KR20170115958A - Melting method, and production method for alkali-free glass plate - Google Patents

Abstract

The present invention relates to a process for producing a glass material which comprises a first chamber (21) into which a glass raw material is injected, a first chamber burner (26), a second chamber (31) A second chamber burner 36 and a throat 41. The raw material has a SiO ₂ content of 54 to 73 mass% and a B ₂ O ₃ content of 0.1 to 12 mass% Alkali glass raw material is used as the first raw burner 26 and one of the oxygen burner and the air burner is used for each of the first and second raw burners 26 and 36, 50 to 100% of the total combustion heat amount per hour is generated by the oxygen combustion burner and 30 to 75% of the total combustion heat amount per hour of all the second room burners 36 is generated by the oxygen combustion burner To a dissolving method.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for producing an alkali-free glass plate,

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

The melting furnace melts raw materials of alkali-free glass. The melting furnace includes a first chamber into which a raw material is injected, a first chamber burner which forms a flame in an upper space of the first chamber, a second chamber through which the 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, and a throat connecting the lower portion of the first chamber and the lower portion of the second chamber.

The first chamber burner or the second chamber burner forms a flame by mixing fuel such as natural gas or heavy oil with gas and burning it. The burner which mainly uses air as gas is called an air combustion burner, and the burner which mainly uses oxygen as gas is called an oxygen combustion burner.

In the case of an air combustion burner, nitrogen gas, which occupies almost the air, is exhausted out of the melting furnace without contributing to combustion. On the other hand, in the case of the oxygen combustion burner, since the amount of exhaust is smaller than that of the air combustion burner, the thermal efficiency is high, and the CO ₂ emission amount and the NO _x emission amount are small.

A burner using a mixed gas in which air and oxygen gas are mixed can be used (see, for example, Patent Document 1). In this case, in the case of the oxygen it fired burner is, of course, there is a case where in comparison with the case of air fired burners, the NO _x emissions increased (for example, see Non-Patent Document 1). Specifically, the oxygen concentration in the gas mixture is less than 93% by volume and in case of more than 25% by volume, compared to the case of the air fired burners, the NO _x emission is increased.

Japanese Patent Application Laid-Open No. 2000-128549

"Research on Energy Saving and Low NOx Combustion by Oxygen Enriched Air", R & D Kobe Seiko, Vol. 51, No. 2 (Sep.2001), pp.

In the case of alkali-free glass, the melting temperature of the raw material is higher than in the case of ordinary soda lime glass, and a bubble layer easily attaches to the liquid surface of the molten glass in the first chamber. The bubble layer is a collection of small bubbles, and the bubbles are caused by generation of gas due to thermal decomposition of the raw materials. The bubble layer is particularly liable to be formed when the SiO ₂ content of the alkali-free glass is 54 to 73 mass%.

If the bubble layer is present, the surface of the molten glass is less likely to be directly exposed to the atmosphere of the upper space. As a result, thermal radiation from the flame of the burner to the molten glass is cut off, and the heating efficiency of the molten glass is low.

In the case of a glass containing a general alkali component, B ₂ O ₃ in the molten glass is liable to volatilize as the alkali content in the molten glass increases. B ₂ O ₃ volatilizes, for example, as a sodium compound.

In contrast, 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 of the upper space, the more easily B ₂ O ₃ in the molten glass is volatilized .

The water content in the molten glass or the moisture content in the atmosphere of the upper space depends on the type of the burner. In the case of the oxygen combustion 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 liable to volatilize. B ₂ O ₃ is considered to volatilize as a hydrogen compound.

Further, when the moisture concentration in the molten glass is high, moisture is easily volatilized in addition to B ₂ O ₃ in the molten glass, so that the molten glass becomes inhomogeneous and the molten glass tends to be generated in the finally obtained alkali-free glass plate .

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a dissolution method and the like capable of efficiently heating a molten glass through a bubble layer and suppressing the volatilization of B ₂ O ₃ and moisture in the molten glass Main purpose.

In order to solve the above problems, according to one aspect of the present invention,

A first chamber in which a raw material of glass is injected, a first chamber burner which forms a flame in an upper space of the first chamber, a second chamber in which molten glass obtained by melting the raw material is supplied from the first chamber, A second chamber burner for forming a flame in an upper space of two chambers and a throat for connecting a lower portion of the first chamber to a lower portion of the second chamber,

The raw material is a non-alkali glass raw material having a SiO ₂ content of 54 to 73 mass% and a B ₂ O ₃ content of 0.1 to 12 mass%

Wherein each of the first chamber burner and the second chamber burner uses either an oxygen combustion burner or an air combustion burner,

50 to 100% of the total combustion heat amount per hour of all the first filament burners is generated by the oxygen burner,

Characterized in that 30 to 75% of the total combustion heat amount per hour of all the second chamber burners is generated by the oxygen combustion burner.

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

1 is a flowchart showing a method for producing an alkali-free glass plate according to an embodiment of the present invention.
Fig. 2 is a cross-sectional view showing a melting furnace used in the melting process of Fig. 1; Fig.
3 is a cross-sectional view showing a melting furnace according to the first modification.
4 is a cross-sectional view showing a melting furnace according to a second modification.
5 is a cross-sectional view showing a melting furnace according to the third modification.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In the drawings, the same or corresponding constituent elements are denoted by the same or corresponding reference numerals, and a description thereof will be omitted. In the present specification, " to " representing a numerical range means a range including numerical values before and after the numerical value.

1 is a flowchart showing a method for producing an alkali-free glass plate according to an embodiment of the present invention. The method for producing an alkali-free glass plate has a dissolving step S12 and a molding step S14.

The alkali-free glass is a glass substantially containing no alkali metal oxide such as Na ₂ O, K ₂ O, Li ₂ O, or the like. In the alkali-free glass according to the present invention, the total content of the alkali metal oxide is 0.2 mass% or less.

Alkali-free glasses can be used, for example, as mass percentage percentages based on oxides,

SiO ₂ : 54 to 73%

Al ₂ O ₃ : 10 to 23%

B ₂ O ₃ : 0.1 to 12%

MgO: 0 to 12%

CaO: 0 to 15%

SrO: 0 to 16%

BaO: 0 to 15%

MgO + CaO + SrO + BaO: 8 to 26%

Lt; / RTI >

The alkali-free glass, when both a high distortion point and a high solubility are compatible, is preferably expressed as mass% based on oxide,

SiO ₂ : 58 to 66%

Al ₂ O ₃ : 15 to 22%

B ₂ O ₃ : 5 to 12%

MgO: 0 to 8%

CaO: 0 to 9%

SrO: 3 to 12.5%

BaO: 0 to 2%

MgO + CaO + SrO + BaO: 9 to 18%

Lt; / RTI >

In order to obtain a particularly high distortion point, the alkali-free glass is preferably expressed in mass% based on oxide,

SiO ₂ : 54 to 73%

Al ₂ O ₃ : 10.5 to 22.5%

B ₂ O ₃ : 0.1 to 5.5%

MgO: 0 to 10%

CaO: 0 to 9%

SrO: 0 to 16%

BaO: 0 to 2.5%

MgO + CaO + SrO + BaO: 8 to 26%

Lt; / RTI >

The content of B ₂ O _{3 in the} alkali-free glass is preferably 9 mass% or less, more preferably 5 mass% or less, further preferably 3 mass% or less, particularly preferably 2 mass% or less, Or less.

The B ₂ O ₃ content of the alkali-free glass is preferably not less than 0.3% by mass, more preferably not less than 0.5% by mass, further preferably not less than 1% by mass, in the case of obtaining high solubility.

The distortion point of the alkali-free glass is preferably 650 占 폚 or higher, more preferably 670 占 폚 or higher, and still more preferably 700 占 폚 or higher.

The T ₂ of the alkali-free glass (the temperature which is the standard for melting and corresponds to a viscosity of 10 ² dPa · s) is 100 ° C. higher than the T ₂ of the ordinary soda lime glass. The T ₂ of the alkali-free glass is preferably 1600 to 1820 ° C, more preferably 1610 to 1770 ° C, and still more preferably 1620 to 1720 ° C.

Β-OH showing a water content in the alkali-free glass plate is preferably 0.2 to 0.4mm ^-1, more preferably from 0.2 to 0.35mm ^{- 1.} The higher the value of β-OH, the greater the water content. This value increases when dissolved in an atmosphere having a high water concentration. The value B of? -OH is calculated by measuring the plate thickness C and the transmittance T of the alkali-free glass plate and substituting the measurement result into the following equation. A general Fourier transform infrared spectrophotometer (FT-IR) is used to measure the transmittance of the alkali-free glass plate.

B = (1 / C) log ₁₀ (T1 / T2)

T1: transmittance of an alkali-free glass plate at a reference wave number of 4000 / cm (unit:%)

T2: minimum transmittance of an alkali-free glass plate in the vicinity of a water absorption wavelength of 3570 / cm (unit:%)

The alkali-free glass plate is used as a substrate for a display such as a liquid crystal display, an organic EL display, and a substrate for a magnetic disk. The use of the alkali-free glass plate may be various. As will be described later in detail, the present embodiment is suitable for a substrate for a liquid crystal display which requires a particularly high quality, because a homogeneous alkali-free glass sheet with few defects such as bubbles can be obtained.

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

The melting property of the raw material of the alkali-free glass affects the formation of the bubble layer. Raw material of, SiO ₂ is difficult to cause the silica sand is melted. The median particle diameter D ₅₀ of the silica sand is preferably 250 탆 or less, more preferably 240 탆 or less, and further preferably 230 탆 or less. When the median particle diameter D ₅₀ of the silica sand is 250 탆 or less, the meltability of the raw material becomes good and the generation of undrawn silica can be suppressed.

The median particle diameter D ₅₀ of the silica sand is preferably 90 占 퐉 or more, more preferably 120 占 퐉, and still more preferably 150 占 퐉 or more. When the median particle diameter D ₅₀ of the silica sand is 90 탆 or more, the increase of the water concentration in the molten glass can be suppressed and the volatilization of B ₂ O ₃ and moisture in the molten glass can be suppressed. If the median particle diameter D ₅₀ of the silica sand is less than 90 탆, the surface area of the particles becomes large and a large amount of water is adhered, so that the water concentration in the molten glass becomes high.

Here, the median particle diameter D ₅₀ means 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 molding step S14 shown in Fig. 1, the molten glass is formed into a plate. The molding method may be a general method, and examples thereof include a float method and a fusion method.

The float process is a process for continuously feeding molten glass onto a molten metal (for example, molten tin) and forming molten glass in a strip shape by flowing the molten glass in a horizontal direction on the molten metal.

The fusion method is also called an overflow down-draw method. The molten glass overflowing from both sides to the left and right sides of the trough is caused to flow down along the both left and right sides of the trough, and the molten glass merged at the lower end of the trough is further caused to flow downward, And is formed into a plate.

Further, a clarifying apparatus (for example, a vacuum degassing apparatus) or an agitating apparatus (for example, a stirring agitator) may be provided between the dissolving step S12 and the molding step S14.

Fig. 2 is a cross-sectional view showing a melting furnace used in the melting process of Fig. 1; 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 filled with a raw material 12 of alkali-free glass. The first chamber (21) melts the raw material (12) and reserves the molten glass (14). The first chamber 21 includes 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 For example, an arched ceiling). The downstream side wall 24 reaches the ceiling 25 as shown in FIG. 2, but it may be higher than the bubble layer 16 and does not need to reach the ceiling 25 as shown in FIG. At the upstream side wall 23, a charging port 23a for the raw material 12 is formed.

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

The first chamber burner 26 ejects flames from the openings of the left and right side walls connecting the upstream side wall 23 and the downstream side wall 24 to the first chamber 21. The first chamber burner 26 may continuously spray the flame, or may spray the flame intermittently.

The first chamber burner 26 is disposed on each of the right and left side walls. The first chamber burners 26 may be disposed laterally symmetrically with the first chamber 21 therebetween, may be arranged in a staggered manner with the first chamber 21 interposed therebetween, They may be arranged in a zigzag manner.

Either an air combustion burner or an oxygen combustion burner is used for each first chamber burner 26. All of the plurality of first yarn burners 26 may be oxygen burners, some of them may be oxygen burners, and the remainder may be air burners.

In the present specification, an air combustion burner refers to the use of air mainly as a gas to be mixed with fuel, and means that the oxygen concentration of the gas is 25% by volume or less. If the oxygen concentration of the gas is 25 vol% or less, a mixed gas of air and oxygen gas may be used, or air may be used.

In the present specification, the term "oxygen combustion burner" refers to the use of oxygen gas mainly as a gas to be mixed with fuel, and means that the oxygen concentration of the gas is 93 vol% or more. If the oxygen concentration of the gas is 93% by volume or more, a mixed gas of oxygen gas and air may be used, or only oxygen gas may be used.

Since each of the first chamber burners 26 is either an air combustion burner or an oxygen combustion burner, the NO _x emission amount can be reduced.

An electrode for energizing the molten glass 14 may be provided in the molten glass 14 of the first chamber 21 for the purpose of assisting the heating of the molten glass 14 by the first chamber burner 26. [

It is preferable not to introduce a dry gas such as nitrogen gas into the upper space of the first chamber 21. [ The reduction of the heat efficiency and the increase of the exhaust gas amount can be prevented.

In the second chamber 31, the molten glass 14 formed by melting the raw material 12 is supplied from the first chamber 21. The second chamber (31) refines the molten glass (14) or adjusts the temperature. The second chamber 31 includes 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, It is enclosed. At the lower portion of the downstream side wall 34, a blow-out port 34a for the molten glass 14 is formed.

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 but may not be integrated as shown in Fig. 4, the bottom wall 32 of the second chamber 31 and the bottom wall 22 of the first chamber 21 may have a step D therebetween. The bottom wall 32 of the second chamber 31 and the bottom wall 22 of the first chamber 21 may be either higher.

2 to 4, the upstream side wall 33 of the second chamber 31 and the downstream side wall 24 of the first chamber 21 are integrated, but they may not be integrated as shown in Fig.

In Figs. 2 to 4, the ceiling 35 of the second chamber and the ceiling 25 of the first chamber 21 are integrated, but they may not be integrated. The case in which the ceiling 35 of the second chamber and the ceiling 25 of the first chamber 21 are not integrated is not limited to the case where the lower side wall 24 of the first chamber 21, And the upstream side wall 33 of the second chamber 31 is not integrated.

The second chamber burner 36 forms a flame by mixing fuel such as natural gas or heavy oil with gas and burning it. 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 ejects flames from the openings of the left and right side walls connecting the upstream side wall 33 and the downstream side wall 34 to the second chamber 31. The second chamber burner 36 may continuously spray the flame, or may spray the flame intermittently.

The second chamber burner 36 is disposed on each of the left and right sidewalls connecting the upstream side wall 33 and the downstream side wall 34. The second chamber burners 36 may be disposed symmetrically with the second chamber 31 interposed therebetween, may be arranged in a zigzag manner with the second chamber 31 interposed therebetween, They may be arranged in a zigzag manner.

For each second chamber burner 36, either an air combustion burner or an oxygen combustion burner is used. Of the plurality of second yarn burners 36, a part is an oxygen combustion burner and the remaining part is an air combustion burner. As a result, the NO _x emission amount can be reduced.

An electrode for energizing the molten glass 14 may be provided in the molten glass 14 of the second chamber 31 for the purpose of assisting the heating of the molten glass 14 by the second chamber burner 36. [

It is preferable not to introduce a dry gas such as nitrogen gas into the upper space of the second chamber 31. [ The reduction of the heat efficiency and the increase of the exhaust gas amount can be prevented.

The throat 41 connects the lower portion of the first chamber 21 and the lower portion 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 of the first chamber 21 is supplied to the second chamber 31 through the throat 41. [

The inlet of the throat 41 is formed in the downstream sidewall 24 of the first chamber 21 in Fig. 2 but may be formed in the bottom wall 22 of the first chamber 21 as well. Similarly, the outlet of the throat 41 is formed in the upstream wall 33 of the second chamber 31 in Fig. 2, but may also be formed in the bottom wall 32 of the second chamber 31. Fig.

However, the T ₂ of the alkali-free glass is 100 ° C or more higher than the T ₂ of the ordinary soda lime glass. Thus, in the present embodiment, the molten glass 14 is heated by using both the first and second seal burners 26 and 36.

In the case of alkali-free glass, the melting temperature of the raw material 12 is high and the bubble layer 16 is easily attached to the liquid surface of the molten glass 14 in the first chamber 21, as compared with the case of ordinary soda lime glass. The bubble layer 16 is a collection of small bubbles, and the bubbles are caused by generation of gas due to pyrolysis of the raw material 12 and the like. Foam layer 16 is liable to be formed especially in the case where the SiO ₂ content of 54 to 73% by weight alkali-free glass. The bubble layer 16 blocks thermal radiation from the flame of the first chamber burner 26 to the molten glass 14.

Therefore, in this embodiment, 50 to 100% (preferably 55 to 100%, more preferably 60 to 100%) of the total combustion heat amount per hour of all the first yarn burners 26 is supplied to the oxygen combustion burner .

In the case of an air combustion burner, nitrogen gas, which occupies almost the air, is exhausted out of the melting furnace without contributing to combustion. On the other hand, in the case of the oxygen combustion burner, since the amount of exhaust is smaller than that of the air combustion burner, the heat efficiency is high, and the CO ₂ emission amount and the NO _x emission amount are small.

It is possible to efficiently heat the molten glass 14 even if the bubble layer 16 is interposed, if 50 to 100% of the total combustion heat amount per hour of all the first chamber burners 26 is due to the oxygen combustion burner, The molten glass 14 can be heated to a desired temperature by the fuel. The total combustion heat amount is obtained by summing the heat amount 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. The molten glass 14 is supplied to the second chamber 31 through the throat 41 and the molten glass 14 is supplied to the second chamber 31 without being influenced by the bubble layer 16 of the first chamber 21 The bubble layer 16 is hardly formed in the second chamber 31 unlike the first chamber 21 because the molten glass 14 is uniformly supplied.

In the second chamber 31, the liquid surface 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 is dissolved in the molten glass 14.

However, in general alkali-containing glass, B ₂ O ₃ in the molten glass tends to volatilize more as the alkali content in the molten glass increases. B ₂ O ₃ volatilizes, for example, as a sodium compound.

In contrast, 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 of the upper space, the more easily B ₂ O ₃ in the molten glass is volatilized .

The water content in the molten glass or the moisture content in the atmosphere of the upper space depends on the type of the burner. In the case of the oxygen combustion 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 liable to volatilize.

Therefore, in the present embodiment, it is preferable that 30 to 75% (preferably 35 to 75%, more preferably 45 to 75%, and even more preferably 50 To 75%) is made by the oxygen combustion burner. In the present embodiment, the ratio of the amount of combustion heat per hour of the oxygen combustion burner in the first chamber 21 to the total combustion heat amount per hour of all the first chamber burners 26 (hereinafter referred to as the first chamber 21 ) Is the ratio of the combustion heat amount per hour of the oxygen combustion burner in the second chamber 31 to the total combustion heat amount per hour of all the second chamber burners 36 (Hereinafter referred to as the oxygen combustion rate of the oxygen-containing gas 31).

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

Here, in the first chamber 21, since the bubble layer 16 is formed and B ₂ O ₃ in the molten glass 14 is hardly volatilized into the upper space, even if the oxygen burning rate is large, the B ₂ O ₃ volatilization Is not much of a problem. However, in the second chamber 31, since the bubble layer 16 is hardly formed, it is necessary to reduce the oxygen combustion rate in order to suppress the volatilization of B ₂ O ₃ .

In the present embodiment, the oxygen combustion rate of the second chamber 31 is 75% or less, whereby the volatilization of B ₂ O ₃ can be suppressed. Further, by setting the oxygen combustion rate of the second chamber 31 to 30% or more, the NO _x emission amount can be reduced.

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

The molten glass 14 is balanced in the first chamber 21 and the second chamber 31 when the distance L1 is 50 to 75% of the reference distance L0 and the distance L2 is 10 to 40% .

In the embodiment of the present invention, among the first room burners 26, a total of one hour of the first room burner 26 installed in an area spaced by 0.5L1 or more from the upstream end of the first room 21 It is assumed that 60% or more (preferably 65% or more, more preferably 70% or more, and more preferably 80% or more) of the combustion heat amount is caused by the oxygen combustion burner.

If at least 60% of the total combustion heat amount per hour of the first chamber burner 26 installed in the above region is due to the oxygen combustion burner, the amount of exhaust gas is reduced, and the molten glass 14 can be efficiently heated , An alkali-free glass sheet can be produced with a small gas consumption. A bubbler or the like 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 dissolution and homogeneity of the glass.

The bubbler is disposed so as to be spaced apart from the melting chamber by a predetermined distance (pitch) across the width direction of the melting furnace (the direction perpendicular to the plane of FIG. 2), and the molten glass in the first chamber 21 and / 14). The number of bubblers arranged in one line in the width direction (the direction perpendicular to the plane of FIG. 2) is preferably 5 to 30, more preferably 7 to 25. The plurality of bubblers may be arranged at regular intervals in the width direction (the vertical direction in FIG. 2), or may not be arranged at equal intervals. The plurality of bubblers may be two or more rows.

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

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

Although the melting furnace, the melting method, the method of producing an alkali-free glass plate, and the embodiment of the alkali-free glass have been described, the present invention is not limited to the embodiments described above, Various modifications and substitutions can be made to the shape.

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

[ Example ]

Hereinafter, examples and comparative examples of the present invention will be described in detail. The present invention is not limited to these materials.

The oxygen burning rate of the first chamber 21 and / or the second chamber 31 is changed so that the atmosphere of the upper space in the first chamber 21 and the second chamber 31 The water content was adjusted. The moisture concentration is determined by calculating the water concentration contained in the gas after combustion based on the composition of fuel and gas burned by the first and second chamber burners 26 and 36, In consideration of flowing toward the outside of the apparatus. Further, the total flow rate of the combustion air used for the air combustion burner of the melting furnace was calculated. The results are shown in Table 1. 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 molten glass surface to the ceiling 25 of the first chamber and the ceiling 35 of the second chamber: 8 m

The first chamber burner 26 and the second chamber burner 36 are partly an oxygen combustion burner and the remaining part 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 rate of the first chamber 21 and / or the second chamber 31 was changed so that the total heating amount of the melting furnace became equal. 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.

Examples 1 to 3 show the case where the oxygen combustion rate of the first chamber 21 is 50 to 100% and the oxygen combustion rate of the second chamber 31 is 30 to 75% The average moisture concentration in the atmosphere of the space was 19 to 23%.

On the other hand, in Example 4, the oxygen combustion rate of the first chamber 21 is 50 to 100%, the oxygen combustion rate of the second chamber 31 is more than 75% The average moisture concentration in the atmosphere was 40%.

As described above, when the moisture concentration in the atmosphere of the upper space in the second chamber 31 is high, B ₂ O ₃ is easily volatilized, so that the oxygen combustion rate of the first chamber 21 is 50 to 100% It was also found that the dissolution method in which the oxygen burning rate of the second chamber 31 is 30 to 75% can suppress the volatilization of B ₂ O ₃ .

In Examples 1 to 3, the total combustion air flow rate of the melting furnace was 100 to 180, relative to 100 as Example 1.

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

The dissolving method in which the oxygen combustion rate of the first chamber 21 is 50 to 100% and the oxygen combustion rate of the second chamber 31 is 30 to 75% can reduce the total combustion air flow rate of the melting furnace , It was found that the NO _x emission amount can be reduced.

As described above, the dissolving method in which the oxygen burning rate of the first chamber 21 is 50 to 100% and the oxygen burning rate of the second chamber 31 is 30 to 75% suppresses the volatilization of B ₂ O ₃ And the amount of NO _x emissions can be reduced.

The present application is based on Japanese Patent Application No. 2016-078125 filed on April 8, 2016, the contents of which are incorporated herein by reference.

12 Ingredients of alkali-free glass
14 Melted glass
16 bubble layer
21 Room 1
22 Lower wall of the first room
23 upstream side wall of the first chamber
23a Inlet of raw material
24 downstream side wall of the first chamber
25 Ceiling of the 1st room
26 1st chamber burner
31 2nd Room
32 Lower wall of the second room
33 upstream side wall of the second chamber
34 downstream side wall of the second chamber
35 Ceiling of the second room
36 2nd room burner
41 throttle

Claims (4)

A first chamber in which a raw material of glass is injected, a first chamber burner which forms a flame in an upper space of the first chamber, a second chamber in which molten glass obtained by melting the raw material is supplied from the first chamber, A second chamber burner for forming a flame in an upper space of two chambers and a throat for connecting a lower portion of the first chamber to a lower portion of the second chamber,
The raw material is a non-alkali glass raw material having a SiO ₂ content of 54 to 73 mass% and a B ₂ O ₃ content of 0.1 to 12 mass%
Wherein each of the first chamber burner and the second chamber burner uses either an oxygen combustion burner or an air combustion burner,
50 to 100% of the total combustion heat amount per hour of all the first filament burners is generated by the oxygen burner,
Wherein 30 to 75% of the total combustion heat amount per hour of all the second room burners is generated by the oxygen combustion burner. The dissolution method according to claim 1, wherein the median particle diameter D ₅₀ of the silica sand contained in the raw material is 90 占 퐉 or more and 250 占 퐉 or less. The non-alkali glass according to claim 1 or 2, wherein the alkali-free glass is represented by mass% based on oxide,
SiO ₂ : 54 to 73%
Al ₂ O ₃ : 10 to 23%
B ₂ O ₃ : 0.1 to 12%
MgO: 0 to 12%
CaO: 0 to 15%
SrO: 0 to 16%
BaO: 0 to 15%
MgO + CaO + SrO + BaO: 8 to 26%
≪ / RTI > A dissolution step comprising the dissolution method according to any one of claims 1 to 3;
And a molding step of molding the molten glass melted in the melting step into a plate.

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