JP2002167223A - Burner for synthesizing porous glass base material and manufacturing method for porous glass base material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a porous glass base material in a short time by increasing buildup efficiency and synthesizing velocity drastically. SOLUTION: In a burner for synthesizing the porous glass base material in which a raw material gas for glass is ejected from the center nozzles and flame is formed by oxygen gas and hydrogen gas blown from the outside periphery to produce fine glass powders by hydrolysis reaction or thermoxydation reaction, the center nozzle is composed of a plurality of glass raw material gas nozzles 6, and each of them is arranged in one line to the moving direction of the glass target rod 2 or the burner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a burner for synthesizing a porous glass base material and a porous glass for producing glass fine particles by subjecting a glass raw material gas to a hydrolysis reaction or a thermal oxidation reaction using oxygen gas and hydrogen gas. More specifically, in a method for manufacturing a preform for an optical fiber by an external VAD method, an optical fiber for efficiently depositing porous glass particles and producing a soot preform having a predetermined diameter in a short time. The present invention relates to a burner for synthesizing a porous glass base material used when manufacturing a base material for use.

[0002]

2. Description of the Related Art As a technique for synthesizing a porous glass base material for producing an optical fiber, there is the following technique. That is, a combustion supporting gas (for example, oxygen gas) and a flammable gas (for example, hydrogen gas) are ejected from the burner to form a flame, and a glass raw material gas (for example, silicon tetrachloride or germanium tetrachloride) is injected into the flame. The glass particles are supplied to produce glass fine particles by a flame hydrolysis reaction or a thermal oxidation reaction. The generated glass fine particles are sprayed onto a glass target rod including the core of the optical fiber until a predetermined diameter is reached. This method is called an external VAD method and is a technique for synthesizing a porous glass base material having excellent productivity.

[0003] Such a burner used in the external VAD method conventionally discharges a glass material gas (for example, silicon tetrachloride) from a single central nozzle and emits a flame of oxygen gas and hydrogen gas from the outer periphery thereof. It is a structure to generate. This structure includes a multi-tube burner type (multi-tube structure) such as a nine-pipe burner that ejects oxygen gas, hydrogen gas, and inert gas from a plurality of ports installed concentrically with the center of the burner around the center nozzle. There is a so-called multi-burner type in which a plurality of small-diameter oxygen ejection ports are arranged around a central nozzle.

[0004]

However, in the case of such a burner that supplies a source gas from one central nozzle (same as a source gas nozzle), the synthesis rate of the porous glass base material [g / min] (1 SiO ₂ deposited per minute
If the diameter of the source gas nozzle is too large, the source gas does not hit the target and escapes when the target, which is the starting base material, is thin, so that the source gas is wasted.

On the contrary, when the diameter of the material nozzle is too small, the gas flow becomes too large, the distance of the hydrolysis reaction of the material gas ejected from the material gas nozzle becomes small, the synthesis rate is saturated, and the deposition efficiency ( reducing the SiO ₂ ratio) deposited against the jetted material gas amount, the soot diameter (soot takes very long time to increase the porous glass fine particles) to a predetermined diameter.

Further, the glass particles which have not adhered are
The glass particles floating in the reaction chamber adhere to the target rod again, causing glass defects such as air bubbles. Further, since the temperature of the suspended glass particles is low, the bulk density (the weight of the porous glass particles per unit deposition) of the porous glass base material is rapidly reduced, and cracks are generated. Dust removal equipment (eg, scrubber)
There are many glass particles that need to be removed by the method, and the burden on the dust removal device and the running cost for the removal are very large.

In order to reduce the cost of an optical fiber,
It is important to reduce the deposition time required to increase the soot diameter to a predetermined diameter, to efficiently deposit the supplied glass raw material gas, and to eliminate glass defects such as bubbles and cracks.

To summarize the above, the problems of the prior art are as follows. (1) Since the deposition efficiency up to the saturated soot diameter and the synthesis rate are low, the deposition time is long. (2)
The SiO ₂ powder that has not adhered floats and causes bubbles and cracks. (3) SiO ₂ to be removed due to (1) above
A large amount of powder increases the burden and running cost of the dust removal device.

Accordingly, an object of the present invention is to solve the above-mentioned problems, dramatically improve the deposition efficiency and the synthesis rate, and make it possible to produce a porous glass base material in a short time. The object of the present invention is to improve the optical fiber characteristics by minimizing non-adhered glass particles that cause bubbles and cracks by improving the optical fiber characteristics.

[0010]

Means for Solving the Problems In order to achieve the above object, the present invention is configured as follows.

(1) The burner for synthesizing a porous glass base material according to the first aspect of the present invention ejects a glass raw material gas from a central nozzle and generates a flame of oxygen gas and hydrogen gas from the outer periphery thereof, thereby hydrolyzing. In a burner for synthesizing a porous glass base material that generates glass fine particles by a reaction or thermal oxidation reaction, the central nozzle is constituted by a plurality of glass material gas nozzles, and each glass material gas nozzle is disposed in the direction in which the target or the burner moves. It is characterized by being arranged in a row.

In the burner for synthesizing a porous glass base material of the present invention, oxygen gas, hydrogen gas and inert gas are spouted from a plurality of ports installed concentrically with the center of the burner around a central nozzle for spouting glass raw material gas. And a multi-tube burner type in which a plurality of small-diameter oxygen jet ports are arranged around a central nozzle.

(2) The invention of claim 2 is characterized in that, in the burner for synthesizing a porous glass base material of claim 1, the plurality of glass material gas nozzles are collectively installed inside an inert gas nozzle. I do.

The reason why the inert gas nozzle (inert gas jet nozzle) is provided is to prevent glass particles from adhering to the tip of the burner. A cylindrical port or a non-cylindrical port formed concentrically with the center of the burner is provided. It may be provided as an annular port, or may be provided as an annular port or a non-annular port formed concentrically with the center of the burner. In any of the embodiments, the inert gas ejection nozzle is not installed concentrically with each of the glass material gas nozzles.

(3) The invention of claim 3 is the invention of claim 1 or 2
In the burner for synthesizing a porous glass base material of the above, the inner diameter of each glass raw material gas nozzle arranged in the above-mentioned one row is calculated from the initial target diameter a and the final diameter b by the following equation

[0016]

(Equation 2)

The average synthesizing speed is set to be maximum.

(4) In the method for manufacturing a porous glass preform according to the invention of claim 4, a glass raw material gas is jetted from a central nozzle of a burner for synthesizing a porous glass preform, and oxygen gas and hydrogen are discharged from the outer periphery thereof. A gas flame is generated, and a hydrolysis reaction or a thermal oxidation reaction is performed to generate glass fine particles, which are reciprocated along an axial direction relative to a rotating target including a core of an optical fiber, In the method for manufacturing a porous glass base material that is sprayed and deposited to a predetermined diameter on the outer periphery of a target, the central nozzle is configured by a plurality of glass raw material gas nozzles as the burner for synthesizing the porous glass base material, A burner in which glass source gas nozzles are arranged in a row in a direction in which the target or the burner moves is used.

(5) The invention according to claim 5 is the method for producing a porous glass base material according to claim 4, wherein an inert gas is blown from around the plurality of glass raw material gas nozzles, and It is characterized in that adhesion of fine particles is prevented.

(6) The invention of claim 6 is the invention of claim 4 or 5
In the method for manufacturing a porous glass preform according to the above, as the burner for synthesizing the porous glass preform, when the inner diameters of the plurality of glass raw material gas nozzles are deposited from an initial target diameter to a final diameter, the average synthesis rate is the maximum. It is characterized by using a burner designed to be as follows.

<The gist of the invention> The gist of the present invention is that the glass raw material gas nozzles of the burner for synthesizing the porous glass base material are arranged in one row, and the direction of the row is the same as the direction in which the target or the burner moves. It is in.

By doing so, (i) when the target which is the starting base material is thin, it is possible to avoid the inconvenience that the source gas does not hit the target and escapes because the diameter of the source gas nozzle is too large. ii) Conversely, if the diameter of the raw material nozzle is too small, the flow of the gas becomes too large, the distance at which the raw material gas ejected from the raw material gas nozzle undergoes a hydrolysis reaction is reduced, and the synthesis rate is saturated, thereby decreasing the deposition efficiency. Inconvenience can be avoided.

Therefore, by using the burner of the present invention, it is possible to improve the deposition efficiency and the synthesis speed, and to shorten the working time (the deposition time).

Further, since the deposition efficiency is improved, the glass fine particles floating in the reaction chamber do not adhere again, and a preform for an optical fiber free of bubbles and cracks can be manufactured.

Another point of the present invention is that, at the moment when silicon tetrachloride ejected from the glass material gas nozzle of the burner comes out of the nozzle during deposition, glass particles produced by a hydrolysis reaction adhere to the tip of the burner. In order to prevent this, the plurality of glass material gas nozzles are collectively installed inside the inert gas nozzle. In this form, as a normal form, an annular port (see the annular port 21 in FIG. 6) is provided around the glass material gas nozzle concentrically with the glass material gas nozzle, and an inert gas (for example, Ar) may be ejected. However, since a plurality of glass material gas nozzles are used in the present invention, preferably, a plurality of glass material gas nozzles are collectively installed inside a cylindrical or non-cylindrical inert gas nozzle. (See FIG. 1).
In any of the embodiments, the present invention is characterized in that an inert gas jet nozzle for preventing glass particles from adhering to the tip of the burner is not provided concentrically with each glass material gas nozzle. .

Another point of the present invention is that a plurality of source gas nozzles are designed such that the average synthesis rate becomes maximum when the inner diameters of the plurality of source gas nozzles are deposited from an initial target diameter a [mm] to a final diameter b [mm]. On the point. The following formula

[0027]

(Equation 3)

The point is to design so that the maximum value is obtained.

<Supplementary Explanation of the Invention> In the present invention, the glass raw material gas nozzles are arranged in a line along the moving direction of the target or the burner, and the larger the number, the more effective. The synthesis speed increases in proportion to the number of nozzles, and the deposition time can be further reduced. The shape of the inert gas nozzle used in the present invention is basically a circle,
It can be oval or square. Similarly, the same effect can be obtained for the shape of the entire burner also for an ellipse or a square.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the illustrated embodiment.

FIG. 4 shows an external VAD method employed in the method of manufacturing an optical fiber preform according to the present embodiment. This method
As shown in FIG. 4, both ends of the glass target are fixed by a chuck 1 using a core glass corresponding to the core of the optical fiber or a glass target rod 2 containing the core glass and a part of the clad as a starting member (target). Rotate around its axis. On the other hand, silicon tetrachloride as a raw material gas, hydrogen as a fuel gas, and oxygen as an auxiliary fuel gas are supplied to one or more soot generation burners 5, and glass fine particles are sprayed from the burner 5 together with the combustion flame 4. . This deposits the porous soot base material 3 by reciprocating the glass target rod 2 and the burner 5 relatively along the axial direction of the target, ie, traversing the glass target rod 2 and the burner 5 while depositing the glass particles on the outer periphery of the rotating target. is there. The speed of the traverse may be the same as or different from the speed of the reciprocating movement in the forward path and the return path.

FIGS. 5 (a) and 5 (b) show graphs of the synthetic speed y [g / min] with respect to the soot diameter x [mm]. The synthesis rate is the weight of SiO ₂ adhered per unit time.
As can be seen from the graph of y (x), when the soot diameter of each burner reaches a certain diameter (saturated soot diameter),
At a soot diameter larger than that, there is a region where the synthesis speed is in a saturated state (saturation synthesis speed) where the synthesis speed does not change much. The soot diameter at which saturation starts is defined as “saturated soot diameter”. Also,
The saturated synthesis rate above the saturated soot diameter is defined as “saturated synthesis rate”. This saturated soot diameter Xs is shown in FIG.
As shown in (a), the tangent line A from the origin of the rise of the curve of y (x) and the value of the saturation synthesis speed Ys (20 g / mi)
Focusing on the straight line B in n), the soot diameter Xs corresponding to the intersection C where the two intersect is obtained. In the case shown, the saturated soot diameter Xs is about 90 mmφ.

By the way, as described above, the average synthesizing speed until the porous glass base material is deposited from the initial target diameter a [mm] to the final diameter b [mm] is f () at an arbitrary target diameter. x), it is obtained by the following equation.

[0034]

(Equation 4)

However, the initial glass target diameter is a [mm]
And the final diameter after deposition is b [mm].

As can be seen from the above equation, f (x) and x
The larger the area enclosed by the axis and the integral range represented by the above equation, the greater the average synthesis rate until one porous glass base material is deposited, and the faster the deposition time. In other words,
This means that the supplied glass raw material gas is efficiently deposited.

Therefore, in order to efficiently and efficiently deposit the supplied glass raw material gas and shorten the deposition time, the saturated soot diameter Xs is reduced and the saturated synthesis speed Y is reduced.
It is understood that s should be increased.

Therefore, it was examined how the important parameters, the saturated soot diameter Xs and the saturated synthesis speed Ys, change with respect to the glass material gas nozzle diameter.

<Comparative Examples 1-4, FIG. 6> As a comparative example, as shown in FIG. 6, a burner 5 having a single central glass nozzle composed of a glass material gas nozzle 6 was experimentally manufactured and used.
The glass material gas, silicon tetrachloride, is supplied from the single central nozzle, and a plurality of small-diameter oxygen nozzles (a plurality of small-diameter oxygen ejection ports) are provided around the glass material gas nozzle 6 concentrically with the center of the burner. 7) was provided, and oxygen was ejected therefrom. Hydrogen was ejected from a port 8 formed by a gap around the plurality of small-diameter oxygen nozzles 7.

Further, the jet structure of the oxyhydrogen has a double structure of the inner layer nozzle 9 and the outer layer nozzle 10. The reason for the double structure is as follows. That is, (i) when the deposited porous glass base material is thin, oxygen on the inside,
The hydrolysis reaction is carried out only with hydrogen, and oxygen and hydrogen on the outer side are ejected in accordance with the gradually increasing diameter of the porous glass base material, thereby preventing a decrease in the bulk density of the fine particles of the porous glass base material. (ii) Further, when a plurality of burners for forming a porous glass base material are arranged side by side, interference of a flame is suppressed as much as possible and deposition efficiency is improved. However, in this experiment, in order to clarify the relationship between the deposition efficiency and the synthesis rate by the glass raw material gas nozzle, oxygen and hydrogen gas were ejected from the inside and outside from the initial stage of the deposition to cause a hydrolysis reaction.

Further, concentric annular ports 21 and 22 are provided around the central nozzle 6 from the central nozzle 6 and silicon tetrachloride as a glass raw material gas.
In order to prevent porous glass particles from adhering to the tip of the burner, argon gas (inside seal A)
r) was ejected. Finally, argon gas (outer seal Ar) is also supplied from the outermost annular nozzle (port 22).
Erupted.

Next, in the configuration shown in FIG. 6, the diameter of one central glass material gas nozzle 6 is 2 mmφ,
Burners having structures of 3 mmφ, 4 mmφ, and 6 mmφ were prepared, and these were designated as Comparative Examples 1 to 4. These were used to compare the synthesis rate [g / min] with the porous glass base material (soot diameter), which gradually increased during deposition.

However, these burner structures have the same dimensions and structure except for the diameter of the glass material gas nozzle 6, and the flow rates of hydrogen gas, oxygen gas, inert gas and silicon tetrachloride gas used at the time of deposition are also the same. I made it. Further, their gas flow rates were kept constant irrespective of the diameter of the porous glass base material gradually increasing. Specifically, silicon tetrachloride = 42 × 2 [g / min], inner oxygen = 17 × 2 [l /
min], inner hydrogen = 32 × 2 [g / min], outer oxygen =
18 × 2 [l / min], outer hydrogen = 38 × 2 [l / min]
], A carrier Ar for transporting silicon tetrachloride = 0.
3 × 2 [l / min], inner seal Ar = 1 [l / min]
] And the outer seal Ar = 15 [min]. The rotation speed of the target and the relative movement speed between the burner and the target were fixed at 40 rpm and 120 mm / min, respectively.

In the experiment, a soot base material having a length of 2000 mm and a diameter of 220 mmφ was manufactured using a 10 mmφ quartz rod as a starting target. Then, deposition was performed while measuring the weight of the attached glass fine particles, and the synthesis rate (the weight of SiO ₂ deposited per minute) was calculated from the weight. FIG. 7 shows the result.

As can be seen from FIG. 7, the saturation synthesis rate is determined by the glass material gas nozzle diameters of φ2, φ3, φ4, φ6.
(Mm). This is because, as the diameter of the glass raw material gas nozzle 6 becomes larger, the flow velocity of the raw material gas becomes smaller, the distance over which the raw material gas ejected from the burner reacts becomes longer, and the distance required for producing glass particles is sufficient. .

However, the larger the diameter of the glass raw material gas nozzle, the larger the diameter at which the synthesis rate starts to saturate. That is, the saturated soot diameter is large. In other words, when the target diameter is small (the soot diameter is small), it indicates that the deposition efficiency is poor. This is because the source gas ejected from the source gas nozzle has a large spread, and some of the glass fine particles generated by reacting with the flame escape without hitting the target, and the glass fine particles are wasted.

In order to improve the deposition efficiency (average deposition efficiency) until the final diameter of the porous glass base material and increase the average synthesis rate, not only the saturation synthesis rate is high but also the
The synthesis speed when the target diameter (soot diameter) is small also becomes important. That is, it is also important to reduce the saturated soot diameter.

FIG. 8 shows the ideal direction of the burner characteristics. In order to improve the synthesis rate and the deposition efficiency, FIG.
The point is to shift the curve to the left and further to the direction of the up arrow, as indicated by the arrow inside.

From the previous experiment, in order to reduce the saturated soot diameter, the diameter of the glass material gas nozzle was reduced in order to shift the burner characteristic in FIG. This is to deposit the source gas.

In order to further increase the saturation synthesis speed, it is necessary to increase the diameter of the glass material gas nozzle in order to shift the burner characteristics in FIG.
That is, by increasing the cross-sectional area of the glass material gas nozzle and decreasing the ejection speed (flow velocity) of the glass material gas, the reaction distance of the glass material gas is increased.

<Burner of the present embodiment> From the above,
The following burner was invented. FIG. 1 shows a structure of a burner 5 according to one embodiment of the present invention. Fig. 6 except for the center nozzle
It has the same structure as.

In order to form a plurality of ports concentrically with the center of the burner around the central nozzle for ejecting the glass raw material gas, cylindrical inert gas nozzles 11 and 13 are provided inside the annular ring for oxygen gas and hydrogen gas. A layer nozzle 9 also has an annular outer layer nozzle 10 for oxygen gas and hydrogen gas. The structure of the inner layer nozzle 9 and the outer layer nozzle 10 is shown in FIG.
Oxygen nozzles 7 composed of a plurality of small-diameter oxygen jet ports are arranged at equal intervals in the circumferential direction around the center nozzle, more precisely, around the inert gas nozzle 13 (port 22). In this structure, hydrogen is ejected from a port 8 formed by a peripheral gap.

The diameter of the glass raw material gas nozzle 6 is 2 mmφ (inner diameter) which has a small saturated soot diameter and can attach fine glass particles to a thin glass target at a pinpoint.
And four of them were arranged in a row in the moving direction of the glass target or the burner. Further, in order to reduce the size of the burner 5, the glass raw material gas nozzles 6 were densely installed without leaving any interval. The glass material gas was supplied to the burner 5 with a single supply port, so that the gas was uniformly supplied to four glass material gas (spouting) nozzles 6.

Accordingly, the total sectional area of the four glass material gas nozzles 6 is a burner-shaped nozzle diameter of 4 mmφ in FIG. 6 in which one glass material gas nozzle is installed at the center of the burner.
Is the same as the cross-sectional area. Therefore, the flow velocity of the glass raw material gas ejected from the burner becomes equal.

The glass raw material gas nozzles 6 arranged in a line are collectively installed in the seal Ar gas region 12 inside the cylindrical inert gas nozzle 11 in order to prevent glass particles from adhering to the tip of the burner. did.

Using the burner of the present invention configured as described above, the relationship between the synthesis rate and the diameter of the porous glass base material (soot diameter) was examined. The conditions of the experiment (the burner structure and dimensions other than the gas flow rate and the source gas nozzle diameter, the target rotation speed, and the moving speed) were all the same as those in the previous experiment. The result is shown in FIG. In FIG. 2, the solid line indicates the burner characteristics of the present invention, and the broken line indicates the burner characteristics of the burner (glass raw material gas nozzle diameter φ4) of FIG.

As is clear from FIG. 2, the burner of the present invention (solid line) has a saturated soot diameter Xs (see FIG. 5) smaller than that of the conventional burner (broken line). That is, in the prior art (broken line), the saturated soot diameter Xs
= X2 is about 100 mmφ, whereas in the burner of the present invention, the saturated soot diameter Xs = x2 is considerably small at about 20 mmφ.

Further, the saturated synthesis rate is equal because the velocity (flow velocity) of blowing the glass raw material gas from the burner of the present invention is equal to the flow velocity of the conventional burner.

Assuming that the initial diameter of the glass target is 10 mmφ and this is deposited to a diameter of 150 mmφ, the average synthesis rate of the burner of the prior art is 11.9 [g / min], whereas the average synthesis rate of the burner of the present invention is 11.9 g / min. The average synthesis rate is 16.1
[G / min]. The improvement is about 1.35 times that of the burner structure of FIG.
As a result, the deposition time (working time) could be reduced by about 26%.

Similarly, the deposition efficiency (the ratio of SiO ₂ adhered to the amount of ejected source gas) is also improved by about 1.35 times, and the glass particles can be adhered to the target without waste.

The porous glass preform deposited by the burner of the present invention and sintered and transparent vitrified did not show any glass defects such as air bubbles, and was a good optical fiber glass preform.

<Other Embodiments> A burner according to the present invention is one in which glass raw material gas nozzles are arranged in a line along the moving direction of a target or a burner, and four burners are arranged in a line as in the above embodiment. In addition, the desired effect of the present invention can be obtained even if the number of lines arranged in one row is changed to two, three, five, six, etc., but the larger the number of glass material gas nozzles, the more effective It is. The synthesis speed increases in proportion to the number of nozzles, and the deposition time can be further reduced.

Although the inert gas jet nozzles (seal Ar nozzles) 11 and 13 used in FIG. 1 are circular, they may be elliptical as shown in FIG. , Pentagon, hexagon, etc. Similarly, the shape of the entire burner can be an ellipse, a polygon such as a square, a pentagon, or a hexagon, and the same effect as in the case of a circle can be obtained.

Further, the nozzle diameter of the plurality of glass raw material gases is 2 mm in inner diameter in the above embodiment, but the following formula is used depending on the initial glass target and the soot diameter after deposition.

[0065]

(Equation 5)

The point is to design so that the maximum value is obtained.

[0067]

As described above, according to the present invention, the glass raw material gas nozzles of the burner for synthesizing the porous glass base material are arranged in one line, and the direction of the line is the same as the direction in which the target or the burner moves. Therefore, it is possible to avoid the disadvantage that the raw material gas nozzle diameter is too large and the raw material gas does not hit the target and escapes when the target as the starting base material is narrow, and (ii) conversely, If the nozzle diameter is too small, the gas flow becomes too large, the distance in which the raw material gas ejected from the raw material gas nozzle undergoes a hydrolysis reaction becomes small, and the inconvenience of reducing the deposition efficiency by saturating the synthesis rate can be avoided. it can.

Therefore, by using the burner of the present invention, the deposition efficiency and the synthesis speed can be improved, and the working time (deposition time) can be reduced.

Further, since the deposition efficiency is improved, the glass fine particles floating in the reaction chamber do not adhere again, and a preform for an optical fiber free of bubbles and cracks can be manufactured.

Also, by adopting such a configuration,
When the inner diameters of the plurality of source gas nozzles are deposited from the initial target diameter to the final diameter, the average synthesis rate can be designed to be maximum.

Further, since the plurality of glass raw material gas nozzles arranged in a line are collectively installed inside the inert gas nozzle, it is possible to collectively prevent glass fine particles generated by each glass raw material gas nozzle from adhering to the tip of the burner. Can be prevented.

[Brief description of the drawings]

FIG. 1 is a view showing a structure of a burner for synthesizing a porous glass base material of the present invention.

FIG. 2 is a view showing a relationship between a soot diameter and a synthesis speed by a burner for synthesizing a porous glass base material of the present invention.

FIG. 3 is a view showing another structural example of a burner for synthesizing a porous glass base material of the present invention.

FIG. 4 is a diagram showing an outline of an external VAD method employed in the method for producing a porous glass base material of the present invention.

5 is a graph showing a relationship between a saturated soot diameter and a saturated synthesis rate in the manufacturing method of FIG.

FIG. 6 is a view showing a structure of a burner for synthesizing a porous glass base material prepared for comparison.

FIG. 7 is a diagram showing characteristics of a comparative burner having the structure of FIG. 6, using a change in the diameter of a glass source gas nozzle at the center thereof as a parameter.

FIG. 8 is a diagram showing the directionality of ideal burner characteristics derived from the characteristics of FIG. 7;

[Explanation of symbols]

 2 Glass target rod 3 Porous soot base material 4 Flame 5 Burner 6 Glass material gas nozzle 7 Oxygen nozzle 8 Port (gap) 9 Inner layer nozzle 10 Outer layer nozzle 11, 13 Inert gas nozzle 12 Seal Ar gas area

Claims (6)

[Claims] 1. A porous glass preform that spouts a glass raw material gas from a central nozzle and generates a flame of oxygen gas and hydrogen gas from the outer periphery thereof, and causes a hydrolysis reaction or a thermal oxidation reaction to generate glass fine particles. A burner for synthesizing a porous glass base material, wherein the central nozzle is constituted by a plurality of glass material gas nozzles, and the glass material gas nozzles are arranged in a line in a direction in which the target or the burner moves. 2. The porous glass preform synthesis burner according to claim 1, wherein said plurality of glass raw material gas nozzles are collectively installed inside an inert gas nozzle. Burner. 3. The burner for synthesizing a porous glass base material according to claim 1, wherein the inner diameter of each of the glass raw material gas nozzles arranged in one row is determined by the following equation from the initial target diameter a and the final diameter b. 1) A burner for synthesizing a porous glass base material, characterized in that the average synthesizing speed is set to be maximum. 4. A glass raw material gas is jetted from a central nozzle of a burner for synthesizing a porous glass base material, and a flame of oxygen gas and hydrogen gas is generated from the outer periphery thereof, and a hydrolysis reaction or a thermal oxidation reaction is carried out to produce glass fine particles. A porous glass mother which is sprayed and deposited to a predetermined diameter on the outer periphery of the target while reciprocating along the axial direction relative to the rotating target including the core of the optical fiber, and depositing the same. In the method for producing a material, as the burner for synthesizing a porous glass base material, the burner in which the central nozzle is constituted by a plurality of glass material gas nozzles, and each glass material gas nozzle is arranged in a row in a direction in which the target or the burner moves. A method for producing a porous glass base material, comprising: 5. The method of manufacturing a porous glass base material according to claim 4, wherein an inert gas is blown from around said plurality of glass raw material gas nozzles to prevent glass particles from adhering to the burner tip. A method for producing a porous glass base material. 6. The method for producing a porous glass base material according to claim 4, wherein the burner for synthesizing the porous glass base material has an inner diameter of the plurality of glass raw material gas nozzles.
A method for producing a porous glass base material, comprising using a burner designed to maximize the average synthesis rate when deposited from an initial target diameter to a final diameter.