Glass forming apparatus and glass ribbon forming method

Abstract

A glass forming apparatus configured to shape a molten glass ribbon is disclosed, the glass forming apparatus including an edge director assembly positioned to immerse at least a portion of a wire dip tool into an edge of the molten glass ribbon to reduce lateral contraction of the molten glass ribbon and improve edge stability. A method of forming a glass ribbon using the edge director is also disclosed.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority under 35 U.S.C. Section 119 of U.S. Provisional Application No. 63 / 336,571, filed April 29, 2022, the entire disclosure of which is incorporated herein by reference.

[0002] (Technical field) The present disclosure relates to a glass forming apparatus, and more particularly, to a glass forming apparatus for forming a glass ribbon using an edge director with a wire dip tool. [Background technology]

[0003] Forming glasses with low liquidus viscosities (e.g., 1 kilopoise (kP) to about 10 kP) is not easily accomplished using typical melting processes in which molten glass is flowed onto converging forming surfaces joined at the bottom edge and drawn therefrom as a glass ribbon. To optimize the properties of the glass ribbon, it may be desirable to reduce edge flow densities that can cause edge instability of the ribbon. In such a situation, molten glass may accumulate and drip from a portion of the forming body, or the ribbon may undergo periodic lateral contraction. Both of these forms of edge instability can prevent the process from running reliably.

[0004] Typically, in a glass ribbon forming process, the viscosity of the ribbon edge is higher than the viscosity of the ribbon center. If the viscosity of the ribbon center drops to remain below the liquidus viscosity, the viscosity of the ribbon edge also drops, causing the edge to become unstable.

[0005] Edge directors have been used since the beginning of the fusion process to help maintain the ribbon width and stabilize the flow of molten glass at the ribbon edges. Because typical edge directors are attached to the forming body and made of platinum or platinum alloy sheets, they cannot be replaced while the process is running, thus requiring extensive downtime to repair the damage. Such edge directors are also difficult to heat, which can lead to devitrification at the glass-contacting surfaces of the edge director. Summary of the Invention [Means for solving the problem]

[0006] Described herein are edge directors spaced apart from the forming body. Such edge directors may include one or more wires shaped to help stabilize the flow of molten glass at the edges of the formed ribbon, and may be easily heated with electrical current passing through the wire(s) if desired. The wires have a small surface area to dissipate heat and a small cross-sectional area to reduce electrical current requirements.

[0007] Edge directors employing one or more wires at least partially immersed in the molten glass flow can be easily replaced in the event of damage or process changes requiring a different design. For example, the wire(s) can be incorporated into a housing or other fixture that can be retracted from the forming process, such as a cartridge design, so that the wire portion of the edge director can be repaired or replaced. Wires that are immersed in the molten glass flow can be easily manufactured by bending. Modeling has shown that such wire configurations are effective in maintaining ribbon width and flow stability. Some glass forming processes may require high flow rates for good ribbon formation, but the flow rates are not practical for production. Wire edge directors have been shown to collect enough flow (e.g., slow the flow of molten glass) that the ribbon edge stabilizes as it leaves the wire. Without being bound by theory, it is believed that a wire edge director with a wire that extends down very close to the edge dam can maintain the ribbon width very close to the length of the forming body due to the faster flow at the edge of the molten glass ribbon.

[0008] Accordingly, in a first aspect, a glass forming apparatus is disclosed that includes a forming body having a first end and a second end opposite the first end and configured to receive a flow of molten glass from the forming body along a draw plane as a molten glass ribbon. The glass forming apparatus further includes an edge director assembly disposed below the forming body and including a wire dip tool positioned to extend from the first end in a direction toward a first vertical plane passing through the forming body that bisects the forming body perpendicular to the draw plane, with at least a portion of the dip tool positioned between the first vertical plane and a second vertical plane that is parallel to the first vertical plane and coincident with the first end of the forming body.

[0009] In a second embodiment, the maximum diameter of the wire immersion tool of the first embodiment is in the range of about 1 mm to about 10 mm.

[0010] In a third aspect, the wire dip tool of either the first or second aspect comprises a platinum group metal.

[0011] In a fourth aspect, the wire immersion tool of any of the first to third aspects is vertically movable.

[0012] In a fifth aspect, the wire dip tool of any of the first to fourth aspects is movable horizontally.

[0013] In a sixth aspect, the wire dip tool of any of the first to fifth aspects is rotatable about an axis of rotation parallel to the drawing plane.

[0014] In a seventh aspect, the wire dip tool of any of the first to sixth aspects is rotatable about a horizontal axis perpendicular to the drawing plane.

[0015] In an eighth embodiment, the forming body of any of the first to seventh embodiments comprises a pair of converging forming surfaces that meet along a bottom edge of the forming body, the bottom edge lying in the drawing plane.

[0016] In a ninth aspect, the glass forming apparatus of any of the first to eighth aspects can further include a forming roll positioned spaced below the edge director and rotatable about an axis of rotation, the forming roll positioned to receive the molten glass ribbon on a surface thereof.

[0017] In a tenth aspect, the glass forming apparatus of the ninth aspect can further include a pair of counter-rotating pull rolls positioned in a spaced relationship below the forming roll, the pair of counter-rotating pull rolls being positioned to receive the second glass ribbon from the forming roll therebetween.

[0018] In an eleventh aspect, the wire dip tool of any of the first to tenth aspects may be connected to a power source configured to apply an electrical current to the wire dip tool.

[0019] In a twelfth aspect, the wire dip tool of any of the first to eleventh aspects may comprise a conductive sheath disposed around the wire dip tool and an electrically insulating material disposed between the wire dip tool and the conductive sheath to electrically isolate the wire dip tool from the conductive sheath.

[0020] In a thirteenth aspect, the conductive sheath of the twelfth aspect can include platinum.

[0021] In a fourteenth aspect, the electrically insulating material of the thirteenth aspect can include a ceramic refractory material.

[0022] In a fifteenth aspect, the glass forming apparatus of the fourth aspect can further include a DC power supply electrically connected between the forming body and the edge director.

[0023] In a sixteenth aspect, the glass forming apparatus of any of the eleventh to fourteenth aspects can further include a DC power source electrically connected between the forming roll and the sheath.

[0024] In a seventeenth aspect, the edge director assembly of any of the first through sixteenth aspects can be positioned spaced below the forming body.

[0025] In an eighteenth aspect, a method of shaping a glass ribbon includes flowing molten glass from a forming body as a molten glass ribbon; and contacting an edge of the molten glass ribbon with an edge director assembly, the edge director comprising a wire dip tool at least partially immersed in the edge.

[0026] In a nineteenth aspect, the edge director assembly of the eighteenth aspect may be positioned spaced below the forming body.

[0027] In a twentieth aspect, the method of any of the eighteenth to nineteenth aspects may further comprise the step of heating the wire dip tool with an electric current directed therethrough.

[0028] In a twenty-first aspect, a DC power source can be connected between the edge director and the forming roll, and the method of the twentieth aspect further includes controlling the adhesion of the molten glass layer to the forming roll by controlling at least one of the voltage or current provided by the DC power source.

[0029] In a twenty-second aspect, the method of the twenty-first aspect can further include the step of controlling the voltage in a range of about -3 volts to about +3 volts.

[0030] In a twenty-third aspect, the method of the twenty-first aspect can further include controlling the current in a range from about 0 amps to about 5 amps.

[0031] In a twenty-fourth aspect, the method of the twentieth aspect can further include a DC power supply connected between the edge director assembly and the forming body.

[0032] In a twenty-fifth aspect, the edge director assembly of the twenty-first or twenty-fourth aspects may include a conductive sheath disposed around the wire immersion tool, with an electrically insulating material disposed between the conductive sheath and the wire immersion tool, and a DC power source electrically connected to the conductive sheath.

[0033] In a twenty-sixth aspect, the method of any of the eighteenth to twenty-fifth aspects can further include receiving the molten glass ribbon onto a rotating forming roll positioned below and spaced from the edge director, the molten glass ribbon covering at least a portion of the forming roll to form a molten glass layer.

[0034] In a twenty-seventh aspect, the method of the twenty-sixth aspect can further include drawing the molten glass layer from the forming roll as a second glass ribbon.

[0035] The foregoing summary and the following detailed description present embodiments that are intended to provide an overview or framework for understanding the nature and features of the embodiments disclosed herein. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. These drawings illustrate various embodiments of the present disclosure, and together with the description explain the principles and operation of the present disclosure. [Brief description of the drawings]

[0036] [Figure 1] FIG. 1 is a front view of an exemplary glass forming apparatus. [Diagram 2] 2 is a front view of a portion of the glass forming apparatus of FIG. 1 in which a molten glass ribbon descending from a bottom edge of a forming body without edge directors splits into multiple streams. [Diagram 3] FIG. 2 is a front view of another exemplary glass forming apparatus. [Figure 4] FIG. 4 is a cross-sectional side view of the glass forming apparatus of FIG. [Diagram 5] 5 is a front view of an edge director for the glass forming apparatus of FIG. 4, the edge director including a wire dip tool. [Figure 6] 5 is a front view of another edge director for the glass forming apparatus of FIG. 4 including another exemplary immersion tool. [Figure 7] 5 is a front view of another edge director for the glass forming apparatus of FIG. 4 including yet another immersion tool. [Figure 8] 5 is a front view of another edge director for the glass forming apparatus of FIG. 4 including yet another exemplary immersion tool. [Figure 9] 5 is a front view of another edge director for the glass forming apparatus of FIG. 4 including another exemplary immersion tool. [Figure 10] 5 is a front view of another edge director for the glass forming apparatus of FIG. 4 including yet another immersion tool. [Figure 11] 5 is a front view of another edge director for the glass forming apparatus of FIG. 4 including yet another exemplary immersion tool. [Figure 12] 5 is a front view of another edge director for the glass forming apparatus of FIG. 4 including another exemplary immersion tool. [Figure 13] FIG. 12 is a front view of the edge director and immersion tool of FIG. 11 showing the power supply connected to the edge director and more particularly to the immersion tool. [Figure 14] 1 is an end view of an exemplary immersion tool illustrating out-of-plane rotation of the immersion tool about an axis of rotation (e.g., the longitudinal axis of a segment of the immersion tool). [Figure 15] FIG. 2 is a side view of an exemplary edge director according to embodiments disclosed herein. [Figure 16] 16 is a cross-sectional view of a portion of the immersion tool of FIG. 15 including an electrically conductive sheath and an electrically insulating layer. [Figure 17] FIG. 1 is a schematic diagram of an exemplary edge director assembly including a first DC power supply electrically connected between the immersion tool and the forming roll and a second DC power supply electrically connected between the forming body and the immersion tool. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0038] As used herein, the term "about" means that quantities, sizes, compositions, parameters, and other quantities and characteristics are not, or need not be, exact, but are approximate and / or larger or smaller, as appropriate, to reflect tolerances, conversion factors, rounding, measurement errors, and the like, as well as other factors known to those of ordinary skill in the art.

[0039] 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 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 further be understood that the endpoints of each range are significant in relation to the other endpoint, and independently of the other endpoint.

[0040] Directional terms used herein, e.g., up, down, right, left, front, back, top, bottom, are merely used with reference to the figures and do not imply absolute orientation.

[0041] Unless expressly stated otherwise, no method described herein should be construed as requiring that its steps be performed in a particular order, nor should any apparatus be construed as requiring a particular orientation. Thus, if a method claim does not actually recite an order that its steps are to be followed, or if any apparatus claim does not actually recite an order or orientation for individual components, or if the claims or specification do not otherwise clearly state that the steps are to be limited to a particular order, or if no particular order or orientation for the apparatus components is recited, no order or orientation is to be implied in any respect. This applies to all possible implicit criteria for interpretation, including logical matters regarding the arrangement of steps, operational flow, order of components, or orientation of components, general meaning derived from grammatical constructions or punctuation, and the number or type of embodiments described in the specification.

[0042] As used herein, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Thus, for example, reference to "an element" includes aspects having two or more such elements unless the context clearly dictates otherwise.

[0043] As used herein, the terms "exemplary," "example," or various forms thereof, mean serving as an example, instance, or illustration. Any aspect or design described herein as "exemplary" or "example" is not to be construed as preferred or advantageous over other aspects or designs. Moreover, examples are provided merely for clarity and understanding and are not meant to restrict or limit in any way the disclosed subject matter or relevant portions of this disclosure. It can be understood that countless additional or alternative examples of varying scope could have been presented, but have been omitted for the sake of brevity.

[0044] As used herein, the terms "comprises" and "including," and variations thereof, unless otherwise indicated, shall be construed as synonymous and non-limiting. A list of elements following the transitional phrase "comprises" or "including" is a non-exclusive list, such that there may be elements other than those specifically recited in the list.

[0045] As used herein, the terms "substantial," "substantially," and variations thereof, are intended to describe a described characteristic being equal or nearly equal to a value or description. For example, a "substantially planar" surface describes a surface that is planar or nearly planar. Furthermore, "substantially" is intended to indicate that two values ​​are equal or nearly equal. In some embodiments, "substantially" can describe values ​​that are within about 10% of each other, such as within about 5% of each other, or within about 2% of each other.

[0046] As used herein, the term "molten glass" in the context of the first molten glass ribbon refers to a glass having a viscosity in the range of about 100 Pascal seconds (1000 poise) to about 20,000 Pa·s (200,000 poise), e.g., in the range of about 100 Pa·s to about 15,000 Pa·s, in the range of about 100 Pa·s to about 12,500 Pa·s, in the range of about 100 Pa·s to about 10,000 Pa·s, in the range of about 7,500 Pa·s, in the range of about 10 By "viscosity range" is meant a molten material having a viscosity in the range of 0 Pa·s to about 5,000 Pa·s, or in the range of about 100 Pa·s to about 2,500 Pa·s, including all ranges and subranges therebetween, which is formulated such that upon proper cooling, the material will form a glass, e.g., a silicate glass (e.g., borosilicate glass, aluminoborosilicate glass, low-alkali or non-alkali aluminoborosilicate glass, etc.). The edge directors disclosed herein are useful over the above-mentioned viscosity ranges, but can be particularly useful for molten glass (e.g., a first molten glass ribbon) having a viscosity in the range of about 100 Pa·s to about 1000 Pa·s, e.g., in the range of about 100 Pa·s to about 750 Pa·s, in the range of about 100 Pa·s to about 500 Pa·s, or in the range of about 100 Pa·s to about 250 Pa·s, including all ranges and subranges therebetween.

[0047] FIG. 1 is a front view of an exemplary apparatus for shaping a glass ribbon comprising a forming body 12, a forming roll 14 positioned downstream of the forming body relative to the direction of flow of molten glass from the forming body, and a plurality of pulling rolls 16 a, 16 b configured to engage the molten glass ribbon as counter-rotating rolls that apply a downward force to the molten glass ribbon.

[0048] Forming body 12 includes a trough 18 disposed on an upper surface of the forming body and at least partially defined by a pair of weirs, and a pair of converging forming surfaces 20 positioned below the weirs, the converging forming surfaces meeting at a bottom edge (root) 22 of forming body 12. Molten glass provided at an inlet end of trough 18 overflows the trough and flows over converging forming surfaces 20 as separate streams of molten glass that meet at or below root 22 and flow downwardly therefrom as a combined stream of molten glass, e.g., first molten glass ribbon 24. Dams 26a, 26b positioned at the ends of forming body 12 contain the lateral flow of molten glass and prevent the molten glass from flowing beyond the ends of the forming body.

[0049] In another embodiment, forming body 12 can comprise a slot draw apparatus, where a vessel configured to receive a flow of molten glass includes a slot extending across a bottom thereof such that molten glass provided to the interior of the vessel flows from the vessel through the slot. In yet another embodiment, forming body 12 can include a vessel configured to receive a flow of molten glass and a distribution pipe extending from a bottom orifice of the vessel, the distribution pipe including a slotted passageway through which molten glass in the chamber can exit as a molten glass ribbon.

[0050] In yet another aspect, the forming body can include a metallic overflow tube configured to receive a flow of molten glass, the overflow tube including a slot extending across a top surface of the overflow tube, where the molten glass is fed into the overflow tube, fills the overflow tube, overflows the overflow tube through the slot, and flows over both sides of the overflow tube before meeting at a bottom of the overflow tube to form a glass ribbon.

[0051] In the apparatus shown in FIG. 1 , the first molten glass ribbon 24 is directed as a molten glass layer 30 onto a downstream forming roll 14 that rotates in a direction that pulls the molten glass downwardly away from the root 22. The molten glass layer 30 deposited on the forming roll 14 rotates with the forming roll through a portion of an arc before being released from the forming roll 14 and drawn from the forming roll as a second glass ribbon 32 by a first pair of counter-rotating pull rolls 16a and a second pair of counter-rotating pull rolls 16b that engage side edges of the second glass ribbon 32 and draw the second glass ribbon from the forming roll in a draw direction 34. Downstream processes (not shown) can be used to separate the second glass ribbon 32 into lengths of individual glass sheets. Such individual glass sheets can then be further processed, such as to remove edge portions contacted by the pull rolls, wash the glass sheets, stack the glass sheets, and / or package the glass sheets.

[0052] As the molten glass moves away from the root 22, surface tension and viscous forces cause the first molten glass ribbon 24 to shrink laterally (e.g., in a direction parallel to the root 22). Thus, the width W1 of the first molten glass ribbon 24 may undergo a significant decrease as a function of distance from the root 22, which in turn reduces the width of the commercially useful portion of the second glass ribbon 32, thereby limiting the size of the glass sheet that may be obtained therefrom. Conservation of mass causes the edges of the first glass ribbon to thicken as the first glass ribbon undergoes lateral shrinkage, such that the thickness at the edges is greater than the thickness of the central portion of the first glass ribbon inboard of the edges. Such thickened edges are generally subsequently removed as they are detrimental to the commercial value of the ribbon, thereby further reducing the useful width of the second glass ribbon. It is desirable to reduce the initial shrinkage of the first glass ribbon in order to increase the commercially useful portion of the second glass ribbon, as well as subsequent glass sheets produced therefrom. That is, an apparatus and / or method for reducing the lateral shrinkage of a first glass ribbon can help increase the width of a subsequent second glass ribbon, for example, by controlling the flow of molten glass at the edges of the first glass ribbon.

[0053] Additionally, flow conditions, such as the flow rate and drop distance for first molten glass ribbon 24 from forming body 12 to forming rolls 14, can cause the stream of molten glass from the forming body to oscillate, that is, the width of the stream of molten glass can change over time. Such flow fluctuations can disrupt the forming process.

[0054] The function of the edge director in a conventional melting process is to ensure that the molten glass wets the end dam at the end of the forming body. In another process, the converging forming surfaces may have a smaller included angle than normal (e.g., 10-20 degrees). The smaller included angle allows the glass to wet the end dam without the edge director blocking the intersection of the end dam and the forming body surface. This allows the edge director to be placed below the base of the forming body without being connected to the forming body. However, without an edge director, voids 40 may appear that separate the single stream into multiple portions (see FIG. 2), which is not acceptable for the manufacturing process.

[0055] 3 and 4 show a front view and a cross-sectional side view, respectively, of an exemplary apparatus 100 for forming a glass ribbon according to the present disclosure. The apparatus 100 comprises a forming body 102 and, optionally, a forming roll 104 rotatable about an axis of rotation 103 and positioned downstream of the forming body relative to the flow of molten glass 105 from the forming body. Although forming body 100 is depicted as being the same as or similar to forming body 12, forming body 102 may be any other suitable forming body, such as other forming bodies described herein (e.g., a slotted forming body). Forming roll 104 may be a driven forming roll, in which case it is coupled to a motor (not shown) configured to rotate the forming roll about axis of rotation 103. The apparatus 100 may further include multiple pull roll pairs 106a, 106b, such as a first pair of counter-rotating pull rolls 106a positioned to engage a first edge of the stream of molten glass drawn from the forming body (or from the forming rolls, if forming rolls are used), and a second pair of counter-rotating pull rolls 106b positioned to engage a second, opposite edge. In the embodiment of Figures 3 and 4, the forming body 102 includes a first end 107a, a second end 107b opposite the first end 107a, and a trough 108 disposed on the upper surface of the forming body between the first end 107a and the second end 107b and defined at least in part by a pair of weirs 110a, 110b. The lower portion of the forming body 102 includes converging forming surfaces 112a, 112b positioned below the weirs on either side of the forming body, the converging forming surfaces 112a, 112b meeting at a bottom edge (root) 114 of the forming body 102. Molten glass 105 provided at the inlet end of the trough 108 overflows the weirs 110a, 110b and flows downwardly over the converging forming surfaces 112a, 112b as separate streams of molten glass which meet at or below the root 114 and flow downwardly therefrom as a combined stream of molten glass, e.g., a first ribbon of molten glass 116. Dams 118a, 118b positioned at either end of the forming body 102 restrict lateral flow of molten glass over the forming body and prevent molten glass 105 from flowing beyond the forming body ends 107a, 107b.In the apparatus shown in Figures 2 and 3, at least a portion of the combined flow of molten glass, including a first edge 120a extending along the length of the first molten glass ribbon 116 and a second edge 120b extending along the length of the first molten glass ribbon 116 opposite the first edge 120a, flows along a drawing plane 122, shown in a side view in Figure 3, which extends through and parallel to the root 114. The drawing plane 122 may be a vertical plane. A first vertical plane 124, which is perpendicular to the drawing plane 122, shown in a side view in Figure 2, may be envisioned as bisecting the forming body 102. That is, the first vertical plane 124 is located midway between the first end 107a and the second end 107b and perpendicular to a longitudinal axis 125 extending through the forming body. The second vertical plane 127a extends parallel to the first vertical plane 124 and coincides with the first end 107a of the forming body. The third vertical plane 127b extends parallel to the first vertical plane 124 and coincides with the second end 107b of the forming body. In some embodiments, the first molten glass ribbon 116 is then directed as a layer 126 of molten glass onto the downstream forming roll 104, which rotates in a direction that pulls the molten glass downward and away from the root 114. The forming roll 104 is particularly useful for glass compositions that exhibit low viscosities at processing temperatures, e.g., viscosities less than about 5,000 Pa·s, and therefore require further cooling, e.g., by depositing the low-viscosity molten glass of the first molten glass ribbon 116 onto a cooled surface, such as the forming roll 104. In other embodiments employing different glass compositions, the molten glass flowing from root 114 can have a sufficient viscosity, for example about 5,000 Pa·s or greater, to omit forming rolls 104 .

[0056] When a forming roll 104 is employed, the root 114 and the forming roll 104 are separated by a predetermined separation distance 128. A layer 126 of molten glass deposited on the forming roll 104 rotates with the forming roll 104 over a portion of an arc before being released from the forming roll and becoming a second glass ribbon 130 that descends from the forming roll. The forming roll 104 can be used, for example, to cool the molten glass layer to increase the viscosity of the molten glass layer 126. For example, the forming roll 104 can include cooling passages (not shown). The cooling passages can be arranged to receive a flow of a coolant, for example a liquid or gas (such as water or air), to cool the surface of the forming roll to a predetermined temperature. The coolant can thus be provided by a cooling system, such as a chilled water system, including a temperature control device for the coolant.

[0057] A counter-rotating pair of pull rolls 106a, 106b positioned below and downstream from the forming body 102, e.g., below and downstream from the forming roll 104, engage the first edge 120a and the second edge 120b to draw a glass ribbon in a drawing direction 132, either the first molten glass ribbon 116 from the root 114 or the second glass ribbon 130 from the forming roll 104 if the forming roll 104 is employed. Downstream processes (not shown) can be used to separate the glass ribbon 32, such as the second glass ribbon 130, into individual glass sheets of predetermined length. Such individual glass sheets can then be further processed, e.g., to remove contacted edge portions, grind or polish the glass sheets as necessary, clean the glass sheets, stack the glass sheets, and / or package the glass sheets. The following description assumes that the forming roll 104 is employed, but it should be understood that in alternative embodiments the forming roll 104 may not be utilized.

[0058] According to embodiments disclosed herein, a pair of edge directors 134a, 134b are positioned below the root 114 and arranged to contact the molten glass of the first molten glass ribbon 116. That is, a portion of each edge director 134a, 134b may extend into and be submerged in the flow of molten glass descending from the root 114, specifically, at the first and second edges 120a, 120b of the first molten glass ribbon 116. The first and second edge directors 134a, 134b may reduce lateral contraction of the first molten glass ribbon 116 that would otherwise reduce the width of the first glass ribbon. Alternatively or additionally, the first and second edge directors 134a, 134b may help stabilize the flow of molten glass from the forming body 102. Without edge control, depending on the viscosity of the molten glass and the separation distance 128 between the root 114 and the forming roll 104, the width of the first molten glass ribbon 116 can vary (e.g., vibrate) uncontrollably, thereby making process control and product uniformity difficult. Edge directors, such as those disclosed herein, can help reduce this vibration. FIG. 5 is an enlarged view of such an edge director (e.g., first edge director 134a) and shows the edge director's relationship to the forming body 102 and forming roll 104. While the following discussion will be directed to the first edge director 134a, it should be understood that the second edge director 134b can be similar or identical to the first edge director 134a.

[0059] As shown in FIG. 5, the first edge director 134a includes a submerged tool 136. As used herein, a "submerged tool" refers to a device including one or more elongated members, such as one or more wires, that can extend into the molten glass and be at least partially submerged in the flow of molten glass from the forming body 102, i.e., the first molten glass ribbon 116. At least a portion of the submerged tool 136 can be positioned between the first vertical plane 124 and the first edge director 134a. The first edge director 134a can further include a housing 138 configured to support the submerged tool 136 and, if necessary, movement of the submerged tool relative to the forming body (e.g., the flow of molten glass from the root 114).

[0060] In the embodiment of FIG. 5, the illustrated submerged tool 136 comprises two tool segments, a first tool segment 140 extending along a first longitudinal axis 142 and a second tool segment 144 extending along a second longitudinal axis 146. The first tool segment 140 and the second tool segment 144 are configured as a continuous member, i.e., the second tool segment 144 is connected to and extends from the first tool segment 140. However, the first and second tool segments 140, 144 need not be homogenous (e.g., formed continuously as one piece). For example, the second tool segment 144 may be joined to the first tool segment 140 by welding, brazing, or the like. The first longitudinal axis 142 forms an angle α with a horizontal axis 148 that intersects the first longitudinal axis 142. The root 114 may be parallel to the horizontal axis 148. Thus, the horizontal axis 148 may coincide with the root 114. The angle α can be positive, negative, or zero. A positive angle α means an upward tilt to the first vertical axis 142 relative to the horizontal axis 148 (from left to right in FIG. 5 , toward the first vertical plane 124), while a negative angle α means a downward tilt to the first vertical axis 142 relative to the horizontal axis 148. An angle α of zero means that the first vertical axis 142 is horizontal (i.e., parallel to the horizontal axis 148). The tilts described herein are evaluated in a clockwise direction (see arrow 149) from the first tool segment to the last tool segment.

[0061] The second tool segment 144 extends downward from the first tool segment 140 along a second longitudinal axis 146. The second longitudinal axis 146 forms an angle β with a vertical axis 150 that intersects the second longitudinal axis 146. The angle β can be positive, negative, or zero. A positive angle β with respect to the vertical axis 150 means that the second longitudinal axis 146 and the second tool segment 144 extend downward toward the first vertical plane 124 (to the right in FIG. 4), while a negative angle α means that the second longitudinal axis 146 and the second tool segment 144 extend downward away from the first vertical plane 124 (to the left in FIG. 5). A zero angle β with respect to the second longitudinal axis 146 means that the second tool segment 144 extends vertically downward from the first tool segment 140 (i.e., parallel to the vertical axis 150).

[0062] 6 illustrates a first edge director 134a with another exemplary submerged tool 236 including a first tool segment 240 extending along a first longitudinal axis 242 and a second tool segment 244 extending along a second longitudinal axis 246. The first tool segment 240 and the second tool segment 244 are constructed as a continuous member. The first tool segment 240 is shown as being identical to the first tool segment 140 of FIG. 5 and forms an angle α with the horizontal axis 148, while the second longitudinal axis 246 and the second tool segment 244 are depicted as extending downward from the first tool segment 240 in a direction away from the first vertical plane 124 at a negative angle β with respect to a vertical axis 150 that intersects the second longitudinal axis 246.

[0063] 7 illustrates a first edge director 134a with another exemplary submerged tool 346 including a first tool segment 340 extending along a first longitudinal axis 342 and a second tool segment 344 extending along a second longitudinal axis 346. The first tool segment 340 and the second tool segment 344 are configured as a continuous member. As illustrated, the first tool segment 340 may be identical to the first tool segment 140 of FIG. 5 or the first tool segment 240 of FIG. 6. However, the second longitudinal axis 346 and the second tool segment 344 are depicted as extending vertically downward from the first tool segment 340 (i.e., at an angle β of zero, parallel to the vertical axis 150 and the first vertical plane 124).

[0064] FIG. 8 illustrates a first edge director 134a with another exemplary immersed tool 436, at least a portion of which extends downward. The immersed tool 436 of FIG. 8 includes a first tool segment 440 that extends inwardly toward the first vertical plane 124 along a first longitudinal axis 442, as shown in FIGS. 5-7. However, the second tool segment 444 of the immersed tool 436 is not shown as a straight line, but as a curve that includes, for example, a portion of a circular arc. In this case, the angle of the curve can be determined from a tangent to the convex curvature of the arc (e.g., the "outside" of the arc) compared to the vertical axis 450 that intersects the tangent. In the example shown in FIG. 8, the tangent 452 extends downward at a positive angle β with respect to the vertical axis 450. Any one or more segments of the immersed tools disclosed herein can include a fully or partially curved portion.

[0065] 9 illustrates a first edge director 134a with yet another exemplary submerged tool 536 including a first tool segment 540 extending along a first longitudinal axis 542 and a second tool segment 544 extending along a second longitudinal axis 546. The first longitudinal axis 542 extends inwardly from the housing 138 toward the first vertical plane 124 at an angle α relative to a horizontal axis 548 that intersects the first longitudinal axis 542. As discussed above, the angle α can be positive, negative, or zero relative to a horizontal axis (e.g., horizontal axis 548). The second longitudinal axis 546 and second tool segment 544 extend downwardly from the first tool segment 540 at an angle β relative to a vertical axis 550 that intersects the second longitudinal axis 546. The angle β can be positive, negative, or zero. The third longitudinal axis 562 and the third tool segment 560 extend leftward from the second tool segment 544, away from the first vertical plane 124 at an angle θ relative to a horizontal axis, e.g., a horizontal axis 570 that intersects the third longitudinal axis 562. The angle θ can be positive, negative, or zero. A positive angle θ means that the third longitudinal axis 562 and the third tool segment 560 are inclined upward from the second tool segment 544 relative to the horizontal axis 570. A negative angle θ means that the third longitudinal axis 562 and the third tool segment 560 are inclined downward from the second tool segment 544 relative to the horizontal axis 570. A zero angle θ means that the third longitudinal axis 562 and the third tool segment 560 extend horizontally from the second tool segment 544.

[0066] 10 illustrates a first edge director 134a with another exemplary submerged tool 636 including four tool segments, a first tool segment 640 extending along a first longitudinal axis 642, a second tool segment 644 extending from the first tool segment 640 along a second longitudinal axis 646, a third tool segment 660 extending from the second tool segment 644 along a third longitudinal axis 662, and a fourth tool segment 664 extending from the third tool segment along a fourth longitudinal axis 666. The first longitudinal axis 642 and the first tool segment 640 extend inwardly from the housing 138 toward the first vertical plane 124 at an angle α with respect to a horizontal axis 648 that intersects with the first longitudinal axis 642. The root 114 can be parallel to the horizontal axis 648. The horizontal axis 648 can be coincident with the root 114. The angle α1 can be positive, negative, or zero. A positive angle α1 means that the first longitudinal axis 642 and the first tool segment 640 are inclined upward relative to the horizontal axis 648. A negative angle α1 means that the first longitudinal axis 642 and the first tool segment 640 are inclined downward relative to the horizontal axis 648. A zero angle α1 means that the first tool segment 640 extends horizontally.

[0067] The second longitudinal axis 646 and the second tool segment 644 extend inwardly from the first tool segment 640 towards the first vertical plane 124 at an angle α2 relative to a horizontal axis 648 that intersects the second longitudinal axis 646. A positive angle α2 means that the second longitudinal axis 646 and the second tool segment 644 are inclined upward relative to the horizontal axis 648. A negative angle α2 means that the second longitudinal axis 646 and the second tool segment 644 are inclined downward relative to the horizontal axis 648. An angle α2 of zero means that the second tool segment 644 extends horizontally from the first tool segment 640.

[0068] The third longitudinal axis 662 and the third tool segment 660 extend downward from the second tool segment 644 at an angle β relative to the vertical axis 670. The angle β can be positive, negative, or zero. A positive angle β relative to the vertical axis 650 intersecting the third longitudinal axis 662 means that the third longitudinal axis 662 and the third tool segment 660 extend downward toward the first vertical plane 124 (to the right in FIG. 10), while a negative angle β means that the third longitudinal axis 662 and the third tool segment 660 extend downward away from the first vertical plane 124 (to the left in FIG. 10). A zero angle β means that the third longitudinal axis 662 and the third tool segment 660 extend vertically downward from the second tool segment 644 (i.e., parallel to the vertical axis 650).

[0069] The fourth longitudinal axis 666 and the fourth tool segment 664 extend outward from the third tool segment 660 in a direction away from the first vertical plane 124 at an angle θ relative to a horizontal axis 670 that intersects the fourth longitudinal axis 666. A positive angle θ means that the fourth longitudinal axis 666 and the fourth tool segment 664 are inclined upward relative to the horizontal axis 670. A negative angle θ means that the fourth longitudinal axis 666 and the fourth tool segment 664 are inclined downward relative to the horizontal axis 670. An angle θ of zero means that the fourth tool segment 664 extends horizontally, parallel to the horizontal axis 670.

[0070] While the exemplary immersion tools of FIGS. 5-10 were supported in respective housings 138 at one end of the immersion tool (e.g., first tool segment 140, 240, 340, 440, 540, 640, respectively), in the embodiment of FIG. 11, the immersion tool 736 is electrically connected to a power source configured to apply electrical current to the immersion tool. The immersion tool 736 of FIG. 11 comprises a first tool segment 740 extending along a first longitudinal axis 742 at a first angle α relative to a horizontal axis 748 that intersects the first longitudinal axis 742. The angle α can be positive, negative, or zero. The second tool segment 744 extends from the first tool segment 540 at an angle β relative to a vertical axis 750 that intersects the second longitudinal axis 746. The angle β can be positive, negative, or zero. The third tool segment 760 extends along a third longitudinal axis 762 at an angle θ relative to a horizontal axis 770 that intersects the third longitudinal axis 762. The angle θ can be positive, negative, or zero. The first tool segment 740 and the third tool segment 760 thus represent ends of an immersion tool. These ends are connected to a power source 772 via conductive lines 774 and 776. The first tool segment 740 and the third tool segment 760 can contact and / or be supported by an electrical insulation member 778. The electrical insulation member 778 can comprise the housing 138. For example, at least a portion of the first tool segment 740 and at least a portion of the third tool segment 768 can be embedded in and extend through the electrical insulation member 778. While the electrical insulation member 778 can be formed from a variety of materials, the location of the first edge director 134a is proximate to the flowing molten glass, which may in some cases exceed 1000°C, meaning that the electrical insulation member 778 may be formed from a heat resistant electrically insulating material. For example, the electrical insulation member 778 can be formed from a refractory material (e.g., ceramic). In some embodiments, the first and third tool segments 740, 760 can be positioned on opposing edges of the electrical insulation member 778, such as adjacent opposing edge surfaces of the electrical insulation member (e.g., upper and lower edge surfaces, see e.g., FIG. 12).However, as shown in FIG. 11, the first and third tool segments 740 and 760 may be embedded within an electrical insulating member 778. In this latter embodiment, the first and third tool segments 740, 760 may be better protected from accidental contact with each other or with equipment that may be positioned near the edge directors, thereby preventing electrical shorts and shock hazards. In some embodiments, a portion of the first tool segment 740 and a portion, e.g., ends, of the third tool segment 760 may be formed with a larger cross-sectional diameter than the remainder of the first and third tool segments to provide improved contact with and / or support by the electrical insulating member 778. However, in embodiments, the ends of the first and third tool segments 740 and 760 may be sleeved, e.g., with a ceramic material 782. The power source may include a controller (not shown) configured to control the magnitude of current passed through the immersed tool and, therefore, the temperature of the immersed tool as the current heats it.

[0071] 12 and 13 show another exemplary submerged tool 836 including a first tool segment 840 extending along a first longitudinal axis 842, a second tool segment 844 extending from the first tool segment 840 along a second longitudinal axis 846, a third tool segment 860 extending from the second tool segment 844 along a third longitudinal axis 862, a fourth tool segment 864 extending from the third tool segment 860 along a fourth longitudinal axis 866, and a fifth tool segment 868 extending from the fourth tool segment 864 along a fifth longitudinal axis 870. The first tool segment 840, the second tool segment 844, the third tool segment 860, the fourth tool segment 864, and the fifth tool segment 868 are configured as a continuous member, for example, as a wire having multiple bends to form a predetermined shape. The embodiment of FIGS. 12 and 13 is similar to the embodiment shown in FIG. 10. For example, the first vertical axis 842 makes an angle α1 with a horizontal axis 848 that intersects the first vertical axis 842. The angle α1 can be positive, negative, or zero. A positive angle α1 means that the first vertical axis 842 is tilted upward with respect to the horizontal axis 848, a negative angle α1 means that the first vertical axis 842 is tilted downward with respect to the horizontal axis 848, and a zero angle α1 means that the first vertical axis 842 is horizontal. Similarly, the second vertical axis 846 makes an angle α2 with a horizontal axis 848 that intersects the second vertical axis 846. The angle α2 can be positive, negative, or zero. A positive angle α2 means that the second vertical axis 846 is inclined upward relative to the horizontal axis 848, a negative angle α2 means that the second vertical axis 846 is inclined downward relative to the horizontal axis 848, and a zero angle α2 means that the second vertical axis 842 is horizontal. The third vertical axis 862 makes an angle β with a vertical axis 850 that intersects the third vertical axis 862. The angle β can be positive, negative, or zero. A positive angle β means that the third vertical axis 862 is inclined toward the first vertical plane 124 (to the right in FIG. 13), a negative angle β means that the third vertical axis 862 is inclined away from the first vertical plane 124 (to the left in FIG. 13), and a zero angle β means that the third vertical axis 842 is vertical. The fourth vertical axis 866 makes an angle θ with a horizontal axis 872 that intersects the fourth vertical axis 866. The angle β can be positive, negative, or zero.A positive angle θ means that the fourth vertical axis 866 is tilted upward relative to the horizontal axis 872, a negative angle θ means that the fourth vertical axis 866 is tilted downward relative to the horizontal axis 872, and a zero angle θ means that the fourth vertical axis 866 is horizontal. The fifth vertical axis 870 makes an angle φ with a horizontal axis 872 that intersects the fifth vertical axis 870. The angle φ can be positive, negative, or zero. A positive angle φ means that the fifth vertical axis 870 is tilted upward relative to the horizontal axis 872, a negative angle β means that the fifth vertical axis 870 is tilted downward relative to the horizontal axis 872, and a zero angle β means that the fifth vertical axis 870 is horizontal.

[0072] The wire dip tool 136, 236, 336, 436, 536, 636, 736, 836, or any other wire dip tool, can have a maximum wire diameter of about 10 millimeters (mm) or less, e.g., about 9 mm or less, about 8 mm or less, about 7 mm or less, about 6 mm or less, about 5 mm or less, about 4 mm or less, about 3 mm or less, about 2 mm or less, e.g., in the range of about 1 mm to about 3 mm. The dip tool 136, 236, 336, 436, 536, 636, 736, 836, and / or any other configuration of wire dip tool can have various wire cross-sectional shapes in planes perpendicular to the respective longitudinal axes for a particular portion of the dip tool. The dip tool, or a portion thereof, e.g., the wire of the dip tool, can have a circular cross-sectional shape, an elliptical cross-sectional shape, or a polygonal shape (e.g., square, rectangular, hexagonal, octagonal, etc.). The diameter and cross-sectional shape of the submerged tool wire need not be uniform and therefore may vary along the length of the wire.

[0073] The immersion tool 136, 236, 336, 436, 536, 636, 736, 836, and / or any other configuration of the wire immersion tool may include a conductive material. For example, in some embodiments, the immersion tool may include a platinum group metal (i.e., at least one of ruthenium, rhodium, palladium, osmium, iridium, or platinum). In some embodiments, a platinum alloy, such as a platinum-rhodium alloy, may be used. The platinum-rhodium alloy may include about 70% to about 90% platinum by weight and about 30% to about 10% rhodium by weight. However, other high temperature metals may be used where appropriate (e.g., depending on the temperature of the molten glass in the first molten glass ribbon), including, but not limited to, molybdenum, tungsten, titanium, tantalum, nickel, and alloys thereof, to name a few. Other suitable materials may include stainless steel, or an iron-chromium-aluminum alloy, such as Kanthal. In some embodiments, the wire is made of a metal alloy, such as an intermetallic material, for example, molybdenum disilicide (MoSi 2 ) or Ti 3 It can be formed using Al.

[0074] At least a portion of the immersion tool can be positioned between the first vertical plane 124 and the second vertical plane 127a (or the third vertical plane 127b). One or more portions of the immersion tool can be fully or partially immersed in the molten glass (e.g., edge 120a or edge 120b) depending on the immersion depth of the respective edge director; that is, the distance the immersion tool extends into the molten glass. One way to determine the immersion depth for any of the several embodiments disclosed herein is to measure the distance 900 between the first end 127a of the dam and the furthest extent of the immersion tool from the first end (or another reference point, if desired). While this measurement does not provide a direct means of determining the length of the immersion tool immersed in the molten glass, it does provide a convenient and measurable indication of the lateral position of the immersion tool, for example, by using a visual scale to compare to a known reference point. Of course, other reference points can be used to determine the position of the immersion tool relative to the reference point.

[0075] The first edge director 134a can be configured to have several degrees of freedom of movement. Referring to FIG. 11 as an example, the first edge director 134a can be movable in a direction along an axis parallel to the root 114, e.g., a horizontal axis 148, to vary the immersion depth of the first submerged tool 136 (or any other submerged tool disclosed herein). That is, a lateral movement parallel to the root allows the submerged tool to be inserted into the flow of molten glass at the edge of the first molten glass ribbon 116. In some embodiments, the first edge director 134a can be configured as a removable cartridge, so that removal and replacement can be easily accomplished when the edge director needs to be removed, e.g., to replace it with another edge director of a different geometry while the glass forming apparatus is in operation.

[0076] As shown in FIG. 14, the first edge director 134a may further be configured to be rotatable about an axis of the submerged tool. Typically, the submerged tool lies on a plane, such as a vertical plane. However, as shown, the first tool segments 140, 240, 340, 440, 540, 640, 740, and 840 may each have a longitudinal axis extending along at least a portion of the length of the first tool segment, e.g., a horizontal first longitudinal axis. Thus, the submerged tools 136, 236, 336, 436, 536, 636, 736, and / or 836, or any other configuration of the submerged tools, may be configured to rotate about the respective first longitudinal axis 142, 242, 342, 442, 542, 642, 742, or 842. 14, for example, shows that the submerged tool can rotate about the first longitudinal axis 142 at angles ±γ relative to the drawing plane 122, as indicated by the bidirectional arc 902 representing the rotation of the submerged tool, such that a portion of the submerged tool can swing out of the drawing plane 122 while at least a portion of the submerged tool 136 remains in the drawing plane. It will be apparent that an upper portion of the submerged tool will remain in the drawing plane 122, while the remaining portion of the submerged tool will extend out of the drawing plane. The extent of the submerged tool rotation will determine how much of the edge of the first molten glass ribbon the submerged tool will remain submerged in.

[0077] The first edge director 134a can be further configured to rotate about an axis 904 that is perpendicular to the drawing plane 122. For example, with reference to FIG. 13, the first edge director 134a, and thus the immersion tool 836, is configured to rotate about the axis 904, as indicated by the double-headed arc 906. The first edge director 134a can be configured to move vertically, as indicated by the double-headed arrow 908 (see, for example, FIG. 12). For example, the first edge director 134a can be coupled to an actuator configured to move the first edge director 134a vertically, either upward (opposite the direction of molten glass flow from the forming body) or downward (the same direction as the direction of molten glass flow from the forming body).

[0078] There are many process variables that can affect the flow characteristics of the molten glass during the forming process, including chemical composition, temperature, viscosity, flow rate, rotational speed of the forming rolls, distance from the root of the forming rolls, etc., and some or all of the variables may be interdependent. Thus, the shape and size of the submerged tool can be varied to obtain the desired reduction in lateral shrinkage that depends on these and other process variables. As an example, the submerged tool 136 of FIG. 5 was described above as having two segments with different angles relative to the horizontal and / or vertical axes. Thus, for example, any one or more of the angles α, β, and / or length of the submerged tool segments can be changed to achieve the desired reduction in lateral shrinkage and / or ribbon stability. Additionally, various segments can be added to or removed from the submerged tool. For example, the submerged tool of FIG. 12 has a more complex shape with more segments than the submerged tool shown in FIG. 11.

[0079] The viscosity of the molten glass in contact with the submerged tool can be altered by establishing an electric current to the submerged tool via a power source 772 and appropriate wiring (e.g., conductive lines 774, 776), and the temperature of the molten glass in contact with the submerged tool can be increased or decreased depending on the magnitude of the electric current, thereby altering the flow characteristics of the molten glass in contact with the submerged tool. Heating the submerged tool can also prevent devitrification of the molten glass in contact with a surface of the submerged tool by maintaining the temperature of the molten glass in contact with the submerged tool above the liquidus temperature of the molten glass.

[0080] It will also be apparent that the positioning of the first edge director 134a relative to the root 114 and the forming roll 104 can be used to control the flow characteristics of the edges of the first molten glass ribbon 116. That is, in embodiments, a first distance 170 from the root 114 to the top segment of the submerged tool and a second distance 172 from the forming roll 104 to the bottom segment of the submerged tool can affect the ability of the first edge director 134a to mitigate lateral contraction of the first molten glass ribbon 116. Thus, in embodiments, the first edge director 134a can be configured to allow for variation of the vertical position of the edge director, and in particular the vertical position of the submerged tool relative to the root 114 and / or the forming roll 104. Any one or more of the above degrees of freedom of movement can be used individually or together, in whole or in part, to control the flow of molten glass at the first molten glass ribbon 116, and in particular the edges. The horizontal position of the first edge director 134a relative to the end of the forming body, e.g., the dam 118a, can be variable. That is, the first edge director 134a, and thus the immersion tool, can be moved inwardly parallel to the drawing plane 122 toward the first vertical plane 124, or outwardly parallel to the drawing plane 122 away from the first vertical plane 124. For example, the first edge director 134a can be coupled to an actuator configured to move the first edge director outwardly toward or away from the first vertical plane 124. Alternatively, the first edge director 134a can be manually movable, e.g., mounted to a fixture that allows translation along an axis parallel to the drawing plane 122. The first edge director can be fixed in any desired position along that axis.

[0081] FIG. 15 illustrates yet another first edge director 134a. The edge director of FIG. 15 comprises an immersion tool 936 including a first tool segment 940, a second tool segment 944 extending from the first tool segment 940, and a third tool segment 946 extending from the second tool segment 944. The first tool segment 940 is joined to or extends from a first thickened wire section 974, while the third tool segment 946 is joined to or extends from a second thickened wire section 976. The first and / or second thickened wire sections 974 and / or 976 may be formed, for example, by welding, brazing, or otherwise joining two or more wires to form a wire having a greater thickness (e.g., diameter) than the first and third tool segments 940 or 946. For example, the first thickened wire section 974 can include an extension of the first tool segment 940 to which one or more additional lengths of wire can be joined to form a thickened wire length having a reduced electrical conductivity compared to the thinner portion of the first tool segment. Similarly, the second thickened wire section 976 can include an extension of the third tool segment 946 to which one or more additional lengths of wire can be joined to form a thickened wire length having a reduced electrical conductivity compared to the thinner portion of the third tool segment. The first and second thickened wire sections 974 and / or 976 can be housed in an electrically insulating member 778. For example, the electrically insulating member 778 can comprise a first refractory member 978, such as a tubular refractory member including a first bore extending through a length of the first refractory member, where the first thickened wire section 974 can extend through the first bore and be connected to a power source 772 at a first end 980 via conductive wires 774, 776 (not shown). Similarly, the electrical insulation member 778 can comprise a second refractory member 982, such as a tubular refractory member including a second bore extending through the length of the second refractory member, where the second thickened wire section 976 can extend through the second bore and connect to the power source 772 at a second end 984. The first refractory member 978 can be coupled to the second refractory member 982 with one or more coupling members 986.The one or more connecting members 986 can be, for example, clamps, ties, additional refractory bodies including one or more holes through which the first and second refractory members 978, 982 can pass, or any other device suitable for connecting the first refractory member 978 to the second refractory member 982. The first and second refractory members 978, 982 provide rigidity to the first and second thickened sections 974, 976 to support the weight of molten glass that may accumulate on the immersion tool while it is immersed in the flow of molten glass (first molten glass ribbon), and also provide electrical insulation between the first and second thickened sections. The first and second refractory members 978, 982 can be formed of alumina, although other high temperature electrically insulating materials can be used. In some embodiments, a single refractory member with two holes, one for each of the two thickened wire sections, can be used. The first and second refractory members 978, 982 can be further supported by a suitable support member 988. The support member 988 can include features that provide the edge director with the degrees of freedom of movement described above. That is, the support member 988 can be configured to provide vertical, horizontal, and / or rotational movement to the first edge director 134a. Such movement can be facilitated by one or more actuators coupled to the first edge director or can be accomplished manually.

[0082] It will be readily apparent that various immersion tool configurations can be utilized as edge directors inserted downstream into the first molten glass ribbon 116 and spaced from the forming body root 114. The molten glass wets the wire of the immersion tool and follows a path downward on the wire. As soon as the molten glass leaves the wire, the glass ribbon thins until its viscosity becomes too high or until it contacts the forming rolls (if present). The wire can be extended downward as far as necessary to reduce the distance the molten glass ribbon thins unsupported. Now referring to FIG. 16, in aspects of the disclosure, including at least all aspects and embodiments disclosed herein in which the immersion tool is configured to conduct electrical current and thereby heat the immersion tool, the immersion tool can comprise an outer sheath 1000 and an electrical insulation layer 1002 disposed between the central wire of the immersion tool and the outer sheath 1000. Because the wire dip tool is positioned in the flow of molten glass descending from the forming body, the wire will need to have sufficient stiffness (e.g., thickness, diameter) to withstand deformation due to the force of the flow. As the wire diameter increases, the electrical resistance of the wire decreases, so an increase in current is required to heat the wire to a sufficient temperature. Thus, in some embodiments, an outer conductive sheath 1000 can be added to provide stiffness without requiring the wire diameter to be increased to obtain the desired heating capacity. For example, the sheath 1000 can include platinum, e.g., 70% to 90% platinum by weight and about 10% to about 30% rhodium by weight. However, other high temperature metals can be used where appropriate (e.g., depending on the temperature of the molten glass in the first molten glass ribbon), including, but not limited to, molybdenum, tungsten, titanium, tantalum, nickel, and alloys thereof, to name a few. The sheath 1000 can be, for example, a tube disposed around the wire dip tool. A cross-section of a portion of the dip tool 1004 is shown in FIG. 16. The electrically insulating layer 1002 should be a non-conductive material that can withstand degradation from the high temperatures imposed by the molten glass in contact with the immersion tool. For example, the electrically insulating layer 1002 can include alumina.An electrically insulating layer isolates the immersion tool from contact with the molten glass.

[0083] Because the molten glass flowing through the glass making equipment is a weak conductor of electricity, it has been found that currents imposed on components of the glass making equipment, such as the melting tank (used to melt the batch materials) and the various metallic conduits and tanks that can be directly heated by establishing an electric current therethrough, can result in stray currents in downstream components of the process. For example, the forming body 102 and the forming roll 104 can be electrical circuit elements. These stray currents can inhibit the adhesion of the molten glass to the forming roll 104 and / or cause blisters (bubbles) to appear on the surfaces of the forming body 102 and / or the forming roll 104.

[0084] In some embodiments, a DC bias voltage can be established between the sheath 1000 and the forming roll 104 to control the adhesion of the molten glass to the forming roll surface. For example, referring to FIG. 17, a first DC power supply 1006 can be electrically connected to the sheath 1000 and the forming roll 104, for example, between the sheath 1000 and the forming roll 104. The polarity and magnitude of the first voltage V1 provided by the first DC power supply 1006 can be selected using a suitable controller (not shown) as needed to control the adhesion. By way of example, the first voltage V1 can be controlled within a range of about -3 volts DC to about +3 volts DC, for example, within a range of about -2 volts DC to about +2 volts DC, and the second current is in a range of about 0 to about 5 amperes. Such a configuration is shown in FIG. 17, using a dip tool 936 for illustration and not limitation.

[0085] A second DC power supply 1008 can be connected between the forming body 100 and the sheath 1000 to mitigate the formation of blisters on the surface of the forming body 102 that contacts the molten glass. This is particularly effective when the forming body 102 is a metal forming body. The second voltage V2 and second current provided by the second DC power supply 1008 may be of different polarity but may be in the same magnitude range as those provided by the first DC power supply 1006.

[0086] To obtain a continuous ribbon, sufficient flow must be available on the immersion tool and throughout the ribbon. Otherwise, voids may form in the ribbon and travel upstream to the root of the forming body, causing the molten glass ribbon to break off into a stream as shown in FIG. 2. As the flow rate is increased at the edge of the molten glass ribbon, the holes close, but the edge flow may become unstable due to a mechanism similar to dripping. Further increases in flow can stabilize the flow at the edge. However, high flow rates may not be practical for production. Thus, a low flow rate at the edge of the molten glass ribbon may be beneficial to the process when stabilized with an edge director. The edge directors described herein can function to gather sufficient flow at the immersion tool to stabilize the ribbon edge as it exits the immersion tool. With the increased flow at the edge of the molten glass ribbon, a wire edge director with a vertical wire very close to the dam can maintain the ribbon width very close to the root length. Thus, the viscosity and flow rate of the molten glass must be considered when determining the appropriate immersion depth, distance from the root, and shape of the submerged tool for any particular equipment and process parameters.

[0087] It will also be apparent that the forming apparatus need not include forming rolls that distribute the molten glass. For example, the edge directors described herein may also be useful in other processes in which the glass ribbon is drawn from a bottom edge of a converging forming surface and drawn down with draw rolls that do not have a forming roll disposed therebetween. Indeed, other forming apparatuses that do not have converging forming surfaces may also be employed. For example, a slot-draw apparatus in which the molten glass ribbon flows out of a slot in the bottom of a vat may be subject to lateral contraction. Thus, the edge directors disclosed herein may be used with such slot-draw apparatuses, or any other down-draw apparatus (i.e., in which the molten glass is drawn downward from the vat as a molten glass ribbon), with the immersion tool of each edge director being at least partially immersed in the edge of the molten glass ribbon.

[0088] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments of the present disclosure without departing from the spirit and scope of the present disclosure, and therefore, the present disclosure is intended to cover all such modifications and variations provided they come within the scope of the appended claims and their equivalents. [Explanation of symbols]

[0089] 100 Exemplary Apparatus According to the Present Disclosure 102 Molded body 103 Rotation axis of forming roll 104 Forming roll 105 Molten Glass 106a,b First pair / second pair of counter-rotating pull rolls 107a,b First end / second end of molded body 108 Trough 114 Bottom edge (base) of molding body 116 First molten glass ribbon 118a,b Dam 120a,b First / second edge of first molten glass ribbon 124 First Vertical Plane 126 Layer of Molten Glass 127a,b 2nd / 3rd vertical plane 128 Separation distance between root and forming roll 130 Second Glass Ribbon 132 Pull-out direction 134a,b 1st / 2nd edge director W Width of first molten glass ribbon

Claims

1. a forming body configured to receive a flow of molten glass, the forming body having a first end and a second end opposite the first end, the molten glass flowing from the forming body as a molten glass ribbon along a drawing plane; an edge director assembly including a wire dip tool positioned below the forming body and extending from the first end in a direction perpendicular to the withdrawal plane toward a first vertical plane that bisects the forming body and passes through the forming body; Equipped with At least a portion of the wire dip tool is positioned between the first vertical plane and a second vertical plane parallel to the first vertical plane and coincident with the first end of the forming body.

2. The glass forming apparatus of claim 1 , wherein the wire dipping tool is vertically movable.

3. The glass forming apparatus of claim 1 , wherein the wire dipping tool is horizontally movable.

4. 10. The glass forming apparatus of claim 1, further comprising a forming roll rotatable about an axis of rotation positioned below and spaced from the edge director, the forming roll positioned to receive the molten glass ribbon on a surface thereof.

5. 10. The glass forming apparatus of claim 1, wherein the wire dip tool is connected to a power source configured to apply an electrical current to the wire dip tool.

6. 6. The glass forming apparatus of claim 5, wherein the wire dip tool comprises a conductive sheath disposed around the wire dip tool and an electrically insulating material disposed between the wire dip tool and the conductive sheath, electrically isolating the wire dip tool from the conductive sheath.

7. The glass forming apparatus of claim 1 , wherein the edge director assembly is positioned below and spaced from the forming body.

8. 1. A method of forming a glass ribbon, comprising: flowing molten glass from a forming body as a molten glass ribbon; contacting an edge of the molten glass ribbon with an edge director assembly, the edge director assembly comprising a wire dip tool at least partially immersed in the edge; A method comprising:

9. The method of claim 8 wherein the edge director assembly is positioned below and spaced from the forming body.

10. The method of claim 8 further comprising heating the wire dip tool with an electrical current directed through the wire dip tool.

11. 11. The method of claim 10, further comprising the step of: connecting a DC power source between the edge director assembly and the forming roll; and controlling the adhesion of the molten glass layer to the forming roll by controlling at least one of a voltage or a current supplied by the DC power source.

12. 12. The method of claim 11, wherein the edge director assembly comprises a conductive sheath disposed around the wire immersion tool, an electrically insulating material disposed between the conductive sheath and the wire immersion tool, and the DC power source electrically connected to the conductive sheath.

13. 10. The method of claim 8, further comprising receiving the molten glass ribbon onto a rotating forming roll positioned below and spaced from the edge director, the molten glass ribbon covering at least a portion of the forming roll to form a molten glass layer.

14. 14. The method of claim 13, further comprising drawing the molten glass layer from the forming roll as a second glass ribbon.

Images