JP3529264B2 - Electric furnace stretching method and stretching apparatus for glass preform for optical fiber - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric furnace drawing method and apparatus for drawing an optical fiber glass preform in an electric furnace so as to have a predetermined outer diameter. In the present specification, the glass preform for optical fiber includes not only a normal glass preform for stretching but also a glass stretch preform obtained by stretching the glass preform, that is, a so-called preform.

[0002]

2. Description of the Related Art Usually, an optical fiber is manufactured by synthesizing a porous glass preform for an optical fiber by a VAD method or an external CVD method, and then dehydrating and sintering the porous glass preform for the optical fiber. It is manufactured by drawing a transparent glass preform for use as an optical fiber, drawing it to an outer diameter suitable for drawing, to obtain a drawn preform for optical fibers (referred to as a preform), and then drawing the preform.

Conventionally, the drawing of the glass preform for optical fibers has been
It has been performed by a burner drawing method with a burner using an oxyhydrogen flame as a heat source. In this burner drawing method, it is relatively easy to control the outer diameter of the drawing base material, but the drawing speed is slow and usually 8
10 to 10 mm / min.

With the recent development of technology, the outer diameter of the porous glass preform for optical fibers synthesized by the VAD method or the external CVD method has become remarkably thicker than the conventional one. Along with this tendency, a burner drawing method using a burner using the oxyhydrogen flame as a heat source has a calorific value for an optical fiber glass preform having an outside diameter of a certain value or more before drawing. Therefore, for the glass base material for an optical fiber having an outer diameter of a certain value or more before drawing, a heating furnace with a large amount of heat, specifically, a heating drawing method by an electric furnace using an electric heater (hereinafter referred to as electric furnace drawing The law) is adopted.

In the electric furnace drawing method, the amount of heat is large, so that the drawing speed can be increased. For example, the drawing speed of the burner drawing method is 8 to 10 mm / min, whereas the drawing speed of the electric furnace drawing method is 30 mm / min or more. Therefore, the electric furnace drawing method is advantageous from the viewpoint of productivity, even in the case of a drawn base material (preform) having a small outer diameter and a preform having a smaller outer diameter produced from this preform. Since this electric furnace drawing method has a wide heating range, it is limited to the vertical type that is long in the vertical direction.
It

In this electric furnace drawing method, it is necessary to connect a support rod for drawing (a glass member for drawing) to the end portion of the glass base material for optical fiber or the glass draw base material (preform) before drawing. Conventionally, this connection is generally performed by flame stretching in a separate step, but it is preferable that this connection be performed in the same electric furnace stretching step.

However, if this connection is made in the same electric furnace drawing step, there is a problem that this connection is difficult. That is, it is necessary to match the shaft center of the end of the glass base material with the shaft center of the end of the support rod for pulling out (glass portion for pulling), but both cores are easily displaced and connected. If the axes are displaced and connected, the stress distribution in the cross section of the connecting portion becomes non-uniform, and the drawn base material is likely to bend, and troubles such as breakage of the connecting portion are likely to occur.

The above-mentioned axial alignment when the optical fiber preform is drawn by an electric furnace is usually performed as follows. That is, two glass members (a glass preform for drawing and a glass member for pulling) having one end gripped in a heated furnace body are inserted from opposite directions and abutted to each other to heat and weld the abutted end faces of the two. After that, the gripping part of the glass preform for drawing is moved downward at a predetermined speed while the gripping member holding the glass member for pulling is lowered at a constant speed, and the glass preform for drawing is pulled to a predetermined outside. Stretch to diameter.

FIG. 11 is a schematic view showing an example of a conventional glass fiber preform for an optical fiber of this type. Figure 11
In the above, reference numeral 91 is a glass preform for drawing (glass preform for optical fiber), and 92 is a glass member for pulling (glass member for pulling out) serving as a dummy. 93 is a furnace body,
A core tube 94 having an electric heater built therein is installed therein. One end of each of the glass preform 91 for stretching and the glass member 92 for pulling is gripped and fixed by gripping members 95 and 96, which are, for example, three-jaw chucks. The gripping members 95, 96 are movable in the vertical direction in FIG. 9 by means of a moving base 97 on which the gripping members 95, 96 are fixed. Reference numeral 98 is a guide rail for guiding the moving portion 97.

The glass preform for optical fibers is drawn in the following manner by the above-described apparatus for drawing preforms for optical fibers. The fixed end portions of the glass preform 91 for drawing and the glass member 92 for pulling are gripped and fixed by gripping members 95 and 96, respectively. The ends of the free ends of the drawn glass base material 91 and the drawn glass member 92 that are fixed are aligned with each other, and the two are connected to the core tube 94.
Move in and match. After heating the core tube 94 to a predetermined temperature to heat and weld the abutting end faces of both to unify them, the holding member 95 holding the glass member 92 for pulling is moved downward, and the glass mother for drawing is drawn. The material 91 is pulled and stretched to a predetermined outer diameter.

[0011]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the above-described conventional stretching apparatus, the glass preform 91 for stretching and the glass member 92 for stretching are drawn.
When heating and welding the abutting end faces of the two in the core tube 94, the two are axially aligned. This axial alignment (alignment) is performed by manually finely moving the fixed ends of the drawing glass base material 91 and the pulling glass member 92 within the range of the play of the gripping members 95, 96, for example, a three-jaw chuck. Align and secure the shaft center of the end tip. The ends of the fixed free ends are abutted in the core tube 94 and visually checked through an observation window 94A provided in the core tube 94 to check the axial alignment.

This conventional centering method has a problem that the centering work takes time and the axis alignment accuracy is not good. For example, conventionally, an axis deviation of ± 1 to 2 mm (5 to 10% of the glass member diameter) occurs in the horizontal plane. If this axis alignment accuracy is poor, the stress distribution in the cross section of the connecting portion between the glass preform 91 for stretching and the glass member 92 for stretching becomes uneven at the time of stretching, causing bending in the base material for stretching, and breaking of the connecting portion. Trouble is likely to occur.

Therefore, it is necessary to perform the above-mentioned alignment with high accuracy.
It

Furthermore, even after accurate alignment, electrical
When the glass base material for optical fiber is drawn in the drawing process by the furnace drawing method , the drawn base material (preform) may be bent or wavy, and the outer diameter may be different from the specified value. Therefore, it is required to improve the accuracy of the outer diameter of this preform. Further, from the viewpoint of productivity, it is also required to improve the drawing speed. The purpose of the present invention is to improve the outer diameter accuracy of the preform for optical fibers, it and fast drawing speed electric furnace drawing method and to provide a manufacturing apparatus.

[0015]

According to a first aspect of the present invention, there is provided an electric furnace drawing method for drawing a glass preform for an optical fiber at a highest temperature portion inside the electric furnace, wherein the heating of the electric furnace is performed. The outer diameter of the glass base material for optical fiber is measured at a position where the meniscus angle of the meniscus portion formed in the stretched portion of the glass base material for optical fiber is 2 degrees or more and 4 degrees or less, and the measured outer diameter value Is fed back to the drawing speed control for drawing the glass base material for an optical fiber, and an electric furnace drawing method for a glass base material for an optical fiber is provided.

[0016] Preferably, the feed for controlling the drawing speed
After starting the back, the stretching speed is set to the stretching speed at the start.
The stretching speed is controlled to gradually increase from the degree .

More preferably, prior to the drawing of the glass preform for optical fiber, the end of the glass preform for optical fiber and the end of the glass member for pulling are attached at the highest temperature inside the electric furnace. the combined unit is heated welded, the maximum temperature portion moves to the extended portion of the optical fiber glass base material side from the hot sealing portion, followed by heating before Symbol electric furnace of the optical fiber glass preform The meniscus portion is formed in the stretching portion, and the stretching is performed.

Also preferably, the glass for optical fiber
Matching part between the end of the base material and the end of the glass member for pulling
When heating and welding, the glass base material end portion for the optical fiber
The outer diameter of the glass is smaller than the outer diameter of the end of the glass member for tensioning.
It

According to a second aspect of the present invention, an electric furnace,
An outer diameter measuring unit for measuring an outer diameter of an optical fiber to be stretched which is located at a lower portion of a core tube surrounded by a furnace body of the electric furnace, and a control means for controlling a stretching speed, In an electric furnace stretching device that stretches the glass preform for optical fiber at the highest temperature part, the control means, via the outer diameter measuring part, the stretching part of the glass preform for optical fiber by heating the electric furnace. The outer diameter of the glass base material for an optical fiber is measured at a position where the meniscus angle of the meniscus portion formed on the substrate is 2 degrees or more and 4 degrees or less, and the glass base material for an optical fiber is referred to with reference to the measured outer diameter value. An electric furnace stretching apparatus for glass preforms for optical fibers is provided, which is characterized by controlling a stretching speed for stretching.

Preferably, the control means is the stretching speed.
After starting feedback of degree control,
Stretching speed control that gradually increases from the stretching speed at the beginning
U

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention described above will be described below.
The operation, the specific configuration and the like will be described in detail.

According to the apparatus for drawing a glass preform for an optical fiber of the present invention, an aligning mechanism having a pair of aligning grips is provided between each end of the furnace tube and both glass member grips. Therefore, the axial alignment of the free ends of both glass members can be performed easily and easily.

According to the method of fixing the optical fiber preform to the drawing device of the present invention, the pair of centering grippers are provided at the free ends of the glass members temporarily fixed by the glass member grippers. Since the alignment is performed by the aligning mechanism, the axis alignment can be performed easily and easily in a short time. After the free ends of both glass members are aligned as described above, the fixed ends of both glass members are permanently fixed, so that the axes of the free ends of both glass members moved into the core tube are Can be butt-connected in a matched state. As a result, the stress distribution in the cross section of the connecting portion of both is uniform, the vicinity of the connecting portion of both is not inclined, and fracture is avoided.

The following is a description of an apparatus for stretching a glass preform for optical fibers according to an embodiment of the present invention and a method for fixing the glass preform for optical fibers to the stretching apparatus with reference to FIGS. 1 to 3. This will be specifically described. In FIG.
1 is a glass preform for drawing (glass preform for optical fiber), 2
Is a glass member for pulling (a glass member for pulling out) which is a dummy. Reference numeral 3 denotes a furnace body. Inside the furnace body 3, a core tube 4 having an electric heater built therein is installed. 4A is a core tube 4
It is an observation window for observing the inside. A gripping member 5 for gripping and fixing the fixed end portion 1A of the upper portion of the glass preform 1 for drawing is provided on the upper portion of the furnace core tube 4. A gripping member 6 for gripping and fixing the fixed end portion 2A of the lower portion of the pulling glass member 2 is provided below the core tube 4. The gripping members 5 and 6 can be moved in the vertical direction by a moving table 7 to which the gripping members 5 and 6 are fixed. Reference numeral 8 is a guide rail for guiding the movable table 7.

The gripping member 5 for gripping and fixing the glass preform 1 for drawing has, for example, two key-shaped glass member supporting claws 5A arranged in parallel as shown in FIG. 2 and supporting two glass members. Above the gap between the claws 5A, there is provided a glass member fixing member 5B having a spherical tip end for fixing the upper portion of the fixed end portion 1A of the glass member for drawing 1 held in the gap between the supporting claws 5A. The glass member fixing member 5B can be moved up and down by hydraulic drive. The glass member fixing member 5B is not limited to hydraulic drive, and other drive sources such as an electric motor, a manual screw, and pneumatic drive can be used. The shape of the gripping member 5 is not limited to that shown in FIG. 2 and may have another shape. The holding member 6 that holds and fixes the fixed end portion 2A of the pulling glass member 2 is, for example, a well-known interlocking chuck having three claws.

In the drawing apparatus for glass preform for optical fiber according to the embodiment of the present invention, the tip of the lower free end 1B of the drawing glass member 1 is aligned between the furnace tube 4 and the holding member 5. A centering mechanism 9 is provided. The aligning mechanism 9
For example, as shown in FIG. 3, a pair of centering grippers 9A having a self-centering function, and a support rod 9B supporting the centering gripper 9A.
And a pedestal 9C having a hydraulically driven moving mechanism that integrally moves the centering gripping tool 9A and the support rod 9B in the left-right direction.
Is equipped with. The moving mechanism provided on the gantry 9C is not limited to the hydraulic drive, but another drive source such as an electric motor, a manual screw, or a pneumatic drive can be used. In the figure, 9D is a guide rail. The pair of centering gripping tools 9A is provided with a V groove 9E in the axial direction of the glass preform 1 for stretching in the center of the facing surface thereof.

The apparatus for stretching a glass preform for optical fibers according to the embodiment of the present invention further includes an upper portion of the pulling glass member 2 between the furnace body 3 and the holding member 6 for holding and fixing the pulling glass member 2. An aligning mechanism 9 shown in FIG. 3 for aligning the tip of the free end portion 2B is provided. The structure of the centering mechanism 9 for aligning the free end 2B tip of the pulling glass member 2 with an axis is the same as that of the aligning mechanism 9 for aligning the free end 1B of the drawing glass base material 1 with an axis. Therefore, details are omitted.
The aligning mechanism 9 is not limited to the shape shown in FIG. 3, and may have another shape.

The method of fixing the glass base material to the optical fiber glass base material stretching apparatus configured as described above is performed as follows. First, the disk-shaped fixed end portion 1A of the upper portion of the glass preform 1 for drawing is mounted between two key-shaped glass member supporting claws 5A arranged on the holding member 5 and temporarily fixed. Next, the tip of the free end portion 1B at the bottom of the glass preform for drawing 1 is held by a pair of aligning mechanisms 9 having a self-aligning function to align the axis of the tip of the free end portion 1B. That is, the free end 1
Since the tip end of B is in a free state, when it is pressed by a pair of centering grips 9A provided with a V groove 9E in the axial direction of the stretching glass member 1, the axis of the free end 1B becomes 2
It is set at the center of the circle inscribed in the two V grooves 9E. At this time, the center of the circle inscribed in the two V grooves 9E is
For example, the axis of the free end portion 1B can be aligned with the axis of the core tube 4 by previously aligning with the axis of the core tube 4.

As described above, the free end 1B of the lower part of the glass preform 1 for drawing is held by the centering mechanism 9 and the free end 1B is held.
After aligning the axial center of the B tip, the disc-shaped fixed end 1A on the upper portion of the glass preform 1 for drawing is gripped and fixed again by the gripping member 5. The fixed end portion 1A is gripped and fixed by pressing the upper portion of the fixed end portion 1A of the glass preform 1 for drawing which is gripped in the gap between the two support claws 5A with a glass member fixing member 5B having a spherical tip. That is, the drawing glass base material 1 has 2
One support claw 5A and one glass member fixing member 5B hold and fix the tip of the free end portion 1B with the centering mechanism 9 centering the shaft. After that, the pair of aligning gripping tools 9A of the aligning mechanism 9 are retracted from the axial center, and the tip of the free end portion 1B is moved to the core tube 4
Set it in place.

Then, the pulling glass member 2 is gripped and fixed by the gripping member 6. The lower fixed end portion 2A of the pulling glass member 2 is temporarily fixed to the grip member 5 in a state with a predetermined backlash. In this state, the tip of the free end 2B at the upper portion of the pulling glass member 2 is gripped by a pair of centering mechanisms 9 having a self-centering function to center the axis of the tip of the free end 2B. Free end 2B
The axial center of the tip is aligned with the free end 1 of the drawing glass base material 1.
The detailed description is omitted because it is the same as the alignment of the B tip. After aligning the axial center of the free end portion 2B of the upper portion of the pulling glass member 2, the fixed end portion 2A of the lower portion of the pulling glass member 2 is aligned.
Is gripped and fixed again by the gripping member 6 in earnest.

At this time, the pulling glass member 2 has the free end 2
The tip end of B is gripped and fixed in a state where the axis is aligned by the aligning mechanism 9. After that, the pair of aligning gripping tools 9A of the aligning mechanism 9 is retracted from the axis to set the tip of the free end 2B at a predetermined position in the core tube 4, and the free end of the glass preform 1 for drawing is set. 1B
The tip and the tip of the free end 2B of the pulling glass member 2 are butted against each other. Since the two free ends 1B and 2B are aligned with respect to the shaft center of the core tube 4, the shaft ends of the two are abutted in a state of being coincident with each other.

After that, the core tube 4 is heated to a predetermined temperature in the same manner as in the prior art to heat and weld the abutting end faces of both to unify them, and then the holding member holding the glass preform for drawing is fixed. While lowering at a speed, the gripping member 6 that grips the pulling glass member 2 is moved downward at a predetermined speed to pull the glass preform 1 for stretching and stretch it to a predetermined outer diameter.

Next, in the electric furnace drawing step, when the end portions of the glass preform for optical fiber and the end portions of the glass member for pulling are brought into contact with each other by heating and welding, the highest temperature portion of the electric furnace is first joined to this joint portion. An electric furnace drawing method will be described in which, after transfer and heat welding, the highest temperature part is moved from the heat welding part to the drawing part on the glass base material side, and then the glass base material is drawn .

FIG. 4 is an explanatory view showing an outline of an electric furnace drawing apparatus according to an embodiment of the present invention and a situation in which a glass base material is drawn by this apparatus. In the figure, 30 is a furnace body, 31 is a core tube, 32 is a heater, 33 is a heat insulating material, 34 and 35 are windows, 36 is an outer diameter measuring device, 37 is a temperature measuring device, and 38 is an outer diameter measuring device of a stretching rod. , 39a, 39b are grips.
Further, 20 is a glass base material for drawing, 21 is a drawing part (outer diameter changing part), 22 is a drawing rod, 23 is a glass member for drawing (for drawing), and 24 is a joining part. The present invention is stretched using such a device. Further, FIG. 5 shows the inside of the electric furnace drawing apparatus, and shows a state before joining the end portion of the glass preform 20 for optical fiber and the end portion of the pulling glass member 23. A dummy material 25 is attached to the end of the glass base material in advance. Further, FIG. 7 shows that the highest temperature portion in the electric furnace is from the connecting portion P1 of both members to the extending portion P on the glass base material side.
It is explanatory drawing which moves to 2 and extends. This distance L
Is, for example, about 10 to 40 mm. By adopting such a method, after the glass base material and the glass member for pulling (glass member for pulling out which becomes a dummy) are joined in the same process, the stretching work can be performed immediately and the efficiency of the stretching work can be improved. improves.

Further preferred embodiments will be described.
It This embodiment relates to the shapes of both ends of the glass preform and the glass member for pulling when joining the ends of the glass preform, and as shown in FIG. The outer diameter d ₁ of the dummy member 25 at the end is made smaller than the outer diameter d ₂ at the end of the pulling glass member 23. By doing so, a preferable and reliable joint can be obtained. The outer diameter of the end portion of the pulling glass member is preferably 2 to 3 times the outer diameter of the dummy material at the end portion of the glass base material for optical fiber. Note that FIG. 6B is an example of defective joining in which the outer diameter of the glass base material end is larger than the outer diameter of the pulling glass member end.

Further, an embodiment of the present invention will be described.
It In the present embodiment, in the highest temperature part inside the electric furnace, when the glass base material for optical fiber is drawn, the temperature, the outer diameter and the drawing speed of the glass base material drawing part are measured to control them. An electric furnace drawing method for glass preforms for optical fibers, characterized in that the drawing speed is gradually increased from the start of drawing while performing the drawing. More preferably, and performs control of the stretching by feeding back the outer diameter value when stretched meniscus angle of the glass preform stretching unit was measured at 4 ° or less to draw speed.

[0037] By performing such control of the stretching, to prevent bending of the rolled Shinhaha material, it is possible to improve the dispersion and accuracy of Matasoto径. It also improves the drawing speed,
It can contribute to productivity.

The stretching speed referred to in the present invention refers to the speed at which a rod is formed after stretching. The stretching speed at the start of stretching is, for example, 20 to 40 mm / min, and the speed is gradually increased so that stretching is performed at 40 to 70 mm / min. This is done to improve productivity.
In the present invention, since the stretching speed is gradually increased, it is necessary to control the temperature of the furnace as well. The stretching speed at the start of stretching is slow, since there is no meniscus portion at the start of stretching, there is no outer diameter measurement data value, and increasing the speed causes trouble, so it is necessary to slow the initial stretching speed. is there.

On the other hand, in the present invention, if the meniscus portion is formed and the outer diameter value of this portion can be measured, the measured outer diameter value of the stretched meniscus portion can be fed back to the stretching speed to control the stretching. Therefore, the stretching speed can be increased. FIG. 8 shows the shape of the glass base material in which the meniscus portion at the initial stage of drawing has not yet been formed.

Further, FIG. 9 shows a situation in which a stretched meniscus portion is formed after a while and the shape of the glass base material is changed. In FIG. 9, the outer diameter measuring portion 21A of the extending portion 21 of the base material 20 is at a position where the meniscus angle θ of the extending meniscus portion 21a is 4 ° or less. The outer diameter measuring portion B is at a position where the meniscus angle exceeds 4 ° (upper part of 21A). In controlling the outer diameter, the outer diameter measurement value at the position where the meniscus angle of the outer diameter measuring portion 21A is 2 to 4 ° is preferable. Since the measuring unit 21B is too close to the base material, the outer diameter is not yet thin, the meniscus angle is large, and the measurement position is high, which makes it difficult to control. Further, if the distance is much lower than the measuring unit 21A, the feedback is delayed and the device becomes large. Further, since the non-control unit is large, waste is also increased. Therefore, it is preferable to use the outer diameter value at a meniscus angle of 2 to 4 degrees for control.

[0041] FIG. 10 is an explanatory view of a main control system related to the embodiment of the present invention. The embodiment of the present invention is
Measure the temperature and outer diameter of the glass base material stretched portion, especially the temperature and outer diameter when the stretching meniscus angle is 4 ° or less, and the stretching speed of the stretching rod, and gradually control from the start of stretching while controlling these. The outer diameter measuring device 3 is used to increase the speed and perform stretching in a steady state.
6, temperature measuring device 37, stretching rod outer diameter measuring device 3
8, each information obtained by the speedometer 42 is input to the control device 40, the stretching speed is controlled by the motor 41, and the temperature of the electric heater is also controlled.

This will be described in more detail. The control device 4
0 is composed of, for example, a computer and performs various control calculations described below. In the present embodiment, the control device 40 is particularly configured to extend the glass base material extending portion (outer diameter changing portion),
In particular, by measuring and controlling the temperature, the outer diameter, and the stretching speed at the position where the meniscus angle in the meniscus portion 21a is in a predetermined range, preferably in the range of 2 to 4 ° The stretching speed is continuously increased up to the stretching speed of. The control device 40 measures the temperature and outer diameter of the stretched portion of the glass preform for optical fibers, particularly the heating temperature and outer diameter when the stretching meniscus angle is 4 ° or less, and the stretching speed of the stretching rod, and controls these. While performing, the stretching speed is gradually improved from the start of stretching, and stretching is performed in a steady state.However, in order to control these, an outer diameter measuring instrument that measures the outer diameter of the stretched portion and measures the meniscus angle 36, a temperature measuring device 37 for measuring the temperature of the stretching portion, a second outer diameter measuring device 38 for measuring the diameter of the stretching rod, and the lowering speed of the lower grip portion 39a by detecting the rotation speed of the motor 41. The information obtained by the speedometer 42 such as a tachometer for detecting the stretching speed is input to the control device 40, and the stretching speed is controlled by the motor 41 as a moving unit that pulls and lowers the lower grip 39a, and the electric furnace is used. Temperature of the electric heater 32 in the 0 also controls. The control device 40 has, in addition to the above-described control,
As an original control process, the measured value of the outer diameter of the second outer diameter measuring device 38 is input to the motor 41 so that the diameter of the drawn glass fiber preform for optical fiber 22 becomes a predetermined outer diameter. And the stretching speed is controlled to control the temperature measuring device 37.
The temperature control of the electric heater 32 in the electric furnace 30 is performed with reference to the measured temperature.

As another embodiment of the present invention, the above-mentioned embodiment
Like the form of, the glass base material stretched portion (outer diameter change portion),
In particular, by controlling by measuring the temperature at the position where the meniscus angle in the meniscus portion 21a is 4 ° or less, the outer diameter, and the stretching speed, the stretching device is provided with a control function of gradually increasing the stretching speed from the start of stretching. electric furnace stretching apparatus comprising Nitsu
I will explain. This action and effect are as described above.

[0044]

The following is a description of the embodiments of the present invention described above.
An example will be described. It was carried out in Example 1 stretching apparatus for a glass preform for an optical fiber shown in FIGS. The glass base material used for this has an outer diameter of 7
The length is 0 mm × the length is 1000 mm, and the outer diameter of the base material end dummy material on the pulling glass member side is 15 mm.
Further, the outer diameter of the end portion of the glass member for pulling is 20 mm. As a result of the implementation, the axial center misalignment of the two free ends 1B, 2B within the core tube 4 is within ± 0.1 to 0.2 mm (0.5 to 1% of the glass member diameter) in the horizontal plane. , Conventional 10
The accuracy is improved to about one-half. In addition, the embodiment described above
Although the glass preform was drawn based on the state, no bending occurred in the glass drawn preform for optical fiber.
Further, the vicinity of the connecting portion was not broken during stretching.

Example 2 A glass preform for drawing having an outer diameter of 65 mm was used. In addition,
A dummy member 25 (upper outer diameter 3
5 mm, lower outer diameter 10 mm, and height 30 mm) are joined together. Further, a glass member for pulling (for drawing) having an outer diameter of 38 mm was used. After welding and connecting the both ends, the highest temperature part in the electric furnace was transferred from the connection part to the drawing part of the glass base material, and the drawing speed was set to 38 mm / min. As a result, there was no bending in the stretched base material, and the outer diameter accuracy could be 34 mm ± 0.5 mm at a total length of 1300 mm.

Example 3 A glass preform for drawing having an outer diameter of 70 mm was used. In addition,
At the tip of this, the dummy material 25 (upper outer diameter 4 shown in FIG.
0 mm, lower outer diameter 10 mm, and height 30 mm) are joined together. Further, a glass member for pulling (for drawing) having an outer diameter of 38 mm was used.

After welding and connecting the both ends, the highest temperature part in the electric furnace was moved from the connecting part to the extending part of the glass base material,
The stretching start speed was 30 mm / min, the stretching speed was gradually increased, and the steady-state stretching speed was 50 mm / min. In this case, the temperature, the outer diameter, and the drawing speed of the glass base material drawing part were measured, and drawing was performed while controlling these.
In addition, the angle of the stretched meniscus portion was controlled using the outer diameter measurement value at 3 °. As a result, there was no bending in the stretched base material, and the outer diameter accuracy could be 36 mm ± 0.5 mm in the entire length.

[0048]

As described above , according to the present invention ,
When the drawing glass base material and the pulling (drawing) glass member are joined prior to the drawing, the axes of both can be accurately aligned, easily and easily. As a result, at the time of stretching, the stress distribution in the cross section of both connecting portions becomes uniform, and the bending of the stretched base material can be prevented. Further, the vicinity of the connecting portion between the two is not inclined, and breakage is avoided.
Further , according to the present invention, in the electric furnace drawing step, the drawing of the glass base material can be started immediately after the welding and joining of the both, and therefore, it is effective in terms of work efficiency. Furthermore, the present invention
According to the method , the stretching speed can be gradually improved from the start of stretching by control, and the outer diameter value at a predetermined position of the stretching portion meniscus portion is used for this control. The speed can be improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an apparatus for stretching a glass preform for optical fibers according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of a holding member for holding and fixing a glass member provided in the optical fiber glass preform stretching device of FIG.

FIG. 3 is an explanatory view showing an example of a centering mechanism for centering the tip of the free end portion of the glass member provided in the glass fiber preform stretching device of FIG.

FIG. 4 is an explanatory diagram showing an outline of an electric furnace drawing apparatus according to an embodiment of the present invention and a situation in which a glass base material is drawn by the apparatus.

FIG. 5 is an explanatory view showing the inside of the electric furnace drawing apparatus of the embodiment of the present invention, in which a dummy material is attached to the end of the glass base material and the end of the glass base material is attached. The situation before connection with the end of the glass member for pulling is shown.

FIG. 6 is an explanatory view showing a state in which a dummy material at the end of the glass base material is connected to the end of the glass member for pulling, (a).
Shows a good connection state and (b) shows a bad connection state .
is there.

[FIG. 7] FIG. 7 shows the first maximum heating part as a connection part P ₁ in the embodiment of the present invention , and then the maximum heating part P _{2 as a} base material extending part.
It is an explanatory diagram to move to, in the illustration, between P _{1 and} P ₂ is 1
It is illustrated that it is about 0 to 40 mm .

FIG. 8 shows a deformed state of the glass base material at the start of stretching in the embodiment of the present invention .

FIG. 9 shows the shape of a glass base material stretched portion when a stretched meniscus portion is formed from the start of stretching in the embodiment of the present invention . In the figure, the measurement unit A is at a position with a meniscus angle of 4 °.

10 is an explanatory view of a main control system related to the embodiment of the present invention.

FIG. 11 is a schematic view showing an example of a conventional glass fiber preform for an optical fiber.

[Explanation of symbols]

1, 91 Drawing glass base material (glass base material for optical fiber) 1A Fixed end portion 1B above drawing glass base material Free end portion 292 below drawing glass base material 2,92 Pulling glass member (for pulling out) Glass mother member) 2A Fixed end portion of lower glass member for pulling 2B Free end portion of upper glass member for pulling 3,93 Furnace body, 4,94 Core tube, 4A, 94A Observation window 5,95 Glass mother for stretching Material gripping member 6, 96 Gripping member for pulling glass member 7, 97 Moving base, 8, 98 Guide rail 9 Aligning mechanism, 9A Aligning gripping tool, 9B Support rod, 9C
Frame 9D Guide rail, 9EV groove 20 Optical fiber glass base material 21 Stretched portion (outer diameter changing portion) 21a A portion of the stretched portion where the meniscus angle is 4 ° or less 21A Outer diameter measuring portion 21B Upper portion of the stretched meniscus angle 21A 22 Draw Base Material 23 Glass Member for Tensioning (Drawing Out) 24 Joining Section 25 Heating Point at Dummy Material P ₁ Connection at End of Glass Base Material, P ₂ Heating Point at Start of Drawing 30 Electric Furnace Body, 31 Core Tube , 32 electric heaters,
33 heat insulating material 34, 35 window 36 outer diameter measuring instrument, 37 temperature measuring instrument, 38 outer diameter measuring instrument for stretched base material 39a glass base material gripping portion, 39b pulling glass member gripping portion 40 control device, 41 motor, 42 speedometer

Continuation of the front page (56) Reference JP-A-63-195139 (JP, A) JP-A-6-239639 (JP, A) JP-A-6-271326 (JP, A) JP-A-10-72226 (JP , A) JP-A-11-106231 (JP, A) JP-A-11-109142 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C03B 37/00-37/16 C03B 20/00 C03B 23/04

Claims (6)

(57) [Claims] 1. An electric furnace drawing method for drawing a glass base material for an optical fiber at a maximum temperature portion inside an electric furnace, wherein the glass base material for an optical fiber is formed by heating the electric furnace. The meniscus angle of the meniscus part is 2
The outer diameter of the glass base material for optical fiber is measured at a position of not less than 4 degrees and not more than 4 degrees, and the measured outer diameter value is fed back to the drawing speed control for drawing the glass base material for optical fiber. Electric furnace drawing method for glass preform for optical fiber. 2. The electric furnace drawing method for a glass preform for an optical fiber according to claim 1, wherein after the feedback of the drawing speed control is started, the drawing speed control is performed to gradually increase the drawing speed from the drawing speed at the start. . 3. Prior to the drawing of the glass preform for optical fiber, the part where the end of the glass preform for optical fiber and the end of the glass member for pulling are joined at the highest temperature inside the electric furnace. hot-sealing the said maximum temperature portion moves from the hot sealing portion extending portion of the optical fiber glass base material side, then extension of the previous SL electric furnace glass preform for optical fiber by heating The electric furnace stretching method for a glass preform for an optical fiber according to claim 1, wherein a meniscus portion is formed on the substrate and the stretching is performed. 4. When the end portion of the glass base material for optical fiber and the end portion of the glass member for pulling are welded together by heating, the outer diameter of the glass base material for optical fiber has the outer diameter. The electric furnace drawing method for a glass base material for an optical fiber according to claim 3, wherein the outer diameter is smaller than the outer diameter of the end portion. 5. An electric furnace, an outer diameter measuring section for measuring an outer diameter of an optical fiber which is located below a core tube surrounded by a furnace body of the electric furnace, and control means for controlling a drawing speed. In the electric furnace stretching apparatus for stretching the glass preform for optical fiber in the highest temperature part of the electric furnace, the control means, via the outer diameter measuring section, by heating the electric furnace The outer diameter of the glass base material for optical fiber is measured at a position where the meniscus angle of the meniscus portion formed in the stretched portion of the glass base material for optical fiber is 2 degrees or more and 4 degrees or less, and the measured outer diameter value is referred to An electric furnace stretching apparatus for a glass base material for an optical fiber, wherein a stretching speed control for stretching the glass base material for an optical fiber is performed. 6. The glass fiber matrix for optical fiber according to claim 5, wherein the control means performs a drawing speed control for gradually increasing the drawing speed from the drawing speed at the start after starting the feedback of the drawing speed control. Electric furnace drawing equipment.