JPH0348152B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention reduces heat transfer to the container by coating the inner surface of the container in which molten metal is transported or smelted, or coats the surface of the molten metal with These are heat-insulating refractory particles that are suspended to reduce contact with the outside air, prevent heat loss from the molten metal, and further prevent reactions between the outside air and the molten metal.

[Prior art] When transporting or refining molten metal in a tundish or ladle, a heat insulating material is applied to the inner surface of the container to reduce heat transfer to the container, and the surface of the molten metal is coated with heat insulating and fire-resistant material. A technical idea whose main purpose is to prevent heat loss from the molten metal surface to the outside air and reaction between the outside air and the molten metal by scattering particles of the molten metal is known.

Traditionally, rice husks or steamed rice husks have been mainly used as insulation materials. However, although this product has the characteristic of being very inexpensive, its main components are silica and carbon, so the silica reacts with calcia etc. to create a compound with a low melting point, and the carbon content and silicon are It is known that the metal is incorporated into the molten metal produced and deteriorates the properties of the metal obtained as a product. For this reason, the use of rice husks was becoming a big problem in high-grade steel, where slight differences in composition are a problem.
In order to solve this drawback of rice husks, several attempts have been made to use substances with low carbon content and low melting point compounds that are difficult to form.

Magnesia is a substance that satisfies these two conditions, but since it itself has high thermal conductivity, attempts are being made to provide it with heat insulating properties. One such method is to coat a foamed material such as pearlite or vermiculite with fine powder of magnesia, which is used to produce various products. However, in these products, it is difficult to increase the magnesia content to 60% or more due to the manufacturing method, which makes it easy to create compounds with low melting points, and the insulation layer and magnesia layer are separated, so the insulation properties are not sufficient. I couldn't say it. Furthermore, these products undergo large shrinkage and decrease in strength at the temperature of the molten metal, so they cannot be used to reduce heat transfer to the container by coating it on the inner surface of the container. In order to improve the heat insulating properties of magnesia bricks, methods for producing foamed magnesia, which is the raw material for magnesia bricks, have been studied. These are, for example, Tokuko Sho 47-47565, Tokko Tokuko 48
-7485 etc. However, the expanded magnesia obtained by the conventional method is of excessive quality for use in the purpose of the present invention, and the product cost is high, so there is a problem that it is difficult to use in practice.

[Problems to be Solved by the Invention] The present invention reduces heat transfer to the container by coating it on the inner surface of the container in which molten metal is transferred or refined, or floats it on the surface of the molten metal and connects it to the outside air. The purpose of the present invention is to provide refractory particles containing magnesia as a component that can be manufactured at low cost and are superior in order to reduce contact between metals, prevent heat loss from the molten metal, and further prevent reactions between the outside air and the molten metal. be.

[Means for solving the problems] The configuration of the present invention for solving the above problems is as follows:
The content of magnesium oxide is 60% or more, the specific surface area is 15 to 1 m ² /gr, preferably 15 to 5 m ² /gr (Bett method), the volume ratio is 0.2 to 1.5, preferably 0.5 to 1.5,
More preferably, the heat-insulating refractory particles have a particle size of 0.35 to 0.60 mm, and a particle size of 0.5 to 15 mm, preferably 1 to 10 mm.

In addition, the above-mentioned heat-insulating refractory particles can be produced by firing magnesite lumps, then crushing them, and sizing them into particles with a particle size of 0.5 to 15 mm, or by firing a magnesium compound so that the MgO content becomes 60% or more. ,
In addition, water or an aqueous solution is mixed with the powder containing 40% or more of lightly calcined magnesia as a magnesium compound, dried, and sized into particles of 0.5 to 15 mm.
This is done by firing.

[Function] It is necessary that the content of magnesium oxide (hereinafter referred to as magnesia purity) in the chemical composition of the heat-insulating refractory particles of the present invention is 60% or more.

As the magnesia purity of the heat-insulating refractory particles increases, the melting point of the refractory particles increases. The specific temperature may vary depending on other coexisting components, or when the purity of magnesia exceeds 60%, the melting of the heat-insulating refractory particles themselves becomes extremely small at the temperature of the molten metal.

As the purity of magnesia increases, the softening caused by the reaction with the slag components accompanying the molten metal decreases.
It was observed that when the magnesia component exceeds 90%, the reaction with the slag component becomes extremely low.

After all, in order to maintain the fire resistance necessary for the heat-insulating refractory particles of the present invention, it is necessary that the magnesia purity is 60% or more. We also check the magnesia purity of our products.
It is effective to produce by the method of the present invention in order to increase the ratio to 60% or more.

It is necessary for the specific surface area of the heat-insulating refractory particles of the present invention to be 1 m ² /gr or more in order to improve the heat-insulating properties. The greater the specific surface area, the greater the heat insulating properties of the refractory particles, which is desirable. However, as the specific surface area increases, the strength of the refractory particles tends to decrease, resulting in problems such as the particles collapsing during transportation, or particles rubbing against each other and turning into powder. Powder produced by particles disintegrating or turning into powder not only flies up when refractory particles are used and becomes a hindrance to operations, but also causes the problem of environmental pollution at the operation site. Taking these things into consideration, the specific surface area of the refractory particles must be 15 m ² /gr or less, and if the above-mentioned thermal insulation properties are also considered, the specific surface area of the refractory particles should be 15 to 5 m ² /gr. desirable.

Further, the heat-insulating refractory particles of the present invention are usually sized to a size of 0.5 to 15 mm. This size can be arbitrarily selected depending on the purpose of use. However, if the particle size exceeds 15 mm, it is too large for the purpose of the present invention, and a phenomenon was observed in which a uniform dispersion state could not be obtained when sprayed on the surface of molten metal. It is particularly desirable that the particle size be 10 mm or less. or,
When the particle size was 0.5 mm or less, adverse effects such as dust generation were observed when the particles were poured onto the surface of the molten metal.

The volume specific gravity of refractory particles is calculated from the weight of a certain volume of particles measured in a graduated cylinder. As the volume specific gravity decreases, the heat insulation properties of the refractory particles improve, but the time for reacting with slag and the like to maintain the shape of the particles becomes shorter, and the strength of the particles also becomes weaker.
If the volume specific gravity of the refractory particles is less than 0.2, the strength of the refractory particles will be significantly reduced, requiring extra costs for packaging, etc. during transportation, and will also increase transportation costs. As the volumetric specific gravity increases, the heat insulating property, which is the object of the present invention, decreases, but the manufacturing cost of the refractory particles tends to decrease. Considering the above costs and effects comprehensively, a volume specific gravity of 0.2 to 1.5 is considered to be an appropriate range.

As the magnesia raw material for producing the refractory particles of the present invention, not only magnesium hydroxide, which is a raw material for seawater magnesia clinker, but also inexpensive raw materials such as natural magnesite can be used.

There are multiple manufacturing methods for the refractory particles of the present invention. The manufacturing method is determined by taking into account available raw materials, factory location, etc. The two methods described below are considered to be particularly excellent methods.

One method is to heat natural magnesite to 1000 to 1450°C using a firing furnace such as a shaft kiln or rotary kiln, although the conditions vary depending on the production area.
By firing at a temperature of 15~
This is a method of sizing magnesium oxide at 1 m ² /gr by crushing, etc. so that most of the particles are 0.5 to 15 mm in size.
Water or an aqueous solution of acid, sodium silicate, etc. is mixed by a method such as dropping into a powder containing 60% or more of MgO and 40% or more of lightly calcined magnesia as a magnesium compound. After drying if necessary, the particles are sized and fired at a temperature of 400°C or higher. In this case, if the content of lightly calcined magnesium in the powder is 40% or more, considerable strength can be developed even with water alone, making it possible to create an economical process.

Hereinafter, the effects of the present invention will be explained with reference to Examples.
In addition, the amount (%) of each component described in the examples is weight %.
It is.

Example 1 A 5-10 cm block of natural magnesite was fired at 1200°C for 2 hours in an electric furnace. This fired product was crushed with a dior crusher, and particles of 5 to 10 mm were sieved. The volume specific gravity of this particle is 0.98,
The specific surface area was 8.2 m ² /gr.

The analytical values of the heat-insulating refractory particles were as follows.

MgO 92% CaO 1.4% Al ₂ O ₃ 1.3% Fe ₂ O ₃ 0.3% SiO ₂ 2.4% [Comparative example] In order to compare the properties with those of Example 1 above, foamed vermiyukilite was coated with natural magnesia powder. manufactured. The chemical composition and physical properties of this product were as follows.

MgO 50.7% CaO 0.6% Al ₂ O ₃ 9.7% Fe ₂ O ₃ 1.8% SiO ₂ 20.5% Na ₂ O 2.5% Ig・loss 10.4% Volume specific gravity 0.50 Heat retention test Place molten iron in a crucible with a diameter of 15 cm and heat to 1550℃. After the temperature was maintained, heat-insulating refractory particles were added to a thickness of 6 cm, and the rate of temperature drop after the addition was measured. The results were as follows.

Temperature drop rate Example 1 11.4°C/min Comparative example 11.8°C/min Slag resistance A certain amount of heat-insulating refractory particles was put into a tundish at a continuous casting site, and the time taken for the particles to disappear was measured and compared. As a result, Example 1 showed 1.5 to 4 times higher slag resistance than Comparative Example in all cases.

Example 2 Natural magnesite containing 92% MgO in terms of fired product was fired at 1100°C for 1 hour and finely pulverized while heating to 110°C in a ball mill to have a specific surface area of 9.
Lightly calcined magnesia of m ² /gr was obtained.

50% of this lightly calcined magnesia and dried fine powder of seawater magnesium hydroxide were mixed, heated to 120°C, and water at about 90°C was added dropwise to obtain a granulated product. This granulated material was fired in a rotary kiln at a maximum temperature of 1450°C.

When particles with a particle size of 0.5 to 10 mm were sieved from this granule, the specific surface area was 7 m ² /gr, the MgO content was 93%,
Insulating refractory particles with a volume specific gravity of 1.04 were obtained.

[Effects of the Invention] As explained above, the heat-insulating refractory particles of the present invention have excellent heat insulating properties at high temperatures, and according to the manufacturing method of the present invention, the manufacturing cost is low, so it is expected that they can be used in a wide range of applications. can.

Claims (1)

[Scope of Claims] 1. A thermal insulation characterized by having a magnesium oxide content of 60% or more, a specific surface area of 15 to 1 m ² /gr, a volume ratio of 0.2 to 1.5, and a particle size of 0.5 to 15 mm. Refractory particles. 2. The heat-insulating refractory particles according to claim 1, wherein the content of magnesium oxide is 90% or more.