JP7140654B2 - Quartz glass molded body manufacturing method and quartz glass molded body manufacturing apparatus - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a molded quartz glass body and an apparatus for manufacturing a molded quartz glass body.

Silica glass, also called silica glass, is a glass material that has been used for a long time. On the other hand, due to the rapid progress in semiconductor manufacturing technology, optical communication technology, image display and imaging technology in recent years, quartz glass, which achieves high levels of optical properties, thermal properties, and chemical resistance, is attracting more and more attention. ing. On the other hand, from the viewpoint of manufacturing technology, it is desired to develop a technology that can supply high-quality quartz glass products at a lower cost and can be suitable for the production of a wide variety of products. .

Patent Literature 1 discloses a first heating means for heating a raw material supplied to the inside of a crucible to form molten glass, and heating the molten glass formed by the first heating means at a temperature higher than that of the first heating means. A second heating means for heating, a resistor (baffle) provided inside the crucible, and a control means for controlling the heating temperature and residence time of the molten glass by the first and second heating means. A quartz glass molding apparatus is disclosed. In this document, the temperature difference inside the crucible can be adjusted to an appropriate value, and the residence time of the molten glass inside the crucible can be extended by providing a resistor (baffle) inside the crucible. is said to be possible.

US Pat. No. 5,300,000 discloses a furnace for melting silica into a desired shape, the furnace including a body having a melting zone and a drawing zone, the melting zone substantially containing a non-reactive barrier material. A furnace is disclosed comprising a refractory wall with an airtight inner lining. Furnaces with substantially gas-tight rhenium, iridium, platinum and/or osmium linings in the melting zone are claimed to have advantages such as the ability to produce products with much lower refractory metal content in the melt.

US Pat. No. 6,300,003 discloses a device for extracting quartz glass cylinders, which has a specific structure. It is said that this makes it possible to easily manufacture a more homogeneous quartz glass cylinder even when the lateral dimension of the quartz glass cylinder is on the order of the size of the inner diameter of a general-purpose melting crucible.

Patent No. 3,637,178 Japanese Patent Publication No. 2004-514634 Patent No. 5,460,707

The heating of the crucible or furnace (crucible or the like) in Patent Documents 1 and 2 is based on an induction heating type heater. Heating of the crucible in Patent Document 3 is based on a resistance heating heater. Thus, quartz glass is conventionally melted by heating a crucible or the like with a heater. The melting temperature of quartz glass exceeds 2000°C. Therefore, when using a heater, the crucible or the like must be heated to that temperature or higher. Refractory metals are commonly used for crucibles and the like as materials that can withstand this. On the other hand, when a refractory metal crucible or the like is used, it is necessary to create a hydrogen atmosphere in the apparatus in order to prevent the crucible from deteriorating. Rare metals such as molybdenum and tungsten are used as refractory metals, and they are not inexpensive. In addition, operation in a hydrogen atmosphere is unavoidable, which has been a major factor in increasing the production cost of quartz glass.

Accordingly, the present invention provides a method and apparatus for manufacturing a quartz glass molded body that does not require the use of a refractory metal in the melting portion of the quartz glass, and that allows the quartz glass to be melted and molded without using a hydrogen atmosphere. for the purpose of providing

The above problems can be solved by the following means.
<1> A melting process in which raw material powder of quartz glass is melted with an oxyhydrogen flame and the melted glass is deposited in the melting zone (however, part of the molten glass deposited in the melting zone is in contact with the sidewall of the melting zone). , the molten glass near the sidewall has low or no fluidity) and
A viscosity adjustment process in which the molten glass outside the vicinity of the side wall in the melting section is allowed to flow down in the preforming section to obtain molten glass with a viscosity suitable for flowing out in the forming section downstream of the preforming section (however, melting in the preforming section The flow of the glass is carried out by its own weight while being isolated from the outside air and under heating),
A molding process in which the molten glass whose viscosity is adjusted is allowed to flow down in the molding part and out of the molding opening, and then,
a cooling process in which the outflowing quartz glass molded member is cooled in a cooling unit;
A method for producing a quartz glass molded body, comprising: a cutting step for obtaining a molded body by cutting a cooled quartz glass molded member at a cutting portion.
<2> The manufacturing method according to <1>, wherein the side walls in the fusion zone are not heated from the outside.
<3> The manufacturing method according to <1> or <2>, wherein the molten glass in the melting section near the inlet of the preforming section flows down to the preforming section due to its own weight.
<4> The manufacturing method according to any one of <1> to <3>, wherein the residence time of the molten glass in the preforming part is set to a time sufficient for bubbles in the molten glass to disappear.
<5> The production method according to any one of <1> to <4>, wherein high-purity oxygen gas and hydrogen gas are used for the oxyhydrogen flame.
<6> The quartz glass molded body is tubular,
The part of the preforming part where the molten glass flows down is cylindrical, and the horizontal cross-sectional shape of the forming part is ring-shaped,
The horizontal cross-sectional shape of the cylindrical portion of the preforming portion through which the molten glass flows is ring-shaped,
the inner diameter of the ring-shaped horizontal cross-section of the pre-molded portion is smaller than the inner diameter of the ring-shaped horizontal cross-section of the molded portion;
The manufacturing method according to any one of <1> to <5>, wherein the outer diameter of the ring-shaped horizontal cross section of the preformed part is larger than the outer diameter of the ring-shaped horizontal cross section of the molded part.
<7> The quartz glass molded body is rod-shaped,
The part of the preforming part where the molten glass flows down is cylindrical, and the part of the molding part where the molten glass flows down is also cylindrical,
The manufacturing method according to any one of <1> to <5>, wherein the horizontal cross-sectional diameter of the portion of the preforming portion where the molten glass flows down is larger than the horizontal cross-sectional diameter of the forming portion.
<8> The manufacturing method according to any one of <1> to <7>, wherein the molded quartz glass flowing out from the molding unit has a viscosity capable of maintaining the molded shape.
<9> The manufacturing method according to any one of <1> to <8>, wherein the molded body obtained by cooling is cut into predetermined lengths downstream of the cooling section to obtain molded bodies.
<10> a melting part having a supply port for raw material powder of quartz glass and an oxyhydrogen flame burner in the upper part, and depositing quartz glass melted by the oxyhydrogen flame;
a preforming section having a cavity for vertically flowing molten glass and having a heating function;
a molding unit having a molding opening for flowing molten glass and molding;
Equipped with a cooling unit for cooling the molded molten glass,
The side walls in the fusion zone are made of refractory bricks,
Having a connecting port for flowing molten glass to the bottom of the melting part and the top of the preforming part,
An apparatus for producing a quartz glass molded body having a connecting port for flowing molten glass to the bottom of the preforming section and the top of the molding section.
<11> The manufacturing apparatus according to <10>, further comprising a cutting section for cutting the cooled molten glass downstream of the cooling section.
<12> The manufacturing apparatus according to <10> or <11>, wherein refractory bricks are laid on the surface of the fusion zone that can come into contact with the oxyhydrogen flame.
<13> The manufacturing apparatus according to any one of <10> to <12>, wherein a heater is provided in the molding section to adjust the temperature of the quartz glass during the molding process to control the shape of the molded body.

According to the present invention, it is not necessary to use a refractory metal in the melting portion of the quartz glass, and the quartz glass can be melted and molded without using a hydrogen atmosphere for that purpose. Furthermore, the improvement of the manufacturing process described above contributes to the reduction of the manufacturing cost of the quartz glass molded body.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side cross-sectional view schematically showing an apparatus for manufacturing quartz glass moldings according to a preferred embodiment of the present invention; FIG. 2 is a side cross-sectional view schematically showing an enlarged periphery of a molding section in the quartz glass molded body manufacturing apparatus of FIG. 1 ; FIG. 2-1 is a cross-sectional view taken along the line II of FIG. 2-1; FIG. 2-2 is a cross-sectional view taken along line II-II of FIG. 2-1; FIG. 4 is a side cross-sectional view schematically showing an enlarged periphery of a forming section of a quartz glass molded body manufacturing apparatus according to another preferred embodiment of the present invention. FIG. 3-1 is a cross-sectional view taken along line III-III in FIG. 3-1; FIG. 3-1 is a cross-sectional view taken along line IV-IV in FIG. 3-1; FIG. 2 is a side cross-sectional view schematically showing a conventional apparatus for manufacturing a quartz glass molding.

Hereinafter, the present invention will be described in more detail based on preferred embodiments. However, the embodiments, including the illustrated ones, are examples of the present invention, and the present invention is not intended to be limited to these embodiments.

The method for manufacturing a quartz glass molded body according to a preferred embodiment of the present invention includes (1) a melting process of melting raw material powder 50 of quartz glass with an oxyhydrogen flame and depositing the molten glass in the melting portion 10A (however, , a part of the molten glass 51a deposited in the melting zone contacts the sidewall in the melting zone, and the molten glass 51a near the sidewall has low or no fluidity); A viscosity adjustment process for obtaining molten glass 52 having a viscosity suitable for flowing out in the molding section 30 downstream of the preforming section 20 by allowing the molten glass 51 in the area other than the vicinity of the side wall 11 in 10A to flow down in the preforming section 20 (however, (3) flow down the molten glass 52 with the adjusted viscosity in the molding section 30, and (4) a molding process in which the outflowing quartz glass 54 molding member is cooled in the cooling section; and (5) the cooled quartz glass molding member 54 is cut in the cutting section. and a cutting step of obtaining a molded body.

Further, the apparatus for manufacturing a molded glass body according to a preferred embodiment of the present invention has a supply port 1a for the raw material powder 50 of quartz glass and a burner 1 for oxyhydrogen flame at the upper part, and the quartz glass 51 melted by the oxyhydrogen flame. and a cavity 21 for vertically flowing molten glass 52, a preforming section 20 having a heating function, and a molding port 3 for flowing and molding the molten glass. A molding section 30 and a cooling section 40 for cooling the molded molten glass are provided. Side walls 11 of the melting section 10A are made of refractory bricks. Connection ports 14 and 24 for flowing down are provided, and connection ports (not numbered in the figure) for flowing molten glass 52 are provided at the bottom of the preforming section 20 and the top of the molding section 30 .

These manufacturing processes will be described in detail below with reference to the drawings schematically showing manufacturing apparatuses that can be suitably used in the present invention.

(Melting process - melting part)
FIG. 1 shows an apparatus for manufacturing a quartz glass molding according to a preferred embodiment of the present invention.

In the melting process of the present embodiment, the raw material powder 50 of quartz glass is supplied in an oxygen and hydrogen stream, and the raw material powder is wrapped in an oxyhydrogen flame F and brought into contact with the material to be melted. The quartz glass material that can be used is not particularly limited, and materials that can be applied to this type of quartz glass can be used as appropriate. Examples of natural raw materials include crystal flakes and purified silica powder. For example, quartz crystal lathka can be used, but from the viewpoint of cost, it is preferable to use silica, which is an aggregate of microcrystals of quartz. The silica is preferably refined by extensive beneficiation and chemical treatment. It is preferable that the concentration of iron or alkali metal is 0.1 ppm or less from the viewpoint of obtaining a high-quality quartz glass molding. Aluminum is generally contained at several ppm.

Synthetic raw materials can also be used as raw materials for quartz glass. For example, synthetic raw materials obtained by converting silicon alkoxide into glass powder by a sol-gel method have been put to practical use as quartz glass raw materials. In addition, a material obtained by gelling and purifying water glass (alkali silicate), or a material obtained by melting silicon and spraying or directly oxidizing it may be used.

In the present invention, the raw material powder 50 of quartz glass is brought into contact with an oxyhydrogen flame F to be heated and melted, and the molten quartz glass is deposited in the melting portion 10 (FIG. 1, deposited quartz glass 51). At this time, in this embodiment, the quartz glass raw material powder 50 is supplied to the burner together with hydrogen gas (H ₂ ) and oxygen gas (O ₂ ). A raw material powder 50 of quartz glass is fed from a raw material supply device 70 through a raw material powder line 71 . In this embodiment, the burner 1 is provided in the upper portion of the melting section 10A in the melting section 10. As shown in FIG. An oxyhydrogen flame F is blown from the flame outlet 1a of the burner 1. The flame blowout port 1a also serves as a supply port for the raw material powder 50, and the raw material powder 50 of quartz glass is sent into the melting chamber V of the melting section so as to be enveloped in the flame F. As shown in FIG.

A method for generating the oxyhydrogen flame F is not particularly limited, and a conventional method can be used. As the oxyhydrogen gas, it is preferable to mix and supply oxygen and hydrogen so that the volume ratio is 1:2. As the oxygen gas and hydrogen gas for the oxyhydrogen flame F, it is preferable to use high-purity products.

It is not necessary to set the flame temperature higher than necessary, and considering the integrity of the refractory bricks, which will be described later, it is preferable to set the flame temperature as low as necessary for melting. From this point of view, the melting temperature is preferably less than 2000.degree. C., more preferably 1800 to 1900.degree.

In this embodiment, refractory bricks are laid on the surface of the fusion zone 10 that can come into contact with the oxyhydrogen flame F. As shown in FIG. Specifically, in this embodiment, the inner wall 11 of the melting section main body (inside the melting section) 10A is made of refractory bricks. As a result, as shown in the figure, refractory bricks can be used as the material for the fusion zone, and for example, the use of refractory metal, which has been required in the past, is not essential (however, in the present invention, the use of refractory metal in the fusion zone (does not preclude Specifically, the refractory material can be selected at a setting of 2000 ° C. or less, silica brick, alumina (α, β-alumina, β-alumina) brick, fired AZS (alumina-zirconia-silica) brick. , zirconia bricks, chromium-containing bricks such as AZSC, mullite bricks, spinel bricks, basic bricks, and the like. These materials are preferably selected from the viewpoint of balancing cost and durability.

In the manufacturing method of the present embodiment, a portion 51a of the molten glass 51 deposited inside the melting section 10A is in contact with the sidewall 11 inside the melting section. Thereby, the molten glass 51a in the vicinity of the side wall 11 has low fluidity or no fluidity. In other words, the portion of the side wall 11 inside the fusion zone 10A is not heated. Thus, it is a feature of preferred embodiments of the present invention that a portion of the fused quartz glass is not heated. That is, since the molten glass 51a near the side wall 11 loses its fluidity, the glass itself acts as a dam against the molten and deposited quartz glass 51, which has the effect of preventing foreign matter from entering from the side wall. Moreover, the point that the heating from the side wall is not essential leads to an advantage in terms of manufacturing cost.

The base/outer wall 12 of the fusion zone does not need to be as heat resistant as the inner wall 11, and a refractory material can be selected with more emphasis on cost, strength, and workability. For example, select high alumina materials, general clay bricks, or refractory mortar materials (magnesium-chromium mortar, high alumina mortar, clay mortar, alumina-zirconia mortar, zircon mortar, silica mortar, etc.) You may In addition, if necessary, the bricks of the inner wall may be joined with the mortar described above.

According to the present invention, it is no longer necessary to use a refractory metal in the fusion zone as described above, so there is no need to place the fusion zone in a hydrogen atmosphere to prevent oxidation of the refractory metal. However, in the present invention, this does not prevent the fusion zone from being in a hydrogen atmosphere.

In the apparatus of this embodiment, the burner 1 is installed on the burner stage 15, the flame outlet 1a is directed into the melting chamber V, and the flame F can be blown into the melting chamber V together with the raw material powder 50. The material of the burner stage 15 is not particularly limited, but since this portion is not heated as much as the inner wall 11, the same material as the base/outer wall 12 may be applied.

In the apparatus of the present embodiment, one burner 1 is provided directly above in the vertical direction, but the present invention should not be construed as being limited to this. For example, two or more units may be arranged in a plane. Alternatively, a plurality of burners 1 may be provided on the side surface of the melting portion to spray the flame and raw material powder. Further, in the present embodiment, the oxyhydrogen flame F and the raw material powder 50 are supplied from the common outlet 1a. It is good also as a mode wrapped.

In the manufacturing apparatus of this embodiment, the inside 10A of the melting section of the melting section has a connecting port 14 at its bottom for allowing the molten glass to flow down to the top of the preforming section 20 . On the other hand, the preforming section 20 has a connecting port 24 at its top for allowing the molten glass to flow down in a position and shape corresponding to the connecting port 14 of the melting section. The amount of quartz glass that flows from the melting section 10 into the preforming section 20 by its own weight can be adjusted by appropriately combining the sizes and shapes of these connection ports. Appropriately adjusting the amount of the molten glass 52 flowing through the preforming section 20 in this manner is an important point in managing the production quality of the molded product, which is a product.

(Viscosity adjustment process - preforming part)
In the manufacturing apparatus of the present embodiment, a preforming section 20 is provided for the purpose of homogenizing and adjusting the viscosity of the molten glass melted in the melting section before forming the molten glass into a molded body. Any member and mechanism for guiding the molten glass 52 in the preforming section 20 can be used. For example, common electric furnace structures and materials can be applied.

It is preferable that the molten glass in the preforming section 20 is allowed to flow down by its own weight while being shielded from the outside air and heated. By doing so, quality deterioration due to oxidation of the quartz glass can be suppressed without circulating reducing gas or the like in the reactor. As described above, in the present embodiment, the molten glass in the melting section near the entrance of the preforming section 20 flows down to the preforming section 20 due to its own weight. The residence time of the molten glass in the preforming section 20 is preferably set to a time sufficient for bubbles in the molten glass to disappear. In this embodiment, the oxyhydrogen flame F is used to envelop and melt the quartz glass powder 50 . In order to obtain a homogeneous quartz glass molded body, it is preferable to extinguish it in the preforming section.

From this point of view, it is preferable that the preformed portion is heated. The heating temperature in the preforming part is preferably about 1700° C. or higher, more preferably 1800° C. or higher, which is the softening point of quartz glass. As for the upper limit, 1900° C. or less is practical due to restrictions on facilities and the like.

(Molding process - molding section)
FIG. 2-1 is a side sectional view schematically showing an enlarged periphery of a molding section in the manufacturing apparatus shown in FIG. 1. FIG. 2-2 is a cross-sectional view taken along line II in FIG. 2-1, and FIG. 2-3 is a cross-sectional view taken along line II-II in FIG. 2-1. In this embodiment, as shown in the figure, the preforming section 20 and the forming section 30 are partitioned by outer walls 22, 32 and inner walls 23, 33 forming the outside. Spaces 21 and 31 are formed therebetween to form a cavity through which molten silica glass flows. The molten silica glass 52 flows through the space 21 of the preforming portion 20 . After that, the molten silica glass 52 reaches the molding opening 3 through the space 31 of the molding section 30 below it, and is shaped along its shape. In other words, this can be said to be a structure having a connection port for flowing molten glass between the bottom of the preforming section and the top of the forming section. However, in the illustrated embodiment, although the connecting port is not indicated by a particular reference numeral, it is shown as a structure in which the preforming portion and the forming portion are continuous.

In this embodiment, the space (cavity) 21 in which the molten glass of the preforming section 20 flows down is made cylindrical by the outer wall 22, and becomes narrower and ring-shaped by the inner wall 23 toward the forming section 30. It is As for the specific shape and dimensions, the horizontal cross-sectional shape of the cylindrical portion of the preforming section 20 where the molten glass flows down is ring-shaped, and the spatial inner diameter D3 of the ring-shaped horizontal cross section of the cylindrical portion is the same as that of the forming section. is smaller than the spatial inner diameter D1 of the ring-shaped horizontal cross section of . Furthermore, in the present embodiment, the spatial outer diameter D4 of the ring-shaped horizontal cross section of the cylindrical portion of the preformed portion 20 is larger than the spatial outer diameter D2 of the ring-shaped horizontal cross section of the molded portion. Such a dimensional relationship between the preformed portion and the main formed portion facilitates stable and homogeneous production of the glass tube, which is preferable.

FIG. 3 is a side cross-sectional view schematically showing an enlarged periphery of a molding section of a manufacturing apparatus for manufacturing rod-shaped moldings, as another preferred embodiment of the present invention. FIG. 3-2 is a cross-sectional view schematically showing a cross-section of the pre-molding portion of FIG. 3-1 taken along line III-III, and FIG. 3-2 is a line IV-IV of the molding portion of FIG. 3-1. FIG. 3 is a cross-sectional view schematically showing a cross section taken along an arrow. In this embodiment, the spatial diameter D5 of the horizontal cross section of the portion (cavity) of the preforming section 20 where the molten glass flows down is made larger than the spatial diameter D6 of the forming section. By adopting such a configuration, it is possible to stably and uniformly produce a rod-shaped molded body of quartz glass.

(Cooling process - cooling section)
In this embodiment, the quartz glass that has passed through the shaping section 30 is sent to the cooling section 40 and cooled there. It is preferable that the quartz glass member flowing out of the molding section has a viscosity that allows it to maintain the molded shape. By doing so, it is possible to obtain a quartz glass molded member 54 of good quality having a desired shape while maintaining stable productivity.

As described above, in the molding section 30 , a molten glass member (molding member) is pulled out by its own weight from the molding opening 3 provided on the bottom surface of the preforming section 20 . The molten glass forming member 54 drawn out is in the shape of a tube of the cylinder material 8 . At this time, instead of relying only on the weight of the molten glass, if necessary, a roller or the like may be installed to pull out the molten glass. That is, in the present invention, the term "flow by its own weight" means that it flows only by its own weight, and also means that it flows by a combination of pull-out force and push-out force from the outside.

In this embodiment, the molding member 54 sent to the cooling unit 40 has a circular cross-sectional shape that matches the cross-section of the molding opening 3, but it may be tapered into a truncated cone shape at this portion. However, it may be rod-shaped.

In the apparatus of this embodiment, the mode of pulling out the molten glass tube by its own weight is shown in the vertical direction, but the present invention should not be construed as being limited to this. For example, it is preferable to install a heater in the molding section or the like to adjust the temperature of the quartz glass tube or bar during the molding process to control the shape of the molded member as an intermediate product or the molded product as a finished product. A rod-shaped glass molded body can also be given as a preferable example of the shape control of the molded body by heating as described above. Alternatively, a mode may be adopted in which the pipe or bar is pulled out not in the vertical direction but in an oblique direction. After pulling out vertically or obliquely, the sheet may be bent at a predetermined position and sent horizontally, for example, by rollers.

(Production process - cutting part)
In the present embodiment, the molded member 54 obtained by cooling is cut into predetermined lengths at a cutting section downstream of the cooling section 40 to obtain a molded body (product). Cutting of the molded member can be carried out in a known manner.

(Example of conventional manufacturing equipment)
FIG. 4 is a cross-sectional view schematically showing a conventional manufacturing apparatus 90. As shown in FIG. In this conventional apparatus 90, a heater 92 is arranged around a crucible 91 so that almost the entire crucible 91 is heated to the softening temperature of quartz glass. Therefore, the crucible 91 is made of a refractory metal, and is continuously supplied with hydrogen as the atmospheric gas. A raw material powder 50 of quartz glass is melted by heating with a heater, and molten glass 52 is filled in the crucible. There is a gap between the mold 93 and the mandrel 94 at the bottom of the crucible, through which the tubular molten glass 54 is pulled out by its own weight. This is slowly cooled to form a tube material, and cut to form a glass tube. This method requires a continuous supply of hydrogen gas. Even so, corrosion and damage to the refractory metal are unavoidable and become factors that increase manufacturing costs. In addition, it is not easy to separate the molding part (mold) and the melting part (crucible), making it difficult to maintain the manufacturing equipment.

REFERENCE SIGNS LIST 10 melting section 10A melting section main body 1 burner 1a flame outlet/raw material supply port 11 inner wall (refractory brick)
REFERENCE SIGNS LIST 12 base/outer wall 14 fusion zone side connection port 15 burner stage 20 preforming part 21 preforming part flowing part (cavity)
22 Flow portion outer wall of preforming portion 23 Flow portion inner wall of preforming portion 24 Preforming portion side connection port 30 Molding portion 3 Molding port 31 Molding portion flow portion (cavity)
32 Flow portion outer wall of molding portion 33 Flow portion inner wall of molding portion 40 Cooling portion 50 Raw material powder of quartz glass 51 Accumulated quartz glass 52 Quartz glass that melts and flows (molten glass)
54 Quartz glass in cooling process 59 Quartz glass molded body 70 Raw material supply device 71 Raw material powder line 8 Cylinder material 90 Conventional device 91 Crucible 92 Heater 93 Mold 94 Mandrel

INDUSTRIAL APPLICABILITY The present invention is useful in fields related to quartz glass moldings (especially tubes or rods). Silica glass tubes and bars are industrially applicable as materials for manufacturing processes of various semiconductor devices, optical equipment, communication equipment, and the like.

Claims (12)

A melting process in which the raw material powder of quartz glass is melted with an oxyhydrogen flame and the molten glass is deposited in the melting zone. The molten glass of has lower fluidity or no fluidity than the molten glass outside the vicinity of the side wall in the melting part ,
A viscosity adjustment process in which the molten glass outside the vicinity of the side wall in the melting section is allowed to flow down within the preforming section to obtain molten glass having a viscosity suitable for flowing out of the forming section downstream of the preforming section , provided that the molten glass is melted in the preforming section. The flow of the glass is done by its own weight while being isolated from the outside air and under heat.
a molding process in which the molten glass with adjusted viscosity is allowed to flow down in the molding unit and out of the molding opening ;
a cooling process in which the outflowing quartz glass molded member is cooled in a cooling unit;
A method for producing a quartz glass molded body, comprising: a step of cutting a cooled quartz glass molding member at a cutting portion to obtain a molded body (provided that the molding portion used in the molding step causes molten glass to flow into the molding opening); (except when the displacement body projecting in the direction is arranged) . 2. The manufacturing method according to claim 1, wherein the sidewalls within the fusion zone are not heated from the outside. 3. The manufacturing method according to claim 1, wherein the molten glass in the melting section near the inlet of the preforming section flows down to the preforming section due to its own weight. The manufacturing method according to any one of claims 1 to 3, wherein the residence time of the molten glass in the preforming part is set to a time sufficient for bubbles in the molten glass to disappear. The quartz glass molded body is tubular,
The part of the preforming part where the molten glass flows down is cylindrical, and the horizontal cross-sectional shape of the forming part is ring-shaped,
The horizontal cross-sectional shape of the cylindrical portion of the preforming portion through which the molten glass flows is ring-shaped,
the inner diameter of the ring-shaped horizontal cross-section of the pre-molded portion is smaller than the inner diameter of the ring-shaped horizontal cross-section of the molded portion;
The manufacturing method according to any one of claims 1 to 4 , wherein the outer diameter of the ring-shaped horizontal cross section of the preformed part is larger than the outer diameter of the ring-shaped horizontal cross section of the molded part. The quartz glass molded body is rod-shaped,
The part of the preforming part where the molten glass flows down is cylindrical, and the part of the molding part where the molten glass flows down is also cylindrical,
The manufacturing method according to any one of claims 1 to 4 , wherein the horizontal cross-sectional diameter of the portion of the preforming portion where the molten glass flows down is larger than the horizontal cross-sectional diameter of the forming portion. The manufacturing method according to any one of claims 1 to 6 , wherein the molded quartz glass discharged from the molding part has a viscosity capable of maintaining the molded shape. The manufacturing method according to any one of claims 1 to 7 , wherein the molded product obtained by cooling is cut into predetermined lengths downstream of the cooling section to obtain molded products. a melting section having a supply port for the raw material powder of quartz glass and an oxyhydrogen flame burner in the upper part and depositing quartz glass melted by the oxyhydrogen flame;
a preforming section having a cavity for vertically flowing molten glass and having a heating function;
a molding unit having a molding opening for flowing molten glass and molding;
Equipped with a cooling unit for cooling the molded molten glass,
The side walls in the fusion zone are made of refractory bricks,
Having a connecting port for flowing molten glass to the inner bottom of the melting section and the top of the preforming section,
An apparatus for manufacturing a quartz glass molded body having a connecting port for flowing molten glass at the bottom of the preforming section and the top of the molding section (however, the molding section has a displacement body protruding in the molding port in the flow direction of the molten glass) (unless it has been modified) . The manufacturing apparatus according to claim 9 , further comprising a cutting section for cutting the cooled molten glass downstream of the cooling section. 11. The manufacturing apparatus according to claim 9 or 10 , wherein refractory bricks are laid on a surface of said fusion zone that can come into contact with an oxyhydrogen flame. 12. The manufacturing apparatus according to any one of claims 9 to 11 , wherein a heater is provided in said molding section to adjust the temperature of the quartz glass during the molding process to control the shape of the molding.

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