Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
1999-12-10
2004-01-06
Sample, David (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S070000
Reexamination Certificate
active
06673730
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to infrared and/or ultraviolet radiation absorbing soda-lime-silica glass composition suitable for architectural and automotive glazing applications. The glass article has high redox values greater than 0.38 which makes the article difficult to melt from batch and refine in a horizontal continuous furnace with a melter and refiner. The melter of the furnace is heated at least partially from overhead fossil fuel fired burners and the melted glass moves and advances along as a pool of molten glass maintained in the melter and through the refiner and to a glass forming operation.
2. Technical Considerations
Infrared and ultraviolet radiation absorbing colored glass substrates have a variety of different applications. In particular, such glasses may be used by architects to glaze buildings and by vehicle designers as automotive windows. Besides providing an aesthetically pleasing color, these glasses may also provide enhanced solar performance as compared to conventional clear glass.
Different materials may be added to the glass in order to provide the desired color and spectral performance. For example, iron, cobalt, nickel, selenium, cerium, and titanium, to name a few, are typically added to provide the desired color composition. As materials are added to change color and enhance solar performance, care must be taken to maintain the visible light transmittance and color required for that particular application. It should also be remembered that changing the thickness of the glass affects these spectral properties so that a particular composition which has acceptable color and performance at a particular thickness may not be acceptable at a different thickness. The conversion of these properties to different thickness of glass is discussed in U.S. Pat. No. 4,792,536 to Pecoraro, et al. at column 15 line 59 through column 16 line 7.
One particular blue composition that provides superior spectral performance is disclosed in U.S. Pat. No. 4,792,536 to Pecoraro, et al. Commercial products covered by this patent were sold by PPG Industries, Inc. under the SOLEXTRA® and AZURLITE® trademarks. This glass incorporates a moderate amount of iron in the composition and has a relatively large portion of the glass in the ferrous state, expressed as FeO. In particular, the glass composition includes a basic soda-lime-silica composition and further includes 0.45 to 1 weight percent total iron (expressed as Fe
2
O
3
). At least 35 percent of the total iron is in the ferrous state. The dominant wavelength of these glasses range from about 486 to 489 nanometers (“nm”) and excitation purity ranges from about 8 to 14 percent. From a processing standpoint, producing the glass disclosed in this patent with a high ratio of ferrous iron to total iron may require additional processing considerations not typically associated with conventional glass melting operations, as are well known in the art.
Horizontal elongated continuous melting furnaces with several different operational sections for the molten pool of glass leads to forming operations at one end to produce flat glass from batch materials and optionally cullet generally introduced to the furnace at the opposite elongated end. The furnaces melt the batch and any cullet through the application of heat to form a pool of molten glass that flows through the furnace for refining and conditioning into formable melted glass withdrawn for forming flat glass. Furnaces of various design have various heat sources such as overhead fossil fuel fired burners and/or electric heat sources. Fossil-fueled furnaces include regenerative furnaces and recuperative furnaces, and electric furnaces include those as illustrated in U.S. Pat. No. 2,225,616 and U.S. Pat. No. 2,225,617. There are fossil fuel-fired furnaces which include electric-boosting electrodes as shown in U.S. Pat. Nos. 2,397,852, 2,600,490, 2,636,914 and 2,780,891. In general, when both electricity and fossil fuels have been used to provide heat to the same glassmaking furnace, the fossil fuels have been employed to melt glass batch in the region of the furnace where batch is advancing freely through the furnace from its charging kilns. Electrodes have been positioned at various locations in the furnace in order to assist in melting batch, to heat molten glass beyond the region of unmelted batch, and to strengthen the convective flow, known as the “spring zone” flow, within the molten glass as shown in U.S. Pat. Nos. 2,512,761, 2,636,914 and Canadian Pat. No. 634,629, and the like.
The solar absorbing glasses, like those with a high redox value of greater than 0.38 with the higher amounts of the reduced form of iron, ferrous iron, and especially with high iron concentration of greater than 0.45 to 1.5, pose challenges in melting and refining and conditioning in horizontal continuous furnaces. The melting and refining and/or conditioning whether in one, an adjoining, or separate sections or zones of the furnace for the refining and conditioning operations can each experience similar and different upsets and impediments in producing these glasses. Although the higher amount of ferrous iron results in glasses that absorb infrared energy, this higher amount of ferrous iron also provides for low effective thermal conductivity in the glass melt. This leads to a more pronounced temperature gradient in the depth of the pool of melted glass than is encountered with lower redox glass melts. Consequences of such a situation depending on the location within the furnace can result in a much lower tolerance to both changes in temperature and depth of the melted glass pool. Results of these situations can range from bubble defects and/or ream defects or imperfections in the flat glass product to premature glassy formations from the molten glass in the furnace. These defects include gradations for each. For instance the bubble defects range from seed defects to partial and to closed bubble defects that can occur at different locations in the depth of the glass product such as top and bottom bubble defects. The ream defect relates to Rayleigh instability as described in U.S. Pat. No. 3,836,349.
Also one way of achieving a higher redox value in glass is the formation of ferrous iron during melting and/or refining of the glass melt for the solar absorbing glasses through the use of reductants and the removal of oxidizers from the batch and/or cullet ingredients. For the refining of a glass melt in horizontal continuous furnaces having overhead fossil fuel firing, chemical fining agents such as sulfur-containing fining agents generally are used. These fining agents assist in the removal or resolution of gaseous inclusions from or in the melt. The dilemma is that the sulfur-containing fining agents are oxidizers which depending on their amounts can shift the balance of the amount of reduced iron, ferrous iron, to oxidized iron, ferric iron, in the glass melt and product creating difficulties in achieving higher redox values. The reduction or removal of sulfur-containing oxidizing fining agents from the batch ingredients can impede the fining operation of the melted glass. A resolution is needed for the use of sulfur-containing fining agents to obtain high quality glass with minimum defects while at the same time limiting the oxidation of iron to achieve higher redox values for the glass.
The favorable acceptance of the SOLEXTRA product makes it advantageous to produce a type of glass having a similar color and enhanced spectral performance using conventional glass melting furnaces. Also the market may find glasses of other colors such as green, blue-green, green gray, blue grey and grey with good spectral properties to be of value. Also the production of solar performing glasses of these other colors with their higher ferrous content could benefit from more facile production processes in more conventional melting furnaces in a manner similar to that for a type of glass like the SOLEXTRA glass.
An object of the present invention is to produce qualit
Bolden Elizabeth A
PPG Industries Ohio Inc.
Sample David
Siminerio Andrew C.
Stachel Kenneth J.
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