Manufacturing method for glass articles

Abstract

To provide a method for manufacturing glass articles using the cold-top melting method, which allows for control of the equilibrium raw material input rate and minimizes the occurrence of unmelted glass raw materials. [Solution] A method for manufacturing a glass article, comprising using glass raw materials containing silica sand A and silica sand B, and melting the glass raw materials by a cold-top melting method, A method for manufacturing glass articles, wherein the volume-based median diameter of silica sand A is greater than the volume-based median diameter of silica sand B, the content of silica sand B relative to the total content of silica sand A and silica sand B is adjusted to a range of 1 to 99% by mass, and silica sand A and silica sand B satisfy the following requirements 1 and 2. Requirement 1: The median diameter based on volume of silica sand A and the median diameter based on volume of silica sand B are both 300 μm or less. Requirement 2: The value obtained by subtracting the volume-based median diameter of silica sand B from the volume-based median diameter of silica sand A is 35 μm or more.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing glass articles. More specifically, this invention relates to a method for manufacturing glass articles by a cold-top melting method. [Background technology]

[0002] Methods for melting glass raw materials when manufacturing glass articles include heating the glass raw materials in a molten tank with a burner or the like, and heating the glass by Joule heating generated by passing an electric current through it. In particular, a melting furnace that uses only the heat generated by passing electricity through the glass to melt it is also called an all-electric melting furnace. All-electric melting furnaces are preferable because they have high thermal efficiency and reduce the amount of energy used during manufacturing. Furthermore, as a method for melting glass using an all-electric melting furnace, the cold-top melting method is known, in which the glass is melted while the surface of the molten glass is covered with solid glass raw material.

[0003] One example of a method for manufacturing glass articles using an all-electric melting furnace is the method using the electric melting furnace described in Patent Document 1. Paragraph 0030 of Patent Document 1 discloses that when manufacturing glass articles using the electric melting furnace described in Patent Document 1, it may be a cold-top type in which the entire molten glass is covered with glass raw material. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-080076 [Overview of the project] [Problems that the invention aims to solve]

[0005] In conventional cold-top melting methods, such as those described in Patent Document 1, the glass raw material is generally melted by the heat from the molten glass, which is melted by applying an electric current, and the glass raw material is introduced from above the molten glass raw material to replenish it. The molten glass is then discharged from the melting furnace at a predetermined rate and used for subsequent clarification processes, etc. In the cold-top melting method, a layer of unmelted glass raw material (hereinafter also referred to as the "blanket") placed above the molten glass suppresses heat dissipation from the molten glass, allowing the glass to be melted in a state of high thermal efficiency.

[0006] As mentioned above, blanket thickness is an important control factor in the cold-top melting method. Generally, blanket thickness is determined by the balance between the blanket melting rate and the rate at which glass raw materials are fed into the blanket. Therefore, when controlling the blanket thickness to be constant, it is usually necessary to control the blanket melting rate and the rate at which glass raw materials are fed into the blanket to be in balance. Here, the blanket melting rate can be said to be equal to the discharge rate of molten glass when the amount of molten glass in the melting furnace is kept constant. Considering the above points, when controlling the blanket thickness to be constant, it is usually necessary to control the rate at which glass raw materials are fed into the furnace and the discharge rate of molten glass to be in balance. In other words, to control the thickness of the blanket to a predetermined thickness, it is usually necessary to control the rate at which the glass raw material is fed and the rate at which the molten glass is discharged to predetermined values. As described above, the rate at which the glass raw material is fed (i.e., the rate at which the molten glass is discharged to an equal value) at which the thickness of the blanket is constant is referred to in this specification as the "equilibrium raw material feeding rate".

[0007] On the other hand, in cold-top melting operations, for example, to melt glass of different compositions, it may be necessary to control the temperature of the molten glass in the melting furnace. To address the above requirements, one possible method is to increase the amount of heat generated by increasing the current flow, thereby raising the temperature of the molten glass. However, as the temperature of the molten glass rises, the thickness of the blanket decreases, increasing heat dissipation from the molten glass and making it difficult to maintain the temperature of the molten glass. Therefore, raising the temperature of the molten glass is generally not easy. Furthermore, adjusting the amount of current as described above often requires tap switching, and since this can cause significant fluctuations in kiln conditions due to the interruption of power supply, there was a need for a method to control the temperature of molten glass by different means.

[0008] On the other hand, in the operation of the cold-top melting method, it may be necessary to control the amount of molten glass discharged. In response to the above requirements, simply reducing the amount of molten glass discharged would, for example, decrease the thickness of the blanket, leading to increased heat dissipation from the molten glass and making it difficult to maintain the temperature of the molten glass. Furthermore, adjusting the amount of electricity supplied, as described above, often requires construction work such as tap switching, and can also cause significant fluctuations in kiln conditions due to the interruption of power supply, thus requiring a different method.

[0009] To meet the above requirements, it is necessary to control the blanket thickness simultaneously with controlling at least one of the following: controlling the temperature of the molten glass and controlling the amount of molten glass discharged. However, as mentioned above, when controlling the blanket thickness to a predetermined thickness, there is usually an equilibrium raw material input rate corresponding to that thickness. Therefore, it is generally difficult to control the blanket thickness while simultaneously controlling the discharge rate of molten glass. Furthermore, since the equilibrium raw material input rate changes depending on the temperature of the molten glass, it is generally difficult to control the blanket thickness while simultaneously controlling the temperature of the molten glass. For the reasons stated above, in the cold-top melting method, there was a need for a method to control the equilibrium raw material input rate independently of controlling the blanket thickness.

[0010] In addition, when melting glass raw materials by the cold top melting method, it is required that there is no unmelted glass raw material remaining.

[0011] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing a glass article in which the equilibrium raw material input rate can be controlled and the occurrence of unmelted glass raw material is less likely to occur in the cold top melting method.

Means for Solving the Problems

[0012] As a result of intensive studies on the above problems, the present inventors have found that by using two types of silica sands that meet predetermined requirements as the silica sand used as the glass raw material and adjusting the mixing ratio thereof, the above equilibrium raw material input rate can be controlled. In addition, by meeting predetermined requirements regarding the silica sand, it has been found that no unmelted glass raw material occurs.

[0013] That is, the inventors have found that the above problems can be solved by the following configuration. 〔1〕 A method for manufacturing a glass article, comprising using a glass raw material containing silica sand A and silica sand B and melting the glass raw material by the cold top melting method, where the median diameter of silica sand A on a volume basis is larger than the median diameter of silica sand B on a volume basis, adjusting the content of silica sand B with respect to the total content of silica sand A and silica sand B within a range of 1 to 99% by mass, and the silica sand A and the silica sand B satisfy the following requirement 1 and requirement 2. Requirement 1: The median diameter of silica sand A on a volume basis and the median diameter of silica sand B on a volume basis are both 300 μm or less. Requirement 2: The value obtained by subtracting the median diameter of silica sand B on a volume basis from the median diameter of silica sand A on a volume basis is 35 μm or more. 〔2〕 The method for manufacturing a glass article according to 〔1〕, wherein the content of silica sand B with respect to the total content of silica sand A and silica sand B is adjusted within a range of 5 to 95% by mass. [3] The method for manufacturing a glass article according to [1] or [2], wherein the content of silica sand B is adjusted to a range of 10 to 90% by mass relative to the total content of silica sand A and silica sand B. [4] A method for manufacturing a glass article as described in any one of [1] to [3], which further satisfies requirement 1-1 below. Requirement 1-1: The median diameter of silica sand A, based on volume, is 100-300 μm, and the median diameter of silica sand B, based on volume, is 20-150 μm. [5] A method for manufacturing a glass article as described in any one of [1] to [4], which further satisfies requirement 2-1 below. Requirement 2-1: The value obtained by subtracting the volume-based median diameter of silica sand B from the volume-based median diameter of silica sand A is 50 μm or more. [6] A method for manufacturing a glass article as described in any one of [1] to [5], which further satisfies requirement 2-2 below. Requirement 2-2: The value obtained by subtracting the volume-based median diameter of silica sand B from the volume-based median diameter of silica sand A is 60 μm or more. [7] A method for manufacturing a glass article as described in any one of [1] to [6], which further satisfies requirement 2-3 below. Requirement 2-3: The value obtained by subtracting the volume-based median diameter of silica sand B from the volume-based median diameter of silica sand A is 200 μm or less. [8] A method for manufacturing a glass article according to any one of [1] to [7], wherein the total content of silica sand A and silica sand B in the above glass raw material relative to the batch raw material is 30 to 90% by mass. [Effects of the Invention]

[0014] According to the present invention, a method for manufacturing glass articles is provided in which the equilibrium raw material input rate can be controlled in the cold-top melting method, and in which unmelted glass raw materials are less likely to occur. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic cross-sectional view of a glass melting apparatus used in the cold-top melting method. [Figure 2] This is a schematic cross-sectional view of a melting furnace used to measure the equilibrium raw material input rate. [Figure 3] This graph shows the relationship between the amount of residual silica sand in a glass raw material melting rate test and the value of the equilibrium raw material input rate measured in an actual machine. [Modes for carrying out the invention]

[0016] The present invention will be described in detail below. The following description of the constituent elements may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.

[0017] The meanings of the terms used in this specification are as follows: A numerical range represented using "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. "ppm" is an abbreviation for parts per million, which means 1 in 1,000,000 (10 -6 ) means.

[0018] In this specification, "silica sand" refers to a powder mainly containing silicon dioxide (silica, SiO2). The silicon dioxide content in silica sand is generally 95% by mass or more, preferably 98% by mass or more, and more preferably 99% by mass or more, based on the total mass of the silica sand. Silica sand may also consist of silicon dioxide. That is, the silicon dioxide content in silica sand may be 100% by mass.

[0019] <Method of manufacturing glass articles> The present invention relates to a method for manufacturing glass articles, in which glass raw materials containing silica sand A and silica sand B, as described later, are melted by a cold-top melting method. First, I will explain the cold-top melting method, referring to the diagram.

[0020] [Cold Top Melting Method] Figure 1 is a schematic cross-sectional view of a glass melting apparatus 10 used in the cold-top melting method. The glass melting apparatus 10 melts the glass raw material GS supplied from the raw material supply unit 50 to produce molten glass GL. The glass raw material GS is usually prepared by mixing several types of materials. The glass raw material GS also contains silica sand A and silica sand B, which will be described later. The glass raw material GS will be discussed in detail later.

[0021] The glass melting apparatus 10 comprises a glass raw material GS, a melting tank 20 that contains molten glass GL obtained by melting the glass raw material GS, and a plurality of electrodes 30 that heat the molten glass GL by applying an electric current. The glass raw material GS is introduced from the raw material supply unit 50 into the liquid surface LS of the molten glass GL, forming a blanket made of the glass raw material GS on the liquid surface LS. The layer (blanket) of glass raw material GS is gradually melted by the heat transferred from the molten glass GL.

[0022] The glass raw material GS layer (blanket) preferably covers 80% or more of the liquid surface LS of the molten glass GL, and more preferably covers 90% or more of the liquid surface LS, in order to suppress the dissipation of heat or evaporated components from the molten glass GL. Furthermore, the maximum surface temperature of the glass raw material GS layer (blanket) is preferably 500°C or less, more preferably 350°C or less, and even more preferably 200°C or less.

[0023] The glass melting apparatus 10 is preferably an all-electric melting furnace that melts the glass raw material GS by only applying electric heating to the molten glass GL. The all-electric melting furnace is equipped with only a plurality of electrodes 30 as a heat source for melting the glass raw material GS. The glass melting apparatus 10 may be of a configuration other than an all-electric melting furnace, and the glass raw material GS may be melted by combining electric heating of the molten glass GL with the heat of combustion of a flammable gas or heavy oil. However, the ratio of the amount of heat from electric heating to the amount of heat per unit time used to melt the glass raw material GS is preferably 80% or more. In the case of an all-electric melting furnace, the above ratio is 100%.

[0024] The melting tank 20 in the glass melting apparatus 10 shown in Figure 1 has a two-story structure (shelf structure) and comprises a first tank 22 and a second tank 24 located below the first tank 22. The first tank 22 has a first side wall 22a surrounding the molten glass GL, a first bottom wall 22b supporting the molten glass GL from below, and a flow opening 22c formed through the first bottom wall 22b. The molten glass GL moves from the first tank 22 to the second tank 24 through the flow opening 22c. Furthermore, the larger the surface area of ​​the molten glass GL (liquid surface LS), the greater the amount of glass raw material GS (glass raw material) that can be input per unit time, thereby increasing the production volume of molten glass GL.

[0025] The second tank 24 has a second side wall 24a extending downward from the periphery of the flow opening 22c and a second bottom wall 24b that supports the molten glass GL from below. An outlet 26 is provided in the second side wall 24a. The outlet 26 for the molten glass GL may be provided in the second bottom wall 24b.

[0026] Furthermore, the melting tank 20 does not necessarily have a shelf structure. That is, the melting tank 20 only needs to have a first tank 22 and does not need to have a second tank 24. If the melting tank 20 does not have a second tank 24, a flow port 22c will not be formed in the first bottom wall 22b. Also, if the melting tank 20 does not have a second tank 24, the outlet 26 for the molten glass GL may be provided in the first side wall 22a or in the first bottom wall 22b.

[0027] The molten tank 20 is made of, for example, refractory bricks. Examples of refractory bricks include zirconia-based electroformed bricks, alumina-based electroformed bricks, alumina-zirconia-based electroformed bricks, alumina-zirconia-silica (AZS)-based electroformed bricks, and dense-fired bricks. The melting tank 20 may be composed of multiple types of refractory bricks.

[0028] In the embodiment shown in Figure 1, the electrode 30 is rod-shaped and protrudes diagonally upward from the first bottom wall 22b. The electrode 30 is not particularly limited, but examples include a molybdenum electrode. A through-hole 22d for inserting the electrode 30 is formed in the first bottom wall 22b. An electrode holder 40 is provided in the through-hole 22d. The electrode holder 40 holds the electrode 30 and cools the electrode 30 to prevent molten glass GL from leaking out of the melting tank 20 through the through-hole 22d. Cooling of the electrode holder 40 is performed by supplying a coolant such as water. The electrode holder 40 may also hold the lower end of the electrode 30. In the embodiment shown in Figure 1, the electrode holder 40 does not protrude above the plane of the paper from the through-hole 22d, but it may protrude.

[0029] It goes without saying that in the present invention, a glass melting apparatus 10 other than the one shown in Figure 1 may also be used.

[0030] [Glass raw materials] In the present invention, the glass raw materials to be melted by the cold-top melting method include silica sand A and silica sand B. Here, the volume-based median diameter of silica sand A is greater than the volume-based median diameter of silica sand B. Furthermore, the content of silica sand B relative to the total content of silica sand A and silica sand B is adjusted to a range of 1 to 99% by mass. Furthermore, silica sand A and silica sand B satisfy the following requirements 1 and 2. Requirement 1: The median diameter based on volume of silica sand A and the median diameter based on volume of silica sand B are both 300 μm or less. Requirement 2: The value obtained by subtracting the volume-based median diameter of silica sand B from the volume-based median diameter of silica sand A is 35 μm or more. That is, let the volume-based median diameter of silica sand A be D 50A (unit: μm), and let the volume-based median diameter of silica sand B be D 50B (unit: μm). In this case, D 50A and D 50B satisfy the following relational expressions (1), (2), and (3). (1) D 50A > D 50B (2) D 50A ≦300, D 50B ≦300 (3) D 50A −D 50B ≧35

[0031] In the method for manufacturing a glass article of the present invention, in the cold top melting method, although the mechanism by which the control of the equilibrium raw material input rate is possible and the remaining unmelted glass raw materials are unlikely to occur is not necessarily clear, the present inventors presume as follows. In the method for manufacturing a glass article of the present invention, the glass raw materials often contain silica sand (SiO2) and other raw materials. Generally, the melting point of SiO2 is often higher than that of other raw materials, and other raw materials often undergo dehydration, decomposition, etc. first and then melt, and a liquid phase mainly composed of other raw materials often occurs. The process by which SiO2 melts into the molten glass is considered to proceed through a dissolution step in which SiO2 dissolves in the generated liquid phase and a diffusion step in which the dissolved SiO2 diffuses in the molten glass in this order. In the process by which SiO2 melts into the molten glass, it is considered that the time required for the above diffusion step is longer than that for the above dissolution step. That is, in the process by which SiO2 melts into the molten glass, usually, the diffusion step in which the dissolved SiO2 diffuses in the molten glass is considered to be rate-determining. In this case, as in the manufacturing method of the glass article of the present invention, when two types of silica sand with different particle sizes (median diameter) are mixed and used, it can be said that the melting of the silica sand with the smaller particle size (silica sand B) proceeds preferentially. If the silica sand with the smaller particle size melts first, it is thought that a large amount of molten material containing a lot of SiO2 generated from the melting of the silica sand with the smaller particle size will be present around the silica sand with the larger particle size (silica sand A). When a SiO2-rich molten material like the one described above is present around large-particle-sized silica sand, the diffusion step described above limits the melting of the large-particle-sized silica sand, resulting in a longer melting time for the silica sand. A longer melting time for the silica sand reduces the blanket melting rate, and consequently, the equilibrium raw material input rate decreases. Furthermore, the amount of SiO2-rich molten material (i.e., the thickness of the SiO2 diffusion layer) can be adjusted by controlling the amount of small-particle-sized silica sand contained in the glass raw materials. Based on the above, it is considered that the equilibrium raw material input rate can be controlled by adjusting the mixing ratio of large-particle-size silica sand to small-particle-size silica sand.

[0032] On the other hand, if the particle size of the silica sand is large, the time required to melt the silica sand tends to be longer, which can easily lead to undissolved glass raw materials. In the method for manufacturing glass articles of the present invention, by setting the median diameter of the silica sand contained in the glass raw materials to 300 μm or less by volume, it is believed that the occurrence of undissolved glass raw materials will be less likely to occur.

[0033] The median diameter of silica sand A and silica sand B based on volume (D above) 50A and D 50B ) is the particle size at which the cumulative frequency of the particle size distribution, obtained by a laser particle size distribution analyzer, reaches 50% in volume percentage. Specifically, the particle size distribution curve is obtained by a laser particle size distribution analyzer under the following equipment and conditions. • Device name: LA960S2 (manufactured by Horiba, Ltd.) ·Dispersion medium: water • Pre-measurement treatment: Ultrasonic treatment (1 minute)

[0034] The median diameter of silica sand A is D, which is the volume-based median diameter. 50A The (unit: μm) is not particularly limited as long as it satisfies the above requirements, but is preferably 80 μm or more, more preferably 100 μm or more, and even more preferably 200 μm or more. Also, D 50A The upper limit is 300 μm or less, preferably 280 μm or less, and more preferably 250 μm or less. 50A The particle size may be 200 μm or less, or 100 μm or less.

[0035] The median diameter of silica sand B is D, which is the volume-based median diameter. 50B The unit (μm) is not particularly limited as long as it satisfies the above requirements, but 10 μm or more is preferred, 20 μm or more is more preferred, and 30 μm or more is even more preferred. 50B The particle size may be 50 μm or larger, or 100 μm or larger. Also, D 50B The upper limit is 265 μm or less, preferably 200 μm or less, and more preferably 150 μm or less.

[0036] Furthermore, it is preferable that silica sand A and silica sand B also satisfy the following requirement 1-1. Requirement 1-1: The median diameter of silica sand A, based on volume, is 100-300 μm, and the median diameter of silica sand B, based on volume, is 20-150 μm. Furthermore, silica sand A and silica sand B satisfy requirement 2 described above.

[0037] With respect to silica sand A and silica sand B, it is also preferable that the following requirements 1-2 be further met. Requirement 1-2: The median diameter of silica sand A, based on volume, is 130-250 μm, and the median diameter of silica sand B, based on volume, is 30-150 μm. Furthermore, silica sand A and silica sand B satisfy requirement 2 described above.

[0038] Furthermore, it is preferable that silica sand A and silica sand B also satisfy the following requirement 2-1. Requirement 2-1: The value obtained by subtracting the median diameter of silica sand B based on volume from the median diameter of silica sand A based on volume is 50 μm or more. Furthermore, silica sand A and silica sand B satisfy requirements 1 and 2 described above.

[0039] Furthermore, it is preferable that silica sand A and silica sand B also satisfy the following requirement 2-2. Requirement 2-2: The value obtained by subtracting the median diameter of silica sand B based on volume from the median diameter of silica sand A based on volume is 60 μm or more.

[0040] Furthermore, it is preferable that silica sand A and silica sand B also satisfy the following requirements 2-3. Requirement 2-3: The value obtained by subtracting the median diameter of silica sand B based on volume from the median diameter of silica sand A based on volume is 200 μm or less. Furthermore, silica sand A and silica sand B satisfy requirements 1 and 2 described above.

[0041] Furthermore, it is preferable that silica sand A and silica sand B also satisfy the following requirements 2-4. Requirement 2-4: The value obtained by subtracting the median diameter of silica sand B based on volume from the median diameter of silica sand A based on volume is 150 μm or less. Furthermore, silica sand A and silica sand B satisfy requirements 1 and 2 described above.

[0042] With respect to silica sand A and silica sand B, the above requirements are met, and the particle size distribution of silica sand A and silica sand B may be unimodal or multimodal, but unimodal is preferred.

[0043] As described above, the glass raw material includes silica sand A and silica sand B. Here, the total content of silica sand A and silica sand B relative to the batch raw material in the glass raw material is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, from the viewpoint of making it easier to control the equilibrium raw material input rate. Furthermore, the total content of silica sand A and silica sand B relative to the batch raw material in the glass raw material is often 95% by mass or less, preferably 90% by mass or less, and more preferably 80% by mass or less. The batch raw materials mentioned above refer to the glass raw materials excluding the cullet raw materials described later. Typically, batch raw materials consist of silica sand A, silica sand B, and other raw materials described later. The batch material content relative to the glass raw material is usually 40% by mass or more, and is often 50% by mass or more. Furthermore, the batch material content relative to the glass raw material may be 100% by mass, but is often 95% by mass or less.

[0044] Other raw materials besides silica sand A and silica sand B included in the glass raw materials include compounds containing elements found in the glass composition described later. Other raw materials are compounds of elements included in the glass composition described later, and raw materials in forms commonly used as glass raw materials can be used as appropriate. Other raw materials include, for example, oxides, hydroxides, and chlorides of elements included in the glass composition described later, as well as carbonates, nitrates, and sulfates containing elements included in the glass composition described later. The median diameter of the other raw materials, based on volume, is preferably 5 μm or more, and more preferably 10 μm or more. Furthermore, the median diameter of the other raw materials, based on volume, is preferably 1000 μm or less, and more preferably 500 μm or less. The volume-based median diameter of the other raw materials can be measured using the same measurement method as for the volume-based median diameters of silica sand A and silica sand B described above.

[0045] The glass raw materials may also include cullet raw materials in addition to the batch raw materials mentioned above. Cullet raw material refers to the raw material obtained by crushing glass. Cullet raw material can be obtained, for example, by crushing leftover glass scraps and off-spec glass items in other processes described later to obtain the desired glass articles. The composition of cullet raw material usually matches the composition of molten glass obtained by melting glass raw materials. The cullet content relative to the glass raw material is often 5% by mass or more. Furthermore, the cullet content is usually 60% by mass or less, and often 50% by mass or less. Note that the glass raw material does not necessarily have to contain cullet.

[0046] The glass raw materials may contain silicon dioxide raw materials other than silica sand A and silica sand B, but it is preferable that they do not contain silicon dioxide raw materials other than silica sand A and silica sand B. When glass raw materials include silicon dioxide raw materials other than silica sand A and silica sand B (other silicon dioxide raw materials), the median diameter of the other silicon dioxide raw materials by volume is preferably 2300 μm or less.

[0047] Furthermore, in the method for manufacturing glass articles of the present invention, the content of silica sand A relative to the total content of silica sand A and silica sand B is adjusted to a range of 1 to 99% by mass. Here, from the viewpoint of making it easier to control the equilibrium raw material input rate, it is preferable to adjust the content of silica sand A relative to the total content of silica sand A and silica sand B to a range of 5 to 95% by mass, more preferably to a range of 10 to 90% by mass, and even more preferably to a range of 15 to 85% by mass.

[0048] The adjustment of the content of silica sand A relative to the total content of silica sand A and silica sand B in the glass raw material can be carried out by known methods. In the embodiment shown in Figure 1 above, the glass raw material GS supplied from the raw material supply unit 50 is supplied after the individual powders constituting the glass raw material GS are mixed together. Here, the above content of silica sand A can be adjusted by adjusting the amount of silica sand A and silica sand B used when mixing the individual powders constituting the glass raw material GS. Furthermore, when continuously supplying the glass raw material GS, it is also preferable to provide a raw material mixing section (not shown) between the raw material supply section 50 and a plurality of raw material storage sections (not shown) that contain each raw material. In this case, when adjusting the above content of silica sand A, the supply rate of silica sand A supplied from the raw material storage section containing silica sand A to the raw material mixing section and the supply rate of silica sand B supplied from the raw material supply section containing silica sand B to the raw material mixing section can be adjusted.

[0049] [Glass composition] In the present invention's method for manufacturing glass articles, the preferred composition of the molten glass obtained by the cold-top melting method will be described. That is, the preferred glass composition of the glass article obtained by the glass article manufacturing method of the present invention will be described. The glass composition may include an alkaline component (e.g., soda glass, soda-lime glass, borosilicate glass, and aluminosilicate glass), or it may be a composition that is substantially free of alkaline components (alkali-free glass). "Substantially free of the above-mentioned alkaline components" means that the content of alkali metal oxides (Li2O, Na2O, K2O) is 1000 ppm by mass or less.

[0050] Examples of alkali-free glass compositions, expressed as mass percent based on oxides, include those containing 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.

[0051] Other compositions of alkali-free glass include, for example, those containing 57-67.5% SiO2, 17-25% Al2O3, 0.1-5.5% B2O3, 2-8.5% MgO, 1.5-8.5% CaO, 0.5-10% SrO, and 0-2.5% BaO, expressed as mass percent on an oxide basis.

[0052] Other alkali-free glass compositions include, for example, those containing 45-75% SiO2, 1-15% Al2O3, 1-30% B2O3, 0.1-13% MgO, 0.1-13% CaO, 0.1-13% SrO, and 0-13% BaO, expressed as mass percent based on oxides.

[0053] [Other processes] The method for manufacturing a glass article of the present invention may include other steps besides those described above. Other processes include, for example, a clarifying process for clarifying the molten glass, a molding process for shaping the molten glass, and a processing process for processing the molded glass articles. In other words, in the method for manufacturing glass articles of the present invention, the obtained molten glass may be clarified, the clarified molten glass may be molded, and a glass article may be obtained. The above-mentioned clarifying, molding, and processing steps can be carried out by known methods.

[0054] <Glassware> A glass article can be obtained by the glass article manufacturing method of the present invention described above. The uses of the resulting glass articles are not particularly limited and can be applied as appropriate to applications in which glass articles have traditionally been used. [Examples]

[0055] The present invention will be described in more detail below based on examples. The materials, quantities, proportions, processing details, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following examples.

[0056] <Melting rate test of glass raw materials> Glass raw materials were prepared to have the following composition. Note that the following composition is expressed in mass percentage based on oxides. SiO2:60%, Al2O3:17%, B2O3:8%, MgO:3%, CaO:4%, SrO:8% Furthermore, the raw material for SiO2 is the median diameter (D) based on volume. 50 Silica sands 1-5 with the following values ​​were used. ·Silica sand 1:D 50 is 37 μm ·Silica sand 2:D 50 is 51 μm ·Silica sand 3:D 50 is 125 μm ·Silica sand 4:D 50 is 147 μm ·Silica sand 5:D 50 is 214 μm ·Silica sand 6:D 50 319 μm

[0057] Glass raw materials containing two types of silica sand selected from silica sand 1 to 6 were uniformly mixed and placed in a vessel. The mixture was then heated to 1550°C and removed from the heating furnace. The heating rate during this heat treatment was 10°C / min. After heat treatment, the contents of the crucible were removed, and the amount of silica sand remaining after heat treatment was quantified by X-ray diffraction measurement. The amount of remaining silica sand was quantified by the amount of SiO2 remaining after heat treatment (amount of remaining silica sand) from the SiO2 / ZnO intensity ratio relative to the SiO2 / ZnO mass ratio prepared in advance. The results are shown in Table 1. In Table 1, the "Silica Sand A Content" column represents the content of silica sand A relative to the total content of silica sand A and silica sand B. Furthermore, in Table 1, the "Difference from Linear Interpolation" column shows the difference between the linear interpolation of the values ​​for when silica sand A is 0% by mass and when it is 100% by mass, and the amount of remaining silica sand when silica sand A is 50% by mass. The larger the value in the "Difference from Linear Interpolation" column, the greater the change in the amount of remaining silica sand when silica sand A and silica sand B are mixed.

[0058] [Table 1]

[0059] The results shown in Table 1 confirm that mixing two types of silica sand changes the amount of silica sand remaining after heat treatment. Comparing Examples 1, 3, and 5, which satisfy requirement 2 above, with Examples 2 and 6, which do not satisfy requirement 2 above, it was confirmed that in Examples 1, 3, and 5, the amount of remaining silica sand changed more significantly when the two types of silica sand were mixed. Furthermore, comparing Examples 1, 3, and 5, which satisfy requirement 1 above, with Example 4, which does not satisfy requirement 1 above, it was confirmed that in Examples 1, 3, and 5, even when two types of silica sand are mixed, the amount of remaining silica sand does not exceed a certain value (specifically, 6.90 mass%) as described later.

[0060] The following examines the relationship between the amount of silica sand remaining after heat treatment and the equilibrium raw material input rate. Furthermore, the following describes the results of an investigation into the relationship between the amount of silica sand remaining after the heat treatment and the undissolved glass raw materials. Specifically, the relationship between the amount of silica sand remaining after heat treatment exceeding 6.90% by mass and the undissolved glass raw materials is examined.

[0061] <Measurement of equilibrium raw material input rate> Based on the principle described above, the amount of silica sand remaining in the melting rate test of the glass raw material is thought to be related to the melting rate of the blanket. In other words, in the above test, if the amount of remaining silica sand is large, the melting rate of the blanket can be controlled to be small, and if the amount of remaining silica sand is small, the melting rate of the blanket can be controlled to be large. Here, we actually measured the equilibrium raw material input rate using a real machine when a predetermined amount of silica sand was mixed and used as a glass raw material. Specifically, the equilibrium raw material input rate was measured in the melting furnace shown in Figure 2 using glass raw materials prepared by mixing the above-mentioned silica sand with other raw materials. The results are shown in the graph in Figure 3. The melting furnace shown in Figure 2 is equipped with a roughly funnel-shaped crucible 1. The opening at the top of the crucible 1 is the input port for the glass raw material. By supplying the glass raw material through the input port while simultaneously removing molten glass from the bottom of the furnace, molten glass can be continuously obtained. An induction heating device 2a is provided on the outer circumference of the molten section 1a at the top of the crucible 1, allowing a temperature gradient to be created in the object to be heated inside the crucible 1, from the low temperature region at the top of the molten section 1a to the high temperature region at the bottom of the molten section 1a. An electric heating device 2b is provided in the extraction section 1b at the bottom of the crucible 1, allowing the extraction amount to be adjusted by adjusting the temperature of the glass flowing inside the extraction section 1b. In this example, a platinum crucible 1 was used, with a molten section 1a diameter of 100 mm and a molten section 1a height of 250 mm. The crucible was heated so that the molten glass temperature (set temperature) in the molten section 1a reached 1600°C. The temperature of the extraction section 1b of crucible 1 was adjusted, the extraction amount was adjusted, and the material was continuously added at an input rate commensurate with the extraction amount. When the input and extraction amounts were balanced, approximately 100 mm from the bottom of crucible 1 was filled with molten glass, and approximately 140 mm from the top was filled with raw material.

[0062] In the graph in Figure 3, the horizontal axis represents the amount of silica sand remaining in the glass raw material melting rate test described above, and the vertical axis represents the equilibrium raw material input rate measured in the actual machine. The equilibrium raw material input rate shown on the vertical axis is a value normalized to the rate when the remaining amount of silica sand is 0.53 mass%. As shown in Figure 3, a strong negative correlation was observed between the amount of silica sand remaining in the glass raw material melting rate test and the value of the equilibrium raw material input rate measured in the actual machine. In other words, it was confirmed that as the amount of silica sand remaining in the glass raw material melting rate test increased, the equilibrium raw material input rate decreased. Therefore, referring to Table 1 above and the results in Figure 3, it can be said that the equilibrium raw material input rate can be controlled by mixing two predetermined types of silica sand. In other words, when using glass raw materials containing silica sand A and silica sand B, and melting the glass raw materials by the cold-top melting method, if the volume-based median diameter of silica sand A is larger than the volume-based median diameter of silica sand B, and the content of silica sand B relative to the total content of silica sand A and silica sand B is adjusted within a predetermined range, and silica sand A and silica sand B satisfy requirement 2 described above, it can be said that it is possible to control the equilibrium raw material input rate.

[0063] Furthermore, in the melting rate test of the glass raw materials described above, when the equilibrium raw material input rate was measured using glass raw materials in which the amount of silica sand remaining after the heat treatment exceeds 6.90% by mass (for example, the glass raw material in Example 4 when the silica sand A content is 100%), undissolved glass raw materials were observed in the molten glass that was extracted. On the other hand, when the equilibrium raw material input rate was measured using glass raw materials in which the amount of silica sand remaining after the heat treatment is 6.90% by mass or less (for example, the glass raw material in Example 6 when the silica sand A content is 100%), no undissolved glass raw materials were observed in the molten glass that was extracted. In other words, if at least one of the volume-based median diameters of silica sand A and silica sand B exceeds 300 μm (i.e., requirement 1 is not met), it can be said that undissolved glass raw materials will occur. On the other hand, if requirement 1 above is met, it can be said that the occurrence of undissolved glass raw materials is less likely to occur. [Explanation of symbols]

[0064] 1 crucible 1a Molten part 1b Extraction section 2a induction heating device 2b Electric heating device 10 Glass melting apparatus 20 Melting tank 22 Tank 1 22a 1st side wall 22b 1st bottom wall 22c Distribution port 22d Through hole 24 Tank 2 24a 2nd side wall 24b 2nd bottom wall 26 Outlet 30 electrodes 40 Electrode holder 50 Raw material supply department

Claims

1. A method for manufacturing a glass article, comprising using glass raw materials containing silica sand A and silica sand B, and melting the glass raw materials by a cold-top melting method, The volume-based median diameter of silica sand A is greater than the volume-based median diameter of silica sand B. The content of silica sand B is adjusted to a range of 1 to 99% by mass relative to the total content of silica sand A and silica sand B. A method for manufacturing a glass article, wherein the silica sand A and the silica sand B satisfy the following requirements 1 and 2. Requirement 1: The median diameter of silica sand A and the median diameter of silica sand B, both based on volume, are 300 μm or less. Requirement 2: The value obtained by subtracting the volume-based median diameter of silica sand B from the volume-based median diameter of silica sand A is 35 μm or more.

2. The method for manufacturing a glass article according to claim 1, wherein the content of silica sand B is adjusted to a range of 5 to 95% by mass relative to the total content of silica sand A and silica sand B.

3. A method for manufacturing a glass article according to claim 1, wherein the content of silica sand B is adjusted to a range of 10 to 90% by mass relative to the total content of silica sand A and silica sand B.

4. A method for manufacturing a glass article according to any one of claims 1 to 3, further satisfying requirement 1-1 below. Requirement 1-1: The median diameter of silica sand A, based on volume, is 100 to 300 μm, and the median diameter of silica sand B, based on volume, is 20 to 150 μm.

5. A method for manufacturing a glass article according to any one of claims 1 to 3, further satisfying requirement 2-1 below. Requirement 2-1: The value obtained by subtracting the volume-based median diameter of silica sand B from the volume-based median diameter of silica sand A is 50 μm or more.

6. A method for manufacturing a glass article according to any one of claims 1 to 3, further satisfying requirement 2-2 below. Requirement 2-2: The value obtained by subtracting the volume-based median diameter of silica sand B from the volume-based median diameter of silica sand A is 60 μm or more.

7. A method for manufacturing a glass article according to any one of claims 1 to 3, further satisfying the following requirements 2-3. Requirement 2-3: The value obtained by subtracting the volume-based median diameter of silica sand B from the volume-based median diameter of silica sand A is 200 μm or less.

8. A method for manufacturing a glass article according to any one of claims 1 to 3, wherein the total content of silica sand A and silica sand B in the glass raw material relative to the batch raw material is 30 to 90% by mass.

Images