Directly Heated Edge Director Assembly

Abstract

The glass manufacturing apparatus includes a forming device having a forming body and a directly electrically heated edge director assembly attached to the forming body, the edge director assembly configured to direct the flow of molten glass from the forming body. The edge director assembly includes a plurality of busbar assemblies connected thereto and configured to receive electrical current. The electrical current can be three-phase current. The busbar assemblies are supported by a three-axis support assembly that supports movement of the busbar assemblies along three orthogonal axes.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority under 35 U.S.C. Section 19 of U.S. Provisional Patent Application No. 63 / 320,330, filed March 16, 2022, the disclosure of which is incorporated herein by reference in its entirety.

[0002] (Technical field) The present disclosure relates to glass manufacturing apparatus, and more particularly to a forming apparatus that includes a forming body and an electrically heated edge director attached to the forming body and configured to control the flow of molten glass from the forming body. [Background technology]

[0003] Typically, glass manufacturing processes include equipment used to form molten material into useful end products, such as glass sheets. The production of glass sheets can take a variety of forms, such as float, rolling, and fusion processes. In particular, in the fusion process, molten material, hereafter referred to as molten glass, is fed into a forming body from which it is drawn downward as a ribbon of molten glass. The ribbon of molten glass cools to form a ribbon of glass that may be wound for future use or cut into individual glass sheets. During the drawing process, surface tension causes the ribbon of molten glass ribbon to contract laterally, thereby reducing the width of the subsequent cooled glass ribbon and the glass article(s) derived therefrom. The lateral contraction causes the edges of the ribbon of molten glass to thicken, resulting in what are known as "beads." To mitigate the lateral contraction and control the formation of beads, devices, referred to herein as "edge directors," are attached to the forming body, which effectively lengthen the forming body to counter the loss of width resulting from the lateral contraction of the ribbon. Summary of the Invention [Problem to be solved by the invention]

[0004] While the forming body may be formed from a refractory ceramic material, the edge director is typically metallic and is attached to the end of the forming body. As the molten glass flows over the surface of the edge director, the temperature of the molten glass drops below the liquidus temperature of the molten glass and the molten glass can crystallize along the edge of the edge director. This crystal growth, referred to herein as devitrification or "devit," can cause defects in the glass ribbon and prevent stable bead growth. What is needed is an effective way to mitigate debits. [Means for solving the problem]

[0005] Accordingly, in a first aspect of the disclosure, a glass forming apparatus is described that includes a forming body including a first converging forming surface and a second converging forming surface, the first and second converging forming surfaces being joined along a bottom edge of the forming body. The glass forming apparatus further includes an edge director assembly disposed at a first end of the forming body, the edge director assembly including a first edge director in contact with the first converging forming surface and a second edge director in contact with the second converging forming surface and joined to the first edge director along an edge portion joint. The glass forming apparatus further includes a first busbar assembly joined to the first edge director, a second busbar assembly joined to the second edge director, and a third busbar assembly joined to the edge director assembly at the edge portion joint. The first, second, and third busbar assemblies are electrically connected to a power source configured to provide alternating current to the edge director assemblies.

[0006] In a second aspect, the first edge director of the first aspect comprises a first thickened bottom edge portion and the second edge director comprises a second thickened bottom edge portion, the first thickened bottom edge portion joined to the second thickened bottom edge portion at an edge portion joint.

[0007] In a third aspect, the first busbar assembly of the second aspect can include a first busbar formed from a first material and joined to a first thick edge portion, and a second busbar formed from a second material different from the first material and joined to the first busbar.

[0008] In a fourth aspect, the second busbar assembly of the second or third aspect may comprise a third busbar formed from a first material and joined to the second thickened edge portion, and a fourth busbar formed from a second material and joined to the third busbar.

[0009] In a fifth aspect, in a glass forming apparatus, the third busbar assembly of the third or fourth aspect can include a central busbar formed from a first material and joined to the edge portion joint, a first branch busbar joined to the central busbar, and a second branch busbar joined to the central busbar, wherein the first branch busbar includes a first busbar segment formed from the first material and joined to the central busbar, and a second busbar segment formed from a second material different from the first material and joined to the first busbar segment, and the second branch busbar includes a third busbar segment formed from the first material and joined to the central busbar, and a fourth busbar segment formed from the second material and joined to the third busbar segment.

[0010] In a sixth aspect, the boundaries of the first and second materials for the first busbar assembly, the second busbar assembly, and the third busbar assembly can be positioned within the surrounding deformable fire-resistant insulation.

[0011] In a seventh aspect, the first edge director and the second edge director of any of the third to sixth aspects may be formed from a first material.

[0012] In an eighth aspect, the first material of any of the third to seventh aspects may comprise platinum.

[0013] In a ninth aspect, the second material of any of the third to eighth aspects can include nickel.

[0014] In a tenth aspect, the edge portion bond of any of the first to ninth aspects may be positioned below a bottom edge of the formed body.

[0015] In an eleventh aspect, the first and second busbar assemblies of any of the first to tenth aspects may be supported by a first and a second three-axis support assembly, respectively, each of the first and second three-axis support assemblies configured to support movement of the respective busbar assembly along three orthogonal axes.

[0016] In a twelfth aspect, the first and second three-axis support assemblies of the eleventh aspect may each include a tiltable stage configured to accommodate tilting of the first and second busbar assemblies, respectively.

[0017] In a thirteenth aspect, each of the first three-axis support assembly and the second three-axis support assembly of the eleventh or twelfth aspects can support the first bus bar assembly and the second bus bar assembly, respectively, using springs.

[0018] In a fourteenth aspect, the first triaxial support assembly of the eleventh aspect can support a first portion of the third busbar assembly, and the second triaxial support assembly supports a second portion of the third busbar assembly.

[0019] In a fifteenth aspect, the first triaxial support assembly of the fourteenth aspect can support a first branch busbar, and the second triaxial support assembly can support a second branch busbar.

[0020] In a sixteenth aspect, the edge director assembly of any of the first to fifteenth aspects can include an end cap joined to the first edge director and the second edge director, the end cap being positioned over a first end of the molded body.

[0021] In a seventeenth aspect, at least one of the first busbar assembly, the second busbar assembly, or the third busbar assembly of any of the first to sixteenth aspects may include a cooling channel configured to pass a cooling fluid therethrough.

[0022] In an eighteenth aspect, the cooling channel can comprise a hollow tube in fluid communication with a cooling fluid source.

[0023] In a nineteenth embodiment, the hollow tube of the eighteenth embodiment is not in contact with the first material.

[0024] In a twentieth aspect, the power source of any of the first to nineteenth aspects may be configured to provide three-phase variable amplitude and phase current to the edge director assembly.

[0025] In a twenty-first aspect, a first phase of the three-phase power source of the twentieth aspect may be connected to a first busbar assembly, a second phase of the three-phase power source of the twentieth aspect may be connected to a second busbar assembly, and a third phase of the three-phase power source of the twentieth aspect may be connected to a third busbar assembly.

[0026] In a twenty-second aspect, a method of forming a glass article is disclosed, the method including providing molten glass to a forming body including a first converging forming surface and a second converging forming surface opposite the first converging forming surface and an edge director assembly disposed at a first end of the forming body, the edge director assembly including a first edge director in contact with the first converging forming surface and a second edge director in contact with the second converging forming surface, each of the first edge director and the second edge director including an outward facing surface. The method further includes flowing molten glass over the converging forming surfaces of the forming body and the outward facing surfaces of the first edge director and the second edge director, heating the edge director assembly by passing an electric current through the edge director assembly, and drawing the molten glass from a bottom edge of the forming body.

[0027] In a twenty-third aspect, the current of the twenty-second aspect may include a three-phase current.

[0028] In a twenty-fourth aspect, a first busbar assembly is joined to a first edge director, a second busbar assembly is joined to a second edge director, and a third busbar assembly is joined to a joining edge joining the first edge director to the second edge director, and the method may further include supplying a first phase of the three-phase current to the first busbar assembly, supplying a second phase of the three-phase current to the second busbar assembly, and supplying a third phase of the three-phase current to the third busbar assembly.

[0029] In a twenty-fifth aspect, the method of the twenty-third aspect can further include varying a magnitude or phase angle of at least one phase of the three-phase current.

[0030] In a twenty-sixth aspect, the magnitude of the first phase of the twenty-fifth aspect of the twenty-fourth aspect can be different from at least one of the magnitude of the second phase or the magnitude of the third phase.

[0031] In a twenty-seventh aspect, the amplitude and phase of the current of the twenty-fourth aspect may be independent of the frequency of the current.

[0032] In a 28th aspect, the method of any of the 23rd to 27th aspects may include supporting the first and second busbar assemblies with a first and a second three-axis support assembly, respectively, each of the first and second three-axis support assemblies configured to support respective movement of the busbar assemblies along three orthogonal axes.

[0033] In a twenty-ninth aspect, the first triaxial support assembly of the twenty-eighth aspect can support a first portion of the third busbar assembly, and the second triaxial support assembly can support a second portion of the third busbar assembly.

[0034] The foregoing summary and the following detailed description present embodiments that are intended to provide an overview or framework for understanding the nature and character of the embodiments disclosed herein. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the present disclosure, and together with the description explain the principles and operation of the present disclosure. [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 is a schematic diagram of an exemplary glass manufacturing apparatus according to the present disclosure. [Diagram 2] FIG. 2 is a cross-sectional perspective view of an exemplary molded body showing a portion of an edge director assembly and a bus bar assembly. [Diagram 3] FIG. 2 is a perspective view of an exemplary edge director assembly and bus bar assembly shown without the molded body. [Figure 4] FIG. 1 is another perspective view of an example edge director assembly and bus bar assembly showing a cooling device attached to the bus bar assembly. [Diagram 5]FIG. 2 is an elevational cross-sectional view of an exemplary forming apparatus showing an edge director assembly and a bus bar assembly. [Figure 6] FIG. 2 is a cross-sectional view of a three-axis support assembly for supporting a busbar assembly. [Figure 7] FIG. 7 is a partial cross-sectional view of the three-axis support assembly of FIG. [Figure 8] 1 is a schematic diagram of an exemplary power supply circuit for powering an edge director assembly. [Figure 9] 9 is a simplified equivalent circuit of the circuit shown in FIG. 8. [Figure 10] FIG. 13 is a perspective view of another example edge director assembly and busbar assembly with the shaped body removed, configured to be heated with a single electrical phase. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Reference will now be made in detail to embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like elements. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0037] As used herein, the term "about" means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not, and need not be, exact, but are approximate and / or may be larger or smaller, as appropriate, to reflect tolerances, conversion factors, rounding, measurement errors, and other factors known to those of ordinary skill in the art.

[0038] Ranges can be expressed herein as from "about" one particular value, and / or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value to the other particular value. Similarly, when values ​​are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another embodiment. It will further be understood that the endpoints of each range are significant in relation to the other endpoint, and independently of the other endpoint.

[0039] Directional terms used herein, e.g., up, down, right, left, front, back, upper and lower, are merely indicated with reference to the illustrated figures and are not intended to imply absolute directions.

[0040] Unless expressly stated otherwise, the methods described herein are not intended to be construed as requiring that their steps be performed in a particular order, or as requiring a particular orientation of any apparatus. Thus, where a method claim does not actually recite an order that its steps are to be followed, or where any apparatus claim does not actually recite an order or orientation with respect to individual components, or where the claims or specification do not otherwise specifically recite that the steps are limited to a particular order, or where no particular order or orientation with respect to the components of the apparatus is recited, no order or orientation is intended to be inferred in any respect. This is true for all possible non-expressive bases for interpretation, including logical considerations regarding the arrangement of steps, operational flow, order of components, or orientation of components, general meaning derived from grammatical construction or punctuation, and the number or type of embodiments described in the specification.

[0041] As used herein, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Thus, for example, reference to "a" element includes aspects having two or more such elements unless the context clearly dictates otherwise.

[0042] The terms "exemplary," "example," or various forms thereof are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "exemplary" or "example" is not to be construed as preferred or advantageous over other aspects or designs. Moreover, the examples are provided merely for clarity and understanding and are not intended to restrict or limit in any way the disclosed subject matter or relevant portions of this disclosure. It can be appreciated that numerous additional or alternative examples of varying scope may be presented, but have been omitted for purposes of brevity.

[0043] As used herein, the terms "comprises" and "including," and variations thereof, unless otherwise indicated, are intended to be synonymous and open ended. A list of elements following the transitional phrase "comprises" or "including" is a non-exclusive list, and there may be elements in addition to the elements specifically listed in the list.

[0044] As used herein, the terms "substantial," "substantially," and variations thereof are intended to note that a described feature is equal or approximately equal to a value or description. For example, a "substantially planar" surface is intended to describe a surface that is planar or approximately planar. Furthermore, "substantially" is intended to indicate that two values ​​are equal or approximately equal. In some embodiments, "substantially" is intended to indicate values ​​that are within about 10% of each other, such as within about 5% of each other, or within about 2% of each other.

[0045] As used herein, a refractory material is a polycrystalline, multiphasic, inorganic, porous, heterogeneous, non-metallic inorganic material suitable as a component of an apparatus or system exposed to temperatures above 538° C. For example, the refractory material can include, but is not limited to, oxides of aluminum, silicon, magnesium, calcium, yttrium, and zirconium. The refractory material can include a binder material.

[0046] As used herein, an electrical bus (e.g., a busbar, a busbar section, a busbar segment, etc.) refers to a solid, rigid metallic member designed to carry electrical current between a power source and a load. In contrast, a cable designed to carry electrical currents of the magnitudes described herein comprises multiple wrapped (e.g., helically wound) metallic conductors (wires) housed within an electrically insulating jacket material.

[0047] 1 illustrates an exemplary glass manufacturing apparatus 10. The glass manufacturing apparatus 10 comprises a glass melting furnace 12 that includes a melting vessel 14. In addition to the melting vessel 14, the glass melting furnace 12 can optionally include one or more additional components, such as heating elements (e.g., combustion burners and / or electrodes) configured to heat and convert raw materials into molten material (hereinafter molten glass). For example, the melting vessel 14 can be an electrically boosted melting vessel that adds energy to the raw materials by both combustion burners and direct heating, where an electric current is passed through the raw materials, whereby the electric current adds energy by Joule heating of the raw materials.

[0048] The glass melting furnace 12 may include other thermal management devices (e.g., thermal insulation components) that reduce heat lost from the melting vessel. The glass melting furnace 12 may include electronic and / or electromechanical devices that facilitate melting the raw materials into a glass melt. The glass melting furnace 12 may include a support structure (e.g., a support chassis, support members, etc.) or other components.

[0049] The melting vessel 14 can be formed from a refractory material, such as a refractory ceramic material including alumina or zirconia, but may alternatively or in any combination include other refractory materials such as yttrium (e.g., yttria, yttria stabilized zirconia, yttrium phosphate), zircon (ZrSiO4), or alumina-zirconia-silica, or even chromium oxide. In some embodiments, the glass melting vessel 14 can be constructed of refractory ceramic bricks.

[0050] The glass melting furnace 12 can be incorporated as a component of a glass manufacturing apparatus configured to produce glass articles such as glass ribbons, although the glass manufacturing apparatus can be configured to form other glass articles, such as, but not limited to, glass rods, glass tubes, glass skins (e.g., glass skins for lighting devices such as light bulbs), and glass lenses. In some embodiments, the glass melting furnace 12 can be incorporated into a glass manufacturing apparatus that includes a slot draw apparatus, a float bath apparatus, a downdraw apparatus (e.g., a fusion downdraw apparatus), an updraw apparatus, a press apparatus, a rolling apparatus, a tube draw apparatus, or any other glass manufacturing apparatus that would benefit from the present disclosure. As an example, FIG. 1 illustrates the glass melting furnace 12 diagrammatically as a component of a fusion downdraw glass manufacturing apparatus 10 for fusion draw forming a glass ribbon and subsequently processing it into individual glass sheets or winding the glass ribbon onto a spool. As used herein, fusion draw forming involves flowing molten glass over sloping, e.g., converging, sides of a forming body, with the resulting streams of molten material meeting or "fusing" at the bottom of the forming body to form a glass ribbon.

[0051] Optionally, glass manufacturing system 10 may include an upstream glass manufacturing apparatus 16 positioned upstream of glass melting vessel 14. In some embodiments, a portion or all of upstream glass manufacturing apparatus 16 may be incorporated as part of glass melting furnace 12.

[0052] As shown in FIG. 1, the upstream glass manufacturing apparatus 16 can include a raw material storage bin 18, a raw material delivery device 20, and a motor 22 coupled to the raw material delivery device 20. The raw material storage bin 18 can be configured to store raw material 24 that can be fed to the melting vessel 14 of the glass melting furnace 12 through one or more feed openings, as indicated by arrow 26. Typically, the raw material 24 includes one or more glass-forming metal oxides and one or more modifiers. In some embodiments, the raw material delivery device 20 can be driven by the motor 22 to deliver a predetermined amount of raw material 24 from the storage bin 18 to the melting vessel 14. In another embodiment, the motor 22 can drive the raw material delivery device 20 to introduce the raw material 24 at a controlled rate based on a level of molten glass sensed downstream from the melting vessel 14 relative to the flow direction of the molten glass. The raw material 24 in the melting vessel 14 can then be heated to form molten glass 28. Typically, the raw material is added to the melting vessel as particulate matter, for example, as various "sands." The feedstock 24 may include scrap glass (i.e., cullet) from previous melting and / or forming operations. A combustion burner may be used to initiate the melting process. In an electrically boosted melting process, once the electrical resistance of the feedstock has been sufficiently lowered by the combustion burner, an electrical boost may be initiated by generating an electrical potential between electrodes placed in contact with the feedstock, which typically establishes an electrical current through the feedstock as it enters or is in a molten state.

[0053] The glass manufacturing system 10 may also include a downstream glass manufacturing system 30 positioned downstream of the glassmelting furnace 12 relative to a flow direction of the molten glass. In some embodiments, a portion of the downstream glass manufacturing system 30 may be incorporated as part of the glassmelting furnace 12. For example, a first connecting conduit 32, described below, or other portions of the downstream glass manufacturing system 30 may be incorporated as part of the glassmelting furnace 12.

[0054] The downstream glass production apparatus 30 may include a first conditioning chamber, such as a fining vessel 34, located downstream of the melting vessel 14 and coupled to the melting vessel 14 via the first connecting conduit 32 described above. In some examples, the molten glass 28 may be gravity fed from the melting vessel 14 to the fining vessel 34 via the first connecting conduit 32. The first connecting conduit 32 thus provides a flow path for the molten glass 28 from the melting vessel 14 to the fining vessel 34. However, other conditioning chambers may be positioned downstream of the melting vessel 14, for example, between the melting vessel 14 and the fining vessel 34. In some embodiments, a conditioning chamber may be employed between the melting vessel and the fining chamber. For example, the molten glass from the primary melting vessel may be further heated in a secondary melting (conditioning) vessel or cooled in the secondary melting vessel to a temperature lower than the temperature of the molten glass in the primary melting vessel before entering the fining chamber.

[0055] The gas bubbles can be removed from the molten glass 28 by a variety of techniques. For example, the raw material 24 can include a polyvalent compound (i.e., a fining agent), such as tin oxide, that undergoes a chemical reduction reaction when heated to release oxygen. Other suitable fining agents can include, but are not limited to, arsenic, antimony, iron, and / or cerium, although arsenic and antimony are toxic and may not be recommended for use in some applications for environmental reasons. The fining vessel 34 is heated, for example, to a temperature higher than the internal temperature of the melting vessel, thereby heating the fining agent to a reaction temperature sufficient for chemical reduction. Oxygen produced by the temperature-induced chemical reduction of one or more fining agents contained within the molten glass can diffuse into the gas bubbles generated during the melting process. The enlarged and now more buoyant gas bubbles then rise to the free surface of the molten glass in the fining vessel and are then evacuated from the fining vessel, for example, through a vent tube in fluid communication with the atmosphere above the free surface.

[0056] The downstream glass production apparatus 30 may further include another conditioning chamber, such as a mixing device 36, e.g., a stirred bed vessel, to mix the molten glass flowing downstream from the fining vessel. The mixing device 36 may be used to reduce chemical and / or thermal inhomogeneities that may be present in the molten glass exiting the fining vessel by providing a homogenous glass melt composition. As shown, the fining vessel 34 may be coupled to the mixing device 36 via a second connecting conduit 38. Thus, the molten glass 28 may be gravity fed from the fining vessel 34 to the mixing device 36 via the second connecting conduit 38. Typically, the molten glass in the mixing device 36 includes a free surface, with a free (e.g., gas) volume extending between the free surface and the top of the mixing device. Although the mixing device 36 is shown downstream of the fining vessel 34 with respect to the flow direction of the molten glass 28, in other embodiments, the mixing device 36 may be positioned upstream of the fining vessel 34. The downstream glass manufacturing equipment 30 can include multiple mixing devices, such as a mixing device upstream from the fining vessel 34 and a mixing vessel downstream from the fining vessel 34. When multiple mixing devices are used, they can be of the same design or of different designs. One or more of the vessels and / or conduits disclosed herein can include static mixing vanes positioned therein to further promote mixing and subsequent homogenization of the molten materials.

[0057] The downstream glass manufacturing apparatus 30 may further include another conditioning chamber, such as a delivery vessel 40 located downstream of the mixing device 36. The delivery vessel 40 may function as an accumulator and / or flow control device to provide a consistent flow of the molten glass 28 to the forming body 42 via an outlet conduit 44. In some embodiments, the molten glass in the delivery vessel 40 may include a free surface from which a free volume extends upwardly to the top of the delivery vessel. As shown, the mixing device 36 may be coupled to the delivery vessel 40 via a third connecting conduit 46, and the molten glass 28 may be gravity fed from the mixing device 36 to the delivery vessel 40 through the third connecting conduit 46.

[0058] The downstream glass manufacturing apparatus 30 may further include a forming apparatus 48 configured to form a glass article, e.g., a glass ribbon. Thus, the forming apparatus 48 may comprise a downdraw apparatus, such as an overflow downdraw apparatus, with the outlet conduit 44 arranged to deliver the molten glass 28 from the delivery vessel 40 to an inlet conduit 50 of the forming body 42. The forming body 42 of the fusion downdraw glass manufacturing apparatus may include a trough 52 positioned on an upper surface of the forming body and opposing converging forming surfaces 54 that converge in a drawing direction 56 along a lower end (root) 58 of the forming body 42. Molten glass delivered to the forming body trough 52 via the delivery vessel 40, the outlet conduit 44, and the inlet conduit 50 overflows the sidewall of the trough 52 and descends along the converging forming surfaces 54 as separate streams of molten glass. The separate streams of molten glass join below and along the root 58 to produce a ribbon of molten glass that is drawn from the root 58 in a drawing direction 56 by applying a downward tension to the molten glass ribbon, such as by gravity and counter-rotating opposing drawing rolls 62. The applied downward tension and the temperature of the molten glass can be used to control the dimensions of the glass ribbon as the molten glass cools and its viscosity increases. Thus, the molten glass ribbon undergoes a viscosity transition from a viscous state, through a viscoelastic state, to an elastic state, and acquires mechanical properties that give the glass ribbon 60 stable dimensional properties. The molten glass ribbon 60 can then be scored and divided into shorter lengths, such as glass sheets 64. Alternatively, the glass ribbon 60 can be wound up. The glass reboscoring apparatus 66 can include a scoring tool 68, a backing bar 70 (e.g., anvil) positioned opposite the scoring tool on an opposite side of the glass ribbon, and one or more nosing members 72 that can be applied to a surface of the glass ribbon to control the movement of the glass ribbon during the scoring operation. The glass ribbon scoring apparatus 80 can include a gantry (not shown) capable of vertical motion along the drawing direction at the drawing speed. The glass sheet can be removed from the glass ribbon by a robot 74.For example, the robot 74 can bend the glass ribbon at cuts to separate the glass ribbon along the cuts to form glass sheets.

[0059] The components of the downstream glass manufacturing equipment 30, including any one or more of the connecting conduits 32, 38, 46, the fining vessel 34, the mixing device 36, the delivery vessel 40, the outlet conduit 44, or the inlet conduit 50, may be formed from a precious metal. Suitable precious metals include platinum group metals selected from the group consisting of platinum, iridium, rhodium, osmium, ruthenium, and palladium, or alloys thereof. For example, the downstream components of the glass manufacturing equipment may be formed from a platinum-rhodium alloy including about 70% to about 90% platinum and about 10% to about 30% rhodium by weight.

[0060] The forming apparatus 48 may further include an enclosure 80, in which the forming body 42 is disposed. The enclosure 80 is configured to aid in maintaining a controlled thermal environment for the glass ribbon as it undergoes a viscosity transition. The enclosure 80 may be a single enclosure or may include multiple sections. For example, the enclosure 80 may include an upper section that houses the forming body 42 and one or more lower sections. A door and / or gate (not shown), often horizontally slidable, may be provided between the upper and lower section(s) to mitigate cooling of the upper environment, for example, from heated air (e.g., stack effect) or upward drafts caused by cooler downstream equipment.

[0061] The enclosure 80 may be formed of refractory materials such as silicon carbide, alumina, and zircon, but may additionally or alternatively include metal components, such as various steel beams, trusses, wall panels, and refractory insulating panels configured to further control the thermal environment within the enclosure. The enclosure 80 may further include a number of thermal elements 82, such as heating and / or cooling elements disposed within the enclosure, for example along the enclosure walls, for heating the forming body and the molten glass therein and for cooling the glass ribbon drawn from the forming body. The heating elements may be coil and / or rod shaped electrical resistance heating elements. The cooling elements may include cooling tubes through which a cooling fluid flows. The glass article (e.g., glass ribbon) formed by the forming body 42 is drawn downwardly through the enclosure 80 and conditioned by a predetermined and carefully controlled temperature profile induced by the multiple thermal elements, which is selected to reduce residual stresses in the glass ribbon that may affect the shape of the glass ribbon.

[0062] As the molten glass 28 flows over the converging forming surfaces 54 and descends from the root 58 of the forming body 42, it contracts laterally in a direction perpendicular to the draw direction 56. This lateral contraction reduces the width of the glass ribbon drawn from the forming body 42. To mitigate the lateral contraction, a first edge director assembly 100a is attached to the forming body 42 at a first end of the forming body and a second edge director assembly 100b is attached to the forming body 42 at a second end of the forming body 42. The edge director assemblies 100a, 100b increase the surface area of ​​the converging forming surfaces 54, effectively increasing the length of the root 58, thereby combating the lateral contraction. Each of the edge director assemblies 100a, 100b comprises a pair of plowshares extending along at least a portion of the length of the forming body. Each edge director assembly 100a, 100b includes two opposing edge directors positioned on either side of the forming body, for a total of two edge director assemblies and four edge directors. A pair of opposing edge directors on either side of the forming body at an end of the forming body are attached to each other to form an edge director assembly. Thus, a first edge director assembly 100a is positioned at the inlet end of the forming body (where the molten glass enters the forming body from the inlet conduit 50) and a second edge director assembly 100b is positioned at the opposite end of the forming body. Although a single edge director assembly 100a located at a first end of the forming body 42 is described below, a second edge director assembly positioned at the opposite second end of the forming body can be substantially similar to the first edge director assembly.

[0063] FIGURE 2 is a perspective view of one end (e.g., the inlet end) of forming body 42 showing a first edge director assembly 100a (only one edge director of the edge director assembly is shown), and FIGURE 3 is a perspective view of edge director assembly 100a showing a pair of opposing edge directors, but with the forming body removed for clarity. That is, edge director assembly 100a comprises a first edge director 102a positioned against a first converging forming surface 54a and a second edge director 102b positioned against a second converging forming surface 54b. First edge director 102a contacts first converging forming surface 54a and comprises a first curved outward facing surface 104a, while second edge director 102b contacts second converging forming surface 54b and comprises a second curved outward facing surface 104b. The first and second edge directors 102a, 102b may further include dams 106a, 106b, respectively, that extend at approximately 90 degrees relative to the forming body 42 (e.g., the converging forming surface 54). The dams 106a, 106b prevent the molten glass from spilling over the edge director assembly. As shown in FIG. 2, the dams 106a, 106b may form part of an end cap 108 positioned over the inlet end of the forming body 42.

[0064] The first and second curved outward surfaces 104a, 104b may be, for example, frustoconical surfaces. The edges of the opposing first and second edge directors 102a, 102b facing inward toward the center of the forming body are joined, for example, by welding, thereby forming a joining edge 112 positioned below the root 58. The first and second bottom edge portions 114a, 114b of the first and second edge directors 102a, 102b may be thickened, for example, by laminating (e.g., welding) additional material to the edge directors, so that the bottom edge portion of each edge director is thicker than the remaining upper portion of each edge director. The joining edge 112 may include first and second thickened bottom edge portions 114a, 114b. That is, the joining edge 112 may be formed by the intersection of the thickened bottom edge portions of each edge director.

[0065] As the molten glass flows down the forming body 42 and over the outwardly facing surfaces 104a, 104b of the first and second edge directors 102a, 102b, the temperature of the molten glass drops and the viscosity increases. All glasses are unstable to one or more crystalline compounds. Given the appropriate temperature transitions, the glass will crystallize. Nucleation and crystal growth are required. The kinetics of nucleation are related to the free energy of formation of a small domain of glass and the transport of atoms to and from that domain. Above a certain critical size, the interfacial energy becomes unimportant and crystal growth can proceed by an interfacial diffusion process. The kinetics of both parts of this process depend on the magnitude of undercooling (T L -T), where T L is the liquidus temperature of the molten glass, and T is the current temperature of the molten glass. The liquidus temperature is the temperature above which the melt remains liquid, and represents the maximum temperature at which crystals can coexist with the melt. In both cases, the competing properties of the thermodynamic driving force, which increases with increasing supercooling, and the diffusion term, which decreases with increasing supercooling, make T L The rate of nucleation and crystal growth is greatest at temperatures below 0.1° C. If the temperature of the molten glass falls below its liquidus temperature and the molten glass remains at that temperature for a sufficient time, crystallization can occur.

[0066] The accidental or uncontrolled formation of crystals in a glass is known as devitrification, and the crystal growth is often referred to as "debits." Debits can be detrimental to the optical and mechanical properties of the glass. In some glasses, the nucleation and crystal growth rate curves are nearly identical, resulting in uniform nucleation and crystal growth over a wide temperature range. In more stable glasses, the combination of high viscosity and low diffusion coefficient at the liquidus temperature eliminates the concern of uniform nucleation. However, non-uniform nucleation can occur at surfaces where impurity particles or other discontinuities are present. Thus, the combination of long residence times at the molten glass-edge director interface and temperatures below the liquidus temperature of the molten glass can lead to the accumulation of debits along the edge director, especially the lower edge (e.g., bottom edge) of the edge director and the lower portion of the dam. Heating the debit to a temperature above the liquidus temperature can return the debit to solution in the molten glass and / or prevent the formation of debits.

[0067] A thermal element 82, such as a resistive heating element, may be positioned along the central portion of the forming body 42 near the root 58 of the forming body and arranged to heat the root 58 of the forming body 42. Such heating elements have been found to be effective in preventing debits along the root. However, the edge director assembly is positioned near the coldest portion of the forming body, i.e., at the end of the forming body closest to the end wall of the housing 80, and while various heating devices have been used to heat the edge directors by radiant heating, such heating devices have limitations, particularly the concentration of other forming equipment near the ends of the forming body, which can prevent effective placement of the heating elements and radiant effectiveness. These other devices have difficulty directing heat to the edge directors, especially the lower edges of the edge directors where debits are most likely to form, and are not completely effective in preventing debits. Debits can cause defects in the glass ribbon and prevent the growth of a stable ribbon edge (bead). The debits can also impede the relief of lateral shrinkage, thereby increasing ribbon attenuation and reducing usable ribbon width. Furthermore, if crystal growth is allowed to continue, pieces of the debit can break off from the edge director and become wrapped around the glass ribbon, forming defects therein.

[0068] To overcome the limitations caused by radiative heating of the edge directors, busbar assemblies are attached to the edge director assemblies and configured to pass electrical current through the edge director assemblies, particularly through the thickened bottom edge portions. A first busbar assembly 200a is attached to the first thickened bottom edge portion 114a of the first edge director 102a, and a second busbar assembly 200b is attached to the second thickened bottom edge portion 114b of the second edge director 102b. A third busbar assembly 200c is attached to the joining edge 112 between the first edge director 102a and the second edge director 102b (e.g., behind the joining edge 112), more particularly at the intersection of the two opposing thickened bottom edge portions 114a, 114b.

[0069] As can be seen in FIG. 4, the first busbar assembly 200a includes a first busbar 202a formed of a first metal and a second busbar 204a formed of a second metal. A first end 206a of the first busbar 202a can be joined, for example, by welding, to the first thickened bottom edge portion 114a of the first edge director 102a. The first busbar 202a can be formed of the same metal as the first edge director 102a. For example, the first metal can include platinum. The first metal can be formed of a platinum alloy, such as a platinum-rhodium alloy including about 70 to about 90 weight percent platinum and about 10 to about 30 weight percent rhodium. However, alternatively or additionally, other platinum group metals can be used, such as ruthenium, palladium, osmium, iridium, or alloys thereof (e.g., alloys with either or both of platinum and rhodium). Other high temperature metals useful for such applications may include molybdenum, titanium, tungsten, or tantalum, which are typically used as alloy metals. The second end 208a of the first busbar 202a may be joined to the first end 210a of the second busbar 204a, for example, by welding. The second busbar 204a is spaced from the first edge director 102a and is positioned entirely or primarily outside the housing 80, as described below, and may be formed from a second metal (e.g., a metal different from the first metal) that has a lower heat resistance compared to the first busbar 202a, such as nickel, copper, silver, alloys thereof, or other metals suitable for the associated operating temperature and expected current carrying capacity. Unless otherwise specified, the first metal and second metal as used herein refer to the first metal and second metal described for at least the first busbar 202a and the second busbar 204a. The joining of the first busbar 202a and the second busbar 204a forms a first boundary 212a between the first busbar 202a and the second busbar 204a, for example between the first metal and the second metal of the first busbar assembly 200a.

[0070] Similarly, the second busbar assembly 200b includes a third busbar 202b formed from a first metal and a fourth busbar 204b formed from a second metal. A first end 206b of the third busbar 202b, arranged similarly to the first busbar assembly 200a, is joined to the second edge director 102b, e.g., to the second thickened bottom edge portion 114b, and a second end 208b of the third busbar 202b is joined to a first end 210b of the fourth busbar 204b. The joining of the third busbar 202b and the fourth busbar 204b forms a second boundary 212b between the third busbar 202b and the fourth busbar 204b, e.g., between the first metal of the third busbar 202b and the second metal of the fourth busbar 204b. The third bus bar 202b can be formed from the same metal as the second edge director 102b, e.g., the same first metal as the first bus bar 202a, and the fourth bus bar 204b, spaced from the second edge director 102b, can be formed from the same second metal as the second bus bar 204a.

[0071] The third busbar assembly 200c includes a central busbar 214 joined, such as by welding, to the joining edge 112 (e.g., at the intersection of the first and second thickened bottom edge portions 114a, 114b) between the first edge director 102a and the second edge director 102b. The first and second branch busbars 216a, 216b extend outwardly from the central busbar 214 and are joined, such as by welding, to the central busbar 214. For example, the first and second branch busbars 216a, 216b can extend in opposite directions, such as orthogonal to the central busbar 214, although other angles are contemplated. That is, the first branch busbar 216a can be disposed 180 degrees from the second branch busbar 216b. For example, the central busbar 214, the first branch busbar 216a, and the second branch busbar 216b may form a "T" shape. The central busbar 214 may be formed from a first metal, such as the first metal of the first busbar 202a. The first branch busbar 216a may further comprise a first busbar segment 218a and a second busbar segment 220a, where the first busbar segment 218a comprises a first metal and the second busbar segment 220a comprises a second metal. The first busbar segment 218a is joined at one end to the central busbar 214 and at an opposite end to the second busbar segment 220a, such as by welding. The joining of the first busbar segment 218a and the second busbar segment 220a forms a third boundary 212c between the first busbar segment 218a and the second busbar segment 220a, e.g., between the first metal and the second metal.

[0072] Similarly, the second branch busbar 216b can include a third busbar segment 218b including a first metal and a fourth busbar segment 220b including a second metal. The third busbar segment 218b is joined, such as by welding, at one end to the central busbar 214 and at an opposite end to the fourth busbar segment 220b. The joining of the third busbar segment 218b to the fourth busbar segment 220b forms a fourth boundary 212d between the third busbar segment 218b and the fourth busbar segment 220b, e.g., between the first metal and the second metal.

[0073] Thus, edge director assembly 100a, first bus bar assembly 200a, second bus bar assembly 200b, and third bus bar assembly 200c may be joined, such as by welding, to form an integral direct heating assembly 300 that is attached to formed body 42. Although not shown in FIGS. 3 and 4, direct heating assembly 300 may include end caps 108.

[0074] 5, while the molded body 42 and edge director assembly 100a (and edge director assembly 100b) are positioned within the housing 80, the first busbar assembly 200a, the second busbar assembly 200b, and the third busbar assembly 200c may extend from the edge director assembly 100a through an opening in the housing 80 from inside the housing 80 to outside the housing 80 to facilitate connection to a power source. That is, at least a portion of each of the first busbar assembly 200a, the second busbar assembly 200b, and the third busbar assembly 200c may extend through an opening in the housing 80 to an environment external to the housing. At least a portion of the first branch busbars 216a of the first busbar assembly 200a and the third busbar assembly 200c may be positioned as busbar pairs 222 extending outwardly from the molded body 42, for example, perpendicular to the respective converging molded surfaces. Similarly, at least a portion of the second branch busbars 216b of the second busbar assembly 200b and the third busbar assembly 200c may be arranged as busbar pairs 224 extending outwardly from the formed body 42, e.g., in an opposite direction from the first busbar assembly 200a and the first branch busbar 216a, e.g., perpendicular to the opposing converging formed surfaces. Thus, the first busbar pair 222 may extend from the first edge director 102a (e.g., the first busbar assembly 200a and a portion of the first branch busbar 216a), and the second busbar pair 224 may extend from the second edge director 102b. The openings through which each busbar pair extends are sized to permit movement of the busbar pairs 222, 224, e.g., along three orthogonal axes.

[0075] Temperature changes within the housing 80, such as during heating up of the top of the housing 80 and the forming body therein, can cause dimensional changes in the forming body 42. That is, the forming body can undergo thermal expansion and / or contraction due to temperature changes within the housing, either as a result of planned temperature changes (e.g., start-up or shutdown of the glass manufacturing process) or unplanned temperature changes (e.g., power loss). Because the edge director assemblies are attached to the forming body and the respective edge directors can be joined to form a unitary structure, movement of the forming body due to, for example, thermal expansion or contraction, will cause associated movement of the direct heating assembly 300, and more particularly, associated movement of the associated bus bar assembly relative to the housing. If the bus bar assembly is constrained and cannot move with the forming body, stresses can be placed on the forming body, edge director assembly, and / or bus bar assembly. If the bus bar assembly cannot move with the forming body, damage can occur to any one or more of the edge director assembly, bus bar assembly, or forming body. Thus, the openings through which the busbar pairs pass can be filled with deformable insulation 230, e.g., a fire-resistant insulation that can accommodate movement of the busbars. As used herein, a deformable insulation is an insulation that flexes when pressed against the edge director assembly, but returns to its original position when pressure is released. For example, the deformable insulation can include fire-resistant wool (e.g., a fibrous fire-resistant material) that is inserted into the housing openings through which the busbar assemblies pass and surrounds the busbars within the openings, although other forms of fire-resistant insulation that are deformable or otherwise capable of accommodating horizontal and / or vertical movement of the busbars in which they are disposed can also be used.

[0076] Additionally, each busbar pair 222, 224 may be supported by a three-axis support assembly configured to accommodate movement of the edge director assembly along any of three mutually orthogonal axes. For example, the first busbar pair 222 may be supported by a first three-axis support assembly 240a, and the second busbar pair 224 may be supported by a second three-axis support assembly 240b. While FIG. 6 illustrates the first three-axis support assembly 240a, it should be understood that the second three-axis support assembly 240b may be similar or identical to the first three-axis support assembly 240a. Each three-axis support assembly may be configured to move along three mutually orthogonal axes (X-axis, Y-axis, and / or Z-axis), and the three-axis support assemblies couple the busbar assemblies to suitable structural supports, such as the building steel structure and / or supporting steel structure of the housing 80. For example, the three-axis support assemblies may comprise a linear slide on which the stage is disposed. The three axes of the first and second three-axis support assemblies 240a, 240b can be arranged, for example, along two orthogonal horizontal axes (e.g., X-axis and Y-axis) and a vertical axis (Z) orthogonal to both the X-axis and Y-axis. With reference to Fig. 6, the first three-axis support assembly 240a can include a pedestal 242, a first rail 244, and a first stage 246 configured to slide along the rail 244 in a first direction, for example, in and out of the page of Fig. 6, represented by an X with a dot at the intersection and further represented as the + / -Y direction. The first three-axis support assembly 240a can further include a second stage 248 configured to slide along a second rail 250 in a second direction, represented by an arrow labeled + / -X, orthogonal to the first direction. The triaxial support assembly 240a may further include a frame 252 coupled to the second stage 248, the frame 252 supporting a pair of spring-loaded cradles (e.g., yokes or other coupling devices) configured to engage the first busbar pair 222 along a + / -Z axis that is orthogonal to the + / -X and + / -Y axes. For example, as shown in FIG. 6, a first cradle 256a of the first triaxial support assembly 240a may support the first busbar assembly 200a, and a second cradle 256b may support a portion of the third busbar assembly 200c.In that case, the first and second cradles 256a, 256b may be supported by first and second springs 258a, 258b that are used to support and counteract the weight of the respective bus bars coupled to the cradles.

[0077] The first and second triaxial support assemblies 240a, 240b may include a tilting feature. During operation, it may be necessary from time to time to tilt the forming body 42, e.g., rotate the forming body about its longitudinal (vertical) axis, to adjust the flow of molten glass on the opposite converging forming surfaces of the forming body. Because the edge director assemblies are attached to the forming body and the busbar assemblies extend outwardly from the forming body (e.g., perpendicular to the longitudinal axis of rotation of the forming body), the busbar assemblies necessarily tilt as the forming body rotates. The triaxial support assemblies may be configured to accommodate the tilt angle imposed on the busbar assemblies by the forming body without stressing the edge director assemblies or the formed article body. Thus, the triaxial support assemblies may be provided with a tilting feature. For example, as shown in FIG. 7, the first and second springs 58a, 258b of the first triaxial support assembly 240a may be coupled to a platform 260 coupled to the frame 252 at a hinge 262 to facilitate tilting of the cradles 256a, 256b. However, other mechanisms may be used to provide the tilt function. The first triaxial support assembly 240a may be provided with a threaded adjustment screw 264. The adjustment screw may be provided with a vernier scale to provide accurate and repeatable tilting of the platform 260 and the cradles 256a, 256b. The busbar assemblies are electrically isolated from the respective triaxial support assemblies. For example, the cradles 256a and 256b may be formed from an electrically insulating material and / or may include a non-conductive material between the cradle and the respective busbar(s).

[0078] As mentioned above, the enclosure 80 is a temperature controlled enclosure with multiple thermal elements to maintain the forming body 42 and the molten glass therein at a temperature consistent with the desired forming viscosity of the molten glass. These temperatures can exceed 1000°C at the top of the enclosure housing the forming body 42. Accordingly, the portions of the busbar assemblies 200a, 200b, 200c exposed to such high temperatures can be formed from a high temperature resistant material, such as a material containing platinum (e.g., a platinum alloy such as platinum-rhodium). On the other hand, the portions of the busbar assemblies 200a, 200b, 200c located away from such temperatures can be formed from a material that is less resistant to high temperatures (e.g., has a lower melting point), such as a material containing nickel. The less heat resistant components can be actively cooled to maintain them within a safe operating temperature range. Accordingly, the second busbar 204a, the fourth busbar 204b, the second busbar segment 220a, and the fourth busbar segment 220b may include cooling elements 232 coupled thereto. For example, such cooling elements 232 may comprise cooling tubes configured to pass a cooling fluid through the second busbar 204a, the fourth busbar 204b, and the second and fourth busbar segments 220a, 220b to reduce the temperature of the second busbar 204a, the fourth busbar 204b, and the second and fourth busbar segments 220a, 220b. A suitable cooling fluid may be water, although other cooling fluids may also be used. The cooling elements 232 may be clamped to the respective busbar assemblies, but are typically welded in place to provide good thermal conduction between the cooling tubes and the respective busbar assemblies.

[0079] The busbar assembly can be positioned such that the second material included in the busbar assembly (e.g., second busbar 204a, fourth busbar 204b, and first and second busbar segments 218a, 220a) is not exposed to the high temperature environment within the forming housing. Due to the high temperature of the molten glass flowing into and out of the forming body 42, components of the molten glass, such as boron, can evaporate from the molten glass into the surrounding environment, and the volatile components can condense on cooler surfaces. To prevent condensation of volatiles on the busbar assembly, particularly on cooled portions of the busbar assembly, the busbar assembly can be configured such that an interface between the first material (e.g., platinum-containing material) and the cooled second material (e.g., nickel-containing material) of the busbar assembly is located outside the internal environment within the housing 80. For example, the interface between the first material and the second material can be located within a refractory insulation, such as a deformable refractory insulation. A portion of the cooling tube 232 will extend into the deformable insulation but will not be exposed within the enclosure.

[0080] As shown in FIGS. 3 and 4, a first busbar assembly 200a is joined to the first thickened bottom edge portion 114a of the first edge director 102a, a second busbar assembly 200b is joined to the second thickened bottom edge portion 114b of the second edge director 102b, and a third busbar assembly 200c (e.g., central busbar 214) is joined to the first and second thickened bottom edge portions 114a, 114b of both the first and second edge directors 102a, 102b to join the two edge directors, i.e., forming a joining edge 112. That is, current is supplied to the edge director assembly 100 through four current paths, namely, two current paths formed by the first and second bus bar assemblies 200a, 200b, and two current paths formed by the first and second branch bus bars 216a, 216b of the third bus bar assembly 200c.

[0081] The first and second busbar assemblies 200a, 200b are electrically connected to a power source configured to provide current to the first and second busbar assemblies 200a, 200b, and thus the edge director assembly 100. The power source provides three-phase current, the three phases being referred to herein as phase A, phase B, and phase C. The first busbar assembly 200a is provided with a first current phase (e.g., phase A, phase B, or phase C), the second busbar assembly 200b is provided with a second current phase that is different from the first current phase provided to the first busbar assembly 200a, and the third busbar assembly 200c is provided with the remaining current phases that are different from the current phases provided to the first and second busbar assemblies 200a, 200b. For purposes of explanation and not limitation, the current phase supplied to the first busbar assembly 200a is designated as phase A, the current phase supplied to the second busbar assembly 200b is designated as phase C, and the current phase supplied to the third busbar assembly 200c is designated as phase B.

[0082] Phase A of the power source 250 is provided to the second bus bar 204a of the first bus bar assembly 200a via a first power cable 252 connected between the power source 250 and the second bus bar 204a. Phase C of the power source 250 is provided to the fourth bus bar 204b via a second power cable 254 connected between the power source 250 and the fourth bus bar 204b. Phase B is connected to the first branch bus bar 216a via a third power cable 256 and also to the second branch bus bar 216b via a fourth power cable 258. For example, the third power cable 256 can connect to the second bus bar segment 220a and the fourth power cable 258 can connect to the fourth bus bar segment 220b.

[0083] When electrical current is applied, the edge director assembly 100 heats up by Joule heating. This type of heating is referred to as direct heating because the current passing through the edge director assembly resistively heats the edge director assembly itself, rather than the edge director being heated by radiation from one or more heating elements external to the edge director. That is, the heating of the edge director assembly occurs as a result of the current passing through the metal of the edge director and the electrical resistance of that metal. Additionally, because the first, second, and third bus bar assemblies 200a, 200b, and 200c are connected to the first and second thickened bottom edge portions 114a, 114b of the edge director assembly, the bottom edge portions heat to a higher temperature than the rest of the edge director assembly, thereby directing heat to the areas of the edge director most prone to accumulating debits.

[0084] The edge director assembly 100a may be supplied with alternating current (AC) from a suitable power system, such as power system 400. For example, the power system may include a power source 402 that supplies power to a primary side of a transformer 404, such as a Δ:Δ (delta:delta) transformer. The secondary side of the transformer 404 is connected to a floating wye load, such as the edge director assembly 100a, shown as an electrical resistance, as shown in FIG. 8. The power source and the load are not electrically grounded.

[0085] The power system may employ a digital power supply 402, such as an AFX3000 series power supply manufactured by Pacific Power Source. Digital power supplies can produce high power outputs with precise waveforms and may include multiple parallel modules, each capable of generating a maximum rated three-phase or single-phase current output over a wide range of voltages, such as from about 5V to about 120Vac. For voltages between 120 and 300Vac, the output may be current limited.

[0086] The power supplies described herein can provide a sinusoidal output waveform. Additionally, the power supplies can be capable of generating waveforms that can be defined by a digital input file. The output frequency can be in the range of about 15 Hertz (Hz) to about 1200 Hz in the absence of voltage limitations, and up to about 3000 Hz in the presence of any voltage limitations.

[0087] The power system can be operated as a three-phase resistive heater with the edge director assemblies themselves functioning as heating elements so that the actual power dissipated on both sides of the edge director assemblies (e.g., right and left edge directors) can be equalized or directly controlled. However, in practical applications it has been found that the actual power passing through the three busbar assemblies is generally not equal. It is often the case that these loads are clearly real (e.g., Z Pt =R+j0), the current term can be derived from the resistance form of Ohm's law:

[0088]

number

[0089] Here, the subscripts L-Pt and R-Pt refer to the right and left edge directors of the edge director assembly, i a and i c and Z refer to the individual phase currents of phase A and phase C, respectively. This circuit can be simplified by reflecting the load impedance to the primary side of the transformer as shown in Figure 9. The phase impedances are Z a , Z b , Z c It is expressed as:

[0090] Since the power system is assumed to be unbalanced, the currents resulting from the input voltages can be found using mesh analysis. Phase currents i a , i b , and i ccan be expressed in terms of mesh currents I1 and I2 by applying Kirchhoff's current law at node n (see FIG. 9).

[0091]

number

[0092] Applying Kirchhoff's voltage law to each loop in the mesh gives us the matrix equation for I1 and I2: a =I1 and i c Note that I = -I2 are independent, the circuit can be designed such that the load to be controlled is assigned to phase A and phase C as per equation 3, resulting in:

[0093]

number

[0094] where Z is the impedance matrix defined by the circuit elements such as sources, lines, and loads, I is the vector of mesh currents, and V is the phase-to-phase differential voltage, i.e.,

[0095]

number

[0096] The variables Z, I, and V can be defined as phasor variables. For example:

[0097]

number

[0098] Here, φ an is the phase angle, V an is the magnitude of the phasor. a and i c Substituting, we get the following:

[0099]

number

[0100] In traditional three-phase power systems, the voltage magnitude and phase angle are fixed by the power source, usually a utility, and the user has little ability to change them. In a balanced three-phase system, the voltage input, load impedance, and phase currents are all identical, making analysis simple. However, in today's unbalanced systems (where magnitude and phase angle can vary), the digital power source can only determine the magnitude of the phase voltages, V an , V bn , and V cn , and the phase angle φ an , φ bn , φ cn Since we can control for , this results in an indeterminate problem with two equations and potentially six unknown variables.

[0101] If the voltage V and impedance Z matrices are fully defined, i.e., all magnitudes and phases are known, then the mesh currents I1 and I2 can be determined by:

[0102]

number

[0103] Once the mesh currents are known, the phase current i a , i b , i c Since the voltages can be specified arbitrarily, a control system can be implemented that drives the phase currents to desired values ​​by adjusting the voltage input definition, resulting in variable amplitude three-phase sinusoidal control of the system that is frequency independent.

[0104] The power supply 402 may include a controller 406, such as a proportional-integral (PI) controller. The control parameters may include a balance control parameter. The control parameters may include a bias control parameter. The control parameters may further include a level control parameter. Each control parameter may be associated with an error function that is the difference between a user-defined set point and a current value for the respective control parameter. Each error function may be used to adjust the value of the control parameter associated with that error function.

[0105] An example controller 406 can be configured as follows: In the following controller description, phase A will be used as the primary reference and the other phases will be controlled relative to phase A.

[0106] Referring to Figure 8-9, the goal of balance control is to balance the right-side resistive load R R-pt and the left resistive load R L-pt (e.g., opposing edge directors of an edge director assembly), which is a |=|i c Therefore, the balance function Δi bal is the phase current i a and i c It can be defined as the difference between

[0107] User-defined balance control setting value Δi ba1,setpt Given, the power balance error function ε bal is the balance control setting value and the balance function Δi bal It can be defined as the difference between

[0108] When using the proportional-integral (PI) control method, the error function u bal It is possible to formulate a power balance control parameter that is proportional to the mesh current and the phase current. a and I2 = i c In the case of , the power balance control parameter u balcan be applied antisymmetrically to the phase voltages.

[0109] Bias function Δi bias Using the phase current i a Phase current i b It is possible to control the magnitude of the difference between the A phase current and the B phase current.

[0110] Similar to the formulation of balance control, the error function ε is defined as the difference between the user-defined bias setting value and the bias function (e.g., the current difference between phase A and phase B). bias Again, by using the proportional-integral (PI) control method, the bias control parameter u, which is proportional to the balance error function and the bias function, can be calculated using the quadratic gain function b1. bias The bias control can be applied in parallel with the balance control.

[0111] Based on the balance control and bias control, the magnitude of the current |i a | can be adjusted.

[0112] The formulation of the level control parameters proceeds in the same way as the balance control and bias control. The level control involves adjusting the magnitude of the current in phase A. Since the power system is a three-phase continuous conduction system, a change in one phase affects the power allocation of all phases. Here, the level error function ε level is the magnitude of phase A current |i a | and a user-defined level setting L setpt This is the difference between...

[0113] Then, the associated PI level control parameter u level is proportional to the level error function via a second quadratic gain function b2. In this case, the level control u level acts on all phases simultaneously to maintain a specific power ratio once the balance and bias control parameters have converged. Thus, the level control parameter u level Using the master voltage gain parameter k Vcan be adjusted.

[0114] The power supplies used in the above system can be used to generate a steady-state output response. The control schemes described herein are designed to drive the system towards a desired operating condition and maintain it there even in the presence of external perturbations. The dynamics associated with the power system can be handled internally within the power supply, leaving only the input commands to the user. Because the PI controller only provides local stability, the initial voltage conditions must be manually specified and reasonably close to the controlled equilibrium state before control begins.

[0115] The power supply may include built-in functionality that can be utilized to achieve this control scheme, or such functionality may be applied externally. In either case, the control may be performed by a suitable controller, with the control parameters implemented through software. A PI controller may include features, circuitry, logic, means, or instructions for controlling the current provided to the busbar assemblies via the control parameters of balance, bias, and level. The controller comprises a processor communicatively coupled to a non-transitory memory storing computer readable and executable instructions that, when executed by the processor, facilitate operation of the power supply.

[0116] An operating voltage and current limit can be specified for each phase of the power output. The primary control method can be determined by the proximity of the output to one of these limits. If the input phase voltage results in a current that exceeds the specified operating limit, that phase can operate in a current control mode, thereby adjusting the phase voltage internally to produce the specified current limit.

[0117] To accomplish this, phase limit currents can be explicitly specified before the controller begins to regulate. Proportional control can then be applied to each phase voltage until the limit current is reached. Once each phase is driven to its limit current, a new voltage can be assigned to the voltage setpoint variable. The controller will increase the voltage until the limit current is reached, and if the resulting current exceeds the phase limit current, the power supply can automatically reduce the voltage.

[0118] Although the above disclosure has emphasized three-phase embodiments of the directly heated edge director assemblies, direct heating using a single electrical phase is also contemplated. For example, FIG. 10 illustrates an embodiment of the edge director assembly 100a without a third busbar assembly. In this manner, a single-phase current can be established between the first busbar assembly 200a and the second busbar assembly 200b through the first and second edge directors 102a, 102b, and more particularly through the first bottom edge portion 114a and the second bottom edge portion 114b.

[0119] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments of the present disclosure without departing from the spirit and scope of the present disclosure, and therefore, the present disclosure is intended to cover all such modifications and variations provided they come within the scope of the appended claims and their equivalents. [Explanation of symbols]

[0120] 100a First Edge Director Assembly 102a First Edge Director 102b Second Edge Director 104a first curved outward surface 104b second curved outward surface 106a Dam 106b Dam 112 Joint Edge 114a first bottom edge portion 114b second bottom edge portion 200a First bus bar assembly 200b Second bus bar assembly 200c Third bus bar assembly 222 First busbar pair 224 Second busbar pair

Claims

1. a forming body comprising a first converging forming surface and a second converging forming surface, the first and second converging forming surfaces being joined along a bottom edge of the forming body; an edge director assembly disposed at a first end of the forming body, the edge director assembly comprising a first edge director in contact with the first converging forming surface and a second edge director in contact with the second converging forming surface and joined to the first edge director along an edge portion joint; a first busbar assembly joined to the first edge director; a second busbar assembly joined to the second edge director; a third bus bar assembly joined to the edge director assembly at the edge portion joint; The glass forming apparatus, wherein the first, second, and third bus bar assemblies are electrically connected to a power source configured to provide alternating current to the edge director assembly.

2. 2. The glass forming apparatus of claim 1, wherein the first edge director comprises a first thickened bottom edge portion and the second edge director comprises a second thickened bottom edge portion, the first thickened bottom edge portion joined to the second thickened bottom edge portion at the edge portion joint.

3. 3. The glass forming apparatus of claim 2, wherein the first bus bar assembly comprises a first bus bar formed from a first material and joined to the first thick edge portion, and a second bus bar formed from a second material different from the first material and joined to the first bus bar.

4. 4. The glass forming apparatus of claim 3, wherein the second bus bar assembly comprises a third bus bar formed from the first material and joined to the second thick edge portion, and a fourth bus bar formed from the second material and joined to the third bus bar.

5. 5. The glass forming apparatus according to claim 3, wherein the third bus bar assembly comprises a central bus bar formed from the first material and joined to the edge portion joint, a first branch bus bar joined to the central bus bar, and a second branch bus bar joined to the central bus bar, the first branch bus bar comprising a first bus bar segment formed from the first material and joined to the central bus bar, and a second bus bar segment formed from the second material different from the first material and joined to the first bus bar segment, and the second branch bus bar comprising a third bus bar segment formed from the first material and joined to the central bus bar, and a fourth bus bar segment formed from the second material and joined to the third bus bar segment.

6. 6. The glass forming apparatus of claim 5, wherein an interface between the first material and the second material for the first bus bar assembly, the second bus bar assembly, and the third bus bar assembly is positioned within a surrounding deformable refractory insulation.

7. The glass forming apparatus of claim 3 , wherein the first edge director and the second edge director are formed from the first material.

8. 2. The glass forming apparatus of claim 1, wherein the first bus bar assembly and the second bus bar assembly are supported by a first three-axis support assembly and a second three-axis support assembly, respectively, each of the first three-axis support assembly and the second three-axis support assembly configured to support movement of a respective bus bar assembly along three orthogonal axes.

9. 9. The glass forming apparatus of claim 8, wherein the first three-axis support assembly and the second three-axis support assembly each comprise a tiltable stage configured to accommodate tilting of the first bus bar assembly and the second bus bar assembly, respectively.

10. 9. The glass forming apparatus of claim 8, wherein the first triaxial support assembly supports a first portion of the third bus bar assembly and the second triaxial support assembly supports a second portion of the third bus bar assembly.

11. 10. The glass forming apparatus of claim 1, wherein at least one of the first bus bar assembly, the second bus bar assembly, or the third bus bar assembly comprises a cooling channel configured to pass a cooling fluid therethrough.

12. 1. A method of forming a glass article, comprising: supplying molten glass to a forming body including a first converging forming surface and a second converging forming surface opposite the first converging forming surface, and to an edge director assembly disposed at a first end of the forming body, the edge director assembly including a first edge director in contact with the first converging forming surface and a second edge director in contact with the second converging forming surface, each of the first edge director and the second edge director including an outward facing surface; flowing the molten glass onto the converging forming surfaces of the forming body and onto the outward facing surfaces of the first edge director and the second edge director; heating the edge director assembly by passing an electric current through the edge director assembly; withdrawing the molten glass from a bottom edge of the forming body; A method comprising:

13. The method of claim 12 , wherein the current comprises a three-phase current.

14. a first busbar assembly joined to the first edge director; a second busbar assembly joined to the second edge director; a third busbar assembly joined to a joining edge joining the first edge director to the second edge director; The method comprises:

14. The method of claim 13, further comprising the steps of supplying a first phase of the three-phase current to the first busbar assembly, supplying a second phase of the three-phase current to the second busbar assembly, and supplying a third phase of the three-phase current to the third busbar assembly.

15. The method of claim 13 further comprising varying the magnitude or phase angle of at least one phase of the three-phase current.

16. 15. The method of claim 14, wherein the size of the first phase is different from at least one of the size of the second phase or the size of the third phase.

17. 17. The method of claim 13, further comprising supporting the first busbar assembly and the second busbar assembly on a first tri-axial support assembly and a second tri-axial support assembly, respectively, each of the first tri-axial support assembly and the second tri-axial support assembly configured to support respective movement of the busbar assemblies along three orthogonal axes.

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