A gradient structure tundish permanent layer castable and a preparation method thereof

Abstract

The present application belongs to the technical field of continuous casting tundish, and particularly relates to a gradient structure tundish permanent layer castable and a preparation method thereof. The gradient structure tundish permanent layer castable provided by the present application comprises bauxite aggregate, sintered mullite, gradient microporous aggregate, silicon powder, cement and deionized water. In the present application, the gradient microporous aggregate is used to replace part of the bauxite aggregate, and the pore structure interface composition is improved. Alumina, magnesia and zircon are used as the main raw materials of the gradient microporous aggregate. During the sintering process, the gradient magnesium aluminate spinel and zircon surrounding microporous and nanoporous structure are formed on the surface of the pore structure. The core-shell structure of alumina coated magnesium carbonate is used as a pore former and added to the gradient microporous aggregate, so as to improve the heat insulation performance of the castable and the slag resistance.

Description

Technical Field

[0001] This invention belongs to the field of continuous casting tundish technology, specifically relating to a gradient structure tundish permanent layer castable and its preparation method. Background Technology

[0002] The tundish is an intermediate storage container between the ladle and the crystallizer, serving functions such as steel storage, flow stabilization, buffering, flow diversion, and purification. It is fundamental to achieving multi-strand continuous casting. With the optimization of continuous casting processes and the increasing demands on the quality of continuously cast billets, the tundish has evolved into a terminal device for steel refining, placing higher requirements on its insulation performance, service life, and effective volume.

[0003] The permanent lining refractory in the tundish is the core material of the tundish lining. During the tundish's reception of molten steel, the temperature rises sharply, and after continuous casting, the temperature drops rapidly. This repeated rapid heating and cooling of the refractory easily induces thermal stress. In the pouring zone, where molten steel resides for the longest time, the working layer at the slag line is severely eroded, and the permanent lining refractory is also corroded. Furthermore, high-alumina refractory has a high coefficient of thermal expansion, making it prone to surface cracks or internal micro-cracks under cyclic thermal shock due to "thermal stress concentration," thus requiring improvement in thermal shock resistance and corrosion resistance. Existing permanent lining refractory materials are typically homogeneous, failing to balance insulation and corrosion resistance. Using lightweight aggregates to improve insulation reduces the lining's bulk density, resulting in insufficient compressive strength at room temperature and significantly weakened resistance to erosion and corrosion. Conversely, using heavy aggregates to improve corrosion resistance increases thermal conductivity, raising the temperature of the tundish's outer wall and increasing heat loss from the molten steel.

[0004] Chinese patent application CN111377715A discloses a tundish castable and its preparation method. The tundish castable includes bauxite aggregate, mullite, alumina powder, silica powder, cement, magnesia-carbon bricks, admixtures, and water. By adding α-alumina powder and magnesia-carbon bricks, the heat resistance and viscosity of the castable are improved. However, the formulation of this castable lacks lightweight insulating aggregates, resulting in poor insulation of the tundish and increased heat loss from the molten steel. The magnesia-carbon bricks have poor compatibility with the matrix components, and the graphite contained in them is easily oxidized during baking, leading to the formation of pores and loose areas, which reduces the slag resistance of the tundish. Furthermore, the main aggregates in its formulation are all high-hardness, low-toughness ceramic phases. Under thermal cycling, the tundish lining develops surface cracks or internal through cracks due to thermal stress exceeding the fracture strength, resulting in insufficient slag resistance and thermal shock resistance. Summary of the Invention

[0005] In order to solve the technical problems of slag resistance and high thermal conductivity in the prior art, the purpose of this invention is to provide a gradient structure tundish permanent layer castable and its preparation method.

[0006] A gradient structure tundish permanent layer castable comprises the following components in parts by weight:

[0007] 40-60 parts of bauxite aggregate, 10-25 parts of sintered mullite, 20-25 parts of gradient microporous aggregate, 5-8 parts of silica fume, 10-15 parts of cement, and 10-15 parts of deionized water.

[0008] The method for preparing the gradient microporous aggregate is as follows: magnesium oxide, calcined alumina and zircon powder are mixed evenly, deionized water is added, and the mixture is ball-milled for 5-6 hours. A pore-forming agent and a binder are added to the ball-milled slurry, and the mixture is stirred at 50-60℃ for 3-4 hours. The mixture is then dried, pulverized, placed in a mold, cold isostatically pressed, sintered, crushed and graded to obtain the gradient microporous aggregate.

[0009] Through the above technical solution, gradient microporous aggregate is used to replace part of the bauxite aggregate. Ball milling of magnesium oxide, calcined alumina, and zircon refines the alumina, magnesium oxide, and zircon, ensuring uniform contact at the microscale. After ball milling, a pore-forming agent and binder are added. During sintering, magnesium oxide and alumina react to form spinel, and the pore-forming agent decomposes in situ at high temperature, forming a micro-nanoporous structure surrounded by gradient magnesium-aluminum spinel and zircon. This achieves the goal of lightweighting the aggregate and reducing thermal conductivity. Simultaneously, the magnesium-aluminum spinel and zircon around the micropores enhance the aggregate's resistance to erosion and slag. When molten slag enters the pores, the spinel solid solution around the pores interacts with the molten slag, absorbing manganese oxide, ferrous oxide, ferric oxide, etc., and dissolving them in the crystal lattice to form a high-melting-point spinel solid solution, increasing the viscosity of the molten slag and slowing its penetration. Furthermore, during sintering, a small amount of zirconium oxide or Mg2Zr5O is generated at the spinel interface. 12 These products can fill the pores at the spinel interface, acting as a grain boundary barrier to further block the direct contact between the slag and the spinel, thereby further improving the aggregate's resistance to erosion and slag.

[0010] Furthermore, the preparation method of the pore-forming agent in the preparation method of gradient microporous aggregate is as follows: magnesium carbonate is added to deionized water and ultrasonically dispersed to form a magnesium carbonate suspension. Then, aluminum nitrate is dissolved in ethanol, citric acid is added, and ammonia is added dropwise to adjust the pH value to 4-5 while stirring. Stirring is continued to form a transparent sol. The magnesium carbonate suspension and the transparent sol are mixed and stirred in a water bath at 55-65℃ for 4-5 hours. The mixture is then filtered, dried, calcined, and ground to obtain the pore-forming agent.

[0011] The above technical solution involves mixing magnesium carbonate suspension with aluminum sol. During stirring, the sol coats the surface of magnesium carbonate, and after sintering, a core-shell structure of magnesium carbonate encapsulated in alumina is obtained. This structure is then added to gradient microporous aggregate. During high-temperature calcination, magnesium carbonate first decomposes into highly active magnesium oxide, which then reacts with the surface-coated alumina to form magnesium aluminum spinel, increasing the strength of the pore structure and thus improving its resistance to erosion and slag. Simultaneously, the carbon dioxide produced during the decomposition of magnesium carbonate leaves a large number of micron-sized pores in situ. The alumina shell shrinks during calcination and reaction to produce nano-sized micropores, forming a micro-nano composite pore structure in the gradient microporous aggregate, effectively improving the thermal insulation performance of the aggregate.

[0012] Furthermore, in the preparation method of the pore-forming agent, the mixing mass ratio of the magnesium carbonate suspension and the transparent sol is 8-12:1.

[0013] Furthermore, the mass ratio of aluminum nitrate to citric acid in the preparation method of the pore-forming agent is 2-3:1.

[0014] Through the above technical solution, citric acid can form a stable, soluble complex with aluminum ions in aluminum nitrate. This complexation effectively reduces the concentration of aluminum ions in the solution, which is a prerequisite for forming a stable, transparent sol. Insufficient citric acid will result in insufficient complexation capacity, causing aluminum ions in the solution to form flocculent precipitates during the addition of ammonia, leading to sol turbidity and ultimately, clumping or island-like defects in the coating layer. Conversely, excessive citric acid will result in carbon residue in the pore-forming agent during calcination.

[0015] Furthermore, the calcination temperature in the preparation method of the pore-forming agent is 400-500℃, the heating rate is 10-15℃ / min, and the calcination time is 1-1.5h.

[0016] Furthermore, in the method for preparing gradient microporous aggregate, the mass ratio of magnesium oxide, calcined alumina and zircon powder is (0.15-0.30):1:(0.04-0.08).

[0017] The above technical solution controls the performance of gradient microporous aggregate by adjusting the mass ratio of magnesium oxide, calcined alumina, and zircon powder. In this aggregate, magnesium oxide acts as a functional component, its core function being to react with alumina to form spinel. Insufficient magnesium oxide content leads to insufficient spinel formation, failing to effectively utilize spinel's resistance to alkali slag. Conversely, excessive magnesium oxide content results in incomplete reaction with alumina, causing it to react with water vapor in the air to form magnesium hydroxide, leading to volume expansion and cracking after aggregate sintering. Alumina, as the framework phase, determines the aggregate's strength and structural stability. Insufficient alumina content further weakens the framework... Insufficient alumina content results in a loose structure and poor performance of the aggregate after sintering. Excessive alumina content leads to an excessive proportion of corundum in the aggregate, increasing the densification degree of the aggregate during sintering. This causes the micropores generated by the pore-forming agent to be filled, losing the heat-insulating advantage of the gradient micropores. At the same time, the high brittleness of corundum also reduces the thermal shock resistance of the aggregate. Zircon powder, as a corrosion-resistant functional phase, determines the erosion resistance of the aggregate. When the zircon powder content is too low, there is insufficient corrosion-resistant phase in the aggregate, making the aggregate easily eroded in alkaline slag. When the zircon powder content is too high, it leads to excessive differences in the thermal expansion coefficients within the aggregate, generating thermal stress during sintering and cooling, inducing microcracks, and reducing strength and corrosion resistance.

[0018] Furthermore, in the method for preparing gradient microporous aggregate, the amount of pore-forming agent is 12%-15% of the total mass of magnesium oxide, calcined alumina and zircon powder; the amount of binder is 2%-5% of the total mass of magnesium oxide, calcined alumina and zircon powder.

[0019] Furthermore, the binder in the preparation method of gradient microporous aggregate is dextrin or a polyvinyl alcohol aqueous solution with a mass percentage of 10%-15%.

[0020] Furthermore, the specific sintering process described in the method for preparing gradient microporous aggregate is as follows: the cold isostatically pressed billet is placed in a box-type resistance furnace, heated to 600℃ at a heating rate of 5-10℃ / h, held for sintering for 0.5-1h, then heated to 1500℃ at a heating rate of 5-10℃ / h, held for sintering for 10-15h, and then cooled with the furnace.

[0021] Through the above technical solution, during the sintering process, the temperature is first raised to 600℃ at a relatively low heating rate and held for sintering for 0.5-1 hours. During this process, the binder is completely decomposed, and cracking of the green body caused by rapid heating is avoided. Then, the temperature is raised to 1500℃ at a relatively low heating rate and held for sintering for 10-15 hours. During this process, the slow heating provides sufficient time for the diffusion of magnesium and aluminum ions, ensuring that spinel is generated uniformly in situ. At the same time, the gas generated by the decomposition of the pore-forming agent slowly escapes, forming stable and closed micropores, avoiding the formation of interconnected pore structures due to excessive heating. The holding sintering process can promote the sintering of corundum grains and the growth of spinel grains. The micropores tend to be stable through surface tension, avoiding collapse.

[0022] Furthermore, the specific crushing and grading process described in the preparation method of gradient microporous aggregate is as follows: the sintered billet is fed into a jaw crusher and crushed to below 50mm, then crushed by a reverse crusher, and a three-layer vibrating screen is used to select coarse aggregate with a particle size of 10-20mm, medium aggregate with a particle size of 3-7mm, and fine aggregate with a particle size ≤1mm, wherein the proportion of coarse aggregate is 40%-50%, the proportion of medium aggregate is 30%-40%, and the proportion of fine aggregate is 10%-20%.

[0023] This invention also provides a method for preparing the gradient structure tundish permanent layer castable, specifically: mixing bauxite aggregate, sintered mullite, gradient microporous aggregate, silica powder and cement, stirring for 15-20 min, then rolling for 20-25 min, adding deionized water, stirring for 1-2 h, pouring into a strip mold, vibrating to form, curing at room temperature for 24 h, demolding, drying at 110-120℃ for 24 h, and then heat-treating at 1500-1600℃ for 3-4 h to obtain the gradient structure tundish permanent layer castable.

[0024] The above technical solution solves the problem of uneven thermal insulation gradient distribution caused by the easy floating or agglomeration of gradient microporous aggregate in traditional wet mixing process through solid material mixing process. It achieves uniform dispersion of bauxite, mullite and gradient microporous aggregate, and improves the overall thermal insulation performance of the material.

[0025] Compared with existing technologies, the gradient structure tundish permanent layer castable and its preparation method provided by this invention have the following technical advantages:

[0026] (1) The present invention uses gradient microporous aggregate to replace part of the bauxite aggregate and improves the pore structure interface composition, which effectively improves the heat insulation performance and slag resistance performance of the tundish permanent layer castable.

[0027] (2) The present invention uses alumina, magnesium oxide and zircon as the main raw materials of gradient microporous aggregate. During the sintering process, a micro-nano pore structure surrounded by gradient magnesium aluminum spinel and zircon is formed on the surface of the pore structure, which can not only improve the heat insulation performance of the castable, but also improve the slag resistance of the castable.

[0028] (3) In this invention, an alumina-encapsulated magnesium carbonate core-shell structure is added to the gradient microporous aggregate as a pore-forming agent. During the sintering process, a micro-nano pore structure is formed in the gradient microporous aggregate, which improves the heat insulation performance of the castable while also improving the slag resistance of the micro-nano pore structure. Attached Figure Description

[0029] Figure 1 This is a scanning electron microscope image of the gradient structure intermediate liner permanent layer castable prepared in Example 4. Detailed Implementation

[0030] The following description, in conjunction with specific embodiments, provides further details, but the present invention is not limited to these embodiments. Those skilled in the art can make various modifications based on the fundamental principles of the present invention, but all modifications that do not depart from the fundamental principles of the present invention are within its scope.

[0031] Example 1

[0032] A gradient structure tundish permanent layer castable comprises the following components in parts by weight:

[0033] 40kg of bauxite aggregate, 25kg of sintered mullite, 25kg of gradient microporous aggregate, 8kg of silica powder, 15kg of cement, and 15kg of deionized water; the graded particle sizes of the bauxite aggregate are: 8-12mm 10kg, 5-8mm 15kg, 1-5mm 10kg, and 0-1mm 5kg.

[0034] The preparation method of gradient microporous aggregate is as follows: 3 kg of magnesium oxide, 20 kg of calcined alumina and 0.8 kg of zircon powder are mixed evenly, 4.8 kg of deionized water is added, and the mixture is ball-milled for 5 hours (ball-to-powder ratio of 5:1, rotation speed of 200 rpm). The ball-milled slurry is transferred to a mixing tank, and 2.86 kg of pore-forming agent and 0.48 kg of dextrin are slowly added dropwise under stirring at 50℃ and 300 rpm. The mixture is stirred at 50℃ for 3 hours, dried at 100℃, pulverized and passed through a 100-mesh sieve. The resulting powder is then placed in a mold for cold isostatic pressing (pressure is increased to 150 MPa at a rate of 10 MPa / min, held for 5 minutes, and then increased at a rate of 5 MPa / min). After depressurization, the formed billet (φ36mm×20mm cylinder) is placed in a box-type resistance furnace and heated to 600℃ at a heating rate of 5℃ / h, held for sintering for 0.5h, then heated to 1500℃ at a heating rate of 5℃ / h, held for sintering for 10h, cooled with the furnace, and the sintered billet is sent to a jaw crusher to be crushed to below 50mm, then crushed by a reverse crusher, and a three-layer vibrating screen is used to select coarse aggregate with a particle size of 10-20mm, medium aggregate with a particle size of 3-7mm and fine aggregate with a particle size ≤1mm, of which coarse aggregate accounts for 40%, medium aggregate accounts for 40%, and fine aggregate accounts for 20%, to obtain gradient microporous aggregate.

[0035] The preparation method of the pore-forming agent is as follows: 10 kg of magnesium carbonate is added to 20 kg of deionized water and ultrasonically dispersed at 60 kHz for 0.5 h to form a magnesium carbonate suspension. Then, 4 kg of aluminum nitrate is dissolved in 10 kg of ethanol, 2 kg of citric acid is added, and ammonia water is added dropwise to adjust the pH value to 4 while stirring. Stirring is continued to form a transparent sol. The magnesium carbonate suspension and the transparent sol are mixed (mixing mass ratio of 8:1), stirred in a 55℃ water bath for 4 h, filtered, dried at 60℃, calcined at 400℃ for 1 h (heating rate of 10℃ / min), and ground to obtain the pore-forming agent.

[0036] The preparation method of the gradient structure tundish permanent layer castable is as follows: bauxite aggregate, sintered mullite, gradient microporous aggregate, silica powder and cement are mixed and stirred for 15 min, then rolled for 20 min, deionized water is added, stirred for 1 h, poured into a 70 mm × 70 mm × 70 mm mold, vibrated for 2 min, cured at room temperature for 24 h, demolded, dried at 110 °C for 24 h, and then heat-treated at 1500 °C for 3 h to obtain the gradient structure tundish permanent layer castable.

[0037] Example 2

[0038] A gradient structure tundish permanent layer castable comprises the following components in parts by weight:

[0039] The composition of the bauxite aggregate is as follows: 60 kg bauxite aggregate, 10 kg sintered mullite, 20 kg gradient microporous aggregate, 5 kg silica powder, 10 kg cement, and 10 kg deionized water. The graded particle sizes of the bauxite aggregate are: 8-12 mm 15 kg, 5-8 mm 20 kg, 1-5 mm 15 kg, and 0-1 mm 10 kg.

[0040] The preparation method of gradient microporous aggregate is as follows: 6 kg of magnesium oxide, 20 kg of calcined alumina, and 1.6 kg of zircon powder are mixed evenly, and 5.6 kg of deionized water is added. The mixture is ball-milled for 6 hours (ball-to-powder ratio of 5:1, rotation speed of 250 rpm). The ball-milled slurry is transferred to a mixing tank, and 4.14 kg of pore-forming agent and 1.38 kg of 10% polyvinyl alcohol aqueous solution are slowly added dropwise under stirring at 60℃ and 500 rpm. The mixture is stirred at 60℃ for 4 hours, dried at 120℃, pulverized and passed through a 100-mesh sieve, and then the obtained powder is placed in a mold for cold isostatic pressing (pressure is increased to 150 MPa at a rate of 10 MPa / min, held for 5 min, and then reduced at 5 MPa / min). The pressure was released at a rate of a / min. The formed billet (φ36mm×20mm cylinder) was placed in a box-type resistance furnace and heated to 600℃ at a heating rate of 10℃ / h. It was then held for sintering for 1h, and then heated to 1500℃ at a heating rate of 10℃ / h. It was held for sintering for 15h and then cooled with the furnace. The sintered billet was then fed into a jaw crusher and crushed to below 50mm. It was then crushed by a reverse crusher and a three-layer vibrating screen was used to select coarse aggregate with a particle size of 10-20mm, medium aggregate with a particle size of 3-7mm, and fine aggregate with a particle size ≤1mm. The proportion of coarse aggregate was 50%, medium aggregate was 40%, and fine aggregate was 10%, resulting in gradient microporous aggregate.

[0041] The preparation method of the pore-forming agent is as follows: 10 kg of magnesium carbonate is added to 20 kg of deionized water and ultrasonically dispersed at 80 kHz for 1 h to form a magnesium carbonate suspension. Then, 6 kg of aluminum nitrate is dissolved in 10 kg of ethanol, 2 kg of citric acid is added, and ammonia water is added dropwise to adjust the pH value to 5 while stirring. Stirring is continued to form a transparent sol. The magnesium carbonate suspension and the transparent sol are mixed (mixing mass ratio is 12:1), stirred in a 65℃ water bath for 5 h, filtered, dried at 70℃, calcined at 500℃ for 1.5 h (heating rate is 15℃ / min), and ground to obtain the pore-forming agent.

[0042] The preparation method of the gradient structure tundish permanent layer castable is as follows: bauxite aggregate, sintered mullite, gradient microporous aggregate, silica powder and cement are mixed and stirred for 20 min, then rolled for 25 min, deionized water is added, stirred for 2 h, poured into a 70 mm × 70 mm × 70 mm mold, vibrated for 2 min, cured at room temperature for 24 h, demolded, dried at 120 °C for 24 h, and then heat-treated at 1600 °C for 4 h to obtain the gradient structure tundish permanent layer castable.

[0043] Example 3

[0044] A gradient structure tundish permanent layer castable comprises the following components in parts by weight:

[0045] 50kg of bauxite aggregate, 20kg of sintered mullite, 23kg of gradient microporous aggregate, 7kg of silica powder, 13kg of cement, and 13kg of deionized water; the graded particle sizes of the bauxite aggregate are: 8-12mm 14kg, 5-8mm 18kg, 1-5mm 12kg, and 0-1mm 6kg.

[0046] The preparation method of gradient microporous aggregate is as follows: 5 kg of magnesium oxide, 20 kg of calcined alumina, and 1.3 kg of zircon powder are mixed evenly, and 5.2 kg of deionized water is added. The mixture is ball-milled for 5.5 h (ball-to-powder ratio of 5:1, rotation speed of 240 rpm). The ball-milled slurry is transferred to a mixing tank, and 3.68 kg of pore-forming agent and 1.05 kg of dextrin are slowly added dropwise under stirring at 55℃ and 400 rpm. The mixture is stirred at 55℃ for 3.5 h, dried at 110℃, pulverized and passed through a 100-mesh sieve. The resulting powder is then placed in a mold for cold isostatic pressing (pressure is increased to 150 MPa at a rate of 10 MPa / min, held for 5 min, and then increased at 5 MPa / min). The pressure was released at a rate of 8℃ / h. The formed billet (φ36mm×20mm cylinder) was placed in a box-type resistance furnace and heated to 600℃ at a heating rate of 8℃ / h. It was then held for sintering for 0.8h, and then heated to 1500℃ at a heating rate of 8℃ / h. It was held for sintering for 13h and then cooled with the furnace. The sintered billet was sent to a jaw crusher to be crushed to below 50mm. Then it was crushed by a reverse crusher. A three-layer vibrating screen was used to select coarse aggregate with a particle size of 10-20mm, medium aggregate with a particle size of 3-7mm, and fine aggregate with a particle size ≤1mm. The proportion of coarse aggregate was 45%, medium aggregate was 35%, and fine aggregate was 20%, resulting in gradient microporous aggregate.

[0047] The preparation method of the pore-forming agent is as follows: 10 kg of magnesium carbonate is added to 20 kg of deionized water and ultrasonically dispersed at 70 kHz for 0.8 h to form a magnesium carbonate suspension. Then, 5 kg of aluminum nitrate is dissolved in 10 kg of ethanol, 2 kg of citric acid is added, and ammonia water is added dropwise to adjust the pH value to 4.5 while stirring. Stirring is continued to form a transparent sol. The magnesium carbonate suspension and the transparent sol are mixed (mixing mass ratio is 10:1), stirred in a 60℃ water bath for 4.5 h, filtered, dried at 65℃, calcined at 450℃ for 1.2 h (heating rate is 13℃ / min), and ground to obtain the pore-forming agent.

[0048] The preparation method of the gradient structure tundish permanent layer castable is as follows: bauxite aggregate, sintered mullite, gradient microporous aggregate, silica powder and cement are mixed and stirred for 18 min, then rolled for 23 min, deionized water is added, stirred for 1.5 h, poured into a 70 mm × 70 mm × 70 mm mold, vibrated for 2 min, cured at room temperature for 24 h, demolded, dried at 115 °C for 24 h, and then heat-treated at 1550 °C for 3.5 h to obtain the gradient structure tundish permanent layer castable.

[0049] Example 4

[0050] A gradient structure tundish permanent layer castable comprises the following components in parts by weight:

[0051] 52kg of bauxite aggregate, 21kg of sintered mullite, 23kg of gradient microporous aggregate, 6kg of silica powder, 13kg of cement, and 14kg of deionized water; the graded particle sizes of the bauxite aggregate are: 8-12mm 13kg, 5-8mm 18kg, 1-5mm 13kg, and 0-1mm 8kg.

[0052] The preparation method of gradient microporous aggregate is as follows: 5 kg of magnesium oxide, 20 kg of calcined alumina, and 1.2 kg of zircon powder are mixed evenly, and 5.0 kg of deionized water is added. The mixture is ball-milled for 5.5 h (ball-to-powder ratio of 5:1, rotation speed of 230 rpm). The ball-milled slurry is transferred to a mixing tank, and 3.67 kg of pore-forming agent and 1.05 kg of 13% polyvinyl alcohol aqueous solution are slowly added dropwise under stirring at 55℃ and 400 rpm. The mixture is stirred at 55℃ for 3.2 h, dried at 110℃, pulverized and passed through a 100-mesh sieve. The resulting powder is then placed in a mold for cold isostatic pressing (pressure is increased to 150 MPa at a rate of 10 MPa / min, held for 5 min, and then increased at 5...). The pressure was released at a rate of MPa / min. The formed billet (φ36mm×20mm cylinder) was placed in a box-type resistance furnace and heated to 600℃ at a heating rate of 8℃ / h. It was then held for sintering for 0.8h, and then heated to 1500℃ at a heating rate of 8℃ / h. It was held for sintering for 11h and then cooled with the furnace. The sintered billet was then fed into a jaw crusher and crushed to below 50mm. It was then crushed by a reverse crusher and a three-layer vibrating screen was used to select coarse aggregate with a particle size of 10-20mm, medium aggregate with a particle size of 3-7mm, and fine aggregate with a particle size ≤1mm. The proportion of coarse aggregate was 47%, medium aggregate was 38%, and fine aggregate was 15%, resulting in gradient microporous aggregate.

[0053] The preparation method of the pore-forming agent is as follows: 10 kg of magnesium carbonate is added to 20 kg of deionized water and ultrasonically dispersed at 70 kHz for 0.8 h to form a magnesium carbonate suspension. Then, 5.2 kg of aluminum nitrate is dissolved in 10 kg of ethanol, 2 kg of citric acid is added, and ammonia water is added dropwise to adjust the pH value to 4.5 while stirring. Stirring is continued to form a transparent sol. The magnesium carbonate suspension and the transparent sol are mixed (mixing mass ratio is 11:1), stirred in a 60℃ water bath for 4.5 h, filtered, dried at 65℃, calcined at 450℃ for 1.4 h (heating rate is 13℃ / min), and ground to obtain the pore-forming agent.

[0054] The preparation method of the gradient structure tundish permanent layer castable is as follows: bauxite aggregate, sintered mullite, gradient microporous aggregate, silica powder and cement are mixed and stirred for 18 min, then rolled for 23 min, deionized water is added, stirred for 1.5 h, poured into a 70 mm × 70 mm × 70 mm mold, vibrated for 2 min, cured at room temperature for 24 h, demolded, dried at 115 °C for 24 h, and then heat-treated at 1550 °C for 3.5 h to obtain the gradient structure tundish permanent layer castable.

[0055] Comparative Example 1

[0056] The tundish permanent layer castable in this comparative example is similar to that in Example 4. The difference between this comparative example and Example 4 is that an equal amount of bauxite aggregate is used instead of gradient microporous aggregate in this comparative example.

[0057] Comparative Example 2

[0058] The intermediate permanent layer castable of this comparative example is similar to that of Example 4. The difference between this comparative example and Example 4 is that an equal amount of magnesium oxide is used to replace zircon powder in the preparation method of the gradient microporous aggregate in this comparative example.

[0059] Comparative Example 3

[0060] The intermediate permanent layer castable of this comparative example is similar to that of Example 4. The difference between this comparative example and Example 4 is that an equal amount of magnesium carbonate is used instead of the pore-forming agent in the preparation method of the gradient microporous aggregate in this comparative example.

[0061] Comparative Example 4

[0062] The tundish permanent layer castable in this comparative example is similar to that in Example 4. The difference between this comparative example and Example 4 is that the mass ratio of aluminum nitrate to citric acid in the preparation method of the pore-forming agent in this comparative example is 8:1.

[0063] Comparative Example 5

[0064] The intermediate permanent layer castable of this comparative example is similar to that of Example 4. The difference between this comparative example and Example 4 is that the sintering heating rate in the preparation method of the gradient microporous aggregate in this comparative example is 20-30℃ / h.

[0065] Test case

[0066] Bulk density and apparent porosity: The tundish permanent layer castables prepared in Examples 1-4 and Comparative Examples 1-5 were tested according to GB / T2997-2015.

[0067] Thermal conductivity: The tundish permanent layer castables prepared in Examples 1-4 and Comparative Examples 1-5 were tested according to YB / T 4130-2005.

[0068] Slag Resistance Test: Holes with a diameter of 40×40 mm were drilled in the top of the tundish permanent layer castable samples prepared in Examples 1-4 and Comparative Examples 1-5. 100g of tundish slag sample from Panzhihua Iron & Steel Group was then placed into the holes. After holding at 1500℃ for 3 hours, the samples were removed and cooled. The samples were then cut in half, and the erosion area and penetration area of ​​the cross-section were measured. The erosion (penetration) index was calculated. The higher the index, the worse the slag resistance. The calculation formula is: Erosion Index = (S / S0) × 100%, where S is the erosion area (mm²). 2 S0 is the area of ​​the central empty cross-section before the test (mm²). 2 ).

[0069] The experimental results are shown in Table 1.

[0070] Table 1 Performance Test Results

[0071]

[0072] As shown in Table 1, the bulk density of the gradient structure tundish permanent layer castable provided by this invention is 3.27-3.50 g / cm³. 3 The apparent porosity is 11%-17%, and the thermal conductivity is 0.60-0.75 W·m. -1 ·K -1 The erosion index is 2.28%-2.67%, which indicates that the gradient structure tundish permanent layer castable provided by the present invention has good thermal insulation and slag resistance.

[0073] In Comparative Example 1, an equal amount of bauxite aggregate was used to replace the gradient microporous aggregate, but the resulting castable showed increased bulk density, apparent porosity, and thermal conductivity, indicating that the gradient microporous aggregate can effectively improve the thermal insulation performance of the castable. In Comparative Example 2, an equal amount of magnesium oxide was used to replace zircon powder, but the resulting castable showed a significant increase in erosion index, indicating that the addition of zircon powder to the gradient microporous aggregate can effectively improve its resistance to slag erosion. In Comparative Example 3, an equal amount of magnesium carbonate was used to replace the pore-forming agent, but the resulting castable showed a significant increase in apparent porosity and erosion index. This is because magnesium carbonate decomposes into magnesium oxide during high-temperature calcination, and a large amount of magnesium oxide... The simultaneous escape of carbon dioxide gas in the castable led to the formation of interconnected pores. Comparative Example 4 changed the mass ratio of aluminum nitrate to citric acid, but the apparent porosity and erosion index of the resulting castable increased. This was because the amount of citric acid was too small, resulting in agglomeration or island defects in the coating layer of the pore-forming agent, and the rapid decomposition of magnesium carbonate at high temperature. Comparative Example 5 increased the sintering heating rate in the preparation method of gradient microporous aggregate, but the apparent porosity and erosion index of the resulting castable increased significantly. This was because the excessively rapid heating rate caused the gas generated by the decomposition of the pore-forming agent to escape rapidly, forming interconnected pore structures, which led to an increase in the apparent porosity and erosion index of the castable.

[0074] Furthermore, the present invention also conducted scanning electron microscopy tests on the gradient structure intermediate tundish permanent layer castable prepared in Example 4, and the test results are shown in [Figure 4]. Figure 1 .Depend on Figure 1 It can be seen that a uniformly dispersed closed-pore structure was formed in the gradient structure intermediate liner permanent layer castable prepared in Example 4.

[0075] The above embodiments are merely illustrative of the present invention and are not intended to limit the invention. Those skilled in the art should not modify the above embodiments without departing from the spirit and scope of the present invention. All equivalent modifications or alterations made by those skilled in the art without departing from the technical concept of the present invention are still within the protection scope of the present invention.

Claims

1. A gradient structure tundish permanent layer castable, characterized in that, The components include the following parts by mass: 40-60 parts of bauxite aggregate, 10-25 parts of sintered mullite, 20-25 parts of gradient microporous aggregate, 5-8 parts of silica fume, 10-15 parts of cement, and 10-15 parts of deionized water. The method for preparing the gradient microporous aggregate is as follows: magnesium oxide, calcined alumina and zircon powder are mixed evenly, deionized water is added, and the mixture is ball-milled for 5-6 hours. A pore-forming agent and a binder are added to the ball-milled slurry, and the mixture is stirred at 50-60℃ for 3-4 hours. The mixture is then dried, pulverized, placed in a mold, and cold isostatically pressed. The cold isostatically pressed blank is placed in a box-type resistance furnace and heated to 600℃ at a heating rate of 5-10℃ / h. The blank is then held at this temperature for 0.5-1 hours. Then, the blank is heated to 1500℃ at a heating rate of 5-10℃ / h and held at this temperature for 10-15 hours. The blank is then cooled in the furnace, crushed, and graded to obtain the gradient microporous aggregate. The pore-forming agent is prepared as follows: magnesium carbonate is added to deionized water and ultrasonically dispersed to form a magnesium carbonate suspension. Then, aluminum nitrate is dissolved in ethanol, citric acid is added, and ammonia is added dropwise to adjust the pH value to 4-5 while stirring. Stirring is continued to form a transparent sol. The magnesium carbonate suspension and the transparent sol are mixed and stirred in a water bath at 55-65℃ for 4-5 hours. The mixture is then filtered, dried, calcined, and ground to obtain the final product. The mass ratio of aluminum nitrate to citric acid is 2-3:

1.

2. The gradient structure tundish permanent layer castable according to claim 1, characterized in that, The mass ratio of the magnesium carbonate suspension to the transparent sol is 8-12:1; the calcination temperature is 400-500℃, the heating rate is 10-15℃ / min, and the calcination time is 1-1.5h.

3. The gradient structure tundish permanent layer castable according to claim 1, characterized in that, The mass ratio of magnesium oxide, calcined alumina and zircon powder is (0.15-0.30):1:(0.04-0.08).

4. The gradient structure tundish permanent layer castable according to claim 1, characterized in that, The amount of the pore-forming agent is 12%-15% of the total mass of magnesium oxide, calcined alumina and zircon powder; the amount of the binder is 2%-5% of the total mass of magnesium oxide, calcined alumina and zircon powder.

5. The gradient structure tundish permanent layer castable according to claim 1, characterized in that, The binder is dextrin or a polyvinyl alcohol aqueous solution with a mass percentage of 10%-15%.

6. The gradient structure tundish permanent layer castable according to claim 1, characterized in that, The specific process of crushing and grading is as follows: the sintered billet is fed into a jaw crusher and crushed to below 50mm, then crushed by a reverse crusher, and a three-layer vibrating screen is used to select coarse aggregate with a particle size of 10-20mm, medium aggregate with a particle size of 3-7mm and fine aggregate with a particle size ≤1mm, wherein the proportion of coarse aggregate is 40%-50%, the proportion of medium aggregate is 30%-40%, and the proportion of fine aggregate is 10%-20%.

7. The method for preparing the gradient structure tundish permanent layer castable according to any one of claims 1-6, characterized in that, Specifically, the following steps are taken: mix bauxite aggregate, sintered mullite, gradient microporous aggregate, silica powder and cement, stir for 15-20 minutes, then roll for 20-25 minutes, add deionized water, stir for 1-2 hours, pour into a strip mold, vibrate to form, cure at room temperature for 24 hours, demold, dry at 110-120℃ for 24 hours, and then heat treat at 1500-1600℃ for 3-4 hours to obtain the gradient structure intermediate ladle permanent layer castable.

Images