JP2013203622A - Drawing furnace and drawing method for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drawing apparatus and a drawing method for an optical fiber, effective for suppressing crossing of a downflow gas stream and upper-flow gas stream at a lower end of a constricted part of a furnace core tube and preventing deposition of soot in an inner diameter direction.SOLUTION: There is provided a drawing apparatus for optical fibers provided with a furnace core tube 13 for inserting a glass preform 11 for optical fiber, a lower extension tube 17 provided under the furnace core tube and having a shutter mechanism 19 at a lower end, and a furnace case 14 housing a heater 15 to heat the glass preform for optical fiber from outside. Optical fiber is drawn by passing an inert gas through the furnace core tube downward from the top. The lower extension tube 17 has an inner diameter larger than the furnace core tube, and a gas stream reversing member 20 composed of a tubular body 20b having a diameter nearly equal to the diameter of the furnace core tube and protruding downward from the lower part of the furnace core tube is placed between the furnace core tube 13 and the lower extension tube 17 to again reverse the gas stream from the lower part.

Description

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

  Drawing of an optical fiber by a drawing furnace is performed by heating and melting a glass preform for optical fiber (hereinafter referred to as a glass preform) with a heater. Since the temperature inside the drawing furnace is about 2200 ° C., which is extremely high, carbon is usually used as the material for the furnace core tube and the like surrounding the glass base material. In an oxygen-containing atmosphere, it is oxidized and consumed. 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 or the like sent into the core tube flows from the top to the bottom of the core tube, and is released to the outside from 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. It is necessary to flow a lot of inert gas etc. to suppress the intrusion of outside air into the furnace core tube, but the inert gas etc. used for the drawing furnace affects the manufacturing cost, so the use of it should be suppressed as much as possible. It is requested.

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. Discloses that a cylindrical lower extension pipe (also referred to as 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 order to lower the temperature to a certain extent and to obtain a cured state.
Further, in Patent Document 2, the shape of the core tube is reduced in a taper shape so as to follow the softened shape of the lower end of the glass base material, and the gas flow at the lower end portion of the glass base material is stabilized. In addition, it is disclosed that a thin base is provided at the fiber outlet.

Japanese Patent No. 2778783 JP-A-8-91862

As a method of suppressing the use of inert gas used in the drawing furnace, as disclosed in Patent Documents 1 and 2, the fiber outlet of the lower extension pipe is narrowed to suppress the outflow of gas. Is valid. It is also effective to provide a reduced diameter portion in order to stabilize the flow of gas.
However, the inert gas that flows downward becomes a gas flow (traction flow) accelerated by the linear velocity of the optical fiber, and most of it flows out of the furnace together with the optical fiber, but a part is the shutter exit part. The gas flow rebounds and flows upward along the inner wall of the lower extension pipe (upper flow). Since the gas flow of the upper flow may have an adverse effect such as reaching the reduced diameter portion of the core tube, as one means for suppressing the gas flow of the upper flow from directly entering the core tube, A configuration in which the inner diameter of the lower extension pipe is enlarged from the reduced diameter part is conceivable.

However, when the lower extension pipe is larger than the core tube, the gas flow of the upper flow hits the upper wall surface to which the lower extension pipe is attached and intersects the main flow downflow gas flow flowing downward from the reduced diameter portion. Hit as you do.
As described above, when the diameter of the lower extension pipe is larger than that of the core tube, and the main downflow gas flow intersects the gas flow by the upper flow, the soot is increased in the inner diameter direction around the lower end portion of the core tube. May accumulate and stick out. In this case, when the soot deposited on the glass fiber comes into contact with the glass fiber, the strength of the glass fiber is lowered, and the frequency of screening disconnection is increased.

  The present invention has been made in view of the above-described circumstances, and suppresses the crossing of the downflow gas flow and the upper flow gas flow at the lower end of the core tube diameter-reduced portion, so that soot accumulates in the inner diameter direction. Therefore, an object of the present invention is to provide an optical fiber drawing device and a drawing method in which the strength of the glass fiber does not decrease.

An optical fiber drawing furnace 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, a lower extension tube having a shutter mechanism at the lower end thereof, and an optical fiber. And an optical fiber drawing furnace and method for drawing an inert gas in a furnace core tube from the top to the bottom. The lower extension tube has an inner diameter larger than that of the core tube, and is formed between the core tube and the lower extension tube from a tubular body having a diameter substantially the same as the core tube and projecting downward from the lower portion of the core tube. The gas flow reversing member for reversing the gas flow from below is provided.
In addition, it is preferable that the protrusion length below the tubular body of a gas flow inversion member is 40 mm-60 mm.

  According to the present invention, the gas flow of the upper flow along the inner wall of the lower extension pipe is reversed downward by the gas flow reversal member, and the intersection with the gas flow of the down flow flowing downward from the core tube is avoided. As a result, accumulation of soot can be suppressed in the inner diameter direction, soot can be prevented from coming into contact with or attached to the glass fiber, and the frequency of disconnection in optical fiber screening can be reduced.

It is a figure explaining an example of the drawing furnace for optical fibers by this invention. It is a figure explaining a prior art example.

  An outline of the drawing furnace for optical fibers of the present invention and the prior art 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), 12 is a glass fiber, 13 is a core tube, 13a is a reduced diameter portion of the core tube, 14 is a furnace housing, 14a is a lower wall, 14b is a central opening, 15 is a heater, 16 is a heat insulating material, 17 is a lower extension tube, 18 is a core tube receiving member, 19 is a shutter mechanism, 19a fiber outlet, 19b is a shutter plate, and 20 is a gas. A flow reversal member, 20a is a horizontal wall, 20b is a tubular body, and 21 is a gap.

  As shown in the drawing, the optical fiber is drawn so that the lower part of the glass base material 11 supported by suspension is heated, and the glass fiber 12 is melted and dripped from the melted lower end portion so as to have a predetermined outer diameter. Done. 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 a 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 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 / deterioration of the furnace core tube 13, an inert gas such as a rare gas such as argon gas or helium gas or a nitrogen gas is introduced into the furnace core tube 13. The inert gas or the like passes through the gap between the glass base material 11 and the core tube 13, and most of the inert gas is released to the outside through the lower extension tube 17 from below the core tube 13.

  The core tube 13 is provided with a reduced diameter portion 13a having a Y-shaped cross section so as to follow the melting shape of the lower end portion of the glass base material at the lower portion, thereby stabilizing the flow of inert gas and the like downward. Although it is possible to block the radiated heat and increase the heating efficiency of the heater 15, a structure without the reduced diameter portion 13a may be used. The core tube 13 is supported in such a manner that it is placed on the lower wall 14a of the furnace casing 14 via a core tube receiving member 18 made of a heat-resistant material such as quartz or carbon. The central opening 14b of the lower wall 14a is formed with substantially the same diameter as the inner diameter of the reduced diameter portion 13a.

  The lower extension pipe 17 has a function of suppressing rapid fluctuation of the glass fiber 12 that has been heated and softened, and at the same time, cooling and hardening to some extent to suppress fluctuations in the outer diameter. Further, the inner diameter of the lower extension pipe 17 is made larger than the inner diameter of the reduced diameter portion 13a of the core tube, and the upper end thereof is attached to the lower wall 14a of the furnace casing 14 so as to be detachable. A shutter mechanism 19 is attached to the lower end of the lower extension pipe 17. The shutter mechanism 19 is formed, for example, by a pair of openable and closable shutter plates 19b having a fiber outlet port 19a having a reduced diameter as shown in Patent Document 1. In addition to this, as shown in Patent Document 2, a thin base may be provided at the fiber outlet.

  In the optical fiber drawing furnace 10 described above, an inert gas or the like is introduced into the furnace core tube 13 from above, and the gas passes between the glass base material 11 and the reduced diameter portion 13a below the lower extension tube 17. The flow is pulled by the high speed drawing of the glass fiber 12 to become a downflow gas flow Q1. A part of the down flow gas flow Q1 is discharged to the outside together with the glass fiber 12 from the fiber outlet 19a of the shutter mechanism 19. However, a part of the downflow hits the shutter plate 19b and rebounds along the inner wall of the lower extension pipe 17. Thus, the upper flow gas flow Q2 flows upward.

In order to prevent the gas flow Q2 of the upper flow from entering the reduced diameter portion 13a of the core tube 13 and affecting the gas flow in the core tube, the inner diameter of the lower extension tube 17 is reduced. Larger than the inner diameter.
In this case, as shown in the conventional example of FIG. 2, the gas flow Q2 of the upper flow hits the wall surface near the central opening 14b of the lower wall 14a of the furnace housing to which the lower extension pipe 17 is attached, Become.

The gas flow Q2 of the upper flow whose flow is changed in the inner diameter direction strikes from the lateral direction so as to intersect the gas flow Q1 of the down flow passing through the center. As the gas flows Q1 and Q2 intersect, soot S (SiC, C, SiO _2, etc.) generated in the core tube is deposited around the lower end of the reduced diameter portion 13a and protrudes in the inner diameter direction. There is. The soot S deposited in the inner diameter direction is likely to contact or adhere to the glass fiber 12 immediately after drawing, which contributes to the deterioration of the optical fiber characteristics such as a decrease in fiber strength and an increase in the frequency of screening disconnection. There is a fear. The periphery of the lower end portion of the reduced diameter portion 13a is a region including the inner diameter surface of the core tube receiving member 18 and the central opening 14b of the lower wall 14a of the furnace casing.

In the present invention, as shown in FIG. 1, a gas flow reversal member 20 is disposed between the lower end of the core tube 13 and the upper end of the lower extension tube 17 so that the gas flow Q2 of the upper flow passes through the center. It is characterized by not hitting the gas flow Q1.
The gas flow reversing member 20 is formed of a heat-resistant material such as quartz or carbon, and has a diameter substantially the same as the inner diameter of the core tube 13 (the reduced diameter portion 13a when there is a reduced diameter portion). It consists of the tubular body 20b which protrudes into. The gas flow reversing member 20 is provided with an annular horizontal wall 20a on the upper portion of the tubular body 20b. For example, the gas flow reversing member 20 includes a horizontal wall 20a and a mounting flange at the upper end of the lower extension pipe 17 and a furnace. It is good also as installing in the form with easy attachment or detachment so that it may support between the lower walls 14a of a housing | casing.

  Further, the gas flow reversing member 20 is supported between the lower extension pipe 17 and the lower wall 14a of the furnace casing as shown in FIG. You may make it support so that the horizontal wall 20a may be pinched | interposed between the member 18 and the lower end of the core tube 13. As shown in FIG. In addition, the horizontal core 20a may be supported between the core tube receiving member 18 and the lower wall 14a of the furnace casing 14 so as to be supported.

  As described above, the tubular body 20b of the gas flow reversing member 20 protrudes downward in a state of being installed between the core tube 13 and the lower extension tube 17, and the core tube 13 (when there is a reduced diameter portion) It is formed to be approximately the same as the inner diameter of the reduced diameter portion 13a). Further, an annular gap 21 is formed between the outer surface of the tubular body 20b and the inner surface of the lower extension pipe 17 so that the upper flow gas flow Q2 flows, and the length of the tubular body 20b for this purpose is as follows. The thickness is preferably about 40 mm to 60 mm.

  In the drawing furnace configured as described above, the glass fiber 12 to be drawn moves at high speed in the furnace core tube 13 and the lower extension tube 17 at a predetermined drawing speed. At this time, the glass fiber 12 is drawn out while discharging a downflow gas flow Q1 pulled by an inert gas or the like introduced into the core tube from the fiber outlet 19a of the shutter mechanism 19 at the lower end of the lower extension pipe 17. .

A part of the downflow gas flow Q1 pulled by the glass fiber 12 hits the shutter plate 19b of the shutter mechanism 19 and rebounds to become an upper flow gas flow Q2 flowing upward along the inner wall of the lower extension pipe 17. This gas flow Q2 is reversed by an annular gap 21 formed by the horizontal wall 20a of the gas flow reversing member 20 and the tubular body 20b, the flow is changed downward, so that it does not intersect with the downflow gas flow Q1. To be. Thereby, it is possible to prevent soot from being deposited so as to protrude in the inner diameter direction in the vicinity of the lower end portion of the reduced diameter portion 13a of the core tube 13, and it is possible to prevent the strength of the glass fiber from being lowered.
In the optical fiber drawing furnace in which the gas flow reversing member is arranged as described above, when the drawing of the optical fiber of 1 million km is performed, the disconnection frequency in screening is approximately compared with the case where the gas flow reversing member 20 is not provided. Decrease by 20%.

DESCRIPTION OF SYMBOLS 10 ... Optical fiber drawing furnace, 11 ... Glass base material (glass base material) for optical fibers, 12 ... Glass fiber, 13 ... Furnace core tube, 13a ... Reduced diameter part, 14 ... Furnace housing, 14a ... Lower wall, 14b ... Center opening, 15 ... Heater, 16 ... Heat insulating material, 17 ... Lower extension pipe, 18 ... Core tube receiving member, 19 ... Shutter mechanism, 19a ... Fiber outlet, 19b ... Shutter plate, 20 ... Gas flow reversing member, 20a ... horizontal wall, 20b ... tubular body, 21 ... gap.

Claims (3)

A furnace containing a furnace tube into which a glass preform for an optical fiber is inserted, a lower extension tube having a shutter mechanism at the lower end thereof and a heater for heating the glass preform from the outside. A drawing furnace of an optical fiber comprising a housing and flowing an inert gas from above to below in the furnace core tube,
The lower extension tube has an inner diameter larger than the core tube, and is a tube projecting downward from the lower portion of the core tube between the core tube and the lower extension tube and having substantially the same diameter as the core tube. An optical fiber drawing furnace comprising a body and a gas flow reversing member for reversing a gas flow from below.   The drawing furnace for an optical fiber according to claim 1, wherein a length of the gas flow reversing member protruding downward from the tubular body is 40 mm to 60 mm. A furnace containing a furnace tube into which a glass preform for an optical fiber is inserted, a lower extension tube having a shutter mechanism at the lower end thereof and a heater for heating the glass preform from the outside. A drawing furnace provided with a housing, and a drawing method of an optical fiber for flowing an inert gas downward from above in the furnace core tube,
The lower extension tube has an inner diameter larger than the core tube, and is a tube projecting downward from the lower portion of the core tube between the core tube and the lower extension tube and having substantially the same diameter as the core tube. An optical fiber drawing method characterized by disposing a gas flow reversal member comprising a body and reversing a gas flow from below again.

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