JP2009519884A - Overflow downdraw glass forming method and apparatus - Google Patents

Abstract

  The present invention discloses an improved method and apparatus for forming glass sheets. In one embodiment, the present invention introduces a reaction force against stress on the molded structure in such a way that the effect of unavoidable thermal creep on the flow characteristics of the glass of the molded structure is minimized. .

Description

Explanation of related applications

  This application claims the invention disclosed in US Provisional Patent Application No. 60 / 751,419 filed on Dec. 15, 2005 under the title "OVERFLOW DOWNDRAW GLASS FORMING METHOD AND APPARATUS". . The benefit of the priority of US provisional applications under 35 USC 119 (e) is claimed hereby and the above-mentioned application is hereby incorporated herein by reference.

  This application is filed on August 8, 2002 and claims the title "OVERFLOW DOWNDRAW GLASS FORMING", filed on August 8, 2002, claiming the invention disclosed in one of the following provisional applications: A pending US patent application filed under the title “OVERFLOW DOWNDRAW GLAST FORMING METHOD AND APPARATUS” on December 7, 2004, which is a divisional application of US Pat. No. 6,889,526, which is “METHOD AND APPARATUS”. This is a continuation-in-part application of No. 11 / 006,251.

1) Provisional patent application No. 60 / 310,989 filed on August 8, 2001 under the name of the invention “SHEEET GLASS FORMING DEVICE”,
2) Provisional patent application No. 60 / 316,676, filed on August 29, 2001, with the title of the invention “SHEEET GLASS FORMING DEVICE”,
3) Provisional patent application No. 60 / 318,726, filed on September 12, 2001, with the title “SHEET GLASS FORMING APPARATUS”,
4) Provisional patent application No. 60 / 318,808 filed on September 13, 2001 under the name of the invention “SHEEET GLASS FORMING APPARATUS”,
5) Provisional patent application No. 60 / 345,464 filed on January 3, 2002, with the title “SHETET GLASS FORMING APPARATUS”,
6) Provisional patent application No. 60 / 345,465 filed on January 3, 2002 under the title “SHEET GLASS FORMING APPARATUS”.

  The benefit of the priority of US provisional applications under 35 USC 119 (e) is claimed here and the above-mentioned applications and patents are incorporated herein.

  The present invention relates generally to the manufacture of glass plates, and more particularly to glass plates used in the manufacture of LCD display devices that are widely used in computer displays.

  Glass for use in semiconductor-powered displays, especially TFT / LCD display devices widely used in computer displays, has an extremely high surface quality to allow the successful application of semiconductor-type materials Must be a thing. The plate glass made using the apparatus described in Patent Document 1 assigned to Corning, Inc. becomes the highest quality glass at the time of molding and does not require post-treatment. In Corning's patent, glass is produced by a manufacturing method called the “overflow process”. Glass made by other methods is not as fine as a surface finish because it requires polishing and / or polishing. Glass plates must meet stringent specifications for thickness variation and distortion. An excellent finished surface is formed mainly from virgin glass coming from the center of the glass stream. This glass is not in contact with the foreign matter surface after the stirring operation.

  The teachings of Patent Document 1 are still the most advanced as it is still practiced. However, this device has limitations.

  One of the main disadvantages of the "overflow process" equipment is that even though excellent glass can be obtained on most surfaces, the surface of the glass plate closest to the inlet is composed of glass flowing near the surface of the raw material supply pipe, There are times when quality falls.

  Another disadvantage of the “overflow process” apparatus is that it recovers very slowly from transient conditions, even if excellent glass is obtained during stable operating conditions. This is partly due to the quiescent zone of the flow of glass in this tube when the tube that sends the glass from the stirrer to the device (of the overflow process) is manufactured in a conventional manner. During unintended process transients, these stationary zones cause the glass of the previous material composition to flow slowly into the glass main process stream and become defective. These defects will eventually subside if the process is stable. However, there are times when the quality of the glass plate is below standard.

  Yet another disadvantage of the “overflow process” apparatus is that the means for controlling the thickness of the formed plate is limited. At present, the glass is not selectively cooled with respect to the width when the plate is formed. The loss of radiant heat from the reverse slope portion below the forming structure is not controlled. This lack of control can greatly affect the flatness (distortion) of the molded plate.

  The thickness control system described in U.S. Pat. No. 6,057,097 can compensate for small thickness errors, but can only redistribute glass over a distance of approximately 5-10 cm.

  Another disadvantage of the “overflow process” device is that the surface tension and volume force have a great influence on the flow of molten glass flowing down the outer surface of the forming device, and the edge of the plate is formed with a narrower plate than the forming device. May cause thick beads.

  Patent Document 3 attempts to compensate for the effect of surface tension, but actually describes an edge director that is a correction for problems caused by constraining the cross-section of the forming device to a single profile on its outer surface. ing.

  Yet another disadvantage of the “overflow process” device is that when the plate is pulled down from the bottom of the device, the plate thickness tends to vary periodically. This periodic thickness variation is a strong function of uncontrolled airflow that tends to occur as equipment ages during manufacturing activities. As the device ages, air leakage through various openings caused by material cracks and differential expansion increases.

  One of the major disadvantages of the “overflow process” device is that during the manufacturing activity, the forming device is deformed in such a way that the glass sheet does not meet the thickness specification. This deformation is a thermal creep of the forming device caused by gravity. This is the main cause that the manufacturing operation ends early. This deformation occurs over a long period of time. While this is happening, the process is continuously changing so that the process must be adjusted to compensate for the slack in the forming apparatus. This adjustment action leads to the loss of products that sell.

Accordingly, there is a need in the art for devices that solve the problems of the prior art.
U.S. Pat. No. 3,338,696 US Pat. No. 3,682,609 US Pat. No. 3,451,798

  In a preferred embodiment of the present invention, all the glass that forms the useful area of the plate is virgin glass that is not contaminated with a flow near the refractory or refractory metal surface after the stirring operation. Also, in this embodiment, the non-uniformity of the glass forming the plate is greatly reduced by eliminating the region of the quiescent flow in the pipe between the stirring device and the plate glass forming device.

  In another preferred embodiment, the present invention introduces a strict thermal control system for redistributing the molten glass stream at the weir, the most important area of the molding process. This thermal control effectively corrects the deterioration of the plate forming apparatus that is unavoidable in manufacturing activities.

  In another embodiment, the width of the outlet opening of the molding chamber is varied to adjust the radiant heat loss from the bottom of the reverse slope of the molding structure in the longitudinal direction.

  In another preferred embodiment, the direction and magnitude of the surface tension and body force stress is varied to produce a variable outer cross section that reduces the adverse effects of surface tension and body force on the plate width.

  In another preferred embodiment, the glass is preferentially cooled in its width direction to generate a forming stress during solidification that essentially flattens the subbing glass sheet.

  In yet another preferred embodiment, the present invention adjusts the internal pressure in each of the main components of the molding apparatus in such a way that the pressure differential in the leakage path to the molding zone approaches zero. Thus, even if cracks and openings exist during initial operation and become larger during manufacture, the air leakage of the device is minimized.

  In yet another preferred embodiment, the present invention provides a forming structure in a manner that minimizes the effect of thermal creep deformation (strain) due to thermal creep on glass sheet thickness variations. The reaction force against the stress caused by gravity is introduced.

  The flow dynamics in all embodiments of the present invention are sufficient because the outer surface of the glass plate comes from the center of the glass stream flowing into the forming apparatus and is not in contact with the surface of the refractory or refractory metal. It is formed from virgin glass mixed with the above. This gives the highest quality surface possible. Such a defect-free surface is essential for the manufacture of LCD / TFT semiconductor display devices. Also, the flow dynamics of all embodiments of the present invention are such that the flow rate of molten glass to the forming wedge at the bottom of the forming structure is substantially uniform across its width.

  Glass “plate forming equipment”, usually designed for use in the “overflow process” (US Pat. No. 3,338,696) dispenses glass in such a way as to form a plate of uniform thickness. Rely on a molded structure specifically shaped for the purpose. The basic shape of this forming structure is described in detail in US Pat. No. 3,338,696. The glass sheet forming step is generally performed at a high temperature of 1150 ° C to 1275 ° C. At these temperatures, the material used to build the molded structure has a characteristic called thermal creep, which is a deformation of the material due to stress applied at high temperatures. Thus, the molded structure deforms due to the stress caused by its own weight and the stress caused by the weight of the molten glass inside and outside the molded structure and the hydrostatic pressure.

  As used herein, stress is the magnitude of the force in the molded structure and strain is the deformation of the molded structure.

  In U.S. Pat. No. 3,519,411, Courtright addressed concerns about the structural integrity of the molded structure. Refractory materials that produce molded structures have high compressive strength and low tensile strength. In order to prevent crushing of the molded structure, a compressive force was applied to the bottom portion of each end of the molded structure for the purpose of “reducing the undesirable effects of tensile stress on the refractory sheet glass molded member”. Regarding this force, since finite element analysis (FEA) was not a technique used by those skilled in the glass industry at that time, static closed-form stress analysis described in US Pat. No. 3,519,411 was used. It was sought after.

  US Pat. No. 3,437,470 (Overman) also provides a design that negates the effect of the gravity of the forming structure on structural integrity. None of these patents contained any text or information on such thermal creep because the thermal creep of the forming structure is related to the thickness of the glass sheet being formed.

  US Pat. Nos. 6,748,765, 6,889,526, 6,895,782, addressing different problems of thermal creep in the overflow process, Nos. 10 / 826,097, 11 / 011,657, 11 / 060,139 and 11 / 184,212 are hereby incorporated by reference. Has been filed by. These patents and patent applications are incorporated herein by reference. These documents describe treating thermal creep as a linear process. Although these methods and apparatus work as described, significant advantages are obtained when considering the non-linear behavior of thermal creep. The present invention further enhances the claims and techniques of the above-cited patents and patent applications by taking into account the non-linear thermal creep characteristics of the refractory molded structure against temperature and stress.

  In the present invention, an accurate calculation of the reaction force against gravity on the forming structure is introduced in such a way that inevitably generated thermal creep has virtually no effect on the glass flow characteristics of the forming structure. The present invention is designed so that this reaction force is appropriate to reduce the non-linear aspects of the thermal creep of the refractory material and is maintained throughout long-term manufacturing activities. For this reason, it is possible to produce a glass sheet according to the original specification for a still longer period using the same molding structure and process parameters.

  Referring to FIGS. 1, 11A and 11B, a general “overflow process” manufacturing system (1) is shown. Glass (10) from the melting furnace (2) and the forehearth (3), which must have a substantially uniform temperature and chemical composition, is fed to the stirring device (4). The stirrer (4) homogenizes the glass sufficiently. Next, the glass (10) is guided to the bowl (6) through the bowl inflow pipe (5) and flows down to the downcomer pipe (7), and between the downcomer pipe (7) and the forming apparatus inflow pipe (8). To the inlet of the overflow molding structure (9) via the joint (14). During the flow from the stirring device (4) to the forming structure (9), the glass (10), in particular the glass forming the surface of the plate, must remain homogeneous. The usual purpose of the bowl (6) is to change the direction of flow from horizontal to vertical and to provide a means for stopping the flow of the glass (10). Depending on the device configuration, a needle (13) is provided to stop the flow of glass. The normal function of the joint (14) between the downcomer pipe (7) and the soot inflow pipe (8) is to make it possible to remove the means for compensating for the thermal expansion of the processing equipment as well as the sheet glass forming device during inspection. It is.

  The molten glass (10) from the melting furnace and fore-haas, which must have a substantially uniform temperature and chemical composition, is fed into the inlet pipe (129) located at the top of the plate forming structure (9) ( 8) through the molding apparatus. The inlet pipe (8) is preferably formed to control the velocity distribution of the incoming molten glass stream. The glass sheet forming apparatus described in detail in both US Pat. No. 3,338,696 and US Pat. No. 6,748,765 (incorporated herein) is a wedge-shaped forming structure. That is, the molding structure (9). A linear sloping weir (115) substantially parallel to the tapered edge of the wedge (116) forms both sides of the ridge (129). The bottom (117) of the ridge (129) and the side surface (118) of the ridge (129) are formed in such a way that the glass is evenly distributed to the top of the weir (115) on both sides. The glass flows over the top of the weirs (115) on both sides, flows down on both sides of the wedge-shaped forming structure (9), and a molten glass plate (11) that can be used at the tapered edge of the route (116); Become. The molten glass plate (11) is cooled when pulled from the route (116) by the pulling roller (111), and becomes a solid glass plate (12) having a substantially uniform plate thickness. An edge roller (110) may be used in combination to stretch the molten glass plate (11). In the prior art, the forming structure (9) is housed in a rectangular muffle (112), the purpose of which is to control the temperature of the forming structure (9) and the molten glass (10). It is customary in the prior art to keep the temperature in the muffle chamber (113) surrounding the forming structure (9) constant. The muffle (112) is heated by the heating element (138) in the heating chamber (119), and this heating element is accommodated in the insulating structure (133). The cooling of the glass during the transition from the molten state to the solid state must be carefully controlled. This cooling process begins with the lower part of the forming device (9), just above the route (116), and continues as the molten glass sheet passes through the muffle door zone (114). The molten glass solidifies substantially by the time it reaches the tension roller (111). Thus, the molten glass becomes a solid glass plate (12) having a substantially uniform plate thickness.

  One of the main elements of the overflow process plate forming apparatus is the forming structure (9). Molding structures (9) include, among those skilled in the art, other, but not limited to, molding rods, molding wedges, molding members, molding devices, molding blocks, rods, pipes, isopipes, fusion pipes, Also known by many names.

Change of Glass Flow Distribution Referring also to FIGS. 2 to 10, in a preferred embodiment of the present invention, the flow path is changed at the inlet of the sheet glass forming apparatus to improve the surface quality. This also facilitates a more uniform flow of glass through the pipe that guides the glass from the stirrer to the sheet glass forming device.

  U.S. Pat. No. 3,338,696 considers only the flow of glass within the forming structure. U.S. Pat. No. 3,338,696 also claims that the entire surface of the plate is molded from virgin glass without being adversely affected by contact with dissimilar surfaces. This is not unconditionally correct. This is because a part of the glass serving as a plate flows in contact with the front surface of the downcomer at the inlet end of the tub. In the present invention, a diversion device is added to the soot inlet so that all usable plate surfaces are formed of virgin glass. The pipe system between the glass stirrer and the glass plate forming apparatus is changed from the configuration in the connecting portion between the downcomer and the forming apparatus inflow pipe in the conventional bowl. Change the flow through the bowl, eliminating or changing the position of the normal flow zone that would otherwise be formed on the front upper surface of the bowl. Since the downcomer is not immersed in the glass of the forming device inlet tube, the static flow zone between the tubes is eliminated.

  2A to 2C show that the glass (10) flowing into the descending supply pipe (7) in the prior art "overflow process" becomes a shaped glass plate. The glass flow (21) near the back of the downcomer (7) is in the center of the stretched plate. The flow (23) near the front of the downcomer (7) is distributed over the entire surface of the glass. However, most attention is paid to about one third of the inlet end side of the plate. This surface glass (23) is disrupted by the surface of the downcomer and the glass in the stationary zone in the bowl (6) and the glass of the downcomer (7) towards the connection (14) of the inflow tube (8). ) The remaining substantially two-thirds of the surface of the plate is molded from the inner virgin glass (22). The other two parts of the glass stream (24) that are symmetrically spaced at an angle of about 45 degrees from the front face become the unusable edge part (25) of the part near the edge at the inlet end of the plate. . Another portion (26) centered at an angle of about 180 degrees goes to the far end (27) of the unusable edge portion.

  3A and 3B show a glass having an inflow pipe (8), a flow diverter (32) (which is the subject of the present invention) located on the surface of the soot inlet, and a glass plate forming apparatus body (9) An embodiment of a plate forming device (31) is shown. The diverter (32) interrupts the flow of the surface glass and diverts it towards the surface of the edge of the plate. Subsequently, the glass from the center of the flow stream of the downcomer reaches the surface of the forming structure and forms the surface of the usable part of the glass plate (11). Note that 10 to 20 percent on either side of the plate is usually not usable for a variety of reasons.

  4A and 4B show that the surface diverter (42) is located below the surface of the glass (10) and causes the surface flow to be redistributed in a slightly but equally effective manner. 4 shows another embodiment of a glass plate forming apparatus (41) that performs the same function as the embodiment shown in FIG. The glass flow (10) at the edge of the plate flows through the central slot (43) of the flow diverter (42). The glass (flowing through this central slot) is the glass that was near the front of the downcomer. The glass from the center of the downcomer then flows to the surface of the forming structure and forms the surface of the usable part of the plate (11). Other glass flowing near the downcomer surface remains immersed.

  5A to 5C show that the glass (10) flowing into the descending supply pipe (7) according to the present invention described in FIGS. 3 and 4 becomes a formed glass plate. The glass flow (21) to the center of the plate is virtually the same as in the prior art. However, the flow (52) forming the outer surface of the formed glass plate does not flow in the vicinity of the front surface of the downcomer pipe (7). The two parts of the glass stream (24), which are symmetrically spaced from the front face at an angle of about 45 degrees and become the unusable edge part (25) at the inlet end of the plate, are substantially affected. Absent.

  FIG. 6 is an embodiment showing the axis of the bowl (66) inclined at an angle such that the main process stream passes through the front of the bowl. This active flow (60) entrains the surface glass (61) against the force of surface tension that would normally create a stationary zone of glass flow (FIG. 8) located at the nose of the bowl. There is a needle (13) to stop the flow of glass.

  7A-7D show that the glass in the tube (75) connecting the stirrer to the bowl is placed on the side of the bowl (76) at an angle (74) to the center line (73) of the molding device (9). ) Shows an embodiment of the present invention that facilitates the crossing movement of the glass within the bowl (76). This effectively causes the flow pattern (70) in the bowl to move so that the stationary zone (81, FIG. 8), usually located at the nose of the bowl, moves to the side (71) of the bowl. Change. Referring again to FIGS. 2A-2C and 5A-5C, depending on the angle of flow (74) in the bowl relative to the center line (73) of the molding apparatus (9), the glass from the stationary zone (81) It becomes the unusable part (25) of the inlet edge, not the surface (23) of the glass plate, or it is otherwise immersed in the center of the glass plate (21). The glass free surface (72) of the bowl is also shown.

  FIG. 8 shows the prior art with a bowl (6) showing a stationary zone (81) of glass located at the front of the bowl (6). The glass is held in place by a combination of low process stream flow (80) in front of the bowl and surface tension.

9A to 9C show that the bottom end (94) of the downcomer pipe (7) is the glass free surface (90) of the forming apparatus inflow pipe (98). 1 illustrates one embodiment of the present invention located substantially above. The molding device inlet (98) is made to a specific size and shape (92). The vertical distance (93) and the size and shape (92) of the forming device inlet (98) are strictly designed to minimize static or vortex flow zones in the glass flow path (91). ing. For this reason, the molten glass (10) becomes a more homogeneous plate (11). This design is determined by the solution of fluid flow equations (Navier-Stokes equations) and experimental testing.

  10A-10C show a downcomer pipe (7) immersed in the surface (100) of the molten glass in a forming apparatus inlet pipe (8) as is well known in the prior art. There is a stationary zone (101) between the two tubes (7) and (8). In the glass flow path (103), an annular glass vortex (102) is formed between the downcomer pipe (7) and the soot inflow pipe (8). There is little mass exchange between the vortex and the main process stream except when the flow transitions (at which time the glass plate becomes defective).

  There are three main defects in homogeneity that may be formed in the downcomer pipe (7) towards the coupling part (14) of the inlet pipe (8). These defects are code defects, bubble defects, and devitrification defects.

  The code is most often described as a glass streak of different viscosity and / or refractive index in the body glass. This is obvious in antique glass as a vortex or line of strain. Insufficient glass mixing can result in cords. Also, if the glass flow in a region is much slower than the body glass, or if volatilization occurs on the surface, cords may be generated in well mixed glass. The chemical composition of glass in many manufacturing operations varies slightly from day to day. There is a possibility that the glass used in the previous day's production gradually flows out and enters the glass used in the same day's production, causing a slight difference in refractive index or viscosity to generate a code. In the glazing process, the code appears as optical distortion caused by refractive index or thickness variations. Thickness variations can also affect the quality of the semiconductor manufacturing process.

  Bubbles are gaseous inclusions or bubbles contained in the glass body. When the bubbles grow, they are called blisters. Foam is very common in molten glass and is kept to the minimum necessary for a particular product by a process called fining or refining. This process is usually chemical and mechanical and is carried out in a fining tank or a fining tank. Electrolysis and fluid flow phenomena can cause bubbles to form in the glass after the clarification step. In the plate glass process, the bubbles become longer and appear as visible defects.

  Devitrification is the crystallization of glass. Glass is amorphous or a completely random mixture of molecules. Molten glass remains amorphous unless its temperature falls below the liquidus temperature. In the case of glass that should be transparent, if the molten glass is cooled in a short time from a temperature higher than the liquidus to a solid below the liquidus, the amorphous state is maintained and the transparency is maintained. It is. When the molten glass is left at a temperature close to the liquidus temperature but less than the liquidus temperature for a certain period of time, crystals that normally have a slightly different chemical composition from the parent glass are slowly formed. The rate at which this devitrification occurs is a function of the glass composition and the difference between the glass temperature and the liquidus temperature. In the glazing process, devitrification appears as an optical defect in the LCD screen.

  46-48 show the sources of homogeneity defects that can occur in the downcomer (7) towards the coupling portion (14) of the inflow pipe (8) as well as the occurrence of these defects depending on the location of the downcomer. It shows in more detail how it affects.

  46A and 46B show the vertical position of the bottom (94) of the downcomer (7) in the same vertical position as the glass free surface (460). The length of the small arrow (461) indicating the streamline of the flow approximates the relative velocity of the glass flow at different locations of the downcomer pipe (7) and inflow pipe (8). At the bottom of the downcomer (7) exposed to factory air at the free surface (460) is a glass flow vortex (462). The length of the vortex arrow (462) is not the same scale as the length of the arrow (461) indicating the streamline of the flow. The glass in the vortex flow (462) portion circulates for a long time, which causes some of the glass chemicals to volatilize, changing the chemical properties and properties of the glass. The magnitude of the vortex flow (462) becomes even greater when the bottom (94) of the downcomer (7) falls below the glass free surface (460).

  According to physical theory, if the downcomer pipe (7) is circular and is completely in the middle of the circular inflow pipe (8), the vortex between the downcomer pipe (7) and the inflow pipe (8) The glass stream (462) is stationary and does not flow out into the glass stream (461) stream. In actual manufacturing sites, a portion of the glass in the vortex (462) will flow out periodically or continuously into the main glass stream (461). Because the glass flowing into the main glass stream is volatile and often has a different chemical composition, code defects may occur. Further, devitrification defects may be formed when the temperature of the glass of the vortex is below the liquidus temperature for a certain period of time.

  FIGS. 49A to 49D show that the temperature of the glass of the vortex (462) is higher than the liquidus temperature by applying heat to the glass at the joint (14) of the downcomer pipe (7) and the inflow pipe (8). An example of raising to This embodiment is useful when glass devitrification at the joint (14) between the downcomer pipe (7) and the inlet pipe (8) is a concern or problem. If it is preferred or desirable that the bottom end (94) of the downcomer (7) is below or below the glass free surface (460), and if devitrification or cords are a problem of homogeneity defects, this is Of particular importance. The applied heat solves the problem of devitrification. This can be done by placing heaters at the top of the inlet pipe (491) and / or the bottom of the downcomer pipe (492).

  In another embodiment, the heater is placed on the seal block (493). There are preferably two symmetrical sealing blocks (493), one of which is shown individually in FIG. 49D. Seal block (493) is manually placed on insulating structure (133) for the purpose of partially sealing free surface (460) from factory air. The key shape of the seal block is the semi-circular inner radius (494), which is part of the outside of the downcomer (7) to partially seal the glass free surface (460) and factory air. Must be in close contact with the diameter (496). The illustrated seal block (493) is semicircular on the outer edge side, but the outer edge shape (495) is rectangular or any other that effectively seals the free surface (460) from air at the top of the insulating structure (133). It may be a complicated shape. Depending on the seal block configuration, more than two seal blocks (493) may be used to properly seal between the free surface (460) and factory air and to conform to the irregular shape of the downcomer (7). May be included.

  US Pat. No. 6,895,782, incorporated herein, describes the flow of glass in a vortex (462) between a downcomer (7) and an inflow tube (8). This patent describes how to shape the bottom of the downcomer (7), how to shape the inflow tube (8), and to control the time the glass is in the vortex (462) Describes how to inter-regulate and what part of the glass stream it flows out of.

  47A and 47B are related to FIG. 9C. The length of the small arrow indicates that the downcomer (7) has a bottom (94) of the downcomer (7) that is substantially above the free glass surface (90) to virtually eliminate vortex flow conditions. And approximates the relative velocity of the glass flow at different locations of the inlet pipe (8). Arrows (471) indicate flow streamlines. The illustrated distance (93) is 0.25 times the inner diameter (476) of the inlet pipe (7). This distance (93) is approximately in the middle of the operating range which varies from 0.05 to 0.65 times the inner diameter (476) of the inflow pipe (7). The optimum distance (93) is a function of the relative diameter of the downcomer pipe (7) and the inlet pipe (8) as well as the viscosity of the glass (10). It is most desirable to position the downcomer pipe (7) in this range with respect to the inflow pipe (8) in the sense that the rate of generation of cord, foam and devitrification defects is reduced.

  The length of the small arrows (481) and (487) in FIGS. 48A and 48B is such that the bottom (94) of the downcomer (7) is on the inner diameter (476) of the downcomer (7) over the glass free surface (480). Approximate the relative velocity of the glass flow in and between the downcomer pipe (7) and inflow pipe (8), with a distance (483) of 1.00 times It is. The glass stream (484) exiting the downcomer (7) narrows as the glass accelerates towards the free surface (480). The streamline arrow (487) in this region (484) is longer than the streamline arrow (481) below the free surface (480), indicating a relative velocity difference. Where the stream enters the free surface (485), a vortex flow (482) similar to that of the free surface (460) as shown in FIG. 46B or the downcomer pipe (7) is generated. The lengths of these arrows (482) are not the same scale as the lengths of arrows (481) and (487) in the streamlines of the flow. At the entry point (485) of the stream (484) towards the free surface (480), bubbles are taken into the flow path where the descending stream (484) and vortex (482) come together. These bubbles are non-uniform bubbles. As the distance (483) becomes longer, the bubble entrapment rate becomes higher.

  50A and 50B show an inflow tube (508) near the free surface (90) to further minimize the generation of static vortices at the junction (14) of the downcomer tube (7) and the inflow tube (508). ) Shows an embodiment of the present invention in which the shape is changed. The inflow pipe (508) extends outward by an angle (505) at the intersection (509) of the free surface (90) and the inflow pipe (508). The divergence angle (505) creates a conical shape in part of the inflow pipe (508). A stationary vortex ((462) in FIG. 46B and (482) in FIG. 48B) is formed in the arrow (502) representing the flow near the intersection (509) between the free surface (90) and the inflow pipe (508). There is a radial component that reduces the tendency. When the angle (505) is increased from 10 to 50 degrees, the tendency to form a static vortex is reduced. Adding this conical portion into the inflow tube (508) increases the range of distance (93) over which the vortices ((462) in FIG. 46B and (482) in FIG. 48B) are minimized.

  In summary, the situation of FIG. 47 is most desirable with little or no vortices (462) and (482) in the downcomer pipe (7) towards the coupling portion (14) of the inflow pipe (8). The state of FIG. 46 where the downcomer is at or below the free surface is acceptable by installing a heater and / or with certain design and operation constraints, the state of FIG. Will be avoided in all situations.

Reduction of Degradation of Sheet Glass Forming Apparatus Referring now to FIGS. 11-16, another embodiment of the present invention is that the degradation of the manufacturing apparatus and the deformation of the forming structure due to thermal creep is caused by the flow distribution of the glass. The shunting of the glass on the forming apparatus is controlled in such a way as to be compensated by thermal control.

  U.S. Pat. No. 3,338,696 relies on a specially shaped forming structure for dispensing glass in such a way that a plate of uniform thickness is formed. The basic shape of this molded structure is described in detail in US Pat. No. 3,338,696. The glass sheet forming step is generally performed at a temperature as high as 1000 ° C. to 1350 ° C. At these temperatures, the material used to construct the molded structure has a characteristic called thermal creep, which is a deformation of the material caused by the applied stress. Therefore, the forming structure is deformed by the influence of the stress caused by its own weight and the stress caused by the hydrostatic pressure of the glass flowing in the cage.

  The materials used to build other parts of the molding equipment also degrade in an unpredictable way (distortion, cracks, changes in thermal properties, etc.), which adversely affects the thickness distribution. The thickness control system of US Pat. No. 3,682,609 can compensate for small thickness errors, but with this system, the glass can only be redistributed at a distance of approximately 5-10 cm. To distribute the thickness significantly across the width of the glass plate, the flow of molten glass that overflows from the weir must be controlled.

  This embodiment of the present invention solves the above problem by introducing a strict thermal control system that redistributes the flow of molten glass at the weir, which is the most important area in the molding process. This thermal control effectively corrects the deterioration of the plate forming apparatus that is unavoidable in manufacturing activities.

  FIG. 12A shows a side view of the forming structure (9). The arrows indicate the flow of molten glass (10) flowing through the forming structure (9) to the side weir (115). FIG. 12B shows a section cut at the center of the forming structure (9) showing the different zones for controlling the molten glass (10) as it flows through the forming apparatus. Zone (121) is the flow in the ridge (129) from the inlet end to the far end of the forming structure, zone (122) is the flow overflowing from the weir, and zone (123) flows down the forming structure. Zone (124) is molten glass (11) drawn from route (116) and cooled to become a solid plate (12). The effect on the thickness of the solid glass plate (12) caused by heating or cooling as the molten glass (10) passes through each zone is different. When the molten glass (10) flows from the inlet end to the far end of the forming structure (9) in the zone (121), energy is added to the molten glass (increasing temperature) or energy is removed from the molten glass. Or a convex thickness profile is produced. The period of change in thickness profile that occurs in zone (121) is approximately the same as the length of the forming structure.

  Changing the energy flux for the molten glass when the molten glass (10) overflows the weir (115) in the zone (122) greatly affects the thickness distribution of the resulting solid glass plate. When the glass is locally cooled in the zone (122), a dam is effectively generated, which greatly affects the glass flow. This is a very sensitive zone and any control strategy other than isothermal must be carefully designed. Zone (123) is important in returning the glass to a substantially linear and uniform temperature distribution in the longitudinal direction so that the subtraction process at route (116) is consistent. Differential cooling in zone (124) is the purpose of US Pat. No. 3,682,609 and is effective in changing the thickness distribution slightly. Cooling at a particular location in the longitudinal direction affects the thickness in one direction at that location, and adversely affects the glass on both sides of the location. This effect is distributed over distances in the centimeter range.

  11A and 11B show a prior art muffle (112), the top surface of which is horizontal, whereas the weir (115) of the forming structure (9) and the trough (129) of the forming structure (9). ) Flowing through the glass (10) is inclined downward from the inflow pipe (8) to the far end of the forming structure (9). Heat transfer at these temperatures between the muffle (115) and the glass (10) is primarily due to radiation. Thus, due to the characteristics of radiation heat transfer, the distance between the muffle (115) and the glass (10) affects the distribution of energy transferred. The heating elements in the chamber (119) are nominally equidistant (136) from the muffle (112). Thus, each element (138) has substantially the same effect on energy transfer from the element (138) to the muffle (112).

  The distance (137) between the muffle (112) and the glass (10) at the inflow end is substantially shorter than the distance (139) between the muffle (112) at the far end and the glass (10). For this reason, the heat transfer at the inflow end is more concentrated than the heat transfer at the far end. As a result, the change in energy of the heating element (138) at the inflow end has a targeted effect on the temperature of the glass (10) rather than the change in energy of the heating element (138) at the far end. . For changing the temperature using a heating element (138) in the chamber (119) and consequently changing the local flow rate of the glass (10) flowing through the forming structure (9), see US Pat. Documented and claimed in 748,765.

  FIGS. 13A and 13B show that the top of the muffle (132) is shaped close to the outer surface of the molten glass (10) flowing in the ridge (129) and the surface of the forming structure (9). One embodiment is shown. The muffle (132) is heated by the heating element (138) in the heating chamber (131) housed in the insulating structure (133). The distance (137) between the muffle (132) and the glass (10) at the inflow end is substantially equal to the distance (139) between the muffle (132) and the far end glass (10), so that the inflow end The heat transfer at is substantially the same as the heat transfer at the far end.

  By designing the muffle (132) to fit the outer shape of the molten glass (10) flowing through the ridge (129) in the forming structure (9), energy is sent to the target area of the molten glass (10). As a result, the temperature distribution can be further controlled. The heating element (138) in the heating chamber (131) has a suitable force to create a suitable temperature state by balancing the energy flux to the forming structure (9).

  14A and 14B show an embodiment of the invention in which molten glass (10) is locally cooled as it overflows from weir (115) in zone (122). Here, the muffle (132) configuration of FIGS. 13A and 13B is used. An air cooling tube (142) functionally similar to the air cooling tube (141) described in US Pat. No. 3,682,609 is directly above the molten glass (10) overflowing the weir (115). The muffle (143) located at the heating chamber side. By locally cooling the glass at this location, a local dam is effectively created, which greatly affects the thickness distribution of the solid glass plate.

  15A and 15B show a multi-chamber muffle (156) with separate heating chambers (151-155) for controlling the temperature of the molten glass (10) as it passes through the various individual zones of the molding process. ) Shows an embodiment of the present invention designed. These zones (121-124) are described in FIGS. 12A and 12B. The multi-chamber muffle (156) has five heating chambers (151 to 155). The heating chamber (153) located above the top of the forming structure (9) affects the glass flow (zone (121)) from the inlet end to the far end of the forming structure (9). The heating chambers (152) and (154) above the top of the weir (115) affect the flow from the weir (115) (zone (122)) and the heating chambers (151) on both sides of the forming structure (9). ) And (155) are used to balance the temperature in the longitudinal direction (zone (123)). Each of the heating chambers (151-155) has a heating element with appropriate force to create a suitable temperature state by balancing the energy flux to the forming structure (9).

  FIGS. 16A and 16B show an embodiment of the present invention in which localized cooling is applied to the molten glass (10) as it overflows the weir (115). This is the zone (122) shown in FIG. 12B. Here, the multi-chamber muffle (156) configuration of FIGS. 15A and 15B is utilized. A specially designed radiant cooler (161) installed in the heating chambers (152) and (154) has a function of selectively cooling the heating chamber side of the muffle surface (162) facing the weir (115). . The radiant cooler has a plurality of adjusters (164) so that the temperature of the bottom surface can be changed in the longitudinal direction. The heat transfer distribution between the radiant cooler (161) and the muffle surface (162) is a function of the distance (163). The sensitivity may be adjusted by reducing the cooling effect by changing the distance (163) between the cooling device (161) and the muffle surface (162). Although not shown, the cooling device (161) can be replaced during operation. The radiant cooler (161) can be inserted from the side instead of from above by appropriately changing the design of the heating chambers (152), (153), and (154).

  In another embodiment, the air cooling tube (142) of FIGS. 14A and 14B can be used in conjunction with the muffle (156) design of FIGS. 15A and 15B, and the radiant cooler (161) of FIGS. 16A and 16B is illustrated. It can be used in combination with the muffle (132) configuration of 13A and 13B.

Reduction of Glass Plate Thickness Variation Referring to FIGS. 17-20, another embodiment of the present invention minimizes the effect of deformation due to thermal creep on glass plate thickness variation. The molding apparatus is supported and compressed. In this embodiment, reaction forces against these stresses on the forming structure are introduced in such a way that inevitably generated thermal creep has a minimal effect on the glass flow characteristics of the forming structure. The present invention is designed so that this reaction force is maintained through long-term manufacturing activities. Therefore, a plate glass can be manufactured for a long time with the same molding structure.

  The refractory material that produces the molded structure and its support structure has high compressive strength and low tensile strength. Like most structural materials, these materials also change shape when stressed at high temperatures. This embodiment was developed because of material characteristics and how these characteristics affect the manufacturing process.

  There are two basic concepts in this embodiment of the invention. First, applying forces and / or moments to the edges of the forming structure reduces the effect of stress caused by gravity and minimizes the effect on molten glass flow caused by thermal creep. Second, the present invention utilizes a compression member that is shaped so that thermal creep that also occurs in the compression member does not substantially alter the force and / or moment.

  17A and 17B show the typical effect of thermal creep on the shape of the molded structure. FIG. 17A shows that the top of the weir (115) and route (116) is curved (171) and the molding structure (9) is slack in the middle so that the curved (171) state of the bottom (117) changes. It shows that it is out. Due to this curvature (171), the molten glass (10) does not overflow from the weir (115) and flow with a constant thickness (172). This curvature (171) allows more glass to flow from the middle of the weir, resulting in a non-uniform distribution of plate thickness. FIG. 17B shows how the hydrostatic pressure (174) from the molten glass (10) in the forming structure (9) releases the weir (115) at the top. This allows more glass to flow to the middle of the forming structure (9), further increasing the middle thickness.

  18A-18D show a sheet glass forming apparatus (180) as known in the prior art. The forming structure (9) is supported by an inlet end supporting the block (181) and a distal end supporting the block (182). The forming structure (9) is equivalent to a beam, and receives bending stress from its own weight, the weight of the glass inside and outside the forming structure, and the pulling force. Since the tensile strength of the molded structure material is low, a compression force (183) is applied to the lower half of the molded structure (9), and the material of the root (116) portion of the molded structure (9) is compressed. Generally, the inlet end support block (181) is constrained in the longitudinal (horizontal) direction (175), so the compressive force (183) is applied to the far end support block (182). The prior art only considers preventing tension at the root (116) of the forming structure (9) and then only considers the starting stress. The effect of thermal creep of the molded structure (9) and its support blocks (181) and (182) on stress is hardly considered.

  19A-19D show one embodiment of a sheet glass forming apparatus (190) having formed end support blocks (191) and (192). The inlet end molded support block (191) is constrained in the longitudinal direction (175). A compressive force (193) is applied to the far end molded support block (192). The shape of the support block is designed in such a way that a force distribution is created in the molded structure (9) that substantially weakens the influence of the weight of the molded structure (9) and the molten glass (10). The applied force (193) is such that all the material of the forming structure (9) is subjected to a compressive stress substantially equal to the longitudinal direction (175). This stress causes thermal creep mainly in the longitudinal direction (175) with little sag as shown in FIG. 17A. Due to the equal compressive stress in the longitudinal direction (175), the forming structure (9) is shortened. Thermal creep also occurs in the molded support block. The cross section of the molded support block is substantially the same in the entire length direction, and the cross section is equally subjected to compressive stress. Thus, when the molded support block is deformed by thermal creep, the block continues to apply substantially the same force distribution to the molded structure (9).

  20A-20D show one embodiment of a sheet glass forming apparatus (200) having four shaped end support blocks (201), (202), (204), (205). There are three molded support blocks (201), (204), (205) at the inlet end, all receiving longitudinal compression forces (206), (207), (208). A compression force (203) is applied to the far end molded support block (202). The shapes and loads of the support blocks (202) and (203) are designed on the same basis as the support blocks (191) and (192) of FIGS. 19A to 19D. The upper two shaped support blocks (204) and (205) are connected to the inlet end of the weir and face inward in such a way as to apply more force on the weir to reduce the influence of hydrostatic pressure that tends to spread the weir. Is at an angle.

  In a preferred embodiment, there is a short (10-25% of length) transition zone (not shown) at the end of the forming structure of the forming support block. In these transition zones, the cross section of the molding support block changes from a cross section of the molding support block to a shape in which a design load is appropriately applied to the molding structure.

Compression Load of Forming Structure FIGS. 42A-42D show a sheet glass forming apparatus (420) representing the prior art. This design is primarily that described by Courtright in US Pat. No. 3,519,411. The forming structure (9) is supported by the inlet end support / compression block (421) and the far end support / compression block (422). The inlet end support / compression block (421) rides on the inlet end structure (423) and is elongated (horizontal) by the adjusting screw (424) and the sealing force (429) of the forming structure (9) inlet. ) Direction (175). The far end support / compression block (422) rides on the far end structure (425) and is supported on the surface (427) by the support / compression block (422) at the far end of the forming structure at the far end compression force (426). Is applied. The force (426) is generated by a far end force application device (428) acting between the support and compression block (422) and the far end structure (425). In one embodiment, the force applicator (428) is a force motor. The force applicator used in the prior art is an air cylinder that produces a substantially constant force. The prior art only considers preventing undesired tension at the root (116) of the forming structure (9).

  A force motor, as defined herein, is a device that generates a substantially constant force in a linear direction and maintains that force for the linear stroke required for the application. The permissible range of force level variation is preferably ± 5 percent or less of the full stroke range. The energy required to maintain this force can be supplied by gravity, air, hydraulic or mechanical means. Some examples of force motors include adjustable spring assemblies, mechanical regulators that are monitored and adjusted regularly or regularly, pneumatic cylinders, pneumatic motors, hydraulic cylinders, hydraulic motors, solenoids, electric motors or weights There is a system using a lever, but it is not limited to this.

  43A-43D, there is a substantial improvement over the prior art described in US Pat. Nos. 6,889,526 and 6,990,834, incorporated herein by reference. Utilizing multiple force applicators, the compression forces (426) and (436) at the root (116) of the forming structure (9) can be kept constant at the desired level throughout the manufacturing activity.

  43A-43D show a sheet glass forming apparatus (430) in which the weight of the forming structure is supported at the inlet end by the surface (431) of the inlet end structure (433). Furthermore, this is constrained in the horizontal direction by a small sealing compression force (429) at the surface (439). The weight of the forming structure is supported at the far end by the surface (432) of the far end structure (435). This surface (432) is designed so that the friction in the horizontal direction is very low, resulting in negligible forces in the horizontal direction. An inlet end compression force (436) is applied to the bottom portion of the forming structure by a compression block (437) designed to reduce friction in the direction of the applied force. This inlet end compression force (436) is generated by the inlet end force application device (438). The compression block (434) also applies a far end compression force (426) to the bottom portion of the forming structure. This far end compression force (426) is generated by a far end force applicator (428). The far end compression force (426) must be slightly greater than the inlet end compression force (436) to compensate for the inlet pipe sealing compression force (429). Molded structure bottom compression forces (426) and (436) are applied with low friction and can be maintained at any level programmed and the same throughout the manufacturing activity. The force application devices (428) and (438) are preferably force motors.

  Another substantial improvement over the prior art is shown in FIGS. 44A-44D. Shown is a sheet glass forming apparatus (440) in which the weight of the forming structure is supported at the inlet end by an inlet end support / compression block (421). The inlet end structure (445) also horizontally restrains the forming structure at the surface (449) by a small sealing compression force (429). The weight of the forming structure is supported at the far end by a far end support / compression block (422). An inlet end compression force (436) is applied to the bottom portion of the forming structure by the support / compression block (421). The inlet end compression force (436) is generated by the inlet end force applying device (448). Further, the far end compression force (426) is applied to the bottom portion of the molding structure by the support / compression block (422). This far end compression force (426) is generated by a far end force applicator (428). The far end compression force (426) must be slightly greater than the inlet end compression force (436) to compensate for the inlet pipe sealing compression force (429). Molded structure bottom compression forces (426) and (436) are maintained at any level that is the same and / or programmed throughout the manufacturing activity. The force application devices (428) and (438) are preferably force motors.

  The force application device applies a force in the longitudinal direction (175) opposite each support / compression block in such a way that the bottom of the forming structure is compressed substantially larger than the top of the forming structure. In a preferred embodiment, the compressive stress at the bottom of the molded structure is 1.25 to 4 times the compressive stress at the top of the molded structure. In another preferred embodiment, the compressive stress at the bottom of the molded structure is 1.75 to 2.5 times the compressive stress at the top of the molded structure. The bottom of the molded structure, which is more resistant to thermal creep than the top of the molded structure, is deformed in the longitudinal direction by the same amount as the top of the molded structure due to thermal creep. As a result, the effect of deformation of the forming structure due to thermal creep on the variation in glass sheet thickness is minimal.

  In another embodiment that can be used in prior art devices, the inlet end adjustment screw (424) is periodically adjusted to cause the forming structure to deform longitudinally by thermal creep during manufacturing activities. Compensates for changes in sealing force (429). The torque on the adjustment screw (424) can also be monitored. However, due to friction, the accuracy of torque as an index of the sealing force (429) actually applied to the molded structure (9) is reduced. This embodiment of the present invention concerns the operator by adjusting the adjustment screw (424) in a direction that reduces the integrity of the glass seal between the inlet tube (8) and the forming structure (9). Therefore, it is counter-intuitive.

Effect of surface tension on the plate In another embodiment of the invention, the width of the forming wedge and the angle of the reverse slope can be changed to change the effect of surface tension and body force on the narrowing of the plate. . Alternatively, the width and the angle of the reverse slope may be increased to make the structure firm and to increase resistance to thermal creep.

  21A-21G show the prior art shape of the molded structure. The cross-section of the wedge-shaped portion, ie, FIGS. 21C-21G, is uniform throughout the usable length of the molded structure. The width (211) of the forming structure and the angle (210) of the reverse slope are the same in each cross section. When the molten glass (10) flows down the vertical part (211) of the forming wedge (9), the influence of surface tension and body force on the plate width (212) is minimal, but the molten glass (10) As it flows down the reverse slope portion (210) of the forming wedge in the vertical direction, surface tension and body force act to narrow the plate (213).

  22A-22G show the same width (211) throughout the length of the molded structure, whereas the reverse slope angle (210) is the same at the center of the molded structure (FIGS. 21D-21F) The angle (220) of the reverse slope at the end is small. This reduced reverse slope (220) has an equilibrium effect on surface tension and body force stress, reducing the narrowing of the plate (223).

  23A to 23G, the width (211) of the forming structure and the angle (210) of the reverse slope are the same at the center of the forming structure (FIGS. 21D to 21F and FIGS. 22D to 22F). It shows that the width (231) of the molding structure at the end and the angle (230) of the reverse slope are reduced. Since the narrowed width (231) and the reverse slope (230) have an equilibrium effect on surface tension and volume force stress than in FIGS. 22A to 22G, the narrowing (233) of the plate is further reduced. .

  FIGS. 24A-24G show the width of the forming structure (211) except that the angle of the reverse slope (240) in the center of the forming structure, ie, FIG. 24E, is substantially larger than the other reverse slopes (210) and (230). ) And (231) and the reverse slope angles (210) and (230) show another embodiment of the invention in which the embodiment of FIGS. 23A-23G is the same. Such a large angle increases the section modulus of the structure, making the structure more rigid and less likely to cause thermal creep. By maintaining the end configuration the same as that in FIGS. 23A to 23G, substantially the same effect as in FIGS. 23A to 23G can be obtained with respect to the surface tension and the volume force stress. Has little effect.

U.S. Pat. No. 3,338,696 only considers the flow of glass in the forming structure, and because of the uniform thickness of the glass flow to the critical point of solidification, It is assumed that the glass drawn from the bottom will have a uniform thickness and flatness. In practice, the glass width direction must be preferentially cooled in order to generate the forming stress that forms the flat plate during solidification. The present invention changes the molding stress and cooling distribution so that the molded plate is essentially flat.

  FIGS. 25A-25D illustrate an embodiment of the present invention in which the shape of the root (116) of the forming wedge (259) is a continuously curved upward convex (250) in the form of a parabola rather than a straight line. . Thereby, the glass drawn from the center of the forming wedge (251) is cooled in a shorter time than the glass drawn from each edge (252) of the forming wedge. As a result, stress is applied to the glass (251) partially solidified at the center of the plate, and the plate becomes flat with little distortion.

  The vertical dimension of the parabola (257) varies between 1% and 10% of the horizontal length (258) of the glass covering the forming structure (259), but the preferred range is 3% to 5%. The angle (254) of the reverse slope of the forming wedge at the inflow end and the far end of the forming structure (259) is the same as the angle (255) of the reverse slope at the center of the forming structure (259).

  26A-26D show that the shape of the root (116) of the forming wedge (269) is a continuously curved upward convex (250) parabola as shown in FIGS. 25A-25D, but the forming structure (269 ) Illustrates another embodiment of the present invention in which the forming wedge reverse slope angle (264) at the inflow end and the far end is substantially smaller than the reverse slope angle at the center of the forming structure (269). . FIG. 26A shows a split line (263) that defines a breakpoint where the top edge start of the reverse slope is horizontal, and FIG. 25A shows a split line that defines a breakpoint where the top edge start of the reverse slope curves parabolically. (253) is shown.

  The equation representing the viscous force in the glass flow is as follows.

F = μ × dv / dx = μ × dv / dz × dz / dx (1)
Where
F = viscous force μ = absolute viscosity v = velocity
dF = μ × d (dv / dx) + (dv / dx) dμ (2)
The equation for the parabola is
z = k × x ² (3)
Where
z = vertical axis x = horizontal axis k = proportional constant When z is differentiated by x,
dz / dx = 2 × k × x (4)
Combining equations (1) and (4),
F = μ × dv / dz × 2 × k × x (5)
Differentiate by x and add up,
dF / dx = 2 × k × (μ × x × d (dv / dz) / dx + x × (dv / dz) × dμ / dx + μ × dv / dz) (6)
When μ is a constant and dv / dz is smaller than x,
dF / dx≈2 × k × μ × dv / dz (7)
It is.

  Equation 4 shows that the shape change of the parabola with respect to x is a constant. Equation 7 shows that if the longitudinal temperature distribution (x direction) can be controlled, the force change with respect to x is substantially constant. Comparing the form of Equation (7) with the form of Equation (4), it is clear that the use of a parabolic shape is consistent with the fluid flow equation.

  Referring to FIGS. 27A to 27E, from the assumptions of the equations (2) and (7), the glass temperature distribution in the zone of the route (116) of the forming structures (259) and (269) where the glass plate is formed is described. Control is important. The change in glass viscosity (dμ) is a strong function of glass temperature at different locations on the shaped glass sheet. In FIGS. 25A and 26A, this is the relative temperature at locations (251) and (252). The process temperature at the weir (115) at the top (259) and (269) of the forming structure is higher than the temperature of the route (116). FIG. 39D shows a typical temperature difference of 50 ° C., which is common in prior art shaped shaped structures (9). Since the respective end portions (256) and (266) of the forming structures (259) and (269) extend below the central portions (255) and (265) and enter the forming zone, there is even greater heat loss. May happen. The large amount of heat lost from the end portions (256) and (266) and the central portions (255) and (265) is the opening provided in the bottom door (272) by the edges (271), (273), (274). Due to the radiation coming from the bottom of the molding chamber (113). In the prior art (FIG. 27E), these doors (272) have a linear inner edge (271) that is lateral to control radiation heat loss by increasing or decreasing the gap (276) between the doors. Moved to. In a preferred embodiment of the present invention, the inner edge (273) of the door is relative to the end portions (256) and (266) and the central portions (255) and (265) of the molded structures (259) and (269). In order to control the heat loss, it is shaped like a parabola (273). In another preferred embodiment, the inner edge (274) of the door is relative to the end portions (256) and (266) and the central portions (255) and (265) of the molded structures (259) and (269). Shaped with a series of straight sections (274) to control heat loss. The exact shape of the inner edges (273) and (274) is preferably determined by heat transfer analysis and / or experimentation.

  In the upper part, it was assumed that the temperature distribution in the longitudinal direction of the route (250) is a constant that satisfies the equation (7). In another preferred embodiment, it is desirable that the temperature at the end (252) of the forming plate be lower than the temperature at the center of the forming plate (251). In this scenario, a longitudinal force distribution according to equation (6) is obtained.

  The shape of the inner edges (271), (273), (274) for controlling radiation heat loss from the bottom portion of the forming structure (9) is a forming having a continuously curved upward convex (250) parabolic shape. It is not limited to the structure, and can be used together with the shaped structure (9) having such a shape that the longitudinal control of the radiation heat loss is necessary.

Reduced air leakage US Pat. No. 3,338,696 relies primarily on careful design and material matching to prevent material cracking and opening. These cracks and openings are the source of air leaks both during initial operation and during manufacturing activities. This embodiment of the present invention provides for individual pressure balancing techniques in such a way that there is a minimum amount of air flowing through the leakage path even if the leakage path exists at the start or spreads out during operation. Is to provide.

  The glass plate is formed by pulling down the glass from the bottom of the overflow forming structure. The molten glass is cooled and solidified in a carefully controlled manner. The most desirable cooling phenomenon is radiation that is substantially equal to the entire thickness of the glass. Convective cooling, which mainly cools the glass surface, is also a factor. Excessive convection cooling has a destabilizing effect on the subtraction process, so convection cooling must be strictly controlled. The observed destabilization phenomenon includes periodic fluctuations in the plate thickness when the plate is pulled down. This is called “pumping” and is one of the phenomena mentioned in virtually all glass downdraw processes.

  The operating temperature of the molding zone in the “overflow process” is typically 1250 ° C., typically at the top of a 3 meter high open bottomed chamber containing an atmosphere of hot air. Because of the approximately 3 meter column of hot air, the atmosphere in the zone where the plate is formed is higher than the pressure outside the forming apparatus. Thus, if there is a crack or opening, there will be a flow path for air, which will allow air to flow into the open bottom of the chamber, lift the chamber, and exit the crack or opening. If this leakage path is such that it substantially increases the convective cooling of the forming zone in the route (116) of the forming structure (9), periodic variations in the plate thickness (pumping) will occur.

  In order for air to flow through the opening, there must be a pressure differential from one side of the opening to the other. The present invention relates to adjusting the internal pressure in each of the main components of the molding apparatus in such a way that the pressure difference in the leakage path to the molding zone approaches zero. For this reason, even if the opening exists or widens, there is only a negligible pressure difference for moving the air flow, so that there is little or no air leakage.

  Referring now to FIGS. 28A-32B, FIGS. 28A and 28B illustrate glass cooling as the glass transitions from a molten state to a solid state. This process must be carefully controlled. This cooling process starts from the underside of the forming device (9) just above the route (116) in the muffle zone (280), with the molten glass sheet (11) passing through the muffle door zone (114). The interval continues and is substantially solidified by the time it exits the transition zone (281). In order to relieve the internal stress of the solidified glass sheet (12), the controlled cooling process is continued in the annular tensioner zone (282).

  Four embodiments for controlling the pressure difference in the molding chamber are shown in FIGS. 29A-32B. These are: a) applying a flow to pressurize, b) limiting the outflow, c) flowing to a vacuum, d) entering the chamber for pressurization. Any of these control methods can be used to control the pressure in the muffle zone (280), muffle door zone (114), transition zone (281) or slow cooling and tensioning device zone (282), depending on the unique design requirements. May be used. However, one important objective is to equalize the pressure on both sides of the membrane separating the factory air or heating or cooling zone from the molding chamber. The invention also applies when performing an “overflow process” where the gas in the molding chamber is a gas other than air, ie nitrogen.

  In particular, FIGS. 29A and 29B show that air that is preferably preheated and introduced into the muffle heating chamber (131) to equalize the pressure in the heating chamber (131) to the pressure in the adjacent molding chamber (113). FIG. 14 illustrates one embodiment of a muffle zone (280) showing (290). The wall (132) that separates the two chambers in the muffle is usually composed of many parts and is therefore susceptible to random leakage. Equalizing the pressure between the two chambers also minimizes leakage flow.

  FIGS. 30A and 30B show one embodiment of a muffle door zone (114) that includes an outlet restriction (300) for the flow of air exiting each muffle door (301). The magnitude of this restriction is variable to maintain the air pressure in the muffle door chamber (302) equal to the air pressure in the adjacent molding chamber (303). The flow of air through the cooling tube (141) to the muffle door (301) typically eliminates the leakage path and increases the internal pressure of the muffle door chamber (302) to the pressure of the adjacent molding chamber (303). Is appropriate.

  51, 52, 53, cooling to the muffle door chamber (302) is another way to minimize leakage from the muffle door (301) through joints or cracks. The air mass flow (511) for cooling and the cooling air mass flow (517) flowing out therefrom may be strictly controlled. FIG. 51 shows that the device (512) controls the cooling air mass flow (511) to the muffle door chamber (302), and the device (516) cools the cooling air mass flow (512) out of the muffle door chamber (302). ) Shows an embodiment of the present invention that controls The total cooling air mass flow (511) to the muffle door (301) is the cooling flow of the individual cooling tubes (141) described in US Pat. No. 3,682,609, incorporated herein by reference. Is adjusted by the measurement and control device (512) as it flows to the individual flow regulators (513). Cooling air flows out of the muffle door (301) via a plurality of outlets (514) to a manifold (515) that leads to a measurement and control device (516) that regulates the outflow of the cooling air mass flow (517). . In this embodiment, since the cooling air mass flow (511) flowing into the muffle door (301) and the cooling air mass flow (512) flowing out from the muffle door (301) are adjusted to the same value, the crack of the muffle door (301) And there is no net air leak from the joint. If all leakage paths outside the muffle door (301) are sealed, there is no leakage from the front (518) of the muffle door (301) to the internal chamber (113) of the molding apparatus. Another feature of this embodiment is that the total cooling air mass flow is controlled to a constant value, which stabilizes the energy loss in the muffle door zone (114).

  In another embodiment, the device (512) measures the cooling air mass flow (511) to the muffle door (301) and the device (516) flows out of the muffle door (301) air mass flow (517). And the outflow air mass flow (517) is controlled to a value equal to the inflow air mass flow (511) as measured by the device (512). The setting of the individual flow regulators (513) determines the speed (511) of the cooling air mass flow.

  In another embodiment, each individual flow regulator functions as a measurement and control device (523) so that the total measurement is equal to the cooling air mass flow (511) to the muffle door (301). . The device (516) measures the air mass flow (517) flowing out from the muffle door (301) and calculates the outflow air mass flow (517) as the inflowing air mass when the total of the measured values of the device (523) is obtained. Control to a value equal to the flow (511).

  31A and 31B show a transition zone (281) with high pressure cooling air (310) entering the cooling chamber (311) and exiting (312) from each of the transition coolers (313) to a regulated vacuum source (314). ). The large amount of air required for cooling in the transition zone typically raises the pressure in the transition cooling chamber (311) higher than the pressure in the adjacent molding chamber (315). For this reason, a vacuum source (314) is required to reduce the pressure, and the pressure in the transition cooling chamber (311) is adjusted to be equal to the pressure in the adjacent molding chamber (315).

  32A and 32B illustrate one embodiment of a slow cooler / tensioner zone (282) that includes a pair of pressure balancing chambers (320) at each end of the slow cooler and tensioner (282). The pressure in the balancing chamber (321) is adjusted to be equal to the pressure in the slow cooling chamber (322). The chamber at each end was selected because there is a bearing and adjustment mechanism for the pulling roller (111) at each end. Alternatively, a single pressure balance chamber (320) or multiple individual pressure balances that accommodates the entire slow cooler and tensioner (282) as required by individual design considerations. There will be a working chamber (320).

Control of Convection Cooling Referring again to FIGS. 51-53, cooling airflow (511) flowing into the muffle door (301) and cooling airflow ((517) and (527)) cooling out therefrom. Accurate control of the working air flow controls convective cooling in the muffle door zone (114). The cooling of the glass when it is formed into a plate by the route (116) of the forming structure (9) is largely due to radiation on the front surface (518) of the muffle door (301) in the muffle door zone (114). The temperature of the front surface (518) of the muffle door (301) is mainly adjusted by the total cooling air mass flow (511). There is also forced convection cooling of the glass in the muffle door zone (114) if there is an air flow from the muffle chamber (113) to the transition zone (281).

  FIG. 52 shows a muffle door (301) with a plurality of vent openings (529) provided on the top surface. These vent openings (529) open to the muffle chamber (113) and provide an air flow (528) for forced convective cooling of the glass in the muffle door zone (114). The cooling air mass flow (511) to the muffle (301) is measured and regulated by individual flow regulators (523) that send the cooling air to the front surface (518) of the muffle door (301). Cooling air flows out of the muffle door (301) via a plurality of measurement and control devices (526) that regulate the outflow mass flow of the cooling air (527). The convective cooling air mass flow (528) exiting from the muffle door is the difference between the cooling air mass flow (511) flowing into the muffle door (301) and the cooling air mass flow (527) flowing out therefrom. equal. The convective cooling air mass flow (528) flows into the molding device chamber (113) through the vent opening (529) and flows down through the muffle door zone (114) to form the molding structure (9 ) Route (116) to provide a controlled amount of forced convection cooling to the molten glass (10) that is formed into the plate (111). As described above in this specification, excessive amounts of forced convection cooling can cause glass flow to circulate ("pumping"), resulting in variations in plate thickness. Another feature of this embodiment is that the total cooling air mass flow is controlled to a constant value, which stabilizes the energy loss in the muffle door zone (114).

  In another embodiment of the invention, the device (512) measures and regulates the cooling air mass flow (511) to the muffle door (301) and the device (516) flows out of the muffle door (301). The mass flow (517) is measured and the outflow air mass flow (517) is equal to the incoming air mass flow (511) minus the desired forced convection cooling air mass flow (528) as measured by the device (512). Control to value.

  The vent opening (529) between the chamber containing the plate forming structure (113) and the muffle chamber (302) is the glass flowing from the muffle door chamber (302) and the route (116) of the wedge shaped plate forming structure (9). The pressure between the two chambers must be large enough so that air does not leak from the cracks and openings between them.

Compensation for Nonlinear Thermal Creep of Refractory The refractory material that produces the molded structure (9) and its support structure has high compressive strength and low tensile strength. Like most structural materials, these materials also change shape when stressed at high temperatures. The latest from US Pat. No. 6,974,786 issued on Dec. 13, 2005, entitled “SAG CONTROL OF ISOPPES USED IN MAKING SHEEET GLAST BY THE FUSION PROCESS”, incorporated herein by reference. Available information defines the characteristics of the zircon thermal creep material. Zircon is a presently preferred material for building the molded structure. The motivation for the present invention was to analyze how these thermal creep characteristics affect the manufacturing process.

  The present invention includes embodiments in which the vertical deformation approaches zero by minimizing the vertical deformation of the forming structure. This increases the yield and delays the end of the production run to replace the forming structure.

  33A-33D show the main parts of a typical “overflow process” manufacturing system. Molten glass (10) from the melting furnace and fore Haas, whose temperature and chemical composition must be substantially uniform, is sent to the forming apparatus and flows into the plate forming structure (9). U.S. Pat.No. 3,338,696 as well as U.S. Pat. Nos. 6,748,765, 6,889,526, 6,895,782 of the present applicant, No. 6,990,834, No. 6,997,017 and U.S. Patent Application Nos. 11 / 006,251, 11 / 060,139, 11/184, The glass sheet forming apparatus described in detail in No. 212 is a wedge-shaped forming structure (9). These patents and patent applications are incorporated herein by reference. The linear inclined weir (115) is substantially parallel to the wedge (116) configuration on either side of the ridge (129) of the forming structure (9). The bottom (117) and side (118) of the reed (129) are formed in such a way that an even distribution of the glass on the top of the weir (115) on both sides is obtained. The glass overflows from the top of the weir (115) on both sides and flows down on both sides of the wedge-shaped forming structure (9), resulting in a molten glass plate that can be used in the route (116). The molten glass is cooled when drawn from the route (116), and becomes a solid glass plate (11) having a substantially uniform thickness.

  The usable width (331) of the shaped plate (11) is approximately 70 percent of the longitudinal length of the route (116) of the shaped structure (9) and is in the middle area of the weir (115) ( 337) from the overflowing glass. The glass overflowing from the inlet end region (336) and the far end region (338) of the forming structure (9) becomes unusable end portions (334) and (335) of the formed plate. For this reason, the middle region (337) of the forming structure (9) can be maintained in a uniform shape in such a way that the thickness of the easy-to-sell part of the plate is constant during the manufacturing activity. Most important.

  Figures 34A-34D show the typical effect of thermal creep on the shape of the molded structure when different compressive forces are applied to the bottom portion of the molded structure (9) near the root (116). FIG. 34A shows the molding structure (9) in such a way that without compression load, the top of the weir (115) and root (116) is curved (171) and the state of curvature (171) of the bottom (117) changes. ) In the middle. Due to this curvature (171), the molten glass (10) does not overflow from the weir (115) and flow with a constant thickness (172). Specifically, this curvature (171) allows more glass to flow from the middle region (337) of the weir (115), resulting in a non-uniform distribution of plate thickness. Molded structure (9) has an initial length (346) defined by temporary lines (344) and (349). If no external load is applied, the weir (115) becomes shorter and the route (116) becomes longer. At the neutral shaft (341), the length of the forming structure (9) does not change. As used herein, the neutral shaft (341) defines a horizontal plane with no deformation in the longitudinal direction when the forming structure (9) is deformed by its own weight without external force. . As used herein, the neutral shaft (341) also distinguishes between the top and bottom portions of the forming structure (9). The top or upper part of the forming structure (9) is above as viewed perpendicular to the neutral axis (341) and the bottom or lower part is below as viewed perpendicular to the neutral axis (341). .

  FIG. 34B shows that sagging of the forming structure is minimized under an optimal compressive load (345) in the lower portion of the forming structure (9) near the root (116). When the optimum load is applied, both the weir (115) and the route (116) are deformed (shortened) by approximately the same length (347). FIG. 34C shows that if too much load (342) is applied to the lower portion of the forming structure (9) near the route (116), the route (116) is overcompressed, and the dredging weir (115), dredging bottom (117) In addition, an upward convex shape (342) is formed in the route (116). As is apparent from the movements with respect to the temporary lines (344) and (349), the route (116) deforms significantly more than the weir (115). 34A-34C illustrate the effect of thermal creep within the same time. FIG. 34D shows the molded structure (9) deformed to a greater extent than the length (348). The increase in the amount of deformation is due to the fact that the time of the manufacturing activity that has become substantially longer is increased and the correct load (345) is applied. Referring again to FIG. 33, the usable plate width (331) is a function of the width of the middle region (337) of the forming structure, so that the usable width of the manufactured plate increases as the amount of deformation increases. (331) is adversely affected. In order to keep the shape of the middle region and to obtain a plate (11) with a uniform thickness of usable width (331) manufactured, the longitudinal deformation at the top of the middle region (337) is , Should be substantially equal to the longitudinal deformation at the bottom of the middle region (337). If the amount of deformation increases in this way over a long period of time, the usable plate width (331) may not be appropriate, so that the manufacturing activity may eventually be terminated.

  The present invention recognizes the highly non-linear characteristics of the thermal creep of the refractory material used to build the molded structure. A preferred refractory material for molded structures at present is zircon, but other materials such as alumina have been used in the past as refractories for molded structures. FIG. 35 is a graph of the zircon thermal creep coefficient as a function of pressure and temperature as defined by the data in US Pat. No. 6,974,786. With the inventor's knowledge, this data is not available from general literature. The data in FIG. 35 is derived from FIGS. 2B, 3A, and 3B of US Pat. No. 6,974,786. Since the raw data is not available, the curve in FIG. 35 is a fit by judgment on the data, and the accuracy is sufficient to represent the trend but is not absolute accuracy. Extrapolation of the data was necessary to obtain the predicted value of the thermal creep coefficient in the stress range predicted by the model.

  36 and 37 show the thermal creep deformation predicted by the prior art, and the creep deformation obtained by the present invention is shown in FIGS. 40 and 41. FIG. These figures are the results of a finite element analysis (FEA) model with a variety of different boundary conditions and material properties and represent 10 times the expected thermal creep deformation for a two-year production period. As will be described later, the variables considered in the analysis include the shape of the block, force load, density, thermal creep coefficient / Young's modulus, but does not include the weight of the glass. ALGOR (registered trademark) software was used for the finite element analysis.

  The FEA grid of the molded structure is shown in FIGS. 39A and 39B. The forming structure is supported vertically at (391) and (392) at the first and second ends, respectively. The forming structure is restrained in the longitudinal direction at (393). FIG. 39B shows the use of a half model assuming symmetry on the vertical surface (394). The area where force is applied to the first and second ends as a uniform pressure is shown as area (395) in FIGS. 39A and 39C.

  The modeled molded structure (9) was for a molded structure root length of 2.00 meters. The finished dimensions of the analyzed fireproof block are 2.20 meters long, 0.66 meters high, and 0.20 meters wide. The bottom of the trough through which the glass flows is horizontal, and the weir slope at the top of the forming structure is minus 5.73 degrees. The angle of the mountain at the bottom of the route is 33.4 degrees. Applicants' knowledge is that the dimensions used are not an exact representation of the actual dimensions used by individual manufacturers utilizing the overflow process. However, this dimension is typical of those selected by those skilled in the art.

The weight of the glass flowing inside and outside the molded structure was not included as part of the total load. Including the weight of the glass, the deformation amplitude has a minimal effect, and the deformation shape has negligible force. To include the weight of the glass, the force applied to the lower portion of the edge of the forming structure needs to increase in proportion to the weight of the glass. The material density of the molding structure (9) used was 4,000 kg / m ³ .

  The thermal creep coefficient used for the calculations in FIGS. 36, 37 and 38 was for the conditions of 250 psi and 1215 ° C. in FIG. When thermal creep was simulated using a linear stress finite element analysis program, the thermal creep coefficient multiplied by time was similar to the reciprocal of Young's modulus. The thermal creep coefficient value used was 2e-8 inches / inch / hour / psi. The Young's modulus used to simulate thermal creep was 11.4e6 psi. The resulting magnification of 40,000 times in FIGS. 36, 37, 38, 40, and 41 represents 10 times the deformation that would occur in two years. The force applied to the lower portion of the first and second ends was 0 (zero) pounds in FIG. 36, 2,250 pounds in FIG. 37, and 3,195 pounds in FIG.

  36, 37, 38, 40, and 41 are graphs showing the FEA results. Using FIG. 36 as an example, the shape of the shading image (361) of the forming structure is the deformation of the forming structure in the case of a specific boundary condition for the calculation result in FIG. 36 with respect to the undeformed grid (362). Show. The shading corresponds to the stress tensor XX in the longitudinal direction, the size of which is defined in the legend in the upper right corner of the corresponding figure.

  36, 37, and 38 are thermal creep results predicted using linear FEA at boundary conditions. The shade formed represents the magnitude of the longitudinal stress tensor on the scale of minus 450,000 to plus 450,000 newtons per square meter.

  The shape of the shaded image (361) in FIG. 36 represents 10 times the thermal creep predicted over a two year period using linear FEA when no compressive load is applied to the lower portion of the molded structure. The shape of the shaded image (371) in FIG. 37 is predicted over two years using linear FEA when using compressive loads on the lower portion of the molded structure described in US Pat. No. 3,519,411. Represents 10 times the thermal creep. The shape of the shaded image (381) in FIG. 38 is predicted over two years using linear FEA to obtain a substantially linear shape at the top of the shaped structure (9) in the middle region (387). It represents 10 times the thermal creep. The middle region ((387) of the forming structure of FIG. 38) is substantially straight, whereas the inlet end region (386) and the far end region (388) are both slightly curved. Note that it is an upward convex shape. This configuration maintains a uniform flow that overflows the weir (115) in the middle region (387), and the altered flow at the weirs in the end regions (386) and (388). The plate to be molded has a constant thickness in the middle part that is easy to sell, but the thickness and shape are different at the unusable end part. The linear shape in the middle part of the top (9) of the forming structure preferably causes deformation or strain in the middle region of the upper part of the forming structure (9) to be reduced under the forming structure (9). It is obtained by making it substantially equal to the deformation or strain in the middle region of the side portion.

  The stress-strain model of the forming structure is a short beam stress-strain model. The stress is distributed and cannot be determined by the simple method of a long beam stress-strain model. The reason is that the end effect is more remarkable in the short beam than in the long beam. When a longitudinal compressive force is applied to the lower part of the forming structure (9), local stress concentrations can be generated as at locations (384) and (385) in FIG. These specific stress concentrations are at the point of application of the longitudinal compressive force.

  The stress and the resulting thermal creep deformation (thermal creep strain) of the molded structure is caused by gravity which generates both shear and bending moments in the molded structure. The vertical shear force is generated by supporting the forming structure at each end and is greater in the end regions (386) and (388). The bending moment is greatest in the middle region of the forming structure. Bending moments produce primary deformations, but the analysis must consider both shear and bending moments. Finite element analysis (FEM) is the preferred technique for designing the compressive load of the molded structure.

  For some molded structural shapes, certain combinations of shear and bending moments make it desirable to implement the multistage compression force technique of US patent application Ser. No. 11 / 184,212.

  FIG. 39D shows the temperature distribution of the molded structure assumed in the nonlinear model. The temperature difference between the top and bottom is 50 ° C. The temperature used may not be an exact representation of the actual difference encountered by a particular manufacturer utilizing the overflow process. However, this difference is typical of the difference that one skilled in the art would select.

  40 and 41 show thermal creep deformation predicted by varying material properties with linear stress FEA in a method that simulates nonlinear thermal creep. The shading formed represents the magnitude of the longitudinal stress tensor on a scale of minus 1,250,000 to plus 250,000 Newtons per square meter.

  The shape of the shaded image (401) in FIG. 40 is 10 times the thermal creep predicted over the course of two years using nonlinear FEA when using the compressive load on the lower part of the shaped structure of FIG. 38 (linear FEA). Represents. This is a non-linear analysis for the load of the configuration of FIG.

  The shape of the shaded image (411) in FIG. 41 is a nonlinear analysis that predicts the minimum thermal sagging state. The force resulting in substantially zero vertical deformation predicted for the molded structure is 6,075 pounds versus 3,195 pounds predicted by the linear analysis shown in FIG. The force of 6,075 pounds that results in a stable forming structure (9) shape is zero longitudinal tension in linear analysis in the forming structure (9) according to the claims of US Pat. No. 3,519,411. Nearly three times the 2,250 pounds of force needed to produce While the middle region (417) of the forming structure of FIG. 41 has a substantially linear shape, the inlet end region (416) and the far end region (418) are both slightly curved. Note that it is upwardly convex. This configuration maintains a uniform flow that overflows the weir (115) in the middle region (417), and the altered flow at the weirs in the end regions (416) and (418). The plate to be molded has a constant thickness in the middle part that is easy to sell, but the thickness and shape are different at the unusable end part. Due to the non-linear thermal creep properties of the zircon refractory, the compressive stress in the middle region of the bottom or lower part of the forming structure (9) is reduced in the middle region of the top or upper part of the forming structure (9). By making it substantially larger than the compressive stress, the linear shape of the middle part of the top of the forming structure (9) is obtained. These stress levels result in equal longitudinal deformation or strain at the top and bottom portions of the middle region (417). When a compressive force in the longitudinal direction is applied to the lower portion of the forming structure (9), local stress concentration as shown in the regions (414) and (415) of FIG. 41 can be generated.

  In the nonlinear analysis, the compressive load necessary to obtain a stable shape (9) shape increases, so that the deformation (413) in the longitudinal direction is predicted to be approximately 16 mm (413). Applying the linear analysis load of FIG. 38 (US Pat. No. 6,889,526) to the non-linear analysis results in a longitudinal deformation or strain (403) of approximately 8 mm as shown in FIG. When the width (331) of the usable plate (11) is important and the design width (346) at the current stage is the limit, the initial structure of the forming structure (9) is compensated for to compensate for this increase in deformation. The length (346) may be much larger.

  The non-linear analysis herein is a simplified example of non-linear analysis that would be performed on a known manufacturing configuration. The grid was extremely rough and the thermal creep coefficient was only repeated in the vertical direction. Also, a refined FEA program is available that can automatically repeat the thermal creep coefficient as a function of stress and temperature level than that used herein.

  Reconsidering the data of US Pat. No. 6,974,786, it can be seen that there are large variations in the test results of samples performed in the same test conditions. Part of this variation is test error. However, for different batches of zircon refractories, there is a high probability that there is significant variation in the magnitude and slope of the thermal creep properties with respect to temperature and stress. For this reason, the thermal creep characteristics of molded structures made with different batches of materials may differ. The analysis described in this specification can be performed by designing the forming structure (9) using the average value of the thermal creep characteristics. However, the deformation of the individual molded structure (9) in the manufacturing environment may differ from the predicted deformation. To correct for such deformation variations, the feedback control strategy described in US patent application Ser. No. 11 / 184,212, incorporated herein by reference, can be utilized.

  In one embodiment, the coated light whose forming structure (9) is restrained in the longitudinal direction (175) by a force applied at one end by an adjustment bolt (424) in place and at the other end by an active horizontal load (426). (Cortriight) (US Pat. No. 3,519,411) may be used to apply a compressive load on the molded structure. The device of this embodiment is shown in FIGS. 42A-42D, where the applied force (426) is significantly greater than the force specified by the Cortlight. During application of this embodiment, the adjustment bolt (424) is periodically adjusted to maintain the load at the desired magnitude according to US Pat. No. 6,990,834.

  In another embodiment shown in FIGS. 43 and 44, US Pat. No. 6,990,834, incorporated herein by reference, forces (426) and (436) as active loads at each end of the molded structure. To be applied.

  In another embodiment shown in FIG. 45, U.S. Pat. No. 6,990,834 induces a third active load (457) at the far end of the forming structure to cause glass (429) to enter the forming structure. ) Sealing force against hydrostatic pressure is obtained. In this embodiment, the compression forces (436) and (456) are the same in magnitude but in opposite directions.

  The basic idea of the present invention is to apply a force and / or moment to weaken the stress caused by gravity to the edge of the forming structure to virtually eliminate the effect of thermal creep on the molten glass flow.

  Although the invention has been described with reference to various embodiments, it will be apparent that various other embodiments are possible in the invention.

  Accordingly, it is to be understood that the embodiments of the present invention described herein are merely illustrative of the application of the principles of the present invention. The detailed description of the exemplary embodiments provided herein is not intended to limit the scope of the claims which describe the features deemed essential to the invention.

"Overflow process" shows the main parts of the glass sheet manufacturing system. FIG. 2 shows a side view of an “overflow process” known in the prior art. It is the cross section cut | disconnected by the line BB of FIG. 2A about the flow of the glass in a downcomer. FIG. 2B is a cross-sectional view taken along line CC in FIG. 2A, where the glass flow in the downcomer pipe looks like a plate in the “overflow process”. 1 shows a side view of a surface diverter in a preferred embodiment of the present invention. 1 shows a top view of a surface diverter in a preferred embodiment of the present invention. FIG. Figure 2 shows a side view of an immersed flow diverter in a preferred embodiment of the present invention. Figure 2 shows a top view of an immersed flow diverter in a preferred embodiment of the present invention. The side view of the "overflow process" in one embodiment of the present invention is shown. It is the cross section cut | disconnected by the line BB of FIG. 5A about the flow of the glass in a downcomer pipe | tube at the time of using a diversion apparatus. It is the cross section which cut | disconnected the part which the flow of the glass in a downcomer pipe | tube at the time of using a flow dividing device looks like a plate with the line CC of FIG. 5A. Fig. 5 shows a bowl with a tilt axis that diffuses a static flow zone at the nose of the bowl in a preferred embodiment of the invention. FIG. 4 shows a top view of a bowl with a lateral inflow moving a static flow zone from the tip of the bowl to the side of the bowl in a preferred embodiment of the present invention. FIG. 7B shows a side view of FIG. 7A. FIG. 4 shows a top view of a bowl with a side inflow that moves a static flow zone from the nose of the bowl to a location about 45 degrees transverse to the center line of the forming apparatus in a preferred embodiment of the present invention. FIG. 7C shows a side view of FIG. 7C. 1 shows an “overflow process” bowl known in the prior art. Fig. 5 shows a downcomer supplying a minimal static flow to the forming device inlet in a preferred embodiment of the present invention. FIG. 9B shows a top view of FIG. 9A. Fig. 3 shows details of the downcomer to the soot inlet connection showing the glass flow pattern in a preferred embodiment of the present invention. Fig. 2 shows the flow between the downcomer and the forming device inlet in an "overflow process" known in the prior art. FIG. 10B shows a top view of FIG. 10A. Fig. 2 shows details of the downcomer to the soot inlet connection showing the glass flow pattern known in the prior art. The main parts of a typical “overflow process” manufacturing system are shown. 11B shows a cross section of FIG. 11A. FIG. 2 shows a side view of glass flowing through a forming structure. FIG. 12B shows a cross section taken at the center of the shaped structure of FIG. 12A showing the cooling zone. Figure 2 shows a modified single heating chamber muffle design in a preferred embodiment of the present invention. FIG. 13B shows a cross section of FIG. 13A. In a preferred embodiment of the present invention, an air-cooled tube is provided for applying local cooling to the molten glass as it overflows from the weir. 14B shows a cross section of FIG. 14A. 1 shows a muffle having a plurality of heating chambers in a preferred embodiment of the present invention. FIG. 15B shows a cross section of FIG. 15A. In a preferred embodiment of the present invention, a radiant cooler is provided that applies local cooling to the molten glass as it overflows the weir. FIG. 16B shows a cross section of FIG. 16A. Figure 2 shows how a prior art molded structure design is deformed by thermal creep. FIG. 17B shows another view of FIG. 17A. 1 shows a forming structure support system known in the prior art. FIG. 18A shows another view of FIG. 18A. FIG. 18A shows another view of FIG. 18A. FIG. 18A shows another view of FIG. 18A. Figure 2 shows a single molded compression block at each end of the molded structure in a preferred embodiment of the present invention. FIG. 19B shows another view of FIG. 19A. FIG. 19B shows another view of FIG. 19A. FIG. 19B shows another view of FIG. 19A. Figure 2 shows a single molded compression block at one end of the molded structure and a plurality of molded compression blocks at the other end in a preferred embodiment of the present invention. FIG. 20B shows another view of FIG. 20A. FIG. 20B shows another view of FIG. 20A. FIG. 20B shows another view of FIG. 20A. Figure 2 shows a molded structure design well known in the prior art. FIG. 21B shows a top view of FIG. 21A. FIG. 21B shows a cross section of the molded structure design shown in FIG. 21A taken along line CC. FIG. 21B shows a cross section of the molded structure design shown in FIG. 21A taken along line DD. FIG. 21B shows a cross section of the molded structure design shown in FIG. 21A taken along line EE. FIG. 21B shows a cross section of the molded structure design shown in FIG. 21A taken along line FF. FIG. 21B shows a cross section of the molded structure design shown in FIG. Figure 5 shows a reduced reverse slope at each end of the forming structure in a preferred embodiment of the present invention. FIG. 22B shows a top view of FIG. 22A. FIG. 22B shows a cross section of the molded structure design shown in FIG. 22A taken along line CC. FIG. 22B shows a cross section of the molded structure design shown in FIG. 22A taken along line DD. FIG. 22B shows a cross section of the molded structure design shown in FIG. 22A taken along line EE. FIG. 22B shows a cross section of the molded structure design shown in FIG. 22A taken along line FF. FIG. 22B shows a cross section of the molded structure design shown in FIG. 22A taken along line GG. Fig. 4 shows another embodiment of the invention with further modified ends. FIG. 23B shows a top view of FIG. 23A. FIG. 23B shows a cross section of the molded structure design shown in FIG. 23A taken along line CC. FIG. 23B shows a cross section of the molded structure design shown in FIG. 23A taken along line DD. FIG. 23B shows a cross section of the molded structure design shown in FIG. 23A taken along line EE. FIG. 23B shows a cross section of the molded structure design shown in FIG. 23A taken along line FF. FIG. 23B shows a cross section of the molded structure design shown in FIG. 23A taken along line GG. 4 illustrates another embodiment of the present invention that may increase structural rigidity. FIG. 24B shows a top view of FIG. 24A. FIG. 24B shows a cross section of the molded structure design shown in FIG. 24A taken along line CC. FIG. 24B shows a cross section of the molded structure design shown in FIG. 24A taken along line DD. FIG. 24B shows a cross section of the molded structure design shown in FIG. 24A taken along line EE. FIG. 24B shows a cross section of the molded structure design shown in FIG. 24A taken along line FF. FIG. 24B shows a cross section of the molded structure design shown in FIG. 24A taken along line GG. In a preferred embodiment of the present invention, a forming structure with a continuously curved, parabolically shaped upward convex root with a constant reverse slope angle that solidifies the central glass ahead of the edge glass. Show. FIG. 25B shows an end view of section BB of FIG. 25A. FIG. 25B shows a top view of FIG. 25A. FIG. 25B is a cross-sectional view taken along DD in FIG. 25A. In a preferred embodiment of the present invention, a forming structure with a continuously curved, parabolically shaped upward convex root with a variable reverse slope angle that solidifies the central glass ahead of the edge glass. Show. FIG. 26B shows an end view of section BB of FIG. 26A. FIG. 26B shows a top view of FIG. 26A. FIG. 26B is a cross-sectional view taken along DD in FIG. 26A. FIG. 26 shows the molded structure of FIGS. 25A-25D housed in a muffle heating chamber with a movable bottom door for controlling radiation heat loss at the bottom. FIG. 27B is a cross-sectional view taken along BB in FIG. 27A. FIG. 27B is a cross-sectional view taken along CC of FIG. 27A in a preferred embodiment of the present invention. FIG. 27B is a cross-sectional view taken along DD of FIG. 27A in a preferred embodiment of the present invention. FIG. 27B is a cross-sectional view taken along the line E-E of FIG. 27A showing the shape of the movable bottom door according to the prior art. Fig. 3 shows the cooling process of an "overflow process" glass sheet forming system known in the prior art. FIG. 28B shows a cross section of FIG. 28A. In a preferred embodiment of the present invention, it is shown how the pressure in the muffle zone can be controlled to minimize leakage. FIG. 29B shows a cross section of FIG. 29A. In one preferred embodiment of the present invention, it is shown how the pressure in the muffle door zone can be controlled to minimize leakage. FIG. 30B shows a cross section of FIG. 30A. In a preferred embodiment of the present invention, it is shown how the pressure in the transition zone can be controlled to minimize leakage. FIG. 31B shows a cross section of FIG. 31A. In one preferred embodiment of the present invention, it is shown how the pressure in the slow cooler and tensioner zone can be controlled to minimize leakage. FIG. 32B shows a cross section of FIG. 32A. It is a side view of the glass which flows in the inside and the outside of the forming structure of the overflow process. FIG. 33B is an in-flow end view of the glass and molded structure shown in FIG. 33A. FIG. 33B is a far end view of the glass and forming structure shown in FIG. 33A. FIG. 33B is a top view of the glass and molded structure shown in FIG. 33A. It is a figure showing the thermal creep deformation | transformation of the glass forming structure under the load by own weight. It is a figure showing the thermal creep deformation | transformation of the glass forming structure under the applied load which minimizes a deformation | transformation of a perpendicular direction. It is a figure showing the thermal creep deformation | transformation of the glass forming structure under the applied load under an excessive applied load. FIG. 6 represents thermal creep deformation of a glass forming structure under an applied load that minimizes vertical deformation over long-term manufacturing activity. It is a graph which shows the characteristic of the heat creep material of the refractory material used for a forming structure. Fig. 4 shows the deformation of a prior art linear FEA for forming structure deformation in the absence of straightening force. Figure 3 shows the deformation of a prior art linear FEA for forming structure deformation under corrective force according to US 3,519,411. Fig. 5 shows the linear FEA deformation of the forming structure deformation with the corrective force when there is virtually no sagging of the forming structure. 1 is a side view of a grid used in FEA and showing dimensions in metric. FIG. 3 is an end view of a grid with dimensions in metric used in FEA. It is an end view of a forming structure showing a case where force is applied to the bottom portion of the forming structure in FEA. The assumed temperature distribution of the cross section of the molded structure is shown. The deformation of the non-linear FEA of the deformation of the forming structure with a corrective force when there is virtually no sagging of the forming structure predicted by the linear FEA is shown. Fig. 5 shows a non-linear FEA deformation of a forming structure deformation with a corrective force when there is virtually no sagging of the forming structure. 1 shows a prior art glass forming structure support and compression system. FIG. 42B shows a cross-sectional view of FIG. 42A. FIG. 42B shows a partial view of FIG. 42A. FIG. 42B shows a cross-sectional view of FIG. 42A. Figure 3 shows a forming structure support system using a forming structure at each end and a support block to support the weight of the individual compression block and force applicator at each end. FIG. 43B shows a cross-sectional view of FIG. 43A. FIG. 43B shows a partial view of FIG. 43A. FIG. 43B shows a cross-sectional view of FIG. 43A. 1 shows a forming structure support system having a support / compression block and a force application device at each end. FIG. 44B shows a cross-sectional view of FIG. 44A. FIG. 44B shows a partial view of FIG. 44A. FIG. 44B shows a cross-sectional view of FIG. 44A. 1 shows a forming structure support system having a support / compression block, a force applying device at each end, and a sealing force applying device at the far end. FIG. 45B shows a cross-sectional view of FIG. 45A. FIG. 45B shows a partial view of FIG. 45A. FIG. 45B shows a cross-sectional view of FIG. 45A. It is a cross section of the downcomer pipe towards the inflow pipe coupling part where the downcomer is sinking below the glass free surface. It is the detail of the flow of the glass in sectional drawing of FIG. 46A. FIG. 6 is a cross-section of the downcomer pipe towards the inflow pipe coupling portion where the downcomer is substantially above the glass free surface. It is the detail of the flow of the glass in the cross section of FIG. 47A. FIG. 6 is a cross-section of the downcomer pipe towards the inflow pipe joint where the downcomer is the same distance as the diameter of the inflow pipe on the glass free surface. It is the detail of the flow of the glass in the cross section of FIG. 48A. The heater in the downcomer toward the inflow pipe coupling part is shown. It is the detail of the flow of the glass in the cross section of FIG. 49A. FIG. 49B is a partial top view of FIG. 49A. FIG. 50 is a detail of an exemplary sealing block used in FIGS. 49A, 49B, 49C. FIG. It is a cross section of the downcomer pipe which goes to the inflow pipe joint part which added the conical part to the inflow pipe. It is the detail of the flow of the glass in the cross section of FIG. 50A. FIG. 6 illustrates an apparatus for tightly controlling the cooling air mass flow into and out of a muffle door chamber to minimize leakage from the muffle door, according to one embodiment of the present invention. 1 illustrates an apparatus for controlling forced convection cooling of glass flowing through a plate forming structure by strictly controlling the cooling air mass flow into and out of a muffle door chamber according to an embodiment of the present invention. The cross section at the time of mounting | wearing the plate forming apparatus with the muffle door in FIG. 52 is shown.

Claims (45)

An apparatus for forming a sheet glass having a trough for receiving molten glass having a side surface attached to a wedge-shaped plate forming structure, wherein the wedge-shaped plate forming structure converges at the bottom of the wedge Having a side surface inclined downward, so that the molten glass overflows from the side surface of the bowl and flows down the side surface inclined downward of the wedge-shaped plate forming structure, and the bottom of the wedge In an apparatus configured to form a glass plate when fusing with
a) at least one inlet end compression block located at the inlet end of the molding structure, the inlet end compression block disposed at the bottom end of the molding structure;
b) at least one far end compression block located at an end opposite to the inlet end compression block of the molding structure, the far end compression block disposed at the bottom end of the molding structure;
c) an inlet end force application device that applies force to the inlet end compression block so that the bottom of the inlet end of the forming structure is deformed in the longitudinal direction by thermal creep;
d) a first far-end force applying device that applies a force to the far-end compression block so that the bottom of the far-end of the forming structure is deformed in the longitudinal direction by thermal creep;
The molding structure is such that the force applying device is deformed in the longitudinal direction by the same size as the top of the molding structure by thermal creep, so that the bottom of the molding structure is more resistant to thermal creep than the top of the molding structure. Applying a force in the opposite longitudinal direction against the respective compression block such that the bottom of the compression structure is compressed substantially larger than the top of the forming structure;
Thus, the apparatus is characterized in that the deformation of the forming structure due to thermal creep has a minimal effect on the thickness variation of the glass sheet.   The apparatus according to claim 1, characterized in that the compressive stress at the bottom of the forming structure is 1.25 to 4 times the compressive stress at the top of the forming structure as measured in the middle region.   The compressive stress at the bottom of the molded structure is 1.75 to 2.5 times the compressive stress at the top of the molded structure as measured in the middle region. apparatus.   The apparatus according to claim 1, wherein the inlet end force applying device is an inlet end adjusting screw.   The inlet end adjustment screw is compressed at the inlet end so that the bottom of the inlet end of the forming structure is deformed in the longitudinal direction opposite to the deformation at the bottom of the far end of the forming structure by thermal creep. The apparatus of claim 4, wherein the apparatus is periodically adjusted to maintain an applied force to the block.   6. A device according to claim 5, characterized in that the compressive stress at the bottom of the forming structure is 1.25 to 4 times the compressive stress at the top of the forming structure as measured in the middle region.   The compressive stress at the bottom of the molded structure is 1.75 to 2.5 times the compressive stress at the top of the molded structure as measured in the middle region. apparatus.   The first far-end force applying device is selected from the group consisting of a force motor, an adjustable spring, an air cylinder, a hydraulic cylinder, an electric motor, and a system using a weight and a lever. The device according to claim 4, characterized in that   The inlet end force application device is selected from the group consisting of a force motor, an adjustable spring, an air cylinder, a hydraulic cylinder, an electric motor, and a system using a weight and a lever. The apparatus according to claim 1.   The first far-end force applying device is selected from the group consisting of a force motor, an adjustable spring, an air cylinder, a hydraulic cylinder, an electric motor, and a system using a weight and a lever. The apparatus according to claim 1, wherein:   The apparatus of claim 1, wherein the inlet end compression block supports the trough.   The apparatus of claim 1, wherein the far end compression block supports the scissors. A second far-end force application device;
The second far-end force applying device applies a force to the top of the far end of the forming structure to generate a sealing force that weakens the liquid pressure of the glass flowing into the forming structure. The apparatus of claim 1.   The second far-end force applying device includes a force motor, an adjusting screw, an adjustable spring, an air cylinder, a hydraulic cylinder, an electric motor, and a system using a weight and a lever. 14. Device according to claim 13, characterized in that it is selected. An apparatus for forming a sheet glass having a trough for receiving molten glass having a side surface attached to a wedge-shaped plate forming structure, wherein the wedge-shaped plate forming structure converges at the bottom of the wedge Having a side surface inclined downward, so that the molten glass overflows from the side surface of the bowl and flows down the side surface inclined downward of the wedge-shaped plate forming structure, and the bottom of the wedge In an apparatus configured to form a glass plate when fusing with
a) at least one inlet end compression block located at the inlet end of the forming structure;
b) at least one far end compression block located at an end opposite to the inlet end compression block of the molding structure,
The inlet end compression block and the far end compression block distribute the force in the molding structure so that the applied force is directed to the refractory in the middle region of the molding structure from the top of the middle region. By applying substantially equal thermal compressive strain in the longitudinal direction, which substantially weakens the influence of the forming structure and the weight of the molten glass, up to the bottom of the middle region, so as to reduce sagging in the middle region A device characterized in that it is shaped to reduce the influence of the weight of the forming structure.   The apparatus of claim 15, wherein the inlet end compression block supports the trough.   The apparatus of claim 15, wherein the far-end compression block supports the scissors. A method for reducing the sagging rate of a forming rod having a longitudinal axis, a middle region, a first end, and a second end opposite the first end,
a) suppressing the molded structure at a lower portion of the first end;
b) From the top to the bottom, all materials in the middle region of the forming structure are given a force distribution that produces a thermal compression strain that is substantially equal in the longitudinal direction, and the influence of the weight of the forming structure and the molten glass. Applying a force to the lower portion of the second end so as to reduce a sag in the middle region by generating a substantially weakening force distribution in the forming structure;
Including methods.   The method of claim 18, further comprising supporting the molded structure at the first end and the second end. An apparatus for forming a sheet glass having a trough for receiving molten glass having a side surface attached to a wedge-shaped plate forming structure, wherein the wedge-shaped plate forming structure converges at the bottom of the wedge Having a side surface inclined downward, so that the molten glass overflows from the side surface of the bowl and flows down the side surface inclined downward of the wedge-shaped plate forming structure, and the bottom of the wedge In an apparatus configured to form a glass plate when fusing with
a) at least one inlet end compression block located at the inlet end of the forming structure;
b) at least one far end compression block located at an end opposite to the inlet end compression block of the molding structure,
The inlet end compression block and the far end compression block have a compression force equal to or greater than the compression force at the top of the molding structure when the applied force is measured at the center in the longitudinal direction of the molding structure. The deformation in the molding structure caused by thermal creep is formed by distributing the force in the molding structure so as to reduce the influence of the weight of the molding structure, as generated in the variation of the thickness of the glass plate. A device characterized in that it has a minimal effect on the device.   21. Apparatus according to claim 20, characterized in that the applied force is greater than the force required to compress the bottom of the forming structure. A method for reducing the sag of a molded structure having a longitudinal axis, a middle region, a first end, and a second end opposite the first end, comprising:
a) suppressing the molded structure at a lower portion of the first end;
b) When measured at the longitudinal center of the molded structure, the compression force measured at the bottom of the molded structure is greater than or equal to the compression force at the top of the molded structure, depending on the weight of the molded structure and the molten glass Applying a force to the lower portion of the second end so as to reduce a sag in the middle region by generating a distribution of forces in the forming structure that substantially reduces the effects;
Including methods.   23. The method of claim 22, further comprising supporting the molded structure at the first end and the second end. An apparatus for forming a sheet glass having a trough for receiving molten glass having a side surface attached to a wedge-shaped plate forming structure, wherein the wedge-shaped plate forming structure converges at the bottom of the wedge Having a side surface inclined downward, so that the molten glass overflows from the side surface of the bowl and flows down the side surface inclined downward of the wedge-shaped plate forming structure, and the bottom of the wedge In an apparatus configured to form a glass plate when fusing with
An apparatus comprising a bottom of a wedge-shaped plate forming structure having a shape that is continuously parabolically curved in an upward convex direction so that a plate formed from the device is flat.   25. Apparatus according to claim 24, characterized in that the reverse slope of the wedge-shaped forming structure is at an angle with respect to the vertical direction.   The angle formed by the reverse slope of the wedge-shaped forming structure with respect to the vertical direction is smaller at the inlet end and the far end than at the center of the wedge-shaped forming structure. The device described. An apparatus for forming a sheet glass having a trough for receiving molten glass having a side surface attached to a wedge-shaped plate forming structure, wherein the wedge-shaped plate forming structure converges at the bottom of the wedge Having a side surface inclined downward, so that the molten glass overflows from the side surface of the bowl and flows down the side surface inclined downward of the wedge-shaped plate forming structure, and the bottom of the wedge In an apparatus configured to form a glass plate when fusing with
Chamber containing the device with a width that varies in the longitudinal direction so that the magnitude of the radiant heat loss in the vertical direction from the chamber containing the device is controlled to a different value in the longitudinal direction A device comprising a bottom opening. An apparatus for molding sheet glass comprising an inflow pipe for delivering molten glass and a ridge for receiving molten glass having a side surface attached to a wedge-shaped sheet molding structure, wherein the wedge shape The plate forming structure has a downwardly inclined side surface that converges at the bottom of the wedge, so that the molten glass overflows from the side surface of the ridge and moves downward in the wedge-shaped plate forming structure. In an apparatus configured to form a glass sheet when flowing down an inclined side surface and fusing at the bottom of the wedge,
A downcomer connected to the end of the inflow pipe opposite to the ridge, the bottom end of the downcomer being located at or below the glass free surface in the inflow pipe, A downcomer pipe, wherein the pipe and the inflow pipe have a predetermined size and shape;
And at least one heater applied to the free surface area to maintain the temperature of the glass at the free surface above the liquidus temperature of the glass.   29. Apparatus according to claim 28, characterized in that the heater prevents the formation of devitrification homogeneity defects.   29. The apparatus of claim 28, wherein the heater is part of the bottom of the downcomer.   29. The apparatus of claim 28, wherein the heater is part of the top of the inflow pipe.   30. The apparatus of claim 28, further comprising at least one sealing block surrounding the downcomer, wherein the heater is part of the sealing block. An apparatus for molding sheet glass comprising an inflow pipe for delivering molten glass and a ridge for receiving molten glass having a side surface attached to a wedge-shaped sheet molding structure, wherein the wedge shape The plate forming structure has a downwardly inclined side surface that converges at the bottom of the wedge, so that the molten glass overflows from the side surface of the ridge and moves downward in the wedge-shaped plate forming structure. In an apparatus configured to form a glass sheet when flowing down an inclined side surface and fusing at the bottom of the wedge,
A downcomer connected to the end of the inflow pipe opposite to the ridge, the bottom end of the downcomer being located above the free glass surface in the inflow pipe, and the downcomer and A downcomer, wherein the inflow pipe has a predetermined size and shape;
And at least one heater applied to the free surface area to maintain the temperature of the glass at the free surface above the liquidus temperature of the glass.   34. Apparatus according to claim 33, characterized in that the heater prevents the formation of devitrification homogeneity defects.   34. Apparatus according to claim 33, characterized in that the heater is part of the bottom of the downcomer.   34. The apparatus of claim 33, wherein the heater is part of the top of the inflow pipe.   34. The apparatus of claim 33, further comprising at least one sealing block surrounding the downcomer, wherein the heater is part of the sealing block. An apparatus for molding sheet glass comprising an inflow pipe for delivering molten glass and a ridge for receiving molten glass having a side surface attached to a wedge-shaped sheet molding structure, wherein the wedge shape The plate forming structure has a downwardly inclined side surface that converges at the bottom of the wedge, so that the molten glass overflows from the side surface of the ridge and moves downward in the wedge-shaped plate forming structure. In an apparatus configured to form a glass sheet when flowing down an inclined side surface and fusing at the bottom of the wedge,
A downcomer connected to the end of the inflow pipe opposite the ridge, and a conical portion at a vertical location of the glass free surface at the junction of the downcomer and the inflow pipe The apparatus is incorporated in the inflow pipe.   40. The apparatus of claim 38, wherein the contained half angle of the conical portion is 10 to 50 degrees and the apex of the conical portion is above the conical portion. An apparatus for forming a sheet glass having a trough for receiving molten glass having a side surface attached to a wedge-shaped plate forming structure, wherein the wedge-shaped plate forming structure converges at the bottom of the wedge Having a side surface inclined downward, so that the molten glass overflows from the side surface of the bowl and flows down the side surface inclined downward of the wedge-shaped plate forming structure, and the bottom of the wedge In an apparatus configured to form a glass plate when fusing with
a) at least one inflow measurement device for measuring the mass flow of air into the muffle door chamber;
b) at least one outflow measuring device for measuring the mass flow of air exiting the muffle door chamber;
The outflow measuring device is equal to the measured value flowing into the muffle door chamber so that air does not leak from the openings and cracks between the glass flowing down from the bottom of the wedge-shaped plate forming structure and the muffle door chamber. Adjusting the cooling air flowing out of the muffle door chamber.   41. The inflow measuring device according to claim 40, wherein the cooling air flowing into the muffle door chamber is adjusted to a constant value so that the energy loss in the muffle door zone is constant. apparatus. An apparatus for forming a sheet glass having a trough for receiving molten glass having a side surface attached to a wedge-shaped plate forming structure, wherein the wedge-shaped plate forming structure converges at the bottom of the wedge Having a side surface inclined downward, so that the molten glass overflows from the side surface of the bowl and flows down the side surface inclined downward of the wedge-shaped plate forming structure, and the bottom of the wedge In an apparatus configured to form a glass plate when fusing with
a) at least one inflow measurement device for measuring the mass flow of air into the muffle door chamber;
b) at least one outflow measuring device for measuring the mass flow of air exiting the muffle door chamber;
c) at least one vent opening provided at the top of the muffle door chamber to allow air flow between the muffle door chamber and the chamber containing the plate forming structure;
The outflow measurement device is equal to the measured value flowing into the muffle door chamber minus the amount of forced convection air mass flow required to cool the glass flowing down from the bottom of the wedge-shaped plate forming structure. Adjusting the cooling air flowing out of the muffle door chamber.   43. The inflow measuring device according to claim 42, wherein the cooling air flowing into the muffle door chamber is adjusted to a constant value so that the energy loss in the muffle door zone is constant. apparatus.   Between the muffle door chamber and the chamber containing the plate forming structure so that air does not leak from the openings and cracks between the glass flowing down from the bottom of the wedge shaped plate forming structure and the muffle door chamber. 43. The apparatus of claim 42, wherein the vent opening of the chamber is large enough to allow the pressure of the muffle door chamber and the pressure of the chamber containing the plate forming structure to be substantially equal.   Between the muffle door chamber and the chamber containing the plate forming structure so that air does not leak from the openings and cracks between the glass flowing down from the bottom of the wedge shaped plate forming structure and the muffle door chamber. 44. The apparatus of claim 43, wherein the vent opening of the chamber is large enough to allow the pressure of the muffle door chamber and the pressure of the chamber containing the plate forming structure to be substantially equal.

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