JP2008179517A - Apparatus and method for producing glass preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for producing a glass preform, capable of avoiding the rise of the temperature of a gas exhausted outside from an upper lid and stabilizing the pressure inside a furnace core pipe by suppressing internal pressure fluctuation in the upper lid. <P>SOLUTION: The apparatus 1 for producing the glass preform heats a glass particulate deposited body 10 using a vertical furnace core pipe. The upper lid 4 is installed on top of the furnace core pipe 2 and has support rod penetrating holes 40A, 42B and 43B through which a support rod 10A penetrates, provided that the support rod supports the glass particulate deposited body 10. The upper lid 4 has three-layered chambers (first chamber 41 to third chamber 43) partitioned into three or more layers in a vertical direction along the support rod 10A. The first chamber 41 to the third chamber 43 have a gas inlet 41B, a gas outlet 42D and a gas inlet 43D, respectively, and have concentric partitions 41C, 42E and 43E between the gas inlet 41B and the support rod penetrating hole 40A, between the gas outlet 42D and the support rod penetrating hole 42B and between the gas inlet 43D and the support rod penetrating hole 43B, respectively. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a glass base material manufacturing apparatus and method using a vertical furnace core tube.

  A glass base material used for optical fiber production or the like generates a glass fine particle deposit (porous glass base material) by a VAD method, an OVD method or the like. It is manufactured by transparent vitrification. Furthermore, if necessary, a heat treatment such as annealing may be performed after forming the transparent glass. In these heat treatment steps, an atmospheric gas is selected and used according to the content of treatment such as dehydration and transparent vitrification. For example, in the first heat treatment, the glass fine particle deposit is dehydrated using He and a dehydrating gas (such as a chlorine-based gas), and in the subsequent second heat treatment, the dehydrated glass fine particle deposit is obtained in an atmosphere containing only He. Transparent glass.

As a specific method of heat treatment using a glass base material manufacturing apparatus,
(1) The glass particulate deposit supported by the support rod is suspended in the core tube, the glass particulate deposit is dehydrated in a chlorine-based gas atmosphere, and further mixed in an inert gas atmosphere or an inert gas and a chlorine-based gas. Or transparent vitrification in the atmosphere, or
(2) After dehydration in the same manner with a chlorine-based gas, F is added using a gas such as SiF _{4 to} adjust the profile (refractive index), and then in an inert gas atmosphere or an inert gas and a halogen-based gas. Transparent vitrification in a mixed atmosphere of
Etc. are known.

  By the way, in the case of such a method, if corrosive gas (halogen-based gas such as chlorine-based gas or fluorine-based gas) leaks from the glass base material manufacturing device, the metal parts of each device in the room where the manufacturing device is installed The amount of metal dust in the indoor atmosphere may increase. Normally, this type of production equipment is often installed in the same room as the glass fine particle deposition equipment that produces glass fine particle deposits. However, as the amount of metallic dust in the room increases, glass fine particles (soot) accumulate. Metal dust in the room atmosphere is mixed in the glass fine particle deposition apparatus, and metal impurities are mixed in the glass base material finally obtained. In addition, when adjusting the profile (refractive index) by adding dehydration or F, if moisture in the air outside the furnace is involved, dehydration failure may occur.

  Usually, most of the corrosive gas flowing out from the glass base material manufacturing apparatus into the room in which the apparatus is installed often flows out from the portion of the upper cover of the core tube where the support rod is inserted. Therefore, as a means to prevent the entry of metallic dust and moisture from the outside of the furnace and at the same time to prevent the corrosive gas from flowing out of the furnace, the upper cover of the core tube is covered with a multilayer covering the outer periphery of the support rod. The thing etc. which comprised the cylindrical tube of a structure are proposed (for example, refer patent document 1).

This will be described below with reference to the drawings.
FIG. 5 shows an example of an upper cover structure of a core tube for sintering a glass particle deposit, and this upper cover has a seal structure having a substantially cylindrical shape attached to the upper end of the core tube 100. Three small chambers 110, 120, and 130 are provided, and a collar 140 that forms the top surface and a collar 150 that forms the bottom surface have holes through which the support rod 160 passes.

  In each of the small chambers 110, 120, and 130, airtight rings 111, 121, and 131 that are loosely fitted to the support rod 160 are movably inserted. The hermetic rings 111, 121, 131 are inserted in the small chambers 110, 120, 130 so as to be movable within a certain range. Therefore, the support rod 160 can freely move up and down and rotate, and even if the support rod 160 moves in the horizontal direction due to vibration or deviation from the central axis of the core tube, the hermetic rings 111, 121, 131 can also be moved.

  Further, only the airtight ring 111 inserted into the small chamber 110 having the exhaust gas port 112 is provided with a groove-like gas passage 111 </ b> A extending in the circumferential direction from the center on the lower surface thereof. Further, the small chamber 130 provided on the upper stage of the small chamber 120 having the seal gas introduction port 122 does not have a port (gas port) for introducing or discharging the seal gas, and the airtight ring 131 inserted in the small chamber 130 is also in the circumferential direction. No groove-like gas passage is provided. Thereby, airtightness is improved and entrainment of outside air is blocked. Further, by reducing the conductance between the small chamber 110 having the exhaust gas port 112 and the small chamber 120 having the seal gas introduction port 122, a pressure difference between the chambers can be ensured, and at the same time, from the exhaust gas port 112 of the small chamber 110. The work gas can be sufficiently discharged by the circumferential groove 111A on the lower surface of the hermetic ring 111.

  As described above, the upper lid has the small chamber 110 having the exhaust gas port 112 and the small chamber 120 having the seal gas introduction port 122. Therefore, the seal gas is introduced from the seal gas introduction port 122 in the small chamber 120, At 110, corrosive gas and the like from the inside of the core tube 100 can be discharged from the exhaust gas port 112 to a scrubber (not shown) together with the seal gas from the seal gas introduction port 122. Further, since the small chamber 130 does not have a port (gas port) for introducing or discharging the seal gas, it is possible to block air from being introduced into the small chambers 110 and 120 and to improve the airtightness.

JP 2002-226218 A

In recent years, due to the increase in the size of the glass base material and the accompanying increase in the inner diameter of the core tube and the increase in the volume, the amount of radiant light reaching the upper lid from the high temperature part of the core tube has increased. When the core tube is used, a large amount of radiant heat is transmitted to the upper lid, and the temperature of the upper lid is increased. As a result, the exhaust temperature of the gas when exhausting from the upper lid to the outside tends to rise excessively. In addition, when the gas in the core tube rises and flows to the top cover, the degree of cooling by contacting the inner wall of the core tube to reduce the inner diameter of the core tube decreases, so the temperature rises and moves toward the top cover. The tendency to move increases. For this reason, the temperature inside the upper lid increases more and more.
Such a rise in the gas temperature inside the upper lid leads to an increase in temperature in equipment such as an exhaust pipe provided on the exhaust downstream side of the upper lid. As a result, the material used for the exhaust pipe or the like is restricted by a highly heat-resistant material such as a nickel alloy, resulting in an increase in cost.

  In addition, the amount of gas supplied to and exhausted from the furnace is increasing due to the increase in the size of the glass base material and the accompanying increase in the size of the equipment. As a result, an increase in the gas flow velocity in the vicinity of the gas supply / exhaust port of the upper lid causes local pressure fluctuations in the circumferential direction and the like in the upper lid, leading to further pressure fluctuations in the furnace. In this way, when the pressure fluctuation in the furnace increases, for example, corrosive gas leaks from the glass base material manufacturing apparatus into the room or the residual water content increases due to the entrainment of outside air, resulting in deterioration of the characteristics of the glass base material. Causes various inconveniences such as the manifestation of.

  The present invention provides a glass base material manufacturing apparatus and manufacturing method capable of avoiding a rise in the temperature of gas exhausted from the upper lid to the outside and stabilizing the pressure in the furnace core tube while suppressing fluctuations in the internal pressure of the upper lid. The purpose is to provide.

  An apparatus for producing a glass base material according to the present invention capable of solving the above problems is a glass base material production apparatus for heating an object to be heated in a vertical furnace core tube, and supports the object to be heated. An upper lid that is provided with an insertion port through which a rod passes and is attached to the upper portion of the core tube includes a plurality of rooms of three or more layers in the vertical direction along the support rod, and each of the chambers has a gas port on the outer periphery. And having a partition wall concentric with the insertion port between the gas port and the insertion port. Here, examples of the object to be heated include a case of both a glass fine particle deposit and a glass base material intermediate that has already been made into a transparent glass.

Moreover, it is preferable that the said partition is formed so that it may continue in the circumferential direction concentric with the said insertion port, and may partially cover the up-down direction in the said room.
Or it is preferable that the said partition is intermittently formed in the circumferential direction concentric with the said insertion port.

  A method for producing a glass base material according to the present invention that can solve the above-described problem is a method for producing a glass base material that heats an object to be heated in a vertical furnace core tube, and supports the object to be heated. An upper lid that is provided with an insertion port through which a rod passes and is attached to the upper portion of the core tube includes a plurality of rooms of three or more layers in the vertical direction along the support rod, and each of the chambers has a gas port on the outer periphery. And having a partition wall concentric with the insertion port between the gas port and the insertion port, with respect to the room of each layer, through the gas port, from the lowermost layer to the upper layer In this case, the introduction of the inert gas and the exhaust of the gas are alternately performed in this order.

  Moreover, it is preferable to use He gas for the inert gas introduced into the lowermost layer.

  According to the present invention, the upper lid attached to the upper part of the core tube is provided with a plurality of chambers partitioned into three or more layers in the vertical direction, and these chambers are penetrated by gas ports and support rods in the outer peripheral portion. Since the partition wall concentric with the insertion port is provided between the insertion port and the insertion port, the gas flow between the gas port and the insertion port diffuses in the circumferential direction in each room. Therefore, the temperature in the upper lid is easily made uniform, and the temperature rise is suppressed. Further, the gas flow rate in the upper lid is also suppressed. Therefore, an increase in the temperature of the gas exhausted from the upper lid to the outside can be avoided, and the internal pressure fluctuation can be suppressed and the pressure in the core tube can be stabilized.

Hereinafter, an example of an embodiment of a manufacturing apparatus and a manufacturing method of a glass base material concerning the present invention is explained in detail, referring to drawings.
FIG. 1 shows a glass base material manufacturing apparatus capable of performing the glass base material manufacturing method of the present embodiment. The glass base material manufacturing apparatus 1 is a heating furnace that heat-treats the glass particulate deposit 10, and has a cylindrical core tube 2 disposed in a vertical shape and a heating source disposed on the outer peripheral side of the core tube 2. And a cylindrical heater 3.

  The core tube 2 is made of quartz and is heated by the heat generated by the heater 3. Thereby, the glass particulate deposit 10 accommodated in the furnace space S inside the furnace core tube 2 can be heated.

The glass particulate deposit 10 is formed integrally with the support bar 10A so as to be suspended from the support bar 10A, and the support bar 10A is held by the holding device 8. Further, the gripping device 8 rotates the glass particulate deposits 10 together with the support rods 10A around its axis by driving means (not shown), and vertically moves the glass by vertically moving means (not shown) for raising and lowering the gripping device 8. The fine particle deposit 10 can be moved.
An upper lid 4 is detachably attached to the upper end of the core tube 2 in order to open and close the opening when the glass particulate deposit 10 is introduced or removed. On the other hand, a lower cover 5 that can be attached and detached as appropriate is attached to the lower end of the core tube 2.

  The heater 3 is made of carbon, and a heat insulating material 31 is disposed around the heater 3. Further, the core tube 2 and the heat insulating material 31 are covered with a furnace body 21 that forms an outer shell of the furnace.

In addition, the glass base material manufacturing apparatus 1 of the present embodiment includes a gas supply control device 6 that supplies a gas used when the glass fine particle deposit 10 is heat-treated into the furnace and controls its supply amount. ing. The gas supply control device 6 supplies atmospheric gas into the furnace core tube 2 from an atmosphere gas introduction part 2 </ b> A provided near the lower end of the furnace core tube 2. As the atmospheric gas, for example, an inert gas such as He and a dehydrated gas (such as a chlorine-based gas) are used at the time of dehydration, and only an inert gas is used at the time of transparent vitrification. In addition, a refractive index adjusting gas such as SiF ₄ is used for adjusting the refractive index of the glass base material, and gases such as H ₂ , O ₂ , and CO are used for controlling lattice defects and improving the characteristics of the glass base material. Sometimes used as atmospheric gas.

  Further, a reactor core pressure monitor 6A is provided in the vicinity of the upper end of the reactor core tube 2 so that the pressure P in the reactor space S can be monitored in a timely manner. The data measured by the reactor core pressure monitor 6A is sent to the gas supply control device 6 and used to adjust the supply amount of the atmospheric gas to the atmospheric gas introduction unit 2A. For example, by maintaining the pressure in the furnace space S at atmospheric pressure or higher, intrusion of outside air into the furnace space S can be prevented, and the quality of the glass base material to be manufactured can be favorably maintained.

  The atmospheric gas in the furnace space S is exhausted to a main exhaust pipe (not shown) that leads to the scrubber through a gas exhaust part 42D (described later) of the upper lid 4. Exhaust gas also flows into the main exhaust pipe from the exhaust sections of other heating furnaces, and is exhausted collectively to the scrubber. In the scrubber, the exhausted gas is cleaned.

Next, the upper lid 4 attached to the glass base material manufacturing apparatus 1 will be described in detail with reference to FIG. FIG. 3 shows a horizontal sectional view of the first chamber 41 (cross sectional view taken along the line III-III in FIG. 2).
In the upper lid 4 of the present embodiment, a support rod insertion port 40A formed at the approximate center of the lid portion 40 is formed on the upper surface of the lid portion 40 facing the furnace space S, and further along the support rod 10A penetrating therethrough. A room (first chamber 41, second chamber 42, third chamber 43) partitioned in three layers in the vertical direction is formed. Each of the first chamber 41 to the third chamber 43 has a short cylindrical shape, and has gas ports (a gas introduction portion 41B, a gas exhaust portion 42D, A gas introduction part 43D) is provided. Further, inside the first chamber 41 to the third chamber 43, the support rod insertion ports 40A, 42B, 43B are substantially concentric with the support rod insertion ports 40A, 42B, 43B and the respective gas ports. Partition walls 41C, 42E, and 43E are provided.

  As shown in FIGS. 2 and 3, the first chamber 41 is configured by a substantially columnar space surrounded by a cylindrical outer peripheral surface 41A, and functions as a gas input layer. The first chamber 41 has a support rod insertion port 40A through which a support rod 10A for supporting the glass particulate deposit 10 is opened at a lower central portion, and a support rod in a state of surrounding the support rod insertion port 40A. A sealing edge 40B extending upward by a height A along the axial direction of 10A is provided to enhance the sealing performance. Further, a support rod insertion opening 42B through which the support rod 10A passes is opened in the upper central portion.

  In addition, gas introduction portions 41B are provided as gas ports for introducing an inert gas at two locations in the circumferential direction of the outer peripheral surface 41A of the first chamber 41, from a gas supply control device (not shown). An inert gas is introduced into the first chamber 41 through the gas introduction part 41B. As the inert gas introduced into the first chamber 41, helium (He) gas is preferably used, thereby reducing the amount of heat received from the atmosphere gas in the core tube 2 flowing in through the support rod insertion port 40A. It becomes possible to suppress, and the amount of heat conduction to the second chamber 42 can be reduced.

  Furthermore, in the first chamber 41, a partition wall 41C that is substantially concentric with the support rod insertion port 40A is suspended downward from the ceiling surface. The partition wall 41 </ b> C is formed in a substantially cylindrical shape that is continuous over the entire circumference of 360 degrees, and partially covers the vertical direction in the first chamber 41. The vertical length of the partition wall 41C is formed such that the position of the lower end thereof is lower than the positions of the upper ends of the gas introduction part 41B and the seal edge 40B. Further, the partition wall 41C is installed closer to the center in the radial direction in the first chamber 41, so that the outer chamber (outer chamber R1) facing the gas introduction portion 41B is formed wider. In this way, the outer chamber R1 is widened to form a laminar flow state without generating turbulent flow in the outer chamber R1, and the inert gas introduced from the gas introduction portion 41B is surrounded in the outer chamber R1. Flow in the direction and diffuse. On the other hand, in the chamber (inner chamber R2) inside the outer chamber R1 partitioned by the outer chamber R1 and the partition wall 41C (inner chamber R2), the inert gas flows from the outer chamber R1 radially inward substantially uniformly in the circumferential direction. It contacts substantially uniformly in the circumferential direction with respect to the atmospheric gas in the core tube 2 flowing in from the support rod insertion port 40A. Then, the inert gas introduced into the first chamber 41 from the gas introduction portion 41B and the atmospheric gas in the core tube 2 are mixed in the inner chamber R2, and a part of the inert gas enters the second through the support rod insertion port 42B. It flows to the chamber 42 in the circumferential direction with a substantially uniform pressure. Further, since the gas flowing into the inner chamber R2 has a substantially uniform flow in the circumferential direction, the temperature distribution in the inner chamber R2 is substantially uniform.

  Similar to the first chamber 41, the second chamber 42 is configured by a substantially columnar space surrounded by a cylindrical outer peripheral surface 42A, and functions as a gas exhaust layer. Similarly to the first chamber 41, the second chamber 42 is also provided with a support rod insertion port 42B through which the support rod 10A penetrates in the lower central portion, and is supported in a state surrounding the support rod insertion port 42B. A seal edge 42C extending in the same manner as the seal edge 40B is provided upward along the axial direction of the rod 10A. In addition, a support rod insertion port 43B through which the support rod 10A passes is opened in the upper central portion.

  Further, gas is provided at two locations in the circumferential direction of the outer peripheral surface 42A of the second chamber 42 as gas ports for exhausting the gas flowing into the second chamber 42 from the support rod insertion port 42B and the support rod insertion port 43B. An exhaust part 42D is provided. That is, from the gas exhaust part 42 </ b> D, the atmospheric gas such as corrosive gas in the furnace core tube 2, the inert gas introduced into the first chamber 41, and the inert gas introduced into the third chamber 43 are exhausted. The gas exhausted from the gas exhaust part 42D is sent to the scrubber through the main exhaust pipe and cleaned.

  In the second chamber 42, a partition wall 42E that is substantially concentric with the support rod insertion opening 40A is suspended downward from the ceiling surface. Similarly to the partition wall 41C of the first chamber 41, the partition wall 42E is formed in a substantially cylindrical shape continuous over the entire 360 degrees, and partially covers the vertical direction in the second chamber 42. . Similarly to the partition wall 41C, the length in the vertical direction is also formed such that the lower end position is lower than the upper end positions of the gas exhaust part 42D and the seal edge 42C. Further, the partition wall 42E is disposed closer to the outer periphery in the radial direction in the second chamber 42, so that the support bar insertion port 42B and the inner chamber R4 facing the support bar insertion port 43B are formed wider than the outer chamber R3. is doing. As described above, by enlarging the inner chamber R4 to ensure a sufficient volume, the gas flowing through the support rod insertion port 42B and the support rod insertion port 43B does not generate turbulent flow in the inner chamber R4. To flow in the circumferential direction and diffuse. Therefore, the temperature distribution in the inner chamber R4 can be made substantially uniform, and the temperature exhausted from the gas exhaust part 42D can be kept low.

  The third chamber 43 is configured by a substantially columnar space surrounded by a cylindrical outer peripheral surface 43A, and functions as a gas input layer. Like the first chamber 41 and the second chamber 42, the third chamber 43 has a support rod insertion port 43 </ b> C through which the support rod 10 </ b> A penetrates in the lower central portion, and the support rod insertion port 43 </ b> C. A seal edge 43C extending in the same manner as the seal edges 40B and 42C is provided upward along the axial direction of the support rod 10A. The lid 44 on the upper surface side of the upper lid 4 that forms the space portion of the third chamber 43 together with the outer peripheral surface 43A is provided with a support rod insertion port 44A at the center, and the periphery of the support rod insertion port 44A. A seal edge 44B similar to the seal edge 43C is formed in the part.

Further, gas introduction portions 43D are provided at two locations in the circumferential direction of the outer peripheral surface 43A as gas ports for introducing an inert gas for sealing, and are inert from a gas supply control device (not shown). Gas is introduced into the third chamber 43 through the gas introduction part 43D. As the inert gas introduced into the third chamber 43, it is inexpensive to use nitrogen (N ₂ ) gas.

  Further, in the third chamber 43, a support rod insertion port 40A and a partition wall 43E that is substantially concentric with the support rod insertion port 40A are suspended downward from the ceiling surface. Similarly to the partition walls 41C and 42E, the partition wall 43E is formed in a substantially cylindrical shape continuous over the entire circumference of 360 degrees, and partially covers the vertical direction in the third chamber 43. Similarly to the partition walls 41C and 42E, the length in the vertical direction is formed such that the lower end position is lower than the upper end positions of the gas introduction part 43D and the seal edge 43C. Further, the partition wall 43E is formed at a substantially intermediate portion in the radial direction in the third chamber 43, but it may be formed closer to the center portion like the partition wall 41C of the first chamber 41. In any case, the sealing gas introduced from the gas introduction part 43D diffuses in the circumferential direction without generating turbulent flow in the outer chamber R5, and flows into the inner chamber R6 in a substantially uniform state in the circumferential direction. The pressure of the gas flowing from the third chamber 43 to the support rod insertion port 43C and the support rod insertion port 44A is substantially uniform in the circumferential direction.

  When the glass particle deposit body 10 is heated using the glass base material manufacturing apparatus 1 configured as described above to be transparent vitrified, the atmospheric gas supplied into the core tube 2 is inserted into the support rod of the upper lid 4. It flows into the first chamber 41 in the upper lid 4 through the opening 40A. In the first chamber 41, He gas is introduced into the outer chamber R1 from the gas introducing portion 41B on the outer peripheral side, diffused in the circumferential direction by the partition wall 41C, and flows into the inner chamber R2 with a substantially uniform flow in the circumferential direction. Since the inner chamber R2 of the first chamber 41 is a concentrically partitioned space, local pressure fluctuations in the circumferential direction due to the inflow of He gas can be suppressed. In the inner chamber R <b> 2, the He gas and the atmospheric gas from the furnace core tube 2 are mixed, and a part thereof flows into the second chamber 42. At this time, the inner chamber R2 has a substantially uniform temperature distribution in the circumferential direction, and local pressure fluctuations are suppressed, so that pressure fluctuations in the core tube 2 are not caused.

  Further, since the temperature of the gas flowing from the first chamber 41 into the second chamber 42 is kept low by the He gas introduced into the first chamber 41, the temperature of the gas exhausted from the gas exhaust part 42D is set to 150 ° C. It can be as follows. As a result, the temperature rise in the main exhaust pipe that exhausts the exhaust gas in a concentrated manner can be suppressed, and the material used for the main exhaust pipe is an expensive high heat resistant material (such as nickel alloy). There is no need. For example, if the exhaust temperature is 200 ° C. or lower, a fluororesin material can be used, and if it is 150 ° C. or lower, a main exhaust pipe using an industrial plastic such as FRP can be used, and the equipment cost can be kept low.

Furthermore, N ₂ gas for sealing is introduced into the third chamber 43 to prevent the gas from flowing from the second chamber 42 into the third chamber 43, and outside air is introduced into the third chamber 43 from the support rod insertion port 44 A. Inflow can also be prevented. This sealing effect is because the pressure fluctuation is suppressed in the first chamber 41, and the gas flow is uniformed in the circumferential direction by the partition walls 42E and 43E in the second chamber 42 and the third chamber 43 as well. By being suppressed, it will be exhibited in a more stable state.

  Further, even if the exhaust pressure varies in the main exhaust pipe installed on the downstream side of the gas exhaust part 42D of the second chamber 42, the pressure variation is diffused in the circumferential direction by the partition wall 42E of the second chamber 42. It is difficult to reach the inside of the core tube 2. As a result, the furnace pressure can be kept more uniform than before.

  The partition walls 41C, 42E, and 43E formed in the first chamber 41, the second chamber 42, and the third chamber 43 have a configuration in which the partition walls are formed in addition to the configuration formed in a continuous state over the entire circumference. It may be formed intermittently in the direction. For example, as shown in FIG. 4, in the partition wall 41 </ b> D having four gaps 41 </ b> E in the circumferential direction, gas flows from the gaps 41 </ b> E into the inner chamber R <b> 2 substantially uniformly in the circumferential direction. However, the gap 41E is not disposed at a location where the gas introduction part 41B and the support rod insertion port 40A are linearly connected, and the gas flow introduced from the gas introduction part 41B strikes the partition wall 41D and diffuses in the circumferential direction. is important. In addition, when the partition wall has an intermittent structure in the circumferential direction in this way, walls other than the gap may block the entire vertical direction of the room.

  In the above embodiment, the glass particulate deposit 10 in the core tube 2 is lowered while rotating. However, the glass particulate deposit 10 is of a type in which the glass particulate deposit 10 is heated while rotating without being lowered. Is applicable.

  Furthermore, in the said embodiment, although it is the structure which provided the upper cover 4 which consists of a three-layer room | chamber of the 1st chamber 41-the 3rd chamber 43 immediately above the cover part 40 which block | closes the upper end opening part of the furnace space S, A five-layer structure is provided in which a fourth chamber constituting a gas exhaust layer on the third chamber 43 and a fifth chamber constituting a gas input layer thereon are provided. In addition, the gas exhaust layer and the gas input layer are combined into two layers, such as a seven-layer structure in which a sixth chamber constituting the gas exhaust layer and a seventh chamber constituting the gas input layer are provided thereon. It is also possible to add a room above it. That is, in order from the lowermost layer to the upper layer, the introduction of the inert gas through the gas port and the exhaust of the gas through the gas port may be performed alternately.

  Moreover, in the said embodiment, although the partition in each chamber | room is formed in single in the radial direction, you may make it form in double or more.

Embodiments according to the present invention will be described. In this example, the same parts as those of the above-described embodiment are denoted by the same reference numerals to avoid redundant description.
In this embodiment, when the glass base material is manufactured, as the glass base material manufacturing apparatus 1, a core tube 2 having an inner diameter of 350 mm formed of quartz is used. The glass particulate deposit 10 is heat-treated. The glass fine particle deposit 10 is made of VAD and has an outer diameter of 300 mm and a length of 1000 mm.

  On the other hand, the upper lid 4 has the configuration shown in FIGS. 1 to 3 and is formed of three layers of the first chamber 41 to the third chamber 43 using quartz, and the first chamber 41 at the lowermost layer is charged with gas. The second chamber 42 in the layer and the central layer is a gas exhaust layer, and the third chamber 43 in the uppermost layer is a gas input layer.

  Using the glass base material manufacturing apparatus 1 having the upper lid 4 having such a configuration, heat treatment is first performed at 1000 ° C. in a chlorine-containing atmosphere in a furnace in which the glass fine particle deposit 10 is installed, and then 1200. Heat treatment is performed at ℃ in a fluorine gas-containing atmosphere, and then the temperature is raised to 1400 ℃ to form a transparent glass. Thus, an F-added quartz glass body was obtained. In addition, He is used for the inert gas introduced into the 1st chamber 41 via the gas introduction part 41B.

Next, for the glass base material manufacturing apparatus 1 of the present example provided with the upper lid 4 having such a configuration, and the comparative example, the same glass fine particle deposit 10 is heat-treated, thereby F-added quartz glass. A comparative experiment was conducted to examine the amount of gas inflow and gas displacement, body temperature, and fluctuations in exhaust pressure and internal pressure. However, the glass base material manufacturing apparatus of the comparative example has a configuration in which the upper chamber 4 has only the second chamber 42 and the third chamber 43 in the upper lid 4 in the glass base material manufacturing apparatus 1 of the present embodiment. In addition, the second chamber 42 and the third chamber 43 have a structure having no partition wall.
By this comparative experiment, the results shown in Table 1 below were obtained. However, the exhaust gas temperature and the internal pressure fluctuation are values at a set temperature of 1400 ° C. in the transparent vitrification process.
Further, the furnace pressure is expressed as a differential pressure from the room where the glass base material manufacturing apparatus is installed. Both Example and Comparative Example are set to −500 [Pa] in order to prevent the diffusion of corrosive gas into the room.

  According to this comparative experiment, in the embodiment, the support rod insertion ports 40A, 42B, and 43B and the concentric partition walls 41C, 42E, and 43E are provided, so that both the gas input layer and the gas exhaust layer are in the circumferential direction. It was confirmed that the air flow was made uniform and local pressure fluctuations could be reduced.

Further, apart from this comparative experiment, in the glass base material manufacturing apparatus 1 provided with the top cover 4 having the same configuration as the present embodiment, the outer diameter of the core tube 2 is larger than 350 mm, in addition to the outer diameter of 350 mm. And the exhaust temperature was investigated about the thing whose outer diameter is smaller than 350 mm.
According to this, it was also found that the temperature rise of the exhaust gas exhausted from the upper lid 4 becomes significant when the inner diameter of the core tube 2 exceeds 300 mm. One reason for this is considered to be that when the inner diameter exceeds 300 mm, the solid angle at which the upper lid 4 is viewed from the furnace center of the heat generating part is likely to increase, and the amount of radiant heat transfer increases.

By the way, when the exhaust temperature exceeds 200 ° C., it becomes difficult to handle heat countermeasures in various apparatuses or facilities in the exhaust system related to the subsequent processing of the exhaust gas exhausted from the upper lid 4. For example, for piping materials used for various exhaust systems or equipment, industrial plastics such as FRP (reinforced plastic) can be used if it is 150 ° C. or lower, but if the temperature is higher than this, Considering the corrosion resistance, pipes made of materials such as Teflon (registered trademark) resin up to 200 ° C., such as expensive nickel, must be used at higher temperatures.
Under these circumstances, as can be seen from the results of the comparative experiments described above, in this embodiment, the exhaust temperature is 150 ° C. as shown in Table 1, and therefore the piping material used in the exhaust system apparatus and equipment However, the use of expensive materials can be avoided.

  Further, since corrosive gas is often used as the atmospheric gas in the furnace, the furnace pressure is often managed at a negative pressure including fluctuations in the internal pressure, but may be managed at a positive pressure. In that case, the absolute value of the differential pressure between the indoor pressure and the external pressure in the first chamber 4 and the third chamber 43 of the lid 4 is set smaller than in the case of managing the negative pressure. In other words, if the internal pressure fluctuation is large, the control value of the furnace internal pressure must be set larger than the negative pressure side, but under these conditions, outside air is likely to be entrained, and as described above, metal impurities are contained in the glass base material. Or the amount of water remaining in the glass base material tends to increase due to the influence of moisture contained in the outside air. In addition, the temperature of the glass particulate deposit decreases in the vicinity of the portion where the outside air is entrained, and the probability that the amount of the refractive index control substance varies or the glass particulate deposit is cracked increases.

  In particular, when the set pressure inside the furnace with respect to the outside of the furnace falls below −500 Pa, such a problem is likely to occur remarkably. On the other hand, also in the case of positive pressure, if +500 Pa is exceeded, problems such as leakage of the gas in the furnace into the room and expansion of the quartz furnace tube tend to occur. In the case of a large furnace core tube, for example, if the glass fine particle deposit is regularly vitrified in a state of 1 kPa to 1.5 kPa, the core tube is surely deformed. Therefore, in this embodiment, a more preferable furnace pressure condition is ensured that is significantly lower than such pressure fluctuation. That is, as can be seen from Table 1 showing the results of the comparative experiment described above, in this example, the fluctuation range in the furnace pressure is suppressed to ± 150 Pa, so that the glass particulate deposit can be stably heat-treated. .

It is a schematic sectional drawing which shows the manufacturing apparatus of the glass base material which attached the upper cover which concerns on this invention. It is sectional drawing which shows the structure of the upper cover shown in FIG. It is the III-III sectional view taken on the line in FIG. It is the III-III sectional view taken on the line which shows the structure of another upper cover. It is sectional drawing which shows the upper cover of the manufacturing apparatus of the conventional glass base material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass base material manufacturing apparatus 2 Furnace core tube 3 Heater 4 Upper cover 6 Gas supply control apparatus 10 Glass particulate deposit body (object to be heated)
10A Support rod 40 Lid 40A, 42B, 43B Support rod insertion port (insertion port)
40B, 42C, 43C Seal edge 41-43 1st chamber-3rd chamber (room)
41A-43A Outer peripheral surface 41B, 43D Gas introduction part (gas port)
41C, 42E, 43E, 41D Bulkhead 42D Gas exhaust part (gas port)
R1, R3, R5 Outer chamber R2, R4, R6 Inner chamber S Furnace space

Claims (5)

A glass base material manufacturing apparatus for heating an object to be heated in a vertical furnace core tube,
An upper lid that is provided with an insertion port through which a support rod that supports the object to be heated passes and is attached to an upper portion of the core tube includes a plurality of rooms of three or more layers in the vertical direction along the support rod,
Each of the rooms has a gas port on the outer periphery, and has a partition wall concentric with the insertion port in the room. It is a manufacturing apparatus of the glass base material of Claim 1, Comprising:
The apparatus for producing a glass base material, wherein the partition wall is formed so as to be continuous in a circumferential direction concentric with the insertion opening and to partially cover the vertical direction in the room. It is a manufacturing apparatus of the glass base material of Claim 1, Comprising:
The said partition is intermittently formed in the circumferential direction concentric with the said insertion port, The manufacturing apparatus of the glass base material characterized by the above-mentioned. A method for producing a glass base material for heating an object to be heated in a vertical furnace core tube,
An upper lid that is provided with an insertion port through which a support rod that supports the object to be heated passes and is attached to the upper portion of the core tube includes a plurality of rooms of three or more layers in the vertical direction along the support rod. Each has a gas port on the outer periphery, and a partition concentric with the insertion port in the room,
A method for producing a glass base material, wherein the introduction of the inert gas and the exhaust of the gas are alternately performed in order from the lowermost layer to the upper layer through the gas ports for the rooms of the respective layers. . It is a manufacturing method of the glass base material of Claim 4,
A method for producing a glass base material, wherein He gas is used as an inert gas introduced into the lowermost room.

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