JP2003300745A - Method for fabricating glass preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for fabricating a glass preform capable of stably stretching the glass preform to a desired diameter. <P>SOLUTION: When the glass preform 3 is melted by heating and is stretched, the heating temperature of the glass preform 3 is lowered from the initial heating temperature at an effective portion 14 of the preform during the course of stretching of the effective portion 14. At this time, the heating of the glass preform 3 is so performed that its heating temperature is lowered by at least ≤20°C than the initial heating temperature of the effective portion 14. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass base material processing method for heating and melting a glass base material used for manufacturing an optical fiber or the like and stretching the glass base material.

[0002]

2. Description of the Related Art Conventionally, as a method for drawing an optical fiber glass preform, those described in JP-A-2000-233938 and JP-A-2000-169171 are known. In these publications, dummy rods are attached to both ends of an optical fiber glass preform, a portion of the glass preform to be stretched (hereinafter referred to as a preform effective portion) is heated, and in that state, the dummy rod is grasped and pulled. Then, a method of stretching the diameter of the effective portion of the base material to a desired diameter is described.

[0003]

However, the above-mentioned prior art has the following problems. That is, when the quartz glass preform is stretched, heat is transferred to the upper side of the glass preform by being heated at a high temperature for a long time. The diameter portion may soften and stretch. When such a stretch occurs, the stretched diameter of the base material effective portion becomes large and not only deviates from the target, but in the worst case, the glass base material may be torn off. There is no choice but to stop the stretching. In this case,
The outer diameter of the base material effective portion deviates greatly from the desired diameter, and it cannot be used as a product.

An object of the present invention is to provide a method for processing a glass base material, which can stably stretch the glass base material to a desired diameter.

[0005]

DISCLOSURE OF THE INVENTION The present invention relates to a method for processing a glass base material in which a glass base material having a base material effective portion is heated and stretched, in which the glass base material is heated while the base material effective portion is being stretched. It is characterized by lowering the temperature.

In the glass base material, in order to form a starting rod by attaching dummy rods to both ends of the glass base material at the time of drawing, a small diameter portion corresponding to the dummy rod is provided at both ends of the base material effective portion. It is common to have When heating and stretching such a glass preform, by lowering the heating temperature during the stretching of the preform effective portion, the thin-diameter portion on the extension end end side of the preform effective portion is less likely to soften,
The thin portion does not easily stretch. Therefore, it is possible to suppress the reduction of the diameter of the drawing end end of the glass base material, and it is possible to stably extend the effective portion of the base material to a desired diameter.

Preferably, the heating temperature of the glass preform is lowered by at least 20 ° C. from the initial heating temperature of the effective part of the preform.
This makes it more difficult for the small-diameter portion of the glass base material on the end-of-stretching side to soften, so that the elongation of the thin-diameter portion can be further reduced.

In this case, preferably, the process of lowering the heating temperature of the glass base material by at least 20 ° C. from the initial heating temperature is 2 times the total length of the base material effective portion when the length from the stretching end end of the base material effective portion is 2. It is started before stretching the portion to be%.
As a result, it is possible to more reliably suppress the elongation of the small diameter portion of the glass base material on the end side of the stretching.

At this time, it is preferable to start lowering the heating temperature of the glass preform after stretching the portion where the length from the stretching end of the preform effective portion is 70% of the entire length of the preform effective portion. . Thereby, the entire base material effective portion can be effectively stretched.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the method for processing a glass base material according to the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an example of a stretching device used in an embodiment of a method for processing a glass base material according to the present invention. In the figure, a stretching device 1 heats and melts a quartz glass base material 3 for an optical fiber to stretch it.

The glass base material 3 is composed of a base material effective portion 14 formed in a substantially cylindrical shape, and base material non-effective portions 18a and 18b provided at both ends of the base material effective portion 14. The base material ineffective portions 18a and 18b are tapered and have a diameter that decreases from the base end side to the tip end side.

The glass base material 3 entirely contains an additive for changing the refractive index. Such additives include Ge, F, B, and so on, in order to obtain a refractive index profile required to achieve desired optical fiber transmission characteristics.
P, Cl, etc. are used.

In such a glass base material 3, first, glass fine particles are deposited on a quartz rod (core rod) by a VAD method, an OVD method or the like to form a glass fine particle deposit, and then the glass fine particle deposit is made into a transparent glass. It is formed by

A stretching device 1 for stretching the above glass base material 3 has a furnace body 2. Inside the furnace body 2, a furnace core tube 4 for heat-treating the glass base material 3, a heater 5 arranged on the outer periphery of the furnace core tube 4 and heating the glass base material 3,
A heat shield 6 arranged outside the heater 5 for preventing heat release from the heater 5 is housed.

A chimney 7 is provided above the furnace body 2. Above the chimney 7, there are a chuck 10 for holding and fixing a support rod 9a attached to one end of the glass base material 3 via a dummy rod 8a, and a lifting device 11 for vertically moving the chuck 10. It is arranged. Below the furnace body 2, a dummy rod 8 is provided on the other end of the glass base material 3.
A chuck 12 that holds and fixes the support rod 9b that is attached via b, and a lifting device 13 that moves the chuck 12 in the vertical direction are arranged. Furthermore, the furnace body 2
And the elevating device 13 between the glass base material 3 after drawing.
A chuck 15 that holds the base material effective portion 14 and a lifting device 16 that moves the chuck 15 in the vertical direction are arranged. The stretching device 1 also has a radiation thermometer 17 for measuring the surface temperature in the core tube 4.

Next, a method of drawing the glass preform 3 using the drawing apparatus 1 as described above will be described. First, dummy rods 8a and 8b made of quartz glass are welded and joined to both ends of the base material non-effective portions 18a and 18b of the glass base material 3,
Make a starting glass rod. Next, the dummy rod 8
Support rods 9a and 9b are attached to both ends of a and 8b. The base material ineffective portion 18b of the glass base material 3 is on the lower side (stretching start end side), and the base material ineffective portion 18a is on the upper side (stretching end end side).
The starting glass rod is inserted into the furnace core tube 4 of the furnace body 2 in the state of being arranged as follows. Next, the support rods 9a, 9
The glass base material 3 is supported by gripping b with the chucks 10 and 12.

Then, the heater 5 is operated to start the temperature rise in the core tube 4. Then, when the inner surface temperature of the furnace core tube 4 reaches the initial heating temperature at which the preform effective portion 14 of the glass preform 3 can be stretched, the stretching of the glass preform 3 is started while maintaining the temperature. The initial heating temperature of the base material effective portion 14 is preferably 1400 ° C to 2000 ° C.

The glass base material 3 is stretched by the lifting devices 11, 1
3 by moving the chucks 10 and 12 downward. At this time, the feeding speed of the chuck 10 is
It is set so as to be slower than the feeding speed of the chuck 12. As a result, the chuck 10 can feed the glass preform 3 into the furnace core tube 4, and the chuck 12 can pull and stretch the glass preform 3.

During the drawing, the outer diameter of the glass base material 3 is measured at a part or a plurality of points of the glass base material 3 which is being stretched,
The feed rates of the chucks 10 and 12 are adjusted so that the value of the outer diameter becomes constant. Moreover, the outer diameter of the glass base material 3 can be kept constant by adjusting the temperature in the furnace core tube 4. Alternatively, a plurality of glass preforms 3 having the same shape may be drawn, an optimum chuck feed rate may be calculated from the results, and the drawing may be performed using the feed rate. In this case, the glass preform 3 is used. Without controlling the outer diameter of
The outer diameter of the glass base material 3 can be stabilized.

In the drawing process of the glass base material 3 as described above, the heating temperature of the glass base material 3 is set to be lower than the initial heating temperature during the drawing of the effective portion 14 of the base material. The heating temperature at this time is at least 20 higher than the initial heating temperature.
It is desirable to lower the temperature by ℃. Needless to say, such a decrease in the heating temperature is performed within a range in which the base material effective portion 14 can be stretched. In the process of lowering the heating temperature, preferably, the length L from the stretching end end (upper end) 14a of the base material effective portion 14 is the entire length of the base material effective portion 14 (the extension of the base material effective portion 14 is completed. The length between the end 14a and the stretching start end 14b) 2% of L ₀ is started before stretching. At this time, the length L from the extension end 14a of the base material effective portion 14 is the entire length L ₀ of the base material effective portion 14.
It is preferable to start lowering the heating temperature of the glass base material 3 from an arbitrary part (for example, near the middle of the base material effective portion 14) after stretching the part where 70% of the glass base material becomes 70%.

By lowering the heating temperature of the glass preform 3 below the initial heating temperature during the stretching of the preform effective portion 14 in this way, the preform non-effective portion 18a of the glass preform 3 on the end side of the stretching is softened. Hard to do. Therefore, even when the base material effective portion 14 is heated for a long time, the base material non-effective portion 18a is less likely to be stretched. Therefore, it is possible to suppress the diameter reduction of the base material non-effective portion 18a due to the stretching, so that the stretched outer diameter of the base material effective portion 14 can be stabilized.

After the stretching process as described above is completed, the preform effective portion 14 is grasped by the chuck 15 with the chuck 10 fixed, and the glass preform 3 is pulled and torn in cooperation with the chuck 12.

Next, an example in which the glass preform is drawn by using the drawing apparatus shown in FIG. 1 will be described.

Example 1 As a glass base material, an effective part of the base material (total length 250 mm)
Has an outer diameter of 35 mm, and Ge (concentration 2
5 wt%) was used and stretched by the method described above. At this time, when the surface temperature in the core tube 4 reached 1600 ° C., stretching of the effective portion of the base material was started. Further, the feeding speed of the chuck 18 is 3 to 4 mm per minute,
The feed rate of the chuck 20 was adjusted to 40 to 60 mm / min. Also, during stretching, the outer diameter of a predetermined portion of the base material ineffective portion on the stretching start end side (lower side) is measured and controlled so that the value becomes 13 mm, and the final target stretched diameter is 11.5 mm. So that Then, when the position of 150 mm in length from the stretching end of the base material effective portion enters the heating region, the heating temperature is gradually lowered, and the position of 100 mm in length from the stretching end end of the base material effective portion Upon entering the heating region, the heating temperature was set to 1550 ° C., and thereafter, this temperature was maintained and the stretching was continued.

As a result of the above stretching, no stretching occurred in the vicinity of the stretching end of the glass base material finally obtained. Moreover, when the outer diameter of the glass base material was measured in the longitudinal direction, it was 11.5 mm ± 1 mm in total length, which was very good.

Example 2 The same glass base material as in Example 1 was used, and stretching was performed while maintaining the surface temperature in the furnace tube 4 at 1600 ° C. The feeding speed of the chucks 18 and 20 at this time is the same as that in the first embodiment,
Also, during stretching, the outer diameter of a predetermined portion of the base material ineffective portion on the stretching start end side (lower side) is measured and controlled so that the value becomes 13 mm, and the final target stretched diameter is 11.5 mm. So that Then, when the position of 20 mm in length from the end of stretching of the base material effective portion enters the heating region, the heating temperature is gradually lowered, and the length 1 from the end of stretching of the base material effective portion 1
When the 0 mm position enters the heating area, the heating temperature is set to 1
The temperature was set to 550 ° C., and this temperature was maintained thereafter to continue the stretching.

As a result of stretching as described above, some stretching occurred in the vicinity of the end of stretching of the glass base material finally obtained. Further, the outer diameter of the glass base material was measured in the longitudinal direction, and it was 12.0 mm ± 1.5 mm in total length.

Comparative Example The same glass preform as in Example 1 was used, and stretching was performed while maintaining the surface temperature in the furnace tube 4 at 1600 ° C. The feeding speed of the chucks 18 and 20 at this time is the same as that in the first embodiment,
Also, during stretching, the outer diameter of a predetermined portion of the base material ineffective portion on the stretching start end side (lower side) is measured and controlled so that the value becomes 13 mm, and the final target stretched diameter is 11.5 mm. So that In addition, the stretching was continued at a temperature of 1600 ° C. throughout the stretching.

As a result, the outer diameter of the glass was increased near the center of the finally obtained glass base material. Further, the outer diameter of the glass base material was measured in the longitudinal direction, and was 13.5 mm ± 3.0 mm in total length.

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the support rods are attached to the dummy rods welded to both ends of the glass base material inserted into the furnace body, but the support rods may be attached to only one of the dummy rods. .

[0032]

According to the present invention, when the glass preform is heated and stretched, the heating temperature of the glass preform is lowered during the stretching of the preform effective part. The diameter can be stably stretched.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a stretching device used in an embodiment of a method for processing a glass base material according to the present invention.

[Explanation of symbols]

1 ... Stretching device, 3 ... Glass base material, 14 ... Base material effective part, 1
8a, 18b ... Base material non-effective portion.

Claims (4)

[Claims] 1. A method of processing a glass base material, comprising heating and stretching a glass base material having a base material effective portion, wherein the heating temperature of the glass base material is lowered during the stretching of the base material effective portion. And the method of processing the glass base material. 2. The method for processing a glass base material according to claim 1, wherein the heating temperature of the glass base material is lower than the initial heating temperature of the effective portion of the base material by at least 20 ° C. 3. The process for lowering the heating temperature of the glass base material by at least 20 ° C. from the initial heating temperature is 2 times the total length of the base material effective portion when the length from the drawing end end of the base material effective portion is 2. The method for processing a glass base material according to claim 2, wherein the processing is started before stretching the portion to be%. 4. The heating temperature of the glass base material is started to be lowered after drawing a portion where the length of the base material effective portion from the drawing end end is 70% of the entire length of the base material effective portion. The method for processing a glass base material according to claim 3, wherein.