KR100643839B1 - Porous Refractories for Gas Purging - Google Patents

Abstract

The present invention does not use chromium oxide that causes environmental problems, and by appropriately adjusting the composition and particle size distribution of the raw material to control the microstructure to have an appropriate porosity and pore size, crystal structure and microstructure excellent in thermal shock resistance It prevents the nozzle hole closing due to the attachment of aluminum and aluminum oxide, thereby suppressing casting unevenness and microcracks, so that the input gas pressure is kept constant so that it can be used multiple times and has high bubbling functionality. It is about.

The constitution is 10 to 40 parts by weight of spherical or square sintered alumina or electrolytic alumina as 1 to 0.5 mm particle diameter, 50 to 80 parts by weight of spherical or square sintered mullite or electrolytic mullite as 0.4 to 0.05 mm particle size, 5-10 parts by weight of plastic alumina of 50 µm or less, and 2 to 6 parts by weight of clay and frit.

Porous refractory materials. Alumina. Mullite

Description

Porous Refractories for Gas Purging

The present invention relates to a porous refractory material for gas injection used in a refining facility for refining molten metal, and more specifically, the porous refractory material is free from cracks due to thermal shock during preheating or casting, and is resistant to physical and chemical reactions. A fire retardant composition having a porosity suitable for impregnating.

In the refining furnaces such as ladle and tundish in the manufacture of steel and nonferrous metals, gas such as argon (Ar) or nitrogen (N ₂ ) is blown into the melt through a porous refractory material and bubbling to impurity. The non-metallic inclusions of flotation are floated to obtain a clean, uniform melt that has been removed.

In addition to the bubbling function of air flow rate and bubble generation ability, the molten steel must be able to withstand chemical and physical erosion by non-metallic inclusions and heat shock during preheating or casting. There should be no cracking and no molten steel adhesion or infiltration.

The most important improvement of the bubbling function among the above requirements depends on the pore size such as microstructure control of the porous refractory material. The larger the size of the bubble that passes through the pores of the refractory material, the lower the trapping ability of the inclusions, but the higher the separation resolution. Therefore, the fine structure of the refractory material of the optimal size, that is, the appropriate pore size and porosity is required.

The pore size is determined by the particle size of the porous refractory material to be produced, and also varies depending on the sintering agent, the firing temperature, the pressing force, and the like.

Uniform pore diameter distribution can minimize the problem of coalescing when the bubble size is formed uniform. In addition, cracks may occur when cracks are generated during use or preheating is insufficient, and if such a problem occurs, the bubbling input gas is not injected into the molten steel and is lost to the outside of the container to maintain a constant bubbling pressure. As a result, the casting nonuniformity caused by the increase in adhesion of inclusions may be increased, thereby causing a problem of casting interruption.

Therefore, in order to improve the service life, cracking should not occur during use as well as the contents of molten steel and non-metallic inclusions. In order to improve this, in addition to the proper porosity and the appropriate pore size, a crystal structure and microstructure having excellent thermal shock resistance are required.

On the other hand, in order to improve the melt damage caused by chemical reactions to molten steel and non-metallic inclusions in addition to physical factors, control of chemical composition is required.

In particular, infiltration of Fe oxides and inclusions by infiltration and oxidation of molten steels causes deterioration of air permeability due to formation and infiltration of constituents and low melts with refractory materials.

Finally, cracks due to heat spalling cause problems of leakage of injected gas, infiltration and leakage of molten steel, and improvement of particle shape, microstructure, and thermal shock by low-expandable minerals.

Conventional refractory materials in this regard are sintered or molten alumina (Al ₂ O ₃ ) or mullite (Mullite) by particle size of 75 to 100 parts by weight, plastic alumina 5-10 parts by weight, clay (clay) and frit (frit) 2 It is comprised at -6 weight part.

However, such a conventional fireproof material has problems such as insufficient strength, solvent resistance, spalling resistance including thermal shock resistance, and insufficient bubble formation ability due to uneven distribution of pore diameter.

On the other hand, a domestic patent (Registration No. 10-0361807) is known as a part to improve the above problems, but the pores formed in the product when using too much alumina may be a cause of waste regeneration and non-uniform pore formation Since chromium oxide (Cr ₂ O ₃ 1 to 8 parts by weight) is used to improve the properties, there have been problems such as not considering environmental problems.

On the other hand, since the melting of the refractory material is rapidly made due to the rapid rise of the temperature at the time of opening by the oxygen during casting or casting, a component having a high melting point for oxygen washing is required. On the other hand, aluminum added as a deoxidizer in molten steel needs to be controlled because it forms an oxide by reacting with oxygen in molten steel or oxygen in a refractory material.SiO ₂ component in the refractory material is easily reduced, so that it is not reduced by aluminum in molten steel. Minimization of _two components is desired. In addition, since the melting loss due to the formation of low melt of the FeO-SiO ₂ system by the chemical reaction with molten steel is easily made, it is necessary to control the chemical composition.

The present invention is to improve the above-mentioned conventional problems, and does not use chromium oxide causing environmental problems, and by appropriately adjusting the composition and particle size distribution of the raw material to have an appropriate porosity and pore size by controlling the microstructure and In addition, it has a crystal structure and microstructure excellent in thermal shock resistance, prevents nozzle hole closure due to adhesion of aluminum and aluminum oxide, and keeps the input gas pressure constant by suppressing casting unevenness and microcracks. An object of the present invention is to provide a porous refractory material having excellent high thermal shock resistance.

The present invention for achieving the above object is 10 to 40 parts by weight of spherical or square sintered alumina or electrolytic alumina, 50 to 80 parts by weight of spherical or square sintered alumina or electrolytic mullite, 5 to 10 parts by weight of plastic alumina, It is made of gas-injected porous refractory material, characterized in that the composition is composed of clay and frit 2 to 6 parts by weight.

In the above composition, it is preferable that the rectangular sintered alumina or the molten alumina has a particle size distribution of 1 to 0.5 mm, and that the spherical or rectangular sintered alumina or the molten aluminite has a particle size distribution of 0.4 to 0.05 mm,

The spherical or rectangular sintered mullite or electromelted mullite is excellent in thermal shock resistance improvement with a coefficient of thermal expansion of about 40% lower than that of alumina and low melt formation due to the reaction between Fe oxide and non-metallic inclusions. In order to minimize the bubbling effect, especially when the current infiltration is excessive, the particle size distribution was set to 0.4 to 0.05 mm to improve the particle size composition and the bubbling effect.

In particular, the present invention can maximize the effect of improving the impact resistance by applying a spherical or angular mullite mineral having excellent thermal shock resistance to improve the material improvement and bubbling performance to prevent clogging for ultra low carbon steels that are a problem when using multiple times. It was made.

The added amount of the mullite is insufficient in the effect of improving the thermal shock resistance at 50 parts by weight or less, and the content of molten steel is lowered at 80 parts by weight or more. Therefore, the range was 50 to 80 parts by weight. The particle size is 0.05 mm or less, and the uniform pore diameter forming ability and bubbling effect are insufficient, and the pore size of 0.4 mm or more is too large to decrease the inclusion removal forming ability.

Spherical or square alumina is 10 to 40 parts by weight because it is difficult to improve the solvent resistance to molten steel only by mullite and reacts with some components in the molten steel.

If it is 10 parts by weight or less, there is a problem of lowering the packing density, and if it is 40 parts by weight or more, the thermal shock resistance is lowered. And 0.5 mm or less reduces the packing density of a product, and 1 mm or more reduces the size of the pore formed, and the ability to remove inclusions falls.

The plastic alumina preferably has a particle size distribution of 50 μm or less, and is preferably 5 to 10 parts by weight since excess pores may cause waste pores and non-uniformity to be formed in the product.

Table 1 shows the examples according to the present invention.

Table 1

  Conventional            Embodiment of the present invention      One      2      3     4   Membership fee, weight part Square or Spherical Alumina 2 ~ 1mm  0-10 Spherical Sintered Alumina 1 ~ 0.5mm 31 Square Electrolytic Alumina 1 ~ 0.5mm 40 Spherical Sintered Alumina 1 ~ 0.5mm 19 Square Electrolytic Alumina 1-0.5mm 10 Spherical Sintered or Electrolytic Alumina 1 ~ 0.2mm  50-80 Electrolytic Mullite 0.4 ~ 0.05mm 60 Spherical Sintered Mullite 0. ~ 0.05mm 50 Electrolytic Mullite 0.4 ~ 0.05mm 70 Spherical Sintered Mullite 0.4 ~ 0.06mm 80 Square or spherical alumina 0.2mm or less  10 to 20 Plastic Alumina 50㎛ or less 10 to 20      6     5     5      8 Cr ₂ O ₃ 50㎛ or less  1 to 5 Clay + frit  2 to 6      3     5     6     2 CaO or MgO containing minerals  1 to 7  Properties Porosity (%) 18-30     33     29     24     32  Volume specific gravity 2.7 to 3.1      2.03      2.5      2.2      2.2 Compressive strength (kg / cm ² ) 400-700      300     400     580     260 Aeration rate (N / min at 0.5Bar) 120-130      140     135     130     145 Heat resistant spalling usually     Great    Great    Great    Great Bubble Formation usually     Great    Great    Great    Great ★★★ Contents   100      96     90       92    95 Inclusion thickness mm   9.5      7     7      8     6       Use High thermal shock resistance for high temperature oxygen cleaning for multi company     Left     Left     Left

★ Comparison of crack initiation time, crack size and number by 1,600 ℃ burner heating

★★ Bubble forming ability comparison at 0.1Bar after applying foaming agent

★★★ Erosion resistance comparison after reacting molten steel and slag at 1,600 ℃ for 2 hours at high frequency induction furnace

★★★★ Inclusion thickness after actual application (180 minutes application, molten steel is 1250 tons)

As described above, the present invention has appropriate porosity and pore size by controlling the microstructure by appropriately adjusting the composition and particle size distribution of the raw material, and having a crystal structure and microstructure excellent in thermal shock resistance to attach aluminum and aluminum oxide. By preventing the closing of the nozzle hole according to the casting non-uniformity and micro-cracks suppress the input gas pressure is kept constant to obtain a high-temperature shock-resistant porous refractory material excellent in bubbling functionality.

Claims (3)

 10 to 40 parts by weight of sintered alumina or electrolytic alumina having a spherical or rectangular shape and having a particle size distribution of 1 to 0.5 mm, 50 to 80 parts by weight of a sintered mullite or electrolytic mullite having a 0.4 to 0.05 mm particle size distribution, A gas-injected porous refractory material for molten metal refining equipment, characterized in that 5 to 10 parts by weight of plastic alumina having a particle size distribution of 50 µm or less, and 2 to 6 parts by weight of clay and frit. delete delete