TWI613158B - Method for producing glass substrate and device for manufacturing glass substrate - Google Patents

Description

Method for producing glass substrate and device for manufacturing glass substrate

The present invention relates to a method and apparatus for producing a glass substrate for manufacturing a glass substrate.

A glass substrate (hereinafter referred to as a "glass substrate for FPD (Flat Panel Display)) for a flat panel display such as a liquid crystal display or a plasma display is a glass plate having a thickness of, for example, 0.5 to 0.7 mm. The glass substrate for FPD has, for example, a size of 300×400 mm in the first generation, but a size of 2850×3050 mm in the tenth generation.

When manufacturing a glass substrate for FPD, there is a case where an overflow down-draw method is used. The overflow down-draw method includes the steps of: forming a sheet glass (sheet glass) under the formed body by overflowing (overflowing) the molten glass from the upper portion of the formed body in the forming furnace; and a cooling step of making the thin glass Slowly cool in a slow cooling furnace. In the slow cooling furnace, the sheet glass is pulled between the paired rolls, and the sheet glass is stretched to a desired thickness by the roller facing downward, and then the sheet glass is slowly cooled. Thereafter, the glass substrate is formed by cutting the sheet glass into a specific size.

In the overflow down-draw method, the slow cooling of the flake glass is performed at a temperature higher than the strain point and lower than the slow cooling point, and the temperature near the roll for conveying the flake glass is kept relatively high (600 when the temperature is high) °C or more). In general, since the rotating shaft for rotating the roller is made of metal, the strength is lowered as the temperature rises, thereby allowing the stress to drop and the risk of deformation of the shaft to rise. When the shaft rotates in a deformed state, the speed at which the roller attached to the front end of the shaft conveys the glass substrate periodically changes, and the longitudinal (stretching) side is generated. The thickness deviation in the upward direction, or the cause of the warpage. Patent Document 1 discloses that in order to prevent deformation of such a rotating shaft, for example, the shaft is hollow and the heat medium flows in the hollow space, whereby the rotating shaft is cooled.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 5-124826

In addition, regarding the molten glass overflowing from the molded body, the temperature distribution in the width direction of the sheet glass is previously designed along the flow direction of the molten glass so that the warpage and strain do not become larger than necessary, and the thin glass is made The temperature distribution is designed in such a way that strict temperature management is performed using a cooling device or a heater. Therefore, it is necessary to maintain the roller in contact with the sheet glass at a certain temperature.

On the other hand, the rotation axis of the cantilever support roller is provided through the furnace wall of the forming furnace to generate a temperature gradient inside and outside the furnace wall. When the temperature gradient in the longitudinal direction of the rotating shaft becomes large, there is a problem that the stress generated on the rotating shaft becomes large, and the rotating shaft is deformed. Materials that allow stresses greater than those due to temperature gradients are also considered for rotating shafts, but materials that can be selected are limited. The glass singular point such as the strain point or the slow cooling point of the glass used for the glass substrate for the low temperature polycrystalline germanium TFT (Thin Film Transistor) for FPD is high, so the temperature at the time of molding is high, after the formation The temperature at the time of slow cooling also becomes high, and the temperature gradient inside and outside the slow cooling furnace becomes large, and the above problems become remarkable.

Accordingly, an object of the present invention is to provide a method and a manufacturing apparatus for a glass substrate which can accurately reproduce the temperature distribution of the sheet glass as designed, and which can reduce the stress generated on the rotating shaft of the sheet for conveying the sheet glass.

In order to solve the above problems, the first aspect of the present invention is characterized in that it is as follows A method for producing a glass substrate, in which a molten glass is poured from a molded body in a forming furnace to form a continuous sheet glass, and the sheet glass is held by a roll in a slow cooling furnace and conveyed downward while being slowly cooled. And the slow cooling furnace has a wall which is divided into a furnace for conveying the sheet glass and an outer space, wherein the roller is supported by a rotating shaft that penetrates the wall of the forming furnace, and is disposed on the slow cooling The temperature gradient adjustment mechanism of the furnace is adjusted to reduce the temperature gradient in the longitudinal direction of the rotating shaft.

The temperature gradient adjusting mechanism may be a heat insulating mechanism that heats the rotating shaft or a heating mechanism that heats the rotating shaft.

The heat insulating means may heat the rotating shaft by a heat insulating material extending from the inner wall surface of the forming furnace toward the roll side of the rotating shaft.

The heating means may heat the rotating shaft by supplying a medium to the inside of the rotating shaft, and the medium transports heat from a portion of the rotating shaft where the roller is provided to a portion penetrating the wall.

Preferably, the temperature gradient in the longitudinal direction of the rotating shaft is adjusted so that the maximum value is 2500 ° C / m or less.

Preferably, the temperature gradient in the longitudinal direction of the rotating shaft at the position of the end portion on the roll side of the heat insulating material is adjusted to be 1300 ° C/m or less.

A second aspect of the present invention provides a glass substrate manufacturing apparatus comprising: a molding furnace having a molded body in which molten glass is overflowed to form a continuous sheet glass; and a slow cooling furnace in which the sheet glass is sandwiched And transporting one side downward to perform slow cooling; the slow cooling furnace includes: a wall which is divided into a furnace for conveying the inside and outside of the sheet glass; a rotating shaft penetrating the wall; a roller disposed at a front end of the rotating shaft and supported by the rotating shaft cantilever; and a temperature gradient adjusting mechanism configured to reduce a temperature gradient in a longitudinal direction of the rotating shaft Adjustment.

According to the present invention, by reducing the temperature gradient in the longitudinal direction of the rotating shaft that supports the roller for conveying the sheet glass, the stress generated on the rotating shaft due to the temperature gradient can be lowered, and deformation of the rotating shaft can be prevented.

30‧‧‧ Roll

31‧‧‧Rotary axis

32‧‧‧Inside

33‧‧‧Insulation materials

100‧‧‧melting device

101‧‧‧melting tank

102‧‧‧Clarification tank

103‧‧‧Stirring tank

103a‧‧‧Agitator

104‧‧‧Transfer tube

105‧‧‧Transfer tube

106‧‧‧Glass supply tube

200‧‧‧Forming device

201‧‧‧Forming furnace

201A‧‧‧Upper forming furnace

201B‧‧‧ Lower forming furnace

202‧‧‧ Slow cooling furnace

2031, 2022, ..., 202n‧‧‧ spacer

203‧‧‧ wall

210‧‧‧Formed body

212‧‧‧ trench

213‧‧‧Lower end

220‧‧‧Interval spacers

230‧‧‧Cooling components

240‧‧‧Cooling device

241‧‧‧End cooling unit

242‧‧‧Central Cooling Unit

242a‧‧‧Upper unit

242b‧‧ mid-unit

242c‧‧‧Next unit

2501, 2502, ..., 250n‧‧‧ transport components

2701, 2702, 270n‧‧‧ temperature adjustment device

300‧‧‧cutting device

MG‧‧‧ molten glass

SG‧‧‧Sheet glass

ST1‧‧‧melting step

ST2‧‧‧Clarification steps

ST3‧‧‧ homogenization steps

ST4‧‧‧ supply steps

ST5‧‧‧ forming steps

ST6‧‧‧ Slow cooling step

ST7‧‧‧cutting steps

Fig. 1 is a view showing the flow of a method of manufacturing a glass substrate.

2 is a schematic view showing a manufacturing apparatus of a glass substrate.

Figure 3 is a schematic view of the forming apparatus shown in Figure 2.

Figure 4 is a cross-sectional view taken along the line of arrows IV-IV of Figure 3 .

Fig. 5 is a cross-sectional view showing the conveying member shown in Figs. 3 and 4;

Fig. 6 is a view showing the relationship between the position in the longitudinal direction of the rotating shaft of the conveying roller and the temperature.

Fig. 7 is a view showing the relationship between the position in the longitudinal direction of the rotating shaft of the conveying roller and the stress.

Hereinafter, a method of producing a glass substrate and a glass substrate manufacturing apparatus of the present invention will be described.

Fig. 1 is a view showing an example of a procedure of a method for producing a glass substrate of the embodiment.

(Overall outline of the manufacturing method of the glass substrate)

The manufacturing method of the glass substrate mainly includes a melting step (ST1), a clarification step (ST2), The homogenization step (ST3), the supply step (ST4), the molding step (ST5), the slow cooling step (ST6), and the cutting step (ST7). In addition, a grinding step, a grinding step, a washing step, an inspection step, a baling step, and the like may also be included. The glass substrate to be produced is transported to the delivery destination by laminating steps as needed.

In the melting step (ST1), molten glass is produced by heating the glass raw material. The heating of the molten glass can be performed by electric heating, and the electric heating causes the electric current to pass, and the molten glass itself generates heat to heat it. Further, the glass raw material may be melted by assisting heating by a flame of a burner.

Further, the molten glass contains a clarifying agent. As the clarifying agent, tin oxide, arsenious acid, cerium, or the like is known, but is not particularly limited. However, in terms of reducing the environmental burden, it is preferred to use tin oxide as a fining agent.

In the clarification step (ST2), by heating the molten glass, bubbles containing oxygen, CO ₂ or SO ₂ contained in the molten glass are generated. The bubble is absorbed by the oxygen generated by the reduction reaction of the clarifying agent, and is floated to the surface of the molten glass to be released. Thereafter, in the clarification step, the temperature of the molten glass is lowered, whereby the reducing substance obtained by the reduction reaction of the clarifying agent is subjected to an oxidation reaction. Thereby, the gas component such as oxygen remaining in the bubbles of the molten glass is again absorbed into the molten glass, and the bubbles disappear. The oxidation reaction and the reduction reaction by the clarifying agent are carried out by controlling the temperature of the molten glass.

Further, the clarification step may also employ a vacuum defoaming method in which bubbles existing in the molten glass are grown and defoamed in a reduced pressure atmosphere. The vacuum defoaming mode is effective in not using a clarifying agent. However, the vacuum defoaming method complicates and enlarges the apparatus. Therefore, it is preferred to use a clarifying method using a clarifying agent to raise the temperature of the molten glass.

In the homogenization step (ST3), the molten glass is stirred by using a stirrer to homogenize the glass component. Thereby, the composition unevenness of the glass which causes a stripe etc. can be reduced.

In the supplying step (ST4), the molten glass after the stirring is supplied to the forming apparatus.

The forming step (ST5) and the slow cooling step (ST6) are carried out in a forming apparatus.

In the forming step (ST5), the molten glass is formed into a sheet glass, and a flow of the sheet glass is formed. An overflow down-draw method is used during forming.

In the slow cooling step (ST6), the sheet glass which is formed and flows has a desired thickness and does not generate internal strain, and is further cooled without causing warpage.

In the cutting step (ST7), a sheet glass substrate is obtained by cutting the slowly cooled sheet glass to a specific length. The cut glass substrate is further cut into a specific size to produce a glass substrate of a target size.

Fig. 2 is a schematic view showing a manufacturing apparatus of a glass substrate on which the melting step (ST1) to the cutting step (ST7) in the present embodiment are performed. As shown in FIG. 2, the manufacturing apparatus of a glass substrate mainly includes the melting apparatus 100, the shaping apparatus 200, and the cutting apparatus 300. The melting apparatus 100 includes a melting tank 101, a clarification pipe 120, a stirring tank 103, transfer pipes 104 and 105, and a glass supply pipe 106.

A heating mechanism such as a burner (not shown) is provided in the melting tank 101 shown in Fig. 2 . The glass raw material to which the clarifying agent is added is supplied to the melting tank, and the melting step (ST1) is performed. The molten glass melted in the melting tank 101 is supplied to the clarification pipe 120 via the transfer pipe 104.

In the clarification pipe 120, the temperature of the molten glass MG is adjusted, and the clarification step (ST2) of the molten glass is performed by the oxidation-reduction reaction of the clarifying agent. The clarified molten glass is supplied to the stirring tank via the transfer pipe 105.

In the stirring tank 103, the molten glass is stirred by the stirrer 103a, and the homogenization process (ST3) is performed. The molten glass which has been homogenized in the agitation tank 103 is supplied to the molding apparatus 200 via the glass supply pipe 106 (supply step ST4).

In the molding apparatus 200, the sheet glass is formed from the molten glass by the overflow down-draw method (forming step ST5), and the cooling is performed (slow cooling step ST6).

In the cutting device 300, a plate-shaped glass substrate cut out from the sheet glass is formed (cutting step) Step ST7).

(Description of forming device)

Fig. 3 is a schematic view of a molding apparatus 200 for a glass substrate, and Fig. 4 is a cross-sectional view taken along the line of arrows IV-IV of Fig. 3.

The furnace wall of the forming apparatus 200 is formed of a refractory such as a refractory brick, a refractory heat insulating brick, or a fiber-based heat insulating material. The internal space of the molding apparatus 200 is divided into a forming furnace 201 (the upper forming furnace 201A and the lower forming furnace 201B) and a slow cooling furnace 202 at the lower portion of the forming furnace 201. The forming step (ST5) is performed in the forming furnace 201, and the slow cooling step (ST6) is performed in the slow cooling furnace 202.

A molded body 210 is provided in the upper forming furnace 201A.

The molten glass is supplied to the molded body 210 from the melting apparatus 100 by the glass supply pipe 106 shown in FIG.

The formed body 210 is an elongated structure composed of refractory bricks or the like, and has a wedge-shaped cross section as shown in Fig. 4 . A groove 212 that serves as a flow path for guiding the molten glass MG is provided on the upper portion of the molded body 210. The groove 212 is connected to the third pipe 106, and the molten glass MG flowing through the third pipe 106 flows along the groove 212. The depth of the groove 212 becomes shallower as the flow of the molten glass MG flows downstream, and therefore, the molten glass MG flowing in the groove 212 gradually overflows from the groove 212, flows down the side walls of the molded body 210, and The lower end portion 213 of the molded body 210 merges and flows downward vertically. Thereby, in the molding apparatus 200, the sheet glass SG which is formed from the molded body 210 toward the vertical direction is formed.

Further, the temperature of the sheet glass SG directly under the lower end portion 213 of the molded body 210 is a temperature corresponding to a viscosity of 10 ^5.7 to 10 ^7.5 poise, for example, 1000 to 1130 °C.

The atmosphere partition member 220 is disposed near the lower side of the lower end portion 213 of the molded body 210, and divides the internal space of the forming furnace 201A into the upper forming furnace 201A and the lower forming furnace 201B. The atmosphere partition member 220 is a pair of plate-shaped heat insulating materials, and is provided on both sides in the thickness direction of the sheet glass SG so as to be sandwiched by the sheet glass SG from both sides in the thickness direction (X direction in the drawing). Between the sheet glass SG and the ambience spacer member 220, the astigmatism spacer member The gap 220 is not provided with a degree of contact with the sheet glass SG. The atmosphere spacing member 220 blocks the movement between the forming furnace 201 above the ambient spacing member 220 and the slow cooling furnace 202 below by separating the internal space of the forming apparatus 200.

A pair of cooling rolls 230 and a cooling mechanism 240 are provided in the lower forming furnace 201B.

The cooling roller 230 and the cooling mechanism 240 are disposed below the ambience spacer 220.

As shown in FIG. 3 and FIG. 4, the pair of cooling rolls 230 are provided on both sides in the thickness direction of the sheet glass SG so as to sandwich the sheet glass SG from both sides in the thickness direction. The cooling roll 230 is cooled such that both end portions in the width direction of the sheet glass SG are lowered to a temperature equal to or lower than a viscosity (for example, 900 ° C) of about 10 ^9.0 poise or more. The cooling roll 230 is hollow and is rapidly cooled by supplying a cooling medium (for example, air or the like) to the inside. The diameter of the cooling roll 230 is smaller than the following conveying members 2501, 2502, ..., 250n, and the length inserted into the furnace is also short, and since it is quenched, the deformation (eccentricity) is less.

The cooling mechanism 240 includes a plurality of cooling units (the end cooling unit 241 and the central cooling unit 242) to cool the sheet glass SG.

The end portion cooling unit 241 cools so that both end portions in the width direction of the sheet glass SG are lowered to a temperature corresponding to a viscosity of 10 ^14.5 poise or more.

The central cooling unit 242 cools the central portion of the sheet glass SG in the width direction from the temperature higher than the softening point to the vicinity of the slow cooling point. Here, the center portion of the sheet glass SG is a region which is manufactured in a region other than the target to be cut after the sheet glass is formed, and is formed so that the sheet thickness of the sheet glass SG becomes uniform.

The central cooling unit 242 includes, for example, three-stage units (upper stage unit 242a, middle stage unit 242b, and lower stage unit 242c) in the up and down direction. The upper stage unit 242a quenches the sheet glass SG away from the lower end 213 of the formed body 210 to the vicinity of the softening point, and the middle stage unit 242b and the lower stage unit 242c cool the sheet glass SG to the vicinity of the slow cooling point by slow cooling.

The slow cooling oven 202 has a wall 203. The wall 203 divides the inside of the furnace for transporting the sheet glass SG of the slow cooling furnace 202 and the outside of the furnace. The slow cooling furnace 202 is provided with a plurality of conveying members 2501, 2502, ..., 250n, a plurality of temperature adjustment devices 2701, 2702, 270n, and a plurality of spacers 2021, 2022, ..., 202n.

The slow cooling furnace 202 is separated from the lower forming furnace 201B by the partition plate 2021, and the internal space of the slow cooling furnace 202 is partitioned into a plurality of spaces in the height direction by a plurality of partition plates 2022, ..., 202n other than the partitioning plate 2021. . Each of the spaces partitioned by the plurality of partition plates 2021, 2022, ..., 202n is provided with transport members 2501, 2502, ..., 250n and a plurality of temperature adjusting devices 2701, 2702, ..., 270n. Specifically, a transport member 2501 and a temperature adjustment device 2701 are provided in a space partitioned by the partition plate 2021 and the partition plate 2022, and a transport member 2502 and a temperature adjustment device are provided in a space partitioned by the partition plate 2022 and the partition plate 2023. 2702.

The partition plate 2022 and the partition plate 202n are also partitioned by a partition plate (not shown), and other transport members (not shown) and temperature adjustment devices are provided in the same space. Further, the lowermost conveying member 250n and the temperature adjusting device 270n are provided in a space below the lowermost partition plate 202n.

Each of the conveying members 2501, 2502, ..., 250n is disposed on both sides in the thickness direction of the sheet glass SG, and includes: a pair of rotating shafts which are equal to the outside of the furnace wall supported by a bearing cantilever (not shown); and a pair of conveying A roller, which is attached to the front end of each of the rotating shafts. Each of the temperature adjustment devices 2701, 2702, ..., 270n includes a pair of heaters provided on both sides in the thickness direction of the sheet glass SG. Each of the heaters has a plurality of heat sources in the width direction of the sheet glass SG, and the amount of heating can be adjusted separately. The plurality of heat sources are, for example, chromium-based heating wires.

The sheet glass SG is cooled by the cooling member 230, the cooling device 240, and the temperature adjusting devices 2701, 2702, ..., 270n so as to have a temperature distribution corresponding to a temperature distribution designed in advance, for example.

In the viscous region, for example, the temperature at the end portion in the width direction of the sheet glass is set to be lower than the temperature in the central portion, and the temperature in the central portion becomes uniform (temperature distribution) (first distribution). Thereby, the shrinkage in the width direction can be suppressed, and the sheet thickness of the sheet glass can be made uniform.

In the viscoelastic region, for example, the temperature of the sheet glass is designed to decrease in temperature in the width direction from the center portion toward the end portion (second distribution).

In the temperature region near the glass strain point, the temperature at which the temperature at the end portion in the width direction of the sheet glass and the temperature at the center portion become substantially uniform are designed.

The warpage and strain (residual stress) of the sheet glass can be reduced by managing the temperature of the sheet glass in accordance with the temperature distribution designed as described above. Further, the central portion of the sheet glass includes a region where the thickness of the object portion is uniform, and the end portion of the sheet glass is included in the region of the object portion to be cut after the production.

As described above, the above-described slow cooling step is carried out so that the warpage and strain of the sheet glass do not exceed the allowable value. In the slow cooling step, the rotating shaft of the conveying roller is moved from the furnace wall to the slow cooling furnace by heat conduction from the contact portion with the sheet glass, radiant heat from the sheet glass, and heat conduction from the atmosphere in the slow cooling furnace 202. The protruding portion of 202 is heated. On the other hand, since the heat insulating property of the furnace wall is high, the outside of the slow cooling furnace 202 is maintained at a lower temperature than that in the slow cooling furnace 202.

The inventors of the present invention have obtained the following observations: in the vicinity of the furnace wall, the temperature gradient in the longitudinal direction of the rotating shaft becomes large, and the stress generated in the rotating shaft becomes larger in accordance with the magnitude of the temperature gradient, and the stress generated in the rotating shaft is used. The adjustment of the temperature gradient of the rotating shaft was studied below the allowable stress in the environment.

In the present invention, the influence on the designed temperature distribution is as small as possible and the maximum value of the temperature gradient in the longitudinal direction of the rotating shaft is equal to or less than a specific value, specifically, 2500 ° C / m or less. , control the temperature of the rotating shaft. Hereinafter, it demonstrates based on an embodiment.

Fig. 5 is a cross-sectional view showing one of the conveying members 2501, 2502, ..., 250n.

The conveyance roller 30 comes into contact with the sheet glass SG in the slow cooling furnace 202, and conveys the sheet glass SG downward. The conveying roller 30 is fixed to the front end portion of the rotating shaft 31. The conveying roller 30 can be formed, for example, by collecting inorganic fibers.

The rotating shaft 31 is a hollow tubular shape. One end of the rotating shaft 31 is blocked, and a conveying roller 30 is fixed to the periphery of the blocked end of the rotating shaft 31. The intermediate portion of the rotating shaft 31 is rotatably inserted into a through hole provided in the wall 203 of the slow cooling furnace 202. That is, the rotating shaft 31 penetrates the wall 203. An end portion of the rotating shaft 31 opposite to the conveying roller 30 is supported by a bearing cantilever (not shown) outside the wall 203, and is connected to a discharge pipe (not shown). The discharge pipe is for discharging the heat medium supplied to the rotary shaft 31 as will be described later.

As the rotating shaft 31, a material excellent in heat resistance and high in hardness can be used. For example, austenite stainless steel can be used for the rotating shaft 31. Specifically, SUS310S, SUS303, SUS304, and SUS316 can be used. Further, the total length of the rotating shaft 31 is, for example, 1500 mm or less, and the amount inserted into the furnace is, for example, 500 mm or less, and the outer diameter can be, for example, 50 mm or less, and the inner diameter can be, for example, 50 to 80% of the outer diameter.

Inside the hollow of the rotating shaft 31, an inner tube 32 having a diameter smaller than the inner diameter of the rotating shaft 31 is disposed apart from the inner wall of the rotating shaft 31. The end of the inner tube 32 on the side of the conveying roller 30 is opened, and the open end is away from the blocked end of the rotating shaft 31. An end portion of the inner tube 32 opposite to the open end is connected to a supply tube (not shown) outside the wall 203. The supply pipe is used to supply the heat medium to the rotating shaft 31 from the inner pipe 32 as described below. The heat medium may be either a gas or a liquid, and since the heat capacity of the liquid is large and the temperature of the rotating shaft 31 is excessively lowered, it is preferably a gas.

In the present embodiment, the heat medium is supplied to the inner tube 32 from the outside of the wall 203. The end portion of the heat medium from the side of the conveying roller 30 of the rotating shaft 31 flows to the side of the wall 203 through the gap between the outer surface of the inner tube 32 and the inner wall surface of the rotating shaft 31, and is discharged to the outside of the slow cooling furnace 202. The heat medium is a medium for moving the heat of the end portion of the rotating shaft 31 on the side of the conveying roller 30 to the end opposite to the conveying roller 30. That is, at the end portion of the rotating shaft 31 on the side of the conveying roller 30, the heat medium absorbs heat to lower the temperature of the rotating shaft, and the heat medium after the temperature rises flows toward the outside of the slow cooling furnace 202 along the length of the rotating shaft 31. Thereby, the end portion of the hot rotating shaft 31 on the side of the conveying roller 30 moves along the longitudinal direction of the rotating shaft 31. Thereby, the reason can be derived from the conveying roller 30 The temperature gradient in the longitudinal direction of the rotating shaft 31 caused by the heat conduction with the contact portion of the sheet glass SG is suppressed to be low. In the present embodiment, by controlling the flow rate of the heat medium, the temperature gradient in the longitudinal direction of the rotary shaft 31 is adjusted to be small. Thereby, the stress caused by the temperature gradient and acting on the rotating shaft 31 can be reduced, so that the deformation of the rotating shaft 31 can be prevented. Here, it is preferable to adjust so that the maximum value of the temperature gradient in the longitudinal direction of the rotating shaft 31 becomes 2500 ° C / m or less. The reason for this is that when the temperature gradient is 2500 ° C / m or less, the stress acting on the rotating shaft 31 is smaller than the allowable stress of the rotating shaft 31 in the atmosphere temperature (700 ° C to 850 ° C) in the slow cooling furnace 202.

Further, the temperature gradient of the rotating shaft 31 can be reduced by heating the rotating shaft 31 by a heat source such as a heater (not shown).

Preferably, the heat insulating material 33 is provided, and the heat insulating material 33 extends from the through hole of the slow cooling furnace 202 through which the rotating shaft is inserted toward the roller 30 side of the rotating shaft 31, and covers the outer surface of the rotating shaft 31. As the heat insulating material 33, a material (for example, heat-resistant brick, fire-resistant heat insulating brick, inorganic fiber, or the like) having heat resistance at an ambient temperature in the slow cooling furnace 202 in which the rotating shaft 31 is disposed can be used. The heat insulating material 33 can be formed in a cylindrical shape so as to cover the outer surface of the rotating shaft 31, but it is not necessarily required to be cylindrical. Further, the heat insulating material 33 does not need to cover the entire outer surface of the rotating shaft 31, and it is preferable that the portion inside the slow cooling furnace 202 of the rotating shaft 31 is at least covered at the end on the side of the wall 203 so as to obtain a desired temperature gradient.

By providing the heat insulating material 33, the temperature rise of the rotating shaft 31 due to the radiant heat from the sheet glass or the heat conduction from the atmosphere in the slow cooling furnace 202 can be suppressed. Thereby, the temperature gradient in the longitudinal direction of the rotating shaft 31 at the portion covered by the heat insulating material 33 can be reduced.

Preferably, the temperature gradient of the rotating shaft 31 at the end portion of the heat insulating material 33 on the side of the roller 30 is 1300 ° C / m or less. At the end portion of the heat insulating material 33 on the side of the roller 30, the portion of the rotating shaft 31 covered with the heat insulating material 33 and the portion not covered with the heat insulating material 33 have a large temperature difference, and the temperature gradient becomes large. The tendency. Moreover, the reason is that the rotating shaft 31 is not The portion covered with the heat insulating material 33 is exposed to the ambient temperature (700 ° C to 850 ° C) in the slow cooling furnace 202 to become a high temperature, so that the allowable stress is small. When the temperature gradient is 1300 ° C / m or less, the stress acting on the rotating shaft 31 is smaller than the allowable stress in the vicinity of the lower end portion of the sheet glass SG in the slow cooling furnace 202 (700 ° C or more).

[Examples]

Hereinafter, the present invention will be specifically described by way of examples.

The rotation axis of the conveying member in the slow cooling furnace is set as shown in Fig. 5 described above. The length of the heat insulating material in the longitudinal direction of the rotating shaft is set to 0.26 m from the furnace wall, the temperature in the slow cooling furnace is set to 800 ° C, and the temperature outside the slow cooling furnace is set to 30 ° C, and the thermal conductivity of the rotating shaft The rate is assumed to be SUS304 and the thermal conductivity W/(m‧K)=0.013*temperature (°C)+15, and the thermal conductivity of the heat insulating material is set to 0.1 W/(m‧K), thereby calculating the rotation The allowable stress of the shaft.

<Comparative example>

The length of the heat insulating material in the longitudinal direction of the rotating shaft is set to 0.26 m from the furnace wall, the temperature in the slow cooling furnace is set to (800) ° C, and the temperature outside the slow cooling furnace is set to (30) ° C, and the rotation is performed. The thermal conductivity of the shaft is assumed to be SUS304 and is set to thermal conductivity W/(m‧K)=0.013*temperature (°C)+15, and the thermal conductivity of the insulating material is set to (0.1)W/(m‧ K), thereby calculating the allowable stress of the rotating shaft.

Fig. 6 is a view showing the relationship between the position in the longitudinal direction of the rotating shaft and the temperature. The position in the longitudinal direction of the rotating shaft is set to the horizontal axis, and the temperature is set to the vertical axis. The position in the longitudinal direction of the rotating shaft is set to be positive with respect to the slow cooling furnace side with the furnace wall as a reference. The embodiment is shown by a solid line, and the comparative example is shown by a broken line.

In the embodiment, the temperature gradient in the longitudinal direction of the rotating shaft is the largest at the position of the furnace wall of the heat insulating material, and the maximum value is 2500 ° C / m. Further, the temperature gradient in the longitudinal direction of the rotating shaft at the end portion of the heat insulating material on the roll side was 1,250 ° C / m.

In the comparative example, the temperature gradient in the longitudinal direction of the rotating shaft was the largest at the position of the furnace wall of the heat insulating material, and the maximum value was 3600 ° C / m. Moreover, the end portion of the roller side of the heat insulating material The temperature gradient in the longitudinal direction of the rotating shaft placed was 2350 ° C / m.

Fig. 7 is a view showing the relationship between the position in the longitudinal direction of the rotating shaft and the stress of the rotating shaft at the temperature of the rotating shaft of Fig. 6. In the examples, the maximum value of the temperature gradient is smaller than that of the comparative example, so that the stress acting on the rotating shaft is small.

The method for producing the glass substrate of the present invention has been described in detail above. The present invention is not limited to the above-described embodiments, and various modifications and changes can be made without departing from the spirit and scope of the invention.

Claims (6)

A method for producing a glass substrate, wherein a molten glass is poured from a molded body in a forming furnace to form a continuous sheet glass, and the sheet glass is held by a roll in a slow cooling furnace and conveyed downward; The furnace has a wall which is divided into a furnace for conveying the sheet glass and an outer space, wherein the roller is supported by a rotating shaft passing through the wall, and the temperature gradient adjusting mechanism provided in the slow cooling furnace is borrowed a heat insulating material that heats the rotating shaft at least the portion on the wall side of the rotating shaft, a heat source that heats the rotating shaft, or flows through the rotating shaft to the rotating shaft The heating medium is heated, and the temperature gradient adjusting mechanism is adjusted to reduce the temperature gradient in the longitudinal direction of the rotating shaft. The method for producing a glass substrate according to claim 1, wherein the heat insulating material extends from an inner wall surface of the forming furnace toward the roll side of the rotating shaft. The method of producing a glass substrate according to claim 1, wherein the heat medium transfers heat from a portion of the rotating shaft on which the roller is provided to a portion penetrating the wall. The method for producing a glass substrate according to any one of claims 1 to 3, wherein the maximum value of the temperature gradient in the longitudinal direction of the rotating shaft is adjusted to be 2,500 ° C / m or less. The method for producing a glass substrate according to any one of claims 1 to 3, wherein a temperature gradient in a longitudinal direction of the rotating shaft at an end portion of the heat insulating material on the side of the roll side is 1300 ° C / m or less Make adjustments. A manufacturing apparatus for a glass substrate, comprising: a forming furnace having a sheet glass formed by overflowing molten glass to form a continuous sheet And a slow cooling furnace, wherein one side of the sheet glass is held and conveyed downward to perform slow cooling; and the slow cooling furnace comprises: a wall which is divided into a furnace for conveying the inside and outside of the sheet glass; a shaft penetrating the wall; a roller disposed at a front end of the rotating shaft and supported by the rotating shaft cantilever; and a temperature gradient adjusting mechanism configured to reduce a temperature gradient in a longitudinal direction of the rotating shaft The temperature gradient adjusting mechanism is a heat insulating material that heats the rotating shaft by heat-insulating at least the portion on the wall side of the rotating shaft, a heat source that heats the rotating shaft, or flows through the above A heat medium that rotates the shaft to heat the rotating shaft.