WO2011090893A1

WO2011090893A1 - Apparatus and methods for fusion drawing a glass ribbon

Info

Publication number: WO2011090893A1
Application number: PCT/US2011/021255
Authority: WO
Inventors: Olus N. Boratav; William A. Whedon
Original assignee: Corning Incorporated
Priority date: 2010-01-19
Filing date: 2011-01-14
Publication date: 2011-07-28
Also published as: JP2013517217A; TWI540107B; CN102762507B; JP5820395B2; CN102762507A; TW201129511A; KR101796804B1; KR20120121897A

Abstract

An apparatus for fusion drawing a glass ribbon includes a forming wedge with a pair of downwardly inclined forming surface portions converging along a downstream direction to form a root. The apparatus further includes an edge director intersecting with at least one of the pair of downwardly inclined forming surface portions, a heating device configured to heat an interface of the molten glass in contact with the edge director, and a cooling device configured to extract heat from a portion of the glass ribbon flowing off of the edge director. Methods are also provided for heating an interface of the molten glass in contact with the edge director and for extracting heat from a portion of the glass ribbon flowing off of the edge director.

Description

APPARATUS AND METHODS FOR FUSION DRAWING A GLASS RIBBON

[0001] This application claims the benefit or priority to US Provisional

Application No. 61/296240 filed on January 19, 2010.

TECHNICAL FIELD

[0002] The present invention relates generally to apparatus and methods for fusion drawing a glass ribbon, and more particularly, to apparatus and methods for fusion drawing a glass ribbon with a heating device and a cooling device.

BACKGROUND

[0003] Glass manufacturing systems are commonly used to form various glass products such as LCD sheet glass. It is known to manufacture sheet glass by downwardly flowing molten glass over a forming wedge and drawing a glass ribbon from the root of the forming wedge. Edge directors are frequently provided at opposed ends of the forming wedge to help achieve a desired glass ribbon width and edge bead characteristics. SUMMARY

[0004] The following presents a simplified summary of the disclosure in order to provide a basic understanding of some example aspects described in the detailed description.

[0005] In one example aspect, a fusion draw method includes the steps of flowing molten glass over a pair of downwardly inclined forming surface portions of a forming wedge, the downwardly inclined forming surface portions converging along a

downstream direction to form a root. The method further includes the step of flowing the molten glass over an edge director intersecting with at least one of the pair of

downwardly inclined forming surface portions. The method also includes the step of drawing a glass ribbon from the root, wherein an edge of the glass ribbon is formed by molten glass flowing off the edge director. The method still further includes the steps of using a heating device to heat an interface of the molten glass in contact with the edge director, and using a cooling device to extract heat from a portion of the glass ribbon flowing off of the edge director.

[0006] In another example aspect, an apparatus for fusion drawing a glass ribbon includes a forming wedge with a pair of downwardly inclined forming surface portions converging along a downstream direction to form a root. The apparatus further includes an edge director intersecting with at least one of the pair of downwardly inclined forming surface portions. The apparatus also includes a heating device configured to heat an interface of molten glass in contact with the edge director, and a cooling device configured to extract heat from a portion of a glass ribbon flowing off of the edge director.

[0007] A first exemplary aspect of the present invention relates to a fusion draw method comprising the steps of: flowing molten glass over a pair of downwardly inclined forming surface portions of a forming wedge, the downwardly inclined forming surface portions converging along a downstream direction to form a root; flowing the molten glass over an edge director intersecting with at least one of the pair of downwardly inclined forming surface portions; drawing a glass ribbon from the root, wherein an edge of the glass ribbon is formed by molten glass flowing off the edge director; using a heating device to heat an interface of the molten glass in contact with the edge director; and using a cooling device to extract heat from a portion of the glass ribbon flowing off of the edge director.

[0008] In certain embodiments of the first aspect of the present invention, the heating device maintains the interface of the molten glass in contact with the edge director above a liquidus temperature of the molten glass.

[0009] In certain embodiments of the first aspect of the present invention, the method comprises a the step of maintaining a temperature of the molten glass below a baggy warp temperature of the molten glass at a location downstream from the root.

[0010] In certain embodiments of the first aspect of the present invention, the cooling device preferentially extracts heat from the edge of the glass ribbon below the root such that the temperature of the edge of the glass ribbon decreases at a higher rate than the temperature of an inner portion of the glass ribbon.

[0011 ] In certain embodiments of the first aspect of the present invention, the cooling device extracts more heat from the edge of the glass ribbon below the root than the heat provided by the heating device to the interface of the molten glass in contact with the edge director.

[0012] In certain embodiments of the first aspect of the present invention, the method further comprises a step of shielding a heating region of the heating device from a cooling region of the cooling device. [0013] In certain embodiments of the first aspect of the present invention, the heating device maintains the interface of the molten glass in contact with the edge director by use of an external heater operating outside of the edge director.

[0014] In certain embodiments of the first aspect of the present invention, the heating device maintains the interface of the molten glass in contact with the edge director by use of an internal heater operating inside the edge director.

[0015] In certain embodiments of the first aspect of the present invention, the cooling device includes a fluid nozzle that extracts heat from the edge of the glass ribbon at a location downstream from the edge director.

[0016] In certain embodiments of the first aspect of the present invention, the method further comprises the step of controlling at least one of the heating device and the cooling device with a control system.

[0017] In certain embodiments of the first aspect of the present invention, the method comprises sensing a temperature and using the sensed temperature to provide feedback to the control system.

[0018] A second exemplary aspect of the present invention relates to an apparatus for fusion drawing a glass ribbon comprising: a forming wedge including a pair of downwardly inclined forming surface portions converging along a downstream direction to form a root; an edge director intersecting with at least one of the pair of downwardly inclined forming surface portions; a heating device configured to heat an interface of molten glass in contact with the edge director; and a cooling device configured to extract heat from a portion of a glass ribbon flowing off of the edge director.

[0019] In certain embodiments of the second aspect of the present invention, the heating device is configured to maintain the interface of the molten glass in contact with the edge director above a liquidus temperature of the molten glass.

[0020] In certain embodiments of the second aspect of the present invention, the cooling device is configured such that the cooling device preferentially extracts heat from the edge of the glass ribbon below the root such that the temperature of the edge of the glass ribbon decreases at a higher rate than the temperature of an inner portion of the glass ribbon.

[0021] In certain embodiments of the second aspect of the present invention, the cooling device is configured such that the cooling device extracts more heat from the edge of the glass ribbon below the root than heat provided by the heating device to the interface of the molten glass in contact with the edge director.

[0022] In certain embodiments of the second aspect of the present invention, the apparatus comprises a thermal shield positioned between a heating region of the heating device and a cooling region of the cooling device.

[0023] In certain embodiments of the second aspect of the present invention, the apparatus comprises a control system configured to control at least one of the heating device and the cooling device.

[0024] In certain embodiments of the second aspect of the present invention, the control system includes a controller and a temperature sensor configured to provide feedback to the controller.

[0025] In certain embodiments of the second aspect of the present invention, the control system is configured to control the cooling device to preferentially extract heat from the edge of the glass ribbon below the root such that the temperature of the edge of the glass ribbon decreases at a higher rate than the temperature of an inner portion of the glass ribbon.

[0026] In certain embodiments of the second aspect of the present invention, the control system is configured to operate at least one of the heating device and the cooling device such that the cooling device extracts more heat from the edge of the glass ribbon below the root than heat provided by the heating device to the interface of the molten glass in contact with the edge director.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] These and other aspects are better understood when the following detailed description is read with reference to the accompanying drawings, in which:

[0028] FIG. 1 is a schematic view of an apparatus for fusion drawing a glass ribbon;

[0029] FIG. 2 is a cross sectional perspective view of the apparatus along line 2-2 of FIG. 1 illustrating portions of a first example apparatus;

[0030] FIG. 3 is a side view illustrating portions of a second example apparatus; and

[0031] FIG. 4 is a side view illustrating portions of a third example apparatus. DETAILED DESCRIPTION

[0032] Examples will now be described more fully hereinafter with reference to the accompanying drawings in which example embodiments are shown. Whenever possible, the same reference numerals are used throughout the drawings to refer to the same or like parts. However, aspects may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0033] FIG. 1 illustrates a schematic view of an apparatus 101 for fusion drawing a glass ribbon 103 for subsequent processing into glass sheets. The apparatus 101 can include a melting vessel 105 configured to receive batch material 107 from a storage bin 109. The batch material 107 can be introduced by a batch delivery device 111 powered by a motor 113. An optional controller 115 can be configured to activate the motor 113 to introduce a desired amount of batch material 107 into the melting vessel 105, as indicated by arrow 117. A glass metal probe 119 can be used to measure a glass melt 121 level within a standpipe 123 and communicate the measured information to the controller 115 by way of a communication line 125.

[0034] The apparatus 10 can also include a fining vessel 127, such as a fining tube, located downstream from the melting vessel 105 and coupled to the melting vessel 105 by way of a first connecting tube 129. A mixing vessel 131 such as a stir chamber, can also be located downstream from the fining vessel 127 and a delivery vessel 133, such as a bowl, may be located downstream from the mixing vessel 131. As shown, a second connecting tube 135 can couple the fining vessel 127 to the mixing vessel 131 and a third connecting tube 137 can couple the mixing vessel 131 to the delivery vessel 133. As further illustrated, a downcomer 139 can be positioned to deliver glass melt 121 from the delivery vessel 133 to an inlet 141 of a forming vessel 143. As shown, the melting vessel 105, fining vessel 127, the mixing vessel 131, delivery vessel 133, and forming vessel 143 are examples of glass melt stations that may be located in series along the apparatus 101.

[0035] The melting vessel 105 is typically made from a refractory material, such as refractory (e.g. ceramic) brick. The apparatus 101 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 metals 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 129, the fining vessel 127 (e.g., finer tube), the second connecting tube 135, the standpipe 123, the mixing vessel 131 (e.g., a stir chamber), the third connecting tube 137, the delivery vessel 133 (e.g., a bowl), the downcomer 139 and the inlet 141. The forming vessel 143 is also made from a refractory material and is designed to form the glass ribbon 103.

[0036] FIG. 2 is a cross-sectional perspective view of the apparatus 101 along line

2-2 of FIG. 1. As shown, the forming vessel 143 includes a forming wedge 201 comprising a pair of downwardly inclined forming surface portions 207, 209 extending between opposed ends of the forming wedge 201. The pair of downwardly inclined forming surface portions 207, 209 converge along a downstream direction 211 to form a root 213. A draw plane 215 extends through the root 213 wherein the glass ribbon 103 may be drawn in the downstream direction 211 along the draw plane 215. As shown, the draw plane 215 can bisect the root 213 although the draw plane 215 may extend at other orientations with respect to the root 213.

[0037] The forming vessel 143 may comprise one or more edge directors intersecting with at least one of the pair of downwardly inclined forming surface portions 207, 209. In further examples, the one or more edge directors can intersect with both downwardly inclined forming surface portions 207, 209. In further examples, an edge director can be positioned at each of the opposed ends of the forming wedge 201 wherein an edge of the glass ribbon 103 is formed by molten glass flowing off the edge director. For instance, as shown in FIG. 2, an edge director 217 can be positioned at a first opposed end 203 and a second identical edge director (not shown) can be positioned at a second opposed end (not shown). Each edge director can be configured to intersect with both of the downwardly inclined forming surface portions 207, 209. Each edge director 217 can be substantially identical to one another although the edge directors may have different characteristics in further examples. Various forming wedge and edge director configurations may be used in accordance with aspects of the present disclosure. For example, aspects of the present disclosure may be used with forming wedges and edge director configurations disclosed in U.S. Pat. No. 3,451,798, U.S. Patent No. 3,537,834, U.S. Patent No. 7,409,839 and/or U.S. Provisional Pat. Application No. 61/155,669, filed February 26, 2009 that are each herein incorporated by reference in its entirety. [0038] FIG. 2 illustrates just one example edge director 217 that may be used with aspects of the disclosure. The first edge director 217 will be discussed with the understanding that the second edge director (not shown), in some examples, may be similar or identical to the first edge director 217. Providing identical edge directors can be beneficial to provide a uniform glass ribbon although the edge directors may have different features to provide varied glass sheet characteristics and/or accommodate various forming vessel configurations.

[0039] FIG. 2 illustrates a first side of the first edge director 217 positioned with respect to the first downwardly inclined forming surface portion 207 of the forming wedge 201. Although not shown, the first edge director 217 further includes a second side positioned with respect to the second inclined forming surface portion 209 of the forming wedge 201. The second side of the first edge director 217 is a mirror image of the first side about the draw plane 215 bisecting the root 213. As shown, the first side includes a first surface 219 that intersects the first downwardly inclined forming surface portion 207 of the forming wedge 201. Although not shown, the second side of the first edge director 217 also includes a substantially identical surface that intersects the second inclined forming surface portion 207 of the forming wedge 201.

[0040] Each opposed end of the forming wedge 201 can be provided with a retaining block 221 designed to help laterally position the corresponding first and second edge directors 217. Optionally, as shown, the first edge director 217 can include an upper portion 223 and a lower portion 225. The lower portion 225 can, in some examples, join the first edge director 217 on the first opposed end 203 with the second edge director on the second opposed end (not shown). Joining the edge directors 217 together can be beneficial to simplify assembly of the edge directors 217 to the forming wedge 201. In further examples, the upper portions 223 of the edge directors 217 may be provided separately. For example, the first edge director 217 can be separate from the second edge director and assembled independently to each of the pair of downwardly inclined forming surface portions 207, 209 of the forming wedge 201. With certain configurations, providing upper portions 223 that are not joined may simplify manufacturing of the edge directors 217. Each edge director 217 can have a variety of orientations and geometries by providing different surfaces relative to the forming wedge 201.

[0041] The apparatus 101 for fusion drawing a glass ribbon can also include at least one edge roller assembly including a pair of edge rollers configured to engage a corresponding edge of the glass ribbon as the ribbon is drawn off the root 213 of the forming wedge 201. The pair of edge rollers facilitates proper finishing of the edges of the glass ribbon. Edge roller finishing provides desired edge characteristics and proper fusion of the edge portions of the molten glass being pulled off opposed surfaces of the edge director associated with the pair of downwardly inclined forming surface portions 207, 209. As shown in FIG. 2, a first edge roller assembly 227 is associated with the first edge director 217 and a second edge roller assembly (not shown) is associated with the second edge director. Each edge roller assembly 227 can be substantially identical to one another although the pairs of edge rollers may have different characteristics in further examples.

[0042] FIG. 2 illustrates an example edge roller assembly that may be used with aspects of the disclosure. The first edge roller assembly 227 will be discussed with the understanding that the second edge roller assembly (not shown), in some examples, may be similar or identical to the first edge roller assembly 227. As shown in FIG. 2, the first edge roller assembly 227 includes a first pair of edge rollers 229 including a first edge roller 231 and a second edge roller 233. The edge rollers 231, 233 are configured to simultaneously engage the first side and the second side of the glass ribbon 103. The first edge roller assembly 227 further includes a first shaft 235 attached to the first edge roller 231 and a second shaft 237 attached to the second edge roller 233. The first and second shafts 235, 237 are configured to be rotatably driven by a motor (not shown).

[0043] As schematically shown in FIG. 2, the apparatus 101 can also include one or more heating devices 239. The heating device 239 is configured to heat an interface of the molten glass in contact with the first edge director 217. In the example shown, the first heating device 239 can be located about the edge director 217 as an external heating device. In one example, the external heating device can be configured to heat the back side of the lower portion 225 of the first edge director 217. As shown in FIG. 3, the heating device 339 can also be located inside the edge director although the heating device may be located on the edge director or in other locations in further examples. Indeed, the heating device can be located in various three-dimensional positions relative to the edge director 217. As shown, a single heating device may be provided although a plurality of heating devices may be provided in further examples.

[0044] The heating device can heat the interface of the molten glass in contact with the first edge director 217 above a liquidus temperature of the molten glass. The liquidus temperature corresponds to a lower temperature range where the glass remains molten without crystal formation. If portions of the molten glass drop below the liquidus temperature, crystallized glass may develop. Portions of crystallized glass, often referred to as a devits within the molten glass, tend to accumulate at a rate proportional to the temperature difference below the glass liquidus temperature. Thus, in one example the heating device 239 is configured to heat the interface of the molten glass in contact with the first edge director to slow down the rate of devit accumulation on the edge director. In another example, the edge director 217 is maintained above the liquidus temperature to substantially reduce or even eliminate any devit accumulation on the edge director.

Elimination of any devit accumulation can result in a devitrification- free edge director apparatus.

[0045] While desirable to reduce devit accumulation on the edge director, the operation of the heating device 239 also tends to reduce the viscosity of the molten glass. As noted by reference number 245 in FIG. 2, a reduced viscosity may undesirably reduce the width of the glass ribbon 103.

[0046] The apparatus 101 can also include one or more cooling devices 241 to counteract undesirable width loss of the glass ribbon 103. As schematically shown in FIG. 2, the cooling device 241 is configured to extract heat from a portion of the molten glass flowing off of the first edge director 217. The cooling device 241 can be comprised of various devices including but not limited to a fluid dispensing apparatus (e.g., an orifice forming an air jet), a relatively cold object held in proximity to the edge of the glass ribbon, a radiative cooler, and/or a plurality of fluid nozzles.

[0047] Cooling devices may be configured to operate in one or more of a variety of ways. For example, the cooling device 241 can be configured such that the cooling device 241 preferentially extracts heat from the edge of the glass ribbon 103 below the root 213 such that the temperature of the edge of the glass ribbon 103 decreases at a higher rate than the temperature of an inner portion of the glass ribbon. In such examples, the inner portion may comprise an intermediate portion, such as a middle portion, disposed between opposed lateral edges of the glass ribbon 103. In addition or alternatively, the cooling device 241 may be configured such that the cooling device 241 extracts more heat from the edge of the glass ribbon 103 below the root 213 than heat provided by the heating device 239 to the interface of the molten glass in contact with the edge director. [0048] Operation of the cooling device 241 at a location below the root 213 helps counteract an undesirable decrease in glass ribbon width that might otherwise occur by operating the heating device 239 alone. Thus, the heating device 239 can be used to reduce devit formation on the edge director while the cooling device 241 can be used to counteract an undesirable loss in glass ribbon width that might otherwise occur by using the heating device 239 without subsequent cooling of the molten glass flowing off of the edge director.

[0049] As shown in FIG. 3, a side view of a second example apparatus 301 including the forming wedge 201, and the edge director 217 of FIG. 2 is shown. In the example of FIG. 3, the heating device 339 is located within the edge director 271. As further shown in FIG. 3, the apparatus 301 can include a pair of edge gates 305 and a pair of central gates 307. Only one of the edge gates 305 and one of the central gates 307 are shown in this view as the other gate in each pair is located on the reverse side of the molten glass. The edge gate 305 and the central gate 307 are located below a lower portion 225 of the edge director 217 to aid in directing the flow of the molten glass. The central gates 307 can be closed more tightly together than the edge gates 305 as the central portion of the molten glass is thinner than the edge portion of the molten glass. The edge gates 305 cannot be closed as tightly due to the additional flow of molten glass from the edge director 217.

[0050] As further shown in FIG. 3, the first and second rollers 231 , 233 may be actively cooled to help reduce the likelihood of molten glass being deposited on the edge rollers 231, 233. For instance, as shown in FIG. 3, an inlet line 309 is configured to extend through each shaft 235 to provide a cooling fluid (i.e. gas or liquid) to the first and second rollers 231, 233. An outlet line 311 also extends through each shaft 235, 237 to return heated liquid to a liquid source 313. A hydraulic pump 315 can draw fluid from the liquid source and passed through a heat exchanger 317 to remove heat transferred from the first and second rollers 231, 233 before cycling back through the inlet line 309 to continue cooling the first and second rollers 231, 233. The cooling can help reduce the likelihood of glass adhering to the rollers. In further examples, the rollers can be cooled at a higher rate to assist the cooling device 241.

[0051] A third example apparatus 401 is shown in FIG. 4. As described above, the heating device 239 heats an interface of the molten glass in contact with the first edge director 217. The cooling device 241 is configured to extract heat from a portion of the molten glass flowing off of the first edge director 217. The third example apparatus 401 can also further include structure for cooling the rollers 231 , 233 or any of the other structure from the other examples.

[0052] In the third example of FIG. 4, an optional thermal shield apparatus is provided with the illustrated thermal shield 411. The thermal shield 411, if provided, can be configured to shield a heating region associated with the heating device 239 from a cooling region associated with the cooling device 241. As further illustrated, a control system 419 may be provided to control at least one of the heating device 239 and the cooling device 241. The control system 419 can operate at least one of the heating device 239 and the cooling device 241 in a variety of ways based on a variety of conditions, including but not limited to monitoring the temperature of the molten glass at different locations and monitoring the width of the glass ribbon 103. In one example, the control system 419 may be configured to control the cooling device 241 to preferentially extract heat from the edge of the glass ribbon 103 below the root 213 such that the temperature of the edge of the glass ribbon 103 decreases at a higher rate than the temperature of an inner portion of the glass ribbon 103. In addition or alternatively, the control system 419 can be configured to operate at least one of the heating device 239 and the cooling device 241 such that the cooling device 241 extracts more heat from the edge of the glass ribbon 103 below the root 213 than heat provided by the heating device 239 to the interface of the molten glass in contact with the edge director.

[0053] In one example, the control system 419 can further include a controller

421 and at least one sensor 423. The at least one sensor 423 in this example is located on the edge director 217 although other positions are possible in further examples.

Furthermore, the sensor can comprise an infrared sensor positioned to sense temperature conditions associated with the edge director. The at least one sensor 423 is configured to sense a temperature associated with the molten glass about the edge director 217 and uses the sensed temperature to provide feedback control to the heating device 239 and the cooling device 241. The at least one sensor 423 can communicate the sensed temperature to the controller 421 through a wired connection or through a wireless connection. The controller 421 is then configured to adjust operation of the heating device 239 and/or the cooling device 241 in response to the sensed temperature. In addition or alternatively, another sensor 425 may be associated with the cooling device 241 to sense a temperature condition of the edge of the glass ribbon 103. The sensor may comprise an infrared sensor although other sensing devices may be provided in further examples. The sensor 425 is configured to sense a temperature associated with the edge of the glass ribbon 103 and uses the sensed temperature to provide feedback to the controller 421. Based on the sensed feedback, the controller 421 can then operate the cooling device 241 at to provide proper cooling conditions.

[0054] Still further, the controller may send a signal along line 417 to activate a motor (not shown) to control positioning of the thermal shield 411 to provide desirable thermal control between the heating region associated with the heating device 239 and the cooling region associated with the cooling device 241.

[0055] A method for forming glass will now be described with respect to the apparatus 401 including the example edge directors 217. It will be appreciated that similar or identical method steps may be performed with further examples, for instance, as described throughout the application. Moreover, example methods of the present invention may omit and/or add additional steps. Moreover, unless noted, the steps can be performed simultaneously, sequentially or in different orders depending on the particular application.

[0056] As shown in FIGS. 1-2 and 4, methods of forming glass with the example apparatus 401 including the edge director 217 are schematically illustrated. In a first example method, a fusion draw method is provided for making a glass ribbon 103. The method includes the step of flowing a molten glass over a pair of downwardly inclined forming surface portions 207, 209 comprising a forming wedge 201, where the pair of downwardly inclined forming surface portions 207, 209 are converging at the bottom of the forming wedge 201 at a root 213. The method further includes the steps of flowing the molten glass over a first edge director 217 intersecting with at least one of the pair of inclined forming surface portions 207, 209 and drawing the molten glass from the root 213 of the forming wedge 201 to form the glass ribbon 103. The method still further includes the steps of using a heating device 239 to heat the interface of the molten glass in contact with the first edge director 217 and using a cooling device 241 to extract heat from a portion of the molten glass flowing off of the edge director 217. Thus, the heating device 239 heats the interface of the molten glass in contact with the first edge director 217 to reduce devit accumulation and the cooling device 241 extracts heat from a location below the edge director 217 to preserve the width of the glass ribbon 103 by

counteracting the width loss that would occur by use of only the heating device 239. In one example, the heating device 239 heats the interface of the molten glass in contact with the first edge director 217 by use of an external heater operating outside of the edge director 217. In another example, the heating device 239 heats the interface of the molten glass in contact with the first edge director 217 by use of an internal heater operating inside the edge director 217. The cooling device 241 can extract heat from the molten glass below the edge director 217 by use of a fluid nozzle in one example.

[0057] The example method can include using the heating device 239 to heat the interface of the molten glass in contact with the first edge director 217 above a liquidus temperature of the molten glass. The liquidus temperature can correspond to where the crystal phase starts to develop. Thus, in one example the heating device 239 is configured to heat the interface of the molten glass in contact with the first edge director 217 to slow down the rate of devit accumulation on the edge director 217. In another example, the edge director 217 is maintained above the liquidus temperature to substantially reduce or even eliminate any devit accumulation on the edge director 217. The additional heat flux required to completely eliminate devit accumulation is that which will ensure no part of the edge director 217 surface operates below the liquidus temperature of the glass being formed. Therefore, aspects of the present disclosure can reduce or elimination devit accumulation that may impact glass ribbon quality. Indeed, when the devit layer becomes too thick the flowing glass can "bridge" to fixed objects in close proximity and cause serious operational issues. Devit accumulation can also disrupt the fusing of the two molten glass ribbons being drawn off the root 213 from the downwardly inclined forming surfaces 207, 209. Fusion disruption at the edge can result in bubble formation in the bead or other imperfections in the glass ribbon.

[0058] The example method can include using the cooling device 241 to extract an amount of heat flux to counteract the use of the heating device 239. The step of using the heating device 239 to heat the interface of the molten glass in contact with the first edge director 217 will cause a width loss, or a contraction, of the resulting glass ribbon 103. The cooling device 241 can be operated to extract an amount of heat flux corresponding to the amount of heat flux applied by the heating device 239 and recover a portion of the width loss. In one example, the amount of heat flux to be applied and then extracted can be estimated from glass ribbon formation models. A glass ribbon formation model can provide guidance for the resulting sheet size for a various temperatures of a molten glass. [0059] In another example, the amount of heat flux to be applied and extracted can be measured during operation of the apparatus. In one example, the cooling device 241 can be operated at different cooling rates to attain a different width loss of the glass ribbon from the different attenuation of the molten glass that occurs. Based on modeling techniques, it was determined that operating the cooling device 241 at different rates may result in the width loss of the resulting glass ribbon being reduced to approximately 57 mm. In another modeling example using a relatively larger cooling rate, it was determined that the width loss of the resulting glass ribbon can be reduced to

approximately 6 mm. In yet another modeling example using a relatively larger cooling rate, the modeling results indicated that the glass ribbon had a width gain of

approximately 11 mm.

[0060] The example method can further include the step of maintaining the temperature of the molten glass at a location below the root 213 below a baggy warp temperature of the molten glass. The baggy warp temperature represents the maximum temperature allowable on the free ribbon before a baggy warp condition is observed. The baggy warp temperature may vary depending on the cooling curve in a region of the molten glass as well as the local mass flow and glass composition. The physical explanation of the baggy warp is a condition wherein the molten glass has a reduced viscosity from the temperature of the molten glass exceeding the baggy warp temperature. Under baggy warp conditions, the viscosity of the molten glass is reduced to the point where it cannot be pulled anymore by the pulling rolls (not shown). Furthermore, under baggy warp conditions, the glass flow exiting the forming wedge may begin to exceed that of a purely rectangular sheet being pulled to a fixed thickness by the pulling rolls located much lower in the plane. In one example method, the heating device 239 maintains the temperature at an edge of the molten glass passing over the edge director 217 within a range from about 3010° C to about 1200° C. The temperature range can correspond to maintaining the molten glass in contact with the first edge director above a liquidus temperature, such as 3010° C, of the molten glass while still maintaining the temperature of the molten glass at a location below the root below the baggy warp temperature, such as 1200° C. The example method can maintain the temperature through use of one of the heating device 239 and the cooling device 241 or through use of both of the heating device 239 and the cooling device 241. [0061] In another alternative, the example method can also further include the step of shielding a heating region of the heating device 239 from a cooling region of the cooling device 241. Shielding the heating region from the cooling region can be achieved with the thermal shield 411 shown in FIG. 4. The thermal shield 411 may configured to help control heat transfer between the heating region and the cooling region.

[0062] The example method can also further include the step of controlling at least one of the heating device 239 and the cooling device 241 with a control system 419. The control system 419 can operate at least one of the heating device 239 and the cooling device 241 in a variety of ways based on a variety of conditions, including the temperature of the molten glass at different locations and the width of the glass ribbon 103. In one example, the control system 419 can include the step of sensing or measuring a temperature associated with the molten glass and using the sensed temperature to provide feedback control for the control system 419.

[0063] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the claimed invention.

Claims

CLAIMS What is claimed is:

1. A fusion draw method comprising the steps of:

flowing molten glass over a pair of downwardly inclined forming surface portions of a forming wedge, the downwardly inclined forming surface portions converging along a downstream direction to form a root;

flowing the molten glass over an edge director intersecting with at least one of the pair of downwardly inclined forming surface portions;

drawing a glass ribbon from the root, wherein an edge of the glass ribbon is formed by molten glass flowing off the edge director;

using a heating device to heat an interface of the molten glass in contact with the edge director; and

using a cooling device to extract heat from a portion of the glass ribbon flowing off of the edge director.

2. The method according to claim 1, wherein the heating device maintains the interface of the molten glass in contact with the edge director above a liquidus temperature of the molten glass.

3. The method according to claim 1 or claim 2, further comprising the step of maintaining a temperature of the molten glass below a baggy warp temperature of the molten glass at a location downstream from the root.

4. The method according to any of the preceding claims, wherein the cooling device preferentially extracts heat from the edge of the glass ribbon below the root such that the temperature of the edge of the glass ribbon decreases at a higher rate than the temperature of an inner portion of the glass ribbon.

5. The method according to any of the preceding claims, wherein the cooling device extracts more heat from the edge of the glass ribbon below the root than the heat provided by the heating device to the interface of the molten glass in contact with the edge director.

6. The method according to any of the preceding claims, further comprising the step of shielding a heating region of the heating device from a cooling region of the cooling device.

7. The method according to any of the preceding claims, wherein the heating device maintains the interface of the molten glass in contact with the edge director by use of an external heater operating outside of the edge director.

8. The method according to any of the preceding claims, wherein the heating device maintains the interface of the molten glass in contact with the edge director by use of an internal heater operating inside the edge director.

9. The method according to any of the preceding claims, wherein the cooling device includes a fluid nozzle that extracts heat from the edge of the glass ribbon at a location downstream from the edge director.

10. The method according to any of the preceding claims, further comprising the step of controlling at least one of the heating device and the cooling device with a control system.

11. The method according to claim 10, further comprising sensing a temperature and using the sensed temperature to provide feedback to the control system.

12. An apparatus for fusion drawing a glass ribbon comprising:

a forming wedge including a pair of downwardly inclined forming surface portions converging along a downstream direction to form a root;

an edge director intersecting with at least one of the pair of downwardly inclined forming surface portions;

a heating device configured to heat an interface of molten glass in contact with the edge director; and

a cooling device configured to extract heat from a portion of a glass ribbon flowing off of the edge director.

13. The apparatus according to claim 12, wherein the heating device is configured to maintain the interface of the molten glass in contact with the edge director above a liquidus temperature of the molten glass.

14. The apparatus according to claim 12 or claim 13, wherein the cooling device is configured such that the cooling device preferentially extracts heat from the edge of the glass ribbon below the root such that the temperature of the edge of the glass ribbon decreases at a higher rate than the temperature of an inner portion of the glass ribbon.

15. The apparatus according to any of claims 12 to 14, wherein the cooling device is configured such that the cooling device extracts more heat from the edge of the glass ribbon below the root than heat provided by the heating device to the interface of the molten glass in contact with the edge director.

16. The apparatus according to any of claims 12 to 15, further comprising a thermal shield positioned between a heating region of the heating device and a cooling region of the cooling device.

17. The apparatus according to any of claims 12 to 16, further comprising:

a control system configured to control at least one of the heating device and the cooling device.

18. The apparatus according to claim 17, wherein the control system includes a controller and a temperature sensor configured to provide feedback to the controller.

19. The apparatus according to claim 17 or claim 18, wherein the control system is configured to control the cooling device to preferentially extract heat from the edge of the glass ribbon below the root such that the temperature of the edge of the glass ribbon decreases at a higher rate than the temperature of an inner portion of the glass ribbon.

20. The apparatus according to any of claims 17 to 19, wherein the control system is configured to operate at least one of the heating device and the cooling device such that the cooling device extracts more heat from the edge of the glass ribbon below the root than heat provided by the heating device to the interface of the molten glass in contact with the edge director.