JP7537271B2 - Float glass manufacturing apparatus and float glass manufacturing method - Google Patents

Description

This disclosure relates to a float glass manufacturing apparatus and a float glass manufacturing method.

A float glass manufacturing device continuously supplies molten glass onto molten metal in a bath, and forms the molten glass into a band-like glass ribbon as it flows over the molten metal. The space above the bath is separated by a partition wall into a spout space on the upstream side and a main space on the downstream side. The main space is much larger than the spout space, and is filled with a reducing gas to prevent oxidation of the molten metal.

A silicon carbide (SiC) heater is provided in the spout space to increase the fluidity of the molten glass (see, for example, Patent Document 1). A silicon carbide heater is provided in the main space to control the temperature distribution of the glass ribbon (see, for example, Patent Document 2). The silicon carbide heater in Patent Document 2 is suspended from above the main space.

JP 2015-134691 A JP 2006-219341 A

Conventionally, silicon carbide heaters have been installed in the space above the bathtub. Silicon carbide heaters have the problem of being prone to creep deformation at high temperatures.

One aspect of the present disclosure provides a technique for improving the creep resistance of a heater installed in the space above a bathtub.

A float glass manufacturing apparatus according to one embodiment of the present disclosure includes a bath, a spout lip, a top roll, and a carbon heater. The bath contains molten metal. The spout lip supplies molten glass onto the molten metal. The top roll forms the molten glass into a band-shaped glass ribbon while flowing the molten glass in a predetermined direction on the molten metal. The carbon heater includes a carbon heating part disposed in a space above the bath, and an electrode part supporting the heating part. The atmosphere in the vicinity of the heating part has a dew point of -35°C or less and an oxygen concentration of 100 ppm by volume or less. The carbon heater includes a pair of windbreak parts that sandwich the heating part when viewed from above and divert an ascending air current generated below the heating part to the outside of the heating part.

According to one aspect of the present disclosure, the creep resistance of a heater installed in the space above a bathtub can be improved.

FIG. 1 is a cross-sectional view showing a float glass manufacturing apparatus according to one embodiment. FIG. 2 is a cross-sectional view of the float glass manufacturing apparatus taken along the line II-II in FIG. FIG. 3 is a plan view showing an example of the arrangement of the carbon heater in the spout space. FIG. 4 is a plan view showing an example of the arrangement of carbon heaters in the spout space and the main space. FIG. 5 is a cross-sectional view of the float glass manufacturing apparatus taken along line VV in FIG. FIG. 6 is a plan view of a carbon heater according to a modified example. FIG. 7 is a view of a carbon heater according to a modified example, viewed from the Y-axis direction. FIG. 8 is a cross-sectional view of a float glass manufacturing apparatus according to a modified example.

Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Note that the same or corresponding configurations in each drawing are given the same reference numerals, and description thereof may be omitted. In each drawing, the X-axis direction, Y-axis direction, and Z-axis direction are mutually perpendicular, the X-axis direction and Y-axis direction are horizontal directions, and the Z-axis direction is vertical. The X-axis direction is the flow direction of the molten glass G and the glass ribbon GR, and the Y-axis direction is the width direction of the molten glass G and the glass ribbon GR. In the specification, "to" indicating a numerical range means that the numerical values before and after it are included as the lower and upper limits.

As shown in FIG. 1, the float glass manufacturing apparatus 1 continuously supplies molten glass G onto molten metal M in a bath 10, and forms the molten glass G into a strip-shaped glass ribbon GR while flowing in a predetermined direction (X-axis direction) above the molten metal M. The glass ribbon GR is pulled up from the molten metal M in the downstream area of the bath 10, then slowly cooled by a slow cooling device (not shown), and cut to a predetermined size by a processing device (not shown). The processing device cuts off both ends of the glass ribbon GR in the Y-axis direction. The glass ribbon GR is processed by the processing device to obtain the product float glass.

The type of glass for float glass includes, for example, alkali-free glass, aluminosilicate glass, borosilicate glass, soda-lime glass, etc. The term "alkali-free glass" refers to glass that does not substantially contain alkali metal oxides such as Na ₂ O and K ₂ O. Here, "substantially does not contain alkali metal oxides" means that the total content of alkali metal oxides is 0.1 mass% or less.

The uses of float glass are not particularly limited, but include, for example, flat panel displays (FPDs) such as liquid crystal displays (LCDs) and organic electroluminescence displays, and for example, glass substrates for FPDs. When float glass is used as a glass substrate for FPDs, the type of glass used for float glass is non-alkali glass.

The float glass is preferably an alkali-free glass substrate containing, in mass % on an oxide basis, SiO ₂ : 54% to 66%, Al ₂ O ₃ : 10% to 23%, B ₂ O ₃ : 6% to 12%, and MgO+CaO+SrO+BaO: 8% to 26%.

In order to achieve a high strain point, the float glass is preferably an alkali-free glass substrate containing, in mass % on an oxide basis, 54% to 68% SiO ₂ , 10% to 25% Al ₂ O ₃ , 0.1% to 5.5% B ₂ O ₃ , and 8% to 26% MgO+CaO+SrO+BaO.

The thickness of the float glass is selected according to the application of the float glass. When the float glass is used as a glass substrate for an FPD, the thickness of the float glass is preferably 0.7 mm or less, more preferably 0.5 mm or less, even more preferably 0.3 mm or less, even more preferably 0.2 mm or less, and particularly preferably 0.1 mm or less.

The thickness of the float glass is measured over the entire Y-axis direction of the glass ribbon GR after cutting off the Y-axis end of the glass ribbon GR.

As shown in FIG. 1, the float glass manufacturing apparatus 1 includes a bath 10. The bath 10 contains molten metal M. As the molten metal M, for example, molten tin is used. In addition to molten tin, molten tin alloys can also be used, and the molten metal M may be any metal that can float the molten glass G.

The bathtub 10 has a box-shaped bottom casing 11 that is open upward, side bricks 12 that protect the side walls of the bottom casing 11 from the molten metal M, and a bottom brick 13 that protects the bottom wall of the bottom casing 11 from the molten metal M.

The float glass manufacturing apparatus 1 includes a spout lip 14. The spout lip 14 supplies molten glass G onto the molten metal M in the bath 10. As shown in FIG. 2, the side jams 16 and 17 sandwich the spout lip 14 in the Y-axis direction to prevent the molten glass G flowing over the spout lip 14 from spilling in the Y-axis direction.

As shown in FIG. 1, the float glass manufacturing apparatus 1 includes a tweel 18. The tweel 18 is movable up and down relative to the spout lip 14, and adjusts the flow rate of the molten glass G flowing over the spout lip 14. The narrower the gap between the tweel 18 and the spout lip 14, the smaller the flow rate of the molten glass G flowing over the spout lip 14.

The twill 18 is made of a refractory material. A protective film 19 that prevents contact between the twill 18 and the molten glass G may be formed on the twill 18. The protective film 19 is made of, for example, platinum or a platinum alloy.

The float glass manufacturing apparatus 1 includes a tile 20. The tile 20 is disposed below the spout lip 14 and contacts the molten glass G above the molten metal M. As shown in FIG. 3, the tile 20 includes a wetback tile 22 that contacts the upstream end of the molten glass G, and restrictor tiles 24, 25 that extend downstream from the wetback tile 22. The restrictor tiles 24, 25 extend obliquely downstream from the wetback tile 22 and expand downstream.

After being supplied onto the molten metal M, the molten glass G forms a main flow F1 that flows in the positive direction of the X-axis and a tributary flow F2 that flows back in the negative direction of the X-axis toward the wetback tile 22. When the tributary flow F2 reaches the wetback tile 22, it splits into left and right flows along the wetback tile 22, then flows along the left and right restrictor tiles 24, 25, and merges with the Y-axis end of the main flow F1. Therefore, the heterogeneous components generated by the contact between the spout lip 14 and the tile 20 and the molten glass G are collected at both ends of the glass ribbon GR in the Y-axis direction. The both ends of the glass ribbon GR in the Y-axis direction are cut off after annealing and do not become part of the product, so that a high-quality float glass is obtained.

As shown in FIG. 1, the float glass manufacturing apparatus 1 has an upper space S above the bathtub 10. A sidewall 26 (see FIG. 5) forms the side surface of the upper space of the bathtub 10. A ceiling 27 forms the upper surface of the upper space S of the bathtub 10. Furthermore, a partition wall 28 divides the upper space S of the bathtub 10 into a spout space S1 on the upstream side and a main space S2 on the downstream side. The partition wall 28 is also called a front lintel.

The temperature range of the molten glass G in the spout space S1 is, for example, a range equivalent to 10 ^3.8 dPa·s to 10 ^4.65 dPa·s in terms of the viscosity of the molten glass G, and preferably a range equivalent to 10 ^4.1 dPa·s to 10 ^4.3 dPa·s in terms of the viscosity of the molten glass G.

The main space S2 is sufficiently larger than the spout space S1. The main space S2 is filled with reducing gas to prevent oxidation of the molten metal M. The reducing gas is, for example, a mixed gas of nitrogen gas and hydrogen gas, and contains 85% to 98.5% by volume of nitrogen gas and 1.5% to 15% by volume of hydrogen gas. The reducing gas is supplied through the joints between the bricks in the ceiling 27 and through holes in the ceiling 27.

As shown in FIG. 4, the float glass manufacturing apparatus 1 includes a top roll 30. The top roll 30 forms the molten glass G into a strip-shaped glass ribbon GR while flowing it in the X-axis direction on the molten metal M. The top roll 30 rotates while pressing the Y-axis end of the glass ribbon GR, and sends out the glass ribbon GR in the X-axis direction. As the glass ribbon GR moves in the X-axis direction, it gradually cools and hardens.

The pair of top rolls 30 are spaced apart in the Y-axis direction to suppress the shrinkage of the glass ribbon GR in the Y-axis direction. The thickness of the glass ribbon GR can be made thinner than the equilibrium thickness. Multiple pairs of top rolls 30 are spaced apart in the X-axis direction. This results in multiple pairs of top rolls 30.

The top roll 30 presses the Y-axis direction end portion of the glass ribbon GR at least in the forming zone A1. The forming zone A1 is a region where the viscosity of the glass ribbon GR is 10 ^4.5 dPa·s to 10 ^7.5 dPa·s. In the forming zone A1, the glass ribbon GR is formed to a predetermined thickness by the top roll 30. The viscosity of the glass ribbon GR is a value obtained by converting the temperature measured at the center of the glass ribbon GR in the Y-axis direction into a viscosity value.

The top roll 30 may press the Y-axis direction end portion of the glass ribbon GR in both the forming zone A1 and the low temperature zone A2. The low temperature zone A2 is a zone that is lower in temperature than the forming zone A1, and is a zone in which the viscosity of the glass ribbon GR is from more than 10 ^7.5 dPa·s to 10 ^7.65 dPa·s. The low temperature zone A2 can also suppress the shrinkage of the glass ribbon GR in the Y-axis direction.

The top roll 30 may further press the Y-axis direction end of the glass ribbon GR in the annealing region A3. The annealing region A3 is a region where the viscosity of the glass ribbon GR exceeds 10 ^7.65 dPa·s. In this case, the Y-axis direction end of the glass ribbon GR is locally heated by a carbon heater 50 described later. Therefore, in the annealing region A3, the top roll 30 can grip the glass ribbon GR.

The top roll 30 has a rotating member 31 and a rotating shaft 32. The rotating member 31 is, for example, disk-shaped, and presses the Y-axis end of the glass ribbon GR with its outer periphery, and sends out the glass ribbon GR in the X-axis direction of the glass ribbon GR. The rotating shaft 32 is driven to rotate by a driving device (not shown), and rotates the rotating member 31. The rotating shaft 32 is made of metal, and since metal has low heat resistance, a refrigerant flow path is formed inside the rotating shaft 32.

As shown in FIG. 3, the float glass manufacturing apparatus 1 includes a carbon heater 50. The carbon heater 50 includes a carbon heating section 51 that is disposed in the space S above the bathtub 10, and electrode sections 52, 53 that support the heating section 51. In this embodiment, the material of the electrode sections 52, 53 is carbon. Since the cross-sectional area of the electrode sections 52, 53 is larger than the cross-sectional area of the heating section 51, the electrical resistance of the electrode sections 52, 53 is lower than the electrical resistance of the heating section 51. Therefore, the electrode sections 52, 53 hardly generate any heat. Here, the cross-sectional area is the area of a cross section perpendicular to the flow of current.

The material of the electrodes 52 and 53 may be molybdenum or tungsten, which has excellent creep resistance. In addition, although the electrodes 52 and 53 are a pair in this embodiment, they may be multiple pairs.

As described above, the space S above the bathtub 10 is filled with a reducing gas to prevent oxidation of the molten metal M. However, air enters the space S above the bathtub 10 through the seal that closes the space between the side bricks 12 and the side wall 26. Therefore, the space S above the bathtub 10 contains oxygen gas. When oxygen gas reacts with hydrogen gas, water vapor is generated. The oxygen gas and water vapor oxidize carbon. When carbon is oxidized, carbon dioxide gas is generated, and the weight of the carbon decreases. Therefore, it was not previously conceivable to use a carbon heater 50 in the space S above the bathtub 10.

The inventors have considered the conditions under which the carbon heater 50 can be used, and have focused on the atmosphere near the heat generating part 51 of the carbon heater 50. Near the heat generating part 51 means an area that is 10 cm or less away from the heat generating part 51. The inventors have found the following conditions through experiments, etc., which will be described later. The atmosphere near the heat generating part 51 that they found has a dew point of -35°C or less and an oxygen concentration of 100 ppm by volume or less. The dew point is an index for understanding the water vapor concentration of the atmosphere. The lower the dew point, the lower the water vapor concentration.

If the dew point is -35°C or lower and the oxygen concentration is 100 ppm by volume or lower, the water vapor concentration and oxygen concentration are low, so the weight loss of the heat generating part 51 is small and the frequency of replacing the heat generating part 51 is about the same as for normal maintenance, for example, about once every three months. Therefore, it is possible to use the carbon heater 50.

From the viewpoint of durability of the heat generating unit 51, the dew point of the atmosphere near the heat generating unit 51 is preferably -45°C or lower, and more preferably -50°C or lower. In addition, from the viewpoint of controllability of the dew point, the dew point of the atmosphere near the heat generating unit 51 is preferably -100°C or higher.

The oxygen concentration in the atmosphere near the heat generating part 51 is preferably 60 ppm by volume or less, more preferably 50 ppm by volume or less, from the viewpoint of durability of the heat generating part 51. The oxygen concentration in the atmosphere near the heat generating part 51 is preferably 5 ppm by volume or more, from the viewpoint of controllability of the oxygen concentration.

The carbon heater 50 has a higher specific rigidity (rigidity/density) than conventional SiC heaters, so creep deformation due to gravity is small. This improves creep resistance. In addition, the carbon heater 50 has a higher maximum operating temperature than conventional SiC heaters, and can be used at temperatures of, for example, 1300°C or higher.

The heat generating portion 51 preferably includes, for example, a number of straight portions 51a arranged parallel to one another and a U-shaped folded portion 51b connecting adjacent straight portions 51a. The straight portions 51a and the folded portions 51b are arranged horizontally. The folded portions 51b can increase the heat generating area per unit area in a plan view. The folded portions 51b can also increase the overall length of the current path, thereby increasing the electrical resistance.

The material of the heat generating portion 51 is preferably a CIP material or a C/C composite material. The CIP material is obtained by the CIP (Cold Isostatic Pressing) method. In the CIP method, carbon raw material is placed in a rubber mold and pressure is applied to the entire rubber mold to form it. The CIP material has a higher electrical conductivity than the C/C composite material.

On the other hand, C/C composite materials are composite materials of carbon fibers and carbon or graphite, and are obtained by the impregnation method or the CVD method. In the impregnation method, a carbon fiber substrate is impregnated with resin or pitch, and then baked to carbonize or graphitize. In the CVD (Chemical Vapor Deposition) method, carbon obtained by pyrolyzing hydrocarbons is deposited on a carbon fiber substrate. C/C composite materials have higher electrical resistivity and strength than CIP materials.

In this embodiment, the material of the heat generating portion 51 is a C/C composite material with high electrical resistivity.

The electrode parts 52 and 53 apply a voltage to both ends of the heat generating part 51, causing a current to flow through the heat generating part 51. The electrode parts 52 and 53 are, for example, rod-shaped and arranged horizontally. The material of the electrode parts 52 and 53 is preferably a CIP material or a C/C composite material, similar to the material of the heat generating part 51. Since the electrode parts 52 and 53 are cantilevers of the heat generating part 51, the material of the electrode parts 52 and 53 is a high-strength C/C composite material in this embodiment.

As shown in FIG. 3, the heating unit 51 is disposed between the pair of restrictor tiles 24, 25 in a plan view, and is disposed so as to overlap the molten glass G. The temperature region between the pair of restrictor tiles 24, 25 is a temperature region in which devitrification of the molten glass G may occur. Devitrification is a phenomenon in which crystals precipitate and transparency decreases. By locally heating the molten glass G with the heating unit 51, it is possible to suppress the precipitation of crystals and thus suppress devitrification.

Devitrification of the molten glass G is likely to occur in areas where the flow of the molten glass G stagnates, and is likely to occur near the downstream ends of the restrictor tiles 24, 25. Near the downstream ends of the restrictor tiles 24, 25 means areas within 10 cm of the downstream ends.

Therefore, it is preferable that the heating section 51 is arranged near the downstream ends of the pair of restrictor tiles 24, 25 in a plan view and overlaps the molten glass G. This can further suppress devitrification of the molten glass G.

As shown in FIG. 4, the heating portion 51 is preferably arranged so as to overlap the Y-axis direction end of the glass ribbon GR in a plan view. This arrangement is adopted at least in the forming zone A1, and may also be adopted in the low temperature zone A2 or the annealing zone A3.

With this arrangement, the Y-axis direction end of the glass ribbon GR is locally heated by the heating section 51 and becomes soft. This improves the grip of the top roll 30 on the glass ribbon GR. As a result, the formability of the glass ribbon GR can be improved, and the flatness of the float glass can be improved.

In addition, when the above arrangement is adopted in the annealing region A3, the insufficient heating of the Y-axis direction end of the glass ribbon GR is eliminated, and the occurrence of a problem in which the glass ribbon GR cracks at the exit of the float glass manufacturing apparatus 1 (the exit of the space S above the bathtub 10) can be prevented. Note that the heating portion 51 may be arranged so as to overlap the inside of the Y-axis direction end of the glass ribbon GR in a plan view.

The heating section 51 is preferably disposed between adjacent top rolls 30 in the X-axis direction in a plan view. The heating section 51 can be heated just before the Y-axis end of the glass ribbon GR is pressed by the top roll 30, which can further improve the grip of the top roll 30 on the glass ribbon GR.

The carbon heater 50 preferably has a pair of connecting parts 54, 55 that connect the pair of electrode parts 52, 53 and the heat generating part 51. One connecting part 54 connects one electrode part 52 and the heat generating part 51, and another connecting part 55 connects the other electrode part 53 and the heat generating part 51. This allows the pair of electrode parts 52, 53 and the heat generating part 51 to be manufactured separately, reducing the manufacturing costs.

As shown in FIG. 5, the connecting portion 54 is formed, for example, in an L-shape and includes a vertical portion 54a to which one end of the electrode portion 52 is connected, and a horizontal portion 54b to which one end of the heat generating portion 51 is connected. Another connecting portion 55 is also formed in a similar L-shape. The connecting portions 54, 55 are made of a CIP material or a C/C composite material. In this embodiment, the connecting portions 54, 55 are made of a CIP material with high electrical conductivity.

The carbon heater 50 further includes a first bolt 56 that fastens the electrode portion 52 and the connecting portion 54. The first bolt 56 is preferably passed through a through hole in the vertical portion 54a of the connecting portion 54 and screwed into a threaded hole in the electrode portion 52. By loosening the first bolt 56, the connecting portion 54 and the heating portion 51 can be replaced. The heating portion 51 is replaced when the heating portion 51 is worn out. After the heating portion 51 is replaced, the first bolt 56 is tightened again. The carbon heater 50 further includes a first bolt (not shown) that connects the electrode portion 53 and the connecting portion 55.

The carbon heater 50 further includes a second bolt 58 that fastens the heat generating part 51 and the connecting part 54. The second bolt 58 preferably passes through a through hole in the horizontal part 54b of the connecting part 54 and is screwed into a threaded hole in the heat generating part 51. The heat generating part 51 can be replaced by loosening the second bolt 58. The heat generating part 51 is replaced when the heat generating part 51 is worn out. After replacing the heat generating part 51, the second bolt 58 is tightened again. The carbon heater 50 further includes a second bolt (not shown) that connects the heat generating part 51 and the connecting part 55.

As shown in FIG. 5, the electrodes 52, 53 of the carbon heater 50 are preferably disposed in the opening 26a of the side wall 26. This allows an operator to stand outside the side wall 26 and install and remove the carbon heater 50. This makes it easy to add, reposition, or replace the carbon heater 50.

The float glass manufacturing apparatus 1 preferably includes a metal casing 60, a first seal member 70, and a second seal member 71. The metal casing 60 includes a tube portion 61 disposed in the opening 26a of the side wall 26, a lid portion 62 that closes the opening of the tube portion 61 on the outside of the side wall 26, and a through hole 63 through which the electrode portion 52 of the lid portion 62 is inserted. The through hole 63 through which one electrode portion 52 is inserted and a through hole (not shown) through which another electrode portion 53 is inserted are provided separately in the lid portion 62. The metal casing 60 and the electrode portions 52 and 53 of the carbon heater 50 are insulated.

The first sealing member 70 seals the gap between the cylindrical portion 61 of the metal casing 60 and the side wall 26. Mortar, for example, is used as the first sealing member 70.

The second seal member 71 seals between the lid portion 62 of the metal casing 60 and the electrode portion 52. For example, an O-ring is used as the second seal member 71. The O-ring surrounding one electrode portion 52 and the O-ring surrounding the other electrode portion 53 are prepared separately. From the viewpoint of heat resistance, the O-ring material is, for example, fluororubber. The second seal member 71 has insulating properties.

The metal casing 60, the first sealing member 70, and the second sealing member 71 prevent air from entering the upper space S of the bathtub 10 (main space S2 in FIG. 5) through the opening 26a of the side wall 26, and prevent oxidation wear of the heat generating portion 51 of the carbon heater 50.

The metal casing 60 preferably has an inlet port 64 in the lid 62 for introducing an inert gas into the internal space IS of the metal casing 60. The inert gas is, for example, nitrogen gas or argon gas. Since the internal space IS of the metal casing 60 is filled with an inert gas, the electrode parts 52 and 53 can be protected from oxygen gas and water vapor in the space S above the bathtub 10.

The metal casing 60 has an opening toward the space S above the bathtub 10. The internal space IS of the metal casing 60 is provided with an insulating member 80 that divides the internal space IS of the metal casing 60 from the space S above the bathtub 10. The insulating member 80 is preferably insulating. The electrodes 52 and 53 of the carbon heater 50 are preferably inserted through the through holes of the insulating member 80. The insulating member 80 is formed with a through hole 81 through which one electrode 52 is inserted and a through hole (not shown) through which another electrode 53 is inserted. From the viewpoint of heat resistance, the insulating member 80 is made of bricks, ceramic boards, quartz glass blocks, etc. This can block radiant heat from the heat generating portion 51 and suppress heating of the metal casing 60. For example, an alumina-based refractory material is used for the bricks.

The through hole 81 of the insulating member 80 supplies the inert gas introduced into the internal space IS of the metal casing 60 by the inlet port 64 to the upper space S of the bathtub 10. As a result, the inert gas can be supplied near the heat generating part 51 of the carbon heater 50, and the oxidative wear of the heat generating part 51 can be further suppressed.

The float glass manufacturing method includes continuously supplying molten glass G onto molten metal M in a bath 10, forming the molten glass G into a band-shaped glass ribbon GR while flowing the molten glass G in the X-axis direction above the molten metal M, and heating the molten glass G or glass ribbon GR with a carbon heater 50.

Heating the molten glass G with the carbon heater 50 can suppress devitrification of the molten glass G. In addition, heating the glass ribbon GR with the carbon heater 50 can improve the grip of the top roll 30 on the glass ribbon GR. As a result, the formability of the glass ribbon GR can be improved, and the flatness of the float glass can be improved.

Next, a carbon heater 50 according to a modified example will be described with reference to Figures 6 and 7. The carbon heater 50 includes a heat generating portion 51. The heat generating portion 51 includes three or more (four in Figure 6) straight portions 51a arranged parallel to each other, and a U-shaped folded portion 51b connecting adjacent straight portions 51a. The straight portions 51a and the folded portions 51b are arranged horizontally. The number of straight portions 51a is not particularly limited, but is, for example, 3 to 20. The number of folded portions 51b is one less than the number of straight portions 51a.

The heating section 51 heats the glass ribbon GR or the molten glass G from above. When the glass ribbon GR or the molten glass G is heated, the atmosphere above it is also heated. As a result, as shown in FIG. 7, an ascending air current is generated below the heating section 51. The gap between adjacent straight sections 51a is narrow, and the ascending air current does not easily pass through the gap. Therefore, the ascending air current flows to avoid the heating section 51. Therefore, the flow speed of the ascending air current is likely to be high at the outer edge of the heating section 51, and oxidation wear is likely to progress. The outer edge of the heating section 51 includes, for example, straight sections 51a at both ends and folded sections 51b.

As shown in FIG. 6, when viewed from above, the width W1 of the straight line portions 51a at both ends may be larger than the width W2 of the straight line portion 51a at the center. The widths W1 and W2 are dimensions in a direction perpendicular to the current path. When the width W1 is larger than the width W2, breaks due to oxidative wear at the straight line portions 51a at both ends can be suppressed, and the useful life of the heat generating portion 51 can be extended. The width W1 is preferably 1.1 times or more the width W2, more preferably 2 times or more the width W2, and even more preferably 3 times or more the width W2. The width W1 may be 10 times or less the width W2.

Furthermore, if the width W1 of the straight portions 51a at both ends is greater than the width W2 of the straight portion 51a at the center, the electrical resistance of the straight portions 51a at both ends will be lower than the electrical resistance of the straight portion 51a at the center. As a result, the heat generation temperature T1 of the straight portions 51a at both ends can be made 30°C or more lower than the heat generation temperature T2 of the straight portion 51a at the center. This makes it possible to suppress breakage due to oxidative wear at the straight portions 51a at both ends. The temperature difference between the heat generation temperature T1 and the heat generation temperature T2 is preferably 100°C or more, more preferably 200°C or more. The temperature difference between the heat generation temperature T1 and the heat generation temperature T2 may be 400°C or less.

As shown in FIG. 6, when viewed from above, the width W3 of the folded portion 51b may be larger than the width W2 of the central straight portion 51a. The width W3 is the dimension in the direction perpendicular to the current path. When the width W3 is larger than the width W2, breaks due to oxidative wear at the folded portion 51b can be suppressed, and the useful life of the heat generating portion 51 can be extended. The width W3 is preferably 1.1 times or more the width W2, more preferably 1.4 times or more the width W2, and even more preferably 2 times or more the width W2. The width W3 may be 5 times or less the width W2.

When viewed from above, the distance G1 between adjacent straight portions 51a is, for example, 5 mm or less. If the distance G1 is 5 mm or less, the gap between adjacent straight portions 51a is narrow and it is difficult for an ascending air current to pass through the gap, so that oxidation wear of the straight portions 51a can be suppressed. The distance G1 is preferably 4 mm or less, and more preferably 3 mm or less. The distance G1 may also be 0.5 mm or more.

The carbon heater 50 may include a pair of windbreaks 41, 42 that sandwich the heat generating part 51 when viewed from above as shown in FIG. 6 and that divert the rising air current generated under the heat generating part 51 to the outside of the heat generating part 51 as shown in FIG. 7. The pair of windbreaks 41, 42 are disposed at a distance from the heat generating part 51 and are disposed, for example, parallel to the straight part 51a of the heat generating part 51.

As shown in FIG. 6, the pair of windbreaks 41, 42 are connected, for example, to a pair of connecting parts 54, 55. The windbreak 41 is connected to the vertical part 54a of the connecting part 54, and the windbreak 42 is connected to the vertical part 55a of the connecting part 55. When viewed from above, the folded part 51b of the heat generating part 51 is disposed between the pair of connecting parts 54, 55 so as to block the rising air current.

The pair of windshield parts 41, 42 may be made of carbon, like the heat generating part 51. The material of the windshield parts 41, 42 is preferably a CIP material or a C/C composite material, more preferably a CIP material. The electrical resistance of the windshield parts 41, 42 is lower than the electrical resistance of the heat generating part 51, and the windshield parts 41, 42 generate almost no heat.

The windshield sections 41 and 42 divert the rising air current away from the heat generating section 51, thereby suppressing the oxidative wear of the heat generating section 51. In addition, unlike the heat generating section 51, the windshield sections 41 and 42 hardly generate heat, and therefore have a lower temperature than the heat generating section 51. Therefore, the oxidative wear of the windshield sections 41 and 42 can also be suppressed.

When viewed from above, the gap G2 between the windshields 41, 42 and the heat generating part 51 is, for example, 5 mm or less. If the gap G2 is 5 mm or less, the gap between the windshields 41, 42 and the heat generating part 51 is narrow, making it difficult for an ascending air current to pass through the gap, thereby suppressing oxidation wear of the heat generating part 51. The gap G2 is preferably 4 mm or less, and more preferably 3 mm or less. The gap G2 may also be 0.5 mm or more.

When viewed from above, the width W4 of the windbreaks 41, 42 is preferably at least 1.0 times the width W2 of the central straight section 51a, and more preferably at least 3 times the width W2. Note that the width W4 may be 10 times or less the width W2.

Next, a float glass manufacturing apparatus 1 according to a modified example will be described with reference to FIG. 8. The float glass manufacturing apparatus 1 preferably includes a metal casing 60, a first seal member 70, and a second seal member 71. The metal casing 60, the first seal member 70, and the second seal member 71 prevent air from entering the upper space S of the bathtub 10 (main space S2 in FIG. 8) from the opening 26a of the side wall 26, and prevent oxidation wear of the heat generating portion 51 of the carbon heater 50.

The float glass manufacturing apparatus 1 preferably includes a carbon box 90 that protrudes from the internal space IS of the metal casing 60 into the upper space S of the bath 10 (main space S2 in FIG. 8) and houses a part of the carbon heater 50. The carbon box 90 prevents oxygen gas and water vapor from entering from the outside to the inside, and prevents oxidation wear of the carbon heater 50. The carbon box 90 is preferably made of CIP material or C/C composite material.

The metal casing 60 preferably has an inlet port 64 for introducing an inert gas into the internal space of the carbon box 90. The inert gas is, for example, nitrogen gas or argon gas. Since the internal space of the carbon box 90 is filled with an inert gas, the heating unit 51 and the electrodes 52 and 53 can be protected from oxygen gas and water vapor in the space S above the bathtub 10.

An opening 91 is formed in the bottom wall of the carbon box 90. When viewed from below, the size of the opening 91 is larger than the size of the heat generating part 51 of the carbon heater 50. A carbon nozzle (not shown) that protrudes downward may be provided on the edge of the opening 91. The carbon nozzle is cylindrical and surrounds the heat generating part 51. Note that when the carbon nozzle surrounds the heat generating part 51, the wind shields 41 and 42 are not necessary.

The inert gas supplied to the internal space of the carbon box 90 passes through the opening 91 of the carbon box 90 and is ejected below the heat generating portion 51 of the carbon heater 50. This makes it possible to prevent the generation of an ascending air current below the heat generating portion 51. In order to allow the inert gas to be ejected evenly below the heat generating portion 51, it is preferable that the distance G3 between the opening edge of the opening 91 and the heat generating portion 51 is 90% to 110% of the distance G1 between the straight portions 51a of the heat generating portion 51. The distance G3 is, for example, 5 mm or less. If the distance G3 is 5 mm or less, the backflow of gas from the outside to the inside of the carbon box 90 can be prevented. The distance G3 is preferably 4 mm or less, more preferably 3 mm or less. The distance G3 may also be 0.5 mm or more.

The gap G4 between the heat generating portion 51 of the carbon heater 50 and the glass ribbon GR (or molten glass G) is, for example, 50 mm or less. If the gap G4 is 50 mm or less, backflow of gas from the outside to the inside of the carbon box 90 can be suppressed, and the glass ribbon GR (or molten glass G) can be efficiently heated. The gap G4 is preferably 30 mm or less, and more preferably 10 mm or less. The gap G4 may also be 0.5 mm or more.

In the following experiment, the relationship between the oxidative wear rate of a carbon test piece and the surrounding atmosphere was investigated. A C/C composite material was used as the carbon test piece. The size of the carbon test piece was 50 mm x 50 mm x 10 mm thick. The oxidative wear rate of the carbon test piece was calculated as the reduction in the mass of the carbon test piece before and after the test (unit: %), with the mass of the carbon test piece before the test being taken as 100%.

In the test, first, a carbon test piece was placed inside the container. Then, while nitrogen gas with an oxygen concentration of 3 ppm by volume or less and a dew point of -75°C or less was flowing inside the container, an electric current was passed through the carbon test piece placed inside the container, and the inside of the container was heated to 1400°C at a temperature increase rate of 300°C/h. Here, the oxygen concentration meter used was the trace oxygen measurement unit TKZ005AU made by Techne Measurement Co., Ltd., and the dew point meter used was the TK-100 dew point transmitter made by Techne Measurement Co., Ltd.

Next, a mixed gas of nitrogen gas, oxygen gas, and water vapor, with the oxygen concentration and dew point controlled to the values shown in Table 1, was supplied to the inside of the container, while an electric current was passed through a carbon test piece placed inside the container, and the inside of the container was heated to 1,400°C for 24 hours.

Finally, the inside of the container was cooled to room temperature while nitrogen gas with an oxygen concentration of 3 ppm by volume or less and a dew point of -75°C or less was passed through the inside of the container, and the carbon test piece was removed from inside the container.

The test results are shown in Table 1.

表１から明らかなように、露点が－３５℃以下であって、且つ酸素濃度が１００体積ｐｐｍ以下であれば、カーボン試験片の酸化消耗速度が０．３質量％／ｈ以下であった。酸化消耗速度が０．３質量％／ｈ以下であれば、３か月に１回程度の交換頻度で、カーボンヒータを使用できる。

As is clear from Table 1, when the dew point was −35° C. or lower and the oxygen concentration was 100 ppm by volume or lower, the oxidation consumption rate of the carbon test piece was 0.3 mass%/h or lower. If the oxidation consumption rate is 0.3 mass%/h or lower, the carbon heater can be used with a replacement frequency of about once every three months.

The float glass manufacturing apparatus and float glass manufacturing method according to the present disclosure have been described above, but the present disclosure is not limited to the above-mentioned embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. Naturally, these also fall within the technical scope of the present disclosure.

10 Bathtub 14 Spout lip 30 Top roll 50 Carbon heater 51 Heating portion 52, 53 Electrode portion M Molten metal G Molten glass GR Glass ribbon

Claims (25)

a bath for containing molten metal;
a spout lip for delivering molten glass onto the molten metal;
A top roll that forms the molten glass into a band-shaped glass ribbon while flowing the molten glass in a predetermined direction on the molten metal;
A carbon heater including a carbon heating part disposed in the space above the bathtub and an electrode part supporting the heating part;
Equipped with
The atmosphere in the vicinity of the heat generating portion has a dew point of −35° C. or less and an oxygen concentration of 100 ppm by volume or less ;
The carbon heater includes a pair of windbreaks that sandwich the heat generating portion when viewed from above and divert an ascending air current generated below the heat generating portion to the outside of the heat generating portion. A side wall is provided to form a side surface of the space above the bathtub,
The float glass manufacturing apparatus according to claim 1 , wherein the electrode portion of the carbon heater is disposed in the opening of the side wall. a metal casing including a cylindrical portion disposed in an opening of the side wall, a lid portion closing the opening of the cylindrical portion on an outside of the side wall, and a through hole through which the electrode portion of the lid portion is inserted;
a first seal member that seals a gap between the cylindrical portion and the side wall of the metal casing;
3. The float glass manufacturing apparatus according to claim 2, further comprising: a second seal member that seals a gap between the cover portion of the metal casing and the electrode portion. The float glass manufacturing apparatus according to claim 3, wherein the metal casing has an inlet port in the lid for introducing an inert gas into the internal space of the metal casing. The metal casing has an opening toward the upper space of the bathtub,
A heat insulating member is provided in the internal space of the metal casing to separate the internal space of the metal casing from the upper space of the bathtub.
5. The float glass manufacturing apparatus according to claim 3, wherein the electrode portion of the carbon heater is inserted into a through hole of the heat insulating member. The float glass manufacturing device according to claim 3 or 4, further comprising a carbon box that protrudes from the internal space of the metal casing into the upper space of the bath and houses a part of the carbon heater. The float glass manufacturing apparatus according to claim 6, wherein the heat generating portion of the carbon heater is positioned so that the distance between the heat generating portion and the molten glass or the glass ribbon on the molten metal is 50 mm or less. a tile below the spout lip for contacting the molten glass above the molten metal;
The tiles include a wetback tile that contacts an upstream end of the molten glass, and a pair of restrictor tiles that extend downstream from the wetback tile;
The float glass manufacturing apparatus according to any one of claims 1 to 7, wherein the heat generating portion of the carbon heater is disposed between a pair of the restrictor tiles in a plan view and is disposed so as to overlap the molten glass. The float glass manufacturing apparatus according to claim 8, wherein the heat generating portion of the carbon heater is disposed near the downstream end of the restrictor tile in a plan view and overlaps the molten glass. The float glass manufacturing device according to any one of claims 1 to 9, wherein the heat generating portion of the carbon heater is arranged so as to overlap the width direction end of the glass ribbon in a plan view. The top roll rotates while pressing the width direction end of the glass ribbon, and sends out the glass ribbon in the predetermined direction,
The float glass manufacturing apparatus according to claim 10, wherein the heat generating portion of the carbon heater is disposed between the top rolls adjacent to each other in the predetermined direction in a plan view. The float glass manufacturing device according to any one of claims 1 to 11, wherein the material of the heat generating portion of the carbon heater is a CIP material or a C/C composite material. The float glass manufacturing device according to any one of claims 1 to 12, wherein the material of the electrode part of the carbon heater is a CIP material or a C/C composite material. The float glass manufacturing device according to any one of claims 1 to 13, wherein the heat generating portion of the carbon heater includes a plurality of straight portions arranged parallel to each other and a U-shaped folded portion connecting adjacent straight portions. The heat generating portion of the carbon heater includes three or more straight portions arranged in parallel to each other,
The float glass manufacturing apparatus according to claim 14, wherein a width of the straight portion at both ends is larger than a width of the straight portion at a center when viewed from above. The heat generating portion of the carbon heater includes three or more straight portions arranged in parallel to each other,
16. The float glass manufacturing apparatus according to claim 14, wherein a width of the folded portion is larger than a width of the central straight portion when viewed from above. The float glass manufacturing device according to any one of claims 1 to 16, wherein the carbon heater has a pair of connecting parts that connect the pair of electrode parts and the heating part. The carbon heater further includes a first bolt that fastens the electrode portion and the connecting portion,
The float glass manufacturing apparatus according to claim 17 , wherein the first bolt passes through a through hole of the connecting portion and is screwed into a screw hole of the electrode portion. The carbon heater further includes a second bolt that fastens the heat generating portion and the connecting portion,
The float glass manufacturing apparatus according to claim 17 or 18, wherein the second bolt passes through a through hole of the connecting portion and is screwed into a screw hole of the heating portion. A method for producing float glass using the float glass producing apparatus according to any one of claims 1 to 19 ,
continuously supplying the molten glass flowing over the spout lip onto the molten metal in the bath;
forming the molten glass into a band-shaped glass ribbon while flowing the molten glass in the predetermined direction on the molten metal;
Heating the molten glass or the glass ribbon with the heat generating portion of the carbon heater;
The float glass manufacturing method according to the present invention comprises the steps of: A float glass manufacturing method using the float glass manufacturing apparatus according to any one of claims 14 to 16,
continuously supplying the molten glass flowing over the spout lip onto the molten metal in the bath;
forming the molten glass into a band-shaped glass ribbon while flowing the molten glass in the predetermined direction on the molten metal;
Heating the molten glass or the glass ribbon with the heat generating portion of the carbon heater;
having
a heat generation temperature of the straight portion at each end being lower by 30° C. or more than a heat generation temperature of the straight portion at a center. The method for producing a float glass according to claim 20 or 21 , wherein an atmosphere in the vicinity of the heat generating portion has a dew point of −45° C. or lower. The method for producing a float glass according to any one of claims 20 to 22 , wherein an oxygen concentration in an atmosphere in the vicinity of the heat generating portion is 60 ppm by volume or less. The method for producing a float glass according to any one of claims 20 to 23, wherein the float glass is an alkali-free glass substrate containing, in mass % on an oxide basis, SiO ₂ : 54% to 66 %, Al ₂ O ₃ : 10 % to 23%, B ₂ O ₃ : 6% to 12%, and MgO + CaO + SrO + BaO: 8% to 26%. The method for producing float glass according to any one of claims 20 to 23, wherein the float glass is an alkali-free glass substrate containing, in mass % on an oxide basis, SiO ₂ : 54% to 68 %, Al ₂ O ₃ : 10 % to 25%, B ₂ O ₃ : 0.1% to 5.5%, and MgO + CaO + SrO + BaO: 8% to 26%.

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