JP2003206147A - Method for drawing glass base material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for drawing a glass base material by which the glass base material can be drawn in high yield without wasting an effective part thereof. <P>SOLUTION: The glass base material to both end parts of which dummy rods are joined, is set in a heating furnace by being grasped with an upper chuck and a lower chuck, is melted by heating and then is drawn by loading stress by adjusting downward sending speed VA of the upper chuck and downward sending speed VC of the lower chuck. In this method for drawing the glass base material, drawing is performed by making VA zero just before a joint between the glass base material and the upper dummy rod is heated at softening temperature and thereafter making VA zero or a minus value. <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 drawing 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 heater 7 of the electric furnace (heating furnace) 6 heats and melts the lower end portion of the glass base material 1 and adjusts the downward feeding speed of the upper chuck 4 and the lower chuck 5 to apply a constant pulling force to a desired value. Stretch to have the outer diameter.

In such a drawing process, it is one of the important issues to obtain a drawn base material having a uniform outer diameter, and in general, a taper portion (neck-down portion) formed under the glass base material is generally used. ), The outer diameter is measured at a fixed position, and the feeding or drawing speed of the glass base material (feeding speed of the upper chuck and lower chuck downward) is adjusted based on the result. It is being appreciated. Various methods have been studied as a technique for improving this method. For example, in Japanese Unexamined Patent Publication No. 5-147971, the outer diameter immediately after the start of the taper portion and the outer diameter immediately before the end of the taper portion are measured to measure the taper. The target value of the outer diameter immediately before the end of the taper part is calculated in advance from the measured value of the outer diameter immediately after the start of the part, and the deviation between the target value and the measured value of the outer diameter immediately before the end of the taper part Has been proposed, and a method of controlling the supply and / or take-off speed of the glass base material according to this deviation value has been proposed.
Further, Japanese Patent Laid-Open No. 2001-10839 proposes a glass base material stretching device provided with a measuring means for measuring the outer diameter of the glass base material at a plurality of different positions along the stretching axis of the glass base material. Has been done.

[0005]

Another problem in the above-mentioned drawing process is that the diameter of the drawing base material is increased at the end of the drawing, and the effective part of the glass base material cannot be used efficiently. . That is, as shown in FIG. 4, when the stretching approaches the end, the joint (dummy joint 8) between the upper end of the glass base material 1 and the upper dummy rod 2 is heated. Upper dummy rod 2 and dummy joint 8
Has a diameter smaller than that of the effective portion of the glass base material 1 and is weak in strength, so that when this portion reaches the softening temperature of the glass, stretching occurs, and a large diameter portion 1c is formed on the upper portion of the base material 1b after stretching. Yield is reduced. Therefore, the dummy joint portion 8 is generally shielded from heat, but there is a problem that it is difficult to partially shield the heat and the device becomes complicated.

An object of the present invention is to solve the above problems in the prior art and to provide a glass base material drawing method capable of drawing with a good yield without wasting an effective portion of the glass base material. And

[0007]

The present invention provides the following methods (1) to (4) as means for solving the above problems. (1) The glass base material having dummy rods bonded to the upper and lower ends thereof is placed in a heating furnace with the upper dummy rod held by the upper chuck and the lower dummy rod held by the lower chuck. From the glass base material and the upper dummy rod, in which the glass base material and the upper dummy rod are stretched by applying a tension by adjusting the downward feeding speeds VA and VC of the upper chuck and the lower chuck. The distance between the joint and the upper end of the heater of the heating furnace is within a predetermined range, VA is gradually decreased to 0 before the joint is heated to the softening temperature, and then VA is gradually decreased to the negative side. A method for stretching a glass base material, comprising the steps of: (2) The time when the VA becomes 0 is within a time when the distance between the joint between the glass base material and the upper dummy rod and the upper end of the heater of the heating furnace is in the range of 150 to 30 mm. The glass base material stretching method of (1) above.

(3) The time when the VA is on the negative side is within the time when the distance between the joint between the glass base material and the upper dummy rod and the upper end of the heater of the heating furnace is in the range of 100 to 0 mm. (1) or (2) characterized by
Method for stretching glass base material. (4) The outer diameter D _{1 in the} vicinity of the upper end of the taper portion below the glass base material formed by stretching and the outer diameter D ₂ at a specific position below the middle are monitored, and VC is the outer diameter throughout the stretching period. D ₂ is controlled according to the deviation from the set value, and VA is controlled according to the deviation from the set value of the outer diameter D ₁ during the steady stretching, according to the above (1) to (3). A method for stretching any one glass preform.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The method of the present invention will be described in detail below with reference to the drawings. 1 and 2 are explanatory views for explaining the stretching method of the present invention. FIG. 1 shows a state during steady stretching, and FIG. 2 shows a state at the final stage of stretching. In FIG. 1, the outer diameter D ₁ near the upper end of the taper portion 9 formed on the lower portion of the glass base material 1 during stretching and the outer diameter D ₂ at a specific position below the middle are monitored to feed the lower chuck 5. The speed VC is controlled according to the equation (1) throughout the stretching period, and is controlled according to the deviation (ΔD ₂ ) of the outer diameter D _{2 from} the set value. Also,
The feed speed VA of the upper chuck 4 is calculated by the formula (2) during the steady stretching.
Accordingly, the outer diameter D ₁ is controlled according to the deviation (ΔD ₁ ) from the set value. VC = VC0 + bΔD ₂ (1) (In the formula, VC0 is the initial value of VC, b is the coefficient determined by the experiment) VA = VA0-aΔD ₁ (2) (In the formula, VA0 is the initial value of VQ, a is the experimental value) The determined coefficient) Note that the stretching speed control method at the time of steady stretching described here is only an example, and as described in the above-mentioned prior art, the outer diameter of the taper portion at a plurality of positions is monitored to feed the upper and lower chucks. It is also possible to control each of the above based on the deviation between the outer diameter and the outer diameter set value at a plurality of locations.

A drawing before reaching the softening temperature (the temperature at which the glass viscosity is sufficiently large and the glass can be stretched by the tension due to the difference between VA and VC) as the stretching progresses and the dummy joint portion 8 is heated near the heater 7. In the state of 2 (a), the descending speed of the upper chuck 4 is gradually reduced and stopped (VA
= 0). At this time, if VA is rapidly set to 0, the load on the grip is too great, so 0.1 to 0.5 m per minute
The distance between the dummy joint portion 8 and the upper end of the heater 7 (s _{1 in} FIG. 2) is 150 to 30 while gradually decreasing at a speed of about m / min.
It is desirable that it becomes 0 within a time in the range of mm.

After that, if necessary, the state of VA = 0 is maintained for a predetermined time, and then VA is gradually increased to the minus side as shown in FIG. 2B (that is, the upper chuck 4 is gradually moved upward while gradually increasing its speed). Move to). The change in speed at this time is preferably about 0.1 to 1.0 mm / minute per minute. In addition, VA is set to the minus side because the distance between the dummy joint portion 8 and the upper end of the heater 7 (s _{2 in} FIG. ₂ )
Is preferably within a time in the range of 100 to 0 mm.

In the case of ordinary stretching, the stretching temperature T ₀ for stretching the stationary portion is in the range of 1800 to 1900 ° C.
In the present invention, VA is reduced from the speed at which the steady portion is stretched to 0, and the stretching temperature T _{1 at} the negative side is in the range of 1750 to 1900 ° C., which is ₀ to 50 ° C. lower than T _0. can do.

As the heater of the heating furnace, the length of the heater (length in the axial direction of the glass base material) is L, the inner diameter of the heater is R,
When the outer diameter of the glass base material is r, L / r is 0.5 to
It is preferable that the heater has a structure in which the ratio of 1.2 and R / r is in the range of 1.3 to 1.6. If L / r is less than 0.5, 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. Becomes 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. When the outer diameter r of the glass base material is 100 mm, these ranges are L
Means that the range of 50 to 120 mm and R of 130 to 160 mm is preferable.

By doing so, the dummy connecting portion 8 is formed.
Is not heated to the softening temperature, the upper dummy rod 2 and the dummy connecting portion 8 can be stretched to the end without stretching, and the yield in the stretching step is improved.

[0015]

EXAMPLE A glass base material was drawn by the method shown in FIG. Length 100mm, inner diameter 160mm as heater
The outer diameter of the stationary part is 100 mm and the length is 400
mm, length of unsteady part (tapered part) at both ends is 100 m
The glass base material 1 having a diameter of m was drawn to produce a drawn base material having an outer diameter of 40 mm. Stretching speed is VA0 = 5mm / min, VC0 = 20m
The outer diameter D _{1 in the} vicinity of the upper end of the lower taper portion of the glass base material 1 and the outer diameter D ₂ in the middle of the lower end of the glass base material 1 to the lower end thereof are monitored, and VA and VC are calculated based on these bodies. It was controlled according to the equations (1) and (2). Formula obtained experimentally
The values of the coefficients in (1) and (2) are b = 200 and a = 15.
Met.

VA is set to 1 when the distance between the dummy joint portion 8 and the upper end of the heater 7 reaches 100 mm as the stretching proceeds.
It will be reduced at a rate of 0.25 mm / min per minute,
When VA = 0, it was held for 5 minutes. Up to this point, VC was controlled according to the above equation (1). After that, VA was continued to the minus side (upward) while increasing the speed by 0.33 mm / min, and finally 5 mm in the opposite direction.
/ Min. As a result, a stretched base material having a length of 1900 mm could be obtained without causing the dummy joint portion 8 to stretch. On the other hand, when the stretching is carried out under the condition of the steady state until the end, the dummy joint portion 8 is formed at the final stage of the stretching.
Was stretched and became unstretchable, and the length of the uniform portion of the obtained stretch base material was 1300 mm.

FIG. 5 shows changes in the upper chuck speed (VA) and the lower chuck speed (VC) at the end of the stretching. In FIG. 5, the time 0 on the horizontal axis indicates the dummy joint portion 8
This is the time when the distance between the heater and the upper end of the heater 7 becomes 100 mm.

[0018]

According to the method of the present invention, the extension of the connecting portion of the upper end of the glass base material with the dummy rod is prevented, and the effective portion of the glass base material is not wasted, and the glass base material is stretched with a high yield. You can

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing a steady state of stretching by the method of the present invention.

FIG. 2 is an explanatory view schematically showing the final state of stretching by the method of the present invention.

FIG. 3 is an explanatory view showing a general process of stretching a glass base material.

FIG. 4 is an explanatory view showing a state of a large diameter portion that occurs at the final stage of stretching the glass base material.

FIG. 5 is a diagram showing changes in the upper chuck speed (VA) and the lower chuck speed (VC) at the final stage of stretching in the example.

[Explanation of symbols]

1 Glass Base Material 1a Base Material Before Stretching 1b Base Material After Stretching 1c Large Diameter Part of Stretching Base Material 2 Upper Dummy Rod 3 Lower Dummy Rod 4 Upper Chuck 5 Lower Chuck 6 Electric Furnace 7 Heater 8 Dummy Joint 9
Tapered part

   ─────────────────────────────────────────────────── ─── 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 (4)

[Claims] 1. A glass preform having dummy rods bonded to the upper and lower ends thereof, the upper dummy rod being held by an upper chuck, the lower dummy rod being held by a lower chuck, and placed in a heating furnace. In the method, in which the glass base material and the upper dummy are drawn by passing through a heating zone from the lower end side to heat and melt, and by applying a tension by adjusting the downward feeding speeds VA and VC of the upper chuck and the lower chuck. The distance between the joint with the rod and the upper end of the heater of the heating furnace is within a predetermined range, VA is gradually reduced to 0 before the joint is heated to the softening temperature, and then VA is reduced to the negative side. A method for stretching a glass base material, comprising the steps of gradually increasing and stretching. 2. The time when the VA becomes 0 is within the time when the distance between the joint between the glass base material and the upper dummy rod and the upper end of the heater of the heating furnace is in the range of 150 to 30 mm. The method for drawing a glass base material according to claim 1. 3. The time when the VA is on the negative side is within the time when the distance between the joint between the glass base material and the upper dummy rod and the upper end of the heater of the heating furnace is in the range of 100 to 0 mm. The method for drawing a glass preform according to claim 1 or 2, which is characterized. 4. The outer diameter D _{1 in the} vicinity of the upper end of the taper portion at the lower portion of the glass base material formed by stretching and the outer diameter D ₂ at a specific position below the middle are monitored, and the VC is throughout the stretching period. controlled according to the deviation from the set value of the outer diameter D _2, any of claims 1 to 3 wherein the VA is in the constant stretching and controlling in response to the deviation from the set value of the outer diameter D ₁ The method for drawing a glass preform according to item 1.