Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B17/00—Forming molten glass by flowing-out, pushing-out, extruding or drawing downwardly or laterally from forming slits or by overflowing over lips
  • C03B17/06—Forming glass sheets
  • C03B17/064—Forming glass sheets by the overflow downdraw fusion process; Isopipes therefor
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B17/00—Forming molten glass by flowing-out, pushing-out, extruding or drawing downwardly or laterally from forming slits or by overflowing over lips
  • C03B17/06—Forming glass sheets
  • C03B17/068—Means for providing the drawing force, e.g. traction or draw rollers

Definitions

• the present specification generally relates to the manufacture of glass sheets and, more specifically, to apparatus and methods for making glass sheets with edge directors.
• Glass manufacturing systems are commonly used to form various glass products such as LCD glass sheets. It is known to manufacture glass sheets by downwardly flowing molten glass over a forming wedge. Edge directors are frequently provided at opposed ends of the forming wedge to help achieve a desired glass sheet width and edge bead
• edge directors glass that passes over the edge directors can cool and devitrify, building up on the edge directors. This buildup can result in shape-related and other defects of the glass as well as necessitate frequent replacement of the edge directors. Accordingly, methods that minimize the buildup of devitrified glass on edge directors are desirable.
• the embodiments described herein relate to apparatus and methods for making glass sheets with edge directors heated through induction.
• a fusion draw method of making a glass sheet includes flowing molten glass over a pair of downwardly inclined foiming surface portions of a foiming wedge, the downwardly inclined foiming surface portions converging along a downstream direction to form a root.
• the method also includes flowing molten glass over an edge director intersecting with at least one of the pair of downwardly inclined foiming surface portions.
• the method includes maintaining a minimum temperature of at least a portion of a surface of the edge director contacting the molten glass above a predetermined amount through heating of the edge director by induction.
• the method further includes drawing the molten glass from the root of the forming wedge to form a glass sheet.
• an apparatus for downwardly drawing sheet glass includes a forming wedge having a pair of downwardly inclined forming surface portions, the downwardly inclined forming surface portions converging at the bottom of the forming wedge forming a root and defining a draw line for molten glass therealong.
• the apparatus also includes an edge director contacting at least one of the pair of downwardly inclined foiming surface portions.
• the edge director includes an induction coil positioned behind the surface of the edge director for maintaining a minimum temperature of at least a portion of a surface of the edge director contacting the molten glass above a predeteimined amount through heating of the edge director by induction.
• FIG. 1 is a schematic view of an apparatus for making glass
• FIG. 2 is a cross sectional perspective view of the apparatus along line 2-2 of FIG. 1 illustrating a first example of a heat shield apparatus
• FIG. 2A is a perspective view of the apparatus with another example of a heat shield apparatus
• FIG. 3 is a perspective view of an induction heated edge director shown with a schematic representation of an induction heating system
• FIG. 4 is a perspective view of an induction coil configuration
• FIGS. 5A and 5B are, respectively, perspective views of alternative embodiments of induction heating system components
• FIGS. 6A and 6B are, respectively, cross-sectional and perspective views of an edge director having a back plate and an induction coil that is positioned behind the back plate; and [0016] FIG. 7 is a perspective view of an edge director having a back plate where an area between an inner surface of the back plate and an inner surface of the edge director contacting the molten glass is filled with thermally conductive beads.
• Glass sheet materials may generally be formed by melting glass batch materials to form molten glass and thereafter forming the molten glass into a glass sheet.
• Exemplary processes include the float glass process, the slot draw process and the fusion down-draw process.
• FIG. 1 illustrates a schematic view of an apparatus 10 for making glass, such a glass sheet 12.
• the apparatus 10 can include a melting vessel 14 configured to receive batch material 16 from a storage bin 18.
• the batch material 16 can be introduced to the melting vessel 14 by a batch delivery device 20 powered by a motor 22.
• An optional controller 24 may be provided to activate the motor 22 and a molten glass level probe 28 can be used to measure the glass melt level within a standpipe 30 and communicate the measured information to the controller 24.
• the apparatus 10 can also include a fining vessel 38, such as a fining tube, located downstream from the melting vessel 14 and coupled to the melting vessel 14 by way of a first connecting tube 36.
• a mixing vessel 42 such as a stir chamber, can also be located downstream from the fining vessel 38 and a delivery vessel 46, such as a bowl, may be located downstream from the mixing vessel 42.
• a second connecting tube 40 can couple the fining vessel 38 to the mixing vessel 42 and a third connecting tube 44 can couple the mixing vessel 42 to the delivery vessel 46.
• a downcomer 48 can be positioned to deliver glass melt from the delivery vessel 46 to an inlet 50 of a forming vessel 60.
• the melting vessel 14, fining vessel 38, the mixing vessel 42, delivery vessel 46, and forming vessel 60 are examples of glass melt stations that may be located in series along the apparatus 10.
• the melting vessel 14 is typically made from a refractory material, such as refractory (e.g. ceramic) brick.
• the apparatus 10 may further include components that are typically made from platinum or platinum-containing metals such as platinum-rhodium, platinum- iridium and combinations thereof, but which may also comprise such refractory 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 36, the fining vessel 38, the second connecting tube 40, the standpipe 30, the mixing vessel 42, the third connecting tube 44, the delivery vessel 46, the downcomer 48 and the inlet 50.
• the forming vessel 60 can also made from a refractory material and is designed to form the glass sheet 12.
• FIG. 2 is a cross sectional perspective view of the apparatus 10 along line 2-2 of FIG. 1.
• the forming vessel 60 includes a forming wedge 62 comprising a pair of downwardly inclined forming surface portions 66a, 66b that can extend between opposed ends 64a, 64b of the forming wedge 62.
• the downwardly inclined forming surface portions 66a, 66b converge along a downstream direction 68 to form a root 70.
• a draw plane 72 extends through the root 70 wherein the glass sheet 12 may be drawn in the downstream direction 68 along the draw plane 72.
• the draw plane 72 can bisect the root 70 although the draw plane 72 may extend at other orientations with respect to the root 70.
• aspects of the disclosure may be used with various forming vessels. For example, aspects of the disclosure may be used with apparatus for reducing radiative heat loss from a forming body disclosed in U.S. Provisional Pat. Application No. 61/180,216, filed May 21, 2009 which is herein incorporated by reference in its entirety.
• the forming vessel 60 may comprise an edge director intersecting with at least one of the pair of downwardly inclined forming surface portions 66a, 66b.
• the edge director can intersect with both downwardly inclined forming surface portions 66a, 66b.
• an edge director can be positioned at each of the opposed ends of the forming wedge 62.
• an edge director 80a, 80b can be positioned at each of the opposed ends 64a, 64b of the forming wedge 62 with each edge director 80a, 80b configured to intersect with both of the downwardly inclined forming surface portions 66a, 66b.
• each edge director 80a, 80b is substantially identical to one another although the edge directors may have different characteristics in further examples.
• forming wedge and edge director configurations may be used in accordance with aspects of the present disclosure.
• 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. Pat. 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.
• FIGS. 2 and 2A illustrate just one example edge director that may be used with aspects of the disclosure.
• the first edge director 80a will be discussed with the understanding that the second edge director 80b, in some examples, may be similar or identical to the first edge director 80a.
• Providing identical edge directors can be beneficial to provide a uniform glass sheet although the edge directors may have different features to provide varied glass sheet characteristics and/or accommodate various forming vessel configurations.
• FIGS. 2 and 2A illustrate a first side of the first edge director 80a positioned with respect to the first downwardly inclined forming surface portion 66a of the forming wedge 62.
• the first edge director 80a further includes a second side positioned with respect to the second inclined forming surface portion 66b of the forming wedge 62.
• the second side of the first edge director 80a is a mirror image of the first side about the draw plane 72 bisecting the root 70.
• the first side includes a first surface 82 that intersects the first downwardly inclined forming surface portion 66a of the forming wedge 62.
• the second side of the first edge director 80a also includes a substantially identical surface that intersects the second inclined forming surface portion 66b of the forming wedge 62.
• Each opposed end 64a, 64b of the forming wedge 62 can be provided with a retaining block 84 designed to help laterally position the corresponding first and second edge directors 80a, 80b.
• the first edge director 80a can include an upper portion 86 and a lower portion 88.
• the lower portion 88 can, in some examples, join the first edge director 80a on the first opposed end 64a with the second edge director 80b on the second opposed end 64b. Joining the edge directors 80a, 80b together can be beneficial to simplify assembly of the edge directors 80a, 80b to the forming wedge 62.
• the upper portions 86 of the edge directors 80a, 80b may be provided separately.
• the first edge director 80a can be separate from the second edge director 80b and assembled independently to each of the pair of downwardly inclined forming surface portions 66a, 66b of the forming wedge 62.
• providing upper portions 86 that are not joined may simplify manufacturing of the edge directors 80a, 80b.
• Each edge director 80a, 80b can have a variety of orientations and geometries by providing different surfaces relative to the forming wedge 62.
• the apparatus 10 for making glass can also include at least one edge roller device including a pair of edge rollers configured to engage a corresponding edge of the glass ribbon as the ribbon is drawn off the root 70 of the forming wedge 62. The pair of edge rollers facilitates proper finishing of the edges of the glass sheet.
• 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 66a, 66b.
• the edge rollers can be located at various positions within the viscous region of the glass being drawn from the 70. For instance, the edge rollers can be located anywhere from immediately below the root 70 to a position about 15 inches below the root 70 although other positions may be contemplated in further examples. In still another example, the edge rollers can be located at a position within a range of from about 8 inches to about 10 inches below the root 70.
• a first edge roller assembly 130a is associated with the first edge director 80a and a second edge roller assembly 130b is associated with the second edge director 80b.
• each edge roller assembly 130a, 130b is substantially identical to one another although the pairs of edge rollers may have different characteristics in further examples.
• FIG. 2 illustrates an example edge roller assembly that may be used with aspects of the disclosure.
• the first edge roller assembly 130a will be discussed with the understanding that the second edge roller assembly 130b, in some examples, may be similar or identical to the first edge roller assembly 130a.
• the first edge roller assembly 130a includes a first pair of edge rollers 132 including a first edge roller 132a and a second edge roller 132b.
• the edge rollers 132a, 132b are configured to simultaneously engage the first side and the second side of the glass sheet 12.
• the first edge roller assembly 130a further includes a first shaft 134a attached to the first edge roller 132a and a second shaft 134b attached to the second edge roller 132b.
• the first and second shafts 134a, 134b extend through a seal plate 136 and are configured to be rotatably driven by a motor (not shown).
• the seal plate 136 is configured to provide closure to an opening leading to the area housing the motor 138.
• the seal plate may comprise a refractory material, steel, or other thermal insulation to protect sensitive components of the motor and/or other mechanisms located within the housing area.
• the forming vessel 60 may also be provided with a thermal shield apparatus including a thermal shield associated with at least one of the edge directors 80a, 80b. The thermal shields are configured to reduce heat loss from the corresponding edge directors 80a, 80b to non-target areas, and in particular, heat loss to the cooled edge rollers.
• Such non-target areas can include nearby areas of the glass making apparatus and/or other locations capable of receiving heat transfer from the edge directors.
• a first thermal shield apparatus 110a includes a first thermal shield 120a associated with the first edge director 80a.
• a second thermal shield apparatus 110b includes a second thermal shield 120b associated with the second edge director.
• each thermal shield apparatus 110a, 110b is substantially identical to one another although the thermal shield apparatus may have different characteristics in further examples. Providing identical thermal shield apparatus can be beneficial to provide similar thermal shielding of the edge directors although the thermal shield apparatus may have different features to accommodate various forming vessel configurations.
• FIG. 2 illustrates just one example thermal shield apparatus that may be used with aspects of the disclosure.
• the first thermal shield apparatus 110a will be discussed with the understanding that the second thermal shield apparatus 110b, in some examples, may be similar or identical to the first thermal shield apparatus 110a.
• the first thermal shield can be positioned below a portion or the entire first edge director, and extends generally in a length-wise direction relative to the long dimension of the forming wedge and in close proximity to the edge roller shafts. As shown in FIG. 2, the first thermal shield 120a may be positioned to be located below only a portion of the first edge director 80a. Providing the first thermal shield 120a at a location underneath only a portion of the first edge director 80a can provide sufficient reduction of heat loss to non-target areas while avoiding possible interference with the molten glass being drawn from the root 70 of the forming wedge 62.
• the first thermal shield can also extend entirely below the first edge director.
• FIG. 2A illustrates another example of a first thermal shield apparatus 210a
• the first thermal shield apparatus 210a includes a thermal plate 222 with an end 224 terminating inside of the corresponding edge 13 of the glass sheet 12.
• the thermal plate 222 only extends relative to one side of the glass sheet 12 thereby allowing the thermal shield to extend below the entire first edge director.
• the thermal plate 222 may include a slot 226 to provide passage of the edge 13 and corresponding edge portion of the glass sheet 12.
• the end 224 of the thermal plate 222 extends relative to both sides of the glass sheet 12 while allowing the thermal shield to extend below the entire first edge director 80a. Positioning the thermal shield to extend below the entire first edge director 80a can minimize heat loss from the first edge director 80a to non-target areas.
• FIG. 3 illustrates an example of an edge director 80' that is assembled to forming wedge 62' having a pair of downwardly inclined forming surface portions 66a', 66b'.
• Edge director 80' includes an upper portion 86' and a lower portion 88' and edge director 80' and forming wedge 62' are shown in FIG. 3 in a bottom-left perspective view.
• Positioned behind the surface of the edge director 80' is an induction coil 90.
• Induction coil 90 comprises a plurality of turns sufficient to result in a desired amount induction heating of edge director 80' upon sufficient application of alternating current to induction coil 90.
• FIG. 3 also shows a schematic representation of an induction heating system 1000 that can be used to facilitate heating of edge director 80' by induction.
• Induction heating system 1000 includes an alternating current power supply 500, a heat station 550, a chiller 400 for supplying cooling fluid, and a controller 600.
• Induction heating system 1000 also includes a cooling fluid input line 402 for directing cooling fluid flow from chiller 400 to alternating current power supply 500, heat station 550, and induction coil 90 as well as a cooling fluid output line 452 for directing cooling fluid flow from induction coil 90 back to chiller 400.
• induction heating system 1000 includes an electrical circuit 502, 504, 506, and 508 between alternating current power supply 500, heat station 550, and induction coil 90.
• Induction heating system 1000 additionally includes a control loop 602 for enabling a controller 600 to provide managed control of induction heating of edge director 80', including the minimum temperature of at least a portion of the surface of the edge director contacting the molten glass.
• the cooling fluid is water.
• alternating current is supplied from alternating current power supply 500 to heat station 550 and induction coil 90 via electrical circuit 502, 504, 506, and 508 while, at the same time, cooling fluid is directed through alternating current power supply 500, heat station 550, and induction coil 90 from chiller 400 via cooling fluid input and output lines 402, 452.
• the amount and frequency of alternating current as well as the flow rate of cooling fluid can be controlled simultaneously via controller 600 and control loop 602 so as to provide managed control of induction heating of edge director 80'.
• Such control can, for example, include or be forwarded to a computer processing unit, and such unit can process, for example, feedback or feedforward control according to process control methods known to persons of skill in the art.
• such control can allow for heating of the edge director by induction such that a minimum temperature of at least a portion of the surface of the edge director contacting the molten glass is maintained in steady state in as close to a constant temperature as possible.
• the minimum temperature of at least a portion of the surface of the edge director contacting the molten class can be maintained at steady state for a predetermined length of time at a predetermined temperature that does not vary for more than ⁇ 10°C, such as not more than ⁇ 5°C, and further such as not more than ⁇ 2°C, and still yet further such as not more than ⁇ 1°C.
• Such predetermined length of time while not limited, can be at least 1 hour, such as at least 10 hours, and further such as at least 25 hours, including from 1 hour to 10 years, such as from 10 hours to 5 years, and further such as from 20 hours to 1 year.
• Such minimum temperature should at least be maintained above the liquidus temperature of the molten glass flowing over the surface of the edge director so as to minimize buildup of devitrified glass on edge director.
• the molten glass is a borosilicate glass and the minimum temperature should be maintained above the liquidus temperature of the borosilicate glass.
• the surface of the edge director contacting the molten glass is maintained above 1150°C, such as above 1200°C, and further such as above 1250°C, including from 1000°C to 1700°C, including from 1100°C to 1600°C, and further including from 1150°C to 1400°C.
• the edge director 80', induction coil 90, and induction heating system 1000 can also be configured so as to enable rapid change of the minimum temperature of at least a portion of the surface of the edge director contacting the molten glass, for example, in response to predetermined factors which would call for such temperature to be changed. For example, if the composition of the glass flowing over the edge director were to change such that its liquidus temperature were to also change, the minimum temperature of at least a portion of the surface of the edge director could correspondingly be changed.
• controller 600 could be integrated into a control algorithm that not only controls induction heating system but also serves to control the entire apparatus shown in FIG.
• the temperature of the surface of the edge director could be changed in response to or anticipation of any number of process parameters or measured or desired glass characteristics, including, but not limited to, glass composition, glass temperature, glass devitrification temperature, glass viscosity, and glass flow rate.
• embodiments disclosed herein include those in wherein the minimum temperature of at least a portion of the surface of the edge director contacting the molten glass can be changed at a rate of at least 10°C per minute, including at least 20°C per minute, such as from 10°C per minute to 30°C per minute at temperatures of at least 1000°C, including at temperatures of from 1000°C to 1400°C.
• Induction coil 90 can be configured behind the surface of edge director 80' in a manner that enables a minimum temperature of at least a portion of a surface of the edge director contacting the molten glass to be maintained above a predetermined amount through direct heating of the edge director 80' by induction.
• induction coil 90 can be configured to have a variable density of coil per unit area of edge director 80' and or be positioned at a variable distance from edge director 80' such that the temperature of a surface of the edge director contacting the molten glass varies from a maximum temperature at one point or area on the surface of the edge director to lower temperatures at other points or areas on the surface of the edge director. In this manner, a temperature profile can exist on the surface of the edge director where the difference between the maximum and minimum temperatures on the surface of the edge director vary by a predetermined amount.
• induction coil 90 is configured to have a greater amount of coil density embedded behind the surface of lower portion 88' of edge director than behind the surface of upper portion 86' of edge director.
• a local maximum temperature of a surface of the edge director would be expected to be at a point or area on lower portion 88' of edge director 80'.
• embodiments could include those in which induction coil 90 has a density of coil per unit area that is more uniform behind the entire surface of edge director 80'. Additional embodiments (not shown) could include those in which induction coil 90 is configured to have a greater amount of coil density embedded behind a surface of upper portion 86' of edge director 80' than behind the surface of lower portion 88' of edge director.
• embodiments disclosed herein include those in which a temperature profile is present on the surface of the edge director such that the maximum temperature on the surface of the edge director contacting the molten glass is at least 25 °C greater, such as at least 50°C greater, and further such as at least 100°C greater than the minimum temperature on the surface of the edge director.
• embodiments disclosed herein can include those in which the difference between the maximum and minimum temperature on the surface of the edge director is from 25°C to 250°C, such as from 50°C to 150°C.
• Such temperature profiles can be approximately linear or nonlinear as a function of temperature versus position on the surface of the edge director.
• Embodiments disclosed herein include those in which the heat provided to the edge director via induction varies as a function of position of the edge director surface according to a predeteirnined profile.
• the heat provided to the edge director via induction can either increase or decrease as a function of vertical position on the edge director surface.
• the heat provided to the edge director via induction increases as the vertical position on the edge director surface decreases.
• the induction coil can be configured in a manner that maximizes the heat transfer efficiency to surfaces of the edge director and/or provides a more uniform degree of heat flux to various surfaces of the edge director.
• the induction coil can be configured such that the coil extends through at least three areas, the first being an area 90A closest to the center of the edge director (hereinafter referred to as "center area”) and the other two areas 90B, 90C, being on either side of the center area (hereinafter referred to as "first wing area” and "second wing area", respectively).
• first wing area an area 90A closest to the center of the edge director
• second wing area being on either side of the center area
• the portion of the coil extending in the center area is configured to protrude forward relative to the first wing area and the second wing area.
• the portion of coil in the center area is configured such the coil extends vertically V to a greater extent than the vertical extension of the portion of coil in first wing area and second wing area, and the portions of the coil in the first wing area and the second wing area are configured such that they extend horizontally H to a greater extent than the horizontal extension of the portion of coil in the center area.
• the portion of coil in the center area has at least three generally parallel loops that loop around a central axis CA and the portion of coil in the first wing area and the portion of coil in the second wing area each have at least two generally parallel loops that loop around a first wing axis 1WA and a second wing axis 2WA, respectively, wherein the first wing axis and the second wing axis intersect at a point X on a plane P that is perpendicular to the central axis.
• Embodiments disclosed herein include those in which the edge director 80'
• edge director 80' comprises platinum.
• Edge director '80 may also comprise an alloy of platinum and tin.
• the thickness of edge director 80' is preferably less than 10 millimeters, such as from 0.5 to 5 millimeters, including about 1 millimeter. Such thickness can be relatively constant or may be variable.
• induction coil 90 should preferably be embedded behind the surface of edge director 80' as close to surface of edge director as possible where maximum temperature of the edge director is desired.
• induction coil 90 can be configured so that the portion of the coil closest to an inner surface of edge director 80' is less than 10 millimeters, such as less than 5 millimeters, and further such as less than 2 millimeters from the inner surface of edge director 80'.
• Embodiments disclosed herein include those in which induction coil 90 comprises at least one material selected from the group consisting of copper, nickel, platinum, gold, silver, and alloys comprising at least one of the same.
• the induction coil 90 comprises copper.
• induction coil 90 may be coated, insulated, sleeved, or embedded with at least one material that provides, for example, thermal, mechanical, and/or corrosion protection.
• induction coil may be sleeved in a fabric material comprising at least one material selected from the group consisting of alumina and silica.
• embodiments herein include those in which induction coil 90 comprises copper tubing having an outer diameter of from 2 to 15 millimeters, such as from 4 to 10 millimeters, and further such as from 4 to 7 millimeters.
• copper tubing can, for example, have a radial thickness of from 0.5 to 1 millimeter.
• the induction coil 90 should preferably be configured to enable induction heating of the platinum, such that a minimum temperature of at least a portion of a surface of the edge director is at least 1000°C, such as at least 1 100°C, and further such as at least 1 150°C, and yet further such as at least 1200°C, and still yet further such as at least 1250°C, and even still yet further such as at least 1300°C, including from 1000°C to 1700°C, such as from 1100°C to 1600°C, and further such as from 1200°C to 1500°C.
• This induction heating will depend on the number of turns per unit area of the induction coil 90, the proximity of the induction coil 90 to the inner surface of the edge director 80' and the amount and frequency of the alternating current being supplied from the alternating current power supply 500 to the induction coil 90.
• preferred embodiments include those in which the power supply provides at least 5 kW of power, such as at least 7.5 kW of power, and further such as at least 10 kW of power, and still yet further such as at least 15 kW of power, including from 2 to 20 kW of power, such as from 5 to 15 kW of power, and an alternating current with a frequency of at least 50 kHz, such as at least 100 kHz, and further such as at least 150 kHz, such as from 50 kHz to 250 kHz.
• the power supply provides at least 5 kW of power, such as at least 7.5 kW of power, and further such as at least 10 kW of power, and still yet further such as at least 15 kW of power, including from 2 to 20 kW of power, such as from 5 to 15 kW of power, and an alternating current with a frequency of at least 50 kHz, such as at least 100 kHz, and further such as at least 150 kHz, such as from 50 kHz to 250 kHz.
• Cooling fluid can be provided at a flow rate and temperature that prevents undesirable softening, deformation, or melting of induction coil 90, while at the same time, keeping alternating current power supply 500 sufficiently cool.
• cooling water can be provided to induction coil 90 from chiller 400 at a temperature of from about 0°C to about 50°C, including about 25°C.
• Cooling fluid flow rate can, for example, range from about 0.5 liters per minute to about 10 liters per minute, such as from about 1 liter per minute to about 5 liters per minute.
• FIG. 3 shows a single induction coil 90 embedded behind the surface of the edge director 80'
• embodiments herein include those in which at least two induction coils (not shown) are embedded behind the surface of an edge director.
• Such induction coils can each be connected to induction heating systems that are operating independently of one another or in concert with each other.
• the at least two induction coils can be separately controlled by, for example, controlling the amount and frequency of alternating current being supplied to each coil from a power supply and/or controlling the flow rate of cooling fluid flowing through each coil.
• such induction coils can be positioned such that, for example, a first of the at least two separately controlled induction coils is positioned in a first area and a second of said at least two separately controlled induction coils is positioned in a second area.
• such coils can be positioned such that electrical power supplied to the first induction coil is at least 10% greater, such as at least 20% greater, and further such as at least 30%> greater, and still further such as at least 40% greater, and still yet further such as at least 50% greater than electrical power supplied to the second induction coil.
• the electrical power supplied to the first induction coil can be in the range of 7.5 kW to 50 kW while the electrical power supplied to the second induction coil can be in the range of 5 kW to 25 kW.
• induction coils when at least two induction coils are embedded behind a surface of an edge director, such induction coils can, in certain exemplary embodiments, be embedded behind different surface areas of the edge director so as to provide a different temperature characteristic or profile on a first surface area of the edge director as compared to a second surface area of the edge director.
• Such different temperature characteristic or profile can be enabled by, for example, supplying differing amounts of electrical power to the at least two induction coils.
• such coils can be embedded behind the edge director such that a first of at least two separately controlled induction coils is embedded behind a first surface area of the edge director and a second of at least two separately controlled induction coils is embedded behind a second surface area of the edge director and wherein electrical power supplied to the first induction coil is at least 10%> greater, such as at least 20%> greater, and further such as at least 30%> greater, and still further such as at least 40%> greater, and still yet further such as at least 50%> greater than electrical power supplied to the second induction coil.
• the electrical power supplied to the first induction coil can be in the range of 7.5 kW to 50 kW while the electrical power supplied to the second induction coil can be in the range of 5 kW to 25 kW.
• such coils can be embedded behind the edge director such that the first surface has a maximum temperature that is at least 10°C greater, such as at least 25°C greater, and further such as at least 50°C greater, and yet further such as at least 100°C greater than a maximum temperature of the second surface.
• the first surface is on a lower portion of the edge director and the second surface is on an upper portion of the edge director.
• a second induction heated edge director (similar to edge director 80') can also be assembled on the opposite end of forming wedge (not shown).
• FIG. 3 shows a single cooling fluid source to which cooling fluid is both supplied and returned (e.g., chiller 400) such that cooling fluid continually circulates within induction heating system 1000
• cooling fluid is supplied from a source other than chiller 400, including more than one source (e.g., a combination of a chiller 400 and house water) and wherein some (if not all) of cooling fluid is not returned to chiller 400 following circulation through input and output lines 402, 452.
• embodiments described above include those in which the portions of the edge director contacting the molten glass are directly heated by induction
• embodiments disclosed herein also include those in which at least one other portion of the edge director (e.g., those not contacting the molten glass) and/or at least one other susceptible material in close proximity to the edge director is directly heated by induction, wherein heat is transferred from the at least one other edge director portion and/or other susceptible material to one or more portions of the edge director contacting the molten glass.
• the portions of the edge director contacting the molten glass are still heated by induction but in a more indirect manner than in the embodiments described above.
• the induction heating system shown in FIG. 3 can be applied to this more indirect induction heating method.
• FIGS. 5 A and 5B schematically illustrate perspective views of alternative embodiments of induction heating system components as disclosed herein.
• induction coil is replaced by a slotted conductive plate 92 that is configured to conduct alternating current supplied by an alternating current power supply.
• Cooling fluid can be circulated through a cooling fluid conduit, such as a cylindrical cooling fluid conduit 94, as shown in FIG. 5A, or a rectangular cooling fluid conduit 96, as shown in FIG. 5B.
• Slotted conductive plate 92 can be configured to be embedded behind an edge director surface that is contacting the molten glass, such as configured to fit snugly beneath an edge director surface that is contacting the molten glass.
• At least one thermally insulative layer can be between the inner edge director surface and slotted conductive plate.
• Slotted conductive plate 92 can also be configured to be easily attached or detached within induction heating system.
• Slotted conductive plate 92 may comprise at least one material selected from the group consisting of copper, nickel, platinum, gold, silver, and alloys comprising at least one of the same.
• slotted conductive plate 92 comprises copper.
• Cooling fluid conduit such as cylindrical cooling fluid conduit 94 or rectangular cooling fluid conduit 96, may comprise at least one material selected from the group consisting of copper, nickel, platinum, gold, silver, and alloys comprising at least one of the same.
• cooling fluid conduit comprises copper.
• FIGS. 6 A and 6B schematically illustrate cross-sectional and perspective views, respectively, of another exemplary embodiment as disclosed herein.
• edge director 80' includes a back plate 180.
• back plate 180 may be made of the same material as the balance of edge director 80', such as at least one material selected from the group consisting of platinum, iridium, palladium, rhodium and alloys comprising at least one of the same.
• back plate 180 comprises platinum.
• Back plate 180 has an inner surface 182 and an outer surface 184 and is preferably positioned such that molten glass does not substantially flow over its outer surface.
• Back plate 180 is directly heated by induction by induction coil 90' that is positioned behind at least a portion of outer surface 184. Heat is then transferred from back plate 180 to a surface of the edge director 80' that directly contacts the molten glass.
• Induction coil 90' should preferably be embedded behind outer surface 184 of back plate 180 as close to outer surface 184 as possible.
• induction coil 90' can be configured so that the portion of the coil closest to outer surface 184 is less than 10 millimeters, such as less than 5 millimeters, and further such as less than 2 millimeters.
• a thermally insulative material 190 may be positioned between outer surface 184 of back plate 180 and induction coil 90' so as to minimize heat transfer between back plate 180 and induction coil 90'.
• suitable thermally insulative materials include those comprising at least one of alumina, alumino-silicate fibers, organic binders, and inorganic binders, such as, for example, KVS high temperature vacuum formed boards and shapes available from Rath.
• Embodiments disclosed herein include those in which heat transfer is facilitated between back plate 180 and one or more surfaces of the edge director 80' that directly contact the molten glass.
• a material having a thermal conductivity ( ⁇ ) wherein ⁇ is at least 10 W/(m-K) at 25°C, such as at least 20 W/(m-K) at 25°C, and further such as at least 30 W/(m-K) at 25°C, and still further such as at least 50 W/(m-K) at 25°C, and yet further such as at least 100 W/(m-K) at 25°C, and even yet further such as at least 200 W/(m-K) at 25°C, including from 10 to 500 W/(m-K) at 25°C, and further including from 20 to 400 W/(m-K) at 25°C, and still further
• FIG. 7 schematically illustrates a perspective view of an edge director 80' having a back plate 180 where an area between an inner surface 182 of the back plate and an inner surface of the edge director 80' contacting the molten glass is filled with a thermally conductive material in the form of thermally conductive beads 200.
• the presence of thermally conductive beads 200 substantially increases the conductive (and overall) heat transfer between back plate 180 and the surface of the edge director contacting the molten glass.
• Thermally conductive beads 200 preferably comprise a material having a thermal conductivity ( ⁇ ), wherein ⁇ is at least 10 W/(m-K) at 25°C, such as at least 20 W/(m-K) at 25°C, and further such as at least 30 W/(m-K) at 25°C, and still further such as at least 50 W/(m-K) at 25°C, and yet further such as at least 100 W/(m-K) at 25°C, and even yet further such as at least 200 W/(m-K) at 25°C, including from 10 to 500 W/(m-K) at 25°C, and further including from 20 to 400 W/(m-K) at 25°C, and still further including from 30 to 300 W/(m-K) at 25°C.
• Thermally conductive beads may, for example, be selected from the group consisting of alumina and beryllium oxide.
• FIG. 7 shows a thermally conductive material in the form of beads
• embodiments herein can include other types or configurations of thermally conductive materials, such thermally conductive granular materials, non-spherically shaped thermally conductive materials, and solid, thermally conductive materials of unitary construction, such as a thermally conductive block that is shaped to be compatible with the interior surface of edge director 80' so as to provide efficient heat transfer between back plate 180 and the surface of the edge director contacting the molten glass and/or heat transfer between back plate 180 and the surface of the edge director contacting the molten glass, such that the temperature of the edge director contacting the molten glass is in accordance with a predetemiined temperature gradient profile.
• Facilitation of heat transfer between back plate 180 and the surface of the edge director contacting the molten glass can further be enhanced in embodiments wherein at least one of inner surface 182 of back plate 180 and an inner surface of the edge director contacting the molten glass is configured to have relatively high emissivity ( ⁇ ), such as wherein 0.5 ⁇ ⁇ ⁇ 1.0, such as 0.6 ⁇ ⁇ ⁇ 1.0, further such as 0.7 ⁇ ⁇ ⁇ 1, yet further such as 0.8 ⁇ ⁇ ⁇ 1, and still yet further such as 0.9 ⁇ ⁇ ⁇ 1.
• ⁇ relatively high emissivity
• At least one of an inner surface of the back plate and an inner surface of the edge director contacting the molten glass is coated with a high emissivity coating, such as a coating having an emissivity ( ⁇ ), wherein 0.5 ⁇ ⁇ ⁇ 1.0, such as 0.6 ⁇ ⁇ ⁇ 1.0, further such as 0.7 ⁇ ⁇ ⁇ 1.0, yet further such as 0.8 ⁇ ⁇ ⁇ 1, and still yet further such as 0.9 ⁇ ⁇ ⁇ 1.
• a high emissivity coating such as a coating having an emissivity ( ⁇ )
• both of an inner surface of the back plate and an inner surface of the edge director contacting the molten glass is coated with a high emissivity coating, such as a coating having an emissivity ( ⁇ ), wherein 0.5 ⁇ ⁇ ⁇ 1.0, such as 0.6 ⁇ ⁇ ⁇ 1.0, further such as 0.7 ⁇ ⁇ ⁇ 1.0, yet further such as 0.8 ⁇ ⁇ ⁇ 1, and still yet further such as 0.9 ⁇ ⁇ ⁇ 1.
• high emissivity materials and coatings include, for example, at least one coating comprising a material from the group consisting of alumina, zirconia and mixtures and multilayers of the same.
• the high emissivity coating may be applied, for example, by plasma spray or flame spray coating techniques.
• heat transfer can, in certain exemplary embodiments, be facilitated from the back plate to one or more surfaces of the edge director contacting the molten glass, such that the temperature difference between the back plate and a surface of the edge director contacting the molten glass is less than 200°C, such as less than 150°C, and further such as less than 100°C, including from 50°C to 200°C, and further including from 100°C to 150°C.
• the temperature of a surface of the edge director contacting the molten glass can be at least 1100°C, such as at least 1150°C, and further such as at least 1200°C, and yet further such as at least 1250°C.
• Embodiments herein can provide advantages over other methods of minimizing buildup of devitrified glass on edge directors, such as those using, for example, resistance heaters near the edge directors (relying on convection and radiation to transfer heat from the resistance heaters to the edge directors). Such methods are not sufficient to transfer enough heat to the edge directors in order to achieve adequate edge director temperature necessary to sufficiently minimize devitrification within the requisite physical space limitations. Such methods may not enable the precise temperature control of the edge directors that can be achieved according to embodiments herein. Moreover, the additional components (such as resistance heaters, etc.) used in such methods can take up substantial amounts of critical physical space near the draw and can result in substantial undesirable (and unnecessary) heating to manufacturing components and equipment located near the edge directors.
• additional components such as resistance heaters, etc.
• the present specification generally relates to the manufacture of glass sheets and, more specifically, to apparatus and methods for making glass sheets with edge directors.
• Glass manufacturing systems are commonly used to form various glass products such as LCD glass sheets. It is known to manufacture glass sheets by downwardly flowing molten glass over a forming wedge. Edge directors are frequently provided at opposed ends of the forming wedge to help achieve a desired glass sheet width and edge bead
• edge directors glass that passes over the edge directors can cool and devitrify, building up on the edge directors. This buildup can result in shape-related and other defects of the glass as well as necessitate frequent replacement of the edge directors. Accordingly, methods that minimize the buildup of devitrified glass on edge directors are desirable.
• the embodiments described herein relate to apparatus and methods for making glass sheets with edge directors heated through induction.
• a fusion draw method of making a glass sheet includes flowing molten glass over a pair of downwardly inclined foiming surface portions of a foiming wedge, the downwardly inclined foiming surface portions converging along a downstream direction to form a root.
• the method also includes flowing molten glass over an edge director intersecting with at least one of the pair of downwardly inclined foiming surface
• the method includes maintaining a minimum temperature of at least a portion of a surface of the edge director contacting the molten glass above a predetermined amount through heating of the edge director by induction.
• the method further includes drawing the molten glass from the root of the forming wedge to form a glass sheet.
• an apparatus for downwardly drawing sheet glass includes a forming wedge having a pair of downwardly inclined forming surface portions, the downwardly inclined forming surface portions converging at the bottom of the forming wedge forming a root and defining a draw line for molten glass therealong.
• the apparatus also includes an edge director contacting at least one of the pair of downwardly inclined foiming surface portions.
• the edge director includes an induction coil positioned behind the surface of the edge director for maintaining a minimum temperature of at least a portion of a surface of the edge director contacting the molten glass above a predeteimined amount through heating of the edge director by induction.
• FIG. 1 is a schematic view of an apparatus for making glass
• FIG. 2 is a cross sectional perspective view of the apparatus along line 2-2 of FIG. 1 illustrating a first example of a heat shield apparatus
• FIG. 2A is a perspective view of the apparatus with another example of a heat shield apparatus
• FIG. 3 is a perspective view of an induction heated edge director shown with a schematic representation of an induction heating system
• FIG. 4 is a perspective view of an induction coil configuration
• FIGS. 5A and 5B are, respectively, perspective views of alternative embodiments of induction heating system components
• FIGS. 6A and 6B are, respectively, cross-sectional and perspective views of an edge director having a back plate and an induction coil that is positioned behind the back plate;
• FIG. 7 is a perspective view of an edge director having a back plate where an area between an inner surface of the back plate and an inner surface of the edge director contacting the molten glass is filled with thermally conductive beads.
• Glass sheet materials may generally be formed by melting glass batch materials to form molten glass and thereafter forming the molten glass into a glass sheet.
• Exemplary processes include the float glass process, the slot draw process and the fusion down-draw process.
• FIG. 1 illustrates a schematic view of an apparatus 10 for making glass, such a glass sheet 12.
• the apparatus 10 can include a melting vessel 14 configured to receive batch material 16 from a storage bin 18.
• the batch material 16 can be introduced to the melting vessel 14 by a batch delivery device 20 powered by a motor 22.
• An optional controller 24 may be provided to activate the motor 22 and a molten glass level probe 28 can be used to measure the glass melt level within a standpipe 30 and communicate the measured information to the controller 24.
• the apparatus 10 can also include a fining vessel 38, such as a fining tube, located downstream from the melting vessel 14 and coupled to the melting vessel 14 by way of a first connecting tube 36.
• a mixing vessel 42 such as a stir chamber, can also be located downstream from the fining vessel 38 and a delivery vessel 46, such as a bowl, may be located downstream from the mixing vessel 42.
• a second connecting tube 40 can couple the fining vessel 38 to the mixing vessel 42 and a third connecting tube 44 can couple the mixing vessel 42 to the delivery vessel 46.
• a downcomer 48 can be positioned to deliver glass melt from the delivery vessel 46 to an inlet 50 of a forming vessel 60.
• the melting vessel 14, fining vessel 38, the mixing vessel 42, delivery vessel 46, and forming vessel 60 are examples of glass melt stations that may be located in series along the apparatus 10.
• the melting vessel 14 is typically made from a refractory material, such as refractory (e.g. ceramic) brick.
• the apparatus 10 may further include components that are typically made from platinum or platinum-containing metals such as platinum-rhodium, platinum-
• the platinum-containing components can include one or more of the first connecting tube 36, the fining vessel 38, the second connecting tube 40, the standpipe 30, the mixing vessel 42, the third connecting tube 44, the delivery vessel 46, the downcomer 48 and the inlet 50.
• the forming vessel 60 can also made from a refractory material and is designed to form the glass sheet 12.
• FIG. 2 is a cross sectional perspective view of the apparatus 10 along line 2-2 of FIG. 1.
• the forming vessel 60 includes a forming wedge 62 comprising a pair of downwardly inclined forming surface portions 66a, 66b that can extend between opposed ends 64a, 64b of the forming wedge 62.
• the downwardly inclined forming surface portions 66a, 66b converge along a downstream direction 68 to form a root 70.
• a draw plane 72 extends through the root 70 wherein the glass sheet 12 may be drawn in the downstream direction 68 along the draw plane 72.
• the draw plane 72 can bisect the root 70 although the draw plane 72 may extend at other orientations with respect to the root 70.
• aspects of the disclosure may be used with various forming vessels. For example, aspects of the disclosure may be used with apparatus for reducing radiative heat loss from a forming body disclosed in U.S. Provisional Pat. Application No. 61/180,216, filed May 21, 2009 which is herein incorporated by reference in its entirety.
• the forming vessel 60 may comprise an edge director intersecting with at least one of the pair of downwardly inclined forming surface portions 66a, 66b.
• the edge director can intersect with both downwardly inclined forming surface portions 66a, 66b.
• an edge director can be positioned at each of the opposed ends of the forming wedge 62.
• an edge director 80a, 80b can be positioned at each of the opposed ends 64a, 64b of the forming wedge 62 with each edge director 80a, 80b configured to intersect with both of the downwardly inclined forming surface portions 66a, 66b.
• each edge director 80a, 80b is substantially identical to one another although the edge directors may have different characteristics in further examples.
• forming wedge and edge director configurations may be used in accordance with aspects of the present disclosure.
• 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. Pat. No. 3,537,834, U.S. Patent No. 7,409,839 and/or U.S.
• FIGS. 2 and 2A illustrate just one example edge director that may be used with aspects of the disclosure.
• the first edge director 80a will be discussed with the understanding that the second edge director 80b, in some examples, may be similar or identical to the first edge director 80a.
• Providing identical edge directors can be beneficial to provide a uniform glass sheet although the edge directors may have different features to provide varied glass sheet characteristics and/or accommodate various forming vessel configurations.
• FIGS. 2 and 2A illustrate a first side of the first edge director 80a positioned with respect to the first downwardly inclined forming surface portion 66a of the forming wedge 62.
• the first edge director 80a further includes a second side positioned with respect to the second inclined forming surface portion 66b of the forming wedge 62.
• the second side of the first edge director 80a is a mirror image of the first side about the draw plane 72 bisecting the root 70.
• the first side includes a first surface 82 that intersects the first downwardly inclined forming surface portion 66a of the forming wedge 62.
• the second side of the first edge director 80a also includes a substantially identical surface that intersects the second inclined forming surface portion 66b of the forming wedge 62.
• Each opposed end 64a, 64b of the forming wedge 62 can be provided with a retaining block 84 designed to help laterally position the corresponding first and second edge directors 80a, 80b.
• the first edge director 80a can include an upper portion 86 and a lower portion 88.
• the lower portion 88 can, in some examples, join the first edge director 80a on the first opposed end 64a with the second edge director 80b on the second opposed end 64b. Joining the edge directors 80a, 80b together can be beneficial to simplify assembly of the edge directors 80a, 80b to the forming wedge 62.
• the upper portions 86 of the edge directors 80a, 80b may be provided separately.
• the first edge director 80a can be separate from the second edge director 80b and assembled independently to each of the pair of downwardly inclined forming surface portions 66a, 66b of the forming wedge 62.
• providing upper portions 86 that are not joined may simplify manufacturing of the edge directors 80a, 80b.
• Each edge director 80a, 80b can have a variety of orientations and geometries by providing different surfaces relative to the forming wedge 62.
• the apparatus 10 for making glass can also include at least one edge roller device including a pair of edge rollers configured to engage a corresponding edge of the glass ribbon as the ribbon is drawn off the root 70 of the forming wedge 62.
• the pair of edge rollers facilitates proper finishing of the edges of the glass sheet. 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 66a, 66b.
• the edge rollers can be located at various positions within the viscous region of the glass being drawn from the 70.
• the edge rollers can be located anywhere from immediately below the root 70 to a position about 15 inches below the root 70 although other positions may be contemplated in further examples. In still another example, the edge rollers can be located at a position within a range of from about 8 inches to about 10 inches below the root 70.
• a first edge roller assembly 130a is associated with the first edge director 80a and a second edge roller assembly 130b is associated with the second edge director 80b.
• each edge roller assembly 130a, 130b is substantially identical to one another although the pairs of edge rollers may have different characteristics in further examples.
• FIG. 2 illustrates an example edge roller assembly that may be used with aspects of the disclosure.
• the first edge roller assembly 130a will be discussed with the understanding that the second edge roller assembly 130b, in some examples, may be similar or identical to the first edge roller assembly 130a.
• the first edge roller assembly 130a includes a first pair of edge rollers 132 including a first edge roller 132a and a second edge roller 132b.
• the edge rollers 132a, 132b are configured to simultaneously engage the first side and the second side of the glass sheet 12.
• the first edge roller assembly 130a further includes a first shaft 134a attached to the first edge roller 132a and a second shaft 134b attached to the second edge roller 132b.
• the first and second shafts 134a, 134b extend through a seal plate 136 and are configured to be rotatably driven by a motor (not shown).
• the seal plate 136 is configured to provide closure to an opening leading to the area housing the motor 138.
• the seal plate may comprise a refractory material, steel, or other thermal insulation to protect sensitive components of the motor and/or other mechanisms located within the housing area.
• the forming vessel 60 may also be provided with a thermal shield apparatus including a thermal shield associated with at least one of the edge directors 80a, 80b.
• the thermal shields are configured to reduce heat loss from the corresponding edge directors 80a, 80b to non-target areas, and in particular, heat loss to the cooled edge rollers.
• Such non-target areas can include nearby areas of the glass making apparatus and/or other locations capable of receiving heat transfer from the edge directors.
• a first thermal shield apparatus 110a includes a first thermal shield 120a associated with the first edge director 80a.
• a second thermal shield apparatus 110b includes a second thermal shield 120b associated with the second edge director.
• each thermal shield apparatus 110a, 110b is substantially identical to one another although the thermal shield apparatus may have different characteristics in further examples. Providing identical thermal shield apparatus can be beneficial to provide similar thermal shielding of the edge directors although the thermal shield apparatus may have different features to accommodate various forming vessel configurations.
• FIG. 2 illustrates just one example thermal shield apparatus that may be used with aspects of the disclosure.
• the first thermal shield apparatus 110a will be discussed with the understanding that the second thermal shield apparatus 110b, in some examples, may be similar or identical to the first thermal shield apparatus 110a.
• the first thermal shield can be positioned below a portion or the entire first edge director, and extends generally in a length-wise direction relative to the long dimension of the forming wedge and in close proximity to the edge roller shafts. As shown in FIG. 2, the first thermal shield 120a may be positioned to be located below only a portion of the first edge director 80a. Providing the first thermal shield 120a at a location underneath only a portion of the first edge director 80a can provide sufficient reduction of heat loss to non-target areas while avoiding possible interference with the molten glass being drawn from the root 70 of the forming wedge 62.
• the first thermal shield can also extend entirely below the first edge director.
• FIG. 2A illustrates another example of a first thermal shield apparatus 210a
• the first thermal shield apparatus 210a includes a thermal plate 222 with an end 224 terminating inside of the corresponding edge 13 of the glass sheet 12.
• the thermal plate 222 only extends relative to one side of the glass sheet 12 thereby allowing the thermal shield to extend below the entire first edge
• the thermal plate 222 may include a slot 226 to provide passage of the edge 13 and corresponding edge portion of the glass sheet 12. As such, the end 224 of the thermal plate 222 extends relative to both sides of the glass sheet 12 while allowing the thermal shield to extend below the entire first edge director 80a. Positioning the thermal shield to extend below the entire first edge director 80a can minimize heat loss from the first edge director 80a to non-target areas.
• FIG. 3 illustrates an example of an edge director 80' that is assembled to forming wedge 62' having a pair of downwardly inclined forming surface portions 66a', 66b'.
• Edge director 80' includes an upper portion 86' and a lower portion 88' and edge director 80' and forming wedge 62' are shown in FIG. 3 in a bottom-left perspective view.
• Positioned behind the surface of the edge director 80' is an induction coil 90.
• Induction coil 90 comprises a plurality of turns sufficient to result in a desired amount induction heating of edge director 80' upon sufficient application of alternating current to induction coil 90.
• FIG. 3 also shows a schematic representation of an induction heating system 1000 that can be used to facilitate heating of edge director 80' by induction.
• Induction heating system 1000 includes an alternating current power supply 500, a heat station 550, a chiller 400 for supplying cooling fluid, and a controller 600.
• Induction heating system 1000 also includes a cooling fluid input line 402 for directing cooling fluid flow from chiller 400 to alternating current power supply 500, heat station 550, and induction coil 90 as well as a cooling fluid output line 452 for directing cooling fluid flow from induction coil 90 back to chiller 400.
• induction heating system 1000 includes an electrical circuit 502, 504, 506, and 508 between alternating current power supply 500, heat station 550, and induction coil 90.
• Induction heating system 1000 additionally includes a control loop 602 for enabling a controller 600 to provide managed control of induction heating of edge director 80', including the minimum temperature of at least a portion of the surface of the edge director contacting the molten glass.
• the cooling fluid is water.
• alternating current is supplied from alternating current power supply 500 to heat station 550 and induction coil 90 via electrical circuit 502, 504, 506, and 508 while, at the same time, cooling fluid is directed through alternating current power supply 500, heat station 550, and induction coil 90 from chiller 400 via cooling fluid input and output lines 402, 452.
• cooling fluid can be controlled simultaneously via controller 600 and control loop 602 so as to provide managed control of induction heating of edge director 80'.
• control can, for example, include or be forwarded to a computer processing unit, and such unit can process, for example, feedback or feedforward control according to process control methods known to persons of skill in the art.
• such control can allow for heating of the edge director by induction such that a minimum temperature of at least a portion of the surface of the edge director contacting the molten glass is maintained in steady state in as close to a constant temperature as possible.
• the minimum temperature of at least a portion of the surface of the edge director contacting the molten class can be maintained at steady state for a predetermined length of time at a predetermined temperature that does not vary for more than ⁇ 10°C, such as not more than ⁇ 5°C, and further such as not more than ⁇ 2°C, and still yet further such as not more than ⁇ 1°C.
• Such predetermined length of time while not limited, can be at least 1 hour, such as at least 10 hours, and further such as at least 25 hours, including from 1 hour to 10 years, such as from 10 hours to 5 years, and further such as from 20 hours to 1 year.
• Such minimum temperature should at least be maintained above the liquidus temperature of the molten glass flowing over the surface of the edge director so as to minimize buildup of devitrified glass on edge director.
• the molten glass is a borosilicate glass and the minimum temperature should be maintained above the liquidus temperature of the borosilicate glass.
• the surface of the edge director contacting the molten glass is maintained above 1150°C, such as above 1200°C, and further such as above 1250°C, including from 1000°C to 1700°C, including from 1100°C to 1600°C, and further including from 1150°C to 1400°C.
• the edge director 80', induction coil 90, and induction heating system 1000 can also be configured so as to enable rapid change of the minimum temperature of at least a portion of the surface of the edge director contacting the molten glass, for example, in response to predetermined factors which would call for such temperature to be changed. For example, if the composition of the glass flowing over the edge director were to change such that its liquidus temperature were to also change, the minimum temperature of at least a portion of the surface of the edge director could correspondingly be changed.
• controller 600 could be integrated into a control algorithm that not only controls induction heating system
• embodiments disclosed herein include those in wherein the minimum temperature of at least a portion of the surface of the edge director contacting the molten glass can be changed at a rate of at least 10°C per minute, including at least 20°C per minute, such as from 10°C per minute to 30°C per minute at temperatures of at least 1000°C, including at temperatures of from 1000°C to 1400°C.
• Induction coil 90 can be configured behind the surface of edge director 80' in a manner that enables a minimum temperature of at least a portion of a surface of the edge director contacting the molten glass to be maintained above a predetermined amount through direct heating of the edge director 80' by induction.
• induction coil 90 can be configured to have a variable density of coil per unit area of edge director 80' and or be positioned at a variable distance from edge director 80' such that the temperature of a surface of the edge director contacting the molten glass varies from a maximum temperature at one point or area on the surface of the edge director to lower temperatures at other points or areas on the surface of the edge director. In this manner, a temperature profile can exist on the surface of the edge director where the difference between the maximum and minimum temperatures on the surface of the edge director vary by a predetermined amount.
• induction coil 90 is configured to have a greater amount of coil density embedded behind the surface of lower portion 88' of edge director than behind the surface of upper portion 86' of edge director.
• a local maximum temperature of a surface of the edge director would be expected to be at a point or area on lower portion 88' of edge director 80'.
• induction coil 90 has a density of coil per unit area that is more uniform behind the entire surface of edge director 80'.
• Additional embodiments could include those in which induction coil 90 is configured to have a greater amount of coil density embedded behind a surface of upper portion 86' of edge director 80' than behind the surface of lower portion 88' of edge director.
• embodiments disclosed herein include those in which a temperature profile is present on the surface of the edge director such that the maximum temperature on the surface of the edge director contacting the molten glass is at least 25 °C greater, such as at least 50°C greater, and further such as at least 100°C greater than the minimum temperature on the surface of the edge director.
• embodiments disclosed herein can include those in which the difference between the maximum and minimum temperature on the surface of the edge director is from 25°C to 250°C, such as from 50°C to 150°C.
• Such temperature profiles can be approximately linear or nonlinear as a function of temperature versus position on the surface of the edge director.
• Embodiments disclosed herein include those in which the heat provided to the edge director via induction varies as a function of position of the edge director surface according to a predeteirnined profile.
• the heat provided to the edge director via induction can either increase or decrease as a function of vertical position on the edge director surface.
• the heat provided to the edge director via induction increases as the vertical position on the edge director surface decreases.
• the induction coil can be configured in a manner that maximizes the heat transfer efficiency to surfaces of the edge director and/or provides a more uniform degree of heat flux to various surfaces of the edge director.
• the induction coil can be configured such that the coil extends through at least three areas, the first being an area 90A closest to the center of the edge director (hereinafter referred to as "center area”) and the other two areas 90B, 90C, being on either side of the center area (hereinafter referred to as "first wing area” and "second wing area", respectively).
• first wing area an area 90A closest to the center of the edge director
• second wing area being on either side of the center area
• the portion of the coil extending in the center area is configured to protrude forward relative to the first wing area and the second wing area.
• the portion of coil in the center area is configured such the coil extends vertically V to a greater extent than the vertical extension of the portion of coil in first wing area and second wing area, and the portions of the coil in the first wing area and the second wing area are configured such that they extend horizontally H to a greater extent than the horizontal extension of the portion of coil in the center area.
• the portion of coil in the center area has at least three generally parallel loops that loop around a central axis CA and the portion of coil in the first wing area and the portion of coil in the second wing area each have at least two
• Embodiments disclosed herein include those in which the edge director 80'
• edge director 80' comprises platinum.
• Edge director '80 may also comprise an alloy of platinum and tin.
• the thickness of edge director 80' is preferably less than 10 millimeters, such as from 0.5 to 5 millimeters, including about 1 millimeter. Such thickness can be relatively constant or may be variable.
• induction coil 90 should preferably be embedded behind the surface of edge director 80' as close to surface of edge director as possible where maximum temperature of the edge director is desired.
• induction coil 90 can be configured so that the portion of the coil closest to an inner surface of edge director 80' is less than 10 millimeters, such as less than 5 millimeters, and further such as less than 2 millimeters from the inner surface of edge director 80'.
• Embodiments disclosed herein include those in which induction coil 90 comprises at least one material selected from the group consisting of copper, nickel, platinum, gold, silver, and alloys comprising at least one of the same.
• the induction coil 90 comprises copper.
• induction coil 90 may be coated, insulated, sleeved, or embedded with at least one material that provides, for example, thermal, mechanical, and/or corrosion protection.
• induction coil may be sleeved in a fabric material comprising at least one material selected from the group consisting of alumina and silica.
• embodiments herein include those in which induction coil 90 comprises copper tubing having an outer diameter of from 2 to 15 millimeters, such as from 4 to 10 millimeters, and further such as from 4 to 7 millimeters.
• copper tubing can, for example, have a radial thickness of from 0.5 to 1 millimeter.
• the induction coil 90 should preferably be configured to enable induction heating of the platinum, such that a minimum temperature of at least a portion of a surface of the edge director is at least 1000°C, such as at least 1 100°C, and further such as at least 1 150°C, and yet further such as at least 1200°C, and still yet further such as at least 1250°C, and even still yet further such as at least 1300°C, including from 1000°C to 1700°C, such as from 1100°C to 1600°C, and further such as from 1200°C to 1500°C.
• This induction heating will depend on the number of turns per unit area of the induction coil 90, the proximity of the induction coil 90 to the inner surface of the edge director 80' and the amount and frequency of the alternating current being supplied from the alternating current power supply 500 to the induction coil 90.
• preferred embodiments include those in which the power supply provides at least 5 kW of power, such as at least 7.5 kW of power, and further such as at least 10 kW of power, and still yet further such as at least 15 kW of power, including from 2 to 20 kW of power, such as from 5 to 15 kW of power, and an alternating current with a frequency of at least 50 kHz, such as at least 100 kHz, and further such as at least 150 kHz, such as from 50 kHz to 250 kHz.
• the power supply provides at least 5 kW of power, such as at least 7.5 kW of power, and further such as at least 10 kW of power, and still yet further such as at least 15 kW of power, including from 2 to 20 kW of power, such as from 5 to 15 kW of power, and an alternating current with a frequency of at least 50 kHz, such as at least 100 kHz, and further such as at least 150 kHz, such as from 50 kHz to 250 kHz.
• Cooling fluid can be provided at a flow rate and temperature that prevents undesirable softening, deformation, or melting of induction coil 90, while at the same time, keeping alternating current power supply 500 sufficiently cool.
• cooling water can be provided to induction coil 90 from chiller 400 at a temperature of from about 0°C to about 50°C, including about 25°C.
• Cooling fluid flow rate can, for example, range from about 0.5 liters per minute to about 10 liters per minute, such as from about 1 liter per minute to about 5 liters per minute.
• FIG. 3 shows a single induction coil 90 embedded behind the surface of the edge director 80'
• embodiments herein include those in which at least two induction coils (not shown) are embedded behind the surface of an edge director.
• Such induction coils can each be connected to induction heating systems that are operating independently of one another or in concert with each other.
• the at least two induction coils can be separately controlled by, for example, controlling the amount and frequency of alternating current being supplied to each coil from a power supply and/or controlling the flow rate of cooling fluid flowing through each coil.
• such induction coils can be positioned such that, for example, a first of the at least two separately controlled induction coils is positioned in a first area and a second of said at least two separately controlled induction coils is positioned in a second area.
• such coils can be positioned such that electrical power supplied to the first induction coil is at least 10% greater, such as at least 20% greater, and further such as at least 30%> greater, and still further such as at least 40% greater, and still yet further such as at least 50% greater than electrical power supplied to the second induction coil.
• the electrical power supplied to the first induction coil can be in the range of 7.5 kW to 50 kW while the electrical power supplied to the second induction coil can be in the range of 5 kW to 25 kW.
• induction coils when at least two induction coils are embedded behind a surface of an edge director, such induction coils can, in certain exemplary embodiments, be embedded behind different surface areas of the edge director so as to provide a different temperature characteristic or profile on a first surface area of the edge director as compared to a second surface area of the edge director.
• Such different temperature characteristic or profile can be enabled by, for example, supplying differing amounts of electrical power to the at least two induction coils.
• such coils can be embedded behind the edge director such that a first of at least two separately controlled induction coils is embedded behind a first surface area of the edge director and a second of at least two separately controlled induction coils is embedded behind a second surface area of the edge director and wherein electrical power supplied to the first induction coil is at least 10%> greater, such as at least 20%> greater, and further such as at least 30%> greater, and still further such as at least 40%> greater, and still yet further such as at least 50%> greater than electrical power supplied to the second induction coil.
• the electrical power supplied to the first induction coil can be in the range of 7.5 kW to 50 kW while the electrical power supplied to the second induction coil can be in the range of 5 kW to 25 kW.
• such coils can be embedded behind the edge director such that the first surface has a maximum temperature that is at least 10°C greater, such as at least 25°C greater, and further such as at least 50°C greater, and yet further such as at least 100°C greater than a maximum temperature of the second surface.
• the first surface is on a lower portion of the edge director and the second surface is on an upper portion of the edge director.
• edge director 80' While only one edge director 80' is shown assembled to forming wedge 62' in FIG. 3, it is understood that a second induction heated edge director (similar to edge director 80') can also be assembled on the opposite end of forming wedge (not shown).
• FIG. 3 shows a single cooling fluid source to which cooling fluid is both supplied and returned (e.g., chiller 400) such that cooling fluid continually circulates within induction heating system 1000
• cooling fluid is supplied from a source other than chiller 400, including more than one source (e.g., a combination of a chiller 400 and house water) and wherein some (if not all) of cooling fluid is not returned to chiller 400 following circulation through input and output lines 402, 452.
• embodiments described above include those in which the portions of the edge director contacting the molten glass are directly heated by induction
• embodiments disclosed herein also include those in which at least one other portion of the edge director (e.g., those not contacting the molten glass) and/or at least one other susceptible material in close proximity to the edge director is directly heated by induction, wherein heat is transferred from the at least one other edge director portion and/or other susceptible material to one or more portions of the edge director contacting the molten glass.
• the portions of the edge director contacting the molten glass are still heated by induction but in a more indirect manner than in the embodiments described above.
• the induction heating system shown in FIG. 3 can be applied to this more indirect induction heating method.
• FIGS. 5 A and 5B schematically illustrate perspective views of alternative embodiments of induction heating system components as disclosed herein.
• induction coil is replaced by a slotted conductive plate 92 that is configured to conduct alternating current supplied by an alternating current power supply.
• Cooling fluid can be circulated through a cooling fluid conduit, such as a cylindrical cooling fluid conduit 94, as shown in FIG. 5A, or a rectangular cooling fluid conduit 96, as shown in FIG. 5B.
• Slotted conductive plate 92 can be configured to be embedded behind an edge director surface that is contacting the molten glass, such as configured to fit snugly beneath an edge director surface that is contacting the molten glass.
• At least one thermally insulative layer (not shown) can be between the inner edge director surface and slotted conductive plate.
• Slotted conductive plate 92 can also be configured to be easily attached or detached within induction heating system. Slotted conductive plate 92 may comprise at least one material
• cooling fluid conduit such as cylindrical cooling fluid conduit 94 or rectangular cooling fluid conduit 96, may comprise at least one material selected from the group consisting of copper, nickel, platinum, gold, silver, and alloys comprising at least one of the same.
• cooling fluid conduit comprises copper.
• FIGS. 6 A and 6B schematically illustrate cross-sectional and perspective views, respectively, of another exemplary embodiment as disclosed herein.
• edge director 80' includes a back plate 180.
• back plate 180 may be made of the same material as the balance of edge director 80', such as at least one material selected from the group consisting of platinum, iridium, palladium, rhodium and alloys comprising at least one of the same.
• back plate 180 comprises platinum.
• Back plate 180 has an inner surface 182 and an outer surface 184 and is preferably positioned such that molten glass does not substantially flow over its outer surface.
• Back plate 180 is directly heated by induction by induction coil 90' that is positioned behind at least a portion of outer surface 184. Heat is then transferred from back plate 180 to a surface of the edge director 80' that directly contacts the molten glass.
• Induction coil 90' should preferably be embedded behind outer surface 184 of back plate 180 as close to outer surface 184 as possible.
• induction coil 90' can be configured so that the portion of the coil closest to outer surface 184 is less than 10 millimeters, such as less than 5 millimeters, and further such as less than 2 millimeters.
• a thermally insulative material 190 may be positioned between outer surface 184 of back plate 180 and induction coil 90' so as to minimize heat transfer between back plate 180 and induction coil 90'.
• suitable thermally insulative materials include those comprising at least one of alumina, alumino-silicate fibers, organic binders, and inorganic binders, such as, for example, KVS high temperature vacuum formed boards and shapes available from Rath.
• Embodiments disclosed herein include those in which heat transfer is facilitated between back plate 180 and one or more surfaces of the edge director 80' that directly contact
• At least a portion of an area between an inner surface of the back plate and an inner surface of the edge director contacting the molten glass can be filled with a material having a thermal conductivity ( ⁇ ), wherein ⁇ is at least 10 W/(m-K) at 25°C, such as at least 20 W/(m-K) at 25°C, and further such as at least 30 W/(m-K) at 25°C, and still further such as at least 50 W/(m-K) at 25°C, and yet further such as at least 100 W/(m-K) at 25°C, and even yet further such as at least 200 W/(m-K) at 25°C, including from 10 to 500 W/(m-K) at 25°C, and further including from 20 to 400 W/(m-K) at 25°C, and still further including from 30 to 300 W/(m-K) at 25°C.
• ⁇ thermal conductivity
• FIG. 7 schematically illustrates a perspective view of an edge director 80' having a back plate 180 where an area between an inner surface 182 of the back plate and an inner surface of the edge director 80' contacting the molten glass is filled with a thermally conductive material in the form of thermally conductive beads 200.
• the presence of thermally conductive beads 200 substantially increases the conductive (and overall) heat transfer between back plate 180 and the surface of the edge director contacting the molten glass.
• Thermally conductive beads 200 preferably comprise a material having a thermal conductivity ( ⁇ ), wherein ⁇ is at least 10 W/(m-K) at 25°C, such as at least 20 W/(m-K) at 25°C, and further such as at least 30 W/(m-K) at 25°C, and still further such as at least 50 W/(m-K) at 25°C, and yet further such as at least 100 W/(m-K) at 25°C, and even yet further such as at least 200 W/(m-K) at 25°C, including from 10 to 500 W/(m-K) at 25°C, and further including from 20 to 400 W/(m-K) at 25°C, and still further including from 30 to 300 W/(m-K) at 25°C.
• Thermally conductive beads may, for example, be selected from the group consisting of alumina and beryllium oxide.
• FIG. 7 shows a thermally conductive material in the form of beads
• embodiments herein can include other types or configurations of thermally conductive materials, such thermally conductive granular materials, non-spherically shaped thermally conductive materials, and solid, thermally conductive materials of unitary construction, such as a thermally conductive block that is shaped to be compatible with the interior surface of edge director 80' so as to provide efficient heat transfer between back plate 180 and the surface of the edge director contacting the molten glass and/or heat transfer between back plate 180 and the surface of the edge director contacting the molten glass, such that the temperature of the edge director contacting the molten glass is in accordance with a predetemiined temperature gradient profile.
• At least one of an inner surface of the back plate and an inner surface of the edge director contacting the molten glass is coated with a high emissivity coating, such as a coating having an emissivity ( ⁇ ), wherein 0.5 ⁇ ⁇ ⁇ 1.0, such as 0.6 ⁇ ⁇ ⁇ 1.0, further such as 0.7 ⁇ ⁇ ⁇ 1.0, yet further such as 0.8 ⁇ ⁇ ⁇ 1, and still yet further such as 0.9 ⁇ ⁇ ⁇ 1.
• a high emissivity coating such as a coating having an emissivity ( ⁇ )
• both of an inner surface of the back plate and an inner surface of the edge director contacting the molten glass is coated with a high emissivity coating, such as a coating having an emissivity ( ⁇ ), wherein 0.5 ⁇ ⁇ ⁇ 1.0, such as 0.6 ⁇ ⁇ ⁇ 1.0, further such as 0.7 ⁇ ⁇ ⁇ 1.0, yet further such as 0.8 ⁇ ⁇ ⁇ 1, and still yet further such as 0.9 ⁇ ⁇ ⁇ 1.
• high emissivity materials and coatings include, for example, at least one coating comprising a material from the group consisting of alumina, zirconia and mixtures and multilayers of the same.
• the high emissivity coating may be applied, for example, by plasma spray or flame spray coating techniques.
• heat transfer can, in certain exemplary embodiments, be facilitated from the back plate to one or more surfaces of the edge director contacting the molten glass, such that the temperature difference between the back plate and a surface of the edge director contacting the molten glass is less than 200°C, such as less than 150°C, and further such as less than 100°C, including from 50°C to 200°C, and further including from 100°C to 150°C.
• the temperature of a surface of the edge director contacting the molten glass can be at least 1100°C, such as at least 1150°C, and further such as at least 1200°C, and yet further such as at least 1250°C.
• Embodiments herein can provide advantages over other methods of minimizing buildup of devitrified glass on edge directors, such as those using, for example, resistance heaters near the edge directors (relying on convection and radiation to transfer heat from the resistance heaters to the edge directors). Such methods are not sufficient to transfer enough heat to the edge directors in order to achieve adequate edge director temperature necessary to
• Such methods may not enable the precise temperature control of the edge directors that can be achieved according to embodiments herein.
• the additional components such as resistance heaters, etc.
• the additional components can take up substantial amounts of critical physical space near the draw and can result in substantial undesirable (and unnecessary) heating to manufacturing components and equipment located near the edge directors.

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• Organic Chemistry (AREA)
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• Glass Melting And Manufacturing (AREA)
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• 2013
  • 2013-12-12 WO PCT/US2013/074512 patent/WO2014099560A1/en active Application Filing
  • 2013-12-12 KR KR1020157019244A patent/KR102166756B1/ko not_active Expired - Fee Related
  • 2013-12-12 CN CN201380067490.0A patent/CN105050969B/zh not_active Expired - Fee Related
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