Intermediate package MgO-CaO quality dry material and preparation method thereof

Abstract

The application relates to the technical field of refractory materials, in particular to a tundish MgO-CaO dry material and a preparation method thereof. The preparation method of the tundish MgO-CaO dry material comprises the following steps: taking 20-50 parts of light-burned dolomite, 40-80 parts of magnesia and 2-9 parts of phenolic resin powder as raw materials, uniformly mixing the raw materials, tamping and shaping, and drying to obtain the tundish MgO-CaO dry material; the light-burned dolomite is prepared by the following method: after dolomite is subjected to high-temperature calcination and decomposition at 300 DEG C-750 DEG C for 2.5-3.5 h, the dolomite is naturally cooled, and then exposed to air for a period of time in a normal-temperature and normal-humidity environment. The tundish MgO-CaO dry material prepared by the application has good hydration resistance, excellent steel liquid purification capacity and low cost.

Description

Technical Field

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

[0002] With the steel industry developing towards large-scale, continuous, and high-cleanliness operations, the proportion of ladle refining and continuous casting processes is constantly increasing. Molten steel is in prolonged contact with slag and refractory materials at high temperatures, requiring furnace linings to not only have a long service life but also minimize secondary pollution of the molten steel. Given that traditional MgO-based refractories can no longer simultaneously meet the requirements of service life and clean steel, MgO-CaO-based refractories, which combine slag resistance and purification functions, have attracted more attention and become one of the important development directions for basic refractories in metallurgy. MgO-CaO-based refractories are highly regarded for their excellent desulfurization, dephosphorization, and inclusion adsorption capabilities; however, the free CaO they contain is highly susceptible to hydration reactions with moisture in the air, leading to material cracking and pulverization, which severely restricts their widespread industrial application. Therefore, studying their hydration mechanism and protective measures is a key research focus in this field.

[0003] Researchers often improve the hydration resistance of dolomite refractories through sintering densification, surface treatment, and sealed packaging. Ke Changming et al. (Ke Changming, Li Nan. Sintering performance and hydration resistance of MgO-CaO-TiO2 materials [J]. Refractory Materials, 2005, 39(1):5.) used dolomite and lightly calcined magnesia as raw materials, introduced TiO2 as an additive, and prepared MgO-CaO-TiO2 materials by holding at 1500~1650 ℃ for 3 h. The study found that the relative density of samples with TiO2 addition of 10%~30% all reached more than 92%. The 2MgO·TiO2 generated during calcination can also promote sintering. At the same time, free CaO is converted into CaO·TiO2, which is not easily hydrated, further improving the hydration resistance of MgO-CaO refractories. Chen et al. (Chen S, Lu P, Chen G, et al. Improved hydration resistance of synthesized magnesia-calciaclinker by surface modification[J]. Journal of the American Ceramic Society.2004, 87(12): 2164-2167.) used two types of CaO particles with low porosity (0.2%) and high porosity (27%) as raw materials, and induced surface carbonation by introducing CO2 at 700 ℃. The results showed that the calcium carbonate film formed by the low porosity material was thinner and denser, and its hydration resistance was better than that of the high porosity material.

[0004] 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

[0005] The purpose of this invention is to address the aforementioned shortcomings of the prior art by proposing an intermediate MgO-CaO dry material with good hydration resistance, excellent steel purification ability, and low cost, as well as its preparation method.

[0006] The first objective of this invention is to provide a method for preparing MgO-CaO dry intermediate pack material, wherein 20-50 parts by weight of lightly calcined dolomite, 40-80 parts by weight of magnesia, and 2-9 parts by weight of phenolic resin powder are mixed evenly, tamped and shaped, and dried to obtain MgO-CaO dry intermediate pack material. The lightly calcined dolomite was prepared using the following method: Dolomite is calcined at 300℃~750℃ for 2.5-3.5 hours until decomposed, and then naturally cooled. After being exposed to air at normal temperature and humidity for a period of time, (Mg2(OH)2CO3)-coated MgO-CaCO3 composite refractory material, namely the lightly calcined dolomite, is obtained.

[0007] Furthermore, it is exposed to air for 5 to 10 days under normal temperature and humidity conditions.

[0008] Furthermore, the dolomite has a CaO content ≥30 wt%, an MgO content ≥20 wt%, and a loss on ignition ≥45 wt%.

[0009] Furthermore, the drying process involves drying at 150℃-300℃ for 24 hours.

[0010] Furthermore, the particle size distribution of lightly calcined dolomite is: Particles smaller than 5 mm and greater than or equal to 3 mm account for 25-35 wt% of lightly calcined dolomite; Particles smaller than 3 mm and greater than or equal to 1 mm account for 35-45 wt% of lightly calcined dolomite; Particles with a diameter less than 1 mm and greater than or equal to 0.088 mm account for 30-35 wt% of lightly calcined dolomite.

[0011] Furthermore, the MgO content of the magnesia is ≥95 wt%.

[0012] Furthermore, the residual carbon content of the phenolic resin powder is ≥45 wt%.

[0013] A second objective of this invention is to provide a dry intermediate MgO-CaO feedstock prepared by the method described above.

[0014] Compared with the prior art, the present 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. Dolomite is one of the main CaO sources in the refractory field, and my country has abundant and low-cost dolomite resources. The main component of dolomite is (Ca, Mg)(CO3)2, a double salt of CaCO3 and MgCO3. In this invention, dolomite is lightly calcined at 300-750℃, causing MgCO3 to decompose into highly active MgO while CaCO3 remains undecomposed, resulting in a MgO-CaCO3 composite refractory raw material. Then, after being exposed to air at normal temperature and humidity for a period of time, basic magnesium carbonate (Mg2(OH)2CO3) forms on the surface of the highly active MgO, hindering the reaction between the internal MgO and water vapor in the air, thus improving the hydration resistance of MgO. The final lightly calcined dolomite is a (Mg2(OH)2CO3)-coated MgO-CaCO3 composite refractory raw material with excellent hydration resistance. The preparation of dry tundish refractories using lightly calcined dolomite and magnesia as the main raw materials effectively solves the problem of easy hydration of refractory materials containing free CaO. During high-temperature operation of the tundish, temperatures can reach as high as 1550℃, and the CaO produced by the decomposition of CaCO3 directly contacts the molten steel, achieving desulfurization and dephosphorization effects.

[0015] Therefore, the MgO-CaO dry tundish material prepared by this invention has good resistance to hydration, excellent ability to purify molten steel, and low cost. Detailed Implementation

[0016] 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.

[0017] To avoid repetition, the materials used in this specific implementation method are described uniformly as follows, and will not be repeated in the examples: The dolomite contained 31.4 wt% CaO, 21.57 wt% MgO, and 46.7 wt% loss on ignition. Lightly calcined dolomite was prepared using the following method: Dolomite was calcined at 750℃ for 3 hours to decompose it. After natural cooling, it was exposed to air at room temperature and humidity for 7 days to obtain lightly calcined dolomite. The particle size distribution of light-burned dolomite is as follows: particles smaller than 5 mm and greater than or equal to 3 mm account for 30 wt% of light-burned dolomite; particles smaller than 3 mm and greater than or equal to 1 mm account for 40 wt% of light-burned dolomite; and particles smaller than 1 mm and greater than or equal to 0.088 mm account for 30 wt% of light-burned dolomite. The magnesia has an MgO content of 96.2 wt%. The residual carbon content of the phenolic resin powder is 45.2 wt%.

[0018] Example 1 Using 24 parts of lightly calcined dolomite, 72 parts of magnesia, and 4 parts of phenolic resin powder as raw materials, the mixture was thoroughly mixed, tamped into shape, and dried at 200 ℃ for 24 h to obtain the intermediate MgO-CaO dry material.

[0019] The MgO-CaO dry material prepared by this invention was tested and found to have a weight gain rate of 0.01% after being placed in a curing chamber with a humidity of 96% and a temperature of 20°C for 20 days; after reacting with molten steel at 1550°C for 90 min, the P and S elements in the steel were 0.023% and 0.006%, respectively.

[0020] Example 2 Using 29 parts of lightly calcined dolomite, 66 parts of magnesia, and 5 parts of phenolic resin powder as raw materials, the mixture was thoroughly mixed, tamped into shape, and dried at 200 ℃ for 24 h to obtain the intermediate MgO-CaO dry material.

[0021] The MgO-CaO dry tundish material prepared by this invention was tested and found to have a weight gain of 0.25% after being placed in a curing chamber with 96% humidity and 20°C for 20 days; and after reacting with molten steel at 1550°C for 90 min, the P and S elements in the steel were 0.020% and 0.005%, respectively.

[0022] Example 3 Using 39 parts of lightly calcined dolomite, 57 parts of magnesia, and 4 parts of phenolic resin powder as raw materials, the mixture was thoroughly mixed, tamped into shape, and dried at 200 ℃ for 24 h to obtain the intermediate MgO-CaO dry material.

[0023] The MgO-CaO dry tundish material prepared by this invention was tested and found to have a weight gain rate of 0.032% after being placed in a curing chamber with 96% humidity and 20°C for 20 days; and after reacting with molten steel at 1550°C for 90 min, the P and S elements in the steel were 0.017% and 0.0042%, respectively.

[0024] Example 4 Using 50 parts of lightly calcined dolomite, 45 parts of magnesia, and 5 parts of phenolic resin powder as raw materials, the mixture was thoroughly mixed, tamped into shape, and dried at 200 ℃ for 24 h to obtain the intermediate MgO-CaO dry material.

[0025] The MgO-CaO dry tundish material prepared by this invention was tested and found to have a weight gain rate of 0.04% after being placed in a curing chamber with a humidity of 96% and a temperature of 20°C for 20 days; and after reacting with molten steel at 1550°C for 90 min, the P and S elements in the steel were 0.012% and 0.003%, respectively.

[0026] For any points not covered above, existing technologies shall apply.

[0027] 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 dry MgO-CaO intermediate batch, characterized in that, Using 20-50 parts by weight of lightly calcined dolomite, 40-80 parts by weight of magnesia, and 2-9 parts by weight of phenolic resin powder as raw materials, mix them evenly, pound them into shape, and dry them to obtain MgO-CaO dry material in intermediate packaging. The lightly calcined dolomite was prepared using the following method: Dolomite is calcined at 300 ℃~750 ℃ ​​for 2.5-3.5 h to decompose it. After natural cooling, it is exposed to air at normal temperature and humidity for a period of time to obtain (Mg2(OH)2CO3) coated MgO-CaCO3 composite refractory material, namely the lightly calcined dolomite.

2. The preparation method according to claim 1, characterized in that, Expose to air at normal temperature and humidity for 5-10 days.

3. The preparation method according to claim 1, characterized in that, The dolomite has a CaO content ≥30 wt%, an MgO content ≥20 wt%, and a loss on ignition ≥45 wt%.

4. The preparation method according to claim 1, characterized in that, The drying process involves drying at 150℃-300℃ for 24 hours.

5. The preparation method according to claim 1, characterized in that, The particle size distribution of the lightly calcined dolomite is: Particles smaller than 5 mm and greater than or equal to 3 mm account for 25-35 wt% of lightly calcined dolomite; Particles smaller than 3 mm and greater than or equal to 1 mm account for 35-45 wt% of lightly calcined dolomite; Particles with a diameter less than 1 mm and greater than or equal to 0.088 mm account for 30-35 wt% of lightly calcined dolomite.

6. The preparation method according to claim 1, characterized in that, The MgO content of the magnesia is ≥94 wt%.

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