Glass melting apparatus, glass manufacturing method, and molten glass base replacement method

Abstract

This glass melting device comprises: a melt tank for accumulating molten glass; an electrode traversing a through-hole in the bottom wall of the melt tank, protruding above the bottom wall, and electrically heating the molten glass; and a cooler surrounding the electrode in the through-hole of the bottom wall. The bottom wall of the melt tank includes a first brick forming a surface layer in contact with the molten glass, and a second brick surrounding the electrode and the cooler in the through-hole of the surface layer. The first brick is superior in corrosion resistance to the second brick. The second brick is such that no reversible transformation occurs in the temperature region of 1000°C to 1200°C.

Description

[Technical field]

[0001] The present disclosure relates to a glass melting apparatus, a glass manufacturing method, and a method for changing the base material of molten glass. [Background technology]

[0002] Patent Document 1 describes a method for changing the raw material of molten glass (for example, changing the composition or color) in a continuous glass melting furnace. In this method, most of the molten glass is once discharged from the melting furnace, and then new glass raw material is charged.

[0003] Patent Document 2 describes a melting furnace equipped with a plurality of electrodes at the bottom. The bottom of the melting furnace has first bricks surrounding the electrodes and second bricks arranged between the first bricks. The first bricks are electrocast bricks, e.g., zirconia-based refractories. On the other hand, the second bricks are dense zircon fired bricks. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent No. 6670460 [Patent Document 2] International Publication No. 2019 / 004434 Summary of the Invention [Problem to be solved by the invention]

[0005] The glass melting apparatus includes a melting tank, an electrode, and a cooler. The melting tank stores molten glass. The electrode passes through a through hole in the bottom wall of the melting tank and protrudes above the bottom wall, and electrically heats the molten glass. The cooler is a water-cooled jacket or the like, and surrounds the electrode with the through hole in the bottom wall, solidifies the molten glass, and seals the through hole.

[0006] In the molten glass raw material change, first, the molten glass stored in the melting tank is discharged to the outside of the melting tank, and the liquid level of the molten glass stored in the melting tank is lowered. Then, glass raw materials for a second molten glass different from the molten glass are poured into the melting tank. As a result, the liquid level of the second molten glass rises.

[0007] During the replacement of the molten glass, the electrode protrudes above the surface of the molten glass and is sublimated by reaction with oxygen gas in the atmosphere. Therefore, after the surface of the second molten glass reaches a preset height, the electrode is inserted upward and the effective length of the electrode is returned to its original length. The effective length of the electrode is the length of the part of the electrode that heats the molten glass, that is, the length of the part of the electrode that protrudes from the bottom wall.

[0008] Before inserting the electrode upward, the supply of refrigerant to the cooler is temporarily stopped in order to soften the molten glass that has solidified in the through hole through which the electrode passes. After the electrode is inserted, the supply of refrigerant to the cooler is resumed. Since the supply of refrigerant to the cooler is stopped and resumed, a large temperature change occurs around the electrode.

[0009] According to Patent Document 2, electroformed bricks are arranged around the electrodes. The most preferred electroformed bricks are electroformed zirconia bricks. Zirconia (ZrO2) has excellent corrosion resistance against molten glass. However, zirconia undergoes reversible transformation in the temperature range of 1000°C to 1200°C. This transformation is accompanied by a large volume change, which generates large internal stress.

[0010] One aspect of the present disclosure provides a technique for reducing stresses induced in the bottom wall of a melting tank during glass replacement and for improving the corrosion resistance of the bottom wall of the melting tank to molten glass. [Means for solving the problem]

[0011] A glass melting apparatus according to one aspect of the present disclosure includes a melting tank for storing molten glass, an electrode that passes through a through hole in a bottom wall of the melting tank and protrudes above the bottom wall to electrically heat the molten glass, and a cooler that surrounds the electrode at the through hole in the bottom wall. The bottom wall of the melting tank includes a first brick that forms a surface layer that contacts the molten glass, and a second brick that surrounds the electrode and the cooler at the through hole in the surface layer. The first brick has higher corrosion resistance than the second brick. The second brick does not undergo reversible transformation in a temperature range of 1000°C to 1200°C. Effect of the Invention

[0012] According to one aspect of the present disclosure, it is possible to reduce stress generated in the bottom wall of the melting tank during base material replacement, and to improve the corrosion resistance of the bottom wall of the melting tank against molten glass. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing a glass manufacturing apparatus according to one embodiment. [Diagram 2] FIG. 2 is a flow chart illustrating a method for producing glass according to one embodiment. [Diagram 3] FIG. 3 is a cross-sectional view showing a glass melting apparatus according to one embodiment. [Figure 4] FIG. 4 is a plan view showing the bottom wall of the dissolution tank of FIG. [Diagram 5] FIG. 5 is a cross-sectional view showing an example of a state during substrate replacement in the melting tank of FIG. [Figure 6] FIG. 6 is an enlarged cross-sectional view showing a portion of the bottom wall of the dissolution tank of FIG. [Figure 7] FIG. 7 is an enlarged perspective view of a portion of the bottom wall of the dissolution tank of FIG. [Figure 8] FIG. 8 is a perspective view showing a groove formed on the upper surface of the surface layer of the bottom wall of FIG. [Figure 9] FIG. 9 is a flowchart showing a method for changing molten glass according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding configurations are denoted by the same reference numerals, and the description may be omitted. In each drawing, the X-axis direction, the Y-axis direction, and the Z-axis direction are perpendicular to each other, the X-axis direction and the Y-axis direction are horizontal directions, and the Z-axis direction is vertical. In addition, in the specification, "~" indicating a numerical range means that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0015] First, a glass manufacturing apparatus 1 according to the present embodiment will be described with reference to Fig. 1. The manufacturing apparatus 1 has a glass melting apparatus 2, a forming apparatus 3, an annealing apparatus 4, and a processing apparatus 5.

[0016] The glass melting device 2 melts glass frits to produce molten glass. The glass frits are prepared by mixing a plurality of materials. For example, when the glass is soda-lime glass, the glass frit M contains, for example, silica sand, limestone, soda ash, boric acid, and a fining agent. The fining agent is, for example, sulfur trioxide, chloride, or fluoride. The glass frit M may contain glass cullet in order to recycle the glass. The glass frit M may be a powdered raw material, or may be a granulated raw material obtained by granulating the powdered raw material.

[0017] The glass raw materials are determined according to the composition of the glass. When the glass is soda-lime glass, the glass contains, in mole percent based on oxides, 50% to 75% SiO2, 0% to 20% Al2O3, 5% to 25% Li2O, Na2O, and K2O in total, and 0% to 20% MgO, CaO, SrO, and BaO in total.

[0018] When the glass is an alkali-containing aluminosilicate glass, the glass contains, in mole % on an oxide basis, 50% to 75% SiO2, 5% to 20% Al2O3, 2% to 20% Na2O, 0% to 6% K2O, 0% to 15% MgO, 0% to 10% in total of CaO, SrO, and BaO, 0% to 5% in total of ZrO2 and TiO2, 0% to 10% B2O3, and 0% to 20% Li2O.

[0019] The glass melting apparatus 2 is of a continuous type, and continuously supplies glass raw materials and produces molten glass. The input amount of glass raw materials per unit time is approximately the same as the output amount of molten glass per unit time. The molten glass is sent from the glass melting apparatus 2 to the forming apparatus 3. The details of the glass melting apparatus 2 will be described later.

[0020] The forming device 3 forms the molten glass obtained in the glass melting device 2 into glass of a desired shape. Forming methods for obtaining plate-shaped glass include the float method, the fusion method, the roll-out method, etc. Forming methods for obtaining tubular glass include the Vello method, the Danner method, etc.

[0021] The annealing device 4 anneals the glass formed by the forming device 3. The annealing device 4 has, for example, an annealing furnace and transport rollers that transport the glass in a desired direction inside the annealing furnace. The transport rollers are arranged, for example, at intervals in the horizontal direction. The glass is annealed while being transported from the entrance to the exit of the annealing furnace. By annealing the glass, glass with little residual distortion can be obtained.

[0022] The processing device 5 processes the glass annealed in the annealing device 4 into a desired shape. The processing device 5 may be, for example, one or more selected from a cutting device, a grinding device, a polishing device, and a coating device. The cutting device cuts the glass annealed in the annealing device 4. The cutting device forms a scribe line in the glass annealed in the annealing device 4, for example, and breaks the glass along the scribe line. The scribe line is formed using a cutter or a laser beam. The grinding device grinds the glass annealed in the annealing device 4. The polishing device polishes the glass annealed in the annealing device 4. The coating device forms a desired film on the glass annealed in the annealing device 4.

[0023] The glass manufacturing apparatus 1 may further include a fining apparatus. The fining apparatus removes bubbles contained in the molten glass obtained in the glass melting apparatus 2 before the molten glass is formed in the forming apparatus 3. The method for removing bubbles may be, for example, one or more methods selected from a method of reducing the pressure of the atmosphere surrounding the molten glass and a method of heating the molten glass to a high temperature.

[0024] Next, a method for manufacturing glass according to this embodiment will be described with reference to Fig. 2. As shown in Fig. 2, the method for manufacturing glass includes melting (step S11), forming (step S12), annealing (step S13), and processing (step S14). A glass melting apparatus 2 performs melting (step S11), a forming apparatus 3 performs forming (step S12), an annealing apparatus 4 performs annealing (step S13), and a processing apparatus 5 performs processing (step S14). The method for manufacturing glass may further include fining. Fining is to remove bubbles contained in molten glass, and is performed after the production of molten glass (step S11) and before forming (step S12).

[0025] Next, the glass melting apparatus 2 according to the present embodiment will be described with reference to Figs. 3 and 4. As shown in Fig. 3, the glass melting apparatus 2 includes a melting tank 10, an electrode 20, a cooler 30, and a charger 50. The melting tank 10 stores molten glass G obtained by melting glass raw material M. The electrode 20 passes through a through hole 12 in the bottom wall 11 of the melting tank 10, protrudes above the bottom wall 11, and electrically heats the molten glass G. The cooler 30 is a water-cooled jacket or the like, and surrounds the electrode 20 with the through hole 12 in the bottom wall 11, solidifies the molten glass G, and seals the through hole 12. The charger 50 charges glass raw material M into the melting tank 10 from above the side wall 13 of the melting tank 10.

[0026] The charger 50 is, for example, a blanket charger, and includes a hopper 51, a conveying pan 52, and a moving mechanism 53. The hopper 51 stores the glass frit M. The conveying pan 52 carries the glass frit M dropped from the hopper 51. The moving mechanism 53 moves the conveying pan 52 toward and away from the melting tank 10 under computer control, charges the glass frit M on the conveying pan 52 into the melting tank 10, and forms a raw material pile Ma on the liquid surface Ga of the molten glass G. The raw material pile Ma floats on the molten glass G and melts by the heat of the molten glass G.

[0027] The melting tank 10 contains molten glass G obtained by melting glass raw material M. A plurality of through holes 12 for passing electrodes 20 are formed in the bottom wall 11 of the melting tank 10. The plurality of through holes 12 form a plurality of (e.g., two) rows along the side wall 13 of the melting tank 10, and a plurality of electrodes 20 form a plurality of (e.g., two) rows along the side wall 13 of the melting tank 10 as shown in FIG. 4. Each of the plurality of electrodes 20 protrudes upward from the bottom wall 11 of the melting tank 10 and heats the molten glass G by passing electricity through it. The material of the electrodes 20 is not particularly limited, but is, for example, Mo (molybdenum). When the molten glass G is heated, convection occurs and the heat is carried throughout the entire melting tank 10.

[0028] A burner (not shown) or the like for heating the molten glass G is provided above the melting tank 10. The burner heats the molten glass G when the base material of the molten glass G is changed. The burner may be an electric heater made of silicon carbide, molybdenum disilicide, or the like, in addition to a burner. The burner may also be used when producing glass. On the other hand, the electrode 20 heats the molten glass G when producing glass, but does not have to heat the molten glass G when the base material of the molten glass G is changed.

[0029] Incidentally, in changing the base material of molten glass G, as shown in Fig. 5, first, the molten glass G stored in the melting tank 10 is discharged to the outside of the melting tank 10, and the liquid level of the molten glass G stored in the melting tank 10 is lowered. Then, glass raw material of a second molten glass different from the molten glass G is charged into the melting tank 10. As a result, the liquid level of the second molten glass rises.

[0030] During the replacement of the molten glass G, the liquid level of the molten glass G is lowered, causing the electrode 20 to protrude above the liquid level of the molten glass G, and the protruding portion is sublimated by reaction with oxygen gas in the atmosphere, shortening the effective length L (see FIG. 3) of the electrode 20. The effective length L of the electrode 20 refers to the length of the portion of the electrode 20 that heats the molten glass G, and refers to the length of the portion of the electrode 20 that protrudes from the bottom wall 11. Therefore, after the liquid level of the second molten glass rises by the introduction of the glass raw material of the second molten glass and reaches a preset height, the electrode 20 is inserted upward, and the effective length L of the electrode 20 is returned to its original length.

[0031] Before inserting the electrode 20 upward, the supply of refrigerant to the cooler 30 is temporarily stopped in order to soften the molten glass G solidified in the through hole 12 through which the electrode 20 passes. Then, after the insertion of the electrode 20 is completed, the supply of refrigerant to the cooler 30 is resumed. Since the supply of refrigerant to the cooler 30 is stopped and resumed, a large temperature change occurs around the electrode 20.

[0032] According to Patent Document 2, electroformed bricks are arranged around the electrodes. The most preferred electroformed bricks are electroformed zirconia bricks. Zirconia (ZrO2) has excellent corrosion resistance against molten glass. However, zirconia undergoes reversible transformation in the temperature range of 1000°C to 1200°C. This transformation is accompanied by a large volume change, which generates large internal stress.

[0033] As shown in FIG. 6, the bottom wall 11 of the melting tank 10 of this embodiment includes a first brick 16 forming a surface layer 15 in contact with the molten glass G, and a second brick 17 surrounding the electrode 20 and the cooler 30 at the through hole 12 of the surface layer 15. The first brick 16 has better corrosion resistance than the second brick 17. The second brick 17 does not undergo reversible transformation in the temperature range of 1000°C to 1200°C. For example, the first brick 16 is an electrocast brick, and the second brick 17 is a dense zircon fired brick. The electrocast brick and the dense zircon fired brick are arranged in the opposite manner between this embodiment and Patent Document 2. Although not shown, the bottom wall 11 may further include a heat-insulating layer under the surface layer 15. The heat-insulating layer is formed by a brick having excellent heat-insulating properties.

[0034] According to this embodiment, dense zircon fired bricks are arranged around the electrode 20. The dense zircon fired bricks mainly contain zircon (ZrSiO4). The dense zircon fired bricks have a zircon content of, for example, 95% by mass. Unlike zirconia, zircon does not undergo reversible transformation in the temperature range of 1000°C to 1200°C. Therefore, even if a large temperature change occurs around the electrode 20 by stopping and restarting the supply of the refrigerant to the cooler 30, the stress generated inside can be reduced.

[0035] Furthermore, dense zircon fired bricks have a lower porosity and a higher electrical resistivity than electroformed bricks. By disposing dense zircon fired bricks with high electrical resistivity around the electrode 20, leakage of electricity to the bottom wall 11 can be suppressed.

[0036] When the temperature of the dense zircon fired bricks exceeds 1500° C., the zircon is decomposed and the dense zircon fired bricks are easily eroded by the molten glass G. According to the present embodiment, the dense zircon fired bricks are disposed near the cooler 30, so that the temperature rise of the dense zircon fired bricks can be suppressed, and as a result, the decomposition of the zircon can be suppressed.

[0037] According to the present embodiment, electrocast bricks are used as the first bricks 16 forming the surface layer 15 that contacts the molten glass G. The electrocast bricks have better corrosion resistance against the molten glass G than the dense zircon fired bricks. Therefore, the corrosion resistance of the bottom wall 11 of the melting tank 10 against the molten glass G can be improved.

[0038] The first brick 16 is, for example, an electroformed alumina-zirconia-silica brick, an electroformed alumina brick, or an electroformed zirconia brick. Among these, electroformed zirconia bricks are preferred, and electroformed high-zirconia bricks are particularly preferred, from the viewpoint of corrosion resistance against the molten glass G. The electroformed high-zirconia brick has a zirconia content of, for example, 90% by mass or more.

[0039] When the glass to be produced is an alkali-containing aluminosilicate glass, the melting temperature of the glass raw material M is higher than when it is soda-lime glass, so that it is preferable to use high-zirconia electroformed bricks as the first bricks 16.

[0040] As shown in Fig. 6, the bottom wall 11 of the melting tank 10 further includes a third brick 18 covering at least a part of the upper surface of the second brick 17. The third brick 18 is an electrocast brick, like the first brick 16. Covering at least a part of the upper surface of the dense zircon fired brick with the electrocast brick can improve corrosion resistance against the molten glass G. The third brick 18 is preferably an electrocast zirconia brick, and more preferably an electrocast high zirconia brick.

[0041] The bottom wall 11 of the melting tank 10 is composed of multiple types of bricks. During heating, the bricks constituting the bottom wall 11 may become misaligned due to differences in thermal expansion between the multiple types of bricks. In order to allow the electrode 20 to be inserted even if the bricks are misaligned, the third brick 18 is positioned farther away from the electrode 20 than the second brick 17 when viewed from above. As a result, the upper surface of the second brick 17, the portion surrounding the electrode 20, is exposed to the molten glass G. The portion of the second brick 17 exposed to the molten glass G is cooled to 1500° C. or less by the cooler 30 to suppress decomposition of zircon.

[0042] 7 and 8, the bottom wall 11 of the dissolution tank 10 includes a groove 19 that forms a step surface on the upper surface of the surface layer 15. A side surface 19a of the groove 19 is the step surface and holds down the third brick 18. A through hole 12 is formed in the bottom surface 19b of the groove 19, as shown in FIG.

[0043] 6, the second brick 17 protrudes upward from a bottom surface 19b of the groove 19. The third brick 18 includes a fitting portion 18a that fits into the groove 19 and a pressing portion 18b that presses the upper surface of the second brick 17. The third brick 18 is, for example, L-shaped when viewed from the side. By fitting the first brick 16, the second brick 17, and the third brick 18 together, it is possible to prevent the bricks from shifting positions.

[0044] As shown in FIG. 7, two rectangular third bricks 18-1 and 18-2 and two T-shaped third bricks 18-3 and 18-4 are interlocked inside the groove 19 when viewed from above. When viewed from above, two L-shaped cutouts 18a are formed in each of the two T-shaped third bricks 18-3 and 18-4. One third brick 18-1 is fitted into the two cutouts 18a, and another third brick 18-2 is fitted into the remaining two cutouts 18a. By interlocking the four third bricks 18-1, 18-2, 18-3, and 18-4 with each other, it is possible to suppress the displacement of the bricks. The four interlocked third bricks 18-1, 18-2, 18-3, and 18-4 form one third brick group. A plurality of third brick groups are arranged in a row at intervals in the Y-axis direction.

[0045] As shown in FIG. 7, when viewed from above, two rectangular third bricks 18-1 and 18-2 face each other in the X-axis direction and are held down by two side surfaces 19a of the groove 19 facing the X-axis direction. On the other hand, when viewed from above, two T-shaped third bricks 18-3 and 18-4 face each other in the Y-axis direction. Both end faces in the X-axis direction of the third brick 18-4 are held down by two side surfaces 19a of the groove 19 facing the X-axis direction. In addition, the end face in the negative Y-axis direction of the third brick 18-3 is held down by the side surface 19a of the groove 19. Although not shown, both end faces in the X-axis direction of the third brick 18-3 may be held down by two side surfaces 19a of the groove 19 facing the X-axis direction. In addition, the end face in the positive Y-axis direction of the third brick 18-4 may be held down by the side surface 19a of the groove 19.

[0046] Taking into consideration the expansion of the bricks when heated, a part of the side surface of the third brick 18 may not be in contact with the side surface 19 a of the groove 19 .

[0047] Next, a method for changing the base material of molten glass G according to this embodiment will be described with reference to Fig. 9. As shown in Fig. 9, the method for changing the base material of molten glass G includes, for example, steps S21 to S27. First, in step S21, power supply to electrode 20 is stopped. Next, in step S22, molten glass G stored in melting tank 10 is discharged to the outside of melting tank 10, and the liquid level of molten glass G stored in melting tank 10 is lowered. As a result, electrode 20 protrudes above the liquid surface of molten glass G, and the protruding portion is sublimated by reaction with oxygen gas in the atmosphere, and the effective length L of electrode 20 is shortened.

[0048] Next, in step S23, glass raw materials for a second molten glass different from the molten glass G are charged into the melting tank 10, and the second molten glass is stored in the melting tank 10. When the liquid level of the second molten glass reaches a preset height, step S24 is performed. In step S24, the supply of the refrigerant to the cooler 30 is stopped. Then, in step S25, the electrode 20 is inserted upward. The effective length L of the electrode 20 is returned to its original length.

[0049] Next, in step S26, the supply of refrigerant to cooler 30 is resumed. Finally, in step S27, the supply of power to electrode 20 is resumed, and the second molten glass is electrically heated by electrode 20. Thereafter, glass production is resumed.

[0050] According to this embodiment, as described above, dense zircon fired bricks are arranged around the electrode 20. Therefore, even if a large temperature change occurs around the electrode 20 by stopping and restarting the supply of the refrigerant to the cooler 30, the stress generated inside can be reduced.

[0051] According to the present embodiment, electrocast bricks are used as the first bricks 16 forming the surface layer 15 that contacts the molten glass G. The electrocast bricks have better corrosion resistance against the molten glass G than the dense zircon fired bricks. Therefore, the corrosion resistance of the bottom wall 11 of the melting tank 10 against the molten glass G can be improved.

[0052] The glass melting apparatus, the glass manufacturing method, and the molten glass base replacement method according to the present disclosure have been described above, but the present disclosure is not limited to the above-mentioned embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These naturally fall within the technical scope of the present disclosure.

[0053] This application claims priority based on Japanese Patent Application No. 2020-170756, filed with the Japan Patent Office on October 8, 2020, the entire contents of which are incorporated herein by reference. [Explanation of symbols]

[0054] 2. Glass melting equipment 10 Dissolution tank 11 Bottom wall 12 Through holes 15 Surface layer 16 First Brick 17 Second Brick 20 electrodes 30 Cooler

Claims

1. A melting tank for storing molten glass; an electrode that passes through a through hole in a bottom wall of the melting tank and protrudes above the bottom wall, and electrically heats the molten glass; a cooler surrounding the electrode at the through hole in the bottom wall, the bottom wall of the melting tank includes a first brick forming a surface layer in contact with the molten glass, and a second brick surrounding the electrode and the cooler at the through hole of the surface layer, The first brick has higher corrosion resistance than the second brick, The second brick does not undergo reversible transformation in the temperature range of 1000°C to 1200°C.

2. the first brick is an electroformed brick, 2. The glass melting apparatus of claim 1, wherein the second brick is a dense zircon fired brick.

3. 3. The glass melting apparatus according to claim 1, wherein the first brick is an electroformed zirconia brick.

4. the bottom wall of the dissolution tank further includes a third brick covering at least a portion of an upper surface of the second brick; The glass melting apparatus according to any one of claims 1 to 3, wherein the third brick is an electroformed brick.

5. The glass melting apparatus according to claim 4 , wherein the third brick is disposed farther from the electrode than the second brick when viewed from above.

6. the bottom wall of the dissolution tank includes a groove forming a step surface on an upper surface of the surface layer, a side surface of the groove is the step surface, and the through hole is formed in a bottom surface of the groove; the second brick protrudes above the bottom surface of the groove; 6. The glass melting apparatus according to claim 4, wherein the third brick includes a fitting portion that is fitted into the groove, and a pressing portion that presses an upper surface of the second brick.

7. The glass melting apparatus according to claim 6 , wherein two of the third bricks having a rectangular shape and two of the third bricks having a T-shape are interlocked with each other inside the groove when viewed from above.

8. Melting glass raw materials for the molten glass using the glass melting apparatus according to any one of claims 1 to 7; forming the molten glass; cooling the formed glass slowly; A method for producing glass, comprising:

9. A method for replacing molten glass obtained by the glass melting apparatus according to any one of claims 1 to 7, comprising the steps of: discharging the molten glass stored in the melting tank to the outside of the melting tank and lowering a liquid level of the molten glass stored in the melting tank; pouring a glass raw material for a second molten glass different from the molten glass into the inside of the melting tank and storing the second molten glass in the melting tank; When the liquid level of the second molten glass reaches a preset height, the supply of the refrigerant to the cooler is stopped and the electrode is inserted upward. The method for changing the base material of molten glass includes the steps of:

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