Glass base material manufacturing apparatus and glass base material manufacturing method

Abstract

To provide a manufacturing apparatus of a glass preform capable of suppressing decentering of the glass preform or non-circularity of a cross-sectional shape of the glass preform; and to provide a manufacturing method of the glass preform.SOLUTION: A manufacturing apparatus of a glass preform includes a furnace core tube capable of storing an untreated base material, a heater provided outside the furnace core tube, a furnace body for storing at least a part of the furnace core tube and the heater, multiple supply ports for supplying gas into the furnace body, and an exhaust port for discharging gas from inside the furnace body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a glass base material manufacturing apparatus and a glass base material manufacturing method. [Background technology]

[0002] Patent Document 1 discloses a manufacturing apparatus for a glass preform (optical fiber preform). This manufacturing apparatus for a glass preform includes a furnace tube capable of accommodating an unprocessed preform, a heater, a furnace body accommodating the furnace tube and the heater, a supply port for supplying gas into the furnace body, and an exhaust port for discharging gas from the furnace body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-124953 Summary of the Invention [Problem to be solved by the invention]

[0004] In general, the temperature of the gas supplied into the furnace through the supply port is often different from the temperature of the heater. When only one supply port is provided to supply gas into the furnace, as in Patent Document 1, a difference occurs between the temperature near the supply port and the temperature of the other areas, making temperature unevenness in the furnace tube more likely to occur. Temperature unevenness in the furnace tube can cause eccentricity of the glass preform and non-circularity of the cross-sectional shape of the glass preform.

[0005] The present invention has been made in consideration of the above circumstances, and aims to provide a glass base material manufacturing apparatus and a glass base material manufacturing method that can suppress eccentricity of the glass base material and non-circularity of the cross-sectional shape of the glass base material. [Means for solving the problem]

[0006] In order to solve the above problem, a glass base material manufacturing apparatus according to one embodiment of the present invention comprises a furnace tube capable of accommodating unprocessed base material, a heater provided outside the furnace tube, a furnace body accommodating at least a portion of the furnace tube and the heater, a plurality of supply ports for supplying gas into the furnace body, and an exhaust port for discharging gas from the furnace body.

[0007] Furthermore, a method for manufacturing a glass base material according to one aspect of the present invention is a method for manufacturing a glass base material that uses a glass base material manufacturing apparatus to perform heat treatment on an untreated base material, and the glass base material manufacturing apparatus includes a furnace tube that can accommodate the untreated base material, a heater provided outside the furnace tube, a furnace body that accommodates at least a portion of the furnace tube and the heater, a plurality of supply ports that supply gas into the furnace body, and an exhaust port that exhausts gas from the furnace body. [Effects of the Invention]

[0008] According to the above aspects of the present invention, it is possible to provide a glass base material manufacturing apparatus and a glass base material manufacturing method that can suppress eccentricity of the glass base material and non-circularity of the cross-sectional shape of the glass base material. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of a glass base material manufacturing apparatus according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along the line II-II in FIG. [Figure 3] FIG. 6 is a cross-sectional view of a glass base material manufacturing apparatus according to a second embodiment. [Figure 4] FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] (First embodiment) Hereinafter, the glass base material manufacturing apparatus and the glass base material manufacturing method according to the first embodiment will be described with reference to the drawings. 1, the glass base material manufacturing apparatus 1A includes a furnace tube 10 capable of accommodating an untreated base material M, a heater 20, a furnace body 30, and a heat insulating material 40. The furnace tube 10 is formed in a cylindrical shape with a bottom, having a furnace tube lower surface 10b and a furnace tube outer circumferential surface (outer circumferential surface of the furnace tube) 10c. A lid L is attached to the open end of the furnace tube 10.

[0011] In this embodiment, the direction along the central axis O of the furnace tube 10 is referred to as the axial direction. Along the axial direction, the side of the lid L is referred to as the upper side, and the side of the lower surface 10b of the furnace tube is referred to as the lower side. A position in the axial direction is simply referred to as the height. A cross section perpendicular to the axial direction is referred to as a transverse cross section. When viewed from the axial direction, a direction intersecting the central axis O is referred to as the radial direction, and a direction going around the central axis O is referred to as the circumferential direction. When viewed from the transverse cross section, the direction approaching the central axis O is referred to as the radially inward direction, and the direction away from the central axis O is referred to as the radially outward direction.

[0012] The untreated preform M is a porous glass body having deposited glass particles. The glass preform is obtained by subjecting the glass particles contained in the untreated preform M to a heat treatment such as sintering. The untreated preform M may be a porous glass body manufactured using a soot method such as the VAD method or the OVD method. When manufacturing an untreated base material M using the soot method, first, oxygen gas, hydrogen gas, inert gas, etc. are flowed from a burner installed in a reaction vessel, and glass raw material gas such as SiCl4 is introduced into the flame that causes these gases to react. This generates glass particles. These glass particles are attached to a target rotating in the reaction vessel, and soot is deposited on the outer periphery of the target. This results in a glass porous body (untreated base material M).

[0013] The glass preform manufacturing apparatus 1A may be, for example, an optical fiber preform manufacturing apparatus. In this case, the target may include a portion that will become the core of the optical fiber. Furthermore, a portion of the target on which soot is not deposited may be used as a support portion 50 described later.

[0014] The lower surface 10b of the muffle tube faces downward, and the outer peripheral surface 10c of the muffle tube faces radially outward. The material of the muffle tube 10 can be, for example, quartz glass. In this embodiment, the outer peripheral surface 10c of the muffle tube is circular in cross section. The muffle tube 10 may be provided with a gas supply port and a gas outlet port (not shown). The gas supply port is a gas supply port for supplying gas to the space (inside the muffle tube 10) in which the untreated base material M is accommodated. The gas outlet port is a gas outlet port for exhausting gas from the space (inside the muffle tube 10) in which the untreated base material M is accommodated. A lid L is attached to the open end (top end) of the muffle tube 10 so as to be freely opened and closed. By opening the lid L, a user can insert the untreated base material M into the muffle tube 10 or remove the sintered base material (glass base material) from the muffle tube 10. When the lid L is closed, the furnace tube 10 is closed, and the inflow of unnecessary gas into the furnace tube 10 is suppressed.

[0015] The untreated base material M is supported within the muffle tube 10 via a support 50. The support 50 penetrates the center of the lid L. Although a detailed description will be omitted, the lid L is configured to be able to seal the inside of the muffle tube 10 with the support 50 penetrating through it. The support 50 may also be configured to be rotatable relative to the lid L. In this case, the untreated base material M can be rotated within the muffle tube 10 by rotating the support 50. In other words, the untreated base material M is supported within the muffle tube 10 in a state where rotation about the central axis O relative to the muffle tube 10 is permitted. When the untreated base material M is heated by the heater 20, rotating the untreated base material M allows the application of heat to the untreated base material M to be uniform in the circumferential direction. Note that the untreated base material M does not necessarily have to be rotatably supported within the muffle tube 10.

[0016] The heater 20 is provided outside the muffle tube 10. In this embodiment, the heater 20 is cylindrical and disposed so as to surround the muffle tube 10 in the circumferential direction. The heater 20 heats the untreated base material M via the muffle tube 10. The heater 20 may be, for example, an electric heater. The heater 20 has a heater outer circumferential surface 20c facing radially outward and a heater inner circumferential surface 20d facing radially inward. The heater inner circumferential surface 20d faces radially opposite the muffle tube outer circumferential surface 10c of the muffle tube 10. Although the heater 20 is a single cylinder in this embodiment, the heater 20 may be divided into multiple parts. In this case, the multiple heaters 20 may surround the muffle tube 10 in the circumferential direction. Alternatively, the multiple heaters 20 may be arranged side by side in the axial direction.

[0017] In this embodiment, the furnace body 30 is a hollow cylindrical container that houses at least a portion of the muffle tube 10 and the heater 20. The furnace body 30 may house the entire muffle tube 10. The furnace body 30 has an upper wall 30a at its upper end, a lower wall 30b at its lower end, and a peripheral wall 30c connecting the upper wall 30a and the lower wall 30b. A through-hole 33 that communicates with the interior of the furnace body 30 is formed in the center of the upper wall 30a and the center of the lower wall 30b. The muffle tube 10 is inserted into each through-hole 33. A user can insert the muffle tube 10 into the furnace body 30 or remove the muffle tube 10 from the furnace body 30 via the through-hole 33.

[0018] An annular sealing mechanism S is provided on the edge of the through hole 33. The sealing mechanism S closes any gap that may occur in the through hole 33 when the furnace muffle tube 10 is inserted through the through hole 33, and prevents gas from flowing out of the furnace body 30 or into the furnace body 30 through the through hole 33. Note that the glass base material manufacturing apparatus 1A does not necessarily have to include the sealing mechanism S.

[0019] Four supply pipes 31 extending radially outward are provided on the furnace body peripheral wall 30c. The number of supply pipes 31 can be changed as needed, and may be any number equal to or greater than two. Four exhaust pipes 32 extending radially outward are provided on the furnace body peripheral wall 30c. The number of exhaust pipes 32 can be changed as needed, and may be one to three, or five or more. The supply pipes 31 are used to supply gas G from outside the furnace body 30 into the furnace body 30. The exhaust pipes 32 are used to exhaust gas G from inside the furnace body 30 to outside the furnace body 30. The gas G supplied to the furnace body 30 through the supply pipes 31 is mainly an inert gas (e.g., argon, helium, nitrogen, etc.). Supplying gas G into the furnace body 30 exhausts oxygen from within the furnace body 30, thereby suppressing oxidation and oxidation-related deterioration of the heater 20 and the insulating material 40.

[0020] The radially inner end of each supply pipe 31 is referred to as a supply port 31a. Similarly, the radially inner end of each exhaust pipe 32 is referred to as an exhaust port 32a. In this embodiment, each supply port 31a and each exhaust port 32a are located on the furnace body peripheral wall 30c. The end of each supply pipe 31 located opposite the supply port 31a is connected to a gas supply device (not shown). Note that, for example, all four supply pipes 31 may be connected to one gas supply device, or each supply pipe 31 may be connected to each of the four gas supply devices. In other words, the configuration of the gas supply device is arbitrary as long as it can supply gas G into the furnace body 30 through each supply pipe 31. Furthermore, the end of each exhaust pipe 32 located opposite the exhaust port 32a is located outside the furnace body 30.

[0021] In this embodiment, the four supply ports 31a and the four exhaust ports 32a are arranged in the axial direction so as to sandwich the heater 20. More specifically, each supply port 31a is provided below the heater 20, and each exhaust port 32a is provided above the heater 20.

[0022] By supplying gas G through each supply port 31a and discharging gas G through each exhaust port 32a, oxygen can be discharged from the furnace body 30. This makes it possible to suppress oxidation of the heater 20 and the heat insulating material 40 and deterioration due to oxidation.

[0023] The temperature of the gas G is often different from the temperature of the heater 20, the temperature of the muffle tube 10, and the temperature of the untreated base material M. For example, when the temperature of the gas G is about room temperature, the temperature of the gas G is likely to be lower than the temperature of the heater 20, the temperature of the muffle tube 10, and the temperature of the untreated base material M. Therefore, a difference is likely to occur between the temperature of the portion of the muffle tube outer peripheral surface 10c that faces each supply port 31a in the radial direction and the temperature of the other portions of the muffle tube outer peripheral surface 10c. In other words, temperature unevenness is likely to occur on the muffle tube outer peripheral surface 10c.

[0024] In contrast, in the glass base material manufacturing apparatus 1A of this embodiment, the four supply ports 31a are arranged in a substantially rotational symmetry with respect to the central axis O of the core tube 10 (see FIG. 2). In other words, the four supply ports 31a are arranged at substantially equal intervals in the circumferential direction. This distributes the supply of gas G in the circumferential direction, thereby suppressing temperature variations in the circumferential direction of the outer peripheral surface 10c of the core tube. Furthermore, the symmetry of the temperature distribution in the circumferential direction of the outer peripheral surface 10c of the core tube can be improved. Therefore, eccentricity (core misalignment) of the glass base material resulting from heat treatment of the untreated base material M and non-circularity of the cross-sectional shape of the glass base material can be suppressed. The terms "substantially rotationally symmetric" and "substantially equally spaced" include cases where the glass base material can be considered rotationally symmetric or equally spaced if manufacturing errors are removed, and cases where the effect of suppressing the above-mentioned eccentricity and non-circularity can be expected even if the glass base material is not completely rotationally symmetric or equally spaced.

[0025] Furthermore, because the gas G is discharged through the exhaust ports 32a, a temperature difference is likely to occur between the portions of the muffle tube outer peripheral surface 10c radially opposite the exhaust ports 32a and the remaining portions of the muffle tube outer peripheral surface 10c. Therefore, temperature variations due to the positions of the supply ports 31a and the exhaust ports 32a may occur on the muffle tube outer peripheral surface 10c. In contrast, the glass base material manufacturing apparatus 1A of this embodiment has four exhaust ports 32a arranged substantially rotationally symmetrically about the central axis O of the muffle tube 10. In other words, the four exhaust ports 32a are arranged at substantially equal intervals in the circumferential direction. This distributes the discharge of the gas G circumferentially, further suppressing temperature variations in the circumferential direction of the muffle tube outer peripheral surface 10c. Furthermore, the symmetry of the temperature distribution in the circumferential direction of the muffle tube outer peripheral surface 10c can be further improved. Therefore, eccentricity of the glass base material and non-circularity of the cross-sectional shape of the glass base material can be further suppressed. It should be noted that "substantially rotationally symmetric" and "substantially equally spaced" include cases where the rotational symmetry or equal spacing can be considered if manufacturing errors are removed, and also cases where the effect of suppressing the above-mentioned eccentricity and non-circularity can be expected even if the rotational symmetry or equal spacing is not perfect.

[0026] The heat insulating material 40 is a member that prevents heat from escaping from the muffle tube 10 to the outside of the furnace body 30. Examples of the heat insulating material 40 include layers of carbon sheets and silicone sponge. In this embodiment, the heat insulating material 40 is cylindrical and circumferentially surrounds the muffle tube 10 and the heater 20. The heat insulating material 40 has an outer heat insulating surface (outer heat insulating surface) 40c facing radially outward and an inner heat insulating surface 40d facing radially inward. The inner heat insulating surface 40d faces radially opposite the outer heat insulating surface 10c of the muffle tube. A recess 41 is formed in the inner heat insulating surface 40d, in which the heater 20 is disposed. The recess 41 is located in the center of the heat insulating material 40 in the axial direction and is recessed radially outward from the inner heat insulating surface 40d. It is also possible to dispose the heater 20 in the gap between the inner peripheral surface 40d of the heat insulating material and the outer peripheral surface 10c of the furnace tube without providing the recess 41. The heat insulating material 40 may be formed of a porous material (for example, a sponge-like material). In this case, the gas G can easily pass through the heat insulating material 40. This allows oxygen in the furnace body 30 to be exhausted more efficiently.

[0027] The outer peripheral surface 40c of the thermal insulator faces the furnace body peripheral wall 30c in the radial direction. In particular, in this embodiment, each supply port 31a is located radially outward of the outer peripheral surface 40c of the thermal insulator. This prevents the gas G supplied from each supply port 31a from directly hitting the outer peripheral surface 10c of the muffle tube, making it possible to prevent temperature variations in the outer peripheral surface 10c of the muffle tube due to the gas G.

[0028] (Glass base material manufacturing method) Next, a method for manufacturing a glass base material using the glass base material manufacturing apparatus 1A configured as above will be described.

[0029] First, an untreated base material M is prepared. The untreated base material M may be, for example, the above-mentioned target on which glass particles are deposited. Next, the untreated base material M is inserted into the furnace tube 10 and arranged along the central axis O of the furnace tube 10 . Next, the lid L closes the furnace tube 10 .

[0030] Next, gas G is supplied into the furnace body 30 from a gas supply device (not shown) through each supply pipe 31. The supply of gas G is continuous. This allows oxygen inside the furnace body 30 to be discharged to the outside of the furnace body 30, thereby suppressing oxidation of the heater 20 and the heat insulating material 40 and deterioration associated with oxidation. At this time, gas G may be supplied so that the air pressure inside the furnace body 30 is higher than the outside air pressure. In this case, a pressure measuring means (e.g., an air pressure sensor, etc.) (not shown) may be provided inside the furnace body 30, and the supply amount of gas G may be controlled based on the measured value of the air pressure inside the furnace body 30. By increasing the pressure inside the furnace body 30, the furnace core tube 10, which is softened by heat in the heat treatment process described below, is prevented from bending radially outward. Unless otherwise specified, the supply of gas G will continue.

[0031] The flow path of the gas G will be described below. First, the gas G supplied from each supply port 31a penetrates the interior of the insulating material 40 or passes through the gap between the insulating material 40 and the inner surface of the furnace body 30 to reach the region where the insulating material inner peripheral surface 40d and the core tube outer peripheral surface 10c face each other. The gas G that reaches this region spreads isotropically in the circumferential direction, as shown in FIG. 2. At the same time, the gas G flows from bottom to top due to the pressure difference in the axial direction within the furnace body 30 (see FIG. 1). Next, the gas G penetrates the interior of the insulating material 40 or passes through the gap between the insulating material 40 and the inner surface of the furnace body 30 to reach each exhaust port 32a and be discharged to the outside of the furnace body 30. In this embodiment, the exhaust port 32a and the supply port 31a are arranged so as to sandwich the heater 20 in the axial direction. More specifically, the supply port 31a is located below the heater 20, and the exhaust port 32a is located above the heater 20. Therefore, the direction of flow of the gas G in the vicinity of the heater 20 is stabilized in an upward direction, and oxygen can be efficiently discharged from the vicinity of the heater 20. Therefore, oxidation and deterioration of the heater 20 can be effectively suppressed.

[0032] After a predetermined time has elapsed since the gas G began to be supplied into the furnace body 30, heat treatment of the untreated base material M is started. More specifically, the heater 20 is operated, and the untreated base material M is heated via the furnace core tube 10. A glass base material is obtained by performing heat treatment on the untreated base material M. Note that the oxygen concentration in the furnace body 30 may be measured using an oxygen concentration meter (not shown) provided in the furnace body 30, and the heat treatment may be started after the measured value falls below a predetermined concentration value.

[0033] When the heater 20 is operated, the gas G expands due to heat. The gas G, which has a reduced density, tends to move upward due to the influence of gravity. This promotes the upward flow of the gas G. In this embodiment, the exhaust ports 32a are located above the supply ports 31a, so that efficient exhaust can be achieved by utilizing the upward movement of the gas G due to thermal expansion. Therefore, oxidation and deterioration of the heater 20 and the insulating material 40 can be more effectively suppressed.

[0034] Furthermore, during the heat treatment of the untreated base material M, the untreated base material M may be rotated appropriately around the central axis O of the furnace tube 10 inside the furnace tube 10. In this case, temperature unevenness of the untreated base material M in the circumferential direction is suppressed, and the effect of suppressing eccentricity of the glass base material and non-circularity of the cross-sectional shape of the glass base material is obtained. This effect is considered to be enhanced as the rotation speed of the untreated base material M increases. On the other hand, the higher the rotation speed of the untreated base material M, the greater the centrifugal force generated in the untreated base material M, and the greater the radial vibration of the untreated base material M. In particular, if the vibration is so great that a part of the untreated base material M touches the inner circumferential surface of the furnace tube 10, the untreated base material M may be damaged. In contrast, the glass base material manufacturing apparatus 1A of this embodiment is designed to have multiple supply ports 31a, and therefore the effect of suppressing the eccentricity and non-circularity can be obtained without increasing the rotation speed of the untreated base material M.

[0035] The heat treatment may be, for example, a sintering process in which glass particles contained in the untreated base material M are sintered. In the sintering process, the glass particles are heated to the glass transition temperature (approximately 1400 to 1500°C). Around this temperature, various physical properties of the glass particles, including transparency and viscosity, change significantly with temperature. Therefore, if temperature unevenness occurs in the untreated base material M during the sintering process, the physical properties of the untreated base material M are likely to become non-uniform. For this reason, eccentricity and non-roundness of the glass base material are particularly likely to occur during the sintering process. In contrast, the glass base material manufacturing apparatus 1A of this embodiment is designed to have multiple supply ports 31a, thereby suppressing eccentricity and non-roundness during the sintering process. The "heat treatment" may also be a dehydration process, a doping process, or the like. The dehydration process or the doping process may be performed before the sintering process.

[0036] When the manufacturing method of the glass preform is, in particular, an optical fiber preform, a drawing step may be performed in addition to the above steps to obtain an optical fiber from the optical fiber preform. In the drawing step, the optical fiber preform is melted and the melted optical fiber preform is stretched in the longitudinal direction to obtain an optical fiber.

[0037] As described above, the glass base material manufacturing apparatus 1A of this embodiment includes a furnace tube 10 capable of accommodating unprocessed base material M, a heater 20 provided outside the furnace tube 10, a furnace body 30 accommodating at least a portion of the furnace tube 10 and the heater 20, a plurality of supply ports 31a for supplying gas G into the furnace body 30, and an exhaust port 32a for discharging gas G from the furnace body 30.

[0038] In the method for producing a glass base material according to the present embodiment, the untreated base material M is subjected to a heat treatment using the above-described glass base material production apparatus 1A.

[0039] These configurations can suppress temperature variations in the circumferential direction of the furnace tube outer peripheral surface 10c compared to when only one supply port 31a is provided, thereby suppressing eccentricity of the glass base material and non-circularity of the cross-sectional shape of the glass base material.

[0040] At least one supply port 31a and exhaust port 32a are arranged axially on either side of the heater 20. This configuration allows oxygen around the heater 20 to be efficiently exhausted, effectively suppressing oxidation and deterioration of the heater 20.

[0041] The supply ports 31a are arranged at approximately equal intervals in the circumferential direction. This configuration improves the symmetry of the temperature distribution in the circumferential direction of the furnace tube outer peripheral surface 10c, and effectively suppresses the eccentricity of the glass preform and the non-circularity of the cross-sectional shape of the glass preform.

[0042] Furthermore, the glass base material manufacturing apparatus 1A of the present embodiment includes a plurality of exhaust ports 32a, which further suppresses temperature variations in the circumferential direction of the furnace tube outer peripheral surface 10c, and further suppresses eccentricity of the glass base material and non-circularity of the cross-sectional shape of the glass base material.

[0043] The exhaust ports 32a are arranged at approximately equal intervals in the circumferential direction. This configuration further improves the symmetry of the temperature distribution in the circumferential direction of the outer circumferential surface 10c of the furnace tube, and more effectively suppresses the eccentricity of the glass preform and the non-circularity of the cross-sectional shape of the glass preform.

[0044] The glass base material manufacturing apparatus 1A of this embodiment further includes a thermal insulator 40 housed in the furnace body 30, and each of the supply ports 31a is located radially outward of the outer peripheral surface 40c of the thermal insulator. This configuration separates the supply ports 31a from the outer peripheral surface 10c of the muffle tube, thereby preventing local temperature changes at the outer peripheral surface 10c of the muffle tube. This reduces the likelihood of the glass base material becoming eccentric or its cross-sectional shape becoming non-circular.

[0045] In the glass base material manufacturing method of this embodiment, the untreated base material M may have deposited glass particles, and the glass particles may be sintered by heat treatment. According to the glass base material manufacturing apparatus 1A of this embodiment, even when sintering is used as the heat treatment, it is possible to suppress eccentricity of the glass base material and non-circularity of the cross-sectional shape of the glass base material.

[0046] Furthermore, in the glass base material manufacturing method of this embodiment, the untreated base material M may be rotated inside the furnace tube 10 during heat treatment. According to the glass base material manufacturing apparatus 1A of this embodiment, it is possible to suppress eccentricity of the glass base material and non-circularity of the cross-sectional shape of the glass base material without increasing the rotation speed of the untreated base material M. Therefore, it is possible to suppress damage to the untreated base material M due to contact with the inner peripheral surface of the furnace tube 10.

[0047] (Second embodiment) Next, a second embodiment of the present invention will be described, but the basic configuration is the same as that of the first embodiment. Therefore, the same components are given the same reference numerals and their description will be omitted, and only the differences will be described. As shown in FIG. 3, in the glass base material manufacturing apparatus 1B of this embodiment, the supply ports 31a and exhaust ports 32a are located radially inward of the outer peripheral surface 40c of the thermal insulator. In the example of FIGS. 3 and 4, the supply pipes 31 and exhaust pipes 32 penetrate the thermal insulator 40 in the radial direction, and the supply ports 31a and exhaust ports 32a are located on the inner peripheral surface 40d of the thermal insulator. This improves the supply rate of the gas G to the region where the inner peripheral surface 20d of the heater and the outer peripheral surface 10c of the muffle tube face each other, thereby improving the rate at which oxygen is removed from the furnace body 30. This effectively prevents oxidation of the heater 20 and the thermal insulator 40 and the associated deterioration.

[0048] As described above, the glass base material manufacturing apparatus 1B of this embodiment includes the thermal insulator 40 housed in the furnace body 30, and each of the supply ports 31a is located radially inward of the outer peripheral surface 40c of the thermal insulator. This configuration improves the speed at which oxygen is removed from the furnace body 30, and effectively suppresses oxidation and deterioration of the heater 20 and the thermal insulator 40. [Example]

[0049] The above embodiment will be described below using specific examples, but the present invention is not limited to the following examples.

[0050] (Comparative Example) Two glass base material manufacturing apparatuses were prepared, each having a furnace body with a diameter of 900 mm and an axial dimension of 1200 mm, a furnace core tube with a diameter of 300 mm, and a heat insulating material. Comparative Example 1 had one supply pipe and one exhaust pipe, and the supply inlet and exhaust outlet were located on the peripheral wall of the furnace body. Comparative Example 2 had one supply pipe and one exhaust pipe, and the supply inlet and exhaust outlet were located on the inner peripheral surface of the heat insulating material.

[0051] (Example) A glass base material manufacturing apparatus 1B according to the second embodiment was prepared. The example included four supply pipes 31 and four exhaust pipes 32, and each supply port 31 a and each exhaust port 32 a was located on the inner peripheral surface 40 d of the heat insulating material.

[0052] For each of Comparative Examples 1 and 2 and the Example, argon gas was supplied from each supply pipe with the furnace body sealed, and the time required for the oxygen inside the furnace body to be sufficiently exhausted was measured. More specifically, the oxygen concentration was measured using an oxygen concentration meter installed near the exhaust port, and the time from the start of argon gas supply until the oxygen concentration reached 210 ppm (parts per million by volume) was measured.

[0053] Next, the same untreated preform M was subjected to a sintering process to manufacture an optical fiber preform. The untreated preform M was a porous glass body obtained by depositing glass particles on a target having a portion that would become the core of the optical fiber. The argon gas supply rate during the sintering process was 2.0 L / m (liters per minute) in total for all supply pipes in all of Comparative Examples 1 and 2 and the Example. The cross-sectional shape of each of the obtained optical fiber preforms was measured at 200 mm intervals in the axial direction, and the maximum eccentricity was evaluated. The eccentricity was defined as (amount of eccentricity) = (amount of deviation between the center of the optical fiber preform and the center of the core) / (outer diameter of the optical fiber preform).

[0054] The maximum time required for oxygen discharge and the amount of eccentricity obtained in the above experiments are summarized in Table 1. Note that in Comparative Example 2 and the Example, the "6 hours or less" in the time required for oxygen discharge means that the oxygen concentration was already below 210 ppm after 6 hours had passed.

[0055] [Table 1]

[0056] As can be seen from the comparison between the Example and Comparative Examples 1 and 2 in Table 1, when multiple supply pipes and exhaust pipes are provided, the eccentricity of the optical fiber preform is smaller than when one supply pipe and one exhaust pipe are provided. Thus, it was confirmed that the eccentricity of the optical fiber preform can be suppressed by providing multiple supply pipes and exhaust pipes. Comparing Comparative Examples 1 and 2, when the supply port is located radially inward from the outer peripheral surface of the insulating material, the time required to discharge oxygen is shorter than when the supply port is located radially outward from the outer peripheral surface of the insulating material. In this way, it was confirmed that oxygen discharge efficiency can be improved by bringing the supply port closer to the inner peripheral surface of the insulating material.

[0057] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0058] For example, each supply pipe 31 and each exhaust pipe 32 may be provided on the furnace body upper wall 30a or the furnace body lower wall 30b. Alternatively, the exhaust pipe 32 may not be provided, for example, one or both of the two sealing mechanisms S may be eliminated, and the gap between the through hole 33 and the furnace core tube 10 may be used as the exhaust port 32a.

[0059] Furthermore, each supply port 31 a and each exhaust port 32 a may be located inside the heat insulating material 40 .

[0060] Furthermore, although the outer circumferential surface 10c of the furnace tube in the above embodiment is circular in cross section, it may also be polygonal in cross section. Similarly, the heat insulating material 40 and the furnace body peripheral wall 30c may also be polygonal in cross section.

[0061] Furthermore, during the heat treatment step in the method for producing a glass base material, the supply amount of gas G may be controlled to prevent significant temperature unevenness at the outer peripheral surface 10c of the muffle tube. For example, the supply amount of gas G may be adjusted so that the difference between the maximum and minimum temperatures at each height in the circumferential direction of the outer peripheral surface 10c of the muffle tube is maintained at 10°C. In this case, a temperature measuring means (e.g., a temperature sensor) for measuring the temperature of the outer peripheral surface 10c of the muffle tube may be provided in the furnace body 30, and the supply amount of gas G may be controlled based on the measured temperature value of the outer peripheral surface 10c of the muffle tube. When these configurations are adopted, eccentricity of the glass base material and non-circularity of the cross-sectional shape of the glass base material can be more reliably suppressed.

[0062] In addition, it is possible to replace the components in the above-described embodiments with well-known components as appropriate, and the above-described embodiments and variations may be combined as appropriate, without departing from the spirit of the present invention. For example, the first and second embodiments may be combined so that some of the multiple supply ports 31a are located radially outside the outer peripheral surface 40c of the insulating material, and the remaining supply ports 31a are located radially inside the outer peripheral surface 40c of the insulating material. [Explanation of symbols]

[0063] 1...Glass base material manufacturing apparatus 10...Mass tube 10c...Outer surface of the furnace tube (Outer surface of the furnace tube) 20...Heater 30...Furnace body 31a...Supply port 32a...Exhaust port 40...Insulating material 40c...Outer surface of the insulating material (Outer surface of the insulating material) M...Untreated base material G...Gas

Claims

1. a furnace tube capable of accommodating untreated base material; a heater provided outside the furnace tube; a furnace body that accommodates at least a portion of the furnace core tube and the heater; a plurality of supply ports for supplying gas into the furnace body; a plurality of exhaust ports for discharging gas from the furnace body; the plurality of exhaust ports are arranged at substantially equal intervals in the circumferential direction of the furnace tube, the exhaust port extends radially outward from the furnace body in the furnace core tube, The apparatus for manufacturing a glass base material, wherein the supply port and the exhaust port are not provided on an upper surface of the furnace body but on a side surface of the furnace body.

2. 2. The apparatus for producing a glass base material according to claim 1, wherein at least one of the supply port and the exhaust port is arranged on either side of the heater in the axial direction of the furnace tube.

3. 3. The apparatus for producing a glass base material according to claim 1, wherein the plurality of supply ports are arranged at approximately equal intervals in the circumferential direction of the furnace tube.

4. Further provided with a heat insulating material housed in the furnace body, The apparatus for manufacturing a glass base material according to claim 1 , wherein at least some of the plurality of supply ports are located radially outward of an outer circumferential surface of the heat insulating material.

5. Further provided with a heat insulating material housed in the furnace body, The apparatus for manufacturing a glass base material according to claim 1 , wherein at least some of the plurality of supply ports are located radially inside the furnace tube with respect to an outer circumferential surface of the heat insulating material.

6. a furnace tube capable of accommodating untreated base material; a heater provided outside the furnace tube; a furnace body that accommodates at least a portion of the furnace core tube and the heater; a plurality of supply ports for supplying gas into the furnace body; a plurality of exhaust ports for discharging gas from the furnace body; the at least two exhaust ports are provided on opposite sides of the furnace tube; the exhaust port extends radially outward from the furnace body in the furnace core tube, The apparatus for manufacturing a glass base material, wherein the supply port and the exhaust port are not provided on an upper surface of the furnace body but on a side surface of the furnace body.

7. a furnace tube capable of accommodating untreated base material; a heater provided outside the furnace tube; a furnace body that accommodates at least a portion of the furnace core tube and the heater; a plurality of supply ports for supplying an inert gas into the furnace body; an exhaust port for discharging gas from the furnace body, the plurality of supply ports are located below the heater, the exhaust port is located above the heater, the supply port or the exhaust port extends radially outward from the furnace body, The apparatus for manufacturing a glass base material, wherein the supply port and the exhaust port are not provided on an upper surface of the furnace body but on a side surface of the furnace body.

8. A method for manufacturing a glass base material, in which an untreated base material is heat-treated using a glass base material manufacturing apparatus, The glass base material manufacturing apparatus includes: a furnace tube capable of accommodating the untreated base material; a heater provided outside the furnace tube; a furnace body that accommodates at least a portion of the furnace core tube and the heater; a plurality of supply ports for supplying gas into the furnace body; a plurality of exhaust ports for discharging gas from the furnace body; the plurality of exhaust ports are arranged at substantially equal intervals in the circumferential direction of the furnace tube, the exhaust port extends radially outward from the furnace body in the furnace core tube, The method for manufacturing a glass base material, wherein the supply port and the exhaust port are not provided on an upper surface of the furnace body but on a side surface of the furnace body.

9. the untreated substrate has glass particles deposited thereon; The method for producing a glass base material according to claim 8 , wherein the glass particles are sintered by the heat treatment.

10. The method for manufacturing a glass base material according to claim 8 or 9, wherein the untreated base material is rotated inside the furnace tube when the heat treatment is performed.

11. 11. The method for manufacturing a glass base material according to claim 8, wherein a difference between a maximum value and a minimum value of a temperature in a circumferential direction of the outer peripheral surface of the furnace tube is kept at 10°C or less at each position in the axial direction of the furnace tube.

12. A method for manufacturing a glass base material, in which an untreated base material is heat-treated using a glass base material manufacturing apparatus, The glass base material manufacturing apparatus includes: a furnace tube capable of accommodating the untreated base material; a heater provided outside the furnace tube; a furnace body that accommodates at least a portion of the furnace core tube and the heater; a plurality of supply ports for supplying gas into the furnace body; a plurality of exhaust ports for discharging gas from the furnace body; the at least two exhaust ports are provided on opposite sides of the furnace tube; the exhaust port extends radially outward from the furnace body in the furnace core tube, The method for manufacturing a glass base material, wherein the supply port and the exhaust port are not provided on an upper surface of the furnace body but on a side surface of the furnace body.

13. A method for manufacturing a glass base material, in which an untreated base material is heat-treated using a glass base material manufacturing apparatus, The glass base material manufacturing apparatus includes: a furnace tube capable of accommodating the untreated base material; a heater provided outside the furnace tube; a furnace body that accommodates at least a portion of the furnace core tube and the heater; a plurality of supply ports for supplying an inert gas into the furnace body; an exhaust port for discharging gas from the furnace body, the plurality of supply ports are located below the heater, the exhaust port is located above the heater, the supply port or the exhaust port extends radially outward from the furnace body, The method for manufacturing a glass base material, wherein the supply port and the exhaust port are not provided on an upper surface of the furnace body but on a side surface of the furnace body.

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