JP2000344530A - Production of porous glass preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of and deposition of rust on the inside walls of piping of a cooling system and to prevent the degradation in heat exchange efficiency by passing cooling water containing a rust preventive into a cooling medium flow passage provided in a reaction vessel where glass particulates are deposited on a starting base material. SOLUTION: The glass particulates formed by vapor phase hydrolysis of gaseous glass raw material in an oxyhydrogen flame are deposited on a base material glass rod 2 to form a soot body 5 in the reactor 1 having the cooling medium flow passage. A cooling pipe 11 made of stainless steel is installed along the vessel wall 12 of the reactor vessel 1 in parallel with the axis of the base material glass rod 2. Thermally insulating materials 16 are mounted at the vessel wall 12 and the outside wall 15 is provided so as to enclose both. The water containing the rust preventive is passed as a cooling medium into the cooling pipe 11 to cool the reaction vessel 1. The rust preventive containing polycarboxylic acid nitrate or the rust preventive containing polycarboxylic acid nitrite and inorg. nitrogen compd. are used as the rust preventive. The amounts of these rust preventives to the cooling water are preferably specified to about 1 to 10 ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a porous glass preform for producing a glass preform used as a raw material of an optical fiber.

[0002]

2. Description of the Related Art An optical fiber is manufactured by drawing a glass rod, a so-called optical fiber preform, having a large diameter glass base material reduced in diameter. This large-diameter glass base material is obtained by sintering a porous base material manufactured by an axis attachment method (VAD method) or an external attachment method (OVD method) by heat treatment to form a transparent glass.

FIG. 1 shows an apparatus for manufacturing a porous glass preform by an external method. In a reaction vessel 1, a base glass rod 2 serving as a starting base material is arranged with both ends thereof supported by a base material holding tool 3. The deposition of the glass particles on the base glass rod 2 is performed by subjecting a glass raw material gas to a gas phase hydrolysis reaction in an oxyhydrogen flame using a glass particle synthesis burner (hereinafter, simply referred to as a burner) 4 to obtain glass particles (soot). ) Is generated by spraying glass fine particles on the peripheral surface of the base glass rod 2 and depositing them in the radial direction, so that the soot body 5 is formed. Until a predetermined outer diameter is obtained, the burner 4 is reciprocated by the moving mechanism 7 along the longitudinal direction of the base glass rod 2 while rotating the base glass rod 2 by the rotating mechanism 6 to perform deposition. to continue.
The combustion exhaust gas is exhausted to the outside of the reaction vessel 1 by the exhaust hood 8.

In this process, in order to maintain the deposition efficiency and prevent contact between the soot body 5 and the burner 4,
According to the growth of the soot body 5, the distance between the soot body 5 and the burner 4 is adjusted by the burner position adjusting mechanism 9. The outer diameter increases with the growth of the soot body 5 and the outer peripheral area increases.
Need to maintain the heat supply per unit area to the
Combustion gas such as hydrogen and oxygen to the burner 4 will be increased. In recent years, as the size of the porous glass base material increases, the amount of gas to be burned increases, and the amount of heat received by the reaction vessel 1 increases.

[0005] The reaction vessel does not receive the radiant heat evenly. When the amount of heat increases, the thermal stress of the reaction vessel increases, which damages the reaction vessel or greatly affects the life. If the reaction vessel is damaged, fine pieces of the plate material or the heat insulating material constituting the reaction vessel may be mixed into the soot body, causing an increase in transmission loss and disconnection of an optical fiber as a final product. To extend the life of the reaction vessel,
Although it is necessary to reduce the amount of heat received by the reaction vessel, reducing the amount of combustion gas lowers the density of the soot body and causes breakage during the manufacturing or transportation of the soot body. Further, when the density decreases, the diameter of the soot body becomes large, and there is a problem that the apparatus needs to be enlarged. As a countermeasure, the temperature of the reaction vessel itself is lowered by using water as a cooling medium to protect the reaction vessel.

[0006]

When cooling a reaction vessel, it is important to select a heat transfer area of the cooling pipe to the reaction vessel and a cooling medium to be used. As for the heat transfer area, there is a method in which the reaction vessel has a double structure, that is, a jacket structure, and a cooling medium flows through the reaction vessel. However, it is difficult to adjust the heat removal balance. Further, when the reaction vessel is damaged, there is a problem that the cooling medium leaks into the reaction vessel. For this reason, in practice, cooling is performed by attaching a cooling pipe to the outside of the reaction vessel.However, in order to remove heat from the reaction vessel with such a limited heat transfer area, a medium having high heat exchange efficiency is used. Is required. As the cooling medium, there are some places where the temperature of the reaction vessel becomes 100 ° C. or higher, so that mineral oil or the like can be cited in terms of boiling point. However, it is not efficient because it has only one fifth heat transfer capacity as compared with water.

Further, when water is used as the cooling medium, a new corrosion problem occurs. In a cooling device using water, oxygen is always supplied to the cooling water by contact with air, and the oxygen and high temperature cause a strong corrosive action, which promotes the generation of rust. The generated rust not only shortens the life of the equipment and cooling system, but also accumulates on the inner wall of the cooling system piping, lowering the heat transfer coefficient and reducing the flow rate by narrowing the pipeline to reduce the heat exchange efficiency. cause. The present invention provides a method for producing a porous glass base material capable of preventing generation and accumulation of rust on a pipe inner wall of a cooling system attached to a reaction vessel and preventing a decrease in heat exchange efficiency. Is an issue.

[0008]

Means for Solving the Problems Usually, when water is used as a cooling medium, a corrosion-resistant material such as a pipe serving as a cooling medium flow path is used in order to make the cooling medium less susceptible to corrosion. In this case, the device becomes very expensive. Incidentally, even stainless steel, which is generally considered to be hardly corroded, rusts. Therefore, the present inventors use water containing a polycarboxylic acid nitrite as a rust preventive agent in water, more preferably, water containing a polycarboxylic acid nitrite and an inorganic nitrogen compound, so that even water at high temperature can be corroded. Did not progress, and completed the present invention.

That is, in the method for producing a porous glass base material of the present invention, a glass raw material gas is produced by gas phase hydrolysis in an oxyhydrogen flame in a reaction vessel provided with a cooling medium flow path. When depositing the glass fine particles on the starting base material, the method is characterized in that water containing a rust inhibitor is flowed into the cooling medium flow path to cool the reaction vessel to form a glass fine particle deposit.
As rust preventives, those containing polycarboxylic nitrite,
Alternatively, a mixture containing a polycarboxylic acid nitrite and an inorganic nitrogen compound is used, and the amount of these added to the cooling water is preferably about 1 to 10 ppm. If the added amount is less than 1 ppm, the desired effect cannot be obtained, and if it exceeds 10 ppm, the effect will be constant, and if it is added in too much amount, it will cause a problem of precipitation in the medium pipeline and the heat exchanger, which is not preferable.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in more detail with reference to the drawings based on examples.

[0011]

FIG. 2 is a schematic cross-sectional view showing an example of a porous glass preform manufacturing apparatus according to the present invention, in which a cooling pipe and a heat insulating material as a cooling medium passage are attached to the vessel wall of a reaction vessel. ing. In this embodiment, a 25 mm square stainless steel cooling pipe 11 is connected in parallel with the axis of the base glass rod 2 by 10 mm.
3, the cooling pipes 11 were fixed (point-welded) using bands 13 at a pitch of 300 mm, and the cooling pipes 11 were fixed at both sides of the cooling pipe 11 at intervals of 0 mm, as shown in FIG. Thermo-cement 14 was added to the structure to increase the heat conduction area. Further, Al ₂ O ₃ and SiO ₂ are placed on the wall 12 of the reaction
Was attached, and an outer wall 15 was provided so as to wrap them, and the space between the vessel wall 12 and the outer wall 15 was completely sealed.

As a cooling medium flowing through the cooling pipe, 6 ppm of polycarboxylic acid nitrite and 5 pp of inorganic nitrogen compound
tolfam water: KH5000
(Manufactured by Shinsei Cooling Systems) was used. When the flow rate of the cooling water was adjusted and the temperature of the cooling water was maintained at 50 ° C. to manufacture the porous glass, the temperature of the inner wall of the reaction vessel was suppressed to 200 ° C. or less, as shown in FIG. Even when used for three months, no deterioration of the cooling effect and brown contamination, which had occurred conventionally, were observed, and the corrosion of the cooling device could be suppressed.

In this embodiment, the temperature of the cooling water is set to 50
Although the flow rate of the cooling water was adjusted so as to maintain the temperature at 0 ° C., it is desirable to use cooling water at 40 to 90 ° C., preferably 50 to 80 ° C. in consideration of dew condensation and cooling efficiency in the reaction vessel.
Although not specified in the present embodiment, since the cooling medium is used for a long period of time in the closed system without being replaced, there is a problem that bacteria grow in the device in addition to rust.
For this reason, it is also important to improve the environment around the device by adding an additive that suppresses the growth of bacteria and the like that adversely affect the human body. A rust preventive agent Regiocrash (manufactured by Aquas) having such a function and containing a bacterial growth inhibitor in addition to the polycarboxylic acid nitrite may be used.

[0014]

According to the method for producing a porous glass base material of the present invention having the above-described structure, the corrosion of the cooling device and the piping of the cooling system can be suppressed, and the heat exchange rate equivalent to that of water can be maintained. Therefore, it was possible to cope with an increase in the amount of heat due to the enlargement of the porous glass base material, and it was possible to improve productivity. Further, since the amount of heat released from the outer wall of the reaction vessel to the outside is suppressed, the working environment is improved, and the load on air conditioning is reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a porous glass preform manufacturing apparatus according to an external attachment method.

FIG. 2 is a schematic cross-sectional view of a reaction vessel according to the present invention.

FIG. 3 is a partial sectional view showing details of a vessel wall of the reaction vessel according to the present invention.

FIG. 4 is a comparative diagram showing a change in a heat removal ratio between an example of the present invention and a comparative example outside the reaction vessel.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction container 2 Substrate glass rod 3 Substrate grasper 4 Burner 5 Soot body 6 Rotating mechanism 7 Moving mechanism 8 Exhaust hood 9 Burner position adjusting mechanism 11 Cooling pipe 12 Container wall 13 Band 14 Thermocement 15 Outer wall 16 Insulation material 17 Exhaust port 18 Burner opening (air intake)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tadakatsu Shimada 2-3-1-1, Isobe, Annaka-shi, Gunma Shin-Etsu Kagaku Kogyo Co., Ltd. Precision Functional Materials Laboratory (72) Inventor Hideo Hirasawa Isobe, Annaka-shi, Gunma 2-13-1 Shin-Etsu Kagaku Kogyo Co., Ltd. Precision Functional Materials Laboratory F-term (reference) 4G014 AH15 4G021 EA03 EB22 4G062 AA06 BB01 CC07

Claims (4)

[Claims] In a reaction vessel provided with a cooling medium flow path,
When depositing glass fine particles generated by vapor-phase hydrolysis of a glass raw material gas in an oxyhydrogen flame on a starting substrate, water containing a rust inhibitor is flowed into the cooling medium flow path to cool the reaction vessel. A method for producing a porous glass base material, wherein a glass fine particle deposit is formed while forming. 2. The method for producing a porous glass base material according to claim 1, wherein the rust inhibitor contains a polycarboxylic acid nitrite. 3. The method for producing a porous glass base material according to claim 1, wherein the rust inhibitor contains a polycarboxylic acid nitrite and an inorganic nitrogen compound. 4. The porous glass mother according to claim 1, wherein the amount of the polycarboxylic acid nitrite and the amount of the inorganic nitrogen compound to be added to the water flowing in the cooling medium flow path are each 1 to 10 ppm. The method of manufacturing the material.