JP6191222B2 - Manufacturing method of glass base material - Google Patents

Description

  The present invention relates to a method for manufacturing a glass base material that is made transparent by sintering a porous glass base material.

  When making the porous glass base material transparent, helium gas, which is usually an inert gas, is allowed to flow in the furnace core tube during sintering. However, since helium gas is expensive and the use of helium gas leads to an increase in cost, there is a need to reduce the amount of helium gas used. Patent Document 1 discloses that the flow rate of helium gas (He) flowing into the furnace can be reduced at the initial stage of sintering when the pressure fluctuation in the furnace is small, thereby reducing the manufacturing cost.

JP 2009-132585 A

  However, for further cost reduction, there is a demand for further reduction of the amount of helium gas used when the porous glass base material is made transparent.

  Accordingly, an object of the present invention is to provide a method for producing a glass base material that can reduce the amount of helium gas used and keep the production cost low.

The method for producing a glass base material of the present invention capable of solving the above problems is a method for producing a glass base material by sintering and transparentizing a porous glass base material composed of an effective part and an ineffective part. ,
A first step of sintering the effective part while supplying helium gas into the sintering furnace;
And a second step of sintering the ineffective portion while supplying at least one of nitrogen gas and argon gas into the sintering furnace.

  According to the present invention, the amount of helium gas used can be reduced and the manufacturing cost can be kept low.

It is a schematic block diagram of the sintering furnace used for the manufacturing method of the glass base material which concerns on one Embodiment of this invention, and is a figure which shows the state which sinters an effective part. It is a schematic block diagram of the sintering furnace used for the manufacturing method of the glass base material which concerns on one Embodiment of this invention, and is a figure which shows the state which sinters an ineffective part.

When the porous glass base material is made transparent by sintering, helium gas, which is an inert gas having high gas solubility in glass, is usually allowed to flow into the furnace tube. If other inert gas such as cheap nitrogen gas or argon gas is used instead of this helium gas, problems such as bubble generation may occur.
The present inventor has that the porous glass base material has an effective portion that is a portion that becomes an optical fiber (product becomes) and an ineffective portion that is a portion that is not made optical fiber (not a product). Pay attention. If the non-effective part is left unsintered, sintering proceeds at the time of drawing the effective part thereafter, and problems such as deformation of the base material occur, so it is necessary to also sinter the non-effective part. However, even if bubbles or the like are generated in the glass of the ineffective portion, the ineffective portion is not drawn, so that there is no problem in the manufactured optical fiber (product).
Thus, as a result of intensive studies, the present inventor has devised a manufacturing method that uses inexpensive nitrogen gas (or argon gas) instead of helium gas while sintering the ineffective portion of the porous glass base material. I found it. Thereby, manufacturing cost can be reduced, maintaining the quality of the optical fiber manufactured.

[Description of Embodiment of Present Invention]
A method for producing a glass base material according to an embodiment of the present invention is as follows:
(1) A method for producing a glass base material by sintering and transparentizing a porous glass base material comprising an effective part and an ineffective part,
A first step of sintering the effective part while supplying helium gas into the sintering furnace;
And a second step of sintering the ineffective portion while supplying at least one of nitrogen gas and argon gas into the sintering furnace.
Helium gas is used for sintering in the effective part (first step), whereas nitrogen gas or argon gas, which is cheaper than helium gas, is used for sintering the ineffective part (second step). Therefore, the cost of the gas used at the time of sintering can be reduced. Since the ineffective portion is a portion that does not become an optical fiber even if sintered, even if bubbles are generated as a result of sintering using nitrogen gas or argon gas, the product optical fiber is not affected. Therefore, the manufacturing cost can be reduced without deteriorating the quality of the obtained optical fiber. In the second step, a slight amount of helium may be mixed.

(2) After the first step of sintering the effective part by supplying helium gas, at least one of nitrogen gas or argon gas is supplied into the sintering furnace to sinter the ineffective part The second step is performed.
The porous glass base material may include an ineffective portion at the upper and lower ends, but if the portion that is an ineffective portion is sintered with nitrogen gas or argon gas before the effective portion is sintered, the effective portion Even if the gas is switched to helium gas, bubbles may be generated in the effective portion. For this reason, helium is first flowed, and after the effective part has been completely sintered, at least one of nitrogen gas and argon gas is supplied to sinter, thereby reliably preventing bubbles from being generated in the effective part. However, the manufacturing cost can be reduced.

(3) In the second step, only nitrogen gas is supplied into the sintering furnace without containing helium.
In the second step, by using nitrogen gas that does not contain any helium gas and is cheaper than argon gas, the cost can be further effectively reduced.

[Details of the embodiment of the present invention]
Specific examples of the method for producing a glass base material according to the embodiment of the present invention will be described below with reference to the drawings.
In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to a claim are included.

  FIG. 1 is a schematic configuration diagram of a sintering furnace used in a method for producing a glass base material according to an embodiment of the present invention, and shows a state in which an effective part is sintered. FIG. 2 is a schematic configuration diagram of a sintering furnace used in the method for producing a glass base material according to an embodiment of the present invention, and shows a state in which an ineffective portion is sintered.

  A sintering furnace 1 shown in FIGS. 1 and 2 heats and sinters a porous glass base material 3 to make it transparent. The sintering furnace 1 includes a furnace core tube 2, a heater 4, a gas supply passage 5, a first intake valve 6, a second intake valve 7, an exhaust passage 8 and an exhaust valve 8a. Yes.

The core tube 2 is a tube formed in a bottomed cylindrical shape into which the porous glass base material 3 is inserted, for example. An upper end wall 9 of the core tube 2 has an opening 11 through which a seed bar 10 extending upward from the upper end of the porous glass base material 3 is inserted so as to be movable up and down.
The heater 4 heats the porous glass base material 3 inserted into the furnace core tube 2. A gas supply flow path 5 is connected to the bottom of the core tube 2. In the middle of the gas supply flow path 5, a first intake valve 6 that opens when supplying nitrogen (N ₂ ) gas or argon (Ar) gas supplied into the core tube 2 and helium (He) gas are provided. A second intake valve 7 that is opened when the supply is performed is provided. Further, an exhaust passage 8 for exhausting the gas in the furnace is connected to the peripheral wall on the upper end side of the core tube 2, and an exhaust valve 8 a is provided in the middle of the exhaust passage 8. A part of the gas supplied to the core tube 2 is discharged to the outside through a gap between the seed rod 10 and the opening 11.

  Moreover, the porous glass base material 3 inserted into the furnace core tube 2 of the sintering furnace 1 has an effective portion 3a that is a portion that is made into an optical fiber and an ineffective portion 3b that is a portion that is not made into an optical fiber. The effective part 3a is a part that has a part that becomes a core of an optical fiber and a part that becomes a clad and becomes a product. 1 and 2, the ineffective portion 3b is a portion above the broken line in the porous glass base material 3, but there may be an ineffective portion at the lowermost end.

[Glass base material manufacturing method]
Next, the manufacturing method of the glass base material of this embodiment is demonstrated.
First, as shown in FIG. 1, the porous glass base material 3 is inserted into the core tube 2 of the sintering furnace 1. At this time, the lower end portion of the porous glass base material 3 (that is, the sintering start end of the effective portion 3 a) is disposed at the height of the heater 4.

(First step)
First, the following first step is performed.
With the first intake valve 6 closed, the second intake valve 7 is opened, and helium gas is supplied into the furnace tube 2 as an inert gas for sintering from the gas supply flow path 5. At this time, the supply / exhaust flow rate of helium gas is adjusted so that the inside of the furnace becomes a positive pressure. The effective portion 3a of the porous glass base material 3 is sintered by performing predetermined heating with the heater 4 in the atmosphere of the supplied helium gas. In this manner, the position of the porous glass base material 3 is gradually lowered while the effective portion 3a is sintered from the lower end side. Then, as shown in FIG. 2, when the position where the porous glass base material 3 is suspended in the core tube 2 reaches a predetermined position (for example, the position where the ineffective portion 3b is the same as the height of the heater 4), the effective portion 3a. The whole is completely sintered.

(Second step)
Next, the following second step is performed.
The second intake valve 7 is closed, the first intake valve 6 is opened, and nitrogen gas or argon gas is supplied into the furnace core tube 2. Even if the helium gas is switched to nitrogen gas or argon gas, it is necessary to keep the inside of the furnace at a positive pressure in order to prevent outside air from being mixed into the furnace. For this reason, the pressure is adjusted while supplying substantially the same amount of nitrogen gas or argon gas as helium. And the ineffective part 3b of the porous glass base material 3 is sintered by performing predetermined heating with the heater 4 in the atmosphere of nitrogen gas or argon gas.

  As described above, the entire porous glass base material 3 is sintered to obtain a transparent glass base material. According to the glass base material manufacturing method of the present embodiment, the amount of helium gas used is reduced by 1/8 to 1/10 compared to the case where the entire porous glass base material 3 is sintered with only helium gas. The manufacturing cost can be reduced by about 10%.

In the above embodiment, an example in which there is an effective portion at the lower portion and an ineffective portion at the upper portion has been described. However, an ineffective portion may also exist at the lower portion of the glass base material. In this case, when the ineffective portion is first sintered with nitrogen gas or argon gas, the gas is switched, and when helium is flowed to sinter the effective portion, bubbles are generated in the effective portion. For this reason, before the effective part is sintered, it is necessary to sinter without flowing nitrogen gas or argon gas. In this case, even the ineffective part needs to be sintered with helium gas. is there.
Further, since nitrogen gas is less expensive than argon gas, in the above embodiment, it is more cost-effective to use nitrogen gas than argon gas.
In the second step, nitrogen gas or argon gas may not be used alone, but nitrogen gas and argon gas may be mixed and supplied. Although a slight amount of helium may be mixed, it is advantageous in terms of cost to use only nitrogen gas as described above.

  Moreover, in the manufacturing method of the glass base material of the said embodiment, in the part of the boundary of the effective part 3a of the porous glass base material 3, and the ineffective part 3b, the end part of sintering end side of the effective part 3a and the ineffective part 3b The time zone which sinters simultaneously the sintering start side edge part of this arises. At the same time as entering this time zone, the process proceeds to the second step, the gas to be supplied is switched from helium gas to nitrogen gas or argon gas, and sintering of the ineffective portion 3b may be started. You may increase the ratio of gas.

DESCRIPTION OF SYMBOLS 1 Sintering furnace 2 Furnace core tube 3 Porous glass base material 3a Effective part 3b Ineffective part 4 Heater 5 Gas supply flow path 6 First intake valve 7 Second intake valve 8 Exhaust flow path 8a Exhaust valve 9 Upper end wall 10 Seed stick 11 Opening

Claims (2)

A method for producing a glass base material by sintering and transparentizing a porous glass base material composed of an effective part and an ineffective part,
A first step of sintering the effective part while supplying helium gas into the sintering furnace;
Look including a second step for sintering by performing predetermined heating by the heater of the invalid portion while supplying at least one of nitrogen gas or argon gas into the sintering furnace,
A method for producing a glass base material , wherein the second step is performed after the first step is completed . The method for producing a glass base material according to claim 1, wherein in the second step, only nitrogen gas is supplied into the sintering furnace without containing helium .

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