JP2014024693A - Method for producing glass preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a glass preform making it possible to produce a good porous glass preform in a highly productive manner.SOLUTION: A method for producing a porous glass preform G, in which fine glass particles are formed utilizing flame hydrolysis reaction, sprayed and deposited on a starting base material 14 using burners 15 and 16 having plural series of combustion gas supplying lines while the starting base material 14 is slowly moved upward, comprises controlling a flow rate of the plural series of combustion gas supplying lines in such a manner that the flow rate is larger at the time of starting the deposition of the fine glass particles than at the time of effective deposition when the deposition is performed at a specified flow rate and then slowly decreased down to the specified flow rate and that the flow rate of one or more of the series is lowered temporarily down to a value less than the specified flow rate for the series before the completion of the effective deposition and then increased up to the specified flow rate.

Description

  The present invention relates to a glass base material manufacturing method for manufacturing a porous glass base material by depositing glass fine particles.

  An optical fiber having a core and a cladding is manufactured by drawing a glass preform for an optical fiber to reduce the diameter. A VAD (Vapor Phase Axial Deposition) method is known as a method for producing a glass base material that is the basis of an optical fiber (for example, see Patent Documents 1 and 2). In this VAD method, glass fine particles are generated in a flame of a burner, and the generated glass fine particles are deposited on a starting base material made of quartz or the like, and the starting base material is gradually pulled up to form a cylindrical porous glass base material. This is a method of forming a (glass fine particle deposit).

Japanese Patent Laid-Open No. 7-242433 JP 2005-314209 A

  When a glass fine particle deposit is produced by synthesizing glass fine particles by the VAD method, it is necessary to deposit glass fine particles having a large bulk density on the starting substrate at the start of the deposition of the glass fine particles. For this reason, the flow rate of the combustion gas made of hydrogen gas is set higher than the predetermined flow rate at the time of depositing the effective portion, and then the flow rate is gradually decreased toward the predetermined flow rate. However, if the flow rate of the combustion gas is reduced, the bulk density of the glass fine particles to be deposited is reduced, and the growth rate of the glass fine particle deposit is increased. For this reason, when the flow rate of the combustion gas supplied to the burner is decreased toward the predetermined flow rate during the effective portion deposition, the growth rate of the glass particulate deposits rapidly increases and the shape of the deposition surface of the glass particulates changes. Or the pulling-up speed of the starting substrate is disturbed, and the glass fine particle deposit is easily deformed.

  As a countermeasure for this, for example, it is conceivable to reduce the rate of reducing the flow rate of the combustion gas to suppress the increase in the growth rate, but in this case, the time until the pulling rate becomes constant and the effective part is deposited. As a result, the manufacturing time of the glass fine particle deposit becomes longer, resulting in a decrease in productivity.

  The objective of this invention is providing the manufacturing method of the glass base material which can manufacture a favorable porous glass base material with sufficient productivity.

A method for producing a glass base material that can solve the above problems is a burner equipped with a plurality of combustion gas supply lines, in which glass fine particles are generated by a flame hydrolysis reaction with a raw material gas and sprayed onto a substrate. A glass base material manufacturing method for gradually raising the base material while producing a glass base material for porous glass while depositing,
The flow rates of the plurality of combustion gases at the start of the deposition of the glass particulates are gradually decreased toward the predetermined flow rate after increasing from the predetermined flow rates at the time of effective portion deposition. The flow rate of at least one system in the system is temporarily made smaller than the predetermined flow rate in the system before depositing the effective part of the glass fine particles, and then the flow rate is increased to the predetermined flow rate.

As the burner, using a multi-tube burner that ejects gas in different layers for each system,
The flow rate of the combustion gas supplied to the outermost layer of the multiple combustion gas systems is temporarily reduced below the predetermined flow rate in the system before the effective portion deposition of the glass particulates, and then the flow rate Is preferably increased to the predetermined flow rate.

  The flow rate that is temporarily less than the predetermined flow rate in the system is preferably 70% or more and 98% or less of the predetermined flow rate.

  According to the present invention, it is possible to suppress a rapid increase in the growth rate of the porous glass base material from the start of the deposition of the glass fine particles to the time when the effective part is deposited. The time will not increase. In addition, it is possible to suppress the occurrence of problems such as disturbance in the pulling speed and deformation of the shape of the deposited surface, and a glass base material can be manufactured stably. That is, a good porous glass base material can be manufactured with high productivity.

It is a schematic sectional drawing of the manufacturing apparatus used for the manufacturing method of the glass base material which concerns on this embodiment. It is a schematic side view in the front-end | tip part of the glass base material to manufacture. 4 is a graph showing a change in pulling rate immediately after the start of deposition of glass fine particles in Example 1. It is a graph which shows the change of the pulling-up speed immediately after the deposition start of the glass fine particle in the comparative example 1.

Hereinafter, an example of an embodiment of a manufacturing method of a glass base material concerning the present invention is explained with reference to drawings.
First, a manufacturing apparatus for manufacturing a glass base material will be described.
As shown in FIG. 1, the manufacturing apparatus 11 includes a reaction container 12 and is an apparatus for manufacturing a glass base material G of a porous glass body in the reaction container 12 by a VAD method. A suspension device 13 is provided on the upper portion of the reaction vessel 12. The suspension device 13 is moved up and down by a drive device (not shown) provided outside the reaction vessel 12. The suspension device 13 holds a starting base material (base material) 14 made of, for example, quartz glass, and the starting base material 14 is axially rotated while being rotated about the axis by the suspension device 13. It is possible to move along.

As shown in FIGS. 1 and 2, the reaction vessel 12 is provided with two burners 15, 16 at the lower part thereof. These burners 15 and 16 eject glass raw material gas and flame gas, generate glass fine particles by a flame hydrolysis reaction, and spray the glass fine particles toward the starting substrate 14. Each of the burners 15 and 16 is installed below the starting base material 14 and is inclined obliquely upward. The burner 15 is a cladding burner, and the burner 16 is a core burner. Each of the burners 15 and 16 is supplied with a glass source gas such as silicon tetrachloride (SiCl ₄ ), a combustion gas such as hydrogen (H ₂ ), an auxiliary combustion gas such as oxygen (O ₂ ), and the like from the gas supply unit 17. A purge gas such as argon (Ar) is supplied in a plurality of systems. The cladding burner 15 and the core burner 16 eject various gases supplied from a plurality of systems, respectively, and synthesize glass particles by flame hydrolysis.

  The burners 15 and 16 are multi-tube burners such as an 8-fold quartz glass burner having a plurality of ports (spout ports) concentrically, and jet gas from ports of different layers for each of a plurality of systems. .

  Glass fine particles synthesized by flame hydrolysis are deposited on the starting substrate 14 by the glass raw material gas and flame gas (combustion gas and auxiliary combustion gas) ejected from the burners 15 and 16. By gradually pulling up the starting base material 14 rotated about the axis while depositing the glass fine particles on the starting base material 14, a cylindrical porous glass body, which is a deposit of glass fine particles, is formed on the starting base material 14. A glass base material G is formed. The glass base material G is then dewatered and sintered into a transparent glass base material for an optical fiber, and the optical fiber base material is drawn to produce an optical fiber.

  A laser device 21 is provided below the reaction vessel 12. The laser device 21 includes a projector 22 that emits laser light L and a light receiver 23 that receives the laser light L. The light projector 22 and the light receiver 23 are provided on the outer side of the lower part of the reaction vessel 12 at positions facing each other with the reaction vessel 12 interposed therebetween. The laser light L emitted from the projector 22 passes through the reaction container 12 and reaches the light receiver 23, and is received by the light receiver 23. Based on the light reception signal from the light receiver 23, the deposition state (position of the deposition surface) of the glass particles on the glass base material G is monitored.

Next, a method for producing a porous glass base material G by depositing glass fine particles on the starting substrate 14 by the production apparatus 11 will be described.
First, the starting base material 14 is suspended from the suspension device 13, and the starting base material 14 is arranged at a predetermined position.

Next, while rotating the starting base material 14 around the axis, glass fine particles generated by flame hydrolysis with the glass raw material gas and the flame gas ejected from the burners 15 and 16 are sprayed onto the starting base material 14, and the glass fine particles are sprayed. To deposit.
In this state, the starting base material 14 is gradually pulled up by the suspending device 13 to form a columnar glass base material G that is a deposit of glass fine particles.

  At this time, the laser device 21 including the projector 22 and the light receiver 23 is used to monitor the deposition state of the glass fine particles, and while monitoring the tip position of the deposition surface, the lifting speed by the suspension device 13 is controlled to thereby reduce the predetermined diameter. The glass base material G is manufactured.

  When the porous glass base material G is produced by synthesizing the glass fine particles by the VAD method, the glass fine particles having a large bulk density are attached to the starting substrate 14 in order to obtain the strength of the deposit at the start of the glass fine particle deposition. There is a need. Therefore, at the beginning of the production of the glass base material G, the flow rate of the combustion gas in each system from the burners 15 and 16 is set to be larger than the predetermined flow rate at the time of depositing the effective part, and then gradually toward the predetermined flow rate. Reduce the flow rate.

  When the flow rate of the combustion gas is reduced, the temperature of the flame is lowered, the bulk density of the glass fine particles is lowered, and the growth rate of the glass base material G is increased. For this reason, when the flow rate is lowered toward the predetermined flow rate at the time of depositing the effective portion in all systems of the combustion gas in the burners 15 and 16, the growth rate of the glass base material G is rapidly increased, so that the starting substrate The glass base material G is likely to be deformed due to a disturbance in the pulling speed of 14 or a change in the shape of the deposition surface of the glass fine particles.

  On the other hand, in this embodiment, the flow rate of the combustion gas supplied to the outermost layer port among the plurality of combustion gas systems in each of the burners 15 and 16 which are multi-tube burners is set as the effective part deposition of glass particulates. After temporarily reducing the flow rate to be less than the predetermined flow rate in the system at the time of depositing the effective portion, the flow rate is increased to the predetermined flow rate.

  As described above, when the flow rate of the combustion gas in at least one system is temporarily made smaller than the predetermined flow rate at the time of depositing the effective part in that system and then gradually increased so as to become the predetermined flow rate, Acts in the direction of decreasing the growth rate. On the other hand, in other combustion gas systems, the growth rate is increased by gradually decreasing the flow rate of the combustion gas.

  Therefore, as a result, a rapid increase in the growth rate of the glass base material G on which the glass fine particles are deposited is suppressed, the pulling speed of the starting base material 14 is disturbed, or the shape of the deposition surface is deformed. There is no defect, and the glass base material G is stably formed.

  In a system in which the flow rate of the combustion gas is temporarily less than the predetermined flow rate at the time of effective portion deposition in the system before the effective portion deposition, the flow rate that is temporarily reduced is 70% or more of the predetermined flow rate at the time of effective portion deposition. % Or less is preferable. If the flow rate is less than 70% with respect to the predetermined flow rate at the time of depositing the effective part of the system, the growth rate is increased at that point, and the deformation of the glass base material is promoted. Further, if the flow rate is larger than 98% with respect to the predetermined flow rate when depositing the effective portion of the system, the effect of lowering the growth rate cannot be obtained sufficiently, and the effect of suppressing the disorder of the pulling rate and the deformation of the deposition surface can be obtained. I can't. The flow rate that is temporarily reduced is more preferably 90% or more and 95% or less of the predetermined flow rate when the effective part of the system is deposited.

  As described above, according to the manufacturing method of the glass base material G according to the present embodiment, the flow rate of the combustion gas of each system at the start of the deposition of the glass fine particles is set higher than the predetermined flow rate at the time of depositing each effective part. While gradually reducing the flow rate toward each predetermined flow rate, the flow rate in at least one combustion gas system is temporarily made smaller than the predetermined flow rate at the time of depositing the effective part in the system before the effective part deposition of the glass particulates. Thereafter, the flow rate is gradually increased so that the predetermined flow rate is obtained. As a result, a rapid increase in the growth rate of the glass base material G can be suppressed, and the glass base material G can be stably manufactured without problems such as disorder of the pulling speed and deformation of the shape of the deposition surface. In addition, the growth rate is slower than necessary and the time until the effective part is deposited does not increase. Thus, a good glass base material G can be manufactured with high productivity.

  Moreover, in the burners 15 and 16 which consist of a multi-tube burner, since a cross-sectional area becomes large as an outer port, the flow volume of the gas sent through an outer port tends to increase more than an inner port. On the other hand, in the combustion gas, the ratio of the change amount of the growth rate to the change amount of the combustion gas flow rate becomes larger in the inner port. Therefore, if the gas flow rate of the combustion gas in the inner port is temporarily greatly reduced, the growth rate may be drastically reduced, and instead deformation may be promoted. Therefore, gradually reducing the gas flow rate of the combustion gas at the inner port from the start of deposition, and temporarily decreasing the flow rate of the outer port and then increasing the flow rate, It is easy to suppress the change and is more preferable.

  In the present embodiment, the VAD method using the cladding burner 15 and the core burner 16 has been described. However, there may be one burner or more than two. In any one or more of the burners to be used, the growth rate of the glass base material G is rapidly increased by applying control for temporarily reducing the flow rate of the combustion gas as described above to a predetermined flow rate at the time of depositing the effective portion. The effect of suppressing the rise is obtained. Further, in the case where the cladding burner 15 and the core burner 16 are used as described above, the above control is performed only on the core burner 16 that deposits glass particles in the vicinity of the starting base material 14 and affects the pulling speed. Even if applied, a sufficient effect can be obtained.

  Even when a burner having a structure other than the multi-tube burner is used, the above control can be applied if there are a plurality of combustion gas systems.

(1) Evaluation method A glass base material of a porous glass body, which is a glass particulate deposit, is manufactured using two octuplicated quartz glass burners, and the pulling speed is disturbed and the glass base material is deformed. The presence or absence was evaluated.
The glass base material includes a core part and a clad part, and the core part and the clad part are formed by two respective burners. The formed glass base material has an outer diameter of the core part of 40 mm and an outer diameter of the clad part of 150 mm.
When manufacturing the glass base material, a part of the laser light from the projector of the laser device is shielded at the tip of the glass base material, and the area of the laser light is constant so that the area of the laser light is constant. The pulling speed was controlled.

(2) Gas flow control (Example 1)
The gas flow rate of the burner for synthesizing the glass particles in the core part was set as shown in Table 1 according to the time from the start of deposition. In each gas supply system, the predetermined flow rate at the time of depositing the effective portion is set after 120 minutes from the start of deposition.
Specifically, the glass raw material gas (SiCl ₄ , GeCl ₄ ) and the auxiliary combustion gas (O ₂ ) were set so that the flow rates gradually increased from 120 minutes after the start. Further, the gas flow rate of the combustion gas (H ₂ ) was set to be larger than the predetermined flow rate at the start of deposition and gradually decreased. In the system of the sixth layer of the combustion gas system, the flow rate is gradually reduced from immediately after the start, and after 90 minutes from the start, the flow rate is temporarily reduced from the predetermined flow rate at the time of depositing the effective portion, Thereafter, the flow rate was set to increase 120 minutes after the start. In addition, the gas flow rate of each layer was set to a constant flow rate as a predetermined flow rate at the time of depositing the effective portion from 120 minutes to the end of deposition. The inert gas (Ar) was always kept at a constant flow rate from the start of deposition.

(Comparative Example 1)
The gas flow rate of the burner for synthesizing the glass particles in the core was set as shown in Table 2 according to the time from the start of deposition.
The difference from Example 1 in Comparative Example 1 is the gas flow rate of the combustion gas (H ₂ ) in the sixth layer. In Comparative Example 1, the flow rate was set to gradually decrease from 120 minutes after the start of all combustion gas systems.

(3) Evaluation results (Example 1)
As shown in FIG. 3, the pulling rate (mm / hour) immediately after the start of deposition of the glass fine particles gradually increases from 120 minutes after the start of deposition, and is almost stable after 120 minutes. The base material could be manufactured.

(Comparative Example 1)
As shown in FIG. 4, the pulling rate immediately after the start of the deposition of the glass fine particles suddenly increased after 90 minutes from the start of the deposition, and after 120 minutes, the pulling rate was disturbed to repeatedly increase and decrease. Further, at this time, the deposition portion of the glass fine particles in the core portion was deformed, and the glass base material could not be manufactured stably.

11: Manufacturing apparatus, 14: Starting base material (base material), 15, 16: Burner, G: Glass base material

Claims (3)

A burner equipped with multiple lines of combustion gas supply lines. While producing fine glass particles by flame hydrolysis reaction with the raw material gas and spraying and depositing them on the base material, the base material is gradually pulled up to form porous glass. A glass base material manufacturing method for manufacturing a glass base material,
The flow rates of the plurality of combustion gases at the start of the deposition of the glass particulates are gradually decreased toward the predetermined flow rate after increasing from the predetermined flow rates at the time of effective portion deposition. A glass mother characterized in that the flow rate of at least one system is temporarily made lower than the predetermined flow rate in the system before depositing the effective portion of the glass fine particles, and then the flow rate is increased to the predetermined flow rate. A method of manufacturing the material. It is a manufacturing method of the glass base material of Claim 1,
As the burner, using a multi-tube burner that ejects gas in different layers for each system,
The flow rate of the combustion gas supplied to the outermost layer of the multiple combustion gas systems is temporarily reduced below the predetermined flow rate in the system before the effective portion deposition of the glass particulates, and then the flow rate Is increased to obtain the predetermined flow rate. A method for producing a glass base material according to claim 1 or 2,
The method for producing a glass base material, characterized in that a flow rate that is temporarily less than the predetermined flow rate in the system is 70% or more and 98% or less of the predetermined flow rate.

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