JP2007204329A - Manufacturing method of optical glass preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stably manufacturing an optical preform with reduced bubbles in a long term. <P>SOLUTION: The manufacturing method of an optical preform comprises spraying glass fine particles on a core material 3 in a chamber 1 by an oxygen-hydrogen burner 2 to grow a porous suit layer 6. From above the chamber 1, air is supplied into the chamber 1 and discharged from the bottom of the chamber 1 to the outside of the chamber 1, and the oxygen-hydrogen burner 2 is made to approach from above the core material 3 to the core material 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing an optical glass base material capable of stably producing an optical glass base material with reduced bubbles for a long period of time.

  As an optical fiber manufacturing method, a glass raw material (for example, silicon tetrachloride) is supplied into a oxyhydrogen flame burner to a core material (core glass target) made of a core and a clad produced by a VAD method or the like. In general, an OVD (external) method is used in which a porous glass base material is produced by spraying glass fine particles formed by a hydrolysis reaction on the core material and growing a porous soot layer. The porous glass base material manufactured by the OVD method is then heated and sintered at a temperature of about 1500 ° C. to become a transparent glass base material.

  In order to grow the soot layer uniformly in the axial direction and circumferential direction of the core material, the core material is supported horizontally in the chamber and rotated around its horizontal central axis, and the oxyhydrogen burner and the core material are aligned with the central axis of the core material. Relatively moved in parallel directions.

  In the conventional method for producing an optical glass base material, the oxyhydrogen burner is formed from below the core material so that an oxyhydrogen flame containing a raw material gas blown from the oxyhydrogen burner to the core material in the chamber is stably formed along with the rising airflow. The oxyhydrogen flame is directed vertically upward, diagonally upward, or horizontally, facing the core material. The exhaust port is provided on the side opposite to the oxyhydrogen burner, that is, above the core material with the core material interposed therebetween.

JP 2003-20242 A Japanese Patent No. 3524426 Japanese Patent Laid-Open No. 9-71430 JP 11-343135 A

  In order to stably manufacture an optical fiber without breaking in the spinning (drawing) process, it is important to reduce bubbles contained in the optical glass base material. Among the glass particles formed by the hydrolysis reaction described above, some of the glass particles that are exhausted without being deposited on the core material adhere to the exhaust port or the inner wall of the chamber, and the glass particles are deposited as a cause of bubbles. It is known that it peels off in the process, falls and adheres to the core material (growing optical glass base material).

  In the conventional method for manufacturing an optical glass base material, as a countermeasure to reduce bubbles contained in the optical glass base material, the glass particles adhered by heating the chamber are made difficult to peel off, or the glass microparticles adhere to the chamber. An independent gas to be reduced is introduced into the chamber. However, these countermeasures have an effect of reducing bubbles in the short term, but it is difficult to stably reduce bubbles in a long period of time such as six months to one year. When used for a long time, the exhaust port and the chamber deteriorate due to corrosive gas such as HCl generated by the hydrolysis reaction, and the deterioration causes foreign matter (for example, rust in the case of a metal chamber) to the exhaust port and the chamber. To do. Since the exhaust port and the chamber are located above the core material, this foreign substance falls on the optical glass base material and causes bubbles.

  Then, the objective of this invention is providing the manufacturing method of the optical glass base material which can manufacture the optical glass base material which reduced the said subject and reduced the bubble for a long term stably.

  To achieve the above object, the present invention provides a method for producing an optical glass base material in which a porous soot layer is grown by spraying glass fine particles onto a core material in a chamber with an oxyhydrogen burner. The air is supplied and exhausted from under the chamber to the outside of the chamber, and the oxyhydrogen burner is made to face the core from above the core.

  The strength of the air flow in the chamber by the supply / exhaust may be set so that glass fine particles not adhered to the core do not go above the core.

  Further, the present invention provides a method for producing an optical glass base material in which a porous soot layer is grown by spraying glass fine particles onto a core material in a chamber with an oxyhydrogen burner, and the above-mentioned chamber is used to supply air into the chamber. The exhaust gas is exhausted from the bottom of the chamber to the outside of the chamber, and the flow rate of the air flow in the chamber by the supply / exhaust is kept at 1.0 m / s or more, and the oxyhydrogen burner faces the core material from above the core material. .

  The present invention exhibits the following excellent effects.

  (1) An optical glass base material with reduced bubbles can be stably produced over a long period.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, according to the method for manufacturing an optical glass base material according to the present invention, air is supplied into the chamber from above the chamber 1 and exhausted out of the chamber from below the chamber 1. As a result, an air stream flowing from above to below is generated, and the oxyhydrogen burner 2 is made to face the core material 3 from above the core material 3, whereby glass particles are sprayed onto the core material 3 from above the core material 3.

  The manufacturing apparatus will be described in detail. An air supply port 4 is formed in the upper portion of the chamber 1 and an air supply duct (not shown) is attached. An exhaust port 5 is formed in the lower portion of the chamber 1 and an exhaust duct (not shown). ) Is attached. Since the drawing is drawn in a simplified manner, the chamber 1 has a simple cylindrical shape, but it does not prevent other shapes or complicated shapes from being formed. The exhaust port 5 may be disposed below the core material 3 and does not need to be directly below the core material 3 as shown. Similarly, the air supply port 4 has only to be arranged on the opposite side of the exhaust port 5 with the core material 3 interposed therebetween, and does not need to be directly above the core material 3 as shown in the figure.

  As a matter of course, a gas (for example, air or nitrogen gas) supplied from the supply port 4 is a clean gas, and a filter (not shown) may be attached to the supply port 4. If the entire manufacturing apparatus shown in the figure is installed in a clean environment, the filter may not be provided.

  The material of the chamber 1 is SUS metal, but quartz glass or other materials may be used.

  The core material 3 is formed in a rod shape in advance, is horizontally supported in the chamber 1 by a rotation support mechanism (not shown), and is rotated around the central axis of the core material.

  The oxyhydrogen burner 2 is installed obliquely above the core material 3. Therefore, the oxyhydrogen burner 2 sprays glass fine particles onto the core material 3 from obliquely above the core material 3.

  The oxyhydrogen burner 2 and the core material 3 can move relative to each other in a direction parallel to the central axis of the core material 3. In this embodiment, the core material 3 is fixed, and the oxyhydrogen burner 2 is reciprocated in the longitudinal direction of the core material (direction perpendicular to the paper surface).

  The manufacturing method will be described in detail. A rod-shaped core 3 supported horizontally in the chamber 1 is rotated around the central axis of the core 3 and glass particles are sprayed on the outer periphery of the core 3 with an oxyhydrogen burner 2. The oxyhydrogen burner 2 is reciprocated in the longitudinal direction of the core material 3 to sequentially deposit and grow a porous soot layer (porous glass deposition layer) 6 on the outer periphery of the core material 3.

  At that time, air is supplied to the chamber 1 from the upper air supply port 4 and exhausted from the lower air supply port 5 to generate an air flow. By maintaining the flow velocity of the air flow at 1.0 m / s or more, the oxyhydrogen flame 7 containing glass fine particles blown out from the oxyhydrogen burner 2 can be stably guided downward.

  Further, the excessive glass fine particles generated when the oxyhydrogen flame 7 is sprayed on the core material 3 can be smoothly flown upward without rising up by keeping the flow velocity of the airflow at 1.0 m / s or more. To be discharged.

  Even if the exhaust port 5 and the chamber 1 deteriorate due to long-term use and foreign matter is generated, the exhaust port 5 and the chamber 1 (deteriorated part) are located below the core material 3, so that the foreign glass is growing. It does not fall on the base material and cause bubbles.

  As a result, the material and atmosphere above the optical glass base material (core material) will always be kept clean, and the generation of bubbles due to the fall of glass particles and foreign matter can be suppressed even after long-term production. , Stable production becomes possible.

  The reason why the flow rate is preferably 1.0 m / s or more depends on the result of the next experiment. In other words, the flow and dirt accumulation were observed experimentally under the conditions of 0.5 m / s, 0.8 m / s, 1.0 m / s, 1.5 m / s, and 2.0 m / s. did. When the flow velocity was 1.0 m / s or more, the soot rising due to the rising air flow was suppressed, and the chamber wall located above the soot deposition position of the core material was hardly contaminated. The higher the flow velocity, the lower the dirt boundary position.

  On the contrary, when the flow velocity is 0.5 m / s and 0.8 m / s, the soot rises upward, soot adheres to the wall of the chamber 1 located above the soot deposition position of the core material 3, and Soot peeling (part) occurred. The slower the flow rate, the more soot was peeled off.

Hydrogen gas 0.06m in multi-tube oxyhydrogen burner made of silica glass ³ / min, supplying oxygen gas 0.03 m ³ / min and silicon tetrachloride 30 g / min, to generate glass particles by hydrolysis, heartwood Starting from a diameter of 35 mm, a porous soot diameter of 150 mm was deposited. The rotation speed of the core material was 40 rpm, and the moving speed of the burner was 120 mm / min.

  Thereafter, transparent vitrification was performed, and the number of bubbles of 0.1 to 1.0 mm generated in the glass at that time was evaluated. The number of bubbles per base material was 0 to 2 when continued for about half a year at a rate of about 1 line / day. In this way, stable optical glass base material production could be realized.

  As a comparative example, a conventional manufacturing apparatus in which an exhaust port is located above the core material and a burner is installed below the core material, and the same deposition conditions (gas concentration, diameter, speed, manufacturing pace, etc.) as in the above example are used. When the number of bubbles was evaluated by performing period production, the number of bubbles was stable until 0 to 3 months, but thereafter, the number of bubbles gradually increased to several tens. As a result of investigating the cause, it was found that the progress of deterioration (corrosion) of the exhaust port almost coincided with the tendency of the increase in the number of bubbles.

  For this reason, air is supplied into the chamber from the top of the chamber and exhausted from the bottom of the chamber to the outside of the chamber, thereby generating an air flow that flows from the top to the bottom of the chamber, and the oxyhydrogen burner on the core. If glass particles are sprayed onto the core material from the top of the core material, glass particles and foreign substances adhering to the chamber and the exhaust port will drop and adhere to the growing optical glass base material. This makes it possible to continue production stably for a long period of time.

It is a fundamental block diagram of the manufacturing apparatus which enforces the manufacturing method of the optical glass base material of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Chamber 2 Oxyhydrogen burner 3 Core material 4 Supply port 5 Exhaust port 6 Soot layer (porous glass deposition layer)
7 Oxyhydrogen flame

Claims (3)

  In a method for manufacturing an optical glass base material in which a porous soot layer is grown by spraying glass fine particles onto a core material in a chamber with an oxyhydrogen burner, air is supplied into the chamber from above the chamber, and from outside the chamber to outside the chamber. And producing the optical glass base material, wherein the oxyhydrogen burner is allowed to face the core material from above the core material.   2. The method for producing an optical glass base material according to claim 1, wherein the strength of the air flow in the chamber by the supply / exhaust is set such that the glass fine particles not adhered to the core material do not go above the core material. . In a method for manufacturing an optical glass base material in which a porous soot layer is grown by spraying glass fine particles onto a core material in a chamber with an oxyhydrogen burner, air is supplied into the chamber from above the chamber, and from outside the chamber to outside the chamber. The optical glass base material is characterized in that the flow rate of the air flow in the chamber by supply and exhaust is maintained at 1.0 m / s or more, and the oxyhydrogen burner is placed on the core material from above the core material. Manufacturing method.

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