Method for manufacturing glass

Abstract

To provide a method for manufacturing glass that can readily remove bubbles from a molten glass.SOLUTION: A method for manufacturing glass includes an adjustment step (step S1) of adjusting a state of a molten glass that is obtained by melting a glass raw material. Conditions of the adjustment step of the step S1 satisfy a first condition that an upper atmosphere of the molten glass has an oxygen concentration of 3% or more and a second condition that an upper atmosphere of the molten glass has a pressure of 0.11 MPa or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing glass. [Background technology]

[0002] As described in Patent Document 1, a method for producing glass includes a step of melting glass raw materials to obtain molten glass. When the molten glass thus obtained contains bubbles, a step of removing the bubbles from the molten glass is required to prevent the bubbles from being mixed into glass products. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 054385 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, there is still room for improvement in terms of easily removing bubbles from molten glass. An object of the present invention is to provide a method for producing glass that makes it possible to easily remove bubbles from molten glass. [Means for solving the problem]

[0005] Various aspects of the glass manufacturing method that solves the above problems will be described. The glass manufacturing method of aspect 1 includes an adjusting step of adjusting the state of molten glass obtained by melting glass raw materials, and the conditions of the adjusting step satisfy a first condition that the oxygen concentration in the atmosphere above the molten glass is 3% or more and a second condition that the pressure of the atmosphere above the molten glass is 0.11 MPa or more.

[0006] The glass manufacturing method of aspect 2 may be the same as that of aspect 1, further comprising a bubble removal step of removing bubbles from the molten glass adjusted in the adjustment step, and the conditions of the bubble removal step may satisfy a third condition that the pressure of the atmosphere above the molten glass is lower than the pressure of the second condition, and a fourth condition that the temperature of the molten glass is higher than the temperature of the molten glass in the adjustment step.

[0007] In the method for producing glass of Aspect 3, in Aspect 2, the pressure of the third condition may be atmospheric pressure. In the glass manufacturing method of the fourth aspect, in the second aspect, the pressure of the third condition may be lower than atmospheric pressure.

[0008] In the glass manufacturing method of aspect 5, in any one of aspects 2 to 3, the maximum temperature of the molten glass in the adjusting step may be in the range of 1500°C or higher and 1649°C or lower, and the temperature of the fourth condition may be 1650°C or higher.

[0009] In the glass manufacturing method of Aspect 6, in any one of Aspects 1 to 5, the oxygen concentration of the first condition may be 22% or more. In the glass manufacturing method of aspect 7, in any one of aspects 1 to 6, the heating method used to heat the molten glass in the adjusting step includes at least one of an electric heating method in which the molten glass is heated by passing electricity through it, and a conductive heating method in which heat from a wall portion in contact with the molten glass is conducted to the molten glass, and the wall portion is heated by at least one of a first wall heating method in which the wall portion is heated by passing electricity through it, and a second wall heating method in which the wall portion is heated by a heating device, and the heating device may be at least one of a resistance heating device and an induction heating device.

[0010] In the method for producing glass of aspect 8, in any one of aspects 1 to 7, the glass may contain, in mass % calculated as oxides, 55 to 70% SiO2, 12 to 25% Al2O3, 0.1 to 15% B2O3, 0 to 8% MgO, 3 to 10% CaO, 0 to 8% SrO, and 0 to 10% BaO as a glass composition, and may be substantially free of alkali metal oxides.

[0011] In the glass manufacturing method of Aspect 9, in any one of Aspects 1 to 8, the molten glass may contain at least one selected from arsenic oxide, antimony oxide, tin oxide, and cerium oxide.

[0012] In the glass manufacturing method of Aspect 10, in any one of Aspects 1 to 9, the atmosphere above the molten glass in the adjusting step may contain at least one oxidizing gas selected from ozone, nitrogen oxides, and halides at a concentration of 21% or more.

[0013] In the glass manufacturing method of Aspect 11, in any one of Aspects 1 to 10, at least a part of the liquid surface of the molten glass in the adjusting step may be covered with a deposition layer of the glass raw material. [Effects of the Invention]

[0014] The present invention exhibits the effect of making it possible to easily remove bubbles from molten glass. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a flow diagram illustrating the glass manufacturing method according to this embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view showing a glass manufacturing apparatus. [Figure 3] FIG. 3 is a schematic front cross-sectional view showing a test apparatus used in a glass production test. [Figure 4] FIG. 4 is a schematic cross-sectional side view showing a test apparatus used in glass production tests. [Figure 5] FIG. 5 is a schematic cross-sectional view showing a modified example of a glass manufacturing apparatus. [Figure 6] FIG. 6 is a schematic cross-sectional view showing a modified example of a glass manufacturing apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of a glass manufacturing method will be described with reference to the drawings. Note that in the drawings, for the sake of convenience, some components may be shown exaggerated or simplified. Furthermore, the dimensional ratios of each part may differ from the actual ratios.

[0017] As shown in Fig. 1, the glass manufacturing method includes an adjusting step (step S1) of adjusting the state of molten glass obtained by melting glass raw materials, and further includes a bubble removing step (step S2) of removing bubbles from the molten glass adjusted in the adjusting step of step S1.

[0018] <Glass raw materials> Examples of glass raw materials include silica sand, lime, aluminum oxide, soda ash, boric acid, colemanite, kaolinite, pyrophyllite, calcium carbonate, dolomite, and zircon. The glass raw materials may contain recycled materials such as cullet and recycled glass fiber. When the glass raw materials contain cullet, the cullet content is preferably 50 mass% or less.

[0019] Examples of glasses obtained from glass raw materials include glass for fibers, alkali-free glass, soda glass, soda lime glass, borosilicate glass, aluminosilicate glass, alkali-containing glass, etc. Examples of glasses for fibers include E glass (glass with an alkali content of 2% or less), D glass (low dielectric constant glass), NE glass (low dielectric constant glass), AR glass (alkali-resistant glass), C glass (acid-resistant glass), S glass (high strength, high elastic modulus glass), R glass (high strength, high elastic modulus glass), H glass (high dielectric constant glass), etc.

[0020] An example of the glass is one containing, in mass % oxide equivalent, 55 to 70% SiO2, 12 to 25% Al2O3, 0.1 to 15% B2O3, 0 to 8% MgO, 3 to 10% CaO, 0 to 8% SrO, and 0 to 10% BaO, and substantially no alkali metal oxides.

[0021] <Adjustment process in glass manufacturing method> The conditions for the adjusting step of step S1 satisfy a first condition, which is a condition for the oxygen concentration of the atmosphere above the molten glass, and a second condition, which is a condition for the pressure of the atmosphere above the molten glass. The first condition, the oxygen concentration, is 3% or more. The second condition, the pressure, is 0.11 MPa or more.

[0022] The unit % for the oxygen concentration in the first condition indicates volume %. Hereinafter, the unit % for the gas concentration always indicates volume %. The oxygen concentration in the first condition is preferably 21% or more, more preferably 22% or more. The oxygen concentration in the first condition is, for example, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or 98% or more. By increasing the oxygen concentration in the first condition in this way, it is possible to obtain molten glass in a state in which bubbles are more easily removed. The upper limit of the oxygen concentration in the first condition is, for example, 100% or less.

[0023] The atmosphere above the molten glass in the adjusting step of step S1 may contain gases other than oxygen, such as nitrogen, carbon dioxide, ozone, nitrogen oxides, halides, etc. When the atmosphere above the molten glass in the adjusting step of step S1 contains at least one oxidizing gas selected from ozone, nitrogen oxides, and halides, the concentration of the oxidizing gas is preferably 21% or more. In this case, molten glass in a state in which bubbles are more easily removed can be obtained.

[0024] Examples of nitrogen oxides include nitric oxide and nitrogen dioxide. Examples of halides include hydrogen fluoride, hydrogen chloride, hydrogen bromide, and hydrogen iodide. The molten glass in the adjusting step of step S1 preferably contains at least one oxide selected from arsenic oxide, antimony oxide, tin oxide, and cerium oxide. These oxides are based on the blending of a fining agent. By including the oxide in the molten glass, it is possible to obtain molten glass in a state in which bubbles are more easily removed.

[0025] More specifically, the oxidation-reduction reaction of the oxide is represented by the following reaction formulas (1) to (4). As2O5⇔As2O3+O2↑…(1) Sb2O5⇔Sb2O3+O2↑…(2) SnO⇔SnO+1 / 2·O↑…(3) CeO2⇔1 / 2·Ce2O3+1 / 4·O2↑…(4) In the adjusting step of step S1, oxygen supplied to the molten glass prioritizes the reactions that proceed from right to left in the above reaction formulas (1) to (4), i.e., the oxidation reaction of oxides. In the molten glass prepared in the adjusting step of step S1, the oxides used as fining agents are more likely to be maintained in an oxidized state. Therefore, when the temperature of the molten glass is increased, the amount of oxygen generated as the reduction reaction of the oxides used as fining agents progresses can be increased. In this way, supplying oxygen to the molten glass in the adjusting step of step S1 can enhance the fining effect of the oxides used as fining agents. The total content of the fining agents in the molten glass is preferably in the range of 0.001% by mass or more and 1% by mass or less. From the viewpoint of reducing environmental impact, it is more preferable to use SnO2 alone as the fining agent. The content of SnO2 in the molten glass is preferably in the range of 0.05% by mass or more and 0.5% by mass or less, more preferably in the range of 0.1% by mass or more and 0.4% by mass or less.

[0026] The pressure P2 of the second condition described above in the adjusting process of step S1 is an absolute pressure. The pressure P2 of the second condition is preferably 0.3 MPa or more. The pressure P2 of the second condition is, for example, 0.35 MPa or more, 0.4 MPa or more, 0.45 MPa or more, or 0.5 MPa or more. By increasing the pressure of the second condition, molten glass can be obtained in a state in which bubbles are more easily removed. The upper limit of the pressure P2 of the second condition is, for example, 1.0 MPa or less, 0.8 MPa or less.

[0027] The maximum temperature T of the molten glass in the adjustment process of step S1 max is preferably in the range of 1500°C or higher and 1649°C or lower. The heating method used to heat the molten glass in the adjusting process of step S1 preferably includes at least one of an electric heating method and a conduction heating method. The electric heating method is a method of heating the molten glass by passing electricity through it. The conduction heating method is a method of conducting heat from a wall portion in contact with the molten glass to the molten glass.

[0028] The wall portion in contact with the molten glass is heated by at least one of a first wall heating method in which the wall portion is heated by passing electricity through the wall portion, and a second wall heating method in which the wall portion is heated by a heating device. The heating device used in the second wall heating method includes at least one of a resistance heating device and an induction heating device.

[0029] It is preferable that at least a part of the liquid surface of the molten glass in the adjusting step of step S1 is covered with a sediment layer where the glass frit is deposited. The entire liquid surface of the molten glass in the adjusting step of step S1 may be covered with a sediment layer. Such a sediment layer has gaps between the glass frit particles, so that an oxygen-containing gas can come into contact with the molten glass that is the layer below the sediment layer. The liquid surface of the molten glass in the adjusting step of step S1 may have a part covered with the sediment layer and an exposed part. In this case, the step of melting the glass frit and the adjusting step of step S1 can be carried out efficiently.

[0030] <Air bubble removal process in glass manufacturing process> The conditions for the bubble removal step of step S2 satisfy a third condition, which is a pressure condition for the atmosphere above the molten glass, and a fourth condition, which is a temperature condition for the molten glass. The pressure for the third condition is lower than the pressure for the second condition. The temperature for the fourth condition is higher than the temperature of the molten glass in the adjusting step of step S1. The heating method for the molten glass in the bubble removal step of step S2, like the heating method for the adjusting step of step S1, preferably includes at least one of the above-mentioned electrical heating method and conductive heating method.

[0031] If the pressure of the second condition is P2 [MPa] and the pressure of the third condition is P3 [MPa], the difference ΔP [MPa] between the pressure P2 [MPa] and the pressure P3 [MPa] (ΔP=P2-P3) is preferably 0.05 or more, more preferably 0.10 or more, and even more preferably 0.15 or more. The pressure of the third condition is preferably, for example, atmospheric pressure or a pressure lower than atmospheric pressure.

[0032] In the bubble removal step of step S2, the gas composition of the atmosphere above the molten glass is not particularly limited. The bubble removal step of step S2 can be performed, for example, in air. The bubble removal step of step S2 can also be performed in an atmosphere with substantially the same gas composition as the adjustment step of step S1.

[0033] The maximum temperature of the molten glass in the adjustment process of step S1 is T max [°C], and the temperature of the fourth condition of the bubble removal process in step S2 is T4 [°C]. max +5 or more is preferable, and T max +10 or more, and more preferably T max +50 or higher. The temperature T4 of the fourth condition is preferably 1650° C. or higher. The upper limit of the temperature T4 of the fourth condition is, for example, 1800° C. or lower.

[0034] <Glass manufacturing equipment> Next, the glass manufacturing apparatus will be described. As shown in Fig. 2, glass manufacturing apparatus 11 includes a melting furnace 12, a fining vat 13, and a molten glass flow path 14. Melting furnace 12 includes an inlet 12a for introducing glass raw material G1 and a first outlet 12b for discharging molten glass G2 into molten glass flow path 14. Glass manufacturing apparatus 11 includes a gas flow path pipe 15 for adjusting the state (composition and pressure) of gas within melting furnace 12. Glass manufacturing apparatus 11 includes a gas supply source (not shown) for supplying gas of a predetermined composition and pressure to gas flow path pipe 15.

[0035] The inlet 12a and the first outlet 12b are provided, for example, on side walls facing each other. A supply device (not shown) is connected to the inlet 12a. The supply device supplies the glass frit G1 to the inlet 12a. An example of the supply device is a screw feeder. The supply device may also be a vibration feeder. The inlet 12a is arranged so as to supply the glass frit G1 onto the molten glass G2. The layout of the inlet 12a, the first outlet 12b, etc. described above is an example, and can be changed as appropriate depending on the shape of the melting furnace 12, etc.

[0036] The walls of the melting furnace 12 are made of, for example, a refractory material. More specifically, the walls of the melting furnace 12 include a bottom wall, side walls, and a top wall. Examples of refractories that make up the walls include electrocast bricks and fired bricks. Examples of electrocast bricks include zirconia-based electrocast bricks, alumina-based electrocast bricks, alumina-zirconia-based electrocast bricks, and alumina-zirconia-silica-based electrocast bricks. Examples of fired bricks include dense zircon bricks, dense chrome bricks, alumina-zircon bricks, and mullite bricks. The melting furnace 12 is configured to be heated by the heating method described above.

[0037] The fining vat 13 is equipped with an inlet 13a through which the molten glass G2 flows in from the molten glass flow path 14, and a second outlet 13b through which the molten glass G2 flows out. The inlet 13a and the second outlet 13b are provided on side walls facing each other. The fining vat 13 can be made of, for example, a refractory material, platinum, a platinum alloy, or the like. The fining vat 13 is equipped with a heating device (not shown). The fining vat 13 is configured so that it can be heated by the heating method described above. The fining vat 13 is configured so that the pressure within the fining vat 13 can be adjusted. For example, by connecting a pressure reducing pump to the fining vat 13, it is possible to set the pressure within the fining vat 13 lower than the pressure outside the fining vat 13.

[0038] Molten glass flow path 14 transfers molten glass G2 from melting furnace 12 to refining vat 13. Glass manufacturing apparatus 11 of this embodiment includes first flow rate control unit 16a that controls the flow rate of molten glass G2 flowing out of melting furnace 12 and second flow rate control unit 16b that controls the flow rate of molten glass G2 flowing out of refining vat 13.

[0039] The adjusting step of step S1 can be performed in melting furnace 12. The bubble removing step of step S2 can be performed in refining vat 13. Furthermore, the duration of the adjusting step of step S1 can be adjusted by controlling the flow rate of molten glass G2 flowing out of melting furnace 12 with first flow rate control unit 16a. Furthermore, the duration of the bubble removing step of step S2 can be adjusted by controlling the flow rate of molten glass G2 flowing out of refining vat 13 with second flow rate control unit 16b.

[0040] The obtained glass can be formed into shapes such as plates, fibers, tubes, blocks, containers, etc. Examples of glass forming methods include the downdraw method, rollout method, float method, blow molding method, press molding method, fiber forming method, and Danner method. Examples of downdraw methods include the overflow downdraw method and the slot downdraw method.

[0041] <Test example> Next, a test example will be described. (Test Example 1-1) In Test Example 1-1, a glass having a predetermined composition was first prepared. The glass was prepared by melting glass raw materials, crushing and classifying them into particles of 2.0 mm or more and 5.6 mm or less, and then washing them. The glass contained, in mass % oxide equivalent, 59% SiO2, 19% Al2O3, 6.5% BO3, 2.5% MgO, 6.5% CaO, 0.5% SrO, and 6% BaO, and was substantially free of alkali metal oxides.

[0042] 3 and 4 show a test apparatus 17 used in Test Example 1-1. The test apparatus 17 includes a heating furnace 18 and a platinum crucible 19 placed in the heating furnace 18. The heating furnace 18 includes a furnace wall 18a and a heater 18b. The test apparatus 17 includes a gas flow pipe 20 for adjusting the state (composition and pressure) of the gas in the heating furnace 18. The test apparatus 17 includes a gas supply source (not shown) for supplying gas of a predetermined composition and pressure to the gas flow pipe 20. The test apparatus 17 includes a pressure-resistant container (not shown) that covers the heating furnace 18, and is configured so that the pressure in the heating furnace 18 can be adjusted.

[0043] In the production of the glass of Test Example 1-1, first, about 100 g of glass having the above composition was placed in platinum crucible 19 and heated using heating furnace 18 at a furnace temperature of 1500°C for 30 minutes to obtain molten glass. In the process of obtaining molten glass in platinum crucible 19 in this manner, an adjusting step of step S1 was performed. The oxygen concentration in the adjusting step of step S1 was 21%, which satisfied the first condition above. The gas in the adjusting step of step S1 contained nitrogen as a base gas other than oxygen. The pressure in the adjusting step of step S1 was 0.3 MPa, which satisfied the second condition above.

[0044] Next, the temperature inside the furnace was maintained at 1500°C, and the atmospheric pressure above the molten glass was changed to standard atmospheric pressure. Subsequently, the temperature inside the furnace was increased to 1650°C, and the molten glass was heated at the furnace temperature of 1650°C for 10 minutes, thereby performing the bubble removal process of step S2. The pressure in the bubble removal process of step S2 was standard atmospheric pressure, which satisfied the third condition above. The temperature in the bubble removal process of step S2 was 1650°C, which satisfied the fourth condition above. Next, the molten glass obtained in the bubble removal process of step S2 was cooled to obtain a block of glass.

[0045] (Test Examples 1-2 and 1-3) In Test Examples 1-2 and 1-3, glasses were obtained in the same manner as in Test Example 1-1, except that the oxygen concentration and pressure in the adjustment process of step S1 were changed as shown in Table 1. In Test Examples 1-2 and 1-3, the oxygen concentration and pressure in the adjustment process of step S1 satisfied the first and second conditions, respectively.

[0046] (Test Examples 2-1 to 2-3) In Test Examples 2-1 to 2-3, glasses were obtained in the same manner as in Test Example 1-1, except that the oxygen concentration and pressure in the preparation step were changed as shown in Table 2.

[0047] (bubble number density) The glass blocks obtained in each test example were processed into disks with a diameter of 40 mm and a thickness of 9 mm, and the surfaces were mirror-finished to prepare samples for measuring the number of bubbles. The number of bubbles contained in each test example sample was measured using an image analyzer. The bubble number density, which is the number of bubbles per 1 kg of glass, was calculated from the total sample mass and the number of bubbles measured. The results are shown in Tables 1 and 2. The bubble number densities shown in Tables 1 and 2 are values rounded to the nearest 1,000.

[0048] [Table 1]

[0049] [Table 2] As shown in Table 1, the number density of bubbles in the samples of Test Examples 1-1 to 1-3 was 3000 [pieces / kg] or less. As shown in Table 2, Test Example 2-1 did not satisfy either the first or second condition in the preparation step. Test Example 2-2 satisfied the second condition but did not satisfy the first condition. Test Example 2-3 satisfied the first condition but did not satisfy the second condition. The number density of bubbles in the samples of Test Examples 2-1 to 2-3 was higher than the number density of bubbles in the samples of Test Examples 1-1 to 1-3.

[0050] <Actions and Effects of the Embodiment> Next, the operation and effects of the embodiment will be described. (1) The method for producing glass includes an adjusting step (step S1) for adjusting the state of molten glass G2 obtained by melting glass raw material G1. The conditions for the adjusting step of step S1 satisfy a first condition that the oxygen concentration in the atmosphere above the molten glass G2 is 3% or more and a second condition that the pressure of the atmosphere above the molten glass G2 is 0.11 MPa or more. According to this method, in the adjusting step of step S1, the amount of dissolved oxygen in the molten glass G2 can be increased compared to when the atmosphere above the molten glass G2 does not contain oxygen. The oxygen in the molten glass G2 expands bubbles in the step of removing bubbles in the molten glass G2. This increases the floating speed of bubbles in the molten glass G2. Therefore, it becomes possible to easily remove bubbles in the molten glass G2.

[0051] (2) The glass manufacturing method further includes a bubble removal step (step S2) for removing bubbles from the molten glass G2 prepared in the preparation step of step S1. The conditions for the bubble removal step of step S2 satisfy a third condition that the pressure of the atmosphere above the molten glass G2 is lower than the pressure of the second condition, and a fourth condition that the temperature of the molten glass G2 is higher than the temperature of the molten glass G2 in the preparation step of step S1.

[0052] By subjecting the molten glass G2 after the adjusting step of step S1 to the bubble removing step of step S2 as described above, for example, it becomes possible to easily remove bubbles in the molten glass G2.

[0053] (3) The molten glass G2 in the adjusting step of step S1 preferably contains at least one selected from arsenic oxide, antimony oxide, tin oxide, and cerium oxide. In this case, the oxygen supplied to the molten glass G2 in the adjusting step S1 can enhance the fining effect of the oxides, thereby making it possible to more easily remove bubbles from the molten glass G2.

[0054] (4) The atmosphere above the molten glass G2 in the adjusting step S1 preferably contains at least one oxidizing gas selected from ozone, nitrogen oxides, and halides at a concentration of 21% or more. In this case, the oxidizing gas can expand bubbles in the molten glass G2, thereby promoting the floating of bubbles in the molten glass G2. Therefore, bubbles in the molten glass G2 can be easily removed.

[0055] (5) In the preparation step of step S1, at least a part of the liquid surface of the molten glass G2 may be covered with a sediment layer formed by the accumulation of the glass frit G1. In this case, by simultaneously performing the preparation step of step S1 and the melting step of melting the glass frit G1, it is possible to simplify, for example, the glass manufacturing equipment. When the total area of the liquid surface of the molten glass G2 is taken as 100%, the area of the liquid surface covered with the sediment layer is preferably 80% or more, more preferably 90% or more. The area of the liquid surface covered with the sediment layer may be 100%.

[0056] <Example of change> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0057] A glass manufacturing method can also be carried out using a glass manufacturing apparatus 21 shown in FIG. 5. The glass manufacturing apparatus 21 shown in FIG. 5 includes a metal container 22. The metal container 22 is sometimes called a pot furnace. Examples of the metal for the container 22 include platinum and platinum alloys. The container 22 is configured so that it can be heated by the heating method described above. The glass manufacturing apparatus 21 includes a gas flow path 23 for adjusting the state (composition and pressure) of the gas in the container 22. The glass manufacturing apparatus 21 includes a flow rate control unit 24 for controlling the flow rate of the molten glass G2 flowing out of the container 22. In this glass manufacturing apparatus 21, the adjustment process of step S1 and the bubble removal process of step S2 can be performed in the same container 22 by adjusting the pressure in the container 22 and the heating temperature of the container 22.

[0058] A glass manufacturing method can also be carried out using glass manufacturing apparatus 25 shown in Fig. 6. Glass manufacturing apparatus 25 shown in Fig. 6 includes a melting furnace 12, a fining vat 13, and a molten glass flow path 26 connecting melting furnace 12 and fining vat 13. Melting furnace 12 and fining vat 13 are configured similarly to melting furnace 12 and fining vat 13 in the above embodiment. Molten glass flow path 26 includes upstream inclined flow path 26a that slopes downward toward the downstream side, downstream inclined flow path 26b that slopes upward toward the downstream side, and horizontal flow path 26c that connects upstream inclined flow path 26a and downstream inclined flow path 26b. Glass manufacturing apparatus 25 includes a gas supply unit 27 that supplies gas into horizontal flow path 26c.

[0059] The adjusting step of step S1 can be performed in melting furnace 12 of glass manufacturing apparatus 25. Molten glass G2 adjusted in the adjusting step of step S1 is transferred to fining vat 13 through molten glass flow path 26. The bubble removal step of step S2 can be performed in fining vat 13. In this glass manufacturing apparatus 25, by supplying gas from gas supply unit 27 into horizontal flow path 26c of molten glass flow path 26, the gas can be bubbled into molten glass G2 passing through horizontal flow path 26c.

[0060] For example, in a flow path located at a height lower than the inner bottom surface of the melting furnace 12, such as the horizontal flow path 26c, the pressure applied to the molten glass G2 due to its own weight is increased. By bubbling an oxygen-containing gas into such molten glass G2, the amount of dissolved oxygen in the molten glass G2 can be easily increased. The gas supplied from the gas supply unit 27 is preferably a gas having an oxygen concentration of 3% or more. In this case, it is possible to further increase the amount of oxygen dissolved in the molten glass G2 adjusted in the adjustment process of step S1. That is, the amount of dissolved oxygen in the molten glass G2 can be further increased. This further enhances the effect described in section (1) above. The oxygen concentration of the gas supplied from the gas supply unit 27 is more preferably 21% or more, even more preferably 22% or more, and most preferably 98% or more.

[0061] Molten glass G2 may contain inorganic salts such as Glauber's salt and sodium chloride as fining agents. The fining tank 13 may be equipped with a stirring device that improves the uniformity of the molten glass G2.

[0062] A burner may be used to heat the molten glass G2. However, from the viewpoint of easily stabilizing the oxygen concentration under the first condition in step S1, the pressure under the second condition, and the pressure under the third condition in step S2, it is preferable to heat the molten glass G2 without using a burner. [Explanation of symbols]

[0063] G1...glass raw material G2...molten glass

Claims

1. an adjusting step of adjusting the state of molten glass obtained by melting glass raw materials, The conditions of the adjusting step include a first condition that the oxygen concentration of the atmosphere above the molten glass is 3% or more; a second condition that the pressure of the atmosphere above the molten glass is 0.11 MPa or more.

2. a bubble removal step of removing bubbles in the molten glass adjusted in the adjusting step, The conditions of the bubble removal step include a third condition in which the pressure of the atmosphere above the molten glass is lower than the pressure under the second condition; The method for producing glass according to claim 1 , wherein a fourth condition is satisfied in which the temperature of the molten glass is higher than the temperature of the molten glass in the adjusting step.

3. The method for producing glass according to claim 2 , wherein the pressure of the third condition is atmospheric pressure.

4. The method for producing glass according to claim 2 , wherein the pressure of the third condition is lower than atmospheric pressure.

5. the maximum temperature of the molten glass in the adjusting step is within a range of 1500°C or higher and 1649°C or lower; The method for producing glass according to claim 2 , wherein the temperature of the fourth condition is 1650° C. or higher.

6. The method for producing glass according to claim 1 , wherein the oxygen concentration of the first condition is 22% or more.

7. a heating method used to heat the molten glass in the adjusting step includes at least one of an electric heating method in which the molten glass is heated by passing electricity through the molten glass and a conduction heating method in which heat from a wall portion in contact with the molten glass is conducted to the molten glass, The wall portion is heated by at least one of a first wall portion heating method in which the wall portion is heated by passing electricity through the wall portion and a second wall portion heating method in which the wall portion is heated by a heating device, The method for producing glass according to claim 1 , wherein the heating device is at least one of a resistance heating device and an induction heating device.

8. The glass has a glass composition of SiO in terms of oxide mass %. ２ :55-70%, Al ２ O ３ : 12-25%, B ２ O ３ 2. The method for producing glass according to claim 1, wherein the glass contains 0.1 to 15% of Al, 0 to 8% of MgO, 3 to 10% of CaO, 0 to 8% of SrO, and 0 to 10% of BaO, and is substantially free of alkali metal oxides.

9. 2. The method for producing glass according to claim 1, wherein the molten glass contains at least one selected from the group consisting of arsenic oxide, antimony oxide, tin oxide, and cerium oxide.

10. 2. The method for producing glass according to claim 1, wherein the atmosphere above the molten glass in the adjusting step contains at least one oxidizing gas selected from ozone, nitrogen oxides, and halides at a concentration of 21% or more.

11. The method for producing glass according to claim 1 , wherein at least a portion of the liquid surface of the molten glass in the adjusting step is covered with a deposition layer formed by deposition of the glass raw materials.

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