WO2016201055A1

WO2016201055A1 - Glass manufacturing apparatus and method with reduced pressure cavity

Info

Publication number: WO2016201055A1
Application number: PCT/US2016/036617
Authority: WO
Inventors: Timothy L Lansberry; Andrew Jerome Muto
Original assignee: Corning Inc
Current assignee: Corning Inc
Priority date: 2015-06-12
Filing date: 2016-06-09
Publication date: 2016-12-15
Anticipated expiration: 2017-12-12
Also published as: CN107750240A; TW201708130A; JP2018516838A; KR20180030410A

Abstract

A glass forming apparatus and method include a glass forming device having an inlet end and a compression end and a trough extending between the inlet end and the compression end. The apparatus also includes a channel below the trough extending at least partially between the inlet end and the compression end. An atmosphere within the channel is maintained at a lower pressure than an atmosphere surrounding the glass forming device.

Description

GLASS MANUFACTURING APPARATUS AND METHOD WITH REDUCED

PRESSURE CAVITY

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S.

Provisional Application Serial No. 62/174,706 filed on June 12^th 2015, the content of which is relied upon and incorporated herein by reference in its entirety.

BACKGROUND

Field

[0002] The present disclosure relates generally to a glass manufacturing apparatus and method and more specifically to a glass manufacturing apparatus with a reduced pressure cavity.

Technical Background

[0003] Methods for the manufacture of glass materials, such as flat panel glass for display applications, including LCD televisions and handheld electronic devices, include the fusion draw method wherein glass flows over opposing sides of a glass forming device and then rejoins to form a glass sheet below the bottom, or root, of the device. Such methods can enable the production of relatively thin, flat glass sheets with high surface quality, which are desirable characteristics of glass intended for use in display applications.

[0004] In such manufacturing processes, there is a continual desire to increase molten glass flow rates. However, increased flow densities can result in several technical challenges with respect to the glass forming device. Such technical challenges can include, for example, a glass forming device that is subject to increased deformation over time, sometimes referred to as creep deformation. Creep deformation of the glass forming device can, for example, lead to undesirable changes in the molten glass flow distribution and thickness profile.

Eventually, creep deformation can result in the need to replace the glass forming device because the thickness profile of the molten glass cannot be kept within specifications.

Accordingly, it would be desirable to minimize the degree of creep deformation of the glass forming device while achieving higher molten glass flow rates. SUMMARY

[0005] Disclosed herein is an apparatus for producing a glass article. The apparatus includes an inlet end and a compression end and a trough extending between the inlet end and the compression end. The apparatus also includes a channel below the trough extending at least partially between the inlet end and the compression end. An atmosphere within the channel is maintained at a lower pressure than an atmosphere surrounding the glass forming device.

[0006] Also disclosed herein is a method of producing a glass article. The method includes introducing molten glass to a glass forming device. The glass forming device includes an inlet end and a compression end and a trough extending between the inlet end and the compression end. The glass forming device also includes a channel below the trough extending at least partially between the inlet end and the compression end. An atmosphere within the channel is maintained at a lower pressure than an atmosphere surrounding the glass forming device .

[0007] In addition, disclosed herein are glass sheets made by the above method as well as electronic devices that include such glass sheets.

[0008] Additional features and advantages of these and other embodiments will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0009] It is to be understood that both the foregoing general description and the following detailed description present embodiments of the present disclosure, and are intended to provide an overview or framework for understanding the nature and character of the embodiments as claimed. The accompanying drawings are included to provide a further understanding of these and other embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of these and other embodiments, and together with the description serve to explain the principles and operations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a schematic view of an apparatus for producing a glass article including a forming device in accordance with aspects of the disclosure; [0011] FIG. 2 is a cross-sectional enlarged perspective view of the forming device of FIG. i;

[0012] FIG. 3 is a perspective view of a glass forming device according to embodiments disclosed herein;

[0013] FIG. 4 is a side cutaway view of a glass forming device according to embodiments disclosed herein;

[0014] FIG. 5 is a side cutaway view of a glass forming device according to embodiments disclosed herein;

[0015] FIG. 6 is a side cutaway view of a glass forming device according to embodiments disclosed herein;

[0016] FIG. 7 is a side cutaway view of a glass forming device according to embodiments disclosed herein;

[0017] FIG. 8 is a top cutaway view of a glass forming device according to embodiments disclosed herein;

[0018] FIG. 9 is a top cutaway view of a glass forming device according to embodiments disclosed herein;

[0019] FIG. 10 is a top cutaway view of a glass forming device according to embodiments disclosed herein;

[0020] FIG. 11 is a side cutaway view of a glass forming device, a pressure reducing unit, and a control unit according to embodiments disclosed herein;

[0021] FIG. 12 is an inlet end view of a portion of a glass forming device after a period of operation, wherein the glass forming device does not contain a reduced pressure cavity; and

[0022] FIG. 13 is an inlet end view of a portion of a glass forming device of a glass forming device after a period of operation, wherein the glass forming device contains a reduced pressure cavity.

DETAILED DESCRIPTION

[0023] Reference will now be made to embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

[0024] FIG. 1 illustrates an exemplary schematic view of a glass forming apparatus 101 for fusion drawing a glass ribbon 103 for subsequent processing into glass sheets. The illustrated glass forming apparatus comprises a fusion draw apparatus although other fusion forming apparatus may be provided in further examples. The glass forming apparatus 101 can include a melting vessel (or melting furnace) 105 configured to receive batch material 107 from a storage bin 109. The batch material 107 can be introduced by a batch delivery device 111 powered by a motor 113. An optional controller 115 can be configured to activate the motor 113 to introduce a desired amount of batch material 107 into the melting vessel 105, as indicated by an arrow 117. A glass level probe 119 can be used to measure a glass melt (or molten glass) 121 level within a standpipe 123 and communicate the measured information to the controller 115 by way of a communication line 125.

[0025] The glass forming apparatus 101 can also include a fining vessel 127, such as a fining tube, located downstream from the melting vessel 105 and fluidly coupled to the melting vessel 105 by way of a first connecting tube 129. A mixing vessel 131, such as a stir chamber, can also be located downstream from the fining vessel 127 and a delivery vessel 133, such as a bowl, may be located downstream from the mixing vessel 131. As shown, a second connecting tube 135 can couple the fining vessel 127 to the mixing vessel 131 and a third connecting tube 137 can couple the mixing vessel 131 to the delivery vessel 133. As further illustrated, a downcomer 139 can be positioned to deliver glass melt 121 from the delivery vessel 133 to an inlet 141 of a forming device 143. As shown, the melting vessel 105, fining vessel 127, mixing vessel 131, delivery vessel 133, and forming device 143 are examples of glass melt stations that may be located in series along the glass forming apparatus 101.

[0026] The melting vessel 105 is typically made from a refractory material, such as refractory (e.g. ceramic) brick. The glass forming apparatus 101 may further include components that are typically made from platinum or platinum-containing metals such as platinum-rhodium, platinum-iridium and combinations thereof, but which may also comprise such refractory metals such as molybdenum, palladium, rhenium, tantalum, titanium, tungsten, ruthenium, osmium, zirconium, and alloys thereof and/or zirconium dioxide. The platinum-containing components can include one or more of the first connecting tube 129, the fining vessel 127 (e.g., finer tube), the second connecting tube 135, the standpipe 123, the mixing vessel 131 (e.g., a stir chamber), the third connecting tube 137, the delivery vessel 133 (e.g., a bowl), the downcomer 139 and the inlet 141. The forming device 143 is made from a refractory material, such as a ceramic, and is designed to form the glass ribbon 103.

[0027] FIG. 2 is a cross-sectional perspective view of the glass forming device 143 along line 2-2 of FIG. 1. As shown, the forming device 143 can include a trough 201 at least partially defined by a pair of weirs comprising a first weir 203 and a second weir 205 defining opposite sides of the trough 201. As further shown, the trough may also be at least partially defined by a bottom wall 207. As shown, the inner surfaces of the weirs 203, 205 and the bottom wall 207 define a substantially U shape that may optionally be provided with round corners. In further examples, the U shape may have surfaces substantially 90° relative to one another. In still further examples, the trough may have a bottom surface defined by an intersection of the inner surfaces of the weirs 203, 205. For example, the trough may have a V-shaped profile. Although not shown, the trough can include further configurations in additional embodiments.

[0028] As shown, the trough 201 can have a depth "D" between a top of the weir and a lower portion (i.e., bottom wall 207) of the trough 201 that varies along a longitudinal axis 209 although the depth may be substantially the same along the axis 209. Varying the depth "D" of the trough 201 may facilitate consistency in glass ribbon thickness across the width of the glass ribbon 103. In just one example, as shown in FIG. 2, the depth "Di" near the inlet of the forming device 143 can be greater than the depth "D2" of the trough 201 at a location downstream from the inlet of the trough 201. As demonstrated by the dashed line 210, the bottom wall 207 may extend at an acute angle relative to the axis 209 to provide a substantially continuous reduction in depth of the trough 201 along a length of the forming device 143 from the inlet end to the opposite end.

[0029] The forming device 143 further includes a forming wedge 211 comprising a pair of downwardly inclined forming surface portions 213, 215 extending between opposed ends of the forming wedge 211. The pair of downwardly inclined forming surface portions 213, 215 converge along a downstream direction 217 to form a root 219. A draw plane 221 extends through the root 219 wherein the glass ribbon 103 may be drawn in the downstream direction 217 along the draw plane 221. As shown, the draw plane 221 can bisect the root 219 although the draw plane 221 may extend at other orientations with respect to the root 219.

[0030] The forming device 143 may optionally be provided with one or more edge directors 223 intersecting with at least one of the pair of downwardly inclined forming surface portions 213, 215. The edge directors 223 can help reduce the attenuation or width reduction of the glass ribbon 103. In further examples, the one or more edge directors can intersect with both downwardly inclined forming surface portions 213, 215. In further examples, an edge director can be positioned at each of the opposed ends of the forming wedge 211 wherein an edge of the glass ribbon 103 is formed by molten glass flowing off the edge director. For instance, as shown in FIG. 2, the edge director 223 can be positioned at a first opposed end 225 and a second identical edge director (not shown in FIG. 2) can be positioned at a second opposed end (see 227 in FIG. 1). Each edge director 223 can be configured to intersect with both of the downwardly inclined forming surface portions 213, 215. Each edge director 223 can be substantially identical to one another although the edge directors may have different characteristics in further examples. Various forming wedge and edge director configurations may be used in accordance with aspects of the present disclosure. For example, aspects of the present disclosure may be used with forming wedges and edge director configurations disclosed in U.S. Pat. No. 3,451,798, U.S. Patent No. 3,537,834, U.S. Patent No. 7,409,839 and/or U.S. Provisional Pat. Application No.

61/155,669, filed February 26, 2009 that are each herein incorporated by reference in its entirety.

[0031] FIG. 3 shows a perspective view of a glass forming device according to embodiments disclosed herein. In the embodiment of FIG. 3, glass forming device 300 includes an inlet end 330, a compression end 340, and a trough 320 extending between the inlet end 330, the compression end 340, a first weir 305 and a second weir 310. Glass forming device is configured such that molten glass may flow from trough 320 over first and second weirs 305, 310, and down the sides of glass forming device and toward root 350 of the glass forming device. As can be seen in FIG. 3, trough 320 has a depth "D" that decreases between inlet end 330 and compression end 340. Accordingly, the cross-sectional area of trough 320 decreases between inlet end 330 and compression end 340. Pier blocks 410, 420 provide compression forces to mitigate sag of the glass forming device 300.

[0032] Glass forming device 300 additionally includes a channel 380 below the trough 320 that extends at least partially between the inlet end 330 and the compression end 340. While FIG. 3 shows channel 380 extending all of the way to inlet end 330, embodiments disclosed herein include those in which the channel extends all of the way to compression end 340, such as the entire longitudinal length of glass forming device between inlet end 330 and compression end 340. As explained in more detail below, channel may extend only partially between inlet end 330 and compression end 340, such as a distance within glass forming device 300 from inlet end 330 or a distance within glass forming device 300 from compression end 340.

[0033] While FIG. 3 shows a generally rectangular-shaped channel 380 wherein the horizontal width of the channel is greater than the vertical height of the channel at the inlet end 330 of the glass forming device 300, it is to be understood that embodiments disclosed herein include those in which the geometrical shape and dimensions of the channel have other configurations, including generally rectangular shapes wherein the vertical height of the channel is greater than the horizontal width of the channel, generally square shapes, wherein the horizontal width and vertical height of the channel are approximately equal, as well as, for example, generally circular, oval, or triangular-shaped channels with different orientations. In addition, while the channel 380 of FIG. 3 is shown having rounded corners, embodiments disclosed herein encompass channels with sharp corners, chamfered corners, or other geometries.

[0034] As will be described in more detail below, embodiments herein include those in which the geometrical dimensions of the channel change between the inlet end 330 and compression end 340 of the glass forming device 300. Embodiments herein also include those in which the geometrical dimensions of the channel are relatively constant along the longitudinal length of the glass forming device 300 between the inlet end 330 and the compression end 340.

[0035] FIG. 4 shows side cutaway view of the glass forming device 300 according to embodiments disclosed herein. In the embodiment shown in FIG. 4, channel 380 extends along axis "A-A" between inlet end 330 and compression end 340 of glass forming device 300. Channel 380 is generally parallel to the bottom of trough 320 along its longitudinal length and height "H" of channel 380 is approximately constant along the longitudinal length of channel 380.

[0036] FIG. 5 shows a side cutaway view of a glass forming device 300' according to embodiments disclosed herein. In the embodiment shown in FIG. 5, channel 380' extends between inlet end 330 and compression end 340 of glass forming device 300'. Channel 380' has a cross-sectional area that changes between inlet end 330 and compression end 340 of glass forming device 300'. Specifically, channel 380' has a height "H" that decreases between inlet end 330 and compression end 340 of glass forming device 300. While, in the embodiment shown in FIG. 5, top of channel 380' is generally parallel to root 350 of glass forming device 300 and bottom of channel 380' is generally parallel to bottom of trough 320, it is to be understood that embodiments disclosed herein include alternate configurations in which a channel has a height that decreases between inlet end 330 and compression end 340.

[0037] In this regard, FIG. 6 shows a side cutaway view of a glass forming device 300" according to embodiments disclosed herein. In the embodiment shown in FIG. 6, channel 380" extends between inlet end 330 and compression end 340 of glass forming device 300". Channel 380" has a height "H" that decreases between inlet end 330 and compression end 340 of glass forming device 300. In the embodiment shown in FIG. 6, top of channel 380" is generally parallel to bottom of trough 320.

[0038] In the embodiments of FIGS. 5 and 6, wherein the height "H" of the channel decreases between inlet end 330 and compression end 340, the height of the channel at the compression end 330 relative to the height of the channel at the inlet end 340, while not limited, may, for example, range from 5% to 95%, such as from 10% to 90%, and further such as from 20% to 80%, and yet further such as from 30% to 70% of the height of the channel at the inlet end.

[0039] In addition, while FIG. 4 shows an embodiment in which the height "H" of the channel is approximately constant along its longitudinal length and FIGS. 5 and 6 shown embodiments in which the height "H" of the channel decreases between inlet end 330 and compression end 340, it is to be understood that embodiments herein include those in which the height of the channel increases between the inlet end and the compression end of the glass forming device (not shown in FIGS. 4-6).

[0040] FIG. 7 shows a side cutaway view of a glass forming device 300'" according to embodiments disclosed herein. In the embodiment in FIG. 7, channel 380'" extends only partially along longitudinal length of glass forming device 300'". Specifically, channel 380'" extends from inlet end 330 and along a partial length of glass forming device 300'".

[0041] While, in the embodiment shown in FIG. 7, the channel has an approximately constant height "H" and is generally parallel to the bottom of trough 320, it is to be understood that embodiments disclosed herein include other configurations, such as configurations similar to those shown in FIGS. 5 and 6, wherein the height "H" of the channel decreases between inlet end 330 and compression end 340, except that the channel 380'" extends only partially along the longitudinal length of the glass forming device.

Embodiments disclosed herein also include those in which the channel extends only partially along the longitudinal length of the glass forming device and the height of the channel increases between the inlet end and the compression end of the glass forming device.

Embodiments disclosed herein further include any of the above with respect to the height of the channel as a function of length where the channel extends from compression end 340 and along a partial length of the glass forming device. [0042] In the embodiments of e.g., FIGS. 4 and 6, the top of the channel 380, 380" is a uniform distance from the trough 320 bottom between the inlet end 330 and the compression end 340. In the embodiment of, e.g., FIG. 5, the top of the channel 380' is a non-uniform distance from the trough 320 bottom between the inlet end 330 and the compression end 340. Specifically, in the embodiment of FIG. 5, the distance between the trough 320 bottom and the top of the channel 380' increases between the inlet end 330 and the compression end 340. Embodiments herein also include those in which the distance between the trough bottom and the top of the channel decreases between the inlet end and the compression end (not shown).

[0043] FIG. 8 shows a top cutaway view of a glass forming device 300" according to embodiments disclosed herein. In the embodiment in FIG. 8, the width "W" of channel 380" is approximately constant along the longitudinal length of the glass forming device between inlet end 330 and compression end 340.

[0044] FIG. 9 shows a top cutaway view of a glass forming device 300 according to embodiments disclosed herein. In the embodiment of FIG. 9, the width "W" of channel 380 decreases between inlet end 330 and compression end 340.

[0045] In the embodiment of FIG. 9, wherein the width " W" of the channel decreases between inlet end 330 and compression end 340, the width of the channel at the compression end 330 relative to the width of the channel at the inlet end 340, while not limited, may, for example, range from 5% to 95%, such as from 10% to 90%, and further such as from 20% to 80%, and yet further such as from 30% to 70% of the width of the channel at the inlet end.

[0046] FIG. 10 shows a top cutaway view of a glass forming device 300'" according to embodiments disclosed herein. In the embodiment of FIG. 10, channel 380'" extends only partially along longitudinal length of glass forming device 300'" and has an approximately constant width "W" along its longitudinal length.

[0047] While, in the embodiment shown in FIG. 10, the channel has an approximately constant width "W", it is to be understood that embodiments disclosed herein include other configurations, such as configurations similar to that shown in FIG. 9, wherein the width "W" of the channel decreases between inlet end 330 and compression end 340 except that the channel extends only partially along the longitudinal length of the glass forming device.

[0048] While FIGS. 8-10 show channels having an approximately constant or decreasing width between inlet end 330 and compression end 340, it is to be understood that embodiments disclosed herein also include those having a channel that increases in width between the inlet end and the compression end of the glass forming device (not shown in FIGS. 8-10).

[0049] Embodiments disclosed herein include those in which the cross-sectional area of the channel remains approximately constant along its longitudinal length or changes between inlet end 330 and compression end 340. For example, in certain preferred embodiments, the cross-sectional area of the channel decreases between the inlet end 330 and the compression end 340.

[0050] In this regard, FIGS. 6 and 8 show, in combination, an embodiment wherein channel 380" has a height "H" that decreases between inlet end 330 and compression end 340 of glass forming device 300 and has a width "W" that is approximately constant along the longitudinal length of the glass forming device between inlet end 330 and compression end 340. Accordingly, the cross-sectional area of channel 380" decreases between the inlet end 330 and the compression end 340 of the glass forming device 300".

[0051] By way of further example, FIGS. 4 and 9 show, in combination, an embodiment wherein channel 380 has a height "H" that is approximately constant along its longitudinal length and a the width "W" that decreases between inlet end 330 and compression end 340. Accordingly, the cross-sectional area of channel 380 decreases between the inlet end 330 and the compression end 340 of the glass forming device 300.

[0052] While FIGS. 6 and 8 and FIGS. 4 and 9 show, in combination, preferred embodiments in which the cross-sectional area of the channel decreases between the inlet end and the compression end, it is to be understood that embodiments herein also include other configurations in which the cross-sectional area of the channel decreases between the inlet end and the compression end. In that regard, embodiments disclosed herein include those in which any of the configurations shown in FIGS. 4-6 are combined with any of those shown in FIGS. 8 and 9 in order to obtain a channel having a cross-sectional area that decreases between the inlet end and the compression end of the glass forming device.

[0053] In embodiments wherein the cross-sectional area of the channel decreases between inlet end 330 and compression end 340, the cross-sectional area of the channel at the compression end 330 relative to the cross-sectional area of the channel at the inlet end 340, while not limited, may, for example, range from 5% to 95%, such as from 10% to 90%, and further such as from 20% to 80%, and yet further such as from 30% to 70% of the cross- sectional area of the channel at the inlet end. [0054] Embodiments disclosed herein also include those in which the cross-sectional area of the channel increases between the inlet end and the compression end of the glass forming device (not shown in FIGS. 4-10).

[0055] FIGS. 7 and 10 show, in combination, an embodiment wherein channel 380'" extends only partially along longitudinal length of glass forming device 300'" and has an approximately constant height "H" and width "W" along its longitudinal length.

Accordingly, the cross-sectional area of channel 380'" remains approximately constant along its longitudinal length.

[0056] While channel 380'" has an approximately constant cross-sectional area along its longitudinal length, embodiments disclosed herein include those in which a channel extends only partially along a longitudinal length of a glass forming device (e.g., extending from an inlet end or from a compression end) and has a cross-sectional area that changes along its longitudinal length, such as increasing between an inlet and compression end or decreasing between an inlet and compression end. Such changes may be the result of changes in channel height, width, or both.

[0057] While FIGS. 4-10 show channels having dimensions or cross-sectional areas that change in a generally linear fashion, it is to be understood that embodiments disclosed herein also include those in which the dimensions or cross-sectional area of the channel change in a non-linear fashion, such as a channel having at least one of a height and width that changes in a curved fashion or a channel having at least one of a height and width that changes in a stepped fashion.

[0058] The glass forming device 300, while not limited to any particular material, may, in certain exemplary embodiments, comprise a refractory material that has minimal reactivity to the molten glass formed using the device. Exemplary materials for the glass forming device include, but are not limited to an isopressed zircon-based ceramic material, such as those disclosed in US patent application publication numbers 2004/0055338 and 2005/0130830, the entire disclosures of which are incorporated herein by reference. Exemplary materials for the glass forming device may also include an isopressed xenotime-based or xenotime-stabilized zircon-based ceramic material, such as those disclosed in US patent application publication number 2009/0131241, the entire disclosure of which is incorporated herein by reference.

[0059] FIG. 11 shows a side cutaway view of a glass forming device 300 having channel 380, wherein a pressure reducing unit 500 is in fluid communication with the channel 380 via conduit 510. While FIG. 11 shows pressure reducing unit 500 on the compression end side of the glass forming device 300, it is to be understood that embodiments disclosed herein include those in which pressure reducing unit 500 is on inlet end side of the glass forming device 300. Pressure reducing unit 500 may comprise a vacuum pump or any other type of mechanism or configuration that enables maintaining an atmosphere within the channel 380 at a lower pressure than an atmosphere surrounding the glass forming device 300.

[0060] The operation of the pressure reducing unit 500 may be controlled by a controller 520, thereby enabling the pressure reducing unit 500 to regulate that pressure of the atmosphere within the channel 380. Although a single controller 520 is shown, multiple controllers may be provided in further embodiments, the term "controller" (e.g., "processor") can encompass all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The processor can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.

[0061] A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages, and it can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

[0062] The processes described herein can be performed by one or more controllers that can comprise one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit) to name a few. [0063] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more data memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Moreover, a computer can be embedded in another device, e.g., a mobile telephone, a personal digital assistant (PDA), to name just a few.

[0064] Computer readable media suitable for storing computer program instructions and data include all forms data memory including nonvolatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[0065] To provide for interaction with a user, embodiments described herein can be implemented on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor, and the like for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, or a touch screen by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, input from the user can be received in any form, including acoustic, speech, or tactile input.

[0066] Embodiments described herein can be implemented in a computing system that includes a back end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the subject matter described herein, or any combination of one or more such back end, middleware, or front end components. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network ("LAN") and a wide area network ("WAN"), e.g., the Internet. [0067] The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.

[0068] Controller 520 may, in certain preferred embodiments, incorporate at least one of a feedback and feedforward control system wherein at least one process condition is measured and inputted to the controller 520 and wherein a control algorithm is used to enable the controller 520 to adjust the pressure of an atmosphere within the channel 380 through operation of pressure reducing unit 500. Process conditions that may be measured and inputted to controller 520 include, but are not limited to, thickness profile characteristics of glass sheets made by the glass forming device and/or thickness profile characteristics of the molten glass ribbon that is flowing below the glass forming device, including glass or ribbon thickness as a function of width along the glass sheets and bead to center mass ratio of the glass or ribbon. Process conditions may also include direct measurement of sag of the glass forming device and direct measurement of the distance between the weirs of the glass forming device, using, for example camera (such as infrared camera) or laser measurement techniques. In addition, process conditions may include the flow rate and temperature of molten glass being processed through the glass forming device 300. Such measurements may be conducted as directed or adjusted by a user or may be done periodically at automatic intervals, such as monthly, weekly, daily, hourly, or several times within an hour.

[0069] Pressure within channel 380 can be periodically adjusted in response to at least one measured characteristic as described above. Accordingly, pressure within channel 380 may differ at different times or under different processing conditions. For at least one given time period, the atmosphere within the channel can be maintained to be at least 2 psi lower than the atmosphere surrounding the glass forming device in order to mitigate the effects of weir spreading over time, which, in turn, enables more uniform flow of molten glass and, hence, increases the useful life of the glass forming device 300 for an increased period of time. The atmosphere within the channel may also be maintained or adjusted to have other pressures relative to the atmosphere surrounding the glass forming device, such as, at least 4 psi lower, and further including at least 6 psi lower, and still yet further including at least 8 psi lower, and even still yet further including at least 10 psi lower, including from 2 to 12 psi lower, and further including from 4 to 10 psi lower than the atmosphere surrounding the glass forming device. In this regard, it is to be understood that while embodiments disclosed herein include maintaining a partial vacuum within channel 380, which may be sufficient to mitigate the effects of weir spreading overtime, embodiments disclosed herein also include maintaining a substantially full vacuum.

[0070] FIGS. 12 and 13 show, respectively, is an inlet end view of a portion of a glass forming device after a period of operation, wherein the glass forming device does not contain a reduced pressure cavity and an inlet end view of a portion of a glass forming device of a glass forming device after a period of operation, wherein the glass forming device contains a reduced pressure cavity. As can be seen from FIG. 12, when glass forming device does not have a reduced pressure cavity, weirs 305 and 310 have a tendency to spread apart over a period of operation such that their distance apart increases to a distance "Wl", which is greater than their distance apart when the glass forming device is first put into operation. As a general rule, as the distance between weirs 305 and 310 increases, glass flow uniformity and predictability decreases, especially since weir spreading tends to be the greatest near the inlet end of the glass forming device due to the height of the weirs being greater relative to their height near the compression end of the glass forming device. Eventually, weir spreading can disrupt glass flow uniformity and predictability to the point that the glass forming device is unusable in producing glass articles, such as glass sheets, of sufficient quality, requiring replacement of the glass forming device.

[0071] In contrast, as shown in FIG. 13, when glass forming device has a reduced pressure cavity 380, weirs 305 and 310, over the same period of operation as in FIG. 12, do not spread apart to the degree shown FIG. 12, such that their distance apart "W2" is less than "Wl". This, in turn, can enable glass flow uniformity and predictability to remain relatively stable and controllable for a longer period of time than when the glass forming device does not contain a reduced pressure cavity. Consequently, the usable life of the glass forming device can be extended, resulting in reduced production expense.

[0072] While specific embodiments disclosed herein have been described with respect to an overflow downdraw process, it is to be understood that the principle of operation of such embodiments may also be applied to other glass forming processes such as flow processes and slot draw processes.

[0073] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments of the present disclosure without departing from the spirit and scope of the disclosure. Thus, it is intended that the present disclosure cover the modifications and variations of these and other embodiments provided they come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. An apparatus for producing a glass article comprising a glass forming device, the glass forming device comprising:

an inlet end and a compression end and a trough extending between the inlet end and the compression end; and

a channel below the trough extending at least partially between the inlet end and the compression end;

wherein an atmosphere within the channel is maintained at a lower pressure than an atmosphere surrounding the glass forming device.

2. The apparatus of claim 1, wherein the cross-sectional area of the channel changes between the inlet end and the compression end.

3. The apparatus of claim 2, wherein the cross-sectional area of the channel decreases between the inlet end and the compression end.

4. The apparatus of claim 3, wherein the width of the channel decreases between the inlet end and the compression end.

5. The apparatus of claim 3, wherein the height of the channel decreases between the inlet end and the compression end.

6. The apparatus of claim 1, wherein the top of the channel is a uniform distance from the trough bottom between the inlet end and the compression end.

7. The apparatus of claim 1, wherein the top of the channel is a non-uniform distance from the trough bottom between the inlet end and the compression end.

8. The apparatus of claim 1, wherein the atmosphere within the channel is maintained to be at least 2 psi lower than the atmosphere surrounding the glass forming device.

9. The apparatus of claim 1, wherein the apparatus further comprises a pressure reducing unit that is in fluid communication with the channel.

10. The apparatus of claim 1, wherein the apparatus further comprises a control unit that regulates that pressure of the atmosphere within the channel.

11. A method of producing a glass article, the method comprising introducing molten glass to a glass forming device, the glass forming device comprising:

12. The method of claim 11, wherein the cross-sectional area of the channel changes between the inlet end and the compression end.

13. The method of claim 12, wherein the cross-sectional area of the channel decreases between the inlet end and the compression end.

14. The method of claim 13, wherein the width of the channel decreases between the inlet end and the compression end.

15. The method of claim 13, wherein the height of the channel decreases between the inlet end and the compression end.

16. The method of claim 11, wherein the top of the channel is a uniform distance from the trough bottom between the inlet end and the compression end.

17. The method of claim 11, wherein the top of the channel is a non-uniform distance from the trough bottom between the inlet end and the compression end.

18. The method of claim 11, wherein the atmosphere within the channel is maintained to be at least 2 psi lower than the atmosphere surrounding the glass forming device.

19. The method of claim 11, wherein the method further comprises operating a pressure reducing unit that is in fluid communication with the channel.

20. The method of claim 11, wherein the method further comprises operating a control unit that regulates that pressure of the atmosphere within the channel.

21. A glass sheet made by the method of claim 11.

22. An electronic device comprising the glass sheet of claim 21.