JP2006232646A - Conductive monolithic refractory for stamping work of dc electric furnace hearth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve conductivity and corrosion resistance in conductive monolithic refractory stamp-worked on the surface of a hearth of a DC electric furnace. <P>SOLUTION: The conductive monolithic refractory for stamping work of the hearth of the DC electric furnace contains a refractory raw material composition consisting of 3-20 mass% scaly graphite, 0.5-8 mass% magnesia fine powder and the balance being a fired magnesia-carbonaceous raw material and a liquid organic binder. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a conductive amorphous refractory that is stamped on the lining surface of a DC electric furnace hearth.

  Steelmaking electric furnaces are classified into AC and DC types. In recent years, DC electric furnaces have become very popular due to low power fluctuations and low electrode costs.

  Since a DC electric furnace generally generates an arc between the upper movable electrode and the hearth electrode, the hearth electrode is subjected to wear damage due to electromagnetic stirring action of molten steel during operation. In addition, erosion by slag occurs during steel output. The hearth electrode is also damaged by contact with scrap put into the furnace.

FIG. 1 is a schematic diagram of a longitudinal section of a DC electric furnace. The DC electric furnace is provided with an electrode 4 at the top, and a steel outlet hole 5 is provided at one end of the side wall. The lining of the hearth 1 having a function as a hearth electrode part is generally composed of 2 magnesia-carbon bricks having both conductivity and corrosion resistance. The magnesia-carbon brick 2 is usually provided with a plurality of layers of a lining and a permanent lining provided on the back thereof as shown in the figure. In order to protect or repair the hearth 1, it is known to apply an amorphous refractory layer on the surface of the magnesia-carbon brick 2. And this amorphous refractory layer uses the conductive amorphous refractory 3 so as not to impair the function of the hearth electrode part (for example, Patent Document 1).
Japanese Patent Laid-Open No. 5-78178

  However, conventional conductive amorphous refractories cannot obtain sufficient conductivity and corrosion resistance due to the low filling rate of the structure of the body during stamping. This invention makes it a subject to improve the electroconductivity and corrosion resistance about this electroconductive unshaped refractory material stamped on the surface of the hearth of a direct current electric furnace.

  The conductive amorphous refractory for DC electric furnace hearth stamping construction of the present invention comprises phosphorous graphite powder 3-20% by mass, magnesia fine powder 0.5-8% by mass, the remainder being fired magnesia-carbonaceous raw material A fire-resistant raw material composition and a liquid organic binder.

  In the conductive amorphous refractory of the present invention, the main aggregate uses a magnesia-carbonaceous raw material. Among the ingredients of this raw material, magnesia has the effect of imparting corrosion resistance and carbon has the effect of imparting conductivity. Magnesia-carbon brick is widely used as a lining material for converters, electric furnaces, etc., but for example, this magnesia-carbon brick is crushed as it is into a conductive amorphous refractory targeted by the present invention. Even if the material is used, a sufficient conductive effect cannot be obtained. This is presumably because magnesia-carbon bricks are generally non-fired products that are heat-treated at about 300 ° C. after molding, and the binder remaining in the refractory structure hinders conductivity.

  The conductive amorphous refractory of the present invention uses a calcined magnesia-carbonaceous material. This magnesia-carbonaceous raw material can be obtained by adding a binder to a blend comprising, for example, magnesia powder and carbon powder, kneading, molding, and firing. At the time of use, this is further pulverized and sieved to a suitable particle size.

  The firing temperature of the magnesia-carbonaceous material is, for example, 700 ° C. or higher. By this firing, the binder that causes conductivity inhibition disappears or carbonizes, and the conductivity of the magnesia-carbonaceous material is improved.

  In the conductive amorphous refractory of the present invention, phosphorus-like graphite powder is further combined with this magnesia-carbonaceous raw material. Carbonaceous powder is a refractory raw material excellent in corrosion resistance and conductivity. Phosphorous graphite is particularly excellent in corrosion resistance and conductivity because of its high crystallization rate and carbon purity among carbonaceous powders.

  However, when an amorphous refractory combined with phosphorus-like graphite is stamped, the amorphous refractory escapes laterally with respect to the hammering direction of the rammer head, and there is a problem that sufficient filling ability cannot be obtained. This is because, in addition to the fact that the magnesia-carbon raw material has a low coefficient of friction due to the inclusion of carbon, the amorphous graphite refractory is struck by stamping due to the flake-like particles having a smooth surface from the crystalline form. In this case, it is considered that the phosphorus-like graphite particles are oriented in the horizontal direction in the refractory composition, and the magnesia-carbonaceous raw material slides on the oriented phosphorus-like graphite particles. If the amorphous refractory is inferior in filling property, the contact area between the blended particles is reduced, and the conductivity effect of the magnesia-carbonaceous raw material and further phosphorus-like graphite is greatly reduced.

  In the present invention, 0.5 to 8% by mass of magnesia fine powder is further blended. As a result, the irregular refractory does not escape from the hitting of the rammer head during the stamping operation, and the filling property is improved. This is because the magnesia fine powder is high in strength and has a small friction coefficient, so that the sliding of the magnesia carbonaceous raw material particles is locked by the spike effect between the magnesia carbonaceous raw material particles and the phosphorous graphite powder. it is conceivable that.

If only the spike effect is expected, the tendency of the effect can be seen even if it is not noticeable even by alumina fine powder, silica fine powder or the like. However, alumina powder, silica powder, etc. react with magnesia in the magnesia-carbonaceous raw material at high temperatures while using amorphous refractories, and spinel (MgO.Al ₂ O ₃ ) or forsterite (2MgO.SiO ₂ ). A low-melting-point substance is produced, and the corrosion resistance necessary as an effect of the present invention is poor.

  The overall particle size of the refractory raw material composition is appropriately adjusted to coarse particles, medium particles, and fine particles so as to obtain a densely packed structure. In this invention, it is preferable that it is the particle size structure which increased the ratio of the particle | grains of a coarse grain and a medium grain by making the ratio for which the fine particle of 1 mm or less is 35 mass% or less. This is because fine particles have a large specific surface area, so that the required amount of binder increases as the blending amount increases, and the porosity of the refractory construction structure increases as the amount of binder added increases. It is because it falls.

  As described above, the amorphous refractory according to the present invention exhibits excellent effects in conductivity, corrosion resistance, and stamping workability required for a DC electric furnace hearth.

  The compounding raw material used for the amorphous refractory of the present invention will be described. First, the phosphorus-like graphite preferably has a fixed carbon content of 85% by mass or more and an ash content of 12% by mass or less. The particle size is preferably 0.5 mm at maximum and 0.15 mm or less on average. If the proportion of phosphorus-like graphite in the refractory raw material composition is less than 3% by mass, the effect of imparting conductivity is poor, and if it exceeds 20% by mass, the corrosion resistance decreases due to oxidation. Moreover, it escapes to the side at the time of stamp construction, and conductivity decreases due to a decrease in filling property.

  The magnesia fine powder may be either a fired product or an electromelted product. Naturally produced magnesite may also be used. The specific example of the particle size is preferably 1 mm or less, more preferably 0.15 mm or less. When the amount of the magnesia fine powder is small, it is preferable that the particle size is small in order to ensure dispersibility.

If the proportion of the magnesia fine powder in the refractory raw material composition is less than 0.5% by mass, the amorphous refractory escapes to the side during stamping, and the filling property of the construction body is lowered, thereby improving the conductivity of the present invention. Cannot be obtained. Since the general volume resistivity of magnesia is as large as about 2 × 10 ⁸ Ω · cm, when it exceeds 8 mass%, the conductivity of the amorphous refractory decreases.

  In addition, the particle size prescribed | regulated by this invention including the particle size of the above-mentioned magnesia fine powder is based on the JIS sieve opening in ceramics operation. Moreover, the display below 1 mm of magnesia fine powder shows the numerical value under sieving. In particular, when the operation of removing the lower particle size particles is not performed, for example, when the particle size is 1 mm or less, particles having a particle size of, for example, 0.5 mm or 0.1 mm are included therein.

  The calcined magnesia-carbonaceous material is prepared by adding a binder to a refractory raw material composition mainly composed of magnesia with 5 to 30% by mass of the carbonaceous material and appropriately adjusted the particle size, and after kneading, press molding. The obtained rough angle is fired and further pulverized.

  The magnesia-based raw material used for the production of the magnesia-carbonaceous raw material is sintered magnesia, electrofused magnesia, or the like. Examples of the carbonaceous raw material include phosphorus graphite, earth graphite, artificial graphite, pitch powder, mesophase carbon, anthracite, and carbon black. The binder is not particularly limited, but a phenol resin, furan resin, epoxy resin, tar or the like having a high residual carbon ratio is preferable in terms of imparting conductivity.

  The firing temperature of the magnesia-carbonaceous material is 700 ° C. or higher, more preferably about 800 to 1300 ° C. As a result, the binder that has been a cause of conductivity inhibition disappears or carbonizes. Further, in the case of a magnesia-carbonaceous raw material produced by using a binder having a high carbon residue as the binder, the carbon bond structure due to carbonization of the binder is enriched, and the conductivity is further improved.

A post-use product of magnesia-carbon brick may be used as the fired magnesia-carbonaceous material. Magnesia-carbon bricks are generally unfired products, but receive a firing effect at high temperatures during use. Some products after use have not received a sufficient firing effect. If the volume resistivity is, for example, 1.0 × 10 ⁻² Ω · cm or less under the test conditions of volume resistivity shown in the column of Examples described later, the conductive effect of the present invention can be obtained.

  In the conductive amorphous refractory of the present invention, a liquid organic binder is added to the above refractory raw material composition in order to impart stamping workability. Examples of the liquid organic binder include oils, phenol resins, furan resins, coal tar and the like. Considering the residual carbon ratio, working environment, economy, etc., novolak type phenol resin having a molecular weight of 500 or less is particularly preferable.

  If the amount of the liquid organic binder used is small, it is difficult to place the liquid organic binder, and if it is too much, the construction body is inferior in conductivity due to the porous structure. The appropriate amount of the liquid organic binder used varies depending on the specific type of the binder. Taking a novolac type phenol resin as an example, 3 to 10 parts by mass is preferable with respect to 100 parts by mass of the refractory raw material composition.

  If necessary, the conductive amorphous refractory according to the present invention may further contain carbonaceous raw material powder other than phosphorus-like graphite powder in a range of 10% by mass or less in the proportion of the refractory raw material composition.

  Specific examples of the carbonaceous raw material powder other than the phosphorus-like graphite powder include, for example, earth graphite, artificial graphite, pitch powder, mesophase carbon, anthracite, carbon black and the like. Since these carbonaceous raw material powders are conductive raw materials, they do not hinder the conductivity-imparting effect of the present invention that phosphorous graphite has. However, unlike phosphorus-like graphite having a high crystallization rate, it easily oxidizes. Therefore, if its blending amount exceeds 10% by mass, it causes oxidative deterioration of the amorphous refractory.

  When combining carbonaceous raw material powders other than the phosphorus-like graphite powder, the total amount with the phosphorus-like graphite powder needs to be 20% by mass or less as a ratio of the refractory raw material composition. When it exceeds 20 mass%, corrosion resistance will fall by oxidation of a carbonaceous raw material.

  For the purpose of preventing oxidation, an appropriate amount of metal powder, carbide powder, nitride powder, boride powder or the like may be added. Examples of the metal powder are Al, Si, or an Al alloy. The addition amount is about 1 part by mass with respect to 100 parts by mass of the refractory raw material composition.

  This conductive amorphous refractory according to the present invention is obtained by thoroughly kneading the above composition with a wet pan mixer, a vortex mixer or the like, and then placing an air rammer on the surface of the hearth lining serving as the hearth electrode part. Install stamps. The thickness is preferably 100 to 300 mm as in the conventional case.

Examples of the present invention and comparative examples thereof are shown below. Table 1 shows the quality values of the magnesia-carbonaceous raw materials used in each example. The magnesia-carbonaceous raw materials A to C were kneaded with the blending composition shown in the same table, and then subjected to pressure molding at a pressure of 245 MPa, followed by heat treatment at each temperature shown in the same table. That is, the magnesia-carbonaceous raw material A was fired at 1100 ° C. and B was fired at a temperature of 800 ° C., and the magnesia-carbonaceous raw material C was obtained by curing the binder at a heating temperature of 300 ° C. It corresponds to goods. The magnesia-carbonaceous raw material D was selected from non-fired bricks having a volume resistivity of 1.0 × 10 ⁻² Ω · cm or less.

  The volume resistivity of each magnesia-carbonaceous raw material shown in Table 1 was measured on a molded body (size: 20 × 20 × 80 mm) before pulverization. In accordance with JIS C2141, the electrical resistance was measured by a two-point method, and the volume resistivity was determined by the following formula.

ρ = R · a / l
ρ: volume resistivity (Ω · cm), R: electrical resistance (Ω), a: cross-sectional area (cm ² ), l: length (cm)
Table 2 shows the irregular refractory composition and test results in each example. The magnesia-carbonaceous material blended in the amorphous refractory material is obtained by pulverizing and sieving the magnesia-carbonaceous material shown in Table 1 above.

  In the test of the construction body shown in Table 2, after kneading the irregular refractory composition composition of each example, a construction body of 100 mm was placed in the mold with an air rammer, and then heated at 300 ° C. × 24 hours. Things were tested.

  In the conductivity test, the electrical resistance was measured by a two-point method based on JIS C2141 for a test piece having a size of 20 × 80 × 20 mm in thickness, and the volume resistivity was obtained by the above formula.

  In the strength test, the compressive strength at room temperature was measured. The dimensions of the test piece were 40 × 40 × 40 mm in thickness, and the pressure during the test was in the thickness direction of the construction body.

  Corrosion resistance was evaluated by a rotational erosion test. As rotary erosion operation, the solvent was used as electric furnace slag, and 1500 ° C. × 0.5 hr was repeated 10 times, and then the erosion dimension was measured. The numerical value of the test result is that the erosion dimension of Comparative Example 4 is 100.

  As shown in the test results shown in Table 2, the irregular refractory according to the embodiment of the present invention does not escape in the horizontal direction even if it is hit by an air rammer during stamping, and all of the obtained constructions are filled to a high degree. Sex was obtained. As a result, as shown in the table, it was possible to obtain excellent effects in conductivity and corrosion resistance required for the amorphous refractory for the DC electric hearth. Moreover, since the construction body is excellent in strength due to its high filling property, it exhibits sufficient resistance to the crushing stress received when scrap is thrown in, and the effect of protecting the hearth lining is obtained.

  Moreover, in the Example which made 1 mm or less into 35 mass% or less about the particle size of the whole refractory raw material composition, even when the addition ratio of the binder was small, it was excellent in workability. And since the addition ratio of the binder was small, the conductivity was further improved.

  Comparative Example 1 uses a non-fired magnesia-carbon material and is inferior in conductivity. Comparative Example 2 does not contain phosphorus-like graphite and is greatly inferior in conductivity and corrosion resistance.

  In Comparative Example 3, since the amount of phosphorus-like graphite is large, the phenomenon that the irregular refractory escapes to the side during stamping is seen, and the filling property of the construction body is insufficient. Comparative Example 4 is an example in which magnesia fine powder is not blended, and the indeterminate refractory escapes to the side during the stamp construction, and the construction body is inferior in fillability. As a result, Comparative Examples 3 and 4 are inferior in conductivity, strength and corrosion resistance.

  Comparative Example 5 is an example in which the blending amount of magnesia fine powder is larger than the range limited in the present invention. Magnesia fine powder is a refractory raw material with low conductivity. In this example having a large amount of magnesia fine powder, the conductivity is poor.

It is a schematic diagram of the longitudinal cross-section of a DC electric furnace.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hearth 2 Magnesia-carbon brick 3 Conductive amorphous refractory 4 Electrode 5 Steel hole

Claims (3)

  DC electric furnace comprising 3-20% by mass of phosphorus-like graphite powder, 0.5-8% by mass of magnesia fine powder, a refractory raw material composition in which the remainder is fired magnesia-carbonaceous raw material, and a liquid organic binder Conductive amorphous refractory for floor stamping.   The refractory raw material composition further contains 10% by mass or less of carbon raw material fine powder other than phosphorus graphite powder, and is the total of the carbon raw material fine powder other than phosphorus graphite powder and the phosphorus graphite powder in a ratio of the refractory raw material composition. The conductive amorphous refractory for DC electric furnace hearth stamp construction according to claim 1, wherein the amount is 20% by mass or less.   The conductive amorphous refractory for DC electric furnace hearth stamp construction according to claim 1 or 2, wherein the proportion of the particle size of the refractory raw material composition is 35% by mass or less.

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