WO2012148642A2

WO2012148642A2 - Apparatus for making a glass article and methods

Info

Publication number: WO2012148642A2
Application number: PCT/US2012/032238
Authority: WO
Inventors: Bradley Frederick BOWDEN; Zagorka Dacic Gaeta; Martin Herbert Goller; Aaron Joshua Hade; James Patrick Murphy
Original assignee: Corning Inc
Current assignee: Corning Inc
Priority date: 2011-04-29
Filing date: 2012-04-05
Publication date: 2012-11-01
Anticipated expiration: 2013-10-29
Also published as: JP2014514239A; TWI565668B; CN103502161A; WO2012148642A3; KR101761457B1; TW201242919A; TWI541208B; JP5993444B2; KR20140025396A; TW201630824A; CN103502161B

Abstract

Methods of making a glass article comprise the step of flowing molten glass into an inlet of a conduit (132, 136), wherein the molten glass entering the inlet includes a flow profile with a first quantity (182) traveling in the conduit at a lower elevation than a second quantity (184) traveling in the conduit. The method further includes the step of twisting the flow profile within the conduit such that the first quantity travels in the conduit at a higher elevation than the second quantity. In further examples, apparatus for making a glass article comprise a helical vane (170) non-rotatably fixed in a conduit (132, 136) and configured to twist a flow profile (180) of a molten glass flowing within the conduit.

Description

APPARATUS FOR MAKING A GLASS ARTICLE AND METHODS

BACKGROUND

[0001] This application claims the benefit of priority under 35 USC § 119 of US Provisional Application Serial No. 61/480,428 filed on April 29, 2011 the content of which is relied upon and incorporated herein by reference in its entirety.

Background

[0002] The present disclosure relates generally to methods and apparatus for making a glass article, and more particularly to apparatus for reorienting glass flow within a conduit and methods of making a glass article including the step of reorienting a flow profile of molten glass within a conduit.

FIELD

[0003] Glass manufacturing systems are commonly used to form various glass articles for example sheet glass that may be used in liquid crystal displays (LCDs). For example, it is known to flow molten glass to an isopipe, forming vessel, debiteuse, or other forming structure, wherein a glass ribbon is formed by a down-draw process, for example a fusion down draw process. The glass ribbon may then be subsequently divided into sheets, for example to provide LCD sheet glass.

[0004] Glass quality attributes requirements for flat glass applications, particularly for the LCD panel applications, are becoming progressively stringent. There are two mutually connected attributes, both associated with the process of glass stirring in the stir chamber: a defect in the flatness of the finished glass surface (known as "mura" or "cord") and precious-metal particle inclusions created by the erosion of the stirrer blades and stir chamber walls. Glass surface corrugation - cord - is a common way in which insufficient homogeneity of glass or insufficient mixing of the glass before delivery expresses itself in the final product. The resulting thickness variation of the panel translates into liquid-crystal gap variation, which may result in faulty LCD operation. Precious-metal inclusions cause discontinuities in the bulk of the glass panel, causing the "black spot" defect in the finished LCD products. SUMMARY

[0005] The purpose of the stirring system is to reduce the chemical variations in the glass that are an artifact of the melting process: batch melting, decomposition products from the tank refractory, etc. Optimal stirring of glass is a balancing act between the two phenomena, glass homogenization and material erosion, both of which are enhanced by increasing the shear between the blades of the stir rod and the stir chamber walls, the former to the advantage, the latter to the detriment of finished glass quality. The present inventors have found solutions to improve glass homogenization without increasing the stir rod speed. Numerical and oil modeling results indicate that glass entering the stirring chamber from the bottom of the finer to stir chamber connecting tube is least mixed by the stirrer. This location also corresponds to the glass with the greatest level of inhomogeneity, the "sludge layer". Thus, the overall homogeneity of glass exiting the stir chamber can be improved by reorienting the least homogeneous incoming glass to a location characterized by improved mixing in the stirrer.

[0006] By reorienting a defined segment of the glass flow stream and guiding it to a location in the stir chamber where it will be effectively mixed, the cord quality of the product glass will improve. Accordingly, two goals may be accomplished: 1. a reduction in cord to meet more stringent customer requirements for glass surface flatness; and 2. a potential reduction of stir speed as a benefit of more effective homogenization in the stir chamber thereby resulting in a reduction in the number platinum particles created in the stir chamber.

[0007] According to one aspect, there is provided a method of making a glass article comprising the steps of:

(I) melting batch material in a glass melter to produce molten glass;

(II) passing the molten glass into a fining chamber;

(III) removing gas bubbles from the molten glass in the fining chamber;

(IV) passing the molten glass from the fining chamber through an inlet of a conduit providing fluid communication between the fining chamber and a stir chamber, wherein the molten glass entering the inlet includes a flow profile with a first quantity traveling in the conduit at a lower elevation than a second quantity traveling in the conduit; (V) twisting the flow profile within the conduit such that the first quantity travels in the conduit at a higher elevation than the second quantity;

(VI) passing the molten glass into the stir chamber from an outlet of the conduit;

(VII) stirring the molten glass in the stir chamber; and

(VIII) passing the quantity of molten glass from the stir chamber to a forming vessel to form the glass article.

[0008] According to a second aspect, there is provided the method according to aspect 1, wherein the forming vessel comprises an isopipe and the glass article comprises a glass sheet formed by a fusion down-draw process.

[0009] According to a third aspect, there is provided the method according to aspect 1 or aspect 2, wherein step (V) includes twisting the flow profile with a device positioned within conduit.

[0010] According to a fourth aspect, there is provided the method according to any one of aspects 1-3, wherein step (V) includes twisting the flow profile with a helical vane.

[0011] According to a fifth aspect, there is provided the method of aspect 4, wherein the helical vane remains nonrotatably fixed relative to the conduit while twisting the flow profile during step (V).

[0012] According to a sixth aspect, there is provided a method of making a glass article comprising the steps of:

(I) melting batch material in a glass melter to produce molten glass;

(II) passing the molten glass through an inlet of a conduit providing fluid communication between the glass melter and a fining chamber, wherein the molten glass entering the inlet includes a flow profile with a first quantity traveling in the conduit at a lower elevation than a second quantity traveling in the conduit;

(III) twisting the flow profile within the conduit such that the first quantity travels in the conduit at a higher elevation than the second quantity;

(IV) passing the molten glass into the fining chamber from an outlet of the conduit;

(V) removing gas bubbles from the molten glass in the fining chamber;

(VI) passing the molten glass from the fining chamber to a stir chamber;

(VII) stirring the molten glass in the stir chamber; and (VIII) passing the quantity of molten glass from the stir chamber to a forming vessel to form the glass article.

[0013] According to a seventh aspect, there is provided the method according to aspect 6, wherein the forming vessel comprises an isopipe and the glass article comprises a glass sheet formed by a fusion down-draw process.

[0014] According to an eighth aspect, there is provided the method according to aspect 6 or aspect 7, wherein step (III) includes twisting the flow profile with a device positioned within conduit.

[0015] According to a ninth aspect, there is provided the method according to any one of aspects 6-8, wherein step (III) includes twisting the flow profile with a helical vane.

[0016] According to a tenth aspect, there is provided the method of aspect 9, wherein the helical vane remains nonrotatably fixed relative to the conduit while twisting the flow profile during step (III).

[0017] According to an eleventh aspect, there is provided an apparatus for making a glass article comprising:

a glass melter configured to melt a batch material into a molten glass;

a fining chamber positioned downstream from the glass melter, wherein the fining chamber is configured to receive molten glass from the glass melter;

a stir chamber positioned downstream from the fining chamber;

a conduit configured to provide a path for molten glass to flow from the fining chamber to the stir chamber;

a helical vane nonrotatably fixed in the conduit and configured to twist a flow profile of the molten glass within the conduit; and

a forming vessel positioned downstream from the stir chamber, wherein the forming vessel is configured to receive molten glass from the stir chamber and form the glass article.

[0018] According to a twelfth aspect, there is provided the apparatus according to aspect 11, wherein the forming vessel comprises an isopipe configured to fusion down- draw the glass article from the molten glass.

[0019] According to a thirteenth aspect, there is provided the apparatus of aspect 11 or aspect 12, wherein the helical vane includes an upstream end and a downstream end, wherein the vane is twisted through an angle between the upstream end and the downstream end within a range from about 90° to about 270°.

[0020] According to a fourteenth aspect, there is provided the apparatus of any one of aspects 11-13, wherein the helical vane further includes an upstream edge positioned at an inclined angle from about 30° to about 60° with respect to a horizontal axis that is perpendicular to an axial flow direction of the conduit.

[0021] According to a fifteenth aspect, there is provided an apparatus for making a glass article comprising:

a glass melter configured to melt a batch material into a molten glass;

a fining chamber positioned downstream from the glass melter;

a conduit configured to provide a path for molten glass to flow from the glass melter to the fining chamber;

a helical vane nonrotatably fixed in the conduit and configured to twist a flow profile of the molten glass within the conduit;

a stir chamber positioned downstream from the glass melter, wherein the stir chamber is configured to receive molten glass from the fining chamber; and

[0022] According to a sixteenth aspect, there is provided the apparatus of aspect 15, wherein the forming vessel comprises an isopipe configured to fusion down-draw the glass article from the molten glass.

[0023] According to a seventeenth aspect, there is provided the apparatus of aspect 15 or aspect 16, wherein the helical vane includes an upstream end and a downstream end, wherein the vane is twisted through an angle between the upstream end and the downstream end within a range from about 90° to about 270°.

[0024] According to an eighteenth aspect, there is provided the apparatus of aspect 17, wherein the angle is about 180°.

[0025] According to a nineteenth aspect, there is provided the apparatus of any one of aspects 15-18, wherein the helical vane further includes an upstream edge positioned at an inclined angle of from about 30° to about 60° with respect to a horizontal axis that is perpendicular to an axial flow direction of the conduit.

[0026] According to a twentieth aspect, there is provided the apparatus of aspect 19, wherein the inclined angle is about 45° with respect to the horizontal axis.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above and other features, aspects and advantages of the present invention are better understood when the following detailed description of the invention is read with reference to the accompanying drawings, in which:

[0028] FIG. 1 is a schematic view of an example apparatus for making a glass article;

[0029] FIG. 2 is a schematic view of the apparatus along line 2-2 of FIG. 1 illustrating portions of the apparatus;

[0030] FIG. 3 is an enlarged portion of the apparatus of FIG. 1;

[0031] FIG. 4 is an enlarged view of an example helical vane nonrotatably fixed in a conduit;

[0032] FIG. 5 is a cross sectional view of the conduit along line 5-5 of FIG. 4 illustrating an upstream edge of the helical vane;

[0033] FIG. 6 is a cross sectional view of the conduit along line 6-6 of FIG. 4 illustrating a downstream edge of the helical vane;

[0034] FIG. 7 is an upstream upper right perspective view of the helical vane of FIG. 4;

[0035] FIG. 8 is a schematic illustration of a computer model demonstrating the reorientation of a flow profile of molten glass when a helical vane is mounted such that the upstream edge is positioned along a horizontal axis of the conduit;

[0036] FIG. 9 is a schematic illustration of a computer model demonstrating the reorientation of a flow profile of molten glass when a helical vane is mounted such that the upstream edge is positioned at an angle of 45° with respect to the horizontal axis of the conduit; and

[0037] FIG. 10 is a schematic view of another example apparatus for making a glass article. DETAILED DESCRIPTION

[0038] The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which example embodiments of the claimed invention are shown. Whenever possible, the same reference numerals are used throughout the drawings to refer to the same or like parts. However, the claimed invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These example embodiments are provided so that this disclosure will be both thorough and complete, and will fully convey the scope of the claimed invention to those skilled in the art.

[0039] FIG. 1 illustrates a schematic view of a fusion draw apparatus 102 for fusion drawing a glass ribbon 104 for subsequent processing into glass sheets. The fusion draw apparatus 102 can include a glass melter 106 configured to receive batch material 108 from a storage bin 110 and melt the batch material 108 into a molten glass 124. The batch material 108 can be introduced by a batch delivery device 112 powered by a motor 114. An optional controller 116 can be configured to activate the motor 114 to introduce a desired amount of batch material 108 into the glass melter 106, as indicated by arrow 118. A probe 120 can be used to measure a level 122 of the molten glass 124 within a standpipe 126 and communicate the measured information to the controller 116 by way of a communication line 128.

[0040] The fusion draw apparatus 102 can also include a fining chamber 130, for example a fining tube, positioned downstream from the glass melter 106. The fining chamber 130 is configured to receive the molten glass 124 from the glass melter 106. For instance, in one example, the fusion draw apparatus 102 includes a first conduit 132 configured to provide a path for molten glass 124 to flow from the glass melter 106 to the fining chamber 130.

[0041] The fusion draw apparatus 102 can further include a stir chamber 134 positioned downstream from the fining chamber 130. The stir chamber 134 is configured to receive the molten glass 124 from the fining chamber 130. For example, the fusion draw apparatus 102 can include a second conduit 136 configured to provide a path for the molten glass 124 to flow from the fining chamber 130 to the stir chamber 134. In one example, the stir chamber 134 can include a plurality of mixing elements 138 mounted to a rotatable shaft 140 for rotating about an axis of the rotatable shaft 140 as indicated by the rotation arrow 142.

[0042] As shown, a forming vessel 152 may be positioned downstream from the stir chamber 134, wherein the forming vessel 152 is configured to receive the molten glass 124 from the stir chamber 134 and form the glass article. For example, the fusion draw apparatus 102 can include a delivery vessel 144, for example a bowl, positioned downstream from the stir chamber 134. The delivery vessel 144 can be configured to receive the molten glass 124 from the stir chamber 134. For instance, the fusion draw apparatus 102 can include a third conduit 146 configured to provide a path for the molten glass 124 to flow from the stir chamber 134 to the delivery vessel 144.

[0043] As further illustrated, the fusion draw apparatus 102 may also include a downcomer 148 positioned to deliver molten glass 124 from the delivery vessel 144 to an inlet 150 of the forming vessel 152 as illustrated by arrow 154.

[0044] Various forming vessels may be used in accordance with aspects of the disclosure depending on the particular application. For example, the forming vessel may be used to provide glass articles having a wide range of configurations for different optical applications. For example, the forming vessel may be designed to provide glass lenses or other optical glass components. In just one example, the forming vessel can comprise an apparatus used to process glass ribbon. Such forming vessels may comprise down-draw, up-draw, float, fusion, press rolling, slot draw, or other forming vessels for producing glass articles. In one example, the forming vessels can be designed to provide a glass ribbon that may be used in various applications. For example, glass ribbon provided by the forming vessel can be further processed for incorporation into liquid crystal displays, electrophoretic displays, organic light emitting diode displays, plasma display panels, or other display or lighting applications.

[0045] In one non-limiting example, FIG. 2 illustrates an example forming vessel 152 that can optionally comprise an isopipe configured, for example, to fusion down-draw the glass article from the molten glass. For instance, FIG. 2 is a cross-sectional perspective view of an example isopipe for the fusion draw apparatus 102 along line 2-2 of FIG. 1. As shown, the forming vessel 152 includes a forming wedge 156 comprising a pair of downwardly inclined forming surface portions 158, 160 extending between opposed ends of the forming wedge 156. The pair of downwardly inclined forming surface portions 158, 160 converges along a downstream direction 162 to form a root 164. A draw plane 166 extends through the root 164 wherein the glass ribbon 104 may be drawn in the downstream direction 162 along draw plane 166. As shown, the draw plane 166 can bisect the root 164 although the draw plane 166 may extend at other orientations with respect to the root 164.

[0046] As shown in FIG. 4, the molten glass 124 within the first conduit 132 and the second conduit 136 includes a flow profile 180 with a first quantity 182 traveling in the conduit at a lower elevation than a second quantity 184 traveling in the conduit. In one example, the first quantity 182 can travel along a lower portion 132a, 136a of the conduit and the second quantity 184 can travel above the first quantity 182. As such, the first quantity 182 can be positioned between the second quantity 184 and the lower portion 132a, 136a of the conduit. In further examples, the second quantity 184 can travel in the conduit at a higher elevation and laterally offset, rather than being positioned above, the first quantity 182.

[0047] The fusion draw apparatus 102 may optionally include a structure within the first conduit 132 and/or the second conduit 136 configured to twist the flow profile 180 within the conduit such that the first quantity 182 travels in the conduit at a higher elevation than the second quantity 184. For instance, in one example, the second quantity 184 can travel below the first quantity 182 such that the second quantity 184 can be positioned between the first quantity 182 and the lower portion 132a, 136a of the conduit. In further examples, the first quantity 182 can travel in the conduit at a higher elevation and laterally offset, rather than being positioned above, the second quantity 184.

[0048] In one example, the structure can include a device positioned within the conduit to twist the flow profile. For example, the device can comprise a helical vane 170 configured to reorient the flow profile 180. As shown, the helical vane 170 can be nonrotatably fixed in the first conduit 132 (as shown in FIG. 10) and/or the second conduit 136 (as shown in FIGS. 1 and 3). As shown in FIGS. 4 and 7, the helical vane 170, if provided, can be configured to twist the flow profile 180 of the molten glass 124 within the conduit 132, 136. [0049] The helical vane 170 can include a wide range of configurations. As shown in FIGS. 4 and 7, the helical vane 170 can comprise a smooth helical configuration to avoid dead flow zones and minimize pressure build up within the conduit. The smooth helical configuration can further avoid ebbing or other disturbances in the glass flow as the glass flow is twisted. As such, the smooth helical configuration can permit twisting of the fluid flow while minimizing interruption of the laminar fluid flow as the flow profile is twisted with the helical vane 170. Still further, the helical vane 170 comprises a simple structure with a smooth configuration that can permit pass through of any bubbles that may unlikely exist in the molten glass passing through the conduit. While it may be intuitive to immediately remove the bubbles with a reorienting device in the flow path, unexpectedly, allowing the gas bubbles to freely pass through can actually simplify subsequent removal of the glass bubbles within the molten glass. Indeed, attempting to dissipate the bubbles with a reorienting device placed within the molten glass path can actually result in accumulation or conglomeration of bubbles that can complicate subsequent removal of the bubbles before forming the glass article. As such, the simple geometry of the helical vane 170 can facilitate pass through of any unlikely bubbles within the molten glass path. The helical nature of the vane can therefore unexpectedly facilitate removal of any gas bubbles within the molten glass by allowing minimized interruption of the gas bubbles that pass through the helical vane 170.

[0050] As shown, the helical vane 170 can include an upstream end 172a and a downstream end 172b defining a continuous helical segment therebetween. Although not shown, a plurality of segments may be stacked in series within the conduit to effect desired reorientation of the flow profile 180 depending on the particular application.

[0051] As further illustrated, in FIG. 7, the helical vane 170 can comprise two helical edges 173a, 173b that may facilitate mounting of the helical vane 170 within the conduit. In one example, the helical edges 173a, 173b are press fit within the conduit although the helical edges can be welded or mechanically attached to the conduit such that the helical vane 170 is nonrotatably mounted within the conduit.

[0052] As further illustrated, the upstream end 172a can include an upstream edge 174a and the downstream end 172b can include a downstream edge 174b. In the illustrated example the edges are substantially fiat although one or both edges may be rounded. Moreover, as shown, the edges are substantially straight although the edges may have a curved shape, for example an S-shape, in further examples.

[0053] As shown in FIG. 7, in one example, the helical vane 170 may comprise a shape generated by rotating a cross sectional axis 176 clockwise between the upstream edge 174a and the downstream edge 174b in an axial flow direction 190. In further examples, the shape of the helical vane 170 may also be generated by rotating the cross sectional axis counterclockwise between the first edge and the second edge. The cross sectional axis 176 may be rotated in a wide range of angles between the upstream end 172a and the downstream end 172b. For example, the cross sectional axis 176 can be rotated such that the helical vane 170 is twisted through an angle between the upstream end 172a and the downstream end 172b within a range from about 90° to about 360°, for example from about 90° to about 270°, or 90° to about 180°. As shown in FIG. 7 and apparent from FIGS. 5 and 6, in one example, the helical vane 170 can be twisted through an angle of about 180° between the upstream end 172a and the downstream end 172b.

[0054] The helical vane 170 can also be mounted with the upstream edge positioned in a wide variety of angles a relative to a horizontal axis 192 that is perpendicular to the axial flow direction 190. For example, the upstream edge can be inclined at an angle a from 0° to 180°, for example from about 30° to about 60° with respect to the horizontal axis 192. As shown in FIG. 5, the upstream edge 174a is positioned at an angle a of about 45° with respect to the horizontal axis 192. As shown, in FIG. 6, with a 180° helical twist, the downstream edge 174b can also be positioned at an angle β of about 45°. As further shown in FIG. 5, when viewing a cross section of the conduit and looking into the axial flow direction 190, four quadrants I, II, III, IV can be viewed wherein the upstream edge 174a is positioned to diagonally extend between quadrants I and III.

[0055] FIGS. 8 and 9 demonstrate computer model using a helical vane similar to the vane shown in FIG. 7 wherein the vane is twisted through an angle of about 180° between the upstream end 172a and the downstream end 172b following a shape generated by a clockwise rotation of the cross sectional axis 176 in an axial flow direction 190. FIG. 8 demonstrates the upstream edge 174a mounted along the horizontal axis 192. The computer model suggests the first quantity 182 of the flow profile 180 being twisted as the molten glass 124 flows downstream through the helical vane 170 from an upstream position 200 at the upstream end 172a of the helical vane 170 to a downstream position 202 at the downstream end 172b of the helical vane 170. As shown in dashed lines, the first quantity 182 of the flow profile 180 is reoriented to be positioned at a higher elevation and within quadrants II and III.

[0056] FIG. 9 demonstrates consequence of mounting the helical vane with the upstream edge 174a positioned at an angle a of about 45 ⁰ with respect to the horizontal axis 192. However, unlike FIG. 5, the mounting of the computer model provides the upstream edge 174a positioned diagonally to extend between quadrants II and IV. As shown, the computer model suggests the first quantity 182 of the flow profile 180 being reoriented as the molten glass 124 flows downstream through the helical vane 170 from an upstream position 200 at the upstream end 172a to a downstream position 202 at the downstream end 172b. As shown, mounting at about a 45° angle a can shift the downstream position 202 such that downstream position 202 is reoriented to be positioned at a higher elevation and substantially above the upstream position 200 along a vertical axis 204 perpendicular to the horizontal axis 192. As shown, the downstream position may be at an elevation of about 50% of the overall height of the conduit. In further examples, the elevation may be greater or less than 50% of the conduit height.

[0057] As shown, the glass melter 106, fining chamber 130, the stir chamber 134, delivery vessel 144, and forming vessel 152 are examples of glass melt stations that may be located in series along the fusion draw apparatus 102.

[0058] The glass melter 106 is typically made from a refractory material, for example refractory (e.g. ceramic) brick. The fusion draw apparatus 102 may further include components that are typically made from platinum or platinum-containing metals for example platinum-rhodium, platinum-iridium and combinations thereof, but which may also comprise such refractory metals for example 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 conduit 132, the fining chamber 130 (e.g., finer tube), the second conduit 136, the standpipe 126, the stir chamber 134 (e.g., a stir chamber), mixing elements 138 and rotatable shaft 140, the third conduit 146, the delivery vessel 144 (e.g., a bowl), the downcomer 148, the inlet 150 and the helical vane 170. The forming vessel 152 is also made from a refractory material and is designed to form the glass ribbon 104. In further examples, the forming vessel 152 can be made from other materials that may not necessarily be refractory materials. For instance, the forming vessel 152 can comprise an all metal or metal cladding although other materials may be used in further examples.

[0059] A method of making a glass article will now be described. As shown in FIG. 1, the method can include the step of melting batch material 108 in the glass melter 106 to produce molten glass 124. As shown in FIG. 3, the molten glass 124 is then passed into the fining chamber 130, for example, by way of the first conduit 132. The method then includes the step of removing gas bubbles 206 from the molten glass 124 in the fining chamber 130 and passing the molten glass 124 from the fining chamber 130 through an inlet 137 of the second conduit 136 providing fluid communication between the fining chamber 130 and the stir chamber 134.

[0060] As shown in FIGS. 3 and 4, the molten glass 124 entering the inlet 137 includes the flow profile 180 with the first quantity 182 traveling in the second conduit 136 at a lower elevation than the second quantity 184 traveling in the second conduit 136. As further shown, the method can also include the step of reorienting the flow profile 180 within the second conduit 136 such that the first quantity 182 travels in the second conduit 136 at a higher elevation than the second quantity 184.

[0061] The method also includes the step of passing the molten glass 124 into the stir chamber 134 from an outlet 139 of the second conduit 136. The molten glass 124 is then stirred within the stir chamber 134. For example, the rotatable shaft 140 can be rotated as indicated by rotation arrow 142 to rotate the mixing elements 138 (schematically shown in FIG. 3). By action of the stir chamber 134, the molten glass 124 can be homogenized prior to passing the quantity of molten glass from the stir chamber to a forming vessel to form the glass article.

[0062] It will be appreciated that the stir chamber 134 is designed to reduce the chemical variations in the molten glass 124 that are a consequence of the melting process. For example, melting of the batch material, and decomposition of portions of the apparatus 102 (for example refractory materials) are examples of sources that can cause chemical variations in the molten glass 124. There is a desire to achieve optimal mixing of the molten glass within the stir chamber 134 to optimize homogenization of the molten glass 124 exiting the stir chamber to the forming vessel. Optimal stirring is a balance between glass homogenization that can be enhanced by increasing the shear between the mixing elements 138 and the walls of the stir chamber 134. On the other hand, increasing the shear can also increase material erosion within the stir chamber 134, thereby adding undesirable chemical components from decomposition of portions of the stir chamber 134.

[0063] It is believed that reorienting the flow profile 180 as discussed above can result in improved glass homogenization without increasing the rotational speed of the mixing elements 138 within the stir chamber 134. In further examples, reorienting the flow profile 180 may allow the same or increased homogenization with a slower rotational speed of the mixing elements; thereby reducing decomposition resulting from shear between the mixing elements 138 and the walls of the stir chamber 134.

[0064] Modeling results indicate that molten glass 124 near the bottom of the flow profile entering the stirring chamber tends to be the location that is least mixed by the stir chamber 134. The bottom location of the flow profile corresponds with the greatest level of inhomogeneity in the molten glass 124 as imperfections tend to settle along a "sludge layer". As such, reorienting the sludge layer found in the first quantity 182 of the flow profile 180 to be at a higher elevation when entering the stir chamber 134 can increase overall homogeneity of the molten glass exiting the stir chamber 134.

[0065] Consequently, turning back to FIG. 1, the homogeneous mixture of molten glass 124 can pass through the third conduit 146, the delivery vessel 144, through the downcomer 148 and into the inlet 150 of the forming vessel 152. As shown in FIG. 2, the forming vessel can comprise an isopipe designed to fusion down-draw a glass ribbon 104 for subsequently processing a glass sheet. As the glass ribbon 104 is being formed from a more homogeneous molten glass 124, glass sheets can be produced with increased flatness of the finished glass surface and avoidance of precious-metal particle inclusions that may otherwise be created by erosion of the stirrer blades and stir chamber walls with less effective mixing procedures.

[0066] As shown in FIGS. 4 and 7, reorienting of the glass mixture can be achieved by twisting the flow profile 180 with the helical vane 170. Moreover, the helical vane 170 can remain nonrotatably fixed relative to the second conduit 136 while twisting the flow profile 180.

[0067] Experimental evidence suggests that enhanced mixing may be achieved by reorienting the flow profile 180 at the first conduit 132 or the second conduit 136. FIG. 10 illustrates another example apparatus 102 where the flow profile is reoriented in the first conduit 132. In such an example, the method includes the initial step of melting the batch material in the glass melter to produce molten glass. The molten glass is then passed through an inlet 208 of the first conduit 132 providing fluid communication between the glass melter 106 and the fining chamber 130. As shown, the molten glass 124 entering the inlet 208 includes a flow profile with a first quantity 182 traveling in the first conduit 132 at a lower elevation than a second quantity 184 traveling in the first conduit 132. The method then includes the step of reorienting the flow profile within the first conduit 132 such that the first quantity 182 travels in the first conduit 132 at a higher elevation than the second quantity 184.

[0068] Reorienting the flow profile within the first conduit 132 can be achieved, for example, by the helical vane 170 previously described. In one example, the helical vane 170 may be located outside electrical flanges 212 designed to provide an electrical heating circuit providing resistance heating through the first conduit 132 between the electrical flanges 212. As such, locating the helical vane 170 at least partially within the glass melter 106 may be possible to avoid interference with the resistance heating circuit. The helical vane 170 in the first conduit 132 also provides additional structural stability to this conduit 132 which can be prone to deformation over time. This embodiment may have the additional benefit of increasing the dissolution rate of melter refractory stones by lowering the saturation of the refractory chemical components in the glass that surrounds them.

[0069] The method then proceeds by passing the molten glass into the fining chamber 130 from an outlet 210 of the first conduit 132. Gas bubbles 206 are then removed from the molten glass 124 in the fining chamber 130. The molten glass is then passed into the stir chamber 134. As shown, the first quantity of material 182 can still be located at an upper portion of the second conduit 136 when entering the stir chamber 134. As such, increased homogeneity of the molten glass and increased quality of the glass articles can therefore be achieved.

[0070] By reorienting the flow profile as described above, increased surface flatness may be observed in the glass articles (e.g., glass sheets). There is also a potential reduction in stir speed of the mixing elements 138 in the stir chamber 134, thereby providing less erosion and consequently more homogenization in the stir chamber. Still further, increased efficiency of mixing may allow the size of the stir chamber 134 to be reduced, thereby significantly reducing the cost to produce the stir chamber 134 that is typically made from precious metals.

[0071] It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. A method of making a glass article comprising the steps of:

(I) melting batch material in a glass melter to produce molten glass;

(II) passing the molten glass into a fining chamber;

(III) removing gas bubbles from the molten glass in the fining chamber;

(IV) passing the molten glass from the fining chamber through an inlet of a conduit providing fluid communication between the fining chamber and a stir chamber, wherein the molten glass entering the inlet includes a flow profile with a first quantity traveling in the conduit at a lower elevation than a second quantity traveling in the conduit;

(V) twisting the flow profile within the conduit such that the first quantity travels in the conduit at a higher elevation than the second quantity;

(VII) stirring the molten glass in the stir chamber; and

2. The method according to claim 1, wherein the forming vessel comprises an isopipe and the glass article comprises a glass sheet formed by a fusion down-draw process.

3. The method according to claim 1 or claim 2, wherein step (V) includes twisting the flow profile with a device positioned within conduit.

4. The method according to any one of claims 1 -3, wherein step (V) includes twisting the flow profile with a helical vane.

5. The method of claim 4, wherein the helical vane remains nonrotatably fixed relative to the conduit while twisting the flow profile during step (V).

6. A method of making a glass article comprising the steps of:

(I) melting batch material in a glass melter to produce molten glass;

(II) passing the molten glass through an inlet of a conduit providing fluid communication between the glass melter and a fining chamber, wherein the molten glass entering the inlet includes a flow profile with a first quantity traveling in the conduit at a lower elevation than a second quantity traveling in the conduit; (III) twisting the flow profile within the conduit such that the first quantity travels in the conduit at a higher elevation than the second quantity;

(V) removing gas bubbles from the molten glass in the fining chamber;

(VI) passing the molten glass from the fining chamber to a stir chamber;

(VII) stirring the molten glass in the stir chamber; and

7. The method according to claim 6, wherein the forming vessel comprises an isopipe and the glass article comprises a glass sheet formed by a fusion down-draw process.

8. The method according to claim 6 or claim 7, wherein step (III) includes twisting the flow profile with a device positioned within conduit.

9. The method according to any one of claims 6-8, wherein step (III) includes twisting the flow profile with a helical vane.

10. The method of claim 9, wherein the helical vane remains nonrotatably fixed relative to the conduit while twisting the flow profile during step (III).

11. An apparatus for making a glass article comprising:

a glass melter configured to melt a batch material into a molten glass;

a stir chamber positioned downstream from the fining chamber;

12. The apparatus according to claim 11, wherein the forming vessel comprises an isopipe configured to fusion down-draw the glass article from the molten glass.

13. The apparatus of claim 11 or claim 12, wherein the helical vane includes an upstream end and a downstream end, wherein the vane is twisted through an angle between the upstream end and the downstream end within a range from about 90° to about 270°.

14. The apparatus of any one of claims 11-13, wherein the helical vane further includes an upstream edge positioned at an inclined angle from about 30° to about 60° with respect to a horizontal axis that is perpendicular to an axial flow direction of the conduit.

15. An apparatus for making a glass article comprising:

a glass melter configured to melt a batch material into a molten glass;

a fining chamber positioned downstream from the glass melter;

16. The apparatus of claim 15, wherein the forming vessel comprises an isopipe configured to fusion down-draw the glass article from the molten glass.

17. The apparatus of claim 15 or claim 16, wherein the helical vane includes an upstream end and a downstream end, wherein the vane is twisted through an angle between the upstream end and the downstream end within a range from about 90° to about 270°.

18. The apparatus of claim 17, wherein the angle is about 180°.

19. The apparatus of any one of claims 15-18, wherein the helical vane further includes an upstream edge positioned at an inclined angle of from about 30° to about 60° with respect to a horizontal axis that is perpendicular to an axial flow direction of the conduit.

20. The apparatus of claim 19, wherein the inclined angle is about 45° with respect to the horizontal axis.