JPH0648744A - Device for heating silica porous preform - Google Patents

Abstract

PURPOSE:To obtain a high-purity uniform quartz glass in good reproducibility by vertically moving a lid part member so that the lid part member is attached to an opening for inserting a silica porous preform of a furnace center pipe when the silica porous preform is taken in and out from the furnace center pipe. CONSTITUTION:A lid part member 11 is hung from a hanging hood 10 from a raising and dropping device 3, a silica porous preform 1 successively synthesized by a vapor-phase axial deposition method is connected from a joint part to a supporting rod 2 and inserted into a furnace core pipe 5 made of quartz glass by using the raising and dropping device 3. In the operation, the hung lid part member 11 is dropped together with the raising and dropping device 3 and set on a flange face 8 of the top of the furnace core part 5. Then, a He gas is circulated from a nozzle 7 at the lower part of the furnace center pipe and the furnace center pipe is heated to about 1,600 deg.C by sending an electric current to a heater 9. In this state, the silica porous preform 1 is gradually dropped while being rotated by a rotary chuck 4, successively heat-treated from the lower part to give transparent quartz glass.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a heating apparatus for a silica porous base material synthesized by a vapor phase axial method, for example, a transparent vitrification treatment, dehydration treatment, dope treatment, calcination treatment and the like. The present invention relates to a heating device that performs heating, and more particularly to a lid member above a furnace core tube of the heating device.

Quartz glass obtained by treating a porous silica preform has high purity and is relatively easy to dehydrate (deoxygenate) and dope other elements. Is expected to be applied.

[0003]

2. Description of the Related Art The vapor axis method is a method in which an oxyhydrogen flame is first formed by a burner, a silicon compound such as silicon halide as a glass raw material is circulated in the oxyhydrogen flame, and a silica fine particle is produced by a hydrolysis reaction. Is generated, the silica fine particles are adhered and deposited on the starting member, and this is pulled up in the axial direction to grow and synthesize the silica porous base material. Then, the porous silica preform is heat-treated in a He atmosphere to densify the voids of the porous silica preform to obtain transparent glass. Also,
At this time, or by performing a pretreatment in an atmosphere containing a gas having an OH group-removing action, dehydration (deoxygenation
H group) treatment can be performed, and the glass can be doped by performing the treatment in an atmosphere containing a gas having a doping element. Further, by performing the calcination treatment, the diameter and bulk density distribution of the porous silica base material are adjusted, and it is possible to suppress the generation of bubbles and the like in the glass as much as possible.

As a heat treatment apparatus used for these heat treatments, a heating apparatus having a structure as shown in FIG. 4 is generally used. That is, this heating device comprises a furnace core tube 5 having an opening for inserting the silica porous matrix 1,
A lid member 11 mounted on the flange portion 8 around the opening in the upper part of the furnace core tube, an electric furnace 6 having a heater 9 for sintering the silica porous base material, and moving the silica porous base material up and down. The lifting and lowering device 3 and the support rod 2 for supporting the silica porous base material on the rotary chuck 4 of the lifting and lowering device.

As a processing method using this heating device,
First, the synthesized silica porous base material 1 is connected to the support rod 2 from the joint portion (FIG. 4 (a)), and this is inserted into the furnace core tube 5 using the elevating device 3, and the lid member 11 (FIG. 4 (b)), the atmosphere gas is circulated into the furnace core tube 5 from the nozzle 7 below the furnace core tube 5, and the rotary chuck 4 is rotated to gradually lower the atmosphere gas to gradually lower the silica porous matrix. Heat treatment is performed in order from the bottom of the material.

During this heat treatment, it is extremely important to suppress the entrainment of external air by adjusting the inner pressure of the furnace core tube in order to obtain highly pure and homogeneous glass with good reproducibility. Due to the inclusion of external air, for example, in the case of dehydration treatment or dope treatment, the concentration distribution of OH groups or the concentration distribution of the doping agent in the obtained glass becomes non-uniform, and in the case of transparent vitrification treatment, This is because it causes the generation of bubbles inside. Therefore, the control of the furnace core tube internal pressure is controlled by the airtightness in the furnace core tube, the gas flow rate, and the exhaust amount.

FIG. 5 shows a furnace core tube upper structure and a lid member which are generally used in the above apparatus. In this figure, the lid member 11 has a through hole 15 through which the support rod 2 penetrates in the central portion, and has a structure having two split surfaces 18 for inserting and removing the porous silica matrix material.
The gas circulated in the furnace core tube is exhausted to the outside of the furnace core tube through the gap 19 between the upper lid member 11 and the support rod. That is,
The exhaust amount is determined by the size of these gaps, and the processing accuracy at this sliding portion is important for highly controlling the internal pressure of the furnace core tube.

[0008]

However, when heat treatment such as transparent vitrification treatment, dehydration treatment, calcination treatment and dope treatment is performed using the heating device having such a lid member, There was a problem.

1) It is difficult to process the sliding portion between the lid member and the support rod, and therefore it is difficult to control the internal pressure of the furnace core tube. As a result, highly pure and homogeneous glass cannot be obtained with good reproducibility.

2) Since the structure of the upper lid member is divided into two, it is difficult to seal the divided surface, and it is difficult to machine the divided surface with high accuracy. In particular, during the temperature rise, the temperature of the lid member was about 200 to 400 ° C., so that sealing was difficult and the airtightness inside the furnace core tube could not be sufficiently maintained. Further, when the lid member is provided with a cooling mechanism for sealing the divided surfaces, the lid member becomes large in size, and the structure becomes complicated, resulting in a marked decrease in workability.

3) In recent years, application to heat resistant materials and optical materials is expected, and it is required to increase the diameter of quartz glass for use for these purposes. However, as the silica porous matrix becomes larger with the increase in size of quartz glass,
Since the upper lid member also becomes larger and heavier, the workability is deteriorated, and the support rod and the lid member may be damaged when the porous silica is taken out and inserted.

4) Although depending on the structure of the electric furnace, the heating method, etc., the length of the supporting rod portion is about 2000 to 4000 mm in order to process the silica porous base material of 500 mm or more. For this reason, it becomes difficult to perform precise machining of the support rod, the misalignment of the axis of the support rod, the surface accuracy, etc. deteriorate, and as a result,
Vibration may occur at the sliding part between the lid member and the support rod,
Occasionally, the support rod and the lid member were damaged.

The present invention has been made in view of the above problems, and an object thereof is to improve the airtightness in the furnace core tube to facilitate the control of the furnace core tube internal pressure, and to handle the core core tube even if the size is increased. It is intended to provide a simple heat treatment apparatus for reproducibly obtaining highly pure and homogeneous quartz glass.

[0014]

DISCLOSURE OF THE INVENTION As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that a heat treatment apparatus having a specific lid member can achieve a predetermined object. The present invention has been completed.

That is, the heating device of the present invention is characterized in that the furnace core tube into which the silica porous base material synthesized by the vapor phase axial method is inserted, and the silica porous base material provided above the furnace core tube. A lid member for closing the material insertion opening, an electric furnace for heat-treating the silica porous base material in the furnace core tube, a support rod extended from the upper end of the silica porous base material, and the support rod In a heat treatment apparatus for a silica porous base material, comprising: an elevating device for vertically suspending the silica porous base material in the furnace core tube by holding an extended upper end of the cover member. Is airtightly mounted in the silica porous base material insertion opening of the furnace core tube, and has a through hole through which the support rod is loosely fitted and penetrates in the central portion without a dividing surface. Mounted so that the lid body and the upper surface of the lid body can slide while maintaining an airtight state. It is closing the through-hole of the lid body,
Further, the support rod is composed of an intermediate lid having a through-hole that substantially slides through and does not have a dividing surface, and the lid member is prepared in a state of being penetrated through the support rod in advance. The means for moving the lid member up and down is provided so that the lid member is mounted in the opening for inserting the porous silica preform of the furnace core tube at the time of inserting into and removing from the furnace core tube.

The present invention will be described in detail below.

The heating device according to the present invention comprises a furnace core tube, a lid member on the upper part of the furnace core tube, an electric furnace for sintering the silica porous base material, and an elevating unit for vertically moving the silica porous base material. There is no particular limitation as long as it is provided with a device and a support rod that supports the silica porous base material on the rotary chuck of the lifting device.

The present invention is characterized by a lid member in a heating device, and this lid member comprises a lid body and an intermediate lid.

The lid main body has a through hole through which the support bar freely fits and has a sufficient gap in the center thereof, and does not have a dividing surface.

The size of the through-hole may be slightly larger than the support rod, or may be several mm to several tens of mm, as long as it does not interfere with the support rod. Good.

The intermediate lid has an outer diameter to be placed on the upper portion of the lid body which is sufficiently larger than the through hole diameter of the lid body, and an inner diameter having such a through bore that there is almost no gap with respect to the support rod, and has a dividing surface. It does not have.

The size of the intermediate lid is not particularly limited as long as the outer diameter of the intermediate lid is large enough to be placed on the lid body and to close the through hole of the lid body. Although it is not a matter of course, if it is made too large, the weight of the intermediate lid is increased, so it is preferable to make the outer diameter as small as necessary. Further, the intermediate lid is provided on the upper surface of the lid main body so as to be slidable in the surface direction while maintaining airtightness at the sliding surfaces of the both.

In the present invention, the lid member is
By using separate members for the intermediate lid and the lid body, the clearance between the through hole of the intermediate lid and the sliding portion of the support rod can be made as small as possible, so that the processing precision of the sliding portion can be improved. Further, even if the lid member becomes large due to the increase in size of the porous silica base material, it is possible to accurately process the intermediate lid without increasing the size of the intermediate lid.

The material of the lid member is not particularly limited as long as it has heat resistance, but it is relatively easy to increase the size (larger diameter), and is easy to process and highly accurate. Further, it is preferably made of quartz glass because it is more resistant to abrasion.

The heating device according to the present invention can be used for any of the heating treatments such as transparent vitrification treatment, dehydration treatment, dope treatment and calcination treatment of the silica porous base material.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail below with reference to the drawings.

The structure of the heating device for the porous silica preform of the present invention is shown in FIG. 1, and the structure of the lid member used in the heating device of the present invention is shown in FIGS. 2 and 3.

The lid member in the present invention is composed of a lid body 12 having a through hole 14 in the center and an intermediate lid 13 having a through hole 15 in the center. The support bar 2 is slidably penetrated through the through hole 15 at the center of the intermediate lid 13 in a state where there is substantially no gap, and the circulating gas in the furnace core tube is
It is discharged only from a very narrow gap 16 between the support rod and the intermediate lid.
The airtightness between the lid body 12 and the furnace core tube 5 is maintained by placing the lid body 12 on the flange portion 8 of the furnace core tube.

By thus forming the intermediate lid 13 and the lid body 12 as separate members, the intermediate lid 13 that slides with the support rod 2 is formed.
Since it is possible to reduce the weight, it is possible to improve the processing accuracy of the sliding part, and even if the lid member becomes large due to the increase in size of the silica porous base material, it can be processed accurately without increasing the size of the intermediate lid. It is possible to

Further, by making the outer diameter of the intermediate lid larger than the through-hole 14 of the lid body so that these surface-joint portions are slid together, the amount of gas exhausted from this slidable portion can be suppressed as much as possible. Further, even if the support rod 2 is shaken, the small weight of the intermediate lid 13 can slide on the lid body 12, so that the misalignment of the axis of the support rod 2 can be absorbed. It is possible to suppress the occurrence of vibrations or the like at the sliding portion between them.

Further, the intermediate lid 13 in this example has a through hole 15 through which the support rod 2 passes in the center thereof, and if the outer diameter is larger than the through hole 14 of the lid body 12, the shape thereof will be changed. It is not particularly limited. For example, as shown in FIG. 2, a disc-shaped one can be cited. In order to keep the furnace core tube more airtight and to secure the pressure in the furnace core tube, the contact area between the supporting rod and the sliding portion at the through-hole is axially long, as shown in FIG. Are preferred.

Further, since the lid member does not have a dividing surface, the airtightness inside the furnace core tube can be maintained, and in particular, the airtightness can be maintained even during the temperature rise, which facilitates the control of the furnace core tube internal pressure. The flow rate of circulating gas can be significantly reduced.

The lid member having the above structure is prepared in such a state that it penetrates through the supporting rod in advance before the supporting rod is suspended by the lifting device, and the porous silica preform is inserted into and out of the furnace core tube. During the removal, the furnace core tube is handled so as to be attached to the silica porous base material insertion opening of the furnace core tube. For this,
The lid member is provided so as to be held and moved by an appropriate vertical moving means such as a cylinder device.

In particular, when the silica porous base material is taken out and inserted, if these lid members are moved up and down together with the support rods by an elevating device for vertically moving the support rods, the lid members are opened and closed. Since it is not necessary to provide a separate means, and relative displacement between the support rod and the lid member can be prevented, damage can be suppressed, which is preferable. For example, as shown in FIG. 1, if the lid member is provided with a hanging mechanism such as the hook 10 and the hook 10 is hung by a lifting device via a wire or the like, the lid member is supported by the lifting device. It becomes easy to move up and down together with (the silica porous matrix).

Test Example The heat treatment apparatus shown in FIG. 1 was used, and further, the quartz glass lid member 11 shown in FIG. 3 was used. That is,
As a lid member, a quartz glass intermediate lid 13 having a through hole 15 in the central portion is placed on the upper portion of a quartz glass lid body 12 having a through hole 14 in the central portion and a hook 10 for hanging. The support rod 2 was used to penetrate the through hole 15 at the center. At this time, the gap 16 between the support rod and the through hole 15 of the intermediate lid was processed to be 0.2 mm.
These lid members are hung from the lifting device 3 by the hanging hooks 10, and subsequently, the silica porous base material 1 synthesized by the vapor phase axis attachment method is connected to the support rod 2 from the joint portion (Fig. 1 (a)), which was inserted into the quartz glass furnace core tube 5 using the elevating device 3. At this time, the suspended lid member 11 is lowered together with the elevating device 3, and the furnace core tube 5
It was set on the upper flange surface 8 (Fig. 1 (b)). Subsequently, He gas was circulated in the furnace core tube from the nozzle 7 in the lower part of the furnace core tube, and the heater 9 was energized to generate 1600 ° C.
The temperature was raised to. In this state, while being rotated by the rotation chuck 4, the silica porous base material 1 was gradually pulled down and heat-treated in order from below to obtain transparent quartz glass. At this time, the pressure in the furnace core tube is adjusted to 10 ± 3 m by adjusting the gas flow rate.
It was possible to control to mH ₂ O. There were no defects such as bubbles in the obtained quartz glass. Further, although these operations were repeatedly performed, the support rod and the lid member were not damaged.

Comparative Example Using the conventional heat treatment apparatus shown in FIGS. 4 and 5, the same procedure as in Example was carried out. However, a gap was formed on the dividing surface 18 and the furnace core tube could not be kept airtight. Many defects such as bubbles were also generated in the obtained glass.

Further, the same procedure as in the example was carried out using the conventional heat treatment apparatus shown in FIGS. 4 and 5, except that the integral lid member having no dividing surface 18 was used. Produced an abnormal noise and eventually the lid member was damaged and could not be reused.

[0038]

As described in detail above, the following effects can be obtained by treating the silica porous matrix with the heat treatment apparatus of the present invention.

1) Since the lid member does not have a dividing surface and the intermediate lid having a small weight is used, the machining accuracy of the through hole of the intermediate lid is improved, and the airtightness in the furnace core tube at the time of temperature rise can be maintained. Further, the internal pressure can be easily controlled by the gas flow rate. Also, the flow rate of the circulating gas can be significantly reduced.

2) If the lid member can be moved up and down together with the lifting device at the time of inserting and removing the silica porous base material,
The workability is remarkably improved, and the lid member and the support rod are hardly damaged. Further, even if the size is increased, there is no change in workability.

3) Even when the shaft center of the support rod is deviated, since the lid body and the intermediate rod are constituted, vibration is generated at the sliding portion between the lid member and the support rod. It is absorbed by sliding against and does not cause vibration.

4) Therefore, highly pure and homogeneous quartz glass can be reproducibly manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a schematic configuration of a heating device for a porous silica preform according to the present invention.

FIG. 2 is a cross-sectional view showing a lid member used in the heating device of FIG.

FIG. 3 is a cross-sectional view showing the configuration of another lid member used in the heating device of the present invention.

FIG. 4 is a diagram showing a schematic configuration of a conventional heating device for a porous silica preform.

FIG. 5 is a diagram showing a lid member used in a conventional heat treatment apparatus.

[Explanation of symbols]

1 ... Silica porous base material 2 ... Support rod 3 ... Lifting device 4 ... Rotating chuck 5 ... Furnace core tube 6 ... Electric furnace 7 ... Nozzle 8 ... Flange surface 9 ... Heater 10 ... Hook 11 ... Lid member 12 ... Lid body 13 ... Intermediate lid 14 ... Through hole 15 ... Through hole 16 ... Gap between support rod and intermediate lid 17 ... Sliding part 18 ... Crack surface 19 ... Gap between lid member and support rod

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eiji Shiota 276-376 Osaki, Hofu City, Yamaguchi Prefecture 276-376 (72) Tomiyoshi Kubo 80, 33, Suemuchu, Kumamatsu City, Yamaguchi Prefecture

Claims (2)

[Claims] 1. A furnace core tube into which a silica porous base material synthesized by a vapor phase axial method is inserted, and a lid member for closing a silica porous base material insertion opening provided in the upper part of the furnace core tube. And an electric furnace for heat-treating the silica porous base material in the furnace core tube, a support rod extended from the upper end of the silica porous base material, and holding the extended upper end of the support rod. In a heat treatment device for a silica porous base material, comprising: an elevating device that vertically suspends the silica porous base material in the furnace core tube, wherein the lid member is the silica porous base material of the furnace core tube. A lid main body which is airtightly mounted in the base material insertion opening and has a through hole through which the support rod is loosely fitted and penetrates in the central portion without a dividing surface, and an upper surface of the lid main body. Attached so as to be able to slide while maintaining an airtight state, to close the through hole of the lid body, and The supporting rod is composed of an intermediate lid having a through-hole that substantially penetrates through and does not have a dividing surface, and the lid member is prepared in a state of being penetrated through the supporting rod in advance. A porous silica preform, which is provided with means for moving the lid member up and down so as to be mounted in the opening for inserting the porous silica preform of the furnace core tube when inserting into and removing from the furnace core tube. Heating device. 2. A means for vertically moving the lid member for attaching the lid member to the opening for inserting the silica porous base material of the furnace core tube when the silica porous base material is inserted into or removed from the furnace core tube. The apparatus for heating a porous silica preform according to claim 1, wherein the heating means is a means for holding the support rod and suspending the support rod by an elevating device for moving the support rod up and down.