Compositions: ceramic – Ceramic compositions – Pore-forming
Reexamination Certificate
1995-04-07
2001-09-04
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Pore-forming
C501S085000, C501S111000, C501S127000, C501S128000
Reexamination Certificate
active
06284688
ABSTRACT:
This invention relates to refractory compositions which are used in their dry state to produce refractory articles, for example linings for furnaces or metallurgical vessels such as ladies, tundishes or launders.
Refractory products, whether they be pre-formed articles for a particular application or linings for furnaces or metallurgical vessels are usually produced by methods, such as ramming, trowelling, spraying or casting, using wet refractory compositions in the form of an aqueous slurry or a mouldable or castable mass. Such methods have disadvantages in that they are time consuming since apart from the initial application or forming process they require a drying step and often additional calcining or sintering steps. It is also necessary to maintain the composition in a suitable condition for application and this can be a problem because the solid materials tend to settle. Some of the methods, for example, spraying, require relatively complex equipment which in use can become blocked, and all the wet methods require an on-site supply of water for producing the compositions in a form suitable for application.
Alternative methods have therefore been proposed which involve the use of substantially dry refractory compositions which can be set or hardened by heat after forming or application.
European Patent Application Publication No. 0064863 describes a method of applying a monolithic refractory layer within a metallurgical vessel using a substantially dry particulate mixture comprising at least 70% by weight of refractory aggregate, at least 0.5% by weight of thermosetting resin, from about 0.5% to 10% by weight of an inorganic binder and optionally from about 0.5% to 10% of an inorganic hydrate.
International Patent Application Publication No. WO 92/09542 describes a thermally activated, dry refractory composition which is used for the production of a new refractory lining or the repair of an existing refractory lining in a furnace or other high-temperature vessel. The composition may consist of from about 35% to about 85% by weight of a refractory aggregate and from about 15% to about 50% by weight of a hydrated material containing from about 5 to about 9 moles of chemically bound water in crystalline form, the water constituting from about 7% to about 35% by weight of the total composition.
The hydrated material is present in a sufficient amount, with respect to the amount of chemically bound water contained therein, to provide moisture to the composition to cause self-flowability of the composition when the composition is applied to a hot surface to be lined or repaired.
It has now been found that the performance of dry refractory compositions containing an inorganic binder having chemically or physically bound water can be improved if the composition also contains an element or compound which will react exothermically with the inorganic binder.
According to the invention there is provided a substantially dry, self-hardening, thermally activated refractory composition comprising a particulate refractory material, an inorganic binder having associated therewith chemically or physically bound water and an element or compound which will react exothermically with the inorganic binder, characterised in that the composition contains 70% to 95% by weight of particulate refractory material, 1% to 15% by weight of the inorganic binder (including the chemically or physically bound water) and 1% to 15% by weight of the element or compound which will react exothermically with the inorganic binder.
The particulate refractory material may be, for example, silica, zircon, silicon carbide, alumina (corundum), magnesia (calcined magnesite), calcined dolomite, chrome magnesite, olivine, forsterite, mullite, kyanite, andalusite, chamotte, carbon or chromite or a mixture of two or more of those materials.
The composition may also contain low density particulate refractory materials such as expanded perlite, expanded vermiculite, diatomaceous earth or fly ash floaters in order to reduce the density of the cured composition if desired.
Examples of suitable inorganic binders having chemically bound water associated therewith are crystalline hydrated salts such as silicates, carbonates, sulphates, nitrates, borates or phosphates. These salts include sodium metasilicate pentahydrate, sodium metasilicate nonahydrate, aluminum sulphate octadecahydrate, magnesium sulphate heptahydrate, sodium tetraborate decahydrate, magnesium carbonate trihydrate, magnesium nitrate hexahydrate, aluminium potassium sulphate dodecahydrate, aluminium sodium sulphate dodecahydrate and tribasic sodium phosphate dodecahydrate. Sodium silicate pentahydrate and tribasic sodium phosphate dodecahydrate are preferred. Examples of suitable inorganic binders having physically bound water associated therewith are micro-encapsulated sodium silicate solution (waterglass) and micro-encapsulated aqueous aluminium orthophosphate solution.
The element or compound which will react exothermically with the inorganic binder may be, for example, ferrosilicon, calcium oxide, magnesium oxide, aluminium or cement. Aluminium is preferred and can be used as a powder or as small particles of foil.
In order to prevent premature reaction between the inorganic binder and the element or compound which will react exothermically with the binder, it may de desirable to include in the composition an inhibitor for example a mineral or vegetable oil. When used the inhibitor will usually constitute from about 0.1% to about 5% by weight of the refractory composition.
The substantially dry refractory compositions of the invention may be prepared by thoroughly mixing together the individual components.
The compositions may be used to produce refractory articles by various means, for example, by filling a suitable mould, or in the case of the production of a lining in a metallurgical vessel by filling the space between the surface to be lined and a suitable former with the composition, and then locally heating the composition to initiate a hardening reaction between the inorganic binder and the element or compound which reacts exothermically with the binder. Local heating of the composition may be achieved by using a mould, former or vessel which is at least partly heated or by applying heat to a portion of the composition, for example by means of a gas torch.
The refractory compositions of the invention are substantially dry flowable powders which may be readily used for a variety of applications, and in particular for producing facing or backing linings for furnaces or for metallurgical vessels such as ladles, tundishes, launders or pot cells used in the smelting of aluminium, and for producing refractory shapes. The compositions have a relatively short curing time so that shapes, linings etc. are ready for use relatively quickly, and they can be formulated so as to produce light-weight, highly heat-insulating articles.
The following Examples will serve to illustrate the invention:
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Fessel Manfred
Mellows Vincent Edward
Stötzel Reinhard
Trinkl Gerd
Foseco International Limited
Group Karl
Nixon & Vanderhye P.C.
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