AN INDUCTION HEATED ENCLOSURE

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Application Serial No. 61/867,707 filed on August 20, 2013 the contents of which are relied upon and incorporated herein by reference in their entirety as if fully set forth below.

BACKGROUND

Field

[0002] The present specification generally relates to the manufacture of glass sheets and, more specifically, to apparatus and methods for making glass sheets with an enclosure housing a molten glass forming apparatus.

Technical Background

[0003] In the manufacturing of glass sheets, it is important to maintain robust temperature control of the glass-forming environment. For example, in the manufacturing of glass sheets using the fusion draw process, it is important to maintain robust temperature control of the environment surrounding the glass forming apparatus (or isopipe) for a variety of reasons including maintenance of the life and integrity of the glass forming apparatus and controlling the quality and dimensional uniformity (e.g., thickness) of the glass.

[0004] During steady state manufacturing operations, it is often necessary to maintain the environment around the glass forming apparatus at temperatures at which radiation is the dominant heat transfer mode. In order to maintain such temperatures, an enclosure can be constructed around the glass forming apparatus and components engineered to facilitate radiation heat transfer via the walls of the enclosure. For example, rods of an electrically resistive material can be placed in close proximity to the walls of the enclosure and subjected to an electric current sufficient to resistively heat the rods to temperatures at which heat is radiated from the rods to the walls of the closure and from the walls of the enclosure to the molten glass and glass forming apparatus.

[0005] Increases in manufacturing run rates and manufacturing temperatures have begun to strain the limits of using resistance heated material to maintain the robust and continual temperature control needed for long-term steady state operation of those processes. For example, as sizes of resistance heated rods have increased in order to compensate for more robust manufacturing environments, their expense has increased while reliability, and useful service life have tended to decrease. Accordingly, it would be desirable to devise alternative or additional methods for maintaining robust temperature control in the environment of the glass forming apparatus.

SUMMARY

[0006] According to one embodiment, the disclosure relates to a method of heating an enclosure for housing a molten glass sheet forming apparatus according to a predetermined thermal profile. The enclosure has a first side wall and a second side wall and the step of heating the enclosure includes heating at least a portion of at least one of first and second sidewalls with at least one induction heating system.

[0007] In another embodiment, the disclosure relates to an apparatus useful in the process of making glass sheets. The apparatus includes an enclosure for housing a molten glass sheet forming apparatus. The enclosure includes a first side wall and a second side wall and a molten glass forming apparatus is situated in the enclosure. The apparatus also includes at least one induction heating system configured to couple energy to at least a portion of at least one of first and second side walls.

[0008] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a perspective view of an enclosure for housing a molten glass forming apparatus, with resistance heated rods and an induction heating system thermally coupled to a portion of each of the side walls of the enclosure;

[0010] FIG. 2 is a cross-sectional perspective end view of the embodiment of FIG. 1 illustrating a molten glass forming apparatus housed in the enclosure; [0011] FIG. 3 is a perspective view of an enclosure for housing a molten glass forming apparatus, with induction heating systems thermally coupled to each of the side walls of the enclosure;

[0012] FIG. 4 is a cross-sectional perspective end view of the embodiment of FIG. 4 illustrating a molten glass forming apparatus housed in the enclosure;

[0013] FIG. 5 is a cross-sectional perspective end view of an alternative embodiment illustrating an intermediate susceptor positioned in proximity to each of the side walls of the enclosure and induction heating systems thermally coupled to each of the immediate susceptors;

[0014] FIG. 6 is a schematic representation of an array of induction heating systems;

[0015] FIGS. 7A and 7B are cross-sectional perspective end views of alternative coil configurations for induction heating systems;

[0016] FIG. 8 is a schematic representation of an induction heating system wherein the coil density and coil distance to a susceptor differ in different regions of the induction heating system; and

[0017] FIG. 9 is a schematic representation of various elements of an induction heating system.

DETAILED DESCRIPTION

[0018] Reference will now be made in detail to various embodiments for use in the manufacture of glass sheets and glass manufacturing processes incorporating the same. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. Glass sheet materials may generally be formed by melting glass batch materials to form molten glass and thereafter forming the molten glass into a glass sheet. Exemplary processes include the float glass process, the slot draw process and the fusion down- draw process.

[0019] FIG. 1 shows a perspective view of an apparatus useful in the process of making glass sheets according to embodiments herein. The apparatus includes an enclosure 100 for housing a molten glass forming apparatus. Enclosure includes a first side wall 102 and a second side wall 104. First, second, and third resistance heated rods, 202, 204, and 206, respectively, are thermally coupled to first side wall 102, and fourth, fifth, and sixth resistance heated rods, 208, 210, and 212, respectively, are thermally coupled directly to second side wall 104. In addition, first induction heating system 302 is thermally coupled to first side wall 102 and second induction heating system 310 is thermally coupled to second side wall 104.

[0020] FIG. 2 shows a cross-sectional perspective end view of the embodiment of FIG. 1 showing molten glass forming apparatus (isopipe) 400 housed in enclosure 100.

[0021] Enclosure 100 is typically made of a refractory material, such as a refractory ceramic material. Examples of refractory ceramic materials that can be used to make enclosure 100 include any dense, thermally conductive material that maintains its structural integrity at operational temperatures while not reacting negatively with glass, such as silicon carbide. Exemplary silicon carbide materials that can be used for enclosure 100 include materials selected from the Hexoloy® family of silicon carbide materials available from Saint-Gobain and reaction bonded silicon carbide available from M-Cubed Technologies.

[0022] In exemplary embodiments, refractory materials of enclosure can include those that substantially retain their strength properties, as well as chemical and physical stability, at temperatures above 1,000°C, such as above 1,200°C, and further such as above 1,400°C, and still yet further such as above 1,600°C such as from 1,200°C to 1,900°C and further such as from 1,400°C to 1,800°C, and yet further such as from 1,600°C to 1,700°C.

[0023] Thickness of side walls, 102 and 104, while not limited, can, for example, range from 0.25 to 6 inches such as from 1 inch to 2.5 inches.

[0024] Resistance heated rods, 202, 204, 206, 208, 210, and 212 can be made of any material having sufficient resistance heating capacity and mechanical robustness to provide steady state radiation heating capability to sidewalls of enclosure. Examples of materials that can be used for resistance heated rods include silicon carbide, molybdenum disilicide, Nichrome, platinum alloys, and various commercial heater compositions known to persons of skill in the art. Commercially available resistance heated rods include silicon carbide Starbars® available from I Squared R Element Co. and Globars™ available from Sandvik.

[0025] The dimensions of resistance heated rods, while not limited, can for example, range from rods having diameters of from 0.5 to 3 inches, such as from 1 to 2.5 inches and axial (longitudinal) lengths of from 15 to 300 inches, such as from 30 to 250 inches. The diameter of resistance heated rods may be constant or may vary along their axial (longitudinal) lengths.

[0026] Resistance heated rods may be placed in appropriate proximity to side wall so as to efficiently couple energy to sidewall while, at the same time, not causing the sidewalls to short from the current flowing through electrically heated rods. While not limited, the shortest distance between the resistance heated rod and the sidewall can, for example, range from 0.125 to 8 inches, such as from 1 to 4 inches.

[0027] In exemplary embodiments, in order to enable sufficient radiation heat transfer to occur between resistance heated rods and side walls, resistance heated rods should be maintained at steady state operational temperatures that enable appropriate levels of heat transfer to occur between the rods and the sidewalls and between the sidewalls and the molten glass and molten glass forming apparatus. In this regard, resistance heated rods maybe maintained at approximately the same temperature or at different temperatures, depending on process conditions, glass composition, and desired glass characteristics and geometry. For example, in certain exemplary embodiments, resistance heated rods that are at relatively higher locations can be maintained at temperatures that are relatively higher than the temperature of resistance heated rods that are at relatively lower locations, such that the temperature of the resistance heated rods decreases as their location is lower. In other exemplary embodiments, resistance heated rods that are at relatively higher locations can be maintained at temperatures that are relatively lower than the temperature of resistance heated rods that are at relatively lower locations, such that the temperature of the resistance heated rods increases as their location is lower. In yet other exemplary embodiments, resistance heated rods that are at relatively mid-level height can be maintained at temperatures that are relatively higher than the temperatures of resistance heated rods at higher and lower locations, such that the temperature of the resistance heated rods increases from a higher location to a mid-level location and then decreases from the mid-level location to a lower location. In still yet other exemplary embodiments, resistance heated rods that are at relatively mid-level height can be maintained at temperatures that are relatively lower than the temperatures of resistance heated rods at higher and lower locations, such that the temperature of the resistance heated rods decreases from a higher location to a mid-level location and then increases from the mid-level location to a lower location. Resistance heated rods may also be configured and/or constructed so as to provide thermal gradients along their longitudinal lengths, as required by the process.

[0028] At steady state operation under any of the above-mentioned embodiments, the temperature of resistance heated rods can range from 100°C to 1650°C, such as from 900°C to 1450°C. For example, resistance heated rods maintained at relatively higher temperatures can, for example, be at least 900°C and can range from 900°C to 1650°C whereas resistance heated rods maintained at relatively lower temperatures can, for example, be less than 900°C and can range from 100°C to 900°C.

[0029] Induction heating systems 302 and 310, can, in exemplary embodiments, include at least one induction coil directly embedded in an insulative material. Insulative material can protect conductive material in induction coil from overheating and can help enable

maintenance of the structural and mechanical integrity of the induction coil. In exemplary embodiments, induction coil is configured in insulative material in a manner that enables heating the enclosure 100 according to a predetermined thermal profile.

[0030] In order to heat enclosure 100 according to the predetermined thermal profile, induction coil and insulative material must be configured in appropriate proximity to a material that is susceptible to induction heating, such as a material that is susceptible to induction heating at least at temperatures corresponding to the desired thermal profile of enclosure during steady state operation.

[0031] As used herein, "susceptible to induction" means a material that is capable of being heated via inductive heating by at least 500°C when the material is within 1 to 50 millimeters of an alternating electrical current having a frequency of from 10 kHz to 250 kHz when supplied by a power supply having 5 kW to 250 kW of power.

[0032] In the embodiment illustrated in FIGS. 1 and 2, induction heating systems, 302 and 310, are thermally coupled directly to first and second sidewalls, 102 and 104, which are, in turn, susceptible to induction heating at least at temperatures corresponding to the desired thermal profile of the enclosure during steady state operation.

[0033] In certain exemplary embodiments, first and second sidewalls, 102 and 104, are susceptible to induction across a wide temperature range, such as at a temperature of at least 20°C, including at least 50°C and further including at least 100°C, such as from 20°C to 1,900°C and further such as from 50°C to 1,800°C and still further such as from 100°C to 1 ,700°C. In such embodiments, first and second sidewalls, 102 and 104, can be susceptible to induction at temperatures of less than 100°C, including less than 50°C, and further including less than 20°C.

[0034] In such embodiments, apparatus, including enclosure 100, can be heated from a cold start condition (e.g., at room temperature) wherein first and second sidewalls, 102 and 104, are being heated at least in part by induction heating systems 302 and 310. Apparatus, including enclosure 100, can continue to be heated at steady state operating temperatures, corresponding to a desired thermal profile, wherein first and second sidewalls, 102 and 104, continue to be heated at least in part by induction heating systems 302 and 310.

[0035] In other exemplary embodiments, first and second sidewalls, 102 and 104, are susceptible to induction across a temperature range that more closely encompasses

temperatures corresponding to the desired thermal profile of the enclosure during steady state operation. Such a temperature range can include temperatures of at least 500°C, including at least 600°C, further including at least 700°C, still further including at least 800°C, and still yet further including at least 900°C, such as from 500°C to 1,900°C, and further such as from 600°C to 1,800°C, and still further such as from 700°C to 1,700°C, and still yet further such as from 800°C to 1 ,600°C, and even still yet further such as from 900°C to 1 ,500°C.

[0036] In such embodiments, apparatus, including enclosure 100, can be heated from a cold start condition (e.g., at room temperature) wherein first and second sidewalls, 102 and 104, are heated in an earlier step with at least one resistance heated rod (e.g., such as at least resistance heated rods 202, 204, 206, 208, 210, and 212) followed by a later step of activating induction heating systems 302 and 310 once the temperature of sidewalls, 102 and 104, have reached sufficient temperature to be susceptible to induction. From that time forward, first and second sidewalls, 102 and 104, continue to be heated at least in part by induction heating systems 302 and 310 in accordance with a desired thermal profile.

[0037] Alternatively, apparatus, including enclosure 100, can be heated from a cold start condition (e.g., at room temperature) wherein first and second sidewalls, 102 and 104, are heated in an earlier step with at least one resistance heated rod (e.g., such as at least resistance heated rods 202, 204, 206, 208, 210, and 212) followed by a later step of replacing at least one of the resistance heated rods with at least one of induction heating systems 302 and 310 once the temperature of sidewalls, 102 and 104, have reached sufficient temperature to be susceptible to induction. From that time forward, first and second sidewalls, 102 and 104, continue to be heated at least in part by induction heating systems 302 and 310 in accordance with a desired thermal profile.

[0038] In certain exemplary embodiments, all of resistance heated rods can be replaced by induction heating systems once the temperature of sidewalls, 102 and 104, have reached sufficient temperature to be susceptible to induction. From that time forward, first and second sidewalls, 102 and 104, continue to be heated by induction heating systems in accordance with a desired thermal profile. [0039] In alternative embodiments, such as those in which first and second sidewalls are susceptible to induction at room temperature, induction heating systems can be initially present along first and second sidewalls, 102 and 104, such that enclosure 100, can be heated from a cold start (e.g., at room temperature) condition wherein first and second sidewalls, 102 and 104, are heated in with induction heating systems from the cold start condition to a steady state operation condition that is in accordance with a desired thermal profile. From that time forward, first and second sidewalls, 102 and 104, continue to be heated by induction heating systems in accordance with the desired thermal profile.

[0040] As noted above, enclosure 100 including first and second sidewalls, 102 and 104, can be made from a ceramic material such as silicon carbide, including dense sintered silicon carbide and reaction bonded silicon carbide. Silicon carbide materials offer good resistance to melting in a high temperature environment, relatively good thermal conductivity, and very low levels of defects that can be transferred from the enclosure 100 to the glass sheet.

[0041] When enclosure 100 including first and second sidewalls, 102 and 104, comprises silicon carbide, such enclosure and walls may consist essentially of silicon carbide. In certain embodiments, enclosure 100 including first and second sidewalls, 102 and 104, may also comprise at least one ceramic material selected from the group consisting of molybdenum disilicide, tin oxide, and lanthanum chromite.

[0042] Examples of sidewall materials that can be used in exemplary embodiments wherein first and second sidewalls are susceptible to induction at room temperature include reaction bonded silicon carbide available from M-Cubed Technologies and silicon carbide materials containing silicon metal and/or other deliberately introduced electrically conductive constituents.

[0043] Examples of sidewall materials that can be used in exemplary embodiments wherein first and second sidewalls are susceptible to induction only at more elevated temperatures (such as across a temperature range that more closely encompasses temperatures corresponding to the desired thermal profile of the enclosure during steady state operation) include dense sintered silicon carbide, such as Hexoloy® family of silicon carbide materials available from Saint-Gobain.

[0044] Ceramic materials, such as silicon carbide, that are susceptible to induction only at elevated temperatures may have superior resistance to melting at high temperatures, such as temperatures of at least 1600°C, and further such as at least 1700°C, and still yet further such as at least 1800°C, and even still yet further such as at least 1900°C, including from 1600°C to 2200°C. Such materials may be engineered to have susceptibility to induction at lower temperatures but this may result in somewhat reduced resistance to melting at high temperatures.

[0045] For example, in certain embodiments, electrically conductive second phase materials may be incorporated into a ceramic-based matrix, such as a silicon carbide-based matrix, via at least one method selected from the group consisting of reaction bonding, co-fire sintering, and temperature lamination/reaction. An example of an electrically conductive second phase material is silicon. The electrically conductive second phase material may be combined with at least one refractory elemental metal so as to impart a higher melting point to the electrically conductive second phase material. Examples of refractory elemental metals include those selected from the group consisting of titanium, vanadium, chromium, zirconium, niobium, molybdenum, ruthenium, rhodium, hafnium, tantalum, tungsten, rhenium, osmium and iridium.

[0046] FIG. 3 shows an embodiment in which a plurality of induction heating systems 302, 304, 306, 308, 310, 312, 314, and 316 are directly coupled to first and second sidewalls, 102 and 104. In the embodiment illustrated in FIG. 3, nearly the entire surface of first and second sidewalls, 102 and 104, are directly coupled to induction heating systems. While the embodiment of FIG. 3 shows insulative material extending over the top of enclosure 100, it is to be understood that embodiments herein include those in which insulative material does not extend over the top of enclosure 100 or only partially extends over the top of enclosure 100. In addition, it is to be understood that embodiments herein include those in which the top of the enclosure is susceptible to induction and at least one induction heating system is thermally coupled directly to the top of the enclosure.

[0047] FIG. 4 shows a cross-sectional perspective end view of the embodiment of FIG. 3 showing molten glass forming apparatus (isopipe) 400 housed in enclosure 100.

[0048] In exemplary embodiments, in order to heat enclosure 100 according to a

predetemiined thermal profile, induction heating systems should be configured in a manner that enables appropriate levels of induction heating to first and second sidewalls, 102 and 104. In this regard, induction heating systems may be configured to couple the same or differing amounts of energy to first and second sidewalls, 102 and 104, such that the temperature profiles of first and second sidewalls, 102 and 104, may be approximately constant across their length and/or height or may vary across their length and/or height according to the predetermined thermal profile. For example, in certain exemplary embodiments, induction heating systems that are at relatively higher locations can couple more energy to first and second sidewalls than induction heating systems that are at relatively lower locations, such that the temperature of the sidewalls decreases from top to bottom. In other exemplary embodiments, induction heating systems are at relatively higher locations can couple less energy to first and second sidewalls than induction heating systems that are at relatively lower locations, such that the temperature of the sidewalls increases from top to bottom. In yet other exemplary embodiments, induction heating systems that are at relatively mid-level height can couple more energy to first and second sidewalls than induction heating systems at higher and lower locations, such that the temperature of the sidewalls increases from a higher location to a mid-level location and then decreases from the mid-level location to a lower location. In still yet other exemplary embodiments, induction heating systems that are at relatively mid-level height can couple less energy to first and second sidewalls than induction heating systems at higher and lower locations, such that the temperature of the sidewalls decreases from a higher location to a mid-level location and then increases from the mid-level location to a lower location.

[0049] FIG. 5 shows a cross-sectional perspective end view of an alternative embodiment as disclosed herein. In the embodiment of FIG. 5, first immediate susceptor 152 is positioned in proximity to first sidewall 102 and second immediate susceptor 154 is positioned in proximity to second sidewall 104. Induction heating systems 302, 304, 306, and 308 are directly coupled to first immediate susceptor 152 and induction heating systems 310, 312, 314, and 316 are directly coupled to second immediate susceptor 154. First immediate susceptor 152 is positioned between induction heating systems 302, 304, 306, and 308 and first sidewall 102 and second immediate susceptor 154 is positioned between induction heating systems 310, 312, 314, and 316 and second sidewall 104. Molten glass forming apparatus (isopipe) 400 is housed in enclosure 100.

[0050] First and second immediate susceptors, 152 and 154, are preferably susceptible to induction at room temperature, including a temperature of at least 20°C, a temperature of less than 50°C, such as a temperature of from 20°C to 1,900°C. In such embodiments, first and second immediate susceptors, 152 and 154, can be heated from a cold start (e.g., at room temperature) condition wherein first and second immediate susceptors, 152 and 154, are heated with induction heating systems from the cold start condition to a steady state operation condition that is in accordance with a desired thermal profile, which, in turn, enables first and second sidewalls, 102 and 104, to be heated from the cold start condition to a steady state operation condition that is in accordance with the desired thermal profile. From that time forward, first and second sidewalls, 102 and 104, continue to be heated by first and second immediate susceptors and induction heating systems in accordance with the desired thermal profile.

[0051] In the embodiment illustrated in FIG. 5, first and second sidewalls, 102 and 104, may or may not be susceptible to induction. For example, in the embodiment illustrated in FIG. 5, first and second immediate susceptors, 152 and 154, may be susceptible to induction at room temperature, whereas first and second sidewalls, 102 and 104, are not susceptible to induction at room temperature, such as when first and second sidewalls are only susceptible to induction at elevated temperatures (e.g., at 500°C or higher) or are not generally susceptible to induction at all.

[0052] FIG. 6 is a schematic representation of an array of induction heating systems, such as an array of induction heating systems that can be directly coupled to a sidewall of an enclosure for housing a molten glass forming apparatus or an immediate susceptor that is positioned between the array of induction heating systems and a sidewall of an enclosure for housing a molten glass forming apparatus. While FIG. 6 shows an array 4x3 array of 12 induction heating systems (with four induction heating systems in the vertical direction and three induction heating systems in the horizontal or longitudinal direction), it is to be understood that arrays of any number of induction heating systems in either direction are contemplated as being within the scope of embodiments disclosed herein. While FIG. 6 shows an array of induction heating systems that are spaced apart from each other, it is to be understood that embodiments disclosed herein include those in which one or more indication heating systems contact or overlap with at least one other induction heating system.

[0053] The array of induction heating systems can comprise heating systems that are configured to heat an enclosure for housing a molten glass forming apparatus according to a predetermined thermal profile or to any number of predetermined thermal profiles that can be selected based on various process conditions, glass composition, and/or desired glass characteristics and geometry. For example, the array of induction heating systems can be configured and/or operated such that each induction heating system in the array couples the same or different amounts of energy as one or more other induction heating systems to a material that is susceptible to induction, depending on the predetermined thermal profile. In addition, the array of induction heating systems can be configured and operated such that, over time, each induction heating system in the array couples the same or differing amounts of energy to a material that is susceptible to induction. For example, during a start-up procedure, one or more induction heating systems in the array may be configured and operated to couple energy to a material that is susceptible to induction, wherein the energy coupled varies as a function of time, such as the time period from a cold start condition to a steady state operational condition. In that regard, each induction heating system in the array may couple the same or differing amounts of energy as one or more other induction heating systems to a material that is susceptible to induction as a function of time.

[0054] For example, in one set of preferred embodiments, an array of induction heating systems can be configured such that the induction heating systems on the outermost horizontal ends of the array, on average, couple less energy to a material that is susceptible to induction than induction heating systems located between the induction heating systems on the outermost horizontal ends of the array (i.e., induction heating systems more centrally located in the horizontal or longitudinal direction). In such embodiments, the induction heating systems can couple the same or differing amounts of energy to a material that is susceptible to induction as a function of their vertical position on the array. For example, in some embodiments, the induction heating systems can couple decreasing amounts of energy to a material that is susceptible to induction as a function of their height, such that induction heating systems configured at a higher point on an array couple less energy to a material that is susceptible to induction than induction heating systems configured directly below them. Alternatively, in other embodiments, the induction heating systems can couple increasing amounts of energy to a material that is susceptible to induction as a function of their height, such that induction heating systems configured at a higher point on an array couple more energy to a material that is susceptible to induction than induction heating systems configured directly below them.

[0055] In alternative embodiments, an array of induction heating systems can be configured such that the induction heating systems on the outermost horizontal ends of the array, on average, couple more energy to a material that is susceptible to induction than induction heating systems located between the induction heating systems on the outermost horizontal ends of the array (i.e., induction heating systems more centrally located in the horizontal or longitudinal direction). In such embodiments, the induction heating systems can couple the same or differing amounts of energy to a material that is susceptible to induction as a function of their vertical position on the array. For example, in some embodiments, the induction heating systems can couple decreasing amounts of energy to a material that is susceptible to induction as a function of their height, such that induction heating systems configured at a higher point on an array couple less energy to a material that is susceptible to induction than induction heating systems configured directly below them. Alternatively, in other embodiments, the induction heating systems can couple increasing amounts of energy to a material that is susceptible to induction as a function of their height, such that induction heating systems configured at a higher point on an array couple more energy to a material that is susceptible to induction than induction heating systems configured directly below them.

[0056] The amount of energy that can be coupled from an induction heating system to a material susceptible to induction can, in some embodiments, be a function of the geometric configuration of the induction heating system. FIGS. 7A and 7B are cross-sectional perspective end views of alternative coil configurations for induction heating systems. In each of FIGS. 7A and 7B, insulation 380 is directly coupled to material (e.g., sidewall) susceptible to induction 180, wherein configuration further includes additional insulation 384 and bracket 182. Induction coil 382 is configured such that current in odd numbered cross sectional areas (e.g., 1, 3, 5, 7) is flowing in the opposite direction as current in even numbered cross sectional areas (e.g., 2, 4, 6). In the embodiment shown in FIG. 7A, induction coil is configured such that the vertical spacing between cross-sectional coil areas is approximately constant. In the embodiment shown in FIG. 7B, induction coil is configured such that there is a vertical distance d between the closest cross-sectional coil areas wherein current is flowing in opposite directions, wherein d is greater than the vertical distance between any two cross- sectional coil areas wherein current is flowing in the same direction. For example, d may be at least 1.5 times, such as at least 2 times, and further such as at least 3 times, including from 1.5 times to 3 times, greater than the vertical distance between any two cross-sectional coil areas wherein current is flowing in the same direction.

[0057] FIG. 8 is a schematic representation of an induction heating system wherein the coil density and coil distance to a material susceptible to induction differ in different regions of the induction heating system. As shown in FIG. 8, induction heating system 320, includes an insulative material 322 and an induction coil having a first segment 324 and a second segment 326. First segment 324 has a higher amount of coil density per unit area than second segment 326, whereas second segment 326 is configured to be closer to material susceptible to induction (not shown) than first segment 324. Alternatively stated, first segment 324 has a greater amount of coil density in the X-Y direction, whereas second segment 326 is closer to material susceptible to induction in the Z direction.

[0058] While FIG. 8 illustrates an embodiment wherein first segment 324 has a higher amount of coil density per unit area and second segment 326 is configured closer to a material that is susceptible to induction, it is to be understood that embodiments disclosed herein include other configurations, including, but not limited to those in which the entire induction coil is approximately the same distance from the material susceptible to induction (susceptor) but the coil density per unit area varies in different areas of the induction heating system. Embodiments herein can also include those in which the entire induction coil has approximately the same coil density per unit area but is configured to be at differing distances from the susceptor in different areas of the induction heating system. In addition, embodiments herein can include those in which the entire induction coil has approximately the same coil density per unit area and is approximately the same distance from the susceptor throughout the entire area of the induction heating system. For example, embodiments herein can include those in which a first segment has both a higher amount of coil density per unit area than a second segment while, at the same time, being configured closer to the susceptor than the second segment. Such embodiments can enable the same or differing amounts of energy to be coupled to different portions of a susceptor. For example, such embodiments can be configured so as to heat at least one portion of a susceptor to a different temperature than at least one other portion of the susceptor.

[0059] At least one induction heating system may also comprises at least two induction coils that are, for example, configured to couple the same or differing amounts of energy to a susceptor. For example, the at least two induction coils can be configured so as to heat at least one portion of a susceptor to a different temperature than at least one other portion of the susceptor.

[0060] The amount of energy that is coupled between induction heating systems and a susceptor can also vary across different induction heating systems as a function of, for example, the coil density per unit area in the induction system and/or the proximity of the coil to the susceptor in the induction heating system. For example, in the embodiment of FIG. 6, the array of induction heating systems can be configured such that at least one induction heating system in the array has a coil density per unit area and/or a coil distance to a susceptor that is greater than or less than that of at least one other induction heating system in the array. For example, if it is desired to have one or more induction heating systems couple more energy to the susceptor than other induction heating systems (such as in the maintenance of a predetermined thermal profile during either a start-up procedure or during steady state operation), the induction heating system or systems that is intended to couple more energy to the susceptor can be configured to have a greater coil density per unit area and/or greater coil proximity to the susceptor than induction heating systems that are intended to couple less energy to the susceptor.

[0061] Embodiments herein can also include those in which a plurality of induction heating systems (such as the array of induction heating systems illustrated in FIG. 6) are each configured to have approximately the same coil configuration with respect to coil density per unit area and coil-susceptor proximity, wherein the amount of energy coupled from each induction heating system to the susceptor varies based on the amount of power supplied to each induction heating system. The power supplied to each induction heating system can also vary in embodiments discussed in the above paragraph, wherein the coil density per unit area and/or the proximity of the coil to the susceptor varies between different induction heating systems. Such embodiments can enable the same or differing amounts of energy to be coupled to different portions of a susceptor. For example, such embodiments can be configured so as to heat at least one portion of a susceptor to a different temperature than at least one other portion of the susceptor.

[0062] In exemplary embodiments, induction coil can include tubing any material that enables sufficient electrical conductivity, while at the same time, having good corrosion resistance to cooling fluid flowing through the tubing. For example, induction coil can comprise at least one material selected from the group consisting of copper, nickel, platinum, gold, silver, and alloys comprising at least one of the same. In a particularly preferred embodiment, the induction coil comprises copper and the cooling fluid comprises water.

[0063] In exemplary embodiments, insulative material can include any material that provides sufficient thermal insulation between susceptor material (e.g., sidewalls 102 and 104) and induction coil while, at the same time, enabling structural and mechanical support for induction coil. For example, insulative material can comprise any nonconductive refractory material suitable for extended high temperature industrial application, such as refractory insulative material comprising at least one compound of alumina, silica, and zirconia.

[0064] In embodiments disclosed herein, induction coil can be configured on a surface of insulative material or be fully or partially embedded in insulative material. When induction coil is embedded in insulative material, insulative material can have a recessed surface area that is patterned to accept the induction coil according to a desired induction coil configuration. When induction coil is partially embedded in insulative material, insulative material can partially surround induction coil. When induction coil is fully embedded in insulative material, insulative material can fully surround induction coil.

[0065] FIG. 9 shows a schematic representation of an exemplary induction heating system 1000 that can be used to facilitate direct heating of a susceptor (not shown) by induction. Induction heating system 1000 includes an alternating current power supply 500, a heat station 550, a chiller 600 for supplying cooling fluid, and a controller 700. Induction heating system 1000 also includes a cooling fluid input line 602 for directing cooling fluid flow from chiller 600 to alternating current power supply 500, heat station 550, and induction coil 330 as well as a cooling fluid output line 652 for directing cooling fluid flow from induction coil 330 back to chiller 600. In addition, induction heating system 1000 includes an electrical circuit 502, 504, 506, and 508 between alternating current power supply 500, heat station 550, and induction coil 330. Induction heating system 1000 additionally includes a control loop 702 for enabling a controller 700 to provide managed control of induction heating of susceptor. While FIG. 9 shows cooling fluid being provided to system components in series, it is to be understood that embodiments disclosed herein include those in which cooling fluid is provided to system components in parallel.

[0066] In addition, while FIG. 9 shows a single cooling fluid source to which cooling fluid is both supplied and returned (e.g., chiller 600) such that cooling fluid continually circulates within induction heating system 1000, it understood that embodiments herein can include those in which the cooling fluid is supplied from a source other than chiller 600, including more than one source (e.g., a combination of a chiller 600 and house water) and wherein some (if not all) of cooling fluid is not returned to chiller 600 following circulation through input and output lines 602, 652.

[0067] In operation, alternating current is supplied from alternating current power supply 500 to heat station 550 and induction coil 330 via electrical circuit 502, 504, 506, and 508 while, at the same time, cooling fluid is directed through alternating current power supply 500, heat station 550, and induction coil 330 from chiller 600 via cooling fluid input and output lines 602, 652. The amount and frequency of alternating current as well as the flow rate of cooling fluid can be controlled simultaneously via controller 700 and control loop 702 so as to provide managed control of induction heating of susceptor. Such control can, for example, include or be forwarded to a computer processing unit, and such unit can process, for example, feedback or feedforward control according to process control methods known to persons of skill in the art.

[0068] When a plurality of induction heating systems are employed, such as the array illustrated in FIG. 6, each induction heating system can be independently controlled, such as in the manner described above, so as to provided managed control of induction heating of susceptor, such as according to a predetermined thermal profile.

[0069] In addition, such control can allow for direct heating of the susceptor by induction such that a minimum temperature of at least a portion of the surface of the susceptor is maintained in steady state in as close to a constant temperature as possible. For example, the minimum temperature of at least a portion of the surface of the susceptor can be maintained at steady state for a predetermined length of time at a predeteimined temperature that does not vary for more than ±10°C, such as not more than ±5°C, and further such as not more than ±2°C, and still yet further such as not more than ±1°C. Such predeteimined length of time, while not limited, can be at least 1 hour, such as at least 10 hours, and further such as at least 25 hours, including from 1 hour to 10 years, such as from 10 hours to 5 years, and further such as from 20 hours to 1 year.

[0070] Such minimum temperature, while not limited, in preferred embodiments should at least be maintained at an operational temperature that corresponds to a predetermined thermal profile. For example in certain preferred embodiments, the surface of the susceptor maintained above 1,000°C, such as above 1,100°C, and further such as above 1,200°C, including from 1,000°C to 1,400°C.

[0071] The susceptor, induction coil 330, and induction heating system 1000 can also be configured so as to enable rapid change of the minimum temperature of at least a portion of the susceptor, for example, in response to predeteimined factors which would call for such temperature to be changed. For example, if the composition of the glass flowing over the molten glass forming apparatus were to change such that its liquidus temperature were to also change, the minimum temperature of at least a portion of the susceptor could correspondingly be changed. Alternatively, if the flowrate of the glass flowing over the molten glass forming apparatus were to change, the minimum temperature of at least a portion of the susceptor could correspondingly be changed. In this regard, controller 700 could be integrated into a control algorithm that not only controls induction heating system but also serves to control the entire glass forming process, wherein the temperature of the susceptor could be changed in response to or anticipation of any number of process parameters or measured or desired glass characteristics, including, but not limited to, glass composition, glass temperature, glass devitrification temperature, glass viscosity, and glass flow rate.

[0072] For example, embodiments disclosed herein include those in wherein the minimum temperature of at least a portion of the susceptor can be changed at a rate of at least 5°C per minute, including at least 10°C per minute, such as from 5°C per minute to 30°C per minute at temperatures of at least 1,000°C, including at temperatures of from 1,000°C to 1,400°C.

[0073] Embodiments disclosed herein include those in which a temperature profile is present on the susceptor (e.g. side wall) such that the maximum temperature on a surface of the susceptor is at least 25°C greater, such as at least 50°C greater, and further such as at least 100°C greater than the minimum temperature on the surface of the susceptor. For example, embodiments disclosed herein can include those in which the difference between the maximum and minimum temperature on the surface of the susceptor is from 25°C to 500°C, such as from 50°C to 250°C. Such temperature profiles can be approximately linear or nonlinear as a function of temperature versus position on the surface of the susceptor.

[0074] Induction coil in each induction heating system should preferably be configured such that it is substantially insulated from susceptor while still close enough to susceptor to enable temperature of susceptor to correspond to a desired thermal profile. While this will vary depending on the application, enclosure configuration, and type and amount of insulative material between induction coil and susceptor, in preferred embodiments, induction coil can be configured so that the portion of the coil closest susceptor is between 1 millimeter and 50 millimeters, such as between 5 millimeters and 25 millimeters.

[0075] In certain exemplary embodiments, one or more induction coils of induction heating systems may be coated, insulated, or sleeved with at least one material that provides, for example, thermal, electrical, mechanical, and/or corrosion protection. For example, in certain exemplary embodiments, induction coil may be sleeved in a fabric material comprising at least one material selected from the group consisting of alumina and silica.

[0076] Embodiments herein include those in which induction coil comprises copper tubing having an outer diameter of from 2 to 15 millimeters, such as from 4 to 10 millimeters, and further such as from 4 to 7 millimeters. In such embodiments, copper tubing can, for example, have a radial thickness of from 0.5 to 1 millimeter. While tubing is most typically of circular or elliptical cross-section, it is to be understood that embodiments herein include those in which tubing is of square or rectangular cross-section.

[0077] While not limited, preferred embodiments include those in which the power supply to each induction heating systems provides at least 5 kW of power, such as at least 7.5 kW of power, and further such as at least 10 kW of power, and still yet further such as at least 15 kW of power, such as from 5 kW to 250 kW of power, and an alternating current with a frequency of at least 10 kHz, such as at least 20 kHz, and further such as at least 50 kHz, such as from 10 kHz to 250 kHz.

[0078] Cooling fluid can be provided at a flow rate and temperature that prevents undesirable softening, deformation, or melting of induction coil, while at the same time, keeping alternating current power supply sufficiently cool. For example, cooling water can be provided to induction coil from a chiller at a temperature of from about 0°C to about 50°C, including about 25°C. Cooling fluid flow rate can, for example, range from about 0.5 liters per minute to about 20 liters per minute, such as from about 1 liter per minute to about 10 liters per minute.

[0079] Embodiments herein can provide advantages over other methods of heating enclosures of molten glass forming apparatuses, such as those, for example, relying exclusively on resistance heated rods to provide heating of the enclosure. Such advantages can include ability to operate at higher temperatures and run rates, lower operating costs (e.g., lower costs associated with maintenance and replacement of resistance heated rods), lower risk of manufacturing upsets, better utilization of existing manufacturing assets, and ability to more precisely control and tune the environment surrounding the glass forming apparatus, including being able to more precisely control and tune the temperature of the side walls of an enclosure for housing a molten glass forming apparatus according to a predetermined thermal profile, including more precise control during the full process range from start up to cool down. [0080] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.