WO2008108943A1

WO2008108943A1 - Apparatus for fining glass

Info

Publication number: WO2008108943A1
Application number: PCT/US2008/002503
Authority: WO
Inventors: Raymond E. Fraley; Lawrence H. Kotacska
Original assignee: Corning Inc
Current assignee: Corning Inc
Priority date: 2007-03-01
Filing date: 2008-02-26
Publication date: 2008-09-12
Anticipated expiration: 2009-09-01
Also published as: JP2010520141A; TWI365859B; TW200909369A; CN101675009A; CN101675009B; KR101454049B1; JP5335700B2; KR20090127308A

Abstract

An apparatus for fining a molten glass comprising a fining vessel, and a cradle for both supporting and preventing oxidation of the fining vessel. High cradle sidewalls which extend above the fining vessel, and a bedding material enhance the support and oxidation prevention capability of the cradle. Keystone refractories engage with channels formed in the bedding material, helping to prevent high-temperature creep of the bedding material and damage to the fining vessel.

Description

APPARATUS FOR FINING GLASS

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

[0001] This invention relates to an apparatus for fining molten glass and, in particular, to the support and protection of precious metal fining vessels.

TECHNICAL BACKGROUND

[0002] An exemplary process for manufacturing glass articles begins with the melting of raw feed materials, such as metal oxides, to form a molten glass. The melting process not only results in the formation of glass, but also the formation of various unwanted byproducts, including various gases such as oxygen, carbon dioxide, carbon monoxide, sulfur dioxide, sulfur trioxide, argon, nitrogen, and water. Unless removed, these gases can continue throughout the manufacturing process, ending up as small, sometimes microscopic gaseous inclusions in the finished glass article. [0003] For some glass articles, the presence of small gaseous inclusions is not detrimental. However, for other articles of manufacture, gaseous inclusions as small as 50 μm in diameter are unacceptable. One such article is the glass sheet used in the manufacture of display devices such as liquid crystal and organic light emitting diode displays. For such applications, the glass must have extraordinary clarity, pristine surfaces, free of distortion and inclusions.

[0004] To remove gaseous inclusions from the molten glass, a fining agent or agents are typically added to the feed material. The fining agent is a multivalent compound that enters a reduced valence state when cooled, absorbing oxygen in the process, and enters a higher valence state when heated thereby releasing the oxygen. The released oxygen serves to cause gases in the molten glass, or melt, to coalesce and rise to the surface of the melt, where it is removed from the process. The heating is typically performed in a high temperature fining vessel. [0005] Typical fining temperatures for display-grade glasses can be as high as 1700⁰C. Temperatures this high require the use of specialized metals or alloys to prevent destruction of the vessel. Platinum or platinum alloys, such as platinum-rhodium are typically used. Platinum advantageously has a high melting temperature and does not easily dissolve in the glass. Nevertheless, at such high temperatures, the platinum or platinum alloy readily oxidizes. Therefore, steps must be taken to prevent contact between the hot platinum fining vessel and atmospheric oxygen. Moreover, because platinum is a precious metal and quite expensive, the walls of the fining vessel are generally manufactured as thinly as possible. Thus, the fining vessel may further require physical support.

SUMMARY

[0006] In accordance with an embodiment of the present invention, an apparatus for fining glass is described comprising a cradle defining a trough, a vessel for conveying molten glass disposed within the trough, a bedding material disposed between the cradle and the vessel comprising channels, and keystones for supporting at least a portion of the bedding material engaged with channels in the bedding material

[0007] In accordance with another embodiment of the present invention, an apparatus for fining glass is disclosed comprising a refractory cradle defining a trough and side walls extending upward from the trough, a vessel comprised of platinum disposed within the trough, a refractory bed disposed between the vessel and the cradle, the refractory bed surrounding the vessel and comprising channels in an upper portion thereof, refractory keystones disposed above the cradle and wherein the refractory keystones engage with the channels to support the refractory bed.

[0008] 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 are incorporated into and constitute a part of this specification. The drawings illustrate an exemplary embodiment of the invention and, together with the description, serve to explain the principles and operations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a cross sectional drawing illustrating an apparatus for fining a molten glass in accordance with an embodiment of the present invention, and including a cradle for supporting the fining vessel and reducing oxidation of the fining vessel. [0010] FIG. 2 is a cross sectional drawing illustrating a portion of the apparatus of FIG. 1 wherein various refractory blocks have been removed for clarity. [0011] FIG. 3 is a perspective view of the cradle of FIG. 1.

[0012] FIG. 4 is a close-up cross sectional view of the refractory bed according to an embodiment of the present invention, showing the channels and flange regions of the bed. [0013] FIG. 5 is a perspective view of the bedding material of FIG. 4, without the fining vessel, showing the channels and flange regions of the refractory bed.

Detailed Description

[0014] 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. [0015] hi accordance with the present invention, and as illustrated in FIGS. 1-3, an apparatus 10 is provided comprising a fining vessel 12, a cradle 14, a bedding material 16, a plurality of refractory blocks 18 of various shapes and sizes, and keystones 20. [0016] Fining vessel 12 is typically constructed from a metal capable of withstanding extremely high temperatures, sometimes in excess of 1700⁰C. Preferably the precious metal vessel comprises a metal selected from the platinum group metals (e.g. platinum, rhodium, iridium, ruthenium, palladium, and osmium), or alloys thereof. However, other high-temperature metals and/or alloys may be used, such as those comprising molybdenum, either separately or in combination with the platinum group metals, or as an alloy with other high temperature metals, hi addition to receiving hot molten glass, such as from a melting furnace, at temperatures sometimes in excess of 1500⁰C, vessel 12 is used to further heat the molten glass. Thus, vessel 12 may be itself heated. In some embodiments, vessel 12 is heated by passing an electric current through the metal vessel. However, other methods of heating vessel 12 as are known in the art may be used, such as, for example, a flame. Fining vessel 12 is preferably in the form of a cylindrical tube. [0017] Cradle 14 defines a trough 22 with sidewalls 24 which extend upward from the trough. Preferably, cradle 14 comprises a U-shaped trough. Cradle 14 is generally formed from a material capable of withstanding high temperatures without mechanical failure. As used herein, unless otherwise stated, a refractory refer to a material capable of withstanding high temperatures. Refractory materials consist largely of single or mixed high melting point oxides of elements such as silicon, aluminium, magnesium, calcium and zirconium. However, non-oxide refractories also exist and include materials such as carbides, nitrides, borides and graphite. The actual composition of a refractory material is dependent on the temperature and atmosphere in which the refractory material will be used, and the materials it will be in contact with. Cradle 14 may be formed from alumina or fused cast zirconia refractories, for example.

[0018] Fining vessel 12 is disposed within cradle 14 and surrounded by bedding material 16. As shown in FIG. 1, cradle sidewalls 24 preferably extend upward above the top of fining vessel 12, and bedding material 16 is disposed between the vessel and the cradle. Preferably, bedding material 16 begins as refractory slurry which is poured into trough 22 to surround tube 12 and which thereafter hardens or cures in place to become a solid refractory material 16 that provides a protective bed for fining vessel 12. As such, bedding material 16 is sometimes termed the "castable" (e.g. castable 16). Bedding material 16 is in intimate contact with fining vessel 12, thereby providing maximum support to the fining vessel, and helping to prevent oxygen from permeating to the outer surface of the vessel. As with cradle 14, bedding material 16 should be capable of withstanding temperatures in excess of 1700⁰C. Bedding material 16 is preferably a refractory composition, and may comprise high purity alumina or zirconia, for example. [0019] Cradle 14 is supported by refractory blocks 18 on the sides and bottom of the cradle, and covered with similar refractory blocks. Cradle 14 and refractory blocks 18 may be further installed within an additional enclosure, such as steel enclosure 25 to provide structural support to the assembly of refractory blocks. Refractory blocks 18 may be, for example, Insalcor® bricks.

[0020] As indicated in FIGS. 1-2, keystones 20 preferably rest on the tops of cradle walls 24. Bedding material 16 is poured into the cradle trough and reaches the tops of keystones 20. As keystones 20 do not touch each other over cradle 14, but instead each extend inward from walls 24 less than half the distance between the walls, bedding material 16 can flow upward and reach the tops of keystones 20. Keystones 20 preferably also comprise a radius on the extended edges 26. The net result is that after bedding material 16 has hardened, bedding material 16 is engaged with keystones 20. That is, channels are formed in the upper portion of the bedding material into which keystone 20 fit. Both bedding material 16 and keystones 20 are topped with additional refractory blocks 18 such that cradle 14 and keystone refractories 20 are encased within refractory blocks. Keystones 20 are preferably formed from a refractory, and may, for example, comprise fused zirconia or alumina.

[0021] Given the high temperatures at which molten glass flows through vessel 12, bedding material 16 is subject to plastic deformation or "creep", which can negatively impact the support function of the bedding material. That is, the bedding material may sag and deform or even crush vessel 12. This is offset in the lower portion of the vessel by the hydrostatic pressure of the molten glass flowing through the vessel. However, molten glass typically does not fill the fining vessel; hence there is a glass level line above which hydrostatic pressure is not applied to the inside of the vessel. In the presence of creep by the bedding material, and the subsequent pressure exerted by the weight of the bedding material on the upper portion of fining vessel 12, and without an internal force (e.g. hydrostatic pressure) to counter the bedding material weight, structural failure at the top of vessel 12 may occur. Keystones 20 overcome this problem by providing a supporting structure for the bedding material.

[0022] FIG. 3 is a close-up of bedding material 16 without cradle 14 and keystones 20 for clarity, showing the region of engagement between the bedding material and the keystones. Also shown is fining vessel 12 and glass level line 28 indicating the level of molten glass 30 within the fining vessel. Without support, bedding material 16 above vessel 12 will creep over time and exert a downward force on the top of vessel 12, thereby deforming vessel 12 and risking structural failure of the vessel. In accordance with the present embodiment, bedding material 16 is formed with opposing channels 32, wherein a thickness "d" between the channels is less the width "D" of flange 34 above the channels. Keystones 20 engage with channels 32 on each side of bedding material 16 such that the upper portion of bedding material 16 is supported by keystones 20 engaged at channels 32. Put differently, keystones 20 extend into a space above vessel 12, which, when filled with the bedding material 16 in its uncured state, covers a portion of the keystones (e.g. over the upper surface of the keystone radius). When bedding material 16 has cured or otherwise transformed into its hardened state, the bedding material forms a shape (i.e. channels 32) complementary to the shape of the extended portions of the keystones. Thus, keystones 20 provide a supporting function by bearing weight from bedding material 16, thereby preventing the upper portions of bedding material 16 from sagging over time due to the high temperature of fining vessel 12. Channels 32 preferably extend longitudinally along the length of bedding material 16 at the same general vertical level in an opposing relationship.

[0023] Referring to FIG. 2, Apparatus 10 may further include at least one thermocouple 36 embedded within bedding material 16 so that a temperature of the fining vessel may be monitored. The at least one thermocouple may be selected based on the expected temperature range to be measured, and the accuracy required for the measurement. For example, type "B" and type "S" thermocouples are typically employed in measurements of the fining vessel (e.g. metal tube 12) temperature. Both thermocouple types are noble metal thermocouples comprising platinum and rhodium. Type "B" thermocouples are typically used in applications up to about 1800⁰C, whereas type "S" thermocouples are generally employed to sense temperatures up to about 1600⁰C. Preferably, a type "B" thermocouple is used to measure upper portions of the fining vessel, whereas type "S" thermocouples are used to measure the mid-point temperatures of the fining vessel. Electrical leads 38 from the at least one thermocouple is connected with measurement equipment (not shown) which may be used to record and/or control the fining vessel temperature.

[0024] In some embodiments, the bottom corners of cradle 14 may be chamfered, as indicated by dotted lines 40. By removing unnecessary material, cradle 14 can be heated more evenly, and cracking of the cradle material can be minimized. [0025] 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 the 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 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.

Claims

What is claimed is:

1. An apparatus for fining glass comprising: a cradle (14) defining a trough (22); a vessel (12) for conveying molten glass (30) disposed within the trough; a bedding material (16) disposed between the cradle and the vessel comprising channels (32); and keystones (20) for supporting at least a portion of the bedding material engaged with the channels.

2. The apparatus according to claim 1 wherein the vessel (12) is a tube.

3. The apparatus according to claim 1 wherein the vessel (12) comprises a metal selected from the group consisting of platinum, rhodium, iridium, ruthenium, palladium, osmium, molybdenum and alloys thereof.

4. The apparatus according to claim 1 wherein sidewalls (24) of the cradle extend above the vessel (12).

5. The apparatus according to claim 1 wherein the bedding material (16) was disposed between the cradle and the vessel as slurry.

6. The apparatus according to claim 1 wherein the bedding material (16) comprises a refractory material.

7. The apparatus according to claim 1 wherein the channels (32) extend along a length of the bedding material (16).

8. An apparatus for fining molten glass comprising: a refractory cradle (14) defining a trough (22) and side walls (24) extending upward from the trough; a vessel (12) comprising platinum disposed within the trough; a refractory bed (16) disposed between the vessel and the cradle, the refractory bed surrounding the vessel and comprising channels (32) in an upper portion thereof; refractory keystones (20) disposed above the cradle; and wherein the refractory keystones engage with the channels to support the refractory bed.

9. The apparatus according to claim 8 wherein bottom corners of the cradle are chamfered.

10. The apparatus according to claim 8 wherein the refractory bed (16) was poured into the trough (22).

11. The apparatus according to claim 8 wherein the sidewalls (24) extend above the vessel (12).

12. The apparatus according to claim 8 further comprising at least one thermocouple (36) embedded within the refractory bed (16) for detecting a temperature of the vessel (12).

13. The apparatus according to claim 8 wherein the channels (32) extend along a length of the refractory bed (16).

14. The apparatus according to claim 13 wherein the channels (32) are in an opposing relationship.