JPH0656541A - Castable refractory - Google Patents

Abstract

PURPOSE:To provide a castable refractory being superior in corrosion resistance and spalling resistance and having durability stabilized in high degree. CONSTITUTION:This castable refractory is formed by incorporating 5-40wt.% alumina.zirconia clinker with >=0.2mm grain diameter incorporating 3-70wt.% ZrO2 and >=1 kind selected from electrofused alumina, sintered alumina, electrofused spinnel, sintered spinnel, electrofused magnesia, and sintered magnesia, and by adding <=1wt.% (in terms of CaO quantity) alumina cement being >=99wt.% in the total quantity of Al2O3 and GaO as a binder. Silicone carbide, carbon, superfine silica, and calcined alumina, etc., can be used in addition to this blended raw materials, and also use of a dispersant and an additive adjusting the workability is not restrained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to castable refractories mainly used for iron-making kilns.

[0002]

2. Description of the Related Art The inner lining of a kiln for steelmaking is labor-saving
For the purpose of improving the working environment, we are shifting from standard refractory materials to non-standard refractory materials. Among the amorphous refractories, castable refractories are widely used due to the compactness and uniformity of the construction structure and the ease of construction.

The performance of castable refractories is greatly affected by the amount of alumina cement used as a binder as well as the grade of aggregate. Therefore, so-called low-cement castable, which reduces the amount of alumina cement and uses ultrafine alumina and calcined alumina instead, is the mainstream.

In iron ladle kilns, ladle whose operating conditions are harsh, burner tiles of secondary refining furnaces and heating furnaces, etc., high refractory raw materials of alumina, spinel and magnesia are used as aggregates of castable refractories. A material that emphasizes corrosion resistance and heat resistance is used.

When chemical erosion is the predominant form of wear in a real furnace, the castable refractory has a good service life, but in a general iron-making kiln with a heat cycle, thermal spalling Peeling occurs and stable durability cannot be obtained.

As a means for improving the spalling resistance of this castable refractory material, JP-A-4-42868 discloses a silica stone having a particle diameter of 0.2 to 3 mm or a particle diameter of 1 to 10.
It has been proposed to add mm mullite. Since this silica stone or mullite has a different coefficient of thermal expansion compared to the main aggregate such as alumina, it is possible to suppress the development of microcracks generated during the process of using the actual furnace.

However, although this is effective as a means for improving the spalling resistance of castable refractories, the silica stone and mullite used are inferior in corrosion resistance and heat resistance to alumina as the main aggregate. There is a problem in applying it to a kiln with severe operating conditions.

Japanese Patent Publication No. 1-58156 proposes to improve spalling resistance by controlling the particle size of alumina cement.
It can be expected that the sintering will be moderated at the initial stage of use and the spalling resistance of the castable refractory will be improved, but CaO will diffuse during long-term use and the spalling resistance will decrease.

[0009]

SUMMARY OF THE INVENTION As described above, the present invention is excellent in corrosion resistance and spalling resistance in view of the fact that there is no compatible corrosion resistance and spalling resistance in the present situation of castable refractories. It is an object of the present invention to provide a castable refractory having high and stable durability.

[0010]

The castable refractory material of the present invention contains ZrO _{2 in an amount} of 3 to 70% by weight and a particle size of 0.
5-4 alumina zirconia clinker of 2 mm or more
It contains 0% by weight and one or more of fused alumina, sintered alumina, fused spinel, sintered spinel, fused magnesia, and sintered magnesia, and contains Al ₂ O ₃ as a binder.
Alumina cement having a total amount of 99% by weight or more of CaO and CaO is added within the range of not more than 1% by weight as the amount of CaO.

In the present invention, in addition to the above-mentioned compounded raw materials, silicon carbide, carbon, ultrafine silica, calcined alumina, etc. can be used. The amount of these used is preferably in a range that does not reduce the corrosion resistance and heat resistance of the castable refractory. Further, there is no problem in using a dispersant or an additive for adjusting workability.

[0012]

[Function] Alumina / zirconia clinker has a smaller coefficient of thermal expansion than alumina, spinel, and magnesia. Therefore, when the castable refractory expands during use, a minute gap is created due to the difference in expansion coefficient. The fine gap relaxes thermal stress and improves spalling resistance.

However, when the particle diameter of the alumina / zirconia clinker used is smaller than 0.2 mm, the gap due to the difference in expansion is absorbed in the voids of the matrix, and the effect of improving the spalling resistance is small.

When the amount of ZrO ₂ in the alumina / zirconia clinker is less than 3% by weight, the difference in expansion from the main aggregate such as alumina is small and the effect of improving spalling resistance is also small. When the amount of ZrO ₂ is more than 70% by weight, the expansion behavior is similar to that of ZrO ₂ , and the difference in expansion with the main aggregate is excessive, and the strength and corrosion resistance are deteriorated, which is not suitable.

The amount of the alumina / zirconia clinker used is limited to the range of 5 to 40% by weight, but if it is less than 5% by weight, it is not sufficient to improve the spalling resistance and exceeds 40% by weight. In the range, the gap due to the difference in expansion becomes excessive, and the strength and corrosion resistance decrease, which is not preferable.

Alumina / zirconia clinker essentially has a small difference in corrosion resistance from alumina and spinel, and
When used in the range of 40% by weight, the corrosion resistance of the castable refractory does not decrease.

When the purity of the binder, alumina cement, is low, the corrosion resistance is lowered because SiO ₂ , TiO _{2 and the} like are increased, and also when the CaO content exceeds 1% by weight, the corrosion resistance is also lowered. This is not preferable.

[0018]

EXAMPLES Castable refractories shown in Table 1 were manufactured and their characteristics were compared.

[0019]

[Table 1] Examples 1 to 6 in Table 1 use alumina / zirconia clinker in a particle size range of 3 to 1 mm and less than 1 to 0.2 mm. Compared with the alumina castable of Comparative Example 1, the corrosion resistance is equivalent, but the spalling resistance is remarkably improved. Particularly, the spalling resistance of Examples 3 to 6 is good. Comparative Example 2 uses an alumina / zirconia clinker having a low ZrO ₂ content.
The spalling resistance is at the same level as in Comparative Example 1 and is not improved. In Comparative Examples 3 and 4, the amount of alumina / zirconia clinker used was outside the range of the present invention. When the amount was small, there was no effect of improving the spalling resistance, and when the amount was large, the binding between coarse particles and the matrix was insufficient. At the same time as the corrosion resistance decreases, the strength deteriorates due to repeated heating, and the effect of improving the spalling resistance is small. Comparative Example 5 is a material to which a zirconia clinker is added, but the corrosion resistance decreases as in the case of using a large amount of alumina / zirconia clinker. Comparative Example 6 is a material in which alumina cement is used in excess of the range of the present invention, and its corrosion resistance is lowered, so that it is difficult to apply it to a kiln under severe operating conditions. Comparative Example 7 uses an alumina-zirconia clinker having a particle size of less than 0.2 mm, but has no effect of improving spalling resistance. The castable refractory material of Example 3 was used on the outer periphery of the CAS crushed pipe. The durability was 1.4 times that of the conventional product and Comparative Example 1, demonstrating the superiority of the present invention.

[0020]

The castable refractory material of the present invention has the following effects.

(1) It has both excellent corrosion resistance and spalling resistance, and has high and stable durability.

(2) Since the basic composition of the conventional castable refractories is not changed, it is possible to obtain a construction body having excellent durability without changing the construction method.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kosuke Kurata, Inventor Kosuke Kurata 1-1 No. 1 Tobata-cho, Tobata-ku, Kitakyushu, Fukuoka (72) Inventor, Saburo Matsuo Tobata-ku, Tobata-ku, Kitakyushu, Fukuoka No. 1 town No. 1 Nippon Steel Corporation Yawata Works

Claims (1)

[Claims] 1. Fused alumina, sintered alumina, fused spinel, sintered spinel, containing 5 to 40% by weight of alumina / zirconia clinker containing ZrO _{2 in an amount} of 3 to 70% by weight and having a particle size of 0.2 mm or more, Contains 1 or 2 or more of electro-melted magnesia and sintered magnesia, and Al as a binder
_A castable refractory made by adding alumina cement having a total content of ₂ O ₃ and CaO of 99% by weight or more within a range of not exceeding 1% by weight as CaO.