JP2003212554A - Method and apparatus for manufacturing fine glass particle deposit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for manufacturing a fine glass particle deposit, in which the back flow of a corrosive gas from a reaction vessel and the rapid spouting of a glass source gas are suppressed when stopping and supplying the glass source gas at both ends of the accumulative layer of the fine glass particle. <P>SOLUTION: The supply of the glass source gas to a burner at both ends of the accumulative layer of the fine glass particle is set to gradually become zero by using a gas flow rate controller. At the time or around the time of setting the supply of the glass source gas to be zero, an inert gas A (N<SB>2</SB>) is changed to the glass source gas (SiCl<SB>4</SB>) at the upstream of the gas flow rate controller 11, a gas flowing from the gas flow rate controller 11 is changed to a burner and an exhaust side at the downstream of the gas flow rate controller 11. An inert gas B (N<SB>2</SB>) is supplied or stopped to the burner at the downstream of the gas flow rate controller 11, and a glass source gas supply passage is purged with the inert gases A and B. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for manufacturing a glass particle deposit body in which glass particles are deposited on a starting glass rod by a flame hydrolysis reaction.

[0002]

2. Description of the Related Art OVD method (external vapor deposition method) is known as a method for producing a cylindrical glass preform such as an optical fiber. In this method, for example, a starting glass rod is reciprocally moved in the axial direction in a reaction vessel and is rotated while a glass raw material gas such as SiCl ₄ or GeCl _{4 is} supplied to the outer periphery thereof, a fuel gas such as H ₂ and O ₂ or the like. It is sprayed from a burner together with the auxiliary gas of No. 3, and glass fine particles are generated and deposited by a flame hydrolysis reaction to prepare a glass fine particle deposit body. Then, the glass fine particle deposit is subjected to dehydration heating treatment in a sintering furnace or the like to be transparent vitrified.

Conventionally, the flow rate of these gases for producing glass particles is controlled by a gas flow rate control mechanism, and the gas supply is stopped when the deposition of glass particles is completed.
Corrosive hydrogen chloride gas (HCl) is generated by the flame hydrolysis reaction during the generation of the glass particles. The corrosive gas is exhausted from the exhaust pipe together with the floating glass particles during the deposition of the glass particles. Further, after the deposition of the glass fine particles is completed and the supply of the glass raw material gas is stopped, an inert gas such as nitrogen is flown into the gas supply passage to discharge the glass raw material gas remaining in the gas supply passage. Be purged.

After the deposition of the glass fine particles, the glass fine particle deposits in the reaction container are left to stand until the temperature drops to a certain extent. During this period, a part of the corrosive gas adsorbed in the glass particulate deposits reacts. Disperse in the container. Therefore, when the supply of gas is stopped, the corrosive gas in the reaction vessel may flow back into the gas supply passage and corrode the pipeline or the gas flow control valve. Therefore, in the VAD method (method with a vapor phase axis), for example, as shown in Japanese Patent Laid-Open No. 8-81234, an on-off valve is provided in the middle of a gas supply passage to provide a glass raw material gas, a combustion gas, a seal gas, etc. When the supply of the gas is stopped, an inert gas is caused to flow in each gas supply passage to prevent the corrosive gas from the reaction vessel from flowing backward.

However, the technique disclosed in the above publication is a countermeasure after the deposition of glass particles is completed and the glass particle deposit is formed. On the other hand, in the OVD method, the starting glass rod and the burner are relatively reciprocally moved in the axial direction, and thin glass particles are laminated in multiple layers in the radial direction of the starting glass rod. The deposition of the glass fine particles, by the gas flow rate control mechanism, gradually reduces the supply of the glass raw material gas to zero on both sides of the effective portion having a uniform outer diameter in the center, or gradually increases from zero to lengthen the effective portion,
The ineffective part is controlled to be as short as possible. However, even if the gas flow rate control mechanism is instructed to supply glass raw material gas to zero, it is difficult to completely reduce the glass raw material gas to zero due to the structure of the gas flow rate control mechanism, and there is a problem that the non-effective portion becomes long. .

At both ends of the glass particulate deposit body, the supply and stop of the glass raw material gas are repeated many times until the final deposition is completed. Then, even if the glass raw material gas is completely suppressed to zero by the gas flow rate control mechanism or the glass raw material gas is completely switched so that the glass raw material gas does not come out from the burner, during the deposition of the glass fine particles, The reaction vessel is constantly evacuated. However, since the supply and stop of the glass source gas are repeated many times, a backflow of corrosive gas from the reaction vessel occurs during the deposition. To prevent the backflow of this corrosive gas,
It is necessary to repeat the operation of stopping the glass raw material gas and simultaneously supplying the inert gas.

However, when the glass material gas and the inert gas are switched on the upstream side of the gas flow rate control mechanism, the gas type suddenly changes, so that the flow rate control of the gas flow rate control mechanism is temporarily disturbed and the control cannot be performed. May be. In this case, the glass raw material gas or the inert gas may be suddenly ejected from the burner into the reaction vessel. The sudden ejection of the glass raw material gas from the burner destabilizes the flame hydrolysis reaction, produces soft glass fine particles, and forms a deposited layer that is easily cracked. Also,
The sudden ejection of gas from the burner damages the deposited layer of glass fine particles, and the foreign matter that has adhered to the inside of the burner or the gas supply path adheres to the deposition surface of the glass fine particles.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and the reaction occurs when the glass raw material gas is stopped and supplied at both ends of the deposition layer of glass fine particles by the OVD method. An object of the present invention is to provide a manufacturing method and a manufacturing apparatus for a glass particulate deposit body, which suppresses the backflow of corrosive gas from a container and the sudden ejection of gas into the reaction container.

[0009]

According to the method for producing a glass fine particle deposit of the present invention, a glass fine particle deposit layer is formed on a starting glass rod that reciprocates in the axial direction and rotates by a burner for producing glass fine particles. A method for producing a glass particle deposit, wherein the gas flow rate control mechanism gradually reduces the supply of the glass material gas to the burner at both ends of the deposited layer of the glass particles, thereby reducing the supply of the glass material gas to zero. At or near the time point, the glass raw material gas and the inert gas A are switched upstream of the gas flow rate control mechanism,
The gas flowing from the gas flow rate control mechanism downstream of the gas flow rate control mechanism and upstream of the burner is switched to the burner side or the exhaust side, and the inert gas B is supplied to the burner downstream of the gas flow rate control mechanism and upstream of the burner. It is characterized in that the glass source gas supply passage is purged with the inert gases A and B so as to be supplied or stopped.

Further, the apparatus for producing a glass fine particle deposit according to the present invention is such that a glass fine particle deposit is formed on a starting glass rod that reciprocates in the axial direction and rotates by a burner for producing glass fine particles. A gas flow rate control mechanism for controlling the supply of the glass raw material gas to the burner, a gas type switching mechanism for switching the glass raw material gas and the inert gas A upstream of the gas flow rate control mechanism, and a gas flow rate. Pipeline switching mechanism that switches the gas flowing from the gas flow rate control mechanism to the burner side or the exhaust side downstream of the control mechanism and upstream of the burner, and inert to the burner downstream of the gas flow rate control mechanism and upstream of the burner A gas supply switching mechanism for supplying or stopping the gas B,
The glass raw material gas supply passage is characterized by being purged with the inert gases A and B.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic view of a reaction vessel for depositing glass particles. In the figure, 1 is a starting glass rod, 2 is a dummy rod, 3 is a deposition layer of glass fine particles, 4 is a supporting rod, 5 is an elevating / rotating device, 6 is a reaction vessel, 7 is an upper chimney, 8 is a lower chimney, and 9 is Burner 10 indicates an exhaust pipe.

The starting glass rod 1 serves as a base material for depositing glass fine particles on the outer peripheral surface, and is made of a glass material of the same quality as the glass formed on the outer peripheral surface.
When manufacturing a glass preform composed of a core part and a clad part for an optical fiber, it is possible to use only a core glass doped with germanium or the like to increase the refractive index, or a core rod made of a core glass and a clad glass. .

Dummy rods 2 made of the same kind of glass material are connected to both ends of the starting glass rod 1 by fusion bonding, and one dummy rod (upper side) is fixed to a support rod 4 and is suspended and supported. The support rod 4 is rotated and reciprocally moved in the vertical direction by an elevating / rotating device 5 to drive and control the starting glass rod 1. The apparatus for producing glass particulate deposits has an upper chimney 7 above the reaction vessel 6 and a lower chimney 8 below. An upper lid is provided on the upper part of the upper chimney 7 so that the starting glass rod 1 can be taken in and out. The reaction vessel 6, the upper chimney 7 and the lower chimney 8 are all made of quartz, and the upper chimney 7 and the lower chimney 8 have such a length that both ends 3a and 3b of the deposition layer 3 of glass particles can be accommodated at the same time. The upper and lower sides of the reaction container 6 are hermetically sealed and combined.

The reaction vessel 6 is provided with a plurality of glass fine particle producing burners 9 for producing glass fine particles. As the burner 9, for example, three burners are provided at 150 mm intervals. This burner 9 is shown in FIG.
As shown in the cross section of (B), the glass raw material gas (S
A port 9a for ejecting iCl ₄ or GeCl ₄ ) and a port 9b for ejecting a seal gas (Ar) are provided outside the port 9a. Outside the port 9b, a port 9c for ejecting hydrogen gas (H ₂ ) for fuel and a large number of small ports 9d for ejecting oxygen gas (O ₂ ) for auxiliary combustion (scattered in the port 9c) are provided. The port 9e is provided coaxially. Further, the reaction container 6 is provided with an exhaust pipe 10 for discharging glass particles and the like floating in the container.

Next, a method for producing a glass particle deposit by using the apparatus having the above-mentioned structure will be described. First, one of the dummy rods 2 attached to both ends of the starting glass rod 1 is attached to the supporting rod 4 of the elevating and rotating device 5, and the elevating and rotating device 5 moves the starting glass rod 1 downward while rotating it. At the time when the starting point (lower end 3a) of the deposition enters the reaction vessel 6 and passes through the burner 9, the glass raw material gas is started to be supplied to the burner 9, and the generation and deposition of the glass particles are started. On the outer peripheral surface of the starting glass rod 1, a deposition layer 3 of glass particles of the first layer (hereinafter, referred to as a deposition layer 3 of the first layer).
Are sequentially formed along the axial direction. In the case where three burners 9 are provided at intervals as shown in the figure, each burner 9 sequentially starts to supply the glass raw material gas as the starting glass rod 1 moves. .

The end of the deposition (upper end 3b) is the burner 9
The supply of the glass raw material gas to the burner 9 is stopped at the time when the passage of the gas has finished. When the three burners 9 are provided at intervals, the supply of the glass raw material gas is sequentially stopped in each burner 9 as the starting glass rod 1 moves. After the deposition of the first stack layer 3 is completed and the stack is evacuated to the lower chimney 8, the starting glass rod 1 is reversed to move upward, and the deposition of the second stack layer is started.

The formation of the second deposited layer is performed in the burner 9 when the upper end 3b enters the reaction vessel 6 and passes through the burner 9, similarly to the formation of the first deposited layer 3. The supply of the glass raw material gas is started, and the glass fine particles are generated and deposited. Then, at the time when the lower end portion 3a finishes passing through the burner 9, the supply of the glass raw material gas to the burner 9 is stopped. After the deposition of the second stack layer 3 is completed and the vehicle is retreated to the upper chimney 7, the starting glass rod 1 returns at the start and is reversed to move downward, so that the deposition of the third stack layer is completed. Be started. Thereafter, this operation is repeated to form a glass particle deposit body having a predetermined outer diameter. Then, the glass fine particle deposit is subjected to dehydration heating treatment in a sintering furnace (not shown) to obtain a glass base material which is made into transparent vitrification.

In the glass particle deposit body, in general, a tapered non-effective portion is formed on both sides of the effective portion where the glass particles are deposited so as to have a uniform outer diameter in the center. In the non-effective portion on both sides, when the deposition of the glass fine particles is performed from the non-effective portion toward the central effective portion, the supply of the glass raw material gas is controlled to gradually increase from zero. On the contrary, when the process is performed from the effective part in the center toward the ineffective parts on both sides, the supply of the glass raw material gas is gradually reduced to zero at the ends. When the supply of the glass raw material gas to the burner becomes zero and is stopped, the corrosive gas in the reaction vessel 6 flows backward into the gas supply passage to corrode the gas supply passage, the gas flow rate control mechanism, and the like. Becomes

FIG. 2 is a schematic view for explaining the glass source gas supply mechanism according to the present invention, and FIGS. 3 and 4 are views showing the opening / closing operation of the opening / closing valve for switching the gas flow.
In the figure, 11 is a gas flow rate control mechanism, 12 is a gas type switching mechanism, 13 is a pipeline switching mechanism, 14 is a gas supply switching mechanism, A
V1 to AV5 are open / close valves, and P1 to P3 are gas supply paths.

The gas flow rate control mechanism 11 controls the gas flow rate using a gas flow rate control valve or the like, and a gas type switching mechanism 12 is connected to the upstream side thereof via a gas supply path P1. The gas type switching mechanism 12 is an opening / closing valve A for supplying / stopping a glass raw material gas (for example, SiCl ₄ ).
V1 and an opening / closing valve AV2 for supplying / stopping an inert gas A (for example, N ₂ ) for purging are provided.

A burner 9 shown in FIG. 1 is connected to the downstream side of the gas flow rate control mechanism 11 via gas supply paths P2 and P3. Between the gas supply paths P2 and P3, an open / close valve AV3 for supplying and stopping the glass raw material gas to the burner 9,
A conduit switching mechanism 13 including an opening / closing valve AV5 that allows the gas from the gas flow rate control mechanism 11 to flow to the exhaust path is connected.
The gas supply path P3 is connected to a gas supply switching mechanism 14 including an opening / closing valve AV4 for supplying / stopping the purging inert gas B (for example, N ₂ ) to the burner 9. The opening / closing valves of each part are referred to as AV1 ... AV5 below.
For short.

Next, the opening / closing operation of the glass source gas supply mechanism shown in FIG. 2 will be described with reference to the example of FIG. As described with reference to FIG. 1, the glass particle deposition layer 3 has tapered non-effective portions on both sides of the central effective portion. The glass raw material gas is zero at both ends 3a and 3b of the ineffective portion, and is supplied so as to increase gradually when it is deposited from the ineffective portion toward the effective portion. On the contrary, when depositing from the effective portion side toward both end portions 3a and 3b of the ineffective portion, the glass raw material gas is gradually reduced to zero at both end portions 3a and 3b.

For example, when glass particles are deposited from one end portion 3a toward the effective portion, a command value for changing the flow rate of the glass raw material gas from zero to high is supplied to the gas flow rate control mechanism 11 at the end portion 3a. Is issued. At the same time, AV
1 is closed and opened, and AV2 is opened and closed. This allows
In the gas flow rate control mechanism 11, the supply of the inert gas A (N ₂ ) is stopped and the supply of the glass raw material gas (SiCl ₄ ) is switched. Further, when the glass raw material gas is supplied to the gas flow rate control mechanism 11 from zero to a large flow rate, AV
3 is closed → open, AV5 is open → closed, and AV4 is open → closed. By this operation, the flow rate of the glass raw material gas is controlled by the gas flow rate control mechanism 11, and the gas supply passage P2 → A
V3 is supplied to the burner through the gas supply path P3.

Next, when glass particles are deposited from the effective portion to the end portion 3b of the ineffective portion, the flow rate of the glass raw material gas is gradually decreased by the gas flow rate control mechanism 11, and the flow rate of the glass raw material gas is increased from a large flow rate to zero. When the command value of
V1 is opened → closed, and AV2 is closed → opened. As a result, the gas flow rate control mechanism 11 has a glass raw material gas (Si
The supply of Cl ₄ ) is stopped and the inert gas A (N ₂ ) is supplied. At the time when the supply of the glass material gas is zero, AV3 is opened → closed, AV5 is closed → opened, and A
Close V4 to open it.

By this opening / closing operation, the inert gas A is exhausted through the gas flow rate control mechanism 11 and the gas supply path P2 → AV5, and the gas flow rate control mechanism 11 and the gas supply path P2.
Purge the route. In addition, the gas supply path P via AV4
The inert gas B is supplied to the burner 3 to prevent the corrosive gas from the reaction vessel from flowing back into the burner, and the gas supply path P3 and the burner are purged. Also, when the deposition direction of the deposition layer 3 of the glass fine particles is reversed to move from the end 3b side to the end 3a side, AV1 to AV1
The same opening / closing operation is performed only by reversing the operation of 5.

By supplying / stopping the glass raw material gas as described above, even if the supply of the glass raw material gas is stopped at both ends of the deposited layer of glass fine particles, the backflow of the corrosive gas from the reaction vessel is caused. Can be completely prevented.
As a result, it is possible to suppress corrosion of the gas supply passage and the on-off valve, and to prevent the corrosive substances from peeling off and adhering to the deposition surface of the glass particles.

FIG. 4 is a diagram showing an example of another opening / closing operation. When the glass particles are deposited from one end 3a toward the effective portion, the gas flow rate control mechanism 11 is provided with a command value for increasing the flow rate of the glass raw material gas from zero. At the same time, the point where AV1 is closed → open and AV2 is opened → close is the same as in the case of FIG. However, AV3 is closed from the time of switching from the inert gas to the glass raw material gas.
The timing of opening, AV5 opening → closing, and AV4 opening → closing is delayed by the timing Ta.

By this operation, the control of the gas flow rate control mechanism 11 is disturbed immediately after switching the gas type between AV1 and AV2,
Even if the glass source gas spouts, the timing Ta
AV3 is kept closed only for the time. Therefore, it is possible to prevent the glass raw material gas from being blown out from the burner by being transmitted to the burner. Then, after the control of the gas flow rate control mechanism 11 becomes stable, the AV
Open 3 and close AV4 and AV5. As a result, it is possible to prevent the glass raw material gas from suddenly ejecting from the burner to cause a flame hydrolysis reaction failure, and to prevent cracking due to adhesion of soft glass fine particles. In addition, it is possible to prevent foreign matter attached to the burner or the gas supply passage from attaching to the deposition surface of the glass particles.

When the glass particles are deposited from the effective portion toward the end portion 3b of the ineffective portion, the gas flow rate control mechanism 11 is provided with a command value for changing the glass raw material gas from a large flow rate to zero. At the same time, AV3 is opened → closed, AV5
Is changed from closed to open and AV4 is closed to open as in the case of FIG. However, from the time of switching the gas source gas flowing from the gas flow control mechanism from the burner side to the exhaust side and supplying the inert gas B to the burner, AV1
Is changed from open to closed and AV2 is changed from closed to open by a timing Tb.

With this operation, before switching between AV1 and AV2, the gas flow rate control mechanism 11 is advanced earlier by the timing Tb.
The gas flowing from is switched from the burner side to the exhaust side. As a result, when the gas type is switched between AV1 and AV2, even if the flow rate control of the gas flow rate control mechanism 11 is disturbed and the glass raw material gas spouts, this spout is made to flow to the exhaust side and to the burner side. It can be prevented from flowing. As a result, similarly to the case of the timing Ta that delays the opening and closing, it is possible to further suppress cracking of the deposition layer of glass fine particles and adhesion of foreign matter.

Timings Ta and Tb for delaying opening and closing
Is the moving speed of the deposition layer of the glass particles, the gas supply path P1
To P3, the switching speed of AV1 to AV5, and the like. However, in reality, the timings Ta and Tb are 0.
If it is less than 5 seconds, the type of gas passing through the gas flow rate control mechanism 11 cannot be completely switched, the flow rate control becomes impossible, and the gas is likely to be ejected. Also, the timing T
If a and Tb exceed 20 sec, it is necessary to make the rate of increase and decrease of the glass raw material gas in the ineffective portion steep, and thus the gas flow rate control mechanism 11 cannot control the gas flow rate. Therefore, the timings Ta and Tb for delaying the opening and closing are preferably set in the range of 0.5 sec to 20 sec.

Next, a specific example 1 in which a glass fine particle deposit is produced by using the reaction vessel of FIG. 1 in the form of supplying the glass raw material gas shown in FIGS. 2 to 4 will be described. The starting glass rod 1 was a core rod composed of a core glass and a clad glass, and had a diameter of 30 mm and a length of 500 mm. Dummy rods 2 having the same diameter were welded to both ends of this starting glass rod 1, and one dummy rod was attached and fixed to the support rod 4. The elevating and rotating device 5 moves the starting glass rod 1 to 40
50mm / min while rotating at rpm
It was moved 1100 mm in the vertical direction at the speed of.

The burner 9 for producing fine glass particles in the reaction vessel 6 was provided with three burners having a diameter of 30 mm at intervals of 150 mm. Each of the burners 9 for producing fine glass particles contains 4 glass raw materials, silicon tetrachloride (SiCl ₄ ).
~6SLM (standard liter / min), 50~80SLM the hydrogen (H ₂₎ to form a flame and oxygen (O
₂ ) was supplied at 40 to 60 SLM, and further 6 SLM of argon (Ar) was supplied as a gas for sealing. Then, a glass fine particle deposit was prepared in which the increased weight of the glass fine particles was 10 kg.

As a result of producing a glass fine particle deposit by opening and closing the glass raw material gas as shown in FIG. 3, the occurrence of cracks in the ineffective portion of the glass particulate deposit layer is 1/100.
It was (body), but foreign matter adhered to the ineffective part was 100 /
Foreign matter adhered to all 100 (body). However, as a second specific example, the timing Ta is set to 5s by the opening / closing operation of FIG.
As a result of producing a glass fine particle deposit body with ec and timing Tb of 2 sec, the occurrence of cracks in the ineffective portion of the deposited layer of glass fine particles was 0/100 (body), and the adherence of foreign matter in the ineffective portion was 0. At 100 / body (body), neither cracks nor foreign matter adhered.

FIG. 5 is a schematic view showing an example of another supply mechanism of the glass raw material gas. In the figure, DV1 and DV2 are direction switching valves, and the other reference numerals are the same as those used in FIG. In FIG. 2, AV1 and AV2 for switching the glass source gas (for example, SiCl ₄ ) and the inert gas A (for example, N ₂ ) are switched at the same time, so that the direction switching valve DV1 can be used. Further, in FIG. 2, the opening / closing valve AV3 for supplying the glass raw material gas to the burner 9 and the opening / closing valve AV5 for flowing the gas from the gas flow rate control mechanism 11 to the exhaust side are simultaneously switched, so that the direction switching valve DV2 Can be used.
By using a direction switching valve for the two opening / closing valves, it is possible to eliminate delay in switching timing and to facilitate operation.

6 and 7 are views showing a comparative example of the present invention, FIG. 6 is a schematic view of a glass raw material gas supply mechanism, and FIG. 7 is a view showing an opening / closing operation of an opening / closing valve for switching a gas flow. Is. The reference numerals used in the drawings are the same as those used in FIGS. This comparative example
As shown in FIG. 6, the gas flow rate control mechanism 11 is provided with a glass raw material gas (SiCl ₄ ) and an inert gas A (N ₂ ) for purging.
Is switched by using AV1 and AV2.

As shown in FIG. 7, as in FIGS. 3 and 4,
The glass raw material gas is zero at both ends 3a and 3b of the ineffective portion of the deposited layer of glass fine particles, and when it is deposited from the ineffective portion toward the effective portion side, it gradually increases from zero to yes. Supplied. On the contrary, in the case of depositing from the effective portion side toward both ends 3a and 3b of the ineffective portion, the glass raw material gas is gradually reduced, and is made zero at both ends 3a and 3b. When glass particles are deposited from one end portion 3a toward the effective portion, the glass raw material gas is supplied from zero at the time of the end portion 3a, and AV1 is closed → opened,
Open and close AV2. As a result, the supply of the inert gas is stopped and the glass raw material gas is supplied to the burner via the gas flow rate control mechanism 11.

Next, when glass particles are deposited from the effective portion to the end portion 3b of the ineffective portion, the flow rate of the glass raw material gas is gradually reduced by the gas flow rate control mechanism 11 to increase the flow rate from a large flow rate to zero. When the command value of
V1 is opened → closed, and AV2 is closed → opened. Further, when a command value for increasing the flow rate of the glass raw material gas from zero is issued, AV1 is opened → closed and AV2 is closed → opened. As a result, the supply of the glass raw material gas is stopped and the inert gas is supplied to the burner via the gas flow rate control mechanism 11.

With the glass raw material gas supply mode shown in FIGS. 6 and 7 described above, a glass particulate deposit was prepared using the reaction vessel of FIG. 1 as in the specific example. As a result, the occurrence of cracks in the ineffective portion of the deposited layer of glass particles was 50/1.
00 (body) and foreign matter adhesion was 100/100 (body).

[0040]

As is apparent from the above description, according to the present invention, even if the supply of the glass raw material gas is stopped at both ends of the deposited layer of glass fine particles, the backflow of the corrosive gas from the reaction vessel is prevented. Can be completely stopped. Further, it is possible to prevent foreign matter attached to the burner or the gas supply passage from attaching to the deposition surface of the glass particles. Further, it is possible to prevent the glass raw material gas from suddenly spouting from the burner to cause a flame hydrolysis reaction failure, and to prevent cracking due to adhesion of soft glass fine particles.

[Brief description of drawings]

FIG. 1 is a schematic view of a reaction container for depositing glass particles used in the present invention.

FIG. 2 is a diagram illustrating a glass source gas supply mechanism of the present invention.

FIG. 3 is a diagram showing an example of opening / closing operation of the opening / closing valve according to the present invention.

FIG. 4 is a diagram showing another example of opening / closing operation according to the present invention.

FIG. 5 is a diagram showing another example of the glass source gas supply mechanism of the present invention.

FIG. 6 is a view showing a glass source gas supply mechanism of a comparative example.

FIG. 7 is a diagram showing an opening / closing operation of a comparative example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Starting glass rod, 2 ... Dummy rod, 3 ... Deposited layer of glass fine particles, 4 ... Support rod, 5 ... Lifting / rotating device, 6 ... Reaction vessel, 7 ... Upper chimney, 8 ... Lower chimney, 9 ... Burner, 10 …
Exhaust pipe, 11 ... Gas flow rate control mechanism, 12 ... Gas type switching mechanism, 13 ... Pipe line switching mechanism, 14 ... Gas supply switching mechanism,
AV1 to AV5 ... Open / close valves, P1 to P3 ... Gas supply paths.

Claims (5)

[Claims] 1. A method for producing a glass particle deposit body, comprising forming a glass particle deposit layer with a burner for producing glass particles on a starting glass rod that reciprocates in the axial direction and rotates. At both ends of the layer, the supply of the glass raw material gas to the burner is gradually reduced to zero by the gas flow rate control mechanism, and the gas flow rate control mechanism is set at or near the time when the supply of the glass raw material gas is zero. Of the glass raw material gas and the inert gas A upstream of the gas flow rate control mechanism, and the gas flowing from the gas flow rate control mechanism downstream of the gas flow rate control mechanism is switched to the burner side or the exhaust side. The inert gas B is supplied to or stopped from the burner by means of, and the glass raw material gas supply path is purged with the inert gases A and B. Method of manufacturing a soot glass deposit body to. 2. When a large command is issued from zero to the gas flow rate control mechanism, the inert gas A is switched to the glass raw material gas, and the gas flow rate control mechanism flows at a timing later than this switching time. The gas is switched from the exhaust side to the burner side, and the supply of the inert gas B supplied to the burner is stopped.
The method for producing a glass particle deposit body according to. 3. When a zero command is issued to the gas flow rate control mechanism, the gas source gas flowing from the gas flow rate control mechanism is switched from the burner side to the exhaust side and an inert gas B is supplied to the burner. Thus, the method for producing a glass fine particle deposit according to claim 1 or 2, wherein the glass raw material gas is switched to the inert gas A at a timing later than the switching time. 4. The late timing is 0.2 to 20.
It is (sec), The manufacturing method of the glass fine particle deposit body of Claim 2 or 3 characterized by the above-mentioned. 5. An apparatus for producing a glass particulate deposit body, wherein a starting layer of glass rods that reciprocates in the axial direction and rotates and forms a deposition layer of glass particulates with a burner for producing glass particulates, comprising: A gas flow rate control mechanism for controlling the supply of the raw material gas, a gas type switching mechanism for switching the glass raw material gas and the inert gas A upstream of the gas flow rate control mechanism, and a gas flow rate downstream of the gas flow rate control mechanism. A gas line switching mechanism for switching the gas flowing from the control mechanism to the burner side or the exhaust side, and a gas supply switching mechanism for supplying or stopping the inert gas B to the burner downstream of the gas flow rate control mechanism, An apparatus for producing a glass fine particle deposit, wherein the glass raw material gas supply path is purged with the inert gases A and B.