JP2003119035A - Method for producing porous glass base material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a porous glass base material by depositing glass particles one by one on a surface of a starting rod while relatively reciprocating a starting rod and a burner for synthesizing glass particles in parallel. A method of manufacturing a porous glass base material capable of suppressing variation in outer diameter in the base material length direction with a simpler device configuration. SOLUTION: In the method, in a state where a burner is set in a reaction vessel, a ventilation port is provided near a burner intake point of the reaction vessel, and a gas such as air or an inert gas is directed from the ventilation port toward a base material. A method for producing a porous glass base material, characterized by supplying.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous glass matrix for depositing glass fine particles synthesized by a burner one by one on the surface of a starting rod while relatively reciprocating a starting rod and a burner for synthesizing glass fine particles. The present invention relates to a method for manufacturing a material.

[0002]

2. Description of the Related Art As a method for producing a large-sized porous glass preform at a high speed, a plurality of burners for synthesizing glass particles are arranged at regular intervals so as to face a starting rod in a reaction vessel, and a rotating starting rod and There is a method (multi-layering method) in which a row of burners is relatively reciprocally moved and glass particles are deposited in layers on the surface of a starting rod to obtain a porous glass preform. In the case of such a method, the outer diameter of the porous glass base material fluctuates due to the difference in the characteristics of each burner, the variation of the folding position and the deposition condition at the end, and the characteristics of the glass obtained from the porous glass base material. It causes fluctuation.

Japanese Laid-Open Patent Publication No. 4-260618 discloses a method for producing a porous glass preform using a plurality of burners, which rapidly and minimally wears due to an end effect, and which is substantially uniform. As a method of obtaining a porous glass base material having characteristics, a method of providing a means for forming an air flow of a uniform flow rate over the entire length of the porous glass base material is disclosed, and the burner array and the porous glass base material are arranged in the vertical direction. When oriented in the horizontal direction, a high-power end heater should be installed in the region of the bottom of the matrix to minimize the effect of thermal gradients along the length of the porous glass matrix. It is stated that the size of the air flow should be selected (increased) to minimize non-uniformities in the base material due to convective air flow along the length of the base material.

According to this method, the apparatus structure becomes complicated, and the reaction vessel has a strong acidic atmosphere, so that the constituent material of the heater is not only expensive, but also glass fine particles that cannot be deposited on the base material are heated. There is also a problem in maintenance such that it is deposited on the surface of the heater and the heat of the heater makes it transparent, which makes it difficult to remove the glass particles from the heater. With a configuration that requires time and effort for equipment maintenance, the preparation time until the next base metal is manufactured becomes longer even if the base metal synthesis rate becomes faster, and as a result, the efficiency of base material production increases in proportion to the improvement in the synthesis rate. Will not be obtained.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned state of the art, the present invention provides a method for producing a porous glass preform capable of suppressing the variation of the outer diameter in the length direction with a simpler device structure. The purpose is to provide.

[0006]

The present invention adopts the following constitutions (1) to (11) as means for solving the above problems. (1) A plurality of glass fine particle synthesizing burners are arranged in opposition to a rotating starting rod supported in a reaction vessel, and the burner is relatively reciprocally moved in parallel with the starting rod and the glass fine particle synthesizing burner. In the method for producing a porous glass preform by depositing the glass particles synthesized in step one by one on the surface of the starting rod, in the state where the burner is set in the reaction vessel, a ventilation port is provided near the burner intake part of the reaction vessel. And a gas is supplied from the ventilation port toward the base material, the method for producing a porous glass base material. (2) The method for producing a porous glass preform according to the above (1), characterized in that the ventilation port is provided around the burner. (3) The gas is supplied from the ventilation port toward the base material at different flow rates in the length direction of the base material.
Alternatively, the method for producing a porous glass base material according to (2). (4) The above-mentioned (1), characterized in that gases having different temperatures are supplied in the length direction of the base material from the ventilation port toward the base material.
Alternatively, the method for producing a porous glass base material according to (2). (5) The method for producing a porous glass preform according to (3), wherein the temperature of the gas supplied from the ventilation port is changed for each ventilation port.

(6) The reciprocating motion is a system in which the burner is fixed and the starting rod is reciprocating, a frame surrounding the entire burner array is provided outside the reaction vessel, and a cover covering the entire burner array is attached to the frame. An air reservoir is formed, a clean gas is supplied into the air reservoir, and the clean gas is supplied from the ventilation port toward the base material. A method for manufacturing a porous glass base material. (7) For each burner, the temperature of the deposition surface on which the glass particles synthesized by each burner are deposited is measured, and the gas supplied from the ventilation port so that the temperature of each deposition surface is kept substantially uniform. The method for producing a porous glass preform according to any one of the above (1) to (6), characterized in that the temperature or the flow rate is adjusted.

(8) The above-mentioned (3), (5), characterized in that the amount of gas supplied from the ventilation port toward the base material is adjusted by adjusting the opening degree of the ventilation port.
(6) The method for producing a porous glass preform according to any one of (6). (9) The above-mentioned (3), (5), characterized in that the amount of gas supplied from the ventilation port toward the base material is adjusted by adjusting the amount of gas supplied to the ventilation port.
(6) The method for producing a porous glass preform according to any one of (6). (10) The method for producing a porous glass preform according to any one of (1) to (9), wherein the gas is air or an inert gas. (11) As the burner for synthesizing glass fine particles, a burner having a flow velocity of gas of 8 m / sec or more ejected from any of ports for ejecting an auxiliary gas or an inert gas is used (1) to (10) The method for producing a porous glass preform according to any one of (10).

The present inventors have found that the problem that the bulk density changes in the length direction of the base material and the outer diameter changes when the large-sized porous glass base material is produced is essentially caused by the deposition of glass fine particles. Since there is a difference in the lengthwise direction of the hot atmosphere in which the base material is wrapped, the method of adjusting the amount of heat generated by each burner was examined first. In order to achieve this, it is necessary to control the supply amount of combustible gas and auxiliary gas supplied to each burner, and if the number of burners is increased to further improve the glass synthesis rate, the gas that needs control Since the number of systems will dramatically increase and the equipment cost will rise accordingly, we decided to consider a method other than this method.

Next, the temperature atmosphere of the entire base material is set to a substantially uniform atmosphere of ± 15 ° C. in which the change in bulk density is within the allowable range,
An attempt was made to eliminate the temperature gradient in the length direction. As a result of studying a gas supply method that can efficiently control the temperature without lowering the deposition efficiency, a ventilation port is provided near the burner intake point of the reaction vessel with the burner set in the reaction vessel. It has been found that supplying gas toward the base material can supply gas to the base material most efficiently. Here, in the part where the burner is incorporated in the reaction container, a gap may be provided between the reaction container and the burner to serve as a ventilation port.

When gas is supplied from a position other than that, the air flow in the reaction vessel is disturbed, and not only the efficiency of adhering the glass particles to the porous glass base material is lowered, but also the floating glass in the reaction vessel is reduced as the adhering efficiency is lowered. As a result of increasing the amount of fine particles and increasing the amount of glass fine particles adhering to the wall surface of the reaction vessel, not only the setup time such as cleaning time is increased, but also the glass fine particles are peeled off from the wall surface and As a result, the frequency of falling onto the high quality glass base material was increased. The peeled glass fine particles adhered to the porous glass base material to generate air bubbles in the base material after sintering and transparency.

In order to control the temperature gradient of the whole base material, the temperature of the deposition surface on which the glass fine particles synthesized by each burner are deposited is measured between each burner and the reaction vessel by a radiation thermometer, and the measurement is performed. Based on the results, the air volume of the gas supplied from each ventilation port was adjusted. In this case, due to the difference in the amount of gas supplied, the flow of gas supplied from each ventilation port interferes with each other, causing a phenomenon that disturbs the burner flame, leading to a decrease in deposition efficiency and an unstable deposition amount. As a result, the amount of deposition changes, which may result in variation in outer diameter.

Therefore, as a result of further studies on the burner structure in order to suppress the turbulence of the flame, it was found that it is preferable to set the flow velocity of the gas from the port for ejecting the auxiliary gas or the inert gas to 8 m / sec or more. As a result, the auxiliary gas or the inert gas guides the flame, the directivity of the burner flame is increased, and the influence of the turbulence of the flow of the supplied gas is reduced, so that the turbulence of the flame can be suppressed.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The method of the present invention will be described below with reference to the drawings. In addition, although the gas to be supplied will be described below as air, in the method of the present invention, an inert gas such as nitrogen can be used instead of air. Figure 1
2 and 2 are explanatory views schematically showing one example of the apparatus configuration for carrying out the method of the present invention. According to the method of the present invention, basically, a plurality of glass fine particle synthesizing burners 4 are arranged at substantially equal intervals in a reaction vessel 2 provided with an exhaust pipe 3 so as to face a starting rod that is supported in the vertical direction and rotates. The starting rod 1 and the burner 4 are relatively reciprocally moved in parallel relative to each other (the starting rod 1 is reciprocated in the vertical direction in the example of the figure), while the glass fine particles synthesized by the burner 4 are moved in the starting rod 1. It is a method of manufacturing the porous glass base material 5 by depositing one layer on the surface.

In these examples, six burners 4 are set in the reaction vessel 2. A gap is provided between each burner 4 and the reaction vessel 2, and a ventilation port 6 is formed so as to surround the periphery of each burner 4. In the method of the present invention, air having different flow rates and / or temperatures is supplied from these ventilation ports 6 so as to form an air flow in the direction of the porous glass base material 5, and the air around the porous glass base material 5 is supplied. The temperature atmosphere is controlled to be a substantially uniform atmosphere of ± 15 ° C. in which the change in bulk density is within the allowable range. In order to prevent foreign matter from adhering to the base material 5, the supplied air is preferably clean air (clean air) that has passed through a filter that can collect 99.97% or more of dust of 0.3 μm or more. More specifically, the air reservoir around the burner in the present invention is class 1
It is preferable that the atmosphere is 00.

In the air supply system in the example of FIG. 1, a cover 7 made of heat-resistant fiber is provided outside the reaction vessel 2 so as to cover each vent hole 6 and the entire row of burners 4, and an air reservoir 8 is provided.
Is formed, clean air from the clean air generator 9 is supplied into the air reservoir 8, and the clean air is supplied into the reaction container 2 from each ventilation port 6. The cover 7 is installed with a gap 10 so that it is not in contact with the reaction container 2, and the supply amount of clean air is adjusted so that clean air leaks from the gap 10 so that outside air does not enter the cover 7. . In this method, when the reaction vessel 2 and the cover 7 are brought into contact with each other, even heat-resistant fibers are deteriorated and damaged during the deposition of glass particles,
This is because it may cause foreign matter to adhere to the base material 5. The ventilation port 6 may be an opening provided in the vicinity of the burner intake portion 15 of the reaction vessel 2 as shown in FIG. 7. The shape of the ventilation port may be rectangular or oval.
The ventilation ports do not have to be provided beside each burner intake location, and for example, every other vent may be provided beside each burner intake location. Further, one elongated ventilation port may be provided beside the plurality of burner intake points.

In order to prevent the entry of outside air into the reaction container 2, it is preferable that the gap 10 is not provided. FIG. 2 shows an example of the structure without the gap 10. The reaction container 2 is provided with a frame 11 surrounding the entire row of the ventilation ports 6 and the burners 4 on the outside of the reaction container 2.
It is installed without providing a gap between and, and a cover 7 is also attached to this frame 11 in a form without a gap to form an air reservoir 8. A detailed view of an example of the air reservoir 8 of this system is shown in FIG. Here, the frame 11 is formed of a material having high heat resistance such as metal, and fins 13 are provided to improve heat dissipation. In FIGS. 1 and 2, the flow of the supplied air is indicated by a dotted line.

In the method of the present invention, the air whose flow rate and / or temperature are changed is supplied from each ventilation port.
Usually, the higher the flow rate, the lower the temperature. The means for adjusting the air flow rate is not particularly limited, but one example thereof is shown in FIG. In this example, as shown in FIG. 4 (c), the metallic adjustment plate 14 is divided into two and has a hole with a diameter larger than that of the burner 4 in the center.
Are attached so as to cover a part of the ventilation port 6 with the burner 4 interposed therebetween, and the opening degree of the ventilation port 14 is adjusted by adjusting the interval. 4A is a sectional view seen from a direction perpendicular to the burner 4, and FIG. 4B is a sectional view seen from above.
This method is suitable for the case where the air reservoir 8 is provided as shown in FIGS. As another means of adjusting the air flow rate, there is also a method of providing an air supply pipe for each ventilation port and adjusting the amount of air supplied to each ventilation port, but the device is more complicated than the method of providing an air reservoir. To do.

The means for adjusting the temperature of the air to be supplied is not particularly limited, but a method is generally used in which an air supply pipe is provided for each ventilation port and a cooling means or a heating means is installed alone or in combination at an appropriate place. is there.

In the method of the present invention, the flow rate and temperature of the air supplied from the ventilation port are substantially uniform within ± 15 ° C. in which the temperature atmosphere around the porous glass base material 5 is within the allowable range of the change in bulk density. Control the atmosphere. As a concrete setting method of the flow rate and temperature of the air to each ventilation port, for example, the temperature at the upper end and the lower end of the porous glass base material is measured and corresponding to the temperature difference, a set value obtained empirically in advance. It is easy to set according to the above. Further, by providing an appropriate temperature measuring means, the temperature of the deposition surface on which the glass particles synthesized by each burner are deposited is measured for each burner (see FIGS. 1 and 2).
A radiation thermometer 12 is provided in the above), and if the flow rate and temperature of the air supplied from the ventilation port are adjusted so that the temperature of each deposition surface is kept substantially uniform, more precise control is possible. Is possible.

In the method of the present invention, as a burner for synthesizing glass fine particles, a burner having as high directivity as possible, for example, a port capable of ejecting a combustion-supporting gas or an inert gas at a flow rate of 8 m / sec or more in a use range. It is desirable to use a burner so that the flow velocity of the gas ejected from either the combustion gas or the port ejecting the inert gas is 8 m / sec or more. This has the effect of suppressing turbulence of the flame due to the flow of air supplied from the ventilation port and stabilizing the amount of accumulation.

As the burner having high directivity, for example, there is a burner having a gas ejection port with a small opening so as to surround the central multi-tube as shown in FIG. In FIG. 5, reference numeral 17 is a raw material gas ejection port for ejecting only a raw material gas such as SiCl ₄ or a raw material gas and a combustible gas such as H ₂ , and 18 and 21 are inert gases for ejecting an inert gas such as Ar or N _2. Ejection ports, 19 are combustible gas ejection ports for ejecting combustible gases such as hydrocarbons such as H ₂ and methane, and 20 and 22 are auxiliary combustion gas ejection ports for ejecting auxiliary combustion gases such as O _2. . Also, a multi-tube burner having a structure as shown in FIG. 6 can be preferably used. In FIG. 6, 23 is a raw material gas ejection port, 24 and 27 are combustible gas ejection ports, and 25 and 2.
8 is an inert gas ejection port, 26 and 29 are auxiliary combustion gas ejection ports, and 30 is a windshield (guide).

In the burner of this type, the flow velocity of the gas ejected from each port is about 1 to 40 m / sec in the burner of the type shown in FIG.
The flow velocity of the gas ejected from 0 is about 10 to 40 m / sec. Further, in the burner of the type 6, the flow velocity of the gas ejected from either the auxiliary combustion gas ejection port 26 or 29 is 8 m / sec or more. In another type of burner, it is preferable that the gas flow rate from the auxiliary gas injection port or the inert gas injection port among the ports, particularly the outermost auxiliary gas injection port, is 8 m / sec or more.

As described above, by supplying the air whose flow rate and temperature are adjusted from the ventilation port provided around the burner to maintain the temperature atmosphere around the porous glass base material substantially uniform, It has the effect of making the bulk density uniform and suppressing fluctuations in the outer diameter. In addition to that, there is an effect that the efficiency of discharging the glass particles, which could not be deposited on the base material during the deposition of the glass particles, from the reaction container is improved, so that the labor for cleaning is reduced and the setup time is reduced.

Generally, the glass fine particles which cannot be adhered to the base material are discharged from the exhaust pipe provided in the reaction container, but they may be deposited on the wall surface of the reaction container. In particular, the glass fine particles attached to the upper part of the reaction vessel have a great influence, and they are peeled off due to their own weight and redeposited on the base material, which causes bubbles to be generated after the sinter is made transparent. According to the method of the present invention, although the air flow from the ventilation port is somewhat disturbed near the ventilation port, it gets on the flame flow of the jet-type burner as it approaches the base metal and forms a smooth flow. This flow is smoothly sucked into the exhaust pipe, and as a result, the glass fine particles not completely attached to the base material are easily discharged. This reduces the risk that the fine particles peeled off from the container wall will reattach.

[0026]

EXAMPLES The method of the present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. A manufacturing test of a porous glass base material was conducted by using the apparatus having the configuration shown in FIG. However, the number of burners 4 is 4,
The gap 10 was 5 mm. The burner 4 used is a multi-tube burner having the structure shown in FIG. 5, and the outer diameter is 60 mm.
belongs to. The diameter of the hole of the reaction vessel 2 where the burner 4 is attached was set to 75 mm, and a gap was formed around the burner 4 to form the ventilation port 6.

(Example 1) Starting rod 1 (diameter 36 m
m, length 1500 mm) and four burners 4 facing each other.
Arranged at 200 mm intervals, starting rod 1 is rotated around the axis
The glass particles are deposited by the method of reciprocating while
went. All the ventilation ports 6 had an outer diameter of 75 mm. Stack
Average blowing flow rate of the clean air generator 9 during the loading process
20m³/ Min, normal temperature clean air (size
The number of dust particles of 0.5 μm or more is 40 / m ³: Laser par
Measured by detecting the scattered light intensity using a tickle counter
Constant) was supplied to the air reservoir 8. As a result
As for the shape of the porous glass base material 5 that has been formed, the outer diameter has an effective portion (length
600mm) 245mm at the top and 260m at the bottom
It was m. Clean air over the entire length of the porous glass base material 5.
By giving the temperature of the porous glass base material 5 in the longitudinal direction.
The difference is relaxed and the obtained porous glass base material is usable
It was a thing.

(Embodiment 2) Porous metal under the same conditions as in Embodiment 1 except that the size of the ventilation port 6 around each burner 4 was adjusted by using the metal adjustment plate 14 as shown in FIG. The quality glass base material 5 was produced. The size of the ventilation port 6 was such that the outer diameter was about 75 mm, 73 mm, 70 mm, and 65 mm in order from the top. As a result, the outer diameter of the base material 5 is 252 mm at the uppermost part of the effective portion (length 600 mm) and 2 at the lowermost part.
It was 60 mm, and the effect of making the outer diameter uniform was noticeable.

(Embodiment 3) As shown in FIG. 7, a ventilation port 6 was provided beside each burner at a position 10 cm away from the burner intake point 15. The vertical length of each ventilation port is constant at 60 mm, and the width is 13, 11, 9, 4 mm, respectively.
The width of the ventilation opening is higher at the top.
The conditions were the same as in Example 2 except for the shape of the ventilation port. The outer diameter of the obtained base metal is 258 mm at the top and 262 m at the bottom.
m, and an effect equivalent to that of Example 2 was obtained.

(Embodiment 4) In the method of Embodiment 2, the radiation thermometer 1 is passed through the gap (ventilation port 6) around each burner 4.
2, the deposition surface temperature was measured, and the porous glass base material 5 was produced while finely adjusting the size of the ventilation port 6 using the adjustment plate 14 so that the deposition surface temperature was 700 ° C. As a result, the outer diameter of the base material 5 was 258 mm at the uppermost part of the effective portion (length 600 mm) and 260 mm at the lowermost part, and a more uniform base material 5 could be obtained.

(Embodiment 5) The reaction vessel 2, the burner 4, and the ventilation port 6 were constructed in the same manner as in Embodiment 1, and piping was provided so that clean air having different temperatures could be supplied to each ventilation port 6. When deposition was started with the supply of clean air at 30 ° C and the supply rate of 4 m ³ / min per burner, the temperature of the deposition surface was 720 ° C at the top of the effective part, At 690 ° C, a temperature difference of about 30 ° C was observed. By applying clean air of uniform temperature to the entire length of the porous glass base material 5, the temperature difference in the length direction of the porous glass base material 5 is relaxed, and the temperature of the deposition surface is ± 1 with respect to the center value.
It could be kept within the range of 5 ° C.

(Embodiment 6) Since a difference in temperature between the upper and lower sides was observed in Embodiment 5, the opening degree of each ventilation port 6 was kept the same, and the temperature of the clean air to be supplied was 30 ° C. and 60 ° from the top.
A porous glass base material 5 was produced at a temperature of 90 ° C., 90 ° C. and 120 ° C. As a result, the outer diameter of the base material 5 is the effective portion (length 600 m
m) was 257 mm at the top and 258 mm at the bottom, and a uniform base material 5 could be obtained. Also, during the deposition, the temperature of the glass deposition surface was 720 ° C. at the top of the effective part.
The lowest part was uniformed at 716 ° C.

[0033]

According to the method of the present invention, in the production of a large-sized porous glass preform, the bulk density in the longitudinal direction of the preform can be made uniform and the outer diameter fluctuation can be suppressed with a simpler apparatus configuration. effective. Further, there is an effect that the efficiency of discharging the glass particles, which could not be deposited on the base material during the deposition of the glass particles, from the reaction container is improved, so that the labor of cleaning is reduced and the setup time is reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing an example of a device configuration for carrying out the method of the present invention.

FIG. 2 is an explanatory view schematically showing another example of the apparatus configuration for carrying out the method of the present invention.

FIG. 3 is a detailed view showing an example of an air reservoir 8 according to the method of FIG.

FIG. 4 is an explanatory view showing an example of a means for adjusting an air flow rate to a ventilation port.

FIG. 5 is a cross-sectional view showing an example of a burner structure that can be preferably used in the method of the present invention.

FIG. 6 is an explanatory view showing another example of a burner structure that can be preferably used in the method of the present invention.

FIG. 7 is an explanatory view showing an example of a ventilation port installation method.

[Explanation of symbols]

1 Starting Rod 2 Reaction Vessel 3 Exhaust Pipe 4
Burner 5 Porous glass base material 6 Vent 7 Cover
8 Air Reservoir 9 Clean Air Generator 10 Gap 11 Frame
12 Radiation thermometer 13 Fin 14 Adjustment plate 15 Burner intake point 17 Raw material gas ejection port 18, 21 Inert gas ejection port 19 Combustible gas ejection port 20, 22 Combustible gas ejection port 23 Raw gas ejection port 24, 27 Flammability Gas ejection ports 25, 28 Inert gas ejection ports 26, 29 Combustible gas ejection port 30 Windshield

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takashi Yamazaki             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works F-term (reference) 4G014 AH14

Claims (11)

[Claims] 1. A plurality of burners for synthesizing glass fine particles are arranged so as to face a rotating starting rod supported in a reaction vessel, and the starting rod and the burner for synthesizing glass fine particles are relatively reciprocated in parallel. While a method for producing a porous glass preform by depositing glass fine particles synthesized by a burner on the surface of the starting rod one by one, in the state where the burner is set in the reaction vessel, near the burner intake point of the reaction vessel. A method for producing a porous glass preform, comprising providing a ventilation port, and supplying gas toward the preform from the ventilation port. 2. The method for producing a porous glass preform according to claim 1, wherein the ventilation port is provided around the burner. 3. The method for producing a porous glass base material according to claim 1, wherein the gas is supplied from the ventilation port toward the base material at different flow rates in the length direction of the base material. 4. The method for producing a porous glass preform according to claim 1, wherein gases having different temperatures are supplied in the length direction of the preform from the ventilation port toward the preform. 5. The temperature of the gas supplied from the ventilation port,
The method for producing a porous glass preform according to claim 3, wherein the method is changed for each ventilation port. 6. The reciprocating motion is a system in which a burner is fixed and a starting rod is reciprocating motion, a frame surrounding the entire burner line is provided outside the reaction vessel, and a cover for covering the entire burner line is attached to the frame. 4. The porosity according to claim 1, wherein a reservoir is formed, a clean gas is supplied into the air reservoir, and the clean gas is supplied from the ventilation port toward the base material. Of manufacturing high quality glass base material. 7. The temperature of a deposition surface on which glass particles synthesized by each burner are deposited is measured for each burner, and the temperature of each deposition surface is supplied from a ventilation port so that the temperature is kept substantially uniform. The method for producing a porous glass preform according to any one of claims 1 to 6, wherein the temperature or flow rate of the gas is adjusted. 8. The method according to claim 3, wherein the amount of gas supplied from the ventilation port toward the base material is adjusted by adjusting the opening degree of the ventilation port. Item 1. A method for producing a porous glass preform according to item 1. 9. The method according to claim 3, wherein the amount of gas supplied from the ventilation port toward the base material is adjusted by adjusting the amount of gas supplied to the ventilation port.
The method for producing a porous glass preform according to any one of 1. 10. The method for producing a porous glass preform according to claim 1, wherein the gas is air or an inert gas. 11. A burner for synthesizing glass particles, wherein a gas flow velocity of 8 m / sec or more is used for jetting from either a port for jetting an auxiliary gas or an inert gas. The method for producing a porous glass preform according to any one of 1 to 10.