Patent Publication Number: US-2020299172-A1

Title: Apparatuses including edge directors for forming glass ribbons

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority of U.S. Provisional Application Ser. No. 62/589,651 filed Nov. 22, 2017 on the contents of which are relied upon and incorporated herein by reference in their entity as if fully set forth below. 
    
    
     BACKGROUND 
     Field 
     The present specification generally relates to methods and apparatuses for making glass ribbons and, in particular, methods and apparatuses including edge directors for forming glass ribbons. 
     Technical Background 
     Glass forming apparatuses are commonly used to form various glass products such as glass sheets used for LCD displays and the like. These glass sheets may be manufactured by downwardly flowing molten glass over a forming wedge to form a continuous glass ribbon, referred to as a fusion process. In the past, fusion processes have used an edge director. The primary purpose of the edge director is to increase the overall width of glass sheets. Generally the upper limit of sheet width is limited by the “dam-to-dam” distance on the vertical section of a forming vessel. In the absence of any type of edge director on the forming vessel “root” section, the four edges of the two opposing glass layers tend to flow toward the center of the forming vessel while each layer as a whole flows toward the root line where the two sides fuse together. The maximum width of a sheet that would result from this scenario would be reduced. 
     Current edge directors may reduce some of this width loss of glass sheets, but while doing so, may create a Y-shaped edge that requires the use of edge rolls to press-fuse prongs of the Y together. As a fusion draw apparatus ages, the Y-shaped edge can become more difficult to fuse, even with edge rolls, and can eventually lead to air holes in the edge portion of the glass ribbon, so called hollow edges. Any asymmetry of the Y shape that develops over time can lead to mismatch in the edges, so called edge mismatch. Both hollow edges and edge mismatch can present ribbon stability issues and limit the life of the fusion draw apparatus. 
     SUMMARY 
     According to one embodiment, an apparatus for downwardly drawing a glass ribbon comprising: a forming vessel comprising: an upper portion including a pair of outside surfaces that extend parallel to each other, the pair of outside surfaces defining a width of the forming vessel; and a forming wedge portion including a pair of downwardly inclined forming surfaces converging along a downstream direction to form a bottom edge; a flow blocking portion that extends alongside the forming wedge; and an edge director comprising: a first flow directing portion formed from an arc portion of a first frustoconical or conical shape that intersects one of the inclined forming surfaces along a first edge of the first flow directing portion and intersects the flow blocking portion along a second edge of the first flow directing portion; and a second flow directing portion formed from an arc portion of a second frustoconical or conical shape that intersects the other of the inclined forming surfaces along a first edge of the second flow directing portion and intersects the flow blocking portion along a second edge of the second flow directing portion; wherein a distance between lowermost endpoints of intersection of the first flow directing portion and the second flow directing portion with the flow blocking portion is no greater than 80 percent of the width of the forming vessel. 
     In another embodiment, an apparatus for downwardly drawing a glass ribbon comprising: a forming vessel comprising: an upper portion including a pair of outside surfaces that extend parallel to each other defining a width of the forming vessel between the outside surfaces; and a forming wedge portion including a pair of downwardly inclined forming surfaces converging along a downstream direction to form a bottom edge; a flow blocking portion that provides a dam that extends alongside the forming wedge; and an edge director comprising a flow directing portion formed from an arc portion of a frustoconical or conical shape that intersects one of the inclined forming surfaces along a first edge of the flow directing portion and intersects the flow blocking portion along a second edge of the flow directing portion; wherein the frustoconical or conical shape has a cone angle of at least 20 degrees, the cone angle measured from a central axis of the frustoconical or conical shape to an outer surface of the frustoconical or conical shape. 
     In yet another embodiment, a method of making a glass ribbon comprising: flowing molten glass over an upper portion of a forming vessel including a pair of outside surfaces that extend parallel to each other defining a width of the forming vessel between the outside surfaces and a forming wedge portion including a pair of downwardly inclined forming surface portions that converge along a downstream direction to form a bottom edge; flowing the molten glass over a flow blocking portion that provides a dam that extends alongside the forming wedge; flowing molten glass over an edge director comprising a first flow directing portion formed from an arc portion of a first frustoconical or conical shape that intersects one of the inclined forming surfaces along a first edge of the first flow directing portion and intersects the flow blocking portion along a second edge of the first flow directing portion; and flowing molten glass over a second flow directing portion of the edge director formed from an arc portion of a second frustoconical or conical shape that intersects the other of the inclined forming surfaces along a first edge of the second flow directing portion and intersects the flow blocking portion along a second edge of the second flow directing portion; wherein a distance between lowermost endpoints of intersection of the first flow directing portion and the second flow directing portion with the flow blocking portion is no greater than 80 percent of the width of the forming vessel. 
     Additional features and advantages of the methods and apparatuses for forming glass ribbons 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 described herein, including the detailed description which follows the claims, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically depicts an apparatus for forming a glass ribbon according to one or more embodiments shown and described herein; 
         FIG. 2  schematically depicts a cross sectional perspective view along line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is a side, perspective view of an edge director for use with the apparatus of  FIG. 1 , according to one or more embodiments shown and described herein; 
         FIG. 4  illustrates a method of forming an edge director, according to one or more embodiments shown and described herein; 
         FIG. 5  illustrates a method of forming an edge director, according to one or more embodiments shown and described herein; 
         FIG. 6  illustrates a method of forming an edge director according to one or more embodiments shown and described herein; 
         FIG. 7  is a side, perspective view of an edge director, according to one or more embodiments shown and described herein; 
         FIG. 8  is a side view of the edge director of  FIG. 7 ; 
         FIG. 9  is a bottom view of the edge director of  FIG. 7 ; 
         FIG. 10  is a front view of the edge director of  FIG. 7 ; 
         FIG. 11  is a side, perspective view of an edge director, according to one or more embodiments shown and described herein; 
         FIG. 12  is a side view of the edge director of  FIG. 11 ; 
         FIG. 13  is a bottom view of the edge director of  FIG. 11 ; 
         FIG. 14  is a front view of the edge director of  FIG. 11 ; 
         FIG. 15  is a side, perspective view of an edge director, according to one or more embodiments shown and described herein; 
         FIG. 16  is a side view of the edge director of  FIG. 15 ; 
         FIG. 17  is a bottom view of the edge director of  FIG. 15 ; 
         FIG. 18  is a front view of the edge director of  FIG. 15 ; 
         FIG. 19  is a side, perspective view of an edge director, according to one or more embodiments shown and described herein; 
         FIG. 20  is a side view of the edge director of  FIG. 19 ; 
         FIG. 21  is a bottom view of the edge director of  FIG. 19 ; 
         FIG. 22  is a front view of the edge director of  FIG. 19 ; 
         FIG. 23  is a side, perspective view of an edge director, according to one or more embodiments shown and described herein; 
         FIG. 24  is a side view of the edge director of  FIG. 23 ; 
         FIG. 25  is a bottom view of the edge director of  FIG. 23 ; and 
         FIG. 26  is a front view of the edge director of  FIG. 23 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments of the methods and apparatuses for forming glass ribbons and edge directors for use with the same, examples of which are illustrated in the accompanying drawings. One embodiment of an apparatus for making glass ribbons is shown in  FIG. 1 , and is designated generally throughout by the reference number  10 . The apparatus  10  generally includes a pair of opposing edge directors located at opposite ends of a forming vessel. As will be described in greater detail below, the edge directors are configured to reduce width loss of the glass ribbon during the forming process. Various embodiments of methods and apparatuses for forming glass ribbons and edge directors for use with the same will be described in further detail herein with specific reference to the appended drawings. 
     Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. 
     Directional terms as used herein—for example up, down, right, left, front, back, top, bottom—are made only with reference to the figures as drawn and are not intended to imply absolute orientation. 
     Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification. 
     As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” component includes aspects having two or more such components, unless the context clearly indicates otherwise. 
     Referring now to  FIG. 1 , one embodiment of a glass forming apparatus  10  for forming a glass ribbon  12  is schematically depicted. The glass forming apparatus  10  generally includes a melting vessel  15  configured to receive batch material  16  used to form glass from a storage bin  18 . The batch material  16  can be introduced to the melting vessel  15  by a batch delivery device  20  powered by a motor  22 . An optional controller  24  may be provided to activate the motor  22  and a molten glass level probe  28  can be used to measure the glass melt level within a standpipe  30  and communicate the measured information to the controller  24 . 
     The glass forming apparatus  10  includes a fining vessel  38  located downstream from the melting vessel  15  and coupled to the melting vessel  15  by way of a first connecting tube  36 . A mixing vessel  42  is located downstream from the fining vessel  38 . A delivery vessel  46  may be located downstream from the mixing vessel  42 . As depicted, a second connecting tube  40  couples the fining vessel  38  to the mixing vessel  42  and a third connecting tube  44  couples the mixing vessel  42  to the delivery vessel  46 . As further illustrated, a downcomer  48  is positioned to deliver glass melt from the delivery vessel  46  to an inlet  50  of a forming vessel  60 . 
     The melting vessel  15  is typically made from a refractory material, such as refractory (e.g., ceramic) brick. The glass forming apparatus  10  may further include components that are typically made from platinum or platinum-containing metals such as platinum-rhodium, platinum-iridium and combinations thereof, but which may also comprise such refractory materials such as molybdenum, palladium, rhenium, tantalum, titanium, tungsten, ruthenium, osmium, zirconium, and alloys thereof and/or zirconium dioxide. The platinum-containing components can include one or more of the first connecting tube  36 , the fining vessel  38 , the second connecting tube  40 , the standpipe  30 , the mixing vessel  42 , the third connecting tube  44 , the delivery vessel  46 , the downcomer  48  and the inlet  50 . The forming vessel  60  can also be made from a refractory material and is designed to form the glass melt into a glass ribbon  12 . 
       FIG. 2  is a cross sectional perspective view of the glass forming apparatus  10  along line  2 - 2  of  FIG. 1 . As shown, the forming vessel  60  includes a forming wedge portion  62  and an open upper portion  61 . The upper portion  61  includes parallel outside surface portions  73 ,  75 , and the forming wedge portion  62  includes a pair of downwardly (i.e., in the −y direction of the coordinate axes depicted in  FIG. 2 ) inclined forming surface portions  66 ,  68  that extend between opposite ends  70 ,  72  of the forming vessel  60 . The downwardly inclined forming surface portions  66 ,  68  converge along a downstream direction  74  to form a bottom edge or root  76 . The root  76  is a boundary where the downwardly inclined forming surface portions  66  and  68  meet or converge. A draw plane  78  extends through the root  76 . The glass ribbon  12  may be drawn from the forming wedge portion  62  in the downstream direction  74  along the draw plane  78 . As depicted, the draw plane  78  bisects an angle σ formed between inclined forming surface portions  66  and  68  and extends through the root  76 . However, it should be understood that the draw plane  78  may extend at other various orientations with respect to the root  76  other than bisecting the angle σ. While  FIGS. 1 and 2  generally depict one embodiment of a glass forming apparatus and a forming vessel, it should also be understood that aspects of the present disclosure may be used with various other forming vessel configurations. 
     Referring to  FIGS. 1 and 2 , in some embodiments, each opposed end  70 ,  72  of the forming vessel  60  can be provided with retaining block assemblies  90  and  92 . Vertically-oriented, planar surfaces  94  and  96  are provided that intersect both of the parallel outside surface portions  73 ,  75  and the downwardly inclined forming surface portions  66 ,  68 . The respective surfaces  94 ,  96  ( FIG. 2 ) can serve as vertical support surfaces for edge directors  80  and  82  that provide lateral barriers on opposite sides of the glass ribbon  12 . The surfaces  94  and  96  with edge directors  80  and  82  are used in limiting migration of the glass ribbon and directing the glass ribbon downwardly toward the root  76 . As can be seen particularly by  FIG. 2 , the surfaces  94  and  96  may extend the entire height or even beyond the entire height of the forming wedge portion  62  (i.e., extend beyond both the root  76  and the upper portion  61  in the y direction). 
     The forming vessel  60  includes the pair of edge directors  80  and  82  each intersecting with the outside surface portions  73  and  75  (see  FIG. 3 ) and the pair of downwardly inclined forming surface portions  66 ,  68 . The edge directors  80 ,  82  help achieve a desired glass ribbon width and edge characteristics by directing the molten glass proximate to the root  76  of the forming vessel  60 . In further embodiments, the edge directors  80  and  82  can intersect with both downwardly inclined forming surface portions  66 ,  68 . In addition, the edge directors  80 ,  82  can be positioned at each of the opposite ends  70 ,  72  of the forming wedge portion  62 . For instance, as shown in  FIG. 1 , the edge director  80 ,  82  can be positioned at each of the opposite ends  70 ,  72  of the forming wedge portion  62  with each edge director  80 ,  82  configured to intersect with both of the downwardly inclined forming surface portions  66 ,  68 . The edge directors  80  and  82  also extend vertically along respective surfaces  94  and  96  forming dams. Each edge director  80 ,  82  may be substantially identical to one another. However, it should be understood that, in alternative embodiments, the edge directors  80 ,  82  may have different configurations and/or geometries depending on the specific characteristics of the glass forming apparatus. The edge directors  80  and  82  will be described in greater detail below. 
     Still referring to  FIG. 1 , the glass forming apparatus  10  can optionally include at least one edge roller assembly  86  for drawing glass ribbon from the root  76  of the forming vessel  60 . It should be understood that various edge roller assembly configurations may be used in accordance with aspects of the present disclosure. 
     A housing  14  encloses the forming vessel  60 . The housing  14  may be formed from steel and contain refractory material and/or insulation to thermally insulate the forming vessel  60 , and the molten glass flowing in and around the forming vessel  60 , from the surrounding environment. 
     Referring again to  FIGS. 1 and 2 , in operation, batch material  16 , specifically batch material for forming glass, is fed from the storage bin  18  into the melting vessel  15  with the batch delivery device  20 . The batch material  16  is melted into molten glass in the melting vessel  15 . The molten glass passes from the melting vessel  15  into the fining vessel  38  through the first connecting tube  36 . Dissolved gasses, which may result in glass defects, are removed from the molten glass in the fining vessel  38 . The molten glass then passes from the fining vessel  38  into the mixing vessel  42  through the second connecting tube  40 . The mixing vessel  42  homogenizes the molten glass, such as by stirring, and the homogenized molten glass passes through the third connecting tube  44  to the delivery vessel  46 . The delivery vessel  46  discharges the homogenized molten glass through downcomer  48  and into the inlet  50  which, in turn, passes the homogenized molten glass into the upper portion  61  of the forming vessel  60 . 
     As molten glass  17  fills the upwardly open upper portion  61  of forming vessel  60 , it overflows the upper portion  61  and flows over the inclined forming surface portions  66 ,  68  and rejoins at the root  76  of the forming wedge portion  62 , thereby forming a glass ribbon  12 . As depicted in  FIG. 2 , the glass ribbon  12  may be drawn in the downstream direction  74  along the draw plane  78  that extends through the root  76 . 
     Referring now to  FIG. 3 , the edge director  80  is illustrated in isolation and generally includes edge director portions  100   a  and  100   b . Referring first to edge director portion  100   a , the edge director portion  100   a  includes a flow directing portion  104   a  that is connected to a flow blocking portion  102   a  (e.g., by welding). The flow blocking portion  102   a  (sometimes referred to as a dam) may be, for example, the surface  94  of the retaining block assembly  90 . In some embodiments, the flow blocking portion  102   a  may be part of the edge director portion  100   a  and connected to the surface  94  of the retaining block assembly  90 . The flow blocking portion  102   a  is generally planar and is shaped to extend alongside the retaining block assembly  90 . While only a portion of a height of the flow blocking portion  102   a  is illustrated by  FIG. 3 , the flow blocking portion  102   a  may extend to or even beyond a top  107  of the retaining block assembly  90  ( FIG. 2 ). The flow directing portion  104   a  extends outwardly from the flow blocking portion  102   a  and generally toward the downwardly inclined forming surface portion  66 . The flow directing portion  104   a  can extend outwardly from the flow blocking portion  102   a  in an increasing fashion from a top  106   a  of the flow directing portion  104   a  toward a bottom  108   a  of the flow blocking portion  102   a  thereby forming a ramped flow directing portion  104   a  of increasing length that increases in a direction outward toward the center of the forming vessel  60  from the flow blocking portion  102   a  from the top  106   a  to the bottom  108   a.    
     Similarly, the edge director portion  100   b  includes a flow directing portion  104   b  that is connected to a flow blocking portion  102   b  (e.g., by welding). The flow blocking portion  102   b  (sometimes referred to as a dam) may, for example, be the surface  96  of the retaining block assembly  90 . In some embodiments, the flow blocking portion  102   b  may be part of the edge director portion  100   b  and connected to the surface  96  of the retaining block assembly  90 . The flow blocking portion  102   b  is generally planar and is shaped to extend alongside the retaining block assembly  90 . While only a portion of a height of the flow blocking portion  102   a  is illustrated by  FIG. 3 , the flow blocking portion  102   a  may extend to or even beyond the top  107  of the retaining block assembly  90  ( FIG. 2 ). The flow directing portion  104   b  extends outwardly from the flow blocking portion  102   b  and generally toward the downwardly inclined forming surface portion  66 . The flow directing portion  104   b  can extend outwardly from the flow blocking portion  102   b  in an increasing fashion from a top  106   b  of the flow directing portion  104   b  toward a bottom  108   b  of the flow blocking portion  102   b  thereby forming a ramped flow directing portion  104   b  of increasing length that increases in a direction outward toward the center of the forming vessel  60  from the flow blocking portion  102   b  from the top  106   b  to the bottom  108   b.    
     The edge director portion  100   a  and the edge director portion  100   b  are connected together at the root  76  of the forming wedge portion  62 . In particular, the flow directing portion  104   a  and the flow directing portion  104   b  extend toward one another to meet at an immersion edge  110 . The immersion edge  110  extends outwardly toward the center of the forming vessel  60  to an immersion point  112 . The immersion edge  110  can have both a horizontal and a vertical component, extending downwardly from the immersion point  112  to tail portions  115 . Although not shown by  FIG. 3 , each flow directing portion includes a tail portion  115  that diverge from one another, away from the immersion edge toward the flow blocking portion  102 . The tail portions  115  extend outwardly from the bottom  108  toward the center of the forming vessel  60  to an intersection  117  with the immersion edge  110 . Thus, the immersion edge  110  and the tail portions  115  may affect the shape of the root line from a straight, horizontal root line portion to a root line having down turned edges, as represented by dotted line  114  in  FIG. 2 . 
     The flow directing portions  104   a  and  104   b  may be curved from edges  120   a  and  120   b  that intersect the flow blocking portions  104   a  and  104   b  inward toward the center of the root to the immersion edge  110 . In particular, referring to  FIGS. 4-6 , the shape of the flow directing portions  104  may be defined by the shape of a cone of a preselected dimension, represented by element  122 . In the example of  FIGS. 4-6 , the cone  122  is selected to have a predetermined cone angle α, which is one half of an apex angle θ that is measured between opposite sides  124  and  126  of the cone  122 . In other words, the cone angle α is the angle between the central axis of the cone  122  and cone surface  130 . As can be appreciated, in the limit of cone angles approaching zero, the cone  122  approaches a line and in the limit of cone angles approaching 90 degrees, the cone  122  approaches a plane. As used herein, the term “large cone angle” refers to cone angles of greater than 20 degrees to form large cone edge directors (LCEDs). While a conical shape is described primarily below, frustoconical shapes may be used. 
     Referring first to  FIG. 4 , the cone  122  is selected to have a preselected cone angle α. To generate a flow directing portion shape, an apex  132  of the cone  122  is placed at where an intersection  134  between the forming wedge portion  62  and the open upper portion  61  intersects the dam or flow blocking portion  102 . The cone  122  extends downward in height to below the root  76 . The flow blocking portion  102  is removed for clarity. The cone  122  is tilted about the z-axis with the apex  132  fixed to a preselected immersion depth (see element  146  of  FIG. 9 ), which is the distance between the immersion point  112  and the flow block portion  102  shown in  FIG. 3 . Referring to  FIGS. 5 and 6 , the cone  122  is then rotated about the x-axis with the apex  132  again fixed to a preselected angle of intersection with the inclined forming surface portion  66  (e.g., between 2 degrees and 10 degrees). The cone  122  is cut below the dam with the draw plane  78  ( FIG. 2 ) so that a tail depth  127  (see  FIG. 9 ) is a preselected percentage of the height of the forming vessel  60  (e.g., between 10 percent and 30 percent). The tail depth  127  is the distance in the z-direction from the flow blocking portion  102  and the intersection point  117  with the immersion edge  110 . The height of the forming vessel is the vertical distance from the root to the intersection  134  between the forming wedge portion  62  and the open upper portion  61 . What is left of the cone is represented by the shaded area A, which corresponds to an arc portion of a frustoconical or conical shape defining a flow directing portion  104  derived from a frustoconical or conical shape of a given cone angle. 
     Referring to  FIG. 7 , an edge director  140  is illustrated in isolation. The edge director  140  includes connected edge director portions  140   a  and  140   b  in a fashion similar to that described above regarding edge director  80 . The edge director  140  includes flow directing portions  144   a  and  144   b . The flow directing portions  144   a  and  144   b  may intersect flow blocking portions  142   a  and  142   b . The flow blocking portions  142   a  and  142   b  may be, for example, the surfaces  94  and  96  of the retaining block assembly  90  ( FIG. 2 ). For simplicity, only the flow blocking portions  144   a  and  144   b  are represented by  FIGS. 7-10  without the retaining block assembly  90 . 
     The flow directing portions  144   a  and  144   b  are formed as described above from cones having a preselected cone angle. In this embodiment, the flow directing portions  144   a ,  144   b  are formed from cones having a cone angle of less than 20 degrees, such as 19.81 degrees. A cone angle of 19.81 degrees provides an immersion depth  146  ( FIG. 9 ) to height  148  of the forming wedge portion, which is the vertical distance from the immersion point  151  to the apex  155  of 0.37. The cone angle of 19.81 degrees also provides a tail height  150  ( FIG. 8 ), which is the vertical distance between the intersection point  153  and the immersion point  151 , to height  148  of the forming wedge portion of 0.22. Knowing coordinates for the apex  155 , the immersion point  151  and the intersection point  153 , the cone angle α can be determined. As can be best seen by  FIG. 9 , the flow directing portions  144   a  and  144   b  are tangent to the flow blocking portions  142   a  and  142   b  at intersections  145   a  and  145   b , providing a relatively wide edge director width  152  of the same width  158  ( FIG. 10 ) as the forming vessel compared to LCEDs. “Edge director width” refers to a distance between lowermost intersections  145   a  and  145   b  along the flow blocking portion  142  where the tail portions  115  intersect the flow blocking portion  142 . As used herein, the term “tangent” refers to an angle of intersection of less than 10 degrees. Dashed lines  154  and  156  of  FIG. 10  are illustrative of glass flow path illustrating edges of the glass flow converging at the root under steady-state operating conditions. 
     Without wishing to be bound by theory, it is believed that providing relatively narrow cone widths can provide improved stability and bead quality compared to wide cone widths. LCEDs can provide such narrower cone widths by intersecting the dams or flow blocking portions in a non-tangential fashion, while being tangent or nearly tangent with the flow directing portions of the forming vessel due to the increased cone angle. 
     Referring to  FIGS. 11-14 , for example, another edge director  160  includes edge director portions  160   a  and  160   b  with flow directing portions  164   a  and  164   b  and flow blocking portions  162   a  and  162   b . In this embodiment, however, the flow directing portions  164   a  and  164   b  are each formed using a cone of increased cone angle compared to  FIGS. 7-10 . In this embodiment, the flow directing portions  164   a  and  164   b  are each formed using a cone having a cone angle of 40.08 degrees. Referring to  FIGS. 12 and 13 , an immersion depth  166  is maintained at 37 percent of a height  168  of the forming wedge portion and a tail height  170  to the height  168  of the forming wedge portion is maintained at 0.22, like the edge director  140  of  FIGS. 7-10 . Unlike the edge director  140 , an edge director width  172  of the edge director  160  is substantially narrower than a width  174  ( FIG. 14 ) of the forming vessel at the open upper portion. In particular, a ratio of edge director width  172  to width  174  of the forming vessel is 0.30. Dashed lines  176  and  178  of  FIG. 14  are illustrative of glass flow path illustrating edges of the glass flow converging at the root  76  under steady-state operating conditions. 
     Referring to  FIGS. 15-18 , another edge director  180  includes edge director portions  180   a  and  180   b  with flow directing portions  184   a  and  184   b  and flow blocking portions  182   a  and  182   b . In this embodiment, the flow directing portions  184   a  and  184   b  are each formed using a cone of increased cone angle compared to  FIGS. 7-10 , but of lower cone angle compared to  FIGS. 11-14 . In this embodiment, the flow directing portions  184   a  and  184   b  are each formed using a cone having a cone angle of 25.90 degrees. Referring to  FIGS. 16 and 17 , an immersion depth  186  is maintained at 37 percent of a height  188  of the forming wedge portion and a tail height  190  to the height  188  of the forming wedge portion is maintained at 0.22. A edge director width  192  of the edge director  180  is also substantially narrower than a width  194  ( FIG. 18 ) of the forming vessel at the open upper portion. In particular, a ratio of edge director width  192  to width  194  of the forming vessel is 0.50. Dashed lines  196  and  198  of  FIG. 18  are illustrative of glass flow path illustrating edges of the glass flow converging at the root  76  under steady-state operating conditions. 
     The Table below provides ratios of edge director width to width of the forming vessel for a number of exemplary cone angles. The Table is generated assuming a zero thickness cone. As can be seen, the ratio of edge director width to width of the forming vessel decreases with increasing cone angle. 
     
       
         
           
               
             
               
                 TABLE 
               
             
            
               
                   
               
               
                 Ratio of Cone Width to Width of Forming Vessel 
               
            
           
           
               
               
               
            
               
                   
                 Ratio of Edge Director Width 
                   
               
               
                   
                 to Width of Forming Vessel 
                 Cone Angle in Degrees 
               
               
                   
                   
               
               
                   
                 0.20 
                 57.78 
               
               
                   
                 0.25 
                 47.47 
               
               
                   
                 0.30 
                 40.08 
               
               
                   
                 0.40 
                 30.90 
               
               
                   
                 0.50 
                 25.88 
               
               
                   
                 0.60 
                 23.00 
               
               
                   
                 0.70 
                 21.33 
               
               
                   
                 0.80 
                 20.39 
               
               
                   
                 0.90 
                 19.93 
               
               
                   
                 1.00 
                 19.81 
               
               
                   
                   
               
            
           
         
       
     
     Referring now to  FIGS. 19-22 , in addition to larger cone angles, the LCEDs may be provided with additional flow control features.  FIG. 19  illustrates a variation of the edge director  180  that includes pedestal structures  208   a  and  208   b . Again, this edge director  200  includes edge director portions  200   a  and  200   b  with flow directing portions  206   a  and  206   b  each derived from a cone having a cone angle of 25.9 degrees and a ratio of cone width  208  to width  210  of forming vessel of 0.5. 
     In this example, each director portion  200   a  and  200   b  is provided with a pedestal structure  208   a  and  208   b  that extends out of planes of flow blocking portions  210   a  and  210   b . Referring to  FIG. 20 , the pedestal structures  208   a ,  208   b  may extend outwardly from the plane of the flow blocking portions  210   a  and  210  at a preselected pedestal incline angle  212  (e.g., of between 2 degrees and 10 degrees, such as about 4 degrees) measured from the vertical flow blocking portions  210   a  and  210   b  to surfaces  211   a  and  211   b  of the pedestal structures  208   a  and  208   b . Further, the pedestal structures  208   a  and  208   b  may terminate along edges  213   a  and  213   b  at a location spaced from a bottom  214  of the flow blocking portions  210   a  and  210   b  and extend downwardly to immersion edge  216  at a pedestal cut angle  220  (e.g., of between 20 degrees and 45 degrees, such as 35 degrees) measured from horizontal as shown by  FIG. 22 . The pedestal structures  208   a  and  208   b  direct glass flow toward the fusion plane. Dashed lines  222  and  224  of  FIG. 22  are illustrative of glass flow path illustrating edges of the glass flow converging at the root  76  under steady-state operating conditions. 
       FIG. 23-26  illustrate another embodiment of an edge director  230  that includes other flow control features. Referring to  FIG. 23 , the edge director is a variation of the edge director  180  that includes both channel structures  232   a  and  232   b  and plate structures  234   a  and  234   b  as flow directing features. The channel structures  232   a  and  232   b  extend along a height of flow blocking portions  236   a  and  236   b  and extend toward each other at immersion edge  238 . The channel structures  232   a  and  232   b  channel glass flow toward the fusion plane and the plate structures  234   a  and  234   b.    
     The plate structures  234   a  and  234   b  extend along a tail portion  240   a ,  240   b  of flow directing portions  242   a  and  242   b . The plate structures  234   a  and  234   b  have a horizontal component normal to the fusion plane and provide an additional surface to oppose forces acting horizontally on the glass flow and direct the glass flow toward the fusion plane. Dashed lines  248  and  250  of  FIG. 26  are illustrative of glass flow path illustrating edges of the glass flow converging at the root  76  under steady-state operating conditions. Any of the pedestal structures, channel structures and plate structures may be used alone or together with the LCEDs. 
     The above-described edge directors can produce a significantly better fused edge at the start of the free ribbon boundary (i.e., the root line or bottom edge). The glass ribbon can be significantly less susceptible to sheet width variation instability where the viscous ribbon width varies with time in an unstable fashion. This reduction in sheet width variation can enable the ability to create thinner beads via end mass flow reduction and can also enable increased pulling speed on the fused glass ribbon for thinner sheet capability. Cone angles can be selected to up to 90 degrees, at which there is no edge director, allowing design optimization for various situations. LCEDs disclosed herein have less out-of-plane protrusion which can allow for reduced heat loss for edge director devit mitigation. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.