Method for manufacturing porous glass body

Abstract

To provide a method for manufacturing a porous glass body, capable of suppressing the quality reduction of the porous glass body due to the existence of an ignition mechanism.SOLUTION: A method for manufacturing a porous glass body comprises: using first and second burners arranged at an interval in the longitudinal direction of a start member; depositing glass fine particles on the start member by igniting a hydrogen gas ejected from the first burner to react a glass raw material gas ejected from the first burner; depositing glass fine particles on the start member by igniting the second burner by inflaming the flame of the first burner to a hydrogen gas ejected from the second burner to react a glass raw material gas ejected from the second burner.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing a porous glass body. [Background technology]

[0002] Patent Document 1 discloses a porous glass body manufacturing device equipped with multiple burners. Hydrogen gas ejected from each burner is burned, and glass raw material gas is reacted with the flame to generate glass particles. The glass particles are deposited on a starting material to obtain a porous glass body that is the base material for optical fibers and the like. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-35813 A Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional porous glass body manufacturing apparatuses, an ignition mechanism was often provided for each burner. In other words, the same number of ignition mechanisms as the number of burners were provided in the reaction chamber. As a result, the structure within the reaction chamber became complicated, and for example, the presence of the ignition mechanisms could disturb the flow of various gases within the reaction chamber, thereby degrading the quality of the porous glass body.

[0005] The present invention has been made in consideration of the above circumstances, and has an object to provide a method for producing a porous glass body that can prevent the quality of the porous glass body from being reduced due to the presence of an ignition mechanism. [Means for solving the problem]

[0006] In order to solve the above problems, a method for producing a porous glass body according to one embodiment of the present invention uses a first burner and a second burner arranged at an interval in the longitudinal direction of a starting member, ignites hydrogen gas ejected from the first burner, reacts with a glass raw material gas ejected from the first burner to deposit glass particles on the starting member, ignites the second burner by igniting hydrogen gas ejected from the second burner with a flame of the first burner, and reacts with a glass raw material gas ejected from the second burner to deposit glass particles on the starting member. Effect of the Invention

[0007] According to the above aspect of the present invention, it is possible to provide a method for producing a porous glass body that is capable of suppressing deterioration in the quality of the porous glass body due to the presence of an ignition mechanism. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a diagram showing an example of a manufacturing apparatus used in the manufacturing method of the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The method for producing a porous glass body according to this embodiment will be described below with reference to the drawings. As shown in FIG. 1, a manufacturing apparatus for a porous glass body (hereinafter, simply referred to as manufacturing apparatus 10) includes a reaction chamber 9, a plurality of burners 3 to 5, and a support section 2. A starting member 1 is accommodated in the reaction chamber 9. The starting member 1 is a member that will be the central part of the porous glass body manufactured by the manufacturing apparatus 10. The starting member 1 is made of quartz glass or the like. The starting member 1 is, for example, in the shape of a round rod. At least one end of the starting member 1 is rotatably held by the support section 2. The reaction chamber 9 is provided with two exhaust ports 8 for discharging unnecessary gas. The number and positions of the exhaust ports 8 can be changed as appropriate.

[0010] The burners 3-5 are supplied with glass raw material gas, oxygen gas, hydrogen gas, inert gas, etc. Each of the burners 3-5 has, for example, a multi-tube structure. In the vicinity of the nozzles of the burners 3-5, a plurality of ports are provided for ejecting each gas alone or in a mixed state. As the glass raw material gas, for example, SiCl4, GeCl4, or an organosilicon compound can be used. A specific example of the organosilicon compound is alkylcyclosiloxane. When the hydrogen gas is burned, a flame (oxyhydrogen flame) is generated in the vicinity of the nozzles of the burners 3-5. The glass raw material gas is reacted in this flame to generate glass particles. The glass particles are deposited on the surface of the rotating starting member 1 to form a deposition layer (soot) of glass particles. As a result, a porous glass body is obtained.

[0011] As the inert gas supplied to the burners 3 to 5, for example, argon, nitrogen, etc. can be adopted. By supplying the inert gas to the burners 3 to 5 together with hydrogen gas, etc., the flow rate of the gas ejected from each nozzle can be increased. This makes it possible to move the flame generation position (combustion start point) away from each nozzle, and to prevent the vicinity of the nozzle from becoming red-hot and being damaged.

[0012] In this embodiment, a case where an optical fiber preform is obtained by a vapor phase axial deposition method (VAD method) will be described. However, this embodiment may be applied to a method other than the VAD method (for example, an outside vapor deposition method (OVD method)). The porous glass body is sintered to obtain an optical fiber preform. In addition to the sintering, the optical fiber preform may be subjected to a dehydration treatment or a doping treatment, if necessary. Moreover, an optical fiber can be obtained by drawing the optical fiber preform.

[0013] (direction definition) In this embodiment, the longitudinal direction of the starting member 1 may be simply referred to as the "longitudinal direction". In the drawings, the vertical direction is represented by the Z axis, with the upper side in the vertical direction being the +Z side, and the lower side being the -Z side. In this embodiment, the longitudinal direction coincides with the vertical direction. However, the longitudinal direction does not have to coincide with the vertical direction.

[0014] In this embodiment, the upper end of the starting member 1 is gripped by the support part 2, and the lower end of the starting member 1 is located inside the reaction chamber 9. The support part 2 has, for example, a chuck that grips the starting member 1 and a moving mechanism that moves the chuck in the vertical direction. The support part 2 is capable of moving the starting member 1 upward while rotating it.

[0015] The burner 3 is disposed at a position where soot 6 can be deposited on the lower end of the starting member 1. The burner 3 is located at the lowest position among the plurality of burners 3 to 5 possessed by the manufacturing apparatus 10. The burner 3 is inclined both vertically and horizontally. However, the position and attitude of the burner 3 may be changed as appropriate. The burner 3 in this embodiment is a core burner, and plays a role in forming a portion that becomes the core of the porous glass body.

[0016] The burners 4 and 5 are disposed at positions where soot can be deposited around the starting member 1. In addition, by moving the starting member 1 upward, the burners 4 and 5 can deposit soot around the soot 6 that becomes the core formed by the burner 3. The burners 4 and 5 in this embodiment are burners for cladding, and play a role in forming the part that becomes the cladding of the porous glass body. The burner 4 is disposed above the burner 3, and the burner 5 is disposed even higher than the burner 4. In other words, the burners 3 to 5 are disposed at intervals along the longitudinal direction of the starting member 1. The burners 4 and 5 extend along a direction (i.e., a substantially horizontal direction) that is substantially perpendicular to the longitudinal direction of the starting member 1. However, the positions and postures of the burners 4 and 5 may be changed as appropriate. The burner 4 is also called a first cladding burner, and the burner 5 is also called a second cladding burner.

[0017] Here, if the hydrogen gas concentration at the combustion start point of each burner 3-5 exceeds 8%, the starting member 1 is likely to be deformed or cracked due to the impact when the hydrogen gas ignites. Therefore, when igniting the burners 3-5, it is preferable to adjust the supply amount of hydrogen gas so that the hydrogen gas concentration at the combustion start point of each burner 3-5 is 8% or less. The "combustion start point" is a point near the nozzle of each burner 3-5, and is the point of the flame generated by the combustion of the hydrogen gas that is closest to the nozzle. The combustion start point is determined for each burner 3-5. More specifically, the combustion start point of each burner 3-5 is determined by the flow velocity of the hydrogen gas ejected from each nozzle and the flame propagation speed of the hydrogen gas. The greater the flow velocity of the hydrogen gas, the farther the combustion start point is from the nozzle. In order to suppress failure of the burners 3-5, the flow velocity of the hydrogen gas is usually set so that the combustion start point is closer to the starting member 1 than each nozzle of the burners 3-5.

[0018] The interval between the nozzles of the burners 3 to 5 in the longitudinal direction of the starting member 1 (vertical direction in this embodiment) is preferably 0.01 m or more and 0.4 m or less. As a result of intensive study by the present inventors, it was found that by setting the interval between the burners 3 to 5 in the longitudinal direction to 0.4 m or less, it was possible to cause ignition between the burners while keeping the hydrogen gas concentration at the combustion start point of each of the burners 3 to 5 to 8% or less. In other words, since the flame of burner 3 can be ignited by burner 4, an ignition mechanism for burner 4 is not required. Similarly, since the flame of burner 4 can be ignited by burner 5, an ignition mechanism for burner 5 is not required.

[0019] In this way, if it is possible to cause ignition between the burners 3 to 5, there is no need to provide an ignition mechanism for the burners 4 and 5 as long as an ignition mechanism is provided for the burner 3, which is ignited first. Therefore, in this embodiment, an ignition mechanism (not shown) is provided only for the burner 3, and no ignition mechanism is provided for the burners 4 and 5. This makes it possible to simplify the structure inside the reaction chamber 9. As the ignition mechanism provided for the burner 3, for example, a spark plug or a glow plug can be used, but other types of ignition mechanisms may also be used.

[0020] The manufacturing apparatus 10 includes a control unit (not shown) that controls the flow rate of each gas supplied to each burner 3 to 5, the timing of supply and stop, and the timing of operation of the ignition mechanism. As the control unit, a microcontroller, an integrated circuit such as an IC (Integrated Circuit), an LSI (Large-scale Integrated Circuit), or an ASIC (Application Specific Integrated Circuit), or an NC (Numerical Control) device can be used. When an NC device or the like is used as the control unit, machine learning may or may not be used.

[0021] Next, a description will be given of a method for manufacturing a porous glass body using the manufacturing apparatus 10. In the following description, the timing of supply and stop of each gas, the flow rate of each gas, the activation timing of the ignition device, and the like may be controlled by a control unit of the manufacturing apparatus 10.

[0022] In this embodiment, prior to depositing the glass particles on the starting member 1, the starting member 1 is preheated (preheating step). Preheating can suppress the occurrence of cracking of the porous glass body and soot falling off. Preheating can be performed by burning hydrogen without supplying glass raw material gas to the burners 3 to 5. By performing preheating until immediately before starting the deposition of the glass particles, it is possible to suppress a decrease in the surface temperature of the heated starting member 1. Therefore, it is preferable to burn hydrogen gas for preheating, and then start supplying glass raw material gas to each of the burners 3 to 5 after a predetermined time has elapsed.

[0023] In the preheating, the target temperature of the surface of the starting member 1 is desirably 100° C. or more higher than the deposition temperature of the glass particles at that portion of the starting member 1, and 1500° C. or less. The manufacturing apparatus 10 may include a non-contact thermometer for measuring the surface temperature of the starting member 1. Furthermore, the measurement result by the non-contact thermometer may be input to the control unit, and the control unit may be configured to control the timing of starting the supply of the glass raw material gas to each of the burners 3 to 5 based on the input.

[0024] When igniting the burner 3, hydrogen gas and inert gas are supplied to the burner 3 and the ignition device is operated. The hydrogen gas concentration at the start of combustion of the burner 3 at the time of ignition is preferably 4% or more and 8% or less. If the hydrogen gas concentration is less than 4%, ignition may not occur even if the ignition device is operated. If the hydrogen gas concentration exceeds 8%, as described above, deformation, cracks, etc. are likely to occur in the starting member 1. As a result of the study by the present inventors, it was possible to make the hydrogen concentration at the start of combustion of the burner 3 at the time of ignition 8% or less by setting the timing of operation of the ignition device to 10 seconds or less from the start of supply of hydrogen gas, etc. to the burner 3.

[0025] After the ignition of the burner 3 is completed, oxygen gas is supplied to the burner 3 while the burners 4 and 5 are not ignited, to preheat the lower end a of the starting member 1. When the surface temperature of the lower end a rises to a target value, the supply of glass raw material gas to the burner 3 is started, and the deposition of glass particles on the lower end a is started. At a timing close to the start of the supply of glass raw material gas to the burner 3, hydrogen gas and an inert gas are supplied to the burner 4. As a result, the flame of the burner 3 ignites the burner 4, and the burner 4 is ignited. After the ignition of the burner 4 is completed, oxygen gas is supplied to the burner 4 to preheat the outer periphery b of the starting member 1. Even while the outer periphery b is being preheated, the burner 3 is operated as usual, and the deposition of glass particles on the lower end a is continued. At this point, the burner 5 may be in an unignited state. In the starting member 1, the part facing the burner 4 is the outer periphery b, and the part facing the burner 5 is the outer periphery c.

[0026] When the surface temperature of the outer periphery b of the starting member 1 is raised to a target value by the preheating by the burner 4, the supply of glass raw material gas to the burner 4 is started, and the deposition of glass particles on the outer periphery b is started. At a timing close to the start of the supply of glass raw material gas to the burner 4, hydrogen gas and an inert gas are supplied to the burner 5. As a result, the flame of the burner 4 ignites the burner 5, and the burner 5 is ignited. After the ignition of the burner 5 is completed, oxygen gas is supplied to the burner 5 to preheat the outer periphery c of the starting member 1. Even while the outer periphery c is being preheated, the burner 4 is operated normally, and the deposition of glass particles on the outer periphery b is continued.

[0027] When the surface temperature of the outer periphery c of the starting member 1 is raised to a target value by preheating with the burner 5, the supply of glass raw material gas to the burner 5 is started, and deposition of glass particles on the outer periphery c is started. This starts deposition of glass particles (soot) by the three burners 3 to 5. In order to finally obtain a porous glass body of a desired shape, the starting member 1 may be moved upward, and soot may be further deposited by the burners 4 and 5 on the soot deposited by the burner 3.

[0028] As described above, the manufacturing method of the porous glass body of the present embodiment uses the burner 3 (first burner) and the burner 4 (second burner) arranged at an interval in the longitudinal direction of the starting member 1. Then, the hydrogen gas ejected from the burner 3 is ignited, and the glass raw material gas ejected from the burner 3 is reacted to deposit glass particles on the starting member 1, and the flame of the burner 3 is ignited to the hydrogen gas ejected from the burner 4 to ignite the burner 4, and the glass raw material gas ejected from the burner 4 is reacted to deposit glass particles on the starting member 1. According to this manufacturing method, it is not necessary to provide an ignition mechanism for the burner 4. Therefore, the number of ignition mechanisms arranged in the reaction chamber 9 can be reduced, and the structure inside the reaction chamber 9 can be simplified. This makes it possible to suppress the quality of the porous glass body from being deteriorated due to the presence of the ignition mechanisms being disturbed in the flow of various gases in the reaction chamber 9. In addition, by reducing the number of ignition mechanisms, the manufacturing apparatus 10 can be reduced in cost.

[0029] Furthermore, the hydrogen concentration at the combustion start point of burner 4, which is determined by the flow velocity of the hydrogen gas ejected from burner 4 and the flame propagation speed of the hydrogen gas, may be within a range of 4 to 8%. When the hydrogen concentration at the combustion start point is 4% or more, it becomes possible for the flame of burner 3 to be reliably ignited by burner 4. Furthermore, when the hydrogen concentration at the combustion start point is 8% or less, it is possible to suppress deformation or cracking of starting member 1 due to the impact at the time of ignition.

[0030] Furthermore, the burners 3 and 4 may be arranged at an interval in the vertical direction, and the vertical distance between the nozzle of the burner 3 and the nozzle of the burner 4 may be 0.4 m or less. In this case, the flame of the burner 3 can ignite the burner 4 while keeping the hydrogen concentration at the combustion start point of the burner 4 at 8% or less.

[0031] The above embodiment will be described below using specific test examples.

[0032] (Test Example 1) A manufacturing apparatus 10 as shown in FIG. 1 was prepared. The vertical distance between the nozzles of the burner 3 and the burner 4 was 0.2 m. The vertical distance between the nozzles of the burner 4 and the burner 5 was 0.1 m. The distance (horizontal distance) between the nozzles of the burners 4 and 5 and the starting member 1 was 0.1 m. After the ignition mechanism was operated to ignite the burner 3, the supply of hydrogen gas to the burner 4 was started so that the hydrogen gas concentration at the combustion start point of the burner 4 was 2%. Under these conditions, a test was performed 10 times to see whether the burner 4 would automatically ignite (i.e., whether the flame of the burner 3 would ignite the burner 4). As a result, the burner 4 ignited within 10 seconds after the supply of hydrogen gas to the burner 4 was started in two of the 10 tests. No deformation or damage of the burner 4 or the starting member 1 due to the impact when the burner 4 ignited was observed.

[0033] (Test Example 2) A manufacturing apparatus 10 similar to that of Example 1 was prepared. After the ignition mechanism was operated to ignite the burner 3, the supply of hydrogen gas to the burner 4 was started so that the hydrogen gas concentration at the combustion start point of the burner 4 was 3%. Under these conditions, a test was performed 10 times to check whether the burner 4 would automatically ignite (i.e., whether the flame of the burner 3 would ignite the burner 4). As a result, the burner 4 ignited within 10 seconds after the supply of hydrogen gas to the burner 4 was started 8 times out of the 10 tests. No deformation or damage of the burner 4 or the starting member 1 due to the impact when the burner 4 ignited was observed.

[0034] (Test Example 3) A manufacturing apparatus 10 similar to that of Example 1 was prepared. After the ignition mechanism was operated to ignite the burner 3, the supply of hydrogen gas to the burner 4 was started so that the hydrogen gas concentration at the combustion start point of the burner 4 was 4%. Under these conditions, a test was performed 10 times to check whether the burner 4 would automatically ignite (i.e., whether the flame of the burner 3 would ignite the burner 4). As a result, in all 10 tests, the burner 4 ignited within 10 seconds after the supply of hydrogen gas to the burner 4 was started. No deformation or damage of the burner 4 or the starting member 1 due to the impact when the burner 4 ignited was observed.

[0035] As described above, it was confirmed that the flame of burner 3 can be ignited by burner 4 if the hydrogen gas concentration at the combustion start point of burner 4 is 4% or more.

[0036] 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.

[0037] For example, in the above embodiment, the longitudinal direction of the starting member 1 coincides with the vertical direction. However, the longitudinal direction of the starting member 1 does not have to coincide with the vertical direction, and may coincide with, for example, the horizontal direction. Furthermore, both ends of the starting member 1 in the longitudinal direction may be supported by the support parts 2. If the longitudinal direction of the starting member 1 coincides with the vertical direction, heat and flame are more likely to be transferred from the burner 3 to the burner 4 due to the influence of gravity, and ignition is more likely to occur. If the longitudinal direction of the starting member 1 coincides with the horizontal direction, for example, the airflow in the reaction chamber 9 can be adjusted so as to flow from the burner 3 to the burner 4, making it easier for ignition to occur from the burner 3 to the burner 4. The airflow in the reaction chamber 9 can be adjusted by the position of the exhaust port 8, the position of the air supply port that supplies the atmospheric gas to the reaction chamber 9, etc.

[0038] In the above embodiment, the timing at which preheating is started by each of the burners 3 to 5 is not the same. That is, preheating is started by the burner 3, and after a predetermined time has elapsed, preheating is started by the burner 4. However, preheating by the burners 3 to 5 may be started simultaneously.

[0039] In addition, within the scope of the spirit of the present invention, 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. [Explanation of symbols]

[0040] 1... Starting member 3... Burner (first burner) 4... Burner (second burner)

Claims

1. using a first burner and a second burner spaced apart in a longitudinal direction of the starting member; The hydrogen gas ejected from the first burner is ignited, and the glass raw material gas ejected from the first burner is reacted with the glass raw material gas to deposit glass particles on the starting member; A method for producing a porous glass body, comprising the steps of: igniting the second burner by causing a flame of the first burner to ignite hydrogen gas ejected from the second burner; and reacting a glass raw material gas ejected from the second burner to deposit glass fine particles on the starting member, The first burner and the second burner are spaced apart in a vertical direction; A distance between the nozzle of the first burner and the nozzle of the second burner in the vertical direction is within 0.4 m, A method for producing a porous glass body, wherein a hydrogen concentration at a combustion start point of the second burner, which is determined by a flow velocity of the hydrogen gas ejected from the second burner and a flame propagation speed of the hydrogen gas, is 4% or more.

2. A method for producing a porous glass body as described in claim 1, wherein the hydrogen concentration at the combustion starting point of the second burner is 8% or less.

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