JP6539609B2 - Sintering apparatus and sintering method - Google Patents

Description

  The present invention relates to an apparatus and method for sintering a porous glass base material.

  VAD method, OVD method, etc. are known as a manufacturing method of the glass base material for optical fibers. In these methods, first, a glass raw material is burned in a flame to generate fine glass particles by hydrolysis. Subsequently, a porous glass base material is formed by adhering the produced | generated glass particulates to the rotating target rod. Furthermore, the porous glass preform is sintered at 1400 to 1600 ° C. to obtain a transparent optical fiber glass preform.

  The porous glass base material is sintered under an atmosphere of a specific composition. If outside air intrudes into a core tube containing a porous glass base during sintering in a sintering apparatus, the quality of the manufactured transparent glass base is degraded. In addition, if the atmosphere in the reactor core leaks to the outside, it pollutes the environment. Therefore, various structures for closing a core tube in a sintering apparatus have been proposed (see, for example, Patent Document 1).

JP, 2002-226218, A

  The structure for closing the core tube during sintering is complicated in structure, difficult to assemble, and difficult to operate. Furthermore, the airtightness is reduced due to the deterioration of parts as the operating time of the sintering apparatus increases. Therefore, a simple and long-life structure is sought to prevent the entry of outside air into the core tube during sintering and the leakage of the gas in the tube.

  According to a first aspect of the present invention, there is provided a sintering apparatus for sintering a porous glass base material, which comprises a core tube surrounded by a heater, which accommodates the porous glass base material, and a porous glass base material. It has an insertion hole through which the combined holding rod is inserted, and has a cover member attached to one end of the core tube, a supply port for introducing a seal gas, and an exhaust port for discharging the seal gas. A cylindrical member which covers a seal chamber provided in a lid member and a holding rod is inserted inside the seal chamber to generate an atmospheric pressure difference between the gas in the core of the furnace core and the gas in the seal chamber And a sintering apparatus characterized by comprising:

  According to a first aspect of the present invention, there is provided a sintering method in which a porous glass base material is contained in a core tube and sintered, and the pressure of the gas in the core tube is maintained higher than atmospheric pressure. A heater surrounding the core tube heats the porous glass base material contained in the core tube, and a holding rod coupled to the porous glass base material and an insertion hole through which the holding rod is inserted A portion of the gas in the pipe is covered in a sealing chamber provided in the lid member so as to cover the insertion hole through the lid member attached to one end and the holding rod and the cylindrical member inserted with the holding rod. Porous glass characterized in that a part of the gas in the pipe discharged and discharged into the seal chamber is discharged from the discharge port provided in the seal chamber together with the seal gas supplied from the supply port provided in the seal chamber. A method of sintering a base material is provided.

  The above summary of the invention does not enumerate all of the features of the present invention. A subcombination of these feature groups can also be an invention.

FIG. 2 is a schematic cross-sectional view showing the structure of a sintering device 10. It is a figure explaining the seal structure in sintering device 10. As shown in FIG. 10 is a graph showing the relationship between the internal pressure of the furnace tube 12 and the flow rate of gas flowing to the cylindrical chamber 24. FIG. 7 is a schematic view illustrating the specification of a cylindrical member 25.

  Hereinafter, the present invention will be described through embodiments of the invention. The following embodiments do not limit the claimed invention. Moreover, not all combinations of features described in the embodiments are essential to the solution of the invention.

  FIG. 1 is a schematic cross-sectional view showing the structure of a sintering apparatus 10. The sintering apparatus 10 includes a heater 11, a core tube 12 and a rotating chuck 15. Further, at the upper end of the core tube 12 in the drawing, a lid member 18, a cylindrical chamber 24, a cylindrical member 25 and an upper lid member 13 are disposed.

  The core tube 12 has an elongated cylindrical shape and has an inner diameter and a length capable of accommodating the porous glass base material 16. The heater 11 is disposed to laterally surround the furnace tube 12. At the bottom of the core tube 12, a gas introduction port 17 is provided inside the core tube 12 to supply an in-pipe gas serving as an atmosphere for sintering the porous glass base material 16. When the porous glass base material 16 is sintered in the sintering apparatus 10, the inside of the core tube 12 is filled with an in-pipe gas based on He or the like.

  The rotary chuck 15 is disposed above the core tube 12 in the figure, and holds the upper portion of the holding rod 14 coupled to the porous glass preform 16 housed in the core tube 12. Further, the rotary chuck 15 raises and lowers the held holding bar 14 and rotates the porous glass base material 16 with the holding bar 14 as a rotation axis. Thereby, the whole porous glass base material 16 can be efficiently heated uniformly.

  A seal structure is formed at the upper end of the core tube 12 to close the core tube 12 containing the porous glass preform 16. In the illustrated sintering apparatus 10, a lid member 18 is placed at the upper end of the core tube 12. The lid member 18 has an insertion hole through which the holding rod 14 is inserted at substantially the center. Further, the lid member 18 is provided with a gas discharge port 21 for communicating the inside and the outside of the furnace tube 12.

  A cylindrical member 25 and a cylindrical chamber 24 which form a sealing structure are disposed on the upper surface of the lid member 18 in the figure. The holding rod 14 is inserted through substantially the center of the cylindrical member 25.

  The cylindrical chamber 24 is disposed on the upper surface of the lid member 18 in the drawing, covering the cylindrical member 25. Furthermore, the upper end of the cylindrical chamber 24 is closed by the upper lid member 13. The holding rod 14 also penetrates the upper lid member 13. The cylindrical chamber 24 and the upper lid member 13 form a seal chamber in the upper portion of the core tube 12.

  FIG. 2 is an enlarged view of a seal structure formed on the upper portion of the core tube 12 in the sintering apparatus 10. As shown in FIG. Elements in common with FIG. 1 are assigned the same reference numerals as in FIG. 1 and redundant explanations are omitted.

  The gas discharge port 21 provided in the lid member 18 communicates the inside of the core tube 12 to the outside, and directly discharges the gas from the inside of the core tube 12 to the outside. Thereby, for example, when the gas pressure in the core tube 12 is rapidly increased, the impact applied to the core tube 12 can be alleviated. The gas in the pipe discharged from the gas discharge port 21 is led to exhaust means and an exhaust treatment device which are not shown.

  The cylindrical chamber 24 has a supply port 22 supplied with the seal gas and an exhaust port 23 for discharging the supplied seal gas on its side. The seal gas may be, for example, the atmosphere. The gas exhausted from the exhaust port 23 includes the seal gas as well as the gas in the pipe leaking from the core pipe 12 to the cylindrical chamber 24. Therefore, the seal gas discharged from the exhaust port 23 is led to the exhaust means and the exhaust treatment device which are not shown.

The cylindrical member 25 has a longitudinally long cylindrical shape. The cylindrical chamber 24 has an inner diameter and height greater than the outer diameter and height of the cylindrical member 25. Therefore, the circular cylinder member 25, within the cylindrical chamber 24, smoothly move along the holding bar 14.

  In the sintering apparatus 10 having the seal structure as described above, the pressure in the core tube 12 is maintained higher than the atmospheric pressure when the porous glass base material 16 is sintered. Thereby, in the sintering device 10, the core tube 12 is passed through the gap between the insertion hole 19 of the lid member 18 and the holding rod 14 and the inner surface of the through hole 26 of the cylindrical member 25 and the holding rod 14. The porous glass base material 16 is sintered while flowing a part of the gas in the core tube 12 into the cylindrical chamber 24.

In the sintering apparatus 10, when the holding rod 14 is inserted through the cylindrical member 25, the pressure difference Δp between the core tube 12 side and the cylindrical chamber 24 side of the cylindrical member 25 is L when the length of the cylinder is L, It is represented by Formula 1 below.

Here, the hydrodynamic equivalent area S is represented by the following equation 2 when the flow passage area is A and the wet etching length is s. Here, the wetted weft length s is the total sum of the lengths of the support rod outer wall surface and the cylinder inner wall surface in contact with the fluid in the flow channel cross section.

Further, when the flow passage area A and the wet contact length s represent the diameter of the holding rod 14 as D and the hole diameter of the cylindrical member as d, they are expressed by the following expressions 3 and 4, respectively.

Furthermore, the flow velocity u of the gas flowing through the gap between the cylindrical member 25 and the holding rod 14 is expressed by the following equation 5 when the gas flow rate flowing through the gap is represented by q.

  Therefore, the pressure difference between the atmospheric pressure and the internal pressure of the core tube 12, the length of the cylindrical member 25 and the diameter of the through hole 26 are determined, and the above equation 1 to 5 are used. The gas in the core tube 12 can be controlled to flow at a predetermined flow rate toward 24. In this case, the value of the diameter D of the holding rod is determined by the design such as the mechanical strength of the device.

  For example, when D = 40 mm, the gas flow rate q flowing through the gap is 0.1 L / min and the pressure difference is 500 Pa, the hole diameter d of the cylindrical member is d = 40.17 mm. It is preferable to reduce the hole diameter of the cylindrical member and narrow the gap with the holding rod, and thus the pressure difference can be increased, but in consideration of the manufacturing accuracy of the outer diameter of the holding rod and the manufacturing accuracy of the hole of the cylindrical member, The lower limit of the difference between the hole diameter d of the cylindrical member and the diameter D of the support rod may be approximately dD = 0.1 mm.

  In the present embodiment, when the outer diameter of the holding rod 14 is 40 mm, the clearance between the inner surface of the insertion hole 19 through which the holding rod 1 is inserted in the cylindrical member 25 and the holding rod 14 is 0.1 mm or more. It was in the range of .15 mm or less. If this clearance is less than 0.1 mm, the possibility of contact between the cylindrical member 25 and the holding rod 14 increases, and there is a concern that the smooth lifting and lowering of the holding rod 14 may be hindered.

  On the other hand, when the above-mentioned clearance exceeds 0.15 mm, the seal gas in the cylindrical chamber 24 easily intrudes into the core tube 12 from the gap between the cylindrical member 25 and the holding rod 14. From the same point of view, by setting the length of the cylindrical member 25 to 100 mm or more, it is possible to effectively prevent the seal gas from entering the core tube 12.

  From the viewpoint of achieving smooth relative movement of the holding rod 14 and the cylindrical member 25, the perpendicularity of the inner surface of the through hole 26 in the cylindrical member 25 is 0.01 mm with respect to the surface contacting the upper surface of the lid member 18. It is preferable that it is the following.

  On the other hand, it is desirable that the upper surface of the cover member 18 and the lower surface of the cylindrical member 25 be in close contact with each other from the viewpoint of blocking the gas flow between the cylindrical chamber 24 and the core tube 12. From such a point of view, it is preferable to set the surface roughness of the surfaces of the lid member 18 and the cylindrical member 25 in contact with each other to Ra 2.0 or less.

  Further, from the viewpoint of smoothly shifting the cylindrical member 25 with respect to the holding rod 14, the cylindrical member 25 preferably has lubricity with respect to the holding rod 14 at least on the inner surface of the through hole 26. Also, the holding rod 14 is at a high temperature, particularly when it is pulled up from the furnace tube 12. Therefore, the cylindrical member 25 preferably has heat resistance to the temperature of the holding rod 14. As a material which has such a characteristic, the bulk material of carbon can be illustrated, for example.

  In the above example, the cylindrical chamber 24 is used as the sealing chamber and the cylindrical member 25 is used as the sealing member, but the shapes of the sealing chamber and the sealing member are not limited to the cylindrical shape, of course.

[Example of experiment]
A cylindrical member 25 having a hole diameter of 40.14 mm and a length of 150 mm was produced and placed in a cylinder provided on the upper lid of the core tube. The outer diameter of the holding rod was 40 mm (design value). The gas flow rate flowing through the gap between the holding rod 14 and the through hole 26 of the cylindrical member 25 was measured while changing the internal pressure of the core tube 12.

  FIG. 3 is a graph showing the measurement results of the above measurement. As shown, there is a strong correlation between the internal pressure of the core tube 12 and the gas flow rate, and it can be seen that the pressure in the core tube 12 can be managed by controlling the gas flow rate. Therefore, it is preferable to control the flow rate of the gas flowing from the furnace tube 12 toward the cylindrical chamber 24 to be a predetermined flow rate.

  In addition, when the pressure in the core tube was set to about 1000 Pa to 2000 Pa in gauge pressure, it was confirmed that the amount of gas flowing in the gap was also suppressed, and it could withstand use. As a result of sintering the porous glass base while maintaining the pressure in the core tube at 1000 Pa, it was confirmed that there is no problem in the optical characteristics of the obtained glass base.

  Thus, in the sintering device 10, the clearance (clearance) between the hole of the cylindrical member provided in the cylinder on the upper lid and the holding bar is 0.1 mm to 0.15 mm, and the length of the cylindrical member is 100 mm or more By flowing the gas from the core tube toward the cylinder and sintering it while exhausting from the exhaust port of the cylinder, it is possible to prevent the entry of outside air from the gap into the core tube, and the glass base material Can be sintered without adversely affecting the properties of

The following equation 6 represents the conditions under which the cylindrical member 25 is lifted by the pressure of the gas in the core tube 12 in the sintering device 10. FIG. 4 is a diagram for explaining values used in Equation 6.

  As described above, when the gas in the core tube 12 reaches the pressure Pc, the cylindrical member 25 floats up. As a result, a large amount of gas in the core tube 12 flows from the core tube 12 to the cylindrical chamber 24 through the wide gap between the upper surface of the lid member 18 and the lower surface of the cylindrical member 25. As a result, the gas pressure in the tube of the furnace tube 12 is rapidly reduced. Therefore, by setting the mass or the like of the cylindrical member 25 in accordance with the pressure resistance of the core tube 12, the upper limit of the internal pressure of the core tube 12 can be restricted to prevent the failure of the core tube 12 due to the increase of the internal pressure.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It is apparent to those skilled in the art that various changes or modifications can be added to the above embodiment. It is also apparent from the scope of the claims that the embodiments added with such alterations or improvements can be included in the technical scope of the present invention.

  The execution order of each process such as operations, procedures, steps, and steps in the apparatuses, systems, programs, and methods shown in the claims, the specification, and the drawings is particularly “before”, “preceding” It is to be noted that “it is not explicitly stated as“ etc. ”and can be realized in any order as long as the output of the previous process is not used in the later process. With regard to the flow of operations in the claims, the specification and the drawings, even if it is described using “first,” “next,” etc. for convenience, it means that it is essential to carry out in this order. It is not a thing.

DESCRIPTION OF SYMBOLS 10 sintering apparatus, 11 heater, 12 core tube, 13 upper lid member, 14 holding rod, 15 rotary chuck, 16 porous glass base material, 17 gas introduction port, 18 lid member, 19 insertion hole, 21 gas discharge port, 22 Supply port, 23 exhaust port, 24 cylindrical chamber, 25 cylindrical member, 26 through hole

Claims (8)

A sintering apparatus for sintering a porous glass base material, comprising:
A heater-wrapped core tube containing a porous glass matrix;
A lid member attached to one end of the core tube, having an insertion hole through which the holding rod coupled to the porous glass base material is inserted
A gas exhaust port provided on the lid member, communicating the inside of the core tube to the outside, and discharging the gas from the inside of the core tube directly to the outside;
A seal chamber provided in the lid member to cover the insertion hole and having a supply port for introducing a seal gas and a discharge port for discharging the seal gas;
The sintered body is characterized by comprising: a cylindrical member which is inserted through the holding rod inside the seal chamber and causes a pressure difference between the gas inside the core tube and the gas inside the seal chamber. Connection device. The sintering apparatus according to claim 1 , wherein the cylindrical member separates from the lid member and reduces the pressure difference when the pressure difference becomes larger than a predetermined threshold value. The sintering apparatus according to claim 1 or 2 , wherein the clearance between the cylindrical member and the holding bar is 0.1 mm or more and 0.15 mm or less, and the length of the cylindrical member is 100 mm or more. . The sintering apparatus according to any one of claims 1 to 3 , wherein a surface roughness of a contact surface of the cylindrical member in contact with the lid member is Ra 2.0 or less. The sintering apparatus according to claim 4 , wherein the perpendicularity of the inner surface of the through hole in the cylindrical member through which the holding bar is inserted is 0.01 mm or less with respect to the contact surface. The sintering apparatus according to any one of claims 1 to 5 , wherein a surface roughness of a surface of the lid member in contact with the cylindrical member is Ra 2.0 or less. A sintering method in which a porous glass base material is contained in a core tube and sintered,
The porous glass base material housed in the core tube is heated by the heater surrounding the core tube while maintaining the pressure of the gas in the core tube higher than the atmospheric pressure,
Between a holding rod coupled to a porous glass base material, and a lid member having an insertion hole through which the holding rod is inserted and attached to one end of the core tube, and the holding rod and the holding rod And a part of the gas in the pipe is discharged to a seal chamber provided in the lid member so as to cover the insertion hole and between the cylindrical member into which the
A part of the gas in the pipe discharged into the seal chamber is discharged to the outside from a discharge port provided in the seal chamber together with a seal gas supplied from a supply port provided in the seal chamber;
A method of sintering a porous glass base material , wherein the gas in the pipe is directly discharged from the inside of the core tube to the outside by a gas exhaust port which communicates the inside of the core tube to the outside . The method of sintering a porous glass base material according to claim 7 , wherein the flow rate of gas flowing from the core tube to the seal chamber is controlled to a predetermined flow rate.

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