JPH01237049A - Heat insulating refractory grain for molten metal - Google Patents

Abstract

PURPOSE:To prevent heat radiation from molten metal surface and oxidation of the molten metal surface by covering the molten metal surface with heat insulating refractory grain composed of gas concrete at center part and coating with MgO or/and CaO at outer circumferential part thereof. CONSTITUTION:On the molten metal surface in a tundish or ladle, the heat insulating refractory-made grain composing of the gas concrete at the center part, coating with MgO or/and CaO at the outer circumferential part thereof and having 0.1-1.0vol. ratio and 0.5-1.5mm granular size is spread to cover the molten metal surface. A part contacting with the molten metal is melted, to become liquid phase and the molten metal surface is perfectly covered and shut off from the outer air, and the refractory grain above this part exists as the one having excellent heat insulating ability, to form the heat insulating layer on the molten metal surface. The molten metal surface is easily prevented from the oxidation and heat radiation.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention suspends molten metal on the surface of the molten metal in a container during transport or scouring treatment, thereby reducing contact between the molten metal and the outside air and improving the molten metal. The present invention relates to heat insulating refractory particles for molten metal that prevent radiation of heat from metal and further prevent oxidation of molten metal due to outside air.

[Prior art] When transporting molten metal such as a tundish or ladle or scouring it, refractory particles are sprinkled on the surface of the molten metal.
It is known to prevent the radiation of heat from the molten metal surface to the outside air and the reaction of the outside air with the molten metal.

Traditionally, rice husks or steamed rice husks have been mainly used as insulation materials. However, although these insulating materials have the advantage of being very inexpensive, because their main components are carbon and silica, the carbon content is incorporated into the molten metal that has been prepared and the properties of the metal obtained as a product are affected. There are drawbacks that reduce the

In order to solve the drawbacks of rice husk, there has been a conventional method of using a foam such as perlite or vermiculite coated with fine powder of magnesia, and various types of heat insulating materials have been produced.

However, in these products, pearlite and vermiculite shrink and melt at low temperatures of 1,250 to 1,300 degrees Celsius, so even if you cover them with magnesia and increase the melting temperature, there are limits.
For example, when it comes into contact with molten steel at 1800°C, it melts in a short period of time and becomes a molten liquid, which has the disadvantage of losing heat insulation properties.

In addition, magnesia is used in large amounts so that it does not melt when it comes into contact with such high-temperature molten metal, or even if it does, it retains its insulation effect for a relatively long time because its melting temperature is close to that of molten metal. This has the disadvantage that the specific gravity increases and the thermal conductivity increases.

There are also heat-insulating and refractory particles made by foaming even higher-purity magnesia, which are used in extremely high-grade applications, but they are generally too high quality to be used in large quantities and are expensive, so their field of use is limited. There is.

[Problem to be solved by the invention m1 The present invention aims to provide relatively inexpensive heat-insulating refractory particles for molten metal, which have a high melting temperature and have heat-insulating properties over a long period of time, and are particularly suitable for molten steel. That is.

[Means for Solving the Problems] The present invention uses cellular concrete particles which retain a large amount of air bubbles at a relatively high shrinking and melting temperature of 1,300 to 1,350° C. and have excellent heat insulation properties.

That is, the particles consist of aerated concrete particles in the center and the outer periphery is coated with magnesia, calcia, or magnesia, calcia, and the volume specific gravity is 0.1 to 1.0, preferably 0.2 to 0.8, and the particle size is is 0.5-15m5. Preferably, the insulating refractory particles for molten metal have a diameter of 1-10 mm.

Moreover, the particles of cellular concrete used for the above-mentioned heat-insulating and refractory particles are those obtained by crushing cellular concrete and sieving it.

The magnesia, calcia, or a mixture of magnesia and calcia to be coated on the aerated concrete should be within the range of a thin coating amount that becomes liquid upon contact with molten steel at teoo°C, depending on the U type used, and insulating refractory particles. Gate
It is divided into those that have a thick coating that maintains its outer shape even if it comes into contact with molten steel at 00°C.

Note that when cellular concrete is coated with magnesia, calcia, or a mixture of calcia and magnesia, when the temperature rises to about 1300° C. during use, the cellular concrete melts and the resulting liquid phase is absorbed by the coating. At this time, if the amount of the coating is small, the coating that has absorbed the liquid phase will also contact the 1600℃ molten steel and become liquid, but if the amount of the coating is large, the generated liquid phase will be large. When absorbed by the coating, the cellular concrete becomes pores, while the coating that has absorbed the liquid phase remains solid and retains heat even at 1600° C., the temperature of molten steel.

In addition, compared to perlite and vermiculite, aerated concrete contains about 30% CaO as one of its main components, so if it is used, the amount of the above-mentioned coating that is restored on the surface of the concrete can be reduced to a relatively minimum amount of all the heat-insulating refractory particles. The mineral composition is such that it is in a solid state at the temperature of molten steel. Therefore, a heat retaining agent with high heat retention properties can be obtained.

To produce such heat-insulating and refractory particles, a drum-type milling machine or a pan (disc) J4! ! The surface of the aerated concrete particles is coated with a magnesium or calcium compound using water glass, pulp waste liquid, etc. as a binder using a molding machine, and then dried and/or fired.

The above magnesium or calcium compounds include:
Examples include magnesium oxides, hydroxides, carbonates, calcium oxides, hydroxides, carbonates, and mixtures of these compounds, as well as dolomite, calcined dolomite powder, and the like.

Further, the temperature at which the coated particles are fired is preferably a temperature that does not melt the product particles, for example, a temperature of 1200° C. or lower.

The heat-insulating refractory particles of the present invention need to have an 8-loss specific gravity of 0.1-1.0 in view of their heat-insulating properties. but,
If the weight is too low, the strength will decrease and the particles may break during transportation, or the particles may rub against each other and turn into powder. The powder generated in this way is thrown up when the refractory particles are used, causing a problem of environmental pollution at the operating site. Furthermore, as the volume specific gravity increases, the heat insulation properties decrease. Taking these things into consideration, it is particularly desirable that the volume specific gravity of the refractory particles be from 0.2 to 0.6.

Further, the heat insulating refractory particles of the present invention are usually 0.5 to 1511+
It is sorted to a size of 11. When it was 0.51 or less, it was found that there was a problem in that dust was generated when it was poured onto the surface of the molten metal.

On the other hand, when the maximum particle size is 15II11 or more, it becomes difficult to obtain a uniform dispersion state when sprayed on the surface of molten metal.
Furthermore, the amount of spraying required to prevent oxidation reactions caused by outside air increases. Therefore, 1 to 10 mm is the most desirable particle size for the dispersion state, IL reaction prevention with outside air, and operation.

By the way, during handling such as bagging and transportation, it is unavoidable that powder of 0.5 mm or less is generated due to damage or abrasion, but since these powders can cause a bad work environment, it is important to avoid powder of 0.5 mm or less. is less than 2096 overall when used,
More preferably, the number is 1596 or less.

Among these, it is particularly desirable that the amount of powder of 0.5 ma+ or less, which causes dust, be 10% or less during use. Similarly, powder having a molecular weight of 15111 or more is used in an amount of 5% or less, more preferably 3% or less. Especially 1-1
It is desirable that the powder of 0s■ is 80% or more.

Aerated concrete shrinks and melts at 1300°C to 1350°C, but there are also heat-insulating refractory particles coated with magnesia, calcia, or a mixture of magnesia and calcia to the extent that they become molten at temperatures lower than 1600°C, which is the temperature of molten steel. Useful. It is especially used when reaction between outside air and molten metal is disliked, or when molten metal comes into contact with outside air to prevent contact between molten metal and outside air. On the surface that comes into contact with the molten metal, the dispersed particles melt into a liquid phase and spread uniformly over the molten metal surface, completely blocking the outside air and the molten metal. The particles melt on the surface that comes into contact with the molten metal, but because the particles have excellent heat insulation properties and the melting point of the particles is close to the temperature of the molten metal, the original composition of the heat insulation properties is maintained immediately behind the surface that comes into contact with the molten metal. It maintains its function as an insulating and refractory particle.

On the other hand, heat-insulating refractory particles coated with magnesia, calcia, or a mixture of magnesia and calcia until the aerated concrete retains its outer shape at a molten steel temperature of 1600°C are used in cases where the molten metal is in contact with molten metal for a long time to retain heat, or when the molten metal is in aerated concrete. It is used in the case of molten metals that do not want to pick up oxygen and silicon from SiO2, which is one of the main components. In this case, the 5i02 in the aerated concrete is separated by magnesia, calcia, or a mixture of magnesia and calcia coated on the outer periphery, and is extremely unlikely to come into contact with molten metal.

[Example] Hereinafter, the present invention will be specifically explained with reference to Examples. In addition,
The amounts (%) of each component described in the examples are weight %.

[Measurement of cooling rate of molten iron] 15 kg of pig iron was placed in an electric induction heating furnace with internal dimensions of 150 n + mφ x 250 m + all, energized, and melted.
After heating to 50℃ and holding for 30 minutes, each sample was heated to a thickness of 60Ill.
I placed it on top of the molten iron and turned off the power after 10 minutes. Continuous i1?
The cooling rate was determined from the cooling curve for 20 minutes at J temperature.

Example 1 A steam-cured lightweight cellular concrete with a high specific gravity of 0.4 was crushed, sieved to 1 to Lots, and the volumetric specific gravity was measured.

The volume specific gravity was 0.23.

While spraying a 3% solution of water glass using a pan-type granulator, magnesia powder was added to coat the mixture with about 70% magnesia. This was fired at 1150°C using a rotary kiln. The volume specific gravity, chemical analysis, and cooling rate of the molten iron were measured for these particles.

The results are shown in Table 1 below.

Example 2 The crushed aerated concrete granules of Example 1 were coated with about 30% of dolomite crushed to 48 mesh or less while spraying a water glass aqueous solution with a concentration of 596 using a pan-type granulator. This was fired using a rotary kiln at a temperature of 1200°C.

Chemical analysis, volume specific gravity, and molten iron cooling rate were measured in the same manner as in Example 1.

Comparative Example 1 In order to compare with the example, foamed pearlite was coated with 70% magnesia powder in the same manner as in the example, chemical analysis,
The volumetric specific gravity and cooling rate of molten iron were determined to be 7Illll.

Table 1 [Effects of the Invention] As explained above, the fireproof and heat insulating particles of the present invention are highly effective in preventing radiation of heat from the surface of molten metal and have excellent fireproof and heat insulating properties.

Claims (1)

[Claims] Particles consisting of aerated concrete particles in the center and coated with magnesia, calcia, or both on the outer periphery, and characterized by having a volume specific gravity of 0.1 to 1.0 and a particle size of 0.5 to 15 mm. Insulating refractory particles for molten metal.