JP2013512184A - Method and apparatus for reducing defects associated with condensates in a glass manufacturing process - Google Patents

Abstract

The present invention relates to a method and apparatus for reducing foreign matter in a glass melt due to fine oxide particles such as platinum oxide, which may condense on the inner surface of the stirring chamber, particularly the stirring shaft, and fall into the glass melt. . The apparatus of the present invention comprises a condensate collection vessel arranged in an annular shape around the agitation shaft of the agitator. The collection container is located above the free surface of the molten glass that occupies the agitation chamber and serves to collect any agglomerated particulates that form in the gaps inside the agitation chamber cover or the cover itself. By collecting the condensate, defects in the final glass product that would otherwise be produced by the condensate can be avoided. A method of stirring the glass melt is also provided.

Description

Cross-reference of related applications

  This application claims the benefit of priority of US Patent Application No. 61 / 265,060, filed Nov. 30, 2009. The contents of this specification, as well as the entire disclosure of the publications, patents and patent documents referred to herein are hereby incorporated by reference.

  The present invention relates generally to a method for reducing foreign matter in a glass melt, and more particularly to a method for reducing condensation-forming foreign matter during a glass agitation process.

  Chemical and thermal homogeneity is a vital part of a good glass forming operation. The function of the glass melting operation is generally to produce a glass with an acceptable level of gaseous or solid inclusions, which usually has a chemically different phase cord (or stripes). (striae) or see-through (ream). These inhomogeneous components of the glass result from various normal events during the melting process, including refractory melting, melting stratification, glass surface vaporization, and temperature differences. The resulting striae is visible in the glass due to color and / or refractive index differences.

  One approach to improve glass homogeneity is to pass molten glass through a vertically extending stirring chamber located downstream of the melting apparatus. Such a stirring chamber comprises a stirrer having a central shaft that is rotated by a suitable motor. A plurality of blades extend from the shaft and serve to mix the molten glass as it passes from the top to the bottom of the stirring chamber. The invention relates to the operation of such a stirring chamber which does not introduce further defects in the resulting glass, in particular defects originating from condensed oxide.

Volatile oxide in the glass stirring chamber can be formed from glass and any components present in the stirring chamber. The most vaporizable and damaging oxides are formed from Pt, As, Sb, B and Sn (platinum, arsenic, antimony, boron and tin). The temporary supply of oxide condensed into the glass melt is the hot platinum surface for PtO ₂ and the glass free surface for B ₂ O ₃ , As ₄ O ₆ , Sb ₄ O ₆ and SnO _2. including. By glass free surface is meant the surface of the glass that is exposed to the atmosphere in the stirring chamber. The atmosphere above the glass free surface, and some or all of the above-mentioned substances that may be included in the atmosphere, or other volatile substances, are hotter than the outside of the agitation chamber, so they are above the glass free surface. The atmosphere tends to naturally flow upward via an arbitrary opening such as via an annular space between the stirrer shaft and the stirring chamber cover. The greater the distance between the stirrer shaft and the glass free surface, the lower the temperature of the stir chamber shaft, so volatile oxides contained in the stir chamber atmosphere will have a shaft and / or cover temperature below the oxide dew point. If so, it will condense on the surface of the shaft. When the resulting condensate reaches a critical size, they can detach and fall into the glass, causing inclusions or bubble defects in the glass product.

  It has been demonstrated that heating the shaft above the glass free surface is only partially successful in reducing particulate foreign matter in the glass melt and only results in the condensate being layered. It was.

  In a broad aspect of the present invention, a condensate collection vessel is provided that attaches to a stirrer rod of a stirrer chamber in a glass melt and glass manufacturing system. The condensate collection container has an annular bottom, and a cylindrical wall is attached to the annular bottom at a predetermined angle relative to the annular bottom. The condensate collection container is provided in a cylindrical stirring chamber configured to hold molten glass. An agitation chamber is a cover that defines a flow path therethrough, a shaft that extends through the cover into the agitation chamber, thereby forming an annular gap between the cover and the shaft. Equipped with a bowl. The shaft is fitted with wings that are used to effectively agitate the molten glass in the chamber.

  The present invention will be more readily understood with reference to the accompanying drawings, which are not intended to be limiting in any way, and that other objects, features, details and advantages will become more apparent in the course of the following description given. Will.

FIG. 1 is a cross-sectional view of an example agitation chamber showing a chamber cover and condensate collection container according to an embodiment of the present invention. FIG. 2 is a partial perspective view of a condensate collection vessel attached to an agitator shaft. FIG. 3 is a cross-sectional view of an example of a condensate collection container.

  FIG. 1 is a diagram showing an example of an apparatus for carrying out a method for homogenizing a glass melt. A stirring chamber 10 shown in FIG. 1 has an inlet pipe 12 and an outlet pipe 14. In the illustrated embodiment, the molten glass flows into the agitation chamber via the inlet pipe 12 as indicated by arrow 13 and flows out of the chamber via the outlet pipe 14 as indicated by arrow 15. The stirring chamber 10 may be other shapes such as oval or hexagonal, but preferably has a cylindrical shape and has at least one wall 16 extending vertically. Preferably, the agitation chamber wall has an inner lining 18 comprised of platinum, platinum alloy, or dispersion strengthened platinum or platinum alloy (eg, zirconia reinforced platinum alloy). Other lining materials having similar fire resistance characteristics including corrosion resistance in addition to conductivity may be used instead. The glass inlet pipe 12 is located at or near the bottom of the agitation chamber 10, while the glass outlet pipe 14 is located near the top of the agitation chamber. However, those skilled in the art will appreciate that the inlet pipe 12 and the outlet pipe 14 may be reversed so that molten glass flows from the top into the stirring chamber and out through the bottom of the stirring chamber. The inlet and outlet pipes may be placed in an intermediate position provided that adequate agitation (ie, the desired amount of homogenization) is achieved. Since the pumping effect generally requires an unacceptably high level of shear stress, it is preferred that the stirrer does not necessarily pump the glass through the stir chamber. Preferably, the stirrer and stir chamber walls are comprised of platinum, platinum alloy, or dispersion strengthened platinum or platinum alloy (eg, zirconia reinforced platinum alloy).

  The agitation chamber 10 further includes an agitator 20 with a shaft 22 and a plurality of vanes 24 extending outwardly from the shaft toward the wall 16 of the agitation chamber. The shaft 22 is generally substantially vertically oriented such that a vane 24 extending from the lower portion of the shaft rotates within the stirring chamber at least partially below a free surface 26 of molten glass. And is rotatably mounted. The surface temperature of the molten glass is usually in the range of 1400 ° C. to 1600 ° C., but may be high or low depending on the glass compounding method. The stirrer 20 is preferably made of platinum, but may be a platinum alloy, or dispersion strengthened platinum or a platinum alloy (eg, zirconia reinforced platinum alloy).

  As shown in FIG. 1, the agitation chamber 10 may have a drain tube 28 for removing glass from the agitation chamber, for example during system shutdown. In addition (or alternatively), the agitation chamber may have an optional sump 30. The stirrer 20 is rotated by a suitable drive source. For example, the agitator 20 may be rotated by an electric motor (not shown) via a suitable gear device or by a belt drive.

  According to this embodiment, the stirring chamber 10 is covered by the chamber cover 32. The chamber cover 32 may be placed directly on the wall portion 16, or a high temperature sealing material may be disposed between the wall portion and the cover, and any seal between the wall portion and the cover may be used. Even if this is the case, it will prevent significant gas flow between the cover and the wall. The cover 32 may have a cover heater 34 to heat the chamber cover and thus help control the free surface temperature of the glass melt stream flowing through the stirring chamber. The cover heater 34 is typically made of platinum and typically has a resistance coil embedded in the chamber cover refractory material. The resistance coil may be a direct current, but is preferably supplied with an alternating current, thereby heating the chamber cover. The chamber cover is usually between about 2 inches (about 5.08 cm) and 3 inches (about 7.62 cm) from the free surface of the glass melt, but can be larger if desired. Accordingly, the volume 35 is defined between the stirring chamber cover 32, the stirring wall 16 and the glass free surface 26.

  The chamber cover 32 includes a passage through which the stirrer shaft 22 passes. The inner surface of this passage may have a lining forming a casing 36. As with the other components of the agitation chamber, the casing is preferably durable against high temperature and corrosive gas corrosion and condensate generated from the molten glass. The casing 36 is usually made of platinum or a platinum alloy. The shaft 22 passing through the chamber cover passage forms an annular gap 38 between the outer surface of the shaft 22 and the passage, or if a casing 36 is used, the annular gap is the outer surface of the shaft. And the inner surface of the casing. For the sake of simplicity, in the following description, reference will be made only to the inner surface of the casing, but it should be construed to mean both examples, whichever applies. It is on the surface defining an annular gap 38 in which a condensate (eg platinum) is formed. When the condensate reaches a predetermined size, the condensate separates and falls into the glass melt 26, thereby creating defects in the final glass product. The portion of the shaft 22 above the chamber cover 32 is surrounded by a refractory material including the shaft heater 46. As with the cover heater 34, the shaft heater 46 preferably comprises a resistance heating element. The heating element is preferably made of platinum, but may be a platinum alloy.

  A heat insulating layer 42 is disposed above the chamber cover 32. The leading edge layer 44 similarly surrounds the shaft heater 46. The annular gap 38 eliminates contact between the rotating shaft and the casing, heater, insulation layer and cover.

  At least one flow tube 50 may extend from the outside of the stirring chamber 10 to the inside of the stirring chamber 10, ie, to the volume 35. The flow tube may be used to cause a gas flow along the agitation shaft, thereby reducing the condensation of volatile oxides along the shaft.

  A condensate collection vessel 40 is disposed on the agitator shaft below the cover 32 and above the glass melt 26. The container has an annular flat bottom 41 arranged substantially perpendicular to the agitation shaft 22. The condensate collection container includes a side wall portion 43 extending in the vertical direction around the outer edge portion. The combination of the bottom 41 and the side wall serves to accommodate any platinum or other condensate that is formed on the inner surface of the annular gap 38 and can subsequently fall. In one embodiment, the bottom area is greater than the cross-sectional area of the annular gap 38. In other embodiments, the distance from the outer surface of the shaft to the side wall of the condensate collection container is between 0.5 and 2 inches (about 1.27 to about 5.04 cm). The height of the side wall may take any value, but in one embodiment is in the range of 0.25 inches (about 0.635 cm) to 1 inch (about 2.54 cm).

  As shown in the partial perspective view of the condensate collection container 40 (FIG. 2), the annular bottom is flush with and surrounds the shaft. The surrounding side wall defines the outer boundary of the container. There is no lid so that the condensate falling from above will land and be contained in a container defined by the annular bottom 41 and the surrounding side wall 43. The condensate collection container 40 may be attached to the shaft by various methods, but in one embodiment, a collar 45 is formed that contacts the shaft 22 along a predetermined length. The collar 45 may be welded to the shaft or otherwise joined. In one embodiment, the condensate collection vessel is attached to the shaft by combining two semi-annular parts and welding them along a radial weld line 47.

  FIG. 3 is a cross-sectional view of the condensate collection container 40. In one embodiment, the angle θA formed by the bottom portion and the outer peripheral wall may be 90 to 120 degrees. In a preferred embodiment, the angle θA formed by the bottom and the outer peripheral wall is 100 degrees. Since the collar 45 is integral with the stirrer shaft 22, the angle θB formed by the bottom and the collar will match the angle of the outer wall of the shaft. In one embodiment, this angle θB is 85-90 degrees.

  The condensate collection container may be made from a material that is known to be capable of withstanding the actual temperature type of the stirring chamber. For example, the condensate collection container may be made of platinum, but may also be made of a platinum alloy, or dispersion strengthened platinum or a platinum alloy (eg, zirconia reinforced platinum alloy).

  In operation, the condensate collection vessel gradually collects the condensed platinum condensate that has left the annular gap as described above. When the glass manufacturing system is shut down for a maintenance process, the condensate in the container is collected and discarded or reused.

  It will be apparent to those skilled in the art that changes and modifications can be made to the present invention without departing from the scope of the invention. Accordingly, it is intended that the present invention encompass the modifications and improvements as long as the modifications and improvements are within the scope of the following claims and their equivalents.

DESCRIPTION OF SYMBOLS 10 Stirring chamber 12 Inlet pipe 14 Outlet pipe 20 Stirrer 22 Shaft 26 Glass free surface 32 Chamber cover 40 Condensate collection container

Claims (5)

A stirring chamber used for stirring and containing molten glass as part of a glass manufacturing system,
A cover having at least one wall and a flow path therethrough;
An agitator comprising a shaft extending through the flow path of the cover, thereby forming a circular gap between the shaft and the cover;
A condensate collection vessel having a volume above the free surface of the molten glass and a flat annular bottom located above the free surface of the molten glass and disposed substantially perpendicular to the shaft of the stirrer, A condensate collection container wherein the bottom has an edge and a vertically extending side wall connected adjacent to the edge, the bottom and the side wall intersecting at an angle between 90 and 120 degrees; ,
A stirring chamber comprising:   The stirring chamber according to claim 1, wherein an angle generated by the intersection of the bottom portion and the side wall portion is 100 degrees.   The agitation chamber of claim 1, wherein the condensate collection vessel further comprises an annular collar for attaching the vessel to the shaft.   The stirred chamber according to claim 1, further comprising at least one gas flow tube that allows gas flow into the chamber and through the volume.   2. The agitation according to claim 1, wherein the distance from the agitation chamber to the side wall of the condensate collection container is between 0.5 and 2 inches (about 1.27 to about 5.04 cm). Chamber.

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