This invention relates to a hydraulic heat-resisting material and a premold product which uses the hydraulic cement as a binder, more particularly to a hydraulic heat-resisting material and a premold product of an improved thermal property which show a high strength and high volume stability under high temperature.
Castable refractories have been widely used for furnaces of various industries due to its readiness in furnace constructing engineering, its easy handling in application and its contribution to the man-power saving.
Generally, such castable refractories substantially consists of a heat-resisting aggregate and a binder, wherein the aluminous cement has been widely used as the binder due to its early high-strength and high heat-resistance.
However, such aluminous cement has following defects, namely, (i) the cement sharply decreases the strength thereof at a low temperature zone due to the change of crystal structure, and (ii) the cement is extremely expensive. Therefore, the aluminous cement has not been used for a general purpose or use.
The present invention has started from the idea to employ the hydraulic cement as a binder for the castable refractories instead of the aluminous cement which have the above-mentioned defects. The hydraulic cement has been used exclusively as a binder of a concrete for civil and architectural engineering.
However, the hydraulic cement contains 3CaO.SiO.sub.2, 2CaO.SiO.sub.2 as the main components thereof.
These components produce a considerable amount of free calcium hydroxide besides the hydrate of the calcium silicate due to the hydration. This free calcium carbonate reacts with the carbon dioxide in the air to produce the calcium carbonate. This reaction increases the speed thereof along with the temperature elevation, and the calcium carbonate is subjected to the decarboxylation above 600.degree. C. to produce the calcium oxide. Meanwhile, the calcium hydroxide is subjected to the dehydration above 450.degree. C. to produce calcium oxide. The calcium oxide produced in the above manner, when being cooled, reacts with the water in the air to produce calcium hydroxide. These chemical reactions provide a physical reaction simultaneously. Namely, the calcium carbonate which was produced by the carbonation of the calcium hydroxide has a high specific gravity and such calcium carbonate is produced with gaps around constituent grains thereof so that the structure thereof is weakened resulting in the poor strength thereof. Furthermore, although the hydration of the calcium oxide produces the calcium hydroxide which has a low specific gravity, such calcium hydroxide provides the expansion thereof and the cracks therein also resulting in the weakening of the structure and the poor strength. These defects of the hydraulic cement has hampered the utilization of the hydraulic cement as a binder of the heat-resisting material.
The inventors have made an extensive research to produce a hydraulic heat-resisting material which can be produced cheaply and has high strength and high volume stability by improving such defects of the hydraulic cement. It has been already known that the above-mentioned defects of the hydraulic cement, e.g. portland cement are derived from the free calcium hydroxide which is produced by the hydration and that several methods are proposed to prevent the ill-effects of the free calcium hydroxide. In concrete industries, one method proposed the addition of various admixing agents, such as soluble terra, fly ash, blast furnace slag to the free calcium hydroxide. However, all these admixing agents reacts very slowly in a long period. Therefore, although the agents may be used in the production of the concrete, they are not suitable for the production of the heat-resisting material where the period from the completion of the casting to the actual servicing is extremely short.
The inventors have further continued the research to improve the reaction speed of an admixing agent with the free calcium hydroxide and have noticed the surface activity and the grain size of the silica particles or grains, and finally, have found out that the ultra-fine amorphous silica could provide the remarkable effect to improve the reaction speed. It was also found that the use of 9.7 to 49.95% by weight of the ultra-fine amorphous silica relative to the 87.3 to 49.95% by weight of the hydraulic cement is most effective. The present invention is completed based on this finding.
The present invention relates to a hydraulic heat-resisting material of early high-strength which consists of 5 to 70 parts by weight of mixture, the mixture being made of 49.95 to 87.3% by weight of the hydraulic cement, 49.95 to 9.7% by weight of ultra-fine amorphous silica and 0.1 to 3% by weight of a dispersing agent, and 95 to 30 parts by weight of the heat-resisting aggregate.
As the hydraulic cement which can be used in the present invention, the portland cement, the blast furnace cement, the fly ash cement, the acidproof cement are considered.
As the ultra-fine amorphous silica, as a primary particulate, the amorphous silica having the particle size of 0.01 to 3.mu. is most preferable. The amount of the amorphous silica should be 9.7 to 49.95% by weight and preferably be 14.55 to 39.96% by weight relative to 49.95 to 87.3% by weight of the hydraulic cement. When the amount of amorphous silica is less than 9.7% by weight, the reaction-speed improving effect is decreased, while when the amount exceeds 49.95% by weight, although the reaction-speed improving effect is maintained, the firing shrinkage increases thereby the volume stability is worsened.
In the structure of a castable refractories using the cement, the cement are generally not dispersed uniformly and the major portion of the cement are segregated in the structure forming granulates having the size of about 40 to 60.mu.. This implies that the cement are not effectively utilized in the structure. To promote the utilization of the cement, if the cement is dispersed uniformly in the structure in a condition of primary particulates, the refractories can obtain the strength greater than the strength of conventional refractories even when the amount of the cement added is small. The dispersing agent of this invention is used for the above dispersion of the cement. As the dispersing agent, the alkali metal salt or the ammonium salt of the alkylsulfonic acid, and the alkali metal or the ammonium salt of the alkylarylsulfonic acid are considered.
The addition amount of the dispersing agent should be 0.1 to 3 parts by weight relative to 49.95% to 87.3% by weight of the cement. When the amount is less than 0.1% by weight, the cement suffers a poor dispersing property and an anhydration, while when the amount is more than 3% by weight, depending on a kind of the dispersing agent, the dispersing property and the anhydration both decrease or although the dispersing and the anhydrating effects are maintained at favorable levels, the dispersing agent becomes expensive and provides an ill-effect on the quality of the heat-resisting material. In the present invention, the addition of the dispersing agent disperses the hydraulic cement uniformly so that the cement necessary for the production of the heat-resisting material can be minimized. Simultaneously, due to the anhydrating effect, the cement water ratio can be lowered whereby the heat-resistance, the volume stability and the strength of the matrix can be greatly improved.
Furthermore, this dispersing agent can sufficiently disperse the co-existing ultra-fine amorphous silica so as to make the silica as carriers of the cement particles, whereby the dispersion and the anhydration of the cement are further enhanced.
The heat-resisting material of the present invention includes the heat-resisting aggregate besides the mixture of the above-mentioned hydraulic cement, the ultra-fine amorphous silica and the dispersing agent.
As the heat-resisting aggregate, agalmatolite, chammotte, sillimanite, kyanite, andalusite, synthetic mullite, bauxite, fired alumina shale, fired alumina, electrofused alumina, silicon carbide, silicon nitride, zircon, zirconia, magnesia, spinel, lime-stone, green dolomite, forsterite, chromite, sandstone, shale, basalt, andesite, rhyolite, granite, diorite, serpentine, slate, gravels, sea sand, river sand, mountain sand are considered.
Although the composition ratio between this heat-resisting aggregate and the mixture consisting of the hydraulic cement, the ultra-fine amorphous silica and the dispersing agent is preferably chosen to provide a desired strength and heat-resistance to the hydraulic heat-resisting material, such ratio should be 5 to 70 parts by weight:30 to 90 parts by weight. When the amount of the mixture is less than 5 parts by weight, the material lowers the strength thereof, while the amount of the mixture exceeds 70 parts by weight, the material lowers the heat-resistance and the volume stability.
Besides the above-mentioned hydraulic cement, the ultra-fine amorphous silica and the dispersing agent, the material of the present invention may include a shrinkage restricting agent for providing the effect of an expansion cement, and a lightweight aggregate such as a alumina balloon, "silasu" balloon (volcanic ash) or pumice or a foamed material such as a foamed styrol or a foamed polyethylene for providing the effect of a heat-insulating cement. Furthermore, the material of the present invention may include steel fiber, stainless steel fiber, glass fiber, ceramic fiber, carbon fiber, alumina fiber which are usually used to increase the strength of the material. Still furthermore, for providing the explosion-resistance at the stage of drying, the material of the present invention may contain metal aluminium or metal silicon as an exothermic material. Still furthermore, the material of the present invention may contain organic fiber or inorganic fiber to increase the heat-insulating effect and the strength of the material.
The manner in which the material of the present invention is used, for example for furnace construction is hereinafter disclosed.
A desired amount of water is added in the material of the present invention which has the above composition and the mixture is applied to furnace lining in the same manner as the conventional concrete or castable refractories, namely by gravity casting, by vibration casting, by vibration molding, by spraying, by injection, by troweling, by slinging, or by ramming. The material may also be applied such that the material is mixed with water to produce a mixture, the mixture is then cast in a mold having a desired shape and size by making use of any one of the methods described above, and after being hardened, a block is removed from the mold and is subjected to an air curing, a steam curing or drying to produce a premold product. It may be possible that after mixing the material of the present invention with water, a mixture is subjected to an extrusion molding and an ensuing press molding to be formed into a desired shape and then is subjected to a natural curing, a steam curing and a heat-drying to produce an unburned brick.
Besides the above uses, the material of the present invention can be used to produce following means or devices all of which belong to the iron and steel industry.
(i) blast furnace PA1 foundation, shaft, heat-proof plate, circular tube, cast house, trough cover, floor of slag processing plant, partition PA1 (ii) hot blast store PA1 foundation, tuyere, hot blast tube PA1 (iii) coke oven PA1 foundation, main chimney, door, cooling chamber of coke-wharf-dry-quenching chamber, upper deck of coke oven, coke guide car PA1 (iv) converter PA1 heat-proof plate, COG duct PA1 (v) others PA1 working floor of mold yard, runner, brick fastener, ingot transport car, foundation of continuous casting machine, foundation of heat treatment furnace such as soaking pit, annealing furnace, inner lining, outer lining, chimney, working floor of strip mill.
Furthermore, the material of this invention is applicable to the similar places or equipments in non-ferrous metal industry and chemical industry, cement industry, or ceramics industry. Still furthermore, the material is applicable to incinerators, nuclear reactor, rocket launch complex or the foundation of various buildings which are conventionally made of cement. The material can also be used in any field with a temperature ranging from 20.degree. to 130.degree. C.