JP2024010830A - Method and apparatus for manufacturing optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress glass particles generated in a drawing furnace from contacting a glass fiber.

SOLUTION: A method for manufacturing an optical fiber comprises the steps of: heating and melting an optical fiber preform in a drawing furnace including a heater and a furnace inner cylinder arranged below from a center of the heater and having an inert gas supplied to the inside to draw a glass fiber; and traveling the drawn glass fiber in the lower chamber including an extension inner cylinder extending below from a lower end of the furnace inner cylinder and a cooling jacket arranged on an outside of the extension inner cylinder. In at least a part in a travel direction of the glass fiber in the lower chamber, a surface temperature T1 of the glass fiber on a plane perpendicular to the travel direction of the glass fiber, a surface temperature T2 of an inner peripheral surface in the extension inner cylinder, and an inner diameter D2 of the extension inner cylinder satisfy: 2(T1-T2)/D2≥5[°C/mm].

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present disclosure relates to an optical fiber manufacturing method and an optical fiber manufacturing apparatus.

Patent Document 1 discloses an optical fiber drawing furnace in which a cooling jacket is provided inside an extension tube connected to the lower end of a furnace tube. By supplying the refrigerant into the cooling jacket, the atmospheric temperature within the extension tube is maintained at a predetermined temperature.

Patent Document 2 discloses an optical fiber drawing furnace in which a coating layer is formed on the inner surface of a carbon core tube. The coating layer suppresses deterioration of the carbon furnace tube due to a reaction between silica vapor generated from the optical fiber base material and the carbon furnace tube.

Patent Document 3 discloses an optical fiber drawing device that recovers and reuses helium gas used in an optical fiber drawing furnace.

Japanese Patent Application Publication No. 9-2832 Japanese Patent Application Publication No. 10-338538 Japanese Patent Application Publication No. 2004-250286

In such a drawing furnace, silica particles (glass particles) evaporated from the surface of the optical fiber base material heated at high temperature float in the drawing furnace and come into contact with the glass fiber, causing the glass fiber to become This may cause wire breakage.

An object of the present disclosure is to suppress glass particles generated in a drawing furnace from coming into contact with glass fibers.

A method for manufacturing an optical fiber according to one aspect of the present disclosure includes:
A step of heating and melting an optical fiber base material and drawing a glass fiber in a drawing furnace that has a heater and a furnace cylinder disposed below the center of the heater, and into which an inert gas is supplied. and,
Running the drawn glass fiber into a lower chamber having an extended inner cylinder extending downward from the lower end of the furnace inner cylinder and a cooling jacket disposed outside the extended inner cylinder;
It is equipped with
In at least a portion of the lower chamber in the running direction of the glass fiber, the surface temperature T1 of the glass fiber on a plane perpendicular to the running direction of the glass fiber, the surface temperature T2 of the inner circumferential surface of the extended inner cylinder, and the The inner diameter D2 of the extended inner cylinder satisfies 2(T1-T2)/D2≧5 [°C/mm].

An optical fiber manufacturing apparatus according to one aspect of the present disclosure includes:
A drawing furnace that heats and melts the base material for optical fiber;
a lower chamber connected to the lower end of the drawing furnace, in which a glass fiber drawn from the heated and melted optical fiber preform runs;
It is equipped with
The drawing furnace has a gas supply port for supplying an inert gas inside, a heater, and an inner furnace cylinder arranged below the center of the heater,
The lower chamber has an extended inner cylinder extending downward from the lower end of the furnace inner cylinder, and a cooling jacket disposed outside the extended inner cylinder,
When the temperature of the glass fiber coming out from the lower chamber is 800 degrees or higher and the drawing speed of the glass fiber is 500 m/min or higher, at least a portion of the lower chamber in the running direction of the glass fiber, The surface temperature T1 of the glass fiber on a plane perpendicular to the running direction of the glass fiber, the surface temperature T2 of the inner peripheral surface of the extension inner cylinder, and the inner diameter D2 of the extension inner cylinder are 2(T1-T2)/D2. ≧5 [°C/mm] is satisfied.

According to the configuration of the present disclosure, it is possible to suppress the glass particles generated in the drawing furnace from coming into contact with the glass fiber.

FIG. 1 is a schematic configuration diagram of an optical fiber manufacturing apparatus according to an embodiment of the present disclosure. FIG. 2 is a partially enlarged view of the optical fiber manufacturing apparatus shown in FIG. FIG. 3 is a diagram showing the relationship between temperature gradient and wire breakage frequency. FIG. 4 is a diagram showing the relationship between pressure loss and disconnection frequency in gas recovery piping.

[Description of embodiments of the present disclosure]
First, embodiments of the present disclosure will be listed and described.

(1) A method for manufacturing an optical fiber according to one aspect of the present disclosure includes:
A step of heating and melting an optical fiber base material and drawing a glass fiber in a drawing furnace that has a heater and a furnace cylinder disposed below the center of the heater, and into which an inert gas is supplied. and,
Running the drawn glass fiber into a lower chamber having an extended inner cylinder extending downward from the lower end of the furnace inner cylinder and a cooling jacket disposed outside the extended inner cylinder;
It is equipped with
In at least a portion of the lower chamber in the running direction of the glass fiber, the surface temperature T1 of the glass fiber on a plane perpendicular to the running direction of the glass fiber, the surface temperature T2 of the inner circumferential surface of the extended inner cylinder, and the The inner diameter D2 of the extended inner cylinder satisfies 2(T1-T2)/D2≧5 [°C/mm].

According to this method, since the temperature gradient (2(T1-T2)/D2) in the radial direction inside the extended inner cylinder is 5 [°C/mm] or more, it occurs in the drawing furnace and flows into the lower chamber. The glass particles that have flowed in become easier to move toward the inner circumferential surface of the extended inner cylinder due to thermophoretic force. Thereby, the glass particles can be attached to the inner peripheral surface of the extension inner cylinder, and the glass particles generated in the drawing furnace and floating in the lower chamber can be suppressed from coming into contact with the glass fiber.

(2) In (1) above, 2(T1-T2)/D2≧10 [° C./mm] may be satisfied in at least a portion of the lower chamber in the running direction of the glass fiber.

According to such a method, the temperature gradient in the radial direction within the extended inner cylinder is further increased, so that the thermophoretic force of the glass particles can be increased. Thereby, more glass particles can be attached to the inner circumferential surface of the extension inner cylinder, and contact of the glass particles with the glass fiber can be suppressed.

(3) In the above (1) or (2), the at least one portion may be a lower end portion of the extended inner tube in the running direction of the glass fiber.

According to this method, the temperature gradient (2(T1-T2)/D2) in the radial direction inside the extension inner cylinder is 5 [°C/mm] or more at the lower end of the extension inner cylinder away from the heat zone. Therefore, glass particles can be attached to the inner circumferential surface of the extended inner cylinder over the entire longitudinal direction of the extended inner cylinder.

(4) In any one of (1) to (3) above, the inert gas may be sucked through a gas suction port of the lower chamber.

According to such a method, glass particles that have flowed into the lower chamber and have not adhered to the inner circumferential surface of the extension inner cylinder can be sucked together with the inert gas. This can prevent glass particles floating in the lower chamber from coming into contact with the glass fibers.

(5) Piping is connected to the gas suction port in (4) above,
The piping may be cleaned when the pressure loss in the piping becomes 150% or more of the pressure loss after the previous cleaning.

According to such a method, it is possible to suppress the increase in pressure loss in the piping and the decrease in the suction force of the inert gas due to the accumulation of glass particles sucked in from the gas suction port inside the piping. Thereby, it is possible to suppress a decrease in the amount of suction of glass particles.

(6) In any one of (1) to (5) above, the inert gas may contain helium gas.

According to such a method, since helium gas has good thermal conductivity, the temperature distribution of the inert gas flowing in the drawing furnace becomes uniform, and disturbances in the flow of the inert gas can be suppressed.

(7) In any one of (1) to (5) above, the inert gas may contain argon gas.

According to this method, since the atoms of argon gas are larger than the atoms of helium gas, the thermophoretic force of the glass particles can be increased compared to helium gas.

(8) An optical fiber manufacturing apparatus according to one aspect of the present disclosure includes:
A drawing furnace that heats and melts the base material for optical fiber;
a lower chamber connected to the lower end of the drawing furnace, in which a glass fiber drawn from the heated and melted optical fiber preform runs;
It is equipped with
The drawing furnace has a gas supply port for supplying an inert gas inside, a heater, and an inner furnace cylinder arranged below the center of the heater,
The lower chamber has an extended inner cylinder extending downward from the lower end of the furnace inner cylinder, and a cooling jacket disposed outside the extended inner cylinder,
When the temperature of the glass fiber coming out from the lower chamber is 800 degrees or higher and the drawing speed of the glass fiber is 500 m/min or higher, at least a portion of the lower chamber in the running direction of the glass fiber, The surface temperature T1 of the glass fiber on a plane perpendicular to the running direction of the glass fiber, the surface temperature T2 of the inner peripheral surface of the extension inner cylinder, and the inner diameter D2 of the extension inner cylinder are 2(T1-T2)/D2. ≧5 [°C/mm] is satisfied.

According to such a device, since the temperature gradient (2(T1-T2)/D2) in the radial direction inside the extended inner cylinder is 5 [°C/mm] or more, it occurs in the drawing furnace and flows into the lower chamber. The glass particles that have flowed in become easier to move toward the inner circumferential surface of the extended inner cylinder due to thermophoretic force. This allows glass particles to adhere to the inner circumferential surface of the extended inner cylinder, thereby suppressing glass particles generated in the drawing furnace and floating in the lower chamber from coming into contact with the glass fiber.

(9) In the above (8), the extension inner cylinder may be configured to be detachable from the lower chamber.

According to such a device, since the extension inner cylinder can be removed from the lower chamber, the extension inner cylinder can be cleaned and glass particles deposited on the inner peripheral surface of the extension inner cylinder can be removed. Alternatively, the extension inner cylinder can be replaced with a new extension inner cylinder. Thereby, it is possible to suppress a decrease in the deposition efficiency of glass particles on the inner circumferential surface of the extended inner cylinder.

(10) In the above (8) or (9), the inner diameter of the extended inner cylinder may be 300 mm or less.

According to such a device, the temperature gradient in the radial direction within the extended inner cylinder increases, and glass particles tend to adhere to the inner circumferential surface of the extended inner cylinder.

(11) In the above (10), the inner diameter of the extended inner cylinder may be 150 mm or less.

According to such a device, since the inner diameter of the inner extended cylinder is smaller, the temperature gradient in the radial direction within the inner extended cylinder becomes larger, and more glass particles can be attached to the inner circumferential surface of the inner extended cylinder. Can be done.

(12) In any one of (8) to (11) above, the lower chamber may include a gas suction port that sucks the inert gas.

According to such a device, glass particles that have flowed into the lower chamber and have not adhered to the inner circumferential surface of the extension inner cylinder can be sucked together with the inert gas. This can prevent glass particles floating in the lower chamber from coming into contact with the glass fiber.

[Details of embodiments of the present disclosure]
DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of an optical fiber manufacturing apparatus and manufacturing method according to the present disclosure will be described with reference to the drawings. In the following description, the same or equivalent elements will be given the same reference numerals or names even in different drawings, and overlapping description will be omitted as appropriate. Further, the dimensions of each member shown in each drawing are for convenience of explanation, and may differ from the actual dimensions of each member.

(Optical fiber manufacturing equipment)
FIG. 1 is a schematic configuration diagram of an optical fiber manufacturing apparatus 1 according to an embodiment of the present disclosure. FIG. 2 is a partially enlarged view of the optical fiber manufacturing apparatus 1. As shown in FIG.

An optical fiber manufacturing apparatus 1 includes a drawing furnace 2 and a lower chamber 3. The drawing furnace 2 is configured to heat and melt the optical fiber preform G1. The lower chamber 3 is connected to the lower end of the drawing furnace 2 . The lower chamber 3 is configured to maintain the atmospheric temperature within the lower chamber 3 at a predetermined temperature. A glass fiber G2 drawn from an optical fiber preform G1 heated and melted in the drawing furnace 2 runs inside the lower chamber 3. The optical fiber manufacturing apparatus 1 further includes a cooling device that cools the glass fiber G2 below the lower chamber 3, a coating device that applies a coating resin to the outer periphery of the glass fiber G2, and a glass fiber G2 coated with the coating resin. A winding device or the like may be provided.

The drawing furnace 2 includes a housing 21 , a furnace core tube 22 , a heater 23 , and a furnace cylinder 24 . The housing 21 is configured to surround the furnace core tube 22, the heater 23, and the furnace cylinder 24. The heater 23 is arranged to surround the furnace core tube 22. A heat insulating material (not shown) is arranged between the heater 23 and the housing 21.

A gas supply port 221 is provided in the furnace core tube 22 . Specifically, the gas supply port 221 is provided on the upper end side of the furnace core tube 22. One end of the gas supply pipe 11 is connected to the gas supply port 221 . An inert gas supplier 12 that supplies inert gas is connected to the other end of the gas supply pipe 11. The inert gas supplied from the inert gas supply device 12 passes through the gas supply piping 11 and is supplied into the furnace core tube 22 from the gas supply port 221. The inert gas is, for example, helium gas.

The furnace tube 24 is arranged within the furnace core tube 22 . Specifically, the furnace tube 24 is arranged below the center of the heater 23 in the longitudinal direction of the furnace core tube 22 . The furnace cylinder 24 may be formed integrally with the furnace core tube 22. In this example, the furnace cylinder 24 has a tapered portion 241 at its upper end, the inner diameter of which decreases downward.

The lower chamber 3 has an extended inner cylinder 31, a cooling jacket 32, and a gas recovery mechanism 33. The extension inner cylinder 31 is connected to the lower end of the furnace cylinder 24 and extends downward from the lower end of the furnace cylinder 24 .

As illustrated in FIG. 2, the extension inner cylinder 31 is provided so that the outlet of the furnace inner cylinder 24 and the inlet of the extension inner cylinder 31 are connected. The upper end of the extension inner cylinder 31 has the same inner diameter D2 as the inner diameter D1 of the lower end of the furnace inner cylinder 24. In this example, the extended inner tube 31 has a cylindrical shape having a constant inner diameter D2 along the longitudinal direction. The inner diameter D2 of the extended inner cylinder is, for example, 300 mm or less, preferably 150 mm or less. Further, the inner diameter D2 of the extended inner cylinder is preferably 30 mm or more.

The extension inner cylinder 31 is provided to be detachable from the lower chamber 3. For example, the extension inner cylinder 31 is provided to be detachable from an opening at the lower end of the lower chamber 3 . In this example, after the gas recovery mechanism 33 is removed from the lower chamber 3, the extension inner cylinder 31 is removed from the opening at the lower end of the lower chamber 3.

The cooling jacket 32 is arranged outside the extended inner cylinder 31. The cooling jacket 32 has a flow path 321 through which a refrigerant flows. A refrigerant supply device (not shown) is connected to the cooling jacket 32, and the supply of refrigerant into the cooling jacket 32 is controlled by the refrigerant supply device.

The gas recovery mechanism 33 includes a gas suction port 331 that sucks cooling gas. In this example, the gas recovery mechanism 33 has an upper shutter 332 and a lower shutter 333, and two gas suction ports 331 are formed on the bottom surface of the lower shutter 333. A gas recovery space S is formed between the upper shutter 332 and the lower shutter 333. The gas passed through the passage hole 332A formed in the upper shutter 332 and collected into the gas recovery space S is sucked by the gas suction port 331 formed in the lower shutter 333 and is discharged to the outside of the lower chamber 3. . In addition, the lower shutter 333 is formed with a fiber outlet 333A through which the glass fiber G2 that has passed through the gas recovery space S exits to the outside of the lower chamber 3.

One end of the gas recovery pipe 13 is connected to the gas suction port 331 . A gas regeneration device 14 is connected to the other end of the gas recovery pipe 13. The gas recovered in the gas recovery space S contains the inert gas supplied into the furnace tube 22 and glass particles generated from the optical fiber preform G1. The gas regeneration device 14 separates and refines an inert gas (for example, helium gas) from the gas sucked through the gas suction port 331, and regenerates the inert gas into a reusable state. Note that the gas regeneration device 14 and the inert gas supply device 12 may be connected through a pipe 15, and the inert gas regenerated by the gas regeneration device 14 may be supplied to the inert gas supply device 12.

The optical fiber manufacturing apparatus 1 configured in this manner has a surface temperature T1 of the glass fiber G2 on a plane perpendicular to the running direction of the glass fiber G2 at the lower end 312 of the extension inner tube 31 in the running direction of the glass fiber; The surface temperature T2 of the inner circumferential surface 311 of the extended inner cylinder 31 and the inner diameter D2 of the extended inner cylinder 31 are configured to satisfy 2(T1-T2)/D2≧5 [° C./mm]. The lower end portion 312 of the extended inner cylinder 31 is an example of at least a portion of the glass fiber G2 in the lower chamber 3 in the running direction.

For example, when the temperature of the glass fiber G2 coming out from the lower chamber 3 is 800 degrees or more and the drawing speed of the glass fiber G2 is 500 m/min or more, 2(T1-T2)/D2≧5 [°C /mm].

Specifically, the extended inner cylinder 31 having a predetermined inner diameter D2 is used so as to satisfy 2(T1-T2)/D2≧5[° C./mm]. Additionally or alternatively, the temperature and flow rate of the refrigerant flowing through the cooling jacket 32 may be set so that the surface temperature T2 of the inner circumferential surface 311 of the extended inner cylinder 31 becomes a predetermined temperature. For example, the temperature of the refrigerant may be adjusted between 20 degrees and 40 degrees.

(Optical fiber manufacturing method)
Next, a method for manufacturing an optical fiber using the optical fiber manufacturing apparatus 1 illustrated in FIG. 1 will be described.

A base material suspension mechanism (not shown) suspends the optical fiber base material G1 within the furnace tube 22 into which inert gas has been introduced, and the heater 23 heats and melts the lower part of the optical fiber base material G1. The molten optical fiber preform G1 is continuously drawn into a glass fiber G2 having a predetermined outer diameter due to the weight and tensile force of the molten glass.

The glass fiber G2 coming out of the drawing furnace 2 passes through the inside of the lower chamber 3. The atmospheric temperature in the lower chamber 3 is maintained at a predetermined temperature, and the glass fiber G2 is not only cooled rapidly but also hardened to some extent.

Gas containing inert gas that has flowed into the lower chamber 3 from the furnace core tube 22 is sucked through the gas suction port 331 . Inert gas is separated and purified from the gas sucked by the gas regeneration device 14 and reused.

Incidentally, as silica evaporates from the surface of the optical fiber preform G1 heated in the drawing furnace 2, silica particles (glass particles P) are generated in the drawing furnace 2. As illustrated in FIG. 2, the glass particles P generated in the drawing furnace 2 are moved into the lower chamber by the pulling flow of the glass fiber G2 and the gas flow of the inert gas supplied from above inside the drawing furnace 2. 3. The glass particles P that have flowed into the lower chamber 3 collide with the glass fiber G2, causing breakage of the glass fiber G2.

Therefore, in the optical fiber manufacturing apparatus 1 according to the present embodiment, the surface temperature T1 of the glass fiber G2 on the plane perpendicular to the running direction of the glass fiber G2 at the lower end 312 of the extension inner cylinder 31, It is configured such that the surface temperature T2 of the peripheral surface 311 and the inner diameter D2 of the extended inner cylinder 31 satisfy 2(T1-T2)/D2≧5 [° C./mm]. That is, since the temperature gradient (2(T1-T2)/D2) in the radial direction of the extended inner cylinder 31 is 5 [°C/mm] or more, the glass particles flowing into the lower chamber 3 as illustrated in FIG. P becomes easier to move toward the inner circumferential surface 311 of the extended inner cylinder 31 due to thermophoretic force. Thereby, the glass particles P can be attached to the inner peripheral surface 311 of the extension inner cylinder 31, and the glass particles P generated in the drawing furnace 2 and floating in the lower chamber 3 can be prevented from coming into contact with the glass fiber G2. It can be suppressed.

Further, in this embodiment, the extension inner tube 31 has a cylindrical shape having a constant inner diameter D2 along the longitudinal direction. Moreover, the surface temperature T1 of the glass fiber G2 becomes lower as the distance from the heat zone increases. Therefore, if 2(T1-T2)/D2≧5 [°C/mm] or more is satisfied at the lower end 312, the portion of the extension inner cylinder 31 closer to the heat zone than the lower end 312 also has 2(T1-T2)/D2. D2≧5[°C/mm] or more is satisfied. Thereby, the glass particles P can be attached to the inner circumferential surface 311 of the extended inner cylinder 31 over the entire longitudinal direction of the extended inner cylinder 31.

Note that the optical fiber manufacturing apparatus 1 may be configured such that the temperature gradient (2(T1-T2)/D2) in the radial direction of the inner extension cylinder 31 is 10 [° C./mm] or more. As a result, the temperature gradient in the radial direction inside the extension inner cylinder 31 becomes even larger, so that more glass particles can be attached to the inner circumferential surface 311 of the extension inner cylinder 31, thereby reducing the amount of glass particles generated in the drawing furnace 2. It is possible to suppress the glass particles from coming into contact with the glass fiber G2.
The larger the temperature gradient (2(T1-T2)/D2) in the radial direction of the extension inner cylinder 31, the more glass particles can be attached to the inner circumferential surface 311 of the extension inner cylinder 31, but this is not possible. The upper limit of the range is about 100[° C./mm].

Further, in this embodiment, the extended inner cylinder 31 has an inner diameter of 300 mm or less, preferably 150 mm or less. As a result, the temperature gradient (2(T1-T2)/D2) in the radial direction inside the extended inner cylinder 31 increases, and the glass particles P tend to adhere to the inner circumferential surface 311 of the extended inner cylinder 31. On the other hand, since the inner diameter D2 of the extended inner tube 31 is 30 mm or more, the glass lumps dropped from the drawing furnace 2 during seed removal performed before wire drawing can pass through the extended inner tube 31.

Further, in this embodiment, the extension inner cylinder 31 is configured to be detachable from the lower chamber 3. As the glass particles adhere to and solidify on the inner peripheral surface 311 of the extended inner cylinder 31 of the lower chamber 3, the temperature gradient inside the lower chamber 3 changes and the glass particle deposition efficiency decreases. . Therefore, by being able to remove the extension inner cylinder 31 from the lower chamber 3, the extension inner cylinder 31 can be cleaned and glass particles deposited on the inner peripheral surface 311 of the extension inner cylinder 31 can be removed. Alternatively, the extended inner cylinder 31 can be replaced with a new extended inner cylinder 31. Thereby, a decrease in the deposition efficiency of glass particles on the inner circumferential surface 311 of the extended inner cylinder 31 can be suppressed. For example, the extension inner cylinder 31 is replaced or cleaned after the plurality of optical fiber preforms G1 are drawn.

Further, in this embodiment, helium gas is used as the inert gas. Since helium gas has good thermal conductivity, the temperature distribution of the inert gas flowing in the drawing furnace 2 becomes uniform, and disturbances in the flow of the inert gas can be suppressed.

Further, in this embodiment, the furnace cylinder 24 has a tapered portion 241 whose inner diameter decreases toward the bottom. Thereby, thermal radiation from the furnace tube 24 can be efficiently transmitted to the optical fiber base material G1.

Further, in this embodiment, inert gas is sucked from the gas suction port 331 of the lower chamber 3. Thereby, glass particles that have flowed into the lower chamber 3 and have not adhered to the inner circumferential surface 311 of the extended inner cylinder 31 can be sucked together with the inert gas. Therefore, it is possible to suppress the glass particles floating in the lower chamber 3 from coming into contact with the glass fiber G2.

Note that when the glass particles P sucked from the gas suction port 331 accumulate in the gas recovery pipe 13, the pressure loss in the gas recovery pipe 13 increases, and the suction force of the inert gas decreases. A decrease in the suction force of the inert gas causes a decrease in the amount of suction of the glass particles P. Therefore, it is preferable to clean the gas recovery piping 13 when the pressure loss in the gas recovery piping 13 becomes 150% or more of the pressure loss immediately after cleaning the gas recovery piping 13. Thereby, it is possible to suppress the increase in pressure loss in the gas recovery pipe 13 due to the accumulation of glass particles in the gas recovery pipe 13, and the decrease in the suction force of the inert gas. For example, if the pressure loss in the gas recovery pipe 13 becomes 150% or more, after the drawing of the optical fiber preform G1 is completed and the next optical fiber preform G1 is inserted into the drawing furnace, Gas recovery piping 13 is cleaned.

(Example)
EXAMPLES Hereinafter, the present disclosure will be described in more detail with reference to Examples, but the present disclosure is not limited in any way by the following Examples.

In the optical fiber manufacturing apparatus 1, after changing the inner diameter D2 of the extension inner tube 31 and the surface temperature T2 of the inner circumferential surface 311 of the extension inner tube 31, the optical fiber base material G1 is drawn, and the drawn glass fiber is produced. The frequency of disconnection of G2 was evaluated. The results are shown in Table 1. The surface temperature T2 of the inner peripheral surface 311 of the extended inner cylinder 31 was changed by changing the temperature and flow rate of the refrigerant flowing through the cooling jacket 32. The surface temperature of the inner circumferential surface 311 of the extended inner cylinder 31 before the start of wire drawing was measured from below the lower chamber 3 using a radiation thermometer.

Furthermore, the temperature gradient in the radial direction inside the extension inner cylinder 31 from the inner diameter D2 of the extension inner cylinder 31, the surface temperature T2 of the inner circumferential surface 311 of the extension inner cylinder 31, and the surface temperature T1 of the glass fiber G2 (2(T1-T2) )/D2) was calculated. FIG. 3 shows the relationship between the calculated temperature gradient and the breakage frequency of the glass fiber G2. Measure the surface temperature of the glass fiber G2 at the fiber outlet 333A of the lower chamber 3, and calculate the surface temperature T1 of the glass fiber G2 by linear interpolation based on the measured surface temperature of the glass fiber G2 and the temperature of the heater 23. did.

As shown in Table 1, it was found that the lower the surface temperature T2 of the inner peripheral surface 311 of the extended inner cylinder 31, the lower the frequency of breakage of the glass fiber G2. It was also found that the smaller the inner diameter D2 of the extended inner tube 31, the lower the frequency of breakage of the glass fiber G2. Moreover, as shown in FIG. 3, it was found that the frequency of breakage of the glass fiber G2 decreased as the temperature gradient increased. For example, it has been found that when the temperature gradient is 5° C./mm or more, the frequency of breakage of the glass fiber G2 does not exceed 1.5 breakages/1,000 km, which is generally said to significantly deteriorate production efficiency. Furthermore, it was found that when the temperature gradient was 10° C./mm or more, the frequency of wire breakage was further reduced.

Furthermore, in the optical fiber manufacturing apparatus 1, the relationship between the pressure loss in the gas recovery pipe 13 connected to the gas suction port 331 and the frequency of breakage of the glass fiber G2 was investigated. Helium gas was used as the inert gas. FIG. 4 shows the relationship between the pressure loss in the gas recovery pipe 13 and the frequency of breakage of the glass fiber G2. In FIG. 4, the horizontal axis indicates the pressure loss when the pressure loss immediately after cleaning the gas recovery piping 13 is set to 1. The pressure loss was calculated as the difference between the two detected pressures by measuring the pressure at two different locations in the gas recovery piping 13.

As shown in FIG. 4, when the pressure loss inside the gas recovery piping 13 is 150% or more of the pressure loss immediately after cleaning the gas recovery piping 13 (that is, 1.5 or more on the horizontal axis), the glass It was found that the frequency of fiber G2 breakages exceeded 1.5 cases/1,000km.

Although the present disclosure has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present disclosure. Further, the number, position, shape, etc. of the constituent members described above are not limited to those in the above embodiment, and can be changed to a suitable number, position, shape, etc. for implementing the present disclosure. Moreover, the elements included in each of the examples described above can be combined with each other.

In the above embodiment, the surface temperature T2 of the inner circumferential surface 311 of the extended inner cylinder 31 is measured from below the lower chamber 3 using a radiation thermometer. However, a measurement window may be provided in the lower chamber 3, and the surface temperature T2 of the inner circumferential surface 311 of the extension inner cylinder 31 on the opposite side to the measurement window may be measured through the measurement window using a radiation thermometer. Alternatively, a thermocouple may be disposed near the surface of the inner peripheral surface 311 of the extended inner cylinder 31 of the lower chamber 3, and the surface temperature T2 of the inner peripheral surface 311 of the extended inner cylinder may be measured by the thermocouple.

In the embodiments described above, helium gas is used as the inert gas. However, the inert gas may contain helium gas as a main component, and may also contain other gases such as argon gas and nitrogen gas. In this case, the content of helium gas is preferably 50% or more.

Further, as the inert gas, for example, argon gas may be used instead of helium gas. Since the atoms of argon gas are larger than the atoms of helium gas, when argon gas is used as the inert gas, the thermophoretic force of the glass particles P can be increased compared to helium gas. Further, the inert gas has argon gas as its main component, and may also contain other gases such as helium gas and nitrogen gas. In this case, the content of argon is preferably 50% or more.

In the above embodiment, the inner diameter D2 of the extended inner cylinder 31 and/or The temperature and flow rate of the refrigerant flowing through the cooling jacket 32 are set. However, for example, the temperature of the heater 23 may be adjusted so that the surface temperature T1 of the glass fiber G2 becomes a predetermined temperature. Note that the temperature of the heater 23 is adjusted within a setting range that is appropriately determined from the viewpoint of the drawing tension of the optical fiber to be manufactured and the glass fiber G2.

In the above embodiment, the temperature and flow rate of the refrigerant flowing through the cooling jacket 32 are set before wire drawing. However, even during wire drawing, the temperature and flow rate of the refrigerant flowing through the cooling jacket 32 and the temperature of the heater 23 are adjusted so that the temperature gradient in the radial direction of the extended inner cylinder 31 is 5 [°C/mm] or more. good.

1: Optical fiber manufacturing equipment 11: Gas supply piping 12: Inert gas supply device 13: Gas recovery piping 14: Gas regeneration device 15: Piping 2: Drawing furnace 21: Housing 22: Furnace core tube 221: Gas Supply port 23: Heater 24: Furnace cylinder 241: Tapered part 3: Lower chamber 31: Extension inner cylinder 311: Inner peripheral surface 312: Lower end 32: Cooling jacket 321: Flow path 33: Gas recovery mechanism 331: Gas suction port 332: Upper shutter 332A: Passing hole 333: Lower shutter 333A: Fiber outlet G1: Optical fiber base material G2: Glass fiber P: Glass particles D1: Inner diameter of furnace inner cylinder D2: Inner diameter of extended inner cylinder S: Gas Recovery space T1: Surface temperature of glass fiber T2: Surface temperature of inner peripheral surface of extension inner cylinder

Claims (12)

A step of heating and melting an optical fiber base material and drawing a glass fiber in a drawing furnace that has a heater and a furnace cylinder disposed below the center of the heater, and into which an inert gas is supplied. and,
Running the drawn glass fiber into a lower chamber having an extended inner cylinder extending downward from the lower end of the furnace inner cylinder and a cooling jacket disposed outside the extended inner cylinder;
It is equipped with
In at least a portion of the lower chamber in the running direction of the glass fiber, the surface temperature T1 of the glass fiber on a plane perpendicular to the running direction of the glass fiber, the surface temperature T2 of the inner circumferential surface of the extended inner cylinder, and the An optical fiber manufacturing method, wherein the inner diameter D2 of the extended inner cylinder satisfies 2(T1-T2)/D2≧5 [°C/mm]. 2. The method for manufacturing an optical fiber according to claim 1, wherein 2(T1-T2)/D2≧10 [° C./mm] is satisfied in at least a portion of the lower chamber in the running direction of the glass fiber. 2. The method for manufacturing an optical fiber according to claim 1, wherein the at least one portion is a lower end portion of the extended inner tube in the running direction of the glass fiber. The method for manufacturing an optical fiber according to claim 1, wherein the inert gas is sucked through a gas suction port of the lower chamber. Piping is connected to the gas suction port,
5. The method for manufacturing an optical fiber according to claim 4, wherein the piping is cleaned when the pressure loss in the piping becomes 150% or more of the pressure loss after the previous cleaning. The method for manufacturing an optical fiber according to any one of claims 1 to 5, wherein the inert gas is a gas containing helium. The method for manufacturing an optical fiber according to any one of claims 1 to 5, wherein the inert gas is a gas containing argon. A drawing furnace that heats and melts the base material for optical fiber;
a lower chamber connected to the lower end of the drawing furnace, in which a glass fiber drawn from the heated and melted optical fiber preform runs;
It is equipped with
The drawing furnace has a gas supply port for supplying an inert gas inside, a heater, and an inner furnace cylinder arranged below the center of the heater,
The lower chamber has an extended inner cylinder extending downward from the lower end of the furnace inner cylinder, and a cooling jacket disposed outside the extended inner cylinder,
When the temperature of the glass fiber coming out from the lower chamber is 800 degrees or higher and the drawing speed of the glass fiber is 500 m/min or higher, at least a portion of the lower chamber in the running direction of the glass fiber, The surface temperature T1 of the glass fiber on a plane perpendicular to the running direction of the glass fiber, the surface temperature T2 of the inner peripheral surface of the extension inner cylinder, and the inner diameter D2 of the extension inner cylinder are 2(T1-T2)/D2. An optical fiber manufacturing device that satisfies ≧5[°C/mm]. The optical fiber manufacturing apparatus according to claim 8, wherein the extension inner tube is configured to be detachable from the lower chamber. The optical fiber manufacturing apparatus according to claim 8, wherein the inner diameter of the extension inner cylinder is 300 mm or less. The optical fiber manufacturing apparatus according to claim 10, wherein the inner diameter of the extension inner tube is 150 mm or less. The optical fiber manufacturing apparatus according to any one of claims 8 to 11, wherein the lower chamber includes a gas suction port that sucks the inert gas.

Images