JP5248092B2 - Synthetic silica glass manufacturing apparatus and synthetic silica glass manufacturing method - Google Patents

Description

  The present invention relates to a synthetic silica glass production apparatus, and more particularly to a closed synthetic silica glass production apparatus and a synthetic silica glass production method including a closed furnace body.

At present, synthetic silica glass having good light transmissivity at a wavelength of 250 nm or less and extremely low impurity content is used as an ultraviolet light transmitting material.
This synthetic silica glass is generally a high-purity silicon compound such as silicon tetrachloride (SiCl ₄ ) for the purpose of avoiding the incorporation of metal impurities that can cause absorption of ultraviolet (400 nm or less) wavelengths. This gas is introduced into an oxyhydrogen flame, flame-hydrolyzed, and deposited on a heat-resistant target in which silica fine particles are directly rotated and melted into a glass to produce transparent glass.

The production apparatus for producing synthetic silica glass is roughly classified into an open production apparatus in which a part of the furnace body is released to the atmosphere and a closed production apparatus in which the furnace body is shut off from the atmosphere. These are used properly depending on the application. For example, when silica glass is doped with a component other than SiO ₂ , a closed production apparatus is used so that toxic gas generated by the reaction does not flow out of the furnace body.
In addition, in order to produce silica glass for a large-diameter optical member, the ingot is also made large-diameter. In this case, an open-type production apparatus that can easily maintain the atmosphere in the furnace body is used.

The open-type manufacturing apparatus includes a furnace body whose lower part is always open to the atmosphere, a refractory installed inside the furnace body, an ingot-forming burner installed inside the refractory, and a target. It comprises exhaust means for exhausting silica particles that have not been deposited.
Using this apparatus, silica particles are deposited on this target while rotating the target around the vertical axis by the flame hydrolysis method, and the distance from the burner to the synthetic surface at the top of the ingot is kept constant according to the deposition rate. The synthetic silica glass is produced while pulling down.

In the closed-system manufacturing apparatus, a burner provided in a closed furnace body is installed with its front end facing the target from the top of the furnace body, and the exhaust means includes an exhaust port, a detoxifying device, and an exhaust fan. Consecutively arranged in the exhaust line.
Using this apparatus, silica fine particles are deposited on the target while rotating the target around the vertical axis by the flame hydrolysis method, and synthetic silica glass is produced while exhausting by the exhaust means.

  On the other hand, the silica fine particles that are not deposited on the target and are floating are discharged out of the furnace body by the exhaust equipment, but are deposited on the wall surface of the furnace body, the wall surface of the furnace structure, the exhaust port, the burner, etc. Go. There is a problem that when the silica deposited on the inside of the furnace or the member peels off and falls onto the ingot melting surface in accordance with the fall or the air flow along the furnace wall, it remains as a defect inside the ingot.

  As a measure to solve this problem, in an open system, in order to prevent silica from adhering to the inner wall of the furnace, a normal temperature inert gas is allowed to flow from the upper surface of the ingot to the lower surface along the inner wall of the furnace. A silica glass production apparatus has been proposed (Patent Document 1), and a method for forming a flame flow along the inner wall surface of a synthesis furnace has been proposed (Patent Document 2).

  In addition, in a closed system, in order to stably obtain an optimal exhaust state for the homogeneity of the refractive index, it is apparent by introducing gas into the exhaust line without changing the amount of exhaust gas from the closed furnace body. An apparatus for producing synthetic silica glass that increases the amount of upper exhaust gas has been proposed (Patent Document 3).

  However, in the case of Patent Document 1, when an inert gas at room temperature is flowed from above the fused silica adhering surface of the ingot to the wall surface of the furnace, the temperature near the fused silica adhering surface is lowered to change the synthesis conditions of the silica glass. There was a drawback that it would. In addition, since the temperature of the burner for allowing the inert gas at room temperature to flow into the furnace body is lowered, silica fine particles may adhere to the melt surface around the burner.

  Moreover, although the thing of patent document 2 has the method of forming the flame flow along the inner wall surface of a synthesis furnace, there exists a possibility of interfering with the flame from a synthesis burner, For this reason, defects, such as striae, are easy to arise. There was a drawback.

Furthermore, since the thing of patent document 3 is not provided with the inlet port, and since the number, inclination of the inlet port, the intake direction of air, etc. are not regulated, the floating silica fine particles cannot be discharged reliably, There was a problem that the silica fine particles adhered to the ingot melting surface to cause defects inside.
JP-A-7-109134 JP 2000-26126 A JP-A-8-165130

The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a synthetic silica glass production apparatus capable of producing synthetic silica glass having no striae and having no defects inside.
Moreover, it aims at providing the synthetic silica glass manufacturing method which can manufacture the synthetic silica glass without a striae and a defect inside.

  In order to achieve the above-described object, a synthetic silica glass manufacturing apparatus according to the present invention is provided with a sealed furnace body, a plurality of air inlets provided at an upper part of the furnace body, and a lower part of the furnace body. An exhaust port connected to the exhaust port, a target for ingot formation that is rotatably installed inside the furnace body, and a silica glass composition provided with a tip facing the target. A burner, and the intake port is always provided at a position lower than the fused silica adhering surface of the ingot, and the gas supplied from the intake port is inclined downward in a direction and horizontally so that the gas does not directly hit the ingot The synthetic silica glass manufacturing apparatus installed as described above, wherein the gas supplied from the intake port is formed as a swirling downward flow that swirls in the same direction as the rotation direction of the target for forming the ingot It is characterized in that.

Thus, in the synthetic silica glass manufacturing apparatus according to the present invention, the gas flow in the furnace is a swirling downward flow along the rotation direction of the ingot. Moreover, by introducing the flow of the intake gas introduced from the intake port in the same direction as the ingot rotation direction, the flow of the exhaust gas is accelerated by merging with the intake gas, and without generating an updraft in the furnace, It can be discharged out of the furnace.
The exhaust gas also includes floating silica particles that have not been deposited as ingots, and the silica particles can be prevented from adhering to the ingot synthetic deposition surface (fused silica adhesion surface), and defects inside the ingot ( (Foam, inclusion) can be suppressed.

  Here, the furnace body includes a refractory muffle having a silica glass synthesis burner installed at the top, an intake furnace portion having a plurality of intake ports provided below the muffle, and the intake furnace. It is desirable to provide an exhaust furnace part having a plurality of exhaust ports provided below the part.

Further, the inner diameter of the muffle is 1.3r to 2.5r, where r is the outer diameter of the ingot, the height in the muffle is 300mm to 800mm, and the inner diameter of the intake furnace section However, when the inner diameter of the muffle is a, it is 1.2a or more and 2.0a or less, the height in the intake furnace section is 150mm or more and 600mm or less, and the inner diameter of the exhaust furnace section is the intake furnace section It is desirable that the inner diameter of the exhaust gas is 1.2b or more and 3.0b or less, and the height in the exhaust furnace section is 300mm or more and 2000mm or less.
When the furnace body has such a dimensional shape, it is possible to obtain synthetic silica glass that is more suppressed in striae and defects and has more uniform physical properties and quality.

Furthermore, it is desirable that a wind direction changing plate having a flange portion extending downward is installed below the ingot forming target.
By using this wind direction changing plate, it is possible to block the upward air flow along the ingot lifting shaft and suppress the occurrence of defects inside the ingot.

  The diameter of the wind direction changing plate is preferably in the range of −10 mm to +10 mm with respect to the diameter of the ingot, and the length below the flange is preferably 50 mm to 100 mm.

  Furthermore, the exhaust equipment includes a differential pressure sensor that measures a pressure difference inside and outside the furnace provided in the exhaust furnace part, an exhaust pipe connected to an exhaust port formed in the exhaust furnace part, An outside air introduction pipe connected to the exhaust pipe and a turning valve for controlling the opening degree of the outside air introduction pipe, and the opening degree of the turning valve is controlled so that the differential pressure of the differential pressure sensor is constant. However, it is desirable that the distribution of the amount of exhaust from the exhaust furnace and the amount of outside air introduced from the outside air introduction pipe can be varied without changing the total amount of exhaust.

  As described above, since the distribution of the exhaust amount from the exhaust furnace part and the outside air introduction amount from the outside air introduction pipe is variable without changing the total exhaust amount, stable exhaust can be performed, and the atmosphere in the furnace can be changed. Can stabilize. Moreover, since the total displacement does not change, it is possible to suppress the adhesion of quartz glass powder in the exhaust pipe. In addition, since stable evacuation can be performed in the furnace, it is possible to obtain a quartz glass with a more uniform refractive index, in which bubbles and foreign substances are further prevented from entering the ingot.

  Further, it is desirable that a detoxifying device is connected to the exhaust pipe, and further an exhaust fan is connected to the detoxifying device.

  Furthermore, it has a horizontal cross section of the muffle constituting the furnace body, a horizontal cross section of an intake furnace portion having a plurality of intake ports provided below the muffle, and a plurality of exhaust ports provided below the intake furnace portion. It is desirable that all horizontal sections of the exhaust furnace section are circular.

  In order to achieve the above-mentioned object, the synthetic silica glass production method according to the present invention is a synthetic silica glass production method in which fused silica is adhered to a target provided in a furnace body using a silica glass synthesis burner. Gas is sucked in from a plurality of air inlets provided at the upper part, and is tilted downward with respect to the direction and the horizontal so as not to directly hit the ingot by the sucked gas, and further swivels in the same direction as the target rotation direction. The target top surface position is adjusted so that a gas flow is formed and air is always drawn from a position lower than the fused silica adhesion surface of the ingot, and fused silica is adhered to the target while exhausting from the vicinity of the lower part of the furnace body. It is said.

Thus, in the synthetic silica glass manufacturing method according to the present invention, the gas flow in the furnace forms a swirling downward flow along the rotation direction of the ingot. Moreover, by introducing the flow of the intake gas introduced from the intake port in the same direction as the ingot rotation direction, the flow of the exhaust gas is accelerated by merging with the intake gas, and without generating an updraft in the furnace, It can be discharged out of the furnace.
The exhaust gas also includes floating silica particles that have not been deposited as ingots, and the silica particles can be prevented from adhering to the ingot synthetic deposition surface (fused silica adhesion surface), and defects inside the ingot ( Bubbles, inclusions).

  According to the synthetic silica glass manufacturing apparatus concerning this invention, the synthetic silica glass manufacturing apparatus which can manufacture the synthetic silica glass which does not have a striae and does not have a defect inside can be provided. Moreover, according to the synthetic silica glass manufacturing method concerning this invention, there can be provided the synthetic silica glass manufacturing method which can manufacture the synthetic silica glass which does not have striae and does not have a defect inside.

  Hereinafter, a synthetic silica glass manufacturing apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a synthetic silica glass manufacturing apparatus according to an embodiment of the present invention, FIG. 2 is a plan view showing an arrangement state of intake ports thereof, and FIG. 3 is a perspective view showing a wind direction changing plate.

As shown in FIG. 1, a synthetic silica glass production apparatus 1 according to an embodiment of the present invention is a closed production apparatus. The furnace body 2 provided in the manufacturing apparatus 1 is hermetically sealed. The furnace body 2 is an air intake having a refractory muffle 3 and a plurality of air inlets 4 a provided on the top of the furnace body 2. The furnace part 4 and an exhaust furnace part 5 having an exhaust port 5 a provided at the lower part of the furnace body 2 are configured.
In addition, the sealed system here includes a substantially sealed state including a completely sealed state and an inevitable open state in terms of design.

  Further, the horizontal cross section of the muffle 3 constituting the furnace body 2, the horizontal cross section of the intake furnace section 4 having a plurality of intake ports 4 a provided below the muffle 3, and provided below the intake furnace section 4. All of the horizontal cross sections of the exhaust furnace portion 5 having a plurality of exhaust ports 5a are formed in a circular shape.

  Further, an ingot forming target 6 that is rotatably installed and an ingot lifting shaft 6 a that rotates and lifts the target 6 are provided inside the furnace body 2. Furthermore, a burner 7 for synthesizing silica glass is provided at the top of the muffle 3 with the tip facing the target 6.

As shown in FIG. 2, a plurality of, for example, four intake ports 4a are provided at regular intervals (every 90 °), and are always provided at a position lower than the fused silica adhering surface 8a of the ingot 8 formed on the target 6. It has been. In addition, the gas supplied from the intake port 4a, for example, air is inclined in a direction (45 ° away from the radial direction of the ingot 8 in FIG. 2) so as not to directly hit the ingot 8 and horizontally downward. is set up.
In addition, it is preferable that the inclination of the intake port 4a is formed at an angle of 5 to 60 ° with respect to the horizontal (in FIG. 1, it is inclined 15 degrees downward and its state is shown). Further, at least two exhaust ports 5a are provided symmetrically with respect to the furnace body 2 and the ingot elevating shaft 6a.

An inner diameter a of the inner wall of the muffle 3 is formed to be 1.3r or more and 2.5r or less, where r is the outer diameter of the ingot 8.
When the inner diameter of the muffle is less than 1.3r, it is difficult to maintain the shape of the ingot 8 due to excessive heat storage inside the muffle 3. As a result, when the shape of the ingot 8 is changed, the synthesis position (the fused silica adhering surface 8a position) is changed, the temperature distribution of the synthetic surface (the fused silica adhering surface 8a) is changed, and is generated by a hydrolysis reaction. This is not preferable because the reaction state of the silica fine particles changes and the physical properties and quality of the synthetic silica glass vary.
Further, since the distance between the inner wall of the muffle 3 and the ingot 8 is reduced, the exhaust gas is difficult to escape to the lower outside (intake furnace section 4) of the muffle 3, and the silica glass powder deposited on the inner wall of the muffle 3, the burner 7, etc. This is not preferable because this increases the amount of slag, which causes flying defects on the synthetic surface (fused silica adhesion surface 8a) of the ingot 8 and the like.

On the other hand, if the inner diameter of the inner wall of the muffle 3 exceeds 2.5r, it is difficult to maintain the high temperature in the muffle 3, and wrinkles occur on the synthetic surface (fused silica adhering surface 8a) of the ingot 8 due to insufficient heat quantity, causing striae. Is not preferable.
Moreover, it is necessary to increase the amount of gas from the burner 7 so that the temperature becomes high, which is not preferable because the manufacturing cost increases. Furthermore, if the amount of gas from the burner 7 is increased, the temperature distribution on the synthetic surface (fused silica adhering surface 8a) of the ingot changes, which causes variations in quality and is not preferable.

Further, the height h1 of the muffle 3 is formed to be 300 mm or more and 800 mm or less.
When the height h1 of the muffle 3 exceeds 800 mm, the amount of gas from the burner 7 necessary for maintaining the temperature inside the muffle 3 is increased, which is not preferable because the manufacturing cost increases.
On the other hand, when the height h1 in the muffle 3 is less than 300 mm, the temperature inside the muffle 3 rises too much, which makes it difficult to maintain the shape of the ingot 8, which is not preferable. Further, exhaust of gas in the muffle 3 deteriorates, silica glass powder adheres to the inner wall surface of the muffle 3, and when this falls, it flies to the synthetic surface of the ingot 8 (fused silica adhesion surface 8a), and there are defects, etc. Since it occurs, it is not preferable.

Further, the inner diameter b of the inner wall of the intake furnace section 4 is formed to be 1.2a or more and 2.0a or less, where a is the inner diameter of the inner wall of the muffle 3.
When the inner diameter of the inner wall of the intake furnace section 4 is less than 1.2a, the temperature inside the intake furnace section 4 rises too much, so it becomes difficult to maintain the outer diameter of the ingot 8, and the shape of the ingot 8 changes, The synthetic position (fused silica adhering surface 8a) changes, the temperature distribution of the synthetic surface (fused silica adhering surface 8a) changes, and the reaction state of the silica fine particles produced by the hydrolysis reaction changes. This is not preferable because it causes variations in physical properties and quality. Moreover, when the temperature in the intake furnace section 4 is high, the internal pressure rises and it is difficult to stably supply intake gas, which is not preferable.

  On the other hand, when the inner diameter of the intake furnace section 4 exceeds 2.0a, a large swirl flow with a reduced flow velocity is generated, so that silica glass powder is likely to be deposited near the upper surface of the intake furnace section 4, and the ingot 8 Since the swirling flow velocity in the vicinity of is reduced, the exhaust efficiency is deteriorated, and an upward air flow is partially generated, thereby causing a defect in the ingot 8, which is not preferable.

Further, the height h2 in the intake furnace section 4 is formed to be 150 mm or more and 600 mm or less.
If the height (length) h2 of the intake furnace section 4 is less than 150 mm, a swirl flow over the entire circumference cannot be formed in the intake furnace section 4, and an upward flow of exhaust gas is generated, and this rise Since the floating silica glass powder or the like adheres to the fused silica adhering surface 8a of the ingot 8 due to the flow and causes defects inside the ingot 8, it is not preferable.

  In addition, if the height (length) h2 of the intake furnace section 4 exceeds 600 mm, the distance between the intake port 4a and the exhaust port 5a is long, and pressure loss occurs and exhaust efficiency decreases, which is not preferable. Further, the swirling flow is not preferable because the flow velocity decreases as it goes downward, and the silica glass powder contained in the exhaust gas adheres to the inner wall surface of the intake furnace section 4.

Further, the inner diameter c of the inner wall of the exhaust furnace section 5 is formed to be 1.2b or more and 3.0b or less, where b is the inner diameter of the intake furnace section 4.
The flow swirling and descending from the intake furnace section 5 descends along the inner wall of the exhaust furnace section 5 and is exhausted from the exhaust port 5a, but there is a part of the airflow that has not reached the exhaust port 5a. The flow circulates in the exhaust furnace section 5. This flow rises along the ingot elevating shaft 6a, and becomes a flow that collides with the swirling flow that descends from the upper portion of the lower surface of the intake furnace portion 5. In order to avoid such a flow collision, it is necessary to sufficiently exhaust the gas circulating in the exhaust furnace unit 5 from the exhaust port 5a and reduce the flow velocity in the exhaust furnace unit 5 to some extent. Therefore, the inner diameter c of the exhaust furnace section 5 needs to be 1.2b to 3.0b, where b is the inner diameter of the intake furnace section 4.

When the inner diameter c of the exhaust furnace part 5 is less than 1.2b, the exhaust gas flow rate in the exhaust furnace part 5 is fast, so the efficiency of exhaust from the exhaust port 5 is poor, and the exhaust furnace part 5 circulates in the exhaust furnace part 5. The gas component (gas flow) to be increased.
In this case, the frequency of collision with the swirling flow descending from the intake furnace unit 4 increases, and the gas flow becomes turbulent in this portion, and an ascending airflow along the ingot elevating shaft 6a is generated. This affects the synthetic surface (fused silica adhering surface 8a) of the ingot 8 and causes a defect inside the ingot 8, which is not preferable. Moreover, the exhaust furnace part 5 becomes very high temperature, deterioration of a member becomes severe, and manufacturing cost increases, which is not preferable.
Further, when the inner diameter c of the inner wall of the exhaust furnace section 5 exceeds 3.0b, the flow rate of the exhaust gas in the exhaust furnace section 5 is slow, so that silica glass powder is easily deposited on the inner wall surface of the exhaust furnace section 5, Since exhaust efficiency falls, it is not preferable.

It is desirable that the height h3 in the exhaust furnace section 5 is 300 mm or more and 2000 mm or less.
When the height h3 of the exhaust furnace section 5 is less than 300 mm, the flow rate in the exhaust furnace section 5 is fast, and therefore the gas components circulating in the exhaust furnace section 5 increase. In this case, the frequency of collision with the swirling flow descending from the intake furnace unit 4 increases, and the gas flow becomes turbulent in this portion, and an ascending airflow along the ingot elevating shaft 6a is generated. This affects the synthetic surface of the ingot 8 (fused silica adhesion surface 8a) and causes defects inside the ingot 8, which is not preferable.

  On the other hand, if the height h3 of the exhaust furnace section 5 exceeds 2000 mm, the distance between the intake port 4a and the exhaust port 5a is long, and this is not preferable because the exhaust efficiency is reduced due to pressure loss. In addition, since the speed of the airflow swirling in the intake furnace section 4 is slow, an ascending airflow is likely to be generated, causing a defect in the ingot 8, which is not preferable.

Further, as shown in FIGS. 1 and 3, a wind direction changing plate 9 having a flange portion 6c extending in the downward direction is installed below the target 6 for forming the ingot.
The wind direction changing plate 9 is formed in a cylindrical shape having a ceiling portion 9a, and a through hole 9b through which the ingot elevating shaft 6a passes is formed in the ceiling portion 9a. Further, the outer peripheral wall (the flange portion 9c) of the wind direction changing plate 9 is extended downward along the ingot elevating shaft 6a.

  The flow swirling and descending from the intake furnace section 4 descends along the inner wall of the exhaust furnace section 5 and is exhausted from the exhaust port 5a, but there is a part of the airflow that has not reached the exhaust port 5a. The flow circulates inside the exhaust furnace section 5.

  As shown by the arrows in FIG. 4, this flow rises along the ingot elevating shaft 6 a and collides with the swirl flow that descends from the upper surface on the lower surface of the intake furnace unit 4. When the frequency of collision with the swirling flow descending from the intake furnace portion 4 increases, the gas flow becomes turbulent in this portion, and an ascending air current along the ingot elevating shaft 6a is generated. This affects the synthetic surface of the ingot 8 (the fused silica adhesion surface 8a) and causes a defect inside the ingot 8.

  On the other hand, when the wind direction changing plate 9 is installed as shown in FIG. 5, the updraft along the ingot lifting shaft 6a is blocked by the flange portion 9c of the wind direction changing plate 9, The occurrence of defects inside the ingot 8 is suppressed.

The diameter of the wind direction changing plate 9 is preferably −10 mm or more and +10 mm or less with respect to the diameter of the ingot 8, and the lower length of the flange is preferably 50 mm or more and 100 mm or less.
The diameter of the wind direction changing plate 9 is desirably equal to the diameter of the desired ingot 8, but the above-described effect can be obtained as long as it is within ± 10 mm with respect to the diameter of the ingot 8. However, when the diameter of the wind direction change plate 9 exceeds 10 mm than the diameter of the ingot 8, the exhaust gas from the intake furnace section 4 collides with the upper surface (outer surface of the ceiling portion) of the wind direction change plate 9, and the upward flow is generated. generate. On the contrary, when the diameter of the wind direction changing plate 9 is less than 10 mm than the diameter of the ingot 8, the upward flow cannot be sufficiently blocked.

If the length of the lower part of the flange is 50 mm or more, the upward flow is received inside the wind direction changing plate 9 and the upward flow is sufficiently convected (changed to the downward flow) inside the wind direction changing plate 9. As a result, the effect of reducing the flow velocity and weakening the upward flow toward the intake furnace section 4 is obtained.
On the other hand, when the length below the flange portion 9c is 50 mm or less, the convection (changed to the downflow) inside the wind direction change plate 9 is insufficient, the flow velocity is not sufficiently lowered, and the upflow from the wind direction change plate 9 Leaks out and forms an upward flow toward the intake furnace section 4.
On the contrary, when the length below the flange portion 9c of the wind direction changing plate 9 exceeds 100 mm, the range in which the upward flow generated outside the flange portion 9c cannot be received increases, and as a result, the upward flow is suppressed. Can not do it.

Further, as shown in FIG. 1, in the manufacturing apparatus 1, an exhaust facility 10 is connected to the exhaust port 5a.
The exhaust facility 10 controls an exhaust pipe 11 connected to an exhaust port 5 a formed in the exhaust furnace section 5, an outside air introduction pipe 12 connected to the exhaust pipe 11, and an opening degree of the outside air introduction pipe 12. A rotary valve 13, a differential pressure sensor 15 for measuring a pressure difference inside and outside the furnace provided in the exhaust furnace section 5, a detoxifying device 17 connected to the exhaust pipe 11, an exhaust fan 18, It has.
The differential pressure sensor 14 is installed below the exhaust port 5a in order to prevent the measurement of the differential pressure from becoming impossible due to the adhesion of silica glass powder in the exhaust gas. In FIG. 1, the abatement apparatus 17 and the exhaust fan 18 connected to the left exhaust pipe 11 are omitted.

  The rotating valve (damper) 12 is rotated by controlling the stepping motor 14 by the control device 15 based on the measurement data from the differential pressure sensor 14. That is, the measurement data from the differential pressure sensor 14 is fed back to the control device 15, and the control device 10 controls the stepping motor 14 (PID control) to adjust the opening degree of the rotary valve 13. It is comprised so that.

  Thus, by adjusting the opening degree of the rotary valve 13, the amount of outside air introduced into the exhaust pipe 11 from the outside air introduction pipe 12 is adjusted, and the amount of exhaust from the exhaust furnace section 5 and the outside air introduction pipe 12 are adjusted. Control is made to vary the distribution of the exhaust amount from the exhaust furnace section 5 and the outside air introduction amount from the outside air introduction pipe 12 without changing the total exhaust amount of the outside air introduction amount from the outside.

  Since the exhaust equipment 10 is configured in this way, the exhaust amount of the exhaust pipe 11 is controlled by using the value of the differential pressure sensor 14 provided in the exhaust part 5 as the outside air introduction pipe 11 provided in the exhaust pipe 10. The amount of exhaust can be controlled so that the differential pressure inside and outside the furnace becomes constant depending on the degree of opening and closing of the rotary valve 12.

Therefore, when the amount of exhaust from the exhaust furnace 5 is large, the opening degree of the outside air introduction pipe 12 is reduced, and the amount of outside air introduced is reduced. On the other hand, when the amount of exhaust from the exhaust section 5 is small, the opening degree of the outside air introduction pipe 12 is increased, and the amount of outside air introduced is increased. In addition, the total exhaust amount, which is the sum of the exhaust amount from the exhaust unit 5 and the outside air introduction amount from the outside air introduction pipe 12, is controlled so as not to change.
The total exhaust amount is determined by the amount of gas supplied from the burner 7, the total amount of exhaust gas from the furnace body 2, the total amount of introduced gas from the intake port 4a, and the secondary gas inlet ( It is necessary to make the total exhaust amount the sum of the amount of gas introduced from the outside air introduction pipe 12).

As a result, stable exhaust from the exhaust furnace unit 5 can be performed, and the atmosphere in the muffle 3 can be stabilized. In addition, since the total displacement is not changed, the silica glass powder can be prevented from adhering to the exhaust pipe 11.
Further, since the total exhaust amount of the exhaust pipe 11 of the synthetic quartz glass manufacturing apparatus does not change, it is economical because a large number of furnace bodies 2 can be connected to one abatement apparatus 17 and exhaust fan 18. .

  Then, by using the synthetic quartz glass production apparatus of the present invention, it is possible to obtain a synthetic quartz glass having a uniform refractive index, in which bubbles and foreign substances are prevented from entering the synthetic quartz glass ingot 8.

Next, the synthetic silica glass production method according to the present invention will be described.
As shown in FIG. 1, a high purity silicon compound such as silicon tetrachloride (SiCl ₄ ) is introduced into an oxyhydrogen flame using a burner 7 that opens into a muffle 3 at about 600 ° C. The synthetic silica glass is decomposed and deposited on the target 6 that directly rotates the glass fine particles and melted into glass, and the distance from the burner 7 to the fused silica adhering surface 8a of the ingot 8 is kept constant in accordance with the deposition speed. Manufacture.

  On the other hand, as shown in FIG. 2, the four intake ports 4a are provided at equal intervals, and are always provided at a position lower than the fused silica adhering surface 8a. In other words, the intake ports 4a are always arranged from the fused silica adhering surface 8a of the ingot 8. The upper surface position of the target 6 is adjusted so that the intake gas is introduced at a low position, and the air supplied from the intake port 4a does not directly hit the ingot 8 and at an angle of 5 to 60 ° with respect to the horizontal. It is tilted downward and introduced.

  The air supplied from the intake port 4a flows as a swirling flow from the upper side to the lower side along the periphery of the ingot 8, and is exhausted out of the furnace body 2 from the exhaust port 5a. Moreover, the gas supplied from the intake port 5a is formed as a swirling downward flow that swirls in the same direction as the rotation direction of the target 6 for forming the ingot.

Since the four intake ports 4a are provided at equal intervals, there is no bias in the furnace atmosphere, and the furnace air always flows as a swirling flow from the upper side to the lower side. It is quickly and reliably exhausted out of the furnace body 2 and does not flow backward and adhere to the fused silica adhering surface 8a and does not remain as a defect inside the ingot 8.
Furthermore, since the ascending airflow along the ingot elevating shaft 6a is blocked by the wind direction changing plate 9, the occurrence of defects inside the ingot 8 can be further suppressed.

  Furthermore, if the amount of gas introduced from the inlet 4a in the exhaust process is increased more than necessary, the air flow in the direction of the melting surface along the inner wall of the furnace is promoted. -10 times or less is preferable.

Further, since the intake port 4a is always provided at a position lower than the fused silica adhering surface 8a of the ingot 8, the silica glass powder around the burner 7 does not decrease the temperature near the fused silica adhering surface 8a. Does not adhere, does not clog the burner 7, and the silica glass powder does not adhere to the molten surface.
In addition, since the intake port 4a is installed in such a direction that the gas supplied from the intake port 4a does not directly hit the ingot 8, there is no possibility of interfering with the flame from the burner 7, and striae, etc. There will be no defects.

  Furthermore, the temperature of the gas supplied from the intake port 4a3 is preferably 30 ° C. or lower, preferably 20 ° C. or lower, and within a range of ± 5 ° C. Thereby, high diameter control becomes possible.

  Further, by introducing normal temperature air from the outside air introduction pipe 12 into the exhaust pipe 11 and lowering the exhaust gas temperature, the exhaust equipment 10 can be protected and the exhaust amount can be easily made constant.

(Example)
The synthetic silica glass manufacturing apparatus according to the present invention as shown in FIGS. 1 and 2 is used, and the inlet is 45 ° (preferably) with respect to a straight line (diameter) connecting the inlet and the synthetic furnace central axis at the same height position. The range was 30 ° to 50 °) so as to introduce gas in the ingot rotation direction, and further, it was inclined 15 ° downward with respect to the horizontal with respect to the intake port and the ingot lifting shaft. The exhaust port was installed below the intake port and provided at two positions symmetrical to the ingot lifting axis (Example).

Using the apparatus of this embodiment, the temperature of the introduced gas from the intake port is 20 ° C., the amount of exhaust gas from the furnace body, the total amount of introduced gas from the four intake ports, and the secondary gas downstream of the exhaust port Add the amount of gas introduced from the inlet to the total exhaust amount, introduce the amount of introduced gas from the inlet to a flow rate five times the amount of exhaust gas discharged from the synthesis furnace, An external air introduction pipe was provided, and the synthetic silica ingot was melted by introducing air into the exhaust pipe.
As a result, no defects inside the ingot were detected.

(Comparative example)
As shown in FIG. 4, the direction of the intake port 4a provided in the furnace body 2 was set toward the ingot elevating shaft 6a, and the synthetic silica ingot was melted in the same manner as in the example. As a result, five defects remaining in the ingot were detected.

The schematic block diagram of the synthetic silica glass manufacturing apparatus which concerns on one Embodiment of this invention. The top view which shows the arrangement | positioning state of the inlet port provided in the synthetic silica glass manufacturing apparatus which concerns on one Embodiment of this invention. The perspective view which shows the wind direction change board shown in FIG. Schematic which shows the gas flow in a furnace when the wind direction change board is not installed. Schematic which shows the gas flow in a furnace when a wind direction change board is installed. The top view which shows the arrangement | positioning state of the inlet port used for the comparative example in a comparative test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Synthetic silica glass manufacturing apparatus 2 Furnace body 3 Muffle 4 Intake furnace part 4a Inlet part 5 Exhaust part 5a Exhaust part 6 Target 7 Burner 8 Ingot 8a Fused silica adhesion surface 9 Wind direction change board 10 Exhaust equipment 11 Exhaust pipe 12 Outside air introduction pipe 13 Rotating valve 15 Differential pressure sensor 16 Control device

Claims (9)

A closed furnace body, a plurality of intake ports provided in an upper portion of the furnace body, an exhaust port provided in a lower portion of the furnace body, an exhaust facility connected to the exhaust port, and the furnace body A target for ingot formation that is rotatably installed inside, and a burner for synthesizing silica glass provided with a tip facing the target,
The intake port is always provided at a position lower than the fused silica adhering surface of the ingot, and is installed so that the gas supplied from the intake port does not directly hit the ingot and is inclined downward with respect to the horizontal. A synthetic silica glass manufacturing device,
The synthetic silica glass manufacturing apparatus, wherein the gas supplied from the intake port is formed as a swirling downward flow swirling in the same direction as the rotation direction of the target for forming the ingot.   The furnace body includes a refractory muffle having a burner for synthesizing silica glass installed at the top, an intake furnace portion having a plurality of intake ports provided below the muffle, and a lower portion of the intake furnace portion. The synthetic silica glass manufacturing apparatus according to claim 1, further comprising: an exhaust furnace section having a plurality of exhaust ports provided in the apparatus. The inner diameter of the muffle is 1.3r to 2.5r, where r is the outer diameter of the ingot, and the height in the muffle is 300mm to 800mm,
The inner diameter of the intake furnace section is 1.2a or more and 2.0a or less when the inner diameter of the muffle is a, and the height in the intake furnace section is 150mm or more and 600mm or less,
The inner diameter of the exhaust furnace part is 1.2b or more and 3.0b or less, where b is the inner diameter of the intake furnace part, and the height in the exhaust furnace part is 300mm or more and 2000mm or less. The synthetic silica glass manufacturing apparatus according to claim 2.   2. The synthetic silica glass manufacturing apparatus according to claim 1, wherein a wind direction changing plate having a flange extending downward is installed below the ingot-forming target.   The diameter of the said wind direction change board exists in the range of -10 mm or more +10 mm or less with respect to the diameter of an ingot, The length below the said collar part is 50 mm or more and 100 mm or less, The said Claim 5 characterized by the above-mentioned. Synthetic silica glass production equipment. The exhaust equipment includes a differential pressure sensor for measuring a pressure difference inside and outside the furnace provided in the exhaust furnace part, an exhaust pipe connected to an exhaust port formed in the exhaust furnace part, and the exhaust pipe And an outside air introduction pipe connected to the rotary valve for controlling the opening degree of the outside air introduction pipe,
The opening of the rotary valve is controlled so that the differential pressure of the differential pressure sensor becomes constant, and the amount of exhaust from the exhaust furnace and the amount of outside air introduced from the outside air introduction pipe can be adjusted without changing the total displacement. 3. The apparatus for producing synthetic quartz glass according to claim 2, wherein the distribution is variable.   The synthetic quartz glass manufacturing apparatus according to claim 6, wherein a detoxifying device is connected to the exhaust pipe, and an exhaust fan is connected to the detoxifying device.   A horizontal cross section of a muffle constituting the furnace body, a horizontal cross section of an intake furnace portion having a plurality of intake ports provided below the muffle, and an exhaust furnace having a plurality of exhaust ports provided below the intake furnace portion 3. The synthetic silica glass manufacturing apparatus according to claim 2, wherein all of the horizontal cross sections of the portions are circular. In the synthetic silica glass manufacturing method in which fused silica is attached to a target provided in the furnace using a silica glass synthesis burner,
Gas is sucked from a plurality of air inlets provided in the upper part of the furnace body, and is inclined downward with respect to the direction and the horizontal so as not to directly hit the ingot by the sucked gas, and further in the same direction as the rotation direction of the target. Forming a swirling gas flow,
In addition, the surface of the target is adjusted so that air is always drawn from a position lower than the fused silica adhesion surface of the ingot, and the fused silica is adhered to the target while exhausting from the vicinity of the lower part of the furnace body. Method.

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