JP2003212576A - Method for elongating glass preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for elongating glass preform which elongates the effective part of a glass preform at a high yield without wasting the part. <P>SOLUTION: In this method, the glass preform is placed in a heating furnace and is elongated while heated and fused from the top end side. Further, the method for elongating the glass preform features that a heating zone is vertically divided into a plurality of temperature zones and each temperature of the zones are independently controlled. <P>COPYRIGHT: (C)2003,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 drawing method for heating and melting a glass base material such as an optical fiber base material to draw it.

[0002]

2. Description of the Related Art A glass base material such as an optical fiber base material is produced by heating a porous glass base material manufactured by an external attachment method (OVD method) or a vapor phase attachment method (VAD) method in a heating furnace. It is manufactured by dehydration and transparent vitrification. The transparent vitrified base material is subjected to surface polishing and core / cladding ratio adjustment by flame polishing, etching, etc., if necessary, and then stretched to the desired outer diameter for the next step, for example, the optical fiber drawing step. Be served.

A general process for stretching a transparent vitrified base material will be described with reference to FIG. Dummy gripping rods (upper dummy rod 2 and lower dummy rod 3) are welded to the upper and lower ends of the glass base material 1 (indicated by the base material 1a before stretching and the base material 1b after stretching) and the upper chuck 4 and It is grasped by the lower chuck 5 and placed in the electric furnace 6. The lower end of the glass base material 1 is heated and melted by the heater 7 of the electric furnace 6, and the downward feeding speed of the upper chuck 4 and the lower chuck 5 is adjusted to apply a constant tensile force to obtain a desired outer diameter. To stretch.

One of the problems in such a drawing step is to obtain a drawn base material having a uniform outer diameter. Generally, the outer diameter is measured at a fixed position of the neck-down portion, and based on the result. A method of adjusting the supply or take-up speed of the glass rod (glass base material) so that the target outer diameter is obtained is performed. However, with the method of monitoring the outer diameter only at a certain position of the neck-down part, it is difficult to absorb the outer diameter fluctuation of the glass base material before stretching, and it is difficult to obtain a stretched base material with a uniform outer diameter. Various methods have been studied as technologies.

For example, in Japanese Patent Laid-Open No. 5-147971, the outer diameter immediately after the start of the neck down portion and the outer diameter immediately before the end of the neck down portion are measured, and the outer diameter immediately after the start of the neck down portion is measured. The target value of the outer diameter immediately before the end of the neck down portion is calculated from the value in advance, and the deviation between the target value and the measured value of the outer diameter immediately before the end of the neck down portion is calculated. A method of controlling the supply and / or the take-up speed of the glass rod according to the above has been proposed. Further, Japanese Patent Laid-Open No. 2001-10839 discloses that
There has been proposed a glass base material stretching apparatus equipped with a measuring means for measuring the outer diameter of the glass base material at a plurality of different positions along the glass base material stretching axis.

[0006]

Another problem in the above-mentioned drawing step is that the portions near the upper and lower ends of the glass base material cannot be uniformly drawn, and the effective portion of the glass base material cannot be used efficiently. There is. That is, as shown in FIG. 3, both end portions of the glass base material 1 are tapered portions 8a, 8
b, the upper dummy rod 2 and the lower dummy rod 3 are welded to the tip thereof. In the vicinity of the end on the effective portion 9 side of the lower taper portion 8b on the lower side, a hard portion 10 that becomes a portion that supports its own weight during the production of the unsintered porous glass preform.
Exists. Since the hard portion 10 is harder than the steady portion 11 of the glass base material 1 and has a high viscosity when melted, it is difficult to stretch when the heating temperature is the same. Therefore, when heated at the same temperature, at the beginning of the stretching, as shown in FIG.
2 occurs, the entire effective portion 9 of the glass preform 1 before stretching cannot be used, and a part thereof is wasted.

Further, the upper taper portion 8a is soft, and when the upper end of the pre-stretched glass base material 1a enters the heating region at the stage before the end of the stretching, the upper taper portion 8a becomes thin and the upper dummy rod 2 Since the joint portion of No. 1 stretches first, the end portion of the effective portion 9 cannot be stretched to the end, and here again, a part of the glass preform 1a before stretching cannot be used.

The present invention solves the above problems in the prior art, in particular, the problem that the portions near the upper and lower ends of the glass base material cannot be uniformly drawn and the effective portion of the glass base material cannot be used efficiently. An object of the present invention is to provide a method for drawing a glass base material, which can be drawn with a good yield without wasting an effective portion of the glass base material.

[0009]

The present invention proposes the following configurations (1) to (5) as means for solving the above problems. (1) In a method in which a glass base material is installed in a heating furnace, heated and melted from the tip side and stretched, the heating zone is divided into a plurality of temperature zones in the axial direction of the glass base material, and the temperature of each temperature zone is divided. A method for stretching a glass base material, characterized in that the stretching is controlled independently. (2) The temperature of the heating zone is controlled by providing a plurality of heaters capable of controlling the temperature independently and controlling the temperature of each heater independently. Stretching method. (3) At the start of stretching, the temperature of the heating zone on the base material take-up side is set to T ₂ which is higher than the temperature T ₁ at the time of steady stretching, and at the time of steady stretching, the temperature of the entire heating zone is maintained at about T ₁ .
At the end of the drawing, the temperature of the heating zone on the feed side of the base material is set to T ₃ which is lower than T _1, and the glass base material drawing method according to (1) or (2) above.

(4) The temperature difference between T ₂ and T ₁ is ΔT
₂ (ΔT ₂ = T ₂ −T ₁ ), the temperature difference between T ₁ and T ₃ is ΔT
₃ (ΔT ₃ = T ₁ −T ₃ ), ΔT ₂ and ΔT
_The method for stretching a glass preform according to the above (3), wherein all ₃ are controlled to be in the range of 50 to 100 ° C. (5) When the temperature of the heating zone on the base material take-up side at the start of stretching is T ₂ , the base material feed length is 10 from the start of stretching.
And until 0 mm, the time for the temperature of the heating zone of the base material feed side during stretching and end T ₃ is 50 the distance between the tapered top end of the top and base metal upper heating zone of the base material feeding side 1
The method for stretching a glass preform according to the above (3) or (4), characterized in that it is in the range of 00 mm.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The method of the present invention will be described in detail below with reference to the drawings. In the case of the conventional method, the heating zone 13 is formed by the heater 7 formed as one body as shown in FIG. Therefore, the temperature T of the heating zone 13 is as shown on the right side of the figure, and once the capacity of the heater 7 is determined, only the temperature can be controlled, and the temperature T required for stretching can be controlled.
After setting to ₁ , partial temperature adjustment is not possible. In the method of the present invention, the heating zone is divided into a plurality of temperature zones in the vertical direction by means of dividing the heater into a plurality of portions, and the temperature of each temperature zone is independently controlled. The present invention solves the problems of the generation of a large diameter portion and the elongation at the end of a simple glass base material.

[0012]

EXAMPLE FIG. 1 schematically shows an example of the temperature control state in the stretching step according to the method of the present invention. In the example of FIG. 1, the heater 7 is divided into two heaters, an upper heater 7a and a lower heater 7b (the entire length of the heating zone is the same as that of the conventional method), whereby the heating zone 13 is divided into the upper zone 13a.
It is divided into a (heating zone on the base material feeding side) and a lower zone 13b (heating zone on the base material receiving side) so that the respective temperatures can be controlled separately.

FIG. 1 (a) is a glass base material 1 at the beginning of drawing.
It shows the state of the time when the hard part 10 under the
At this time, the temperatures of the heater 7a and the heater 7b are different.
Control the temperature of the heating zone as shown on the right side of the figure.
T is the temperature T of the lower zone 13b₂Is the upper zone 13a
Temperature (temperature for heating the steady part 11 of the glass base material 1)
T ₁) Is higher than Like this
Therefore, the hard portion 1 having a higher viscosity when melted than the stationary portion 11
It was shown in Figure 4 by heating 0 at a higher temperature.
It is possible to prevent the large diameter portion 12 from being generated, and
The end of the material 1 can be effectively used.

FIG. 1 (b) shows the state at the time when the stationary part 11 of the glass base material 1 is stretched. At this time, as shown on the right side of the figure, the temperature T of the heating zone is equal to that of the upper zone 13a. T and the temperature of the lower zone 13b are almost constant
Control to be ₁ .

Next, when the stretching is approaching the end, the output of the upper heater 7a is lowered or the heating is stopped before and after the upper taper portion 8a enters the heating zone, and as shown in FIG. the temperature T, is controlled so that the temperature remains upper zone 13a to hold the temperature of the lower zone 13b to stretchable temperatures T ₁ becomes lower T ₃ than T _1. As a result, it is possible to prevent the extension of the upper taper portion 8a of the glass base material 1 in the small diameter portion and the extension of the dummy rod in the vicinity of the connecting portion between the glass base material 1 and the upper dummy rod 2.
It is possible to effectively use the vicinity of the end of the glass base material 1.

In the case of ordinary stretching, the temperature T ₁ of the heating zone during the stretching of the stationary portion is in the range of 1850 to 1950 ° C. In the present invention, the temperature of the heating zone of the base material take-up side at the start stretching, the high T ₂ than the temperature T ₁ of the steady state stretching during stretching ends than T ₁ the temperature of the heating zone of the base material feeding side and lower T ₃ but, from 1,950 to 2,050 ° C. as the T _2, as T ₃ is from 1750 to 185
A range of 0 ° C is suitable.

The temperature difference between T ₂ and T ₁ is ΔT
₂ (ΔT ₂ = T ₂ −T ₁ ), the temperature difference between T ₁ and T ₃ is ΔT
₃ (ΔT ₃ = T ₁ −T ₃ ), ΔT ₂ and ΔT
_By controlling all ₃ to be in the range of 50 to 100 ° C., the viscosity at the terminal end of the base material can be made substantially the same as the viscosity at the time of stretching in the steady part at the beginning and near the end of stretching. Have confirmed.

Usually, the size of the base material is
The length is 450 to 500 mm, and the length of the taper part at both ends is the same.
80 to 200 mm and outer diameter of 80 to 100 mm, respectively
However, the heating zone on the base material take-up side at the start of stretching
The temperature of (lower zone 13b in FIG. 1) is set to T₂Time to
Between the start of stretching and the feed length of the base material up to 100 mm
Then, at the end of the stretching, the heating zone on the feed side of the base material (upper part of Fig. 1
The temperature of zone 13a) is T ₃The time to
Distance between the upper end of the heating zone and the upper end of the taper part above the base metal
Is preferably in the range of 50 to 100 mm.
Yes.

The heater for forming the heating zone is of a type in which the temperature can be controlled by dividing the heating zone into a plurality of heating zones in the axial direction of the glass base material, and a structure in which a plurality of heaters are combined, or A type in which the temperature can be controlled by dividing into a plurality of heating zones with one heater can be used. Although FIG. 1 shows an example of a heater having two heating zones, it goes without saying that the number of heating zones may be three or more.

When the length of the heater (the length of the entire heating zone) is L, the inner diameter of the heater is R, and the outer diameter of the glass base material is r, L / r is 0.5 to 1.2, R / R is 1.3-1.
The range of 6 is preferable. L / r is 0.
If it is less than 5, it will be difficult to melt the glass during stretching, and a large load will be applied to the glass gripping portion. If it exceeds 1.2, the melting range will be too wide and control will be difficult. Further, when R / r exceeds 1.6, the temperature distribution spreads and the melting range becomes too wide, which makes control difficult, and when R / r is less than 1.3, the base material may come into contact with the core tube when the base material is mounted. There is not preferable. These ranges mean that, for example, when the outer diameter r of the glass base material is 100 mm, L is preferably 50 to 120 mm and R is preferably 130 to 160 mm.

In the method of the present invention, at the end of the drawing, the temperature of the heating zone on the feed side of the base material is set to T ₃ which is lower than T ₁ which is the temperature at the time of steady drawing. Before the temperature reaches the end of the glass base material, an inert gas such as N ₂ gas is blown near the end of the glass base material and the temperature is further increased to 20 to 5
It is effective to lower it by 0 ° C.

As a method of suppressing the outer diameter variation when the steady portion is stretched, the outer diameter is measured at a fixed position or a plurality of positions of the neck down portion as described above, and the target outer diameter is obtained based on the result. As described above, a method of adjusting the supply or take-up speed of the glass rod (glass base material) can be adopted. Although the present invention has been described above based on the form of FIG. 1, the present invention is not limited to this form.

[0023]

According to the method of the present invention, the problems that the portions near the upper and lower ends of the glass base material cannot be uniformly drawn and the effective portion of the glass base material cannot be used efficiently, Stretching can be performed with high yield without wasting the effective portion of the base material.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing an example of a temperature control state in a stretching step according to the method of the present invention.

FIG. 2 is an explanatory view showing a general process of stretching a glass base material.

FIG. 3 is an explanatory view showing a state of a glass base material in which dummy rods are connected to upper and lower ends.

FIG. 4 is an explanatory view showing a state of a large diameter portion generated at the start of stretching due to the influence of the hard portion of the glass base material.

FIG. 5 is an explanatory view schematically showing an example of a state of temperature control in a stretching step by a conventional method.

[Explanation of symbols]

1 Glass Base Material 1a Base Material Before Stretching 1b Base Material After Stretching 2 Upper Dummy Rod 3 Lower Dummy Rod 4
Upper chuck 5 Lower chuck 6 Electric furnace 7 Heater 7
a Upper heater 7b Lower heater 8a Upper tapered portion 8b Lower tapered portion 9 Effective portion 10 Hard portion 11 Steady portion 12
Large-diameter portion 13 Heating zone 13a Upper zone 13b Lower zone

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Motonobu Nakamura             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works (72) Inventor Toshihiro Oishi             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works F-term (reference) 4G015 BA02 BB05                 4G021 BA00

Claims (5)

[Claims] 1. A method of placing a glass base material in a heating furnace, heating and melting the glass base material from the tip side and stretching the glass base material, the heating zone is divided into a plurality of temperature zones in the axial direction of the glass base material, and each temperature zone is divided. A method for stretching a glass preform, wherein the temperature of the glass is controlled independently. 2. The control of the temperature of the heating zone is performed by providing a plurality of heaters capable of controlling temperature independently and controlling the temperature of each heater independently. Method for stretching glass base material. 3. The temperature of the heating zone on the base material take-up side at the start of stretching is set to T ₂ which is higher than the temperature T ₁ at the time of steady stretching, and the temperature of the entire heating zone is maintained at about T ₁ at the time of steady stretching to perform stretching. at the end, characterized in that the temperature of the heating zone of the base material feed side and lower T ₃ than T ₁ claim 1
Or the glass base material stretching method described in 2 above. 4. The temperature difference between T ₂ and T ₁ is ΔT ₂ (ΔT
₂ = T ₂ −T ₁ ) and the temperature difference between T ₁ and T ₃ is ΔT ₃ (ΔT
_The method for stretching a glass preform according to claim 3, wherein ΔT ₂ and ΔT ₃ are both controlled to be in the range of 50 to 100 ° C. when ₃ = T ₁ −T ₃ ). 5. The temperature of the heating zone on the base material take-up side at the start of stretching is T ₂ from the start of stretching to the base material feeding length of 100 mm, and the temperature at the base material feeding side at the end of stretching is The time when the temperature of the heating zone is T ₃ is set such that the distance between the upper end of the heating zone on the base material feeding side and the upper end of the taper portion above the base material is in the range of 50 to 100 mm. The method for stretching a glass base material according to 3 or 4.