JPS6126577A - Manufacture of lightweight alumina burnt product - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention relates to a method for producing a lightweight alumina fired product, and a method for manufacturing a lightweight alumina fired product (Special V), in which a urethane foam molded product containing mixed alumina powder as the main raw material is dried and fired at a high temperature. This article relates to a method for producing quality alumina fired products.

(Prior art) A-alumina obtained by calcining aluminum hydroxide at a temperature of about 1000 to 1 loo0c is called calcined alumina, and since this calcined alumina has excellent sinterability, it has a central particle size of 5 microns. A mixed composition liquid made by mixing a foamable polyurethane forming composition liquid into an alumina slurry made by mixing a certain amount of calcined alumina powder with water is poured into a mold, and the mixture is reacted and foamed.
It is known to dry this urethane foam molded product and then fire it at a high temperature to obtain a lightweight 7 μm molded product (for example, Japanese Patent Laid-Open No. 71851/1983).

On the other hand, sintered alumina made by further heating the above calcined alumina to a temperature close to the melting point of 2050°C, or ￥4i, i@alumina heated to a temperature above the melting point in an electric furnace, has excellent heat resistance, chemical resistance, and wear resistance. It has excellent properties such as elasticity, mechanical strength, and electrical insulation, and by taking advantage of these excellent properties, it can be used as a tool for high-temperature firing of non-industrial products, such as bases, shelves, plywood, or setters. Widely used as a material.

(Problem to be solved) Lightweight alumina molded products made from the above calcined alumina have excellent strength, but have insufficient thermal shock resistance, and are exposed to severe thermal conditions such as rapid heating and cooling. Not suitable for use with kiln tools.

Furthermore, since most of the firing parts such as kiln tools made of the above-mentioned sintered alumina and fused alumina are formed by the plenue method or casting method, their specific gravity is 2.6 to 8.
．． 2. If the molded product is large and has a large shape, it is heavy and requires a lot of labor to fill the kiln, making it difficult to work with. Further, since these firing members have a large specific gravity, their heat capacity is also large, and a large amount of thermal energy is required to heat them together with the product, which is not preferable from the point of view of energy saving. Furthermore, since sintered alumina or fused alumina has poor sinterability, products made only of sintered alumina or fused alumina obtained by applying the manufacturing method for lightweight alumina molded products using calcined alumina as a raw material have bending strength. , the thermal shock resistance deteriorates and it cannot be used for kiln tools.

(Means for Solving the Problems) The present invention is a method for manufacturing lightweight alumina molded products using mixed alumina powder, which is a mixture of fused alumina, sintered alumina, and a small amount of calcined alumina, as a raw material.

That is, the present invention provides fused alumina with a center particle diameter of 20 to 400 microns and sintered alumina with a center particle diameter of 70 to 400 microns.
Water or water and an active hydrogen-containing compound are added to a mixed alumina powder of 1% by weight of 95% by weight and 5 to 30% by weight of calcined alumina with a center particle size of 5 microns or less to make it alumina-free, and this alumina-free is foamed. This method of producing a lightweight alumina fired product is characterized by injecting a mixed composition solution containing a polyurethane forming composition solution into a mold, omitting reaction foaming, drying the urethane foam molded product, and then firing it at a high temperature.

Fused alumina and sintered alumina serve as aggregates for fired products, and their median particle size is 20 to 400 microns, preferably 50 to 250 microns. contraction is large,
Moreover, coarse particles protrude on the surface of the fired product, impairing the surface smoothness, and further reducing the sinterability of the fired product, making it impossible to obtain the desired strength and heat resistance. When the center particle size is less than 100 microns, the strength is high and the surface smoothness is good, but the thermal shock resistance is decreased.

Calcined alumina acts as a binder for fired products, and its center grain size is less than 5 microns.If it exceeds 5 microns, it becomes a binder phase and does not function adequately, resulting in poor strength and thermal shock resistance. is not enough.

The particle diameter corresponds to the median cumulative value (50%) in the particle size cumulative curve.

The mixing ratio of fused alumina and/or sintered alumina and calcined alumina is 70 to 95% by weight for the former and 5% by weight for the latter.
~ Weighted amount %. Mixing ratio of calcined alumina is 5% by weight
If it is less than that, the sinterability will be insufficient and the strength of the fired product will be low.
If it exceeds % by weight, the sintering properties will be too high, the strength will be too high, the thermal shock resistance will decrease, and the firing shrinkage will increase.

The above mixed alumina powder is blended with one or more inorganic oxides of magnesium oxide, calcium oxide, and silica as a sintering aid, or an inorganic compound generated during firing of these inorganic oxides. In this case, the sinterability of the fired product is improved, the firing temperature can be lowered, and the strength and thermal shock resistance of the fired product are improved. The blending ratio of the sintering aid is preferably 3% by weight or less based on the total amount of the mixed alumina powder and the sintering aid,
If more than this is mixed, the heat resistance may be lowered or the structure may be damaged.

~60 parts by weight of water for 100 parts by weight of the above mixed alumina powder
The weight parts are mixed to form an alumina slurry.

An active hydrogen-containing compound that reacts with the polyisocyanate compound in the foamable polyurethane forming composition liquid may be mixed with the alumina-free material.

Examples of the active hydrogen-containing compound include polypropylene glycol, polyethers such as polyethylene glycol, polyesters such as polyisocyanate, and mixtures thereof, and triethanolamine,
Compounds having a relatively low molecular weight in glycerin solution and various mixtures thereof can be used. Further, as the polyisocyanate compound which is another component of the foamable polyurecne forming composition liquid which is mixed with the alumina slurry and foamed by reaction, various usual polyisocyanate compounds are used, such as tolylene diisocyanate (TD Engineering),
Liquid diphenylmethane-4゜4゛-diisocyanate (
MDI), polyisocyanates such as crude MDI, and urethane prepolymers having free incyanate groups at the ends obtained by reacting the polyisocyanate compound with the active hydrogen-containing compound are used. Furthermore, catalysts and surfactants commonly used in the polyurethane industry, as well as deflocculants and binders commonly used in the company kiln industry, can be appropriately blended as auxiliaries for the above-mentioned foaming reaction and preparation of the alumina slurry. .

Amu minanura above! A mixed composition prepared by mixing 5 to (1) parts by weight of the foamable polyurethane forming composition to 100 parts by weight of J-100 is poured into a mold and reacted and foamed. After the foaming is completed, resin formation is completed and hardened. The above-mentioned foaming reaction is due to the foaming of carbon dioxide gas generated by the reaction between the water or active hydrogen-containing compound in the alumina slurry and the isocyanate-F group in the foamable polyurethane forming composition liquid. Foaming may be carried out by adding a low boiling point compound, for example trichlorofluoromethane, to the foamable polyurethane forming composition in advance.

Next, the urethane foam molded product cured in the mold is taken out from the mold, and then dried with hot air while still at room temperature, and this dried product is fired at a high temperature of 1500 to 1800°C.

In this firing process, polyurethane begins to thermally decompose at 200 to 300'C and is scattered, so at approximately 400°C
At step 1, the temperature will gradually rise. When a top sintering aid is added to the mixed alumina powder, the firing temperature is 1501')'C.
It is possible to obtain a fired product with predetermined characteristics.

In the case of mixed alumina powder with high purity and relatively coarse pieces, the firing temperature is approximately 1800'C. Of course, it can be changed accordingly.

(Example) ゛ Electro-fused alumina powder ζ with different center grain sizes is made by mixing water with mixed alumina powder of sintered alumina and calcined alumina with center grain size R, and making this alumina slurry. A mixture of various () foamable polyurethane producing compositions was poured into a mold, reacted and foamed at room temperature, and the urethane foam molded product was heated at 80°C and I2
Poetry 1'l (+ After drying, heat at 400° for 6 to 7 hours.
C. and then fired for 15 to 18 hours to obtain a light crab alumina fired product. Table 1 below shows the blending amount of the alumina slurry, the foamable polyurethane forming composition, and Table 2 shows the physical properties of the lightweight alumina fired product.

Table 2 (Physical property values) In Table 1, urethane composition liquid U1 contains 9 parts of triethanolamino 8N, polypropylene glycol (average molecular weight 70
00) 7 parts by weight, 111 parts by weight of crude MD, and a small amount of surfactant (trade name H, EtX-607, manufactured by Toshi Silicone Co., Ltd.), and triethanolamine was mixed in advance without alumina. R2 was prepared by mixing 1 mole of an ethylene oxide-propylene oxide copolymer (average molecular μ5000, ethylene oxide content 70% by weight) using ethylene glycol as an initiator and 3 moles of TD.

This is a hydrophilic urethane prepolymer (N00 value 7.2% by weight, NC010H molar ratio 6.8) obtained by reacting at 120° C. for 13 hours. UIA is the above-mentioned U1 in which no surfactant was blended.

The bulk specific gravity and porosity in Table 2 are measured values using J-K5-R2205. The strength of the song is 1011m+, thickness 10
A sample cut to a length of 60 ff was measured using a universal testing machine using a three-point bending method with a span of 50 mm. Thermal shock resistance was determined by placing the above sample in an electric furnace at 300°C and holding it for 1 hour, then taking it out of the electric furnace and quickly placing it in water at 15°C, drying it, measuring the bending strength, and It is expressed as a bending strength retention rate (96) with respect to the bending strength before being put into the furnace. The drying shrinkage rate is 80 for the urethane foam molded product.
The dimensional shrinkage ratio before and after drying at 12 hours at °C is shown, and the firing shrinkage ratio is the dimensional shrinkage ratio before and after high-temperature firing.

As shown in Tables 1 and 2, if the central particle size of fused alumina is large, the bending strength and thermal shock resistance are low, and the drying shrinkage rate is large; The smaller the ratio zFi, the higher the bending strength, but the lower the thermal shock resistance. Ratio 3, in which the central grain size of sintered alumina is large, has lower bending strength and thermal shock resistance than ratio 1, and also has a large drying shrinkage rate. The larger the central grain size of calcined alumina, the lower the bending strength and thermal shock resistance. Ratio 5, in which the mixing ratio of calcined alumina to fused alumina is large, increases the bending strength, but the thermal shock resistance is insufficient and the firing shrinkage rate is large. Ratio 6, which uses only fused alumina, has low bending strength and insufficient thermal shock resistance. Ratio 7, which uses only calcined alumina, has low thermal shock resistance and high firing shrinkage.

(Effect of the invention) The lightweight alumina fired product obtained by the method of the present invention is lightweight and porous with a specific gravity of 1.3 to 25 and a porosity of ~7oΦ, and has excellent strength and thermal shock resistance. In addition to being excellent, the drying shrinkage rate and firing shrinkage rate are small even though it is porous. Therefore, it is suitable as a kiln tool.

Claims (1)

[Scope of Claims] [1] 70 to 95% by weight of fused alumina and/or sintered alumina with a center particle size of 20 to 400 microns, and 5 to 30% by weight of calcined alumina with a center particle size of 5 microns or less. Water or water and an active hydrogen-containing compound are added to the mixed alumina powder to form an alumina slurry, and the mixed composition liquid prepared by mixing the alumina slurry with a foamable polyurethane forming composition liquid is poured into a mold to cause reaction foaming, and this urethane foam molding is performed. A method for producing lightweight alumina fired products, which is characterized by drying the material and then firing it at a high temperature. [2] Add one or two of magnesium oxide, calcium oxide, and silica to the mixed alumina powder as a sintering aid.
2. The method for producing a lightweight alumina fired product according to claim 1, which comprises blending one or more inorganic oxides or an inorganic compound generated during firing of these inorganic oxides. [3] The specific gravity of the lightweight alumina fired product is 1.3 to 2.5,
The method for producing a lightweight alumina fired product according to claim 1 or 2, wherein the porosity is 30 to 70%.