Tundish microporous MgO-CaO dry material and preparation method thereof

Abstract

The invention relates to the technical field of refractory materials, in particular to a tundish microporous MgO-CaO dry material and a preparation method thereof. A preparation method of a tundish microporous MgO-CaO dry material comprises the following steps: taking 15-55 parts by mass of CaCO3 coated microporous limestone clinker, 40-80 parts by mass of fused magnesite and 2-8 parts by mass of phenolic resin powder as raw materials, uniformly mixing, ramming for forming, drying, and preserving heat at 1400-1650 DEG C for 2.5-3 hours to obtain the tundish microporous MgO-CaO dry material. The tundish microporous MgO-CaO dry material prepared by the preparation method disclosed by the invention is good in hydration resistance, strong in slag corrosion resistance, excellent in molten steel purification capability and easy to disintegrate.

Description

A microporous MgO-CaO dry material for intermediate packaging and its preparation method Technical Field

[0001] This invention relates to the field of refractory materials technology, and in particular to a microporous MgO-CaO dry refractory material for tundishes and its preparation method. Background Technology

[0002] With the increasing demand for high-quality clean steel, the interaction between refractory materials and molten steel has received more and more attention. The tundish, as a container that directly contacts molten steel in the metallurgical industry, plays an indispensable role. MgO-based refractory materials are widely used in the working layer of the tundish due to their excellent high-temperature resistance.

[0003] Compared to MgO-based refractories, CaO-based refractories possess superior thermodynamic stability and are less prone to dissolving and oxygenating into molten steel. Furthermore, CaO can absorb phosphorus and sulfur from molten steel to form calcium phosphate and calcium sulfide, thus achieving dephosphorization and desulfurization effects. However, CaO readily reacts with water in the air to form Ca(OH)₂, accompanied by volume expansion. This can easily cause cracks or disintegration on the dense calcium oxide surface, damaging the CaO-based refractories. Its poor resistance to hydration limits the application of CaO-based refractories. Luo Ming et al. (Luo Ming, Li Nan, Zheng Haizhong, et al. Effects of admixtures on sintering and hydration resistance of dolomite [J]. Refractory Materials, 2001, 35(1): 14-15.) studied the effects of steel slag, Al2O3, Fe2O3 and composite rare earth oxides on the sintering and hydration resistance of dolomite. They found that all of them promoted the sintering of dolomite to a certain extent and improved its hydration resistance, among which the addition of composite rare earth oxides had the best effect. Ke Changming et al. (Ke Changming, Li Nan. Sintering properties and hydration resistance of MgO-CaO-TiO2 materials[J]. Refractory Materials, 2005, (01): 36-40.) prepared MgO-CaO-TiO2 materials with different compositions using dolomite, industrial titanium dioxide and lightly calcined magnesia as raw materials. After calcination at 1550℃~1600℃, the samples all achieved good sintering with a relative density of over 92%. All CaO in the original batch was converted into CaO·TiO2, which is not easily hydrated. Therefore, all samples showed excellent hydration resistance. GM Othman et al. (Othman AGM, Abou El-Maaty MA, Serry M A. Hydration-resistant limerefractories from Egyptian limestone and ilmenite raw materials[J]. Ceramicsinternational, 2001, 27(7): 801-807.) mixed 2.0-3.0 wt.% ilmenite into Egyptian limestone powder, and after calcination at 1500 ℃, they obtained dense lime particles with excellent hydration resistance. Wu Zhande et al. (Wu Zhande, Yang Yang. Preparation of high-quality magnesia-calcium sand by ultra-high temperature calcination and its performance study[J]. Refractories and Lime, 2018, 43(6): 1-8.) used natural dolomite and magnesite as raw materials, pressed at 140 MPa, and calcined at 1700~2000 ℃ to prepare MgO-CaO refractory materials, which showed significantly improved density and a pulverization rate as low as 2%.High-temperature calcination can promote grain growth to increase the density of materials, thereby improving the hydration resistance of MgO-CaO refractory materials. However, since the temperature required for complete sintering of CaO in industry is above 1800 ℃, the high-temperature calcination method consumes a lot of energy and places high demands on sintering equipment, which increases production costs.

[0004] Applying a waterproof layer to the surface of refractory materials through surface treatment can improve their hydration resistance. Chen et al. (Shujiang Chen, Pingge Lu, Guorong Chen, et al. Improved hydration resistance of synthesized magnesia-calcia clinker by surface modification[J].Journal of the American Ceramic Society, 2004, 87(12): 2164-2167.) used magnesite and dolomite as raw materials, calcined at 1800 ℃ to produce magnesia-calcium sand, and then surface-modified magnesia-calcium sand was obtained by surface modification with oleic acid, stearic acid and oleic acid-stearic acid composite acid. The results of the hydration resistance test showed that the magnesia-calcium sand modified with composite acid had the best hydration resistance effect. When 5% (w) was added, the hydration mass increase rate of magnesia-calcium sand was almost zero. This is because the terminal carboxyl groups of the modifier can react with calcium ions on the surface of magnesia-calcium sand to generate corresponding calcium oleate and calcium stearate, forming an organic coating layer on the material surface, which isolates water vapor. Wu Daojun (A method for preparing a dry vibratory material for a magnesium-calcium tundish, CN201611044224.8) prepared a dry vibratory material for a magnesium-calcium tundish by mixing magnesium sand and limestone as the main raw materials. The main component of limestone is CaCO3, which does not react with water. However, CaCO3 decomposes at high temperature to release carbon dioxide, causing the undesirable phenomenon of boiling of molten steel.

[0005] Improving the hydration resistance of CaO-containing refractories through high-temperature calcination densification and surface treatment with additives is costly. There is a need to find a more cost-effective and widely applicable method to enhance the hydration resistance of CaO-containing refractories. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned shortcomings of the prior art by proposing a microporous MgO-CaO dry material for tundishes with good hydration resistance, low thermal conductivity, strong slag erosion resistance, excellent ability to purify molten steel, and easy disintegration, as well as its preparation method.

[0007] The first objective of this invention is to provide a method for preparing a microporous MgO-CaO dry material in an intermediate ladle. The method involves using 15-55 parts by weight of CaCO3-coated microporous limestone clinker, 40-80 parts by weight of fused magnesia, and 2-8 parts by weight of phenolic resin powder as raw materials. These materials are mixed evenly, tamped into shape, dried, and then held at 1400℃-1650℃ for 2.5-3 h to obtain the microporous MgO-CaO dry material in an intermediate ladle. The CaCO3-coated microporous limestone clinker is prepared by calcining limestone at 1000℃-1500℃ for 2.5-3.5 h. After the calcination, the temperature is lowered to 500-700℃, and a mixture of CO2 and H2O is introduced into the furnace. The mixture reacts with the calcined limestone in the furnace, and after natural cooling, the CaCO3-coated microporous limestone clinker is obtained. The limestone contains ≥50 wt% CaO and ≤10% SiO2. wt%, loss on ignition ≥40 wt%.

[0008] Furthermore, the volume ratio of CO2 to H2O in the CO2 and H2O mixture is 30~80: 35~75.

[0009] Furthermore, the drying process involves drying at 200 ℃ for 24 hours.

[0010] Furthermore, the intermediate ladle was kept at 1400℃~1650℃ for 3 h to obtain microporous MgO-CaO dry material.

[0011] Furthermore, the particle size distribution of the CaCO3-coated microporous limestone clinker is as follows: particles with a diameter less than 5 mm and greater than or equal to 3 mm account for 25-35 wt% of the microporous limestone clinker; particles with a diameter less than 3 mm and greater than or equal to 1 mm account for 35-45 wt% of the microporous limestone clinker; and particles with a diameter less than 1 mm and greater than or equal to 0.088 mm account for 30-35 wt% of the microporous limestone clinker.

[0012] Furthermore, the MgO content of the fused magnesia is ≥96 wt%.

[0013] Furthermore, the residual carbon content of the phenolic resin powder is ≥45 wt%.

[0014] The second objective of this invention is to provide a microporous MgO-CaO dry intermediate bag material prepared by the preparation method described above.

[0015] Compared with existing technologies, this invention has the following advantages: The ease with which refractory materials containing free CaO hydrate, leading to disintegration or even pulverization, is a major factor limiting their application. Limestone is one of the main CaO sources in the field of refractory materials, with CaCO3 as its main component. After one-step calcination, it yields a bulk density of 1.3~1.6 g·cm³. -3Microporous limestone clinker particles (mainly composed of CaO) with an apparent porosity of 30-37% and a pore size ≤10 μm absorb the volume expansion stress caused by CaO hydration through these micropores. Simultaneously, the high-temperature calcination of limestone produces microporous limestone clinker particles. When the furnace temperature drops to 500℃-700℃, a mixture of CO2 and H2O is introduced into the furnace. This gas reacts with the CaO in the microporous limestone clinker particles, forming a dense CaCO3 protective layer on the surface of the particles. This dense CaCO3 layer effectively isolates water vapor from the air, significantly reducing the hydration reaction. The micron-sized pores absorb the volume expansion caused by a small amount of CaO hydration, effectively solving the problem of easy hydration in CaO-based refractory materials. Furthermore, the use of microporous limestone clinker increases the porosity of the dry refractory material, resulting in lower thermal conductivity, which is beneficial for the insulation of the tundish.

[0016] The limestone used in this invention contains a certain amount of SiO2. The limestone clinker formed by calcination mainly consists of CaO and dicalcium silicate (Ca2SiO4, abbreviated as C2S). As can be seen from equations (1) to (2), CaO can absorb [P] and [S] in the molten steel, thus purifying the molten steel. The introduced SiO2 can also dissolve in the slag at high temperatures, increasing the viscosity of the slag and thereby improving its resistance to slag erosion.

[0017] 3CaO(s)+2[P]+5[O]=Ca3(PO4)2(s)(1)CaO(s)+[S]+3[O]=CaSO4(s)(2)Finally, after the intermediate ladle has been working for a certain period of time, it needs to be taken offline to replace the dry material. Usually, the residual dry material in the inner lining is removed manually or mechanically, which is quite labor-intensive. In this invention, the limestone clinker contains C2S. C2S is very easy to decompose at temperatures below 500℃, with a density of 3.28 g. cm -3 The β-type transformation has a density of 2.97 g. cm -3 The γ-type crystal structure, accompanied by a volume expansion of about 10%, leads to material cracking or even disintegration. During the cooling process after the tundish is removed from the production line, the C2S crystal transformation makes the residual dry liner material easier to disintegrate, which is beneficial for the replacement of the tundish dry liner material.

[0018] The microporous MgO-CaO dry material prepared by this invention was tested and found to have an apparent porosity of 22-40% and a thermal conductivity of 1-5 W·m at 800℃. -1 ·K -1The room temperature compressive strength is 20~36 MPa, and the room temperature compressive strength is 18~33 MPa after being placed in air for 15 days; after reacting with molten steel at 1550 ℃ for 90 min, the [P] and [O] contents in the steel are 0.04~0.22 wt% and 780~1460 ppm, respectively; after reacting with tundish slag at 1550 ℃ for 3 h, the percentage of eroded area is 12.0~16.3%.

[0019] Therefore, the microporous MgO-CaO dry material prepared by this invention has good resistance to hydration, strong resistance to slag erosion, excellent ability to purify molten steel, and is easy to disintegrate. Detailed Implementation

[0020] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0021] To avoid repetition, the materials used in this specific embodiment are described uniformly as follows, and will not be repeated in the examples: the limestone has a CaO content of 53.4 wt%, a SiO2 content of 4.5%, and a loss on ignition of 42.1 wt%; the CaCO3-coated microporous limestone clinker is prepared by the following method: the limestone is calcined and decomposed at 1100℃ for 3 hours, and after the holding time is completed, the temperature is lowered to 550℃, and a mixture of CO2 and H2O (volume ratio of 50:50) is introduced into the furnace. The mixture reacts with the limestone after calcination and decomposition in the furnace, and after natural cooling, the CaCO3-coated microporous limestone clinker is obtained.

[0022] The particle size distribution of the CaCO3-coated microporous limestone clinker is as follows: particles smaller than 5 mm and greater than or equal to 3 mm account for 30 wt% of the microporous limestone clinker; particles smaller than 3 mm and greater than or equal to 1 mm account for 40 wt% of the microporous limestone clinker; particles smaller than 1 mm and greater than or equal to 0.088 mm account for 30 wt% of the microporous limestone clinker; the MgO content of the fused magnesia is 96.5 wt%; and the residual carbon content of the phenolic resin powder is 45.9 wt%.

[0023] Example 1 uses 24 parts of the above-mentioned CaCO3-coated microporous limestone clinker, 72 parts of fused magnesia, and 4 parts of phenolic resin powder as raw materials. They are mixed evenly, tamped and shaped, dried at 200 ℃ for 24 h, and then kept at 1550 ℃ for 3 h to obtain intermediate ladle microporous MgO-CaO dry material.

[0024] The microporous limestone dry material prepared by this invention was tested and found to have an apparent porosity of 22.6% and a thermal conductivity of 3.88 W·m at 800℃. -1 ·K -1The room temperature compressive strength is 31.2 MPa, and the room temperature compressive strength is 26.9 MPa after being placed in air for 15 days. After reacting with molten steel at 1550℃ for 90 min, the [P] and [O] contents in the steel are 0.18 wt% and 1290 ppm, respectively. After reacting with tundish slag at 1550℃ for 3 h, the percentage of eroded area is 15.7%.

[0025] Example 2 uses 29 parts of CaCO3-coated microporous limestone clinker, 66 parts of fused magnesia, and 5 parts of phenolic resin powder as raw materials. The mixture is evenly mixed, tamped and shaped, dried at 200 ℃ for 24 h, and then kept at 1550 ℃ for 3 h to obtain a microporous MgO-CaO dry material in the intermediate ladle.

[0026] The microporous limestone dry material prepared by this invention was tested and found to have an apparent porosity of 27.8% and a thermal conductivity of 4.1 W·m at 800℃. -1 ·K -1 The room temperature compressive strength is 29 MPa, and the room temperature compressive strength is 24.6 MPa after being placed in air for 15 days. After reacting with molten steel at 1550℃ for 90 min, the [P] and [O] contents in the steel are 0.15 wt% and 1150 ppm, respectively. After reacting with tundish slag at 1550℃ for 3 h, the percentage of eroded area is 14.9%.

[0027] Example 3 uses 39 parts of CaCO3-coated microporous limestone clinker, 57 parts of fused magnesia, and 4 parts of phenolic resin powder as raw materials. The mixture is evenly mixed, tamped and shaped, dried at 200 ℃ for 24 h, and then kept at 1550 ℃ for 3 h to obtain intermediate ladle microporous MgO-CaO dry material.

[0028] The microporous limestone dry material prepared by this invention was tested and found to have an apparent porosity of 31.2% and a thermal conductivity of 1.7 W·m at 800℃. -1 ·K -1 The room temperature compressive strength is 25 MPa, and the room temperature compressive strength is 21.2 MPa after being placed in air for 15 days. After reacting with molten steel at 1550℃ for 90 min, the [P] and [O] contents in the steel are 0.085 wt% and 1010 ppm, respectively. After reacting with tundish slag at 1550℃ for 3 h, the percentage of eroded area is 14.1%.

[0029] Example 4 uses 50 parts of CaCO3-coated microporous limestone clinker, 45 parts of fused magnesia, and 5 parts of phenolic resin powder as raw materials. The mixture is evenly mixed, tamped and shaped, dried at 200 ℃ for 24 h, and then kept at 1550 ℃ for 3 h to obtain intermediate ladle microporous MgO-CaO dry material.

[0030] The microporous limestone dry material prepared by this invention was tested and found to have an apparent porosity of 38% and a thermal conductivity of 1.3 W·m at 800℃. -1 ·K -1 The room temperature compressive strength is 22.5 MPa, and the room temperature compressive strength is 18.2 MPa after being placed in air for 15 days. After reacting with molten steel at 1550℃ for 90 min, the [P] and [O] contents in the steel are 0.05 wt% and 790 ppm, respectively. After reacting with tundish slag at 1550℃ for 3 h, the percentage of eroded area is 12.5%.

[0031] For any points not covered above, existing technologies shall apply.

[0032] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a microporous MgO-CaO dry material for intermediate packaging, characterized in that, Using 15-55 parts by weight of CaCO3-coated microporous limestone clinker, 40-80 parts by weight of fused magnesia, and 2-8 parts by weight of phenolic resin powder as raw materials, the mixture is thoroughly mixed, tamped, dried, and then kept at 1400℃-1650℃ for 2.5-3 h to obtain a microporous MgO-CaO dry material with intermediate lamination. The CaCO3-coated microporous limestone clinker is prepared by the following method: limestone is calcined at 1000℃-1500℃ for 2.5-3.5 h to decompose it. After the calcination is completed, the temperature is lowered to 500-700℃, and a mixture of CO2 and H2O is introduced into the furnace. The mixture reacts with the calcined limestone in the furnace, and after natural cooling, the CaCO3-coated microporous limestone clinker is obtained. The limestone has a CaO content ≥50 wt%, a SiO2 content ≤10 wt%, and a loss on ignition ≥40 wt%.

2. The preparation method according to claim 1, characterized in that, The volume ratio of CO2 to H2O in the CO2 and H2O mixture is 30~80:35~75.

3. The preparation method according to claim 1, characterized in that, The drying process involves drying at 200 ℃ for 24 hours.

4. The preparation method according to claim 1, characterized in that, The tundish was heated at 1400℃~1650℃ for 3 h to obtain microporous MgO-CaO dry material.

5. The preparation method according to claim 1, characterized in that, The particle size distribution of the CaCO3-coated microporous limestone clinker is as follows: particles with a diameter less than 5 mm and greater than or equal to 3 mm account for 25-35 wt% of the microporous limestone clinker; particles with a diameter less than 3 mm and greater than or equal to 1 mm account for 35-45 wt% of the microporous limestone clinker; and particles with a diameter less than 1 mm and greater than or equal to 0.088 mm account for 30-35 wt% of the microporous limestone clinker.

6. The preparation method according to claim 1, characterized in that, The fused magnesia contains ≥96 wt% MgO.

7. The preparation method according to claim 1, characterized in that, The residual carbon content of the phenolic resin powder is ≥45 wt%.

8. A microporous MgO-CaO dry material prepared by the preparation method according to any one of claims 1-7.