JP6631372B2 - Melting method and method for producing alkali-free glass plate - Google Patents

Description

  The present invention relates to a melting method and a method for producing an alkali-free glass plate.

  The melting furnace melts the raw material of the alkali-free glass. The melting furnace has a first chamber in which the raw material is charged, a first chamber burner for forming a flame in the upper space of the first chamber, a second chamber in which a molten glass obtained by melting the raw material is supplied from the first chamber, A second chamber burner for forming a flame in the upper space of the two chambers, and a throat connecting the lower part of the first chamber and the lower part of the second chamber are provided.

  The first-chamber burner and the second-chamber burner form a flame by mixing and burning a fuel such as natural gas or heavy oil with the gas. A burner that mainly uses air as a gas is called an air-fired burner, and a burner that mainly uses oxygen as a gas is called an oxy-fuel burner.

In the case of an air combustion burner, nitrogen gas, which makes up the majority of the air, is exhausted out of the melting furnace without contributing to combustion. On the other hand, if the oxygen combustion burner, than in air-fuel combustion burner, since the amount of exhaust is small, high thermal efficiency, CO ₂ emissions and NO _x emissions is small.

A burner using a mixed gas obtained by mixing air and oxygen gas can also be used (for example, see Patent Document 1). In this case, of course in the case of oxygen-fired burners, as compared with the case of air combustion burner, sometimes NO _x emissions increased (e.g., see Non-Patent Document 1). More specifically, in the case where the oxygen concentration in the mixed gas is more than 25% by volume less than 93% by volume, as compared with the case of air combustion burner, becomes large NO _x emissions.

JP-A-2000-128549

R & D Kobe Steel Engineering Reports, Vol. 51, No. 2 (Sep. 2001), p. 8-12, "Study on energy saving and low NOx combustion by oxygen-enriched air"

In the case of non-alkali glass, the melting temperature of the raw material is higher than in the case of general soda lime glass, and a foam layer is easily formed on the liquid surface of the molten glass in the first chamber. The foam layer is an aggregate of small bubbles, and the bubbles are caused by gas generation due to thermal decomposition of the raw material. The foam layer is easily formed particularly when the SiO ₂ content of the alkali-free glass is 54 to 73% by mass.

  The presence of the foam layer makes it difficult for the molten glass surface to be directly exposed to the atmosphere in the upper space. Therefore, heat radiation from the flame of the burner to the molten glass was blocked, and the heating efficiency of the molten glass was low.

In the case of a glass containing a general alkali component, the higher the alkali content in the molten glass, the more the B ₂ O ₃ in the molten glass is likely to evaporate. B ₂ O ₃ evaporates, for example, as a sodium compound.

On the other hand, in the case of alkali-free glass containing almost no alkali component such as Na in the molten glass, the higher the moisture concentration in the molten glass or the higher the moisture concentration in the atmosphere in the upper space, the higher the B ₂ content in the molten glass. O ₃ is easily volatilized.

The amount of water in the molten glass or the amount of water in the atmosphere in the upper space depends on the type of burner. In the case of the oxyfuel burner, the concentration of water contained in the gas after combustion is higher than in the case of the air combustion burner, and B ₂ O ₃ in the molten glass is easily volatilized. B ₂ O ₃ is considered to evaporate as a hydrogen compound.

Further, when the water concentration in the molten glass is high, in addition to B ₂ O ₃ in the molten glass, the water tends to volatilize, so that the molten glass becomes inhomogeneous and striae on the finally obtained alkali-free glass plate. And reaming are likely to occur.

The present invention has been made in view of the above problems, and is a melting method capable of efficiently heating molten glass via a foam layer and suppressing volatilization of B ₂ O ₃ and moisture in the molten glass. The main purpose is to provide such information.

In order to solve the above problems, according to one embodiment of the present invention,
A first chamber into which a raw material for glass is charged, a first chamber burner for forming a flame in an upper space of the first chamber, and a second glass from which the molten glass obtained by melting the raw material is supplied from the first chamber. Melting the raw materials in a melting furnace having a chamber, a second chamber burner for forming a flame in the upper space of the second chamber, and a throat connecting the lower part of the first chamber and the lower part of the second chamber; Dissolving method,
The raw material is a non-alkali glass raw material having a SiO ₂ content of 54 to 73% by mass and a B ₂ O ₃ content of 0.1 to 12% by mass,
For each of the first chamber burners and each of the second chamber burners, one of an oxyfuel burner and an air combustion burner is used,
50-100% of the total heat of combustion of all the first chamber burners per hour is generated by the oxyfuel burner;
A melting method is provided, wherein 30-75% of the total heat of combustion per hour of all said second chamber burners is generated by said oxy-fuel burner.

According to one aspect of the present invention, there is provided a melting method capable of efficiently heating molten glass via a foam layer and suppressing volatilization of B ₂ O ₃ and moisture in the molten glass.

1 is a flowchart illustrating a method for manufacturing an alkali-free glass plate according to an embodiment of the present invention. It is sectional drawing which shows the melting furnace used in the melting process of FIG. It is sectional drawing which shows the melting furnace by a 1st modification. It is sectional drawing which shows the melting furnace by 2nd modification. It is sectional drawing which shows the melting furnace by 3rd modification.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In the drawings, the same or corresponding components are denoted by the same or corresponding reference numerals, and description thereof is omitted. In this specification, “to” indicating a numerical range means a range including numerical values before and after the numerical range.

  FIG. 1 is a flowchart illustrating a method for manufacturing an alkali-free glass plate according to an embodiment of the present invention. The method for producing an alkali-free glass plate includes a melting step S12 and a forming step S14.

Alkali-free glass is glass that does not substantially contain an alkali metal oxide such as Na ₂ O, K ₂ O, and Li ₂ O. In the alkali-free glass according to the present invention, the total content of the alkali metal oxides is 0.2% by mass or less.

Alkali-free glass is, for example, expressed in terms of mass percentage on an oxide basis,
SiO _2: 54~73%
Al ₂ O ₃ : 10 to 23%
B ₂ O _3: 0.1~12%
MgO: 0 to 12%
CaO: 0 to 15%
SrO: 0 to 16%
BaO: 0 to 15%
MgO + CaO + SrO + BaO: 8 to 26%
It contains.

When the alkali-free glass has both a high strain point and high solubility, it is preferably expressed in terms of mass% on an oxide basis,
SiO _2: 58~66%
Al ₂ O _3: 15~22%
B ₂ O _3: 5~12%
MgO: 0-8%
CaO: 0-9%
SrO: 3 to 12.5%
BaO: 0-2%
MgO + CaO + SrO + BaO: 9 to 18%
It contains.

When an alkali-free glass is required to obtain a particularly high strain point, preferably, it is expressed in mass% based on oxide,
SiO _2: 54~73%
Al ₂ O ₃ : 10.5 to 22.5%
B ₂ O _3: 0.1~5.5%
MgO: 0 to 10%
CaO: 0-9%
SrO: 0 to 16%
BaO: 0-2.5%
MgO + CaO + SrO + BaO: 8 to 26%
It contains.

The B ₂ O ₃ content of the alkali-free glass is preferably 9% by mass or less, more preferably 5% by mass or less, still more preferably 3% by mass or less, and particularly preferably 2% by mass or less, when a high strain point is obtained. is there.

The B ₂ O ₃ content of the alkali-free glass is preferably at least 0.3% by mass, more preferably at least 0.5% by mass, further preferably at least 1% by mass, in order to obtain high solubility.

  The strain point of the alkali-free glass is preferably 650 ° C. or higher, more preferably 670 ° C. or higher, and further preferably 700 ° C. or higher.

T _{2 of the} alkali-free glass (a temperature that is a measure of melting and corresponding to a viscosity of 10 ² dPa · s) is 100 ° C. or more higher than T _{2 of} general soda lime glass. _{T 2} of the non-alkali glass is preferably 1,600 to 1,820 ° C., more preferably 1,610 to 1,770 ° C., more preferably 1,620-1,720 ° C..

Β-OH indicating the water content of the alkali-free glass plate is preferably 0.2 to 0.4 mm ⁻¹ , more preferably 0.2 to 0.35 mm ⁻¹ . The higher the value of β-OH, the higher the water content. This value increases when dissolved in an atmosphere having a high moisture concentration. The value B of β-OH is calculated by measuring the thickness C and the transmittance T of the alkali-free glass plate, and substituting the measurement results into the following formula. To measure the transmittance of the alkali-free glass plate, a general Fourier transform infrared spectrophotometer (FT-IR) is used.
B = (1 / C) log ₁₀ (T1 / T2)
T1: transmittance of alkali-free glass plate at reference wave number 4000 / cm (unit:%)
T2: Minimum transmittance of alkali-free glass plate near hydroxyl absorption wave number 3570 / cm (unit:%)

  The non-alkali glass plate is used as a substrate for a display such as a liquid crystal display and an organic EL display, a substrate for a magnetic disk, and the like. The applications of the alkali-free glass plate may be of a wide variety. As will be described in detail later, according to the present embodiment, a homogeneous alkali-free glass plate having few defects such as bubbles can be obtained, and thus it is suitable for a substrate for a liquid crystal display, which particularly requires high quality.

  In the melting step S12 shown in FIG. 1, a raw material of non-alkali glass is put into a melting furnace, and the raw material is melted to obtain a molten glass.

The meltability of the raw material of the alkali-free glass affects the formation of a foam layer. Among the raw materials, silica sand, which is a source of SiO ₂ , is most difficult to melt. Median particle diameter _{D 50} of the silica sand is preferably 250μm or less, more preferably 240μm or less, more preferably not more than 230 .mu.m. When the median particle diameter D ₅₀ of the silica sand but 250μm or less, the melting of the raw material is improved, silica raw fusion foreign matter can be prevented from occurring.

Further, the median particle diameter _{D 50} of the silica sand is preferably 90μm or more, more preferably 120 [mu] m, more preferably 150μm or more. When he median particle diameter D ₅₀ of the silica sand is more than 90 [mu] m, and prevent the water concentration in the molten glass increases, B ₂ O ₃ and the moisture in the molten glass can be prevented from volatilizing. Incidentally, if less than the median particle diameter D ₅₀ of the silica sand is 90 [mu] m, the surface area of the particles is increased and water to increase adhesion, the water concentration in the molten glass increases.

Here, the median particle diameter D ₅₀ refers to the particle diameter when the cumulative frequency is 50% in the particle size distribution of the powder measured by the laser diffraction method.

  In the forming step S14 shown in FIG. 1, the molten glass is formed into a plate shape. The molding method may be a general one, such as a float method or a fusion method.

  In the float method, a molten glass is continuously supplied on a molten metal (for example, molten tin), and the molten glass is caused to flow in a horizontal direction on the molten metal to form a strip.

  The fusion method is also referred to as an overflow down draw method, in which molten glass overflowing from the gutter to the left and right sides is caused to flow down along the left and right sides of the gutter, and the molten glass joined at the lower end of the gutter is further caused to flow downward. Thereby, it is formed into a strip.

  In addition, between the dissolving step S12 and the forming step S14, a fining device (for example, a vacuum degassing device) or a stirring device (for example, a stirring stirrer) may be provided.

  FIG. 2 is a sectional view showing a melting furnace used in the melting step of FIG. The melting furnace has a first chamber 21, a first chamber burner 26, a second chamber 31, a second chamber burner 36, a throat 41, and the like.

  The first chamber 21 is for charging the raw material 12 of non-alkali glass. The first chamber 21 melts the raw material 12 and stores the molten glass 14. The first chamber 21 is surrounded by a horizontal bottom wall 22, an upstream side wall 23 perpendicular to the bottom wall 22, a downstream side wall 24 parallel to the upstream side wall 23, a ceiling 25 (e.g., an arched ceiling), and the like. . The downstream side wall 24 reaches the ceiling 25 as shown in FIG. 2, but may be higher than the foam layer 16, and does not have to reach the ceiling 25 as shown in FIG. 3. An inlet 23 a for the raw material 12 is formed in the upstream side wall 23.

  The first chamber burner 26 forms a flame by mixing and burning a fuel such as natural gas or heavy oil with the gas. The first chamber burner 26 forms a flame in the upper space of the first chamber 21 and heats the raw material 12 and the like input from the input port 23a. The raw material 12 is melted by radiant heat of a flame formed by the first chamber burner 26 and gradually melts into the molten glass 14.

  The first chamber burner 26 blows out the flame to the first chamber 21 from the opening of the left and right side walls connecting the upstream side wall 23 and the downstream side wall 24. The first chamber burner 26 may continuously emit the flame or may intermittently emit the flame.

  The first chamber burners 26 are disposed on the left and right side walls, respectively. The first chamber burners 26 may be arranged symmetrically with respect to the first chamber 21, may be arranged in a staggered manner with the first chamber 21 interposed therebetween, or may be arranged partly symmetrically and partly. A staggered arrangement may be used.

  Either an air combustion burner or an oxyfuel burner is used for each first chamber burner 26. Of the plurality of first chamber burners 26, all may be oxyfuel burners, or some may be oxyfuel burners and the rest may be air combustion burners.

  In this specification, an air combustion burner refers to a gas that mainly uses air as a gas to be mixed with fuel, and refers to a gas in which the oxygen concentration of the gas is 25% by volume or less. As long as the oxygen concentration of the gas is 25% by volume or less, a mixed gas of air and oxygen gas may be used, or only air may be used.

  Further, in the present specification, the oxyfuel combustion burner means a gas mainly using oxygen gas as a gas to be mixed with fuel, and means a gas having an oxygen concentration of 93% by volume or more. If the gas has an oxygen concentration of 93% by volume or more, a mixed gas of oxygen gas and air may be used, or only oxygen gas may be used.

Each first chamber air combustion burner to the burner 26, for either oxygen combustion burner is used, it can be reduced NO _x emissions.

  For the purpose of assisting the heating of the molten glass 14 by the first chamber burner 26, an electrode for electrically heating the molten glass 14 may be provided in the molten glass 14 of the first chamber 21.

  It is preferable that no dry gas such as nitrogen gas be introduced into the upper space of the first chamber 21. A decrease in thermal efficiency and an increase in the amount of exhaust gas can be prevented.

  The second chamber 31 is supplied with the molten glass 14 obtained by melting the raw material 12 from the first chamber 21. The second chamber 31 clarifies the molten glass 14 and adjusts the temperature. The second chamber 31 is surrounded by a horizontal bottom wall 32, an upstream side wall 33 perpendicular to the bottom wall 32, a downstream side wall 34 parallel to the upstream side wall 33, a ceiling 35, and the like. An outlet 34a for the molten glass 14 is formed below the downstream side wall 34.

  Although the bottom wall 32 of the second chamber 31 and the bottom wall 22 of the first chamber 21 are integrated as shown in FIG. 2, they may not be integrated as shown in FIG. Further, as shown in FIG. 4, there may be a step D between the bottom wall 32 of the second chamber 31 and the bottom wall 22 of the first chamber 21. Either the bottom wall 32 of the second chamber 31 or the bottom wall 22 of the first chamber 21 may be higher.

  Although the upstream side wall 33 of the second chamber 31 and the downstream side wall 24 of the first chamber 21 are integrated, they may not be integrated as shown in FIG.

  Although the ceiling 35 of the second room and the ceiling 25 of the first room 21 are integrated, they need not be integrated. When the ceiling 35 of the second room and the ceiling 25 of the first room 21 are not integrated, for example, as shown in FIG. 5, the downstream side wall 24 of the first room 21 and the upstream side wall 33 of the second room 31 are formed. There is a case where they are not integrated.

  The second chamber burner 36 forms a flame by mixing and burning a fuel such as natural gas or heavy oil with the gas. The second chamber burner 36 forms a flame in the upper space of the second chamber 31 and heats the molten glass 14 supplied from the first chamber 21.

  The second chamber burner 36 blows out the flame to the second chamber 31 from the openings on the left and right side walls connecting the upstream side wall 33 and the downstream side wall 34. The second chamber burner 36 may eject the flame continuously or may emit the flame intermittently.

  The second chamber burners 36 are disposed on left and right side walls connecting the upstream side wall 33 and the downstream side wall 34, respectively. The second chamber burners 36 may be arranged symmetrically with respect to the second chamber 31, may be arranged in a staggered manner with the second chamber 31 interposed therebetween, or may be arranged partly symmetrically and partly. A staggered arrangement may be used.

Each of the second chamber burners 36 uses either an air combustion burner or an oxyfuel burner. Part of the plurality of second chamber burners 36 is an oxyfuel burner, and the rest is an air combustion burner. Therefore, NO _x emissions can be reduced.

  In order to assist the heating of the molten glass 14 by the second chamber burner 36, an electrode for electrically heating the molten glass 14 may be provided in the molten glass 14 of the second chamber 31.

  It is preferable that a dry gas such as nitrogen gas is not introduced into the upper space of the second chamber 31. A decrease in thermal efficiency and an increase in the amount of exhaust gas can be prevented.

  The throat 41 connects the lower part of the first chamber 21 and the lower part of the second chamber 31. The throat 41 is filled with the molten glass 14. A plurality of throats 41 may be provided. The molten glass 14 in the first chamber 21 is supplied to the second chamber 31 via the throat 41.

  The inlet of the throat 41 is formed on the downstream side wall 24 of the first chamber 21 in FIG. 2, but may be formed on the bottom wall 22 of the first chamber 21. Similarly, the outlet of the throat 41 is formed on the upstream side wall 33 of the second chamber 31 in FIG. 2, but may be formed on the bottom wall 32 of the second chamber 31.

Meanwhile, T ₂ of the non-alkali glass is higher 100 ° C. or higher than T ₂ of the general soda-lime glass. Therefore, in the present embodiment, the molten glass 14 is heated using both the first chamber burner 26 and the second chamber burner 36.

In the case of non-alkali glass, the melting temperature of the raw material 12 is higher than in the case of general soda lime glass, and the foam layer 16 is more likely to spread on the liquid surface of the molten glass 14 in the first chamber 21. The foam layer 16 is an aggregate of small air bubbles, and the air bubbles are caused by gas generation due to thermal decomposition of the raw material 12. The foam layer 16 is easily formed particularly when the SiO ₂ content of the alkali-free glass is 54 to 73% by mass. The foam layer 16 blocks heat radiation from the flame of the first chamber burner 26 to the molten glass 14.

  Therefore, in the present embodiment, 50 to 100% (preferably 55 to 100%, more preferably 60 to 100%) of the total combustion heat per hour of all the first chamber burners 26 is due to the oxygen combustion burner. I do.

In the case of an air combustion burner, nitrogen gas, which makes up the majority of the air, is exhausted out of the melting furnace without contributing to combustion. On the other hand, if the oxygen combustion burner, than in air-fuel combustion burner, since the amount of exhaust is small, high thermal efficiency, CO ₂ emissions and NO _x emissions is small.

  If 50 to 100% of the total combustion heat per hour of all the first chamber burners 26 is due to the oxyfuel burner, the molten glass 14 can be efficiently heated even through the foam layer 16 and requires less fuel. The molten glass 14 can be heated to a desired temperature. The total heat of combustion can be obtained by adding the heat generated when the fuel used in each burner is completely burned.

  The molten glass 14 melted in the first chamber 21 is supplied to the second chamber 31. Since the molten glass 14 is supplied to the second chamber 31 through the throat 41, the homogeneous molten glass 14 is supplied to the second chamber 31 almost without being affected by the foam layer 16 of the first chamber 21. In the second chamber 31, unlike the first chamber 21, the foam layer 16 is hardly formed.

  In the second chamber 31, the liquid level of the molten glass 14 is exposed, and the molten glass 14 is exposed to the atmosphere in the upper space of the second chamber 31. The gas in the atmosphere in the upper space of the second chamber 31 melts into the molten glass 14.

By the way, in the case of a general alkali-containing glass, the higher the alkali content in the molten glass, the more easily the B ₂ O ₃ in the molten glass is volatilized. B ₂ O ₃ evaporates, for example, as a sodium compound.

On the other hand, in the case of alkali-free glass containing almost no alkali component such as Na in the molten glass, the higher the moisture concentration in the molten glass or the higher the moisture concentration in the atmosphere in the upper space, the higher the B ₂ content in the molten glass. O ₃ is easily volatilized.

The amount of water in the molten glass or the amount of water in the atmosphere in the upper space depends on the type of burner. In the case of the oxyfuel burner, the concentration of water contained in the gas after combustion is higher than in the case of the air combustion burner, and B ₂ O ₃ in the molten glass is easily volatilized.

  Therefore, in the present embodiment, 30 to 75% (preferably 35 to 75%, more preferably 45 to 75%, even more preferably 50 to 75%) of the total combustion heat per hour of all the second chamber burners 36. ) Is based on the oxyfuel burner. Further, in the present embodiment, the ratio of the amount of combustion heat per hour of the oxyfuel burner of the first chamber 21 to the total amount of combustion heat per hour of all the first chamber burners 26 (hereinafter, the oxyfuel combustion of the first chamber 21) The ratio of the amount of combustion heat per hour of the oxyfuel burner of the second chamber 31 to the total amount of combustion heat per hour of all the second chamber burners 36 (hereinafter referred to as the oxyfuel combustion ratio of the second chamber 31). ) May be larger.

  The oxygen combustion ratio of the first chamber 21 is adjusted by changing the number of air combustion burners and oxygen combustion burners or the flow rates of fuel and gas for the plurality of first chamber burners 26. Similarly, the oxyfuel combustion ratio of the second chamber 31 is adjusted by changing the number of air combustion burners and oxyfuel burners or the flow rates of fuel and gas for the plurality of second chamber burners 36.

Here, in the first chamber 21, the foam layer 16 is formed, and B ₂ O ₃ in the molten glass 14 is hardly volatilized in the upper space. Therefore, even if the oxygen combustion ratio is large, the volatilization of B ₂ O ₃ is prevented. It doesn't matter much. However, since the foam layer 16 is hardly formed in the second chamber 31, it is necessary to reduce the oxygen combustion ratio in order to suppress the volatilization of B ₂ O ₃ .

In the present embodiment, volatilization of B ₂ O ₃ can be suppressed by setting the oxygen combustion ratio of the second chamber 31 to 75% or less. Also, by the oxygen combustion ratio of the second chamber 31 to 30% or more, it can be reduced NO _x emissions.

  The distance L1 in the flow direction (left-right direction in FIG. 2) between the upstream end and the downstream end of the first chamber 21 is preferably 50 to 75% of the reference distance L0, more preferably 55 to 70% of the reference distance L0. . The distance L2 between the upstream end and the downstream end of the second chamber 31 in the flow direction (left-right direction in FIG. 2) is preferably 10 to 40% of the reference distance L0, and more preferably 15 to 35% of the reference distance L0. It is. The reference distance L0 is a distance between the upstream end of the first chamber 21 and the downstream end of the second chamber 31 in the flow direction.

  When the distance L1 is 50 to 75% of the reference distance L0 and the distance L2 is 10 to 40% of the reference distance L0, the molten glass 14 is heated in the first chamber 21 and the second chamber 31 with good balance. Can be.

  In one embodiment of the present invention, the total amount of combustion heat per hour of the first chamber burner 26 provided in the first chamber burner 26 in a region separated from the upstream end of the first chamber 21 by 0.5 L1 or more. 60% or more (preferably 65% or more, more preferably 70% or more, and still more preferably 80% or more) of the oxygen combustion burner.

  If 60% or more of the total combustion heat per hour of the first-chamber burner 26 provided in the region is due to the oxy-combustion burner, the amount of exhaust gas is reduced, so that the molten glass 14 can be efficiently heated and reduced. An alkali-free glass plate can be manufactured with the amount of gas used. Further, for example, a bubbler may be provided on the bottom walls 22 and 32 of the first chamber 21 and / or the second chamber 31 in order to promote melting and homogeneity of the glass.

  The bubbler is disposed at a predetermined interval (pitch) over the width direction of the melting furnace (perpendicular to the paper surface of FIG. 2), and circulates the molten glass 14 in the first chamber 21 and / or the second chamber 31. Form. The number of the bubblers arranged in one row in the width direction (the direction perpendicular to the paper surface of FIG. 2) is preferably 5 to 30, and more preferably 7 to 25. The plurality of bubblers may be arranged at equal intervals in the width direction (the direction perpendicular to the paper surface of FIG. 2), or may not be arranged at equal intervals. The plurality of bubblers may be in two or more rows.

  The inner diameter of each bubbler is preferably from 10 mm to 300 mm, more preferably from 20 mm to 200 mm. When the inner diameter of each bubbler is 10 mm or more, the clogging of the bubbler by the molten glass 14 can be suppressed. When the inner diameter of each bubbler is 300 mm or less, the residence time of the circulating flow of the molten glass 14 is ensured for a predetermined time, so that the homogenization of the molten glass 14 is promoted.

  As the gas supplied from the bubbler, air, nitrogen, oxygen, helium, argon, or the like is used. When platinum or a platinum alloy is used as the material of the bubbler, it is preferable to use a gas that does not contain oxygen, such as nitrogen, helium, or argon, as the gas supplied from the bubbler. The flow rate of the gas is preferably 0.3 to 20 L / min, and more preferably 0.5 to 10 L / min. When the flow rate of the gas is 0.3 L / min or more, the bubbler can be prevented from being clogged by the molten glass 14. When the flow rate of the gas is 20 L / min or less, the production cost of the glass article due to the use of the gas can be suppressed.

  As described above, the melting furnace, the melting method, the method for manufacturing an alkali-free glass plate, and the embodiment of the alkali-free glass have been described. However, the present invention is not limited to the above-described embodiment and deviates from the scope of the present invention. Without departing from the invention, various modifications and substitutions can be made to the above-described embodiment.

  For example, the melting furnace of the above embodiment has the first chamber 21 and the second chamber 31, but may further have a third chamber to which the molten glass 14 is supplied from the second chamber 31. The number of melting furnace rooms may be four or more.

  Hereinafter, Examples and Comparative Examples of the present invention will be specifically described. Note that the present invention is not limited to these descriptions.

  In the above melting furnace, the oxygen concentration in the first chamber 21 and / or the second chamber 31 was changed to adjust the moisture concentration in the atmosphere in the upper space in the first chamber 21 and the second chamber 31. The moisture concentration is calculated based on the composition of the fuel and gas burned by the first chamber burner 26 and the second chamber burner 36, and the like. The calculation was performed in consideration of flowing outward. In addition, the total flow rate of combustion air used for the air combustion burner of the melting furnace was calculated. Table 1 shows the results. Examples 1 to 3 are Examples and Examples 4 to 6 are Comparative Examples.

The dimensions of each part in the melting furnace were as follows.
Reference distance L0: 15m
Distance L1: 10m
Distance L2: 5m
Distance from the surface of molten glass to ceiling 25 of first room and ceiling 35 of second room: 8 m

  Part of the first chamber burner 26 and second chamber burner 36 is an oxyfuel burner, and the rest is an air combustion burner. The fuel of the first chamber burner 26 and the second chamber burner 36 is natural gas. In Examples 1 to 6, the oxygen combustion ratio of the first chamber 21 and / or the second chamber 31 was changed so that the total heating amount of the melting furnace was the same. Here, the total heating amount of the melting furnace is a value calculated by subtracting the heat amount of the exhaust gas from the sum of the total combustion heat amount of the first chamber burner 26 and the total combustion heat amount of the second chamber burner 36.

  In Examples 1 to 3, the oxygen combustion ratio of the first chamber 21 is 50 to 100%, the oxygen combustion ratio of the second chamber 31 is 30 to 75%, and the average The water concentration was 19-22%.

  On the other hand, in Example 4, the oxyfuel combustion ratio of the first chamber 21 is 50 to 100%, but the oxyfuel combustion ratio of the second chamber 31 is more than 75%. The water concentration was 40%.

As described above, when the moisture concentration in the atmosphere in the upper space in the second chamber 31 is high, B ₂ O ₃ is easily volatilized, so that the oxygen combustion ratio in the first chamber 21 is 50 to 100% and the second dissolution method oxyfuel ratio of the chamber 31 is 30 to 75 percent _were found to be suppressed volatilization of B 2 _{O 3.}

  In Examples 1 to 3, the total flow rate of combustion air in the melting furnace was 100 to 180, which was a relative value with respect to Example 1 as 100.

  On the other hand, in Example 5, the oxygen combustion ratio of the first chamber 21 was 50 to 100%, but the oxygen combustion ratio of the second chamber 31 was less than 30%, and the total combustion air flow rate of the melting furnace was 229. . In Example 6, the oxygen combustion ratio of the second chamber 31 was 30 to 75%, but the oxygen combustion ratio of the first chamber 21 was less than 50%, and the total combustion air flow rate of the melting furnace was 250. .

Oxyfuel ratio 50 to 100% of the first chamber 21, and dissolution method oxyfuel ratio of the second chamber 31 is 30 to 75 percent, can be reduced combustion air total flow rate of the melting furnace is, NO _x emissions Was found to be able to be reduced.

As described above, the melting method in which the oxygen combustion ratio of the first chamber 21 is 50 to 100% and the oxygen combustion ratio of the second chamber 31 is 30 to 75% can suppress the volatilization of B ₂ O ₃ , It has been found that NO _x emissions can be reduced.

12 Raw material of non-alkali glass 14 Molten glass 16 Foam layer 21 First chamber 22 Bottom wall 23 of first chamber 23 Upstream side wall 23a of first chamber 23 Input port 24 for raw material 25 Downstream side wall 25 of first chamber Ceiling 26 of first chamber 1 room burner 31 2nd room 32 Bottom wall 33 of 2nd room Upstream side wall 34 of 2nd room Downstream side wall 35 of 2nd room Ceiling 36 of 2nd room Burner 41 of 2nd room Throat

Claims (4)

A first chamber into which a raw material for glass is charged, a first chamber burner for forming a flame in an upper space of the first chamber, and a second glass from which the molten glass obtained by melting the raw material is supplied from the first chamber. Melting the raw materials in a melting furnace having a chamber, a second chamber burner for forming a flame in the upper space of the second chamber, and a throat connecting the lower part of the first chamber and the lower part of the second chamber; Dissolving method,
The raw material is a non-alkali glass raw material having a SiO ₂ content of 54 to 73% by mass and a B ₂ O ₃ content of 0.1 to 12% by mass,
For each of the first chamber burners and each of the second chamber burners, one of an oxyfuel burner and an air combustion burner is used,
50-100% of the total heat of combustion of all the first chamber burners per hour is generated by the oxy-fuel burner;
A melting method, wherein 30 to 75% of the total amount of combustion heat per hour of all the second chamber burners is generated by the oxyfuel burner. The material median particle diameter _{D 50} of the silica sand contained in the 90μm or more and 250μm or less, dissolution method according to claim 1. The alkali-free glass is represented by mass% on an oxide basis,
SiO _2: 54~73%
Al ₂ O ₃ : 10 to 23%
B ₂ O _3: 0.1~12%
MgO: 0 to 12%
CaO: 0 to 15%
SrO: 0 to 16%
BaO: 0 to 15%
MgO + CaO + SrO + BaO: 8 to 26%
The dissolving method according to claim 1, comprising: A dissolution step comprising the dissolution method according to any one of claims 1 to 3,
Forming a molten glass melted in the melting step into a plate-like shape.

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