JP2013035742A - Apparatus and method for drawing optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and method for drawing an optical fiber, which maintains the pressure in a furnace tube at a predetermined or higher value to the drawing velocity of an optical fiber to thereby suppress the involvement of outside air.SOLUTION: A shutter tube section 19 is installed under a fiber lead-out port. If the outer diameter of a glass fiber 12 is taken as 2r; the inner diameter of the shutter tube 19, as 2r; the drawing velocity of the glass fiber 12, as V; and the flow volume of an inert gas flowing down a furnace tube 13, as Q, expression [1] is satisfied. It is preferable that the inner diameter of the shutter tube is 5 mm to 15 mm, and the length thereof is ≥30 mm and ≤500 mm.

Description

  The present invention relates to an optical fiber drawing apparatus and a drawing method for drawing an optical fiber by heating and melting a glass base material for an optical fiber.

  An optical fiber is manufactured by heating and melting an optical fiber glass base material (hereinafter referred to as a glass base material) using a dedicated drawing furnace, drawing the glass fiber, and applying a protective coating to the outer surface thereof. When drawing a glass fiber, heat-resistant carbon is used for a furnace core tube into which a glass base material is inserted. This carbon is oxidized and consumed in a high-temperature oxygen-containing atmosphere. In order to prevent this, a rare gas such as argon gas or helium gas or nitrogen gas (hereinafter referred to as an inert gas) is sent into the furnace core tube.

  Most of the inert gas sent into the core tube flows downward from the top of the core tube, and is discharged to the outside through the fiber outlet along with the glass fiber drawn from the lower end of the glass base material. In this case, if the fiber outlet is wide open, outside air easily enters the core tube, leading to deterioration of carbon parts such as the core tube. Although it is necessary to flow a lot of inert gas to suppress the intrusion of outside air into the furnace core tube, the inert gas used in the drawing furnace affects the manufacturing cost, so it is desired to suppress the use of it as much as possible. Has been.

  For this reason, for example, in Patent Document 1, a shutter is provided at the fiber outlet, and until the glass fiber in a softened state drawn from the lower end of the glass base material comes out of the drawing furnace. In order to obtain a cured state by lowering the temperature to some extent, it is disclosed that a cylindrical partition wall (also called a lower chimney) is provided at the lower end of the core tube, and a shutter is provided at the lower end of the partition wall.

In Patent Document 2, the shape of the core tube is reduced in a taper shape so as to follow the softened shape (neck down shape) of the lower end of the glass base material, and the inert gas at the lower end portion of the glass base material is reduced. It is disclosed that the flow is stabilized and fluctuations in the outer diameter of the glass fiber are suppressed, and that a thinner cap is provided at the fiber outlet of the tapered extension tube (also referred to as a lower chimney).
Patent Document 3 discloses that a tubular nozzle having a small diameter and a length of 10 times or more the diameter is provided as a shutter for the fiber outlet.

Japanese Patent No. 2778783 JP-A-8-91862 Japanese Patent Laid-Open No. 2-92938

  As a method for suppressing the use of an inert gas used in a drawing furnace, it is effective to narrow the fiber outlet and suppress the outflow of gas as shown in Patent Documents 1 to 3 above. If the outlet is narrowed, the drawn glass fiber may come into contact and break. Further, when the production speed of the optical fiber is increased, outside air may be involved depending on conditions such as the internal pressure of the outlet of the optical fiber and the linear speed of the optical fiber.

  In Patent Documents 2 and 3, it is proposed to provide a thin tube at the outlet of the optical fiber, but the relationship between the drawing speed of the optical fiber and the amount of gas released to the outside is clear. In addition, there is a possibility that outside air may be caught in the fiber outlet portion of the tube.

  The present invention has been made in view of the above-described situation, and the drawing of an optical fiber that suppresses the entrainment of outside air by maintaining the pressure in the core tube at a positive pressure equal to or higher than a predetermined value with respect to the drawing speed of the optical fiber. An object is to provide an apparatus and a drawing method.

を満足することを特徴とする。
なお、シャッター管部の内径が５ｍｍ〜１５ｍｍであり、シャッター管部の長さは、３０ｍｍ以上５００ｍｍ以下とするのが好ましい。 An optical fiber drawing apparatus and a drawing method according to the present invention include a furnace core tube into which a glass preform for an optical fiber is inserted, and a furnace housing that houses a heater that heats the furnace core tube from the outside. An optical fiber drawing apparatus and drawing method for flowing a gas from the upper side to the lower side, leading out the glass fiber drawn from the fiber outlet at the bottom of the core tube, and discharging the inert gas to the outside. is there.
Then, a shutter tube portion is provided below the fiber outlet, the outer diameter of the glass fiber is 2r ₁ , the inner diameter of the shutter tube is 2r ₂ , the drawing speed of the glass fiber is V ₁ , and the non-flowing gas flows below the core tube. When the active gas flow rate is Q,

It is characterized by satisfying.
The inner diameter of the shutter tube portion is 5 mm to 15 mm, and the length of the shutter tube portion is preferably 30 mm or more and 500 mm or less.

  According to the present invention, even when the drawing speed of the optical fiber is high, an optical fiber can be manufactured while maintaining the pressure in the furnace core tube at a positive pressure equal to or higher than a predetermined value and suppressing entrainment of outside air. .

It is a figure explaining an example of an embodiment of an optical fiber drawing furnace used by the present invention. It is a figure explaining the other example of embodiment of FIG. It is a figure for demonstrating the gas flow rate and pressure loss in a shutter pipe | tube. It is a figure which shows the relationship between the internal diameter of a shutter pipe | tube with respect to every gas flow rate, and a pressure loss gradient. It is a figure which shows the relationship between the gas flow rate and pressure loss by every length of a shutter pipe | tube. It is a figure which shows the relationship between the gas flow rate by the inside diameter of a shutter pipe | tube, and a pressure loss gradient.

  An outline of the optical fiber drawing apparatus of the present invention will be described with reference to FIGS. In the figure, 10 is an optical fiber drawing furnace, 11 is an optical fiber glass base material (glass base material), 11a is a lower end portion of the glass base material, 12 is a glass fiber, 13 is a furnace core tube, 14 is a furnace housing, 15 is a heater, 16 is a heat insulating material, 17 is an extension tube (lower chimney), 18 is a core tube receiving member, 19 and 20 are shutter tubes, 20a is a large diameter portion, 20b is a tapered portion, and 20c is a small diameter portion. .

  As shown in FIG. 1, the drawing of the optical fiber is performed such that the lower part of the glass base material 11 supported by suspension is heated, and the glass fiber 12 is melted and drooped from the melted lower end part 11a to have a predetermined outer diameter. It is done by drawing a line. For this purpose, the optical fiber drawing furnace 10 is provided with a heater 15 so as to surround a furnace core tube 13 into which the glass base material 11 is inserted and supplied, and a heat insulating material is provided so that the heat of the heater 15 is not dissipated to the outside. 16, and the entire outside thereof is surrounded by a furnace casing 14.

  The glass base material 11 is suspended and supported by a base material suspension mechanism (not shown), and is sequentially controlled to move downward as the optical fiber is drawn. The furnace casing 14 is made of a metal having excellent corrosion resistance such as stainless steel, and a cylindrical furnace core tube 13 made of high-purity carbon is arranged at the center. In order to prevent oxidation and deterioration of the core tube 13, a rare gas such as nitrogen, argon, helium, or nitrogen gas is introduced into the core tube 13. The inert gas or the like passes through the gap between the glass base material and the core tube 13, and most of the inert gas is discharged to the outside through the extension tube 17 from below the core tube 13.

  Similarly, an inert gas such as nitrogen, argon, or helium is poured into the furnace casing 14 in order to prevent oxidation and deterioration of the carbon heater 15 and the heat insulating material 16. The gas that flows into the furnace casing 14 is controlled separately from the gas that flows into the furnace core tube 13, but the same gas is usually used. An extension pipe (also called a lower chimney) 17 is connected to the lower end of the furnace core tube 13 below the furnace casing 14.

  The extension tube 17 has a function of reducing the outer diameter fluctuation by cooling and hardening to some extent while simultaneously relaxing the rapid cooling of the heated and softened glass fiber 12. The extension pipe 17 is formed so as to be separable from the core tube 13 in terms of maintenance and the like, and is detachably attached to the lower wall 14a of the furnace casing 14 so as to communicate with the core tube 13. A joint portion between the core tube 13 and the extension tube 17 is supported by being placed on the lower wall 14a of the furnace casing 14 via a core tube receiving member 18 made of a heat-resistant electrical insulating material such as quartz. 13 and the furnace casing 14 are electrically insulated so as not to cause a large short-circuit accident. However, the core tube receiving member 18 is not limited to quartz but may be made of carbon or the core tube 13 and the extension tube 17 may be directly joined without using the core tube receiving member 18.

  The present invention is characterized in that instead of providing a plate-like shutter member at the lower end of the extension pipe 17, a shutter pipe 19 which is a pipe having a shape as shown in FIG. 1 is used. The shutter tube 19 can be formed of, for example, a metal having excellent corrosion resistance. The shutter tube 19 is a tube having an inner diameter of 5 mm to 15 mm and a uniform diameter as described later, and is formed with a length (Ls) of 30 mm or more. The extension tube 17 may be provided with a tapered portion so as to communicate smoothly with the inner diameter of the shutter tube 19, but may have a shape without the tapered portion.

FIG. 2 is a diagram showing another embodiment, which is different from the embodiment of FIG. 1 in that the shutter tube has a tapered portion.
In addition, the core tube 13 of FIG. 1, FIG. 2 stabilizes the flow of the inert gas which flows downward by providing the reduced diameter part 13a so that the shape of the lower end part 11a of the glass base material 11 may be followed. In addition to this, the heating efficiency by the heater 15 can be increased. That is, by reducing the diameter of the core tube below the lower end portion 11a of the glass base material 11, heat radiated downward can be cut off to save energy.

Moreover, the flow of an inert gas can be stabilized by making the diameter-reduced tube part 13b below the diameter-reduced part 13a thinner than the diameter of the upper part of the core tube 13. And when connecting the extension pipe 17 to the lower end of the reduced diameter pipe portion 13b as in the example of FIG. 1, the inner diameter of the extension pipe 17 may be different from the inner diameter of the reduced diameter pipe portion 13b. The inner diameter is preferably the same.
A shutter tube is provided at the lower end of the reduced diameter tube portion 13b or the lower end of the extension tube 17 as in the case of FIG. 1, but the shutter tube 20 has a tapered portion.

The shutter tube 20 having the tapered portion is divided into, for example, three a, b, and c portions of a large-diameter portion 20a, a tapered portion 20b, and a small-diameter portion 20c, and the lengths of the respective portions are the total length (Ls) of the shutter tube. 1/3 of each. The inner diameter or the like of the shutter tube, as will be described later, 'below 15mm and small-diameter portion 20c (inner diameter 2r ₂ large diameter portion 20a (inner diameter 2r _2)' a ') not less than 5 mm, a length (Ls) is 30mm It is formed as described above. In addition, if the large diameter side is 15 mm or less and the small diameter side is in the range of 5 mm or more, the large diameter portion 20a and the small diameter portion 20c having a uniform diameter may be omitted. Moreover, the length of the taper part 20b may be shorter than 1/3 of the entire length, and the taper angle θ is greater than 0 ° (in the case of a straight pipe) and less than 90 °, depending on the length of the taper part 20b. be able to. Note that when the taper angle is 90 ° or more, the gas flow becomes unstable.

  In FIGS. 1 and 2, the shutter tubes 19 and 20 have been described as being connected via the extension tube 17, but are configured to be directly connected to the lower end of the core tube 13 without using the extension tube 17. Also good. In addition, the shutter tubes 19 and 20 may be formed integrally with the extension tube 17, or may have a shape in which a thick plate is hollowed out in addition to the tube shape.

FIG. 3 is a schematic diagram for analyzing the flow of the inert gas or the like in the shutter tubes 19 and 20 described above. In the figure, it is assumed that the glass fiber 12 has a fiber diameter of 2r ₁ and travels in the Z direction at a travel speed (linear speed) V ₁ . It is assumed that the shutter tubes 19 and 20 have an inner diameter of 2r ₂ and an inert gas having a flow rate Q and a viscosity coefficient μ flows from the upper side to the lower side in the tube.

Assuming that the Hagen-Poiseuille flow is generated by the movement of the optical fiber in the shutter tube, the following theoretical formula can be used. In the formula, P is pressure, _VZ is speed in the Z direction, and r is radial distance.

が得られる。 Here, when the fluid velocity of the surface of the optical fiber having the radius r ₁ is V ₁ and the fluid velocity of the inner surface of the shutter tube having the radius r ₂ is zero,

Is obtained.

が得られる。 If the total flow rate in the shutter tube is Q (m ³ / s),

Is obtained.

となり、圧力損失（圧損）の評価式を得ることができる。 Substituting the above A and B into this and summing up with dP / dz,

Thus, an evaluation formula for pressure loss (pressure loss) can be obtained.

が得られる。この式により、圧力勾配（ｄＰ／ｄｚ）が、ゼロとなる点（クロスポイント）を求めることができる。 From the pressure loss evaluation formula above,

Is obtained. From this equation, a point (cross point) where the pressure gradient (dP / dz) becomes zero can be obtained.

This cross point depends on only the linear velocity V ₁ of the optical fiber and the inner diameter r _{2 of the} shutter tube, regardless of the type of gas, and the horizontal axis represents the gas flow rate and the vertical axis represents the pressure loss as shown in FIG. In the graph shown for each length of the different shutter tube, it is indicated by an intersection point K that intersects at one point regardless of the tube length. The gas flow rate at the cross point K is the minimum gas flow rate necessary to prevent outside air from entering the shutter tube. That is, by setting the gas flow rate to be equal to or higher than the Q value at the cross point K, it is possible to prevent outside air from entering the shutter tube.

On the other hand, if the gas flow rate Q is constant, increases the pressure loss by reducing the internal diameter 2r ₂ of the shutter tube, it is possible to secure a predetermined positive pressure. FIG. 4 is a graph when the horizontal axis is the shutter tube inner diameter (mm), the vertical axis is the pressure loss gradient (Pa / m), and the gas flow rates in the tube are 10, 20, and 30 (L / min), respectively. As described above, the smaller the gas flow rate, the more advantageous in terms of cost, and the gas flow rate is desirably 30 L / min or less. 4A is an example in which the inner diameter of the shutter tube is calculated to be 30 mm or less, and FIG. 4B is an enlarged view of a region P in FIG.

  From this figure, it was found that an effective pressure loss gradient cannot be obtained unless the inner diameter of the shutter tube is 15 mm or less. The positive pressure in the shutter tube is preferably at least 5 Pa or more with respect to the atmospheric pressure, and the inner diameter of the shutter tube is preferably 15 mm or less from the viewpoint of securing this positive pressure. However, the smaller the inner diameter of the shutter tube, the larger the pressure loss gradient can be obtained. However, if the inner diameter of the shutter tube is too small, there is a risk of contact with the optical fiber, and the minimum inner diameter of the shutter tube is preferably 5 mm or more empirically.

In FIG. 5, the horizontal axis represents the gas flow rate (L / min), the vertical axis represents the pressure loss (Pa), the inner diameter of the shutter tube is 10 mm, and the length (Ls) is 0, 30, 50, 100, 200, respectively. It is a graph when it is set to 500 (mm).
From this figure, it can be seen that if the inner diameter of the shutter tube is constant and the length is constant, the pressure loss can be increased by increasing the gas flow rate. On the other hand, if the inner diameter of the shutter tube is constant and the gas flow rate is constant, the pressure loss can be increased by increasing the length of the shutter tube. For example, in order to obtain a pressure loss of 10 Pa, a gas flow rate of 24 L / min is required when there is no shutter tube (Ls = 0), whereas a gas flow rate when a shutter tube is present (Ls = 500 mm). Is 7 L / min. That is, in this case, the gas flow rate of 17 L / min can be reduced by attaching a shutter tube.

  Even if the length Ls of the shutter tube is short, an increase in pressure loss can be expected as compared with the case where it is not attached at all (Ls = 0 mm). For example, in order to secure the positive pressure in the reactor core tube to +5 Pa or more with respect to the atmospheric pressure, if the shutter tube length Ls is about 30 mm from the graph of FIG. This is expected to reduce the gas flow rate by about 1/3 compared to the gas flow rate of Ls = 0 mm. Therefore, the length Ls of the shutter tube is preferably at least 30 mm.

  On the other hand, if the shutter tube is too long, the shutter tube and the optical fiber may come into contact with each other when vibration (for example, an earthquake) occurs in the equipment or the optical fiber. Further, since a long shutter tube requires a distance in the height direction of the drawing device, it is restricted from the viewpoint of equipment. For this reason, it is desirable that the length of the shutter tube is empirically set to 500 mm or less.

FIG. 6 is a graph when the horizontal axis is the gas flow rate (L / min), the vertical axis is the pressure loss gradient (Pa / m), and the inner diameter (2r ₂ ) of the shutter tube is 5, 10, and 15 (mm), respectively. It is.
FIG. 6 shows the relationship between the pressure loss gradient and the gas flow rate in FIG. 4 because the desirable inner diameter of the shutter tube is 5 mm to 15 mm. If the inner diameter of the shutter tube is constant, the pressure drop gradient is It increases in proportion to the flow rate.
In the shutter tube having the tapered portion shown in FIG. 2, for example, the inner diameter on the small diameter side of the taper is 10 mm, the inner diameter on the large diameter side is 15 mm, and the length of the tapered portion is 1/3 of the entire length. In this case, a graph passing near the middle between the 10 mm inner diameter tube and the 15 mm inner tube can be a pressure loss gradient of the tapered tube.

DESCRIPTION OF SYMBOLS 10 ... Optical fiber drawing furnace, 11 ... Glass base material, 11a ... Lower end part of glass base material, 12 ... Glass fiber, 13 ... Core tube, 13a ... Reduced diameter part, 13b ... Reduced diameter pipe part, 14 ... Furnace housing Body, 15 ... heater, 16 ... heat insulating material, 17 ... extension tube, 18 ... core tube receiving member, 19, 20 ... shutter tube, 20a ... large diameter portion, 20b ... taper portion, 20c ... small diameter portion.

Claims (4)

A furnace core tube into which a glass base material for optical fibers is inserted; and a furnace housing that houses a heater for heating the furnace core tube from the outside, and flowing an inert gas in the furnace core tube from above to below, An optical fiber drawing device that guides the glass fiber drawn from the fiber outlet at the bottom of the core tube to the outside and discharges the inert gas to the outside,
A shutter tube is provided below the fiber outlet,
When the outer diameter of the glass fiber is 2r ₁ , the inner diameter of the shutter tube is 2r ₂ , the drawing speed of the glass fiber is V ₁ , and the flow rate of the inert gas flowing below the furnace core tube is Q,

An optical fiber drawing device satisfying the above requirements.   2. The optical fiber drawing device according to claim 1, wherein an inner diameter of the shutter tube portion is 5 mm to 15 mm.   3. The optical fiber drawing device according to claim 2, wherein a length of the shutter tube portion is 30 mm or more and 500 mm or less. A furnace core tube into which a glass base material for optical fibers is inserted; and a furnace housing that houses a heater for heating the furnace core tube from the outside, and flowing an inert gas in the furnace core tube from above to below, An optical fiber drawing method for drawing out a glass fiber drawn from a fiber outlet at a lower part of a furnace core tube to the outside and discharging the inert gas to the outside,
A shutter tube is provided below the fiber outlet,
When the outer diameter of the glass fiber is 2r ₁ , the inner diameter of the shutter tube is 2r ₂ , the drawing speed of the glass fiber is V ₁ , and the flow rate of the inert gas flowing below the furnace core tube is Q,

An optical fiber drawing method characterized by satisfying

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