JP2005320193A - Method of manufacturing optical fiber preform and apparatus for manufacturing optical fiber preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an optical fiber preform which enables safe manufacturing operation by effectively preventing a gas from leaking out to the outside of a furnace by a simple and convenient technique. <P>SOLUTION: The optical fiber preform is obtained by heat treating a porous base material in a furnace core tube 3 in a gas atmosphere containing a chloric gas while sucking and exhausting the gas in a cover 11, by installing the cover 11 to cover the upper end part of the furnace core tube 3 of a heat treating furnace having the furnace core tube 3 and an upper lid 4, and the upper lid 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical fiber preform manufacturing method and manufacturing apparatus. More specifically, the present invention provides a manufacturing method and a manufacturing apparatus that can easily increase the safety when heat-treating a porous optical fiber preform to obtain an optical fiber preform.

  As a method for manufacturing an optical fiber preform, first, a porous preform is produced by a VAD method or the like, and then the porous preform is dehydrated and heated in a heating furnace to obtain a transparent optical fiber preform. Is generally well known.

  FIG. 6 is a schematic view of a general heating furnace used for manufacturing an optical fiber preform. In the figure, a porous base material 1 is connected to an upper dummy rod 2 and inserted into a core tube 3 of a heating furnace, and an upper lid 4 is attached to the upper portion of the core tube 3 with an upper dummy rod 2. It is provided so as to be pivotable. Further, one end of the upper dummy bar 2 is connected to the upper rotating mechanism 5 and is rotatable around the axis. In addition, the heating furnace is provided with a heater 6 for heating the porous base material 1, and is provided with a gas introduction pipe 7 and an exhaust pipe 8 that are introduced into the furnace core tube 3 during the heat treatment. .

  In the dehydration and heat treatment using such a heating furnace, first, the porous base material 1 is connected to the upper dummy rod 2, lowered toward the core tube 3, and suspended in the core tube 3. Thereafter, the upper part of the core tube 3 is connected to the upper dummy bar 2 or closed with an independent upper lid 4. Thereafter, while rotating the porous base material by the upper rotating mechanism 5, it is gradually lowered and heated by the heater 6 while introducing a predetermined gas from the gas introduction pipe 7 and discharging it from the exhaust pipe 8. Heat treatment such as dehydration and sintering is performed.

  In such dehydration and heat treatment in a heating furnace, when a porous base material is dehydrated, for example, a gas containing a chlorine-based gas such as chlorine or thionyl chloride is used. These chlorinated gases are effective in efficiently dehydrating the porous base material during processing, and are contained in the processing gas for that purpose. On the other hand, these chlorinated gases are very harmful to the human body and should be avoided as much as possible from the outside in terms of safety. Chlorine-based gas is also a corrosive gas, so even if the concentration is low enough to have little impact on the human body, if the surrounding metal part leaks and is exposed for a long time, it will gradually It will be corroded. Therefore, sufficient care must be taken so that these gases do not leak outside the furnace.

  In order to prevent the in-furnace gas from flowing out of the furnace, the upper part of the core tube 3 is closed by the upper cover 4, but the sealing property between the upper cover 4 and the upper part of the core tube 3 is insufficient. If so, the chlorine-based gas may leak. However, it is difficult to completely seal between the upper lid 4 and the upper part of the core tube 3. This is because another problem arises when the space between the upper lid 4 and the upper portion of the core tube 3 is completely sealed.

  That is, in order to completely seal between the upper lid 4 and the upper portion of the core tube 3 and prevent gas leakage, the upper lid 4 and the upper end portion of the core tube 3 are gripped and fixed with a clip or the like, for example. However, when the upper lid 4 and the core tube 3 are fixed in this manner, when the upper dummy bar 2 comes into contact with the upper lid 4 due to slight axial misalignment or bending, a force is applied to the upper lid or the upper dummy rod. There is a risk of damage.

  Therefore, the top cover 4 and the core tube 3 cannot be completely fixed. Therefore, in practice, the top cover 4 having a bottom surface that is flush with the top surface of the core tube 3 is mounted on the top end of the core tube 3. And the space between the core tube 3 and the upper lid 4 was sealed by the load of the upper lid 4 itself. In such a configuration, when the above-described upper dummy bar 2 comes into contact with the upper lid 4 due to slight axial deviation, bending, etc., the gas in the furnace may leak out of the furnace.

  Further, a gap is provided between the through hole provided in the upper lid 4 and the upper dummy bar 2 so that the upper dummy bar 2 penetrating the upper lid 4 can be rotated and moved up and down. When the sealing performance of the gap is insufficient, the gas introduced into the core tube 3 from the gap may leak out of the furnace.

In a vitrification furnace having a furnace core tube, Patent Document 1 discloses a manufacturing apparatus with improved sealing performance between a through hole of a lid body and a support rod of a porous base material. It is disclosed that a ring provided with a multi-stage groove facing the support rod is attached to the through-hole wall, and a seal gas is supplied to that portion to be discharged via an exhaust hood. However, the apparatus of Patent Document 1 requires an extra pipe for flowing gas into the lid. In addition, since the support rod has a slight axis deviation or the like, when the support rod hits the lid body due to the rotation of the support rod and the lid body is displaced in the horizontal direction, the pipe line is displaced following that. If the pipe diameter is increased to prevent this, the pressure inside the core tube becomes unstable. Further, if the lid is fixed so that the lid does not shift in the horizontal direction, there is a possibility that other parts such as the support rod may be damaged as described above. In addition, considering the heat retention in the cover and the possibility of long-term contact with a very small amount of chlorine-based gas, no suitable material can be found for the pipe. In other words, plastic materials have problems with heat resistance, metal materials have problems with corrosion resistance and effects on the quality of optical fibers, and carbon materials have problems with strength in the case of thin tubes. . Further, when a seal gas is allowed to flow inside the lid body, as a result, the inside of the lid body is pressurized, so that gas flows from the space between the through hole around the support rod to the exhaust hood side. Since the inside becomes positive pressure due to the supply of seal gas, if gas in the furnace leaks from between the core tube and the lid, this gas penetrates through the support rod provided in the exhaust hood. There was a risk of leakage outside the furnace through the gap between the hole and the support rod. Furthermore, the structure of the quartz ring with multi-stage grooves is complicated, and the sealing performance may not be sufficient depending on the finishing accuracy.
JP 2003-238188 A

  As described above, when a porous base material is dehydrated and heat-treated in a heating furnace, a gas containing a chlorine-based gas used for the processing may leak out of the furnace from the heating furnace. Fixing the tube to the core tube to make it airtight may cause another problem. In addition, the technique disclosed in Patent Document 1 may cause gas leakage.

  The present invention advantageously solves the above-described problems, effectively prevents gas from leaking out of the furnace by a simple method, and provides a method for manufacturing an optical fiber preform that enables safe manufacturing operation. It is intended to be provided together with its advantageous manufacturing apparatus.

  The present invention provides an optical fiber preform in which a porous preform is heat-treated in a gas atmosphere containing a chlorine-based gas in the furnace tube of a heat treatment furnace having a reactor core tube and an upper cover to obtain an optical fiber preform. In this manufacturing method, a cover for covering the upper end portion of the core tube and the upper cover is provided, and the gas in the cover is sucked and exhausted.

  In the optical fiber preform manufacturing method of the present invention, it is preferable that the pressure inside the cover is lower by 0.1 Pa or more than the pressure outside the cover.

  Moreover, in the manufacturing method of the optical fiber preform of the present invention, it is more preferable that the pressure inside the cover is lower by 1 Pa to 30 Pa than the pressure outside the cover.

  Furthermore, in the optical fiber preform manufacturing method of the present invention, the gas in the cover can be sucked and exhausted, and the gas in the inner space of the upper lid can be sucked and exhausted.

  The optical fiber preform manufacturing apparatus of the present invention includes a cover that covers the core tube and the upper cover, an exhaust port that communicates with the inside of the cover and sucks and exhausts the gas in the cover, and an internal space of the upper cover. And an exhaust port for sucking and exhausting the gas.

  In the present invention, when a gas is leaked from between the upper end of the core tube and the upper lid by providing a cover that covers the upper end of the core tube and the upper lid and sucking and exhausting the gas in the cover. Even in this case, the leaked gas stays in the cover and is sucked and exhausted from the cover to the exhaust gas treatment device, so that it is possible to effectively prevent the in-furnace gas from leaking out of the furnace.

  In the optical fiber preform manufacturing method of the present invention, in order to solve the two conflicting problems described above, a cover that covers the upper end of the core tube and the upper cover is provided, and the gas in the cover is sucked and exhausted. . This will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of the vicinity of an upper portion of a heating furnace as a preferable manufacturing apparatus to which the manufacturing method of the present invention is applied, and FIG. 2 is a perspective view thereof. 1 and 2, an upper lid 4 is provided at the upper end of the core tube 3 of the heating furnace so that the upper end surface of the core tube 3 and the bottom surface of the upper lid 4 are in the same plane. The space between the core tube 3 and the upper lid 4 is sealed with a load. A cover 11 is provided so as to cover the entire upper lid 4 and also cover the surface where the core tube 3 and the upper lid 4 are in contact.

  The cover 11 is a housing having a through hole 11b through which the upper dummy rod 2 is pivotably penetrated in the upper surface portion 11a and an opening slightly larger than the outer diameter of the core tube 3 in the lower surface portion 11c. The lower surface portion 11 c is positioned lower than the upper end surface of the core tube 3. An exhaust port 12 is attached to the side surface portion 11 d of the cover 11. An exhaust pipe 13 connected to an exhaust gas treatment device (not shown) is connected to the exhaust port 12, and the gas in the cover 11 is sucked and exhausted by the exhaust gas treatment device.

  Thus, even if gas leaks between the core tube 3 and the upper lid 4 by covering the upper periphery of the core tube 3 with the cover 11 and exhausting the gas in the cover 11, the leaked gas is Since the gas stays in the cover 11 and the gas in the cover 11 is sucked and exhausted and discharged to an exhaust gas treatment device (not shown), it does not leak into the environment around the heating furnace, and safe dehydration and heat treatment can be performed. In addition, the metal around the heating furnace is not corroded. Further, since it is not necessary to fix the furnace core tube 3 and the upper lid 4 in order to prevent leakage of gas in the furnace, there is no problem of damage to the upper lid 4 and the upper dummy rod 2 that occurs when processing is performed in a fixed manner. In addition, the gas leakage prevention equipment itself is simply provided with the cover 11 in the existing heating furnace, and no complicated equipment is required, so that the installation is easy, and the work simply sucks the gas in the cover 11. It is easy because it only exhausts. Moreover, since the gas in the cover 11 can be treated by the exhaust gas treatment device connected to the gas exhaust pipe 8 attached to the core tube 3 of the heating furnace, it is not necessary to provide a new exhaust gas treatment device.

  The cover 11 not only covers the vicinity of the connection surface between the upper end portion of the core tube 3 and the upper lid 4, but also a gap provided in the upper lid 4 so that the upper dummy rod 2 can be rotated and moved up and down. Since the gas is leaked from the gap 4a, the leaked gas stays in the cover 11 and the gas in the cover is sucked and exhausted. It is possible to prevent the gas in the furnace from leaking out of the furnace.

  In order to prevent gas from leaking outside the cover 11, it is sufficient that the pressure inside the cover 11 is sucked and exhausted, but preferably 0.1 Pa or more than the pressure outside the cover (atmospheric pressure). It is preferably low, more preferably 1 Pa or more. However, even if the pressure inside the cover 11 is made too low than the pressure outside the cover, no further effect can be expected and the burden on the suction / exhaust equipment increases, so the pressure outside the cover may be lower than 30 Pa. preferable.

  Since the material of the cover 11 is provided in the vicinity of the upper end portion of the heating furnace that is heated at a high temperature, it is basically required to have high heat resistance. In this respect, any material having high heat resistance may be used. Although it is not, it is preferable to have corrosion resistance because it may come into contact with gas containing chlorine-based gas, and transmission to an optical fiber obtained by drawing an optical fiber preform manufactured in a heating furnace Considering the impact on loss, it is preferable to avoid materials that can contaminate the optical fiber preform. Considering these viewpoints, it is desirable that the material of the cover 11 is mainly carbon. However, in the present invention, the cover 11 is not limited to carbon.

  Further, as shown in the perspective view of FIG. 2, the cover 11 can be constituted by cover members 111 and 112 that are divided by a plane including the central axis, for example. Thus, by making the cover 11 into a split type, the operation | work to attach to the core tube 3 and the upper cover 4 vicinity becomes still easier.

  For example, the cover 11 can be supported by being placed on a cover support plate 14 having a predetermined height. The cover support plate 14 may be a cover installation base, or may be a case where the heating furnace has a height that penetrates a plurality of floors of a manufacturing facility, and the upper end of the core tube 3 is located on the upper floor. In the case of protruding upward from the floor surface on the side, the floor surface on the upper floor side may be used. Moreover, although the position of the cover support plate 14 in the height direction depends on the size of the cover 11, it is preferable that the position is 5 cm to 50 cm below the upper end of the core tube in order to make the cover 11 easier to install.

  FIG. 3 is a fragmentary cross-sectional view showing another example of a heating furnace as a suitable manufacturing apparatus used in the manufacturing method of the present invention. In FIG. 3, the same members as those in FIGS. 1 and 2 are denoted by the same reference numerals, and redundant description is omitted.

  In the heating furnace shown in FIG. 3, the table 15 is provided on the cover support plate 14 in the vicinity of the outer peripheral surface of the core tube 3, the cover 11 is provided on the table 15, and the core tube is provided. 3 is provided in the gap between the outer peripheral surface 3 and the opening of the cover 11. By providing such a table 15, the degree of freedom in arranging the cover 11 in the height direction is increased. Therefore, when the cover support plate 14 is an upper floor and it is difficult to adjust the height of the cover support plate, it is advantageous to provide the cradle 15. Further, by providing the sealing material 16 in the gap between the outer peripheral surface of the core tube 3 and the opening of the cover 11, the airtightness in the cover 11 can be further enhanced. Therefore, gas leakage can be more effectively prevented, and the differential pressure inside and outside the cover 11 can be easily increased. For the sealing material 16, flame retardant fibers such as carbon fibers can be used as materials that can withstand high temperature heating, and glass fibers can also be used. In addition, a stopper 17 can be provided at a position outside the cover 11 on the cradle 15 to prevent the cover 11 from moving on the cradle 15.

  4 and 5 show another example of a heating furnace as a manufacturing apparatus suitable for use in the manufacturing method of the present invention. FIG. 4 is a cross-sectional view of the main part in the vicinity of the upper portion of the heating furnace, and FIG. 4 and 5, the same members as those in FIGS. 1 to 3 are denoted by the same reference numerals, and redundant description is omitted below.

  In the heating furnace shown in FIGS. 4 and 5, an exhaust port 21 is attached to the upper lid 4, and an exhaust pipe 22 connected to a gas exhaust device (not shown) is provided at the exhaust port 21. The gas is sucked and exhausted. Thus, by the structure which sucks and exhausts the gas in the internal space of the upper lid 4, the gas in the furnace is along the gap 4 a (through hole) for enabling the upper dummy rod 2 provided on the upper lid 4 to rotate. Therefore, according to the present invention, the gas leakage in the cover can be effectively prevented in combination with the suction and exhaust of the gas in the cover. it can.

  In the heating furnace shown in FIGS. 4 and 5, the ring 23 is attached to the upper dummy rod 2 so as to be close to the gap 4 a immediately above the upper lid 4. Since this ring 23 can suppress gas leakage from the gap 4a, in combination with the above-described gas suction / exhaust of the inner space of the upper lid 4 and gas suction / exhaust in the cover, It becomes possible to prevent leakage more effectively.

  The present invention has been described above with reference to the drawings. However, these drawings show examples, and the present invention is not limited thereby.

  Using the heating furnace shown in FIG. 1, the optical fiber preform was manufactured with the pressure inside the cover being 5 Pa lower than the pressure outside the cover. In this case, a small amount of chlorine-based gas leaked about once or twice a month due to slight axial misalignment or bending of the upper dummy rod 2 for 6 months. No leakage to the outside of the furnace occurred.

It is sectional drawing of the upper part vicinity of the suitable heating furnace which applies the manufacturing method of this invention. FIG. 2 is a perspective view of FIG. 1. It is principal part sectional drawing of another suitable heating furnace which applies the manufacturing method of this invention. It is principal part sectional drawing of another suitable heating furnace which applies the manufacturing method of this invention. FIG. 6 is a plan view of FIG. 5. It is a schematic diagram of the general heating furnace used for manufacture of the preform | base_material for optical fibers.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous base material 2 Upper dummy rod 3 Core tube 4 Upper lid 4a Gap part 5 Upper rotation mechanism 6 Heater 7 Introducing pipe 8 Exhaust pipe 11 Cover 12 Exhaust port 13 Exhaust pipe 14 Cover support plate 15 Stand 16 Sealing material 17 Stopper 21 Exhaust Port 22 exhaust pipe 23 ring

Claims (5)

In a method for manufacturing an optical fiber preform, a porous preform is heat-treated in a gas atmosphere containing a chlorine-based gas in the furnace tube of a heat treatment furnace having a furnace tube and an upper lid, and an optical fiber preform is obtained. ,
A method for producing an optical fiber preform, comprising: a cover that covers an upper end portion of the furnace core tube and the upper lid; and a gas in the cover is sucked and exhausted.   The method for producing a preform for an optical fiber according to claim 1, wherein the pressure inside the cover is lower by 0.1 Pa or more than the pressure outside the cover.   The method for manufacturing an optical fiber preform according to claim 1, wherein the pressure inside the cover is lower by 1 Pa to 30 Pa than the pressure outside the cover.   The method for manufacturing an optical fiber preform according to any one of claims 1 to 3, wherein the gas in the cover is sucked and exhausted, and the gas in the internal space of the upper lid is sucked and exhausted. A cover that covers the core tube and the upper cover, an exhaust port that communicates with the inside of the cover and sucks and exhausts the gas in the cover, and an exhaust port that sucks and exhausts the gas in the inner space of the upper cover. Manufacturing equipment for optical fiber preforms.

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