JP2014001114A - Method for drawing glass rod and apparatus for drawing glass rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for drawing a glass rod by which a top bearing bar mounted at the upper end of the glass rod is shortened and by which the inside of a heating furnace is isolated from outside air.SOLUTION: The drawing method, in which both ends of a glass rod 30 are respectively mounted with a top bearing bar 31 and a bottom bearing bar 32 which have a diameter smaller than that of the glass rod 30, in which the glass rod 30 which is mounted with these bearing bars is charged into a heating furnace 13 and softened by heating, and in which the glass rod 30 is drawn so that the glass rod has a specified outer diameter, comprises isolating the inside of the heating furnace 13 from outside air by placing the first seal body 16 at the top end face 13a of the heating furnace 13 so that first seal body 16 covers the top opening 17 when the top end face 30a of the glass rod 30 is located outside the heating furnace 13 and by placing the second seal body 18 on the top of the first seal body 16 so that the second seal body 18 covers the top opening 17 of the heating furnace 13 when the top end face 30a of the glass rod 30 is located inside the heating furnace 13.

Description

 The present invention relates to a glass rod stretching method and a glass rod stretching apparatus.

A quartz glass-based optical fiber is generally manufactured by the following method.
First, a glass fine particle deposit including a core portion is produced by a VAD (Vapor Phase Axial Deposition) method, and the glass fine particle deposit is heated at a high temperature to form a transparent glass. obtain. Next, glass fine particles are deposited on the outer side of the intermediate base material stretched to have a predetermined outer diameter, and again subjected to heat treatment at a high temperature to form a transparent glass, thereby obtaining an optical fiber base material. An optical fiber is manufactured by drawing the optical fiber preform thus manufactured.

Conventionally, as a stretching apparatus used in a stretching method for stretching a glass rod such as an intermediate base material, the one shown in FIG.
The stretching apparatus 100 is schematically configured from a heating furnace 103 including a heater unit 101 for heating the glass rod 200 and a heat insulating material 102 surrounding the heater unit 101, a feeding chuck 104 for the glass rod 200, and a take-up chuck 105 for the glass rod 200. Has been.

In order to install the glass rod 200 in the stretching apparatus 100, as shown in FIG. 4A, the upper support rod 201 attached to the upper end of the glass rod 200 is held by the feed chuck 104 and the lower end of the glass rod 200. The lower support rod 202 attached to the holder is picked up and gripped by the chuck 105.
As shown in FIG. 4 (a), the glass rod 200 is inserted into the heating furnace 103 from the lower end, and the glass rod 200 is heated in the heating furnace 103, as shown in FIGS. 4 (b) and 4 (c). By lowering the take-up chuck 105, the molten glass rod 200 can be stretched to have a predetermined outer diameter. On the other hand, by lowering the delivery chuck 104, the drawing lower end of the glass rod 200 is adjusted to be positioned in the vicinity of the heater portion 101 as shown in FIG.

 Since the furnace core tube and the heater unit 101 constituting the heating furnace 103 are widely made of carbon, when the outside air flows into the heating furnace 103, the oxygen contained in the outside air causes the core tube and the heater to be heated. It is necessary to prevent the portion 101 from being oxidized. Further, when outside air flows into the heating furnace 103, the melted portion of the glass rod 200 changes due to pressure fluctuations in the heating furnace 103, and the stretched diameter becomes unstable. Therefore, conventionally, the inside of the heating furnace 103 is set to an inert gas atmosphere, and the upper end surface side of the heating furnace 103 has a through hole through which the upper support rod 201 can pass, and the glass rod 200 inserted into the heating furnace 103 is provided. A cylindrical upper seal body 107 covering the entire upper end and the upper opening 106 of the heating furnace 103 is provided, and a through hole through which the lower support rod 202 can pass is provided on the lower end surface side of the heating furnace 103, A lower seal body 109 is provided to cover the lower opening 108 of 103. Here, by reducing the gap between the upper support rod 201 and the upper seal body 107 and the gap between the lower support rod 202 and the lower seal body 109, the pressure in the heating furnace 103 is made higher than the atmospheric pressure. Then, the inside of the heating furnace 103 is shut off from the outside air.

 In order to insert the glass rod 200 into the heating furnace 103 without the delivery chuck 104 hitting the upper seal body 107, the length of the upper support rod 201 is at least the length of the glass rod 200 (of the glass rod 200). The distance from the upper end surface to the heater unit 101 must be equal to or greater than the distance. However, it is desired to make the length of the upper support bar 201 shorter. This is because the upper support rod 201 is inserted into the heating furnace 103, and a high-purity quartz glass rod is used as the upper support rod 201 in order to prevent impurities from entering the heating furnace 103. This is because the length of the upper support bar 201 needs to be shortened in order to decrease. In recent years, the size of the glass rod 200 has been increased in order to facilitate the transportation and installation in the stretching apparatus 100 and to reduce the cost. For this reason, before the glass rod 200 is installed in the stretching apparatus 100, a building with a high ceiling is required to make the upper support rod 201 stand by.

In order to solve such a problem, for example, a bellows-like cylinder having airtightness, flexibility and heat resistance is provided at a position surrounding the glass base material insertion portion at the upper part of the heating furnace, and a certain distance from the upper chuck is maintained. However, there has been disclosed an optical fiber preform stretching apparatus that has a mechanism for interlocking the bellows-shaped cylinder and that can expand and contract as the upper chuck moves (for example, see Patent Document 1).
In addition, when the optical fiber preform is placed in a heating furnace and heat-treated, a tube portion for shutting off the outside air is installed on the furnace core tube into which the optical fiber preform is inserted at the top of the heating furnace, A glass rod heat treatment apparatus whose height is variable is disclosed (see, for example, Patent Document 2).
Also, a heating furnace and an upper chuck that supports the upper end side of the optical fiber preform disposed in the shield pipe are connected to the furnace and are connected to the furnace in a vertically long shield pipe. On the other hand, the optical fiber preform is configured such that the shield pipe is configured to be vertically expandable and contracted, and when the optical fiber preform is set, the lower end of the shield pipe is lifted upward to reduce the size so that the upper chuck is exposed. A material stretching apparatus is disclosed (for example, see Patent Document 3).

Japanese Patent Laid-Open No. 6-256034 JP 11-349342 A JP 2005-281078 A

 However, the apparatuses disclosed in Patent Documents 1 to 3 have a problem that a large-scale mechanism such as an extendable outside air blocking section and a drive system of a lifting / lowering means synchronized with the feeding of the optical fiber preform is required. In addition, since the seal body covers the feed chuck or becomes a large seal body that interlocks, when installing the optical fiber preform in the stretching apparatus or taking out the optical fiber preform from the stretching apparatus There was a problem of inconvenience.

 The present invention has been made in view of the above circumstances, and the length of the upper support rod attached to the upper end of the glass rod can be further shortened, and the inside of the heating furnace can be blocked from the outside air. An object of the present invention is to provide a glass rod stretching method and a glass rod stretching apparatus that can be used.

 In order to solve the above-mentioned problem, the present invention is provided with an upper support bar and a lower support bar each having an outer diameter smaller than that of the glass rod attached to both ends of the glass rod, and the upper support bar and the lower support bar attached. A glass rod is softened by being inserted into a heating furnace and heat-treated, and the softened glass rod is stretched so as to have a predetermined outer diameter, the upper end surface of the glass rod Is disposed outside the heating furnace, a first sealing body that surrounds the outer periphery of the glass rod and has a through-hole through which the glass rod can pass is disposed on the upper end surface of the heating furnace, By covering the upper opening of the heating furnace with the sealing body, the inside of the heating furnace is shielded from the outside air, and the upper support is provided when the upper end surface of the glass rod is in the heating furnace. A second seal body having a through hole that surrounds the outer periphery of the upper support rod and allows the upper support rod to pass therethrough is overlaid on the first seal body, and the second seal body is used to upper the heating furnace. Provided is a glass rod stretching method that covers the opening to block the inside of the heating furnace from the outside air.

 In the glass rod stretching method of the present invention, the first seal body is preferably a seal ring.

 In the glass rod stretching method of the present invention, the second seal body is preferably a seal ring.

 In the glass rod stretching method of the present invention, the seal ring is preferably a quartz seal ring.

 The present invention is a glass rod stretching device comprising a heating furnace for heating a glass rod, and a feeding chuck and a take-off chuck for the glass rod, the glass rod being allowed to pass through, and the heating When the upper end surface of the glass rod is outside the heating furnace, the first sealing body that covers the upper opening portion of the heating furnace has an upper end surface of the heating furnace. The upper end of the heating furnace is provided so as to surround the outer periphery of the glass rod, is attached to the upper end of the glass rod, and allows an upper support rod having a smaller outer diameter than the glass rod to pass therethrough. When the upper end surface of the glass rod is in the heating furnace, it overlaps on the first sealing body and covers the upper opening of the heating furnace. Providing stretching apparatus for a glass rod Lumpur body formed.

 In the glass rod stretching apparatus of the present invention, the first seal body is preferably a seal ring.

 In the glass rod stretching apparatus of the present invention, the second seal body is preferably a seal ring.

 In the glass rod stretching apparatus of the present invention, the seal ring is preferably a quartz seal ring.

 According to the present invention, the length of the upper support rod attached to the upper end of the glass rod can be shortened, the structure of the upper seal body covering the upper opening of the heating furnace can be simplified, Since the inside of the heating furnace can be shielded from the outside air, the cost can be reduced.

It is a schematic diagram which shows the extending | stretching apparatus used for 1st embodiment of the extending | stretching method of the glass rod of this invention. It is the figure which expanded a part of FIG. It is a schematic diagram which shows a part of extending | stretching apparatus used for 2nd embodiment of the extending | stretching method of the glass rod of this invention. It is a schematic diagram which shows the extending | stretching apparatus used for the extending | stretching method of the conventional glass rod.

An embodiment of the glass rod stretching method of the present invention will be described.
Note that this embodiment is specifically described in order to better understand the gist of the invention, and does not limit the present invention unless otherwise specified.

(1) 1st embodiment FIG. 1: is a schematic diagram which shows the extending | stretching apparatus used for 1st embodiment of the extending | stretching method of the glass rod of this invention. FIG. 2 is an enlarged view of a part of FIG.
The stretching apparatus 10 according to the present embodiment includes a heater unit 11 that heats the glass rod 30 and a heating furnace 13 that includes the heat insulating material 12 that surrounds the heater unit 11, a feeding chuck 14 for the glass rod 30, and a take-up chuck 15 for the glass rod 30. It is roughly composed of
Here, examples of the glass rod 30 include an intermediate base material and an optical fiber base material.
An upper support bar 31 and a lower support bar 32 having a smaller outer diameter than the glass rod 30 are attached to both ends of the glass rod 30. In addition, the glass rod 30, and the upper support bar 31 and the lower support bar 32 are connected so that the central axes thereof are substantially overlapped (substantially the same). Moreover, the glass rod 30 has a cylindrical shape as a whole, and its upper end also has a cylindrical shape.

In addition, the flat plate-shaped first upper seal body 16 having a through hole 16a through which the glass rod 30 can pass surrounds the outer periphery on the upper end side of the glass rod 30 on the upper end surface 13a of the heating furnace 13, It is provided so as to cover the upper opening 17 of the heating furnace 13.
In addition, a flat plate-like second upper seal body 18 having a through hole 18a through which the upper support bar 31 can pass surrounds the outer periphery of the upper support bar 31 on the first upper seal body 16, and It is provided so as to cover the upper opening 17 of the heating furnace 13.
Further, a flat lower seal body 19 having a through hole 19a through which the lower support rod 32 can pass surrounds the outer periphery of the lower support rod 32 on the lower end surface 13b side of the heating furnace 13, and the lower opening of the heating furnace 13 is opened. It is provided so as to cover the part 20.
The first upper seal body 16 and the second upper seal body 18 are separate bodies.

 As the heating furnace 13, the delivery chuck 14, and the take-off chuck 15, those similar to those used in a general glass rod drawing apparatus are used.

The shape of the first upper seal body 16 in plan view is not particularly limited, and is appropriately adjusted according to the shape of the upper opening 17 of the heating furnace 13. The shape of the first upper seal body 16 in plan view is, for example, a circular shape, a square shape, or a rectangular shape.
Moreover, the magnitude | size and thickness of the 1st upper seal body 16 are not specifically limited, The magnitude | size of the heating furnace 13 covered with the 1st upper seal body 16 (sealed), and its upper opening part It adjusts suitably according to the magnitude | size of 17 etc.
As the first upper seal body 16, while having a through-hole 16a through which the glass rod 30 can pass, that is, surrounding the glass rod 30 with a slight gap between the outer periphery on the upper end side, Although it will not specifically limit if it has the through-hole 16a which can let the glass rod 30 pass (penetrate), A seal ring is preferable and a quartz seal ring is more preferable.
Further, when the first upper seal body 16 is provided so as to surround the outer periphery of the glass rod 30, the through hole 16 a of the first upper seal body 16 and the upper opening 17 of the heating furnace 13 overlap each other. It has become.

The shape of the second upper seal body 18 in plan view is not particularly limited, and is appropriately adjusted according to the shape of the upper opening 17 of the heating furnace 13. The shape of the second upper seal body 18 in plan view is, for example, a circular shape, a square shape, or a rectangular shape.
The size and thickness of the second upper seal body 18 are not particularly limited, and the size of the heating furnace 13 covered (sealed) by the second upper seal body 18 and the upper opening thereof. It adjusts suitably according to the magnitude | size of 17 etc.
The second upper seal body 18 has a through hole 18a through which the upper support bar 31 can pass, that is, the upper support body 31 is surrounded by a slight gap between the upper support bar 31 and the outer periphery. Although it will not specifically limit if it has the through-hole 18a which can let the support rod 31 pass (penetrate), A seal ring is preferable and a quartz seal ring is more preferable.
Further, when the second upper seal body 18 is provided so as to surround the outer periphery of the upper support rod 31, the through hole 18a of the second upper seal body 18, the through hole 16a of the first upper seal body 16, and The upper opening 17 of the heating furnace 13 overlaps.

Further, the first upper seal body 16 and the second upper seal body 18 are arranged so as to surround the outer circumferences of the glass rod 30 and the upper support rod 31 in which the respective central axes substantially overlap (substantially be the same). Therefore, the center of the through hole 16a of the first upper seal body 16 and the center of the through hole 18a of the second upper seal body 18 are substantially collinear (on the central axes of the glass rod 30 and the upper support bar 31). Exists.
Furthermore, since the outer diameter of the upper support rod 31 is smaller than the outer diameter of the glass rod 30, the inner diameter of the through hole 18a of the second upper seal body 18 through which the upper support rod 31 is inserted is inserted through the glass rod 30. The inner diameter of the through hole 16a of the first upper seal body 16 is smaller.

The shape when the lower seal body 19 is viewed in plan is not particularly limited, and is appropriately adjusted according to the shape of the lower opening 20 of the heating furnace 13. The shape of the lower seal body 19 when viewed in plan is, for example, a circular shape, a square shape, or a rectangular shape.
Further, the size and thickness of the lower seal body 19 are not particularly limited, and may vary depending on the size of the heating furnace 13 covered (sealed) by the lower seal body 19 or the size of the lower opening 20 thereof. It is adjusted accordingly.
The lower seal body 19 has a through-hole 19a through which the lower support bar 32 can pass, that is, the lower support bar 32 is surrounded by a slight gap between the lower support body 32 and the outer periphery of the lower support bar 32. Although it will not specifically limit if it has the through-hole 19a which can let pass (penetrate), A seal ring is preferable and a quartz seal ring is more preferable.
Further, when the lower seal body 19 is provided so as to surround the outer periphery of the lower support rod 32, the through hole 19 a of the lower seal body 19 and the lower opening 20 of the heating furnace 13 overlap each other.

Next, a method for stretching the glass rod of this embodiment will be described.
In order to install the glass rod 30 in the stretching device 10, as shown in FIG. 1A, the upper support rod 31 attached to the upper end of the glass rod 30 is fed out and held by the chuck 14, and the lower end of the glass rod 30 is installed. The lower support bar 32 attached to the holder is picked up and gripped by the chuck 15.

At this time, as shown in FIGS. 1 (a) and 2 (a), the glass rod 30 is inserted into the through hole 16a of the first upper seal body 16, and the first upper seal body 16 is moved to the heating furnace. 13 on the upper end surface 13a.
Further, as shown in FIGS. 1A and 2A, the upper support rod 31 is inserted into the through hole of the second upper seal body 19, and the second upper seal body 18 is attached to the glass rod 30. It arrange | positions to the upper end surface 30a.
Further, as shown in FIG. 1A, the lower support bar 32 is inserted into the through hole 19 a of the lower seal body 19, and the lower seal body 19 is disposed on the lower end surface 13 b of the heating furnace 13.

 As shown in FIG. 1A, the glass rod 30 is inserted into the heating furnace 13 from the lower end, and the take-up chuck 15 is lowered while heating the glass rod 30 in the heating furnace 13. As described above, when heating of the glass rod 30 is started, the first upper seal body 16 and the second upper seal body 18 are separated from each other.

As shown in FIGS. 1A, 1 </ b> B, and 2 </ b> A, the upper end of the glass rod 30 is outside the heating furnace 13, that is, the upper end surface 30 a of the glass rod 30 is the upper opening 17 of the heating furnace 13. The upper opening 17 of the heating furnace 13 is covered with the first upper seal body 16 when the upper side is higher than the outside, so that the inside of the heating furnace 13 is shut off from the outside air, and the inflow of the outside air into the heating furnace 13 is prevented. To prevent.
At this time, the glass rod 30 passes through the through hole 16 a of the first upper seal body 16, but the inside of the heating furnace 13 is blocked from the outside air by the first upper seal body 16. In this way, the inside of the heating furnace 13 can be shielded from outside air because the first upper seal body 16 covers the upper opening 17 of the heating furnace 13 on the upper end surface 13a of the heating furnace 13, This is because there is only a slight gap between the glass rod 30 and the outer periphery.

 As shown in FIGS. 1C and 2B, when the glass rod 30 is stretched and the entire glass rod 30 is fed into the heating furnace 13, that is, the upper end surface 30a of the glass rod 30 is heated. When in the furnace 13, the second upper seal body 18 is overlaid on the first upper seal body 16, and the second upper seal body 18 covers the upper opening 17 of the heating furnace 13 to heat it. The inside of the furnace 13 is shut off from the outside air to prevent the outside air from flowing into the heating furnace 13.

 At this time, the upper support rod 31 passes through the through hole 18a of the second upper seal body 18, but the inside of the heating furnace 13 is blocked from the outside air by the second upper seal body 18. As shown in FIG. 2B, when the upper end surface 30a of the glass rod 30 is fed into the heating furnace 13, a gap is generated between the through-hole 16a of the first upper seal body 16 and the glass rod 30, and remains as it is. Then, outside air will flow into the heating furnace 13 through the through hole 16 a of the first upper seal body 16. Therefore, as shown in FIG. 2 (b), the second upper seal body 18 is disposed on the upper end surface 13 a of the heating furnace 13, and is stacked on the first upper seal body 16 to open the upper opening of the heating furnace 13. By covering a part (outer edge) of the through-hole 16a of the part 17 and the first upper seal body 16, the inside of the heating furnace 13 is blocked from the outside air. In this way, the inside of the heating furnace 13 can be shielded from the outside air by the fact that the center of the through hole 16a of the first upper seal body 16 and the center of the through hole 18a of the second upper seal body 18 are almost the same. The first upper seal body 16 and the second upper seal body 18 are disposed so as to exist on the same straight line, and the inner diameter of the through hole 18a of the second upper seal body 18 is set to be equal to the first upper seal body 18. This is because it is smaller than the inner diameter of the through hole 16a of the seal body 16 and there is only a slight gap between the second upper seal body 18 and the outer periphery of the upper support rod 31.

 Further, the upper end surface 30 a of the glass rod 30 is fed into the heating furnace 13, and at the same time, the second upper seal body 18 overlaps the first upper seal body 16. To do this, the distance between the first upper seal body 16 and the second upper seal body 18 is adjusted in advance at the time when heating of the glass rod 30 is started in accordance with the length of the glass rod 30.

 Then, by continuing the heating of the glass rod 30 and the lowering of the take-up chuck 15, the molten glass rod 30 can be stretched to have a predetermined outer diameter.

 In order to send the glass rod 30 into the heating furnace 13, the length of the upper support bar 31 is at least the distance from the heater portion 11 to the upper end surface 13 a of the heating furnace 13, the first upper seal body 16 and the second upper seal body 16. The length combined with the thickness of the upper seal body 18 is required. On the other hand, in the conventional glass rod stretching method, as shown in FIG. 4, the length of the upper support rod 201 is at least the distance from the heater unit 101 to the upper end surface 103 a of the heating furnace 103, and the glass rod 200. When the stretching apparatus 100 is installed, it is necessary to have a length that combines the thickness of the upper seal body 107 that covers the upper end of the glass rod 200 outside the heating furnace 103. According to the glass rod stretching method of the present embodiment, the upper seal body 107 used in the conventional glass rod stretching method is not necessary, and the upper support rod 31 attached to the upper end of the glass rod 20 by the thickness thereof. Can be shortened. That is, the structure of the first upper seal body 16 and the second upper seal body 18 covering the upper opening 17 of the heating furnace 13 can be simplified, and the inside of the heating furnace 13 can be blocked from the outside air. As a result, costs can be reduced.

(2) Second Embodiment FIG. 3 is a schematic view showing a part of a stretching apparatus used in the second embodiment of the glass rod stretching method of the present invention.
The stretching apparatus 50 of the present embodiment includes a heating furnace 51 including a heater unit (not shown) for heating the glass rod 70 and a heat insulating material (not shown) surrounding the heater unit, a feeding chuck (not shown) for the glass rod 70, , And a take-up chuck (not shown) of the glass rod 70.
Here, examples of the glass rod 70 include an intermediate base material and an optical fiber base material.
An upper support bar 71 and a lower support bar (not shown) having an outer diameter smaller than that of the glass rod 70 are attached to both ends of the glass rod 70, respectively. The glass rod 70 is connected to the upper support bar 71 and the lower support bar so that their central axes substantially overlap (substantially be the same). The glass rod 70 has a substantially cylindrical shape as a whole, and the upper end portion 70A has a tapered shape in which the outer shape gradually increases from the upper end surface 70a of the glass rod 70 toward the lower end surface side. .

In addition, a flat plate-shaped first upper seal body 52 having a through hole 52a through which the glass rod 70 can pass surrounds the outer periphery on the upper end side of the glass rod 70 on the upper end surface 51a of the heating furnace 51, It is provided so as to cover the upper opening 53 of the heating furnace 51.
Also, the first upper portion is formed so that the cylindrical third upper seal body 54 having a size capable of accommodating the upper end portion 70A of the tapered glass rod 70 surrounds the outer periphery of the upper end portion 70A having the tapered shape. It is provided on the seal body 52.
Further, a flat plate-like second upper seal body 55 having a through-hole 55a through which the upper support bar 71 can pass surrounds the outer periphery of the upper support bar 71 on the third upper seal body 54, and It is provided so as to cover the upper opening 53 of the heating furnace 51.
Further, a lower seal body (not shown) having a through hole (not shown) through which the lower support bar (not shown) can pass surrounds the outer periphery of the lower support bar on the lower end surface (not shown) side of the heating furnace 51. At the same time, it is provided so as to cover the lower opening (not shown) of the heating furnace 51.

The first upper seal body 52 and the third upper seal body 54 may be integrated or separate.
Further, the first upper seal body 52 and the third upper seal body 54 and the second upper seal body 55 are separate bodies.

 As the heating furnace 51, the delivery chuck, and the take-up chuck, the same ones as those used in a general glass rod stretching apparatus are used.

The shape of the first upper seal body 52 in plan view is not particularly limited, and is appropriately adjusted according to the shape of the upper opening 53 of the heating furnace 51. The shape of the first upper seal body 52 in plan view is, for example, a circular shape, a square shape, or a rectangular shape.
Moreover, the magnitude | size and thickness of the 1st upper seal body 52 are not specifically limited, The magnitude | size of the heating furnace 51 covered by the 1st upper seal body 52 (sealed), and its upper opening part According to the size of 53, etc., it is adjusted appropriately.
The first upper seal body 52 has a through hole 52a through which the glass rod 70 can pass, that is, the outer periphery on the upper end side of the glass rod 70 (the portion excluding the upper end portion 70A having a tapered shape). Is not particularly limited as long as it has a through-hole 52a that allows the glass rod 70 to pass (penetrate) while providing a slight gap between and a seal ring, Quartz seal rings are more preferred.
Further, when the first upper seal body 52 is provided so as to surround the outer periphery of the glass rod 70, the through hole 52 a of the first upper seal body 52 and the upper opening 53 of the heating furnace 51 overlap. It has become.

The shape of the third upper seal body 54 in plan view is not particularly limited, and is appropriately adjusted according to the shape of the upper opening 53 of the heating furnace 51. The shape of the third upper seal body 54 in plan view is, for example, a circular shape, a square shape, or a rectangular shape.
The size and thickness of the third upper seal body 54 are not particularly limited, depending on the outer diameter and height of the upper end portion 70A of the glass rod 70 covered by the third upper seal body 54. And adjusted as appropriate.
The third upper seal body 54 has a space (through portion) 54a having a size capable of accommodating the upper end portion 70A of the tapered glass rod 70, that is, an inner diameter larger than the outer diameter of the upper end portion 70A. And having a thickness larger than the height of the upper end portion 70A (the length in the longitudinal direction of the glass rod 70) is not particularly limited.
Further, when the third upper seal body 54 is provided so as to accommodate the upper end portion 70 </ b> A of the glass rod 70, the space 54 a of the third upper seal body 54 and the through hole 52 a of the first upper seal body 52. And the upper opening 53 of the heating furnace 51 overlaps.

The shape of the second upper seal body 55 in plan view is not particularly limited, and is appropriately adjusted according to the shape of the upper opening 53 of the heating furnace 51. The shape of the second upper seal body 55 in plan view is, for example, a circular shape, a square shape, or a rectangular shape.
The size and thickness of the second upper seal body 55 are not particularly limited, and the third upper seal body 54 and the heating furnace 51 covered (sealed) by the second upper seal body 55 are not limited. The size is appropriately adjusted according to the size of the upper opening 53 of the heating furnace 51 and the like.
The second upper seal body 55 has a through hole 55a through which the upper support rod 71 can pass, that is, the upper support rod 71 is surrounded by a slight gap between the upper support rod 71 and the outer periphery. Although it will not specifically limit if it has the through-hole 55a which can let the support rod 71 pass (penetrate), A seal ring is preferable and a quartz seal ring is more preferable.
Further, when the second upper seal body 55 is provided so as to surround the outer periphery of the upper support rod 71, the through hole 55a of the second upper seal body 55 and the through hole 52a of the first upper seal body 52, The space 54 a of the third upper seal body 54 and the upper opening 53 of the heating furnace 51 overlap each other.

Further, the first upper seal body 52, the second upper seal body 55, and the third upper seal body 54 are respectively formed of the glass rod 70 and the upper support rod 71 whose central axes are substantially overlapped (substantially the same). Since it is arranged so as to surround the outer periphery, the center of the through hole 52a of the first upper seal body 52, the center of the through hole 55a of the second upper seal body 55, and the space of the third upper seal body 54 The center of the (penetrating portion) 54a is substantially on the same straight line (on the central axis of the glass rod 70 and the upper support rod 71).
Furthermore, since the outer diameter of the upper support rod 71 is smaller than the outer diameter of the glass rod 70, the inner diameter of the through hole 55a of the second upper seal body 55 through which the upper support rod 71 is inserted is inserted through the glass rod 70. The inner diameter of the through hole 52a of the first upper seal body 52 is smaller.

The shape of the lower seal body in plan view is not particularly limited, and is appropriately adjusted according to the shape of the lower opening of the heating furnace 51. The shape when the lower seal body is viewed in plan is, for example, a circular shape, a square shape, or a rectangular shape.
In addition, the size and thickness of the lower seal body are not particularly limited, depending on the size of the heating furnace 51 covered (sealed) by the lower seal body, the size of the lower opening, and the like. Adjust as appropriate.
The lower seal body has a through-hole through which the lower support rod can pass, that is, passes through the lower support rod while penetrating the lower support rod with a slight gap between it and the outer periphery of the lower support rod. The seal ring is not particularly limited as long as it has a through hole that can be made to pass through, but a seal ring is preferable, and a quartz seal ring is more preferable.
In addition, when the lower seal body is provided so as to surround the outer periphery of the lower support rod, the through hole of the lower seal body and the lower opening of the heating furnace 51 overlap each other.

Next, a method for stretching the glass rod of this embodiment will be described.
In order to install the glass rod 70 in the stretching device 50, the upper support bar 71 attached to the upper end of the glass rod 70 is held by the feed chuck, and the lower support bar attached to the lower end of the glass rod 70 is taken out by the chuck. Hold it.

At this time, as shown in FIG. 3A, the glass rod 70 is inserted into the through hole 52 a of the first upper seal body 52, and the first upper seal body 52 is inserted into the upper end surface 51 a of the heating furnace 51. Deploy.
3A, the glass rod 70 is inserted into the space (through portion) 54a of the third upper seal body 54, and the third upper seal body 54 is moved to the first upper seal body. 52.
3A, the upper support rod 71 is inserted into the through hole 55a of the second upper seal body 55, and the second upper seal body 55 is disposed in the vicinity of the upper end surface 70a of the glass rod 70. To place.
Further, the lower support rod is inserted into the through hole of the lower seal body, and the lower seal body is disposed on the lower end surface of the heating furnace.

 The glass rod 70 is inserted into the heating furnace 51 from the lower end, and the take-up chuck is lowered while heating the glass rod 70 in the heating furnace 51. As described above, when heating of the glass rod 70 is started, the first upper seal body 52, the third upper seal body 54, and the second upper seal body 55 are separated from each other.

As shown in FIG. 3A, the base end on the heating furnace 51 side in the tapered shape of the upper end portion 70A of the glass rod 70 (the base end on the lower end side of the glass rod 70, in FIGS. 3A and 3B, When the portion on the line indicated by α) is outside the heating furnace 51, the upper opening 53 of the heating furnace 51 is covered with the first upper seal body 52 to block the inside of the heating furnace 51 from the outside air, Inflow of outside air into the heating furnace 51 is prevented.
At this time, the glass rod 70 passes through the through hole 52 a of the first upper seal body 52, but the inside of the heating furnace 51 is blocked from the outside air by the first upper seal body 52. In this way, the inside of the heating furnace 51 can be shielded from the outside air because the first upper seal body 52 covers the upper opening 53 of the heating furnace 51 on the upper end surface 51a of the heating furnace 51, This is because there is only a slight gap between the glass rod 70 and the outer periphery.

 As shown in FIG. 3 (b), the glass rod 70 has been extended, and the proximal end of the upper end portion 70A of the glass rod 70 on the heating furnace 51 side (the proximal end on the lower end side of the glass rod 70, FIG. a), when the portion on the line indicated by α in (b) is fed into the heating furnace 51, the second upper seal body 55 is overlaid on the third upper seal body 54, and the second By covering the upper opening 53 of the heating furnace 51 with the upper seal body 55 and the third upper seal body 54, the inside of the heating furnace 51 is shut off from the outside air and the inflow of outside air into the heating furnace 51 is prevented. .

 At this time, the upper support rod 71 passes through the through hole 55a of the second upper seal body 55, but the inside of the heating furnace 51 is blocked from the outside air by the second upper seal body 55. As shown in FIG. 3B, when the proximal end on the heating furnace 51 side in the tapered shape of the upper end portion 70A of the glass rod 70 is fed into the heating furnace 51, the through hole 52a of the first upper seal body 52 and A gap is generated between the glass rods 70, and as it is, outside air flows into the heating furnace 51 through the through hole 52 a of the first upper seal body 52. Therefore, as shown in FIG. 3 (b), the second upper seal body 55 is overlaid on the third upper seal body 54 on the first upper seal body 52, and the upper opening of the heating furnace 51. 53 and a part (outer edge) of the through hole 52a of the first upper seal body 52 are covered to block the inside of the heating furnace 51 from the outside air. In this way, the inside of the heating furnace 51 can be shielded from the outside air by the center of the through hole 52a of the first upper seal body 52, the center of the through hole 55a of the second upper seal body 55, and The first upper seal body 52, the second upper seal body 55, and the third upper seal body so that the centers of the spaces (penetrating portions) 54a of the third upper seal body 54 are substantially collinear. 54, the inner diameter of the through hole 55a of the second upper seal body 55 is smaller than the inner diameter of the through hole 52a of the first upper seal body 52, and the second upper seal body 55 This is because there is only a slight gap between the upper support rod 71 and the outer periphery.

 Further, the proximal end on the heating furnace 51 side in the tapered shape of the upper end portion 70 </ b> A of the glass rod 70 is fed into the heating furnace 51, and at the same time, the second upper seal body 55 overlaps the third upper seal body 54. To. In order to do this, the distance between the second upper seal body 55 and the third upper seal body 54 is adjusted in advance at the time when heating of the glass rod 70 is started in accordance with the length of the glass rod 70. .

 Then, by continuing the heating of the glass rod 70 and the lowering of the take-up chuck, the molten glass rod 70 can be stretched to have a predetermined outer diameter.

 According to the glass rod stretching method of the present embodiment, the inside of the heating furnace 51 can be shut off from the outside air even if the upper end portion 70A of the glass rod 70 has a tapered shape.

 EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to a following example.

[Example 1]
With reference to FIGS. 1 and 2, the method for stretching the optical fiber preform of Example 1 will be described.
The outer shape is cylindrical, and an upper support rod having an outer diameter of 25 mm and a length of 390 mm and a lower support rod having an outer diameter of 25 mm and a length of 300 mm are fused to both ends of an optical fiber preform having an outer diameter of 50 mm and a length of 500 mm, respectively. Connected.
First, the upper support rod attached to the upper end of the optical fiber preform is gripped by the feeding chuck of the stretching device, and the lower support rod attached to the lower end of the optical fiber preform is gripped by the take-up chuck of the stretching device. .
At this time, the optical fiber preform is inserted into a through hole provided in the central portion of the first upper seal body made of a disc-shaped seal ring having a thickness of 20 mm, and the first upper seal body is moved to the heating furnace. It was arranged on the upper end surface of. Further, an upper support rod is inserted into a through hole provided in the center of the second upper seal body made of a disc-shaped seal ring having a thickness of 20 mm, and the second upper seal body is placed on the glass rod. Arranged on the end face.
Note that the first upper seal body and the second upper seal body were spaced apart. Further, the length of the upper support bar is 390 mm, the distance from the heater part of the heating furnace to the upper end surface of the heating furnace is 200 mm, the thickness of the first upper seal body is 20 mm, and the thickness of the second upper seal body is 20 mm. And the length of the portion where the upper support rod is gripped by the delivery chuck is equal to the total length of 150 mm.
Further, a lower support rod was inserted into a through hole provided in the central portion of the lower seal body made of a disc-shaped seal ring having a thickness of 20 mm, and the lower seal body was disposed on the lower end surface of the heating furnace.

Next, the optical fiber preform was inserted into the heating furnace from the lower end, and the take-up chuck was lowered while heating the optical fiber preform in the heating furnace.
Here, when the upper end portion of the optical fiber preform is outside the heating furnace, the inside of the heating furnace is shut off from the outside air by covering the upper opening of the heating furnace with the first upper seal body, Inflow of outside air into the water was prevented.
When the optical fiber preform is extended and the entire optical fiber preform is fed into the heating furnace, the second upper seal body is overlaid on the first upper seal body. By covering the upper opening of the heating furnace, the inside of the heating furnace was shut off from the outside air, and the inflow of outside air into the heating furnace was prevented.
Then, by continuing the heating of the optical fiber preform and the lowering of the take-up chuck, the molten optical fiber preform was stretched so that the outer diameter was 25 mm.

 In the first embodiment, as described above, the upper opening of the heating furnace is covered with the first upper sealing body or the second upper sealing body according to the position of the upper end portion of the optical fiber preform with respect to the heating furnace. As a result, the inside of the heating furnace was blocked from outside air, and the inflow of outside air into the heating furnace could be prevented.

[Comparative Example 1]
The outer shape is cylindrical, and an upper support rod having an outer diameter of 25 mm and a length of 670 mm and a lower support rod having an outer diameter of 25 mm and a length of 300 mm are fused to both ends of an optical fiber preform having an outer diameter of 50 mm and a length of 500 mm, respectively. Connected.
First, the upper support rod attached to the upper end of the optical fiber preform is gripped by the feeding chuck of the stretching device, and the lower support rod attached to the lower end of the optical fiber preform is gripped by the take-up chuck of the stretching device. .
At this time, in order to cover the upper end portion (length: 300 mm) of the optical fiber preform outside the heating furnace, the upper support rod is inserted into the through hole provided in the central portion of the cylindrical upper seal body having a height of 320 mm. The insertion upper seal body was disposed on the upper end surface of the heating furnace.
In addition, the height of the upper seal body is 320 mm, the length of the upper end portion of the optical fiber preform outside the heating furnace is 300 mm, the thickness of the upper end portion of the upper seal body is 10 mm, the upper end surface and the upper portion of the optical fiber preform. It was made equal to the length combined with the size of the gap 10 mm for preventing the seal body from contacting.

Next, the optical fiber preform was inserted into the heating furnace from the lower end, and the take-up chuck was lowered while heating the optical fiber preform in the heating furnace.
Here, regardless of the position of the upper end portion of the optical fiber preform with respect to the heating furnace, the upper opening of the heating furnace was covered with the upper seal body.
Then, by continuing the heating of the optical fiber preform and the lowering of the take-up chuck, the molten optical fiber preform was stretched so that the outer diameter was 25 mm.

[Example 2]
With reference to FIG. 3, the extending | stretching method of the optical fiber preform | base_material of Example 2 is demonstrated.
The outer shape is cylindrical, and an upper support rod having an outer diameter of 25 mm and a length of 420 mm and a lower support rod having an outer diameter of 25 mm and a length of 300 mm are fused to both ends of an optical fiber preform having an outer diameter of 50 mm and a length of 500 mm, respectively. Connected.
In addition, the upper end part of the optical fiber preform before stretching was tapered. The tapered shape has a shape in which the outer shape gradually increases from the upper end surface of the optical fiber preform toward the lower end surface, and occurs over a length of 30 mm from the upper end surface of the optical fiber preform toward the lower end surface. It was.
First, the upper support rod attached to the upper end of the optical fiber preform is gripped by the feeding chuck of the stretching device, and the lower support rod attached to the lower end of the optical fiber preform is gripped by the take-up chuck of the stretching device. .
At this time, the optical fiber preform is inserted into a through hole provided in the central portion of the first upper seal body made of a disc-shaped seal ring having a thickness of 20 mm, and the first upper seal body is moved to the heating furnace. It was arranged on the upper end surface of. Moreover, the optical fiber preform was inserted into the space (through portion) of the cylindrical third upper seal body having a height of 30 mm, and the third upper seal body was disposed on the first upper seal body. Further, the upper support rod is inserted into the through hole provided in the center of the second upper seal body made of a disc-shaped seal ring having a thickness of 20 mm, and the second upper seal body is placed on the glass rod. Arranged on the end face.
Note that the third upper seal body and the second upper seal body were spaced apart. The length of the upper support rod is 420 mm, the distance from the heater part of the heating furnace to the upper end surface of the heating furnace is 200 mm, the thickness of the first upper seal body is 20 mm, and the thickness of the second upper seal body is 20 mm. The height of the third upper seal body is equal to 30 mm, and the length of the portion where the upper support rod is gripped by the feed chuck is 150 mm.
Further, a lower support rod was inserted into a through hole provided in the central portion of the lower seal body made of a disc-shaped seal ring having a thickness of 20 mm, and the lower seal body was disposed on the lower end surface of the heating furnace.

Next, the optical fiber preform was inserted into the heating furnace from the lower end, and the take-up chuck was lowered while heating the optical fiber preform in the heating furnace.
Here, when the proximal end on the heating furnace side in the tapered shape of the upper end portion of the optical fiber preform is outside the heating furnace, the upper opening of the heating furnace is covered with the first upper seal body, thereby Was cut off from outside air to prevent inflow of outside air into the heating furnace.
Further, when the optical fiber preform is stretched and the proximal end on the heating furnace side in the tapered shape of the upper end portion of the optical fiber preform is fed into the heating furnace, the second upper seal body is moved to the third upper portion. The inside of the heating furnace is shut off from the outside air by covering the upper opening of the heating furnace with the second upper sealing body and the third upper sealing body over the sealing body, and the outside air into the heating furnace is blocked. Inflow was prevented.
Then, by continuing the heating of the optical fiber preform and the lowering of the take-up chuck, the molten optical fiber preform was stretched so that the outer diameter was 25 mm.

 In the second embodiment, as described above, depending on the position of the upper end portion of the optical fiber preform with respect to the heating furnace, the first upper seal body, or the second upper seal body and the third upper seal body. By covering the upper opening of the heating furnace, the inside of the heating furnace was shielded from the outside air, and the inflow of outside air into the heating furnace could be prevented.

DESCRIPTION OF SYMBOLS 10,50 ... Stretching apparatus, 11 ... Heater part, 12 ... Heat insulating material, 13, 51 ... Heating furnace, 14 ... Delivery chuck, 15 ... Take-off chuck, 16, 52 .... First upper seal body, 17, 53 ... upper opening, 18, 55 ... second upper seal body, 19 ... lower seal body, 20 ... lower opening, 30, 70 ... Glass rod, 31, 71 ... Upper support bar, 32 ... Lower support bar, 54 ... Third upper seal body.

Claims (8)

At both ends of the glass rod, an upper support bar and a lower support bar having a smaller outer diameter than the glass rod are attached, and the glass rods to which the upper support bar and the lower support bar are attached are inserted into a heating furnace and heated. The glass rod is softened by treatment, and the softened glass rod is stretched so as to have a predetermined outer diameter.
When the upper end surface of the glass rod is outside the heating furnace, a first sealing body that has a through hole that surrounds the outer periphery of the glass rod and allows the glass rod to pass therethrough is formed on the upper end surface of the heating furnace. By placing and covering the upper opening of the heating furnace by the first seal body, the inside of the heating furnace is shut off from the outside air,
When the upper end surface of the glass rod is in the heating furnace, a second seal body surrounding the outer periphery of the upper support rod and having a through-hole through which the upper support rod can pass is provided as the first seal. A method for stretching a glass rod, wherein the interior of the heating furnace is shielded from outside air by covering the body and covering the upper opening of the heating furnace with the second sealing body.  The glass rod stretching method according to claim 1, wherein the first seal body is a seal ring.  The glass rod stretching method according to claim 1, wherein the second seal body is a seal ring.  The method of drawing a glass rod according to claim 2 or 3, wherein the seal ring is a quartz seal ring. A glass rod drawing apparatus comprising: a heating furnace for heating a glass rod; and a feeding chuck and a take-off chuck for the glass rod,
The glass rod is allowed to pass through, and has a through hole that overlaps the upper opening of the heating furnace, and when the upper end surface of the glass rod is outside the heating furnace, the upper opening of the heating furnace is A first sealing body to be covered is provided on the upper end surface of the heating furnace so as to surround the outer periphery of the glass rod,
An upper support rod attached to the upper end of the glass rod and having an outer diameter smaller than that of the glass rod is allowed to pass through, and has a through hole that overlaps the upper opening of the heating furnace. An apparatus for stretching a glass rod, wherein a second seal body is provided that overlaps with the first seal body and covers an upper opening of the heating furnace when an end face is in the heating furnace.  6. The glass rod stretching apparatus according to claim 5, wherein the first seal body is a seal ring.  The glass rod stretching device according to claim 5 or 6, wherein the second seal body is a seal ring.  The glass rod stretching device according to claim 6 or 7, wherein the seal ring is a quartz seal ring.

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