WO2012148411A1

WO2012148411A1 - Apparatus and method for purging contaminants from a glass making system

Info

Publication number: WO2012148411A1
Application number: PCT/US2011/034481
Authority: WO
Inventors: David M. Lineman; Matthew C. Morse; Steven R. Moshier
Original assignee: Corning Incorporated
Priority date: 2011-04-29
Filing date: 2011-04-29
Publication date: 2012-11-01

Abstract

A purging apparatus is disclosed for varying a level of molten glass in a glass making system, thereby purging molten glass contaminated with condensed particulate, such as platinum or platinum alloy particulate, from a standpipe connected with a vessel or conduit for holding or conveying molten glass, or from the vessel itself. The purging apparatus, comprising nested tubes and sealing gaskets, is inserted into the standpipe and sealed thereto, and a pressurized gas may be forced into the standpipe through the purging apparatus. The increased pressure in the standpipe forces the contaminated molten glass from the standpipe into the vessel or conduit so that it can be removed, such as by flowing through and out of the glass making system. The apparatus may also be used to apply a vacuum to the standpipe, wherein the decreased pressure in the standpipe or vessel increases a level of the molten glass to wash contaminants from the system.

Description

APPARATUS AND METHOD FOR PURGING CONTAMINANTS

FROM A GLASS MAKING SYSTEM BACKGROUND FIELD

[0001] The present invention related to a method for purging contaminated glass from a glass making system by varying the level of molten glass in the glass making system.

TECHNICAL BACKGROUND

[0002] In the manufacture of optical quality glass, such as glass for display applications, the batch material is melted in a refractory furnace and the resultant molten glass material is then transported to the forming machine through high temperature resistant metal conduits. These conduits are often formed from a platinum group metal, for example, platinum or a platinum alloy such as platinum-rhodium. Certain conduits or vessels contain molten glass having a free surface. Examples include finers for fining the molten glass (e.g. removing gaseous inclusions) and molten glass stirring apparatus. These vessels and/or conduits may include a vent pipe in fluid communication with the atmosphere above the molten glass free surface. Additionally, other vessels and/or conduits may be completely filled with molten glass, but include a standpipe to provide access to the molten glass, such as for determining a level of the molten glass.

[0003] As those skilled in the art of glass making know, molten glass has a tendency to release gases resulting from the volatilization of the molten glass constituent. For example, boron (e.g. boron oxide), is a common glass constituent that vaporizes readily. However, such volatilized materials are not limited to the glass materials themselves, but may include portions of the glass making system itself. For example, platinum (or alloys thereof) from the transport system conduits and/or vessels can also be volatilized. Such volatilized materials, either from the glass or from the glass making apparatus can condense on surfaces in the glass making system that are exposed to a free surface of the molten glass. Such surfaces include portions of the interior surface of the level probe standpipe. Contaminants can also come from wear products that fall into the molten glass. However, in the absence of mechanisms to dislodge or remove such contaminants (e.g. condensates) that find their way onto the inside surface of the vessel or standpipe, these condensates tend to remain attached to the surfaces thereof. On the other hand, because the temperature at the surface of the molten glass in a standpipe is stagnant and therefore likely cooler than the temperature in the bulk molten glass flowing through the conduit to which the standpipe is attached, volatilized materials have a tendency to condense on the surface of the molten glass as well as the standpipe itself. And, since the molten glass in the standpipe is essentially static, the condensates or other contaminants, and in particular the platinum condensates, tend to accumulate. In time, these contaminants can accumulate to the point where they are unexpectedly released into the flow of molten glass and find their way to the finished product as defects. To prevent such unexpected release, the contaminants must be flushed from the glass making system.

[0004] The current method of flushing contaminants from the glass making system, and in particular standpipes and vent tubes, is to reduce the level of molten glass throughout the system by reducing the addition of batch materials into the furnace so that the inflow of materials is less than the outflow of molten glass from the system. The level of molten glass in the vessel and/or standpipe is thereby lowered. The lowered level of molten glass in the vessel, and in particular a standpipe and/or vent tube, allows contaminated glass from the standpipe and/or vent pipe to become entrained in the glass flow and pass through the system. However, reducing the level of molten glass throughout the system in this manner requires significant time.

SUMMARY OF THE INVENTION

[0005] Although dislodged molten glass constituents may melt back into the glass composition, other dislodged contaminants, like platinum or platinum alloy condensates, are carried through the glass making system and end up in the final product. For optical quality glass, such as display glass, such inclusions, are unacceptable. Current methods of cleaning a vessel and/or standpipe involve reducing the level of the molten glass throughout the glass making system. Lowering the molten glass level and reestablishing the proper operating level of molten glass can take many days. Glass resulting from the cleaning process is typically high in inclusions and therefore unusable. In addition, there are frequently blisters generated for days or weeks after completing such a procedure. Lowering the glass level through the whole melting system is a drastic procedure solely to purge glass from such a small tube. Also, the current technique for purging the level probe standpipe is so expensive that it is typically only performed in cases where platinum inclusion levels are extremely high and cannot be fixed by any other method. Any procedure that accomplishes the same task in less time can save significant revenue in lost glass. In addition, a less costly technique might be used more often and give process engineers another tool for increasing glass product yields.

[0006] In other circumstances it may be desirable to increase the level of molten glass in a vessel, such as a vessel including a free surface of molten glass (and therefore a gaseous atmosphere above the free surface) to wash the inside surfaces of the vessel with the molten glass. In this instance, a vacuum can be applied through the standpipe to the vessel, wherein the negative pressure (relative to ambient air pressure) will cause the level of molten glass in the vessel (or the standpipe) to rise. Increasing and decreasing the level of molten glass can be practiced together (sequentially), in any order, to wash the inside surfaces of a vessel, conduit, standpipe or vent tube as needed. Although the exemplary case of a standpipe connected to a conduit is described below, wherein molten glass is flowing through the conduit, the present invention is equally applicable to a vent tube, and may also generally include a vessel having little or no flow of molten glass therethrough in place of a conduit.

[0007] Accordingly, in one embodiment, an apparatus for purging contaminants from a glass making system is disclosed comprising a first tube comprising a passage extending through at least a portion of the first tube and further comprising a threaded portion. A collar is engaged with the threaded portion. The apparatus further comprises a second tube comprising a passage extending between a first end and a second end of the second tube, the second tube further comprising a first flange attached to the first end of the second tube and a second flange attached to the second end of the second tube. The first tube is positioned within the passage of the second tube and a washer is positioned around the second tube and between the second flange and the collar. A first gasket is positioned between the first flange and a third flange attached to the first tube. The apparatus may be used, for example, to purge molten glass from a standpipe or vessel by lowering a level of the molten glass in the standpipe or vessel. Alternatively, the apparatus may be used to apply a vacuum to the standpipe and/or the vessel, to increase a level of the molten glass in the standpipe or the vessel. The apparatus is generally referred to as a purging apparatus, as the apparatus is used to purge contaminated material from the glass making system. [0008] The apparatus may further comprise a second gasket positioned between the second flange and the washer. In some embodiments, a face of the first flange makes an angle of between 0 degrees and 70 degrees relative to a plane perpendicular to the second tube. In other embodiments a face of the first flange makes an angle of between 5 degrees and 20 degrees relative to a plane perpendicular to the second tube.

[0009] The first tube preferably comprises an output port positioned on a side of the first tube for exhausting a gas from the first tube, and in some embodiment the first tube may comprise a plurality of output ports configured to exhaust a gas from a side of the first tube. Alternatively, a vacuum may be applied to the first tube, wherein gas is drawn into the first tube from the standpipe through the output port or ports.

[0010] The apparatus may optionally further comprise a heat shield attached to an end of the first tube.

[0011] In another embodiment, a method of purging contaminants from a standpipe is disclosed comprising providing a vessel connected to the standpipe, the vessel and the standpipe containing a molten glass material. An end of a purging apparatus is inserted into the standpipe. The purging apparatus comprises a first tube comprising a passage extending through at least a portion of the first tube and further comprising a threaded portion, a collar engaged with the threaded portion, a second tube comprising a passage extending between a first end and a second end of the second tube, and wherein the first tube is positioned within the passage of the second tube. The second tube further comprises a first flange attached to the first end of the second tube and a second flange attached to the second end of the second tube and a first gasket positioned between the first flange and a third flange attached to the first tube. The method further comprises rotating the collar engaged with the threaded portion of the first tube to compress the first gasket and press the first gasket against an interior surface of the standpipe. A pressurized gas is flowed into the standpipe through the purging apparatus to increase a pressure in the standpipe between the molten glass material and the first gasket, thereby decreasing a level of the molten glass material in the standpipe. The first gasket may be, for example, a fibrous ceramic material.

[0012] The method may further comprise a washer positioned between the second flange and the collar and a second gasket positioned between the second flange and the washer. Rotating the collar engaged with the threaded portion of the first tube compresses the second gasket and seals an end of the second tube. The pressurized gas preferably comprises nitrogen or argon, and may, for example be air. Generally, the gas is preferably non- combustible. Preferably, a pressure inside the standpipe while flowing the pressurized gas is equal to or greater than 500 Pa and equal to or less than 2700 Pa.

[0013] The pressurized gas may be flowed into the standpipe in a direction toward the molten glass material. However, the pressurized gas is preferably flowed into the standpipe at an angle that is perpendicular to a side of the first tube to prevent excessive cooling of the molten glass material. Preferably, the pressurized gas is flowed into the standpipe through a plurality of outlet ports.

[0014] In some embodiments, a face of the first flange makes an angle equal to or greater than 5 degrees and equal to or less than 20 degrees relative to a plane perpendicular to a longitudinal axis of the second tube.

[0015] In some embodiments, the vessel is a conduit and molten glass material flows through the conduit. Preferably, the standpipe comprises a platinum group metal, including platinum, rhodium, iridium, ruthenium, palladium, osmium, and alloys thereof.

[0016] In still another embodiment, a method of varying a level of molten glass material in a standpipe or vessel is described comprising providing a vessel connected to a standpipe, the vessel containing the molten glass material, and inserting an end of a purging apparatus in the standpipe. The purging apparatus comprises a first tube comprising a passage extending through at least a portion of the first tube and further comprising a threaded portion, a collar engaged with the threaded portion, a second tube comprising a passage extending between a first end and a second end of the second tube, and wherein the first tube is positioned within the passage of the second tube. The second tube further comprises a first flange attached to the first end of the second tube and a second flange attached to the second end of the second tube and a first gasket positioned between the first flange and a third flange attached to the first tube. The method further comprises rotating the collar engaged with the threaded portion to compress the first gasket and press the first gasket against an interior surface of the standpipe, and flowing a gas through the first tube to vary a level of the molten glass material. The purging apparatus may further comprise a washer positioned between the second flange and the collar and a second gasket positioned between the second flange and the washer. Rotating the collar engaged with the threaded portion compresses the second gasket and seals an end of the second tube. If gas is flowed into the standpipe, in some embodiments the gas is a pressurized gas flowed in a direction toward the molten glass material. Preferably, the gas is non-combustible and can be for example, air, nitrogen, argon, or other inert or non-flammable gases or gaseous mixtures. A pressure inside the standpipe while flowing the gas is preferably equal to or greater than 500 Pa and equal to or less than 2700 Pa. Alternatively, the pressurized gas can be flowed into the standpipe at an angle that is perpendicular to a side of the first tube to prevent excessive cooling of the molten glass material. In some embodiments the gas is flowed into the standpipe through a plurality of outlet ports in the first tube. Preferably, a face of the first flange makes an angle equal to or greater than 5 degrees and equal to or less than 20 degrees relative to a plane perpendicular to a longitudinal axis of the second tube.

[0017] In another embodiment, a vacuum can be applied to first tube such that gas is withdrawn from the standpipe through first tube (e.g. through the outlet port or ports). In this instance the gas may be air containing, for example, various volatilized materials such as boron or platinum.

[0018] Additional features and advantages of the invention 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 invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0019] It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and constitute a part of this specification. The drawings illustrate various embodiments of the invention and, together with the description, serve to explain the principles and operations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a perspective view of a portion of a conduit or vessel for holding or transporting a molten glass;

[0021] FIG. 2 is a cross sectional view of the conduit and standpipe of FIG. 1 showing a portion of a purging apparatus installed in the standpipe; [0022] FIG. 3 is a side view of a purging apparatus according to an embodiment of the present invention;

[0023] FIG. 4 is a cross sectional view of the embodiment of FIG. 3;

[0024] FIG. 5 is a side view of another embodiment of a purging apparatus of the present invention optionally comprising a plurality of gas outlet ports;

[0025] FIG. 6 is a cross sectional view of another embodiment of a purging apparatus according to the present invention comprising an optional heat shield and also showing an optional plurality of outlet ports;

[0026] FIG. 7 is a schematic diagram of an experimental setup used to test an example purging apparatus;

[0027] FIG. 8 is a plot of molten glass level drop obtained as a function of air pressure used in the experimental setup of FIG. 7;

[0028] FIG. 9 is a cross sectional view of another embodiment of a portion of a purging apparatus according to the present invention wherein a vacuum is applied to the purging apparatus;

[0029] FIG. 10 is a cross sectional view of the conduit and standpipe of FIG. 1 showing a portion of a purging apparatus installed in the standpipe, and wherein a vacuum applied to the standpipe and an atmosphere above a free surface of the molten glass causes a level of the molten glass to rise.

DETAILED DESCRIPTION

[0030] 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 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 the present invention. Finally, wherever applicable, like reference numerals refer to like elements.

[0031] Shown in FIGS. 1 is an illustration of a portion of an example vessel, conduit 10, for transporting a molten glass in a glass making process. Conduit 10 comprises a standpipe 12 connected thereto. Preferably, conduit 10 and standpipe 12 comprise a platinum group metal (e.g. platinum, rhodium, palladium, iridium, rhenium, ruthenium and osmium), or alloys thereof. Standpipe 12 is typically, although not necessarily, welded to conduit 10. FIG. 2 shows a cross sectional view of conduit 10 and standpipe 12 transverse to a longitudinal axis of conduit 10 including molten glass 14 contained therein. A portion of a purging apparatus 16 is shown inserted into standpipe 12. Molten glass 14 contained within conduit 10 has a free surface 15 exposed to an atmosphere within standpipe 12.

[0032] FIG. 3 is a side view of an example embodiment of purging apparatus 16 for purging condensates from a standpipe in a glass making system, such as a standpipe for use with a level probe. FIG. 4 shows a cross sectional side view of the purging apparatus of FIG. 3. Purging apparatus 16 comprises a partially threaded first tube 18 having a passage 20 through a length thereof. First tube 18 is preferably metallic, and can be formed from steel or stainless steel, or another high temperature material for example. A collar 22 (e.g. a threaded nut or split shaft collar) is engaged with threaded portion 19 of first tube 18. A second tube 24 comprises a first end 26 and a second end 28 positioned opposite the first end 26 and a passage 30 extending between the first and second ends. Second tube 24 is also preferably metallic, and can also be formed from steel, stainless steel or another high temperature material. Second tube 24 includes a first flange 32 attached at the first end 26 of second tube 24 and a second flange 34 attached at the second end 28 of second tube 24. First flange 32 and second flange 34 may be, for example, washers that are welded in place so that the seam between the washers and second tube 24 are sealed to prevent gas flow. Second tube 24 is positioned around first tube 18 such that first tube 18 can move within passage 30 with respect to second tube 24. First flange 32 attached to first end 26 may also be a flat washer, but is preferably a conical section or convex, and may be formed, for example, from a Belleville washer that is welded in place. Second fiange 34 attached to second tube 24 at second end 28, is preferably flat, and may be, for example, a flat washer welded to the second tube. Third flange 36, is positioned on first tube 18 near the bottom of the tube such that when first tube 18 is positioned within second tube 24, first flange 32 and third flange 36 are in an opposite and opposing orientation. Third flange 36 may also be convex or comprise a conical section, and may, for example, be formed from a Belleville washer that is welded to first tube 18. A portion 38 of first tube 18 extends below third flange 36. Portion 38 comprises outlet port or ports 49 extending from an outside surface of first tube 18 to passage 20. A washer 42 is positioned on first tube 18 below threaded portion 19 and above second flange 34 (i.e. between collar 22 and second flange 34) and is free to move on first tube 18. Washer 42 is preferably a flat washer.

[0033] FIGS. 5 - 6 show another embodiment of purging apparatus 16. FIG. 5 depicts a side view of purging apparatus 16 showing first gasket 46 and second gasket 48 installed on purging apparatus 16. First gasket 46 comprises a high temperature resistant material positioned between first flange 32 and third flange 36 such that first gasket 46 can be compressed between first flange 32 and third flange 36. Square braided ceramic rope, such as is available from Gaskets Incorporated (part # GBOL), is a high temperature material suitable for first gasket 46. Other high temperature materials and/or products could also work for first gasket 46 provided they do not appreciably degrade at temperatures equal to or greater than approximately 200°C, are preferably compressible, and have a compressed density high enough to reduce or eliminate significant gas flow through it.

[0034] Second gasket 48 is a gasket positioned between second flange 34 and washer 42 such that second gasket 48 can be pressed between second flange 34 and washer 42 when collar 22 engaged with threaded portion 19 is rotated. If a compliant material is used, the pressing between second flange 34 and washer 42 will compress the gasket material, thereby causing the gasket material to seal passage 30 at second end 28 of second tube 24. Second gasket 48 can be a silicon rubber, Kalrez® or Viton® gasket, but a compliant gasket material that is resistant to high temperatures (e.g. equal to or greater than about 200°C) is preferred.

[0035] In accordance with FIG. 5, first tube 18 optionally comprises a plurality of outlet ports 49 extending through the side of first tube 18 for directing the gas supplied to the opposite end of first tube 18 through passage 20 into standpipe 12. In this configuration, all gas flow is directed towards the standpipe instead of toward the molten glass such that cold gas is not blown directly on molten glass 14 in standpipe 12, thereby avoiding undue glass cooling. Additionally, the gas linear velocity decreases with a plurality of gas outlet ports. The slower gas linear velocity allows the gas temperature to rise faster and cooling of the glass and standpipe is reduced.

[0036] FIG. 6 illustrates a portion of another embodiment of purging apparatus 16 comprising optional heat shield 47 to reduce the temperature of the rest of the apparatus by reducing radiant heat transfer from the molten glass. Heat shield 47 enables lower temperature materials to be used for the rest of the apparatus. The heat shield could be made of platinum, rhodium, a platinum-rhodium alloy, or other materials capable of withstanding high temperatures. In some embodiments heat shield 47 could be a ceramic heat shield. A peripheral shape of heat shield 47 is generally the same shape as the inside shape of the standpipe. For example, for a cylindrical standpipe, the heat shield should have a circular shape.

[0037] Figure 6 shows the angle a on the surface or face of first flange 32 and third flange 36. The angle a is preferably equal to or greater than 0 degrees and equal to or less than 70 degrees relative to a plane perpendicular to a longitudinal axis of first tube 18 or second tube 24. Preferably, a is between 5° to 20°, inclusive, to ensure first gasket 46 is axially compressed to radially expand and contact the standpipe to reduce gas flow through or around the gasket.

[0038] The following explains how the purging apparatus may be used to purge glass from a standpipe in a glass manufacturing system. Purging apparatus 16 shown in FIGS. 3 - 6 may be used to isolate and pressurize gas introduced above the free surface 15 of the molten glass in standpipe 12. The end of purging apparatus 16 (e.g. first end 26 of second tube 24), including first gasket 46 positioned between first flange 32 and third flange 36, is inserted into standpipe 12. Collar 22 engaged with threaded portion 19 is rotated such that first gasket 46 is axially compressed between first flange 32 and third flange 36 and forced against the inside surface of standpipe 12, closing off that portion of the standpipe below the gasket (i.e. between the molten glass material and gasket). As collar 22 is rotated, thereby compressing first gasket 46 between first flange 32 and third flange 36, second gasket 48 is similarly compressed between second flange 34 and washer 42, thereby sealing the top of second tube 24 and passage 30 to prevent hot gases from within standpipe 12 from escaping from passage 30. It should be noted that contact between first gasket 46 and the inside surface of standpipe 12 need not be an airtight. Some gas flow through and/or around first gasket 46 is acceptable. However, any gas flow used to create gas pressure between molten glass 14 and first gasket 46 should not cause molten glass 14 to substantially cool and solidify. In one embodiment the gas can be heated, thereby mitigating any solidification of molten glass 14 do to leakage at first gasket 46. Gas 50 is then flowed into first tube 18 from a source (not shown). The gas may be any gas that is non-combustible and preferably non-toxic such as air, nitrogen or an inert gas such as helium or argon. The gas flows through passage 20 and exits first tube 18, either through a single outlet port at the opposite end (i.e. bottom) of first tube 18, or through a plurality of outlet ports at the side of first tube 18 within portion 38, wherein the pressure within standpipe 12 increases and forces molten glass 14 down into conduit 10 (as represented by arrow 52 in FIG. 7). A typical gas pressure of from about 0.2 to 0.4 lb/in² (about 1379 Pa to about 2757.9 Pa) is sufficient to push the molten glass from the standpipe into the conduit. Molten glass flowing in conduit 10 then carries the molten glass volume forced from the standpipe through the glass making system and eventually into the final glass product. Glass product containing the defect-ridden glass from the standpipe is may thereafter be discarded. This may be necessary for a period of time after the purging operation is completed.

[0039] In a test of the preceding method, a standpipe/conduit mockup was assembled in a furnace. Figure 7 is a schematic of the mockup comprising a platinum-rhodium box representing a vessel or conduit 10, standpipe 12 and purging apparatus 16, all positioned within furnace 54. For this experiment purging apparatus 16 comprised first tube 18 having a diameter of approximately 0.25 inches (0.64 cm) and second tube 24 having a diameter of approximately 0.625 inches (1.588 cm). Both the first and second tubes were constructed of steel. In practice, the tube diameters could be any size as practical for a given standpipe diameter. The level of molten glass inside the standpipe could not be directly measured. Therefore, the box dimensions were designed such that a 5 inch (12.7 cm) glass level drop inside the standpipe would equal a 1 inch (2.54 cm) glass level rise inside the box. The glass level was measured in the box with an alumina probe (dipstick). Care was taken to exclude the effects of any molten glass meniscus on the glass level measurement. An approximately 4 inch (10 cm) length of the standpipe was obtained from a working glass making system in operation for over one year. This length section was then welded to a 90% platinum - 10% rhodium tube for the mockup standpipe. The approximately 4 inch (10 cm) standpipe section was not cleaned prior to assembly and therefore was representative of the upper portion of a standpipe used on a manufacturing melting system.

[0040] The standpipe mockup was positioned in furnace 54 with the temperature in the furnace at 1450°C. An initial glass level measurement of the molten glass in the box was taken with the alumina dipstick to establish the molten glass level at ambient pressure with no gas flowing through purging apparatus 16. Gas was then flowed through the purging apparatus to increase the gas pressure above the molten glass in the standpipe. Although air was used for this experiment, many other gases could be used for this purpose. For example, nitrogen is a suitable gas to be used. The relationship between gas flow rate, gas pressure, and glass level in the standpipe was determined with the preceding set up. The gas flow rate was varied from 0 to 2.25 L/min to obtain a gas pressure from 0 to 0.38 pounds/inch² (0 to 2620 Pa). The resulting glass level drop in the standpipe was 0 to about 5 inches (0 to about 12.7 cm).

[0041] Figure 8 is a graph of air pressure in Pascal (Pa) versus glass level drop (in cm) in the standpipe generated with this experiment. The scatter in the data is primarily due to inadequate time between pressure readings - about 10 minutes between each data point. However, molten glass is very viscous at 1450°C and was still moving after 10 minutes. The dipstick method of glass level measurement is thought to have also contributed some error to this graph.

[0042] After the initial experiment at 1450°C (diamonds), the furnace temperature was dropped to 1400°C and the glass was allowed to cool. Two data points (squares) were obtained at 1400°C. The 1400°C data point at zero pressure had a lower glass level than the previous point (1450°C) at zero pressure. This is due in part to glass adhering to the walls of the platinum - rhodium box. The second data point at 1400°C was at 0.3 pounds/inch² (2068.4 Pa) pressure. The glass was given about 20 minutes to move to the new level after the pressure change. The glass level at 0.3 pounds/inch² (2068.4 Pa) was very close to the 1450°C linear curve fit. This indicated that the glass movement at 1400°C was very similar to glass movement at 1450°C. This also indicated that glass cooling due to the gas flow was not a significant concern at 1400°C.

[0043] The relationship between air pressure and glass level in FIG. 8 matches the theoretical relationship based on fluid density. In theory, 1 inch (2.54 cm) of a display-type glass having a density of about 2.5 g/cm³ equals 0.90 pounds/inch² (620.53 Pa) air pressure. Referring to FIG. 8, the slope (0.0041 cm/Pa) and offset (0.0817 cm) of the linear fit curve 56 indicates that a depth (or change in depth) of 2.54 cm of such a glass equals a depth change of approximately 600 Pa, indicating that the observed change in depth tracked well with the expected change. Linear fit curve 56 indicates a range of standpipe pressures equal to or greater than 0 and equal to or less than about 2700 Pa. Thus, suitable standpipe pressures during the purging process can be equal to or greater than, for example, 500 Pa, equal to or greater than 1000 Pa, equal to or greater than 1500 Pa, equal to or greater than 2000 Pa, and equal to or greater than 2500 Pa. It should be noted that the pressure needed will depend on the level of molten glass material in the standpipe (the depth of the molten glass material), the amount of molten glass material desired to be purged (the change in level of molten glass material desired during the purging process) and the glass density. In some embodiments the pressure in the standpipe may be greater than 2700 Pa.

[0044] It should be noted that although the present application has been described generally in terms of a standpipe used to determine the molten glass level in a glass making system, embodiments of the present invention can be used to clear molten glass from other standpipes and vent tubes that may be used throughout the vessels and conduits of a glass making system, including vent tubes of a glass fining vessel. In particular, in some embodiments, rather than injecting a pressurized gas through first tube 18 to decrease the level of molten glass in the standpipe (or vent tube, as the case may be), a vacuum could instead be applied to first tube 18 such that the molten glass level in the standpipe rises. As previously described, material condensing on surfaces of the glass making system as a result of their proximity to the free surface of the molten glass, and volatilized material derived therefrom, raising the level of the molten glass can be used to wash material from the inside surfaces of the glass making system. This does not require that the molten glass be at a level within the standpipe or vent tube prior to the application of the vacuum. For example, the vessel may have a molten glass level which only partially fills the vessel, and the standpipe is in fluid communication with the free space above the molten glass. A vacuum may then be applied to first tube 18 as shown in FIG. 9. The vacuum is communicated to the free space above the molten glass in the vessel, thereby causing the level of molten glass to rise in the vessel. A vacuum can be used in combination with pressure to raise and lower the glass level sequentially to improve the washing and purging effectiveness. [0045] 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 purging apparatus (16) for purging contaminants (14) from a glass making system comprising;

a first tube (18) comprising a passage (20) extending through at least a portion of the first tube and further comprising a threaded portion (19);

a collar (22) engaged with the threaded portion;

a second tube (24) comprising a passage (30) extending between a first end (26) and a second end (28) of the second tube, the second tube further comprising a first flange (32) attached to the first end of the second tube and a second flange (34) attached to the second end of the second tube and wherein the first tube is positioned within the passage (30) of the second tube (24);

a washer (42) positioned around the second tube and positioned between the second flange and the collar; and

a first gasket (46) positioned between the first flange and a third flange (36) attached to the first tube.

2. The purging apparatus according to claim 1, further comprising a second gasket (48) positioned between the second flange (34) and the washer (42).

3. The purging apparatus according to claim 1, wherein a face of the first flange (32) makes an angle equal to or greater than 0 degrees and equal to or less than 70 degrees relative to a plane perpendicular to a longitudinal axis of the second tube.

4. The purging apparatus according to claim 1, wherein a face of the first flange makes an angle equal to or greater than 5 degrees and equal to or less than 20 degrees relative to a plane perpendicular to a longitudinal axis of the second tube.

5. The purging apparatus according to claim 1, wherein the first tube (18) comprises an output port (49) positioned on a side of the first tube for exhausting a gas (50) from the first tube.

6. The purging apparatus according to claim 1, wherein the first tube (18) comprises a plurality of output ports (49) configured to exhaust a gas (50) from a side of the first tube.

7. The purging apparatus according to claim 1, further comprising a heat shield (47) attached to an end of the first tube (18).

8. A method of purging contaminants from a glass making system comprising;

providing a vessel (10) connected to a standpipe (12), the vessel containing a molten glass material (14);

inserting an end (26) of a purging apparatus (16) into the standpipe, the purging apparatus comprising:

a collar (22) engaged with the threaded portion;

a second tube (24) comprising a passage (30) extending between a first end (26) and a second end (28) of the second tube, wherein the first tube is positioned within the passage (30) of the second tube, the second tube further comprising a first flange (32) attached to the first end (26) of the second tube and a second flange (34) attached to the second end (28) of the second tube; and

a first gasket (46) positioned between the first flange (32) and a third flange (36) attached to the first tube;

rotating the collar to compress the first gasket and press the first gasket against an interior surface of the standpipe; and

flowing a gas (50) through the first tube to vary a level of the molten glass material.

9. The method according to claim 8, wherein the purging apparatus (16) further comprises a washer (42) positioned between the second flange (34) and the collar (22) and a second gasket (48) positioned between the second flange and the washer (42), and wherein rotating the collar compresses the second gasket and seals an end of the second tube (24).

10. The method according to claim 8, wherein the gas (50) is flowed into the standpipe (12) from the first tube (18) in a direction toward the molten glass material.

11. The method according to claim 8, wherein the gas (5) is flowed into the standpipe (12) from the first tube (18) in a direction toward a side of the first tube (18).

12. The method according to claim 8, wherein the first gasket (46) is a fibrous ceramic material.

13. The method according to claim 8, wherein the gas (50) is flowed into the standpipe (12) through a plurality of output ports (49).

14. The method according to claim 8, wherein a face of the first flange (32) makes an angle equal to or greater than 5 degrees and equal to or less than 20 degrees relative to a plane perpendicular to a longitudinal axis of the second tube (24).

15. The method according to claim 8, wherein a pressure inside the standpipe (12) during the flowing the gas is equal to or greater than 500 Pa and equal to or less than 2700 Pa.

16. The method according to claim 8, wherein the vessel (10) is a conduit and molten glass material (14) flows through the conduit.

17. The method according to claim 8, wherein the standpipe (12) comprises a platinum group metal.

18. The method according to claim 8, wherein a vacuum is applied to first tube (18) and the gas is withdrawn from the standpipe through first tube (18).

19. The method according to claim 8, wherein the gas is a pressured gas that is flowed into the standpipe (12) through first tube (18).

20. The method according to claim 8, wherein a pressure and a vacuum are sequentially applied to the standpipe (12).