JP5831181B2 - Glass base material manufacturing method and manufacturing apparatus - Google Patents

Description

  The present invention relates to a glass base material manufacturing method and a manufacturing apparatus for manufacturing a glass base material for an optical fiber by inserting a glass rod into a glass pipe and heating and integrating them.

  As a method of manufacturing a glass base material suitable for manufacturing an optical fiber having a complicated refractive index distribution such as a dispersion compensating fiber or a dispersion shifted fiber, a glass rod is inserted into a glass pipe and then both are heated and integrated. The rod-in collapse method is known.

  As a method for manufacturing a glass base material by this rod in collapse method, as shown in FIG. 4, excess gas supplied from a gas supply pipe 27 is released to a gas exhaust pipe 31 via a bypass pipe 41, A method is known in which the flow rate of gas flowing into 41 is measured, and the continuous integration process is started after the difference between the measured gas flow rate and the gas flow rate supplied from the gas supply pipe falls below a predetermined value (for example, , See Patent Document 1).

  According to this manufacturing method, it is possible to accurately detect the progress of integration in the portion hidden in the heating furnace, and by controlling the gas supply into the glass pipe according to the detection result, In addition to avoiding breakage, it is possible to prevent the occurrence of inconvenience such as entrainment of the outside air on the downstream side, and to manufacture a glass base material having a stable quality.

JP 2005-162531 A

  By the way, in the above manufacturing method, when the start of integration is detected, the supply of gas from the gas supply pipe 27 is stopped, and the gas supply side is sucked by the vacuum suction device 47 to start the continuous integration process. For this reason, when the integration at the integration start end is incomplete (a gap is left), the gas is sucked from the gas supply side, so that the unclean gas on the gas exhaust side where water vapor or the like remains is glass. There is a possibility that moisture, impurities, etc. may be taken into the optical fiber preform after collapsing into the pipe. When an optical fiber is manufactured from such a base material in which moisture or the like is taken in, an absorption loss (OH loss) due to the OH group increases in the optical fiber.

  The objective of this invention is providing the manufacturing method and manufacturing apparatus of a glass base material which can manufacture a high quality glass base material smoothly.

The method for producing a glass base material of the present invention capable of solving the above-described problem is to connect a gas supply pipe to the primary side consisting of one end side of a glass pipe into which a glass rod is inserted and from the other end side of the glass pipe. A state in which a gas exhaust pipe is connected to the secondary side, and a bypass pipe for passing an excess of gas supplied from the gas supply pipe to the glass pipe is connected between the gas supply pipe and the gas exhaust pipe so,
A starting end integration process is performed in which a part of the glass pipe in the axial direction is heated by a heating means to integrate a part of the glass pipe in the axial direction and a part of the glass rod in the axial direction, A glass base material manufacturing method for obtaining a glass base material by performing a continuous integration process in which a heating means is moved relative to the glass pipe to integrate the glass pipe and the glass rod in the axial direction. And
The starting end integration process and the continuous integration process are performed while the primary pressure of the glass pipe is always maintained to be equal to or higher than the secondary pressure.

  In the method for producing a glass base material of the present invention, a gas suction device is provided only on the secondary side of the glass pipe, and the gas on the secondary side is supplied by the gas suction device during the start-end integration processing and the continuous integration processing. It is preferable that the primary pressure of the glass pipe is always maintained at or higher than the secondary pressure by suction from the gas exhaust pipe.

The glass base material manufacturing apparatus of the present invention is a glass base material manufacturing apparatus that manufactures a glass base material by heating and integrating in a state where a glass rod is inserted into a glass pipe,
A gas supply pipe connected to a primary side composed of one end side of the glass pipe into which the glass rod is inserted;
A gas exhaust pipe connected to the secondary side consisting of the other end of the glass pipe;
Flow rate control means for adjusting the flow rate to the gas supply pipe and feeding the gas;
A bypass pipe connected between the gas supply pipe and the gas exhaust pipe to flow an excess of gas supplied from the gas supply pipe to the glass pipe;
Heating means for moving the glass pipe and the glass rod together by moving relative to the glass pipe along the axial direction of the glass pipe while heating a part of the glass pipe in the axial direction;
A gas suction device that is provided only on the secondary side of the glass pipe and sucks the gas on the secondary side from the gas exhaust pipe so as to maintain the primary side pressure of the glass pipe at or above the secondary side pressure;
It is characterized by providing.

  According to the present invention, the integration process is performed while the primary pressure of the glass pipe is always maintained at or above the secondary pressure. Thereby, even if integration at the starting end of the glass pipe is incomplete, gas does not flow from the secondary side to the primary side in the glass pipe. Therefore, the backflow of the secondary side exhaust gas into the glass pipe can be prevented, and mixing of moisture and impurities can be prevented and a high-quality glass base material can be manufactured. That is, an optical fiber with low transmission loss and high reliability can be manufactured from the manufactured glass preform.

It is a schematic block diagram which shows an example of the manufacturing apparatus of the glass base material which concerns on this invention. It is a schematic block diagram which shows the state after the start of an integration process with the manufacturing apparatus shown in FIG. It is a schematic block diagram which shows the modification of the manufacturing apparatus of FIG. It is a schematic block diagram which shows an example of the manufacturing apparatus of the conventional glass base material.

Hereinafter, an example of an embodiment of a glass base material manufacturing method and manufacturing apparatus according to the present invention will be described with reference to the drawings.
As shown in FIG. 1, the glass base material manufacturing apparatus 21 according to the present embodiment obtains a glass base material having a predetermined length by a so-called rod-in collapse method.

  The manufacturing apparatus 21 includes a first seal box 29 as a pipe joint that hermetically connects the gas supply pipe 27 to the primary side that is one end side of the glass pipe 25 into which the glass rod 23 is inserted, and the other end of the glass pipe 25. A second seal box 33 is provided as a pipe joint for airtightly connecting the gas exhaust pipe 31 to the secondary side. The first seal box 29 and the second seal box 33 are supported by the base 35, and thereby the glass pipe 25 in which the glass rod 23 is inserted and held is supported horizontally.

  The manufacturing apparatus 21 includes a heating furnace 37 as a heating means for heating the glass pipe 25. The heating furnace 37 is configured by disposing a substantially annular heater 37b in a substantially annular furnace body 37a surrounding the outer periphery of the glass pipe 25, and can heat the glass pipe 25 substantially uniformly in the circumferential direction. The heating furnace 37 is installed so as to be movable along the direction of the central axis of the glass pipe 25 as indicated by an arrow A in FIG. The heating furnace 37 may be fixed and the glass pipe 25 may move along the axial direction, or both may move relatively.

  A gas supply means (not shown) is connected to the gas supply pipe 27, and a predetermined gas is supplied from this gas supply means. In the middle of the gas supply pipe 27, a flow rate control means (MFC) 39 for controlling the flow rate of the gas supplied from the gas supply means to the gas supply pipe 27 is provided.

The gas supply means supplies an etching gas such as sulfur hexafluoride (SF ₆ ) to the gas supply pipe 27 in the step of etching the inner peripheral surface of the glass pipe 25 before inserting the glass rod 23 into the glass pipe 25. When performing the start end integration process, a chlorine (Cl ₂ ) gas having a high dehydrating effect is supplied to the gas supply pipe 27.

A bypass pipe 41 is connected to the gas supply pipe 27 and the gas exhaust pipe 31. The bypass pipe 41 is provided with a gas amount adjusting valve 43 and an automatic valve 49 for releasing excess gas to the bypass pipe 41 so that the gas pressure supplied from the gas supply pipe 27 into the glass pipe 25 does not exceed a certain level. Is provided. In the middle of the bypass pipe 41, a bypass flow rate measuring means (MFM) 45 for detecting the flow rate of the flowing gas is provided.
The gas exhaust pipe 31 is connected to a vacuum suction device 48 that is a gas suction device. The vacuum suction device 48 sucks the gas in the gas exhaust pipe 31.

  The manufacturing apparatus 21 includes a control device (CPU) 60. The control device 60 calculates the difference between the gas flow rate measured by the bypass flow rate measuring means 45 and the gas flow rate supplied from the gas supply pipe 27.

  In the glass pipe 25, dummy pipes 26a and 26b are airtightly bonded to both ends in advance. The primary dummy pipe 26 a is connected to the gas supply pipe 27 via the first seal box 29, and the secondary dummy pipe 26 b is connected to the gas exhaust pipe 31 via the second seal box 33. .

  The glass pipe 25 having the dummy pipes 26a and 26b connected to both ends is connected to the first seal box 29 and the second seal box 33 with the glass rod 23 not inserted, and an etching gas is caused to flow therein. The inner peripheral surface is etched. After the etching process, the first seal box 29 and the second seal box 33 are once removed and the glass rod 23 is inserted and held. The first seal box 29 and the second seal box are once again held. 33, the start end integration process and the continuous integration process for integrating the glass rod 23 and the glass pipe 25 are sequentially performed.

Next, an example of the procedure of the glass base material manufacturing method by the manufacturing apparatus 21 will be described.
A glass rod 23 serving as a core portion of the optical fiber and a glass pipe 25 serving as a part of the clad portion of the optical fiber are prepared in advance. As shown in FIG. 1, the glass pipe 25 is prepared with dummy pipes 26a and 26b joined to both ends.

  First, dummy pipes 26 a and 26 b at both ends of the glass pipe 25 are attached to the first seal box 29 and the second seal box 33, and the gas supply pipe 27 and the gas exhaust pipe 31 are connected to both ends of the glass pipe 25. To the state.

Thereafter, SF ₆ gas and Cl ₂ gas are respectively supplied to the glass pipe 25 at a predetermined flow rate by the gas supply means, the flow rate control means 39 and the gas supply pipe 27, and gas is supplied to the gas exhaust pipe 31 by the vacuum suction device 48. Pull in. Thereby, the inside of the glass pipe 25 is replaced with these gases. An etching process is performed in which the glass pipe 25 is heated using the heating furnace 37 while the gas is flowing, and the inner surface of the glass pipe 25 is etched.

  In this etching process, the heating furnace 37 is moved at a substantially constant speed in a range that is an effective portion of the optical fiber in the glass pipe 25 so that the etching amount becomes substantially constant. The etching is terminated after the inner diameter of the glass pipe 25 reaches a predetermined value by this etching process.

Next, the second seal box 33 is removed from the glass pipe 25, and the glass rod 23 is inserted and held inside the glass pipe 25.
Then, after the second seal box 33 is attached to the glass pipe 25 again, the vacuum suction device 48 is supplied while Cl ₂ gas is supplied into the glass pipe 25 by the gas supply means, the flow rate control means 39 and the gas supply pipe 27. Then, gas is drawn into the gas exhaust pipe 31.

  Thus, when the pressure in the gap between the glass rod 23 and the glass pipe 25 is higher than the outside air pressure, the outside air enters the inside of the glass pipe 25 from the connecting portion with the first seal box 29 or the second seal box 33. Intrusion is prevented.

Then, after the inside of the glass pipe 25 is sufficiently replaced with Cl ₂ gas, the glass pipe 25 is heated in the heating furnace 37 while the pressure inside the glass pipe 25 is kept higher than the pressure outside the glass pipe 25, and dehydration treatment is performed. I do. Thereby, the water | moisture content adhering to the outer peripheral surface of the glass rod 23 and the inner surface of the glass pipe 25 is removed.

Thereafter, the automatic valve 49 is opened, and a part of the glass pipe 25 in the axial direction and a part of the glass rod 23 in the axial direction are heated and integrated at an arbitrary position (hereinafter referred to as a starting position) on the secondary side of the glass pipe 25. The starting end integration process is implemented. At this time, gases such as Cl ₂ , O ₂ , and N ₂ are supplied to the gas supply pipe 27, and all of the gases supplied to the gas supply pipe 27 still flow toward the glass pipe 25, It is discharged to the exhaust pipe 31.

  After the start end integration process is started, the detection value of the bypass flow rate measuring means 45 is monitored. When the glass pipe 25 and the glass rod 23 are welded and integration is started, the gap in the glass pipe 25 is narrowed and the gas does not easily flow to the gas exhaust pipe 31 side. Therefore, the pressure in the glass pipe 25 increases with the progress of integration. Thereby, the primary side pressure P1 of the glass pipe 25 is kept more than the secondary side pressure P2 of the glass pipe 25.

  Then, the primary pressure P1 of the glass pipe 25 increases, and surplus gas exceeding the preset reference pressure flows to the bypass pipe 41. That is, as the start-end integration progresses, the amount of gas flowing to the bypass pipe 41 increases, and the progress of the start-end integration is detected by monitoring the amount of gas flowing to the bypass pipe 41. Can do.

  After the start-end integration process is started, the gas on the secondary side of the glass pipe 25 is also collected by the vacuum suction device 48 after the inflow of gas from the gas supply pipe 27 to the bypass pipe 41 starts to increase as the integration progresses. Is drawn into the gas exhaust pipe 31, and the primary pressure P1 of the glass pipe 25 is always maintained to be equal to or higher than the secondary pressure P2.

  In addition, after the inflow of gas from the gas supply pipe 27 to the bypass pipe 41 starts to increase with the progress of integration, the gas supply quantity to the gas supply pipe 27 is gradually decreased by the flow rate control means 39. The conditions of the primary side pressure P1 and the secondary side pressure P2 of the glass pipe 25 may be changed so that an unnecessary pressure does not act on the glass pipe 25. Moreover, you may change the kind of gas supplied from a gas supply means.

  When the integration by the start end integration process is completed in the circumferential direction of the glass pipe 25, the inside of the glass pipe 25 at that portion is sealed, and gas cannot pass from the glass pipe 25 to the gas exhaust pipe 31 side. Therefore, the total amount of gas supplied to the gas supply pipe 27 flows to the bypass pipe 41.

  Therefore, when the bypass flow rate measuring means 45 is monitored and the entire amount of the gas supplied to the gas supply pipe 27 flows to the bypass pipe 41, it can be considered that the start end integration process has been completed.

  After the start end integration process is completed, as shown in FIG. 2, the heating furnace 37 is gradually moved from the integration start position to the primary side of the glass pipe 25 to shrink the glass pipe 25 (so-called collapse). Thus, a continuous integration process is performed in which the heating integrated region of the glass pipe 25 and the glass rod 23 is extended to the primary side and integrated in the axial direction. Thereby, both the glass pipe 25 and the glass rod 23 are integrated over predetermined length.

  Even during this continuous integration process, the secondary side gas P1 of the glass pipe 25 is drawn into the gas exhaust pipe 31 by the vacuum suction device 48, and the primary side pressure P1 of the glass pipe 25 is always higher than the secondary side pressure P2. To keep.

  As described above, in the present embodiment, the starting end integration process and the continuous integration process are performed while the primary pressure P1 of the glass pipe 25 is constantly maintained at the secondary pressure P2 or higher. Therefore, even when the integration of the glass pipe 25 and the glass rod 23 is incomplete during the start-end integration process, gas does not flow from the secondary side to the primary side in the glass pipe 25. Accordingly, the backflow of the secondary side exhaust gas into the glass pipe 25 can be prevented, and mixing of moisture and impurities can be prevented and a high-quality glass base material can be manufactured. Thereby, an optical fiber with low transmission loss and high reliability can be manufactured from the manufactured glass preform.

  Further, in the manufacturing apparatus 21 described above, the vacuum suction device 48 is provided only on the secondary side of the glass pipe 25 as a gas suction device that sucks the secondary side gas during the start-end integration process and the continuous integration process. Compared with the manufacturing apparatus of FIG. 4 which is a conventional example in which the pressure is adjusted by sucking the primary side gas, the primary side gas suction device and the gas processing apparatus can be dispensed with. Cost reduction can be achieved.

  In the manufacturing apparatus 21 described above, gas is drawn into the gas exhaust pipe 31 by one vacuum suction device 48 provided on the secondary side. However, as in the manufacturing apparatus 21A shown in FIG. A vacuum pump 51 for strong suction different from the suction device 48 is provided, and a valve 52 provided on the upstream side of the vacuum pump 51 at the time of suction of the secondary gas in the continuous integration process after the start end integration process. May be opened and the vacuum pump 51 may be operated to suck the secondary gas with the vacuum pump 51 having a stronger suction than the vacuum suction device 48.

  In this way, the vacuum suction device 48 and the vacuum pump 51 are appropriately used together to perform suction in the start end integration process and the continuous integration process, thereby adjusting the pressure on the primary side and the secondary side in the continuous integration process. Can be performed with high accuracy. Note that both suction by the vacuum suction device 48 and suction by the vacuum pump 51 may be performed during suction in the continuous integration process after the start-end integration process.

21, 21A: Manufacturing apparatus, 23: Glass rod, 25: Glass pipe, 27: Gas supply pipe, 31: Gas exhaust pipe, 37: Heating furnace (heating means), 39: Flow control means, 41: Bypass pipe, 48 : Vacuum suction device (gas suction device), 51: Vacuum pump (gas suction device), P1: Primary pressure, P2: Secondary pressure

Claims (3)

A gas supply pipe is connected to the primary side consisting of one end of the glass pipe into which the glass rod is inserted, and a gas exhaust pipe is connected to the secondary side consisting of the other end of the glass pipe. In a state where a bypass pipe for flowing excess gas supplied to the glass pipe is connected between the gas supply pipe and the gas exhaust pipe,
A starting end integration process is performed in which a part of the glass pipe in the axial direction is heated by a heating means to integrate a part of the glass pipe in the axial direction and a part of the glass rod in the axial direction, A glass base material manufacturing method for obtaining a glass base material by performing a continuous integration process in which a heating means is moved relative to the glass pipe to integrate the glass pipe and the glass rod in the axial direction. And
The method for producing a glass base material, wherein the starting end integration process and the continuous integration process are performed while the primary pressure of the glass pipe is always maintained to be equal to or higher than the secondary pressure. It is a manufacturing method of the glass base material of Claim 1,
A gas suction device is provided only on the secondary side of the glass pipe, and the glass pipe sucks the secondary side gas from the gas exhaust pipe by the gas suction device during the start end integration process and the continuous integration process. A method for producing a glass base material, characterized in that the primary pressure is always maintained to be equal to or higher than the secondary pressure. A glass base material manufacturing apparatus for manufacturing a glass base material by heating and integrating with a glass rod inserted into a glass pipe,
A gas supply pipe connected to a primary side composed of one end side of the glass pipe into which the glass rod is inserted;
A gas exhaust pipe connected to the secondary side consisting of the other end of the glass pipe;
Flow rate control means for adjusting the flow rate to the gas supply pipe and feeding the gas;
A bypass pipe connected between the gas supply pipe and the gas exhaust pipe to flow an excess of gas supplied from the gas supply pipe to the glass pipe;
Heating means for moving the glass pipe and the glass rod together by moving relative to the glass pipe along the axial direction of the glass pipe while heating a part of the glass pipe in the axial direction;
A gas suction device that is provided only on the secondary side of the glass pipe and sucks the gas on the secondary side from the gas exhaust pipe so as to maintain the primary side pressure of the glass pipe at or above the secondary side pressure;
An apparatus for producing a glass base material, comprising:

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