WO2016057368A1

WO2016057368A1 - Method of modifying a flow of molten glass and apparatus therefor

Info

Publication number: WO2016057368A1
Application number: PCT/US2015/053936
Authority: WO
Inventors: Olus Naili Boratav; William Anthony Whedon
Original assignee: Corning Incorporated
Priority date: 2014-10-06
Filing date: 2015-10-05
Publication date: 2016-04-14
Also published as: JP2017530932A; CN107001099A; TW201619077A; KR20170066487A

Abstract

A method of modifying a flow of molten glass comprising flowing the molten glass from a forming body as a molten glass ribbon and intersecting the molten glass ribbon with a flow member spaced apart from a bottom edge of the forming body and extending into the molten glass ribbon a predetermined distance from an edge thereof such that the molten glass flows over first and second opposing major surfaces of the flow member.

Description

METHOD OF MODIFYING A FLOW OF MOLTEN GLASS AND APPARATUS

THEREFOR

[0001] This application claims the benefit of priority under 35 U.S.C. § 1 19 of U.S.

Provisional Application Serial No. 62/060,205, filed on October 6, 2014, the content of which is relied upon and incorporated herein by reference in its entirety.

BACKGROUND

Field

[0002] The present disclosure relates generally to forming a glass ribbon by a down draw method, and more particularly to controlling the flow of molten glass drawn from a forming body.

Technical Background

[0003] In one method of forming thin, high quality glass for such purposes as the manufacture of display devices, a molten precursor material, hereinafter molten glass, is flowed from a forming body to form a ribbon of molten glass that cools into a solid glass ribbon in an elastic state as the ribbon descends from a bottom edge of the forming body. The ribbon may then be cut into separate sheets of glass that may be further processed and then shipped to equipment manufacturers.

[0004] As the ribbon of molten glass descends from the forming body, the ribbon width decreases, and the lateral edges of the ribbon thicken Such thickened edge portions are commonly referred to as beads. Both effects decrease the total useable area of the glass ribbon and constitute a manufacturing loss. Thus, manufacturing yield can be increased by increasing the ribbon width and/or decreasing the size of the unusable edge portions.

[0005] In other cases, the size of the lateral edges themselves, rather than the width of the ribbon, may be of primary concern, such as for ultra-thin glass.

SUMMARY

[0006] The ribbon-shaped flow of molten glass from a forming body, such as from the forming body of a fusion down-draw process, or a slot draw process, can undergo lateral attenuation, wherein lateral edges of the ribbon draw inward. On the other hand, the reduced lateral extension causes the edge portions of the glass ribbon to increase in thickness. This can make those thickened edge portions (beads) commercially unusable. In accordance with embodiments disclosed herein, a flow member is disclosed that, when inserted into the edges of the glass ribbon such that the glass ribbon flows over the flow member, can produce thinner beads, increase usable glass, thereby increasing manufacturing efficiency, and reduce the amount of precious metal (e.g. platinum) utilized in the manufacturing process.

[0007] In one aspect, a method of modifying a flow of molten glass is described comprising flowing molten glass from a forming body as a molten glass ribbon; and intersecting the molten glass ribbon with a flow member, the flow member spaced apart from the forming body and extending into the molten glass ribbon a predetermined distance such that the molten glass ribbon flows over and around the flow member.

[0008] The step of flowing molten glass from the forming body can comprise flowing the molten glass from a bottom edge of the forming body where converging forming surfaces of the forming body converge.

[0009] In some embodiments the flow member can be movable in a vertical direction. In some embodiments the flow member can be movable in a horizontal direction. In some embodiments the flow member can be movable in both a vertical and horizontal direction.

[0010] The flow member may have a plate-like construction wherein the flow member comprises first and second major surfaces over which the molten glass ribbon flows, and the first and second major surfaces may be parallel with each other.

[0011] In some embodiments the flow member may have a plate-like construction wherein the flow member can comprise first and second major surfaces over which the molten glass ribbon flows, and the first and second major surfaces of the flow member are parallel with a vertical plane passing through a bottom edge of the forming body.

[0012] In some embodiments the flow member comprises first and second major surfaces over which the molten glass ribbon flows, and the molten glass ribbon flows over an entire surface area of the first and second major surfaces.

[0013] The flow member may be positioned between an upper-most edge roll and the bottom edge of the forming body.

[0014] In some embodiments the flow member can be heated, for example by establishing an electric current within a heating element positioned on or in the flow member.

[0015] In some embodiments the flow member is substantially submerged within the glass ribbon, such as when the flow member is configured as a wire or rod, or an elongated flat strip.

[0016] In some embodiments a surface area of the flow member wetted by the molten glass can be varied. [0017] In some embodiments a distance between an upper most edge of the flow member wetted by the molten glass ribbon and a bottom edge of the forming body can be varied.

[0018] The method may further comprise intersecting the molten glass ribbon with a plurality of flow members, each flow member of the plurality of flow members extending into the molten glass ribbon a predetermined distance from an edge thereof such that at least a portion of a total surface area of the flow members is wetted by the molten glass.

[0019] In another aspect, an apparatus for drawing a molten glass ribbon is described comprising a forming body from which molten glass ribbon is drawn and a flow control apparatus comprising a flow member positioned vertically beneath and spaced apart from the forming body, the flow member comprising opposing planar surfaces, the flow member spaced apart from the forming body in a vertical plane passing through a bottom edge of the forming body and positioned a predetermined distance L from a vertical plane extending through the forming body and perpendicular to a longitudinal axis of the forming body, such that the molten glass ribbon from the forming body can flow over the major surfaces of the flow member, where L is measured from a distal end of the flow member to the vertical plane.

[0020] The flow control apparatus may further comprise a positioning device configured to vary the distance L. The flow control apparatus may be configured to move the flow member in a vertical direction, in a horizontal direction, or both a vertical and a horizontal direction.

[0021] The apparatus for drawing a molten glass ribbon may further comprise a plurality of flow control apparatus, each flow control apparatus of the plurality of flow control apparatus comprising a flow member.

[0022] In yet another aspect, a method of modifying a flow of molten glass is disclosed comprising flowing molten glass from a forming body as a molten glass ribbon and intersecting the molten glass ribbon with a flow member comprising first and second major surfaces, the flow member spaced apart from a bottom edge of the forming body from which the molten glass is drawn and extending into the molten glass ribbon a predetermined distance such that the molten glass ribbon flows over the flow member.

[0023] Additional features and advantages of the embodiments disclosed herein will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings. [0024] It is to be understood that both the foregoing general description and the following detailed description present embodiments of the disclosure, and are intended to provide an overview or framework for understanding of those embodiments. The accompanying drawings are included to provide a further understanding of the embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the disclosure and together with the description serve to explain the principles and operations of the embodiments.

BRIEF DESCRIPTION OF THE FIGURES

[0025] FIG. 1 is an elevational view of an example glass making apparatus according to an embodiment of the present disclosure;

[0026] FIG. 2 is a stylized cross sectional view of a glass ribbon formed by a down draw process, illustrating the beads (edge portions) of the ribbon and the quality region;

[0027] FIGS. 3 A and 3B show perspective views of fusion-style forming bodies comprising conventional edge directors;

[0028] FIG. 4 is a cross sectional end view of the forming body of FIG. 1 illustrating a flow member submerged within the flowing molten glass ribbon according to an embodiment disclosed herein;

[0029] FIG. 5 is a perspective view of a flow control apparatus comprising a generally rectangular flow member according to an embodiment of the present disclosure;

[0030] FIG. 6 is a front view of a flow control apparatus according to another embodiment of the present disclosure comprising a triangular flow member;

[0031] FIGS. 7A - 7C are schematic views of various flow member shapes according to embodiments disclosed herein;

[0032] FIGS. 8A and 8B are cross sectional edge views of flow members according to embodiments disclosed herein comprising at least one curved major surface;

[0033] FIG. 9 is a front view of a flow control apparatus according to another embodiment of the present disclosure comprising an elongated strip-like flow member;

[0034] FIG. 10 is a front view of a flow control apparatus according to another embodiment of the present disclosure comprising a rod-like or wire flow member;

[0035] FIG. 11 is a photograph of an experimental set up showing a comparison between the performance of a conventional edge director (right side) and an embodiment of a flow member according to an embodiment of the present disclosure (left side), where the flow member is completely submerged in the edge flow of the molten glass ribbon;

[0036] FIG. 12 is a photograph of another experimental set up showing a comparison between the performance of a conventional edge director (right side) and a flow member according to another embodiment of the present disclosure (left side) where the flow member is only partially extended into the edge flow of the molten glass ribbon.

[0037] FIG. 13 is a stylized cross sectional view of a glass ribbon formed by the example down draw process of FIG. 1, illustrating a bead (thickened edge portion) of the ribbon wherein the two flows that formed the ribbon are not fully joined; and

[0038] FIG. 14 is a stylized cross sectional view of the glass ribbon formed by the example down draw process of FIG. 1, illustrating a formed airline.

DETAILED DESCRIPTION

[0039] Reference will now be made in detail to various embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. While embodiments of flow control apparatus described herein may be used in different down draw glass making processes, including without limitation slot draw and fusion processes, the following embodiments are described in the context of a fusion process.

[0040] FIGS. 1 is a side view of an example glass forming apparatus 10 according to the present disclosure comprising melting vessel 12, fining vessel 14, stirring vessel 16, delivery vessel 18 and delivery vessel exit conduit 20. Melting vessel 12 is coupled to fining vessel 14 via melting- vessel-to-fining- vessel connecting conduit 22, and fining vessel 14 is joined to mixing vessel 16 via fining- vessel- to-stirring-vessel connecting conduit 24. Glass raw materials, hereinafter "batch", is fed to melting vessel 12 as indicated by arrow 26 and heated to a first temperature Tl to produce a viscous molten material, hereinafter molten glass 28. By way of example and not limitation, Tl for glass compositions suitable for the manufacture of display panels, e.g. aluminoborosilicate glasses, may be at a temperature in a range from about 1500°C to about 1600°C.

[0041] Molten glass 28 flows to fining vessel 14 through melting-vessel-to-fining- vessel connecting conduit 22. At fining vessel 14 the molten glass 28 is heated to a second temperature T2 greater than the melting temperature Tl in melting vessel 12, thereby further reducing the molten glass viscosity. By way of example and not limitation, T2 for glass compositions suitable for the manufacture of display panels may be a temperature in a range from about 1600°C to about 1700°C. The viscosity reduction in molten glass 28 produced by an increase in temperature from Tl to T2 aids the rise of bubbles within the molten glass to a free surface of the molten glass within fining vessel 14. In addition, multivalent compounds included in the molten glass, commonly called fining agents and typified by, for example, oxides of tin (Sn), cerium (Ce), arsenic (As) and/or antimony (Sb), chemically reduce at the fining vessel temperature T2, thereby releasing oxygen into the molten glass as bubbles. These bubbles rise through the low- viscosity molten glass to the free surface 30 of the molten glass within fining vessel 14, collecting other gases produced during the melting process as the bubbles rise. At free surface 30, the gases comprising the bubbles are released and vented from the fining vessel.

[0042] The molten glass flows from fining vessel 14 to mixing vessel 16 where the molten glass is mechanically mixed to homogenize the molten glass. For example, mixing vessel 14 may be a stirring vessel comprising a stirrer 32 rotatably mounted in the stirring vessel that stirs the molten glass within the stirring vessel. However, in other embodiments, mixing vessel 14 may be a static mixing vessel including non-moving vanes configured to alter a flow of the molten glass. The molten glass flows from mixing vessel 16 to delivery vessel 18 through mixing-vessel-to-delivery-vessel connecting conduit 34. The molten glass is also cooled to a temperature at or near the forming temperature during its transit to delivery vessel 18. A direction of flow of the molten glass is changed within delivery vessel 18, for example from a substantially horizontal flow to a substantially vertical flow, and the molten glass subsequently delivered via exit conduit 20 to inlet conduit 36 of forming body 38.

[0043] Forming body 38 may include converging forming surfaces 40 on an exterior of forming body 38 that meet along a bottom edge 42 of the forming body. Forming body 38 may further comprise a trough 44 positioned in an upper surface of the forming body to which molten glass 28 is supplied by inlet conduit 36. The molten glass flows from inlet conduit 36 into trough 44 and overflows the trough walls. The overflowing molten glass flows over converging forming surfaces 40 as separate streams of molten glass that join at bottom edge 42 to form a molten glass ribbon 46 that is drawn downward in a draw direction 48 by a combination of gravity and suitably positioned rolls such as edge rolls and/or pulling rolls. [0044] As molten glass ribbon 46 descends downward, surface tension causes the ribbon to decrease in width while the molten glass ribbon is still at a formable viscosity, a phenomenon referred to hereinafter as attenuation. The attenuation causes edge portions 50 (See FIG. 2) of the molten glass ribbon to increase in thickness relative to a central region of the ribbon. These edge portions 50 of increased thickness are known as beads. The useable area of the glass ribbon is that central area of the glass ribbon between the beads having a generally uniform thickness, i.e., quality area 52, as shown in a lateral cross sectional view of an example glass ribbon 46 in FIG. 2. Typically, the thickness of the quality area once the ribbon has reached a final thickness is equal to or less than about 2 millimeters, for example equal to or less than about 1 millimeter, or equal to or less than about 0.7 millimeter. In some embodiments a thickness of the quality area after the ribbon has reached a final thickness is in a range from about 0.1 millimeter to about 0.7 millimeter. In still other embodiments, the final thickness of the quality area can be in a range from about 0.01 millimeter to about 0.1 millimeter. As described, the edge portions 50 represent a deviation from the desired ribbon thickness. Moreover, for ultra-thin glass ribbon, for example glass ribbons where a thickness of the quality area is on the order of 0.1 millimeter or less, the thickened edge portions may be an impediment to rolling the glass ribbon into a roll shape, for example on a receiving spool during a winding process. Accordingly, the thickened edge portions may be removed. In some processes, the thickened edge portions are removed from individual sheets of glass cut from the glass ribbon. In other processes, the thickened edge portions may be removed directly from the ribbon during the drawing process. In either case, at least because the molten glass ribbon both decreases in overall width and edge portions 50 of the molten glass ribbon become thicker than the quality area 52 and must eventually be removed, attenuation decreases the commercially usable width of glass ribbon 46.

[0045] Returning to FIG. 1 , the molten glass ribbon is drawn from bottom edge 42 of forming body 38 both by the influence of gravity and, for example, by counter-rotating pairs of opposing pulling rolls 54 positioned such that the opposing rolls of each pair of pulling rolls grip the thickened edge portions 50 and apply a downward pulling force on the molten glass ribbon 46. Other rolls, generally referred to as edge rolls 56, may be positioned above and/or below the pulling rolls to assist in the drawing process. Edge rolls apply a downward pulling force on the molten glass ribbon, but also counteract the inward contraction of the glass ribbon, thereby minimizing such contraction of the glass ribbon in a direction orthogonal to the draw direction. Like pulling rolls, edge rolls 56 are also arranged in opposing relationship when engaging the edge portions of the glass ribbon. Edge rolls 56 may be driven or un-driven, depending on their location and specific function. Rotational axes of edge rolls 56 may be horizontal or angled with respect to a horizontal reference plane. There is, however, a limit to how close to bottom edge 42 of forming body 38 that the uppermost edge rolls 56 can be located, owing at least to the placement of other equipment, such as heating and cooling equipment used to control the temperature and viscosity of the molten glass ribbon and thereby its thickness. Thus, there can be a region of the molten glass ribbon immediately below bottom edge 42 of forming body 38 and above the upper-most edge rolls 56 that is un-contacted by either the edge rolls or the pulling rolls and therefore subject to attenuation.

[0046] Prior art methods of increasing ribbon width have employed a web surface 58 ("edge director") extending between the downwardly converging forming surfaces 40 of forming body 38 and a projecting edge portion or dam 60, as illustrated in FIG. 3A. U.S. Patent No. 3,451 ,798, for example, discloses such a web surface that terminates at its lowest extent at a horizontal plane passing through the bottom edge of the forming body, the line along which the downwardly converging forming surfaces of forming body meet. U.S. Patent No. 3,537,834 discloses a forming apparatus comprising a web surface similar to that disclosed in U.S. Patent No. 3,451 ,798 which, at its lowest point may be extended below the bottom edge of the forming body. Such an edge director 58 is shown in FIG. 3B.

US7409839 discloses yet another edge director that includes at least two planar surfaces positioned at angles to one another, and, as disclosed in U.S. Patent No. 3,537,834, at its lowest point may be extended below the bottom edge of the forming body.

[0047] While the foregoing edge directors are effective at reducing or preventing lateral attenuation of the molten glass ribbon, they tend nevertheless to enlarge the beads beyond what would normally occur in the absence of those edge directors. The edge directors also use a significant amount of platinum in their construction and therefore represent a significant cost. As described above, the beads are undesirable as they represent a localized increase in the thickness of the glass ribbon and must be removed prior to sale of a glass sheet cut from the ribbon. As such, the beads represent waste and an undesirable cost to the manufacturing process. Thus, the use of edge directors as described in the prior art involves a tradeoff: increased ribbon width at the expense of increased bead size and capital expense.

[0048] During ordinary usage, the prior art edge directors described above typically provide for a net gain in useable ribbon area, which is to say the overall increase in ribbon width tends also to increase the quality area of the ribbon more than the increase in bead size reduces the ribbon quality area, resulting in a net gain in ribbon width. However, the ever- present need to reduce manufacturing costs warrants additional innovation to increase the useable area of the ribbon. To that end, an apparatus is described herein that can produce an effective increase in ribbon width over that attainable even if a glass ribbon is drawn from a bare bottom edge of the forming body (i.e. in the absence of the foregoing prior art edge directors), while producing a smaller thickened edge portion than if traditional edge directors are employed.

[0049] Accordingly, and referring to FIGS. 1 , 4 - 6, a flow control apparatus 62 is positioned below bottom edge 42 of forming body 38 and above the upper-most set of edge rolls 56. Flow control apparatus 62 comprises a flow member 64 positioned below and spaced apart from (separate from) bottom edge 42 of forming body 38, and above the uppermost set of edge rolls 56. Although there may be a plurality of flow control apparatus 62, a single flow control apparatus will be described with the understanding a second similar or identical flow control apparatus 62 may be employed. For example, a similar or identical second flow control apparatus 62 may be positioned laterally opposite from a first flow control apparatus. In other embodiments, multiple flow control apparatus 62 may be positioned along an edge of the glass ribbon, vertically spaced apart.

[0050] As shown in FIG. 1, flow member 64 is positioned below and spaced apart from bottom edge 42 proximate a first end 66 of forming body 38 (a second flow member 64, comprising a second flow control apparatus 62, may be positioned below and spaced apart from bottom edge 42 proximate a second end 67 of forming body 38). The upper-most edge 68 of each flow member 64 can be positioned, for example, a distance of at least 1 cm below bottom edge 42 of forming body 38, for example in a range from about 1 cm to about 5 cm. Thus, flow member 64 is not in contact with forming body 38. The lack of connection between a flow member 64 and forming body 38 makes replacement of the flow member and/or the flow control apparatus 62 easier than if the flow member was attached to the forming body. In accordance with the present embodiment, flow member 64 is configured with first and second major surfaces, i.e. first major surface 70 and second major surface 72. An example flow control apparatus 62, as shown in FIG. 5, comprises a flow member 64 including the foregoing first major surface 70 and a second major surface 72. First and second major surfaces 70 and 72 may, for example, be planar, and may be parallel such that flow member 64 is of a plate-like configuration. Moreover, first major surface 70 and second major surface 72 may be parallel to a vertical plane 74 passing through bottom edge 42 (see FIG. 4). The flow member illustrated in FIG. 5 is of a generally rectangular shape. An alternative embodiment wherein the flow member is generally triangular in shape is shown in FIG. 6. In still other embodiments, flow member 64 may include one or more curved edges. It should be further noted that major surfaces 70, 72 need not be planar, or parallel. For example, major surfaces 70, 72 may be curved. For example, FIGS. 7A and 7B illustrate alternative embodiments of flow member 64 comprising a curved edge 69. FIG. 7C illustrates another embodiment of a triangular forming member configured as a right triangle. FIGS. 8A and 8B illustrate still other embodiments of a flow member 64 comprising at least one curved major surfaces 70 and/or 72.

[0051] In still other examples, shown in FIGS. 9 and 10, each flow member 64 may be formed as elongated strips (FIG. 9) extending generally in the length- wise direction of the ribbon or in other examples as a rod or wire-style flow member 64 (FIG. 10) that is submerged within the bead region of molten glass ribbon 46, again extending in a generally lengthwise direction of the ribbon (e.g. along draw direction 48). The rod or wire may be bent to conform to the shape of a desired ribbon lateral edge contour, since the lateral edge of the molten glass ribbon flowing over the rod or wire will generally follow the contour of the rod or wire. Additionally, such wire- form flow members minimize material usage and therefore cost (it should be noted that because of the harsh environment presented by the molten glass, flow members according to the present disclosure may be constructed from similar materials as edge directors, for example platinum or a platinum alloy such as a platinum-rhodium alloy).

[0052] Flow member 64 is configured to intersect the free flow of glass from bottom edge 42 of the forming body 38 before the molten glass reaches the first set of edge rolls 56 such that edge portions (beads) 50 of the molten glass ribbon flow over and around at least a portion of the flow member. That is, flow member 64 not only contacts the glass flow, but is extended into the flow of molten glass ribbon 46 such that the molten glass flows over at least a portion of both major surfaces 70, 72 of flow member 64. It should be noted that the flow of molten glass may not necessarily cover the entirety of the major surfaces of the flow member. Thus, a portion of the major surfaces of the flow member may remain un- wetted by the molten glass. For example, in FIG. 5 the diagonally hatched portion of first major surface 70 (and second major surface 72, although not shown in the figure) depicts that portion of the surface area of flow member 64 that may be wetted by the molten glass in certain embodiments.

[0053] Flow control apparatus 62 may include a mounting arm 76 to which flow member 64 is coupled, or mounting arm 76 may be an integral part of flow member 64. A mounting arm 76 may be used to couple flow member 64 to a respective mounting apparatus 78 configured to mount and position the flow member in the flow of molten glass (molten glass ribbon 46). In some embodiments, a mounting arm may not be necessary as the flow member may be coupled directly to the mounting apparatus.

[0054] Flow member 64 is formed from a rigid material that is not easily deformed by the flow of molten glass in contact with the flow member and which is compatible with the molten glass. By compatible what is meant is that the material comprising the flow member does not easily dissolve in the molten glass or shed particulate into the molten glass, and is capable of prolonged exposure to the high temperature of the molten glass without significant material degradation or shape deformation. The molten glass of the molten glass ribbon to which flow member 64 can be exposed may be, for example, at a temperature equal to or greater than about 700°C, equal to or greater than 800°C, or even equal to or greater than 900°C, for example, in a temperature range from about 700°C to about 1200°C. As described supra, each flow member 64 may comprise platinum or a platinum alloy such as a platinum- rhodium alloy or a platinum-iridium alloy. Alternative materials can include ZrSi0₄, or a Haynes® alloy. Compatible materials may also include materials that are dissolvable over time but which dissolved material becomes a non-detrimental part of the overall molten glass composition that does not materially affect the performance of the resultant glass article. In some embodiments, each flow member 64 may comprise a suitable silicate or a non-silicate glass, or comprise a suitable ceramic material.

[0055] Mounting apparatus 78 may include a positioning device 80 for adjusting a position of flow member 64, either by moving the flow member in a direction 82 toward or away from vertical plane 84 extending through the forming body (i.e. the molten glass ribbon) perpendicular to a longitudinal axis of the forming body, thus increasing or decreasing the surface area of the flow member wetted by the molten glass, or in a vertical direction 86 toward or away from bottom edge 42 of forming body 38. Vertical plane 84 may correspond to a centerline of the molten glass ribbon.

[0056] Positioning device 80 can be used to attain an optimal position for flow member 64 that maximizes the width of the molten glass ribbon while minimizing the bead size

(thickness and/or width) for the molten glass ribbon for the particular design of the flow member. In certain embodiments mounting apparatus may also be configured to provide rotational movement to flow member 64, thereby effecting a change in attack angle of the flow member relative to the flow of molten glass. In some embodiments, each mounting apparatus 78 may be substantially stationary, or configured such that positioning of flow member 64 is not readily undertaken. For example, each mounting apparatus 78 may be rigidly coupled to a structural member (not shown) such as structural steel beams that support one or more other components of the draw apparatus or the structure containing it. In such embodiments, repositioning of flow member 64 may require decoupling mounting apparatus 78 from the structural member and recoupling it at another location or in another position.

[0057] FIGS. 1 1 and 12 are photographs illustrating experiments carried out on a mock forming body configured to emulate a working industrial forming body as described supra. A petroleum product (oil or wax) having a viscosity substantially equal to the viscosity of a molten glass flowing over a forming body in an actual glass making process is used to simulate the flow of molten glass over and from the forming body. The exact viscosity will depend on the glass composition being emulated. The use of a simulated molten glass, for example paraffin, can be beneficial in that experiments can be conducted at room

temperature, or at least at a temperature than can be readily observed and performance of the flow member analyzed. Positioned to the right of FIGS. 1 1 and 12 is a conventional edge director extending between the converging forming surfaces of the forming body and the dam located at the right side end of the forming body (as viewed on the drawing page). Positioned on the left is a flow member 64 as described above, the flow member fully submerged in the flow of molten glass coming from the forming body. The particular flow member illustrated in FIG. 1 1 is of a triangular design, with a downward-pointing peak. That is, the top edge of the triangular form is substantially horizontal, whereas the additional two side edges converge in the draw direction. Dashed line 90 and dashed and dotted line 92 show the relative positions of the bottom edge 42 of forming body 38 and the top edge of flow member 64, respectively. As FIG. 1 1 shows, the flow of simulated molten glass (as represented by the size of the right-hand and left-hand beads) for the flow member (left-hand side of the drawing) is generally the same as the flow of molten glass from the conventional edge director shown at the right-hand side of the drawing, indicating that the flow member of FIG. 1 1 is at least equally as effective as the conventional edge director for a reduced amount of material (e.g., platinum or platinum alloy as would be used in a conventional edge director). In contrast to FIG. 1 1 , FIG. 12 illustrates the same set-up as for FIG. 1 1 , with the exception that flow member 64 at the left side of the figure is not fully submerged within the flow of molten glass, having only a portion of its major surfaces wetted by the molten glass. In the embodiment of FIG. 12, the ribbon attenuates more sharply on the flow member side of the molten glass flow (left-hand side) when compared to the molten glass flow at the

conventional edge director (right hand side), but with a significantly reduced edge portion size (e.g., width and/or thickness). Accordingly, FIGS. 1 1 and 12 demonstrate that the width profile of the molten glass ribbon, and the size (e.g., thickness) of the edge portions(s), can be manipulated by positioning of the flow member inward toward a centerline of the molten glass ribbon, or outward, away from the centerline of the molten glass ribbon in order to optimize the size of the quality area. The optimal positioning of the flow member to maximize the width of the quality area and minimize the thickness and width of the beads will depend, inter alia, on the shape of the flow member, the flow rate of the molten glass, and the temperature (viscosity) of the molten glass.

[0058] Modeling has shown that more generally, varying the surface area of the flow member wetted by the molten glass varies the velocity of the molten glass flowing over the major surfaces of the flow member. As the velocity of the molten glass flow over the surfaces of the flow member is reduced, attenuation is also reduced. It has also been found that a narrower flow member in a generally vertical direction produced a less pronounced (smaller) edge portion. Accordingly, a long narrow flow member, such as the flow members of FIGS. 9 and 10, may be more effective at maximizing the width of the quality area while minimizing the size of the thickened edge portions than a wide (in a direction perpendicular to the flow direction), short (in the flow direction) flow member.

[0059] In some embodiments, one or more heating elements 93 (see FIG. 5) may be positioned on and/or in flow member 64. The heating elements may be used to locally control the temperature, and therefore viscosity, of the molten glass flowing over the flow member. Heating of flow member 64, either continuously or intermittently, can be used to prevent devitrification of the glass, for example if the glass is being drawn at a temperature below the liquidus temperature of the glass. Indeed, the use of flow members according to embodiments described herein can be used to intentionally draw glass ribbon at temperatures below the liquidus temperature of the glass. Or, in the case where devitrification buildup occurs at the flow member, devitrification can be removed by the heating. The heating element can be of the resistance type, wherein an electric current is established through heating element 93 and Joule heating occurs. Alternatively, other methods of heating the flow member as are known in the art, such as by microwaves, can be used.

[0060] In addition to reducing thickened edge portion size and reducing attenuation, using a flow member according to embodiments of the present disclosure can aid in enhanced joining of the separate glass flows. FIG. 13 illustrates an example of a thickened edge portion 50 wherein one flow of molten glass from the forming body (a flow coming from one converging forming surface of forming body 38) has not been fully joined with the opposite flow of molten glass, thereby forming an indent or dimple 94 in the edge portion 50. In some cases, shown in FIG. 14, this dimpling can result in an airline 96. Such edge anomalies, and in particular airlines, can disrupt the cutting process, for example by causing the cut line to deviate from its intended path during the time when a distinct sheet of glass is being cut from the glass ribbon. Or, such edge anomalies can produce stress in the ribbon edge that negatively impacts the shape of the central portion (quality area) of the ribbon or the sheet of glass cut therefrom. In still other cases, the existence of airlines can result in uncontrolled cracking of the ribbon. Modeling has shown that the formation of these dimples and/ or airlines can be mitigated using embodiments of the flow members described herein.

[0061] It will be apparent to those skilled in the art that various modifications and variations can be made to embodiments of the present disclosure without departing from the spirit and scope of the disclosure. Thus it is intended that the present disclosure cover such modifications and variations provided they come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. A method of modifying a flow of molten glass comprising:

flowing molten glass from a forming body as a molten glass ribbon; and

intersecting the molten glass ribbon with a flow member, the flow member spaced apart from the forming body and extending into an edge of the molten glass ribbon a predetermined distance such that at least a portion of the flow member is submerged within the molten glass ribbon.

2. The method according to claim 1 , wherein the step of flowing molten glass from the forming body comprises flowing the molten glass from a bottom edge of the forming body where converging forming surfaces of the forming body converge.

3. The method according to claim 2, wherein the flow member comprises opposing first and second major surfaces over which the molten glass flows, and the first and second major surfaces of the flow member are parallel with a vertical plane passing through the bottom edge of the forming body.

4. The method according to claim 2, wherein the flow member is positioned between an upper-most edge roll and the bottom edge of the forming body.

5. The method according to claim 2, further comprising varying a distance between an upper most edge of the flow member wetted by the molten glass ribbon and the bottom edge of the forming body.

6. The method according to claim 1 , further comprising moving the flow member in a vertical direction.

7. The method according to claim 1 , further comprising moving the flow member in a horizontal direction.

8. The method according to claim 1 , wherein the flow member comprises opposing first and second major surfaces over which the molten glass flows, and the first and second major surfaces are parallel with each other.

9. The method according to claim 1 , wherein the flow member comprises opposing first and second major surfaces over which the molten glass flows, and the molten glass contacts an entire surface area of the first and second major surfaces.

10. The method according to claim 1 , further comprising heating the flow member with a heating element positioned on or in the flow member.

1 1. The method according to claim 1 , wherein the flow member is entirely submerged within the molten glass ribbon.

12. The method according to claim 1, further comprising varying a surface area of the flow member wetted by the molten glass.

13. The method according to claim 1, wherein the step of intersecting the molten glass ribbon further comprises intersecting the molten glass ribbon with a plurality of flow members, each flow member of the plurality of flow members extending into the molten glass ribbon a predetermined distance.

14. An apparatus for drawing a molten glass ribbon comprising:

a forming body from which molten glass ribbon is drawn; and

a flow control apparatus comprising a flow member positioned vertically beneath and spaced apart from the forming body, the flow member comprising opposing planar surfaces, the flow member spaced apart from the forming body in a vertical plane passing through a bottom edge of the forming body and positioned a predetermined distance L from a vertical plane perpendicular to a longitudinal axis of the forming body and bisecting the bottom edge of the forming body such that molten glass from the forming body can flow over the opposing planar surfaces of the flow member, where L is measured from the vertical plane to a distal end of the flow member closest to the vertical plane.

15. The apparatus according to claim 14, wherein the flow control apparatus further comprises a positioning device coupled to the flow member and configured to vary the distance L.

16. The apparatus according to claim 14, wherein the flow control apparatus is configured to move the flow member in a vertical direction.

17. The apparatus according to claim 14, wherein the flow control apparatus is configured to move the flow member in a horizontal direction.

18. The apparatus according to claim 14, further comprising a plurality of flow control apparatus, each flow control apparatus of the plurality of flow control apparatus comprising a flow member.

19. The apparatus according to claim 14, wherein the flow member comprises a triangular shape.

20. A method of modifying a flow of molten glass comprising:

flowing molten glass from a forming body as a molten glass ribbon and

intersecting the molten glass with a flow member comprising first and second major surfaces, the flow member spaced apart from a bottom edge of the forming body from which the molten glass ribbon is drawn and extending into the molten glass a predetermined distance such that the molten glass flows over both the first and second major surfaces of the flow member.