JPH08277138A - Production of glass base material for optical fiber - Google Patents

Abstract

PURPOSE: To provide a method for producing a glass base material for optical fiber glass facilitating the operation for hermetically closing and the securing to maintain the hermetically closed state for conducting a melt-adhesion process under a reduced pressure in dealing with the tendency of enlarging the diameter of glass pipe without using a glass lath. In addition, to facilitate the operation for the hermetically closing and the securing to maintain the hermetically closed state while enabling the changing and adjusting of a C/C, the effective utilization of the raw material and the correction of its eccentricity. CONSTITUTION: This method for producing a glass base material for an optical fiber comprises forming a sealed bottom 1a by sealing the opening of the one end side of a glass pipe 1 in advance in a glass pipe sealing process, then piercing the glass pipe through a heating furnace having a ring shaped heater in a inserting arrangement process and vertically supporting it by grasping the upper end with the first chuck 3 and the rod like end of the lower end 1b with the third chuck 5, inserting a glass rod 2 from the opening 1c at the upper end until the sealed bottom and grasping a glass rod part 2a with the second chuck 4, hermetically closing the part between the first and second chucks by covering with a below like blocking member 6 in a hermetically closing process, heating by lowering ascending/ discending means 9, 10, 11 while keeping the inside under a reduced pressure for melt-adhering both of these gradually in a melt-adhesion process. At this stage, each of the transferring speeds is changed and adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a glass preform for optical fibers by applying a rod-in-tube method in which a glass rod for core is covered with a glass pipe for clad and both are welded and integrated.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing a glass preform for optical fibers by a rod-in-tube method, a method using a glass lathe is generally known (see, for example, Japanese Patent Publication No. 1-34938). This is because the clad glass pipe is supported horizontally on the glass lathe, the core glass rod is inserted and placed in the glass lathe, and then the two are sequentially welded by rotating relative to the heating source while rotating around the axis. It is made to be integrated. Then, in this case, a method as shown in FIG. 3 is adopted in order to accelerate the shrinkage of the glass pipe during the welding by performing the above-mentioned welding under a pressure lower than the atmospheric pressure. That is, the outer peripheral surface of the glass pipe 51 on the left end side in the longitudinal direction is heated at a few places to form inwardly projecting portions (partial stop portions) 52, 52 partially in the circumferential direction. After supporting the left end of the glass rod 53 by the stoppers 52, 52 in a state of floating at the axial center position of the glass pipe 51,
While rotating the glass pipe 51 and the glass rod 53, only the right end portion is heated and the inner peripheral surface of the glass pipe 51 at the right end portion is welded to the outer peripheral surface of the glass rod 53, so that the glass pipe 51 and the glass rod 53 The right end side of the space therebetween is sealed (see 55 in the figure). Then, the glass pipe 51 is forcibly sucked from the left end side to bring the space 54 between the glass pipe 51 and the glass rod 53 into a state in which the pressure is lower than atmospheric pressure, and while maintaining this, the heating source 56.
And the glass pipe 51 and the glass rod 53 are relatively moved in the longitudinal direction. Reference numeral 57 is a supporting auxiliary glass pipe welded to the other end of the glass pipe 51, and 58 is a chuck for supporting the glass pipe 51 or the glass rod 53.

On the other hand, when the glass pipe has a large diameter (thickness) in order to increase the size of the glass base material, there is a possibility that the welding in the above-mentioned horizontal supporting state causes a bending due to an increase in its own weight. On the other hand, since the heating source 56 in the glass lathe is insufficient in heat power and cannot perform sufficient welding integration, an electric resistance furnace having a ring-shaped heater is used as a heating source, and a glass pipe or the like is used for this. A method has also been proposed in which a glass pipe having a relatively large diameter is subjected to a welding process by supporting it vertically and heating it while relatively moving it upward in a non-rotating state (for example, see Japanese Patent Laid-Open No. 4-42831).

[0004]

However, in the case of the above proposed method, thin auxiliary glass pipes are respectively joined to the upper and lower openings of a relatively thick glass pipe and extended in the vertical direction to obtain the upper auxiliary glass. Since a cap-shaped jig is fitted on both the upper end of the pipe and the lower end of the lower auxiliary glass pipe to hermetically close the inside of the glass pipe, a welding process under reduced pressure is possible. However, this closing work will be troublesome. In addition, since both the upper end of the upper auxiliary glass pipe and the lower end of the lower auxiliary glass pipe are vertically held by chucks, the glass pipe is welded by the ring heater in the welding process. When heating from one end to the other end of the glass pipe, the auxiliary glass pipe near the end of the glass pipe also melts, causing shrinkage, displacement, etc. This heat effect extends to the end and a predetermined vertical support state Not only cannot be maintained, but cracks may occur at the boundary between the end of the glass pipe and the end of the auxiliary glass pipe. In addition, the heat effect may impair the airtightness between the end portion of the auxiliary glass pipe and the cap-shaped jig, making it impossible to maintain a reliable sealed state. These fears tend to increase as the diameter of the glass pipe increases.

Further, in supporting the glass rod, since the lower end of the glass rod is only supported together by the cap-shaped jig attached to the lower end of the lower auxiliary glass pipe, the glass rod is supported with respect to the auxiliary glass pipe. Since the relative position is fixed, eccentricity may occur due to variations in the shape and dimensions of the glass rod, and it becomes impossible or extremely difficult to correct the eccentricity.
In this case, it is conceivable that the glass rod is supported by a chuck provided separately from the glass pipe, but in that case, the sealing work by the cap jig cannot be performed.

Further, when the glass pipes and glass rods have variations in shape and size, particularly in length, it is desired to effectively utilize a portion in the longest possible range according to the variations to efficiently form the glass preform. There is a request.
For this purpose, it is necessary to make the glass pipe chuck and the separately provided glass rod chuck movable independently of each other. Then, as in the above case, the sealing work by the cap jig is performed. Cannot be done.

On the other hand, in the method proposed above, since the glass pipe and the glass rod are simply moved upward with respect to the ring-shaped heater, the outer diameter of the cladding relative to the outer diameter of the clad with respect to the outer diameter of the core of the glass base material after welding. The ratio (C / C) depends on the shape and dimensions of the glass pipe and the glass rod as forming materials, and when the shape and dimensions of the glass pipe and the glass rod vary, the C of the glass base material
In addition to the fact that / C also varies, there is the inconvenience that C / C cannot be changed and adjusted to a predetermined constant value even if there is no variation in the above-mentioned shape dimensions.

The present invention has been made in view of the above circumstances, and an object of the present invention is to perform a welding process under a reduced pressure when coping with an increase in diameter of a glass pipe without using a glass lathe. It is to ensure the easy and reliable sealing work for performing the above, and to maintain the sealed state. In addition, while making it possible to change and adjust C / C, effectively use the material according to the dimensional variation of the material, and correct the eccentricity, it is possible to perform the above-mentioned easy and reliable sealing work and maintenance of the sealed state. is there.

[0009]

In order to achieve the above object, the invention according to claim 1 comprises the following glass pipe sealing step, insertion placement step, sealing step, and welding step. To do. That is, in the glass pipe sealing step, the opening on one end side in the longitudinal direction of the cladding glass pipe is sealed in advance to form a sealing bottom. Next, in the inserting and arranging step, the glass pipe after the glass pipe sealing step is pierced into a heating furnace having a ring-shaped heater, and at least the other end in the longitudinal direction is held by the first supporting means to vertically move the glass pipe. After being supported by the second end, the core glass rod is inserted from the other end side opening to the sealing bottom in the glass pipe, and the glass rod portion protruding from the other end side opening is grasped.
The supporting means supports the glass rod at the axial center position of the glass pipe. Then, in the sealing step, the first
By covering the space between the supporting means and the second supporting means with a cylindrical shielding member, the space between the glass pipe and the glass rod from the opening on the other end side to the sealing bottom becomes a closed space, and in the welding step. While maintaining the closed space at a pressure lower than atmospheric pressure, the glass rod and the glass pipe are heated while being relatively moved from the one end side to the other end side with respect to the ring-shaped heater, and both are sequentially heated. It is configured to be fused and integrated.

According to a second aspect of the present invention, in the welding step of the first aspect of the invention, the first supporting means and the second supporting means are vertically moved by the elevating means with respect to the ring-shaped heater fixedly positioned. It is configured such that they are moved at a constant speed in synchronization with each other.

According to a third aspect of the invention, in the second aspect of the invention, one end side of the glass pipe is supported by a third supporting means connected to an independent elevating means, and the third supporting means is vertically arranged. When performing the welding process by moving the first supporting means and the second supporting means to the same side, the moving speed of the third supporting means is made relatively faster than the moving speed of the first and second supporting means, The glass pipe and the glass rod between the one end side and the other end side are drawn.

According to a fourth aspect of the present invention, in the third aspect of the invention, the first supporting means and the second supporting means can be moved vertically independently of each other by individual elevating means. Then, in the sealing step, a bellows-shaped shielding member formed to be expandable / contractible in the vertical direction is used to shield the first supporting means and the second supporting means so that the relative distance between them in the vertical direction can be changed, and the welding is performed. In the step, after welding the one end side of the glass pipe and the glass rod, the first supporting means,
The configuration is such that the relative movement speed with respect to the second support means is changed and adjusted.

According to a fifth aspect of the present invention, in the first aspect of the invention, the first supporting means and the second supporting means are arranged such that the relative distance between them in the vertical direction can be changed, and the inserting and arranging step is performed. The glass pipe and the glass rod are connected to the supporting position of the glass pipe by the first supporting means and the second pipe.
The supporting position of the glass rod by the supporting means is supported so as to be relatively changeable in the vertical direction. In the sealing step, the bellows-shaped shielding member formed so as to be capable of expanding and contracting in the vertical direction is used for shielding.

The invention according to claim 6 is the same as claim 1.
In the invention described above, a relative position between the second supporting means and the elevating means in two directions orthogonal to each other on a horizontal plane between the second supporting means and the elevating means for moving the second supporting means in the vertical direction. A horizontal position changing means for changing the position is interposed. Then, in the inserting and arranging step, the relative position of the second supporting means and the elevating means is changed by the horizontal plane position changing means so that the glass rod is positioned at the axis of the glass pipe, and the horizontal direction is set in the sealing step. The configuration is such that a deformable bellows-shaped shielding member is used for shielding.

[0015]

According to the above-mentioned structure, according to the first aspect of the present invention,
The opening on one end side of the glass pipe is sealed in advance by the glass pipe sealing step to form a sealing bottom before the glass rod insertion and placement step, so in the subsequent sealing step,
In addition to the labor saving of the sealing work on the one end side of the glass pipe, the sealed state can be ensured as compared with the conventional case in which the glass pipe is covered with a cap-shaped jig. Further, in this case, since the glass pipe is sealed before the glass rod is inserted, the sealing work cannot be performed when the glass rod is inserted and arranged in the glass pipe by the glass lathe (see FIG. 3). It becomes possible to clean the fine particles of quartz glass that occur during the difficult sealing work, and it is possible to prevent the generation of residual bubbles at the interface between the glass pipe and the glass rod due to the adhesion of the fine particles.

Further, since the glass pipe and the glass rod are supported by the first and second separate supporting means in the inserting and arranging step, the glass rod is fixed by the cap-shaped jig covering the auxiliary glass pipe. As compared with the conventional case of supporting, the thermal deformation of the glass pipe does not affect the supporting state of the glass rod, and the vertical supporting state is surely maintained even if the diameter of the glass pipe is increased.

Further, in the sealing step, the other end side of the glass pipe is sealed by covering both of the first and second supporting means with a shielding member, and the glass pipe and the glass rod after the inserting and arranging step are sealed. A space is provided, and together with the formation of the sealing bottom by the glass pipe sealing step, the sealing work is facilitated and the sealed state is maintained regardless of the size of the glass pipe diameter. Then, the glass pipe is brought into a depressurized state by sucking it from a part of the shielding member or the like, so that the shrinkage of the glass pipe in the welding step is promoted.

According to the second aspect of the invention, in addition to the operation of the first aspect of the invention, the welding step is performed by moving the glass pipe and the glass rod with respect to the ring-shaped heater whose position is fixed. On the contrary, as compared with the case where the ring-shaped heater is moved, relative movement of the glass pipe and the glass rod and the ring-shaped heater becomes easier.
Further, at this time, since the first and second supporting means are synchronized and are moved at a constant speed, even if the glass pipe and the glass rod are individually supported, the welding process by the relative movement to the heater is surely performed. .

According to the third aspect of the invention, in addition to the action of the second aspect of the invention, third supporting means for supporting one end side of the glass pipe, first supporting means for supporting the other end side, and the glass are provided. When the welding process is performed by moving the second supporting means that supports the rod in the same vertical direction, the moving speed of the third supporting means is set relatively higher than the moving speeds of the first and second supporting means. Therefore, the glass pipe and the glass rod are stretched, and a glass base material having a predetermined C / C is formed from the glass pipe and the glass rod as materials by setting the moving speeds of the both.

According to the invention described in claim 4, in addition to the operation according to the invention described in claim 3, after the welding of the one end side of the glass pipe and the glass rod, the relative moving speed of the first supporting means and the second supporting means. Since the C / C of the glass base material after welding is changed, the moving speeds of the other end side of the glass pipe and the other end side of the glass rod are different because C is changed and adjusted. That is, when the moving speed of the first supporting means is relatively slowed down, the cladding portion of the glass base material becomes thick, and conversely, when the moving speed of the second supporting means is relatively slowed down, the diameter of the core portion becomes large. Therefore, even if the glass pipe or the glass rod as the material has a dimensional variation, the glass base material having a predetermined C / C can be reliably formed by correcting the dimensional variation.
Further, at this time, since the bellows-shaped shielding member seals the space between the first and second supporting means, the relative vertical movement between the first and second supporting means is adjusted by changing and adjusting the relative moving speed. Even if the interval changes, the shielding member expands and contracts according to the change, and the depressurized state can be reliably maintained. Therefore, both fine correction of C / C and reliable maintenance of the reduced pressure state can be achieved at the same time.

According to the invention of claim 5, in addition to the operation of the invention of claim 1, the glass pipe projecting from the other end side of the glass pipe by the first and second supporting means. Since both supporting positions of the rod portion and the rod portion are supported so that they can be changed in the vertical direction, even if the glass pipe and / or the glass rod as a material have variations in length, By changing the supporting positions of the first and / or second supporting means, it becomes possible to effectively use the longest possible range of the material in forming the glass preform. In addition, at this time, even if the vertical relative distance between the first and second supporting means is changed, since the both are sealed by the bellows-like shielding member, the other end of the glass pipe is reliably sealed. In addition, the hermetically sealed state is reliably maintained. Therefore, it is possible to achieve both effective use of the material according to variations in dimensions and reliable maintenance of the reduced pressure state.

Further, in the invention described in claim 6, in addition to the operation according to the invention described in claim 1, in the inserting and arranging step, the relative position between the second supporting means and the elevating means is changed by the horizontal plane position changing means to the horizontal plane. The glass rod is positioned at the axis of the glass pipe by changing the position in the two directions orthogonal to each other. Moreover, even if the relative position of the second support means is changed, the second support means and the first support means are sealed by the bellows-shaped shield member, so that the shield member is in the horizontal direction. The glass pipe is deformed in the horizontal direction in accordance with the change of the relative position of the glass pipe, and the other end side of the glass pipe is surely sealed, and the sealed state is surely maintained. Therefore, it is possible to reliably prevent the occurrence of eccentricity due to the dimensional variation of the material and to reliably maintain the depressurized state.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an apparatus for manufacturing a glass preform for optical fibers for carrying out an embodiment of the present invention, in which 1 is a glass pipe for cladding in which a sealing bottom 1a is formed on the lower end side which is one end side. Reference numeral 2 is a glass rod for core which is coaxially inserted and arranged in the glass pipe 2, 3 is a first chuck as a first supporting means for holding an upper end side which is the other end side of the glass pipe 1, and 4 is the above A second chuck as a second supporting means for holding the upper end side of the glass rod 2, a third chuck 5 for holding the lower end side of the glass pipe, and a first chuck 6
And a cylindrical shielding member that shields between the second chucks, 7 is a ring-shaped heater of an electric furnace as a heating furnace, 8 is a guide rail arranged in the vertical direction, and 9, 10 and 11 are the first and the first It is an elevating means for elevating and lowering the second and third chucks along the guide rail.

The first chuck 3 is a chuck body 3a.
And a donut plate-shaped bracket 3b for supporting the chuck body 3a, and the upper end peripheral edge of the lower cover cylinder 12 is airtightly fixed to the outer peripheral position of the lower surface of the bracket 3b so that the glass pipe 1 It covers the outer peripheral surface of the upper end side. The bracket 3b is connected to the elevating means 9, and the first chuck 3 is vertically moved as the elevating means 9 is moved up and down.

The second chuck 4 is composed of upper and lower two stages of chuck bodies 4a, 4a, and chuck bodies 4a, 4a.
A bracket 4b having a donut plate shape for supporting 4a is provided, and the lower end peripheral edge of the upper cover cylinder 13 is airtightly fixed to the inner peripheral side position of the upper surface of the bracket 4b. The bracket 4b is connected to the elevating means 10 via an XY table 14 as a horizontal plane position changing means, and the second chuck 4 is vertically moved as the elevating means 10 is moved up and down. It has become.
The XY table 14 is arranged such that the relative position of the second chuck 4 to the elevating means 10 is orthogonal to each other on a horizontal plane.
The intermediate plate 14a and the X-direction drive unit 14b and the Y-direction drive unit 14 arranged at the upper and lower positions sandwiching the intermediate plate 14a are to be changed.
and c. Then, these X-direction drive units 14b
The horizontal relative position of the second chuck 4 with respect to the elevating means 10 (that is, the guide rail 8) is adjusted by driving the and Y-direction drive portions 14c, respectively.

Further, the third chuck 5 is provided with a chuck body 5a and a donut plate-shaped bracket 5b which supports the chuck body 5a. Then, the bracket 5b is an XY including the intermediate plate 15a, the X-direction drive unit 15b, and the Y-direction drive unit 15c having the same configuration as described above.
It is connected to the lifting means 11 via the table 15,
The third chuck 5 is driven by the lifting drive of the lifting means 11.
Moves up and down in the vertical direction, while the XY table 15 moves the lifting means 11 (that is, the guide rail 8).
The horizontal relative position of the third chuck 5 with respect to is adjusted. By adjusting the positions of the XY table 15 and the XY table 14, the glass rod 2 is positioned at the axial center position of the glass pipe 1.

Incidentally, the above-mentioned first to third chucks 3, 4,
5 indicates each chuck body 3a based on the guide rail 8,
The closing operation centers of 4a and 5a are set in advance so as to be positioned in the vertical direction.

On the other hand, the shielding member 6 is formed in a bellows shape with a metal material such as stainless alloy, and the upper and lower peripheral edges thereof are the upper surface of the bracket 3b of the first chuck 3 and the bracket 4b of the second chuck 4. It is designed to be airtightly and detachably attached to the lower surface of the. It should be noted that one of the upper and lower peripheral edges of the shielding member 6 is previously attached to one of the first chuck 3 side and the second chuck 4 side, and the other peripheral edge is an open end. A socket member 16 is screwed onto the outer peripheral surface of the lower end of the lower cover tubular body 12, and the inner peripheral surface of the socket member 16 is brought into contact with the outer peripheral surface of the glass pipe 1 to form the socket member. A ring-shaped sealing member 17 made of a heat-resistant resin that hermetically closes the gap between 16 and the glass pipe 1 is screwed. The seal member 17 is cut at one position in the circumferential direction and has an end with a predetermined gap, and the screw member is screwed into the socket member 16 so that the gap is closed and the outer peripheral surface of the glass pipe 1 is closed. It comes into close contact with. The upper cover tube 13 is covered with a lid 13a in an upper end opening in an airtight manner, and a suction means (not shown) is connected to the upper cover cylinder 13. The suction means forcibly exhausts the space between the glass pipe 1 and the glass rod 2. And the space between the shielding member 6 and the glass rod portion 2a protruding upward from the first chuck 3 are set to a depressurized state lower than atmospheric pressure.

Next, a method for producing a glass preform for optical fibers using the production apparatus having the above-described structure will be described. The glass preform is made of a glass pipe and glass rod whose both ends are open. The pipe sealing step, the insertion placement step, the sealing step, and the welding step are performed in this order to manufacture. Hereinafter, each step will be described in detail.

In the glass pipe sealing step, before being set in the manufacturing apparatus, one end side in the longitudinal direction of the glass pipes at both ends is heated to be reduced in diameter to form a solid rod-shaped end portion 1b. . As a result, the glass pipe 1 having one end sealed as the sealing bottom 1a and the other end left as the opening 1c is formed.

In the inserting and arranging step, first, the glass pipe 1 is arranged with the sealing bottom 1a facing downward so that the vicinity of the sealing bottom 1a penetrates the ring-shaped heater 7 of the manufacturing apparatus. The rod-shaped end 1b of the pipe 1 is gripped by the third chuck 5 and the upper end thereof is gripped by the first chuck 3, respectively, to support the glass pipe 1 vertically. At this time, when the glass pipe 1 or the rod-shaped end portion 1b has a variation in dimension, the axis of the glass pipe 1 is vertically adjusted by finely adjusting the horizontal relative position of the third chuck 5 by the XY table 15. Correct so that Next, the upper end of the glass rod 2 is held by the second chuck 4 which is in the upper position by the raising operation of the raising and lowering means 10, and the raising and lowering means 10 is lowered in this grasped state to move the glass rod 2 into the glass pipe 1. Inserted from the top opening 1c of the glass rod 2
The lowering operation is stopped when the lower end of is lowered to a position close to the sealing bottom 1a. Originally, the glass rod 2 is positioned at the axial center position of the glass pipe 1 by this insertion operation. However, when eccentricity occurs due to variations in the dimensions of the glass rod 2 or the like, the XY table 14 is used to move the second chuck. The glass rod 2 is corrected so as to be coaxial with the glass pipe 1 by finely adjusting the relative position of the glass pipe 4 in the horizontal direction. As a result, both are vertically supported with the glass rod 2 inserted and arranged at the axial center position of the glass pipe 1. When the glass pipe 1 is arranged, the seal member 17 is loosely fitted in the glass pipe 1.

In the sealing step, the open end side of the shielding member 6 is airtightly attached to the bracket 3b of the first chuck 3 or the bracket 4b of the second chuck 4 and both brackets 3b of the first and second chucks 3 and 4 are attached. , 4b are shielded and hermetically sealed. Then, the sealing member 17 is screwed into the socket member 16 to seal the gap between the outer peripheral surface of the glass pipe 1 and the lower cover cylinder 12, and the lid 13a is airtightly fitted into the upper end opening of the upper cover cylinder 13. This allows
A space between the inner peripheral surface of the glass pipe 1 whose lower end is sealed by the sealing bottom 1a and the outer peripheral surface of the glass rod 2, and this space, the upper end opening 1c of the glass pipe 1, and the chuck body 3.
The space inside the shielding member 6 and the space inside the lower cover cylinder 12 which communicate with each other through the gap a, and this space and the chuck body 4.
The space inside the upper cover cylinder 13 communicating with the space a is a sealed space.

Then, in the welding step, the closed space is depressurized by driving the suction means and forcibly exhausting. Then, in this state, the ring-shaped heater 7 of the electric furnace is operated to move the glass pipe 1 to approximately 20
While heating to 00 ° C., three lifting means 9, 10, and 11
Are moved downward along the guide rails 8 in synchronization with each other. As a result, the glass pipe 1 is heated from the sealing bottom 1a side to the upper end side, and the glass pipe 1 contracts from the sealing bottom 1a side and is sequentially welded to the glass rod 2 to be collapsed.

At this time, the moving speeds of the two upper lifting means 9 and 10 are set equal to each other, while the moving speed of the lower lifting means 11 is relatively faster than that of the two lifting means 9 and 10. By setting such that, when the glass pipe 1 and the glass rod 2 are collapsed, the lower end side thereof is forcibly advanced and stretched more than the upper end side thereof. Therefore, by adjusting the above-mentioned respective moving speeds, a predetermined C /
A glass base material having C can be manufactured.

Further, during the above-mentioned stretching, after the glass pipe 1 and the glass rod 2 near the sealing bottom 1a are collapsed, both moving speeds of the upper two elevating means 9 and 10 are lowered to the lower side. C / of the collapsed glass base material is set by making them different from each other within the range of the moving speed of the means 11 or less.
C can be different from that based on the glass pipe 1 and glass rod 2 of the original material. That is, by making the elevating means 9 on the glass pipe 1 side relatively slower than the elevating means 10 on the glass rod 2 side, the glass pipe 1 is stretched more and the core outer diameter at C / C becomes relatively large. Conversely, by slowing down the elevating means 10 relatively, the glass rod 2 is stretched more and the outer diameter of the core becomes relatively smaller.

In the manufacturing method having the above structure, the glass rod 2
Prior to the step of inserting and arranging into the glass pipe 1, the one end side of the glass pipe 1 is previously sealed by the glass pipe sealing step to form the sealing bottom 1a. It is possible to save labor in the sealing work on one end side of the glass pipe 1, and to ensure the sealed state as compared with the conventional case where the glass pipe 1 is covered with a cap-shaped jig. If a glass lathe is used (see FIG. 3), the glass pipe 51
The glass rod 53 and the glass rod 53 were integrally set by the sealing portion 55, and cleaning of the inner peripheral surface of the glass pipe 51 or the like was impossible or difficult, whereas in the present embodiment, it was sealed. The glass pipe 1 can be washed in this state,
It is possible to prevent the generation of residual bubbles that accompany the adhesion of fine particles of quartz glass during the sealing operation.

In addition, in the inserting and arranging step, both upper end portions of the glass pipe 1 and the glass rod 2 are attached to the first and second ends.
Since they are individually supported by the chucks 9 and 10, a reliable vertical support state can be obtained regardless of the size of the glass pipe, and the glass rod is covered by the cap-shaped jig that covers the auxiliary glass pipe. It is possible to ensure the maintenance of the vertical support state as compared with the conventional case in which the thermal deformation of the auxiliary glass pipe for supporting the glass rod may affect the support state of the glass rod. Since the lower end of the glass pipe 1 is supported by gripping the solid rod-shaped end 1b by the third chuck 1b, it is different from the conventional case in which the hollow auxiliary glass pipe is gripped and supported. In comparison, the vertically supported state can be reliably maintained without instability in the supported state due to thermal deformation. In addition, both upper ends of the glass pipe 1 and the glass rod 2 are independently supported by the two chucks 9 and 10 and the two elevating means 9 and 10 so that their relative positions in the vertical direction can be changed. Therefore, even when the glass pipe 1 and / or the glass rod 2 has a variation in length, the upper ends of the glass pipe 1 and the glass rod 2 can be gripped according to the variation. Therefore, the longest possible area of the material can be effectively used for manufacturing the glass preform. Further, the horizontal relative position between the second chuck 4 and the elevating means 10 and the horizontal relative position between the third chuck 5 and the elevating means 11 are changed and adjusted by the XY table 14 or 15, respectively. 2 can be reliably positioned at the axial center of the glass pipe 1, and eccentricity due to dimensional variation of materials and the like can be reliably corrected.

Further, since the bellows-shaped shielding member 6 is used for sealing in the sealing step, the vertical relative distance between the first and second chucks 9 and 10 changes depending on the material in the above-described insertion and placement step. Even in such a case, the shielding member 6 expands and contracts, so that the sealing work can be performed easily and reliably.
Also, in the insertion and placement process, the first and second chucks 9, 1
Even if the horizontal relative position of 0 slightly shifts due to the eccentricity correction, the shielding member 6 is deformed in the horizontal direction.
The sealing work can be performed easily and surely. Moreover,
Even when the relative moving speeds of the first and second chucks 9 and 10 are changed in the subsequent welding step, the shielding is performed by following the change in the relative distance between the first and second chucks 9 and 10 due to the change. Since the member 6 expands and contracts, it is possible to reliably maintain the reduced pressure state.

In the welding process, since the first and second chucks 9 and 10 are moved at the same speed in synchronization with each other, even if both upper ends of the glass pipe 1 and the glass rod 2 are individually supported, they are ring-shaped. The welding process by the relative movement in the vertical direction with respect to the heater 7 can be reliably performed. Further, by making the moving speed of the lifting / lowering means 11 of the third chuck 5 faster than the moving speed of both the lifting / lowering means 9 and 10 of the first and second chucks 3 and 4, the C / C corresponding to the dimension of the material can be obtained. The glass base material can be drawn, and further, by making the relative moving speeds of the elevating means 9 and 10 of the first and second chucks 3 and 4 different, C / Corrects minute fluctuations in C to ensure that C /
A glass base material having C can be formed.

In summary, in the case of coping with an increase in diameter without using a glass lathe, the present embodiment is such that the sealing work for performing the welding step under reduced pressure is easy and reliable, and the sealed state is maintained. In addition to the above, it is possible to improve the C / C change and adjust the C / C, effectively use the material according to the dimensional variation of the material, and correct the eccentricity. As a result, it is possible to ensure the reliability and the maintenance of the sealed state.

<Manufacturing test> As a material, an outer diameter of 65 mm,
Glass pipe 1 with a wall thickness of 18.5 mm and a length of 500 mm
And a glass rod 2 having an outer diameter of 18 mm and a length of 500 mm, a glass base material is manufactured by the manufacturing apparatus and the manufacturing method of the above-mentioned embodiment, and the glass base material is drawn into an optical fiber, The transmission loss and eccentricity of the fiber were investigated.

-Manufacturing condition setting- The pressure reduction state in the welding process is 500 mmHg, the heating temperature of the ring-shaped heater 7 is approximately 2000 ° C., and the moving speeds of the two lifting means 9 and 10 on the upper end side (feeding speed to the heater 7) are set. The moving speed of the lower elevating means 11 (take-off speed from the heater 7) was set to 8 mm / min and 16 mm / min, respectively.

-Evaluation of glass base material-Outer diameter 45 mm, length 10 by manufacturing under the above-mentioned condition setting
A glass base material of 00 mm was obtained. The transmission loss of the formed optical fiber is 0.33 dB / km for a wavelength of 1.31 μm and 0.1 for a wavelength of 1.55 μm.
9 dB / km, and both have a reference value of 0.35 dB / k
It was smaller than m and was good. Further, the eccentricity amounts were 0.19 μm and 0.25 μm at both end positions, which were smaller than the reference value of 0.30 μm and were favorable.

<Other Embodiments> The present invention is not limited to the above embodiments, but includes various other modifications. That is, although the shielding member 6 is made of metal in the above-described embodiment, the present invention is not limited to this, and the shielding member may be made of a rubber elastic body, a reinforcing core material or the like as long as it can withstand decompression.

In the above embodiment, the sealing bottom 1a is formed by forming the rod-shaped end portion 1b in the glass pipe sealing step, but the present invention is not limited to this, and as shown in FIG. The glass pipe 21 having a sealed bottom may be formed by welding a relatively thick circular glass bottom plate 21a to one end opening of the glass pipe. In this case,
The circumference of the glass bottom plate 21a may be held by the third chuck 5.

In the above-mentioned embodiment, the sealing bottom 1a of the glass pipe 1 is located at the bottom, but the invention is not limited to this.
You may make it support a glass pipe vertically in the state which is located above. In this case, the manufacturing apparatus of FIG. 1 may be turned upside down and the glass rod 2 may be inserted from the bottom to the top.

In the above embodiment, the first to third chucks 3,
Although the Nos. 4 and 5 are provided, the third chuck 5 and the elevating means 11 may be omitted if the stretching is not performed.

In the above embodiment, two XY tables 1 are used.
The relative position in the horizontal direction is adjusted by 4, 15 but at least the XY table 14 on the glass rod 2 side.
The eccentricity correction can be performed by adjusting only.

In the above embodiment, the upper cover cylinder 13 is provided and forced exhaust is performed from here, but the invention is not limited to this.
Forced exhaust may be performed from a part of the shielding member 6. Also,
The upper cover cylinder 13 may be omitted by forming the bracket 4b of the second chuck 4 into a disk shape instead of a donut shape.

[0051]

As described above, according to the method for producing a glass base material for an optical fiber in the first aspect of the present invention, the opening on one end side of the glass pipe is inserted into the glass before the step of inserting and arranging the glass rod. Since the sealing bottom is formed by pre-sealing in the pipe sealing process, it is impossible or difficult in the conventional case where the sealing work is performed with the glass rod being inserted and arranged in the glass pipe. It is possible to clean the glass pipe, and it is possible to prevent the generation of residual bubbles at the interface between the glass pipe and the glass rod due to the adhesion of fine particles of quartz glass during the sealing operation. Moreover, in the subsequent sealing step, the sealing work for the one end side of the glass pipe can be saved, and the sealed state is ensured as compared with the conventional case in which the glass pipe is covered with a cap jig. Can be achieved.

Further, since the glass pipe and the glass rod are supported by the first and second individual supporting means in the inserting and arranging step, the vertical pipe is surely vertical regardless of the diameter of the glass pipe. In the conventional case where the supporting state of the glass rod can be brought into a supported state, and the thermal deformation of the auxiliary glass pipe that supports the glass rod by the cap-shaped jig covering the auxiliary glass pipe may affect the supporting state of the glass rod. In comparison, it is possible to ensure the maintenance of the vertical support state.

Further, in the sealing step, the space between the first and second supporting means is covered with the shielding member to perform the sealing work. Therefore, the sealing bottom is formed by the glass pipe sealing step. Together, the sealing work can be facilitated and the sealed state can be reliably maintained regardless of the size of the glass pipe.

In the welding step, since the closed space is heated in the depressurized state in the sealing step, it is possible to ensure the promotion of shrinkage of the glass pipe.

As described above, when coping with an increase in diameter without using a glass lathe, the sealing work for performing the welding step under reduced pressure should be easy and reliable, and the sealed condition should be maintained. You can

According to the invention of claim 2, in addition to the effect of the invention of claim 1, the welding step is performed by moving the glass pipe and the glass rod with respect to the ring-shaped heater whose position is fixed. Therefore, as compared with the case where the ring-shaped heater is moved, the relative movement between the glass pipe and the glass rod and the ring-shaped heater can be performed easily, and at this time, the first and second support Since the means are synchronously moved at the same speed, even if the glass pipe and the glass rod are individually supported, the welding process by the relative movement to the heater can be surely performed.

According to the invention of claim 3, in addition to the effect of the invention of claim 2, third supporting means for supporting one end of the glass pipe and first supporting means for supporting the other end of the glass pipe are provided. And the second supporting means for supporting the glass rod are moved to the same side in the vertical direction to perform the welding step, the moving speed of the third supporting means is relatively faster than the moving speed of the first and second supporting means. The glass pipe and the glass rod can be effectively drawn because of the high speed, and the glass pipe and the glass rod as materials form a glass base material having a predetermined C / C by setting the moving speed of both. It can be performed.

According to the invention described in claim 4, in addition to the effect of the invention described in claim 3, after the one end side of the glass pipe and the glass rod are welded to each other, the first supporting means and the second supporting means are moved relative to each other. Since the moving speed is changed and adjusted, there is a difference in moving speed between the other end of the glass pipe and the other end of the glass rod, so that the C / C of the glass base material after welding can be changed. . Therefore, even if the outer diameter of the glass pipe or the glass rod as the material has a dimensional variation, a minute variation in C / C due to the variation is corrected to reliably form the glass base material with a predetermined C / C. be able to. Further, at this time, since the bellows-shaped shielding member is used to seal the space between the first and second supporting means, the first and second supporting means can be adjusted by changing the relative moving speed.
Even if the vertical relative distance between the supporting means changes, the shielding member expands and contracts according to the change, and the depressurized state can be reliably maintained. Therefore, it is possible to achieve both fine correction of C / C and reliable maintenance of the reduced pressure state.

According to the invention of claim 5, in addition to the effect of the invention of claim 1, the first and second aspects are provided.
Since the supporting means supports the other end of the glass pipe and the glass rod portion projecting from the other end so as to be vertically changeable, the glass pipe and / or the glass as a material. Even if there are variations in the length of the rod, depending on the variation, the first
And // By changing the supporting position of the second supporting means, the glass base material can be formed by effectively utilizing the longest possible range of the material. Moreover, at this time, even if the vertical relative distance between the first and second supporting means is changed, the both are sealed by the bellows-like shielding member, so that the other end side of the glass pipe is surely secured. Not only can it be hermetically sealed, but also the hermetically sealed state can be reliably maintained. Therefore, it is possible to achieve both effective use of the material according to variations in dimensions and reliable maintenance of the reduced pressure state.

Further, according to the invention of claim 6, in addition to the effect of the invention of claim 1, in the inserting and arranging step, the relative position between the second supporting means and the elevating means is changed within the horizontal plane. 2 which are orthogonal to each other on the horizontal plane by
Since the glass rod is positioned at the axial center of the glass pipe by changing the position with respect to the direction, it is possible to easily and reliably correct the eccentricity due to the dimensional variation of the material and the like. Moreover, even if the relative position of the second support means is changed, the second support means and the first support means are sealed by the bellows-shaped shield member, so that the shield member is in the horizontal direction. The glass pipe is deformed in the horizontal direction in accordance with the change in the relative position, and the other end side of the glass pipe can be reliably sealed, and the sealed state can also be reliably maintained. Therefore, it is possible to achieve both eccentricity correction due to dimensional variation of materials and reliable maintenance of the reduced pressure state.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a manufacturing apparatus for carrying out an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view showing another mode of forming a sealed bottom of a glass pipe.

FIG. 3 is an explanatory diagram of a conventional manufacturing method using a glass lathe.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 glass pipe 1a sealing bottom 1c upper end opening (opening on the other end side) 2 glass rod 2a glass rod part 3 first chuck (first supporting means) 4 second chuck (second supporting means) 5 third chuck (third chuck) Supporting means) 6 Shielding member 7 Ring heater (heating furnace) 9, 10, 11 Lifting means 14 XY table (horizontal plane relative position adjusting means)

Claims (6)

[Claims] 1. A glass pipe sealing step of previously sealing an opening on one end side in the longitudinal direction of a cladding glass pipe to form a sealing bottom, and a glass pipe after the glass pipe sealing step is provided with a ring-shaped heater. After the glass pipe is penetrated into the heating furnace and at least the other end in the longitudinal direction is held by the first supporting means to vertically support the glass pipe, the glass rod for core is sealed from the opening on the other end side in the glass pipe. An inserting and arranging step of supporting the glass rod at the axial center position of the glass pipe by a second supporting means which is inserted to the bottom and holds the glass rod portion protruding from the opening on the other end side; The space between the glass pipe and the glass rod from the other end side opening to the sealing bottom is made a closed space by covering the space between the two supporting means with a cylindrical shielding member. Steps, while maintaining the closed space at a pressure lower than atmospheric pressure, sequentially heating the glass rod and the glass pipe relative to the ring-shaped heater while moving relatively from the one end side to the other end side. A method of manufacturing a glass preform for an optical fiber, comprising a welding step of welding and integrating both. 2. The welding process according to claim 1, wherein the first supporting means and the second supporting means are moved at a constant speed in the vertical direction in synchronization with each other by the elevating means with respect to the ring-shaped heater fixedly positioned. A method for manufacturing an optical fiber preform, characterized in that 3. The glass pipe according to claim 2, wherein one end side of the glass pipe is supported by a third support means connected to an independent lifting means, and the third support means is vertically aligned with the first and second support means. When the welding process is performed by moving the third supporting means to the side, the moving speed of the third supporting means is set relatively higher than the moving speed of the first and second supporting means so that the one end side and the other end side are moved. A method for producing a glass preform for optical fibers, which comprises stretching a glass pipe and a glass rod between them. 4. The first support means and the second support means according to claim 3, wherein the first support means and the second support means can be moved independently of each other in the vertical direction by individual elevating means, and are formed to be vertically expandable and contractable in the sealing step. A bellows-shaped shielding member is used to shield the first supporting means and the second supporting means so that the relative distance in the vertical direction can be changed, and in the welding step, after welding one end side of the glass pipe and the glass rod. A method for manufacturing a glass preform for optical fibers, characterized in that the relative moving speed of the first supporting means and the second supporting means is changed and adjusted. 5. The first support means and the second support means according to claim 1, wherein the vertical relative distance between the first support means and the second support means is changeable, and the glass pipe and the glass rod in the insertion and placement step are attached to the first support means. The supporting position of the glass pipe by the means and the supporting position of the glass rod by the second supporting means are supported so as to be relatively changeable in the vertical direction, and a bellows-like member formed to be vertically expandable and contractable in the sealing step. A method of manufacturing a glass preform for an optical fiber, which comprises shielding using a shielding member. 6. The second supporting means and the elevating and lowering means in two directions orthogonal to each other on a horizontal plane between the second supporting means and the elevating and lowering means for moving the second supporting means in the vertical direction. The horizontal position changing means for changing the relative position to the means is interposed, and in the inserting and arranging step, the second supporting means and the elevating means are moved by the horizontal position changing means so that the glass rod is positioned at the axis of the glass pipe. A method for manufacturing a glass preform for optical fibers, which comprises shielding using a bellows-shaped shielding member formed so as to be deformable in a horizontal direction in a sealing step of changing a relative position to.