JP6418455B2 - Process and apparatus for clarifying molten glass - Google Patents

Description

Explanation of related applications

  This application claims the benefit of priority under 35 USC 119 of US Provisional Patent Application No. 61 / 756,186, filed January 24, 2013. The present specification depends on the content of the specification of the provisional patent application, and the content of the specification of the provisional patent application is incorporated herein by reference in its entirety.

  The present disclosure relates generally to processes and apparatus for making glass, and more particularly to processes and apparatus for improving glass quality in a molten glass clarification process. This process produces glass that can be used in a variety of products.

  Production of glass by melting the selected raw materials (batch) in a melting furnace is then formed and cooled to produce a viscous molten material (hereinafter, molten glass) that becomes a glass product. However, the melting process also produces undesirable by-products that, if not removed from the molten glass, can pass through the glass making process and appear as visible defects in the finished product. In the case of gaseous by-products, such defects are variously referred to as bran bubbles, blisters or gaseous foreign bodies. In addition, chemical inhomogeneities within the molten glass can cause several other visible defects, commonly referred to as striae, striations or cords. In particular, for optical quality glasses, such as glasses that are intended to be substrates for optical lenses or flat panel displays (eg, liquid crystal displays), defects such as striae, cords, and bran bubbles are for the intended purpose. An unacceptable defect that can greatly affect the suitability of the finished product.

  Therefore, it is necessary to remove such defects or prevent the formation of defects before the glass article reaches a finished form.

The process of melting batch materials to make molten glass produces various gaseous byproducts. These gaseous by-products can be dissolved in the glass itself or can be dispersed as bubbles in the glass. Such gases can include, by way of example and not limitation, CO ₂ and SO ₂ . One method used to remove these melting-related defects is by adding a fining agent, such as an arsenic, antimony, tin, cerium or boron oxide, during the initial melting process. For example, the fining agent can be added to the batch material supplied to the melting furnace. In a later step in the manufacturing process, the molten glass is heated to a predetermined temperature sufficiently higher than the initial melting temperature in order to generate oxygen bubbles in the fining agent by changing the valence state. In other words, the fining agent is reduced and releases excess oxygen. Furthermore, the higher the temperature, the lower the viscosity of the molten glass and the easier it is for oxygen bubbles to float through the molten glass. As the oxygen bubbles move upward through the molten glass, the melting-induced gas diffuses into the oxygen bubbles and is transported to the free surface of the molten glass where it is released to the atmosphere above the free surface.

  Some glass making processes use precious metal delivery systems to deliver molten glass to subsequent forming equipment. This is especially true for high purity glasses intended for optical and other high value applications where high light transparency is required. The problem with the formation of oxygen bubbles is that if some of the glass treatment tanks and clarification tanks made of noble metal or noble metal alloy have been in contact for some time to allow some oxygen bubbles to appear, The inner surface can be corroded. Such corrosion, if left unchecked, can weaken the vessel wall and ultimately cause the vessel to crack. Thus, the molten glass is generally subjected to a refining (or more commonly simply referred to as “clarification”) process in which gaseous foreign objects (bubbles) are removed from the molten glass.

  Furthermore, it is also necessary to homogenize the molten glass in order to remove striations and cords and to prevent the accumulation of stagnant glass caused by non-uniform manufacturing process flow of the molten glass. Generally, the molten glass is stirred or mixed after clarification but before the molten glass is cooled to a temperature at which the viscosity of the molten glass is such that it is difficult to stir or mix the molten glass. However, the effectiveness of such a conventional process is limited by the cooling already experienced by molten glass downstream of the clarification process.

  Another problem is related to the high temperature and corrosivity of the molten glass contained in the melting furnace, in that the melting furnace can be gradually melted into the molten glass when the molten glass is formed in the melting furnace. For example, zirconium oxide (hereinafter zirconia) is one such ceramic material that can be used in the construction of a melting furnace. The zirconia that constitutes the melting furnace can be melted into the molten glass during the formation of the molten glass, can remain in the glass until the end of the process, and can remain as a component of the finished glass product. If the zirconia is evenly dispersed and dissolved in the molten glass at a low concentration, it will not pose a serious problem or affect the finished product. However, if the zirconia is not uniformly mixed throughout the molten glass and is not effectively dissolved, and there is a significant concentration of zirconia in the localized area, the zirconia will crystallize from the solution as the molten glass cools. Resulting in visible defects in the finished product. Thus, crystallization prior to homogenization cannot be tolerated because the mixing performed during homogenization is of little use in removing crystals once formed. According to embodiments of the present disclosure, the molten glass has a lower temperature than the temperature in the glass manufacturing process, where the viscosity of the molten glass has a deleterious effect on mixing efficiency and allows the formation of crystalline components in the glass. It is homogenized early, close to the melting process, before the glass is cooled.

Therefore,
Flowing molten glass from a melting furnace to a clarified metal tank through a first metal conduit disposed between the melting furnace and the clarified metal tank, the clarified metal tank having a first region and a second region;
Flowing molten glass vertically upward through the first region of the clarification tank;
Stirring the molten glass while the molten glass flows vertically upward;
Increasing the temperature of the molten glass while the molten glass flows vertically upward, and changing the direction of the molten glass flow from vertically upward to non-vertical in the second region of the clarification tank;
Including
The molten glass in the first and second regions of the clarification tank is a continuous interface with the atmosphere above the free surface of the glass to allow escape of bubbles in the molten glass into the atmosphere. Having a free glass surface,
A method for clarifying molten glass in a glass manufacturing process is disclosed.

  In some embodiments, the non-vertical direction is a horizontal direction.

  The step of stirring can include a step of actively mixing the molten glass using a rotating member. In some embodiments, the agitating step imparts an upward pumping action on the molten glass.

  The step of raising the temperature of the molten glass includes passing an electric current through the wall of the first region (ie, in the wall of the first region).

  The method can further include flowing molten glass from a clarification tank to a stirring tank disposed downstream of the clarification tank through a second metal conduit disposed between the clarification tank and the stirring tank, The molten glass flowing in the two metal conduits does not have a free glass surface, and the molten glass is agitated in a stirred vessel.

In another embodiment,
A melting furnace formed of refractory material and configured to melt batch material to form molten glass,
A clarified metal bath having a first region having a vertical axis and a second region coupled to the first region having a non-vertical axis;
A first metal conduit extending between the melting furnace and the first region of the clarified metal layer such that molten glass flowing from the melting furnace to the clarification tank passes through the first metal conduit;
An agitation tank located downstream of the clarification tank,
A second metal conduit extending between the clarification vessel and the agitation vessel so that molten glass flowing from the clarification vessel to the agitation vessel passes through the second metal conduit;
A stirring member disposed in the first region and configured to agitate the molten glass while the molten glass flows upwardly through the first region; and the first region attached to the first region Electrodes configured to allow current to flow through the walls of the
A glass processing apparatus comprising: In some embodiments, the axis of the second region can be orthogonal to the axis of the first region.

  The agitation member can include a rotatable stirrer. The rotatable stirrer can include, for example, a stirring element coupled to the shaft and extending outwardly from the shaft, wherein the distance between the floor surface of the first region and the top point of the extension member is Greater than the distance between the floor and the lowest point on the inner surface of the wall of the second region. The stirring member is configured to provide an upward pumping action to the molten glass.

  In some embodiments, the axis of the first conduit is orthogonal to the axis of the first region.

In another embodiment,
A first region having a first axis and a second region having a second axis; the first axis is vertical; the second axis is non-vertical;
A stirring member disposed in the first region;
At least one air passage penetrating the wall of the second region so that the internal space of the second region communicates with the atmosphere outside the second region, and attached to the first region, Electrodes configured to allow current to flow through the wall,
A clarification tank for clarification of molten glass having is disclosed. The agitation member can include a rotatable stirrer. In some embodiments, the agitating member is configured to provide an upward pumping action on the molten glass when the rotatable member is rotated.

  The rotatable stirrer may include a stirring element coupled to the shaft and extending outwardly from the shaft, the distance between the floor surface of the first region and the top point of the stirring element being the floor surface of the first region. Greater than the distance between the lowest points on the inner surface of the wall of the second region.

  During operation, the electrode can be in electrical contact with the power source. The first region and the second region of the clarification tank can comprise platinum, and in some embodiments, the end of the second region intersects the wall of the first region.

  The first axis of the clarification tank can be orthogonal to the second axis.

  Additional features and advantages are set forth in the following detailed description, and to some extent will be readily apparent to those skilled in the art from the description, or in the description and claims of this specification, and in the accompanying drawings. It will be appreciated by practicing the embodiments as described. It is to be understood that both the foregoing general description and the following detailed description are exemplary only, and are intended to provide an overview or framework for understanding the nature and nature of the claims.

  The accompanying drawings are included to provide a further understanding and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiments, and together with the description serve to explain the principles and operations of the various embodiments.

FIG. 1 is a schematic diagram of the main functional parts of an example glass making apparatus incorporating a clarification tank as described herein. FIG. 2 is a cross-sectional view of an example formed body according to an embodiment of the present disclosure. FIG. 3 is a perspective view of a clarification tank according to one embodiment of the present disclosure. FIG. 4 is a schematic diagram of a clarification tank according to one embodiment of the present disclosure. FIG. 5 is a perspective view of a portion of the movable member making up the clarification tank according to an embodiment described herein. FIG. 6 is a perspective view of a portion of another movable member that constitutes a clarification tank according to an embodiment described herein. FIG. 7 is a schematic illustration of a clarification tank having a stationary agitation member in accordance with embodiments described herein.

  Examples are provided to describe embodiments of the present invention in more detail with reference to the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings to refer to the same or like elements. The examples and embodiments given illustrate the concepts of the invention, but should not be construed to limit the invention to the embodiments given herein.

  FIG. 1 is a schematic view of an example glass manufacturing apparatus 10. The glass making apparatus 10 can be used to produce a glass substrate for a flat panel display, such as a liquid crystal display (LCD) or an organic light emitting diode (OLED) display. Glass making apparatus 10 provides fluid flow between melting furnace 12, clarification tank 14, melting furnace 12 and clarification tank 14, through which molten glass passes between melting furnace 12 and clarification tank 14. A conduit that flows, the connecting tube 16, the agitation chamber 18, a conduit that provides fluid flow between the clarification vessel 14 and the agitation chamber 18, through which molten glass flows between the clarification vessel 18 and the agitation chamber 18. A connection tube 20, a collection vessel 22, a conduit that provides fluid flow between the agitation chamber 18 and the collection vessel 22 and through which molten glass flows between the agitation chamber 18 and the collection vessel 22 A tube 24, a downcomer tube 26, an inlet 28 and a former 30 are provided.

  According to some embodiments, the molded body 30 is a wedge-shaped body having a trough 32 on its upper surface and an outer convergent molding surface 34, the converging molded surface being along the length of the bottom of the molded body. Meet at the lower apex of the convergent molding surface along the extending line 36, the route 36. Molten glass 38 is supplied from the collection tank 22 to the trough 32, and the molten glass overflows the trough and individually flows on the converging molding surface 34. A cross-sectional view of the molded body is shown in FIG. The individual molten glass streams merge at route 36 (i.e., coalesce), thus forming a single continuous stream of molten glass, i.e., glass ribbon 40, that cools and becomes a viscous liquid to an elastic solid. A pull roll 42 is disposed below the compact 30 and engages the edge of the glass ribbon 10 to assist in pulling the glass ribbon as it solidifies from the root of the compact. Subsequently, a dividing device (not shown) separates the individual glass plates from the glass ribbon. Although the above example describes a fusion draw mechanism as part of the entire glass making apparatus 10, a slot draw mechanism or similar mechanism could be used as the molding apparatus instead of the fusion draw mechanism.

  The melting furnace 12 and the molded body 30 are generally formed by melting the component raw materials (batch) charged into the melting furnace 12 (arrow 44) into a molten glass 38 and molding the molten glass into a glass product such as a glass ribbon 40. It is composed of a heat and fire resistant material, such as a ceramic material, that can withstand the temperatures required to do so. The temperature required to form the molten glass can vary from below 1300 ° C. to above 1550 ° C., depending on the type of glass to be made and the required raw materials. For example, if the glass is an aluminoborosilicate glass, which can be used for certain display applications, the final melting temperature can be in the range of 1550 ° C to 1570 ° C. Other types of glass may be similar or have different melting temperatures. Examples of suitable refractory materials utilized in melting furnaces include zirconium and / or aluminum oxides.

  During the clarification process, the molten glass is generally heated above the temperature of the molten glass in the melting furnace. For example, for an aluminoborosilicate glass having a melting temperature of about 1550 ° C., suitable clarification temperatures are about 1600 ° C. or more, more commonly in the range of about 1600 ° C. to about 1650 ° C., in some embodiments Is between about 1600 ° C and about 1700 ° C. As the temperature of the molten glass increases, one or more fining agents contained within the molten glass are reduced, with the fining agent releasing oxygen as bubbles. Suitable fining agents include, but are not limited to, arsenic, antimony, tin, cerium and iron oxides. However, some fining agents, such as arsenic oxide and antimony oxide, are extremely toxic. This would result in a less toxic refining agent such as tin oxide being selected.

When oxygen bubbles are generated by the fining agent, the buoyancy of the oxygen bubbles raises the bubbles through the molten glass to the free surface of the glass where it releases the contained gas into the atmosphere above the free surface of the glass. These bubbles serve as accumulation points for gases generated by the melting process (eg, CO ₂ and SO ₂ ), and the melt-induced gas, in the form of another bubble or dissolved gas, accumulates in the oxygen bubbles and reduces the size of the bubbles. Enlarging, increasing buoyancy and facilitating the rise of the glass to the free surface. The bubbles rupture at the free surface of the glass, releasing the encapsulated gas into the atmosphere above the free surface of the glass. The released gas is then discharged from the clarification tank.

  It should be noted that the molten glass flowing out of the melting furnace is not homogeneous. In addition to the presence of the melting-induced gas described above, the molten glass flowing out of the melting furnace has various thermal (eg, viscosity) and chemical inhomogeneities that are present in the glass making apparatus 10. Visible artifacts can be produced in the finished glass product made in. Furthermore, the flow of molten glass at different points in the cross section of the flowing molten glass stream can be different. This difference in flow can cause a stagnant region of molten glass in which the molten glass flows at a much slower rate than the other regions of the molten glass and does not flow at all in the worst case. As a result of the stagnation, such regions of the molten glass may also have different thermal and / or chemical properties than the general molten glass flow. However, such stagnant regions of molten glass can be drawn into the overall molten glass flow unexpectedly, resulting in thermally and / or chemically non-uniform molten glass regions. Furthermore, the refractory material constituting the melting furnace, such as zirconium oxide or aluminum oxide, gradually melts into the molten glass as time passes. If the zirconium is not sufficiently dissolved in the molten glass and is not evenly distributed throughout the molten glass, the zirconium can crystallize in the molten glass and can affect the quality and composition of the finished glass product. In some cases, the finished glass article may not serve a specific purpose that has been scheduled. Therefore, the molten glass should be completely homogenized during the manufacturing process.

  The clarification tank 14, the stirring chamber 18, the collection tank 22, the downcomer pipe 26 and other accompanying molten glass transport conduits and tanks (eg, the connecting pipes 16, 20, 24 and the inlet 28) are formed of a noble metal or a noble metal alloy. can do. Such noble metals are generally selected from platinum group metals including ruthenium, rhodium, palladium, osmium, iridium, platinum and alloys thereof. For example, the noble metal can be pure platinum or platinum alloyed with one or more other noble metals, such as rhodium or iridium. Suitable noble metal alloys can include platinum-rhodium alloys including platinum in the range of about 80% to about 90% by weight and rhodium in the range of about 10% to about 20%. In some embodiments, the clarification vessel 14 and the connecting tubes 16 and 20 can be tubes having a circular cross section. The circular cross-sectional shape for at least a part of the clarification tank 14 facilitates the use of a rotating member disposed inside the clarification tank. However, the connecting tube or part thereof and the clarification tank or part thereof could have other cross-sectional shapes, such as oval or oval. Here, the cross section is taken perpendicular to the axis of the vessel or connecting pipe. Non-circular shapes can be used, for example, when passive mixing is used.

  Referring now to FIGS. 1, 3 and 4, the clarification tank 14 is a first region, a tubule 46 directly connected to the connecting tube 16, and a channel 48, which is a second region. Have The soot tube 46 can extend vertically between the clarification tank inlet 50 and the soot tube outlet 52. The soot outlet 52 also serves as an inlet to the channel 48. The channel 48 extends outwardly away from the soot tube 46 and provides a flow path between the soot tube outlet 52 and the clarification tank outlet 54 through which molten glass flows. In some embodiments, one end of the channel 48 intersects the wall of the soot tube 46 at the soot outlet 52. In some embodiments, the soot tube 46 has a vertical axis 57. In some embodiments, channel 48 has a horizontal axis 59. In some cases, soot tube 46 and channel 48 are substantially orthogonal to each other. That is, the angle between the axis 57 and the axis 59 is 90 ° ± 5 °. In yet another embodiment, the soot tube 46 can be vertical and the channel 48 can be horizontal. Therefore, during the operation of the glass manufacturing apparatus 10, the molten glass 38 formed in the melting furnace 12 flows through the connecting pipe 16 and flows into the clarification tank 14 at the clarification tank inlet 50. The flow of the molten glass is indicated by white arrows 53 in FIG. The molten glass then flows upward through the soot tube 46, from the soot tube outlet 52 through the channel 48 to the outlet 54 of the clarification tank 14 and into the connecting tube 20. In some embodiments, the axis 58 of the connecting tube 16 is parallel to the axis 60 of the connecting tube 20 (see FIG. 4), but this is not necessarily so.

  While the molten glass 38 flows upwardly through the soot tube 46 and then along the channel 48, the molten glass forms a continuous free glass surface 62 within both the soot tube 46 and the channel 48. As used herein, a free glass surface is the surface of the glass flowing through the fining vessel 14 that is exposed to an atmosphere 64 disposed in the space above the flowing molten glass. Is surrounded by the walls of the clarification tank. Free glass surface 62 is the interface between atmosphere 64 and molten glass 38. It should be noted that neither the connecting tube 16 nor the connecting tube 20 has a free glass surface while molten glass during operation of the glass making apparatus 10 flows through the connecting tube 16 and the connecting tube 20.

  Subsequently, the molten glass that enters the clarification tank 14 from the connecting pipe 16 at the clarification tank inlet 50 can be heated in the tub pipe 46 while the molten glass 38 flows upward through the tub pipe 46. . For example, the molten glass in the soot tube 46 heats the soot tube, and thus the molten glass flowing in the soot tube, a resistive heating element disposed on or around the outer surface of the soot tube 46 (Not shown) can be indirectly heated. Alternatively, the soot tube 46 can be directly heated by flowing an electric current directly heating the soot tube by Joule heating through the soot tube itself. For example, two or more electrodes 66 can be attached to the soot tube 46 and / or channel 48 so that current can be applied to the soot tube 46 and / or channel 48 from a power source (not shown). In the embodiment of FIG. 4, four electrodes are attached to the clarification bath 14, including two electrodes attached to the canal 46 and two electrodes attached to the channel 48. In another embodiment, the top electrode 66 attached to the soot tube 46 can be removed, in which case the clarification tank will have three electrodes 66. Whether indirect or direct heating, the heated soot tube heats the molten glass flowing in the soot tube so that the molten glass can achieve a predetermined clarification temperature.

  According to embodiments disclosed herein, the molten glass flowing upward through the slag tube 46 can also be agitated. For example, as shown in FIG. 1, the molten glass can be actively agitated by a movable member 68, such as an agitating member, disposed in a tub tube 46 that mixes and homogenizes the molten glass. .

  The movable member 68 in the cannula 46 is placed in a location where the molten glass can be heated during the glass making process and oxygen bubbles are generated for the clarification process. Agitation problems can be mitigated. That is, during the process steps downstream of the clarification process, the temperature of the molten glass can be significantly lower than the clarification temperature, and thus the molten glass exhibits a higher viscosity. Removal of bubbles from the molten glass becomes difficult as the viscosity increases. Thus, in contrast to such downstream process steps, a wide range of options are available for stirring the molten glass in the cannula 46.

  As shown in FIGS. 1, 3 and 4, the movable member 68 can have a rotatable shaft 70 and one or more agitation elements 72 coupled to the shaft and extending outwardly from the shaft. The shaft 70 extends from the soot tube 46 and is coupled to a rotational motion source, such as a hydraulic motor or an electric motor (not shown). This rotational motion source is coupled directly or indirectly to the shaft 70. For example, the shaft 70 can be directly coupled to the motor shaft in the same straight line, or can be indirectly coupled to the motor shaft via a drive mechanism, such as a gearbox or chain drive. The at least one stirring element can take a variety of structural forms.

  In one embodiment, the agitation element 72 can include one or more vanes extending outwardly from the shaft, wherein the vanes stir or circulate the molten glass as the molten glass rises through the cannula 46. Or it can be made to rotate. The vanes can be flattened or curved or can exhibit more complex shapes necessary to achieve a predetermined mixing efficiency. For example, the blades shown in FIGS. 1, 3 and 4 are flat plates, and the surface of the blade is parallel to the axis of the shaft 70. It should be noted that the axis of the shaft 70 can be parallel to and coincide with the axis of the soot tube 46. The movable member 68 can be designed to have vanes that pass near the vertical wall of the soot tube 46 in order to sweep away bubbles from the surface of the soot tube 46 wall and into the center of the molten glass flow.

  The flow of molten glass from the melting furnace 12 through the connecting pipe 16 to the clarification tank inlet 20, up the tub 46, and then exit the tub outlet 52 and through the channel 48 is at least partially clarified. This is achieved by the pressure exerted by the molten glass in the melting furnace 12, which is at a higher level than the molten glass in the chemical bath 14. However, the movement of the molten glass can also be achieved by the use of a pump for moving the molten glass from the melting furnace 12 through the connecting tube 16, raising the soot tube 46 and through the channel 48. Thus, in addition to mixing and homogenizing the molten glass, using at least one stirrer element 72 to move or “pump” the molten glass by actively promoting the upward movement of the molten glass through the cannula You can also.

  In some embodiments, the shaft and stirrer can be formed as a screw that spirals up the shaft toward the free glass surface with a suitable twist rate by one or more helical stirrers 72. For example, a portion of the movable member 68 with a plurality of helical stirring elements 72 coupled to the shaft 70 is shown in FIG. Alternatively, a single helical stirring element could be used. In another embodiment, shown in FIG. 6, the agitation element 72 is coordinated to impart upward thrust to the molten glass and move the molten glass and oxygen bubbles upward toward the free glass surface. It can be formed as a blade in the form of a propeller or fan. In the embodiment of FIG. 6, the face of the blade is not parallel to the axis of the shaft 70.

  The agitation element 72 of the movable member 68 need not be completely submerged in the flow of molten glass 28 as desired for the mixing step downstream of the clarification vessel 14. In the downstream mixing step, the exposed stirring element extending through the free glass surface causes the free glass surface to be kneaded, so that the gas placed on the free glass surface can be taken into the molten glass. As explained above, since the molten glass cools as it moves downstream from the clarification tank, the higher viscosity of the molten glass downstream of the clarification tank can make removal of such trapped gas pockets difficult. .

Arranging the movable member so that at least a portion of the agitation element is on or on the free glass surface 62 in the clarification tank 14 ensures that the bubbles contained in the molten glass are evenly distributed over the free glass surface. And thus can be beneficial in providing enhanced interaction with the molten glass stream of foam. As shown in FIG. 4, at least a part of the uppermost stirring element 71 extends upward from the free glass surface 62 by a distance d ₁ . The movable member 68 can have a shaft 70 and a rotatable stirrer coupled to the shaft and extending outwardly from the shaft, including a stirring element 72, the rotating member within the tub tube 46 and the first of the clarification tank 14. The distance d ₂ between the floor surface 74 of the region (the soot tube 46) and the top point 76 on the stirring element 72 is on the inner surface of the wall surface 81 of the floor surface 74 of the soot tube 46 and the second region (channel 48). to be larger than the distance d ₃ between the lowermost point 78 of is disposed.

  As shown in FIG. 7, in some other embodiments, stirring of the molten glass in the cannula 46 is performed by flowing the molten glass over or through a stationary member 80 disposed in the cannula 46. The stationary member 80 can passively redirect the flow of the molten glass, thus facilitating the stirring and mixing of the molten glass. For example, a stationary member (e.g., a baffle) can be coupled to the inner surface of the soot tube 46 to extend into the molten glass stream, and at least within the vicinity of the baffle, a layer of molten glass 38 is substantially absent. The molten glass stream, which should become a stream, can be coordinated to be converted to a non-laminar flow. The stationary component can define a passage through the stationary component to obtain more intense turbulence. Such stationary components for diverting molten glass in a cannula can have a variety of forms that may be necessary to obtain adequate agitation without unnecessarily restricting the flow of molten glass. It is natural. In some embodiments, both a movable member and a stationary member can be used in the soot tube 46.

  The movable member 68 or the stationary member 80 can be formed of a noble metal or a noble metal alloy as described above (for example, a platinum group metal or a white metal metal alloy such as pure platinum or a platinum-rhodium alloy).

As in the clarification tank 14, stirring of the molten glass within a short distance from the melting furnace 12, where the molten glass has the highest temperature, and thus the lowest viscosity, or would be for a short time,
1) Eliminate uneven flow of molten glass. Unstirred molten glass tends to flow faster in the center of the flow, thus forming stagnant glass along the periphery of the flow, affecting glass quality and consistency.
2) eliminate chemical inhomogeneities that can cause striae, striations or cords that can cause visible defects in the finished glass product, and 3) during the melting process, such as zirconium oxide or aluminum oxide Thoroughly mix the ceramic material that can be dissolved in the glass into the molten glass, thus preventing crystallization of such material,
You can also.

  Agitation and heating of the molten glass in the soot tube 46 can also help in the formation of oxygen bubbles, and free glass without significant corrosion of the soot tube wall when the soot tube wall is substantially vertical. Movement of oxygen bubbles to the surface 62 can be facilitated. When the bubbles containing oxygen come into contact with the metal inner surface of another structure of the glass making apparatus 10 made of a clarification tank or a noble metal or a noble metal alloy, the metal surface is corroded. If left untreated, such corrosion can weaken the structure and ultimately cause destruction of the structure. This is a particularly reasonable consideration for the clarification tank, as it is most likely that the clarification tank has the greatest accumulation of bubbles dispersed in the molten glass, closest to the melting furnace. . By aligning the soot tube 46 substantially vertically, bubbles rising through the soot tube 46 are not in contact with the surface of the soot tube for an appreciable amount of time, directly to the free glass surface 62. To rise. That is, bubbles contained in the molten glass occupying the soot tube 46 rise through the soot tube and are released through the free glass surface into the atmosphere 64 in the soot tube and do not stay on the noble metal surface of the soot tube. . The same is true while the molten glass travels along the channel 48 because the free glass surface 62 extends over the entire length of the channel 48 and is continuous with the free glass surface in the soot tube 46. Therefore, the molten glass has a free glass surface that extends from the top of the tub tube 46 along the channel 48 to the outlet 54 of the clarification tank 14 throughout the time that the molten glass passes through the clarification tank 14. , Bubbles will pass through the free glass surface 62 into the atmosphere 64 in the clarification layer.

  The atmosphere 64 can be exhausted through the exhaust pipe 84 to the atmosphere outside the clarification tank 14 in order to exclude gas that has exited the molten glass through the free glass surface 62 and entered the atmosphere 64. An exhaust pipe 84 is provided that extends through the wall of the clarification tank (eg, wall 81) and forms a passage through the wall between the atmosphere 64 contained in the clarification layer and the atmosphere outside the clarification tank. be able to. If desired, the exhaust pipe 84 can be coupled to a pollution control system (not shown). In another embodiment, the exhaust tube 84 can be coupled to a vacuum source to actively draw gas from the atmosphere 64.

  The exhaust tube 84 may be provided near the downstream end of the clarification vessel 14, such as, for example, near the clarification vessel outlet 54 (eg, on the channel 48). Additional exhaust pipes can be provided. In some embodiments, the shaft 70 extends upward through a cover 86 disposed at the top of the soot tube 46. The cover 86 can be formed of a heat insulating refractory material such as alumina. Cover 86 defines a passage through which shaft 70 extends, and the passage forms an air gap 88 between shaft 70 and cover 86. The void 88 can be used as an additional exhaust path for the gas in the clarification tank atmosphere 64. In some embodiments, an air passage for adding conditioned gas to the atmosphere 64 can also be provided in the clarification vessel 14. For example, FIG. 4 illustrates that the atmosphere 64 in the clarification tank 14 (eg, the tub tube 46) is coupled to the cover 86 so that one or more conditioning gases can be added to the atmosphere 64. An air supply tube 90 is shown extending in FIG. In some embodiments, the conditioning gas can be an inert gas such as helium, argon or other inert gas and combinations thereof.

  In some embodiments, the length of the channel 48 depends on the time it takes for all or substantially all of the bubbles to escape through the free glass surface 62 while the molten glass flows along the channel 48. It is determined. The rate at which the bubbles rise through the molten glass, the depth of the molten glass 38, and the flow rate or average velocity of the molten glass as the molten glass flows down the channel 48 causes the bubbles to reach the free glass surface 62 and free glass. A factor that can determine how long it takes to exit through the surface 62 and thus helps determine the shortest length of the channel 48.

  The bubble velocity as the bubble rises through the molten glass depends on the density difference between the bubble and the molten glass 38, the minimum radius of the bubble (the smaller the bubble, the more slowly the bubble moves) and the viscosity of the molten glass To do. An equation based on Stokes' law to calculate the velocity of bubbles through molten glass:

Or a similar formula can be used. Where ν _B is the velocity of the bubble as it rises through the molten glass, η is the kinematic viscosity of the molten glass, g is the gravitational constant, a is the radius of the bubble, ρ ′ is the density of the bubble, and ρ is the melt It is the density of the glass.

That is, since the bubble substantially all having a larger radius than the minimum radius defined in advance to determine the shortest length x _C required for channel 48 to get out through the glass free surface, initially, above [nu _B It is determined using an equation or a similar equation. Next, the time t _B for the bubbles to move from the floor of the channel 48 to the free glass surface is determined using the velocity equation t _B = x _H / ν _B , where x _H is the channel 48 This is the distance from the floor to the free glass surface. The shortest length required for channel 48 is then calculated by another form of this equation x _C = v _G t _B. Here, v _G is the average flow rate of the molten glass in the channel 48. This assumes that the molten glass in the channel 48 has a steady state flow rate with no significant pressure change and that the channel shape is substantially uniform.

  As the molten glass exits the clarification tank 14 at the clarification tank outlet 54, the molten glass enters the stirring chamber 18 where it can flow through the connecting tube 20 to allow further homogenization of the molten glass 38 downstream. . The stirring chamber 18 has a stirring tank 92 and a stirrer 94 attached to the stirring tank in a rotatable manner. The stirrer 94 can have a shaft 96 and a plurality of stirring elements 98 (eg, vanes or blades) coupled to the shaft that mix and homogenize the molten glass. As shown in FIG. 1, the molten glass can flow down through the stirring chamber 18. The stirrer 94 can be designed to be a flow neutral stirrer that is arranged such that the stirring element does not provide an appreciable pumping action to the molten glass flowing through the stirring chamber 18 during rotation. The agitation element 98 is also below the second free glass surface 100 such that the stirrer 94 does not disturb the second free glass surface 100 while molten glass flows through the agitation chamber 18. The second free glass surface 100 is the interface between the molten glass 38 and a second atmosphere 102 placed in a stirred tank 92 above the molten glass. Further, since the molten glass flowing through the stirring chamber 18 is at a lower temperature than the molten glass flowing through the clarification tank 14, the viscosity of the molten glass flowing through the stirring chamber 18 is clarified in the clarification tank 14. Higher than the viscosity of the molten glass flowing through. Accordingly, the placement of the agitation chamber 18 along the flow path of the molten glass 38 is determined, at least in part, by the maximum viscosity that can be effectively agitated by the stirrer 94.

  As the molten glass exits the agitation chamber 18, the molten glass flows into a collection vessel 22, from which the molten glass is directed to the shaped body 30 by the downcomer tube 26, where the molten glass is formed into a glass ribbon 40. obtain.

  It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the invention. Since those skilled in the art may envision modifications, combinations, subcombinations and variations of the disclosed embodiments which incorporate the spirit and substance of the present invention, the present invention includes the appended claims and their equivalents. It should be understood that everything is included within the scope of.

DESCRIPTION OF SYMBOLS 10 Glass preparation apparatus 12 Melting furnace 14 Clarification tank 16, 20, 24 Connection pipe 18 Stirring chamber 22 Collection tank 26 Downcomer pipe 28 Inlet 30 Molded body 32 Trough 34 Converging molding surface 36 Route 38 Molten glass 40 Glass ribbon 42 Pull roll 46 Soot pipe 48 Channel 50 Clarification tank inlet 52 Soot pipe outlet 54 Clarification tank outlet 57, 58, 60 Axis 59 Channel axis 62, 100 Free glass surface 64 Atmosphere 66 Electrode 68 Movable member 70 Shaft pipe shaft 72 Stirring element of the soot pipe 74 Floor surface of the soot pipe 76 The highest point of the stirring element 78 The lowest point of the inner surface of the channel wall 80 The stationary member 81 The wall of the channel 84 The exhaust pipe 86 The soot pipe cover 88 The gap 90 The air supply pipe 92 The stirring tank 94 The stirrer 96 Stirrer shaft 98 Stirrer stirring element

Claims (10)

In a method for clarifying molten glass in a glass manufacturing process,
A step of flowing molten glass from a melting furnace to a metal clarification tank having a first region and a second region through a first metal conduit disposed between the clarification tank and the melting furnace. ,
Flowing the molten glass vertically upward through the first region of the clarification tank;
Stirring the molten glass while the molten glass flows vertically upward;
Increasing the temperature of the molten glass while the molten glass flows upward in the vertical direction, and the direction of the flow of the molten glass from the vertical upper direction to the non-vertical direction in the second region of the clarification tank. Changing process,
Including
The molten glass in the first region and the second region of the clarification tank has a continuous free glass surface, the free glass surface being an interface with the atmosphere above the free glass surface. Allowing the bubbles in the molten glass to escape into the atmosphere;
A method characterized by that.   The method of claim 1, wherein the non-vertical method is horizontal.   The method according to claim 1, wherein the agitating step includes a step of actively mixing the molten glass with a rotating member.   The method according to any one of claims 1 to 3, wherein the agitating step imparts an upward pumping action to the molten glass.   The method according to claim 1, wherein the step of increasing the temperature of the molten glass includes a step of passing an electric current through a wall of the first region. The step of flowing the molten glass from the clarification tank to a stirring tank disposed downstream of the clarification tank through a second metal conduit disposed between the clarification tank and the stirring tank. The molten glass flowing in the second metal conduit does not have a free glass surface, and the step of stirring the molten glass in the stirring vessel,
The method according to any one of claims 1 to 5, further comprising: In glass processing equipment,
A melting furnace, formed of a refractory material and configured to melt batch material to form molten glass,
A first region having a vertical axis, and having a non-vertical axis, which are connected to the first region, a metal fining vessel and a second region,
A first metal conduit extending between the melting furnace and the clarification tank so that molten glass flowing from the melting tank to the clarification tank passes through the first metal conduit;
An agitation tank disposed downstream from the clarification tank;
A second metal conduit extending between the clarification tank and the agitation tank so that molten glass flowing from the clarification tank to the agitation tank passes through the second metal conduit;
An agitation member disposed within the first region configured to agitate the molten glass while the molten glass is flowing upwardly through the first region; and the first region An electrode attached to the first region configured to allow current to flow through the walls of the first region;
Equipped with a,
The molten glass in the first region and the second region of the metal clarification tank has a continuous free glass surface, and the free glass surface is an interface with the atmosphere above the free glass surface. The glass processing apparatus is configured to allow bubbles in the molten glass to escape into the atmosphere . The glass processing apparatus according to claim 7, wherein the axis of the second region is orthogonal to the axis of the first region. The agitation member has a rotatable stirrer that includes an extension member coupled to the shaft and extending outwardly from the shaft, wherein the distance between the floor surface of the first region and the uppermost point of the extension member is glass processing apparatus according to claim 7 or 8, wherein the greater than the distance between the lowest point on the inner surface of the floor and walls of the second region of the first region. The stirring member is configured to give an upward pumping action to the molten glass, and at least a part of the extension member is on the free glass surface in the metal clarification tank or on the free glass surface. glass processing apparatus according to claim 9, characterized that you have been configured.

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