Fused Cast AZS block is also called electro Zircon corundum block, which is abbreviated as AZS because it contains Al2O3－ZrO2－SiO2. Alumina-zirconia-silica (AZS) fused-cast refractories began to increase in popularity in glass furnace applications for the glass contact and. fused Cast AZS refractories are the most widely used materials both in glass contact and superstructure of glass melting products are made of.
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Year of fee payment: A refractory composition includes a first set of components and a colloidal silica binder. The first set of components includes alumina and zirconia.
More particularly, this invention relates to colloidal silica refractories for the lining of furnaces, such as glass and brass furnaces.
Glass melting furnaces are refractory lined vessels shaped as containers for melting and holding glass. The glass-making materials usually include a mixture of cullet and batch materials. Cullet is crushed glass from the manufacturing process. Batch materials include sand silicalime limestone or calcium carbonate reduced to calcium monoxidesoda ash sodium monoxideand sometimes other materials such as feldspar, salt cake, and metal oxides. During the melting operation, the cullet melts first to increase the heat transfer to the batch materials and to reduce the melting time.
Glass melting furnaces include pot furnaces, glass tanks, tank furnaces, and the like. Glass may be constructed of separate refractory brick or blocks within a frame. The blocks fit together without mortar and typically are arranged in a rectangular shape to hold molten glass. The mechanical pressure from the frame and outer blocks holds the blocks together. The refractory blocks usually receive considerable wear from the molten glass and the charging of glass making materials.
Molten glass is highly corrosive. The refractory blocks usually are made of composite clays having alumina, zirconia, and silica AZS.
The AZS refractory blocks are made from molten material cast into molds, which are machined after hardening. The refractory blocks can become deeply scored and may develop wear spots or portions where the molten glass has eroded or dissolved the refractory.
The wear spots typically grow until the refractory fails to hold the molten glass. The wear spots shorten the service life of glass tanks and often are unpredictable, thus disrupting production of molten glass. Brass furnaces are refractory lined vessels shaped as containers for melting brass. Brass scrap is collected and transported to the foundry where it is melted in the furnace and recast into billets. The furnace is also used to heat up billets extruded the brass into the right form and size.
In one aspect, this invention provides a refractory composition especially useful for furnaces. The refractory composition has been found to provide excellent corrosion resistance. The refractory composition includes a first set of components mixed with a colloidal silica binder.
In another aspect, a method of preparing a refractory includes providing a first set of components and a colloidal silica binder.
The refractory composition is formed on the surface of a furnace. The foregoing and other features and advantages of the present invention will become apparent from the following detailed description of the presently preferred embodiments, when read in conjunction with the accompanying examples.
The present invention will now be further described. In the following passages, different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.
The present invention provides a colloidal silica refractory composition that is especially useful for glass melting furnaces. In particular, the refractory composition includes alumina, zirconia, and silica. The colloidal silica refractory provides surprisingly good resistance to high temperature corrosive environments. The refractory composition disclosed herein may also be used in other types of furnaces, such as brass furnaces. The refractory comprises a mixture of a colloidal silica binder with a first set of components.
The alumina, zirconia, and silica provide strength and corrosion resistance. The alumina may be provided by a high aluminum aggregate such as tabular or white fused alumina. The alumina may be reactive or calcined. The zirconia may be provided by zircon flour or a zirconia bearing material.
The silica may be provided by fumed silica, mullite aluminum silicatemicrosilica, colloidal silica, or the like. The various components are available from AluChem, Inc. Reading, OhioAlcan, Inc. Montreal, Canadaand other conventional suppliers. The colloidal silica binder holds or binds the first set of components together in a monolithic form. In one embodiment, the colloidal silica may have an average particle diameter in the range of about 4 nm through about nm. In one embodiment, the refractory composition does not include an effective amount of any other type of binder, such as a hydraulic cement binder.
Refractory materials that include cement tend to be difficult to dry when setting, especially at lower temperatures. Further, some cement refractories can generate low melting phases at the high temperatures typical of glass melting furnaces, thus leading to higher corrosion rates.
The median particle size of the first set of components may be greater than 40 microns. It is known that particle size effects the properties of the liquid refractory compositions such as pumpabilityas well as the mechanical and chemical properties of the final refractory. Proper particle provides good particle packing for reduced porosity, which leads to greater strength and less glass penetration in the refractory. The particle size of the refractory material allows for a multi-functional material which can be easy shotcreted, pumped or cast.
Fused AZS particles consist of particles each comprising alumina, zirconia, and silica. In contrast, the present composition preferably does not include fused AZS particles. Instead, the first set of components includes particles selected from alumina, zircon, silica, mullite, and the like.
The alumina particles preferably have an average particle size greater than 1 mm. The first set of components may contain no silica. Other proportions of the aza set of components may be used. The first set of components may include other compounds such as a setting agent. The first set of components may include about 0. The amount of setting agent may be adjusted to increase or decrease the setting time for the colloidal system refractory.
The first set of components also may include a flow modifier to enhance or alter the flow properties for forming the colloidal silica refractory prior to setting. The first set of components may be mixed prior to the addition of the colloidal silica binder.
The refractory composition may be cast into blocks for subsequent use in a glass tank or other furnace, or may be formed directly onto the wear portion of a glass tank or other furnace. Besides glass furnaces, the refractory composition may be used rffractory brass, copper, and bronze furnaces. The refractory composition may be formed on the wear portion using one or more refractory forming methods such as casting, pumping, or shotcreting formless pumping with a setting accelerant.
The refractory composition may be formed on one or more portions of the sidewall or hearth. The refractory composition may be formed directly on the wear portion without the replacement of refractory blocks in a glass melting furnace.
For illustration purposes and not as a limitation, Table 1 provides exemplary types and proportions of first set of components for the colloidal silica refractory system. For each Example, the first set of components was mixed together prior to mixing with the colloidal silica binder. The mixture cured into a colloidal silica refractory.
Thus, the refractory of Example 1 had azzs higher amount of zirconia than the refractory of the Comparative Example. To simulate the harsh conditions in a glass melting furnace, refractory corrosion tests were performed on the colloidal silica refractories to evaluate their resistance to molten glass.
The fingers were dipped into molten glass at a high temperature. After the test, the samples were cooled refractorh analyzed to determine the resistance of the refractory composition to the harsh conditions. The test was repeated for each sample for a total of two tests for each composition.
The cross sectional area of the pencil lost during the test was measured and the results were averaged. The pencil prepared from the formula of Comparative Example A lost an average of The pencil prepared from the formula of Example 1 lost only an average of Thus, the pencils prepared from the composition of Example 1 were surprisingly resistant to corrosion.
Thus, the colloidal silica refractories disclosed herein show superior resistance under harsh conditions compared to a prior art refractory. To simulate the harsh conditions in a glass melting furnace, refractory corrosion tests were performed to evaluate resistance to sodium hexametaphosphate.
Thin pencils of the refractory compositions of Example 1 and Comparative Example A were prepared. The pencils were dipped into sodium hexametaphosphate at a high temperature. After the test, the aazs were analyzed to determine the resistance of the refractory composition to the harsh conditions. A composition prepared according to Example 1 was applied in a brass furnace.
The furnace was operated for a period of time and the composition was found to perform well throughout the furnace. For Comparative Example B, the alumino-silicate product worked as above the bath line and the alumina-silicon carbide product worked well below the bath line, but neither material held up at the interface. The composition of Example 1 showed superior performance to the composition of Comparative Example B, especially at the bath line.
Various embodiments of the invention have been described and illustrated. However, the description and illustrations are by way of example only. Other embodiments and implementations are possible within the scope of this invention and will be apparent to those xzs ordinary skill in the art. Therefore, the invention is not limited to the specific details, representative embodiments, and illustrated examples in this ass.
Accordingly, the invention is not to be restricted refrsctory in light as necessitated by the accompanying claims and their equivalents. A refractory composition comprising: The refractory composition reftactory claim 1 wherein the refractory composition does not include an effective ass of a hydraulic cement.