JP2021195289A - Method of manufacturing glass article - Google Patents

Abstract

To prevent a glass article manufactured during and after base material changing from decreasing in quality.SOLUTION: A method of manufacturing a glass article comprises: a preparation process of preparing a state in which the difference ΔHa between a height H1 of a liquid level of molten glass in a refractory material tank 5 and a height H2 of an upper end part 9a of a discharge port 9 of the refractory material tank 5 is 170 mm or larger; and a product class change process of changing the product class of molten glass discharged from the discharge port 9 by an extrusion method from a first product class to a second product class. In the product class change process, the product class of the molten glass discharged from the discharge port 9 is changed from the first product class to the second product class while the state in which the difference ΔHa in height is 170 mm or larger is maintained.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for manufacturing a glass article by changing the substrate of molten glass.

The glass melting furnace produces molten glass by heating the glass raw material charged into the melting tank (melting tank) from the raw material supply unit (input port) with a heating device such as a burner or an electrode. The generated molten glass is discharged from a glass melting furnace and molded by a molding apparatus or the like to become a glass article.

When changing the type of glass article, the base material of the molten glass is changed. As a method for changing the substrate, a substrate extraction method and an extrusion method are known (see, for example, Patent Document 1). For example, in the extrusion method, the molten glass of the first type that was previously produced in the glass melting furnace is extruded downstream by the molten glass of the second type that is produced later, and then the molten glass of the second type is used. The production of glass articles will be started.

Japanese Unexamined Patent Publication No. 2017-65533

When the molten glass of the glass melting furnace is replaced by the extrusion method, the molten glass of the first kind is extruded from the glass melting furnace by the molten glass of the second kind, but all of them are discharged from the glass melting furnace. However, a part of it may remain in the glass melting furnace. Specifically, the molten glass that has reached the stagnant layer existing in the upper layer of the molten glass in the glass melting furnace may remain in the glass melting furnace. The molten glass of the stagnant layer tends to be denatured to become foreign glass due to the volatilization of some components or the mixing of foreign substances.

In this case, if the molten glass of the first type remaining in the stagnant layer in the glass melting furnace is mixed with the molten glass of the second type during and after the substrate change, bubble defects and the like occur in the glass article. It may occur and cause quality deterioration.

The present invention has been made in view of the above circumstances, and it is a technical subject to prevent deterioration of the quality of glass articles manufactured during and after the substrate change.

The present invention is for solving the above-mentioned problems, and is a method of manufacturing a glass article from molten glass having a liquid level in a refractory tank composed of a refractory, wherein the refractory tank is the above-mentioned. A preparatory step of preparing a state in which a discharge port for discharging the molten glass is provided and the difference between the height of the liquid level of the molten glass and the height of the upper end of the discharge port in the refractory tank is 170 mm or more. A type change step of changing the type of the molten glass discharged from the discharge port from the first type to the second type by the extrusion method is provided, and in the type change step, the height of the liquid level of the molten glass is high. The type of the molten glass discharged from the discharge port is changed from the first type to the second type while maintaining the state where the difference between the height and the height of the upper end portion of the discharge port is 170 mm or more. It is characterized by that.

According to this configuration, in the product type change process, the difference between the height of the liquid level of the molten glass and the height of the upper end of the discharge port in the refractory material tank is set to 170 mm or more, so that the refractory material tank is used after the product type change process is completed. The molten glass of the first type remaining in the stagnant layer inside is less likely to be mixed with the molten glass of the second type discharged from the discharge port. This makes it possible to prevent the occurrence of defects in the glass article due to the mixing of the molten glass according to the first type. Therefore, it is possible to prevent quality deterioration of the glass article related to the intermediate variety between the first variety and the second variety manufactured during the execution of the variety change process and the glass article related to the second variety manufactured after the completion of the variety change process. can.

In this method, the capacity of the molten glass in the refractory tank ^{may be 15 m 3} or more. The refractory tank may include a first refractory tank and a second refractory tank connected to the first refractory tank. The discharge port may include a first discharge port formed in the first refractory tank and a second discharge port formed in the second refractory tank. In the preparation step and the product type change step, the difference between the height of the liquid level of the molten glass in the first refractory tank and the height of the upper end portion of the first discharge port is 170 mm or more, and The difference between the height of the liquid level of the molten glass in the second refractory tank and the height of the upper end portion of the second discharge port may be 170 mm or more.

According to this configuration, since the capacities of the first refractory tank and the second refractory tank are 15 m ³ or more, the capacity is large and the amount of the stagnant layer tends to be large. In this case, in the product type change step, the difference between the height of the liquid level of the molten glass in each refractory tank and the height of the upper end of each discharge port in each refractory tank is set to 170 mm or more. Later, it is possible to prevent a large amount of the molten glass of the first variety present in the stagnant layer from being mixed with the molten glass of the second variety for a long period of time.

The refractory tank may include a melting tank that heats a glass raw material to produce the molten glass and a clarification tank that defoams the molten glass. The melting tank and the clarification tank tend to have a large capacity, and the amount of the stagnant layer also tends to be large. If the above-mentioned invention is applied to such a melting tank and a clarification tank, the effect of being able to produce a high-quality glass article with few foam defects and the like becomes remarkable.

The refractory tank may include a distribution tank having a plurality of the discharge ports. A stagnant layer can also be formed in the distribution tank. By applying the above-mentioned invention to such a distribution tank, it is possible to produce a high-quality glass article having few foam defects and the like.

The density of the molten glass according to the second kind may be higher than the density of the molten glass according to the first kind. In the variety change step, the molten glass of the second variety having a high density flows so as to slip under the molten glass of the first variety having a low density. As a result, the molten glass of the first type tends to remain above the second molten glass in the refractory tank, and is less likely to be mixed with the molten glass of the second type even after the end of the type change process.

In this method, the number of bubbles of 100 μm or more contained in the glass article produced during the execution of the product type changing step may be 0.05 cells / kg or less. In this way, it is possible to maintain high quality of the glass article related to the intermediate variety between the first variety and the second variety produced during the execution of the variety change process. Along with this, it is possible to maintain high quality of the glass article related to the second variety manufactured immediately after the execution of the variety change step.

According to the present invention, it is possible to prevent the quality of the glass article manufactured during and after the substrate change from being deteriorated.

It is a side view which shows the manufacturing apparatus of a glass article. It is sectional drawing which shows the glass melting furnace and the clarification tank. It is sectional drawing of the glass melting furnace and the clarification tank which shows the substrate change process. It is sectional drawing of the glass melting furnace and the clarification tank which shows the substrate change process.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. 1 to 4 show an embodiment of a method for manufacturing a glass article according to the present invention.

1 and 2 show a glass article manufacturing apparatus. The manufacturing apparatus 1 includes a glass melting furnace 2 that heats a glass raw material to generate molten glass GM, a clarification tank 3 that defoams the molten glass GM, and a molding apparatus that forms the molten glass GM in order from the upstream side. Mainly equipped with 4.

The glass melting furnace 2 includes a connecting portion (hereinafter referred to as “first connecting portion”) 7 connecting the first melting tank 5, the second melting tank 6, the first melting tank 5 and the second melting tank 6. To prepare for.

The first melting tank 5 is a refractory tank (first refractory tank) made of a refractory material. Examples of refractory materials include refractory bricks (for example, zirconia-based electric cast bricks, alumina-based electric cast bricks, alumina-zirconia-based electric cast bricks, AZS (Al-Zr-Si) -based electric cast bricks, dense fired bricks, etc.). Be done. The capacity (volume) of the molten glass GM in the first melting tank 5 is preferably 15 m ³ or more, more preferably 30 m ³ or more. On the other hand, the upper limit of the capacity is, for example, 600 m ³ .

As shown in FIG. 2, the first melting tank 5 includes a raw material supply unit 8 for supplying a glass raw material, a heating device such as a burner and an electrode for heating the glass raw material and the molten glass GM (not shown), and the molten glass GM. It is mainly provided with a discharge port (hereinafter referred to as “first discharge port”) 9 for discharging the glass.

As shown in FIG. 2, the molten glass GM produced by the first melting tank 5 has a liquid surface (free surface) FS. Here, the "liquid surface (free surface)" means a surface (interface with the gas phase) that comes into contact with the gas phase in the molten glass GM (hereinafter, the same applies).

The second melting tank 6 is a refractory tank (second refractory tank) made of a refractory material. As the refractory material of the second melting tank 6, refractory bricks and the like are used as in the case of the first melting tank 5. The capacity of the molten glass GM in the second melting tank 6 is preferably 15 m ³ or more, more preferably 30 m ³ or more. On the other hand, the upper limit of the capacity is, for example, 600 m ³ .

The second melting tank 6 discharges the heating device (not shown) such as a burner and electrodes for heating the molten glass GM, the supply port 10 connected to the first connecting portion 7, and the molten glass GM to the clarification tank 3. The discharge port (hereinafter referred to as “second discharge port”) 11 is provided. The molten glass GM housed in the second melting tank 6 has a liquid level FS.

The first connection portion 7 constitutes a flow path for transferring the molten glass GM of the first melting tank 5 to the second melting tank 6. The first connection portion 7 connects the first discharge port 9 of the first dissolution tank 5 and the supply port 10 of the second dissolution tank 6. The first connecting portion 7 is formed in a hollow shape by a refractory material such as refractory bricks, platinum, a platinum alloy, or the like. The molten glass GM flowing through the first connecting portion 7 does not have a liquid surface (free surface).

The clarification tank 3 performs a defoaming treatment on the molten glass GM supplied from the second melting tank 6. The clarification tank 3 is composed of refractory materials such as refractory bricks. The clarification tank 3 includes a heating device (not shown) that heats the molten glass GM so as to have a predetermined temperature gradient, a supply port 12 for the molten glass GM, and a discharge port 13. The molten glass GM housed in the clarification tank 3 has a liquid level FS.

The clarification tank 3 is connected to the second melting tank 6 via a connecting portion (hereinafter referred to as “second connecting portion”) 14. The second connection portion 14 constitutes a flow path for transferring the molten glass GM of the second melting tank 6 to the clarification tank 3. The second connection portion 14 connects the second discharge port 11 of the second dissolution tank 6 and the supply port 12 of the clarification tank 3. The second connecting portion 14 is formed in a hollow shape by a refractory material such as refractory bricks, platinum, a platinum alloy, or the like. The molten glass GM flowing through the second connecting portion 14 does not have a liquid level.

The discharge port 13 of the clarification tank 3 is connected to the molding apparatus 4 via the glass supply path 15. The molten glass GM flowing through the glass supply path 15 does not have a liquid level. If necessary, a stirring tank for stirring the molten glass with a stirrer and a state adjusting tank for adjusting the state (for example, viscosity and flow rate) of the molten glass may be provided on the path of the glass supply path 15.

The molding apparatus 4 includes a molded body (not shown) that molds the molten glass GM supplied from the glass supply path 15 into a predetermined shape. The molded body is formed by molding the molten glass GM into a predetermined shape such as a glass ribbon by an overflow down draw method or various other molding methods. In addition, the molding apparatus 4 may be configured to mold the molten glass GM by the float method.

Hereinafter, a method of manufacturing a glass article by the manufacturing apparatus 1 having the above configuration will be described.

This method includes a melting step of heating a glass raw material in a glass melting furnace 2 to generate a molten glass GM, a clarification step of defoaming the molten glass GM, and a molding step of forming the molten glass GM into a predetermined shape. And mainly prepare.

In the melting step, the glass raw material supplied from the raw material supply unit 8 into the first melting tank 5 is heated by a heating device. As a result, the glass raw material is melted and molten glass GM is produced. The molten glass GM flows into the second melting tank 6 through the first connecting portion 7. In the second melting tank 6, the temperature of the molten glass GM is maintained constant by heating the molten glass GM. The molten glass GM in the second melting tank 6 flows into the clarification tank 3 through the second connecting portion 14.

A clarifying agent is blended in the glass raw material, and gas (foam) is generated in the molten glass GM heated in the clarifying tank 3 by the action of the clarifying agent. In the clarification step, the gas contained in the molten glass GM is removed in the clarification tank 3. After that, the molten glass GM is transferred from the clarification tank 3 to the molding apparatus 4 through the glass supply path 15.

In the molding step, the molten glass GM supplied from the clarification tank 3 through the glass supply path 15 is molded into a predetermined shape by a molded body. When molding a glass ribbon, the molded glass ribbon becomes a glass article (glass plate) through various steps such as a slow cooling step, a cutting step, and an inspection step. In the cutting step, after the glass plate is cut out from the glass ribbon, the selvage portion of the glass plate is removed. If necessary, a re-cutting step, an end face processing step, and a cleaning step may be provided. In the re-cutting process, the glass plate is cut to obtain the desired dimensions, in the end face processing process, the end face of the glass plate is ground and polished to remove microcracks, and in the cleaning process, the glass plate is mainly used. Removes dirt adhering to the surface. The glass plate thus obtained is suitable for, for example, a glass substrate for a display and a cover glass.

In the above method for manufacturing a glass article, when a glass article having a composition different from that of the glass article being manufactured is manufactured, the base material changing step is executed. In the substrate changing step, the variety of the molten glass GM produced in the glass melting furnace 2 is changed from the first variety to the second variety by the extrusion method while continuing the operation of the manufacturing apparatus 1. Hereinafter, the molten glass according to the first type of glass article is referred to as the first molten glass GM1, and the molten glass produced from the glass raw material according to the second type of glass article is referred to as the second molten glass GM2.

The substrate changing process includes a preparation process and a product type changing process. In the preparatory step, the difference between the height H1 of the liquid level of the first molten glass GM1 in the first melting tank 5 and the height H2 of the upper end portion 9a of the first discharge port 9 in the first melting tank 5 ΔHa (ΔHa). = H1-H2) is 170 mm or more, preferably 300 mm or more. On the other hand, the upper limit of the difference ΔHa is, for example, 1200 mm.

In the preparatory step, the difference between the height H3 of the liquid level of the first molten glass GM in the second melting tank 6 and the height H4 of the upper end 11a of the second discharge port 11 in the second melting tank 6 ΔHb (ΔHb). = H3-H4) is 170 mm or more, preferably 300 mm or more. On the other hand, the upper limit of the difference ΔHb is, for example, 1200 mm.

In the preparatory step, the difference ΔHc (ΔHc = H5-H6) between the height H5 of the liquid level of the first molten glass GM1 in the clarification tank 3 and the height H6 of the upper end portion 13a of the discharge port 13 in the clarification tank 3 is. , 170 mm or more, preferably 300 mm or more. On the other hand, the upper limit of the difference ΔHc is, for example, 1200 mm.

These height differences ΔHa to ΔHc can be adjusted, for example, by changing conditions such as the input amount of the glass raw material according to the first molten glass GM1 and the heating temperature by the heating device.

In the process of the melting step and the preparation step, as shown in FIGS. 2 and 3, in the first melting tank 5, the wall portion side on which the first discharge port 9 is formed is located, and the first discharge port 9 is more than the first discharge port 9. A layer (stagnation layer) SL in which the molten glasses GM and GM1 are stagnant is formed at an upper position. Similarly, the stagnant layer SL is formed in the second dissolution tank 6 and the clarification tank 3. The stagnant layer SL in the second melting tank 6 and the clarification tank 3 is located on the wall side where the supply ports 10 and 12 are formed, in addition to the wall side where the discharge ports 11 and 13 are formed. May also be formed (sometimes formed as a whole).

The first molten glass GM of the stagnant layer SL of the first melting tank 5, the second melting tank 6 and the clarification tank 3 is altered and different due to some components volatilizing from the liquid surface or foreign matter being mixed. It tends to be glass.

In the product type changing step, the glass material according to the second type is supplied from the raw material supply unit 8 into the first melting tank 5, and the glass material is heated by the heating device related to the first melting tank 5.

As shown in FIG. 3, in the product type changing step, the glass raw material according to the second product supplied to the first melting tank 5 is heated by the heating device to generate the second molten glass GM2. As a result, in the first melting tank 5, the first molten glass GM1 and the second molten glass GM2 are in a mixed state.

The second molten glass GM2 mixes with the first molten glass GM1 while extruding the first molten glass GM1, and the first connecting portion 7, the second melting tank 6, the second connecting portion 14, the clarification tank 3, and the glass supply path. It is supplied to the molding apparatus 4 via 15. Hereinafter, the molten glass in which the first molten glass GM1 and the second molten glass GM2 are mixed may be referred to as “mixed molten glass”.

In the product type changing step, the difference ΔHa between the height H1 of the liquid level of the molten glass GM1 and GM2 in the first melting tank 5 and the height H2 of the upper end portion 9a in the first discharge port 9 of the first melting tank 5 is The height H1 of the liquid level is adjusted so that the state of 170 mm or more, preferably 300 mm or more is maintained.

As a result, in the first melting tank 5, the first molten glass GM1 of the stagnant layer SL is maintained in a state in which it is difficult to flow, so that the second molten glass GM2 flows so as to slip under the stagnant layer SL. Therefore, due to the formation and flow of the second molten glass GM2 in the first melting tank 5, most of the first molten glass GM1 in the first melting tank 5 excludes the first molten glass GM1 of the stagnant layer SL. , Extruded from the first outlet 9. Further, in the stagnant layer SL of the first melting tank 5, the first molten glass GM1 continues to stay in the first melting tank 5 for a long period of time even after the end of the product type changing step.

The difference ΔHb between the height H3 of the liquid levels of the molten glasses GM1 and GM2 in the second melting tank 6 and the height H4 of the upper end portion 11a in the second discharge port 11 of the second melting tank 6 is 170 mm or more. The height H3 of the liquid level is adjusted so that the state of preferably 300 mm or more is maintained.

As a result, in the second melting tank 6, the first molten glass GM1 of the stagnant layer SL is maintained in a state in which it is difficult to flow, so that the second molten glass GM2 flows so as to slip under the stagnant layer SL. Due to the flow of the second molten glass GM2, most of the first molten glass GM1 in the second melting tank 6 is extruded from the second discharge port 11 except for the first molten glass GM1 of the stagnant layer SL. Further, in the stagnant layer SL of the second melting tank 6, the first molten glass GM1 continues to stay in the second melting tank 6 for a long period of time even after the end of the product type changing step.

The difference ΔHc between the height H5 of the liquid level of the molten glass GM1 and GM2 in the clarification tank 3 and the height H6 of the upper end portion 13a at the discharge port 13 of the clarification tank 3 is 170 mm or more, preferably 300 mm or more. The height H5 of the liquid level is adjusted so that the state is maintained.

As a result, in the clarification tank 3, the first molten glass GM1 of the stagnant layer SL is maintained in a state in which it is difficult to flow, so that the second molten glass GM2 flows so as to slip under the stagnant layer SL. Due to the flow of the second molten glass GM2, most of the first molten glass GM1 in the clarification tank 3 is extruded from the discharge port 13 except for the first molten glass GM1 of the stagnant layer SL. Further, in the stagnant layer SL of the clearing tank 3, the first molten glass GM1 continues to stay in the clearing tank 3 for a long period of time even after the end of the product type changing step. As a result, the state shown in FIG. 4 is reached, and the product type changing process is completed.

According to the method for manufacturing a glass article according to the present embodiment described above, in the preparation step and the product type changing step, the liquid level heights H1, H3, H5 of the molten glass GM1 and GM2 and the first melting which is a refractory tank. The product type change step by setting the difference ΔHa, ΔHb, ΔHc from the height of the upper ends 9a, 11a, 13a of the discharge ports 9, 11, 13 of the tank 5, the second dissolution tank 6, and the clarification tank 3 to 170 mm or more. The first molten glass GM1 (heterogeneous glass) remaining in the stagnant layer SL of the first melting tank 5, the second melting tank 6, and the clarification tank 3 flows into the discharge ports 9, 11 and 13 during and after the execution of the above. It becomes difficult to do.

Therefore, it is possible to prevent the occurrence of bubble defects and the like in the glass article due to the mixing of the first molten glass GM1 (heterogeneous glass) of the stagnant layer SL into the mixed molten glass and the second molten glass GM2. This makes it possible to prevent deterioration of the quality of the glass article related to the second kind during and after the execution and completion of the substrate replacement process.

Here, while the product type changing process is executed, an inspection is performed on the glass article (hereinafter referred to as "intermediate type glass article") produced by the mixed molten glass (inspection process). In this inspection step, the presence, type, size, etc. of foreign matter and bubbles (air bubbles) in the glass article of the intermediate variety are inspected. In the product type change process, the liquid level heights H1, H3, H5 of the molten glass GM1, GM2 and the discharge ports 9, 11, of the first melting tank 5, the second melting tank 6, and the clarification tank 3, which are refractory tanks, By setting the difference ΔHa, ΔHb, ΔHc from the height of the upper end portions 9a, 11a, 13a of 13 to 170 mm, the number of bubbles having a maximum dimension of 100 μm or more is 0.05 cells / kg in the glass article of the intermediate variety. It was about the same even after the product type change process was completed. Further, when the height differences ΔHa, ΔHb, and ΔHc were set to 300 mm, the number of bubbles was 0.03 / kg, which was about the same even after the end of the product type change process. On the other hand, when the height difference ΔHa, ΔHb, ΔHc was 100 mm, the number of bubbles increased to 3.0 cells / kg. In each case, the capacity of the first melting tank 5 was 500 m ³ , the capacity of the second melting tank 6 was 150 m ^3, and the capacity of the clarification tank 3 was 150 m ³ .

The density of the second molten glass GM2 is preferably higher than the density of the first molten glass GM1. In this case, the second molten glass GM2 flows and easily reaches the lower layer, and the first molten glass GM1 flows and easily reaches the upper layer. Therefore, the first molten glass GM1 of the stagnant layer SL tends to stay on during the execution and after the end of the product type change step, and the occurrence of bubble defects and the like in the glass article can be more reliably prevented.

The present invention is not limited to the configuration of the above embodiment, and is not limited to the above-mentioned action and effect. The present invention can be modified in various ways without departing from the gist of the present invention.

In the above embodiment, the manufacturing apparatus 1 provided with two melting tanks (first melting tank 5, second melting tank 6) is exemplified, but the present invention is not limited to this configuration. The present invention is also applicable to the case where a glass article is manufactured by the manufacturing apparatus 1 having only one melting tank (first melting tank 5).

The glass melting furnace 2 may be provided with a distribution tank after the clarification tank 3. The distribution tank is connected to the clarification tank 3 via a hollow connection portion. The distribution tank includes a supply port connected to the connection portion and a plurality of discharge ports. The molding apparatus 4 is connected to each of the plurality of discharge ports via the glass supply path 15.

With this configuration, the distribution tank can distribute the molten glass to the plurality of glass supply paths 15 and the plurality of molding devices 4. The molten glass in the distribution tank has a liquid level. In the substrate changing step (preparation step and product type changing step), the difference between the height of the liquid level of the molten glass in the distribution tank and the height of the upper end of each discharge port in the distribution tank is 170 mm or more, preferably 170 mm or more. It is 300 mm or more. The capacity of the molten glass in the distribution tank is preferably 15 m ³ or more, more preferably 30 m ³ or more.

3 Clarification tank 5 First melting tank (first refractory tank)
6 Second melting tank (second refractory tank)
9 First discharge port 9a Upper end of the first discharge port 11 Second discharge port 11a Upper end of the second discharge port 13 Discharge port of the clarification tank 13a Upper end of the discharge port of the clarification tank FS liquid level (free surface)
GM1 1st molten glass GM2 2nd molten glass H1 height of the liquid level of the molten glass in the 1st melting tank H2 height of the upper end of the 1st discharge port in the 1st melting tank H3 molten glass in the 2nd melting tank H4 Height of the upper end of the second discharge port in the second melting tank H5 Height of the liquid level of the molten glass in the clarification tank H6 Height of the upper end of the discharge port in the clarification tank ΔHa molten glass Difference between the height of the liquid level of the first discharge port and the height of the upper end of the first discharge port ΔHb Difference between the height of the liquid level of the molten glass and the height of the upper end of the second discharge port Difference from the height of the upper end of the discharge port in

Claims (6)

A method of manufacturing a glass article from molten glass having a liquid level in a refractory tank composed of a refractory material.
The refractory tank has a discharge port for discharging the molten glass.
A preparatory step for preparing a state in which the difference between the height of the liquid level of the molten glass and the height of the upper end of the discharge port in the refractory tank is 170 mm or more, and the discharge from the discharge port by an extrusion method. It is equipped with a variety change process that changes the variety of molten glass from the first variety to the second variety.
In the product type changing step, the molten glass discharged from the discharge port is discharged from the discharge port while maintaining a state in which the difference between the height of the liquid level of the molten glass and the height of the upper end portion of the discharge port is 170 mm or more. A method for producing a glass article, which comprises changing a variety from the first variety to the second variety. The capacity of the molten glass in the refractory tank is 15 m ³ or more.
The refractory tank includes a first refractory tank and a second refractory tank connected to the first refractory tank.
The discharge port includes a first discharge port formed in the first refractory tank and a second discharge port formed in the second refractory tank.
In the preparation step and the product type change step, the difference between the height of the liquid level of the molten glass in the first refractory tank and the height of the upper end portion of the first discharge port is 170 mm or more, and The method for manufacturing a glass article according to claim 1, wherein the difference between the height of the liquid level of the molten glass in the second refractory tank and the height of the upper end portion of the second discharge port is 170 mm or more. The method for producing a glass article according to claim 1 or 2, wherein the refractory tank includes a melting tank that heats a glass raw material to generate the molten glass and a clarification tank that defoams the molten glass. .. The method for manufacturing a glass article according to any one of claims 1 to 3, wherein the refractory tank includes a distribution tank including a plurality of discharge ports. The method for producing a glass article according to any one of claims 1 to 4, wherein the density of the molten glass according to the second kind is higher than the density of the molten glass according to the first kind. The method for producing a glass article according to any one of claims 1 to 5, wherein the amount of bubbles of 100 μm or more contained in the glass article produced during the execution of the product type changing step is 0.05 cells / kg or less.

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