JPH092831A - Fiber drawing method of optical fiber and fiber drawing furnace - Google Patents

Abstract

PURPOSE: To provide a method for the fiber drawing of an optical fiber and a fiber drawing furnace, not requiring the supply of a large amount of an inert gas, capable of preventing the convection of an atmospheric gas in an upper chamber and stably drawing the optical fiber having a uniform diameter. CONSTITUTION: The fiber drawing furnace for an optical fiber having a furnace core tube 13 to which a preform for the optical fiber 14 is supplied, a heater 16 surrounding the furnace core tube 13 and an upper chamber 22 accommodating the preform for the optical fiber 14 by linking to the upper end of the furnace core tube 13 and through which a supporting rod 17 supporting the preform for the optical fiber 14 penetrates, is constituted by installing a circulating flow forming means for forming the circulating flow of an atmospheric gas along the inner circumferential wall of the upper chamber 22 and suppressing the convecting phenomenon of the atmospheric gas along its longitudinal direction in the upper chamber 22 so as to make the flow of the atmospheric gas around the lower end part of the preform for the optical fiber 14 a stable state and to stabilize the line diameter of the optical fiber 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber drawing method capable of suppressing fluctuations in wire diameter and an optical fiber drawing furnace used therefor.

[0002]

2. Description of the Related Art Usually, an optical fiber is drawn by heating and softening a rod-shaped base material for an optical fiber in an optical fiber drawing furnace and stretching it. As one means of reducing the manufacturing cost of this optical fiber, it has been attempted to lengthen the optical fiber preform and reduce the number of setup changes, and it is possible to achieve continuous drawing work of optical fibers for hundreds of kilometers. ing.

An optical fiber drawing furnace used for drawing such a lengthened base material for an optical fiber is
As disclosed in Japanese Patent Application Laid-Open No. 2-6349, a furnace core tube surrounded by a heater for heating the lower end of the optical fiber preform is extended upward, and this portion is formed of the optical fiber preform. It is formed as a chimney-shaped upper chamber that houses the upper portion and forms a semi-enclosed space. Then, an inert gas such as helium or nitrogen is supplied to the upper end of the upper chamber, the upper chamber and the inside of the core tube communicating with the upper chamber are held in a non-oxidizing atmosphere, and the base material for an optical fiber in a heated and melted state is The optical fiber is drawn from the lower end. Further, the inert gas supplied into the core tube is discharged to the outside from the lower end portion of the core tube.

[0004]

In the optical fiber drawing furnace in which the upper chamber is formed, the optical fiber preform is shortened as the optical fiber drawing work progresses, and the optical fiber occupies the upper chamber. Since the storage space for the base material gradually becomes vacant, the flow velocity of the inert gas in the storage space also tends to slow down.

In this upper chamber, the temperature is high in the lower part close to the heater, and the temperature is low in the upper part, so that natural convection tends to occur. As the drawing work of the optical fiber progresses, the storage space of the optical fiber preform described above gradually becomes larger and the temperature difference between the upper part and the lower part thereof becomes large, and as a result, the flow velocity of the inert gas becomes slow, Vertical natural convection will occur in the upper chamber.

When such a natural convection of an inert gas occurs, the gas flow forming the atmosphere at the lower end of the optical fiber preform in the heat-softened state also becomes unstable, and the diameter of the drawn optical fiber is reduced. The fluctuation tends to be considerably large, and it becomes difficult to obtain a desired quality as a product.

In order to prevent such a convection phenomenon of the inert gas in the upper chamber, in JP-A-2-6349, an inert gas having a flow velocity capable of destroying the convection phenomenon is supplied to the upper chamber. It is suggested to do so.

However, at least 0.4 per second is possible with this method.
Since it is necessary to ensure a flow velocity of ~ 0.5 m, for example, when the inner diameter of the core tube and the upper chamber is 100 mm, the length of 50 cm in the up-down direction along the inner peripheral wall of the upper chamber is 0. In order to form a swirling flow with a flow velocity of 5 m,
The diameter of the support rod is 25 mm, and 221 liters of inert gas must be supplied per minute. Even if the volume of the inert gas expands several times due to the high temperature atmosphere in the furnace,
It is necessary to supply as much as 60 to 80 liters of inert gas per minute in the standard state at a minimum, which increases running cost.

[0009]

It is an object of the present invention to prevent the convection phenomenon of atmospheric gas in the upper chamber without supplying a large amount of inert gas into the furnace and to stably draw an optical fiber having a uniform diameter. (EN) Provided is an optical fiber drawing method and a drawing furnace therefor.

[0010]

The first aspect of the present invention is as follows.
A core tube to which the optical fiber base material is supplied, a heater surrounding the core tube, and a support rod connected to the upper end of the core tube to accommodate the optical fiber base material and to support the optical fiber base material. An optical fiber drawing furnace having an upper chamber through which the lower end of the optical fiber preform is heated and melted to draw an optical fiber, wherein an inner peripheral wall of the upper chamber is provided. The optical fiber drawing method is characterized in that a swirl flow of the atmospheric gas is formed along the line.

Here, it is effective that the swirl flow of the atmospheric gas is formed at the upper end of the upper chamber.
In particular, it is desirable to form it at an intermediate portion between the upper end of the upper chamber and the upper end of the optical fiber preform. Then, an inert gas may be supplied into the furnace along the swirl flow of the atmospheric gas from the upper end of the upper chamber.

On the other hand, according to a second aspect of the present invention, a furnace core tube to which the optical fiber preform is supplied, a heater surrounding the furnace core tube, and the optical fiber preform connected to the upper end of the furnace core tube In an optical fiber drawing furnace having an upper chamber which is housed and through which a supporting rod for supporting the optical fiber preform penetrates, a swirling flow formation for forming a swirling flow of an atmospheric gas along an inner peripheral wall of the upper chamber An optical fiber drawing furnace characterized by comprising means.

Here, it is effective that the swirl flow forming means is provided so that the swirl flow of the atmospheric gas is formed at the upper end portion of the upper chamber. It is desirable to incorporate the elevating means so as to be formed at an intermediate portion between the upper end of the upper chamber and the upper end of the optical fiber preform. Further, the swirl flow forming means may include an annular radial fan that rotatably surrounds the periphery of the support rod, and a driving means that drives and rotates the radial fan.

[0014]

According to the present invention, since the swirling flow of the atmospheric gas is formed along the inner peripheral wall of the upper chamber by the swirling flow forming means, the convection phenomenon of the atmospheric gas along the longitudinal direction in the upper chamber is suppressed. To be done. Particularly, when the swirling flow of the atmospheric gas is formed in the intermediate portion between the upper end of the upper chamber and the upper end of the optical fiber preform by the elevating means, the effect of suppressing the convection phenomenon of the atmospheric gas becomes large. However, even when the swirling flow of the atmospheric gas is formed at the upper end of the upper chamber, the swirling flow is gradually formed over the entire upper chamber due to the viscosity of the atmospheric gas, so that the convection phenomenon of the atmospheric gas is suppressed. It will be. As a result, the flow of the atmospheric gas around the lower end of the optical fiber preform becomes stable, and the diameter of the optical fiber drawn from the lower end of the optical fiber preform also becomes stable.

Further, in the one in which the swirl flow forming means has an annular radial fan that rotatably surrounds the periphery of the support rod, and drive means for driving and rotating the radial fan,
The radial fan is driven and rotated by operating the driving means, and a swirling flow of the atmospheric gas is formed along the inner peripheral wall of the upper chamber.

[0016]

1 is a sectional view showing an embodiment of an optical fiber drawing furnace capable of realizing an optical fiber drawing method according to the present invention, and FIG. 2 and FIG. It will be described in detail with reference to FIG. 3 showing a sectional structure taken along line III-III.

Around a cylindrical core tube 13 provided at the center of a stainless steel furnace body 12 lined with a heat insulating material 11, an optical fiber preform 14 supplied inside the core tube 13 is provided. An annular carbon heater 16 for heating and melting the lower end portion of the core to draw the optical fiber 15 is provided concentrically with the core tube 13.
The heat insulating material 11 is arranged so as to surround the upper and lower sides and the outer peripheral side of the carbon heater 16 so that the heat generated in 1 is not escaped to the outside as much as possible. The upper end of the optical fiber preform 14 is connected to the lower end of the support rod 17, and the upper end of the support rod 17 is suspended by a chuck (not shown), and the optical fiber 15 is drawn to the core tube 13 side. They are sent in order.

An extension tube 19 which projects downward from the furnace body 12 and forms a lower chamber 18 inside is connected to a lower end of the core tube 13, and an optical fiber 15 is connected to a lower end of the extension tube 19. A seal plate 21 having a through-opening 20 formed at the center is attached.

At the upper end of the core tube 13, the furnace body 1
A base material storage cylinder 23 that projects upward from 2 and forms an upper chamber 22 inside is connected to the upper end of the core tube 13.
An annular fan casing 24 having a groove-shaped cross section is attached to the upper end of the base material storage cylinder 23, and the top plate portion 25 of the fan casing 24 and the shutter ring 26 superposed on the top plate portion 25 are centered. The openings 27 and 28 through which the support rod 17 penetrates are formed concentrically with the core tube 13. In this case, the size of the opening 27 formed in the top plate portion 25 is set to be sufficiently larger than the outer diameter size of the support rod 17, but the size of the opening 28 formed in the shutter ring 24 is set to this shutter ring. It is set as small as possible so as not to hinder the lowering operation of the support rod 17 with respect to 24, so that atmospheric gas in the furnace is prevented from leaking out of the furnace as much as possible.

An annular radial fan 29 is rotatably housed inside the fan casing 24, and the radial fan 29 in this embodiment has a plurality of blades 30 radially arranged at equal intervals. , These feathers 3
The radial fan 29 has an annular upper plate 31 and a lower plate 32 for holding the upper end and the lower end of 0, respectively.
An annular bearing groove 33 having a V-shaped cross section is formed in the lower plate 32. Further, an annular bearing groove 34 having a V-shaped cross section corresponding to the bearing groove 33 is formed in the bottom plate portion 35 of the fan casing 24 concentrically with the core tube 13.
A plurality of bearing balls 36 made of stainless steel, ceramics or the like are rotatably held between these bearing grooves 33, 34, and the radial fan 29 with respect to the fan casing 24 is supported via these bearing balls 36. It is held so that it can be turned freely. Further, an external gear 37 is integrally formed on an outer peripheral edge portion of an upper plate 31 of the radial fan 29, and the external gear 37 is attached to a tip end portion of a spindle 39 of a fan drive motor 38. By engaging the pinion 40 and energizing the fan drive motor 38, the radial fan 29 is driven and rotated in the fan casing 24 in the clockwise direction in FIG. 3, and the upper chamber 22 has its upper end portion along the inner peripheral wall thereof. A swirl flow of the internal atmosphere gas is formed.

That is, the fan casing 24, the radial fan 29, the bearing balls 36, and the fan drive motor 3 described above.
8, the pinion 40, etc., constitute the swirl flow forming means of the present invention.

In the present invention, the radial fan 29 does not have a component for flowing the atmospheric gas in the vertical direction of the furnace, that is, the rotation of the radial fan 29 causes the atmospheric gas to move along the longitudinal direction of the core tube 13. In order not to tilt, each blade 30 is set parallel to the longitudinal direction of the core tube 13 without inclining along the circumferential direction.

Further, in the present embodiment, the inert gas supply pipe 41 is connected to the side wall portion 42 of the fan casing 24 in order to prevent the material constituting the core tube 13 and the like from being oxidized.
An inert gas such as helium or nitrogen is supplied into the core tube 13 from an inert gas supply source (not shown) through the inert gas supply pipe 41. in this case,
In order to prevent the swirl flow formed by the radial fan 29 from being disturbed by the supply of the inert gas from the inert gas supply pipe 41, the fan casing 24 is provided with a fan along the swirl flow of the atmospheric gas. It is connected in the tangential direction of the casing 24.

Here, using the above-described optical fiber drawing furnace, a radial fan 29 having an outer diameter of 140 mm and an inner diameter of 100 mm is used with respect to a core tube having an inner diameter of 100 mm, and is driven and rotated at a rate of 180 rpm. At the same time, the inert gas supply pipe 4 is adjusted so that the nitrogen gas as the inert gas is converted into the standard state of 0 ° C. and 1 atm at a rate of 10 liters per minute.
1 was supplied into the upper chamber 22 and the optical fiber preform 14 having a diameter of 80 mm was drawn into the optical fiber 15 having a diameter of 125 μm. The peripheral velocity of the swirling flow of the atmospheric gas in the inner peripheral wall of the upper chamber 22 was measured. Is 0.94 m / min, and the convection phenomenon of the atmospheric gas in the upper chamber 22 does not occur, so that the optical fiber 15 could be drawn with an accuracy of 125 ± 0.1 μm.

On the other hand, as a result of drawing the optical fiber 15 under the same conditions as described above with the rotation of the radial fan 29 stopped, it was possible to draw with an accuracy of 125 ± 0.1 μm at the initial stage of the drawing work. However, it was found that the accuracy gradually began to decrease with the consumption of the optical fiber preform 14 from the middle of the process, and became 125 ± 0.5 μm just before the end of the drawing work.

In the above-mentioned embodiment, the radial fan 29 is provided with the external gear 37 so that the radial fan 29 is driven and rotated by the pinion 40. However, the cylindrical drive shaft is mounted coaxially with the support rod 17, The radial fan 29 may be rotated by externally driving this drive shaft.

Further, although the radial fan 29 is rotatably held in the fan casing 24 in this embodiment, the radial fan 29 can be moved up and down along the longitudinal direction of the core tube 13 if necessary. Is. In this case, the swirl flow of the atmospheric gas is formed at the intermediate position between the upper end of the upper chamber 22 and the upper end of the optical fiber preform 14 at a descending speed that is almost half the descending speed of the optical fiber preform 14. It is effective to lower the radial fan 29.

[0028]

According to the present invention, the swirling flow forming means forms the swirling flow of the atmospheric gas along the inner peripheral wall of the upper chamber, so that the convection phenomenon of the atmospheric gas in the upper chamber is suppressed. As a result, it is possible to stably manufacture a good optical fiber with a small wire diameter fluctuation. In particular, when the swirling flow of the atmospheric gas is formed in the intermediate portion between the upper end of the upper chamber and the upper end of the optical fiber preform, the convection phenomenon of the atmospheric gas can be efficiently suppressed.

Further, as a result of suppressing the convection phenomenon of the atmospheric gas in the upper chamber, it is sufficient to supply the inert gas in an amount necessary to maintain the non-oxidizing atmosphere in the furnace, which is more than the conventional case. The consumption of inert gas can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic structure of an embodiment of an optical fiber drawing furnace capable of realizing an optical fiber drawing method according to the present invention.

FIG. 2 is an enlarged view of an arrow II portion in FIG.

FIG. 3 is a sectional view taken along the line III-III in FIG.

[Explanation of symbols]

 11 Heat Insulation Material 12 Furnace Body 13 Core Tube 14 Optical Fiber Base Material 15 Optical Fiber 16 Carbon Heater 17 Support Rod 18 Lower Chamber 19 Extension Tube 20 Opening 21 Seal Plate 22 Upper Chamber 23 Base Material Storage Tube 24 Fan Casing 25 Top Plate Section 26 Shuttering 27, 28 Opening 29 Radial fan 30 Blade 31 Upper plate 32 Lower plate 33, 34 Bearing groove 35 Bottom plate part 36 Bearing ball 37 External gear 38 Fan drive motor 39 Spindle 40 Pinion 41 Inert gas supply pipe 42 Side wall part

Claims (8)

[Claims] 1. A furnace core tube to which a base material for an optical fiber is supplied, a heater surrounding the furnace core tube, an upper end of the furnace core tube to accommodate the base material for the optical fiber, and the base material for the optical fiber. Using an optical fiber drawing furnace having an upper chamber through which a supporting rod that supports the optical fiber drawing method, wherein a lower end of the optical fiber preform is heated and melted to draw an optical fiber, An optical fiber drawing method, characterized in that a swirling flow of an atmospheric gas is formed along an inner peripheral wall of an upper chamber. 2. The optical fiber drawing method according to claim 1, wherein the swirling flow of the atmospheric gas is formed at an upper end portion of the upper chamber. 3. The optical fiber drawing method according to claim 1, wherein the swirl flow of the atmospheric gas is formed at an intermediate portion between an upper end of the upper chamber and an upper end of the optical fiber preform. . 4. The inert gas is supplied into the furnace along the swirl flow of the atmospheric gas from the upper end of the upper chamber, according to any one of claims 1 to 3. Optical fiber drawing method. 5. A furnace core tube to which the optical fiber preform is supplied, a heater surrounding the furnace core tube, an upper end of the furnace core tube connected to accommodate the optical fiber preform, and the optical fiber preform. In an optical fiber drawing furnace having an upper chamber through which a supporting rod for supporting the gas flows, a swirl flow forming means for forming a swirl flow of an atmospheric gas along an inner peripheral wall of the upper chamber is provided. Optical fiber drawing furnace. 6. The optical fiber drawing furnace according to claim 5, wherein the swirl flow forming means is provided so that a swirl flow of the atmospheric gas is formed at an upper end portion of the upper chamber. 7. The swirl flow forming means is provided with an elevating means so that the swirl flow of the atmospheric gas is formed at an intermediate portion between an upper end of the upper chamber and an upper end of the optical fiber preform. The optical fiber drawing furnace according to claim 5, wherein: 8. The swirl flow forming means includes an annular radial fan that rotatably surrounds the periphery of the support rod, and a driving means that drives and rotates the radial fan. The optical fiber drawing furnace according to any one of claims 5 to 7.