JPH07126080A - Production of light-weight sintered alumina clinker - Google Patents

Abstract

PURPOSE:To produce a light-weight sintered alumina clinker having excellent spalling resistance and heat-insulation, a high porosity and strength to suppress the temperature drop of a furnace made of a refractory containing the clinker as an aggregate and small shrinkage in reheating. CONSTITUTION:The objective sintered material composed of sufficiently developed corundum crystals and having a high porosity and a low bulk density is produced by using a raw material having an average particle diameter of 5-60mum and composed of two or more kinds of mixed powder having different alumina crystal forms, granulating or compression-molding the raw material together with a proper amount of a binder and a proper amount of water and baking the granules or the compression-molded article at >=1800 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention manufactures an alumina sintered body having a high purity, a low density, a large number of pores, a large strength, a small reheat shrinkage and a high heat insulating property, using a Bayer method alumina as a raw material. The present invention relates to a method for manufacturing a lightweight sintered alumina clinker.

[0002]

2. Description of the Related Art Conventionally, a high-purity alumina granule pressure-molded product used as a porous aggregate of a refractory material is a high-purity alumina powder raw material to which flammable organic substances such as wood powder and oil coke and water are added. Then, after granulation or pressure molding, it is dried and calcined to remove organic substances to form voids, which are then heated to a high temperature and sintered.

[0003]

However, it takes a long time to remove organic substances by heating, and in the case of sintering in a rotary kiln, calcination in another firing furnace is required in advance, and the degree of firing is Therefore, the carbonaceous material remains, and a sintered body having sufficient strength cannot be obtained in many cases.

The present invention has been made in view of the above problems and was devised to solve the problems. The object of the present invention is to have excellent spalling resistance and heat insulation. It is an object of the present invention to provide a method for producing a lightweight sintered alumina clinker that is porous and has a high strength and that has a small reheat shrinkage and that suppresses a temperature decrease in a furnace using a refractory having an aggregate as an aggregate.

[0005]

The inventors of the present invention have conducted various studies on a method for inexpensively producing the above-mentioned lightweight sintered alumina clinker, and as a result, have reached the present invention.

The present invention uses, as a raw material, two or more kinds of alumina having different crystallinities, which are obtained by firing aluminum hydroxide obtained from the bauxite ore by the Bayer method, and these are mixed or mixed and ground to obtain alumina. The particle size of the raw material mixed powder is adjusted to an average particle size of 5 μm to 60 μm, or the particle size of the alumina raw material mixed powder is 5 μm or more and 25% or more of particles having an average particle size of 12 μm or more and 1 μm or less. This is a method for producing a lightweight sintered alumina sintered body having a large porosity by adjusting particles to 5% or less, molding the particles, and then firing the particles.

Since the clinker used in the refractory is exposed to high temperature conditions for a long time, the lightweight sintered alumina clinker of the refractory raw material used in this application is fired and sintered at high temperature. 1500 ° C to 1, which is the operating temperature
It is necessary that there is almost no shrinkage due to reheating even when reheated to 700 ° C.

For this purpose, it is necessary that the lightweight sintered alumina clinker has a crystal diameter of 10 μm or more. The porosity is 1 from the viewpoint of heat insulation effect and erosion resistance.
It is desirable to be 5% or more and 30% or less.

In order to produce such a porous clinker, two or more kinds of alumina having different crystal shapes are mixed or mixed and pulverized to have an average particle size of 5 μm or more, preferably 7 μm.
The above raw materials are used, or more preferably, two kinds of alumina having different crystal shapes are used, and the average particle diameter is 5 μm or more,
Preferably, 7% or more and 12 μm or more particles account for 25% or more, preferably 50% or more, and 1 μm or less particles account for 5%.
Used by mixing or mixing and pulverizing so as to be not more than%.

A vibrating ball mill, a tube mill or the like can be used for mixing or pulverizing the raw materials.

Next, a small amount of organic binder and a proper amount of water are added, and the mixture is molded using a device such as a pan pelletizer and a briquette machine.

The alumina granulated and shaped as described above is heated and sintered. The sintering can also be carried out using a static furnace such as a gas furnace or an electric furnace. It is desirable to use a rotary kiln for cost reduction.

The heating temperature required for sintering is 1800 ° C. or higher, preferably in the range of 1850 ° C. to 1900 ° C.,
By this heating, the alumina granulated product molded body becomes a sintered body in which the crystal grains are sufficiently grown without breaking the original shape and the strength is high and the porous body is formed.

[0014]

The present invention will be described in detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples, and various modifications can be made without departing from the spirit of the present invention. Of course you can get it.

[Experimental Example] A Bayer method alumina single crystal powder having a size of 5 μm and a single crystal size of 0.5 μm
2 kinds of powders are mixed and pulverized by a mill to adjust the particle size, and 0.5% by weight binder and 10% by weight water are added to the mixture to form a 15 mmΦ × 15 mmL compact by a press molding machine. The molded body was heated in an electric furnace at a temperature of 1850 ° C. for 20 minutes to be sintered. The results of measuring the physical properties of the sintered body at this time are shown in Table 1.

[0016]

[Table 1]

Example 1 Alumina having a single crystal particle size of 0.5 μm was crushed by a ball mill so that the average particle size was 5 μm, and 50% to 100% of alumina having a single crystal particle size of 5 μm was crushed. Add and mix, and add 0.3% of an organic binder (Metronose 90sh-15000 manufactured by Shin-Etsu Chemical Co., Ltd.) and 11% of water to the mixture, and knead with a kneader. At a pressure of 300 Kg / cm ² with a press molding machine. After molding and drying at 110 ° C. for 24 hours with a drier, heating was performed at a temperature of 1850 ° C. for 10 minutes in an electric furnace for sintering. The results are shown in Table 2.

[0018]

[Table 2]

[Example 2] Two kinds of alumina raw materials having different crystal shapes were subjected to an average particle diameter of 19 µm to 3 by a continuous vibration mill.
Particles of 0 μm and 12 μm or more are 54% to 70% and 1
Particles with a size of μm or less are mixed and pulverized so as to be 1.5% to 3%, and 0.5% of methylcellulose and lignin (Sun Extract P252 manufactured by Nippon Paper Industries Co., Ltd.) is added thereto, and water is added to 14% to 1%.
8% was added, and the mixture was granulated using a pan pelletizer, dried, and then heated in a rotary kiln (400 mmΦ × 5500 mmL, passage time 180 minutes) to a firing temperature of 1850 ° C. to 1900 ° C. to produce a sintered body. Table 3 shows the average particle size composition after pulverizing the raw materials and the physical property values of the sintered body.

[0020]

[Table 3]

The above sintered body was crushed to a particle size of 1 mm or less by a roll crusher, and 15% by weight of commercially available sintered alumina 325meshF was mixed with it. %, 5.0% by weight of water are added and kneaded, and pressurized at 300 Kg / cm ² with a press molding machine,
A 0 mm × 25 mm × 20 mm molded body was prepared. This 11
After drying at a temperature of 0 ° C., heating and holding at a temperature of 1700 ° C. for 2 hours and cooling, reheat shrinkage was determined from the difference between the length before heating and the length after heating. Table 4 shows the results and the physical properties of the test piece after heating.

[0022]

[Table 4]

Comparative Example 1 A commercially available alumina raw material was crushed with a ball mill so that the average particle diameter was 5 μm, and 20% by weight of wood powder and a binder (methylcellulose)
After adding 0.5% by weight and 13% by weight of water and kneading, press molding was performed at a pressure of 300 Kg / cm ^{2 with} a press molding machine, and this was dried at a temperature of 100 ° C. for 3 hours, and then the temperature inside the electric furnace 10
After calcination at 00 ° C., it was heated at a temperature of 1850 ° C. in a gas furnace to obtain a sintered body. Table 5 shows the physical property values.

[0024]

[Table 5]

[0025]

As is apparent from the above description, according to the method for manufacturing a lightweight sintered alumina clinker according to the present invention, a refractory material using this lightweight sintered alumina is used in a contact operation part with molten steel. In this case, since it is porous and lightweight, the thermal conductivity is reduced, heat loss can be improved, the decrease in molten steel temperature can be reduced, and the adhesion of deoxidized molten steel products can be achieved. It is possible to suppress buildup due to. Further, since it is lightweight, the amount of refractory used per unit volume of the furnace body can be reduced.

Claims (2)

[Claims] 1. A raw material having an average particle size of two or more kinds of mixed powders of different alumina crystal shapes of 5 μm or more and 60 μm or less is granulated or pressure molded with an appropriate amount of binder and an appropriate amount of water, Light-weight sintered alumina characterized in that the granulated product or the pressure-molded product is fired at a temperature of 1800 ° C. or higher to obtain a sintered product having a high porosity and a low bulk specific gravity, which is composed of fully developed corundum crystals. Method for producing clinker. 2. The particle size of alumina according to claim 1,
The particles of 2 μm or more are crushed so that 25% or more and the particles of 1 μm or less are 5% or less, and granulated or pressure-molded with an appropriate amount of binder and an appropriate amount of water, and the granulated product or pressed A method for producing a lightweight sintered alumina clinker, which comprises firing a molded product at a temperature of 1800 ° C. or higher to obtain a sintered body having a high porosity and a low bulk specific gravity.