阅读说明：本技术 光纤用玻璃母材的延伸方法 (Method for elongating glass base material for optical fiber ) 是由 三田怜 于 2020-03-03 设计创作，主要内容包括：本发明是将大径的玻璃母材延伸而制造更细径的玻璃杆的方法,且是在将玻璃母材直体部的一端具有透明玻璃锥部、另一端具有包含不透明玻璃部的锥部的玻璃母材延伸时,在该延伸之前,将包含不透明玻璃部的锥部的一部分切断,以该切断面为下端,将连接于延伸装置的牵引机构的牵引虚设件熔接的延伸方法,该切断面为圆形且该切断面的外径为135mm以上160mm以下。(The present invention is a method for producing a glass rod having a smaller diameter by elongating a glass base material having a large diameter and a tapered portion including an opaque glass portion at one end of a glass base material straight portion, and is an elongating method for, before elongation, cutting off a part of the tapered portion including the opaque glass portion, and welding a pulling dummy member connected to a pulling mechanism of an elongating apparatus with the cut surface as a lower end, wherein the cut surface is circular and an outer diameter of the cut surface is 135mm to 160 mm.)

1. A method for elongating a glass base material for an optical fiber, comprising: the method is a method for manufacturing a glass rod with a smaller diameter by extending a glass base material with a larger diameter, and is an extension method for cutting a part of a tapered part including an opaque glass part before extending the glass base material when extending the glass base material having a tapered part including the transparent glass part at one end of a glass base material straight part and a tapered part including the opaque glass part at the other end, and welding a pulling dummy member connected to a pulling mechanism of an extension device with the cut surface as a lower end, wherein the cut surface is circular and the outer diameter of the cut surface is 135mm to 160 mm.

2. The method for elongating an optical fiber glass preform according to claim 1, wherein: a transparent glass portion and an opaque glass portion are present in the cut surface, the opaque glass portion is circular, a relationship between x and y satisfies the following expression 1 when an outer diameter of the cut surface is x and an outer diameter of the opaque glass portion of the cut surface is y,

[ formula 1]

0.0698x²-19.003x+1352.6≦y≦-0.2067x²+62.567x-4620。

3. The method for elongating an optical fiber glass parent material according to claim 1 or 2, wherein the outer diameter of the glass parent material straight portion before elongation is 150mm or more and 190mm or less.

Technical Field

The present invention relates to a method for elongating a glass base material for an optical fiber into a glass rod having a smaller diameter by heating the glass base material.

Background

The following method is used in the manufacture of a silica glass rod such as represented by an optical fiber preform: after a large glass base material is manufactured in advance, it is heated and elongated by an elongation apparatus equipped with a heating furnace to form a glass rod having a smaller diameter. Since the glass rod extended by the extension device has a relatively large variation in outer diameter of, for example, ± 3%, it is precisely extended again by the extension device using a burner called a glass lathe as a heat source, and adjusted to the variation in outer diameter required for the product, for example, within ± 1%.

In recent years, when an optical fiber is produced from an optical fiber preform, it is advantageous in terms of equipment operation rate to produce a larger optical fiber preform, and therefore, an optical fiber preform having a larger outer diameter than a conventional general optical fiber preform having an outer diameter of 80mm, for example, an optical fiber preform having a larger outer diameter of more than 150mm is required. However, if the preform has a large diameter of 150mm in outer diameter, it is difficult to perform outer diameter adjustment by a glass lathe. This is because heating by the burner is performed in an open atmosphere, and therefore cooling by radiation occurs simultaneously with heating, and the effect of cooling by radiation increases as the outer diameter increases, and the temperature cannot be sufficiently increased.

Therefore, even a preform having a large diameter of 150mm in outer diameter is required to suppress the variation in outer diameter of the glass rod obtained by the elongating apparatus to within ± 1% or close to ± 1% required for the final product.

In recent years, various methods have been proposed for obtaining a glass rod having high outer diameter accuracy and high surface cleanliness by using a drawing apparatus. For example, patent document 1 discloses the following method: a glass base material manufactured by using a porous glass base material is arranged such that a tapered portion including an unsintered opaque glass portion is positioned on the lower side and a tapered portion which is vitrified into a transparent glass as a whole is positioned on the upper side, and further, a pulling dummy member is welded and extended at a cut surface formed by cutting the opaque glass portion arranged on the lower tapered portion, whereby the glass base material is extended at low cost and with high accuracy.

[ Prior art documents ]

[ patent document ]

[ patent document 1] Japanese patent No. 5766157

Disclosure of Invention

[ problems to be solved by the invention ]

However, in the method disclosed in patent document 1, since a large amount of gas is contained in the inside of the non-sintered opaque glass portion, the contained gas expands when heated to a high temperature, and as a result, there is a problem that the opaque glass portion is cracked and broken. When a crack occurs, the following problems occur: after the glass base material is taken out from the elongating apparatus after the elongation is stopped and the crack generating portion is cut and removed by the cutter, the glass base material itself must be returned into the elongating apparatus again to be elongated, and the glass base material itself is bent by an impact at the time of generating the crack.

As a result, the yield and productivity are deteriorated, and a dangerous work of removing the glass portion having the crack is required. Patent document 1 discloses a method in which, although it is preferable that when cutting is performed using an opaque glass portion, the closed cells are not left and the closed cells are cut at the closed cell portions, it is extremely difficult to distinguish whether the closed cells or the closed cells are present in the opaque glass portion, and colored ink is allowed to penetrate into the closed cells to distinguish between the closed cells and the closed cells.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for elongating a glass base material for an optical fiber, which can obtain a glass rod having high outer diameter accuracy at low cost.

[ means for solving problems ]

After careful study, it was found that when a part of the tapered portion including the opaque glass portion is cut, cracks generated when the opaque glass portion is extended are likely to be generated if the area of the opaque glass portion is too large. If the opaque glass portion is too large, the amount of gas contained in the opaque glass portion increases, and the opaque glass portion expands due to heating and is likely to be damaged. In order to suppress the cracks during the drawing, it is effective to reduce the opaque glass portion, but in order to reduce the opaque glass portion, it is necessary to heat the glass further than before to form the transparent glass during the sintering, and thus the tapered portion may be excessively stretched or the transparent glass portion may be crystallized as described above. Further, when heating is performed so that the opaque glass portion becomes as small as possible in the sintering process, the time required for each batch becomes long, and the throughput is lowered, or precise and complicated manufacturing management is required.

The method for elongating a glass base material for an optical fiber according to an embodiment of the present invention is a method for manufacturing a glass rod having a smaller diameter by elongating a glass base material having a larger diameter. In the case of elongating a glass base material in which one end of a glass base material straight portion has a transparent glass tapered portion and the other end has a tapered portion including an opaque glass portion, a portion of the tapered portion including the opaque glass portion may be cut before the elongation, and a pulling dummy material connected to a pulling mechanism of an elongating apparatus may be welded with the cut surface as a lower end. The cut surface may be circular and the outer diameter of the cut surface may be 135mm to 160 mm.

In addition, a transparent glass portion and an opaque glass portion may be present in the cut surface, and the opaque glass portion may be circular. Preferably, when the outer diameter of the cut surface is x and the outer diameter of the opaque glass portion of the cut surface is y, the relationship between x and y satisfies the following expression 1. The outer diameter of the glass base material straight portion before drawing may be 150mm to 190 mm.

[ formula 1]

0.0698x²-19.003x+1352.6≦y≦-0.2067x²+62.567x-4620

Drawings

Fig. 1 is a schematic longitudinal sectional view showing an example of an extension device.

Fig. 2 is a schematic view showing an example of a cut surface cut at a tapered portion including an opaque glass portion.

Fig. 3 is a diagram showing a relationship between the outer diameter of the cut surface (horizontal axis X) and the outer diameter of the opaque glass portion in the cut surface (vertical axis Y).

[ description of reference numerals ]

1 Heater

2 Heat insulation Material

3 Water-cooled Chamber

4 Top Chamber

5 hanging shaft

6 connect the gauge

7 feeding mechanism

8 lower part gas seal

9 guide roller

10 carry over pinch rolls (Upper)

11 carry over pinch rolls (lower)

12 glass base material

13 hanging dummy

14-pulling dummy

15 transparent glass part

16 opaque glass part

17 core rod part

18 cut surface outer diameter

19 outer diameter of opaque glass part

Detailed Description

An example of an extension device for extension will be described with reference to fig. 1. The stretching apparatus is substantially composed of 3 parts of a heating furnace, a feeding part and a drawing part. The heating furnace has a heater 1 and a water-cooled chamber 3 containing a heat insulating material 2 therein, a top chamber 4 is connected to an upper part of the water-cooled chamber 3, and a lower gas seal 8 is attached to a lower part of the water-cooled chamber 3.

The feeding part comprises a feeding mechanism 7 which is arranged at the upper part of the top chamber 4 and can move up and down, a suspension shaft 5 connected with the feeding mechanism 7 and a connecting jig 6. The suspension shaft 5 is inserted into the top chamber 4.

The traction part comprises a guide roller 9, a traction roller (upper) 10 and a traction roller (lower) 11 which are arranged at the lower part of the heating furnace and can be grabbed and released. The guide roller 9 is formed of a heat-resistant roller such as carbon, and is responsible for guiding the pulling dummy 14 or the glass rod to the axial core of the apparatus. The pulling rolls 10 and 11 are driven by a motor, and function to lower the pulling dummy member 14 or the glass rod gripped by the pulling rolls and to extend the glass parent material 12 to an appropriate diameter.

The glass base material 12 is mechanically connected to the connection jig 6 at the upper end of the suspension dummy 13 provided on the upper portion of the glass base material 12, and is connected to the feeding mechanism 7 via the suspension shaft 5, so as to be movable up and down. The pulling dummy member 14 is connected to the lower end of the glass base material 12. In the glass base material 12 produced by the porous glass base material, the opaque glass portion 16 is present on one tapered portion. During the elongation, the pulling dummy member 14 is lowered by the pulling rolls 10 and 11 at a speed faster than that of the glass parent material 12 while lowering the glass parent material 12 by the feeding mechanism 7, thereby obtaining a glass rod having a smaller diameter from the glass parent material 12.

Such an opaque glass portion 16 existing in the one-side tapered portion may remain in the sintering step of transparentizing the porous glass base material. Since the porous glass base material is vitrified in the sintering step sequentially from the lower portion while being suspended in the longitudinal direction, when the sintering reaches the upper tapered portion, the entire weight of the vitrified ingot (transparent glass portion) is applied to the heating portion, and when the upper tapered portion is vitrified completely, the tapered portion is excessively expanded by the weight. In order to prevent excessive expansion of the taper, the opaque glass portion 16 remains in the upper taper.

In the elongating method of the present embodiment, when elongating a glass base material in which one end of a glass base material straight body portion has a tapered portion of transparent glass and the other end has a tapered portion including an opaque glass portion, a portion of the tapered portion including the opaque glass portion is cut, and a pulling dummy member connected to a pulling mechanism of an elongating apparatus is welded and elongated with the cut surface as a lower end, and it is found that, when an outer diameter of the cut surface is 135mm or more and 160mm or less, generation of a crack in the opaque glass portion during elongation can be prevented, and a preform having more excellent appearance and outer diameter accuracy can be obtained.

Specifically, when the outer diameter of the cut surface is less than 135mm, the sintering for transparentizing the porous glass base material in the pre-drawing step cannot be achieved without excessive heating, and there is a high possibility that the preform is excessively stretched or the preform is crystallized at a tapered portion, which adversely affects the optical characteristics and the appearance of the preform. Further, when the cut surface outer diameter is larger than 160mm, it is difficult to sufficiently heat the cut surface at the time of sintering, so that the opaque glass portion in the cut surface becomes large, and the amount of gas contained in the opaque glass portion remaining in the vicinity of the cut surface becomes large, and the gas easily expands and cracks are generated at the time of heating at the initial stage of elongation or the like.

In addition, when the opaque glass portion 16 is circular except that the cut-surface outer diameter 18 is 135mm to 160mm, and the outer diameter 18 of the cut surface is x and the outer diameter of the opaque glass portion 16 of the cut surface is y, the crack generation during elongation can be further suppressed when the relationship between x and y satisfies the following relational expression.

In the present embodiment, the circular shape is not limited to a perfect circle, but falls within the scope of a circular shape as long as it is a non-circular shape that does not impair the function of the optical fiber preform.

[ formula 1]

0.0698x²-19.003x+1352.6≦y≦-0.2067x²+62.567x-4620

Even if the cut surface outer diameter 18 is 135mm or more and 160mm or less, when the outer diameter of the opaque glass portion 16 is large beyond the upper limit of the relational expression, the amount of gas remaining in the opaque glass portion in the vicinity of the cut surface is still large, and the gas easily expands and cracks are generated at the time of heating in the initial stage of elongation or the like. On the other hand, when the outer diameter of the opaque glass portion 16 is smaller than the lower limit of the relational expression, it is necessary to further progress the transparentization to the inside in the sintering step although the outer diameter of the porous glass base material is large, and it is very difficult to adjust the sintering conditions for achieving the transparentization without adversely affecting the appearance or the optical characteristics.

The present embodiment will be described in detail below based on comparative examples and examples, but the present invention is not limited to the embodiment described below, and various forms are possible within the claims.