TWI380965B - Glass manufacturing method and vacuum degassing device - Google Patents

Description

Glass manufacturing method and vacuum degassing device

The present invention relates to a glass production method and a vacuum degassing apparatus comprising a process for defoaming molten glass under reduced pressure in a vacuum degassing tank.

Conventionally, in order to improve the quality of a molded glass product, a clarification process for removing bubbles generated in the molten glass is performed before the molten glass obtained by melting the raw material in the melting furnace is formed by a molding apparatus. Clarification treatment.

Among the methods of the clarification treatment, it is known that the molten glass is introduced into a reduced pressure environment, and in the reduced pressure environment, the bubbles in the continuously flowing molten glass are largely grown and floated, and bubbles are formed on the surface of the molten glass. A vacuum degassing method which removes the foam and removes it, and then discharges it from a reduced pressure environment.

In this clarification process, various methods have been proposed in order to promote the growth of bubbles in the molten glass flow or to break the bubbles.

Patent Document 1 is intended to improve the performance characteristics of the clarification operation, and it is proposed to add various clarification accelerators to the vitrifiable material, that is, to the glass raw material. Further, in Patent Document 1, the element that affects the growth of the bubble during the clarification period under the reduced pressure condition includes, for example, the property of the gas on the molten material, that is, the property of the gas on the molten glass.

Further, Patent Document 2 discloses a foam destruction means for destroying foam generated by decompression of molten glass in a clarification treatment chamber. As a means of foam destruction, a mechanical rotating body for expanding and breaking bubbles is disclosed. Use, or cause the jet to collide with the foam.

Patent Document 1: Japanese Patent Publication No. 2001-515453 Patent Document 2: Japanese Laid-Open Patent Publication No. 2003-89529

In Patent Document 1, the method for changing the properties of the gas on the molten glass includes the selection of the partial pressure of the air, the selection of the environment for the concentrated nitrogen form of the inert gas, and the selection of the partial pressure of the inert gas of the nitrogen form. The nature of the gas on the molten glass, which promotes the growth of the bubble, is not revealed at all. Further, when clarification is carried out under reduced pressure, the volatile gas component from the molten glass and the gas component of the bubbles contained in the molten glass are largely released, so that the partial pressure of the selected air and the selected nitrogen form are selected. The partial pressure of the inert gas is liable to be lowered. There is also the problem that the environmental gas composition is easily changed by the environment of the selected intensive nitrogen form of the inert gas.

Further, in the method described in Patent Document 2, the destruction of the foam generated in the clarification treatment chamber is not always sufficient. That is, the use of the mechanical rotating body or the jet stream can destroy the existing foam on the molten glass, but it will cause turbulent flow in the molten glass flow, and as a result, it will become a cause of new bubbles. Further, in the clarification treatment chamber, the foam may be partially destroyed, but the foam generated on the downstream side of the mechanical rotating body or the jet stream cannot be broken. Moreover, the use of mechanical rotating bodies may become a source of contamination of the molten glass, and the use of the jet stream may lower the temperature of the molten glass, so that the glass The quality of the glass is reduced.

In addition, in theory, it is necessary to increase the degree of decompression of the environment (the lower the absolute pressure of the environment), the more the defoaming effect under reduced pressure, the more the bubbles in the molten glass flow are reduced. However, in fact, when the degree of decompression of the environment (the absolute pressure of the environment) reaches a certain stage, the bubble generation rate is higher than the bubble elimination rate of the bubble breaking, and the bubble layer is enlarged on the surface of the molten glass, so that the pressure is reduced. The defoaming ability is reduced. This phenomenon is called "the bubble layer hypertrophy caused by over-decompression". As a result, the bubbles in the molten glass flow increase instead. Therefore, the range of the degree of pressure reduction of the environment in which the vacuum degassing effect can be sufficiently exhibited is extremely small, and thus an external factor such as a change in atmospheric pressure or the like is formed to affect the problem of the vacuum degassing effect.

In order to solve the above problems of the prior art, an object of the present invention is to provide a glass manufacturing method which is excellent in a vacuum degassing effect, and more particularly to provide a method for preventing decompression of a bubble layer caused by over-decompression. A glass manufacturing method for a bubble effect.

Further, it is an object of the present invention to provide a vacuum degassing apparatus suitable for the glass manufacturing method of the present invention.

As a result of intensive studies to achieve the above object, the inventors of the present invention found that the gas component generated by the bubble breaking on the surface of the molten glass is retained above the molten glass flowing in the vacuum degassing vessel, so that the pressure is removed. The bubble effect will be reduced. Hereinafter, in the present specification, a gas component generated by breaking a bubble on a surface of a molten glass is referred to as "from a molten glass. In the gas component, the gas component from the molten glass is retained above the molten glass flowing through the vacuum degassing vessel, and is referred to as "the retention of the gas component from the molten glass".

When the gas component from the molten glass stays, the environment above the molten glass (the upper space inside the vacuum degassing tank), the partial pressure of the gas component from the molten glass becomes high, and thus floats on the surface of the molten glass. The bubbles are not easily broken, so the defoaming effect under reduced pressure is lowered.

Moreover, the inventors of the present invention have found that by releasing the gas component from the molten glass, the bubble breaking speed on the surface of the molten glass is improved, and the bubble layer hypertrophy due to excessive decompression can be suppressed.

Further, the gas component derived from the molten glass differs depending on the glass composition, and examples thereof include HCl, H ₂ SO ₄ , a boric acid compound, and HF.

The present invention is based on the above-described findings of the inventors of the present invention, and provides a method for producing a glass, which is a glass manufacturing method including a process of defoaming a molten glass under reduced pressure in a vacuum degassing tank, characterized in that Flowing over the molten glass of the vacuum degassing vessel, at least one selected from the group consisting of a gas flow in a flow direction of the molten glass and a gas flow in a direction opposite to a flow direction of the molten glass flow.

Moreover, the present invention provides a glass production method comprising a process for defoaming molten glass under reduced pressure in a vacuum degassing vessel, characterized in that the molten glass flows through the vacuum degassing vessel. Upper, forming phase The flow direction of the molten glass is a gas flow in the orthogonal direction.

In the method for producing a glass of the present invention, it is preferable that the gas forming the gas stream does not substantially contain a gas component generated by the molten glass.

In the method for producing a glass of the present invention, the gas forming the gas stream is preferably hydrogen (H ₂ ), nitrogen (N ₂ ), oxygen (O ₂ ), air, carbon monoxide (CO), carbon dioxide (CO ₂ ), At least one selected from the group consisting of argon (Ar), helium (He), neon (Ne), krypton (Kr), xenon (Xe), hydrocarbon gas, fluorocarbon gas, and ammonia (NH ₃ ) .

In the method for producing a glass of the present invention, it is preferable that the gas for forming the gas stream is introduced at a position close to the surface of the molten glass.

Moreover, the present invention provides a vacuum degassing apparatus for molten glass, which has a reduced pressure outer casing that is drawn by a reduced pressure, and is provided in the decompression outer casing for decompressing decompression of molten glass. a bubble tank; an introduction means for introducing the molten glass before decompression under reduced pressure into the vacuum degassing tank; and a connection means for connecting to the vacuum degassing tank; A vacuum degassing apparatus for molten glass which is a deriving means for deriving a molten glass obtained by degassing under reduced pressure from the vacuum degassing vessel, further characterized by further comprising: introducing a gas into the aforementioned vacuum degassing A gas introduction means for the gas introduction means in the upper space inside the groove and a gas flow forming means for guiding the gas from the upper space.

In the vacuum degassing apparatus for molten glass of the present invention, the gas flow forming means is provided on the top or side surface of the vacuum degassing tank in which the upper space is formed above the molten glass in the vacuum degassing tank.

According to the invention, since the gas flow is formed above the molten glass flowing through the vacuum degassing vessel, the retention of the gas component from the molten glass can be released. Since the retention of the gas component from the molten glass can be released, it is possible to prevent a decrease in the vacuum degassing effect. Further, since the retention of the gas component from the molten glass can be released, the bubble layer hypertrophy due to excessive decompression is less likely to occur. As a result, the degree of pressure reduction in the vacuum degassing tank can be further improved, and the effect of decompression and defoaming can be improved.

Hereinafter, the present invention will be described with reference to the drawings.

Fig. 1 is a cross-sectional view showing a configuration example of a vacuum degassing apparatus of the present invention. In the vacuum degassing apparatus 10 shown in Fig. 1, a cylindrical decompression degassing tank 12 is housed and disposed in the decompression housing 11 so that its long axis is oriented in the horizontal direction. A riser 13 oriented in the vertical direction is attached to the lower side of the upstream side of the vacuum degassing tank 12, and a downcomer 14 is attached to the lower side of the downstream side. Further, the upstream side and the downstream side of the vacuum degassing tank 12 represent the upstream side and the downstream side in the flow direction of the molten glass G flowing through the vacuum degassing tank 12. The riser 13 and the downcomer 14 are such that a part thereof is positioned in the decompression housing 11.

As shown in FIG. 1, the riser 13 is an introduction means for communicating with the vacuum degassing tank 12 to introduce the molten glass G from the melting tank 20 into the vacuum degassing tank 12. Therefore, the lower end portion of the riser pipe 13 is the molten glass G embedded in the open end of the upstream groove 22 and immersed in this upstream groove 22 .

The downcomer 14 is a means for deriving the pressure reducing degassing tank 12 for lowering the molten glass G after degassing under reduced pressure from the vacuum degassing tank 12, and then discharging it to a treatment tank (not shown) of a post-process . Therefore, the lower end portion of the downcomer 14 is the molten glass G which is embedded in the open end of the downstream groove 24 and is immersed in this downstream groove 24.

In the pressure-reduced outer casing 11, a heat insulating material 15 such as a heat insulating brick that heat-shields these members is disposed around the vacuum degassing tank 12, the riser pipe 13, and the down pipe 14.

In the vacuum degassing apparatus 10 shown in Fig. 1, since the vacuum degassing tank 12, the riser pipe 13, and the down pipe 14 are pipes of the molten glass G, heat resistance and corrosion resistance to molten glass are good. Materials to make. As an example, a hollow tube made of platinum or platinum alloy is used. Specific examples of the platinum alloy are platinum-gold alloy and platinum-rhodium alloy. Moreover, if other examples are mentioned, it is made of a ceramic non-metallic inorganic material, that is, a hollow tube made of a dense refractory material. Specific examples of the dense refractory include an electroformed refractory such as an alumina-based electroformed refractory, a zirconia-based electroformed refractory, an alumina-zirconia-ceria-based electroforming refractory, and a dense oxidation. A compact refractory such as an aluminum refractory, a dense zirconia-ceria-based refractory, or a dense alumina-zirconia-ceria-based refractory. The decompression housing 11 for accommodating the decompression degassing tank 12 and accommodating one of the riser tube 13 and the down tube 14 is made of metal, and is made of, for example, stainless steel.

In the vacuum degassing apparatus 10 of the present invention shown in Fig. 1, the upstream side and the downstream side of the top portion of the vacuum degassing tank are provided for monitoring and subtraction. The windows 122, 123 inside the defoaming tank 12 are pressed. The windows 122 and 123 are made of platinum or platinum alloy, or a hollow tube made of a dense refractory material, one end of which is connected to the upstream side and the downstream side of the top of the day of the vacuum degassing tank 12, and the other end is a decompression point. The wall of the outer casing 11 is located outside the decompression housing 11.

The vacuum degassing apparatus 10 shown in Fig. 1 has a gas flow forming means including a gas introduction means and a gas discharge means.

In the vacuum degassing apparatus 10 shown in Fig. 1, the window 122 is also a gas introduction means 30 for introducing a gas into the upper space 121 inside the decompression degassing tank 12. The gas 40 introduced into the upper space 121 inside the vacuum degassing tank 12 from the window 122 is formed in the same direction as the flow direction of the molten glass G above the molten glass G flowing through the inside of the vacuum degassing tank 12. The gas stream 41, that is, the gas stream 41 from the upstream side of the vacuum degassing tank 12 toward the downstream side. Next, the gas 42 is discharged to the outside from the window 123 provided on the downstream side of the vacuum degassing tank 12. That is, in the vacuum degassing apparatus 10 shown in FIG. 1, the window 123 is also a gas discharge means 31 for discharging the gas 42 from the upper space 121 of the vacuum degassing tank 12.

The vacuum degassing apparatus 10 shown in Fig. 1 forms a gas flow 41 above the molten glass G flowing through the inside of the vacuum degassing tank 12 to release the gas component from the molten glass. That is, the gas component from the molten glass does not stay, but is transported by the gas stream 41, and is discharged from the window 123 (gas outlet means 31) to the outside.

When the gas component from the molten glass stays, the environment above the molten glass G (the upper space 121 of the vacuum degassing tank 12) is from the melting Since the partial pressure of the gas component of the glass becomes high, the bubbles floating on the surface of the molten glass G are not easily broken, and the defoaming effect under reduced pressure is lowered.

In the present invention, since the retention of the gas component from the molten glass can be released, the decompression and defoaming effect is not lowered, and the vacuum degassing effect is good.

Further, when the gas component from the molten glass is retained, the bubble layer is enlarged due to the excessive pressure reduction, so that the vacuum degassing effect is greatly reduced, but in the present invention, the gas component from the molten glass does not remain, and Since it is conveyed by the gas stream 41 and is discharged to the outside from the gas discharge means 31, even if the degree of pressure reduction of the vacuum degassing tank 12 is increased more than in the past, the bubble layer hypertrophy due to over-decompression can be further suppressed. . Therefore, the degree of pressure reduction of the vacuum degassing tank 12 can be increased more than in the past (the absolute pressure of the vacuum degassing tank 12 can be lowered more than in the past), and the decompression and defoaming effect can be further improved.

Further, the release of the gas component from the molten glass to improve the decompression and defoaming effect is a new inventor of the present invention. In Fig. 1, the pressure in the upper space 121 is a so-called vacuum state of a pressure of only about 38 to 460 mmHg (51 to 613 hPa) as will be described later. It has never been thought in the past that the gas component from the molten glass will remain in the upper space 121 which forms a so-called vacuum state. As a result of the review by the inventors of the present invention, it was found that the gas component from the molten glass stays in the upper space 121 in a so-called vacuum state as described above, and it is found that the retention of the gas component from the molten glass affects the vacuum degassing effect.

As can be understood from the above points, the present invention forms the gas stream 41 above the molten glass G in order to release the retention of the gas component from the molten glass. Therefore, the gas stream 41 formed above the molten glass G is preferably not included. Contains gas components from molten glass. Further, it is preferable that the gas forming the gas stream 41 is a gas which does not adversely affect the molten glass, the glass product to be produced, and the glass manufacturing equipment, particularly the vacuum degassing apparatus.

The gas satisfying the above conditions is hydrogen (H ₂ ), nitrogen (N ₂ ), oxygen (O ₂ ), carbon monoxide (CO), carbon dioxide (CO ₂ ), argon (Ar), helium (He), neon (Ne), Kr (Kr), xenon (Xe), hydrocarbon gas, fluorocarbon gas, ammonia (NH ₃ ), and the like. These gases may be used singly or as a mixture of two or more.

Further, as long as the retention of the gas component from the molten glass can be released, the gas flow formed above the molten glass G is not limited to the molten glass in the vacuum degassing tank 12 as shown by the gas flow 41 in Fig. 1 . The flow direction of G is the same direction, and may be opposite to the flow direction of the molten glass G in the vacuum degassing tank 12, that is, the gas flow from the downstream side of the vacuum degassing tank 12 toward the upstream side. In this case, the gas inlet means is formed in the window 123 on the downstream side of the top of the vacuum degassing tank for 12 days, and the gas outlet means is formed in the window 122 on the upstream side of the top of the vacuum degassing tank 12 days. .

In the first embodiment, the gas flow 41 in the same direction as the flow direction of the molten glass G is formed throughout the longitudinal direction of the vacuum degassing vessel 12, but the gas component from the molten glass can be released. A plurality of gas streams may also be formed above the molten glass G. The plurality of gas streams may be in the same direction as the flow direction of the molten glass G or in the opposite direction. Further, the flow directions of the plurality of gas streams may be the same or opposite directions. Furthermore, the number of gas deriving means and gas introduction means is not limited to one, There may also be a plurality of them.

For example, a plurality of gas streams can be formed above the molten glass G by forming the following configuration.

[Configuration Example 1]

In the vacuum degassing apparatus 10 shown in Fig. 1, a window for forming a gas discharge means is also provided in the central portion in the longitudinal direction of the top portion of the vacuum degassing tank for 12 days, and the window 123 is used as a gas introduction means. The gas introduced from the window 122 as the gas introduction means forms a gas flow in the same direction as the flow direction of the molten glass G on the upstream side of the molten degassing tank 12, and then is placed at the top of the decompression degassing tank for 12 days. The window in the central portion of the long side direction is released to the outside. The gas introduced from the window 123 as the gas introduction means forms a gas flow in the opposite direction to the flow direction of the molten glass G on the downstream side of the molten degassing tank 12, and then is provided from the degassing degassing tank 12 The window in the center of the long side is released to the outside.

[Configuration Example 2]

In the vacuum degassing apparatus 10 shown in Fig. 1, a window for forming a gas introduction means is also provided at a central portion in the longitudinal direction of the top portion of the decompression degassing tank for 12 days, and windows 122 and 123 are used as a gas deriving means. . One part of the gas introduced into the window in the center portion in the longitudinal direction of the top portion of the vacuum degassing tank 12 days, and the gas flow in the opposite direction to the flow direction of the molten glass G is formed on the upstream side of the molten defoaming tank 12 It is discharged from the window 122 forming the gas export means to the outside. And was introduced in the reduction The other portion of the gas in the window at the center in the longitudinal direction at the top of the 12th day of the pressure degassing tank forms a gas flow in the same direction as the flow direction of the molten glass G on the downstream side of the molten degassing tank 12, and then forms a gas from the gas. The window 123 of the export means is released to the outside.

In the first embodiment, the gas inlet 40 is introduced from the window 122 provided on the upstream side of the top of the vacuum degassing tank for 12 days. However, as long as the gas flow can be formed above the molten glass G (in the case of Fig. 1, The gas flow 41 in the same direction in the flow direction of the molten glass G is used to release the gas component from the molten glass, and a window may be formed on the upstream end surface of the vacuum degassing vessel 12, and the gas may be introduced from the window. In this case, the window formed on the end surface (side surface) on the upstream side of the vacuum degassing tank 12 is a gas introduction means.

In the first view, the gas 123 is discharged to the outside from the window 123 provided on the downstream side of the top of the vacuum degassing tank for 12 days, but the gas flow can be formed above the molten glass G (the case of Fig. 1) In the gas flow 41) in the same direction as the flow direction of the molten glass G, the gas component from the molten glass is released, and a window is formed on the downstream end surface of the vacuum degassing vessel 12, and gas is discharged from the window. . In this case, the window formed on the end surface (side surface) of the vacuum degassing tank 12 is a gas deriving means.

In addition, the vacuum degassing tank 12 shown in Fig. 1 has a vertically long shape which is long in the flow direction of the molten glass G. However, the vacuum degassing tank is a width shape having a short length in the flow direction of the molten glass G. . In the case of such a vacuum degassing tank, a gas flow in a direction orthogonal to the width direction of the vacuum degassing vessel, that is, in a direction perpendicular to the flow direction of the molten glass, may be formed. In order to form a gas flow in the width direction of the vacuum degassing tank, for example, as long as two of the degassing tanks are under reduced pressure A side window is provided, one window is used as a gas introduction means, and the other window is used as a gas export means.

Fig. 2 is a view showing an example of a preferred embodiment of the glass manufacturing apparatus of the present invention. In the vacuum degassing apparatus 10 shown in FIG. 2, the window 122 provided on the upstream side of the vacuum degassing tank 12 is inserted with a platinum or platinum alloy or a ceramic containing alumina or zirconia. Hollow tube 300. In the vacuum degassing tank 12, the front end of the hollow tube 300 is positioned above the molten glass G.

In the vacuum degassing apparatus 10 shown in FIG. 2, the hollow tube 300 is a gas introduction means 30 for introducing a gas into the upper space 121 inside the decompression degassing tank 12. The gas 40 introduced into the upper space 121 inside the decompression degassing tank 12 from the hollow tube 300 is formed in the same direction as the flow direction of the molten glass G above the molten glass G flowing inside the decompression degassing tank 12. The gas flow, that is, the gas flow 41 from the upstream side of the vacuum degassing tank 12 toward the downstream side. Next, the gas 42 is discharged to the outside from the window 123 provided on the downstream side of the vacuum degassing tank 12.

Further, the hollow tube 300 as the gas introduction means is not limited to the one shown in Fig. 2, and any of the above-described states may be used. For example, when gas is introduced from the downstream side of the vacuum degassing tank 12, a hollow tube as a gas introduction means may be inserted into the window 123 provided on the downstream side of the vacuum degassing tank 12, and the pressure is to be reduced. When a gas is introduced into the center portion of the longitudinal direction of the defoaming tank, a hollow tube as a gas introduction means may be inserted into a window provided at the center in the longitudinal direction of the decompression degassing tank. Further, when gas is introduced from the upstream end surface or the downstream end surface of the vacuum degassing vessel, it may be inserted as a gas introduction means in a window provided on the upstream end surface or the downstream end surface. Hollow tube. Further, when introducing a gas from the side surface of the vacuum degassing vessel, a hollow pipe as a gas introduction means may be inserted into a window provided on the side surface of the vacuum degassing vessel.

In the second drawing, the position of the front end of the hollow tube 300 is not particularly limited, and may be appropriately selected as needed. For example, in order to release the gas component remaining above the molten glass G, it is preferable to form the gas flow 41 near the surface (liquid surface) of the molten glass G, so that the front end of the hollow tube 300 can also come close to the molten glass G. The position of the surface (liquid level).

Further, since the gas flow 41 is to be formed in the vicinity of the surface (liquid surface) of the molten glass G, an interference plate for guiding the gas flow to the lower side may be provided inside the top of the decompression degassing tank for 12 days.

Further, in the second drawing, the hollow tube 300 having a straight tube shape whose front end faces downward is shown. However, the shape of the hollow tube is not limited thereto, and the shape of the hollow tube may be appropriately selected. For example, in order to guide the gas 40 introduced into the vacuum degassing tank 12 in the downstream direction, a hollow tube whose tip end is curved in the flow direction of the molten glass G (the downstream side in FIG. 2) may be used.

The glass production method of the present invention is a process comprising defoaming a molten glass under reduced pressure in a vacuum degassing vessel, and is characterized in that a flow direction of the molten glass is formed above the molten glass flowing through the vacuum degassing vessel. The gas flow, the gas flow in the opposite direction to the flow direction of the molten glass, or the gas flow of both. Further, as described above, a plurality of gas streams having the same flow direction or the opposite directions may be formed above the molten glass.

For the upper square of the molten glass G circulating in the vacuum degassing tank 12 As the gas flow 41, the vacuum degassing apparatus of the present invention described in Fig. 1 may be used. Further, in the method for producing a glass of the present invention, the effect obtained by forming a gas stream above the molten glass flowing through the vacuum degassing vessel is described in the vacuum degassing apparatus of the present invention. Omitted.

Further, in the present invention, since the gas flow is formed above the molten glass, it is only necessary to release the gas component from the molten glass. Therefore, in the practice of the vacuum degassing, it is not necessary to use the molten glass in advance. A gas flow is formed above it. Therefore, if a gas flow can be formed above the molten glass to release the gas component from the molten glass, the gas flow can be periodically formed during the vacuum degassing, for example, 1 to 30 can be formed every hour. A flow of gas around a second. Further, the gas flow is periodically formed, and the gas may be periodically introduced from the gas introduction means. For example, the gas may be supplied to the solenoid valve of the window 122 of the vacuum degassing apparatus 10 shown in Fig. 1 periodically (not shown). Show) Regularly open and close.

In the glass production method of the present invention, the gas flow can be formed in the same manner as in the conventional glass production method except that a gas flow is formed above the molten glass flowing through the vacuum degassing vessel. For example, when vacuum degassing is performed, the inside of the vacuum degassing tank 12 is 1100 ° C to 1600 ° C, and it is particularly preferable to form a temperature range of 1150 ° C to 1450 ° C by heating. Further, the absolute pressure inside the vacuum degassing tank 12 is preferably reduced to 38 to 460 mmHg (51 to 613 hPa), more preferably to 60 to 350 mmHg (80 to 467 hPa). Further, the flow rate of the molten glass G flowing through the vacuum degassing tank 12 is preferably from 1 to 2,000 tons per day from the viewpoint of productivity.

The glass manufacturing method of the present invention preferably has a vacuum degassing process, and has a raw material melting process and a forming process as a front process and a post process. This raw material melting process can be, for example, a conventionally known process, for example, a process in which the raw material is melted by heating to about 1400 ° C or more depending on the type of the glass. The raw material to be used is not particularly limited as long as it is a material suitable for the glass to be produced. For example, a material which is prepared by blending a conventionally known raw material such as cerambi, boric acid or limestone with the composition of the final glass product may be used. The desired clarifying agent. Further, the molding process may be, for example, a conventionally known process, such as a float molding process, a roll flat forming process, a melt forming process, and the like.

The glass produced by the present invention is not limited as long as it is a glass produced by a heat fusion method. Therefore, it may be an alkali-free glass, or may be an alkali-containing glass such as soda lime ceria-based glass or alkaline borosilicate glass typified by soda lime glass. The present invention is particularly suitable for the production of alkali-free glass and even alkali-free glass used for glass substrates for liquid crystal displays.

Example

Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited to this.

In the examples, vacuum degassing of molten glass was carried out using the vacuum degassing apparatus shown in Fig. 1. The molten glass is an alkali-free glass.

The temperature in the vacuum degassing tank 12 was maintained at 1400 °C. The inside of the decompression housing 11 is exhausted by a vacuum pump, thereby indirectly exhausting the inside of the decompression defoaming tank 12 housed in the decompression housing 11. That is, the decompression housing 11 is sealed and inner The outer portion is blocked, but an opening portion is provided in a portion of the vacuum degassing tank 12 that is in contact with the upper space of the molten glass, and is in communication with the inside of the pressure reducing casing. Therefore, when the inside of the decompression housing is exhausted, the decompression tank is naturally decompressed. In the vacuum degassing implementation, the barometric pressure meter is often used to monitor the atmospheric pressure. The degree of pressure reduction in the vacuum degassing tank 12 is adjusted by adjusting the gauge pressure of the vacuum pump, and the absolute pressure in the vacuum degassing tank 12 is controlled.

In addition, the change in the liquid level of the molten glass G in the vacuum degassing tank 12 due to the adjustment of the degree of pressure reduction in the vacuum degassing tank 12 is corrected by moving the position of the pressure reducing casing 11 up and down.

The liquid level of the molten glass G was visually monitored from a window 122 provided on the upstream side of the top of the vacuum degassing tank for 12 days. A scale (not shown) indicating the distance from the bottom surface of the vacuum degassing tank 12 to the liquid surface of the molten glass G is provided at a position inside the vacuum degassing tank 12 that can be confirmed from the window 122. By comparing the scale with the liquid surface of the molten glass G, the presence or absence of the change in the liquid surface of the molten glass G and the change in the thickness of the bubble layer generated in the surface layer of the molten glass G are monitored.

(Comparative Example 1)

In order to maintain the absolute pressure in the vacuum degassing tank 12 at 300 mmHg (400 hPa), the pressure reduction in the vacuum degassing tank 12 is adjusted according to the change in atmospheric pressure, and decompression under reduced pressure is performed. The change in the liquid level of the molten glass G in the vacuum degassing tank 12 due to the adjustment of the degree of decompression is corrected by moving the position of the decompression housing 11 up and down. At this time, the thickness of the bubble layer observed from the window 122 is about 30 mm. Therefore, it is understood that the glass produced by the degassing under reduced pressure in the vacuum degassing vessel has a poor bubble. The shape will increase.

(Example 1)

Vacuum degassing was carried out in the same manner as in Comparative Example 1. However, in the vacuum degassing implementation, nitrogen gas (N ₂ ) was introduced into the vacuum degassing tank 12 at a flow rate of 100 L/min from the window 122 provided on the upstream side of the top of the vacuum degassing tank for 12 days. Upper space 121. The thermocouple (not shown) inserted into the window 122 is known to have a reduced temperature after introduction of nitrogen. Further, the thermocouple (not shown) inserted into the window 123 on the downstream side of the top of the vacuum degassing tank for 12 days is known to have a temperature rise after the introduction of nitrogen gas. The change in the temperature indicates that the nitrogen gas introduced into the upper space 121 inside the vacuum degassing vessel 12 flows above the molten glass G flowing inside the vacuum degassing vessel 12 to form a flow direction with the molten glass G. The gas flow 41 in the same direction, that is, the gas flow 41 from the upstream side of the vacuum degassing tank 12 toward the downstream side, is discharged from the window 123 to the outside.

Further, in comparison between the first embodiment and the comparative example 1, it is understood that the thickness of the bubble layer observed from the window 122 is reduced by 20 mm or more, and the foaming on the surface of the molten glass G is active, that is, the defoaming effect under reduced pressure. Promoted. Therefore, it is understood that the glass produced by the degassing under reduced pressure in the vacuum degassing vessel is reduced in the case of poor foaming.

(Example 2)

Vacuum degassing was carried out in the same manner as in Example 1. However, it is a window 123 from the downstream side of the top of the decompression degassing tank for 12 days, with a flow of 100 L/min. The amount of nitrogen gas is introduced into the upper space 121 inside the vacuum degassing tank 12. The thermocouple (not shown) inserted into the window 123 is known to have a lowered temperature after the introduction of nitrogen. Further, the thermocouple (not shown) inserted into the window 122 on the upstream side of the top of the vacuum degassing tank for 12 days is known to have a temperature rise after the introduction of nitrogen gas. The change in the temperature indicates that the nitrogen gas introduced into the upper space 121 inside the vacuum degassing vessel 12 from the window 123 is formed above the molten glass G flowing inside the vacuum degassing vessel 12 to form a molten glass G. The gas flow in the opposite direction to the flow direction, that is, the gas flow from the downstream side of the vacuum degassing tank 12 toward the upstream side, is discharged to the outside from the window 122 provided on the upstream side of the vacuum degassing tank 12.

Further, in comparison between the second embodiment and the comparative example 1, it is understood that the thickness of the bubble layer observed from the window 122 is reduced by 20 mm or more, and the foaming on the surface of the molten glass G is active, that is, the defoaming effect under reduced pressure. Promoted. Therefore, it is understood that the glass produced by the degassing under reduced pressure in the vacuum degassing vessel is reduced in the case of poor foaming.

In the second embodiment, on the opposite side (window 122) of the introduction side of the nitrogen gas (the window 122), the foaming is also actively performed, and therefore it is known that the pressure degassing of the entire vacuum degassing tank is formed by forming a gas flow. The effect will improve. Further, as is clear from the results of Examples 1 and 2, in the case where a gas flow in the same direction as the flow direction of the molten glass G and a gas flow in the opposite direction to the flow direction of the molten glass G are formed, the pressure is reduced. The defoaming effect will increase.

(Comparative Example 2)

Vacuum degassing was carried out in the same manner as in Comparative Example 1. However, the absolute pressure in the vacuum degassing tank 12 is changed within the range of 307 to 319 mmHg (409 to 425 hPa).

(Example 3)

Vacuum degassing was carried out in the same manner as in Example 1. However, the absolute pressure in the vacuum degassing tank 12 is changed within the range of 295 to 315 mmHg (393 to 420 hPa).

Comparative Example 2 and Example 3 were to collect the molten glass G discharged to the downstream groove 24, and to measure the number density of the bubbles by the naked eye after the gradual cooling. Fig. 3 is a graph showing the correlation between the bubble density measurement results in the downstream grooves 24 of Comparative Example 2 and Example 3 and the absolute pressure in the vacuum degassing tank 12. Here, the bubble density is represented by a relative value in which the bubble density of the absolute pressure of 315 mmHg (420 hPa) of Example 3 is assumed to be 1. As can be understood from Fig. 3, in Comparative Example 2, the absolute pressure is a minimum value of about 312 mmHg (416 hPa), and the bubble density is increased on both sides where the absolute pressure is higher and the side where the absolute pressure is lower. . That is, at 312 mmHg (416 hPa), it is understood that bubbles are increased due to excessive pressure reduction. On the other hand, in Example 3, as in Comparative Example 2, the bubble density was increased on the side where the absolute pressure ratio was about 312 mmHg (416 hPa), but the bubble density was reduced to about 307 mmHg on the lower side of the absolute pressure. (409hPa), even if the absolute pressure is assumed to be as low as about 295 mmHg (393 hPa), no increase in bubble density is observed. From this result, it is understood that Example 3 is more resistant to over-decompression than Comparative Example 2. As a result of the increase in the number of bubbles, a glass having a small bubble density can be obtained.

[Industrial use possibility]

The present invention is suitable for the production of high quality glass products with few bubbles, and is particularly suitable for the production of alkali-free glass used for glass substrates for liquid crystal displays and the like.

In addition, the contents of the specification, the scope of the application, the drawings and the abstract of the Japanese Patent Application No. 2007-020417 filed on Jan. 31, 2007, are hereby incorporated by reference.

10‧‧‧Decompression defoaming device

11‧‧‧Relief casing

12‧‧‧Decompression defoaming tank

121,122‧‧‧Upper space

123,124‧‧‧Window

13‧‧‧ riser

14‧‧‧Down tube

15‧‧‧Insulation

20‧‧‧melting tank

22‧‧‧ upstream groove

24‧‧‧ downstream groove

30‧‧‧ gas introduction means

300‧‧‧ hollow tube

31‧‧‧ gas export means

40‧‧‧ gas (introduced gas)

41‧‧‧ gas flow

42‧‧‧ gas (emission of gas)

G‧‧‧ molten glass

Fig. 1 is a cross-sectional view showing a configuration example of a vacuum degassing apparatus of the present invention.

Fig. 2 is a cross-sectional view showing a configuration example of a preferred embodiment of the vacuum degassing apparatus of the present invention.

Fig. 3 is a graph showing the correlation between the bubble density measurement result in the downstream groove 24 and the absolute pressure in the vacuum degassing tank 12 in Comparative Example 2 and Example 3.

10‧‧‧Decompression defoaming device

11‧‧‧Relief casing

12‧‧‧Decompression defoaming tank

13‧‧‧ riser

14‧‧‧Down tube

15‧‧‧Insulation

20‧‧‧melting tank

22‧‧‧ upstream groove

24‧‧‧ downstream groove

30‧‧‧ hollow tube

31‧‧‧ gas export means

40‧‧‧ gas (introduced gas)

41‧‧‧ gas flow

42‧‧‧ gas (emission of gas)

121‧‧‧Upper space

122‧‧‧Window

123‧‧‧Window

G‧‧‧ molten glass

Claims (9)

A method for producing a glass, which is a method for producing a glass comprising a process of defoaming a molten glass under reduced pressure in a vacuum degassing vessel, characterized in that the molten glass which flows through the vacuum degassing vessel is formed from the above At least one gas stream selected from the group consisting of a gas flow in a flow direction of the molten glass and a gas flow in a direction opposite to a flow direction of the molten glass. A method for producing a glass, which is a method for producing a glass comprising a process of defoaming a molten glass under reduced pressure in a vacuum degassing vessel, characterized in that it is formed above the molten glass flowing through the vacuum degassing vessel The flow direction of the molten glass is a gas flow in the orthogonal direction. The method for producing a glass according to the first or second aspect of the invention, wherein the gas forming the gas stream does not substantially contain a gas component generated by the molten glass. The glass manufacturing method according to claim 3, wherein the gas forming the gas stream is hydrogen (H ₂ ), nitrogen (N ₂ ), oxygen (O ₂ ), air, carbon monoxide (CO), a group consisting of carbon dioxide (CO ₂ ), argon (Ar), helium (He), neon (Ne), krypton (Kr), xenon (Xe), hydrocarbon gas, fluorocarbon gas, and ammonia (NH ₃ ) At least one of the choices. The method for producing a glass according to the first or second aspect of the invention, wherein the gas forming the gas stream is introduced at a position close to a surface of the molten glass. The method for producing a glass according to the third aspect of the invention, wherein the gas forming the gas stream is introduced at a position close to a surface of the molten glass. The glass manufacturing method according to claim 4, wherein the gas forming the gas flow is introduced at a position close to the surface of the molten glass. A vacuum degassing device for molten glass, comprising: a reduced pressure outer casing that is drawn by a reduced pressure; a vacuum degassing tank provided in the decompression outer casing for performing vacuum degassing of molten glass; Provided in the vacuum degassing tank, an introduction means for introducing molten glass before decompression under reduced pressure into the decompression degassing tank; and a vacuum degassing tank connected to the decompression degassing tank for degassing under reduced pressure The vacuum degassing apparatus for molten glass of the deriving means derived from the vacuum degassing tank after the molten glass is further characterized by further comprising: introducing a gas into the upper space inside the decompression degassing tank The gas introduction means and the gas flow forming means for introducing the gas from the upper space. The vacuum degassing apparatus for molten glass according to claim 8, wherein the gas flow forming means is provided at the top of the vacuum degassing tank in which the upper space is formed above the molten glass inside the vacuum degassing tank. Or on the side.