JPS62265141A - Production of base material for optical fiber - Google Patents

Abstract

PURPOSE:To stably and efficiently produce a porous base material for an optical fiber by maintaining the distance between the end face of a burner and the deposition surface of granular glass in an optimum range in the deposition stage of the granular glass to a starting material. CONSTITUTION:A method for producing the porous glass base material by ejecting a glass raw material from the combustion burner, depositing the granular glass formed by the same on the rotating starting material or arbor and growing the same in the rotation axis direction is executed in the following manner: The burner 1 is gradually moved distant from the granular glass deposition surface 3 along the Z-axis direction 2 of the burner 1 by which the relative distance between the burner 1 and the surface 3 is maintained within the specified range until the normal state is attained. The operations as in the conventional practice may be executed when the stationary state is attained. The attainment of the normal state refers to the initial production stage since the start of the deposition of the granular glass on the starting material or arbor until the outside diameter of the porous glass base material becomes normal.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for manufacturing a base material for optical fiber, which particularly requires high purity, and more particularly, to a method for efficiently and stably manufacturing a porous glass base material. It is related.

[Conventional technology]

Generally, in the production of porous glass base materials, combustion gas, glass raw materials, etc. are mixed and ejected from a combustion burner, and granular glass produced by a chemical reaction of the glass raw materials, etc. in the flame is placed on a rotating starting material or mandrel. A method of depositing the material is used.

In this method, the position of the combustion burner has conventionally been determined by focusing only on the optimal manufacturing conditions when the porous glass base material is steady (the state where the growth of the base material is steady). In other words, for K to fully react with the raw material to form glass fine particles, there needs to be a certain distance between the deposition surface and the reaction starting point, and conversely, if the distance is too far, the particle flow will spread, which will reduce the deposition efficiency (raw material yield). ) will fall, so normally the fLK burner etc. is fixed to the point where it is most efficient in a steady state.

[Problem that the invention seeks to solve]

By the way, when producing a large-sized base material by the above-mentioned conventional method, the diameter of the starting material or the mandrel is very small compared to the diameter of the porous glass base material that is usually produced, and the starting material or the mandrel is It takes a considerable amount of time from the time the granular glass begins to be deposited until the growth of the porous glass matrix reaches a steady state, ie, this early manufacturing stage. However, in conventional methods, even during the initial production stage, the relative position of the starting material or mandrel and the combustion burner remains fixed at a position that is optimal in the steady state of growth of the glass porous matrix.

That is, in the initial manufacturing stage, the relative distance between the granular glass deposition surface and the combustion burner becomes shorter every moment.

There are also problems in that it takes a long time to reach a steady state or that cracks occur during deposition.

The present invention solves these problems and provides a method that can shorten the time required to reach a steady state even when manufacturing large-sized base materials, and stably manufacture porous base materials with a high raw material yield. It is intended.

[Means for solving problems]

The present invention solves the above problems by recognizing that the relative distance between the combustion burner and the granular glass deposition surface is important.

That is, the present invention provides a method for producing a porous glass base material by ejecting glass raw material from a combustion burner, depositing granular glass produced by a rotating starting material or mandrel, and growing it in the direction of the rotation axis. The method is characterized in that the distance between the burner end face and the surface on which the granular glass is deposited is maintained within an optimum range during the manufacturing stage from when the granular glass begins to be deposited on the starting material or the mandrel until the outer diameter of the porous glass base material becomes constant. This is a method for manufacturing a base material for Hikari 7 eyewear. In the present invention, it is one of the preferred embodiments that the distance between the burner end face and the granular glass deposition surface is kept within a certain range.

FIG. 1 is a sectional view for schematically explaining the present invention,
The initial manufacturing stage of the porous glass matrix is shown. In Figure 1 h
By gradually moving the combustion burner 1 away from the granular glass deposition surface 3 along the two axial directions 2 of the emotional burner 1, the combustion burner 1 and the granular glass deposition surface 3 are kept in contact with each other until a steady state is reached. The relative distance between can be kept within a certain range. Once a steady state is reached, the process can be carried out in the conventional manner.

In addition, the black arrow part in @1 figure indicates the above-mentioned relative distance, the white arrow 4 indicates the moving direction of the combustion burner 1, and 4 indicates the shaft.

In the present invention, reaching a steady state refers to the initial manufacturing stage from when the granular glass begins to be deposited on the starting material or mandrel until the outer diameter of the porous glass preform becomes steady. As mentioned above, even while the outer diameter of the porous glass base material reaches a steady state, the relative distance between the combustion burner and the granular glass deposition surface is kept within a certain range, and even in the initial stage, the deposition surface It is possible to maintain an optimal positional relationship between the source and the raw material spout in which the particles grow sufficiently and the spread of the particle flow is small. Therefore, since the yield at this initial stage (unsteady state) is improved, the time required to reach a certain diameter can be shortened, and efficient and stable production becomes possible. At the same time,
By keeping the relative distance between the combustion burner and the surface on which the granular glass is deposited within a certain range, the porous glass base material can be exposed to flames of various strengths, and as a result, the bulk density of the porous glass base material can be reduced. It increases uniformly, and cracks do not occur, making it possible to manufacture efficiently and stably in this respect as well.

〔Example〕

Example 1 According to the configuration shown in FIG. 1, a concentric multi-tube burner was used as the combustion burner 7, and hydrogen was supplied to it at a rate of 30 liters per minute.
Oxygen was supplied at 35 liters per minute, argon was supplied at 12 liters per minute, and silicon tetrachloride was supplied at 700 ml per minute as a glass raw material9. As the mandrel 4, a pure quartz rod was used. The granular glass was sequentially deposited from the upper part of the mandrel 4, while the burner 1 was moved back in the direction of its Z-axis 12 by 5 minutes and Ic, 5+m. In this case, the distance between the end face of the burner 11 and the granular glass deposition surface 13 was maintained in the range of 71 to 9tx. After 50 minutes, when the outer diameter of the porous glass base material reached approximately 100 m, the position of the burner 11 was finally fixed, and from then on, the porous glass base material was lifted while pulling the mandrel 14 at a speed of 70 mm/hour. It was grown in the direction of its rotation axis. With this method, production could be continued without cracking the porous glass base material in the initial stage, and the raw material yield was improved by about 10 times compared to the conventional method.

Comparative Example 1 The flow of raw materials and combustion gas was the same as in the above embodiment, and the position of the burner 11 was fixed at the same position as in the above embodiment during regular production. Started depositing glass. After 55 minutes, cracks appeared in the upper part of the porous glass matrix.

When ten porous glass preforms were produced in the same manner, three of them cracked in the early stages of production.

In the above embodiment, a center rod is used, but the same effect can be obtained without a center rod.

〔Effect of the invention〕

As explained above, in the production of optical fiber preforms, the present invention gradually moves the combustion burner in the Z-axis direction in the initial stage of production until the outer diameter of the porous preform becomes constant, and By keeping the distance between the spout and the granular glass deposition surface within the range of optimal positional relationship for deposition, cracking of the porous glass base material during the initial stage can be prevented and the raw material yield can be improved. It has the effect of Therefore, the present invention is an excellent method for stably manufacturing a porous preform for optical fibers more efficiently than the conventional method.

[Brief explanation of drawings]

FIG. 1 is a sectional view schematically explaining an embodiment of the present invention.

Claims (2)

[Claims] (1) In the method of manufacturing a porous glass base material by ejecting glass raw materials from a combustion burner, depositing the resulting granular glass on a rotating starting material or mandrel and growing it in the direction of the rotation axis, the above-mentioned The method is characterized in that the distance between the burner end face and the surface on which the granular glass is deposited is maintained within an optimum range during the manufacturing stage from when the granular glass begins to be deposited on the starting material or the mandrel until the outer diameter of the porous glass base material becomes constant. A method for producing a base material for optical fiber. (2) The method for manufacturing an optical fiber preform according to claim (1), wherein the distance between the burner end face and the granular glass deposition surface is within a certain range.