JPH01180761A - Nozzle refractory for casting molten metal - Google Patents

Abstract

PURPOSE:To obtain a nozzle refractory having excellent spalling resistance, oxidizing resistance and wear resistance by continuously or stepwisely increasing graphite content from outer wall surface side toward inner wall surface side of the nozzle and improving crack developing resistance at the time of using. CONSTITUTION:Components except graphitic quality in a composite material content oxide material series components of alumina, silica, zirconia, etc., as main component, and SiC, B4C, etc., in the above components may be contained to the max. prescribed concns. In the case of continuously varying the graphite content, a cylindrical mold for forming is set at center of rotation of a rotating table and while rotating the mold at high speed, refractory raw material is charged little by little to manufacture the refractory raw material filling body, in which the graphite content is continuously increased from the outside toward the inside. As the components except the graphite are heavy, they are filled much toward the outside with centrifugal force. This filling body is pressurizing-formed by an isotropic pressurized forming method and further, produced through purning. The graphite is less than the oxide in these thermal expansion ratio and on the other hand, the oxide is more than the graphite in these breakage stress resistance. By this method, the nozzle refractory having excellent spalling resistance and oxidizing resistance can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a casting nozzle which has a cylindrical shape and allows molten metal to flow down through its inner bore.

BACKGROUND OF THE INVENTION Conventional techniques and their problems Nozzles used in continuous casting of molten metal, especially steel, are important refractories that play roles such as preventing oxidation of molten steel, preventing entrainment of air, etc., and preventing splashing.

At the start of casting, the nozzle is rapidly heated by the contact flow of the high temperature molten steel down the wall surface of the inner hole, but the outer circumference remains at a preheated temperature or lower. Therefore, a large temperature difference is generated between the inner wall surface and the outer wall surface of the nozzle refractory, and the tensile stress generated on the nozzle outer wall surface tends to cause troubles such as vertical cracks, cracks such as ring cuts, or breakage.

Conventionally, the materials used for nozzle refractories have been fused silica with low thermal expansion, or graphite-containing oxide materials with high thermal conductivity such as graphite-magnesia and graphite-alumina. Because graphite-containing oxide-based refractories have excellent corrosion resistance, they are the mainstream of today's continuous casting nozzle refractories.

Graphite-containing refractories utilize the characteristics of graphite such as low thermal expansion, low elasticity, and high thermal conductivity, as well as the excellent stress relaxation ability of graphite and the binder carbon in the joints, to improve resistance to cracking, that is, heat resistance. It has improved spalling properties and is also resistant to molten steel and slag.
, it also has the advantage of relatively excellent corrosion resistance due to its lack of eutectic properties.

The reason why graphite-containing oxide refractories such as graphite-magnesia and graphite-alumina have come to be widely used in place of conventional oxide refractories is largely due to the excellent properties of graphite. However, it is also a well-known fact that graphite has the disadvantage of being easily oxidized in air at high temperatures. Therefore, from the viewpoint of heat spall resistance, it is desirable to use a material with as high a graphite content as possible, but in reality, materials with a graphite content of 40% or more are difficult to use because the outer wall in contact with the air suffers significant oxidation loss. It is. In other words, the graphite content of the nozzle refractories currently in general use is unavoidably limited to 35% or less from the viewpoint of oxidation resistance, which often causes problems in terms of heat spall resistance. This is the reality.

When the nozzle is rapidly heated by the contact flow of high temperature molten steel down the inner hole wall surface, compressive stress acts on the inner wall side due to thermal expansion, and tensile stress acts on the unilateral wall side. If the tensile stress acting on the outer wall exceeds the breaking stress of the material, cracks will occur. Therefore, it can be seen that in order to make cracks less likely to occur, it is effective to reduce the stress acting on the outer wall and/or to increase the breaking stress of the outer wall material.

Means for Solving the Problems Generally, in graphite-oxide composite materials, graphite has a lower coefficient of thermal expansion than oxides, while oxides have higher fracture stress. The inventor of the present invention utilized the unique properties of this graphite-oxide material to obtain a nozzle with excellent spall resistance and oxidation resistance. The inventors have discovered that the desired objective can be achieved by increasing the graphite content sequentially from the inner wall surface toward the inner wall surface, and have completed the present invention.

That is, the present invention provides a graphite-oxide nozzle refractory for molten metal casting, in which the graphite content is increased continuously or stepwise from the outer wall side to the inner wall side of the nozzle, thereby preventing the occurrence of cracks during use. The present invention provides a nozzle refractory for molten metal casting, which is characterized by increased resistance.

The material of the graphite-oxide composite material nozzle in the present invention usually has a graphite content (indicated by the amount added to 100 parts by weight of components other than graphite) of the part of the nozzle outer wall with the lowest graphite content of 10 to 30 parts by weight. % (hereinafter simply referred to as %)
, preferably 15 to 25%, and the graphite content of the inner wall portion with the highest graphite content is usually 30 to 50%, preferably 35 to 45%.

If the amount of graphite in the nozzle outer wall is less than 10%, the spalling resistance will essentially be insufficient, and if it exceeds 30%, the oxidation resistance will be insufficient. In addition, the amount of graphite on the inner wall of the nozzle is 30%.
If it is less than 50%, the spall resistance will essentially be insufficient.
If the value exceeds , the wear and tear caused by the molten steel flow will increase.

The graphite content of the nozzle inner wall material and outer wall material may be changed stepwise or continuously, and is not particularly limited, but it is more effective to change it continuously. .

Components other than graphite in the composite material used in the present invention are mainly oxide components such as alumina, silica, zirconia, zircon, spinel, magnesia, and lime.
iCSB4 C, Si2 N4, BN, AQN, Si
etc. may be contained up to about 50%.

The nozzle refractory according to the present invention is manufactured as follows.

First, when changing the graphite content continuously, a cylindrical mold is set on the rotation center of the rotary table,
By gradually introducing clay while rotating the mold at high speed, a clay filling body in which the graphite content continuously increases from the outside to the inside is produced. This is because components other than graphite are heavier than graphite, and are therefore filled in larger amounts on the outside due to centrifugal force. Thereafter, this filled body is pressure-molded by an isostatic pressing method in a conventional manner, and is further fired to produce the filler.

In addition, when changing the graphite content in stages, one or more concentric partition plates are set in a cylindrical mold, and the clay produced by changing the graphite content is Starting from the smallest amount of clay, it is introduced from the outside of the space inside the mold formed by the partition plate. Thereafter, the partition plate is removed to produce a clay filling body in which the graphite content changes stepwise. Thereafter, this filled body is pressure-molded by an isostatic pressing method in a conventional manner, and is further fired to produce the filler.

Effects of the Invention According to the present invention, a graphite-oxide nozzle refractory for molten metal casting which has excellent spall resistance, oxidation resistance, and wear resistance can be obtained.

EXAMPLES Hereinafter, examples will be shown to clarify the features of the present invention.

Example High purity alumina (AQ20399.5%) 65%, 5i
Clay A1B and C were prepared by mixing and kneading 20%, 30% and 40% of natural graphite with respect to 100 weight of a compound consisting of 20% C and 15% fused silica, and the three types shown in Table 1 were prepared. After filling the clay into a rubber mold using the method described in 1.
Molding was performed using an isostatic press at a pressure of 000 kgf/cJ.

AQ2 in the sample nozzle after reduction firing at 1000℃
Thermite powder consisting of 6% and Fe20374% was filled, and the nozzle inner hole was rapidly heated by direct ignition, and the presence or absence of cracks on the outer surface of the nozzle was examined.

A molded body made by a conventional method with graphite distributed homogeneously throughout the body (
In Comparative Example 1), large cracks occurred in the longitudinal direction of the nozzle. On the other hand, in Example 1, no cracks were observed at all,
In addition, in Example 2, only slight surface cracks occurred,
The high spall resistance of the product of the present invention was confirmed.

On the other hand, samples after reduction firing at 1000°C were placed in a furnace maintained at 1000°C, SiC abrasive grains were sprayed onto the sample surface, and weight loss or volume reduction index due to wear was compared.

In Examples 1 and 2, the wear index was 1/2 or less as compared to Comparative Example 1, and a significant improvement in oxidation resistance was observed.

Claims (1)

[Claims] (1) In graphite-oxide nozzle refractories for molten metal casting, the graphite content is increased continuously or stepwise from the outer wall side to the inner wall side of the nozzle to improve cracking resistance during use. A nozzle refractory for molten metal casting, which is characterized by a high temperature.