Patent Publication Number: US-2017349471-A1

Title: Methods and apparatuses including edge directors for forming glass ribbons

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Ser. No. 62/478,670 filed on Mar. 30, 2017 and Provisional Application Ser. No. 62/344,767 filed on Jun. 2, 2016 the contents of which are relied upon and incorporated herein by reference in their entirety 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. Any asymmetry of the Y shape that develops over time can lead to air-holes in the edges, so called hollow edges. Both hollow edges and edge asymmetry 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; and a forming wedge portion including a pair of downwardly inclined forming surfaces converging along a downstream direction to form a bottom edge; and an edge director comprising a flow blocking portion including an upper portion extending along one of the pair of outside surfaces and a lower portion that extends along one of the pair of downwardly inclined forming surfaces and is negatively inclined relative to vertical, the lower portion of the flow blocking portion extending outwardly and downwardly from the upper portion of the flow blocking portion toward the bottom edge. 
     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; and a forming wedge portion including a pair of downwardly inclined forming surfaces converging along a downstream direction to form a bottom edge; and a first edge director comprising a first flow blocking portion; and a second edge director located at an opposite side of the forming vessel from the first edge director, the second edge director comprising a second flow blocking portion; wherein a horizontal distance between the first edge director and the second edge director increases along a height of the forming wedge portion toward the bottom edge. 
     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 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 an edge director intersecting with at least one of the pair of outside surfaces and at least one of the pair of downwardly inclined forming surface portions, the edge director comprising a flow blocking portion including an upper portion that extends along one of the pair of vertical surfaces and a lower portion that extends along one of the pair of downwardly inclined forming surfaces and is negatively inclined relative to vertical, the lower portion extending downwardly from the upper portion toward the bottom edge; and drawing the molten glass from the bottom edge of the forming wedge portion to form the glass ribbon. 
     In yet another embodiment, an apparatus for downwardly drawing a glass ribbon comprising: a forming vessel including a pair of downwardly inclined forming surface portions converging along a downstream direction to form a bottom edge; and an edge director comprising a flow blocking portion that extends outwardly from at least one of the downwardly inclined surface portions and a flow directing portion that engages both the flow blocking portion and the at least one of the downwardly inclined surface portions; wherein a cross-flow direction angle of the flow directing portion is provided a constant preselected angle α to the flow blocking portion between about 95 degrees and about 105 degrees to provide a planar flow directing portion. 
     In yet another embodiment, an apparatus for downwardly drawing a glass ribbon comprising: a forming wedge portion including a pair of downwardly inclined forming surface portions converging along a downstream direction to form a bottom edge; and an edge director comprising a flow blocking portion that extends outwardly from the pair of downwardly inclined surface portions and a first planar flow directing portion that intersects both the flow blocking portion and one of the pair of downwardly inclined surface portions and a second planar flow directing portion that intersects both the flow blocking portion and the other of the downwardly inclined surface portions; wherein the first planar flow directing portion intersects the second planar flow directing portion at an immersion edge below the bottom edge. 
     In yet another embodiment, a method of making a glass ribbon comprising: flowing molten glass over a pair of downwardly inclined forming surface portions of a forming vessel, the pair of downwardly inclined forming surface portions converging along a downstream direction to form a bottom edge; flowing the molten glass over an edge director intersecting with at least one of the pair of downwardly inclined forming surface portions, the edge director comprising: a flow blocking portion that extends outwardly from the at least one of the downwardly inclined surface portions and a flow directing portion that intersects both the flow directing portion and the at least one of the downwardly inclined surface portions; wherein a cross-flow direction angle of the flow directing portion is provided a constant preselected angle α to the flow blocking portion between about 95 degrees and about 105 degrees; and drawing the molten glass from the bottom edge of the forming wedge to form the glass ribbon. 
     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, ad 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  is a side view of the edge director of  FIG. 3 ; 
         FIG. 5  is another side, perspective view of the edge director of  FIG. 3 ; 
         FIG. 6  is a top view of the edge director of  FIG. 3 ; 
         FIG. 7  is a schematic, section view of the edge director connecting to a forming wedge along line  7 - 7  of  FIG. 2 ; 
         FIG. 8  is a schematic, front view of another embodiment of an edge director according to one or more embodiments shown and described herein; 
         FIG. 9  is a side view of the edge director of  FIG. 8 ; 
         FIG. 10  is a bottom view of the edge director of  FIG. 8 ; 
         FIG. 11  is a schematic, front view of another embodiment 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 schematic, front view of another embodiment of an edge director according to one or more embodiments shown and described herein; 
         FIG. 15  is a side view of the edge director of  FIG. 14 ; 
         FIG. 16  is a bottom view of the edge director of  FIG. 14 ; 
         FIG. 17  is a schematic, front view of another embodiment of an edge director according to one or more embodiments shown and described herein; 
         FIG. 18  is a side view of the edge director of  FIG. 17 ; 
         FIG. 19  is a bottom view of the edge director of  FIG. 17 ; 
         FIG. 20  is a horizontal view of a glass ribbon edge at a location below an edge director, such as the edge director of  FIGS. 8-10 , with a line of sight contained in the draw plane illustrating operation of the edge director using an oil that is used to simulate glass flow during a down draw process; 
         FIG. 21  is a schematic, perspective view of another embodiment of an edge director according to one or more embodiments shown and described herein; 
         FIG. 22  is a front view of the edge director of  FIG. 21 ; 
         FIG. 23  is a schematic, perspective view of another embodiment of an edge director according to one or more embodiments shown and described herein; 
         FIG. 24  is a front view of the edge director of  FIG. 23 ; 
         FIG. 25  illustrates an end view of another embodiment of an edge director according to one or more embodiments shown and described herein; 
         FIG. 26  is a schematic illustration of edges of glass flows using various edge directors according to one or more embodiments shown and described herein; and 
         FIG. 27  is a chart of normalized mass flow versus distance from outer edge of a glass ribbon using an edge director having positive and negative inclination according to one or more embodiments shown and described herein. 
     
    
    
     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 −x 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 blocks  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 +/−x directions). 
     The forming vessel  60  includes the pair of edge directors  80  and  82  intersecting with the outside surface portions  73  and  75  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 connected 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 blocking portion  102   a  (sometimes referred to as a dam) and a flow directing portion  104   a  that is connected to the flow blocking portion  102   a  (e.g., by welding). The flow blocking portion  102   a  is generally planar and is shaped to extend alongside the surface  94  of the retaining block  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  105  of the surface  94  ( 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 directing portion  104   a  in an increasing fashion from a top  106   a  of the flow directing portion  104   a  toward a bottom  108  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 from the flow blocking portion  102   a  from the top  106   a  to the bottom  108 . 
     Similarly, the edge director portion  100   b  includes a flow blocking portion  102   b  and a flow directing portion  104   b . The flow blocking portion  102   b  is generally planar and is shaped to extend alongside the planar surface  94  of the retaining block  90 . Again, while only a portion of a height of the flow blocking portion  102   b  is illustrated by  FIG. 3 , the flow blocking portion  102   a  may extend to or even beyond a top  107  of the surface  96  ( 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 the bottom  108  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 from the flow blocking portion  102   b  from the top  106   a  to the bottom  108 . 
     The edge director portion  100   a  and the edge director portion  100   b  extend generally toward one another and 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 from the flow blocking portion  102  to an immersion point  112 . Referring also to  FIG. 4 , the immersion edge  110  can have both a horizontal and a vertical component, extending downwardly from the immersion point  112  to the flow blocking portion  102 . Thus, the immersion edge  110  may affect the shape of the root line from a straight, horizontal root line portion to a root line having down turned, linear edges, as represented by dotted line  114  in  FIG. 2 . In some embodiments, the immersion edge  110  may be arranged at an angle β between about 10 degrees to about 45 degrees from horizontal (or the root  76 ). A length X of the immersion edge  110  between the immersion point  112  and bottom  108  of the flow blocking portion  102  may be between about 5 cm and about 15 cm. 
     Referring to  FIG. 5 , the flow directing portions  104   a  and  104   b  extend toward one another to form a V-shape that is sized to receive the downwardly inclined forming surface portions  66  and  68  of the forming vessel  60  ( FIG. 2 ). In some embodiments, the flow directing portions  104   a  and  104   b  may extend toward each other at flow direction angles θ from vertical. In some embodiments, the flow direction angles θ may be the same and between about 10 degrees and about 25 degrees, such as about 17.6 degrees and constant along the entire height of the flow directing portions  104   a  and  104   b . The size of the flow direction angle θ depends, at least in part, on the width of the downwardly inclined forming surface portions  66  and  68 . In some embodiments, a width W at the top  106  of the flow directing portions  104   a  and  104   b  may be between about 12 cm and about 30 cm. 
     As can be appreciated by  FIGS. 3-5 , the flow directing portions  104   a  and  104   b  are both planar (i.e., without any curves) and extend outwardly from their respective flow blocking portions  102   a  and  102   b . Referring briefly to  FIG. 6 , the flow directing portions  104   a  and  104   b  may extend outwardly from their respective flow blocking portions at oblique cross-flow direction angles α from their respective flow blocking portion  102   a ,  102   b , thereby providing flow directing portions  104   a  and  104   b . In some embodiments, the cross-flow direction angles α of the flow directing portions  104   a  and  104   b  may be the same and between about 95 degrees and about 105 degrees and constant along an entire height of the flow directing portions  104   a  and  104   b.    
     Referring again to  FIG. 3 , outer edges  120   a  and  120   b  of the flow blocking portions  102   a  and  102   b  extend along the surfaces  94  and  96  of the retaining blocks  90  and  92  ( FIGS. 1 and 2 ). In the illustrated embodiment, the outer edges  120   a  and  120   b  may also extend at an angle τ to vertical to intersect at the immersion edge  110 . The angles τ may be greater than the flow direction angles θ to provide some area of the flow blocking portions  102   a  and  102   b  to mount against the planar surfaces  94  and  96  of the retaining blocks  90  and  92 , while also intersecting at the immersion edge  110 . Providing the outer edges  120   a  and  120   b  with the angles τ can reduce areas of the flow blocking portions  102   a  and  102   b  compared to embodiments having vertical outer edges, which can reduce an amount of refractory material used to form the flow blocking portions  102   a  and  102   b.    
     Referring to  FIG. 7 , a cross-section view of the forming wedge portion  62  illustrates the edge director  80  positioned on the forming wedge portion  62  and the planar surfaces  94  of the retaining block  90 . The flow direction angles θ ( FIG. 5 ) of the flow directing portions  104   a  and  104   b  can be selected to approach the off-vertical angles of the downwardly inclined forming surface portions  66 ,  68 . Because of the cross-flow direction angles α, the flow directing portions  104   a  and  104   b  close a gap  122  provided between the downwardly inclined forming surface portions  66 ,  68  and the flow directing portions  104   a  and  104   b . Also, because of the angle β ( FIG. 4 ), the immersion edge  110  closes a gap  124  provided between the root  76  of the forming wedge portion  62  and the immersion edge  110 . 
       FIGS. 8-10  illustrate an alternative embodiment of an edge director  140  that includes many of the features described above with edge director  80  including edge director portions  142   a  and  142   b  with flow blocking portions  144   a  and  144   b  and flow directing portions  146   a  and  146   b . The flow blocking portions  144   a  and  144   b  are generally planar and are shaped to extend alongside the surfaces  94  and  96  ( FIGS. 1 and 2 ). The flow directing portions  146   a  and  146   b  extend outwardly from the flow blocking portions  144   a  and  144   b  and generally toward the downwardly inclined forming surface portions  66  and  68 . In this embodiment, however, outer edges  148   a  and  148   b  are vertical and parallel, terminating at a bottom edge  150 . The bottom edge  150  is located at (i.e., within about 13 mm or less, such as within 6 mm or less) of immersion edge  152 . The vertical arrangement of the outer edges  148   a  and  148   b  can provide additional area of the flow blocking portions  144   a  and  144   b  against the surfaces  94  and  96  compared to edge director  80 . 
       FIGS. 11-13  illustrate a negatively inclined orientation of the edge director  140  where the flow blocking portions  144  are inclined an angle γ (e.g., less than about 10 degrees, such as less than about eight degrees) relative to vertical. As used herein, the term “negatively inclined” refers to an angle resulting in an outward slope from top to bottom of the edge director  140  (away from a center of the forming vessel), thereby increasing a horizontal distance between opposing edge directors moving vertically toward the root line (see −γ of  FIG. 12 ). “Positively inclined” refers to an angle resulting in an inward slope from top to bottom of the edge director  140  (toward the center of the forming vessel), thereby decreasing a horizontal distance between opposing edge directors moving vertically toward the root line (see +γ of  FIG. 12 ). In these embodiments, the surfaces  94  and  96  may be inclined in a fashion similar to the edge director  140 . The negatively inclined arrangement can provide a wider horizontal distance X′ (X′ is about 1.25X of  FIG. 4 ) as bottom  145  of the edge director  140  is farther outboard than top  147 . Glass flow that would otherwise flow straight down the flow blocking portions  144   a  and  144   b  in a vertical arrangement is instead urged toward the flow directing portions  146   a  and  146   b  and directed by the flow directing portions  146   a  and  146   b  toward the fusion plane. The glass flow then converges at the fusion plane at or above the root line, which can provide a thinner ribbon at edges of the glass flow since the edges of the glass flow is spread over a wider horizontal distance X′. 
       FIGS. 14-16  illustrate a variation of the edge director  140  where channel members  152   a ,  152   b  are provided as flow directing features. The channel members  152   a  and  152   b  extend along a height of the flow blocking portions  154   a  and  154   b  and extend toward each other at the immersion edge  156 , decreasing a distance between the channel members  152   a  and  152   b  as they approach the immersion edge  156 . The channel members  152   a  and  152   b  channel the glass flow from the flow blocking portions  154   a  and  154   b  toward the fusion plane. Dashed lines  158  represent an illustrative glass flow path illustrating edges of the glass flow converging at the root line. 
       FIGS. 17-19  illustrate another variation of the edge director  140  where ledge members  162   a  and  162   b  are provided as a flow directing features to provide edge director  160 . Where the channel members  152   a  and  152   b  of  FIG. 14  may be sized to inhibit glass flow thereover, the ledge members  162   a  and  162   b  may be of reduced dimension (height) to allow flow thereover, while providing some guidance of the glass flow toward the fusion plane. Dashed lines  168  represent and illustrative glass flow path illustrating edges of the glass flow converging at the root line. 
     Referring to  FIG. 20 , an end view of the edge director  140  is shown in operation during a down draw process, such as that described above. While the operation is shown with regard to the edge director  140  of  FIGS. 8-10 , there may be variation in form of the material flow depending on shape characteristics of the particular edge director. As can be seen, lobes  170  of material flow are provided below the bottom edge  150  of the edge director  140  when viewed from the end of the edge director  140 . These lobes  170  are oriented generally transverse to the fusion plane, thus rendering a T-shaped edge  172  immediately below the edge director  140 . The ends  174  and  176  of the T-shape can move directly toward the fusion plane when a pulling force is applied and the ribbon edge becomes essentially fused with little residual T-shape. 
     Referring to  FIGS. 21 and 22 , another embodiment of an edge director  200  is generally plate-like in shape that includes edge director portions  202   a  and  202   b . As can be seen, the edge director portions  202   a  and  202   b  are formed as flow blocking portions  204   a  and  204   b , without the flow directing portions described above. While the edge director  200  includes the edge director portions  202   a  and  202   b , only edge director portion  202   a  can be seen and is described. It should be understood that edge director portion  202   b  may include the same features. Further, while only one edge director  200  is illustrated, another edge director may be located at an end of the forming vessel opposite the edge director  200 . The edge director portion  202   a  may extend vertically from a top edge  206  located above an upper portion  212  of forming vessel  210  to a bottom edge  208  located at root  214 . 
     The edge director portion  202   a  is divided into an upper portion  216  and a lower portion  218  that intersects the upper portion  216  at an intersection  220 . The upper portion  216  extends vertically along a an outside surface portion  222  of the upper portion  212  and the lower portion  218  extends downwardly along an inclined forming surface  224  of forming wedge portion  226 . The intersection  220  may be located at a break line or horizontal plane  228  dividing the upper portion  212  and the forming wedge portion  226 . In some embodiments, the plane  228  may intersect the intersection  220 . 
     The lower portion  218  is negatively inclined at an angle −γ relative to vertical resulting in an outward slope extending from the intersection  220  to the bottom edge  208 . The angle −γ can be limited to one half of a root angle σ defined between the inclined forming surfaces  224  of the forming wedge portion  226  ( FIG. 2 ). In some embodiments the angle −γ may be about 10 degrees or less, such as between about five degrees and about 10 degrees, such as about eight degrees. Limiting the angle −γ to at or below 0.56 can improve control over the flow pattern such that the separate glass flows on opposite sides of the forming vessel  210  converge to the fusion plane slightly below the root  214 , as represented by arrow  230 .  FIGS. 23 and 24  illustrate a lower portion  232  having a greater negatively inclined angle −γ providing a glass flow pattern where the glass flows converge to inclined forming surfaces  234  above root  236  represented by arrow  238 . 
     Referring to  FIG. 25 , an end view of a variation of the edge directors described with reference to  FIGS. 21-24  includes flow blocking portions  250   a  and  250   b  including outer edges  252   a  and  252   b . The outer edges  252   a  and  252   b , rather than being vertical and parallel as illustrated by  FIGS. 21-24 , extend at an angle τ to vertical at intersections  254   a  and  254   b  between upper portions  256   a  and  256   b  and lower portions  258   a  and  258   b  to intersect at bottom  254 . Providing the outer edges  252   a  and  252   b  with the angles τ can reduce areas of the flow blocking portions  250   a  and  250   b  compared to embodiments having vertical outer edges, which can reduce an amount of refractory material used to form the flow blocking portions  250   a  and  250   b.    
     Referring to  FIG. 26 , section views of glass ribbon edges are illustrated resulting from use of various edge director structures. Line  240  represents an edge boundary at the upper portion as the molten glass enters the forming wedge portion. Examples (i)-(iii) illustrate various examples where no negative incline is present. Example (i) illustrates a Y-shaped glass ribbon edge flowing from an edge director with an edge directing portion. As can be seen, there is some width loss in Example (i). Example (ii) illustrates a vertical only flow blocking portion with no negatively inclined lower portion. As can be seen, the edges stop at the line  240  with flaring. Example (iii) represents no edge director at the forming wedge portion such that the glass flow has no flow blocking surface to travel along. Omitting the edge director at the forming wedge portion allows edges of the glass flow to flow towards the center of the forming vessel due to attenuation resulting in width loss. Example (iv) represents the negatively inclined lower portion, as described above with regard to  FIGS. 21-24 . Because the lower portion is negatively inclined, the glass ribbon widens as the glass flows toward the root and the edges are elongated with a resulting fused end edge with little to no Y-shape. 
     Referring to  FIG. 27 , a chart of normalized mass flow versus distance from the horizontal position  240  (at zero) along the width of the forming vessel of the upper portion is illustrated. Line A is the normalized mass flow for incoming molten glass flowing from the upper portion of the forming vessel and crossing the break line onto the forming wedge portion. Lines B-D represent mass flow crossing the bottom edge of the forming wedge portion. As represented by line A, mass flow crosses the break line outward to the origin zero edge position and increases from the zero edge position inward toward a center of the forming wedge portion until a relatively steady mass flow is reached. Relative to the incoming molten glass normalized mass flow shown by line A, the negatively inclined lower portion normalized mass flow represented by line B reduces mass flow over the initial 50 mm and increases mass flow over the next 50 mm. The negative incline of the lower portion provides mass flow outward beyond the zero position and as represented by Example (iv) above. As the inclination of the lower portion goes positive shown by lines C and D, a reduction of mass flow over the initial 50 mm from the zero position continues along with a reduction in overall glass ribbon width. 
     While the lower portions described with reference to  FIGS. 21-24  are illustrated as being planar and angled along a line, the lower portions could be curved, multi-linear (multiple intersecting lower portions), etc. The termination point of the lower portions may be located below the root and the general shape can be any suitable shape. 
     The above-described edge directors can produce a fully fused edge at the start of the free ribbon boundary (i.e., the root line or bottom edge). The negatively inclined edge director can have an impact on edge thickness due to the ability to spread the typical amount of mass flow over a greater horizontal distance. Spreading the mass flow over a wider horizontal distance can also provide for a wider glass ribbon. 
     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.