KR20020047773A - A method of coating porous refractory for resisting penetration of melt - Google Patents

Abstract

PURPOSE: Provided is a method for coating porous refractory, conventional alumina refractory, with graphite to prevent infiltration of molten steel and attachment of nonmetallic materials, and improve Ar-gas bubbling. CONSTITUTION: The coating is performed by spreading a coating solution on the surface of porous alumina refractory such as tundish upper nozzle, in a thickness of 0.01-1.0mm, The coating solution comprises 50-70wt.% of graphite, 10-30wt.% of sodium silicate, and water. The porous alumina refractory with 23-28% of porosity comprises 86-88wt.% of spherical Al, 3-5wt.% of Zr, 1-5wt.% of Cr2O3 and inevitable impurities. Afterwards, the coated refractory is dried at room temperature over 24hrs. or at 100-500deg.C over 6hrs.

Description

Coating method of porous fireproofing material to prevent molten steel infiltration {A METHOD OF COATING POROUS REFRACTORY FOR RESISTING PENETRATION OF MELT}

The present invention relates to a coating of a porous refractory material, and more particularly, to a coating method of a porous refractory material for coating a graphite-containing coating solution to prevent molten steel infiltration.

In continuous casting process, the technology to prevent the nozzle clogging of tundish is one of the important management factors. Normally, as shown in FIG. 1, when molten steel flows through the upper nozzle 1 into the ladle in the tundish, Ar or the side of the nozzle 1 is prevented to prevent clogging of the upper nozzle. Blowing is carried out by blowing N ₂ gas, and at this time, a porous refractory material is applied to the upper nozzle for blowing gas. One of the biggest problems of this porous refractory material is the problem of infiltration of molten steel. Infiltration of molten steel or molten steel significantly reduces the bubbling performance of the porous refractory material, which may cause problems of separation of inclusions and control of flow rate of molten steel, and difficulty in casting due to excessive adhesion of alumina inclusions generated during the refining process. It may also cause. In particular, in recent years, as the high-resistance is required for the performance of soft-casting by refractories, clogging due to deoxidation inclusions attached to various refractory materials increases due to a long casting time, which is limited due to problems such as deterioration of molten steel quality. In this regard, the improvement of porous refractory material has emerged as a very important issue.

In addition to the bubbling performance of air flow rate and bubble generation ability, the basic characteristics of the porous refractory material must not only resist chemical and physical erosion by molten steel or non-metallic inclusions during use, but also have no cracking due to thermal shock during preheating or casting. Of course, above all, it must be possible to minimize molten steel adhesion or infiltration. In order to satisfy the above basic conditions in the porous refractory material, the refractory material has an appropriate pore size and porosity.

As a representative example, Korean Patent Laid-Open Publication No. 2000-40918 discloses spherical aluminum: 88 to 90% by weight, SiO ₂ : 4.5 to 5.0%, zirconia: 3 to 3.5% by weight, and Cr ₂ O ₃ : 1.5 to 1.8% by weight. Alumina porous refractory materials for tundish upper nozzles having a porosity of 25 to 27% and an average pore size of 16 to 20 μm are disclosed. However, until now, the porous refractory materials such as the porous refractory materials disclosed in the above-mentioned patents have improved the thermal shock resistance of the refractory material by controlling the microstructural aspects such as porosity and pore size and the composition of the refractory material, and bubbling by molten steel infiltration. In addition to improving performance, the service life is still insufficient. In particular, the porosity and pore size control method has limitations in improving the contents of the refractory material.

The present invention has been proposed to solve such a conventional problem is to prevent the infiltration of molten steel and the adhesion of non-metallic inclusions by coating graphite on the surface of the existing alumina porous refractory material such as a tundish upper nozzle.

1 is a block diagram of a tundish upper nozzle;

* Explanation of symbols for the main parts of the drawings *

1 ..... Upper nozzle 2 ....... Porous fireproof material

The present invention for achieving the above object is formed on the surface of the alumina refractory material of less than 0.1mm graphite: 50 ~ 70% by weight, sodium silicate: 10 ~ 30% by weight and the coating solution composed of the remaining water to a thickness of 0.01 ~ 1.0mm It relates to a coating method of porous refractory material which is then dried.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

First of all, as the refractory material corresponding to the porous refractory material of the present invention, any refractory material may be used, and preferably, an alumina refractory material containing no SiO ₂ is used. More preferably, a refractory having a spherical aluminum content of 86 to 88% by weight, zirconia: 3 to 5% by weight and Cr ₂ O ₃ : 1 to 5% by weight and having a porosity of 23 to 28% is used.

The refractory material having such a composition has an appropriate porosity, a compressive strength of about 250 to 400 kgf / cm 2, and a volume specific gravity of about 2.7 to 3.0, which is very advantageous for improving bubbling.

The coating method of the present invention is to coat with a graphite component having a low wettability against molten steel while maintaining excellent bubbling performance of the conventional porous refractory material. Preferably, the graphite powder has a size of 0.1 mm or less. If the size of the graphite powder is large, rather than blocking the internal pores of the refractory material may limit the bubbling performance. The graphite coated on the refractory reacts with components such as Mn, Cr, and SiO ₂ , which are reducing components in molten steel, to suppress the formation of Fe oxide and low melting point on the surface of the refractory material.

Graphite-containing coating solution in accordance with the present invention is to use a solution composed of 50 to 70% by weight of the graphite of less than 0.1mm and 10 to 30% by weight of sodium silicate and composed of the balance water.

When the graphite content in the coating solution is 50% by weight (hereinafter, only '%') or less than 30% of sodium silicate, the concentration of the solution is too low to penetrate the coating solution into the refractory material and may adversely affect bubbling. In addition, the coating layer and the thickness may be too small, which is undesirable. On the contrary, if the graphite content is 70% or more, and the sodium silicate is 10% or more, the viscosity is too high, so that the thickness of the coating layer may be too thick and uneven, and even the coating itself may be difficult, which is not preferable.

The coating thickness may be up to 0.01mm to 1.0mm, but if too thick, there is a problem in bubbling and too little, there is a problem that the effect of preventing infiltration and inclusion adhesion of molten steel is reduced.

In the present invention, the coating method is not particularly limited. For example, it may be coated with a brush or a cotton swab, and may be coated with a vinyl or the like so that the porous outer surface is not coated, and then deposited.

In addition, the drying method after coating is also not particularly limited and can be carried out by a conventional method. For example, in the case of natural drying, it may be maintained for 24 hours or more, and dried for 6 hours or more at 100 ° C or more and 500 ° C or less.

Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

By weight%, using alumina refractory material (porosity of 25%) comprising a spherical aluminum: 87%, zirconia: 4% and Cr ₂ O ₃ : 3% to prepare a tundish upper nozzle as shown in FIG. The coating solution shown in Table 1 was applied to the surface.

After mounting the upper nozzle thus prepared in a tundish, the degree of clogging of the nozzle during continuous casting was observed and the results are shown in Table 1. At this time, the nozzle clogging rate was expressed as a percentage of the top nozzle clogging charge to the production charge, and the nozzle clogging was judged as whether or not casting without problems during continuous casting.

In addition, the infiltration test was expressed as the penetration length of the molten steel generated by immersing the nozzle for 120 minutes in the molten steel in the induction furnace.

division Composition of Coating Solution (wt%) Coating layer thickness (mm) Infiltration degree (㎛) Nozzle Clogging Rate (%) Graphite Size black smoke bookbinder water Comparative Example 1 0.1mm or less 40 10 Remainder 0.02 0.1 5.0 Inventive Example 1 0.1mm or less 50 20 Remainder 0.05 0.1 1.0 Inventive Example 2 0.1mm or less 60 30 Remainder 0.07 0.15 1.5 Inventive Example 3 0.1mm or less 70 30 Remainder 0.09 0.15 1.5 Comparative Example 2 0.2mm or less 10 5 Remainder 0.20 0.80 8.6 Comparative Example 3 0.2mm or less 20 40 Remainder 0.15 0.10 10.7 Comparative Example 4 0.2mm or less 30 50 Remainder 0.20 1.00 20.9 Comparative Example 5 0.3mm or less 30 60 Remainder 0.30 1.50 14.1

As shown in Table 1, inventive examples (1 to 3) in which the coating layer was formed according to the present invention had a relatively low degree of infiltration and were found to be very good in the field nozzle clogging test results.

On the other hand, in Comparative Examples (1 to 5), it was found that not only the molten steel infiltration but also the nozzle clogging rate were greatly increased. In particular, as in Comparative Examples (2 to 5), as the graphite grain size increases, the size of the pores through which Ar passes decreases, and it is determined that Ar does not contribute to the prevention of nozzle clogging.

As described above, when the graphite coated on the surface of the tundish upper nozzle according to the present invention, not only can improve the bubbling performance by Ar gas, but also prevent infiltration of molten steel and adhesion of nonmetallic inclusions. There is an effect that the work can be done very smoothly.

Claims (2)

Characterized in that the coating solution of 0.1 mm or less graphite: 50 ~ 70% by weight, sodium silicate: 10 ~ 30% by weight on the surface of the alumina refractory material is formed to a thickness of 0.01 ~ 1.0mm and dried Coating method of porous refractory material for preventing molten steel infiltration. The method of claim 1, The alumina refractories are composed of spherical aluminum: 86 to 88% by weight, zirconia: 3 to 5% by weight, Cr ₂ O ₃ : 1 to 5% by weight and other inevitable impurities, characterized in that the porosity is 23 to 28% Coating method of porous refractory material for preventing molten steel infiltration.