JPH11255533A - Apparatus and method for sintering optical fiber preform - Google Patents

Abstract

(57) [Problem] To provide an apparatus for sintering an optical fiber preform made of a porous glass fine particle laminate. The present invention relates to a heating furnace having a furnace tube, an isolation booth having a closed structure constructed on a side of the core tube into and out of an optical fiber preform, and an isolation booth.
, An opening / closing lid 5 provided between the reactor core tube 2, a pipeline 7 for filling the isolation booth 4 with an inert gas, and an isolation booth 4 which is attached to a part of the isolation booth 4 so as to be openable and closable. The opening / closing means 8 for taking the optical fiber preform M in and out is provided in the optical fiber preform sintering device. Can be suppressed as much as possible, and the operation can be performed with the heating temperature of the heating furnace 1 kept at the oxidizing temperature of the furnace tube 2 and the heater 3 or the like. Workability can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for sintering an optical fiber preform made of a laminate of porous glass fine particles.

[0002]

2. Description of the Related Art In order to manufacture a preform for an optical fiber (a so-called transparent optical fiber preform after sintering) using a VAD method or the like, a laminate of porous glass fine particles is first formed by a VAD method or the like. It is necessary to prepare an optical fiber preform (a so-called porous optical fiber preform before sintering), dehydrate it, and make it transparent.

[0003] This dehydration and clarification is performed by a furnace tube (muffle).
Using a sintering apparatus consisting of a heating furnace with, an optical fiber preform before sintering comprising the porous glass fine particle laminate,
It is inserted into the furnace tube and heated. This core tube
Generally, it is made of quartz, alumina, carbon, or the like, and its bottom side has a supply port for gas introduction, but basically has a closed structure integrated with the main body of the furnace tube.

[0004] During sintering, an inert gas such as argon or helium is usually introduced into a furnace tube to remove oxygen in the tube as much as possible. Because the furnace tube is heated to about 1600 ° C. at this time, if oxygen is present, the furnace tube itself or a heating carbon heater mounted on the outer periphery of the furnace tube may be oxidized and deteriorated. Because there is.

[0005]

However, in the conventional sintering apparatus, when inserting the optical fiber preform before sintering or when drawing out the optical fiber preform after sintering that has been dehydrated and made transparent,
Since the furnace tube and the like of the normal heating furnace are open to the outside air, the heating furnace, that is, when the temperature inside the furnace tube is still high, when the optical fiber preform before and after the sintering is put in and taken out, the furnace tube and There was a risk that the heater and the like would be oxidized.

Therefore, ideally, after the sintering is completed, when the temperature of the heating furnace falls below the temperature at which the furnace tube and heater are not oxidized or hardly oxidized (non-oxidizing temperature), the light after sintering is reduced. To pull out the fiber preform and then put the unsintered optical fiber preform into the furnace tube,
The furnace tube, heater, etc. should be carried out at a temperature lower than the non-oxidizing temperature. Between them, there is a problem that a considerably long waiting time occurs and workability deteriorates.

Therefore, the present inventors made a space portion (isolation booth) of a closed structure on the opening side of the furnace tube of the heating furnace in which the optical fiber preform before and after the sintering operation was carried out, and this space portion was formed. Through this, I thought of putting the optical fiber preform in and out.

The present invention has been made based on such an idea. When the optical fiber preform is put in and taken out, the space portion of the sealed structure is used to minimize the intrusion of oxygen from the outside air into the heating furnace. In addition to this, even more positively, even if the heating temperature of the heating furnace remains at or above the oxidation temperature,
An object of the present invention is to provide a sintering apparatus and a sintering method for an optical fiber preform, in which the optical fiber preform can be taken in and out while suppressing oxidation of a furnace tube and a heater.

[0009]

According to the present invention, there is provided a heating furnace provided with a furnace tube, an isolation booth having a closed structure constructed on a side of the furnace tube into and out of an optical fiber preform. An opening / closing lid provided between the isolation booth and the core tube, a pipeline for filling the isolation booth with an inert gas, and an isolation openably attached to a part of the isolation booth. An optical fiber preform sintering apparatus, comprising: opening and closing means for taking the optical fiber preform into and out of the booth.

According to a second aspect of the present invention, there is provided the apparatus for sintering an optical fiber preform according to the first aspect, wherein an oxygen sensor is provided in the isolation booth.

According to a third aspect of the present invention, an isolation booth having a closed structure is constructed on the side of the furnace core tube of the heating furnace where the optical fiber preform is taken in and out, and an opening / closing lid is provided between the isolation booth and the furnace core tube. When the optical fiber preform is taken in and out of the core tube of the heating furnace, the interior of the isolation booth is rendered inactive by filling an inert gas into the isolation booth, and the heating temperature of the heating furnace is reduced. A method for sintering an optical fiber preform, characterized in that the optical fiber preform can be taken in and out while maintaining the temperature at or above the oxidation temperature of the heating furnace.

[0012]

FIG. 1 shows one embodiment of an optical fiber preform sintering apparatus according to the present invention, and FIGS. 2 to 4 show an opening / closing lid portion of the sintering apparatus. is there.

In the figure, 1 is a heating furnace, 2 is a furnace tube made of quartz glass or the like, 2a is a supply port for gas introduction on the bottom side of the furnace tube 2, and 3 is a heating tube installed on the outer periphery of the furnace tube 2. And a heater 4 made of carbon or the like, an isolation booth having a hermetic structure constructed on the side of the opening 2b on the side where the optical fiber preform of the furnace tube 2 is inserted and withdrawn, and 5 opens and closes the opening 2b of the furnace tube 2. Lid 6 for the optical fiber preform M before and after sintering (porous or transparent as described above)
Traverser that holds the robot vertically, 7 is an isolation booth 4
A pipe for filling the inside with an inert gas such as argon or helium, 7 'is a pipe for exhausting the gas, and 8 is mounted on one side of the isolation booth 4 so as to be openable and closable. Opening / closing means such as a closed-type opening / closing door for taking in and out the optical fiber preform M before and after sintering, 9 is an oxygen sensor installed in the isolation booth 4, and 10 is an optical fiber preform M before and after sintering. It is a transporting unit composed of a cart or the like for taking in and out of the isolation booth 4.

The isolation booth 4 is constructed on a floor 100 provided in a hollow portion on the ceiling side of the heating furnace 1 and isolates outside air in the factory from the opening 2b of the furnace tube 2 of the heating furnace 1. It consists of a kind of room to do.

The opening / closing lid 5 is not particularly limited, but preferably has a kind of shutter structure as shown in FIGS. 2 to 4, for example. In this case, a disk-shaped lid plate 51 is used.
And a lid holder 52 such as a ring-shaped (rectangular or the like) having an inner hole 52a having an inner diameter through which the opening 2b of the furnace tube 2 passes while the lid plate 51 is simply placed, and the lid holder 52 And a guide 53 formed of a shaft pin or the like that guides the cover plate 51 so that the cover plate 51 can move up and down. A drive unit 56 is attached to the shaft member 55 and is rotatable and vertically movable by a built-in drive source such as a motor or a gear mechanism (not shown).

Accordingly, when opening and closing the opening 2b of the core tube 2, the lid holder 52 on which the lid plate 51 is placed, for example, at the retracted position of the chain line shown in FIG.
2, as shown in FIG. 2, the core holder 2 is positioned on the opening 2 b of the furnace tube 2, and then, as shown in FIG. Then, the lid plate 51 is guided by the guides 53, 53, and the opening 2b of the core tube 2 is owed to its own weight.
And the opening 2b is closed. At this time, a cover plate 5 is provided in the opening 2b of the core tube 2.
Since only an own weight is applied and an excessive load is not applied, even a core tube 2 made of quartz glass or the like and having a low strength can be used for a long time.

On the other hand, contrary to the above, the lid holder 52 is raised by the ascending drive of the drive unit 56 to lift the lid plate 51, and thereafter, the lid plate 51 is placed by the rotational drive of the drive unit 56. When the closed lid holder 52 is rotated to the retracted position indicated by the dashed line in FIG. 4, the opening 2b of the core tube 2 is opened and released.

The traverser 6 is arranged along the standing shaft 61 by a standing shaft 61 erected in the isolation booth 4 and a drive source such as a built-in motor or a gear mechanism (not shown). A drive unit 62 that moves up and down, an arm 63 that extends from the drive unit 62 in the horizontal direction,
3 and a chuck portion 64 suspended near the tip end.
The optical fiber preform M before and after sintering is supported by the chuck portion 64 via a dummy rod L on the upper side thereof.

The use of a closed-type opening / closing door as the opening / closing means 8 of the isolation booth 4 corresponds to the case where a carriage is used as the conveying means 10 of the optical fiber preform M before and after sintering. An automatic door that is automatically opened and closed is preferred. However, the present invention is not limited to this, and for example, an accordion curtain type having an excellent sealing function may be used. Further, when a traveling hanger suspended from the ceiling side is employed as the transporting means 10, for example, a sheet-like curtain which can be simply opened and closed can be used.

The carriage of the transfer means 10 includes:
For example, as shown in FIG. 1, a base frame 11, a plurality of wheels 12 attached to the bottom surface thereof, a standing shaft 13 erected on the base frame 11, and mounted on two positions above and below the standing shaft 13. Sliders 14, 14, and the sliders 14, 14
And a chuck / arm 16 extending in the horizontal direction from the sliders 14. In this truck, the optical fiber mother before and after sintering is used. The material M is attached to the chuck arm 16, 16 via the upper and lower dummy rods L, L and the like.
16.

With the sintering apparatus configured as described above,
The sintering of the pre-sintered optical fiber preform (porous optical fiber preform made of a porous glass fine particle laminate) may be performed as follows.

First, the optical fiber preform M before sintering is set on the carriage of the conveying means 10, and the opening / closing door which is the opening / closing means 8 of the isolation booth 4 is opened, brought into the isolation booth 4, and taken into the traverser 6. And set it down.

Prior to carrying in the optical fiber preform M before sintering, the opening 2b of the furnace tube 2 is filled with an inert gas such as argon or helium in the isolation booth 4. Is closed by the opening / closing lid 5. by this,
Even if the inside of the isolation booth 4 is opened to the outside air, it is possible to minimize the entry of oxygen in the outside air into the furnace tube 2. Further, after closing the opening / closing lid 5, the inert gas in the isolation booth 4 is drawn out through the pipe 7 ', so that entry into the isolation booth 4 can be made safe.

When the setting of the optical fiber preform M before sintering on the traverser 6 is completed as described above, the opening / closing door as the opening / closing means 8 is closed, and argon or the like is introduced into the isolation booth 4 through the pipe 7. Fill with an inert gas such as helium. The filling of the inert gas is monitored by an internal oxygen sensor 9 and stopped when the oxygen concentration in the isolation booth 4 becomes about 50 ppm or less.

Next, the lid 5 is opened, and the traverser 6 is opened.
Is lowered, and the optical fiber preform M before sintering is inserted into the opening 2b of the furnace tube 2 and lowered to perform predetermined sintering. Here, the inside of the furnace tube 2 of the heating furnace 1 is controlled to have a exactly predetermined heating temperature so that the optical fiber preform M can be sintered. An inert gas such as argon or helium is supplied to the furnace tube 2 from a gas inlet 2a so that the furnace tube 2 and the heater are not oxidized even at the above-mentioned heating temperature. The concentration is also controlled to be about 50 ppm or less.

When sintering is completed in this way, the traverser 6 is raised, and the sintered optical fiber preform M (dehydrated and transparent transparent optical fiber preform) M is placed in the furnace tube 2. It is withdrawn from the opening 2b and once held in the isolation booth 4. At the same time, the opening / closing lid 5 is closed and the opening 2b of the furnace tube 2 is closed.

During the insertion and withdrawal of the optical fiber preform M before and after the sintering, the opening 2b of the furnace tube 2 also
Since it is connected to the isolation booth 4 filled with the inert gas, the outside air, that is, oxygen does not enter the furnace tube 2, and as a result, the heating temperature of the heating furnace 1 is reduced by the furnace tube 2 and the heater. 3 or the like, that is, without lowering the furnace tube 2 and the heater 3 to a temperature at which the furnace tube 2 and the heater 3 are not oxidized or hardly oxidized (non-oxidizing temperature).
It can be carried out. As a result, the waiting time for the temperature decrease of the heating furnace 1 is almost eliminated, so that the working time can be greatly reduced.

After the extraction of the optical fiber preform M after the sintering is completed, the inert gas such as argon or helium filled in the isolation booth 4 is extracted through the pipes 7 and 7 '. The opening / closing door, which is the opening / closing means 8 of 4, is opened to open the isolation booth 4 to the outside air, and the carriage of the conveying means 10 is carried in to carry out the sintered optical fiber preform M to the outside. . Thus, a series of sintering operations is completed. The sintering of the optical fiber preform M before the next sintering may be performed by repeating the above steps.

Incidentally, when the present inventors measured the oxygen concentration in the furnace core tube 2 at the time of extracting the optical fiber preform M after the sintering, it was 60 ppm on average and about 70 ppm at the maximum. Was. From this, even if work such as opening the opening / closing door as the opening / closing means 8 of the isolation booth 4 and opening the isolation booth 4 to the outside air is performed, the opening / closing portion 2b of the core tube 2 is closed by the opening / closing lid 5; It can be seen that the oxygen concentration is kept at a low value which is not much different from the oxygen concentration at the time of sintering (about 50 ppm).

This means that, in other words, as described above, the isolation booth 4 is opened and closed while the heating temperature of the heating furnace 1 is kept at the oxidation temperature of the furnace tube 2 and the heater 3 or higher. Since the preform M can be replaced, it means that a large number of optical fiber preforms M can be continuously inserted and extracted.

[0031]

As is apparent from the above description, the following excellent effects can be obtained by the apparatus and method for sintering an optical fiber preform according to the present invention.

(1) First, an isolation booth having a closed structure is formed on the side of the core tube of the heating furnace where the optical fiber preform is taken in and out.
Since the optical fiber preform is put in and taken out through the isolation booth and the opening / closing lid inside, it is possible to prevent the outside air from entering the heating furnace as much as possible. Thereby, oxidation of the furnace tube itself on the heating furnace side, the heater for heating, and the like can be suppressed, and the life of the heating furnace can be extended.

(2) The function of preventing oxygen from entering the heating furnace side allows the optical fiber preform to be taken in and out while keeping the heating temperature of the heating furnace at or above the oxidation temperature of the furnace tube and heater. Therefore, unlike the related art, there is almost no waiting time for the temperature of the heating furnace to drop, and the working time can be greatly reduced.

(3) The fact that the heating temperature of the heating furnace can be maintained at a constant high temperature while maintaining the heating temperature at or above the oxidation temperature is as follows.
The stress caused by temperature fluctuations in the furnace can be small, and from this point, the life of the heating furnace can be prolonged.

(4) Further, the fact that the heating furnace can be maintained at a constant high temperature as described above means that the work of taking in and out a large number of optical fiber preforms continuously can be performed without lowering the temperature of the heating furnace. This also makes it possible to expect a significant improvement in workability.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing one embodiment of an optical fiber preform sintering apparatus according to the present invention.

FIG. 2 is an enlarged vertical cross-sectional view showing an opening and closing operation of an opening and closing lid in the optical fiber preform sintering apparatus of FIG.

FIG. 3 is an enlarged longitudinal sectional view showing a closed state of an opening / closing lid in the optical fiber preform sintering apparatus of FIG. 1;

FIG. 4 is an enlarged plan view showing an opening / closing lid in the optical fiber preform sintering apparatus of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Furnace tube 2b Opening 3 Heater 4 Sealing structure isolation booth 5 Opening / closing lid 6 Traverser 7, 7 'Pipe line 8 Opening / closing means 9 Oxygen sensor 10 Transport means M Optical fiber preform

Claims (3)

[Claims] 1. A heating furnace provided with a furnace tube, an isolation booth having a closed structure constructed on a side of the furnace tube into and out of an optical fiber preform, and a heating device provided between the isolation booth and the furnace tube. An open / close lid, a conduit for filling an inert gas into the isolation booth, and an openable / closable part of the isolation booth for moving the optical fiber preform into and out of the isolation booth. An apparatus for sintering an optical fiber preform, comprising an opening and closing means. 2. An apparatus for sintering an optical fiber preform according to claim 1, wherein an oxygen sensor is installed in said isolation booth. 3. An isolation booth having a closed structure is constructed on the side of the core tube of the heating furnace into and out of which the optical fiber preform is inserted and removed.
An opening / closing lid is provided between the isolation booth and the furnace tube, and when an optical fiber preform is taken in and out of the furnace tube of the heating furnace, by filling an inert gas into the separation booth,
The isolation booth is in an inactive state, and the heating temperature of the heating furnace is kept at or above the oxidation temperature of the heating furnace, so that the optical fiber preform can be taken in and out. Sintering method.