JP3536886B2 - Method for producing porous refractory for gas-blown porous plug - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a porous refractory for a gas-blown porous plug having both durability and high gas permeability.

[0002]

2. Description of the Related Art Temperature control, uniform composition of molten steel,
In order to remove non-metallic inclusions, an inert gas such as argon is blown into molten steel from the bottom of a molten steel container. The properties required for the gas-injected porous plug are gas permeability, corrosion resistance, and molten steel slag permeability (hereinafter simply referred to as penetration resistance).

As a porous refractory for a gas-blown porous plug having these characteristics, the applicant of the present application has proposed an alumina-zircon material in JP-A-59-203756. According to this material, zircon _(ZrO 2 · SiO ₂₎ is dissociated by high temperature in use, SiO ₂ is produced by it is integrated into the contact point of the aggregate (alumina) with surface tension at a molten state, SiO ₂ reacts with the alumina of the aggregate to form mullite (3Al ₂ O ₃ .2SiO ₂ ). Then, the mullite firmly bonds between the aggregate particles, and becomes a material having excellent corrosion resistance even with high gas permeability. In addition, Japanese Patent Application Laid-Open No. 63-166752 proposes a zirconia-mullite-alumina refractory for a porous plug. This material has excellent spalling resistance due to the low expansion property of zirconia / mullite, and has the effect of improving the permeation resistance by reacting the zirconia / mullite with molten steel slag to increase the viscosity.

[0004]

In recent years, however, various kinds of alloys have been introduced into molten steel as compared with the prior art, and with this, a larger amount of inert gas has been added to make the components uniform. Gas-blown operations have begun. In accordance with this, the refractories for porous plugs are also becoming porous. However, this porosity simultaneously promotes clogging due to penetration of molten steel slag.
The clogging reduces the gas permeation function, so the molten steel slag that has infiltrated the upper end of the porous plug is washed and removed by oxygen blowing during the suspension of operation of the molten metal container. Porous plugs are severely damaged by poling. In addition, since the oxygen cleaning is troublesome and the durability is low, the operating rate of the molten steel vessel is reduced.

[0005] Among the above-mentioned conventional materials used as refractories for porous plugs, alumina-zircon is excellent in corrosion resistance, but is not sufficient in gas permeability and permeation resistance. On the other hand, zirconia-mullite-alumina is excellent in permeation resistance but inferior in gas permeability. Therefore, these conventional materials cannot provide sufficient gas permeability and durability at the same time, and have a problem that they cannot sufficiently meet the recent demand for porous refractories for porous plugs. An object of the present invention is to obtain a porous refractory for a porous plug having both sufficient gas permeability and durability.

[0006]

According to the present invention, a composition containing 1 to 10% by weight of fused silica, 0.5 to 8% by weight of zirconia, and a balance containing a refractory aggregate mainly composed of alumina is formed after kneading. And a method for producing a porous refractory for a gas-blown porous plug characterized by firing. In the present invention, a mullite bond is generated by a reaction between fused silica and alumina during firing, whereby the refractory structure becomes strong and the corrosion resistance is improved. Further, during use in the molten metal container, a permeation resistance is improved by forming a silica film coming from the fused silica between the refractory aggregate particles.

[0007] Zirconia transforms in the temperature range of 1000 to 1200 ° C. And, by the volume expansion accompanying the transition at the time of sintering, it has an effect of generating countless fine cracks serving as gas vents in the refractory structure. As compared with the voids between the refractory aggregate particles, the voids generated by the cracks due to the zirconia transition are fine, but the gas permeability is remarkably improved due to the extremely large number of voids. In addition, the fineness of the voids is extremely effective in improving the penetration resistance to molten steel slag. Further, the silica film is viscous at a high temperature, deforms following firing at the time of zirconia transformation during firing, and then forms a mullite (3Al ₂ O ₃ .2SiO ₂ ) bond by reaction with alumina. Presumably for this reason, the porous refractory for a porous plug according to the present invention is excellent in corrosion resistance despite the fact that a large number of fine cracks are present therein.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The particle size of fused silica, zirconia and alumina used in the present invention is not particularly limited. However, in order to obtain a gas-permeable porous material by forming voids between the particles, As with the material, it is preferable to reduce the ratio of the intermediate particles to make the particle size composition mainly composed of coarse particles. Among them, the ratio of fused silica and zirconia is small, so that the particle size is 1 mm or less, more preferably 0.5 mm or less. Alumina is adjusted to a particle size distribution such that, for example, particles having a particle size of 0.15 to 2 mm become 70% by weight or more in order to form voids between particles.

Fused silica is obtained by fusing silica stone, silica sand, quartz, quartz, and the like, and is sometimes referred to as quartz glass, fused quartz, or the like. As described above, the combination with zirconia has the effect of improving penetration resistance and corrosion resistance. The ratio of the fused silica is 1 to 10% by weight. If it is less than 1% by weight, there is no effect of permeation resistance, and if it exceeds 10% by weight, the corrosion resistance is poor. As described above, zirconia has the effect of obtaining high gas permeability due to volume expansion accompanying the transition. Zirconia is generally produced by fusing and desiliconizing zircon in an electric furnace, and stabilized zirconia and semi-stabilized zirconia to which CaO, MgO, etc. are added are known. As a material used in the present invention, unstabilized zirconia having a large volume expansion accompanying the transition is preferable. The mixing ratio of zirconia is 0.5 to 8% by weight. 0.5% by weight
If it is less than 8% by weight, the gas permeability is inferior.

Alumina, which is the main component of the aggregate, is preferably a high purity product such as fused alumina and sintered alumina from the viewpoint of corrosion resistance and spalling resistance. The shape of the particles is spherical,
Any non-spherical product (crushed product) may be used. A preferable ratio in the refractory aggregate is 82 to 98.5% by weight. In the present invention, chromium oxide may be further added to the refractory aggregate composition comprising silica, zirconia, and alumina. Silica and zirconia components easily react with the molten steel component to form a low melt that causes a reduction in corrosion resistance, but when chromium oxide is added, the molten steel component that causes the low melt product reacts with chromium oxide. Producing a solid solution having a high fire resistance has the effect of further improving corrosion resistance.

The proportion of chromium oxide is 5 parts by weight or less, preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the refractory aggregate according to the above-mentioned composition. If the amount is less than 0.5 part by weight, the effect of improving the corrosion resistance is not obtained, and if it exceeds 5 parts by weight, oversintering is caused and the spalling resistance is poor. As chromium oxide, it is preferable to use fine powder having an average particle diameter of 1 to 2 μm from the viewpoint of reactivity and dispersibility.

In the present invention, the refractory aggregate having the above composition is used as a main material, and a binder such as clay, bentonite, dextrin and CMC is added to the refractory aggregate.
About 1 to 8 parts by weight is added to 00 parts by weight and an appropriate amount of water is added. The mixture is kneaded, molded and then fired. The kneading is performed by adding a suitable binder and using a mixer or the like. The molding is performed by pressure molding such as a friction press or a hydraulic / hydraulic press. The firing temperature is set to, for example, 1000 to 18 so that zirconia is transformed.
Set to 00 ° C. The porous refractory thus obtained is described in, for example, Japanese Utility Model Application Laid-Open No. 58-121327 and JP-A-1-33285.
As seen in No. 6, etc., it is used as a porous plug by connecting to a gas supply pipe and surrounding the outer periphery with a dense refractory.

[0013]

EXAMPLES Examples of the present invention and comparative examples are shown below.
Table 1 shows the chemical analysis values of the main compounding raw materials used in each example. Table 2 shows the composition ratio of the composition according to the examples of the present invention and the test results of the porous refractory obtained from the composition. Table 3 is a comparative example. In each of the examples and comparative examples of the present invention, 2% by weight of a pulp waste liquid was added as a binder to the mixture, and the mixture was kneaded with a mixer, pressed into a predetermined shape by a friction press, and then dried. After that, the resultant was fired at 1700 ° C. × 5 hours to produce a porous refractory. The particle size of chromium oxide is "SK Laser Micron Sizer 7" manufactured by Seishin Enterprise.
000S ".

The test methods in Tables 2 and 3 are as follows. Corrosion resistance; Rotational erosion test at 1650 ° C. × 3 hours was performed using a combination of steel and ladle slag at a weight ratio of 1: 1 as an erosion agent to measure erosion dimensions. It was shown by an index with the erosion dimension of Comparative Example 1 being 100. The smaller the value, the better the corrosion resistance. Gas permeability: The porosity was measured according to JIS: R2205-74, and used as an index of gas permeability. Porosity and gas permeability are proportional. The higher the porosity, the better the gas permeability.

[0015] Slag penetration resistance to molten steel: A test piece was embedded in the bottom of a high-frequency induction furnace using steel as a solvent, and after operating at a temperature of 1650 ° C, the penetration size was measured. Sparing resistance: The operation of heating in an electric furnace at 1500 ° C. for 30 minutes, then taking out and air-cooling was repeated, and the number of service times until the start of peeling was measured.

Examples 3 and 7, Comparative Examples 2 and 9 were tested on actual machines. The porous refractory of the porous plug used in the actual machine test has a lower diameter of 110
mm, an upper diameter of 80 mm, a height of 130 mm, and a truncated cone. Around this porous refractory, a 25 mm-thick dense refractory made of an alumina castable refractory is provided. A structure to attach an introduction pipe was adopted.
Using this porous plug attached to a 300-t molten steel ladle, the time required to remove molten steel slag that had permeated the porous refractory by oxygen washing was examined. The shorter the required time, the better the penetration resistance. As the durability, the wear rate after using 10 charges was measured.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

The porous refractories obtained according to the examples of the present invention are all excellent in corrosion resistance, gas permeability, molten steel slag penetration and spalling resistance. Among them, Examples 6 to 9 to which chromium oxide was added are particularly excellent in corrosion resistance and penetration resistance. Further, in the actual machine test, it was confirmed that the oxygen cleaning time was short in the example and the excellent durability was obtained. In particular, Example 7 to which chromium oxide was added was excellent. The oxygen cleaning time mainly depends on the gas permeability and the resistance to molten steel slag penetration, and in the embodiment of the present invention, since the gas permeability and the resistance to molten steel slag penetration are excellent, no actual machine test was performed. In other examples, it can be easily presumed that the oxygen cleaning time is short. Further, the wear rate mainly depends on the corrosion resistance and the oxygen cleaning time. In the embodiment of the present invention, the corrosion resistance is excellent and the oxygen cleaning time is short. It is easy to guess that the speed is low.

On the other hand, Comparative Example 1 is made of alumina-silica-zircon, and is particularly poor in permeation resistance. Comparative Example 9
Is obtained by adding chromium oxide to alumina-silica-zircon, but is inferior in permeation resistance and spall resistance.
Comparative Example 2 is alumina-zirconia mullite,
Poor gas permeability. Comparative Example 3 is an alumina-fused siliceous material, and is particularly inferior in gas permeability because zirconia is not blended.

Comparative Example 4 was made of alumina-silica-zirconia, and its structure was weakened due to abnormal expansion of the silica.
Poor corrosion resistance. Comparative Examples 5 and 6 were both alumina-
Although it is a fused silica-zirconia material, Comparative Example 5 is inferior in corrosion resistance because the proportion of fused silica is too large, and Comparative Example 6 is too large in proportion of zirconia. Comparative Example 7 is alumina-fused silica-zirconia mullite, and is inferior in gas permeability and spalling resistance, possibly due to oversintering of zirconia mullite and fused silica. Comparative Example 8 was obtained by adding chromium oxide to alumina-silica-zirconia, and was excellent in corrosion resistance, but was inferior in spalling resistance due to too much chromium oxide.

[0023]

As described above, the refractory for a gas-injected porous plug obtained by the present invention has both gas permeability, penetration resistance and corrosion resistance as described above, and can cope with recent large-volume gas-injection operations. Can be. In addition, the improvement in the penetration resistance to the slag can significantly reduce the cleaning time by oxygen blowing and improve the durability, thereby greatly contributing to the improvement in the operation rate of the molten steel container. Furthermore, in its production, the gas permeability can be adjusted by the amount of zirconia and the penetration resistance can be adjusted by the amount of fused silica. Therefore, the gas permeability and the gas resistance of the refractory for a porous plug can be adjusted according to the use conditions such as steel type. There is also an effect that the permeability can be easily adjusted.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-166752 (JP, A) JP-A-61-97161 (JP, A) JP-A-59-169978 (JP, A) JP-A-59-16978 169977 (JP, A) JP-A-9-52168 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 38/00-38/10, 35/10 C21C 7/072

Claims (2)

(57) [Claims] The present invention is characterized in that a composition containing 1 to 10% by weight of fused silica, 0.5 to 8% by weight of zirconia, and a balance containing a refractory aggregate mainly composed of alumina is kneaded, molded and then fired. For producing porous refractories for gas-injected porous plugs. 2. A kneaded mixture comprising 1 to 10% by weight of fused silica, 0.5 to 8% by weight of zirconia, and 100% by weight of a refractory aggregate mainly composed of alumina and 5% by weight or less of chromium oxide. A method for producing a porous refractory for a gas-blown porous plug, characterized by firing after molding.