RADIATION SHIELD FOR SHAPING THIN GLASS

Abstract

Disclosed herein are systems for shaping a glass structure comprising a shaping mold; a radiation heating source; and a radiation shield, wherein the radiation shield is positioned substantially between the radiation source and the glass structure and wherein the radiation shield comprises an outer wall defining a cavity having a first opening disposed to face the glass structure and a second opening disposed to face the radiation heating source. Also disclosed herein are methods for shaping a glass structure comprising positioning the glass structure on a shaping mold; introducing the shaping mold and glass structure into a furnace comprising a radiation heating source; and heating the glass structure, wherein a radiation shield is positioned substantially between the glass structure and the radiation heating source. Methods and systems employing multiple, e.g., concentric, radiation shields are also disclosed.

Claims

1. A system for shaping a glass structure comprising: (a) a shaping mold; (b) a radiation heating source; and (c) a radiation shield; wherein the radiation shield is positioned substantially between the radiation heating source and the glass structure, and wherein the radiation shield comprises an outer wall defining a cavity having a first opening disposed to face the glass structure and a second opening disposed to face the radiation heating source.

2. The system of claim 1, wherein the radiation heating source comprises a plurality of radiant heating elements.

3. The system of claim 1, wherein the radiation heating source further comprises at least one first heating zone comprising at least one first radiant heating element and at least one second heating zone comprising at least one second radiant heating element.

4. The system of claim 3, wherein the glass structure comprises at least one first region and at least one second region, the at least one first heating zone being substantially aligned with the at least one first region and the at least one second heating zone being substantially aligned with the at least one second region.

5. The system of claim 4, wherein the at least one first heating zone operates at a first temperature and the at least one second heating zone operates at a second temperature different from the first temperature.

6. The system of claim 5, wherein the first temperature ranges from about 600 C. to about 1000 C. and wherein the second temperature ranges from about 400 C. to about 700 C.

7. The system of claim 1, further comprising a furnace, the furnace housing the shaping mold, radiation shield, and radiation heating source, wherein the radiation shield is supported by and attached to the furnace.

8. The system of claim 1, wherein the radiation shield is supported by and attached to the shaping mold.

9. The system of claim 1, wherein the radiation shield has an emissivity ranging from about 0.01 to about 1.

10. The system of claim 1, wherein the glass structure is selected from the group consisting of a single sheet of glass, multiple sheets of glass in a single stack, a glass-glass laminate structure, and a glass-polymer laminate structure.

11. The system of claim 1, further comprising at least one second radiation shield comprising an inner wall disposed within the cavity defined by the outer wall and defining at least one second cavity having a first opening disposed to face the glass structure and a second opening disposed to face the radiation heating source.

12. The system of claim 11, wherein the radiation heating further comprises at least one first heating zone comprising at least one first radiant heating element, at least one second heating zone comprising at least one second heating element, and at least one third heating zone comprising at least one third radiant heating element.

13. The system of claim 12, wherein the glass structure comprises at least one first region, at least one second region and at least one third region, the at least one first heating zone being substantially aligned with the at least one first region, the at least one second heating zone being substantially aligned with the at least one second region, and the at least one third heating zone being substantially aligned with the at least one third region.

14. The system of claim 13, wherein the at least one first heating zone has a temperature ranging from about 600 C. to about 1000 C., wherein the at least one second heating zone has a temperature ranging from about 500 C. to about 700 C., and wherein the at least one third heating zone has a temperature ranging from about 400 C. to about 600 C.

15. A method for shaping a glass structure comprising: (a) positioning the glass structure on a shaping mold; (b) introducing the shaping mold and glass structure into a furnace comprising a radiation heating source; and (c) heating the glass structure; wherein a radiation shield is positioned substantially between the glass structure and the radiation heating source, and wherein the radiation shield comprises an outer wall defining a cavity having a first opening disposed to face the glass structure and a second opening disposed to face the radiation heating source.

16. The method of claim 15, wherein the radiation heating source further comprises at least one first heating zone comprising at least one first radiant heating element and at least one second heating zone comprising at least one second radiant heating element.

17. The method of claim 16, wherein the glass structure comprises at least one first region and at least one second region, the at least one first heating zone being substantially aligned with the at least one first region and the at least one second heating zone being substantially aligned with the at least one second region.

18. The method of claim 17, wherein the at least one first heating zone operates at a first temperature and the at least one second heating zone operates at a second temperature different from the first temperature.

19. The method of claim 18, wherein the first temperature ranges from about 600 C. to about 1000 C. and the second temperature ranges from about 400 C. to about 700 C.

20. The method of claim 15, further comprising at least one second radiation shield, which is concentric with the first radiation shield.

21. The method of claim 14, wherein the glass structure is selected from the group consisting of a single sheet of glass, multiple sheets of glass in a single stack, a glass-glass laminate structure, and a glass-polymer laminate structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The following detailed description can be best understood when read in conjunction with the following drawings, where like structures are indicated with like reference numerals and in which:

[0015] FIG. 1 illustrates a system for shaping glass according to one embodiment of the disclosure;

[0016] FIG. 2 is a deviation plot illustrating the theoretically predicted part shape obtained using prior art uniform radiation heating methods;

[0017] FIG. 3A is a thermal distribution illustrating a theoretical temperature differential between the edges and center of a glass structure shaped according to one embodiment of the disclosure;

[0018] FIG. 3B is a theoretical model illustrating the predicted part shape obtained using the differential thermal distribution of FIG. 3A;

[0019] FIG. 3C is a deviation plot illustrating the theoretically predicted part shape obtained using the differential thermal distribution of FIG. 3A;

[0020] FIG. 4 is a theoretical model illustrating a system implementing a differential thermal distribution and radiation shield according to one embodiment of the disclosure;

[0021] FIG. 5 is a plot illustrating glass temperature as a function of distance from the center of the glass using a prior art method and methods according to various embodiments of the disclosure;

[0022] FIG. 6 is a plot illustrating glass temperature as a function of distance from the center of the glass as it relates to the ratio between the length of the radiation shield (L), and the distance between the glass structure and the radiation heating source (H);

[0023] FIG. 7 is a theoretical model illustrating a system implementing a differential thermal distribution and two concentric radiation shields according to one embodiment of the disclosure; and

[0024] FIG. 8 is a plot illustrating glass temperature as a function of distance from the center of the glass using a prior art method and methods according to various embodiments of the disclosure.

DETAILED DESCRIPTION

[0025] Disclosed herein are systems and methods for shaping glass structures comprising a shaping mold, a radiation heating source, and a radiation shield, wherein the radiation shield is positioned substantially between the radiation heating source and the glass structure(s), and wherein the radiation shield comprises an outer wall defining a cavity having a first opening disposed to face the glass structure(s) and a second opening disposed to face the radiation heating source. Exemplary glass structures include, but are not limited to, a single sheet of glass, multiple sheets of glass in a single stack, a glass-glass laminate structure, and a glass-polymer laminate structure, to name a few.

[0026] Systems

[0027] With reference to FIG. 1, one embodiment of an exemplary system for shaping glass structures according to the disclosure is illustrated, which comprises a shaping mold 110 on which glass structures G may be positioned. The shaping mold may comprise any object that has a surface on or around which the glass can be shaped. The shaping mold may have any shape and size suitable for producing a shaped glass product for a particular application. For instance, the shaping mold may be designed so as to impart a desired curvature to a glass sheet, for example, in the case of windshields and rear or side windows for an automobile. Other shapes and configurations are envisioned and within the scope of the application. In some embodiments, the shaping mold may be a gravity bending ring mold, a fixed shape gravity ring, a multi-shape articulated gravity sag ring, a full surface mold optionally with vacuum assist. The above molds may be used, for example, with an optional pre-tensioning mechanism. Of course, disclosure should not be limited to gravity bending methods as embodiments described herein may also be applicable to press assist bending methods.

[0028] The glass structure G may be conveyed or otherwise introduced into a furnace or any other heating means comprising a radiation heating source 120. The radiation heating source provides radiant heat to at least a portion of the glass structure. It is to be understood that while, in certain embodiments, radiant heat may be the dominant heating source, the glass heating can involve all heat transfer modes, including convection and conduction heating. For instance, in some embodiments, radiant heating may make up greater than about 50% of the overall heating, such as greater than about 60%, greater than about 70%, greater than about 80%, or greater than about 90% of the total heating. Other combinations of heating modes are envisioned and intended to fall within the scope of the application.

[0029] The radiation heating source may comprise, in certain exemplary embodiments, a plurality of radiant heating elements. The furnace or heating means may therefore be divided into two or more differential temperature zones, such as a first zone 135 comprising at least one first heating element, such as a first plurality of heating elements 115 and a second zone 145 comprising at least one second heating element, such as a second plurality of heating elements 125. The first plurality of heating elements 115 may operate at a temperature different than the second plurality of heating elements 125, for example, the first heating elements 115 may be cooler than the second heating elements 125, or vice versa. The first zone 135 may be substantially aligned with a first portion of the glass structure G and the second zone 145 may be substantially aligned with a second portion of the glass structure G. In some embodiments, such as the embodiment illustrated in FIG. 1, the first zone 135 may be aligned with the periphery of the glass structure G, and the second zone 145 may be aligned with the central region of the glass structure G.

[0030] Although not illustrated, several heating zones may be created using additional heating elements or pluralities of heating elements operating at differing temperatures. Thus, the depiction in FIG. 1 should not limit the scope of the claims appended herewith. For example, several portions of the glass structure may be heated at different temperatures. In some embodiments, a central region of the glass structure may be heated to a first temperature, an outer region of the glass structure may be heated to a second temperature, and a peripheral region of the glass structure may be heated to a third temperature, these regions optionally being concentric with one another. The radiation shield(s) and heating zone(s) can be arranged in any manner so as to produce a desired temperature differential between various portions of the glass structure as necessary to make the desired glass shape part.

[0031] A radiation shield 130 can be positioned substantially between the shaping mold 110 and the radiation heating source 120. The radiation shield may, in certain exemplary embodiments, serve to direct radiant heat away from one portion of the glass structure and toward another portion of the glass structure so as to establish a desired temperature differential between the portions of the glass structure. For instance, the radiation shield may direct radiant heat having a higher temperature away from the glass edges and toward the glass center and/or direct radiant heat having a cooler temperature away from the center of the glass and toward the glass edges. The radiation shield 130 can be positioned substantially between the radiation heating source 120 and the glass structure G so as to redirect the radiant heat and create the desired temperature differential.

[0032] Although not illustrated, the radiation shield may be attached to and supported by the shaping mold 120. Alternatively, when a furnace comprises the radiation heating source, the shaping mold may be attached to and supported by the furnace, for example, attached to the roof of the furnace. The radiation shield may likewise be attached to any structure housing the radiation heating source. The radiation shield 130 may comprise an outer wall defining a cavity. The outer wall may, in some embodiments, be a continuous wall defining a cavity, e.g., an annulus. In FIG. 1, the radiation shield 130 is illustrated as a circular annulus, comprising a cavity having a first opening 140 disposed to face the glass structure G and a second opening 150 disposed to face the radiation heating source 120. The radiation shield 130 may, however, have any variety of shapes and cross-sections which are not illustrated in FIG. 1, such as an ovoid, square, rectangular, rhomboid, or polygonal cross-sectional shape, to name a few.

[0033] The radiation shield may also have a vertical length L. The distance between the glass structure G and the radiation heating source 120 or, in certain embodiments, the height of the furnace roof, may be represented by H. The ratio L/H may vary to achieve the desired temperature differential (T) between, e.g., the edges and the center of the glass structure G to be shaped. A higher ratio L/H can result in more shielding and thus a higher T, whereas a lower ratio L/H can provide less shielding and thus a lower T. In certain non-limiting embodiments, the radiation shield 130 may have a vertical axis along the vertical length L, which may be substantially perpendicular to the direction in which the glass structure is conveyed, e.g., into and out of a furnace.

[0034] While FIG. 1 illustrates the radiation heating source 120 as positioned above the glass structure G, this arrangement is not intended to be limiting, as the radiation heating source 120 could be positioned beneath the glass structure G, or both above and below, and variations thereof. The orientation of the glass structure and the radiation heating source may vary, so long as one or more radiation shields are present and positioned substantially between the glass structure and the radiation source. The radiation shield 130 may, in certain embodiments, block radiation from the first zone 135 to the center of the glass structure and from the second zone 145 to the edges of the glass structure. The first opening 140 may be substantially aligned with the center of the glass while the second opening 150 may be substantially aligned with the second zone 145. Although not illustrated, one or more additional radiation shields may be used, e.g., concentrically, in coordination with various heating zones so as to create a multi-step differential heating profile. This embodiment is further discussed in conjunction with FIG. 7.

[0035] According to various embodiments, the outer wall of the radiation shield may comprise various materials, such as, for example, metal alloys such as INCONEL alloys, e.g., INCONEL 600, ceramics such as silicon carbide, refractory materials, and high temperature metals such as nickel. In certain embodiments the walls of the shield cavity may be coated with at least one reflective material. For example, gold or jade mirrors may be deposited on the shield walls, e.g., as a colloidal solution. Alternatively, a foil may be applied to the shield walls. The reflective material may have a thickness, e.g., ranging from about 1 m to about 500 m, such as from about 5 m to about 400 m, from about 10 m to about 300 m, from about 20 m to about 200 m, or from about 50 m to about 100 m, including all ranges and subranges therebetween. By way of a non-limiting example, the deposition of gold on INCONEL can be achieved by first spraying the shield cavity walls with a suspension of silicon carbide powder in epoxy resin followed by the vacuum deposition of gold.

[0036] The radiation shield may have a wide range of emissivity values, depending on various parameters such as the shield material, the optional reflective coating, and other parameters such as shield texture, to name a few. In some embodiments, the radiation shield may have an emissivity ranging, for example, from about 0.01 to about 1, from about 0.02 to about 0.9, from about 0.03 to about 0.8, from about 0.05 to about 0.7, from about 0.1 to about 0.6, from about 0.2 to about 0.5, or from about 0.3 to about 0.4, including all ranges and subranges therebetween. By way of a non-limiting embodiment, a radiation shield comprising electroplated nickel may have an emissivity of approximately 0.03, whereas a black body may have an emissivity of approximately 1. According to various embodiments, the shield may be machined to create a texture or microtexture on the surface(s), which may further assist in the redirection of radiation.

[0037] Without wishing to be bound by theory, it is believed that the systems disclosed herein, e.g., the system illustrated in FIG. 1, may serve to create two or more regions on a glass structure surface having discrete temperatures with a significant differential between the temperatures of the two regions. In the case of a sag bending shaping process, such a temperature differential may be achieved, e.g., by blocking cold radiation factors from reaching the center of the glass structure and blocking hot radiation factors from reaching the edges of the glass structure. The systems disclosed herein may thus provide marked improvement in terms of achieving target shape as compared to prior art methods employing uniform heating profiles. Such prior art methods are further illustrated in FIG. 2, which is a plot showing the shape deviation (mm) between the target part shape and the predicted part shape obtained by implementing a uniform heating profile for a 0.7 mm thick glass structure during a sag bending process. Regions denoted by A indicate over-sagging and the region denoted by B indicates under-sagging. The deviation plot illustrates that the glass region just inside the four edges of the structure has over-sagged by as much as about 20 mm, whereas the center of the structure has the approximate target shape. This bathtub phenomenon is particularly prevalent when shaping thin glass structures, e.g., glass structures having thicknesses less than about 3.0 mm, such as between about 0.3 mm and about 2.0 mm, or between about 0.5 mm and about 1.5 mm, including all ranges and subranges therebetween. Modeling results for thicker glass structures, such as those having conventional thicknesses of greater than about 3.0 mm, for example, about 3.2 mm or about 5.0 mm, show that the bathtub effect is not as severe.

[0038] Thus, especially for thinner glasses, Applicants seek to provide shaping systems and methods implementing a differential heating profile across the glass structure. For instance, in the case of the target part shape of FIG. 2, it would be advantageous to employ a differential heating profile in which the peripheral region of the glass structure is heated at a lower temperature so as to maintain higher glass viscosity and limit viscous flow, while the center region of the glass structure is heated at a higher temperature to achieve the desired shape. Such a differential heating profile is illustrated in FIG. 3A, where an exemplary thermal distribution contemplates a central region of the glass structure at about 720 C. and the peripheral region of the glass structure at about 640 C. Thus, a temperature differential (T) of approximately 80 C. exists in the theoretical model of FIG. 3A. FIG. 3B illustrates the predicted part shape obtained by implementing the differential heating profile of FIG. 3A in a sag bending process, expressed as out of plane deformation (mm). FIG. 3C is a plot showing the shape deviation (mm) between the target part shape and the predicted part shape obtained by implementing the differential heating profile of FIG. 3A for a 0.7 mm thick glass structure during a sag bending process. In FIG. 3C the central region A is at the approximate target shape and the peripheral region B is slightly undersagged. Thus, as compared to prior art FIG. 1, there is a marked reduction of over-sagging at the periphery.

[0039] FIG. 4 illustrates a two-dimensional thermal model created using ANSYS FLUENT software, in which a furnace 400 is divided into two zones: (i) a hot zone 445 operating at a temperature of about 650 C. and (ii) a cold zone 435 operating at a temperature of about 400 C. A radiation shield 430 with a length L is present between the furnace top wall (comprising a radiation heating source) and the glass structure G. H represents the distance between the furnace top wall and the glass structure G. The following assumptions were made: (i) the side walls 405 of the furnace were assumed to be insulated, (ii) the initial temperature of the glass structure G was assumed to be about 400 C., and (iii) the residence time in the furnace 400 was assumed to be about 5 minutes. A shaping mold is not illustrated in the model but is assumed to be present. The model furthermore only illustrates one portion of the system, and symmetry is assumed to exist along lines A and B.

[0040] FIG. 5 illustrates the glass surface temperature distribution using the model presented in FIG. 4 after a 5-minute residence time. The glass temperature is plotted as a function of distance from the center of the glass. Plot A represents the glass temperature distribution achieved using a radiation shield with reflective walls (=0.1). Plot B represents the glass temperature distribution achieved using a radiation shield not coated with a reflective material (=0.9). Plot C represents the glass temperature distribution achieved in the absence of a radiation shield. FIG. 5 thus demonstrates that without a radiation shield (Plot C), a more or less linear temperature drop from the center of the glass structure is realized, whereas the introduction of a radiation shield can create a hotter glass center and substantially cooler glass edges. Moreover, the temperature differential (T) between the hot and cold regions of the glass structure can be adjusted by adjusting the reflectivity of the radiation shield walls, where a greater reflectivity (Plot A) results in a greater T as compared to a radiation shield with no reflectivity (Plot B).

[0041] The temperature differential (T) can also be adjusted by adjusting the length L of the shield relative to the distance H between the glass structure and the furnace top wall (or radiation heating source). FIG. 6 demonstrates the effect of the ratio L/H on the glass T. Plot D represents the glass temperature distribution achieved using a ratio L/H=0.84. Plot E represents the glass temperature distribution achieved using a ratio L/H=0.6. Plot F represents the glass temperature distribution achieved using a ratio L/H=0.4. Plot G represents the glass temperature distribution achieved without shielding (L/H=0). As demonstrated by FIG. 6, as the length L of the radiation shield increases, e.g., as the ratio L/H increases, the sharper the distinction between the hot and cold regions generated on the glass structure and the larger the T between the center and edges of the glass structure.

[0042] As discussed above, certain embodiments can employ more than one radiation shield. For example, multiple concentric radiation shields can be used in conjunction with variable heating zones to create multiple discrete temperature regions on the glass surface. FIG. 7 illustrates one such non-limiting configuration, in which a furnace 700 is divided into three zones: (i) a hot zone 745 operating at a temperature of about 650 C., a moderate zone 755 operating at a temperature of about 500 C. and (ii) a cold zone 735 operating at a temperature of about 400 C. Two concentric radiation shields 730 with a length L are present between the furnace top wall and the glass structure G. The radiation shields 730 thus may form inner and outer walls defining inner and outer cavities.

[0043] The shields 730 may be aligned so as to form radiation barriers between the hot zone 745 and the moderate zone 755 and between the moderate zone 755 and the cold zone 735. As such, the hot zone 745 may be aligned with a central region of the glass structure G, whereas the moderate zone 755 may be aligned with an outer region of the glass structure G and the cold zone 735 may be aligned with the peripheral region of the glass structure G, although other configurations are envisioned and intended to fall within the scope of the disclosure. It will also be apparent to one skilled in the art that additional shields may be used in conjunction with a furnace having additional heating zones so as to create multiple discrete temperature regions on the surface of the glass structure. A shaping mold is not illustrated in the model but is assumed to be present. The model furthermore only illustrates one side of the system, and symmetry is assumed to exist along line A.

[0044] FIG. 8 illustrates the glass surface temperature distribution using the model presented in FIG. 7 after a 5-minute residence time. The glass temperature is plotted as a function of distance from the center of the glass. Plot H represents the glass temperature distribution achieved using concentric radiation shields with reflective walls (=0.1). Plot I represents the glass temperature distribution achieved using concentric radiation shields not coated with a reflective material (=0.9). Plot J represents the glass temperature distribution achieved in the absence of radiation shields. FIG. 8 further demonstrates that without a radiation shield (Plot J), a more or less linear temperature drop from the center of the glass is realized, whereas the use of two concentric radiation shields can create three discrete temperature regions on the glass surface. Once again, the temperature differential (T) between the different regions of the glass structure can be adjusted by adjusting the reflectivity of the radiation shield walls, where a greater reflectivity (Plot H) results in a greater T as compared to radiation shields with no reflectivity (Plot I).

[0045] The systems disclosed herein may be used to shape glass structures that are thinner than those shaped by current systems. For example, the methods and systems disclosed herein may be used to shape thin glass structures having a thickness ranging from about 0.3 mm to about 3 mm, such as from about 0.5 mm to about 2 mm, or from about 0.7 mm to about 1.5 mm, including all ranges and subranges therebetween. Alternatively, the systems disclosed herein may be used to shape thicker glass structures, for example, glass structures having a thickness greater than about 3 mm, such as greater than about 4 mm, or greater than about 5 mm. As noted above, exemplary glass structures include, but are not limited to, a single sheet of glass, multiple sheets of glass in a single stack, glass-glass laminate structures, and glass-polymer laminate structures.

[0046] Methods

[0047] According to the methods disclosed herein, a glass structure may be positioned on a shaping mold and introduced into a furnace comprising a radiation heating source. The glass structure may then be heated, e.g., to its forming or softening temperature. A radiation shield may be positioned substantially between the glass structure and the radiation heating source, the radiation shield comprising an outer wall defining a cavity having a first opening disposed to face the glass structure and a second opening disposed to face the radiation heating source.

[0048] The glass structure may be introduced into a furnace or other heating device in any manner known in the art. According to various embodiments, the glass structure may be introduced into a furnace using a conveyer, such as a roller or belt conveyor. In certain embodiments, the glass structure may be heated to a forming or softening point, e.g., a point at which the structure can be effectively molded into a new shape. According to various embodiments, the glass structure may be heated to a temperature ranging from about 400 C. to about 1000 C., such as from about 500 C. to about 900 C., from about 600 C. to about 800 C., or from about 650 C. to about 750 C., including all ranges and subranges therebetween.

[0049] The radiation heating source may, in certain embodiments, be a differential radiation heating source and may comprise two or more radiant heating elements or pluralities of radiant heating elements operating at differing temperatures. For example, a first heating element or plurality of heating elements may operate at a temperature ranging from greater than about 600 C. to about 1000 C., such as from about 650 C. to about 900 C., or from about 700 C. to about 800 C. and a second heating element or plurality of heating elements may operate at a different temperature ranging from about 400 C. to about 700 C., such as from about 450 C. to about 650 C., or from about 500 C. to about 600 C., including all ranges and subranges therebetween. Other combinations of temperature ranges are possible and are intended to be part of this disclosure. In such a case, the furnace can be effectively divided into two or more zones, each operating at differing temperatures.

[0050] In additional embodiments, the furnace may be divided into three or more zones, such that the differential radiation heating source comprises three or more radiant heating elements or pluralities of radiant heating elements. For instance, a first heating element or plurality of heating elements may operate at a temperature ranging from about 400 C. to about 600 C., a second heating element or plurality of heating elements may operate at a different temperature ranging from about 500 C. to less than about 700 C., and a third heating element or plurality of heating elements may operate at a different temperature ranging from about 600 C. to about 1000 C. Other combinations of temperature ranges are possible and are intended to be part of this disclosure. Furthermore, the disclosure is not limited to any number of radiation shields, furnace zones, or radiant heating elements.

[0051] Upon introduction into the furnace or heating means, the glass structure can be heated as described above for a given residence time. The residence time may vary depending on the particular system and application. By way of non-limiting example, the residence time may range from about 1 to about 60 minutes or more, such as from about 5 to about 45 minutes, from about 6 to about 30 minutes, from about 12 to about 24 minutes, or from about 15 to about 20 minutes, including all ranges and subranges therebetween. After the given residence time, the glass structure may then exit the furnace or heating means and may undergo various additional processing steps known to those skilled in the art.

[0052] It will be appreciated that the various disclosed embodiments may involve particular features, elements or steps that are described in connection with that particular embodiment. It will also be appreciated that a particular feature, element or step, although described in relation to one particular embodiment, may be interchanged or combined with alternate embodiments in various non-illustrated combinations or permutations.

[0053] It is also to be understood that, as used herein the terms the, a, or an, mean at least one, and should not be limited to only one unless explicitly indicated to the contrary. Thus, for example, reference to a radiation shield includes examples having two or more such shields unless the context clearly indicates otherwise. Likewise, a plurality is intended to denote more than one. As such, a plurality of radiant heating elements includes two or more such heating elements, such as three or more such heating elements, etc.

[0054] Ranges can be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, examples include from the one particular value and/or 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 aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0055] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that any particular order be inferred.

[0056] While various features, elements or steps of particular embodiments may be disclosed using the transitional phrase comprising, it is to be understood that alternative embodiments, including those that may be described using the transitional phrases consisting or consisting essentially of, are implied. Thus, for example, implied alternative embodiments to a system that comprises A+B+C include embodiments where a system consists of A+B+C and embodiments where a system consists essentially of A+B+C.

[0057] It will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the spirit and scope of the disclosure. Since modifications combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the disclosure may occur to persons skilled in the art, the disclosure should be construed to include everything within the scope of the appended claims and their equivalents.