Carbon-free steel ladle filling sand and preparation process thereof

Abstract

The invention relates to the technical field of metal smelting auxiliary materials, and particularly provides carbon-free steel ladle filling sand and a preparation technology thereof.The preparation technology comprises the steps that chromium ore, quartz sand, electric smelting magnesium chromium sand, high-aluminum balls and alumina-coated zircon sand are accurately weighed respectively; the mass percent of the chromium ore sand is 30%-57%, the mass percent of the quartz sand is 8%-15%, the mass percent of the electric smelting magnesium-chromium sand is 15%-30%, the mass percent of the high-aluminum balls is 5%-15%, and the mass percent of the zircon sand coated with aluminum The preparation method comprises the following steps: firstly adding chromium ore sand and fused magnesium chromium sand, uniformly stirring, then adding quartz sand and high-aluminum balls, finally adding zircon sand coated with aluminum oxide, continuously stirring and heating until the water content of the material does not exceed 0.2%; and metering and packaging. The properties of the carbon-free steel ladle filling sand are close to those of carbonaceous steel ladle filling sand, the cost is not obviously increased, the preparation process is simple and easy to operate, large-scale production can be achieved, and the smelting requirements of special steel types such as low-carbon steel, ultra-low-carbon steel and high-purity steel can be met.

Description

Technical Field

[0001] The invention relates to the technical field of metal smelting auxiliary materials, in particular to carbon-free ladle filling sand and a preparation process thereof. Background Art

[0002] Ladle filling sand is a bulk filler material added to the ladle's sliding nozzle before steel is tapped. Before molten steel is poured, the sand is injected through the sliding nozzle at the bottom of the ladle, leveraging its fluidity to guide the molten steel outflow and ensure a smooth pouring process. It also prevents molten steel from solidifying at the bottom of the ladle, avoiding nozzle blockage and ensuring continuous pouring. It also provides thermal insulation, minimizing heat loss during the pouring process and maintaining a stable temperature. It reduces direct impact of the molten steel on the nozzle, reducing wear and erosion, and extending its service life. It also reduces inclusions and bubbles in the molten steel, improving its purity and quality.

[0003] Currently, chromium filling sand is one of the more commonly used ladle filling sands, with good drainage effects and moderate costs. Traditional chromium drainage sand is made from chromium ore sand, quartz sand, and carbon additives. Carbon additives play an important role in improving the thermal conductivity, lubricity, resistance to slag erosion, and mechanical strength of ladle filling sand. However, the addition of carbon additives not only causes carbonization of molten steel, but may also chemically react with components in certain steel grades, affecting the performance of the steel. Therefore, carbon-containing filling sand cannot be used in the production of ultra-low carbon steel, low carbon steel, non-oriented silicon steel, oriented silicon steel, high-alloy stainless steel, titanium-stabilized stainless steel, high-purity ferritic stainless steel, special-purpose steel, and other steel grades. In addition, carbon additives may oxidize to generate gas at high temperatures, leading to nozzle blockage.

[0004] For this purpose, this application is filed. Summary of the Invention

[0005] In order to solve the above deficiencies in the prior art, the present invention proposes a carbon-free ladle filling sand and a preparation process thereof.

[0006] The technical solution of the present invention is achieved as follows:

[0007] In one aspect, the present invention provides a process for preparing carbon-free ladle filling sand, comprising the following steps:

[0008] S1. Accurately weigh chromium ore, quartz sand, fused magnesia-chrome sand, high-alumina balls, and alumina-coated zircon sand respectively;

[0009] S2. First, chromium ore and fused magnesia-chrome sand are put into a mixing device. After stirring for a period of time, quartz sand and high-alumina balls are added. After continuing to stir for a period of time, alumina-coated zircon sand is added. The mixture is stirred until uniformly mixed. Finally, stirring and heating are performed until the moisture content of the material does not exceed 0.2%;

[0010] S3, measurement and packaging;

[0011] in:

[0012] The mass percentages of the components in S1 are: chromium ore sand 30%-57%, quartz sand 8%-15%, fused magnesia-chrome sand 15%-30%, high-alumina balls 5%-15%, and alumina-coated zircon sand 8%-12%;

[0013] The weight percentage of Gr2O3 in the chromium ore is at least 46%;

[0014] The weight percentage of SiO2 in the quartz sand is ≥98wt%;

[0015] The weight percentage of MgO in the fused magnesia-chrome sand is 60%-80%, the weight percentage of Gr2O3 is 15%-40%, the weight percentage of MgO+Gr2O3 is ≥95%, the weight percentage of Fe2O3 is <0.5wt%, and the weight percentage of C is ≤0.1wt%;

[0016] The high-alumina ball is a high-alumina ball with an alumina content of 95% and / or 99%, wherein the weight percentage of Fe2O3 is less than 0.5wt% and the weight percentage of C is less than 0.1wt%;

[0017] The ZrO2 in zircon sand has high refractoriness, high specific gravity, low thermal expansion coefficient, and good corrosion resistance. However, it decomposes slightly at high temperatures and easily reacts with CaO, FeO, and other substances in the ladle to form low-melting-point silicates, leading to excessive sintering between particles and blocking drainage channels. Coating it with alumina can not only optimize its high-temperature sintering properties, thereby improving the reliability of the filling sand and the quality of the molten steel, but also reduce the amount of zircon sand added and reduce production costs. It should be noted that:

[0018] (1) Strictly control the moisture content of the filling sand to not exceed 0.2%. If it exceeds 0.2%, after it is added to the ladle nozzle, the high temperature of the water vapor generated will react with SiO2 to form a silica gel product, causing the filling sand to stick together and affecting the automatic pouring of molten steel.

[0019] (2) The mixing order of the materials in S2 cannot be adjusted. If the order of addition is adjusted or the materials are directly mixed and stirred and then dried to a specified moisture content, the performance of the product obtained by direct mixing and stirring is far inferior to that of the product obtained by the above preparation process, provided that the composition is completely consistent. Obviously, the performance of carbon-free ladle filling sand depends not only on its specific composition but also on its preparation process.

[0020] Compared with the existing technology, the present invention optimizes the raw material composition and ratio of ladle filling sand, and adopts zircon sand coated with alumina. The raw materials work synergistically to finally obtain a carbon-free ladle filling sand with performance close to that of traditional carbon-containing ladle filling sand, without significantly increasing the cost, having a simple preparation process, easy operation, scalability, and the ability to meet the smelting requirements of special steel grades such as low carbon steel, ultra-low carbon steel, and high-purity steel.

[0021] Furthermore, the weight percentage of MgO in the fused magnesia-chrome sand of the present invention is 70%-80%, the weight percentage of Gr2O3 is 15%-25%, and the weight percentage of Fe2O3 is less than 0.2wt%.

[0022] Furthermore, the weight percentage of MgO in the fused magnesia-chrome sand is 75%-80%, the weight percentage of Gr2O3 is 15%-20%, and the weight percentage of Fe2O3 is less than 0.1wt%.

[0023] The fused magnesia-chrome sand containing the above-mentioned components has high magnesium and low chromium, and its preparation cost is close to that of traditional chromium ore sand, so it will not cause a significant increase in cost. Moreover, the high content of MgO makes the fused magnesia-chrome sand have good fluidity and corrosion resistance, and the low content of Gr2O3 can balance the corrosion resistance and addition cost of the fused magnesia-chrome sand. The fused magnesia-chrome sand partially replaces the chromium ore sand and is used as an aggregate together with the chromium ore sand. Compared with the ladle filling sand using a single chromium ore sand as an aggregate, it has higher refractory properties, slag corrosion resistance, sintering performance and pouring performance, and can also extend the service life. Further, in S1, the mesh sizes of chromium ore sand, quartz sand, fused magnesia-chrome sand, high-alumina balls, and alumina-coated zircon sand are all 20-70 meshes, respectively.

[0024] Specifically, in chromium ore sand, the gradation ratio of each particle size is: 50wt% for 20-40 mesh, 30wt% for 40-60 mesh, and 20wt% for 60-70 mesh; in quartz sand, the gradation ratio of each particle size is: 30wt% for 20-40 mesh, 40wt% for 40-60 mesh, and 30w% for 60-70 mesh; in fused magnesia-chrome sand, the gradation ratio of each particle size is: 40wt% for 20-40 mesh, 40wt% for 40-60 mesh, and 20wt% for 60-70 mesh; in high-alumina balls, the gradation ratio of each particle size is: 20wt% for 20-40 mesh, 50wt% for 40-60 mesh, and 30wt% for 60-70 mesh; and in alumina-coated zircon sand, the gradation ratio of each particle size is: 60wt% for 40-60 mesh, and 40wt% for 60-70 mesh.

[0025] In the present invention, chromium ore sand is mainly used to provide good fluidity, support and reactivity; quartz sand is mainly used to increase the melting point and thermal stability of the filling sand and improve fluidity; fused magnesia-chrome sand is mainly used to enhance high-temperature strength and corrosion resistance; high-alumina balls are mainly used to improve refractoriness and sintering characteristics; and alumina-coated zircon sand serves as the high-temperature stable skeleton of the entire filling sand. It prevents sintering and thermal shock failure through its ultra-high melting point and low thermal expansion, protects the purity of molten steel through chemical inertness, and ensures rapid pouring by controlling the addition ratio. Each material is matched according to the above-mentioned grading requirements: coarse particles (20-40 mesh, including 20 mesh and excluding 40 mesh) can ensure that the filling sand can be quickly spread and cover the bottom of the ladle, medium particles (40-60 mesh, including 40 mesh and 60 mesh) fill the gaps between the coarse particles to improve the density, and fine particles (60-70 mesh, excluding 60 mesh and including 70 mesh) provide a larger specific surface area and accelerate the reaction speed. Then, the materials are compounded according to the mass percentage specified in the present invention. The obtained filling sand does not collapse during use, and there is a certain looseness between the particles. The fluidity, filling density, reaction speed and anti-sintering performance of the ladle are maximized and balanced. Whether in the preparation of the filling sand or in its use, no obvious particle segregation will be caused, the sintered layer will not be too thick, and the particles are tightly matched and the gaps are extremely small, which can effectively prevent the penetration of molten steel and improve the automatic pouring rate of the ladle.

[0026] Furthermore, the fused magnesia-chrome sand is prepared according to the following operation: natural magnesite and natural chromite are used as the main raw materials, the natural magnesite and chromite are mixed according to the target MgO / Gr2O3 ratio, and 0.5%-1% of the total mass of the natural magnesite and natural chromite by aluminum powder is added as an auxiliary material, and it is prepared by electric arc furnace smelting in a weak oxidizing atmosphere.

[0027] The electric arc furnace smelting process is mature and stable, suitable for large-scale production. In a weakly oxidizing atmosphere, the synergistic effect of aluminum powder reduction and the weakly oxidizing atmosphere can cause Fe2O3 and C in the raw materials to leave the raw materials relatively completely, avoiding residual residues in the product and adverse effects on the performance of the filling sand.

[0028] In this embodiment, preferably, the natural magnesite contains MgO ≥ 47%, SiO2 ≤ 0.4%, CaO ≤ 0.7%, and calcination ≤ 2%. The fused magnesia-chrome sand used in the present invention uses natural magnesite that meets the above-mentioned composition and performance requirements as raw material. Compared with traditional high-refractory fused magnesia-chrome sand, its requirements for natural magnesite are relatively lower. Therefore, from the raw material level, the preparation cost is lower than that of traditional fused magnesia-chrome sand. When compared with the electric arc furnace smelting method, the cost of the fused magnesia-chrome sand used in the present invention is basically the same as that of high-grade chromium ore.

[0029] In this embodiment, the natural chromite preferably contains the following components, by mass percentage: Gr2O3 25%-32%, Al2O3 24%-28%, SiO2 7%-10%, Fe2O3 12%-15%, CaO 0.6%-1%, and MgO 18%-21%. The fused magnesia-chrome sand used in the present invention is produced using the aforementioned low-grade chromite as raw material, contributing to efficient resource utilization and reducing reliance on high-grade chromite. Furthermore, the production process is relatively environmentally friendly, reducing waste emissions and aligning with the development trend of green metallurgy.

[0030] In this embodiment, preferably, the arc furnace temperature during smelting is 2150-2300°C, the oxygen flow rate is 1.5-2.5m 3 / ton of main raw materials, the smelting time is not less than 2h, and after the smelting is completed, it is cooled and then crushed, screened and other post-processing is carried out. The present invention has been repeatedly tested and confirmed that when the temperature of the electric arc furnace is 2150℃, the smelting is 3h, and the amount of aluminum powder added is 0.5%, the weight percentage of MgO in the fused magnesia-chrome sand is 60%-70%, the weight percentage of Gr2O3 is 25%-40%, and the weight percentage of Fe2O3 is less than 0.4wt% (product 1); when the temperature of the electric arc furnace is 2250℃, the smelting is 5h, and the amount of aluminum powder added is 0.7%, the weight percentage of MgO in the fused magnesia-chrome sand is less than 0.4wt% (product 1). The weight percentage of MgO is 70%-80%, the weight percentage of Gr2O3 is 15%-25%, and the weight percentage of Fe2O3 is less than 0.2wt% (product 2); when the arc furnace temperature is 2300°C, the smelting is 2h, and the amount of aluminum powder added is 0.85%, the weight percentage of MgO in the fused magnesia-chrome sand is 75%-80%, the weight percentage of Gr2O3 is 15%-20%, and the weight percentage of Fe2O3 is less than 0.1wt% (product 3). The above three products are all suitable for use as the capacitor magnesia-chrome sand described in the present invention, but there are differences in their use effects. Product 3 is better than Product 2, and Product 2 is better than Product 1.

[0031] Furthermore, the coating amount of alumina is 3wt%-8wt% of the pure zircon sand, and the alumina is γ-Al2O3.

[0032] In the present invention, the mesh number of the alumina-coated zircon sand is between 40 and 70 meshes. Within this particle size range, when the alumina coating amount is 3 wt% to 8 wt% of the pure zircon sand, it can form a complete and dense coating layer on the surface of the pure zircon sand. This neither causes sintering of the coating layer itself nor reduces fluidity, but can effectively inhibit the high-temperature decomposition of the zircon sand and reduce the amount of zircon sand added, thereby achieving a balance between cost and performance.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) In the prior art, some chromium ore sands contain impurities such as FeO and NaO, which not only seriously affect the refractoriness, sintering performance and self-opening rate of the filling sand. The chromium ore sand used in the present invention is chemically stable, and is combined with fused magnesia-chrome sand with specific parameter characteristics in a specific ratio to form a composite aggregate, which has better sintering resistance than single chromium ore sand. It is speculated that: on the one hand, the high content of oxides in the fused magnesia-chrome sand has high thermal conductivity, and can form products such as forsterite and chromium silicate with SiO2 in chromium ore sand or other components at high temperature, which can improve the thermal conductivity and lubricity of the filling sand; on the other hand, high-aluminum balls, fused magnesia-chrome sand and chromium ore sand diffuse into each other, and Al 3+ Entering the surface layer of fused magnesia chrome sand, Mg 2+ 、Al 3 + Entering the surface of chromium ore, Mg 2+ 、Gr 3+ Then it enters the surface of the high-alumina ball and eventually forms a complex phase spinel layer Mg(Gr,Al)2O4 with high activity and many lattice vacancy defects, which can absorb impurities in the steel slag, thus helping to improve the resistance to slag permeability. Moreover, the continuous diffusion reaction enhances the bonding strength between the materials, improves the sintering resistance and mechanical strength of the material; the high-alumina ball, fused magnesia-chrome sand and chromium ore sand work synergistically, and the slag erosion resistance, thermal shock stability and mechanical strength of the filling sand are significantly enhanced, and the overall performance of the filling sand is effectively improved.

[0035] (2) The surface of zircon sand is coated with γ-Al2O3 of appropriate thickness. When the filling sand is put into the smelting furnace, γ-Al2O3 forms high-temperature resistant α-Al2O3 at high temperature and is accompanied by volume shrinkage and densification. The resulting coating layer not only inhibits the high-temperature decomposition of zircon sand, effectively improves the reliability of the filling sand and the quality of molten steel, but also reduces the amount of zircon sand added, achieving a balance between performance and cost.

[0036] (3) The particle size of each raw material is reasonably matched, and the gaps between the particles are small, which neither produces obvious particle segregation nor has good resistance to molten steel penetration. The erosion and melting loss effect is obvious during the entire refining process, which can ensure a good automatic pouring rate of the ladle.

[0037] (4) The key raw materials in the present invention are obtained in-house, and the methods of making them are all conventional technical means in the field, which will not significantly increase the cost of the raw materials. The chemical component content of the raw materials obtained in-house is determined and the chemical properties are stable, thus ensuring that the preparation process is repeatable and the product quality is stable.

[0038] On the other hand, the present invention also provides a carbon-free ladle filling sand, which is prepared by the above-mentioned preparation process and is tested by an arc combustion infrared sulfur-carbon analyzer, and no carbon is detected.

[0039] Furthermore, the carbon-free ladle filling sand has a refractoriness of 1700-1800° C., a self-casting rate of ≥99%, and a corrosion rate of ≤8%.

[0040] Furthermore, the bulk density of the carbon-free ladle filling sand is 1.8-2.1 g / cm 3 , tap density is 2.1-2.2g / cm 3 .

[0041] The carbon-free ladle filling sand proposed in the present invention has various properties similar to those of carbon-containing ladle filling sand, and the cost is not significantly increased. It has high refractoriness and self-casting rate, good fluidity, and strong resistance to molten steel penetration. It also avoids the problem of carbon-containing filling sand introducing carbon impurities into molten steel and contaminating the molten steel during use. Its preparation process is simple, easy to operate, and scalable. It can meet the smelting requirements of special steel grades such as low-carbon steel, ultra-low-carbon steel, and high-purity steel, and is very beneficial for maintaining the purity of special steel grades. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0043] Figure 1 This is a schematic diagram of the use of the carbon-free ladle filling sand proposed by the present invention;

[0044] Figure 2 A photo of the carbon-free ladle filling sand proposed in the present invention;

[0045] Figure 3 for Figure 2 Launch photos of the products shown. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0047] In the following embodiments and comparative examples, the preparation method of fused magnesia-chrome sand is as follows: natural magnesite (purchased from a domestic magnesite mine, wherein: MgO ≥ 47%, SiO2 ≤ 0.4%, CaO ≤ 0.7%, calcination vector ≤ 2%) and natural chromite (purchased from a domestic chromite mine, wherein: the natural chromite contains the following components by mass percentage: Gr2O3 25%-32%, Al2O3 24%-28%, SiO2 7%-10%, Fe2O3 12%-15%, CaO 0.6%-1%, MgO The product is prepared by an electric arc furnace smelting method, wherein the electric arc furnace temperature is 2150-2300℃, the smelting time is 2-5h, and 2m3 of aluminum powder is added into each ton of the main raw materials. 3 The oxygen in the final fused magnesia-chrome sand is 60%-80% by weight of MgO, 15%-40% by weight of Gr2O3, 95% by weight of MgO+Gr2O3, <0.5wt% by weight of Fe2O3, and 0.1wt% by weight of C. Specifically, there are three types of fused magnesia-chrome sand: the first type has a MgO weight percentage of 60%-70%, a Gr2O3 weight percentage of 25%-40%, a Fe2O3 weight percentage of <0.4wt%, and a sintering factor of ≤1%. The preparation conditions are: an arc furnace temperature of 2150°C, smelting for 3 hours, and an aluminum powder addition amount of 0.5%; the second type has a MgO weight percentage of 70%-80%, a Gr2O3 weight percentage of 15%-25%, a Fe2O3 weight percentage of 10%-15%, and a C weight percentage of 0.1wt%. The weight percentage of MgO is 75%-80%, the weight percentage of Gr2O3 is 15%-20%, the weight percentage of Fe2O3 is less than 0.1wt%, the sintering vector is ≤1%, the preparation conditions are: the arc furnace temperature is 2250℃, the smelting is 5h, and the amount of aluminum powder added is 0.7%; the third type, the weight percentage of MgO is 75%-80%, the weight percentage of Gr2O3 is 15%-20%, the weight percentage of Fe2O3 is less than 0.1wt%, the sintering vector is ≤1%, the preparation conditions are: the arc furnace temperature is 2300℃, the smelting is 2h, and the amount of aluminum powder added is 0.85%.

[0048] In the following examples and comparative examples, alumina-coated zircon sand was prepared by a sol-gel method, wherein the specific operations are as follows: (1) pure zircon sand was first soaked in dilute hydrochloric acid for at least 1 h, then rinsed with deionized water until neutral and dried, and then calcined at 520°C for 2 h to enhance the activity of surface hydroxyl -OH groups; (2) aluminum isopropoxide was dissolved in anhydrous ethanol at a ratio of 1 g:10 ml, stirred in a 65°C water bath until completely dissolved, and then deionized water was slowly added dropwise with continuous stirring to form a sol, and the molar ratio of deionized water to Al was 1:1. The mass ratio of zircon sand to alumina is 3:1; (3) the zircon sand obtained in step (1) is first added to the sol of step (2) according to the mass ratio of zircon sand to alumina of 100:5, and then 0.8wt% polyvinyl alcohol is added as a dispersant and ultrasonicated for at least 30min with an ultrasonic power of 500W, and finally the temperature is slowly raised to 80°C and stirred until the sol loses fluidity; (4) the product of the previous step is first vacuum dried at 75°C, then ground and sieved, and finally sintered at 750°C for 2h to finally obtain zircon sand with a coating layer of γ-phase alumina.

[0049] Of course, the above-mentioned fused magnesia-chrome sand and alumina-coated zircon sand can also be purchased commercially, as long as their relevant technical parameters are within the range defined by the present invention.

[0050] In the following examples and comparative examples, the raw material chromium ore sand in the carbon-free ladle filling sand was commercially available, and its chemical composition was: Gr2O3 46%-46.5%, Al2O3 13-16%, SiO2 1-1.8%, Fe2O3 25.5%-28%, CaO 0-1%, and MgO 9%-11%.

[0051] In the following embodiments and comparative examples, the quartz sand is quartz sand with a weight percentage of SiO2 ≥ 98wt%; the high-alumina balls are high-alumina balls with an alumina content of 95%, in which the weight percentage of Fe2O3 is <0.5wt% and the weight percentage of C is ≤0.1wt%; the remaining raw materials not specifically mentioned are all purchased from commercial manufacturers, and the manufacturer is not limited, as long as the quality meets the relevant requirements.

[0052] The equipment or operations used in the following examples and comparative examples are all conventional equipment and operations in this field. The technical means not explicitly described are all conventional technical means in this field. The following statistics on automatic pouring rate are based on the carbon-free ladle filling sand shown in each example and comparative example, which was respectively applied to the smelting of a steel plant in Tianjin. The ladle capacity was 150T, the steel grade was ultra-low carbon steel, the temperature of the molten steel entering the ladle was 1610-1650℃, the waiting time for steel was more than 60min, the refining furnace type was RH, the nozzle inner diameter was 72mm, and the number of furnaces counted was 1000.

[0053] Example 1

[0054] A carbon-free ladle filling sand is prepared according to the following steps:

[0055] S1. Accurately weigh chromium ore, quartz sand, fused magnesia-chrome sand, high-alumina balls, and alumina-coated zircon sand according to the following mass percentages: chromium ore 45%, quartz sand 10%, fused magnesia-chrome sand 25%, high-alumina balls 10%, and alumina-coated zircon sand 10%;

[0056] Among them, each raw material is 20-70 mesh, and the gradation requirements are: in chromium ore sand, the gradation ratio of each particle size is: 20-40 mesh 50wt%, 40-60 mesh 30wt%, 60-70 mesh 20wt%; in quartz sand, the gradation ratio of each particle size is: 20-40 mesh 30wt%, 40-60 mesh 40wt%, 60-70 mesh 30w%; in fused magnesia chrome sand, the gradation ratio of each particle size is: The proportions are: 20-40 mesh 40wt%, 40-60 mesh 40wt%, 60-70 mesh 20wt%; in high-alumina balls, the gradation ratios of each particle size are: 20-40 mesh 20wt%, 40-60 mesh 50wt%, 60-70 mesh 30wt%; in alumina-coated zircon sand, the gradation ratios of each particle size are: 40-60 mesh 60wt%, 60-70 mesh 40wt%;

[0057] The fused magnesia-chrome sand comprises 75% to 80% by weight of MgO, 15% to 20% by weight of Gr2O3, <0.1% by weight of Fe2O3, ≤0.1% by weight of C, and ≥95% by weight of MgO + Gr2O3.

[0058] S2. First, chromium ore and fused magnesia-chrome sand are put into a mixing device. After stirring for a period of time, quartz sand and high-alumina balls are added. After continuing to stir for a period of time, alumina-coated zircon sand is added. The mixture is stirred until uniformly mixed. Finally, stirring and heating are performed until the moisture content of the material does not exceed 0.2%;

[0059] S3. Measurement and packaging.

[0060] Example 2

[0061] Compared with Example 1, the composition of the fused magnesia-chrome sand in S1 is changed. The weight percentage of MgO in the fused magnesia-chrome sand is 70%-80%, the weight percentage of Gr2O3 is 15%-25%, the weight percentage of Fe2O3 is less than 0.2wt%, the weight percentage of C is ≤0.1wt%, and the weight percentage of MgO+Gr2O3 is ≥95%. The rest are consistent with Example 1.

[0062] Example 3

[0063] Compared with Example 1, the composition of the fused magnesia-chrome sand in S1 is changed. The weight percentage of MgO in the fused magnesia-chrome sand is 60%-70%, the weight percentage of Gr2O3 is 25%-40%, the weight percentage of Fe2O3 is less than 0.4wt%, the weight percentage of C is ≤0.1wt%, and the weight percentage of MgO+Gr2O3 is ≥95%. The rest are consistent with Example 1.

[0064] Example 4

[0065] Compared with Example 1, the mass percentages of the raw materials in S1 are adjusted, specifically: 50% chromium ore sand, 15% quartz sand, 15% fused magnesia-chrome sand, 8% high-alumina balls, and 12% alumina-coated zircon sand. The rest remain the same as in Example 1.

[0066] Example 5

[0067] Compared with Example 1, the mass percentages of the raw materials in S1 are adjusted, specifically: 30% chromium ore sand, 13% quartz sand, 30% fused magnesia-chrome sand, 15% high-alumina balls, and 12% alumina-coated zircon sand. The rest remain the same as in Example 1.

[0068] Example 6

[0069] Compared with Example 1, the mass percentages of the raw materials in S1 are adjusted, specifically: 57% chromium ore sand, 8% quartz sand, 20% fused magnesia-chrome sand, 5% high-alumina balls, and 10% alumina-coated zircon sand. The rest remain the same as in Example 1.

[0070] Example 7

[0071] Compared with Example 1, the mass percentages of the raw materials in S1 are adjusted, specifically: 50% chromium ore sand, 12% quartz sand, 18% fused magnesia-chrome sand, 12% high-alumina balls, and 8% alumina-coated zircon sand. The rest remain the same as in Example 1.

[0072] Comparative Example 1

[0073] Compared with Example 1, the fused magnesia-chrome sand in S1 is adjusted to chromium ore sand of equal mass, that is, the aggregate of the filling sand is chromium ore sand, and the rest is consistent with Example 1.

[0074] Comparative Example 2

[0075] Compared with Example 1, the chromium ore sand in S1 is adjusted to fused magnesia-chrome sand of equal mass, that is, the aggregate of the filling sand is fused magnesia-chrome sand, and the rest is consistent with Example 1.

[0076] Comparative Example 3

[0077] Compared with Example 1, the alumina-coated zircon sand in S1 was adjusted to zircon sand without any coating, and the added masses of other raw materials remained the same as in Example 1.

[0078] Comparative Example 4

[0079] Compared with Example 1, the gradation requirements in S1 are changed. Specifically, in chromium ore sand, the gradation ratio of each particle size is: 20-40 mesh 40wt%, 40-60 mesh 30wt%, 60-70 mesh 30wt%; in quartz sand, the gradation ratio of each particle size is: 20-40 mesh 20wt%, 40-60 mesh 40wt%, 60-70 mesh 40w%; in fused magnesia chrome sand, the gradation ratio of each particle size is: 2 0-40 mesh 30wt%, 40-60 mesh 40wt%, 60-70 mesh 30wt%; in the high alumina balls, the gradation ratio of each particle size is: 20-40 mesh 10wt%, 40-60 mesh 50wt%, 60-70 mesh 40wt%; in the alumina-coated zircon sand, the gradation ratio of each particle size is: 40-60 mesh 50wt%, 60-70 mesh 50wt%; the rest are consistent with Example 1.

[0080] Comparative Example 5

[0081] Compared with Example 1, the gradation requirements in S1 are changed. Specifically, in chromium ore sand, the gradation ratio of each particle size is: 20-40 mesh 60wt%, 40-60 mesh 30wt%, 60-70 mesh 10wt%; in quartz sand, the gradation ratio of each particle size is: 20-40 mesh 40wt%, 40-60 mesh 40wt%, 60-70 mesh 20w%; in fused magnesia chrome sand, the gradation ratio of each particle size is: 2 0-40 mesh 50wt%, 40-60 mesh 40wt%, 60-70 mesh 10wt%; in high alumina balls, the gradation ratio of each particle size is: 20-40 mesh 30wt%, 40-60 mesh 50wt%, 60-70 mesh 20wt%; in alumina-coated zircon sand, the gradation ratio of each particle size is: 40-60 mesh 70wt%, 60-70 mesh 30wt%; the rest are consistent with Example 1.

[0082] Comparative Example 6

[0083] Compared with Example 1, the mass percentages of chromium ore and fused magnesia-chrome sand in S1 are adjusted, specifically: 25% chromium ore, 10% quartz sand, 45% fused magnesia-chrome sand, 10% high-alumina balls, and 10% alumina-coated zircon sand. The rest remain the same as in Example 1.

[0084] Comparative Example 7

[0085] Compared with Example 1, the mass percentages of chromium ore and fused magnesia-chrome sand in S1 are adjusted, specifically: 60% chromium ore, 10% quartz sand, 10% fused magnesia-chrome sand, 10% high-alumina balls, and 10% alumina-coated zircon sand. The rest remain the same as in Example 1.

[0086] Comparative Example 8

[0087] Compared with Example 1, the mass percentages of chromium ore and alumina-coated zircon sand in S1 are adjusted, specifically: 40% chromium ore, 10% quartz sand, 25% fused magnesia-chrome sand, 10% high-alumina balls, and 15% alumina-coated zircon sand. The rest remain the same as in Example 1.

[0088] Comparative Example 9

[0089] Compared with Example 1, the mass percentages of chromium ore and alumina-coated zircon sand in S1 are adjusted, specifically: 50% chromium ore, 10% quartz sand, 25% fused magnesia-chrome sand, 10% high-alumina balls, and 5% alumina-coated zircon sand. The rest remain the same as in Example 1.

[0090] The specific composition of the carbon-free ladle filling sand disclosed in Examples 1 to 12 and Comparative Examples 1 to 9, as well as the automatic pouring rate during specific applications, whether there is steel infiltration, and the steel infiltration rate (steel infiltration rate = number of steel infiltration furnaces / total number of furnaces * 100%) are shown in Table 1.

[0091] Table 1

[0092]

[0093]

[0094] From Table 1 we can see that:

[0095] (1) From the comparison of the test results of Examples 1 to 7, it can be seen that the carbon-free ladle filling sand prepared by the present invention has an automatic pouring rate of more than 99%, and no steel seepage occurs.

[0096] (2) Comparison of the test results of Comparative Examples 1, 2, 6, and 7 with those of Example 1 shows that if the aggregate in the carbon-free ladle filling sand is entirely chromite sand or entirely fused magnesia-chrome sand, the refractoriness and automatic pouring rate of the product are not high, while mixing the two as aggregate significantly improves the refractoriness and automatic pouring rate. However, when the two are mixed, such as when there is less chromite and more fused magnesia-chrome sand or when there is more chromite and less fused magnesia-chrome sand, the degree of improvement in the refractoriness and automatic pouring rate of the product is low. Only when they are mixed according to the addition ratio specified in the present invention can the refractoriness and automatic pouring rate of the resulting product be significantly improved.

[0097] (3) Comparison of the test results in Comparative Example 3 and Example 1 demonstrates that, in the present invention, the alumina coating of the zircon sand significantly improves the refractoriness, impermeability, and automatic pouring rate of the fill sand. Clearly, alumina coating of the zircon sand is essential; its addition significantly improves the overall performance of the fill sand, ensuring smooth ladle pouring and safe operation.

[0098] Comparing the test results of Comparative Examples 8 and 9 with those of Example 1 shows that the amount of alumina zircon sand added significantly impacts the filler sand. Too little addition yields minimal improvement in filler sand performance, while too much leads to a significant cost increase. In the present invention, the preferred amount of alumina zircon sand added is 8%-12%.

[0099] (4) Comparison of the test results of Comparative Examples 4 and 5 with those of Example 1 shows that, when grading, if the particles in the carbon-free ladle filling sand are too small or too large, the refractoriness and the automatic pouring rate will decrease. According to the grading limited by the present invention, the obtained product has good air permeability, which can ensure the smooth discharge of gas during molten steel pouring; has moderate sinterability, can be sintered in time at high temperature, and forms a stable drainage channel; has a uniform strength distribution, and the particles are tightly bonded, which can resist the scouring of molten steel, and ultimately has a higher refractoriness and a higher automatic pouring rate.

[0100] To sum up: the carbon-free ladle filling sand proposed in the present invention has various properties similar to those of carbon-containing ladle filling sand, and the cost is not significantly increased. It is easy to operate and can be scaled up, and can meet the smelting requirements of special steel grades such as low carbon steel, ultra-low carbon steel, and high-purity steel.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A process for preparing carbon-free ladle filling sand, characterized in that: The steps are as follows: S1. Accurately weigh chromium ore, quartz sand, fused magnesia-chrome sand, high-alumina balls, and alumina-coated zircon sand respectively; S2. First, chromium ore and fused magnesia-chrome sand are put into a mixing device. After stirring for a period of time, quartz sand and high-alumina balls are added. After continuing to stir for a period of time, alumina-coated zircon sand is added. The mixture is stirred until uniformly mixed. Finally, stirring and heating are performed until the moisture content of the material does not exceed 0.2%; S3, measurement and packaging; in: The mass percentages of the components in S1 are: chromium ore sand 30%-57%, quartz sand 8%-15%, fused magnesia-chrome sand 15%-30%, high-alumina balls 5%-15%, and alumina-coated zircon sand 8%-12%; The weight percentage of Gr2O3 in the chromium ore is at least 46%; The weight percentage of SiO2 in the quartz sand is ≥98wt%; The weight percentage of MgO in the fused magnesia-chrome sand is 60%-80%, the weight percentage of Gr2O3 is 15%-40%, the weight percentage of MgO+Gr2O3 is ≥95%, the weight percentage of Fe2O3 is <0.5wt%, and the weight percentage of C is ≤0.1wt%; The high-alumina ball has an alumina content of 95% and / or 99%, wherein the weight percentage of Fe2O3 is less than 0.5wt% and the weight percentage of C is less than or equal to 0.1wt%.

2. The preparation process according to claim 1, characterized in that The weight percentage of MgO in the fused magnesia-chrome sand is 70%-80%, the weight percentage of Gr2O3 is 15%-25%, and the weight percentage of Fe2O3 is less than 0.2wt%.

3. The preparation process according to claim 2, characterized in that The weight percentage of MgO in the fused magnesia-chrome sand is 75%-80%, the weight percentage of Gr2O3 is 15%-20%, and the weight percentage of Fe2O3 is less than 0.1wt%.

4. The preparation process according to claim 1, characterized in that In S1, the mesh sizes of chromium ore sand, quartz sand, fused magnesia-chrome sand, high-alumina balls, and alumina-coated zircon sand are all 20-70 meshes.

5. The preparation process according to claim 4, characterized in that: In the chromium ore, the gradation ratio of each particle size is: 20-40 mesh 50wt%, 40-60 mesh 30wt%, 60-70 mesh 20wt%; In the quartz sand, the gradation ratio of each particle size is: 20-40 mesh 30wt%, 40-60 mesh 40wt%, 60-70 mesh 30w%; In the fused magnesia-chrome sand, the gradation ratio of each particle size is: 20-40 mesh 40wt%, 40-60 mesh 40wt%, 60-70 mesh 20wt%; In the high-alumina balls, the gradation ratio of each particle size is: 20-40 mesh 20wt%, 40-60 mesh 50wt%, 60-70 mesh 30wt%; In the alumina-coated zircon sand, the gradation ratio of each particle size is: 40-60 mesh 60wt%, 60-70 mesh 40wt%.

6. The preparation process according to claim 1, characterized in that The fused magnesia-chrome sand is prepared by the following operation: natural magnesite and natural chromite are used as main raw materials, the natural magnesite and chromite are mixed according to the target MgO / Gr2O3 ratio, and 0.5%-1% of the total weight of the natural magnesite and natural chromite by aluminum powder is added as auxiliary material, and the fused magnesia-chrome sand is prepared by electric arc furnace smelting in a weak oxidizing atmosphere; Preferably, the natural magnesite contains MgO ≥ 47%, SiO2 ≤ 0.4%, CaO ≤ 0.7%, and calcination vector ≤ 2%; Preferably, the natural chromite contains the following components in mass percentage: Gr2O3 25%-32%, Al2O3 24%-28%, SiO2 7%-10%, Fe2O3 12%-15%, CaO 0.6%-1%, MgO 18%-21%; Preferably, the arc furnace temperature is 2150-2300°C, the melting time is not less than 2 hours, and the oxygen flow rate is 1.5-2.5m 3 / ton of main raw materials.

7. The preparation process according to claim 1, characterized in that The coating amount of aluminum oxide is 3wt%-8wt% of the pure zircon sand, and the aluminum oxide is γ-Al2O3.

8. A carbon-free ladle filling sand, characterized in that: It is prepared by the preparation process according to any one of claims 1 to 7.

9. The carbon-free ladle filling sand according to claim 8, characterized in that: Its refractoriness is 1700-1800℃, self-casting rate is ≥99%, and erosion rate is ≤8%.

10. The carbon-free ladle filling sand according to claim 8, characterized in that: Bulk density 1.8-2.1g / cm 3 , tap density is 2.1-2.2g / cm 3 .

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