JPH0710583A - Dehydration sintering furnace - Google Patents

Abstract

PURPOSE:To improve the durability of a core pipe and facilitate the exchange working of the core pipe in a dehydration sintering furnace for dehydrating and transparently vitrifying by heating a preform while rotating and moving in the core pipe. CONSTITUTION:A central thick part 12 is formed so that the thickness of the central thick part 12 in the vicinity of a heater 2 is sufficiently durable against heat deformation due to the heater 2. The thickness of an upper thin part 11 and a lower thin part 13 away from the heater 2 is made thinner. The furnace core pipe is constituted preferably by separately producing the upper thin part 11, the central thick part 12 and the lower thin part 13 and joining them with flanges. If the central thick part 12 is deformed due to the heat of the heater 2, only the central thick part 12 is exchanged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a process for performing a dehydration treatment for removing water contained in an optical fiber preform (preform) made by depositing glass fine particles and a vitrification treatment for making a preform transparent glass. The present invention relates to a dehydration sintering furnace for reform.

[0002]

2. Description of the Related Art An optical fiber has a preform made by depositing glass fine particles introduced into a dehydration sintering furnace and heated while being rotated to remove water contained in the preform.
It is made into transparent glass, and then, the molten meniscus portion at the tip of the preform is drawn and spun in a drawing furnace.

An example of a dehydration / sintering furnace for dehydrating and vitrifying such a preform is shown in FIG.
The structure shown in Fig. 1 is known. In FIG.
A quartz core (core) tube 1B is provided at the center of the dehydration / sintering furnace, and a heater (heater) 2 is provided around the core tube 1B.
Are arranged. A heat insulating material 3 is arranged around the heater 2, and an inert gas sealed space 40 for accommodating the heater 2 and the heat insulating material 3 together with a part of the outer wall of the furnace core tube 1B.
The outer wall 4 of the furnace body that defines An inert gas supply port 5 is provided in the outer wall 4 of the furnace body, and an inert gas such as argon gas is supplied from the inert gas supply port 5 to the inert gas sealed space 40. A processing gas supply port 6 is provided below the furnace core tube 1B, and a processing gas discharge port 61 is provided above the furnace core tube 1B. The processing gas is introduced from the processing gas supply port 6, rises in the furnace core tube 1B, and is discharged from the processing gas discharge port 61. The preform 9 is suspended from the support rod 91 and is housed in the furnace core tube 1B. As the support rod 91 rotates and moves downward, each part of the preform 9 sequentially passes through the heat zone by the heater 2, and the dehydration and transparent vitrification treatment of the preform 9 are sequentially performed.

In the above-mentioned dehydration sintering furnace, the portion of the furnace core tube near the heater 2 becomes extremely hot due to the heating of the heater 2 and its strength is lowered and deformed. Therefore, the furnace core tube 1B is frequently replaced. There is a problem of having to do it. In order to solve this problem, if the overall thickness of the furnace core tube 1B is increased in order to increase the heat resistance of the furnace core tube 1B, the price of the furnace core tube 1B increases. In recent years, along with the demand for cost reduction of optical fibers, the size of preforms has increased, especially
The outer diameter of the preform tends to be large, and the diameter of the furnace core tube also needs to be large. As a result, the deformation of the furnace core tube due to heating becomes more conspicuous, and the furnace core tube is replaced more frequently. On the other hand, the larger the diameter of a quartz furnace core tube, the more the manufacturing cost increases dramatically in terms of both material cost and processing cost, and the furnace core tube itself becomes expensive. Therefore, if the furnace core tube is frequently replaced or repaired due to deformation, etc., the cost of the furnace core tube will rise, and the work efficiency will decrease, increasing the running cost of the dehydration sintering furnace, and There is a problem that the manufacturing cost of the fiber becomes high.

Several methods have been proposed to solve the above problems. JP-A-4-342433 discloses that the core tube near the heater is allowed to deform due to heating, and then the core tube is provided with a central core portion near the heater and an upper part of the upper part of the central core portion. The core part and the lower core part below the central core part are divided into three parts to be manufactured, and the upper core part, the central core part, and the lower core part are integrally combined to form a core tube, and Disclosed is a dehydration sintering furnace in which only a violent central core part can be replaced.

Further, Japanese Patent Laid-Open No. 3-109228 discloses a core tube having a central core portion near a heating element (heater), an upper core portion above the central core portion, and a lower core portion below the central portion. The upper core part, the central core part and the lower core part are made of the same material, for example, high-purity carbon coated with a silicon carbide film, a silicon carbide sintered body coated with a silicon carbide film, or Made of silicon, the central core is fitted between the upper core and the lower core, and the inner cylinder made of heat-resistant material is in contact with the central core and is formed inside the central core with the heat resistant member. And a dehydration sintering furnace fitted in the lower core part is disclosed. In this dehydration sintering furnace, a core main body outer wall is provided across the upper core part and the lower core part into which the central core part and the inner cylinder are fitted, and the core main body outer wall, the central core part, the upper core part and An inert gas sealed space is defined together with the lower core part, and a heater and a heat insulating material are arranged in this space. That is, this dehydration-sintering furnace has three core tubes as disclosed in Japanese Patent Application Laid-Open No. 4-342433.
In addition to splitting, the core tube near the heater is a double core tube in which the central core and the inner tube are combined to have a structure with improved heat resistance.

[0007]

[Patent Document 1] Japanese Patent Application Laid-Open No. 4-34243
The method of dividing the core tube into three parts disclosed in Japanese Patent Publication No. 3 and Japanese Patent Application Laid-Open No. 3-109228 is the dehydration sintering described with reference to FIG. 3 when a part of the core tube in the vicinity of the heater is deformed. It is not necessary to replace the entire core tube as in a furnace, and only the central core portion near the heater needs to be replaced, which has the advantage of reducing core tube replacement costs. However, in the method disclosed in JP-A-4-342433, the durability of the core tube near the heater is the same as that shown in FIG.
The replacement frequency itself is substantially the same as the replacement frequency of the core tube in the dehydration / sintering furnace shown in FIG. Therefore, it is still impossible to solve the problem that the workability of the optical fiber manufacturing is deteriorated due to the replacement of the central core.

In the method disclosed in Japanese Patent Laid-Open No. 3-109228, since the vicinity of the heater is substantially thickened to improve the heat resistance, compared with the method disclosed in Japanese Patent Laid-Open No. 4-342433. There is a possibility that the frequency of replacement of the central portion of the core tube may be reduced to solve the problem described in Japanese Patent Laid-Open No. 4-342433. Moreover, JP-A-3-109228
The method disclosed in the publication has a structure in which only the core tube near the heater can be replaced.

However, when the contents disclosed in JP-A-3-109228 are analyzed, various practical problems listed below are expected. First, the central core and the inner side of the central core are brought into face-to-face contact with the central core in the vicinity of the heater that is heated as the core is deformed, and the inner cylinder is improved in accuracy with the central core and the upper core and lower core. Problems due to the need to fit in are expected. Specifically, the length of the central core and the length of the inner cylinder are perfectly matched, and the inner surface of the central core and the outer surface of the inner cylinder are completely matched so that the mechanical strength is extremely high. The central core and inner cylinder must be manufactured precisely. Even if the central core and the inner cylinder are manufactured with extremely high mechanical accuracy in this way, they are exposed to extremely high temperatures.In particular, the outer wall and inner cylinder of the central core near the heater are Because the degree of heating is different,
The magnitude of thermal expansion between the central core and the inner cylinder is different. As a result, there is a high possibility that a difference in thermal expansion will occur between the central core portion fitted between the upper core portion and the lower core portion and the inner cylinder, resulting in a gap in the fitted portion. In addition, when the material of the central core and the material of the inner cylinder are different, there is a high possibility that a gap will occur. In Japanese Patent Laid-Open No. 3-109228, such a gap is connected to a portion in which an inert gas is filled. Therefore, when a gap is generated, the inert gas sealed space and the processing gas space inside the core tube communicate with each other, and there is a possibility that an inert gas such as argon gas and the processing gas such as helium are mixed. Furthermore, JP-A-3-10
Japanese Patent No. 9228 describes a case where a furnace tube is manufactured from high-purity carbon coated with a silicon carbide film in order to enhance heat resistance. However, carbon may be evaporated by a heater, and the evaporated carbon Adherence to the preform in the core tube may reduce the quality of the optical fiber produced.

As mentioned above, Japanese Patent Laid-Open No. 4-342433
The methods disclosed in both JP-A No. 3-109228 and JP-A-3-109228 still have problems. Incidentally, contrary to JP-A-3-109228, a method of controlling the temperature so that the thickness of the core tube in the vicinity of the heater is made thinner than other portions and the temperature distribution is made different along the axial direction Has also been proposed (for example, the method of Japanese Patent Laid-Open No. 4-260631). However, this method has a problem that it is necessary to provide a long heater in the axial direction and perform complicated temperature control.

The present invention solves the above-mentioned problems and increases the durability of the core portion caused by heating without lowering the price of the dehydration / sintering furnace, and thus the manufacturing cost of the optical fiber, and lowering the replacement frequency thereof. Moreover, it is an object of the present invention to provide a dehydration sintering furnace having excellent maintainability.

[0012]

[Means for Solving the Problems] The above problems are solved,
In order to achieve the above object, in the dehydration / sintering furnace of the present invention, the furnace core tube facing the heater is formed thick so as to have heat resistance. Preferably, the furnace core tube is manufactured by being divided into a thick portion and a thin portion above and below the thick portion, and is constructed by assembling these, and an inert gas is sealed in the outer periphery of the thick portion to form a heater. The thick portion is manufactured so that the space for arranging is defined.

[0013]

[Function] The heat resistance is enhanced by increasing the thickness of the portion of the furnace core tube near the heater which is susceptible to thermal deformation. This reduces the replacement frequency of the furnace core tube. Preferably, the furnace core tube is divided into three parts, that is, the thick portion and the thin portions above and below the thick portion, and these are assembled to form the furnace core tube. In other words, if the thick portion having improved heat resistance is used for a long time, it may be deformed and need to be replaced. Therefore, only the thick portion can be replaced. When the furnace core tube is manufactured by dividing it into thick-walled parts, upper thin-walled parts and lower thin-walled parts, and assembling these, the airtightness of these connecting parts becomes a problem, but the thick-walled part is equipped with a heater. Since the space for enclosing the inert gas is defined, the inert gas and the processing gas are not mixed even if a gap is created in the connecting portion due to thermal expansion.

[0014]

FIG. 1 is a cross-sectional view of the first embodiment of the dehydration / sintering furnace of the present invention. This dehydration / sintering furnace has an upper thin portion 11,
The furnace core tube 1 in which the central thick portion 12 and the lower thin portion 13 are integrally configured is used. The upper thin portion 11, the central thick portion 12, and the lower thin portion 13 are made of the same quartz. A processing gas supply port 6 is provided below the lower thin portion 13, and a processing gas discharge port 61 is provided above the upper thin portion 11. The preform 9 is introduced into the furnace core tube 1 by being suspended from the upper portion of the furnace core tube 1 by a supporting rod 91 that rotates. A furnace body outer wall 4 is provided on the outer periphery of the central thick portion 12, and the central thick portion 12 and the furnace body outer wall 4 form an inert gas sealed space 40.
Is prescribed. In this inert gas sealed space 40, a heater (heater) 2 is arranged around the central thick portion 12, and a heat insulating material 3 is arranged so as to surround the heater 2. The inert gas sealed space 40 is filled with an inert gas, for example, argon gas, from the inert gas supply port 5. The preform 9 supported by the support rod 91 is heated by the heat from the heater 2 in the processing gas atmosphere in which the processing gas introduced from the processing gas supply port 6 such as helium is discharged from the processing gas discharge port 61. Then, it is dehydrated and made into transparent glass.

In the dehydration / sintering furnace shown in FIG. 1, the central thick portion 12 near the heater 2 has high heat resistance.
It is made thick. Therefore, as compared with the conventional case, it takes time until the furnace core tube 1 needs to be replaced due to thermal deformation caused by the heater 2, and the replacement frequency of the furnace core tube 1 is significantly reduced. Therefore, the running price of the dehydration sintering furnace is lowered, and the manufacturing cost of the optical fiber is lowered. In particular, the thickness of the central thick portion 12 may be configured so as to ensure heat resistance, and the upper thin portion 11 and the lower thin portion 13 may be formed as shown in FIG.
It can be made considerably thinner than the core tube 1 having the integral structure shown in FIG. In other words, the furnace core tube 1 shown in FIG. 3 is formed to have a predetermined thickness so that the whole furnace core tube 1 has heat resistance, but the furnace core tube 1 of the present embodiment has the central thick portion 12. The material cost of the entire furnace core tube 1 can be substantially reduced by increasing the wall thickness of the chisel.

As a method of manufacturing the upper thin portion 11, the central thick portion 12 and the lower thin portion 13, for example, the upper thin portion 11, the central thick portion 12 and the lower thin portion 13 are independently manufactured and heated. Assembled integrally by processing. The part which is heat-processed and assembled together is apart from the heater 2, and the heat of the heater 2 causes these processed parts to thermally expand, so that no gap is generated. Of course, the upper thin portion 11, the central thick portion 12 and the lower thin portion 13 may be integrally manufactured.

FIG. 2 is a sectional view showing the second embodiment of the dehydration / sintering furnace of the present invention. The dehydration sintering furnace shown in FIG.
The furnace core tube 1A is composed of an upper thin portion 11A, a central thick portion 12A and a lower thin portion 13A, which are separately manufactured by being divided into three parts. Upper thin part 11A
And the central thick portion 12A are combined with flanges 14 and 15
And the flanges 16 and 17 are joined to the combination of the central thick portion 12A and the lower thin portion 13A. Upper thin part 1
The thickness of 1A is substantially the same as the thickness of the upper thin portion 11 shown in FIG. 1, and the thickness of the central thick portion 12A is substantially the same as the thickness of the central thick portion 12, The thickness of the lower thin portion 13A is substantially the same as the thickness of the lower thin portion 13. Upper thin portion 11A, central thick portion 12A, lower thin portion 13A
Are manufactured from the same quartz. Other components of the dehydration-sintering furnace shown in FIG. 2 are practically the same as those of the dehydration-sintering furnace shown in FIG.

By using the central thick portion 12A, even if the central thick portion 12A is deformed after a long period of use, only the central thick portion 12A needs to be replaced. This replacement work is easy because the flanges 14 and 15 and the flanges 16 and 17 may be removed. That is, according to the second embodiment, in addition to lowering the replacement frequency by using the central thick portion 12A, the replacement work can be completed in a short time, lowering the running price of the dehydration / sintering furnace, and eventually The manufacturing cost of the optical fiber can be reduced.

As illustrated in FIG. 2, the central thick portion 12A is provided between the flanges 15 and 16 of the central thick portion 12A.
It should be noted that the furnace body 4 defines the inert gas sealed space 40, and the heater 2 and the heat insulating material 3 are disposed in the inert gas sealed space 40. In other words, the connection between the flanges 14 and 15 and the flange 1
It should be noted that the connections of 6, 17 are not included in the inert gas sealed space 40 and are separated from the heater 2. In Japanese Patent Laid-Open No. 3-109228, the fitting positions of the central core portion into the upper core portion and the lower core portion are included in the portion defining the inert gas sealed space 40. As a result, the inert gas sealed space 40 and the processing gas space in the furnace core tube 1 may communicate with each other due to generation of a gap due to heating. In the present embodiment, since the joint portion of the flanges 14 and 15 and the joint portion of the flanges 16 and 17 are not included in the inert gas sealed space 40, JP-A-3-109.
The problem in the dehydration sintering furnace disclosed in Japanese Patent No. 228 is solved. Further, in this embodiment, the flange 1
Since the joints 4 and 15 and the joints of the flanges 16 and 17 are located away from the heater 2, a gap is generated in these joints due to thermal expansion due to heating of the heater 2. Never.

[0020]

As described above, according to the present invention, the frequency of replacement of the furnace core tube can be reduced by particularly strengthening the heat resistance of the portion of the furnace core tube which is likely to be deformed by heating. On the other hand, the thickness of the other core tube portions can be reduced, and the cost of the core tube can be practically reduced. Further, according to the present invention, it is only necessary to replace a part of the furnace core tube, that is, the central thick portion, so that the replacement work can be shortened and the cost of the furnace core tube is reduced. Further, according to the present invention, it is possible to prevent the inert gas sealing space and the processing gas space from communicating with each other due to expansion of the core tube due to heating.

[Brief description of drawings]

FIG. 1 is a sectional view of a dehydration / sintering furnace according to a first embodiment of the dehydration / sintering furnace of the present invention.

FIG. 2 is a sectional view of a dehydration / sintering furnace according to a second embodiment of the dehydration / sintering furnace of the present invention.

FIG. 3 is a sectional view of a conventional dehydration sintering furnace.

[Explanation of symbols]

 1 to 1B ··· Furnace core tube 11, 11A · · Upper thin portion 12, 12A · · Central thick portion 13, 13A · · Lower thin portion 14, 15, 16, 17 · · Flange 2 · · Heater 3 ·・ Insulating material 4 ・ ・ Outer wall of furnace body 5 ・ ・ Inert gas supply port 6 ・ ・ Processing gas supply port 9 ・ ・ Preform 61 ・ ・ Processing gas discharge port 91 ・ ・ Support rod

Claims (2)

[Claims] 1. A dehydration / sintering furnace in which an optical fiber preform is heated in a furnace while being heated in a furnace core tube for dehydration and transparent vitrification, wherein a thickness of a portion of the furnace core tube facing the heater The dehydration sintering furnace is characterized in that it is formed thick so as to have heat resistance. 2. The furnace core tube is constructed by assembling a thick portion at a position facing the heater and thin portions above and below the thick portion, and an inert gas is filled in the outer periphery of the thick portion. The dehydration / sintering furnace according to claim 1, wherein the thick portion is manufactured and arranged so that a space for arranging the heater is defined.