Glass melting apparatus and glass manufacturing method

Abstract

To provide a technology that improves heating power (W) for molten glass having high electrical resistivity.SOLUTION: A glass melting apparatus includes: a dissolver for storing a glass raw material and molten glass that is made by melting the glass raw material; and a plurality of electrodes for electrically heating the molten glass. The molten glass has an electrical resistivity of 0.5 Ωm or more at 1600°C. The plurality of electrodes forms an energization passage having a shortest distance of 1800 mm or less.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a glass melting apparatus and a glass manufacturing method.

Background Art

[0002] Patent Documents 1 and 2 describe an electric melting furnace that electrically heats molten glass. The electric melting furnace includes a flame space, an upper pool, and a lower pool in this order from the upper side to the lower side. When viewed from above, the upper pool is hexagonal, and molybdenum electrodes are provided near each vertex of the hexagon. Six molybdenum electrodes electrically heat the molten glass.

[0003] The electric melting furnace described in Patent Document 3 includes a plurality of electrodes on its bottom wall portion. The plurality of electrodes electrically heat the molten glass. This electric melting furnace is a fully electric melting furnace that melts glass raw materials only by electrically heating the molten glass. Patent Document 3 describes that the combustion heat of gas and electric heating may be used in combination to melt glass raw materials. Patent Documents 4 and 5 also describe the electric heating of molten glass.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0005] As shown in Figures 1 to 3, a melting tank 120 is known that is polygonal when viewed from above. Electrodes 130 are provided near each vertex of the polygon. Multiple electrodes 130 heat the molten glass by passing an electric current through them. When viewed from above, the multiple electrodes 130 form an electric current path 131 along the diagonal line passing through the center of the polygon.

[0006] Two electrodes 130 are electrically connected by wiring 132 to each current-carrying path 131. In Figures 1 to 3, for the sake of the drawings, only one of the multiple wirings 132 is shown. A transformer 133 is provided in the middle of each wiring 132. The transformer 133 applies an AC voltage to the multiple electrodes 130. The phase of the AC voltage is adjusted so that current flows through each current-carrying path 131.

[0007] AC voltage has an upper limit set for safety reasons. Therefore, the upper limit of the heating power for molten glass depends on the electrical resistance of the molten glass. Power (P) is the product of the square of the voltage (V) and the reciprocal of the electrical resistance (R) (1 / R) (P=V 2 This is because (R) is the case. The greater the electrical resistance of the molten glass, the lower the upper limit of the heating power for the molten glass.

[0008] Glass with higher electrical resistivity than typical soda-lime glass, such as alkali-free glass, is sometimes manufactured. When electrically heating molten glass with high electrical resistivity, using a long current path 131 as in the conventional method can result in excessively high electrical resistance (R), leading to insufficient heating power.

[0009] One aspect of this disclosure provides a technology for improving the heating power (W) of molten glass with high electrical resistivity. [Means for solving the problem]

[0010] A glass melting apparatus according to an aspect of the present disclosure includes a melting tank that houses a glass raw material and molten glass formed by melting the glass raw material, and a plurality of electrodes that electrically heat the molten glass. The molten glass has an electrical resistivity of 0.5 Ωm or more at 1600°C. The plurality of electrodes form an energization path having a shortest distance of 1800 mm or less. The melting tank comprises a first tank and a second tank positioned below the first tank. The first tank has a first side wall surrounding the molten glass, a first bottom wall supporting the molten glass from below, and a flow port formed in the first bottom wall. The second tank has a second side wall extending downward from the periphery of the flow port and a second bottom wall supporting the molten glass from below. When viewed from above, the first side wall is polygonal. When viewed from above, the plurality of electrodes form the current-carrying path along at least one side of the polygon.

Advantages of the Invention

[0011] According to an aspect of the present disclosure, by using an energization path having a shortest distance of 1800 mm or less, it is possible to improve the heating power (W) of molten glass having a high electrical resistivity.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is a plan view showing an electrode and an energization path according to a first reference example. [Figure 2] FIG. 2 is a plan view showing an electrode and an energization path according to a second reference example. [Figure 3] FIG. 3 is a plan view showing an electrode and an energization path according to a third reference example. [Figure 4] FIG. 4 is a cross-sectional view showing a glass melting apparatus according to an embodiment. [Figure 5] FIG. 5 is a plan view showing an electrode and an energization path according to an embodiment. [Figure 6] FIG. 6 is a plan view showing an electrode and an energization path according to a first modification. [Figure 7] FIG. 7 is a plan view showing an electrode and an energization path according to a second modification. [Figure 8] FIG. 8 is a plan view showing an electrode and an energization path according to a third modification. [Figure 9] FIG. 9 is a plan view showing an electrode and an energization path according to a fourth modification. [Figure 10] FIG. 10 is a plan view showing an electrode and an energization path according to a fifth modification. [Figure 11]FIG. 11 is a plan view showing an example of the inclination of the electrode as viewed from above. [Figure 12] FIG. 12 is a plan view showing an example of the angle formed by the first reference line and the electrode. [Figure 13] FIG. 13 is a cross-sectional view showing an example of the inclination of the electrode as viewed from the first direction. [Figure 14] FIG. 14 is a plan view showing an example of the angle formed by the second reference line and the electrode. [Figure 15] FIG. 15 is a plan view showing an example of the inclination of the electrode as viewed from the second direction.

Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and the description thereof may be omitted. In the specification, "~" indicating a numerical range means that the numerical values described before and after it are included as the lower limit value and the upper limit value.

[0014] Referring to FIG. 4, a glass melting apparatus 10 according to an embodiment will be described. The glass melting apparatus 10 manufactures molten glass G2 by melting a glass raw material G1. The glass raw material G1 is prepared by mixing a plurality of types of materials. The glass raw material G1 may contain a clarifying agent. The glass raw material G1 may contain glass cullet in order to recycle glass. The glass raw material G1 may be a powder raw material or a granulated raw material obtained by granulating the powder raw material. The glass raw material G1 is determined according to the composition of the glass.

[0015] The glass melting apparatus 10 includes a melting tank 20 that houses the glass raw material G1 and the molten glass G2 obtained by melting the glass raw material G1, and a plurality of electrodes 30 that electrically heat the molten glass G2. The glass raw material G1 is introduced from above with respect to the liquid surface LS of the molten glass G2 and forms a layer on the liquid surface LS. The glass raw material G1 is gradually melted by the heat transmitted from the molten glass G2.

[0016] The layer of glass raw material G1 preferably covers 80% or more of the liquid surface LS of the molten glass G2, and more preferably covers 90% or more of the liquid surface LS, in order to suppress the escape of heat or volatile components from the molten glass G2. Furthermore, the maximum surface temperature of the layer of glass raw material G1 is preferably 500°C or less, and more preferably 350°C or less.

[0017] The glass melting apparatus 10 is preferably an all-electric melting furnace that melts the glass raw material G1 by only electrically heating the molten glass G2. The all-electric melting furnace has only a plurality of electrodes 30 as a heat source for melting the glass raw material G1. The glass raw material G1 melts gradually due to the heat transferred from the molten glass G2. The electrodes 30 are not particularly limited, but for example, they are molybdenum electrodes.

[0018] The glass melting apparatus 10 does not necessarily have to be an all-electric melting furnace; the glass raw material G1 may be melted by a combination of electric heating of the molten glass G2 and combustion heat of a flammable gas or heavy oil. However, the ratio of electric heating to the amount of heat per unit time used to melt the glass raw material G1 is preferably 80% or more. An all-electric melting furnace is one where this ratio is 100%.

[0019] The larger the surface area LS of the molten glass G2, the greater the amount of glass raw material G1 that can be input per unit time, enabling mass production of molten glass G2. 2 The number N of the energizing paths 31 is preferably 0.4 or more. If the number N of the energizing paths 31 is 0.4 or more, sufficient heating power (W) can be obtained for the amount of glass raw material G1 input. The number N of the energizing paths 31 is 50 or less.

[0020] The melting tank 20 has, for example, a two-story structure (double-decker structure) and includes a first tank 21 and a second tank 22 located below the first tank 21. The first tank 21 has a first side wall 21a surrounding the molten glass G2, a first bottom wall 21b supporting the molten glass G2 from below, and a flow opening 21c formed through the first bottom wall 21b. The molten glass G2 moves from the first tank 21 to the second tank 22 through the flow opening 21c.

[0021] The second tank 22 has a second side wall 22a extending downward from the periphery of the flow opening 21c, and a second bottom wall 22b that supports the molten glass G2 from below. An outlet 23 for the molten glass G2 is provided in the second side wall 22a. The outlet 23 for the molten glass G2 may be provided in the second bottom wall 22b instead of the second side wall 22a.

[0022] Furthermore, the dissolution tank 20 does not necessarily have a double-decker structure, nor does it necessarily have a second tank 22. The dissolution tank 20 only needs to have a first tank 21. If the dissolution tank 20 does not have a second tank 22, a flow port 21c is not formed in the first bottom wall 21b. Also, if the dissolution tank 20 does not have a second tank 22, the outlet 23 for the molten glass G2 is provided in the first side wall 21a, but it may also be provided in the first bottom wall 21b.

[0023] The melting tank 20 is made of refractory bricks. Refractory bricks include, for example, zirconia-based electroformed bricks, alumina-based electroformed bricks, alumina-zirconia-based electroformed bricks, AZS (Al-Zr-Si)-based electroformed bricks, or densely fired bricks. The melting tank 20 may be composed of multiple types of refractory bricks.

[0024] The electrode 30 is rod-shaped and protrudes, for example, diagonally upward or directly upward (diagonally upward in Figure 4) from the first bottom wall 21b. Compared to the case where the electrode 30 protrudes horizontally inward from the first side wall 21a, current is more easily conducted throughout the entire vertical direction of the electrode 30, current concentration at the tip of the electrode 30 can be suppressed, and melting of the electrode 30 can be suppressed. The electrode 30 is positioned outside the flow opening 21c of the first bottom wall 21b. Therefore, the distance between the two electrodes 30 facing each other across the flow opening 21c is long.

[0025] When two electrodes 30 facing each other across the flow opening 21c form an electrical path, the electrical resistance of the electrical path (see electrical path 131 in Figures 1 to 3) becomes high. Therefore, as will be explained in more detail later, in this embodiment, the electrical path 31 is formed along the sides of the polygon drawn by the first side wall 21a when viewed from above (see Figures 5 to 10). This shortens the electrical path 31, reduces the electrical resistance of the electrical path 31, and improves the heating power of the molten glass G2.

[0026] Preferably, the electrode 30 protrudes diagonally upward from the first bottom wall 21b and is inclined to move away from the first side wall 21a as it extends upward. By positioning the upper end of the electrode 30 further away from the first side wall 21a than the lower end of the electrode 30, the flow of electricity through the first side wall 21a can be suppressed. As a result, the erosion rate of the first side wall 21a can be slowed down, and the lifespan of the dissolution tank 20 can be extended. This is particularly effective when the current path 31 is formed along the sides of the polygon formed by the first side wall 21a when viewed from above (see Figures 5 to 10).

[0027] Patent documents 1 and 2 describe inserting a rod-shaped electrode at an angle. However, in this embodiment, when viewed from above, the current path 31 is formed along at least one side of the polygon drawn by the first side wall 21a. This allows the current path 31 to be shortened, the electrical resistance of the current path 31 to be reduced, and the heating power of the molten glass G2 to be improved, compared to the case where the current path 131 is formed along the diagonal passing through the center of the polygon as shown in Figures 1 to 3.

[0028] However, when viewed from above, if the current path 31 is formed along at least one side of the polygon, the current will flow closer to the first side wall 21a compared to when the current path 131 is formed along the diagonal passing through the center of the polygon. If the current were to flow through the first side wall 21a, there is a risk that the heating power of the molten glass G2 would decrease.

[0029] By tilting the electrode 30 as in this embodiment, the current path 31 is separated from the first side wall 21a. This does not merely mimic known configurations (configurations in Patent Documents 1 and 2), but rather, when combined with configuring the current path 31 along the sides of the polygon, it fully demonstrates the effect of safely supplying high power, resulting in a greater effect than a simple combination.

[0030] As shown in Figure 4, a through hole 21d for inserting the electrode 30 is formed in the first bottom wall 21b. The through hole 21d is set to be inside the first side wall 21a and outside the second side wall 22a. Therefore, there are structural constraints on the position of the through hole 21d. The position of the lower end of the electrode 30 is determined by the position of the through hole 21d. Consequently, there are structural constraints on the distance between the lower end of the electrode 30 and the first side wall 21a. Therefore, in this embodiment, the upper end of the electrode 30 is set to be further away from the first side wall 21a than the lower end of the electrode 30.

[0031] An electrode holder 40 is provided in the insertion hole 21d. The electrode holder 40 holds the outer circumference of the electrode 30 and cools the electrode 30, thereby preventing the molten glass G2 from leaking out of the melting tank 20 through the insertion hole 21d. A coolant such as water is supplied to the electrode holder 40. The coolant dissipates the heat from the electrode holder 40 to the outside. The electrode holder 40 may also hold the lower end of the electrode 30. In addition, the electrode holder 40 does not protrude upward from the insertion hole 21d, but it may protrude.

[0032] Molten glass G2 has an electrical resistivity of 0.5 Ωm or higher at 1600°C. Alkali-free glass is an example of molten glass G2 with high electrical resistivity. Alkali-free glass is glass that does not substantially contain alkali metal oxides such as Na2O and K2O. Here, substantially free of alkali metal oxides means that the total amount of alkali metal oxides contained is 0.1% by mass or less.

[0033] Alkali-free glass, for example, contains 54% to 73% SiO2, 10% to 23% Al2O3, 0.1% to 12% B2O3, 0% to 12% MgO, 0% to 15% CaO, 0% to 16% SrO, 0% to 15% BaO, and a total of 8% to 26% MgO, CaO, SrO, and BaO. Here, B2O3, MgO, CaO, SrO, and BaO are optional components, not essential ones.

[0034] Furthermore, the electrical resistivity of molten glass G2 at 1600°C is preferably 2.5 Ωm or less.

[0035] Next, the electrodes 30 and the current-carrying paths 31 will be described with reference to Figures 5 to 10. Two electrodes 30 are electrically connected by wiring 32 in each current-carrying path 31. A transformer 33, for example, is provided in the middle of the wiring 32. The transformer 33 applies an AC voltage to the multiple electrodes 30. The phase of the AC voltage is adjusted so that current flows through each current-carrying path 31.

[0036] AC voltage has an upper limit set for safety reasons. Therefore, the upper limit of the heating power for molten glass G2 depends on the electrical resistance of molten glass G2. Power (P) is the product of the square of the voltage (V) and the reciprocal of the electrical resistance (R) (1 / R) (P=V 2 This is because (R) is the case. The greater the electrical resistance of the molten glass G2, the smaller the upper limit of the heating power for the molten glass G2 becomes.

[0037] Glass with higher electrical resistivity than typical soda-lime glass, such as alkali-free glass, can sometimes be manufactured. When electrically heating molten glass G2 with high electrical resistivity, using a long current path 131 (see Figures 1-3) as in the conventional method results in a high electrical resistance in the current path 131.

[0038] In this embodiment, the multiple electrodes 30 are located at the shortest distance L min (See Figure 11) This forms an energizing path 31 with a length of 1800 mm or less. This reduces the electrical resistance of the energizing path 31, allowing sufficient heating power to be obtained, and provides the shortest distance L minThe minimum distance L is preferably 1800 mm or less, and more preferably 1500 mm or less. min From the viewpoint of uniformity of the temperature history (hereinafter simply referred to as "temperature history") from the time the glass raw material G1 is introduced into the melting tank 20 until the molten glass G2 is removed from the melting tank 20, it is preferably 100 mm or more.

[0039] Furthermore, as shown in Figure 11, when the electrode 30 is tilted, the shortest distance L min L is the distance between the upper ends of the electrodes 30. In this case, the current path 31 is formed mainly on the straight line connecting the upper ends of the electrodes 30. On the other hand, when the electrodes 30 are standing vertically, the shortest distance L min This is the distance between two electrodes 30 at the same height. In this case, the current-carrying path 31 is formed along the entire vertical direction of the electrode 30.

[0040] As shown in Figures 5 to 10, the first side wall 21a is polygonal when viewed from above. The polygon is not limited to a hexagon (see Figures 5, 7, and 10), a heptagon (see Figure 9), or a dodecagon (see Figures 6 and 8). The polygon may be a triangle to a pentagon, an octagon to an eleven-sided polygon, or a polygon with 13 or more sides. The polygon may be an even-numbered or odd-numbered polygon. From the viewpoint of the symmetry of the temperature distribution of the molten glass G2, the polygon is preferably a regular polygon, or a regular polygon with chamfered corners (a polygon with alternating long and short sides (see Figure 8)). By chamfering the corners of the regular polygon, the area that cannot be heated by electricity (dead space) can be reduced. The polygon is preferably symmetrical with respect to the outlet 23.

[0041] Although not shown in the diagram, when viewed from above, if the first side wall 21a is a polygon, then the second side wall 22a is a similar, scaled-down version of the first side wall 21a and is also a polygon. When viewed from above, the center of the polygon drawn by the second side wall 22a coincides with the center of the polygon drawn by the first side wall 21a. Note that the first side wall 21a and the second side wall 22a do not have to be similar; for example, the first side wall 21a may be a dodecagon and the second side wall 22a may be a hexagon.

[0042] As shown in Figures 5 to 10, when viewed from above, the multiple electrodes 30 form a current-carrying path 31 along at least one side of the polygon. Compared to the case where a current-carrying path 131 is formed along a diagonal passing through the center of the polygon, as shown in Figures 1 to 3, the current-carrying path 31 can be shortened, the electrical resistance of the current-carrying path 31 can be reduced, and the heating power of the molten glass G2 can be improved.

[0043] In this specification, the current path 31 being aligned with one side of the polygon includes both the current path 31 being perfectly parallel to one side of the polygon and the current path 31 being inclined within a range of ±10° with respect to one side of the polygon. Compared to the case where the current path 31 is inclined beyond the above range with respect to one side of the polygon, it is easier to arrange multiple current paths 31 symmetrically.

[0044] As shown in Figures 7 to 10, when viewed from above, it is preferable that the multiple electrodes 30 form current-carrying paths 31 along each side of the polygon. Compared to the case where the current-carrying paths 31 do not follow the sides of the polygon, the areas where current heating cannot be conducted (dead spaces) can be reduced, and the uniformity of the temperature history can be improved.

[0045] As shown in Figure 10, it is preferable that the three electrodes 30 form two current-carrying paths 31 along at least one side (preferably each side) of the polygon. Not only can the current-carrying paths 31 be shortened, but the number of electrodes 30 and electrode holders 40 can be reduced compared to the case where four electrodes 30 form two current-carrying paths 31. As a result, the amount of refrigerant used can be reduced and the heating efficiency of the molten glass G2 can be improved.

[0046] As shown in Figures 5 to 10, it is preferable that the electrodes 30 be placed near each vertex of the polygon when viewed from above. Here, placing the electrodes 30 near each vertex means that, if the diameter of a circle with the same area as the polygon is taken as 100%, the center of the upper surface of the electrode 30 is placed within a range of 20% from each vertex. Placing the electrodes 30 near each vertex reduces areas that cannot be heated by current (dead space).

[0047] Next, the inclination of the electrode 30 will be explained with reference to Figures 4 and 11-15. As described above, as shown in Figure 4, the electrode 30 is rod-shaped and protrudes diagonally upward from the first bottom wall 21b, and is inclined to move away from the first side wall 21a as it goes upward. As shown in Figure 11, when viewed from above, it is preferable that the center of the upper surface of the electrode 30 is displaced toward the center P20 of the dissolution tank 20 compared to the center of the lower surface of the electrode 30.

[0048] As shown in Figure 12, when viewed from above, it is preferable that the angle α1 between the first reference line L1, which connects the center of the lower surface of electrode 30 and the center P20 of the dissolution tank 20, and the straight line PL, which connects the center of the lower surface of electrode 30 and the center of the upper surface of electrode 30, is within the range of ±5°. Furthermore, when viewed from above, the first reference line L1 coincides with the first vertical plane P1 described below.

[0049] As shown in Figure 13, when viewed from a first direction (arrow XIII direction) perpendicular to the first vertical plane P1 shown in Figure 12, it is preferable that the inclination angle β1 of the straight line PL connecting the center of the lower surface of electrode 30 and the center of the upper surface of electrode 30, with respect to the vertical line L3 passing through the center of the lower surface of electrode 30, is within the range of 5° to 45°.

[0050] As shown in Figure 14, when viewed from above, it is preferable that the first side wall 21a is polygonal, and the angle α2 between the second reference line L2, which is perpendicular to the side of the polygon closest to the center of the bottom surface of the electrode 30 and passes through the center of the bottom surface of the electrode 30, and the straight line PL connecting the center of the bottom surface of the electrode 30 and the center of the top surface of the electrode 30, is within the range of ±30°. Furthermore, when viewed from above, the second reference line L2 coincides with the second vertical plane P2 described below.

[0051] As shown in Figure 15, when viewed from a second direction (arrow XV direction) perpendicular to the second vertical plane P2 shown in Figure 14, it is preferable that the angle β2 between the inner wall surface of the first side wall 21a and the straight line PL connecting the center of the lower surface of the electrode 30 and the center of the upper surface of the electrode 30 is in the range of 5° to 60°. The inner wall surface of the first side wall 21a may be inclined outward as it goes upward.

[0052] Next, a glass manufacturing method will be described. The glass manufacturing method comprises producing molten glass G2 using a glass melting apparatus 10, and producing a glass article by shaping the molten glass G2 into a desired shape and cooling it. The glass article is, for example, a glass substrate for a display. However, the shape of the glass article is not limited to a plate shape.

[0053] The glass melting apparatus and glass manufacturing method described above are not limited to the embodiments described herein. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These also naturally fall within the technical scope of this disclosure. [Explanation of symbols]

[0054] 10 Glass melting apparatus 20 Dissolution tank 30 electrodes 31 Power supply path

Claims

1. A glass melting apparatus comprising a melting tank for containing glass raw materials and molten glass obtained by melting the glass raw materials, and a plurality of electrodes for electrically heating the molten glass, The molten glass has an electrical resistivity of 0.5 Ωm or more at 1600°C. Multiple electrodes form an energizing path with a minimum distance of 1800 mm or less. The dissolution tank comprises a first tank and a second tank located below the first tank. The first tank has a first side wall surrounding the molten glass, a first bottom wall supporting the molten glass from below, and a flow opening formed in the first bottom wall. The second tank has a second side wall extending downward from the periphery of the flow opening and a second bottom wall supporting the molten glass from below. When viewed from above, the first side wall is polygonal, A glass melting apparatus in which, when viewed from above, the plurality of electrodes form the current-carrying path along at least one side of the polygon.

2. Area of ​​the molten glass liquid surface: 1 m² ２ The glass melting apparatus according to claim 1, wherein the number of energizing paths for the glass is 0.4 or more.

3. The glass melting apparatus according to claim 1, wherein, when viewed from above, the three electrodes form two current-carrying paths along at least one side of the polygon.

4. The glass melting apparatus according to claim 3, wherein, when viewed from above, the electrodes are provided near each vertex of the polygon.

5. The glass melting apparatus according to claim 3, wherein the electrode is rod-shaped, protrudes diagonally upward from the first bottom wall, and is inclined to move away from the first side wall as it extends upward.

6. When viewed from a first direction perpendicular to the first vertical plane, the angle of inclination of the line connecting the center of the lower surface of the electrode and the center of the upper surface of the electrode, with respect to a vertical line passing through the center of the lower surface of the electrode, is in the range of 5° to 45°. The glass melting apparatus according to claim 5, wherein, when viewed from above, the first vertical plane coincides with a first reference line connecting the center of the lower surface of the electrode and the center of the melting tank.

7. When viewed from a second direction perpendicular to the second vertical plane, the angle between the inner wall surface of the first side wall and the straight line connecting the center of the lower surface of the electrode and the center of the upper surface of the electrode is in the range of 5° to 60°. The glass melting apparatus according to claim 5, wherein, when viewed from above, the first side wall is polygonal, and the second vertical plane coincides with a second reference line that is perpendicular to the side of the polygon closest to the center of the lower surface of the electrode and passes through the center of the lower surface of the electrode.

8. The glass melting apparatus according to claim 5, wherein, when viewed from above, the angle between the first reference line connecting the center of the lower surface of the electrode and the center of the melting tank and the straight line connecting the center of the lower surface of the electrode and the center of the upper surface of the electrode is within the range of ±5°.

9. The glass melting apparatus according to claim 5, wherein, when viewed from above, the first side wall is polygonal, and the angle between a second reference line perpendicular to the side of the polygon closest to the center of the lower surface of the electrode and passing through the center of the lower surface of the electrode, and a straight line connecting the center of the lower surface of the electrode and the center of the upper surface of the electrode, is within the range of ±30°.

10. The glass melting apparatus according to any one of claims 1 to 3, wherein the molten glass is alkali-free glass.

11. The glass melting apparatus according to any one of claims 1 to 3, wherein the ratio of the amount of electrical heating to the amount of heat per unit time used to melt the glass raw material is 80% or more.

12. The glass melting apparatus according to any one of claims 1 to 3, wherein the glass raw material covers 80% or more of the liquid surface of the molten glass.

13. The molten glass is manufactured using the glass melting apparatus described in any one of claims 1 to 3, A method for manufacturing glass, comprising: shaping the molten glass into a desired shape and cooling it to produce a glass article.

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