JP2000034131A - Apparatus and method for producing porous glass body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a high-quality porous glass body having an outer diameter and a relative refractive index difference stabilized in a longitudinal direction, which is optimal as a base material of an optical fiber, by a VAD method. SOLUTION: Glass fine particles generated by burners 21, 22, and 23 are deposited on the lower end of a rotating target rod 12, and the target rod 12 is pulled up in accordance with the deposition to form a glass fine particle deposited body 11 in a columnar shape. I do.
At this time, the lower end position of the glass particle deposit body 11 is detected by the position detecting device 31, and the computer 32 controls the rotary pulling device 13 in accordance with the detected position to change the pulling speed so that the lower end position becomes constant. The flow control device 33 controls the flow rate of the hydrogen gas supplied to the burner 21 according to the lifting speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for producing a porous glass body by a VAD method, which is suitable for producing a glass preform of an optical fiber.

[0002]

2. Description of the Related Art At present, there is a remarkable demand for optical fibers for the spread of optical communication and multimedia. The VAD method is important as a manufacturing method for making this optical fiber. The VAD method is a method for producing a porous glass body using a gas phase reaction process, and is particularly suitable for producing a high-purity porous glass body for use as a glass base material of an optical fiber. Known as the method.

In this VAD method, a combustible gas (such as hydrogen gas or propane gas) and a combustible gas (oxygen gas) are sent to a burner to generate an oxyhydrogen flame, and a glass such as silicon tetrachloride is generated in the flame. By introducing a raw material gas and causing a hydrolysis (partially oxidizing) reaction, glass fine particles are generated, and the generated glass fine particles are deposited on the tip of a rotating target, thereby forming a glass fine particle deposit in a circle. A columnar porous glass body (glass fine particle deposit, soot preform) is formed. At this time, a plurality of burners are used, and a single core burner forms a central core portion, and a plurality of clad burners forms part or all of a surrounding clad portion.

When an optical fiber is formed from a porous glass body produced by such a deposition step, a step of dehydrating and sintering the porous glass body to form a transparent glass body (sintering step). I do. After that, a fine glass body (fiber) is drawn by a spinning furnace.

In the above-described deposition step, the target rod is pulled up as the porous glass body grows at the tip of the target rod, so that the porous glass body is always deposited at the tip. Therefore, there is provided a mechanism for adjusting the pulling speed so that the growth position of the core portion is always kept constant.

[0006]

However, in the prior art, it has been difficult to obtain a porous glass body having characteristics stable in the longitudinal direction, and the low cost required as the optical fiber demand has expanded as described above. There is a problem that can not respond to the change. In other words, in order to reduce the cost, it is important not only to increase the size and speed of production of the base material, but also to improve the quality. However, the instability of the characteristics in the longitudinal direction is a bottleneck for the improvement in quality. I have.

[0007] A factor that hinders the stability of the characteristics in the longitudinal direction is considered to be a fluctuation in the pulling speed of the target rod. Even if the conditions of the burner and the conditions such as the flow rates of the raw material gas, the combustible gas, and the auxiliary gas are kept constant, the growth position of the core portion fluctuates. As a result, the pulling speed fluctuates. Despite the fluctuation of the pulling speed, when the growth is performed under the same conditions, the adhesion state of the glass fine particles in the clad portion fluctuates according to the growth change of the core portion, and the porous glass body has An accident may occur in which the fluctuation of the outer diameter becomes large, or in extreme cases, the soot may be broken. When the outer diameter variation of the base material is large, problems such as poor controllability of the diameter of the base material at the time of stretching, and large variation in the longitudinal direction occur. For this reason, in the past, attempts have been made to adjust the amount of exhaust of the deposition chamber, but this has not been achieved sufficiently.

SUMMARY OF THE INVENTION In view of the above, the present invention provides an apparatus and a method for manufacturing a porous glass body, which have been improved so that a high quality porous glass body whose characteristics are stable in the longitudinal direction can be manufactured by the VAD method. The purpose is to provide.

[0009]

In order to achieve the above-mentioned object, in the apparatus for manufacturing a porous glass body according to the present invention, a burner for producing glass particles and a target rod on which the glass particles are deposited at a lower end are provided. A rotation pulling device that pulls up while rotating, a control device that monitors the growth point of the glass particle deposit growing at the lower end of the target rod and controls the pulling speed, and a control device that controls the pulling speed to be constant. And a flow rate control device for controlling the flow rate of the flammable gas supplied to the burner.

In order to achieve the above object, in the method of manufacturing a porous glass body according to the present invention, the target rod is pulled up while depositing glass fine particles generated from a burner on the lower end of a rotating target rod. In the step of forming the fine particle deposit, the growth point of the glass fine particle deposit growing at the lower end of the target rod is monitored to control the above-mentioned pulling speed, and the burner is controlled so that the pulling speed is constant. It is characterized by controlling the flow rate of flammable gas supplied to the fuel cell.

As a result of the investigation by the present inventors, it has been found that the growth rate of the glass fine particle deposit has a correlation with the temperature at the growth point. That is, the growth rate increases as the temperature decreases, and decreases as the temperature increases. It was also found that the temperature at the growth point was related to the relative refractive index difference.

Therefore, if the growth rate becomes slow and the pulling rate becomes low, the temperature of the growth point is lowered by reducing the flammable gas such as hydrogen gas or propane gas (and the auxiliary gas), thereby increasing the growth speed. Conversely, when the pulling speed increases, a large amount of combustible gas (and auxiliary gas) is supplied to increase the temperature at the growth point and slow down the growth. In this manner, by keeping the growth rate, that is, the pulling rate, constant, the adhesion state of the glass fine particles is stabilized in the longitudinal direction. Therefore, the variation in the diameter in the longitudinal direction and the variation in the relative refractive index difference in the longitudinal direction are small. For example, a high-quality porous glass body whose characteristics are stable in the longitudinal direction can be produced.

At this time, in order to perform optimal control while preventing overshoot and the like, the change amount and the change interval (interval time) of the flammable gas supply amount should be appropriately pursued for each individual device. Generally speaking, it is desirable that the change amount be within 10% of the set value and the interval time be 10 seconds or more. The reason why the interval time is lengthened is that the response time until the change in the supply amount of the combustible gas affects the change in the growth rate is long.

[0014]

Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an apparatus for producing a porous glass body by a VAD method according to the present invention. In this figure, a plurality (three in this example) of burners for producing glass fine particles near the lower end of a target rod 12 are shown. 21, 22, and 23 are arranged. Combustion gas of hydrogen gas and oxygen gas is supplied to these burners 21, 22, and 23, and an oxyhydrogen flame is generated. Further, a glass source gas such as silicon tetrachloride is supplied to these burners 21, 22, and 23. Burner 21, 2
Reference numerals 2 and 23 denote a multi-tube structure in which cylindrical nozzles are arranged concentrically, and a glass material gas (silicon tetrachloride, and for the burner 21, silicon tetrachloride and germanium tetrachloride for the burner 21). ), Hydrogen gas, oxygen gas from the third layer nozzle, and oxygen gas from the fourth layer nozzle, respectively.

In these burners 21, 22, and 23, fine glass particles (fine particles of silicon dioxide) are generated by feeding the glass raw material gas into the oxyhydrogen flame, and the fine glass particles adhere to the lower end of the target rod 12. Can be The upper end of the target rod 12 is gripped by the rotation pulling device 13 and is pulled up while being rotated. The target rod 12 is pulled up while being rotated in this manner, so that a deposit (soot preform) 1 of the attached and deposited glass fine particles is obtained.
1 grows cylindrically downward from the lower end of the target rod 12.

The burner 21 is a core burner for forming a core located at the center, and the burners 22, 23 are clad burners for forming a clad occupying the outer periphery of the core. Here, the clad portion is formed by two deposited layers. Burner 21 for core
In addition to silicon tetrachloride gas, which is a glass source gas,
A germanium tetrachloride gas or the like, which is a source gas of a dopant for controlling the refractive index, is sent.

Glass fine particle deposit 11, target rod 1
2 is disposed in a chamber (reaction vessel) 14 and has a burner 2
1 to 23 are attached to the side wall and the like of the chamber 14, and the deposition process of the glass fine particles is performed in the chamber 1.
4 is performed. Of this chamber 14,
The exhaust pipe 1 is provided on the side opposite to the side where the burners 21 to 23 are arranged.
5 is attached, and is exhausted by suction by a suction device (not shown).

The position of the lower end of the glass particle deposit 11 growing in the chamber 14 is detected by the position detecting device 31. This position detecting device 31 is, for example,
It comprises a TV camera that captures an image near the lower end and an image processing device that analyzes the image. The detection signal is sent to the computer 32, and the computer 32 controls the rotation pulling device 13 based on the detection signal. Thereby, the lifting speed of the target rod 12 is adjusted so that the lower end position of the glass fine particle deposit body 11 is always the same.

Information on the lifting speed of the target rod 12 is sent to the flow controller 33. The flow control device 33 controls the gas flow supplied to the burner 21 according to the lifting speed. That is, the supply amount of the hydrogen gas to be ejected from the nozzle of the second layer of the burner 21 having the multi-tube structure is controlled.

That is, when the growth speed of the glass fine particle deposit 11 is reduced and the pulling speed is lowered, the hydrogen gas is reduced to lower the temperature at the growth point, thereby increasing the growth speed. When the temperature increases, a large amount of hydrogen gas is supplied to increase the temperature at the growth point and slow down the growth. Thus, the growth rate, that is, the pulling rate, can be kept constant.

As a result, the temperature at the deposition position can be stabilized, so that the adhered state of the glass fine particles is reduced.
1 in the longitudinal direction. Accordingly, the variation in the outer diameter of the glass fine particle deposit body 11 in the longitudinal direction is reduced, and the variation in the relative refractive index difference in the longitudinal direction is reduced. Thus, a high-quality porous glass body whose properties are stable in the longitudinal direction can be produced.

It is to be noted that the change amount and the change interval (interval time) of the hydrogen gas supply amount should be appropriately pursued for each individual device so as to realize an optimum control while preventing an overshoot or the like. In general, it is preferable to set the interval time to 10 seconds or more because the response time until the change in the supply amount of the hydrogen gas affects the change in the growth rate is long. In addition, it can be said that the amount of change in the supply amount of hydrogen gas is preferably within 10% of the set value in consideration of, for example, not causing overshoot. In the above description, the flow control device 33 controls only the supply amount of the hydrogen gas to the burner 21, but may also control the supply amount of the oxygen gas.

[0023]

Embodiment 1 Further, a specific embodiment will be described in detail. The conditions of the flow rate of each gas supplied to the burners 21, 22, and 23 were as shown in the following table, to produce the glass particle deposit 11 having a diameter of about 150 mm and a length of about 1000 mm. Silicon tetrachloride Hydrogen gas Oxygen gas Burner 21 0.3 7.0 10 Burner 22 2.0 9.0 10 Burner 23 3.0 16.0 12 Unit SLM: Standard Litere Minutes (Flow rate in standard state: liter / minute) In the first embodiment, the burner is controlled by the flow controller 33 so that the hydrogen gas flow rate is reduced by 5% when the pulling speed is 2% slower than the set speed, and is increased by 5% when the pulling speed is 2% faster. The flow rate of hydrogen gas supplied to 21 was controlled. At that time, the pulling speed was taken in at a rate of once every 15 seconds to 2 minutes, and the flow rate was changed as described above accordingly.

As a result, the pulling speed was within the range of ± 3% as shown by the solid line in FIG. 2, and became very stable in the longitudinal direction of the glass fine particle deposit (soot) 11. The outer diameter of the soot 11 also has a variation within ± 3% as shown by the solid line in FIG. 3 and is stable in the soot length direction. Further, the characteristics of the glass particle deposit body 11, that is, the relative refractive index difference Δ (%) are also stable in the length direction as shown by the solid line in FIG.

[0025]

Example 2 For reference, as a second example, a glass particle deposit 11 having a diameter of about 150 mm and a length of about 1000 mm was produced under the configuration (FIG. 1) and gas flow conditions (table) of the above example. However, the hydrogen gas flow rate control according to the lifting speed is not performed at all (the flow rate control device 33
Inactive). As a result, the pulling speed became as shown by the dotted line in FIG. 2, and fluctuated greatly in the longitudinal direction. The variation in the soot diameter also increased correspondingly, and the tolerance was 5% or more as shown by the dotted line in FIG. The relative refractive index difference Δ in the longitudinal direction also fluctuated greatly as shown by the dotted line in FIG.

[0026]

[Embodiment 3] As a third embodiment, a diameter of about 150 m was obtained with the configuration of the above embodiment (FIG. 1) and gas flow conditions (table).
In this case, not only the hydrogen gas flow rate but also the oxygen gas flow rate was controlled by the flow rate control device 33 in accordance with the pull-up speed. The control interval is set to 15 seconds to 2 minutes, and the gas flow rate is reduced by 5% when the lifting speed is 2% slower than the set speed, and 5% when the speed is increased by 2%.
The rate of change to increase is also the same, and this is
Control was applied to both hydrogen gas and oxygen gas supplied to 1.

In this case, the pulling speed varies in the longitudinal direction,
With respect to the variation in the soot diameter in the longitudinal direction and the variation in the relative refractive index in the longitudinal direction, the results were not significantly different from those in the first example (results close to the solid line in FIG. 2, the solid line in FIG. 3, and the solid line in FIG. 4, respectively). It became.)

[0028]

Embodiment 4 For reference, the interval time of the hydrogen gas flow rate control by the flow rate control device 33 in accordance with the lifting speed was set to 5 seconds. The fourth embodiment is different from the first embodiment in that the glass fine particle deposit 11 having a diameter of about 150 mm and a length of about 1000 mm is manufactured under the configuration (FIG. 1) and the gas flow conditions (table) of the above embodiment. It is the same as the example.

In the fourth embodiment, the fluctuation of the pulling speed in the soot longitudinal direction is as shown by the solid line in FIG. It is probable that the change rate of the hydrogen gas flow rate was too fast with respect to the response speed of the system, or that the control amount was too large and the overshoot was large, resulting in such a result.

[0030]

As described above, according to the apparatus and method for manufacturing a porous glass body of the present invention, the supply amount of the flammable gas is controlled in accordance with the lifting speed of the target rod in the VAD method. Pulling speed (growth speed)
In other words, the temperature at the deposition point can always be constant, thereby stabilizing the deposition state of the glass particles,
A high-quality porous glass body in which characteristics such as the outer diameter and the relative refractive index difference of the porous glass body are stabilized in the longitudinal direction can be easily manufactured. Therefore, it is possible to greatly contribute to the reduction of the manufacturing cost of the optical fiber.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a soot length and a pulling speed in Examples 1 and 2.

FIG. 3 is a graph showing the relationship between soot length and soot diameter for Examples 1 and 2.

FIG. 4 is a graph showing a relationship between a soot length and a relative refractive index difference in Examples 1 and 2.

FIG. 5 is a graph showing a relationship between a soot length and a pulling speed in Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Glass fine particle deposit body 12 Target rod 13 Rotation | pulling-up apparatus 14 Chamber 15 Exhaust pipe 21, 22, 23 Burner 31 Position detection apparatus 32 Computer 33 Flow rate control apparatus

Continuation of the front page (72) Inventor Koichi Takahashi 1440 Mutsuzaki, Sakura-shi, Chiba Prefecture F-term Co., Ltd. F-term in Sakura Plant 4G014 AH14 4G021 EA01 EB26 5H307 AA02 BB04 DD02 DD17 EE02 FF21 GG04 GG20 HH04

Claims (2)

[Claims] 1. A burner for producing glass fine particles, a rotary pulling device for pulling up while rotating a target rod on which the glass fine particles are deposited at a lower end, and a growth point of a glass fine particle deposit growing at the lower end of the target rod. A porous glass, comprising: a control device for monitoring the pulling speed by monitoring the flow rate; and a flow control device for controlling a flow rate of the flammable gas supplied to the burner so that the pulling speed is constant. Body manufacturing equipment. 2. A process in which glass particles generated from a burner are deposited on the lower end of a rotating target rod, and the target rod is pulled up to form a glass particle deposit. Manufacturing the porous glass body, wherein the growth point of the deposit is monitored to control the pulling speed, and the flow rate of the flammable gas supplied to the burner is controlled so that the pulling speed is constant. Method.