JP2013245141A - Method and apparatus for producing glass preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for producing a glass preform, whereby the glass preform of high quality can be obtained by satisfactorily performing sintering while preventing increase in cost.SOLUTION: A method for producing a glass preform comprises, while feeding inert gas from a lower part of a furnace core tube 11, moving a glass particulate deposited body 14 placed inside the furnace core tube 11 downward or upward, thereby heating and sintering the same by heat in a heat zone in the furnace core tube 11. A lid 12 is installed at an upper part of the furnace core tube 11, and a partition plate 20 is installed above the glass particulate deposited body 14. When the glass particulate deposited body 14 is located above a prescribed position, the partition plate 20 is moved with the glass particulate deposited body 14. When the glass particulate deposited body 14 is located below the prescribed position, the partition plate 20 is placed at a stop position that is ≥500 mm below an upper end of the lid 12 and only the glass particulate deposited body 14 is moved.

Description

  The present invention relates to a glass base material manufacturing method and manufacturing apparatus for heating and sintering a glass particulate deposit in a heating furnace.

  The glass base material that is the base material of the optical fiber is a glass base material in which glass fine particles are deposited on a starting rod is inserted into the core tube, and an inert gas such as helium gas is supplied from the lower end of the core tube. It is obtained by heating and sintering the fine particle deposit while rotating around the axis.

  When sintering the glass particulate deposit as described above, heat shields are placed above and below the glass particulate deposit to control the escape of radiant heat and suppress temperature irregularities and natural convection in the core tube. Is known (see, for example, Patent Document 1).

  Also, when drawing an optical fiber from the optical fiber preform, a partition plate that vertically defines a space other than the vicinity of the surrounding wall surface of the drawing chamber in the upper space of the optical fiber preform in the drawing chamber is provided. It is also known to keep the wire diameter variation small (for example, see Patent Documents 2 and 3).

JP 2000-219519 A JP-A-5-147969 Japanese Patent Laid-Open No. 11-343137

  By the way, when the glass fine particle deposit is moved from the upper side to the lower side in the furnace core tube and the sintering proceeds, the upper space of the glass fine particle deposit body in the furnace core tube becomes larger. In this upper space, turbulent flow may occur due to the rising airflow of the inert gas. When such a turbulent flow occurs, the pressure fluctuation in the reactor core tube becomes large and becomes negative pressure, and external air may be caught in the reactor core tube through a gap between the dummy rod connected to the starting rod and the top cover of the reactor core tube. Thereby, impurities may be mixed in the glass base material during sintering, and transmission loss of the optical fiber obtained by drawing from the glass base material after sintering may increase. In order to prevent this, it may be possible to suppress the entrainment of outside air by increasing the amount of inert gas supplied into the furnace core tube, but this increases the amount of gas used, resulting in an increase in cost.

  According to the technique of Patent Document 1, it is possible to control the radiant heat escape by the heat shield to suppress the temperature unevenness and natural convection of the core tube, but it is difficult to suppress the entrainment of outside air. In addition, in the techniques of Patent Documents 2 and 3, the fluctuation of the diameter of the optical fiber can be suppressed to a small level, but the technique of simply suppressing the fluctuation of the diameter of the optical fiber when the optical fiber is drawn is used for sintering of the glass fine particle deposit. Even if it is used, it is difficult to satisfactorily sinter the glass particulate deposit.

  An object of the present invention is to provide a glass base material manufacturing method and a manufacturing apparatus capable of obtaining a high-quality glass base material by satisfactorily sintering a glass particulate deposit while suppressing an increase in cost. .

The method for producing a glass base material of the present invention capable of solving the above-described problem is to supply an inert gas from the lower part of the core tube into the core tube, while lowering or upward the glass particulate deposit disposed in the core tube. A method of manufacturing a glass base material that is heated and sintered by heat of a heat zone in the furnace core tube,
A lid is provided at the top of the furnace core tube, a partition plate is provided above the glass particulate deposit,
When the glass particulate deposit is above a predetermined position, the partition plate is moved together with the glass particulate deposit,
When the glass particulate deposit is below a predetermined position, the partition plate is disposed at a stop position 500 mm or more below the upper end of the lid, and only the glass particulate deposit is moved. Features.

An apparatus for producing a glass base material of the present invention includes a furnace tube that accommodates a glass particulate deposit suspended by a starting seed bar so as to be movable up and down,
A lid provided at the top of the furnace core tube;
A gas supply unit for supplying an inert gas into the furnace core tube from a lower part of the core tube;
A heat source provided on the outer peripheral side of the core tube,
A partition plate provided on the starting seed bar above the glass particulate deposit;
A partition plate holding part that is provided on the starting seed bar and supports the partition plate in the vicinity of the upper part of the glass particulate deposit;
A fastening part arranged to fasten the partition plate at a stop position 500 mm or more away from the upper end of the lid part, and
When the glass particulate deposit is above a predetermined position, the partition plate is moved together with the glass particulate deposit while being supported by the partition plate holder,
When the glass particulate deposit is located below a predetermined position, movement of the partition plate is restricted by the retaining portion, and only the glass particulate deposit is moved.

According to the present invention, when the glass particulate deposit is disposed on the lower side in the core tube, a buffer space is formed between the partition plate and the upper end of the core tube. Therefore, even if turbulent flow is generated in the upper space of the glass particulate deposit, this turbulent flow is blocked by the partition plate, and pressure fluctuations caused by the turbulent flow are absorbed in the buffer space. Therefore, outside air is not involved by turbulent flow, and this does not affect the sintered portion of the glass fine particle deposit. Accordingly, it is possible to prevent impurities from being mixed into the glass base material during sintering, and an optical fiber obtained by drawing the glass base material after sintering can have good transmission characteristics.
In addition, if a space serving as a buffer is provided in the core tube in advance, the manufacturing apparatus itself is increased in size and a large amount of inert gas is required to suppress the occurrence of turbulent flow due to the expansion of the upper space. Therefore, in the present invention, when the glass particulate deposit is disposed on the upper side of the core tube, the partition plate is moved together with the glass particulate deposit, so that the upper space of the glass particulate deposit does not expand, and the space is disturbed in this space. There is no flow. For this reason, it is not necessary to increase the supply amount of the inert gas so much, and the facility is not increased in size. In this manner, a high-quality glass base material can be obtained while suppressing an increase in manufacturing costs and equipment costs.
If the partition plate can be moved together with the glass fine particle deposit until the end of sintering, it is considered that turbulent flow will not occur in the upper space of the glass fine particle deposit, but the buffer space becomes turbulent and becomes turbulent. In the present invention, the partition plate is locked at a predetermined position because problems such as easy flow generation and the partition plate entering the heat zone occur.

It is a schematic block diagram which shows one Embodiment of the manufacturing apparatus of the glass base material which concerns on this invention. It is a figure which shows the sintering operation state of a glass base material, Comprising: (a) And (b) is a schematic block diagram which shows the state of a manufacturing apparatus when a sintering operation advances from the state of FIG. 1, respectively. It is a schematic block diagram of the manufacturing apparatus which is not provided with the partition plate. It is a graph which shows the relationship between the gas flow rate in a furnace, and the transmission loss defect rate of an optical fiber.

Hereinafter, an example of an embodiment of a glass base material manufacturing method and a manufacturing apparatus according to the present invention will be described with reference to the drawings.
As shown in FIG. 1, the manufacturing apparatus 10 for manufacturing the glass base material of the present embodiment is capable of moving up and down a glass particulate deposit 14 whose upper part is closed by a lid 12 and suspended by a starting seed rod 15. And a heater 13 which is a heat source provided on the outer peripheral side of the core tube 11. The manufacturing apparatus 10 also includes a gas supply unit 17 that supplies an inert gas such as helium gas into the core tube 11, and a gas discharge unit 18 that discharges unnecessary gas from the core tube 11.

  The glass particulate deposit 14 is suspended in the core tube 11 by a starting seed rod 15. The glass particulate deposit 14 is obtained by depositing glass particulates on a starting seed rod 15, and the upper portion of the starting seed rod 15 is connected to a dummy rod. The starting seed bar 15 has its dummy bar portion held by a holding mechanism (not shown). The starting seed bar 15 gripped by the gripping mechanism is moved from above to below while being rotated about the axis by the gripping mechanism. The manufacturing apparatus 10 forms a heat zone at a predetermined position in the furnace core tube 11 by the heater 13, and heats and sinters the glass fine particle deposit 14 disposed in the heat zone. Thereby, the glass particulate deposit 14 is heated and sintered sequentially from the lower side by the heat from the heat zone while being moved downward. At that time, an inert gas is supplied from the gas supply unit 17 to the lower portion of the core tube 11, and unnecessary gas in the core tube 11 is discharged from the upper portion of the core tube 11 through the gas discharge unit 18.

  The starting seed bar 15 is provided with a partition plate holding portion 16 that projects outward in the radial direction of the starting seed bar 15 in the vicinity of the upper portion of the glass particulate deposit 14. In addition, the starting seed bar 15 is provided with a partition plate 20 above the partition plate holding portion 16. The partition plate 20 is disposed in the vicinity of the upper portion of the glass particulate deposit body 14 while being locked to the partition plate holding portion 16 in a state where the starting seed rod 15 is inserted into the insertion hole 21 formed in the center. The outer diameter of the partition plate 20 is slightly smaller than the inner diameter of the core tube 11. Thereby, the partition plate 20 is movable together with the glass fine particle deposit 14. And the buffer space S is formed between the partition plate 20 and the cover part 12 of the core tube 11 by moving the partition plate 20 below.

  A retaining portion 22 is provided on the inner surface of the core tube 11 above the heater 13, and the retaining portion 22 projects radially inward from the inner surface of the reactor core tube 11. And the partition plate 20 moved downward together with the glass fine particle deposit 14 is locked to the fastening portion 22. As a result, the downward movement of the partition plate 20 from the time when it is locked by the fastening portion 22 is restricted, and thereafter, only the glass particulate deposit 14 is moved downward. The stop position of the partition plate 20 whose downward movement is restricted by the fastening portion 22 is separated by 500 mm or more below the upper end position (that is, the upper end of the core tube 11 in this example) on the inner surface of the flat lid portion 12. Position.

Next, the case where the glass fine particle deposit body 14 is sintered will be described.
First, the starting seed bar 15 is inserted into the insertion hole 21 of the partition plate 20 and is locked to the partition plate holding portion 16.
Further, the glass seed deposit 14 is suspended from the upper side of the core tube 11 by causing the starting seed bar 15 to be gripped by the gripping mechanism (see FIG. 1).

  Next, the inside of the core tube 11 is heated to about 1500 ° C. by the heater 13, thereby forming a heat zone at a predetermined position in the core tube 11 (a range surrounded by the heater 13). Then, the lower part arrange | positioned in the heat zone in the glass particulate deposit 14 is heated and sintered.

  Further, an inert gas such as helium gas is supplied from the gas supply unit 17 to the lower part of the furnace core tube 11. Then, this inert gas passes between the inner peripheral surface of the core tube 11 and the outer peripheral surface of the glass fine particle deposit 14 and is sent to the upper side of the glass fine particle deposit 14. Discharged.

By lowering the glass fine particle deposit 14 together with the starting seed bar 15 by the gripping mechanism, the sintering position in the heat zone is gradually moved to the upper side of the glass fine particle deposit 14.
In this way, the partition plate 20 moves downward together with the glass particulate deposit 14. Thereby, a buffer space S that gradually expands is formed between the partition plate 20 and the lid portion 12 of the core tube 11.

  Further, when the glass particulate deposit 14 is lowered and reaches a predetermined position (position shown in FIG. 2A), the partition plate 20 is locked to the fastening portion 22. Then, after that, the partition plate 20 does not move downward together with the glass fine particle deposit 14, but stays at a stop position that is a locking position with the fastening portion 22 that is separated by 500 mm or more from the upper end of the lid portion 12. It will be. After that, as shown in FIG. 2 (b), only the glass particulate deposit 14 is lowered.

  When the glass fine particle deposit 14 moves downward in the core tube 11 and the upper space of the glass fine particle deposit 14 increases in the core tube 11, turbulent flow is generated in the upper space due to the rising air flow of the inert gas. There is.

  When such a turbulent flow occurs, as shown in FIG. 3, in an apparatus that does not include the partition plate 20, the pressure fluctuation in the core tube 11 becomes large and a negative pressure is generated. Outside air is likely to be caught in the core tube 11 through the gap with the seed rod 15. Thereby, impurities are likely to be mixed into the glass base material during sintering, and when the optical fiber is drawn from the sintered glass base material, transmission loss of the optical fiber may increase. In this case, if the amount of inert gas supplied into the core tube 11 is increased to suppress the entrainment of outside air, the amount of gas used increases and the cost increases.

  On the other hand, in this embodiment, when the glass particulate deposit 14 is lowered, a buffer space S is formed between the partition plate 20 and the lid portion 12 of the core tube 11. Therefore, even if a turbulent flow occurs in the upper space of the glass particulate deposit 14, the turbulent flow is blocked by the partition plate 20 as shown in FIGS. The pressure fluctuation caused by the turbulent flow is absorbed in the buffer space S and does not affect the sintered portion of the glass particulate deposit 14. Therefore, mixing of impurities into the glass base material during sintering can be prevented, and an optical fiber having good transmission characteristics can be obtained by drawing an optical fiber from the glass base material after sintering. be able to.

  Further, since the partition plate 20 is moved together with the glass fine particle deposit 14 when the glass fine particle deposit 14 is disposed on the upper side of the core tube 11, the upper space of the glass fine particle deposit 14 does not expand, and this space There is no turbulence. Therefore, it is possible to eliminate the need to increase the supply amount of the inert gas in order to suppress the entrainment of outside air. In addition, it is not necessary to increase the size of the facility in which a space serving as a buffer is provided in the core tube 11 in advance. As described above, it is possible to obtain a high-quality glass base material by satisfactorily sintering and reducing a defect rate while suppressing an increase in manufacturing cost and equipment cost.

  If the buffer space S does not have a dimension in the height direction of 500 mm or more, the outside air may pass through the buffer space S and enter the glass particulate deposit 14 side when the outside air is involved. Therefore, in the present embodiment, the partition plate 20 is disposed at a stop position separated by 500 mm or more from the upper end of the lid portion 12 to sufficiently secure the thickness of the buffer space S and prevent the outside air from being caught. . However, if the buffer space S becomes too large, turbulent flow is likely to occur in the buffer space S and the partition plate 20 enters the heat zone. Therefore, at least the partition plate 20 above the heat zone. Is arranged.

  In the above embodiment, the case where the glass fine particle deposit 14 is lowered to sinter along the longitudinal direction is exemplified. However, the glass fine particle deposit 14 can be sintered while being raised. In this case, first, the glass particulate deposit 14 is arranged on the lower side in the core tube 11 and the glass particulate deposit 14 is raised. The partition plate 20 is disposed at a stop position (position locked by the fastening portion 22) at the start of sintering, and only the glass fine particle deposit 14 is raised and sintered. The partition plate 20 is also moved upward together with the glass fine particle deposit 14 from the middle of the rise of the glass fine particle deposit 14 (predetermined position shown in FIG. 2A). Even in this case, although the upper space of the glass particulate deposit 14 becomes large in the furnace core tube 11 at the start of sintering, the partition plate 20 can perform the sintering without the influence of turbulent flow or pressure fluctuation.

  Moreover, in the said embodiment, although the flat cover part 12 was illustrated and demonstrated, the shape of a cover part is not restricted to this. It is good also as a cap-shaped lid part in which a buffer space is formed further above the upper end position of the core tube.

  An example in which a glass fine particle deposit is sintered in order to confirm the effects of the method and apparatus for producing a glass base material according to the present invention will be described.

Inner diameter of the core tube: 250 mm
Outer diameter of glass particulate deposit: 200mm
Sintering temperature: 1500 ° C

  As an example, the glass fine particle deposit is fired using a manufacturing apparatus (see FIG. 1) in which a partition plate is provided on the upper part of the glass fine particle deposit and the partition plate stays at a position 500 mm from the upper end of the lid. Tie. Further, as a comparative example, the glass fine particle deposit is sintered by a manufacturing apparatus (see FIG. 3) that does not include a partition plate.

  In each of the examples and comparative examples, the glass fine particle deposits are sintered by changing the supply amount of the inert gas, an optical fiber is manufactured from the obtained glass base material, and the transmission loss of each optical fiber is measured. FIG. 4 shows the result of calculating the occurrence rate of the defective fiber at each furnace gas flow rate, with the measured transmission loss being higher than the reference value as a defective fiber. In FIG. 4, the gas flow rate supplied to the extent that the turbulent flow does not affect the glass base material in a manufacturing apparatus (see FIG. 3) that does not include a partition plate is set to 100 (%). In both examples, the gas flow rate is expressed in proportion to this.

  As shown in FIG. 4, in the embodiment, even if the furnace gas flow rate is reduced by 20%, the transmission loss defect rate of the optical fiber does not increase. That is, it can be seen that in the example, the gas flow rate in the furnace can be reduced to 80% and the cost can be reduced without increasing the transmission loss defect rate.

  On the other hand, in the comparative example, the transmission loss defect rate of the optical fiber is rapidly increased by reducing the gas flow rate in the furnace. For example, when the gas flow rate in the furnace is reduced by 20%, the transmission loss defect rate of the optical fiber increases to exceed 80%. For this reason, in a manufacturing apparatus that does not include a partition plate, it is necessary to increase the supply amount of inert gas to prevent entrainment of outside air, resulting in an increase in cost because the amount of gas used is greater than in the embodiment. I understand that.

10: Manufacturing apparatus, 11: Core tube, 12: Lid, 13: Heater, 14: Glass particulate deposit, 16: Partition plate holder, 20: Partition plate, 22: Fastener

Claims (2)

While supplying an inert gas from the lower part of the core tube, the glass particulate deposit disposed in the core tube is moved downward or upward to be heated by the heat of the heat zone in the core tube and sintered. A method for producing a glass base material,
A lid is provided at the top of the furnace core tube, a partition plate is provided above the glass particulate deposit,
When the glass particulate deposit is above a predetermined position, the partition plate is moved together with the glass particulate deposit,
When the glass particulate deposit is below a predetermined position, the partition plate is disposed at a stop position 500 mm or more below the upper end of the lid, and only the glass particulate deposit is moved. The manufacturing method of the glass base material characterized. A reactor core tube that accommodates the glass particulate deposit suspended by the starting seed rod so as to be movable up and down;
A lid provided at the top of the furnace core tube;
A gas supply unit for supplying an inert gas into the furnace core tube from a lower part of the core tube;
A heat source provided on the outer peripheral side of the core tube,
A partition plate provided on the starting seed bar above the glass particulate deposit;
A partition plate holding part that is provided on the starting seed bar and supports the partition plate in the vicinity of the upper part of the glass particulate deposit;
A fastening part arranged to fasten the partition plate at a stop position 500 mm or more away from the upper end of the lid part, and
When the glass particulate deposit is above a predetermined position, the partition plate is moved together with the glass particulate deposit while being supported by the partition plate holder,
The glass base material manufacturing apparatus, wherein when the glass particulate deposit is below a predetermined position, the partition plate is restricted from moving by the fastening portion and only the glass particulate deposit is moved. .

Images