JP2004115289A - Manufacturing process of ingot for optical fiber preform and hanging member used in the process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing process of an ingot for an optical fiber preform with which a large-sized porous preform is sintered even in an atmosphere containing high temperature carbon and a hanging member used in the process. <P>SOLUTION: The manufacturing process of the ingot for the preform comprises forming a porous preform 3 by depositing soot around the starting material, hanging down the porous preform in a sintering furnace, dehydrating and sintering it for vitrification to obtain a transparent glass. A hanging member made of silicon nitride covered with silicon carbide is used for hanging the porous preform 3. The hanging member consists of a hanging fixture 2 and a shaft 1. They are screwed together. The porous preform 3 is fixed to the fixture 2 with a pin 6 via its quartz shaft 4 or a dummy 5 mounted on the shaft. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing an optical fiber preform ingot (hereinafter, simply referred to as a preform ingot) for sintering a porous preform and turning it into a transparent glass, and a suspension member used for the method.
[0002]
[Prior art]
In a preform ingot used for manufacturing an optical fiber, a cladding portion is deposited on the surface of a starting core member by an OVD (external attachment) method to form a porous preform, which is then dehydrated in a dehydration furnace and then dehydrated. In the sintering step, a porous preform is attached to a shaft, suspended in a sintering furnace, heated by a heater, and a transparent vitrification treatment is performed at a temperature of 1350 ° C to 1500 ° C.
[0003]
The supporting member used for suspending the porous base material is required to have strength and heat resistance to withstand the load of the porous base material, including a columnar shape made of a graphitized carbon material (graphite carbon). Alternatively, a member obtained by joining cylindrical members in series can be cited (see Patent Document 1).
However, with the increase in the size of the base material ingot, a material having higher strength has been demanded, and a material made of ceramics that has higher strength than graphite carbon and can reduce the weight of the supporting member has been proposed (see Patent Document 2). ).
[0004]
[Patent Document 1]
JP-A-2002-114533 (page 2)
[Patent Document 2]
JP-A-5-24876 (page 2, FIG. 1)
[0005]
[Problems to be solved by the invention]
Graphite carbon materials are relatively inexpensive, have excellent heat resistance and workability, and are also excellent in handling performance.However, this graphite carbon rod is used as a support member for a porous base material, and is used for mounting jigs and shafts. When sintering, the strength is insufficient, and there is a drawback that it cannot withstand a load when producing a large-sized porous base material or when dehydrating and vitrifying the same.
For this reason, the lack of strength has been dealt with by increasing the diameter of the shaft, but the size of each member increases, which hinders assembly.
[0006]
In addition, ceramic materials, for example, silicon nitride have higher strength than graphite carbon materials and can reduce the size of the members.However, in an atmosphere containing high-temperature carbon, they are used as a sintering aid when sintering silicon nitride. Alumina may be scattered in the process atmosphere and adhere to the surface of the base material ingot, causing adverse effects such as devitrification.
On the other hand, silicon carbide has high strength and stability even at high temperatures, but because of its brittleness, it was extremely difficult to connect members using a screw structure.
[0007]
An object of the present invention is to provide a method for manufacturing a base material ingot, which can sinter a large-sized porous base material even in an atmosphere containing high-temperature carbon, and a suspension member used for the method.
[0008]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-described problems, a coating layer serving as a protective layer is formed on the surface of silicon carbide so that silicon nitride is not directly exposed to an atmosphere containing carbon. However, the present inventors have found that alumina contained in silicon nitride can be prevented from jumping into the process atmosphere, and have achieved the present invention.
[0009]
That is, the manufacturing method of the base material ingot of the present invention is to form a porous base material by depositing soot around the starting member, suspending in a sintering furnace, dehydrating and sintering to form a transparent vitrified glass, For suspending the porous base material, a suspending member in which silicon nitride is coated with silicon carbide is used.
[0010]
Further, the suspension member for an optical fiber preform ingot of the present invention (hereinafter simply referred to as a suspension member) forms soot around a starting member to form a porous preform, and is suspended in a sintering furnace. The hanging member used for hanging the porous base material is formed by coating silicon nitride on silicon carbide when the glass material is lowered by dehydration and sintering to form a transparent glass. It consists of a lowering jig and a shaft, and is screw-connected. In addition, a porous base material is fixed to the hanging jig with a pin via the quartz shaft or a dummy portion provided on the quartz shaft.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto, and various modes are possible.
[0012]
FIG. 1 is a schematic partial cross-sectional view showing a suspended state of a porous base material using a suspension member of the present invention in a sintering furnace.
Each of the suspension members comprises a shaft 1 and a suspension jig 2 coated with silicon carbide on silicon nitride material, and the shaft 1 and the suspension jig 2 gripped by a rotary gripping mechanism (not shown) are screwed. The connection, that is, a male screw is formed on one side and a female screw is formed on the other side and screwed together. The screw hole has a structure that does not penetrate to prevent the screw portion from being exposed to the atmosphere.
[0013]
The porous base material 3 to be sintered has a dummy part 5 of a quartz shaft 4 protruding from an upper part thereof inserted into a receiving part of a hanging jig 2 and fixed by a ceramic pin 6. The dummy portion 5 has a hole for inserting the pin 6 in advance. Although silicon carbide or the like can be used for the pin 6, a pin obtained by coating silicon nitride on silicon nitride having the same coefficient of thermal expansion is suitable.
[0014]
FIG. 2 is a schematic partial cross-sectional view showing a connection structure of a shaft made of silicon nitride coated with silicon carbide, and shows an example in which a plurality of shafts 1 are connected to each other by screws to make them longer. At this time, in order to prevent the screw portion from being exposed to the atmosphere, the female screw side does not penetrate.
[0015]
The hanging member of the present invention is a silicon nitride material coated with silicon carbide, and the silicon carbide coating method includes a CVD method and a plasma method, and the plasma method is compared with the CVD method. Suitable for easy peeling.
Although it is difficult to coat the screw portion, screw connection is performed so that the screw portion is not exposed to the atmosphere. Care must be taken because if the screw is exposed to the atmosphere, the alumina will jump out into the atmosphere from that part.
[0016]
【Example】
Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples.
(Example 1)
A dehydrated soot (porous base material) having a diameter of 299 mmφ and a total length of 1800 mm was attached to a hanging member gripped by a rotary gripping mechanism in a graphite core furnace tube provided in a sintering furnace. The suspending member is configured by screwing a suspending jig to the lower end of a shaft having a diameter of 35 mmφ, inserting a dummy part of a soot into a receiving portion of the suspending jig, and inserting a pin having a diameter of 10 mmφ, The hanging member and the soot were fixed. The shaft, the hanging jig, and the pin used were all obtained by applying silicon carbide coating to a silicon nitride material.
The soot suspended in the furnace tube was sintered in a vacuum (20 Pa) at 1475 ° C. for 12 hours. After sintering, the diameter of the base material ingot was reduced to 149 mmφ, and the base material ingot was sufficiently vitrified. No change such as peeling was observed on the surface of the shaft or the hanging jig.
[0017]
(Example 2)
Using the same suspending member used in Example 1, a dehydrated soot having a diameter of 307 mm and a total length of 1750 mm was suspended in a graphite core furnace tube, and sintered at 1490 ° C. and atmospheric pressure for 10 hours. After sintering, the diameter was reduced to 155 mmφ, and the glass was sufficiently vitrified. No change such as peeling was observed on the surface of the shaft or the hanging jig.
[0018]
(Comparative Example 1)
Dewatered soot having a diameter of 300 mm and a total length of 1780 mm was used at 1475 ° C. by using a hanging member made of silicon nitride having the same shape and size as those used in Example 1, but not coated with silicon carbide. Was sintered in a vacuum core (20 Pa) for 12 hours in a graphite core furnace tube.
After sintering, the diameter became 149 mmφ, the surface of the silicon nitride shaft turned green, and devitrification was observed on the surface of the sintered base ingot. When the devitrified portion was analyzed, alumina was detected.
[0019]
【The invention's effect】
According to the present invention, the silicon carbide coating allows a silicon nitride suspension member to be used in a stable state even in an atmosphere containing high-temperature carbon, and a silicon nitride suspension not coated with silicon carbide. No alteration of the surface of the silicon nitride or devitrification of the surface of the base material ingot occurs in the case of the member. Even if the base material ingot becomes large, a jig or a shaft having sufficient strength can be manufactured.
[Brief description of the drawings]
FIG. 1 is a schematic partial cross-sectional view showing a suspended state of a porous base material using a hanging member of the present invention.
FIG. 2 is a schematic partial sectional view showing a connection structure of a shaft.
[Explanation of symbols]
1 ... shaft,
2 ... hanging jig,
3 ... porous base material,
4 ... Quartz shaft,
5 ... Dummy part,
6 ... Pin.

Claims (4)

Soot is deposited around the starting member to form a porous base material, suspended in a sintering furnace, dehydrated and sintered to form a transparent glass. A method for producing an optical fiber preform ingot, comprising using a suspension member coated with silicon carbide. A soot is deposited around a starting member to form a porous base material, and is suspended in a sintering furnace, and is used for suspending the porous base material when dehydrating and sintering to form a transparent glass. Wherein the silicon nitride is coated with silicon carbide. The suspension member for an optical fiber preform ingot according to claim 2, wherein the suspension member comprises a suspension jig and a shaft, and is screw-connected. The suspension member for an optical fiber preform ingot according to claim 2 or 3, wherein a porous preform is fixed to the suspension jig via a quartz shaft or a dummy portion provided on the quartz preform. .

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