The disclosure relates generally to the field of glass production, and more particularly to an apparatus and method for minimizing the inclusion of platinum group metal particulate matter into molten glass during the glass manufacturing process.
A system 100 for making glass comprises a series of interconnected components, as illustrated in the schematic of
Flat display devices such as liquid crystal displays (LCDs) are made from flat glass substrates or sheets formed from molten glass. Reactions which occur during the melting stage release gases which form bubbles in the glass melt. Seeds may also be generated by interstitial air trapped between particles of the feed materials. In any event, these gas bubbles and seeds (collectively referred to herein as gaseous inclusions) must be removed to produce high quality glass. The removal of gaseous inclusions is generally accomplished by “fining” the glass melt. For clarity, gaseous inclusions formed as a result of the melting process, whether as reaction products or interstitial gases, may also be referred to as “blisters” or “bubbles.”
A common method of fining a glass melt is by chemical fining. In chemical fining, a fining agent is introduced into the glass melt, such as by addition to the feed material. The fining agent may be a multivalent oxide material that is reduced (loses oxygen) at high temperatures, and is oxidized (recombines with oxygen) at low temperatures. Oxygen released by the fining agent may then diffuse into the seeds formed during the melting process causing seed growth. The buoyancy of the seeds is thereby increased, wherein they rise to the surface of the glass where the gas is released out of the melt. Ideally, it is desirable that the fining agent releases oxygen late in the melting process, after most of the seeds have formed, thereby increasing the effectiveness of the fining agent. To that end, although large seeds may be eliminated in the melting vessel, the glass typically undergoes additional fining in a fining vessel, where the temperature of the glass melt is typically increased above the melting temperature. The increase in temperature of the glass melt within the fining vessel reduces the viscosity of the glass, making it easier for seeds in the glass melt to rise to the surface of the glass, and a multivalent oxide fining agent will release a fining gas (oxygen) to the glass melt to cause seed growth and assist with the seed removal process. Once the glass melt has been fined, it may be cooled and stirred, and thereafter formed, such as into a glass sheet, through any one of a variety of available forming methods known in the art.
At temperatures above about 1000 degrees C., however, released oxygen from the fining process, or present in the open finer since the finer is open to ambient air through a vent, causes exposed platinum group metal particulates from the inner surfaces of the system components to oxidize according to the following equations:
Pt(s)+O2(g)<->PtO2(g)
Rh(s)+O2(g)<->RhO2(g)
Similar oxidation/reduction reactions occur with other platinum group metals. Platinum and rhodium are shown here as examples. If the temperature is lower in one part of the system than another, then some of the PtO2 and RhO2 gas will be reduced into platinum and rhodium or combination of metal particulates. If this platinum and rhodium particulate deposits or accumulates on the molten glass, then the glass surface of the subsequently formed glass sheet may include these particles, resulting in an unacceptable finished glass sheet. Alternatively, if the exposed platinum and rhodium surfaces above the molten glass line are cooler, then the particulate matter is most likely to deposit thereon, forming a strong diffusion bond on the platinum or platinum/rhodium surfaces, thus significantly reducing the amount of platinum or platinum/rhodium particulate that may be included in the molten glass.
As will be appreciated, while the deposition or bonding of platinum or platinum/rhodium particulate matter on the inner surfaces of the finer, or other system component, results in a shortened equipment lifetime, any particulate that does accumulate on the inner surfaces of the finer, or other system components, that are not in contact with the molten glass 126 significantly reduces the amount of particulate available to form inclusions in the molten glass 126. As a result, and to the extent that less platinum or platinum/rhodium inclusions/depositions do not get into the molten glass 126, the quality and quantity of finished glass sheets increases. Nonetheless, because the flanges in one embodiment are greater than a meter apart, there is substantial molten glass surface area between the flanges where the particulate form or deposit on the surface of the molten glass.
Thus, one aspect of the present disclosure is directed to an apparatus used in the manufacture of glass, which will facilitate reduction of undesirable particulate on or in the molten glass in the space between the flanges. The apparatus comprises a first conduit, such as a finer, which is formed of platinum group metals, such as platinum/rhodium, and comprises a top wall portion, a side wall portion, an outer surface, and a length. A heat sink, also formed of platinum group metals, or other material of sufficient thermal conductivity, is affixed directly and substantially continuously to the outer surface of the first conduit and extends longitudinally along at least a portion of the length of the first conduit, proximate the top wall portion for the dissipation of heat therefrom. As used herein, the term “heat sink” refers to a material that is added to an apparatus or device for the purpose of absorbing and dissipating heat. The heat sink material may comprise one or a combination of forms, including solids, liquids, or gasses. Also, as used herein, the term “continuously” means uninterrupted, unbroken, and without substantial gaps or openings. In one embodiment, this means at least about 70% of the heat sink is in direct contact with the first conduit.
A further aspect of the present disclosure is directed to a process for minimizing the inclusion of platinum group metal particles into molten glass during glass manufacture in a system comprising platinum group metal components, such as vessels, conduits, standpipes, etc. The method comprises the step of processing or conveying molten glass through a conduit or vessel, wherein the conduit or vessel comprises a top wall portion not in direct contact with the molten glass, a side wall portion that is in direct contact with the molten glass, and an inner surface area. A heat sink is located on the outside top wall portion of the conduit or vessel which is not in direct contact with the molten glass. When the molten glass formed during the manufacturing process is conveyed or held within the conduit or vessel, the heat sink creates a selected temperature differential between the maximum temperature in the conduit or vessel and the heat sink. Furthermore, the heat sink creates cold spots inside the conduit or vessel top wall portion. The heat sinks/cold spots are designed such that they are in close proximity to the hottest areas inside the top wall portion of the conduit or vessel. Thus, particulate formed during the manufacturing process will form, or deposit, on the inner surface cold spots of the top wall portion not in contact with the molten glass. In an embodiment, this comprises deposition on the top wall portion between about 5% and 50% of the top wall surface area not in contact with the molten glass 126. In other words, in an embodiment the cold spot comprises 5% to 50% of the top wall surface above the glass. It has been found that a temperature differential (between the hot and cold spots inside the conduit or vessel) as high as 150 degrees C. will create the desired effect; however, in one embodiment, the temperature differential, T(max inside top wall)−T(min inside top wall) is between 10 degrees C. and 50 degrees C. A lower temperature differential permits the system temperature within the vessel to be maximized, but maintained below the melting point of the platinum group metal.
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 embodiments as described in the written description and claims hereof, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.
The accompanying drawings are included to provide a further understanding, 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 principles and operation of the various embodiments.
Examples will now be described more fully herein with reference to the accompanying drawings in which example embodiments are shown. Whenever possible, the same reference numerals are used throughout the drawings to refer to the same or like parts. However, aspects may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.
Referring now in general to
As described above, the inventors have discovered that platinum group metal particulate will form or bond beneath the flanges 107 at each end of the finer 106, as shown in
Referring now to
As shown in
Turning now to
Yet another embodiment of the heat sink of the present disclosure is illustrated in
Turning lastly to
Unless otherwise expressly stated, it is in no way intended that the 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 any particular order be inferred.
It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the invention. For example, the various heat sink configuration described herein may be affixed to conduits by methods other than welding. Since modifications combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and their equivalents.