Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
1999-11-18
2001-09-11
Marcantoni, Paul (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S128000
Reexamination Certificate
active
06287994
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
A ceramic fiber insulation material is disclosed that is useful in high temperature applications. There is also taught a method for producing the insulation material.
2. Description of the Prior Art
Insulating materials for use in high temperature applications were historically made from asbestos. Besides its excellent thermal insulative properties, asbestos can be manufactured into various geometric shapes for particular applications. For example, annular discs of asbestos can be used to form an outer insulating cover for high temperature roller conveyors. A roller conveyor can be made with an inner metal shaft and an outer insulating cover. The asbestos discs are stacked onto the shaft, and pressed together axially, as discussed, for example, in U.S. Pat. No. 3,802,495. The discs can also be pressed together by hydraulic means as taught in U.S. Pat. No. 3,116,053. Asbestos, in conjunction with a binder, may be formed into numerous shapes besides annular discs, e.g., board product or end caps for furnaces. The health consequences of asbestos exposure has created a need for asbestos-free insulation.
Ceramic fiber has been successfully used as a replacement for asbestos in certain applications. For example, it is taught in U.S. Pat. Nos. 5,205,398 and 5,378,219 to use ceramic fiber as a roll cover. Annular discs of bulk ceramic fiber are stacked onto an inner metal shaft and may be axially compressed at greater than about 50 percent of the fiber's original density. The compressed discs on the metal shaft may be perfused with colloidal silica and dried. The discs are then recompressed and held permanently in compression. Insulating roll covers produced by this process can offer improved insulating properties over asbestos and are substantially free of fugitive binders. The resulting product can have a density above about 40 pounds per cubic foot. A variation of this technology, as described in U.S. Pat. No. 5,355,996, obtains improved wear resistance by periodically sandwiching perforated, rigid, metal discs between the ceramic discs.
Ceramic fibers have also been used as a replacement for asbestos in those areas requiring complex shapes. Fiber is commonly blended with a suitable binder to produce a mixture. A vacuum draws the fiber and colloidal mixture into a mold and substantially removes the binder. A porous fiber product remains. This technology permits ceramic fiber components to be fashioned into various shapes. However, unlike compression techniques, vacuum-forming does not compact the ceramic fibers to a high density and may not imbue the article with desirable strength. The resultant product is of low density, typically no more than 18 pounds per cubic foot. The surface of the product is rigid, but the interior may be weak and friable. Attempts have been made to improve the strength of vacuum-formed articles, e.g., by forming the article around an internal metal mesh.
Despite these improvements in ceramic fiber insulation technology, there is still a need in the industry for an improved, asbestos-free, insulating material, which may be fashioned without compression into a wide variety of shapes yet retain the ruggedness and long service life of asbestos. Current technologies, which compress ceramic fiber, possess excellent properties but cannot easily be fashioned into complex-shapes. Vacuum-formed, ceramic fiber articles may be formed into various shapes but lack the strength and durability of articles formed by compression.
SUMMARY OF THE INVENTION
The present invention describes a new insulating composition which combines the ruggedness of compressed fiber with the fabrication ease of a fiber slurry. Most always the new insulating blend comprises a gelled colloid blended with ceramic fiber filler. The use of other fillers, which fillers may be in combination with the ceramic fiber filler, is also contemplated. The blend may be applied to a surface, such as troweled onto a metal surface, or molded into complex shapes. After drying, the resultant ceramic fiber insulation material possesses excellent insulative properties in high temperature applications, and possesses a surface. exhibiting retarded wetting by molten metals, such as zinc and aluminum.
In a first aspect, the invention pertains to a ceramic fiber insulation blend comprising a gelled colloid and an at least substantially ceramic fiber filler, which insulation blend comprises between about 10 weight percent and about 40 weight percent of the ceramic fiber filler and between about 60 weight percent and about 90 weight percent of the gelled colloid, which gelled colloid has a viscosity above about 5,000 centipoise and comprises a colloid of an aqueous suspension of inorganic oxides.
In another aspect, the invention is directed to the above-described blend wherein the gelled colloid is a colloidal-blend of an anionically stabilized colloidal silica and a cationically stabilized colloidal alumina, with the anionically stabilized colloidal silica comprising from about 20 weight percent to about 65 weight percent of the gelled colloid, and the cationically stabilized colloidal alumina comprising from about 35 weight percent to about 80 weight percent of the gelled colloid.
In yet another aspect, the invention generally is directed to the above-described blend comprising a colloid of a metal oxide and a gelling agent, and more specifically such a blend that comprises colloidal silica in mixture with an at least substantially water-soluble, nonionic polymeric gelling agent. In a related aspect, the invention is directed to the above-described blend comprising a colloid of colloidal silica, colloidal alumina, colloidal zirconia, colloidal titania, or their mixtures.
A further aspect of the invention pertains to a blend comprising a gelled colloid and a filler, which gelled colloid is a gelled colloid as more particularly described hereinbefore and which is present in an amount as also described hereinabove. The filler may be blended with ceramic fiber filler or may be other than ceramic fiber filler.
Another aspect of the invention pertains to a method for producing a ceramic fiber insulation blend from an aqueous colloid of an inorganic oxide, which method comprises:
(a) establishing the aqueous colloid in ungelled form and at a viscosity below 5,000 centipoise;
(b) gelling the colloid to a gelled colloid having a viscosity above about 5,000 centipoise; and
(c) blending the gelled colloid with an at least substantially ceramic fiber filler in an amount providing between about 10 weight percent and about 40 weight percent of the ceramic fiber filler in the resulting insulation blend.
A still further aspect of the invention is directed to a gelled colloid adapted for blending with a filler to form an insulation blend, the gelled colloid comprising an aqueous suspension of inorganic oxide, with the gelled colloid having a viscosity above about 5,000 centipoise.
Still another aspect of the invention is the ceramic fiber insulating material produced by drying any above-described insulation blend, which material is for use in high temperature applications. Drying typically yields an insulating material having a density within the range between about 20 pounds per cubic foot and about 70 pounds per cubic foot.
As noted hereinabove, the blend may be molded into a shape, or may be troweled onto a surface. It is also pumpable and can be gunnable. Then, the insulating material obtained on drying can be virtually shrink-free.
Other details, objects and advantages of the invention will become apparent in the following description of the present preferred embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Most commonly, for providing the insulation blend, fillers will include fibers and the fibers used will be inorganic refractory fibers and contain some ceramic fiber, e.g., from about 20 weight percent to 100 weight percent of the total amount of refractory fiber present, and usually greater than about 50 weight percent will be ceramic fiber. Other refractory fibers
Freer John J.
Global Consulting, Inc.
Marcantoni Paul
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