JPH02180728A - Heating furnace for producing high-purity quartz preform - Google Patents

Abstract

PURPOSE:To prevent the intrusion of the atmosphere into a heating atmosphere with a short device and simple structure by providing a means for vertically separating a furnace core tube in a heating furnace for passing a glass body vertically through the inside of the furnace core tube piercing the furnace body having a hollow zone heater. CONSTITUTION:A carbon heater 4 and the furnace core tube 3 are provided inside the furnace body 5 in the heating furnace. A quartz partition 23 pierced with a gas passage hole 24 is provided at the protruding part of the tube 3 above the furnace body 5. A high-purity quartz porous glass preform 1 is firstly fixed through a support 2 to a rotatable and liftable chuck, the upper lid 37 of the tube 3 is opened, and the preform 1 is lowered into the upper part 34 of the tube 3. In this case, the partition 23 is closed, and a purging gaseous N2 is introduced into the tube 3 from an inlet 7 for the atmospheric gas in the furnace core tube. Accordingly, the atmosphere is not introduced even when the upper lid 37 is opened. When the treated preform is discharged from the furnace, the preform is raised above the partition 23, the atmospheric gas is exhausted from an exhaust port 21 while introducing gaseous N2 from the inlet 7, the inside of the tube 3 is filled completely with the N2 atmosphere, the partition 23 is closed, and the upper lid 37 is opened.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a heating furnace for a high-purity quartz glass base material used in the production of optical fibers, and more specifically, the present invention relates to a heating furnace for a high-purity quartz glass base material used in the production of optical fibers, etc. , dopant addition, sintering)
This invention relates to a heating furnace that uses transparent high-purity quartz glass as a base material for manufacturing optical fibers and the like.

Conventional techniques and problems to be solved 1 In heating furnaces used to manufacture glass preforms for optical fibers, conventional techniques have been used, for example, in Japanese Patent Publications No. 58-42136 and No. 58-58299 and Japanese Patent Application Laid-open No. 60-86049.
As shown in the publication, it has been proposed to use a quartz glass tube as a furnace core tube. However, a serious problem with quartz glass tubes is that they are easily deformed at high temperatures. In fact, when a heating furnace is used at temperatures above 1500°C, the quartz glass tube will deform and become unusable unless the method of supporting the furnace core tube and the differential pressure inside and outside the furnace core tube are strictly controlled. Also, if you use it for a long time at 1150℃ or higher,
Devitrification (crystallization) occurs in the quartz glass tube. Since the glass layer and the devitrification layer have different coefficients of thermal expansion, there is also the problem that the furnace core tube may be destroyed by the resulting strain.

In order to solve this problem, the present inventors have already found that a carbon tube is effective as a furnace core tube (see, for example, International Application Publication No. WO38106145). Carbon tubes are not only stable at temperatures above 2000°C and have excellent heat resistance, but also have an ash content of 20 ppm or less, making them easy to purify, and are also a reactive gas useful for heat treatment of glass base materials for optical fibers. (CQ2,CCa,,S
It has the advantage of not reacting with iF, SF CC (hF2, etc.). Carbon tubes have good processing accuracy, so they can be assembled and cost-cut, and the outer surface can be coated with SiC or carbon to improve airtightness, making it possible to use even higher quality glass base materials for optical fibers. Obtainable.

A conventional heating furnace is configured as shown in FIG. 3, for example. This heating furnace is an example of a heating furnace that performs heat treatment using a hollow zone heater, and a carbon heater 4 and a furnace core tube 3 are provided inside a furnace body 5. This heating furnace has a nitrogen gas inlet 6 for purging the furnace body, a lower atmosphere gas in the furnace core tube, and a glass base material support jig 2.
A porous glass body 1 is inserted into a heating furnace. The furnace core tube 3 is composed of an upper part 34, a central part 35, and a lower part 36. At least the central part 35 is made of carbon, and the surface of the carbon is coated with SiC or carbon.

Sometimes.

Since the conventional heating furnace is constructed as shown in FIG. 3, the atmosphere (the atmosphere of the working chamber) gets mixed into the furnace core tube when the glass body is taken in and out. FIG. 4 is a schematic diagram of the apparatus used in the experiment to measure the amount of atmospheric air mixed in.
It also has a zone furnace (not shown) around the furnace core tube 101. The inner diameter of the furnace core tube 101 is 150 mm,
The tip of the gas sampling tube was fixed at a point 1 m from the opening of the furnace core tube. The results are shown in the graph of FIG.

It can be seen that air is mixed into the furnace core tube, and that it is impossible to prevent air mixing even if the purge nitrogen gas flow rate is increased.

Such atmospheric contamination causes the following problems. However, the inside of the furnace core tube is contaminated with dust in the atmosphere. The dust is composed of 5jOz, A<2xOs, Fe2O3, etc. Among these, AQ203 is the base metal devitrification.
Fe, O, causes an increase in loss.

Second, oxidation occurs on the inner surface of the carbon furnace tube. It is known that when carbon fired bodies are oxidized, tar and pitch used as binders are first oxidized. Therefore, the remaining graphite particles fall off, scatter, and fly around in the furnace.

Since these particles adhere to the surface of the sintered glass base material, a fiber made from this glass base material will contain many low-strength portions. Also, as a matter of course, the life of the carbon furnace tube becomes extremely short.

The first method for preventing such oxidation of the furnace core tube is to set the temperature at which the glass body is taken in and out to 400° C. or lower, at which point carbon is not oxidized. However, with this method, the operating rate of the furnace decreases significantly, and since the carbon furnace core tube is porous, once exposed to the atmosphere, a considerable amount of oxygen and moisture in the atmosphere will be adsorbed into the furnace core tube. Therefore, oxidative consumption cannot be completely prevented.

The second method is to provide a front chamber in the upper part of the furnace core tube, store the porous glass base material in the front chamber, replace the gas, and then move the porous glass base material into the furnace core tube. It is disclosed in the published application WO88106145. A schematic cross-sectional view of this furnace core tube with a front chamber is shown in FIG.

A carbon heater 2 and a carbon furnace core tube 4 are installed inside the furnace body 5.
is provided. This silent furnace has a nitrogen gas inlet 6 for purging the furnace body, a lower atmosphere gas inlet in the furnace core tube, a glass base material support jig 2, a front chamber 1L, a front chamber gas outlet 14, a front chamber purge gas inlet 15, and a partition 16. The porous glass body 7 is inserted into the heating furnace.

To insert the porous glass body into the sintering furnace of FIG. 6, proceed as follows.

(2) Attach the porous glass body 1 via the support rod 2 to a chuck that can move up and down 66 rotations.

2. Open the upper lid of the front chamber 11 and lower the porous glass body l into the front chamber 11.

3. Close the top lid and fill the front chamber with inert gas (N).

or He, etc.).

4. Open the partition 16 that separates the front chamber 11 from the heating atmosphere, and introduce the porous glass body l into the heating atmosphere that has been maintained at the heat treatment temperature in advance.

5. Close the partition 16.

Further, in order to take out the base material from this heating furnace, it is rubbed in the following manner.

1. Open the partition 16.

2. Remove the base material l after heat treatment from the heating atmosphere to the front chamber 1.
Raise it to 1. At that time, the temperature of the heating atmosphere does not necessarily need to be lowered.

3. Close the partition L6.

4. Open the top lid of the front chamber 11 and take out the base material I.

Although this device has an excellent effect in preventing oxidation, the overall length of the device is too long, and the partition
6 has a drawback that it has a complicated structure. FIG. 7 is an example of the total length of the device when the total length of the porous glass base material is 800 mm and the length of the seed rod is 200 mm.

In this case, 6,760 mm is required at the lower end of the chuck, and 8,000 m is required considering the space required for design and work.
It ends up being close to m.

In addition, the partition 16 must be compatible with both cases when the porous glass base material support jig penetrates and when it does not, so it must be divided into two parts with the holding rod section cut out and the support jig penetration section. It was necessary to partition the front chamber and the furnace core tube with a total of 3 parts including the part that blocks the front chamber.

[Means for Solving the Problems] The present invention was made in view of the drawbacks of such conventional heating furnaces, and the gist thereof is to provide a furnace body having a hollow zone heater, and a furnace penetrating the furnace body. In a heating furnace that has a core tube and heat-treats a high-purity quartz porous glass base material by passing it in the vertical direction inside the furnace core tube, in the part where the furnace core tube protrudes from the upper part of the furnace body. The present invention relates to a heating furnace for producing a high-purity quartz base material, which is characterized by having means for partitioning the interior space of the furnace core tube into upper and lower parts.

The present invention will be specifically described with reference to the accompanying drawings.

FIG. 1 shows a specific example of the heating furnace of the present invention. In FIG. 1, a carbon heater 4 and a furnace core tube 3 are provided inside a furnace body 5. Furnace core tube 3 has S on the surface of high-purity carbon.
It consists of a central part 35, a lower part 36, an upper part 34 made of quartz, and a top lid 37, which are coated with iC coating or carbon coating.

This heating furnace includes a nitrogen gas inlet 6 for purging the furnace body, a lower atmosphere gas in the furnace core tube, a glass base material support 2, a furnace core tube atmosphere gas exhaust port 21. The furnace core tube has a nitrogen gas inlet 22 for gas replacement in the upper part of the furnace core tube, and a quartz partition 23 having small holes 24 for gas passage, and a porous glass base material 1 is inserted into the furnace core tube. The partition 23 can be opened and closed from the outside using a quartz partition moving jig 26. The means need not be the small holes 24 as long as the structure is such that the gas flows from the bottom to the top of the furnace core tube through a slight gap when the partition 23 is closed. Further, when the glass base material 1 is present in the inner space of the furnace core tube above the partition 23, a heater 25 capable of heating it to 100°C to 800°C may be installed. This heater may be a resistive heating element or an infrared heating lamp.

The glass base material 1 needs to be completely accommodated in the space above the partition 23, but the partition 23 may be positioned anywhere as long as it is above the heater 4, and is not limited to the illustrated position. Generally, it is placed in the upper part of the furnace body 5.

The porous glass body is inserted into the sintering furnace of FIG. 1 as follows.

(2) Attach the porous glass body 1 via the support rod 2 to a chuck that can be rotated up and down once.

2. Open the upper lid 37 of the furnace core tube 3 and lower the porous glass body into the upper part 34 of the furnace core tube 3. At this time, the partition 23 is closed, and nitrogen gas for purging is introduced into the furnace core tube 3 from the furnace core tube atmosphere gas input lower, and the small hole 24 of the partition 23
It flows into the space in the upper part 34 of the furnace core tube. Therefore, the space in the middle and lower part of the furnace core tube is in a nitrogen gas atmosphere, and even if the upper lid 35 is opened, the atmosphere will not be drawn in because of the presence of the partition 23.

3. Close the upper lid 37, introduce nitrogen gas from the furnace core tube upper nitrogen persillo 22, and replace the space inside the furnace core tube upper part 34 with nitrogen gas. At this time, the porous glass body l is heated by the heater 25.
When heated, the gas adsorbed in the porous glass body is released more efficiently.

4. Open the partition 23 and lower the porous glass body to the processing start position (for example, to the position where the bottom end of the porous glass body is at the top end of the heater). Gas supply from the upper purge gas inlet 22 is stopped, the heater 25 is also turned off, and the sintering process of the porous glass body is started.

Further, the base material is taken out from the sintering furnace shown in FIG. 1 in the following manner.

(2) Pull up the overtreated base material to the top of the partition 23. While nitrogen gas is introduced from the furnace core tube atmosphere gas introduction lower, the atmosphere gas is exhausted from the exhaust port 21 to completely replace the inside of the furnace core tube 3 with a nitrogen atmosphere.

2. Close the partition 23. The flow rate of nitrogen gas introduced from the introduction lower may be reduced, but the upper gas continues to flow through the small hole 24 so as not to get caught up in the middle and lower parts.

3. Open the upper lid 37 and take out the base material 1.

[Example] Examples of the present invention are shown below.

Example 1 An apparatus suitable for a porous glass base material having a total length of 800 mm and a seed rod length of 200 mm, as shown in FIG. 7, was designed in accordance with the present invention. The minimum required dimension was 5560 mm at the lower end of the chuck, as shown in FIG. The total height of the actually designed device, including the space required for design and work, was 6,800 mm. It has been found that the cost is approximately 1.2++ lower than the apparatus shown in FIG. 7 which processes the same size of base material.

Example 2 The heating furnace shown in Figure 1 was used.

The porous glass body was placed in the upper part of the furnace core tube, the upper lid of the furnace core tube was closed, and nitrogen gas was flowed into the upper part at 10M min for 10 minutes, and nitrogen gas was continued to flow from the lower part at 10A/min. High-purity carbon tubes whose outer surfaces were coated with a gas-impermeable carbon film or a SiC film were used as the central and lower parts of the furnace core tube.

The partition was opened and a transparent glass base material for optical fiber was manufactured. Note that the conditions for dehydration and sintering were as follows.

Dehydrated He IOL'min CO2500 CC/min Traverse speed 8 mm/min Temperature 1100°C Sintered He 10a/min Traverse speed 3 mm 1 min Temperature 1650° A glass base material was used as the core material, and a separately prepared fluorine material was used as the cladding. A pure silica co-angle mode optical fiber was created by using a doped glass vibrator and integrating them in a resistance furnace.Furthermore, the optical fiber base material with a glass layer attached by the external method for adjusting the outer diameter was drawn. , 0°18 dB/km (at an optical wavelength of 1-55 pm), and the loss was low.

Example 3 A porous glass body was sintered in the same manner as in Example 2.
Performed 0 times. The weight loss of the carbon furnace core tube during this period was 14g.
(corresponding to 35 μm of oxidation consumption in the heating section). This amount indicates that the carbon furnace core tube can be used for about two years.

Comparative example 1 A conventional heating furnace shown in FIG. 6 was used.

The porous glass body was placed in the front chamber, the upper lid of the front chamber was closed, and nitrogen gas was flowed into the front chamber at a rate of 10 Q/min for 10 minutes to replace the inside of the front chamber with nitrogen gas. Thereafter, the partition was opened, the porous glass body was moved from the front chamber into the furnace core tube, and after the partition was closed, heat treatment was performed to produce a transparent glass preform for optical fiber.

When taking out the base material, the partition was first opened, the glass base material was moved to the front chamber, the partition was closed, and then the ball was opened and the glass base material was taken out. When an optical fiber was made using this glass base material as a core material, the result was O, 18 dB/k.
m (at a light wavelength of 1.55 pm), and the loss was low.

Comparative Example 2 A porous glass body was heat-treated 40 times in the same manner as in Comparative Example 1. The weight loss of the carbon furnace core tube during this period was 20
g (corresponding to oxidative wear of 50 μm from the surface). This amount indicates that the carbon furnace core tube can be used for about 1.5 years.

The difference in the amount of wear of the furnace core tube between Example 3 and Comparative Example 2 is that of Example 3.
In this case, nitrogen was also supplied from the lower part of the furnace core tube, Comparative Example 1 had more complicated partitions and a larger displacement section volume, and Example 3 had a porous glass body located closer to the heater during displacement. This is considered to be the result of a combination of three factors: gas release from the porous glass body progressed due to the

Example 4 The replacement time was increased to 20 minutes under the same conditions as in Example 2, and the porous glass body was heated with an 800W infrared lamp during the replacement. During substitution, the porous glass body was rotated to ensure uniform heating. The amount of wear of the 40 carbon furnace core tubes after the sintering treatment was 69 (wear of 15 μm from the surface). This amount indicates that the carbon furnace tube can be used for about 5 years.

[Effect of the invention] The effects of the present invention are as follows.

Air (work room atmosphere) is no longer mixed into the heating atmosphere, and contamination by impurities in the furnace core tube is eliminated. Therefore,
This prevents devitrification of the glass base material and improves transparency.

When the furnace core tube is manufactured from carbon, the oxidative consumption of carbon is suppressed and the life of the furnace core tube is extended. Also, compared to the conventional heating furnace type, which has a front chamber for the same purpose,
Although the structure and mechanism are simple, the same or better effects can be achieved, and the overall height of the device can be reduced.

Since the temperature of the furnace body is not lowered when the glass base material is taken in and out, the furnace operation rate is high.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a specific example of the heating furnace of the present invention, FIG. 2 is a schematic diagram showing the total height required for the heating furnace of the present invention, and FIG. 3 is a schematic cross-sectional view of a specific example of the heating furnace of the present invention. 4 is a schematic diagram of a device for measuring the amount of air entering the furnace core tube, and FIG. 5 is a cross-sectional view of the furnace core tube of a conventional heating furnace measured with the device shown in Figure 4. FIG. 6 is a cross-sectional view of another example of the heating furnace of the prior art, and FIG. 7 is a schematic diagram showing the total height of the heating furnace of FIG. 6. l...Glass base material, 2...Glass base material support jig,
3... Furnace core tube, 4... Carbon heater, 5... Furnace body, 6... Nitrogen gas inlet for furnace body barge, 7... Atmosphere gas inlet in furnace core tube, 21... Furnace Core tube atmosphere gas exhaust port, 22...atmosphere gas inlet for upper gas replacement of the furnace core tube;
23... Partition, 24... Small hole, 25... Heater. Patent Applicant Sumitomo Electric Industries Co., Ltd. Representative Patent Attorney Blue and White Ao Haka1 Famous Confectionery Figure 4 Figure S ◇ Park! (7 minutes) Figure 6 Procedural Amendment (To the Commissioner of the Own Ship's Patent Office February 17, 1999 Patent application No. 10,000, Showa 1999) Name of invention Address of heating furnace for manufacturing high-purity quartz base material 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Name
(213) Sumitomo Electric Industries Co., Ltd. Representative Kawakami
Tetsu Department 4, Acting address: 2-1-61, Chuo District, Osaka City, Osaka Prefecture, Osaka Prefecture Target of correction: Figure 2, Figure 4, Figure 5, Purge Nitto! , 77 Suf, 1 CJli minute) Figure 3 Figure 6 Figure 7 Figure 7. Contents of amendment The following sections in the detailed description of the invention in the description will be amended. (1) On page 5, line 3, "Figure 4" was corrected to "Figure 5." (2) On page 12, line 14, the text "Figure 7" was changed to [Figure 1]. (3) Page 12, line 20, corrected. ``Figure 7'' has been changed to ``Procedural amendment for Figure 6 and above August 31, 2006.''

Claims (1)

[Claims] 1. A furnace body having a hollow zone heater and a furnace core tube passing through the furnace body, with a high-purity quartz porous glass base material passing vertically inside the furnace core tube. A heating furnace for producing high-purity quartz base material, characterized in that the heating furnace is provided with means for partitioning the inner space of the furnace core tube into upper and lower parts at a portion where the furnace core tube projects above the furnace body. . 2. The heating furnace according to claim 1, wherein the upper space of the partitioned furnace core tube has a volume that can completely accommodate the quartz porous glass base material. 3. The heating furnace according to claim 1, wherein the furnace core tube portion located below the partition means is made of high-purity carbon. 4. The heating furnace according to claim 1, wherein the furnace core tube portion above the partition means is made of quartz. 5. The heating furnace according to claim 1, which has a heat source around the upper space of the partitioned furnace core tube.