WO2011149800A2

WO2011149800A2 - Apparatus and method for controlling thickness of a flowing ribbon of molten glass

Info

Publication number: WO2011149800A2
Application number: PCT/US2011/037492
Authority: WO
Inventors: Soongyup Lee; Shawn R. Markham
Original assignee: Corning Incorporated
Priority date: 2010-05-26
Filing date: 2011-05-23
Publication date: 2011-12-01
Also published as: JP5974145B2; JP2013528148A; KR20130090790A; WO2011149800A3; TW201141796A; JP2015214487A; JP5778761B2; CN102906036B; KR20180041256A; CN102906036A; KR101850164B1; KR101959697B1; TWI530463B

Abstract

In the formation of sheet material from molten glass, a heat sink is positioned in the forming area for absorbing heat energy from discrete localized portions of the molten glass proximate a draw line or root to control local thickness variations in the sheet and thereby provide a uniform glass sheet thickness across the width of the sheet. The heat sink may be disposed in a fixture configured to rotate or pivot the heat sink (i.e. cooling member) about at least one axis, thereby absorbing heat from the flowing molten glass. The heat sink may also be inserted or withdrawn toward or away from the flowing molten glass to vary the amount of heat energy extracted by the cooling member (and thereby the viscosity and thickness of the local region cooled by the cooling member). The cooling is accomplished without directing a cooling gas from the cooling member toward the flowing molten glass.

Description

APPARATUS AND METHOD FOR CONTROLLING THICKNESS OF A FLOWING

RIBBON OF MOLTEN GLASS

CLAIMING BENEFIT OF PRIOR FILED U.S. APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application Serial No.

61/348,512, filed on May 26, 2010. The content of this document and the entire disclosure of publications, patents, and patent documents mentioned herein are incorporated by reference.

FIELD

[0002] This invention relates to a method and apparatus for controlling the thickness of a flow of molten glass, and more particularly to controlling the thickness of a continuous flow of molten glass in a downdraw glass sheet forming process.

BACKGROUND

[0003] When molten glass is drawn into sheet form, the glass is stretched or attenuated from an initial delivered thickness to a final sheet thickness. In the overflow downdraw process, where molten glass flows downwardly along opposed converging sides of a forming member and is withdrawn as a single ribbon of glass from the root or bottom edge thereof, the initial thickness of the glass ribbon is measured close to the bottom edge of the forming member, which represents the draw line in such an operation. Single sheets of glass are then separated from the free end of the drawn ribbon.

[0004] Obtaining thickness uniformity of the ribbon has been a problem in both updraw and downdraw processes where the thickness characteristics of the final sheet are determined during the attenuation process by both the uniformity of initial thickness and by the uniformity of the glass viscosity. That is, a given thickness variation in the final sheet may be the result of inaccurate metering, imperfections in the glass-contacting sides of the forming member, or by imbalances in the temperature environment of the glass that cause

imperfections in the viscosity profile of the glass flowing toward the draw line.

[0005] Thickness variation in sheet glass is a problem that has been considered by the industry to be inherent in sheet drawing processes, and may manifest itself in several general types of defects, such as wedge, long period wave variations, and short period wave variations. Wedge is a gross thickness variation in which the ribbon or sheet is thicker at one edge than the other edge. Long wave variations are those that have considerable amplitude and extent, such as in excess of several inches, and can be measured by gauging the ribbon along a path in a direction transverse to the direction of the draw. Short wave variations are of small amplitude and pitch, such as about three inches or less, and are generally superimposed on the long wave variations.

[0006] It has been found that to make distortion- free sheet glass, it is necessary to minimize or compensate for local temperature variations or fluctuations within and around the glass in the zone of ribbon formation. Such local variations in temperature in the vicinity of the draw line cause waves, or alternate thick and thin portions running longitudinally in the vertically drawn ribbon. The longitudinal waves or thickness variations, in turn, cause distortion that is highly objectionable from an optical standpoint, particularly when objects are viewed through the glass at a sharp angle to the waves.

[0007] Prior art methods of controlling these thickness variations included flowing air against the molten glass from cooling tubes arrayed along the length of the forming body. The straight cooling tubes were arranged at equal intervals along the forming body length, and positioned so the central longitudinal axis of each tube was perpendicular to a vertical plane passing through the root. Moreover, the cooling tubes were shrouded by an outer tubular shield. Thus, the tubes were rigidly positioned in relationship to the forming body and the glass flow.

[0008] Unfortunately, thickness defects in the glass ribbon may not be positionally stable over long periods of time, nor may the lateral position of the ribbon itself be constant. Thus, the pre-positioned and immovable cooling tubes may at a first instance be properly positioned, but at a second time be ill-positioned to effectively control thickness due to movement of the defect or ribbon.

[0009] Other methods included using cooling tubes mounted in a fixture that provided for swinging the cooling tubes about one or more axes to extend the range of a single tube and permit enhanced cooling effects from the flow of cooling gas.

[0010] The present invention is directed to an improved method of substantial reducing the general type of localized thickness variation identified as short wave variation having a width of several inches or less, and an apparatus therefor. SUMMARY

[0011] When forming a sheet of glass from molten glass, a heat sink is positioned in the forming area proximate a surface of the flowing molten glass to absorbing heat energy from discrete localized portions of the molten glass, and in particular at a location proximate a draw line or root to control local thickness variations in the sheet and thereby provide a uniform glass thickness. The heat sink, or cooling member, may be disposed in a fixture configured to rotate or pivot the heat sink (i.e. cooling member) about at least one axis, thereby allowing for changing the presentation of the cooling member relative to the flowing glass (and the forming body). This facilitates removing heat from the flowing molten glass, and varying the magnitude of this heat removal based on downstream characteristics of the glass, such as thickness. The cooling member may be inserted or withdrawn toward or away from the flowing molten glass, respectively, to vary the amount of heat energy extracted by the cooling member (and thereby the viscosity and thickness of the local region cooled by the cooling member)., or the cooling member may be rotated or pivoted about an axis. The cooling is accomplished without the need to direct a cooling gas from the cooling member toward the flowing molten glass as is done in conventional localized cooling methods.

[0012] In accordance with an embodiment of the present invention, an apparatus for forming a continuous ribbon of molten glass in a downdraw glass making process is disclosed comprising a forming body comprising converging forming surfaces that converge at a root, an enclosure disposed about the forming body, at least one thickness control unit for modifying a local temperature of the molten glass coupled to the enclosure, the thickness control unit comprising an elongate cooling member extending into close proximity of a flow of molten glass flowing over the forming body; and wherein the thickness control unit does not include a mechanism for supplying a flow of air through the cooling member (i.e.

wherein a flow of air is not directed from the cooling member toward the molten glass). The cooling member is preferably rotatable about a vertical axis, meaning the cooling tube can be pivoted or swung about the vertical axis thereby changing the angular orientation of the cooling member relative to the forming body. The cooling member comprises a distal end that is closest to the flow of molten glass, and a proximal end that is farthest from the flow of molten glass (relative to the distal end). Preferably, a distance between the distal end of the elongate cooling member and the forming body can be varied, such as by withdrawing the cooling member away from the molten glass, or by inserting the cooling member closer to the molten glass. The distance between the distal end and the forming body (and flow of molten glass) can also be accomplished by pivoting the cooling member about the vertical axis described above. The cooling member may be a tube having a hollow interior, or a solid rod. However, a solid rod does not pose a risk of creating an air leak between an interior of the enclosure and the environment outside the enclosure through a hollow interior, and can provide better heat conduction. As used herein, a rod is intended to mean an elongate body, and is therefore not construed to mean only a cylindrical rod. Indeed, the elongate body may have a different shape, and the shape of the rod may vary along the length of the body. In some instances, the distal end of the elongate body (cooling member) may have I shape different from a region of the elongate body immediately next to the distal end. For example, a width of the distal end is greater than a width of a proximal end of the cooling member. The distal end might be bulbous, but have a uniform cylindrical shape as one moves down the length of the elongate body away from the bulbous distal end. Put another way, a shape of the distal end is different than a shape of the cooling member adjacent the distal end.

[0013] The apparatus may further comprising a plurality of thickness control units and a plurality of elongate cooling members arrayed horizontally adjacent a length of the forming body, such that the array has a substantially uniform height relative to the forming body root. In other embodiments, a distance between distal ends of the plurality of cooling members and the forming body may not be uniform. This can occur due to a variation in the vertical height of the individual thermal control units, or because the distal ends of each cooling member has been varied by rotating the cooling members about an axis of rotation that is not vertical, e.g. a horizontal axis. Preferably, the distal end of the cooling tube is positioned such that a viscosity of the molten glass proximate the distal end is in a range between 35,000 Poise and 1,000,000 Poise.

[0014] In some embodiments the apparatus may further comprising a temperature modifier disposed about the cooling member configured to varying a temperature of the cooling member and thereby vary a temperature difference between a distal end of the cooling member and the continuous ribbon of molten glass. For example, the temperature modifier can be an electric heating coil or a cooling coil that conveys a flow of coolant. The temperature modifier is used to vary a temperature of the cooling member and thereby alter a temperature difference between the cooling member (and particularly the distal end of the cooling member) and the flow of molten glass proximate the distal end of the cooling member.

[0015] In accordance with another embodiment, a method of controlling a thickness of a continuous ribbon of glass in a fusion downdraw process is described comprising flowing molten glass over converging forming surfaces of a forming body, the converging forming surfaces meeting at a root to form the ribbon of glass, varying a viscosity of a localized area of the flowing molten glass with an elongate cooling member placed in close proximity of the flowing molten glass and wherein the viscosity of the localized area of the flowing molten glass is varied without directing a flow of cooling gas from the elongate cooling member toward the flowing molten glass. The elongate cooling member comprises a proximal and a distal end, the distal end being closer to the flow of molten glass than the proximal end, and wherein a shape of the distal end is different than a shape of the elongate cooling member adjacent to the distal end. The method may also include a plurality of elongate cooling members, wherein a distance between the distal ends of the plurality of elongate cooling members and the flowing molten glass is not uniform. This can arise, for example, if the individual cooling members are rotated or pivoted about an axis of rotation, such as a vertical axis. In some embodiments a distance between the elongate cooling member (the distal end thereof) and the flowing molten glass is varied, such as by inserting or withdrawing the elongate cooling member toward or away from the flowing glass.

[0016] In certain embodiments, an angle between a longitudinal axis of the elongate cooling member and a vertical plane in which the root lies is varied. That is, the cooling member can be rotated or pivoted about an axis passing through the cooling member perpendicular to a central longitudinal axis of the cooling member, which varies an angle between the central longitudinal axis and the forming body (and therefore the flowing molten glass) proximate the cooling member.

[0017] In certain embodiments the central longitudinal axis of the at least one cooling member is perpendicular to a vertical plane within which the root lies. In other words, the central longitudinal axis of the cooling member is perpendicular to the root.

[0018] In certain other embodiments, a temperature of the cooling member is varied to vary an amount of heat extracted from the flowing molten glass in response to a measured thickness of a glass sheet obtained from the glass ribbon. For example, a cooling or heating coil can be brought into contact with, or into the vicinity of, the cooling member, which changes a temperature of the cooling member and a temperature difference between a distal end of the cooling member and the flow of molten glass proximate the distal end. This can be accomplished in response to a thickness measurement conducted downstream of the forming body root. In still other embodiments, an angular position of the cooling member can be modified to vary an amount of heat extracted from the flowing molten glass in response to a measured thickness of a glass sheet obtained from the glass ribbon.

[0019] In yet another embodiment, a distance between a distal end of the cooling member to the flow of molten glass is varied to vary an amount of heat extracted from the flowing molten glass in response to a measured thickness of a glass sheet obtained from the glass ribbon.

[0020] Varying an angular position, distal end distance from the molten glass flow or a temperature of the cooling member can be conducted separately, or in various combinations of each other, as needed.

[0021] Additional features and advantages of the invention are set forth in the detailed description that follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. It is to be understood that the various features of the invention disclosed in this specification and in the drawings can be used in any and all combinations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a cross sectional view of an exemplary fusion downdraw apparatus for producing sheet glass showing the placement of cooling members for controlling localized thickness of a glass ribbon flowing from a forming body.

[0023] FIG. 2 is a side view of the apparatus of FIG. 1 showing placement of a plurality of thickness control units comprising elongate cooling members in a horizontal array across at least a portion of a length of the apparatus and thus a length of the forming body within.

[0024] FIG. 3 is a side view of the apparatus of FIG. 1 showing placement of a plurality of thickness control units comprising elongate cooling members in a horizontal array across at least a portion of a length of the apparatus and thus a length of the forming body within, wherein a vertical height of each thickness control unit relative to the forming body root is not uniform.

[0025] FIG. 4 is a cross sectional view of a portion of a cooling member used in the apparatus of FIG. 1 , showing its placement within a fixture that facilitates at least a side -to- side yaw motion to the elongate cooling member.

[0026] FIG. 5 is a front view of the fixture for manipulating an elongate cooling member, and showing brackets for mounting the fixture on the apparatus of FIG. 1.

[0027] FIG. 6 is a perspective view of a pivot member coupled to an elongate cooling member to form a pivot member - cooling member unit according to an embodiment of the present invention.

[0028] FIGS. 7 and 8 illustrate respectively a view of the pivot member - cooling member unit of FIG. 6 looking straight on at an end of the elongate cooling member and showing the placement of a key in a keyway for coupling the pivot member to a platform, and a partial cross section of the platform showing the placement of the key in a keyway of the platform.

[0029] FIG. 9 is a perspective view of the pivot member - cooling member unit of FIG. 6 showing side-to-side yaw of the elongate cooling member via rotation of the pivot member about a vertical axis.

[0030] FIG. 10 is a perspective view of the pivot member - cooling member unit of FIG. 6 showing up and down pitch of the elongate cooling member via rotation of the pivot member about a horizontal axis.

[0031] FIG. 11 is a perspective view of a cylindrical pivot member - cooling member unit.

[0032] FIG. 12 is a cross sectional view of a portion of the fixture of FIG. 5 illustrating the complementary mating surfaces of the socket members.

[0033] FIG. 13 is an exemplary pivot member - cooling member unit according to an embodiment of the present invention having an arcuate sheet-like distal end to the elongate cooling member.

[0034] FIG. 14 is top view of a plurality of cooling members displayed in an array, and wherein a distance between a distal end of each cooling member and the flowing molten glass is not uniform across the array. [0035] FIG. 15 is top view of a plurality of cooling members displayed in an array, and wherein an angular orientation of each cooling member is not uniform across the array.

DETAILED DESCRIPTION

[0036] In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to one having ordinary skill in the art, having had the benefit of the present disclosure, that the present invention may be practiced in other embodiments that depart from the specific details disclosed herein. Moreover, descriptions of well-known devices, methods and materials may be omitted so as not to obscure the description of the present invention. Finally, wherever applicable, like reference numerals refer to like elements.

[0037] Shown in FIG. 1 is an apparatus 10 for drawing a glass ribbon according to an exemplary fusion downdraw process. Apparatus 10 comprises forming body 12 having an upper channel or trough 14 disposed therein. Forming body 12 includes converging forming surfaces 16a, 16b that converge at a lower edge or draw line 18 from where the molten glass is drawn from the forming body. Lower edge 18 may also be referred to as root 18. Molten glass 20 is supplied to trough 14, and overflows the trough such that the molten glass flows over upper edges of the trough and down converging forming surfaces 16a, 16b as two separate flows of molten glass. These separate flows of molten glass reunite, or fuse, at the forming body root, and continue downward in direction 21 from the root as a single ribbon of glass 22. Hence, the process is sometimes referred to as the fusion process, or the fusion downdraw process. Those portions of the molten glass contacting the forming surfaces of forming body 12 are positioned within the interior of the ribbon drawn from the root 18, leaving the outer surfaces of the ribbon in a pristine condition. Glass ribbon 22 transitions from a viscous liquid at forming body 12 to a visco-elastic material, and finally to an elastic material. Once the ribbon has reached an elastic state, the ribbon is separated, such as by scoring and snapping, to form an individual glass sheet or pane 23.

[0038] To control the thermal environment surrounding the molten glass, forming body 12 is positioned within a refractory enclosure or muffle 24 having structural support members 26 disposed around the refractory material of the muffle. Muffle doors 28 are positioned below muffle 24 along opposite sides of glass ribbon 22, and can be moved inwardly or outwardly along support rails 30. To prevent air leakage or drafts, any space between muffle 24 and muffle doors 28 may be filled with a suitable refractory insulating material 32, such as mineral wool fibers. Outer shield members 34 are affixed to muffle 24 and extend

downward, skirt-like, between muffle 24 to the top of the muffle doors 28, and are typically formed from metal, such as stainless steel. Shield members 34 serve to further eliminate potential drafts resulting from an exchange of air between the atmosphere within the muffle and the atmosphere outside the muffle. However, because each muffle door is configured to move inward or outward relative to the glass ribbon, the outer shield members 34 are not permanently attached to muffle doors 28. In some embodiments, shield members 34 may be an integral part of muffle 24, such as extensions of support members 26.

[0039] A plurality of thickness control units 38 are positioned along sides of forming body 12 near root 18. For example, thickness control units 38 may be coupled to outer shield members 34. Each thickness control unit 38 includes an elongate cooling member 40 spaced apart from adjacent elongate cooling members of adjacent thickness control units, preferably in a substantially horizontal plane 41 (see FIG. 2). However, the position of the elongate cooling units need not be all within the same horizontal plane. For example, in some embodiments the elongate cooling members can be vertically staggered if desired (FIG. 3). Preferably, each cooling member is vertically positioned adjacent a region of the glass ribbon that falls within a viscosity range of between about 35,000 poise and 1,000,000 poise. Each thickness control unit may further comprise a fixture 42 (FIG. 4) that encloses a portion of each cooling member and, if needed, couples the cooling member to the outer shield member. Bracket 44 of fixture 42 can be used to couple each thickness control unit to outer shield member 34 and maintains the elongate cooling members in a spaced apart relationship on outer shield member 34. Each elongate cooling member 40 terminates in close proximity of forming body 12, and in particular in close proximity to root 18. For example, each elongate cooling tube can be within about 6 cm to about 13 cm of the forming body.

[0040] Each elongate cooling member 40 is formed from a material capable of resisting deformation at the high temperature within volume 36, e.g. in excess of 1250°C. In its simplest form, the cooling member is an elongate body extending into close proximity of the forming body, and in particular, into close proximity of the forming body root, preferably less than about 10 cm from the surface of the molten glass. A cooling member may be a solid rod, or hollow, such as a hollow tube. In some embodiments, the cooling member may be glass or quartz, a ceramic or a glass-ceramic. In other embodiments the cooling member may be metallic, such as a metal rod. A solid cooling member advantageously prevents heated air within the confines of the muffle to escape through the cooling member, and therefore reduces the effect of the cooling member on the overall thermal environment within the muffle interior, although a hollow tube comprising baffles or barriers internal to the tube can accomplish this as well. A solid cooling member also has greater thermal mass than a hollow tube, and is more effective in drawing heat energy from the flowing molten glass. Metallic cooling members generally have greater heat conduction properties (conduct more heat energy from the molten glass) than ceramic or glass cooling tubes, but his rapid heat extraction may in some instances be undesirable by creating larger temperature and viscosity variations in the molten glass than needed. Also, the high temperatures encountered in some glass making processes in such proximity to the molten glass may preclude the practical use of metallic cooling members.

[0041] Elongate cooling members 40 are typically circular in a cross section perpendicular to the longitudinal axis of the cooling member (see for example FIG. 7), but may comprise other geometric shapes as well. For example, the cooling members may have oval cross sections, square cross sections, triangular cross sections and so forth. The cooling members may also be substantially flattened such that they form generally rigid strips having a predetermined finite horizontal width. The thickness of each strip can vary over the length of the strip. The appropriate vertical thickness of each strip can be easily determined so as to aid in preventing bending or other deformation.

[0042] Each cooling member serves as an adjustable heat sink that, when brought into close proximity of the flow of molten glass descending the forming body, affects the temperature of a small, localized area of the flowing molten glass, and therefore the viscosity of the molten glass, and ultimately the local thickness of the molten glass. By local thickness what is meant is a thickness of the flowing molten glass along a horizontal strip of the glass that is less than about 2 cm across. It is important to note that a cooling member according to embodiments disclosed herein accomplishes thickness control without the use of a flowing gas that issues from the cooling member, as used by prior art methods, but only by adjusting the proximity of the cooling member to the flow of glass. Thus, the cooling member acts through the heat conductivity of the cooling member. This is largely the result of radiative heat loss from the flowing glass to the cooling member.

[0043] Referring to FIG. 7, each cooling member 40 may be coupled to a pivot member 46, wherein each pivot member includes a passage 48 through which the cooling member extends. The cooling member may be rigidly bonded within pivot member passage 46, such as with high temperature cement, or the cooling member may be held by other methods, such as a compression fitting or clamping that allow movement of the cooling member inward and outward relative to the flow of molten glass descending the forming body. For example, in certain embodiments, a cooling member 40 may be brought closer to a surface of the flowing glass closest to the cooling member, or the cooling member can be withdrawn so that it is farther from the surface of the flowing molten glass. The proximity of the distal end of the cooling member to the surface of the flowing glass material affects the amount of heat energy removed from the molten glass by the cooling member. The cooling member can be oriented so that a longitudinal axis of the cooling member is perpendicular to a vertical plane 47 passing through the root of the forming body, or the longitudinal axis of the cooling member can be angled with respect to vertical plane 47. In the case where cooling member 40 is a flattened strip, the longitudinal axis of the strip is to be construed as an axis running lengthwise through the strip and equidistant from side edges of the strip and equidistant between upper and lower surfaces of the strip (assuming a strip of uniform proportions, i.e. uniform thickness and width).

[0044] In accordance with one embodiment, best shown in FIGS. 5 and 6, each pivot member 46 may be substantially spherical in shape, and may, for example, be a metallic sphere defining the aforementioned passage 48. By substantially spherical what is meant is that a major portion of the outside surface of the pivot member is spherical, or at least those portions that contact the mating surfaces of socket members described more fully herein below. It is acceptable that other portions of the pivot member that do not contact complementary mating surfaces of the socket members are not spherical (or otherwise complementary, as long as these other surface portions do not impede movement of the pivot member along a desired rotation.

[0045] Pivot member 46 may be coupled to a platform 50, comprising a precision rotary stage 51 that allows precise movement of the pivot member about axis of rotation 52 of the platform. Pivot member 46 may be keyed to platform 50 to prevent relative rotational movement between the pivot member and the platform about vertical axis 52. Consequently, key 54 may be positioned between pivot member 46 and platform 50 via corresponding slots or keyways 56, 58, respectively, in each of the platform and pivot member (shown in FIGS. 7 and 8 with the key removed for clarity). Key 54 may be tightly fixed within either the platform keyway or the pivot member keyway (or both). Alternatively, key 54 may be tightly fixed to one of the platform keyway or the pivot member keyway, and only slidably fit within the other. For example, key 54 may be tightly fixed within a spherical pivot member keyway 58, and slidably fit within corresponding and complimentary keyway 58 on platform 50, thereby allowing the spherical pivot member to rotate not only about vertical axis of rotation 52, but to also rotate about a horizontal axis of rotation 53, giving the pivot member, and the cooling member, two degrees of rotational freedom. FIGS. 9 and 10 illustrate movement about these two degrees of freedom, i.e. a horizontal swing or yaw in FIG. 9, and a vertical swing or pitch in FIG. 10. Since the space between the muffle door and the muffle is generally very narrow, however, rotation of the pivot member about a horizontal axis of rotation, that is pitch, is generally limited by contact between the cooling member and elements of the muffle and/or muffle doors. It should be readily apparent that eliminating the key and relying on a clamping force, described farther below, pivot member 46 can be moved in a variety of directions, and not limited to simply pitch and yaw.

[0046] Integrating pivot member 46 and cooling member 40 into a single unit that is not permanently coupled to platform 50 facilitates easy replacement of the pivot member and cooling member combination. For example, a particular cooling member can be easily replaced by removing the broken pivot member - cooling member combination, and simply inserting a new pivot member - cooling member unit. The key - keyway connection between the platform and the new pivot member - cooling member, if used, allows the new pivot member and cooling member to be deployed in the precise angular orientation as the original pivot member. Thus, the pivot member - cooling member unit can be removed without disturbing the position of platform 50 and key 54, and a new pivot member - cooling member unit reinstalled into the same horizontal angular position as the broken unit.

[0047] In the case that only rotation about a vertical axis of rotation is desired (yaw), pivot member 46 may be cylindrical, wherein the central longitudinal axis of the cylindrical pivot member coincides with the platform axis of rotation 52 (FIG. 11). In such cases, the mating surfaces of the socket members described in more detail herein below should be cylindrical to be complimentary to the cylindrical pivot member.

[0048] Elongate cooling member 40 extends through pivot member 46 via passage 48 such that a first portion 60 of cooling member 40 extends from the pivot member in a direction toward the flowing molten glass, and a second portion 62 of the cooling member extends from pivot member 46 away from the glass ribbon. Cooling member 40 includes two ends: proximal end 64 disposed farthest from the flow of molten glass and distal end 66 closest to the flow of molten glass. Proximal end 64 may, if desired, be heated or cooled by a suitable temperature modifier 67, thereby regulating the thickness control afforded by the particular cooling member by varying a temperature of the cooling member, and thereby also varying a temperature difference between the distal end of the cooling member and the flow of molten glass proximate the distal end. For example, the proximal end of cooling member 40 can be coupled with an optional heating or cooling coil (FIG. 1) that heats or cools the cooling member via an electric current or a flowing coolant that circulates through the cooling coil and carries heat from the cooling member. For example, chilled water can be circulated through the cooling coil. The coolant can be subsequently flowed through a heat exchanger to eliminate the heat from the coolant. By increasing the differential temperature between the cooling member and the flowing glass and/or forming body, the cooling effect of the cooling member can be increased.

[0049] Conversely, a cooling member can be heated by an electric winding or coil, thereby retarding the ability of the cooling member to absorb heat from the flowing glass and forming body. By narrowing the differential temperature between the cooling member and the flowing glass and/or forming body, the cooling effect of the cooling member can be reduced.

[0050] Heating and cooling of individual cooling members by a temperature modifier, such as the heating and cooling coils described above, can be incorporated into a feedback loop whereby a local thickness of the glass ribbon can be measured downstream of the cooling members such as near a bottom of the ribbon, or in a glass sheet separated from the ribbon, and the obtained thickness data used to regulate the one or more cooling members. Thickness of the glass can be determined, for example, using laser triangulation methods. Suitable measurement equipment for making thickness measurements includes the GTS2 thickness and profile measurement sensor from LMI Technologies. For example, if the thickness of a local area of the glass ribbon is less than a target thickness, the effectiveness of a cooling member can be enhanced - by moving the cooling member closer to the glass, by increasing flow of coolant to a cooling coil thermodynamically coupled to the cooling member or by decreasing a temperature of the coolant flow. If desired, the feedback loop can be automated by including controller 71 in communication with the thickness measurement detector through control line 73 and further in communication with one or more actuators (not shown) coupled to the cooling member of each thermal control unit through control lines 75 (see FIG. 3). It should be noted that other temperature modifiers can be used to vary a temperature of a cooling member, such as electric strip heaters, thermoelectric cooling elements and the like, and the illustration of a cooling coil in FIG. 3 is not for the purpose of limitation.

[0051] Fixture 42 further comprises front or first socket member 74 and rear or second socket member 76, best seen in FIG. 12 and shown without pivot member 46 for clarity. First socket member 74 includes an interior surface 78 where at least a portion of the interior surface is complimentary to a portion of the pivot member. An opening 80 extends through a thickness of the first socket member such that when pivot member 46 is in contact with the

complimentary portion of socket interior surface 78, cooling member 40 extends through opening 80. Opening 80 is sized to allow movement of the pivot member and cooling member without obstruction over the intended range of movement. That is, opening 80 is sized to allow the pivot member to rotate at least about axis 52 and therefore cooling member 40 to swing or yaw within the opening. Preferably, cooling member 40 is free to swing through an angle of at least about 40 degrees. Similarly, second socket member 76 includes an interior surface 82 where at least a portion of interior surface 82 is complimentary to pivot member 46, and a second opening 84 through which cooling member 40 extends that allows the second portion of cooling member 40 to swing when pivot member 46 is rotated.

[0052] Rear socket member 76 is coupled to front socket member 74 such that pivot member 46 disposed between the front and rear socket members is held stationary. For example, the front and rear socket members can be coupled one to the other via bolts, screws, clips or other suitable attachment methods so that pivot member 46 is clamped between the socket members. For example, socket members 74 and 76 are shown coupled with bolts in FIG. 11. Pivot member 46 can be first positioned such that cooling member 40 is within a predetermined proximity and location of the flowing molten glass, the clamping elements (e.g. bolts) tightened to lock the pivot member, and the cooling member, in the desired orientation.

[0053] The ability of the pivot member according to the present embodiment to rotate about axis 52 and therefore "swing" cooling member 40 through a horizontal arc facilitates a reduction in the number of thickness control units 38 needed to reach a width of the molten glass compared to fixed cooling members. For example, elongate cooling member 40 can be rotated via pivot member 46 through an angle of at least about 10 degrees, 20 degrees, 30 degrees, or even more than 40 degrees. In addition, by relying on the thermal conductive properties of the cooling member rather than the emission of a cooling gas, the cooling members are simpler to install and maintain (e.g. no external piping to deliver cooling gas and no complicated gas metering).

[0054] In contrast with prior cooling methods, and in accordance with the present

embodiment, cooling members 40 can be spaced farther apart than fixed cooling members. If cooling is required in a particular region of the flowing molten glass, owing to a thickness disruption, a cooling member located closest to the defect can be laterally swung into position by rotating platform 50, and thereby cooling member 40, so the cooling member can be brought into close proximity to the defect region. Additionally, each cooling member may be withdrawn (away from the flow of molten glass), or inserted (toward the flow of molten glass), to vary the distance between the flow of molten glass and the distal end of the cooling member. As a result, the number of openings into the muffle interior volume is reduced. Reducing the number of openings reduces the risk of an uncontrolled draft into (or out of) volume 36 surrounded by muffle 24 due to a leak. Each elongate cooling member need not be moved in unison with other cooling members, either rotationally via pivot member 46, or inwardly or outwardly toward or away from the flow of molten glass.

[0055] In some embodiments, elongate cooling member 40 is straight, and has a uniform cross sectional shape perpendicular to the longitudinal axis of the cooling. However, in other embodiments each cooling member may comprise a modified distal end that has a shape different than a portion of the cooling member adjacent to the distal end. A pivot member may include, for example a crescent-shaped distal end, a partially cylindrical distal end, or a disk-shaped distal end. FIG. 13 shows an elongate cooling member 40 having an arcuate shaped end similar to a portion of a cylindrical wall. The cooling member may include a more complicated distal end as desired to control a localized area of the flowing glass, such as combined portions of different geometric shapes. These modified cooling members have a distal end that is wider (in a direction perpendicular to the longitudinal axis 88 of the elongate cooling member) than the proximal end of the cooling members.

[0056] It should be apparent, based on the preceding disclosure, that positioning of individual cooling members can be used to effectively control the local thickness of a ribbon of glass drawn from molten glass, and ultimately, the thickness of individual glass sheets or panes separated from the ribbon. In accordance with the embodiments described herein, individual cooling members can be rotated (pivoted) about one or more axes to vary the angular orientation of the cooling member relative to the forming body and the molten glass. For example, individual cooling members can be pivoted about a vertical axis so that a side-to- side swing can be produced. Individual cooling members can be inserted closer to the flow of molten glass, thereby reducing the distance between a distal end of the cooling member and the flow of molten glass. Alternatively, individual cooling members can be withdrawn so that the distance between the flow of molten glass and the distal end of the cooling member is increased. Accordingly, the angular orientation of an individual cooling member, and the distance from the distal end of each individual cooling member and the flow of molten glass, can be effected independently of the angular orientation and distal end distance of another cooling member in an array of cooling members. Thus, a cooling profile across a width of the flowing glass appropriate for a particular glass making setup can be introduced. FIG. 14 depicts an exemplary array of cooling members seen from the top, wherein the individual cooling members are positioned at different distances from the flow of molten glass (where here, the downward flow of molten glass is represented by the edge-on view of plane 100). Each cooling tube of FIG. 14 is represented as a straight rod, but in accordance with an earlier description, the size and shape of each cooling member can be varied depending on need. Similarly, FIG. 15 depicts an array of cooling members having different angular orientation to produce a different cooling profile across a width of the flow of molten glass, again looking down on the array of cooling members. In FIG. 15, cooling members are shown adjusted for both distance of the distal end of each cooling member and the flow of molten glass, and angular position. [0057] Exemplary, non-limiting embodiments include:

[0058] CI . An apparatus for forming a continuous ribbon of molten glass in a downdraw glass making process comprising:

a forming body comprising converging forming surfaces that converge at a root; an enclosure disposed about the forming body;

at least one thickness control unit for modifying a local temperature of the molten glass coupled to the enclosure, the thickness control unit comprising an elongate cooling member extending into close proximity of a flow of molten glass flowing over the forming body; and

wherein a flow of air is not directed from the cooling member toward the molten glass.

[0059] C2. The apparatus according to CI, wherein the cooling member is rotatable about a vertical axis.

[0060] C3. The apparatus according to CI or C2, wherein the cooling member comprises a distal end closest to the flow of molten glass, and a distance between the distal end of the elongate cooling member and the forming body can be varied.

[0061] C4. The apparatus according to any of CI to C3, wherein the cooling member is a solid rod.

[0062] C5. The apparatus according to any of CI to C4, wherein the cooling member comprises a distal end closest to the flow of molten glass, and wherein a shape of the distal end is different than a shape of the cooling member adjacent the distal end.

[0063] C6. The apparatus according to any of C5, wherein a width of the distal end is greater than a width of a proximal end of the cooling member.

[0064] C7. The apparatus according to any of CI to C6, further comprising a plurality of elongate cooling members arrayed horizontally adjacent a length of the forming body.

[0065] C8. The apparatus according to C7, wherein a distance between distal ends of the plurality of cooling members and the forming body are not uniform.

[0066] C9. The apparatus according to any of CI to C8, wherein a distal end of the cooling member is positioned such that a viscosity of the molten glass proximate the distal end is in a range between 35,000 Poise and 1,000,000 Poise. [0067] CIO. The apparatus according to any of CI to C9, further comprising a temperature modifier configured to vary a temperature of the cooling member and thereby vary a temperature difference between a distal end of the cooling member and the continuous ribbon of molten glass.

[0068] CI 1. The apparatus according to any of CI to CIO, further comprising a plurality of cooling members, and a vertical height of a first cooling member of the plurality of cooling members relative to the root is different from a vertical height of a second cooling member of the plurality of cooling members relative to the root.

[0069] CI 2. A method of controlling a thickness of a continuous ribbon of molten glass in a fusion downdraw process comprising:

flowing molten glass over converging forming surfaces of a forming body, the converging forming surfaces meeting at a root to form a ribbon of glass;

varying a viscosity of a localized area of the flowing molten glass with an elongate cooling member placed in close proximity of the flowing molten glass; and

wherein the viscosity of the localized area of the flowing molten glass is varied without directing a flow of cooling gas from the elongate cooling member toward the flowing molten glass.

[0070] C13. The method according to CI 2, wherein the elongate cooling member comprises a proximal and a distal end, the distal end being closer to the flow of molten glass than the proximal end, and wherein a shape of the distal end is different than a shape of the elongate cooling member adjacent to the distal end.

[0071] C14. The method according to any of C12 or C13, wherein a distance between the elongate cooling member and the flowing molten glass is varied.

[0072] C15. The method according to any of C12 to CI 4, wherein an angle between a longitudinal axis of the elongate cooling member and a vertical plane in which the root lies is varied.

[0073] C16. The method according to any of C12 to C15, wherein a portion of a longitudinal axis of the at least one cooling member is perpendicular to a vertical plane within which the root lies.

[0074] C17. The method according to any of C12 to C16, further comprising modifying a temperature of the cooling member to vary an amount of heat extracted from the flowing molten glass in response to a measured thickness of a glass sheet obtained from the glass ribbon.

[0075] C18. The method according to any of C12 to C17, further comprising modifying an angular position of the cooling member to vary an amount of heat extracted from the flowing molten glass in response to a measured thickness of a glass sheet obtained from the glass ribbon.

[0076] C19. The method according to any of C12 to C18, further comprising modifying a distance between a distal end of the cooling member to vary an amount of heat extracted from the flowing molten glass in response to a measured thickness of a glass sheet obtained from the glass ribbon.

[0077] C20. The method according to any of C12 to C19, wherein the varying step comprises a plurality of elongate cooling members, each cooling member comprising a proximal and a distal end, and wherein a distance between the distal ends of the plurality of elongate cooling members and the flowing molten glass is not uniform.

[0078] It should be emphasized that the above-described embodiments of the present invention, particularly any "preferred" embodiments, are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiments of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.

Claims

What is claimed is:

1. An apparatus (10) for forming a continuous ribbon of molten glass (22) in a downdraw glass making process comprising:

a forming body (12) comprising converging forming surfaces (16a, 16b) that converge at a root (18);

an enclosure (24) disposed about the forming body;

at least one thickness control unit (38) for modifying a local temperature of the molten glass coupled to the enclosure, the thickness control unit comprising an elongate cooling member (40) extending into close proximity of a flow of molten glass flowing over the forming body; and

2. The apparatus according to claim 1, wherein the cooling member (40) is rotatable about a vertical axis.

3. The apparatus according to claim 1 or claim 2, wherein the cooling member (40) comprises a distal end closest to the flow of molten glass, and a distance between the distal end (66) of the elongate cooling member and the forming body (12) can be varied.

4. The apparatus according to any of claims 1 to 3, wherein the cooling member (40) is a solid rod.

5. The apparatus according to any of claims 1 to 4, wherein the cooling member (40) comprises a distal end (66) closest to the flow of molten glass, and wherein a shape of the distal end is different than a shape of the cooling member adjacent the distal end.

6. The apparatus according to claim 5, wherein a width of the distal end (66) is greater than a width of a proximal end (64) of the cooling member (40).

7. The apparatus according to any of claims 1 to 6, further comprising a plurality of elongate cooling members (40) arrayed horizontally adjacent a length of the forming body (12).

8. The apparatus according to claim 7, wherein a distance between distal ends (66) of the plurality of cooling members (40) and the forming body (12) are not uniform.

9. The apparatus according to any of claims 1 to 8, wherein a distal end (66) of the cooling member (40) is positioned such that a viscosity of the molten glass proximate the distal end is in a range between 35,000 Poise and 1,000,000 Poise.

10. The apparatus according to any of claims 1 to 9, further comprising a temperature modifier (67) configured to vary a temperature of the cooling member (40) and thereby vary a temperature difference between a distal end (66) of the cooling member and the continuous ribbon (22) of molten glass.

11. The apparatus according to any of claims 1 to 10, further comprising a plurality of cooling members (40), and a vertical height of a first cooling member of the plurality of cooling members relative to the root (18) is different from a vertical height of a second cooling member of the plurality of cooling members relative to the root.

12. A method of controlling a thickness of a continuous ribbon (22) of molten glass in a fusion downdraw process comprising:

flowing molten glass over converging forming surfaces (16a, 16b) of a forming body (12), the converging forming surfaces meeting at a root (18) to form a ribbon of glass;

varying a viscosity of a localized area of the flowing molten glass with an elongate cooling member (40) placed in close proximity of the flowing molten glass; and

13. The method according to claim 12, wherein the elongate cooling member (40) comprises a proximal end (64) and a distal end (66), the distal end being closer to the flow of molten glass than the proximal end, and wherein a shape of the distal end is different than a shape of the elongate cooling member adjacent to the distal end.

14. The method according to claim 12 or claim 13, wherein a distance between the elongate cooling member (40) and the flowing molten glass is varied.

15. The method according to any of claims 12 to 14, wherein an angle between a

longitudinal axis of the elongate cooling member (40) and a vertical plane in which the root (18) lies is varied.

16. The method according to any of claims 12 to 15, wherein a portion of a longitudinal axis of the at least one cooling member (40) is perpendicular to a vertical plane within which the root (18) lies.

17. The method according to any of claims 12 to 16, further comprising modifying a temperature of the cooling member (40) to vary an amount of heat extracted from the flowing molten glass in response to a measured thickness of a glass sheet obtained from the glass ribbon.

18. The method according to any of claims 12 to 17, further comprising modifying an angular position of the cooling member (40) to vary an amount of heat extracted from the flowing molten glass in response to a measured thickness of a glass sheet obtained from the glass ribbon (22).

19. The method according to any of claims 12 to 18, further comprising modifying a distance between a distal end (66) of the cooling member (40) to vary an amount of heat extracted from the flowing molten glass in response to a measured thickness of a glass sheet obtained from the glass ribbon (22).

20. The method according to any of claims 12 to 19, wherein the varying step comprises a plurality of elongate cooling members (40), each cooling member comprising a proximal end (64) and a distal end (66), and wherein a distance between the distal ends of the plurality of elongate cooling members and the flowing molten glass is not uniform.