JPH0661603B2 - Method for manufacturing molten metal heat insulating material - Google Patents

Description

Detailed Description of the Invention

[Industrial applications]

TECHNICAL FIELD The present invention relates to a method for manufacturing a heat insulating material that floats on the surface of a molten metal contained in a container to keep it warm.

[Prior art]

For example, in continuous casting of steel, the molten steel held in the tundish has a wide molten surface and a large heat radiation amount, even though the temperature difference between the initial and final stages of pouring from it should not be large. Therefore, I have to try to keep it warm as much as possible. Traditionally used for this purpose is mainly baked chaff. Baked rice husk is cheap, but because it is fine and light (the specific gravity of the bulk is about 0.1), when poured on the surface of the bath,
It has a drawback that it is easily scattered by the rising airflow caused by the high temperature. Its components are as shown in the analysis example below, And that there is a risk of carburization against the molten steel, there is a risk of increasing the silicon content by the reaction of _{SiO 2 + C → SiO + CO} , Al 2
Since the presence of O ₃ is also unfavorable, the baked rice husk thermal insulation material is not suitable for a molten metal of special steel, whose composition is strictly controlled. It has been attempted to use a dolomite powder granulated and fired as a molten metal heat insulating material without such a worry.
The heat retention effect that is not fully satisfactory is not obtained. On the other hand, the heat retaining effect of the molten metal is determined by the thickness of the layer formed on the surface of the molten metal, not by the weight of the heat insulating material charged. Therefore, if a thick heat insulating layer can be formed on the surface of the molten metal with a small amount of heat insulating material, the amount of slag generated can be reduced and the heat insulating effect can be improved.

[Problems to be Solved by the Invention]

The purpose of the present invention is a heat retaining material, which is used for the purpose of reducing the cooling of metal melt represented by molten steel held in a tundish for continuous casting due to heat radiation from the surface, because the heat retaining effect is high. An object of the present invention is to provide a method for producing a heat insulating material that lasts relatively well and that produces a small amount of slag.

[Means for Solving the Problems]

As shown in FIGS. 1 to 3, the method for producing a molten metal heat insulating material according to the present invention uses expanded polystyrene beads as a core (1) (FIG. 1) and applies a solvent to the surface to dissolve only the surface. Alternatively, it is swollen, and a powder (4) of magnesium carbonate, calcium carbonate, dolomite, slaked lime or a mixture of two or more thereof is attached thereto, and then an aqueous slurry of these powders is added and granulated. A heavy sphere (Fig. 2), the double sphere (2) is fired to burn off the expanded polystyrene beads of the core, and a hollow body made of a sintered body of magnesia, calcia, calcined dolomite or a mixture thereof. Form a sphere (3) (Fig. 3)
It consists of The size of expanded polystyrene beads used as the core is 5 to 5 mm in diameter.
A typical length is 15 mm, particularly 7 to 8 mm. The heat insulating material can be selected in a wide range of sizes, but the outer shape is 5 to 20 m.
m, usually within 10 mm, is convenient for manufacture and use. The granulating means is optional, and for example, a pan pelletizer is useful. Granulation often requires the addition of a binder to the aqueous slurry. The binder is also preferably one that will be burned off later, and such as molasses liquid is suitable. Prior to firing the double spheres, it is preferable to dry them once. Air drying is sufficient, but it goes without saying that heating will accelerate the process. The heating is performed by maintaining the granular material in the temperature range of 100 ° C. to 300 ° C. for 10 minutes to 2 hours. However, rapid heating may cause holes in the granular material, so it is preferable to air-dry to some extent. The firing step is performed by a rotary kiln or any other means. The atmosphere of the heating furnace is preferably oxidizable in order to burn out the core and binder. The firing temperature should be such that the sintered body of magnesia, calcia, etc. has an appropriate strength, the porosity of itself is kept relatively high, and the burnout of the synthetic resin used as the binder or core is complete. Select from 1100 ° C to 1300 ° C and heat for 30 minutes to several hours.

[Work]

The surface of expanded polystyrene beads is generally hydrophobic, and it is not easy to granulate by adhering powder even if an aqueous binder is used. As a method for facilitating the incorporation of expanded polystyrene beads into cement mortar, it has been proposed to apply a solvent to dissolve or soften the surface (JP-A-57-63335). Although this method was confirmed to be useful in the practice of the present invention, the solvent used was acetone / water or gasoline /
It was found that a mixture of chlorinated hydrocarbon and LPG was more effective than a mixture of kerosene. When the surface of the beads is dissolved or swelled by applying the solvent to the expanded polystyrene beads, the above-mentioned mineral powder is likely to adhere. As will be readily appreciated, the dissolved or swollen polystyrene acts as a type of adhesive and traps the mineral powder, thus forming its coating layer. Then, if an aqueous slurry is added and granulated, the powders are successively deposited on the powder that is the coating layer, and finally an outer skin of a thickness that covers the whole is formed, and a double spherical shape is formed. I have a body. The foamed synthetic resin used as the core is contracted by the heat of the drying step to obtain a hollow body. The contracted resin particles are burned off in the next firing step. When it is expected to burn off the core resin or the binder used for granulation due to oxidation, by forming a granular body with a relatively coarse raw material powder and by adopting a high temperature such as 1300 ° C, External O ₂ supply and generated CO,
It is possible to diffuse CO ₂ , H ₂ O, or a gas of a volatile component to the outside.

Example 1 Expanded polystyrene beads (diameter 6.7 to 7.9 mm) were used as a core, and 5 to 15% of 1,1,1-trichloroethane was added to LPG on the surface of the core to form an anticorrosive solution (“Pandeau 1”).
8A ", manufactured by ThreeBond Co., Ltd., and dolomite powder (50% passes 44μ, all passes 297μ)
95% by weight and silica powder (90% passing 44μ) 5
A mixture consisting of wt.% Was applied. An aqueous slurry containing molasses as a binder was added to the same powder mixture as above, and granulated with a pan pelletizer. The obtained double spheres had a diameter of 9.5 to 11.1 mm. This is put in a dryer and heated at a rate of 2 ° C./minute to obtain 200
When the temperature reached ℃, it was held for 30 minutes. Then, it was heated in an electric furnace at 1,300 ° C. for 1 hour.
The heat insulating material thus obtained had almost the same diameter as the above, and the apparent specific gravity was 0.50. A product obtained by granulating the same dolomite powder into the same size and firing without using a core of expanded polystyrene beads had an apparent specific gravity of 0.72, so that the heat insulating material of the present invention was obviously lightened. Is. The heat insulating material of the present invention was put on the molten steel in the tundish to form a layer having a thickness of 20 mm on the slag. For comparison, heat retention was also performed using the above mere dolomite granulated and fired product. In this case, about 40% more heat insulating material was required to form the heat insulating material layer having the same thickness. The heat insulating material of the present invention had a higher heat insulating effect than the comparative example, although the heat insulating material was used in a smaller amount.

Example 2 A powder mixture prepared by spraying "Pandeau 18A" (described above) on the surface of expanded polystyrene beads (diameter: 6.7 to 7.9 mm) and blending 99% by weight of magnesia clinker and 1% by weight of methylcellulose ( The particle size is 44 μm or less). An aqueous slurry containing 5% of "Yonerin R-20" (manufactured by Yoneyama Chemical Co., Ltd.) of the above-mentioned magnesia clinker powder as a binder was added thereto, and the mixture was attached by granulating with a pan pelletizer, and a double layer was prepared. A spherical body A was obtained. Using the same magnesia clinker powder, but coarse particles (particle size 44 to 74 μm), the double spherical body B was prepared by the same operation as described above. Double sphere C was produced by the same procedure as the production of double sphere A except that the core of expanded polystyrene beads was not used. These double spheres were dried in the same manner as in Example 1, and then heated in an electric furnace at 1400 ° C. for 2 hours to obtain a heat insulating material A,
B and C were obtained. Their physical properties are shown below.

Example 3 "Pandau 18A" (described above) was sprayed onto the surface of expanded polystyrene beads (diameter: 5.7 to 6.7 mm), and silicone oil "AFP-1" (manufactured by Shin-Etsu Chemical Co., Ltd.) was added. Slaked lime (special slaked lime for industrial use) was attached. On top of that, the same slaked lime slurry was added and further deposited. Also in this case, a pan pelletizer was used. The double spheres were air-dried overnight, placed in a drier, heated to 200 ° C. at 2 ° C./min and held for 2 hours, then heated to 300 ° C. over 30 minutes and held for 1 hour. The heat insulating material obtained had a particle size range of 6.7 to 7.9 mm in 23% and a particle size range of 7.9 to 9.5 mm in 77%. The apparent specific gravity of the latter was 0.34.

【The invention's effect】

The production of the molten metal heat insulating material of the present invention can be carried out using inexpensive raw materials and common equipment, and consumes little energy, so that the cost is low. The molten metal heat insulating material produced by this method has no fear of scattering when floated on the surface of the molten metal and used for heat retention, and also does not cause unfavorable component fluctuations with respect to the metal. The heat retaining effect is high and lasts for a relatively long time. Moreover, since the amount of use is small, the amount of slag generated can be reduced. Therefore, this heat insulating material has the greatest significance when it is used to heat the molten steel in the tundish in the continuous casting of steel.

[Brief description of drawings]

1 and 2 are for explaining the steps of the method for producing a molten metal heat insulating material according to the present invention, wherein FIG. 1 shows expanded polystyrene beads as a core, and FIG. 2 shows the outside thereof. The double spherical body granulated by adhering mineral powder is shown. FIG. 3 is a cross-sectional view of the molten metal heat insulating material obtained by firing the granular body of FIG. 1 ... Expanded polystyrene beads 2 ... Double spheres 3 ... Heat insulating material 4 ... Mineral powder outer shell 5 ... Hollow shell 6 ... Space

Claims (2)

[Claims] 1. A foamed polystyrene bead is used as a core, and a solvent is applied to the surface to dissolve or swell only the surface, and magnesium carbonate, calcium carbonate, dolomite, slaked lime, or a powder of a mixture of two or more thereof. And then add an aqueous slurry of these powders to granulate to form a double spherical body, and burn the double granular body to burn out the expanded polystyrene beads of the core, as well as magnesia, calcia, and firing. A method for producing a molten metal heat insulating material, which comprises forming hollow spheres made of a sintered body of dolomite or a mixture thereof. 2. The method according to claim 1, wherein a mixture of chlorinated hydrocarbon and LPG is used as the solvent applied to the surface of the expanded polystyrene beads.