JP2003192468A - Low thermal conductive and gas-permeable refractory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas-permeable refractory in which a necessary permeability is secured when it is used as a porous plug and the reliability of bubbling and durability are improved. <P>SOLUTION: A refractory fine powder and a refractory aggregate are used as main raw materials, and thin refractory bubbles, each having a particle diameter of ≤2 mm and a thickness of 1/4 to 1/20 of the outer diameter, are incorporated in an amount of 20 to 90 mass % as the refractory aggregate, so that the thermal conductivity becomes ≤2.0. Thereby, the thickness of the infiltrated layer of molten steel can be reduced, and the reliability of bubbling and the durability are improved. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a breathable refractory which is attached to the bottom of a molten metal vessel for refining molten steel and is used as a porous plug for injecting gas into the molten steel to stir the molten steel.

[0002]

2. Description of the Related Art Conventionally, for refining molten steel, a porous body called a porous plug for injecting a gas into the molten steel for the purpose of stirring or a breathable refractory having through-holes formed therein has been used.

The life of this porous plug is 5-30 times of refining at best, and damage due to crack peeling caused by thermal shock at the start of use, wear action when stirring molten steel, infiltration of molten steel, erosion of slag, After repeated wear such as removal work by oxygen cleaning of the solidified molten steel infiltration layer, the usage limit is reached and the product is discarded.

One of the important characteristics required for a porous plug is the reliability in bubbling, and it is nothing but blowing gas into molten steel when necessary. The causes of the decrease in the reliability of bubbling include interruption of gas injection, molten steel infiltrating into pores during casting, and formation of a solidified layer after heat removal. Block the air flow and cause poor ventilation.

As an attempt to shallow the solidified layer due to the infiltration of molten steel that causes poor ventilation and reduce its effect, for example, in Japanese Patent Publication No. 2-23502, a porous brick itself is formed from a spherical raw material. Therefore, it has been proposed to form a pore size as small as possible to give efficient breathability, but there is a problem that the breathability of the core brick itself is deteriorated and it becomes difficult to secure the whole ventilation amount. .

In addition, "Refractory Material, No. 141: 199
In 6 ”, it is proposed to form porous bricks with a material that is difficult to wet molten steel to suppress molten steel infiltration. However, reaction with molten steel components gradually progresses and the properties of the operating surface change and wet the molten steel. The hard property is impaired and the infiltration suppressing effect of molten steel is lost.

Further, Japanese Patent Application Laid-Open No. 11-61235 discloses a gas injection through-hole plug made of a mixture of a dense refractory aggregate and a hollow aggregate. The surface of the hollow aggregate located on the surface is also worn away and a hollow part appears, and molten metal accumulates in the hollow part, which is used as a spark during oxygen cleaning, and cleaning of the slag that covers the pores of the through-hole plug Has been shown to do.

However, in this case, the hollow aggregate is used for accumulating molten steel, so that the one having a large grain size is used, and the surface thereof is used in a state where it is easily worn, so that oxygen cleaning is performed. However, the wear of the surface of the working surface is likely to proceed, and the durability of the plug itself is deteriorated.

[0009]

DISCLOSURE OF THE INVENTION The present invention provides a breathable refractory which can reduce the thickness of a molten steel infiltration layer when applied to a porous plug and can secure a required amount of ventilation, and which improves bubbling reliability and durability. provide.

[0010]

[Means for Solving the Problems] The reason why the porous plug has poor ventilation due to the increase of the molten steel infiltration layer and the bubbling reliability is lowered is because the lower part communicates with the outside air through a metal case, The operating surface is cooled by heat dissipation in contact with the molten steel, the internal temperature of the porous plug bricks gradually decreases from the upper surface downward, and the amount of heat absorbed by the infiltrated molten steel gradually increases as it moves downwards, and at certain positions When it reaches the temperature, it is cooled to below the melting point and solidifies.

That is, according to the present invention, the thickness of the molten steel infiltration layer on the working surface of the porous plug using a porous porous brick (hereinafter referred to as porous brick) which is a breathable refractory is determined by the temperature distribution inside the porous plug. It is based on the finding that it may depend greatly.

According to the experience so far, for example, Al ₂
The life of the Al ₂ O ₃ —SiO ₂ material having low thermal conductivity and low corrosion resistance and fire resistance may be longer than that of the O ₃ material porous plug. As a result of investigating the used products, Al
_{In the 2} O ₃ -SiO ₂ porous plug, attention was paid to the fact that metal infiltration was small and the internal temperature distribution was large. Therefore, by using a refractory bubble in the porous brick, heat insulation and low thermal conductivity are imparted to suppress the infiltration of molten steel.

That is, the low heat conductive breathable refractory material of the present invention is mainly composed of refractory fine powder and refractory aggregate, and the refractory aggregate has a particle diameter of 2 mm or less and a wall thickness of the outer diameter. Of 1
20 ~ with fire resistant bubbles that are / 4 to 1/20 as aggregate
It is characterized by containing 90% by mass.

The particle size of the refractory bubble is 2 m in the refractory aggregate.
If it exceeds m, the heat insulating property is deteriorated, and the pore diameter becomes large, so that the molten steel easily infiltrates, which is not preferable.
However, if the particle size is too small, a substantially hollow state cannot be obtained. From this, the lower limit of the particle size is not specified, but 0.2
It is desirable that the thickness is at least mm.

The thickness of the outer wall of the fire-resistant bubble is 1 / outer diameter
If it is less than 4, the thinner the better, the better, but in order to avoid crushing during kneading, it is desirable to secure a wall thickness of 1/20 or more.

Further, if the thickness of the bubble is too thick, the low thermal conductivity cannot be achieved, and if it is too thin, not only the strength is low, but also during the firing of the porous brick, the reaction firing with the refractory fine powder to be the matrix thereof is performed. The wall of the bubble is destroyed by the bond,
You lose the function of the beads, which are hollow. In other words, in order to maintain the heat insulating property, it is preferable to use a thin hollow bubble within a range that the strength can allow, and a bubble that floats on water.

The bubbles may contain a pulverized product in some industrial production methods, and some of them may have a low hollowness, but they are essentially hollow and have a fire resistance within the applicable range. If the outer diameter as an average value and the wall thickness range are complied with in the amount used, there is no problem in fulfilling the function of the present invention.

The refractory bubbles that can be used in the present invention include refractory hollow beads such as shirasu balloons and fly ash balloons obtained naturally or by-products.

As materials, alumina, mullite,
It is more preferable to use a material having a relatively high purity such as silica and a fire resistance of 1500 ° C. or higher. The usage is 2
If it is less than 0% by mass, the heat insulating property and low thermal conductivity will be poor, leading to an increase in the infiltrated layer of molten steel, and the bubbling reliability will be poor. If it exceeds 90% by mass, the strength as a breathable refractory material is reduced. An artificially similar chemical composition with a better sphericity and hollowness is also available on the market, but it has a good shape, but it also has a fire resistance of up to about 1300 ° C that cannot be used. is there.

Besides, refractory fine powder and other refractory aggregates can be combined and used in an amount of 10% by mass or more. As the refractory fine powder, in addition to zirconia mullite fine powder or zircon fine powder, fused silica, alumina fine powder, clay fine powder, chromium oxide fine powder and the like are blended in a range of 10 to 1% by mass. If the refractory fine powder exceeds 10% by mass, the number of joints becomes excessive, and the air permeability decreases as much as the number of pores decreases, resulting in a lack of bubbling reliability. If the amount is less than 1% by mass, the number of bonded portions will be small and the strength will be low, making it difficult to form the porous brick itself.

As aggregates other than the refractory bubbles, 0 to 7 are used.
Alumina spherical raw materials, mullite raw materials, and other refractory raw materials can be used within a range of 9% by mass, and air permeability can be maintained by using them in combination with refractory bubbles.

In the present invention, the aggregate is 0.2
It means a refractory material of mm or more, and is a raw material for mainly forming pores, and fine powder is less than 0.2 mm and mainly forms a bond for bonding aggregates.

The porous brick using the low thermal conductive breathable refractory material of the present invention exhibits excellent molten steel infiltration resistance by controlling the thermal conductivity within a certain range due to its heat insulating property.

Although its thermal conductivity λ has temperature dependence,
Based on the value at 350 ° C measured by the hot wire method specified in JIS R2618, the thermal conductivity of ordinary porous brick is about λ is 2.7 Kcal / mH ° C, while using a refractory bubble. λ is 2.0 Kcal / mH
By setting the temperature to be not higher than 0 ° C, a sharp temperature gradient can be given in the axial direction of the porous brick, and it is very effective in suppressing the infiltration of molten steel. That is, by making the material forming the porous brick have a heat insulating property, the internal temperature of the porous plug is suddenly changed, and the position where the solidification of molten steel or the viscosity of molten steel increases is brought close to the operating surface, The thickness of the infiltration layer can be reduced. By reducing the thickness of the molten steel infiltration layer, it is possible to secure a sufficient amount of gas during refining, prevent airflow obstruction due to the infiltration of molten steel, and lead to stable operation.

Furthermore, since the refractory bubble can reduce the weight of the porous brick itself, the work of replacing the porous plug is lightened.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to Examples shown in Table 1 in which alumina bubbles are used as refractory bubbles.

[0027]

[Table 1] The refractory bubbles used have three types of alumina purity of 98% and wall thicknesses of 0.4 mm, 0.2 mm and 0.1 mm. Particle diameters of 2 to 1 mm and 2 to 0.2 mm were used.

Phenolic resin as a binder and water were added to the mixture of the refractory aggregate and the refractory fine powder, and the mixture was kneaded and molded,
After drying, firing was carried out at 1700 ° C. or higher, and various characteristics were evaluated with respect to the cut and sampled porous brick in the actual shape obtained.

In Examples 1 to 6, an alumina bubble B having a thickness of 0.2 mm and an alumina bubble C having a thickness of 0.1 mm were used.
It was used. Comparative Examples 1 to 3 are examples using alumina bubbles A having a wall thickness of 0.4 mm, and Comparative Example 4 is a formulation not using alumina bubbles.

For each sample, hot bending,
The air permeability and the thermal conductivity were measured. In addition, each of the porous plugs made of porous bricks is 3
The bubbling reliability, oxygen cleaning property, and molten steel infiltration depth were evaluated based on the results of analysis after repeated use. The bubbling reliability in the actual ladle evaluation was evaluated based on the presence or absence of gas protrusion failure and whether or not the required flow rate was obtained as a result of using it three times. Poor protrusion
Indicated by. Oxygen cleaning was evaluated by the time until the recovery of the required flow rate, and less than 2 minutes was marked with ◯, 2 to 5 minutes was marked with Δ, and more than 5 minutes was marked with x. The molten steel infiltration depth was evaluated by observing the cross section of the porous plug after use.

In Examples 1 to 6, in each of the usage examples of the alumina bubbles B and C, lower thermal conductivity was achieved as compared with Comparative Example 4 which is a conventional product. Due to the heat insulation effect due to this low thermal conductivity, the depth of molten steel infiltration is shallow. Therefore, even in an actual furnace, there was no problem in bubbling reliability and oxygen cleaning performance, and it was highly durable.

Since Comparative Examples 1 to 3 have the same particle size as those of the Examples, there is no problem about the air permeability, but their thermal conductivity is 2.1 to 2.4 Kcal / mH ° C., and their high thermal conductivity is high. The solidification of the molten steel is delayed due to the property, the infiltration of the molten steel progresses, the flow rate of the bubbling is insufficient, and the gas ejection failure is generated, resulting in low reliability. Furthermore, it took time to recover the required flow rate for oxygen cleaning. Comparative Example 4 has a thermal conductivity of 2. because it does not contain refractory bubbles.
It was as high as 4 Kcal / mH ° C., which was inferior in all characteristics as compared with the porous plug made of the breathable refractory material of the present invention.

[0033]

The low-heat-conductivity breathable refractory material of the present invention can provide porous bricks with low heat-conductivity and heat-insulating properties, and can reduce the thickness of the molten steel infiltration layer.
As a result, the degree of wear due to oxygen cleaning can be reduced and the time can be shortened when using an actual furnace, the amount of gas required during refining can be secured in a short time, and bubbling reliability can be obtained. This will lead to stable operation through prevention of heat, improve durability, and reduce the work load due to oxygen cleaning under high heat.

Further, since the porous brick itself can be reduced in weight by using the low heat conductive breathable refractory material of the present invention,
The work of replacing the porous plug can be lightened.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) F27D 23/04 F27D 23/04 F term (reference) 4E014 MA12 MA20 4G019 LA09 LB01 LD02 4K013 CA23 CC02 4K056 AA02 AA06 CA02 EA14 4K070 AB16 AB17 CG02 CG06 EA07 EA13 EA14

Claims (2)

[Claims] 1. A refractory material comprising a refractory fine powder and a refractory aggregate as a main material, the refractory aggregate having a particle size of 2 mm or less and a wall thickness of 1/4 to 1/20 of an outer diameter. 20 to 9 sex bubbles
A low thermal conductive breathable refractory material containing 0% by mass. 2. The low thermal conductive breathable refractory material according to claim 1, which has a thermal conductivity of 2.0 or less.