Float glass manufacturing method

Abstract

To provide a technique capable of suppressing burn-out of a carbon member while suppressing occurrence of dross defects.SOLUTION: A method for manufacturing float glass comprises: withdrawing a glass ribbon molded on molten metal stored in a float bus from the float bus by n (n is a natural number of 2 or more) conveyance rollers provided in the inside of a dross box to send the glass ribbon to a slow cooling furnace; contacting a carbon member to each of the n conveyance rollers in a lower space of the dross box; supplying an inert gas to the first space in the lower space; and supplying a reduction gas to an i-th space (i is a natural number of 2 or more and n or less) of the lower space. A space positioned at a k-th position toward the downstream side from the upstream side in the conveying direction in n+1 spaces obtained by dividing the lower space with the carbon member in the direction of conveying the glass ribbon is defined as a k-th space.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a float glass manufacturing method. [Background technology]

[0002] The float glass manufacturing method includes forming a glass ribbon on molten metal stored in a float bath, drawing the formed glass ribbon from the float bath by a plurality of conveying rolls provided inside a dross box, and sending the formed glass ribbon to an annealing furnace. The float glass manufacturing method also includes cutting the glass ribbon into a desired size and shape after annealing in the annealing furnace. The float glass is obtained by cutting the glass ribbon.

[0003] The inside of the float bath is filled with reducing gas to suppress oxidation of the molten metal. Meanwhile, the inside of the annealing furnace is filled with air flowing in from the outlet of the annealing furnace. As a result, reducing gas flows into the inside of the float bath, and air flows in from the inside of the annealing furnace. Air also flows into the inside of the dross box through holes (e.g. holes through which the transport rolls pass) formed in the outer wall of the dross box, or through the gap between the dross box and the annealing furnace.

[0004] The float glass manufacturing method includes contacting a carbon member with a transport roll in a dross box to remove foreign matter adhering to the transport roll. The foreign matter includes, for example, oxides of molten metal brought into the dross box together with the glass ribbon, so-called dross. When air flows into the dross box, the carbon member is oxidized and consumed by oxygen gas in the air, making it difficult to remove the dross. As a result, scratches are generated on the lower surface of the glass ribbon. Furthermore, when air flows into the dross box, the molten metal adhering to the lower surface of the glass ribbon is oxidized, resulting in the generation of dross defects.

[0005] Patent Document 1 discloses a technique for suppressing the inflow of air from the inside of an annealing furnace into the inside of a dross box by using an atmosphere partition device. The atmosphere partition device includes a partition member and a lifting mechanism for vertically moving the partition member. The partition member separates a space below a conveying path along which a glass ribbon is conveyed in the dross box from a space below the conveying path in the annealing furnace.

[0006] Patent Document 2 discloses a technique in which a gas flow forming means is used to shield a removal member that removes molten tin adhering to a transport roll with a non-oxidizing gas. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2016-050160 A [Patent Document 2] JP 2011-132099 A Summary of the Invention [Problem to be solved by the invention]

[0008] According to Patent Document 1, it is possible to prevent air from flowing into the dross box from inside the annealing furnace, but air may flow into the dross box through holes (e.g., holes through which a transport roll passes) formed in the outer wall of the dross box or through a gap between the dross box and the annealing furnace. Therefore, the technology described in Patent Document 1 cannot sufficiently prevent air from flowing into the dross box. Therefore, it cannot sufficiently prevent the carbon member from being oxidized and worn out by oxygen gas in the air. In addition, it cannot sufficiently reduce dross defects occurring on the lower surface of the glass ribbon.

[0009] The interior of the dross box includes an upper space above the glass ribbon G and a lower space below the glass ribbon G. Reducing gas flows into the upper space of the dross box from inside the float bath. The flowing in reducing gas may flow from above the glass ribbon to below it, and may flow back from the lower space of the dross box toward the inside of the float bath. If the backflowing reducing gas is supplied between the lower surface of the glass ribbon and the upper surface of the molten metal, the molten metal is likely to be brought into the dross box together with the glass ribbon, and the number of dross defects occurring on the lower surface of the glass ribbon increases.

[0010] According to Patent Document 2, deterioration of the removal member due to oxidation can be prevented, but tin adhering to the surface of the transport roll oxidizes, and tin adhering to the surface of the glass ribbon oxidizes while being transported by the transport roll, resulting in a deterioration in the quality of the float glass.

[0011] One aspect of the present disclosure provides a technique for suppressing oxidative wear of a carbon member while suppressing the occurrence of dross defects. [Means for solving the problem]

[0012] A float glass manufacturing method according to one embodiment of the present disclosure includes: drawing out a glass ribbon formed on molten metal stored in a float bath from the float bath by n (n is a natural number of 2 or more) conveying rolls provided inside a dross box, and sending the glass ribbon to an annealing furnace. The float glass manufacturing method includes bringing a carbon member into contact with each of the n conveying rolls in a lower space below the glass ribbon inside the dross box. Among n+1 spaces obtained by dividing the lower space by the carbon members in the conveying direction of the glass ribbon, the space located k-th from the upstream side to the downstream side in the conveying direction is defined as the k-th space. The float glass manufacturing method includes supplying an inert gas to a first space of the lower space, and supplying a reducing gas to an i-th space (i is a natural number of 2 or more and n or less) of the lower space. The float glass manufacturing method includes supplying a reducing gas toward the transport roll on the upstream side in the transport direction in the i-th space. Effect of the Invention

[0013] According to one aspect of the present disclosure, by supplying an inert gas to the most upstream first space, the pressure in the first space can be increased, and the inflow of air into the first space can be suppressed. In addition, by supplying an inert gas to the most upstream first space, the reducing gas concentration in the first space can be reduced while suppressing the inflow of the reducing gas from the space directly above the first space into the first space, and the backflow of the reducing gas from the first space into the inside of the float bath can be suppressed. Furthermore, by supplying a reducing gas to the i-th space, the pressure in the i-th space can be increased, and the inflow of air into the i-th space can be suppressed. Furthermore, by supplying a reducing gas to the i-th space, oxygen gas in the air that has flowed into the i-th space can be changed into water vapor or the like, and oxidation by oxygen gas can be suppressed. As a result, the generation of dross defects can be suppressed while oxidative wear of the carbon member can be suppressed. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view showing a float glass manufacturing apparatus according to one embodiment. [Diagram 2] FIG. 2 is an enlarged cross-sectional view of the dross box of FIG. [Diagram 3] FIG. 3 is an enlarged cross-sectional view of a dross box according to a first modified example. [Figure 4] FIG. 4 is a perspective view showing a nozzle disposed in the second space shown in FIG. [Diagram 5] FIG. 5 is a perspective view showing a nozzle according to a second modified example. [Figure 6] FIG. 6 is a perspective view showing a nozzle according to a third modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding configurations are denoted by the same reference numerals, and description thereof may be omitted. In each drawing, the X-axis direction, the Y-axis direction, and the Z-axis direction are mutually perpendicular, the X-axis direction and the Y-axis direction are horizontal directions, and the Z-axis direction is vertical. The X-axis direction is the conveying direction of the glass ribbon G, and the Y-axis direction is the width direction of the glass ribbon G. In the specification, "~" indicating a numerical range means that the numerical values ​​described before and after it are included as the lower limit and upper limit.

[0016] A float glass manufacturing apparatus 1 according to one embodiment will be described with reference to FIG. 1. The float glass manufacturing apparatus 1 includes a float bath 2, a dross box 3, and an annealing furnace 5, arranged from the upstream side to the downstream side in the conveying direction of a glass ribbon G. The float glass manufacturing apparatus 1 forms a glass ribbon G on molten metal M stored in the float bath 2, and pulls out the formed glass ribbon G from the float bath 2 by a plurality of conveying rolls 31 provided inside the dross box 3, and sends it to the annealing furnace 5. In addition, the float glass manufacturing apparatus 1 anneals the glass ribbon G inside the annealing furnace 5, and then cuts it into a desired size and shape. Float glass is obtained by cutting the glass ribbon G.

[0017] The float glass is, for example, alkali-free glass, aluminosilicate glass, borosilicate glass, soda-lime glass, etc. The alkali-free glass means glass that does not substantially contain alkali metal oxides such as Na2O, K2O, etc. Here, "substantially does not contain alkali metal oxides" means that the total content of alkali metal oxides is 0.1 mass% or less.

[0018] The use of float glass is not particularly limited, but for example, it is a cover glass for a display (for example, a liquid crystal display or an organic EL display). When the float glass is used as a cover glass, the float glass is a glass for chemical strengthening. Unlike non-alkali glass, the glass for chemical strengthening contains an alkali metal oxide.

[0019] Chemically strengthened glass contains, for example, in mole percentages based on oxides, SiO2: 62% to 68%, Al2O3: 6% to 12%, MgO: 7% to 13%, Na2O: 9% to 17%, and K2O: 0% to 7%, and the difference obtained by subtracting the Al2O3 content from the total content of Na2O and K2O is less than 10%, and if ZrO2 is contained, its content is 0.8% or less.

[0020] Another chemically strengthened glass contains, in mole percentages based on oxides, 65% to 85% SiO2, 3% to 15% Al2O3, 5% to 15% Na2O, 0% to less than 2% K2O, 0% to 15% MgO, and 0% to 1% ZrO2, and the total content of SiO2 and Al2O3, SiO2+Al2O3, is 88% or less.

[0021] Another chemically strengthened glass contains, in mole percentages based on oxides, 50% to 75% SiO2, 9% to 20% Al2O3, 10% to 20% Na2O, 0% to 6% K2O, 0% to 15% MgO, 0% to 10% CaO, SrO, and BaO in total (CaO+SrO+BaO), 0% to 5% ZrO2 and TiO2 in total (ZrO2+TiO2), 0% to 10% B2O3, and 0% to 20% Li2O.

[0022] The float glass may be used as a glass substrate for forming a thin film transistor or a color filter of a display. When the float glass is used as a glass substrate, the float glass is an alkali-free glass. Unlike chemically strengthened glass, the alkali-free glass does not substantially contain an alkali metal oxide.

[0023] The alkali-free glass contains, for example, in mass % on an oxide basis, SiO2: 50% to 73%, Al2O3: 10.5% to 24%, B2O3: 0% to 12%, MgO: 0% to 10%, CaO: 0% to 14.5%, SrO: 0% to 24%, BaO: 0% to 13.5%, MgO+CaO+SrO+BaO: 8% to 29.5%, and ZrO2: 0% to 5%.

[0024] In the case where alkali-free glass is to achieve both a high strain point and high solubility, it preferably contains, in mass % on an oxide basis, 58% to 66% SiO2, 15% to 22% Al2O3, 5% to 12% B2O3, 0% to 8% MgO, 0% to 9% CaO, 3% to 12.5% ​​SrO, 0% to 2% BaO, and 9% to 18% MgO+CaO+SrO+BaO.

[0025] When a particularly high strain point is desired, the alkali-free glass preferably contains, in mass % on an oxide basis, 54% to 73% SiO2, 10.5% to 22.5% Al2O3, 0% to 5.5% B2O3, 0% to 10%, CaO: 0% to 9%, SrO: 0% to 16%, BaO: 0% to 2.5%, and 8% to 26% MgO+CaO+SrO+BaO.

[0026] The thickness of the float glass is selected depending on the application of the float glass. When the float glass is used as a cover glass for a display, the thickness of the float glass is, for example, 0.1 mm to 2.0 mm. On the other hand, when the float glass is used as a glass substrate for a display, the thickness of the float glass is, for example, 0.1 mm to 0.7 mm.

[0027] Next, referring again to FIG. 1, a float bath 2 according to one embodiment will be described. The float bath 2 includes a bath 21. The bath 21 contains a molten metal M. As the molten metal M, for example, molten tin is used. In addition to molten tin, a molten tin alloy can also be used, and the molten metal M may be any metal having a higher density than the molten glass. The molten glass is continuously supplied onto the molten metal M, and is formed into a band-shaped glass ribbon G by utilizing the smooth liquid surface of the molten metal M.

[0028] The float bath 2 has a ceiling 22 that forms a space above the bath 21. The inside of the float bath 2 is filled with reducing gas and maintained at a pressure higher than atmospheric pressure to prevent oxidation of the molten metal M. The reducing gas is, for example, a mixed gas of nitrogen gas and hydrogen gas, containing 85 volume % to 98.5 volume % of nitrogen gas and 1.5 volume % to 15 volume % of hydrogen gas. The reducing gas is supplied from the joints between the bricks of the ceiling 22 and holes in the ceiling 22.

[0029] The dross box 3 includes a transport roll 31 that pulls up the glass ribbon G. The transport roll 31 is rotationally driven by a driving device (not shown) such as a motor, and transports the glass ribbon G obliquely upward by the driving force. The driving device is provided outside the dross box 3. Therefore, a hole is formed in the outer wall of the dross box 3 to allow the transport roll 31 to pass through.

[0030] A plurality of transport rolls 31 are arranged at intervals in the transport direction (X-axis direction) of the glass ribbon G inside the dross box 3. The number of transport rolls 31 is three in FIG. 1 , but may be two or more as long as it is more than one. The axial direction of the transport rolls 31 is the same as the width direction (Y-axis direction) of the glass ribbon G.

[0031] The dross box 3 includes a carbon member 32 that is in contact with the transport roll 31. The carbon member 32 is disposed in the lower space of the dross box 3. The lower space of the dross box 3 is a space below the glass ribbon G. The carbon member 32 is in contact with the outer peripheral surface of the transport roll 31, and removes foreign matter adhering to the outer peripheral surface of the transport roll 31. The foreign matter includes, for example, oxides formed by oxidation of the molten metal M brought into the inside of the dross box 3 together with the glass ribbon G, that is, so-called dross.

[0032] The carbon member 32 is, for example, a rectangular parallelepiped. The carbon member 32 may be a trapezoid or an inverted trapezoidal quadrangular prism when viewed in the X-axis direction. A plurality of carbon members 32 may be provided in the axial direction of the transport roll 31. The number of carbon members 32 arranged along each transport roll 31 is determined according to the width of the glass ribbon G (dimension in the Y-axis direction) or the axial length of the transport roll 31 (dimension in the Y-axis direction).

[0033] The dimension of the carbon member 32 in the Y-axis direction is, for example, 300 mm to 1000 mm, and preferably 400 mm to 800 mm. The dimension of the carbon member 32 in the Z-axis direction is, for example, 50 mm to 200 mm, and preferably 70 mm to 150 mm. The dimension of the carbon member 32 in the X-axis direction is, for example, 20 mm to 100 mm, and preferably 30 mm to 80 mm.

[0034] The carbon member 32 may contain graphite powder. The maximum particle size of the graphite powder is, for example, 0.1 mm to 3 mm, and preferably 0.5 mm to 2.5 mm. When the maximum particle size of the graphite powder is 0.1 mm to 3 mm, the strength of the carbon member 32, which is a compact of the graphite powder, can be ensured.

[0035] The shore hardness of the carbon member 32 is, for example, 20 HS to 90 HS, and preferably 30 HS to 80 HS. When the shore hardness of the carbon member 32 is 20 HS to 90 HS, the abrasion resistance of the carbon member 32 against the transport roll 31 can be ensured.

[0036] The dross box 3 may include a biasing member 33 that presses the carbon member 32 against the transport roll 31. The biasing member 33 includes, for example, a metal spring. The spring is a leaf spring. Instead of a leaf spring, the biasing member 33 may include a coil spring, a compression coil spring, a disc spring, a volute spring, a ring spring, or the like. The biasing member 33 may include a fluid pressure cylinder such as an air pressure cylinder.

[0037] The dross box 3 may include a support member 34 that supports the carbon member 32 so that it can be raised and lowered. The support member 34 is disposed on a bottom wall 35 of the dross box 3. The support member 34 has a U-shaped cross section perpendicular to the Y-axis direction, and the carbon member 32 and the biasing member 33 are disposed inside the support member 34. The support member 34 prevents the carbon member 32 and the biasing member 33 from shifting in the X-axis direction.

[0038] The dross box 3 may include a heater 37 to adjust the temperature of the glass ribbon G. The heater 37 may be provided below the glass ribbon G. In the dross box 3, the temperature of the glass ribbon G is preferably (Tg-50°C) to (Tg+30°C) based on the glass transition point Tg of float glass.

[0039] The dross box 3 is provided with a hood 38 above the glass ribbon G, a heat insulating material 39 disposed on the hood 38, and a drape 40 penetrating a part of the heat insulating material 39 and the hood 38 and suspended from the lower surface of the hood 38. The drape 40 is a plate-like member made of a fire-resistant material such as steel or glass.

[0040] The drape 40 divides the upper space of the dross box 3 into multiple spaces in the conveying direction (X-axis direction) of the glass ribbon G. The upper space of the dross box 3 is a space above the glass ribbon G. The drape 40 is disposed, for example, directly above the rotation center line of each conveying roll 31. The drape 40 extends in the axial direction (Y-axis direction) of each conveying roll 31.

[0041] The annealing furnace 5 anneals the glass ribbon G to a temperature equal to or lower than the strain point of the glass while conveying it by the conveying rolls 51. The annealing furnace 5 is provided with heaters (not shown) on the ceiling and bottom wall in order to adjust the temperature of the glass ribbon G. The conveying rolls 51 are driven to rotate by a driving device (not shown) such as a motor, and convey the glass ribbon G in the horizontal direction by the driving force. The annealing furnace 5 is open to the outside at an outlet on the downstream side. Therefore, air flows into the inside of the annealing furnace 5.

[0042] Incidentally, air may flow into the dross box 3 from the inside of the annealing furnace 5. Air may also flow into the dross box 3 from holes (not shown) formed in the outer wall of the dross box 3 (for example, holes through which the transport rolls 31 are inserted) or a gap GP between the dross box 3 and the annealing furnace 5.

[0043] Conventionally, there has been a problem that when air flows into the dross box 3, the carbon member 32 is oxidized and worn away by oxygen gas in the air, making it difficult to remove the dross adhering to the transport roll 31. In addition, conventionally, there has been a problem that when air flows into the dross box 3, the molten metal M adhering to the lower surface of the glass ribbon G is oxidized, resulting in the generation of dross defects.

[0044] In addition, reducing gas may flow into the upper space of the dross box 3 from inside the float bath. Conventionally, the reducing gas flows from above the glass ribbon G downward. nothing This sometimes resulted in a backflow from the lower space of the dross box 3 toward the inside of the float bath 2. The backflowing reducing gas made it easier for the molten metal M to be carried into the dross box 3 together with the glass ribbon G, which caused a problem of an increase in dross defects occurring on the lower surface of the glass ribbon G.

[0045] Next, the dross box 3 according to one embodiment will be described in detail with reference to Fig. 2. A plurality of transport rolls 31, carbon members 32, biasing members 33, and support members 34 are arranged at intervals in the transport direction (X-axis direction) of the glass ribbon G. The axial direction of the transport rolls 31 is the same as the width direction (Y-axis direction) of the glass ribbon G.

[0046] The dross box 3 includes n (n is a natural number of 2 or more) transport rolls 31 in the lower space of the dross box 3, each of which has a carbon member 32 in contact with the roll. Although n is 3 in FIG. 2, it may be 2 or 4 or more.

[0047] In this specification, the kth space is defined as the kth space among the n+1 spaces partitioned by carbon members 32 in the conveying direction (X-axis direction) of the glass ribbon G, the space located kth from the upstream side to the downstream side in the conveying direction.

[0048] In addition, in this specification, among the n transport rolls 31 provided inside the dross box 3, the transport roll 31 located at the kth position from the upstream side to the downstream side in the transport direction is defined as the kth transport roll 31-k.

[0049] Furthermore, in this specification, the carbon member 32 that contacts the kth transport roll 31-k is defined as the kth carbon member 32-k. Also, the biasing member 33 that biases the kth carbon member 32-k is defined as the kth biasing member 33-k. Furthermore, the support member 34 that supports the kth carbon member 32-k is defined as the kth support member 34-k.

[0050] The lower space of the dross box 3 is divided into four spaces S1, S2, S3, and S4 by, for example, three transport rolls 31-1, 31-2, and 31-3. In any two adjacent spaces among the four spaces S1, S2, S3, and S4, gas may flow from one space to the other, and the gases may mix.

[0051] As shown in Figure 2, when viewed in the Y-axis direction, the first space S1 is surrounded by an upstream wall 41 facing the float bath 2 of the dross box 3, a bottom wall 35 of the dross box 3, a first conveying roll 31-1, a first carbon member 32-1, and a first support member 34-1.

[0052] When viewed in the Y-axis direction, the second space S2 is surrounded by the first conveying roll 31-1, the first carbon member 32-1, the first support member 34-1, the bottom wall 35 of the dross box 3, the second conveying roll 31-2, the second carbon member 32-2, and the second support member 34-2.

[0053] When viewed in the Y-axis direction, the third space S3 is surrounded by the second conveying roll 31-2, the second carbon member 32-2, the second support member 34-2, the bottom wall 35 of the dross box 3, the third conveying roll 31-3, the third carbon member 32-3, and the third support member 34-3.

[0054] The fourth space S4 is surrounded by, when viewed in the Y-axis direction, the third conveying roll 31-3, the third carbon member 32-3, the third support member 34-3, the bottom wall 35 of the dross box 3, and the downstream wall 42 of the dross box 3 facing the annealing furnace 5.

[0055] The dross box 3 is equipped with a first nozzle 43 that supplies an inert gas to the first space S1. The first nozzle 43 is inserted into the dross box 3, for example, from an outer wall of one or both ends in the Y-axis direction of the dross box 3, and injects the inert gas into the first space S1. The injection direction of the first nozzle 43 is the Y-axis direction, but may also be the positive Z-axis direction (upward).

[0056] The first space S1 is the most upstream space. The inert gas supplied to the first space S1 is, for example, nitrogen gas or a rare gas such as argon gas. The inert gas supplied to the first space S1 may contain nitrogen gas or a rare gas, or may be a mixed gas of nitrogen gas and a rare gas. No reducing gas is supplied to the first space S1.

[0057] According to this embodiment, the pressure in the first space S1 can be increased by supplying an inert gas to the first space S1. This can prevent the air from flowing into the first space S1 through holes in the outer wall of the dross box 3. This can prevent the carbon member 32 from being oxidized and worn out by oxygen gas in the air. In addition, it can prevent dross defects from being caused by oxygen gas in the air.

[0058] The pressure in the first space S1 is, for example, 1 Pa to 15 Pa higher than atmospheric pressure. If the pressure in the first space S1 is 1 Pa or more higher than atmospheric pressure, it is possible to prevent air from flowing into the first space S1 through holes in the outer wall of the dross box 3. As a result, it is possible to prevent oxidation wear of the carbon member 32. Also, it is possible to reduce dross defects. If the pressure difference between the pressure in the first space S1 and atmospheric pressure is 15 Pa or less, the flow rate of the inert gas supplied to the first space S1 can be reduced.

[0059] Furthermore, according to this embodiment, by supplying an inert gas to the first space S1, the pressure in the first space S1 can be increased while the concentration of the reducing gas in the first space S1 can be reduced. Therefore, the concentration of the reducing gas in the first space S1 can be reduced while preventing the reducing gas from flowing into the first space S1 from the space directly above the first space S1. Therefore, the backflow of the reducing gas from the first space S1 into the inside of the float bath 2 can be prevented, and the molten metal M can be prevented from being brought into the inside of the dross box 3 together with the glass ribbon G. Therefore, dross defects occurring on the lower surface of the glass ribbon G can be reduced.

[0060] The hydrogen gas concentration in the first space S1 is, for example, less than 5 volume %, and preferably 3 volume % or less. If the hydrogen gas concentration in the first space S1 is less than 5 volume %, the amount of hydrogen gas that flows back from the first space S1 into the inside of the float bath 2 is small. The hydrogen gas concentration in the first space S1 is, for example, 1 volume % or more, and preferably 3 volume % or more.

[0061] The oxygen gas concentration in the first space S1 is, for example, 100 ppm by volume or less, and preferably 10 ppm by volume or less. If the oxygen gas concentration in the first space is 100 ppm by volume or less, it is possible to suppress the generation of dross defects and the oxidative wear of the carbon member 32. The oxygen gas concentration in the first space S1 may be 0 ppm by volume or more.

[0062] The dross box 3 includes a second nozzle 44 that supplies reducing gas to the i-th space (i is a natural number between 2 and n). The second nozzle 44 supplies reducing gas to spaces other than the first space S1 at the most upstream side and the (n+1)-th space S4 at the most downstream side (for example, the fourth space S4). The reducing gas can change oxygen gas into water vapor or the like, thereby reducing the oxygen gas concentration.

[0063] As described above, the first space S1 is supplied with an inert gas, not with a reducing gas. In order to avoid a shortage of reducing gas in the second space S2 adjacent to the first space S1, it is preferable that the second nozzle 44 supplies reducing gas to at least the second space S2. In other words, it is preferable that the i-th space includes at least the second space S2. The second nozzle 44 may supply reducing gas to the third space S3.

[0064] The reducing gas supplied to the i-th space contains, for example, hydrogen gas, carbon monoxide gas, or acetylene gas. Hydrogen gas, carbon monoxide gas, and acetylene gas have excellent reducing properties. The reducing gas supplied to the i-th space may contain hydrogen gas or the like, and may further contain an inert gas.

[0065] The reducing gas supplied to the i-th space preferably contains 0.1% to 20% by volume of hydrogen gas, and more preferably 10% to 20% by volume of hydrogen gas. If the hydrogen gas concentration is 0.1% by volume or more, the effect of reducing oxygen gas is easily obtained. Also, if the hydrogen gas concentration is 20% by volume or less, the reducing gas is easily managed.

[0066] The second nozzle 44 is inserted into the dross box 3 from, for example, one or both outer walls in the Y-axis direction of the dross box 3, and discharges the reducing gas into the i-th space. The discharge direction of the second nozzle 44 may be the Y-axis direction as shown in Fig. 2, or the positive Z-axis direction (upward) as shown in Figs. 3 and 4.

[0067] As shown in Fig. 3 and Fig. 4, the second nozzle 44 may include, for example, a horizontal pipe 441 extending in the Y-axis direction and a vertical pipe 442 extending upward from a slit (not shown) formed along the horizontal pipe 441. The horizontal pipe 441 is inserted into a hole in the outer wall of one end in the Y-axis direction of the dross box 3. The vertical pipe 442 is open upward and discharges reducing gas upward. As shown in Fig. 4 and Fig. 5, the dimension of the vertical pipe 442 in the Y-axis direction is not particularly limited, and the vertical pipe 442 may be disposed only at one or both ends of the i-th space in the Y-axis direction, or the vertical pipe 442 may be disposed over the entire i-th space in the Y-axis direction.

[0068] 6, the second nozzle 44 may include a horizontal pipe 441 extending in the Y-axis direction and an outlet hole 443 formed in the horizontal pipe 441. A plurality of outlet holes 443 may be provided at intervals in the Y-axis direction. The outlet holes 443 may be arranged only at one or both ends of the i-th space in the Y-axis direction, or the outlet holes 443 may be arranged over the entire i-th space in the Y-axis direction. The outlet hole 443 is open upward and discharges the reducing gas upward.

[0069] 3, the second nozzle 44 may eject the reducing gas toward the upstream transport roll 31 (for example, the first transport roll 31-1). In the vicinity of the outer circumferential surface of the first transport roll 31-1, an airflow is generated in the rotation direction of the first transport roll 31-1. The airflow can supply the reducing gas to the first carbon member 32-1, and the oxygen gas concentration in the vicinity of the first carbon member 32-1 can be efficiently reduced.

[0070] According to this embodiment, the pressure in the i-th space can be increased by supplying a reducing gas to the i-th space. This makes it possible to prevent the air from flowing into the i-th space through holes in the outer wall of the dross box 3. This makes it possible to prevent the carbon member 32 from being oxidized and worn out by oxygen gas in the air. In addition, it makes it possible to prevent dross defects from being caused by oxygen gas in the air.

[0071] The pressure in the ith space is, for example, 1 Pa to 15 Pa higher than atmospheric pressure. If the pressure in the ith space is 1 Pa or more higher than atmospheric pressure, it is possible to prevent air from flowing into the ith space through holes in the outer wall of the dross box 3. As a result, it is possible to prevent oxidation wear of the carbon member 32. In addition, it is possible to reduce dross defects. If the pressure difference between the pressure in the ith space and atmospheric pressure is 15 Pa or less, it is possible to reduce the flow rate of the reducing gas supplied to the ith space.

[0072] Moreover, according to the present embodiment, by supplying a reducing gas to the i-th space, the oxygen gas flowing into the i-th space can be changed to water vapor or the like, and oxidation by the oxygen gas can be suppressed. Therefore, the carbon member 32 can be prevented from being consumed by oxidation. Also, the occurrence of dross defects can be suppressed.

[0073] The hydrogen gas concentration in the i-th space is, for example, 1 volume % to 20 volume %, and preferably 2 volume % to 10 volume %. If the hydrogen gas concentration in the i-th space is 1 volume % or more, oxygen gas in the air that flows into the i-th space is easily reduced. On the other hand, if the hydrogen gas concentration in the i-th space is 20 volume % or less, it is easy to manage the reducing gas supplied to the i-th space.

[0074] The oxygen gas concentration in the i-th space is, for example, 100 ppm by volume or less, and preferably 50 ppm by volume or less. If the oxygen gas concentration in the i-th space is 100 ppm by volume or less, it is possible to suppress the generation of dross defects and the oxidative wear of the carbon member 32. The oxygen gas concentration in the i-th space may be 0 ppm by volume or more.

[0075] The (n+1)th space is the most downstream space, for example, the fourth space S4. The reducing gas supplied to the (n+1)th space contains, for example, hydrogen gas, carbon monoxide gas, or acetylene gas, and may further contain an inert gas. The inert gas supplied to the (n+1)th space is, for example, nitrogen gas or a rare gas such as argon gas.

[0076] According to this embodiment, by supplying an inert gas or a reducing gas to the (n+1)th space, the pressure in the (n+1)th space can be increased. This makes it possible to prevent air from entering the (n+1)th space through holes in the outer wall of the dross box 3. This makes it possible to prevent the carbon member 32 from being oxidized and worn out by oxygen gas in the air. In addition, it makes it possible to prevent dross defects from being caused by oxygen gas in the air.

[0077] The pressure in the (n+1)th space is, for example, 1 Pa to 15 Pa higher than atmospheric pressure. If the pressure in the (n+1)th space is 1 Pa or more higher than atmospheric pressure, it is possible to prevent air from flowing into the (n+1)th space through the gap GP between the dross box 3 and the annealing furnace 5. As a result, it is possible to prevent the oxidation wear of the carbon member 32. In addition, it is possible to reduce dross defects. If the pressure difference between the pressure in the (n+1)th space and atmospheric pressure is 15 Pa or less, the flow rate of gas supplied to the (n+1)th space can be reduced.

[0078] The hydrogen gas concentration in the (n+1)th space is, for example, 1 volume % to 20 volume %, and preferably 2 volume % to 10 volume %. If the hydrogen gas concentration in the (n+1)th space is 1 volume % or more, oxygen gas in the air that flows into the (n+1)th space is easily reduced. On the other hand, if the hydrogen gas concentration in the (n+1)th space is 20 volume % or less, it is easy to manage the reducing gas supplied to the (n+1)th space.

[0079] The oxygen gas concentration in the (n+1)th space is, for example, 100 ppm by volume or less, and preferably 50 ppm by volume or less. If the oxygen gas concentration in the (n+1)th space is 100 ppm by volume or less, it is possible to suppress the occurrence of dross defects while suppressing the oxidative wear of the carbon member 32. The oxygen gas concentration in the (n+1)th space may be 0 ppm by volume or more. EXAMPLES

[0080] Experimental data will be described below. Example 1 below is a comparative example, and Example 2 is an embodiment. In Examples 1 and 2, float glass was produced under the conditions shown in Table 1 using a dross box 3 shown in FIG. 3. In Examples 1 and 2, float glass was produced under the same conditions, except that in Example 1, no hydrogen-containing gas was supplied to the second space S2, whereas in Example 2, hydrogen-containing gas was supplied to the second space S2. The hydrogen-containing gas used contained 12 volume % hydrogen gas and 88 volume % nitrogen gas.

[0081] [Table 1] As shown in Table 1, float glass was produced under the same conditions in Example 1 and Example 2, except that in Example 1, hydrogen-containing gas was not supplied to the second space S2, whereas in Example 2, hydrogen-containing gas was supplied to the second space S2.

[0082] In Table 1, the hydrogen gas concentration in the second space S2 is the same in Example 1 and Example 2 because the supply of hydrogen-containing gas was performed at the center of the dross box 3 in the Y-axis direction, while the measurement of the hydrogen gas concentration was performed at one end of the dross box 3 in the Y-axis direction.

[0083] However, as is clear from Table 1, in Example 2, since the hydrogen-containing gas was supplied to the second space S2, the pressure in the second space S2 was higher than in Example 1. In addition, in Example 2, since the hydrogen-containing gas was supplied to the second space S2, the hydrogen gas concentration in the third space S3 was higher than in Example 1 due to the infiltration of the hydrogen-containing gas.

[0084] In Examples 1 and 2, the end face of the float glass was irradiated with light in a dark room, the surface of the float glass that had been in contact with the molten metal M was inspected, and the number of dross defects per unit area with a major axis exceeding 20 μm was examined. The examined numbers are shown in relative values ​​in Table 1. As is clear from Table 1, in Example 2, N2 gas was supplied to the first space S1 and a hydrogen-containing gas was supplied to the second space S2, so that the number of dross defects was reduced compared to Example 1.

[0085] In addition, in Examples 1 and 2, float glass was continuously produced for 50 days under the conditions shown in Table 1, and whether or not oxidation wear of the carbon member 32 occurred was visually examined over the 50 days. In Table 1, the evaluation of the carbon member 32 as "◯" means that oxidation wear was not observed visually, and the evaluation of the carbon member 32 as "×" means that oxidation wear was observed visually. As is clear from Table 1, in Example 2, N2 gas was supplied to the first space S1 and a hydrogen-containing gas was supplied to the second space S2, so that oxidation wear of the carbon member 32 could be suppressed compared to Example 1.

[0086] Although the float glass manufacturing method according to the present disclosure has been described above, the present disclosure is not limited to the above-mentioned embodiments, etc. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These naturally fall within the technical scope of the present disclosure. [Explanation of symbols]

[0087] 1. Float glass manufacturing equipment 2. Float Bath 3 Dross Box 31 Transport roll 32 Carbon materials 5 Annealing furnace M Molten metal G Glass ribbon

Claims

1. A method for producing float glass, comprising: drawing out a glass ribbon formed on molten metal stored in a float bath by n conveying rolls (n is a natural number of 2 or more) provided inside a dross box, from the float bath, and sending the glass ribbon to an annealing furnace, In a lower space inside the dross box and below the glass ribbon, a carbon member is brought into contact with each of the n conveying rolls, Among the n+1 spaces obtained by dividing the lower space by the carbon member in the conveying direction of the glass ribbon, the space located at the kth position from the upstream side to the downstream side in the conveying direction is defined as a k-th space, supplying an inert gas to a first space of the lower space; and supplying a reducing gas to an i-th space (i is a natural number equal to or greater than 2 and equal to or less than n) of the lower space; supplying a reducing gas toward the transport roll on an upstream side in a transport direction in the i-th space.

2. The float glass manufacturing method according to claim 1 , wherein the i-th space includes at least a second space.

3. 3. The method for producing float glass according to claim 1, further comprising: supplying an inert gas or a reducing gas to the (n+1)th space of the lower space.

4. 4. The method for producing a float glass according to claim 1, wherein the reducing gas supplied to the i-space contains hydrogen gas, carbon monoxide gas or acetylene gas.

5. 5. The method for manufacturing a float glass according to claim 1, wherein the reducing gas supplied to the i-space contains 0.1 volume % to 20 volume % of hydrogen gas.

6. 6. The method for producing a float glass according to claim 1, wherein a hydrogen gas concentration in the first space is less than 3 volume %.

7. 7. The method for manufacturing a float glass according to claim 1, wherein a hydrogen gas concentration in the i-space is 1 to 20% by volume.

8. 8. The method for manufacturing a float glass according to claim 1, wherein a pressure in the i-th space is 1 Pa to 15 Pa higher than atmospheric pressure.

9. 9. The method for producing a float glass according to claim 1, wherein an oxygen gas concentration in the i-space is 100 ppm by volume or less.

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