insertion port of the optical fiber preform 1 in the inclined base 21 may be the same as the diameter of the upper end opening, but may be slightly longer or shorter. However, when the diameter of the insertion opening is shorter than the diameter of the upper end opening, the base material diameter that can be drawn becomes smaller.

  By having such a shape, the inclined base 21 can hold the seal member 22 in a state where the inner peripheral side is inclined downward from the horizontal direction compared to the outer peripheral side due to the inclined surface. As shown in FIGS. 3 (B) and 3 (C), this holding is performed on the inclined surface of the inclined base 21, or by a guide pin 23 pointed to, the sealing member is formed in a shape inclined downward by overlapping the discontinuous ends. This can be realized by fixing the seal 22 and holding the seal member 22 with the pressing member 24.

When assembling, first, the seal member 22 is formed in an inverted conical shape by overlapping the non-continuous portions so that the pin holes 22c at both ends which are discontinuous overlap, and each pin hole 22c is formed in each guide pin 23 on the inclined base 21. Then, the pressing member 24 is mounted. The holding member 24 also has an inclined surface that matches the inclined surface of the inclined table 21, and an insertion hole for inserting each guide pin 23 is also formed. When the pressing member 24 is mounted, the seal pin 22 is inserted into each insertion hole so that the position of the sealing member 22 is not shifted between the inclined base 21 and the pressing member 24. Can be pinched.
As a result, as shown in FIG. 2A, the seal member 22 can be held while being sandwiched between the inclined base 21 and the pressing member 24.

  At this time, as described above, the bendable region on the inner peripheral side of the seal member 22 is configured so that the inclined base 21 and the pressing member 24 do not protrude on the lower side and the upper side in the vertical direction of the region. That is, the inclined base 21 and the pressing member 24 hold at least the slit 22b so as to hold a region (outer peripheral region) outside the region where the slit 22b having the same length in the seal member 22 is cut. What is necessary is just to hold | maintain so that it may be pinched | interposed from the up-and-down side, leaving the area | region currently occupied. In addition, although you may comprise so that there may exist the circumferential direction area | region where the slit 22b is not cut at all in the part which is not clamped, the slit 22b is cut as much as possible in the part which is not clamped as mentioned above. It is preferable that the configuration be such that

  In this way, the tilt base 21 and the pressing member 24 hold the seal member 22 including the tip 22a obliquely. And since the sealing member 22 containing the slit 22b is arranged diagonally, even if the diameter fluctuation of the optical fiber preform 1 is large, it strikes obliquely with respect to the side surface of the optical fiber preform 1, so that the tip 22a is bent. It is easy to absorb the fluctuations in the longitudinal direction and the circumferential direction of the optical fiber preform 1.

That is, in the seal structure 20, the optical fiber preform 1 descends as shown by the arrow in FIG. 2A due to the progress of drawing, and the outer diameter of the optical fiber preform 1 is assumed to be, for example, the minimum diameter φ _1. 1 to the maximum diameter φ ₂ (> φ ₁ ), the state in which the tip 22a of the seal member 22 is in contact with the side surface of the optical fiber preform 1 (the side is pressed) is maintained. The gap 15 can be sealed. Furthermore, since the seal structure 20 according to the present invention has a structure in which each of the tip portions 22a divided by the slits 22b independently presses the side surface of the optical fiber preform 1, the diameter of the optical fiber preform 1 is the same. A case where the cross section is not constant, that is, a case where the cross section has a non-circular cross section can be dealt with.

Thus, the seal structure 20 can automatically absorb the diameter variation of the optical fiber preform 1. Therefore, if an inert gas or the like (N ₂ , Ar, He, or the like) is allowed to flow in the furnace, the furnace pressure can be maintained at a positive pressure even with respect to fluctuations in the diameter of the optical fiber preform 1.
Furthermore, since one surface of the sealing member 22 is basically formed from one member, there are fewer portions to stop the sealing member than the technique described in Patent Document 3 formed from many members. On top of that, mounting can be done with high accuracy, so there is no worry that the parts will fall into the furnace.

Further, as shown in FIGS. 2A and 4, an example in which three sealing members 22 are arranged is given here. In this case, it is preferable that the slits 22b are arranged so as not to be in the same position in the upper and lower sides. The number of the sealing members 22 is not limited to three, but may be one, two, or four or more, but the sealing member 22 has the slits 22b at the same position at the top and bottom (that is, adjacent sealing members 22). It is preferable that two or more sheets are stacked while being shifted so as not to occur.
Further, not only the number of the sealing members 22 but also the interval and the number of the slits 22b may be appropriately selected according to the outer diameter, the outer diameter fluctuation amount, the bending amount, etc. of the optical fiber preform 1 to be used. Basically, the larger the number of sealing members 22, the easier it is to achieve airtightness, but the flexibility is reduced and the diameter variation that can be dealt with becomes smaller.

  In addition, the inner diameter of the insertion opening of the inclined base 21 and the radial length of the seal member distal end portion 22a protruding from the inclined base 21 may be determined as appropriate so that the gap 15 can be filled. In the example of FIG. 1, the width of the gap 15 is a value obtained by subtracting the diameter φ of the optical fiber preform 1 from the diameter d of the core tube 12 and halving it. However, since the diameter of the optical fiber preform 1 actually varies, the inner diameter of the tilt base 21 and the gap 15 are preferably determined based on the distance (preferably assumed maximum distance) that is assumed in consideration of the fluctuation. What is necessary is just to determine the length of the radial direction of the front-end | tip part 22a (part bent in the front-end | tip part 22a). For example, when the diameter φ of the optical fiber preform 1 is 150 mm and is formed with a diameter variation of ± 10 mm, the diameter d of the core tube 12 may be about 180 mm, so the width of the gap 15 (d− φ) / 2 is about 10 to 20 mm.

  Further, the seal member 22 has heat resistance, and preferably has heat resistance of 200 ° C. or higher. The sealing member 22 is preferably made of carbon, and more preferably a carbon sheet (that is, a carbon sheet). This is because carbon not only has excellent heat resistance, but also can be processed with a small coefficient of friction (a soft material), so there is no fear of damaging the optical fiber preform 1. Furthermore, it is preferable to use what is called high-purity carbon as the material of the carbon sheet, and more preferable is a flexible carbon sheet that has been subjected to compression processing after being foamed by a high-temperature expansion treatment.

Carbon is also preferred because it can be easily molded by press molding. The thickness of the seal member 22 may be, for example, 0.2 mm, and is preferably in the range of 0.1 to 0.4 mm in view of bending, and the bending is made of a material so that the radius of curvature is about 10 mm. It is preferable to determine (such as Young's modulus) and structure (such as slit length).
Note that other materials such as a heat-resistant glass cloth may be employed as the seal member 22.

  In addition, it is preferable that the inclined base 21, the pressing member 24, and the guide pin 23 have a high heat resistance, and it is preferable that the heat resistance of 200 ° C. or more is the same as that of the seal member 22. As the tilt table 21 and the pressing member 24, metal, quartz, carbon, or the like can be used. As the guide pin 23, metal, quartz, carbon, ceramics, or the like can be used. In the case where any one of the members 21 to 24 that does not have high heat resistance is adopted, a mechanism (for example, a water cooling method) for cooling the member may be taken.

As described above, in the present invention, even when the outer diameter φ of the optical fiber preform 1 changes, the seal member 22 can always keep the state in contact with the optical fiber preform 1 as much as possible. That is, according to the present invention, the gap 15 generated between the upper end opening of the drawing furnace body 10 and the optical fiber preform 1 can be sealed even if the optical fiber preform has a large diameter variation. Inflow of outside air from the upper and lower parts can be prevented. As a result, deterioration of the in-furnace parts can be prevented, and the drawing can be performed without increasing the diameter variation of the optical fiber 3 to be formed.
Furthermore, according to the present invention, since the seal member 22 that can be formed by processing one component is held, there is no fear of dropping into the furnace, and spikes and disconnections are not caused. In addition, by using a heat-resistant member as a component such as the seal member 22, it is not melted by heat.

Actually, the optical fiber preform 1 having a diameter of 150 mm and an outer diameter variation of about 10% was drawn while being sealed with the above-described seal structure 20, thereby producing an optical fiber 3 of 125 μm. As a result, the obtained optical fiber 3 was free from spikes and breaks, and the carbon parts in the furnace were not deteriorated, so that it was confirmed that the optical fiber 3 had a sufficient sealing property.
On the other hand, an optical fiber preform having a diameter of 140 to 155 mm was drawn using a seal structure in which three cut carbon sheets described in Patent Document 2 were laminated, and as a result, drawing was started. Many spikes were being drawn, and white smoke slightly rose from the upper part of the road and stopped. Furthermore, at this time, the carbon sheet was partially bent, and it was confirmed that the carbon parts in the furnace were oxidized and consumed.

FIG. 5 is a view showing another example of the seal structure according to the present invention, and is a cross-sectional view showing details of the seal structure in FIG. The seal structure 20 of FIG. 2 has three seal members 22 stacked, but the seal structure 20 illustrated in FIG. 5 is a stack of three seal members 22 stacked with an intermediate member 27 interposed therebetween. It is assumed that an insertion hole for the guide pin 23 is also drilled in this intermediate member.
Further, here, an example in which two sets of the seal member 22 are stacked is given, but the intermediate member 27 may be sandwiched between the sets of three or more sets similarly. In addition, although the example in which the number of the seal members 22 and the seal members 26 is three is given, it is not limited to this, and the number of both may be different, and the number is also limited to three. Absent.

Here, the thickness of the intermediate member 27 may be determined so that the distal end portion 22a of the seal member 22 and the distal end portion 26a of the seal member 26 are not affected by mutual bending. Thereby, the front-end | tip part 22a and the front-end | tip part 26a can contact | abut to the side surface of the optical fiber preform 1 without being influenced by mutual bending.
Further, a gas vent (not shown) may be provided in the intermediate member 27 so that an inert gas or the like flows also between the seal member 22 and the seal member 26.

In addition, although the example using a carbon sheet with a uniform internal diameter was demonstrated, you may use the carbon sheet from which an internal diameter differs. For example, a carbon sheet having an inner diameter φ of 125 mm and a carbon sheet having an inner diameter φ of 145 mm, each having one or more stacked sheets with the smaller inner diameter carbon sheet on the lower side, is set as one set, or Several sets may be stacked via the intermediate member 27. The numerical value of the inner diameter of the carbon sheet described above is a value of the inner diameter after being attached to the holding portion, and is not a value of the inner diameter of the carbon sheet in a planar state.
The size of the inner diameter is not limited to that described above, and a carbon sheet having an inner diameter that is considered to be optimal may be selected as appropriate in accordance with the outer diameter of the optical fiber preform 1 and the amount of fluctuation in outer diameter. Further, the carbon sheets having the respective diameters may be stacked in any number, or the number of both may be different. Further, the types of inner diameter are not limited to two types, and may be three or more types.

Next, the lid 30 in FIG. 1 will be described.
In the configuration in which the support rod 2 is provided on the optical fiber preform 1 as shown in FIG. 1, the support rod 2 is lowered to the position of the core tube 12 by the progress of the drawing process, that is, the support rod 2 is drawn. There is a scene located below the upper end portion 11a of the furnace body 10.

  In order to keep the inside of the furnace sealed even in such a situation, the sealing structure of the drawing furnace for an optical fiber according to the present invention is a lid in addition to the sealing structure 20 of FIGS. 2 and 5 as shown in FIG. 30 is preferred. The lid 30 is a lid that penetrates the support rod 2 and is placed on the upper side of the optical fiber preform 1, and has a through hole 30a and a shoulder 30b for the support rod 2 as shown. Examples of the material of the lid body 30 include quartz and metal.

By providing the lid 30, the optical fiber preform 1 is detached from the seal member 22 (and the seal member 26) even when the drawing of the optical fiber 3 is advanced and the optical fiber preform 1 and the support rod 2 are lowered. Before the operation, the lower end surface of the lid body 30 shifts to a state in contact with the seal structure 20, and the sealed state can be maintained.
In addition, although it demonstrated on the assumption that the cover body 30 has the shoulder part 30b, the cover body 30 may be a shape which just opened the through-hole 30a of the support bar 2 in the disk. Even in such a shape, transition between states as described above is possible as well.

  In the above description, the sealing structure according to the present invention has been described with reference to a drawing furnace for drawing an optical fiber preform. However, the sealing structure in a drawing furnace for drawing an optical fiber preform can be similarly applied. In addition to a drawing furnace and a drawing furnace, the present invention can also be applied to a glass heat processing furnace having an equivalent equipment configuration.

DESCRIPTION OF SYMBOLS 1 ... Optical fiber preform, 2 ... Support rod, 3 ... Optical fiber, 10 ... Drawing furnace body, 11 ... Furnace housing | casing, 11a ... Upper end part, 12 ... Core tube, 13 ... Heater, 14 ... Thermal insulation, 15 DESCRIPTION OF SYMBOLS ... Gap, 16 ... Discharge hole, 20 ... Seal structure, 21 ... Inclined base, 22, 26 ... Seal member, 22a, 26a ... End of seal member, 22b ... Slit, 22c ... Pin hole, 23 ... Guide pin, 24 DESCRIPTION OF SYMBOLS ... Pressing member, 25 ... Housing, 25a ... Gas inlet, 27 ... Intermediate member, 30 ... Lid, 30a ... Through-hole, 30b ... Shoulder.

Claims (3)

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 preform inserted from the upper end opening;
A ring-shaped seal member in which a plurality of slits are cut on the inner peripheral side, and a holding portion that holds the seal member in a state in which the inner peripheral side is inclined downward from the horizontal direction compared to the outer peripheral side,
The seal member is cut out part of the ring to make it non-continuous, overlaps both ends that are made non-continuous, and has a shape inclined downward, and is held by the holding part,
A sealing structure for a drawing furnace for an optical fiber, wherein the gap is sealed by bringing a distal end portion on the inner peripheral side of the sealing member into contact with a side surface of the optical fiber preform.   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 preform inserted from the upper end opening;
  A ring-shaped seal member in which a plurality of slits are cut on the inner peripheral side, and a holding portion that holds the seal member in a state in which the inner peripheral side is inclined downward from the horizontal direction compared to the outer peripheral side,
  One or more of the seal members having different inner diameters are stacked,
  A sealing structure for a drawing furnace for an optical fiber, wherein the gap is sealed by bringing a distal end portion on the inner peripheral side of the sealing member into contact with a side surface of the optical fiber preform.   The sealing structure for an optical fiber drawing furnace according to claim 1 or 2, wherein two or more of the seal members are stacked so as to be shifted so that the slits are not at the same position in the vertical direction.

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