WO2013081827A1

WO2013081827A1 - Down-draw apparatus and methods for providing a clean glass -making environment

Info

Publication number: WO2013081827A1
Application number: PCT/US2012/065006
Authority: WO
Inventors: Robert Delia; Bulent Kocatulum; Shawn Rachelle Markham; Karl Patrick PFEIFER; Michael Andrew SCHROEDER
Original assignee: Corning Incorporated
Priority date: 2011-11-28
Filing date: 2012-11-14
Publication date: 2013-06-06
Also published as: CN104379517A; TW201326061A; JP2015508371A; CN104379517B; KR101854958B1; JP6165161B2; TWI588101B; KR20140105741A

Abstract

A down-draw glass making apparatus (10), for providing a clean glass-making environment, including an enclosure (12), a forming body (30) disposed within the enclosure, an inlet pipe (36) disposed so as to deliver molten glass to the forming body, and a conduit (40) having an outlet disposed so as to deliver fluid to the enclosure whereby the enclosure may be pressurized. The conduit is made of a material that itself does not generate particles causing onclusion formation, and is located at the same elevation as the forming body The enclosure may be a muffle chamber that includes a muffle door (20) at a bottom thereof and through which there exits glass formed by the forming body, wherein the outlet of the conduit is located within the muffle chamber and outside the muffle door. There may also be included a source of gas (44) connected to the conduit, wherein the source of gas is configured to deliver gas of an airborne particulate cleanliness class 100 or cleaner.

Description

DOWN-DRAW APPARATUS AND METHODS FOR PROVIDING A CLEAN

GLASS -MAKING ENVIRONMENT

BACKGROUND

[0001] This application claims the benefit of priority of US Provisional Application Serial No. 61/563,927 filed on November 28, 2011 the content of which is relied upon and incorporated herein by reference in its entirety.

Field

[0002] The present invention relates to apparatus and methods for making glass and, more particularly to apparatus and methods for making glass lengths by a down draw process.

Technical Background

[0003] The fusion process of sheet glass production has become a preferred method of forming glass due to its ability to produce exceptional glass surface quality. In the fusion process, glass overflows a forming body such that two separate molten streams fuse into one ribbon of glass and, in doing so, preserve the surface quality of both outer surfaces. The glass surface quality is of utmost importance for customers who use the glass to manufacture displays, for example, flat panel displays, Liquid Crystal Displays (LCDs), OLED displays, plasma displays, and field emission displays. Even small surface defects may cause retardation differences or other problems which the end user (a TV watcher, for example) may see as defect, a dark or light spot in the picture. Typical liquid crystal cell gaps are in the range of <5μιη, and so even a 1 μιη surface artifact results in a 20% change in the path length of the light from the surrounding areas. In extreme cases, surface defects could be large enough to bridge the cell gap completely, resulting in a short circuit. High quality LCD panels necessitate exceptional surface quality in the component glass. The effects of surface defects are extremely significant for large Gen size panels (for example Gen 8 and Gen 10) where even one defect could make the entire sheet unusable. One type of such glass defect is described as an "onclusion".

[0004] Onclusions are particulate type defects that attach to the surface of the molten glass during ribbon forming and may become partially embedded in the glass. Onclusion is a general term for the nature of the defect, and many root sources are possible. The fusion draw machine (FDM) for making glass is open at the bottom and air circulates up the draw freely. This air can carry particulate matter (that causes defects) upwards and onto the molten glass. In addition, general refractory components of the FDM itself could shed or become agitated by vapor or temperature thereby creating particulate matter which gets entrained in the air currents within the FDM or otherwise forms defects on the surface of the glass. All of these fit the onclusion category, and result in glass losses. Their location on the sheet surface makes onclusions a significant defect class.

[0005] Attempts have been made to reduce the amount of air floating up from the bottom of the FDM by the so-called chimney effect and, thereby, attempt to reduce the amount of onclusions. Generally, these attempts involve managing pressure in the FDM.

SUMMARY

[0006] The inventors have found that merely managing pressure within the FDM is not sufficient to maintain a low level of onclusions on the glass surface. In addition, the manner in which the pressure within the FDM is managed impacts the ability of pressurization to reduce onclusions while maintaining thickness control, i.e., low thickness variation across the width of the glass. Specifically, the inventors have found that pressurization while establishing a clean air environment within the FDM at the point where onclusions are likely to form is a robust and sustainable manner for attaining onclusion reduction. A clean air environment may be established within the FDM by appropriately selecting the equipment through which gas is delivered to pressurize the FDM, the quality of the gas itself in terms of the particulate matter contained therein, and the location of the gas delivery to the FDM, each of which impact the ability to reduce onclusions. The present disclosure is directed to apparatuses and methods for appropriately (i.e., while establishing a clean air environment) increasing the pressure within the FDM and, thereby, reducing onclusions while maintaining thickness control.

[0007] Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the various aspects as exemplified in the written description and the appended drawings. It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the various aspects, and are intended to provide an overview or framework to understanding the nature and character of the invention as it is claimed.

[0008] The accompanying drawings are included to provide a further understanding of principles of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain, by way of example, principles and operation of the invention. It is to be understood that various features disclosed in this specification and in the drawings can be used in any and all combinations. By way of non-limiting example the various features may be combined with one another as set forth in the following aspects:

[0009] According to a first aspect, there is provided a down-draw glass making apparatus comprising:

an enclosure;

a forming body disposed within the enclosure;

an inlet pipe disposed so as to deliver molten glass to the forming body; and a conduit having an outlet disposed so as to deliver fluid to the enclosure whereby the enclosure may be pressurized, wherein the conduit is made of a material that does not react or corrode at the temperatures in the FDM, up near the forming body.

[0010] According to a second aspect, there is provided the apparatus according to aspect 1, wherein the conduit is made of ceramic, glass-ceramic, glass, platinum, iridium, palladium, rhodium, or nickel.

[0011] According to a third aspect, there is provided the apparatus according to aspect 1 or aspect 2, further comprising a source of gas connected to the conduit, wherein the source of gas is configured to deliver gas of an airborne particulate cleanliness class 100 or cleaner.

[0012] According to a fourth aspect, there is provided the apparatus according to any one of aspects 1 -3, wherein the conduit is located at the same elevation as the forming body.

[0013] According to a fifth aspect, there is provided the apparatus according to any one of aspects 1 to 4, wherein the enclosure is a muffle chamber that includes a muffle door at a bottom thereof and through which there exits glass formed by the forming body, wherein the outlet of the conduit is located within the muffle chamber and outside the muffle door.

[0014] According to a sixth aspect, there is provided the apparatus according to aspect 5, wherein the muffle door includes a front plate facing the root, wherein the front plate is made of a material having high thermal conductivity, and further comprising a muffle door chamber disposed on a side of the front plate opposite that on which the root is disposed.

[0015] According to a seventh aspect, there is provided a method of making a length of glass comprising:

flowing molten glass over a forming body, disposed within an enclosure, so as to flow downwardly therefrom in the form of a ribbon;

delivering fluid through a conduit to the enclosure so as to pressurize the enclosure, wherein the conduit is made of a material that does not react or corrode at the temperatures in the FDM, up near the forming body; flowing the ribbon out of the enclosure; and

cutting the ribbon to form a length of glass.

[0016] According to an eighth aspect, there is provided the method of aspect 7, wherein the conduit is made of ceramic, glass-ceramic, glass, platinum, iridium, palladium, rhodium, or nickel.

[0017] According to a ninth aspect, there is provided the method of aspect 7 or aspect 8, wherein the fluid is gas of an airborne particulate cleanliness class 100 or cleaner.

[0018] According to a tenth aspect, there is provided the method of any one of aspects 7 to 9, further comprising delivering the fluid at the elevation of the forming body.

[0019] According to an eleventh aspect, there is provided the method of any one of aspects 7 to 10, wherein the enclosure is a muffle chamber having a muffle door through which he ribbon exits the muffle chamber, and further comprising delivering the fluid within the muffle chamber and outside the muffle door.

[0020] According to a twelfth aspect, there is provided the method of aspect 1 1, wherein the muffle door includes a front plate facing the root, wherein the front plate is made of a material having high thermal conductivity, further comprising a muffle door chamber disposed on a side of the front plate opposite that on which the root is disposed.

[0021] According to a thirteenth aspect, there is provided a down-draw glass making apparatus comprising:

an enclosure;

a forming body disposed within the enclosure;

an inlet pipe disposed so as to deliver molten glass to the forming body; and a conduit having an outlet disposed so as to deliver fluid to the enclosure whereby the enclosure may be pressurized; and

a source of gas connected to the conduit, wherein the source of gas is configured to deliver gas of an airborne particulate cleanliness class 100 or cleaner.

[0022] According to a fourteenth aspect, there is provided the apparatus according to aspect 13, wherein the conduit is located at the same elevation as the forming body.

[0023] According to a fifteenth aspect, there is provided the apparatus according to aspect 13 or aspect 14, wherein the enclosure is a muffle chamber that includes a muffle door at a bottom thereof and through which there exits glass formed by the forming body, wherein the outlet of the conduit is located within the muffle chamber and outside the muffle door.

[0024] According to a sixteenth aspect, there is provided a method of making a length of glass comprising: flowing molten glass over a forming body, disposed within an enclosure, so as to flow downwardly therefrom in the form of a ribbon;

delivering fluid through a conduit to the enclosure so as to pressurize the enclosure, wherein the fluid is gas of an airborne particulate cleanliness class 100 or cleaner;

flowing the ribbon out of the enclosure; and

cutting the ribbon to form a length of glass.

[0025] According to a seventeenth aspect, there is provided the method of aspect 16, further comprising delivering the fluid at the elevation of the forming body.

[0026] According to an eighteenth aspect, there is provided the method of aspect 16 or aspect 17, wherein the enclosure is a muffle chamber having a muffle door through which he ribbon exits the muffle chamber, and further comprising delivering the fluid within the muffle chamber and outside the muffle door.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a schematic illustration of a fusion draw machine.

[0028] FIG. 2 is a schematic illustration of a relationship between the number of onclusions and the amount of pressure in the muffle enclosure.

[0029] FIG. 3 is a schematic illustration of a relationship between the amount of thickness variation and the pressure in the muffle door.

[0030] FIG. 4 is a schematic illustration of a glass making apparatus.

DETAILED DESCRIPTION

[0031] In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth to provide a thorough understanding of various principles of the present invention. However, it will be apparent to one having ordinary skill in the art, having had the benefit of the present disclosure, that the present invention may be practiced in other embodiments that depart from the specific details disclosed herein. Moreover, descriptions of well-known devices, methods and materials may be omitted so as not to obscure the description of various principles of the present invention. Finally, wherever applicable, like reference numerals refer to like elements.

[0032] Directional terms as used herein— for example up, down, right, left, front, back, top, bottom— are made only with reference to the figures as drawn and are not intended to imply absolute orientation.

[0033] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; the number or type of embodiments described in the

specification.

[0034] As used herein, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a "component" includes aspects having two or more such components, unless the context clearly indicates otherwise.

[0035] The present disclosure is directed toward apparatuses and methods for pressurization while establishing a clean air environment within a fusion draw machine (FDM) at the point where onclusions are likely to form, and that provide a robust and sustainable manner for attaining onclusion reduction.

[0036] One manner of establishing a clean air environment in the FDM involves the delivery of gas through equipment that itself will not generate particles that will form onclusions. This may be done by an appropriate choice of material for the conduit through which the gas is delivered to the FDM so as to pressurize an area of the FDM. The entire conduit need not be made of such a material, as long as the fluid-delivery lumen thereof is made of such a material. The inventors have found that a conduit made of high-melting-point material that, when in contact with nitrogen or oxygen rich fluid sources, does not react, degrade, or corrode— which would lead to particle generation— at the temperatures typically found in the FDM, up near the forming body, e.g. 900-1300 degrees C, is well suited to delivering gas without itself generating particles that lead to onclusions. For example, the conduit may be made of ceramic, glass-ceramic, or glass. Also, the conduit may be made of metals, like platinum, iridium, rhodium, palladium, or nickel, for example.

[0037] A second manner of establishing a clean air environment in the FDM involves the use of gas that itself does not include a high amount of particles that lead to onclusions. The inventors have found that gas meeting an airborne particulate cleanliness class of 100 (M3.5) or cleaner, as measured by US Federal Standard 209E entitled "Airborne Particulate

Cleanliness Classes" (available from the Institute of Environmental Sciences and

Technology, 940 East Northwest Highway, Mount Prospect, IL, 60056, USA), is suitable for increasing pressure within the FDM while itself not being a source of particles that lead to onclusions. [0038] A third manner of establishing a clean air environment in the FDM involves the location at which the gas is delivered to the FDM. More specifically, the inventors have found that delivering the gas to the FDM at the level of the forming body, in the muffle chamber, but outside of the muffle door, leads to low levels of onclusions.

[0039] One embodiment of a fusion draw machine (FDM) that includes a clean air environment will be explained with reference to FIG. 1. The FDM 10 includes an upper enclosure or muffle chamber 12 wherein a glass ribbon 4 is formed, and a lower enclosure 14 through which the glass ribbon 4 is pulled and thermally conditioned until exiting the FDM 10 at a lower opening 16. A glass sheet 8 is then separated from the lower end of the ribbon 4 using techniques known in the art. Although a sheet 8 is shown as being separated from the ribbon 4, instead, any length of the ribbon 4 may be formed before being separated from the remainder of the ribbon 4 as, for example, when the glass is rolled. Thus, it is to be understood that "glass sheet" is used through the specification for convenience of reference only, and that such term may also include lengths of glass that are rolled.

[0040] The muffle chamber 12 surrounds a forming body 30 that forms the glass ribbon 4. The forming body 30 receives molten glass from an inlet pipe 36. The glass flows over opposite converging sides 32 of the forming body 30 in two separate flows that recombine at the root 34 of the forming body 30 to form the glass ribbon 4 having a thickness 6.

[0041] A pair of muffle door housings 20 is located at the bottom of the muffle chamber 12, and is used to control variations in thickness 6 across the glass ribbon 4, i.e., in a direction into and out of the plane of FIG. 1. One muffle door housing 20 is disposed on each side of the ribbon 4, whereby the muffle door housings 20 form an opening through which the glass ribbon 4 extends to the lower enclosure 14. The muffle door housings 20 have the same structure and, therefore, only one will be described in detail. Similarly, various principles may be explained in connection with one of the shown muffle door housings 20, with the understanding that those same principles may apply equally to the other muffle door housing 20. The muffle door housing 20 is disposed so as to face the forming body 30, and the glass ribbon 4 when the glass ribbon 4 has a viscosity above its softening point. The muffle door housing 20 includes a front plate 22, a muffle door chamber 24, and a plurality of tubes 26. Each of the tubes 26 includes an outlet within the muffle door chamber 24.

[0042] The front plate 22 is formed of a material having high conductivity, low thermal expansion, and a high emissivity constant with time and temperature. Preferably the front plate 22 is formed of a silicon carbide slab and the back surface thereof, except for the bounding borders, is free from contact with any supporting structure which would cause thermal discontinuity across the face of the slab.

[0043] A fluid source 28 is coupled so as to deliver fluid to the tubes 26. Although only one tube 26 is shown on either side of the forming body 30, typically there will be a plurality of tubes 26 disposed along the width direction of the glass ribbon 4; any suitable number of tubes 26 may be employed on each side of the forming body 30, wherein the number generally depends upon the width of the glass ribbon 4. The fluid may be air, compressed air, any other suitable gas, for example. Throughout the specification, the term "air" or "airflow" is used for convenience but is meant to include all suitable types of gas or other fluid. The fluid is delivered from the fluid source 28, through the tubes 26, and into the muffle door chamber 24 so as to impinge on and locally control the temperature of the front plate 22. The local temperature of a spot on the front plate 22 then influences the temperature, and thus viscosity and accordingly thickness, of an adjacent portion of the glass ribbon 4. The flow of fluid through each tube 26 may be individually regulated, in a manner known in the art, to control the thickness gradient across the ribbon 4.

[0044] Within the lower enclosure 14, there are various structures used to move and/or guide the glass ribbon 4 in a downward direction, although these structures are not shown, for purposes of simplification in illustration. Also, there may be various other structures present in enclosure 14 for thermally conditioning the ribbon 4, or controlling heat loss from the ribbon 4 as it moves through the enclosure 14.

[0045] Within both the muffle chamber 12 and the lower enclosure 14, there are various openings that allow air to leak from the FDM 10. These openings may include intended openings— for electrical connection, for fluid connection, for entry and/or access to the equipment within the FDM 10, for water cooling ports, for resistance heaters, for coil windings for thermo couples, and/or for tubes 26, for example— and/or unintended cracks or holes. Even when seals are provided for the devices inserted through the intended openings, there may still be leaks in the seal allowing flow out of the FDM 10. Because of the air leaking from the FDM 10, as well as thermal gradients within the FDM 10 itself, there is a current that flows upward in the direction of arrow 13. This current draws air through the bottom opening 16, and may carry with it particles, either from the area outside of the FDM 10, or from particle generation sources within the lower enclosure 14. If the particles travel up through the FDM 10 to the area of the muffle door housings 20, they may stick to or otherwise embed within the glass ribbon 4 thereby forming onclusions as explained above. It is thus desirable to minimize the upward current in the FDM 10, especially in the area of the muffle door housings 20.

[0046] One manner of minimizing the current in the FDM 10, especially in the region of the muffle door housings 20, is to pressurize the muffle chamber 12. However, to reduce onclusions, it is not enough to merely pressurize the muffle chamber 12. Additionally, a clean air environment should be established. A pressurized clean air environment may be established within the muffle chamber 12 by appropriately selecting: the equipment through which gas is delivered to pressurize the muffle chamber 12; the quality of the gas itself; and the location of the gas delivery, each of which impact the ability to reduce onclusions.

[0047] One manner of establishing a clean air environment in the FDM involves the delivery of gas through equipment that itself will not generate particles that will form onclusions. This may be done by an appropriate choice of material for the conduit through which the gas is delivered to the FDM so as to pressurize an area of the FDM. The entire conduit need not be made of such a material, as long as the fluid-delivery lumen thereof is made of such a material. The inventors have found that a conduit made of high-melting-point material that, when in contact with nitrogen or oxygen rich fluid sources, does not react, degrade, or corrode— which would lead to particle generation— at the temperatures typically found in the FDM, up near the forming body, e.g. 900-1300 degrees C, is well suited to delivering gas without itself generating particles that lead to onclusions. For example, the conduit may be made of ceramic, glass-ceramic, or glass. Also, the conduit may be made of metals, platinum, iridium, rhodium, palladium, or nickel, for example. As a practical matter, the melting point of the material should be chosen to be higher than the highest expected temperature in the FDM; but this requirement is a minimum. In addition, as noted above, the material chosen should be one that does not react, degrade, or corrode when in contact with nitrogen or oxygen rich fluid sources, as such reaction, degradation, or corrosion, will generate particles that lead to onclusion formation. By using a conduit that itself does not generate particles that will form onclusions, the equipment for conditioning and/or filtering the fluid (to make sure that the fluid does not include particles that lead to onclusion formation) to be delivered can be disposed outside of the high-temperature environment of the FDM. Not only does this lead to longer equipment life, but such makes it easier to perform maintenance service on that equipment.

[0048] With reference to FIG. 1, according to one embodiment, a conduit 40 having an outlet 42 extends into the muffle chamber 12. The other end of the conduit 40 is disposed outside of the high-temperature environment within the FDM. The outlet 42 is disposed within the muffle chamber 12 so as to deliver gas from a fluid source 44. The conduit 40 may be made of ceramic, glass-ceramic, glass, platinum, iridium, rhodium, palladium, or nickel, for example. Although only one conduit 40 is shown on each side of the forming body 30, any suitable number of such conduits may be used to achieve the desired pressurization of muffle chamber 12. The conduits 40 may be disposed at various points along the width direction (extending perpendicular to the plane of FIG. 1) of the muffle chamber 12. Additionally, the conduits 40 may be disposed at the ends of the muffle chamber, i.e., so as to extend in a direction parallel to the width of the muffle chamber 12. The gas delivered into the muffle chamber 12 pressurizes the muffle chamber 12 whereby there is reduced the effect of the updraft current in the direction of arrow 13 and, accordingly, the chance that particles in that updraft will form onclusions on the glass ribbon 4. Moreover, because the equipment used to deliver the pressurizing air, i.e., conduit 40 made of a material that does not itself generate particles that would form onclusions, there is formed a clean air environment within the muffle chamber 12.

[0049] A second manner of establishing a clean air environment in the FDM involves pressurizing the FDM with gas that itself does not include a high amount of particles that lead to onclusions. The inventors have found that gas meeting an airborne particulate cleanliness class of 100 (M3.5) or cleaner, as measured by US Federal Standard 209E, is suitable for increasing pressure within the FDM while itself not being a source of particles that lead to onclusions. Fluid source 44 is configured to deliver gas of the stated cleanliness (i.e. having an airborne particulate cleanliness class of 100 (M3.5) or cleaner) to conduit 40. Fluid source 44 may be, for example, an air compressor, pump, fan, blower, or other air handler, having high efficiency particle attraction (HEP A) filtration of a sufficient degree on its output so as to deliver air of the stated cleanliness. Alternatively, if gas of suitable cleanliness is readily available, the fluid source 44 need not include filtration on its output. Although a fluid source 44 is shown as being connected to only one conduit 40, one such fluid source 44 may be connected to as many conduits 40 as practical to deliver the desired amount of pressurized gas to the muffle chamber 12. For example, one fluid source 44 may be connected to conduits 40 on both sides of the forming body 30. Further, although the fluid source 44 is shown as being separate from the fluid source 28, such need not be the case. That is, a fluid source 44 may be connected to both conduits 40 and tubes 26.

[0050] A third manner of establishing a clean air environment in the FDM involves the location at which the pressurizing gas is delivered to the FDM. More specifically, the inventors have found that delivering the gas to the FDM near the same elevation as that of the forming body, in the muffle chamber, but outside of the muffle door chamber, leads to low levels of onclusions.

[0051] According to one aspect of the third manner of establishing a clean air environment, with reference to FIG. 1, the conduit 40 is disposed so that outlet 42 is positioned at substantially the same elevation within the FDM 10 as is the forming body 30. That is, the forming body 30 is disposed within the FDM 10 at an elevation above the lower opening 16. Supplying air at the elevation of the forming body 30 increases the pressure near the root 34 and sides 32, whereby there is minimized the amount of particles reaching the glass at a point wherein the particles may form onclusions on the glass surface.

[0052] According to another aspect of the third manner of establishing a clean air environment, again with reference to FIG. 1, the outlet 42 is disposed inside of the muffle chamber 12, but outside of the muffle door chamber 24.

[0053] Supplying air into the muffle door chamber 24 in an attempt to pressurize the muffle chamber 12 is not desirable. In particular, as the total volume of air is increased in the muffle door housing 20, the pressure in the muffle chamber 12 is increased, which helps to reduce onclusion levels, as schematically shown in FIG. 2. However, the additional air supplied into the muffle door housing 20 leads to a pressure increase in the muffle door chamber 24, whereby air leaks out towards the glass ribbon 4 in an uncontrolled manner resulting in localized thickness variation, as shown schematically in FIG. 3. That is, thickness variation is negatively impacted when pressure inside the muffle door housing 20, i.e., within muffle door chamber 24, is used to increase total pressure within the muffle chamber 12. On the other hand, when the muffle door chamber 24 was actively evacuated to prevent air from leaking toward the ribbon 4, an increase in the level of onclusions was observed. Thus, to increase pressure within the muffle chamber 12 (to reduce onclusions) without increasing the pressure inside the muffle door housing 20 (which leads to undesirable thickness variations), air may be supplied inside the muffle chamber 12 but outside of the muffle door chamber 24. Additionally, this location— inside the muffle chamber, but outside the muffle door housing— minimizes the impact on other airflow cells within the muffle.

[0054] In order to retro-fit existing FDMs to practice the concepts described herein, existing tubes 26 that are unneeded for thickness control may be used to assist in reducing onclusions according to the above-described concepts. Particularly, tubes 26 may be retracted from their original positions so that their outlets are outside of muffle door chamber 24, yet still within muffle chamber 12. Then, fluid from source 28 may be delivered to the muffle chamber 12 so as to increase the pressure therein. Additionally, instead of using fluid from source 28, a fluid source 44 (i.e., one that delivers air of an airborne particle cleanliness class of 100 or cleaner) may be connected to such existing tubes 26 that have had their outlets outside of the muffle door chamber 24 yet still within muffle chamber 12. With such an arrangement, air having an airborne particulate cleanliness class of 100 or cleaner may be delivered to the muffle chamber 12. Accordingly, existing tubes 26 may be used to assist in creating a clean environment within the FDM 10.

[0055] A method of making glass sheets 8, utilizing the concepts described herein will now be described.

[0056] FIG. 4 illustrates an exemplary glass manufacturing system 100 that uses a fusion process, and in which the above-described concepts may be used to make glass sheets 8. The glass manufacturing system includes a melting vessel 1 10, a fining vessel 1 15 (e.g., finer tube), a mixing vessel 120 (e.g., stir chamber), a delivery vessel 125 (e.g., bowl), and an FDM 10. Glass materials are introduced into a melting vessel 1 10 as shown by arrow 1 12 and melted to form molten glass 126. The fining vessel 1 15 includes a high temperature processing area that receives the molten glass 126 (not shown at this point) from the melting vessel 1 10 and in which bubbles are removed from the molten glass 126. The fining vessel 1 15 is connected to the mixing vessel 120 by a connecting tube 122. The mixing vessel 120 is connected to the delivery vessel 125 by connecting tube 127. The delivery vessel 125 delivers the molten glass 126 through a down-comer 130 into the FDM 10 which includes an inlet 36, a forming body 30, and a pull roll assembly 140. The molten glass flows from the down- comer 130 into inlet 36 which leads to the forming body 30. The forming body 30 includes a trough that receives the molten glass 126 which then overflows and runs down two sides 32 of the forming body 30 before fusing together at the root 34. The root 34 is where the two sides 32 join together and where the two overflows or walls of molten glass 126 rejoin (e.g., refuse) to form the glass ribbon 4 which is drawn downward by the pull roll assembly 140. The details of the FDM 10 are as explained above in connection with FIG. 1. It should be noted that while certain details of an exemplary glass manufacturing system are described, forming bodies and glass manufacturing systems are known in the art and one of ordinary skill could readily select an appropriate forming body and/or glass manufacturing system.

[0057] Referring back to FIG. 1, as the molten glass is being delivered to the forming body 30, a clean air environment is established within the FDM 10 by appropriately pressurizing an area within the FDM 10 so as to reduce the chances of particles reaching the glass at a point where the particles may form onclusions. Specifically, any one or more of the following concepts may be used, either alone or in any and all combinations, to create such a clean air environment within the FDM: gas can be delivered to the FDM 10, so as to pressurize the FDM 10, via a conduit 40 that is made of low particulate emitting material (i.e., one that, when in contact with nitrogen or oxygen rich fluid sources, does not react, degrade, or corrode, at the temperatures typically found in the FDM near the forming body - 900 to 1300 degrees C), for example, ceramic, glass-ceramic, glass, platinum, iridium, rhodium, palladium, or nickel; gas may be delivered to the FDM 10 at the same elevation as that of the forming body 30 so as to pressurize the FDM 10; gas may be delivered to the muffle chamber 12, but outside of the muffle door enclosure 24, so as to pressurize the FDM 10; and the gas delivered to the FMD 10 may be of an airborne particulate cleanliness class of 100 or cleaner.

[0058] It should be emphasized that the above-described embodiments of the present invention, particularly any "preferred" embodiments, are merely possible examples of implementations, merely set forth for a clear understanding of various principles of the invention. Many variations and modifications may be made to the above-described embodiments of the invention without departing substantially from the spirit and various principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.

[0059] For example, although the above description is made in terms of a fusion draw, a slot- draw forming body could be used as the forming body 30.

Claims

What is Claimed is:

1. A down-draw glass making apparatus comprising:

an enclosure;

a forming body disposed within the enclosure;

an inlet pipe disposed so as to deliver molten glass to the forming body; and a conduit having an outlet disposed so as to deliver fluid to the enclosure whereby the enclosure may be pressurized, wherein the conduit is made of a material that, when in contact with nitrogen or oxygen rich fluid sources, does not react, degrade, or corrode at temperatures in the range of 900-1300 degrees C.

2. The apparatus according to claim 1, wherein the conduit is made of ceramic, glass- ceramic, glass, platinum, iridium, rhodium, palladium, or nickel.

3. The apparatus according to claim 1 or claim 2, further comprising a source of gas connected to the conduit, wherein the source of gas is configured to deliver gas of an airborne particulate cleanliness class 100 or cleaner.

4. The apparatus according to any one of claims 1-3, wherein the conduit is located at the same elevation as the forming body.

5. The apparatus according to any one of claims 1 to 4, wherein the enclosure is a muffle chamber that includes a muffle door at a bottom thereof and through which there exits glass formed by the forming body, wherein the outlet of the conduit is located within the muffle chamber and outside the muffle door.

6. The apparatus according to claim 5, wherein the muffle door includes a front plate facing the root, wherein the front plate is made of a material having high thermal conductivity, and further comprising a muffle door chamber disposed on a side of the front plate opposite that on which the root is disposed.

7. A method of making a length of glass comprising:

delivering fluid through a conduit to the enclosure so as to pressurize the enclosure, wherein the conduit is made of a material that, when in contact with nitrogen or oxygen rich fluid sources, does not react, degrade, or corrode at temperatures in the range of 900-1300 degrees C;

flowing the ribbon out of the enclosure; and

cutting the ribbon to form a length of glass.

8. The method of claim 7, wherein the conduit is made of ceramic, glass-ceramic, glass, platinum, iridium, palladium, rhodium, or nickel.

9. The method of claim 7 or claim 8, wherein the fluid is gas of an airborne particulate cleanliness class 100 or cleaner.

10. The method of any one of claims 7 to 9, further comprising delivering the fluid at the elevation of the forming body.

1 1. The method of any one of claims 7 to 10, wherein the enclosure is a muffle chamber having a muffle door through which he ribbon exits the muffle chamber, and further comprising delivering the fluid within the muffle chamber and outside the muffle door.

12. The method of claim 11, wherein the muffle door includes a front plate facing the root, wherein the front plate is made of a material having high thermal conductivity, further comprising a muffle door chamber disposed on a side of the front plate opposite that on which the root is disposed.

13. A down-draw glass making apparatus comprising:

an enclosure;

a forming body disposed within the enclosure;

14. The apparatus according to claim 13, wherein the conduit is located at the same elevation as the forming body.

15. The apparatus according to claim 13 or claim 14, wherein the enclosure is a muffle chamber that includes a muffle door at a bottom thereof and through which there exits glass formed by the forming body, wherein the outlet of the conduit is located within the muffle chamber and outside the muffle door.

16. A method of making a length of glass comprising:

flowing the ribbon out of the enclosure; and

cutting the ribbon to form a length of glass.

17. The method of claim 16, further comprising delivering the fluid at the elevation of the forming body.

18. The method of claim 16 or claim 17, wherein the enclosure is a muffle chamber having a muffle door through which he ribbon exits the muffle chamber, and further comprising delivering the fluid within the muffle chamber and outside the muffle door.