JPH11199261A - Glass rod stretching method - Google Patents

Abstract

(57) [Problem] To provide a glass rod stretching method capable of stretching a glass rod so as to have a uniform outer diameter from the start to the end of stretching. A glass rod stretching method in which a glass rod (1A) is sequentially heated and softened from one end and stretched while holding and moving a dummy rod (1B) fusion-bonded to both ends of the glass rod (1A). Rod 1A
The total content of _{GeO 2, TiO 2, B 2} O 3, P 2 0 5 and Al ₂ 0 ₃ 100
A core portion 9 formed of more than 0 wt.ppm SiO ₂ ,
Is formed around the core portion _{9, GeO 2, TiO 2,} B 2 O 3, P 2 0 total content of ₅ and Al ₂ 0 ₃ has a cladding portion 10 made of SiO ₂ below 1000 wt · ppm , The dummy rod 1B is made of GeO ₂ , Ti
_{O 2, B 2 O 3,} P 2 0 5 and Al ₂ 0 total content of ₃ have a glass portion 11 composed of SiO ₂ below 1000 wt · ppm, clad portion 10 and the glass portion 11 TogaToru It is characterized by being bonded and joined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drawing a glass rod such as a preform for an optical fiber.

[0002]

2. Description of the Related Art Conventionally, as a method for stretching a glass rod such as a base material for an optical fiber into a glass rod having a smaller diameter, Japanese Patent Application Laid-Open No. Hei 4-331734 or Japanese Patent Laid-Open No.
A method described in, for example, Japanese Unexamined Patent Publication No. 1 is known. In these methods, a dummy rod fusion-bonded to the upper and lower ends of a glass rod is held by a chuck, and a part of the glass rod is softened by heating with a burner or a heating furnace, and at the same time, the upper and lower chucks are provided with a speed difference. The glass rod is moved and stretched by applying a tensile force to the glass rod. At this time, the outer diameter of the drawn glass rod is made uniform by controlling the moving speed of the chuck based on the outer diameter of the glass rod in the drawing process.

[0003]

However, in the stretching method as described above, even if the outer diameter of the glass rod after being stretched is controlled to be uniform, immediately after the start of stretching and immediately before the end of stretching, There is a problem that the outer diameter of the stretched glass rod is liable to fluctuate, and the outer diameters at both ends of the stretched glass rod are not uniform. As a result of intensive studies on the cause, the inventors have found that it largely depends on the fusion bonding state between the glass rod and the dummy rod.

[0004] The present invention has been made based on the above findings, and provides a glass rod stretching method capable of stretching a glass rod so that the outer diameter becomes uniform from the start to the end of stretching. Aim.

[0005]

The invention according to claim 1 is
The first rod and the second rod are gripped by the first rod and the second rod, and the first rod and the second rod are held at a higher speed than the second rod. While moving the two gripping parts in the longitudinal direction of the glass rod, in a glass rod stretching method in which the glass rod is sequentially heated and softened and stretched from the first gripping part side end,
Glass rod is made of germanium dioxide, titanium dioxide,
A core portion formed of silicon dioxide having a total content of diboron trioxide, diphosphorus pentoxide, and aluminum oxide of more than 1000 wt.ppm, and germanium dioxide, titanium dioxide, dioxide trioxide formed around the core portion; Boron, diphosphorus pentoxide and a cladding portion made of silicon dioxide with a total content of aluminum oxide of 1000 wt.ppm or less, the dummy rod is germanium dioxide, titanium dioxide, diboron trioxide, diphosphorus pentoxide and It has a glass part made of silicon dioxide having a total content of aluminum oxide of 1000 wt.ppm or less, and is characterized in that the clad part and the glass part are fusion-bonded.

In the invention according to claim 1, the glass rod and the dummy rod are made of a clad portion and a glass portion made of silicon dioxide having a total content of germanium dioxide, titanium dioxide and diboron trioxide of 1000 wt.ppm or less. , The viscosity during softening from the glass rod to the dummy rod becomes substantially uniform. For this reason, the viscosity at the time of softening from the glass rod to the dummy rod is only partially different, so that only this portion is not easily elongated. As a result, according to the first aspect of the present invention, when heating and stretching the vicinity of the fusion bonding surface with the dummy rod at both ends of the glass rod, poor stretching caused by non-uniformity of viscosity during softening is prevented. can do.

According to a second aspect of the present invention, the bonding area between the clad portion and the glass portion on the fusion bonding surface between the glass rod and the dummy rod is 85% of the area of the entire fusion bonding surface.
It is characterized by occupying the above.

In the invention according to the second aspect, most of the tensile force acting on the fusion bonding surface between the glass rod and the dummy rod is increased by 85% or more of the fusion bonding surface between the cladding portion and the glass portion. Can be received at the junction. For this reason,
Since the viscosity at the time of softening from the glass rod to the dummy rod becomes more uniform, it is possible to prevent the vicinity of the fusion bonding surface from being locally stretched when the vicinity of the fusion bonding surface is heated and stretched. As a result, it is possible to more effectively prevent poor stretching caused by uneven viscosity at the time of softening.

According to a third aspect of the present invention, the outer diameter of the dummy rod and the outer diameter of the fusion bonding surface are 50% of the outer diameter of the glass rod.
It is characterized by being 100%.

According to the third aspect of the present invention, by setting the outer diameter of the dummy rod to 50% to 100% with respect to the outer diameter of the glass rod, the tensile stress applied to the glass rod during stretching (per unit area) (Tension) and the tensile stress applied to the dummy rod can be reduced. As a result, concentration of stress on the fusion bonding surface is suppressed, and poor stretching can be more effectively prevented.

Even if the outer diameter of the dummy rod is 50% to 100% of the outer diameter of the glass rod, the bonding at the fusion bonding surface is incomplete and the outer diameter of the fusion bonding surface is small. If so, stress will be concentrated on the fusion bonding surface. For this reason, not only the outer diameter of the dummy rod but also the outer diameter of the fusion bonding surface needs to be 50% to 100% of the outer diameter of the glass rod.

Here, if the outer diameter of the dummy rod and the outer diameter of the fusion bonding surface are less than 50% of the outer diameter of the glass rod, the tensile stress acting on the glass rod and the dummy rod and the fusion bonding may be reduced. The difference from the tensile stress acting on the surface increases, and stress concentrates on the fusion bonding surface where the outer diameter changes greatly. For this reason, the vicinity of the fusion bonding surface is locally stretched, and the glass rod to be stretched is not stretched due to the reaction, which may cause poor stretching.

On the other hand, if the outer diameter of the dummy rod and the outer diameter of the fusion bonding surface exceed 100% of the outer diameter of the glass rod, both the glass rod and the dummy rod increase in diameter. , Making it difficult to melt soften, making it difficult to perform fusion bonding. In addition, it becomes difficult to chuck the dummy rod, which makes it impractical.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a stretching apparatus for carrying out a method for stretching a glass rod according to the present invention will be described with reference to FIG.

FIG. 1 shows a state where the glass rod 1A is being stretched. The lower part of the non-stretched portion 1a of the glass rod 1A is heated and softened by the heating furnace 4 and stretched at a tapered portion 1b (a portion shown by oblique lines in FIG. 1), and a stretched portion 1c is further formed below the tapered portion 1b. Have been. The glass rod 1A has only the non-stretched portion 1a before stretching, but as the stretching progresses, the tapered portion 1b is formed, and the stretched portion 1c is formed below the tapered portion 1b.

A dummy rod 1B is fusion-bonded to the upper end and the lower end of the glass rod 1A, respectively. The dummy rod 1B is chucked by the first grip 2 and the second grip 3, respectively. The first gripper 2 and the second gripper 3 are connected to drive motors 6 and 7, respectively, and are moved by the drive motors 6 and 7 in the longitudinal direction of the glass rod 1A (vertical direction in FIG. 1). The drive motors 6 and 7 are connected to the control unit 8 and change the speeds of the first grip 2 and the second grip 3 based on a signal from the control unit 8.

A heating furnace 4 is disposed between the first grip 2 and the second grip 3. The heating furnace 4 has a cylindrical shape, and heats and softens the glass rod 1A inserted at the center thereof. As the heating furnace 4, a resistance furnace using heat generated by electric resistance or an induction furnace using high-frequency induction heating is used. Although depending on the outer diameter of the glass rod 1A, a burner can be used instead of the heating furnace 4 as long as the glass rod 1A can be sufficiently softened. In the vicinity of the lower portion of the heating furnace 4, a non-contact type outer diameter measuring device 5 for measuring the outer diameter of a specific position 1d of the tapered portion 1b which is inserted into the heating furnace 4 and softened by heating is provided.

The process of stretching the glass rod 1A by the above-described apparatus will be described below.

First, the first grip 2 and the second grip 3 are
Each of them is moved downward by the drive motors 6 and 7 which receive the signal from the control unit 8, respectively. The moving speed of the first holding unit 2 is set to be faster than the moving speed of the second holding unit 3.
A tensile force is applied to A.

The portion of the glass rod 1A inserted into the heating furnace 4 is softened by the amount of heat given from the heating furnace 4,
The tapered portion 1b is formed by being stretched by the above-described tensile force. The tapered portion 1b solidifies after exiting the heating furnace 4 and moves to the stretched portion 1c. The outer diameter of the specific position 1d near the lower end of the tapered portion 1b is measured by the outer diameter measuring device 5, and the measured value is sent to the control unit 8. Based on the measured value, the moving speed of the first grip 2 and the second grip 3 (or one of them) is controlled so that the outer diameter of the stretched portion 1c is constant.

Next, the glass rod 1 stretched by the above-described device and having the dummy rods 1B fused to both ends is bonded.
A will be described.

The glass rod 1A includes a core portion 9 formed at the center thereof and a clad portion 10 formed around the core portion 9.

The core 9 is made of a dopant (refractive index adjuster).
As germanium dioxide (GeO ₂ ), titanium dioxide (Ti
O _2), boron oxide (B ₂ O _3), silicon dioxide containing at least one of diphosphorus pentoxide (P ₂ 0 ₅₎ and aluminum oxide _{(Al 2 0 3) (SiO} 2) GeO ₂ , TiO ₂ , B
₂ O _3, the total content of P ₂ 0 ₅ and Al ₂ 0 ₃ is more than 1000 wt · ppm (parts per million by weight). The core part 9 is a part for transmitting light when the glass rod 1A is drawn into an optical fiber.

On the other hand, the cladding portion 10 is made of GeO ₂ , TiO ₂ , B ₂
O _3, P ₂ 0 ₅ and Al ₂ 0 ₃ of the total content of less 1000 wt · ppm, i.e., is formed by SiO ₂ which is substantially free of dopants. As described above, by making the core portion 9 contain a dopant, the refractive index of the core portion 9 is made higher than the refractive index of the clad portion 10.

The dummy rod 1B is entirely composed of GeO ₂ , Ti
_{O 2, B 2 O 3,} P 2 0 5 and Al ₂ 0 ₃ of the total content of less 1000 wt · ppm, i.e., the glass portion 11 made of SiO ₂ which is substantially free of dopants, in its entirety is formed ing. In some cases, a part of a glass rod that could not be made into a product (such as an end piece of a drawn glass rod) may be used as the dummy rod 1B, and thus has a core portion at the center. A thing may be used as dummy rod 1B.

The fusion bonding portion between the glass rod 1A and the dummy rod 1B will be described in detail. In addition, the above-mentioned fusion bonding portions are formed on both ends of the glass rod in exactly the same manner. Therefore, hereinafter, only one of the two fusion bonding portions will be illustrated and described, and the illustration and description of the other fusion bonding portion will be omitted.

As shown in FIG. 2, the shapes of both ends of the glass rod 1A and the dummy rod 1B are adjusted by a grinder or the like, and then heated and softened. Then, the dummy rod 1B is pressed against both ends of the glass rod 1A and fused. Join. In this fusion bonding, the clad portion 10 on the glass rod 1A side and the glass portion 11 on the dummy rod 1B side are reliably fused. Here, the surface where the glass rod 1A side and the dummy rod 1B are fusion bonded is referred to as a fusion bonding surface P.

The clad portion 10 and the glass portion 11 are made of SiO ₂ which does not substantially contain the above-mentioned dopant, and when the clad portion 10 and the glass portion 11 are fusion-bonded, a fusion bonding surface is formed. The viscosity at the time of softening in the vicinity of P becomes substantially uniform. For this reason, even when the fusion bonding surface P is located in the vicinity of the heating furnace 4 (immediately after the start of stretching or immediately before the end of stretching), the viscosity at the time of softening becomes substantially uniform from the glass rod 1A to the dummy rod 1B. In addition, poor stretching due to non-uniformity can be prevented.

On the other hand, if the clad portion 10 and the glass portion 11 are not fusion-bonded, a portion having a non-uniform viscosity from the glass rod 1A to the dummy rod 1B during softening is formed, and only this portion is easily stretched. As a result, the glass rod 1A to be stretched by the reaction does not stretch and causes poor stretching. Clad part 10 and glass part 1
FIG. 4 shows a case in which No. 1 is not fusion-bonded.

In the case shown in FIG. 4, the glass rod 1A
When the dummy rod 1 </ b> B is fusion-bonded to the core member 9, the core portion 9 is expanded and the dummy rod 1 </ b> B is fusion-bonded only to the core portion 9. The core portion 9 containing the dopant described above has a lower viscosity when softened than the clad portion 10 and the glass portion 11.

For this reason, when the glass rod 1A is stretched in the fusion-bonded state as shown in FIG. 4, when the fusion-bonded surface P is located near the heating section 4 (immediately after the start of stretching or immediately before the end of stretching). However, the low-viscosity core portion 9 in the vicinity of the fusion bonding surface P is stretched, and the glass rod 1A to be stretched is not stretched and the diameter becomes large. In the worst case, the glass rod 1A and the dummy rod 1B break in the vicinity of the fusion bonding surface P.

Next, the glass rod 1A and the dummy rod 1
The respective dimensions of the fusion bonded portion after fusion bonding with B will be described with reference to FIG.

As shown in FIG. 3, the dummy rod 1B
Is approximately equal to the outer diameter R3 of the fusion bonding surface P,
The outer diameter R2 and the outer diameter R3 are equal to the outer diameter R1 of the dummy rod 1a.
Is in the range of 50% to 100%. In the fusion bonding surface P, the bonding area between the clad portion 10 and the glass portion 11 occupies 85% or more of the total area of the fusion bonding surface P.

As described above, the outer diameter R2 and the outer diameter R3 are
Since it is 50% to 100% with respect to the outer diameter R1, the tensile stress acting on the glass rod 1A side and the dummy rod 1
There is no significant difference between the tensile stress acting on the B side and the fusion bonding surface P. For this reason, the concentration of stress near the fusion bonding surface P where the outer diameter changes can be suppressed, and the local extension near the fusion bonding surface P can be more effectively prevented.

Here, the outer diameter R2 of the dummy rod 1B and the outer diameter R3 of the fusion bonding surface P are equal to the outer diameter R of the glass rod 1A.
If the ratio is less than 50% of 1, the difference between the tensile stress on the glass rod 1A side and the tensile stress on the dummy rod 1B side and the fusion bonding surface P increases, and the stress concentrates near the fusion bonding surface P. Would. On the other hand, the outer diameter R2 and the outer diameter R3 are equal to the outer diameter R1.
If it seems to exceed 100%, the glass rod 1
A and the dummy rod 1B both have a large diameter, and both are melted and softened, so that it is difficult to perform fusion bonding. Also, since the dummy rod 1B becomes thicker, it becomes difficult to chuck,
It is not realistic.

Also, even if the outer diameter R2 of the dummy rod 1B is
Is in the range of 50% to 100% with respect to the outer diameter R1 of the glass rod 1A, as shown in FIG. 5, the fusion bonding is incomplete and the outer diameter R3 of the fusion bonding surface P is glass. Rod 1
If it becomes 50% or less with respect to the outer diameter R1 of A, the fusion bonding surface P
Stress concentrates in the vicinity. Therefore, both the outer diameter R2 of the dummy rod 1B and the outer diameter R3 of the fusion bonding surface 1B are 50% to 100% of the outer diameter R1 of the glass rod 1A.
Must be in the range of

The bonding area between the clad portion 10 and the glass portion 11 is equal to the area of the entire fusion bonding surface P as described above.
It accounts for more than 85%. Therefore, most of the tensile force acting on the fusion bonding surface P is transferred to the cladding portion 10 and the glass portion 11.
And can be received at the junction. As a result, from the glass rod 1A to the dummy rod 1B, the viscosity at the time of softening can be made more uniform, and the vicinity of the fusion bonding surface P can be more effectively prevented from being locally stretched. .

As described above, in some cases, a glass rod that has failed to be extended is used as a dummy rod. In this case, as shown in FIG. 6, the dummy rod 1B 'is used.
Also the total content of _{GeO 2, TiO 2, B 2} O 3, P 2 0 5 and Al ₂ 0 ₃ is 1000w
The core portion 9B has more than t · ppm. When such a dummy rod 1B 'is used, the bonding area between the clad part 10 and the glass part 11 on the fusion bonding surface P includes the bonding area between the clad part 10 and the core part 9B of the dummy rod 1B' and the glass. Part 11 and core part 9A of glass rod 1A
Needless to say, it does not include the bonding area with the above.

Further, according to the above-described stretching method in which the clad portion and the glass portion are fusion-bonded to each other, a large amount of heat is applied to the glass rod and a heating furnace that softens the glass rod over a wide range is used. Even so, it is possible to precisely stretch the glass rod to a constant outer diameter by one stretching. For this reason, even a glass rod having a large outer diameter of 50 mm or more, which cannot be stretched unless a large amount of heat is applied, can be precisely stretched by a single stretching.

Conventionally, when only a heating furnace is used, poor stretching occurs immediately after the start of stretching and immediately before the completion of stretching as described above. When only a burner is used, a large amount of heat is applied to the glass rod. Was not able to
It was not possible to precisely stretch a glass rod having a large outer diameter by a single stretching. Therefore, conventionally, when a glass rod having a large outer diameter is precision-drawn, the glass rod is once drawn in a heating furnace to reduce the diameter, and then precisely drawn using a burner.

The burner cannot stretch a glass rod having a large outer diameter at a time, but can locally heat the glass rod and can finely control the amount of heat applied to the glass rod. there were.
Once the diameter of the glass rod was once reduced by the heating furnace, the glass rod could be precisely stretched even by using a burner that gives a limited amount of heat to the glass rod.

With the two steps as described above, even if there is a slight variation in the outer diameter at the time of drawing in the heating furnace, the drawing can be performed precisely at the time of drawing with the burner. It was not preferable from the viewpoint of improving the properties. The above-mentioned stretching method can solve such a problem,
It can also be suitably used in the case where a glass rod having a large outer diameter is precisely stretched by a single stretching using a heating furnace. For example, a glass rod having a diameter of 50 mm or more can be precisely stretched in one stretch, and a glass rod having a considerably large outer diameter of about 200 mm can be stretched to about 50 mm.

In order to confirm the effects of the present invention, tests were conducted for the following relationships.

The relationship between the outer diameter of the glass rod and the outer diameter of the dummy rod and the fusion bonding surface Relation of the area occupied by the clad portion and the glass portion on the fusion bonding surface. In the following test, a glass rod and a dummy rod in which a clad portion and a glass portion were fusion-bonded were used.

Relationship Between the Outside Diameter of the Glass Rod and the Outside Diameter of the Dummy Rod and the Fusion Bonding Surface Regarding the case where the glass rod 1A whose outside diameter before stretching is 100 mm is stretched so that the outside diameter after stretching becomes 50 mm. Tested. In order to set the outer diameter of the dummy rod 1B and the fusion bonding surface P to 40 mm and the outer diameter after stretching to 50 mm, the target outer diameter at the specific position 1d measured by the outer diameter measuring device 5 is fixed to 58 mm. The case where the speeds of the first gripper 2 and the second gripper 3 are controlled is shown in (1) in the graph of FIG. At this time, the ratio of the bonding area of the clad portion 10 and the glass portion 11 to the entire area of the fusion bonding surface P is 95%. In such a case, it can be seen that the outer diameter variation of the glass rod 1A is large immediately after the start of the drawing and immediately before the end of the drawing. The maximum outer diameter fluctuation amount is as large as 15 mm on the drawing end end side.

Next, a test was conducted on a case where the glass rod 1A having an outer diameter of 100 mm before stretching was stretched so as to have an outer diameter of 50 mm by changing the target outer diameter of the specific position 1d without fixing it. That is, the target outer diameter at the specific position 1d is set to 58 until the length of the drawn glass rod 1A becomes about 1300 mm.
mm, and thereafter, it was controlled by gradually changing it to 54 mm at the end of stretching. This case is shown in the graph of FIG.
It is shown in (2). In this case, the variation of the outer diameter of the glass rod 1A immediately after the start of stretching is not different from (1), but the variation of the outer diameter immediately before the end of stretching is smaller than that of (1). But,
Even in the case of (2), the outer diameter variation is still large.
The outer diameter variation is 5.1 mm on the stretching start end side and
7.0 mm. In practice, it is desired to suppress the outer diameter variation of the glass rod 1A to 10% or less of the standard value. If the outer diameter standard value of the glass rod 1A after stretching is 50 mm, the maximum outer diameter variation is 5.
I want to keep it below 0mm.

Therefore, while controlling the speed by the first gripper 2 and the second gripper 3 by variably controlling the target outer diameter at the specific position 1d, the glass rod 1A having an outer diameter of 100 mm before stretching is moved to the outer diameter. The test was performed by changing the outer diameters of the dummy rod 1B and the fusion bonding surface P variously in the case of stretching to 50 mm. Note that the variation control of the target outer diameter at the specific position 1d is 58 mm until the length of the drawn glass rod 1A becomes a specific length (depending on the outer diameter of the dummy rod 1B and the fusion bonding surface P). Thereafter, it was controlled by gradually changing it to 54 mm at the end of stretching. The table shown in FIG. 8 shows the test results. As can be seen from the table shown in FIG. 8, the outer diameter of the dummy rod 1B and the fusion bonding surface P must be 50 mm or more, that is, the glass rod 1A before stretching, in order to make the outer diameter fluctuation amount 5.0 mm or less. It is understood that the diameter should be 50% or more of the outer diameter.

The case where the outer diameter of the dummy rod 1B and the fusion bonding surface P in the table shown in FIG. 8 is 70 mm is shown in the graph (3) of FIG. At this time, the fluctuation control of the target outer diameter at the specific position 1d is set to 58 mm until the length of the drawn glass rod 1A becomes about 1500 mm, and thereafter is gradually changed to 54 mm at the end of drawing. Controlled. In this case, the outer diameter fluctuation amount is 2.5 m on the stretching start end side.
m, which is improved to 2.1 mm at the end of stretching.

Also, in the table shown in FIG. 8, the case where the outer diameters of the dummy rod 1B and the fusion bonding surface P are equal, that is, the case where the fusion bonding is normally performed, is shown in FIG. The case where the fusion bonding was incomplete as shown was also tested.

Therefore, the target outer diameter at the specific position 1d is variably controlled to control the speed by the first gripper 2 and the second gripper 3 while the glass rod 1A having the outer diameter of 100 mm before stretching has the outer diameter of 100 mm. In the case of stretching to be 50 mm, the outer diameter of the dummy rod 1B was fixed to 70 mm, and the outer diameter of the fusion bonding surface P was variously changed and tested. At this time,
The ratio of the bonding area of the cladding part 10 and the glass part 11 to the entire area of the fusion bonding surface P is 95%. The table shown in FIG. 9 shows the test results. As can be seen from the table shown in FIG. 9, not only the outer diameter of the dummy rod 1B but also the fusion bonding surface P
It is understood that the outer diameter of the glass rod 1A needs to be 50 mm or more, that is, 50% or more of the outer diameter of the glass rod 1A before stretching.

Relationship between the area occupied by the clad portion and the glass portion on the fusion bonding surface The target outer diameter at the specific position 1d is controlled to be variable, and the speed is controlled by the first gripper 2 and the second gripper 3 before stretching. In the case where a glass rod 1A having an outer diameter of 100 mm was stretched so as to have an outer diameter of 50 mm, a test was performed by fixing the outer diameter of the dummy rod 1B and the fusion bonding surface P to 60 mm. Here, the ratio of the bonding area between the clad portion 10 and the glass portion 11 to the entire area of the fusion bonding surface P was variously changed. The above-described change in the ratio was performed by changing the diameter of the core portion 9. The table shown in FIG. 10 shows the test results.

As can be seen from the table shown in FIG.
It can be seen that in order to make the variation in outer diameter 5.0 mm or less, the ratio of the bonding area between the clad portion 10 and the glass portion 11 to the entire area of the fusion bonding surface P needs to be 85% or more.

[0053]

In the method for stretching a glass rod according to the present invention, the glass rod to be drawn has a total content of germanium dioxide, titanium dioxide, diboron trioxide, diphosphorus pentoxide and aluminum oxide of 1000 wt.ppm. A core portion formed by more silicon dioxide and a silicon dioxide formed around the core portion and having a total content of germanium dioxide, titanium dioxide, diboron trioxide, diphosphorus pentoxide and aluminum oxide of 1000 wt.ppm or less. A dummy rod having a cladding portion made of silicon and being fusion-bonded to a glass rod has a total content of germanium dioxide, titanium dioxide, diboron trioxide, diphosphorus pentoxide and aluminum oxide.
Since it has a glass part made of silicon dioxide of 1000 wt.ppm or less and is characterized in that the clad part and the glass part are fusion-bonded, the outer diameter becomes uniform from the start of drawing to the end of drawing The glass rod can be stretched as follows.

[Brief description of the drawings]

FIG. 1 is a side view of a drawing apparatus for performing a glass rod drawing method according to the present invention.

FIG. 2 is a perspective view showing a fusion bonding portion between a glass rod and a dummy rod.

FIG. 3 is a cross-sectional view showing a fusion bonding portion between a glass rod and a dummy rod.

FIG. 4 is a cross-sectional view showing a fusion bonded portion (failure example) between a glass rod and a dummy rod.

FIG. 5 is a cross-sectional view showing a fusion bonding portion (failure example) between a glass rod and a dummy rod.

6A is a perspective view showing a fusion bonding portion between a glass rod and a dummy rod (with a core portion), and FIG. 6B is a cross-sectional view taken along a fusion bonding surface.

FIG. 7 is a graph showing test results.

FIG. 8 is a table showing test results (when the outer diameter of the dummy rod and the fusion bonding surface is changed).

FIG. 9 is a table showing test results (when the outer diameter of the fusion bonding surface is changed).

FIG. 10 is a table showing test results (when the ratio of the bonding area is changed).

[Explanation of symbols]

1A: Glass rod, 1B: Dummy rod, 10: Cladding part, 11: Glass part, 2: First gripping part, 3: Second gripping part, 9: Core part, P: Fusion bonding surface.

Claims (3)

[Claims] 1. A dummy rod fusion-bonded to both ends of a glass rod is gripped by a first gripper and a second gripper,
While moving the first gripping portion and the second gripping portion in the longitudinal direction of the glass rod so that the first gripping portion is at a higher speed than the second gripping portion, the glass rod is moved in the first direction. In the method for stretching a glass rod, which is sequentially heated and softened from the end on the gripping part side and stretched, the glass rod has a total content of germanium dioxide, titanium dioxide, diboron trioxide, diphosphorus pentoxide and aluminum oxide of 1000 wt. A core formed of more than ppm of silicon dioxide, and formed around the core;
Germanium dioxide, titanium dioxide, diboron trioxide,
Total phosphorus pentoxide and aluminum oxide content is 1000wt
A cladding portion made of silicon dioxide of not more than ppm, wherein the dummy rod has a total content of germanium dioxide, titanium dioxide, diboron trioxide, diphosphorus pentoxide and aluminum oxide of not more than 1000 wt.ppm. A method for stretching a glass rod, comprising: a glass part comprising: a clad part and the glass part are fusion-bonded. 2. A bonding area between the clad portion and the glass portion at a fusion bonding surface between the glass rod and the dummy rod is 85% of an area of the entire fusion bonding surface.
The method for stretching a glass rod according to claim 1, wherein the above is occupied. 3. An outer diameter of the dummy rod and an outer diameter of the fusion bonding surface are 50% to 100% of an outer diameter of the glass rod.
The method for stretching a glass rod according to claim 1 or 2, wherein: