A double-layered intermediate package cover agent pellet

Abstract

This invention relates to the field of tundish covering agent technology, and specifically discloses a double-layer tundish covering agent pellet, comprising the following components by mass percentage: limestone 30%–37%, dolomite 18%–28%, lightly calcined magnesia powder 10%–15%, expanded perlite 22%–30%, expanded graphite 1%–4%, binder 1%–3%, and magnesium chloride 2%–4%. The purpose of this invention is to solve the problem of potential quality hazards in molten steel caused by the melting of rice husks in traditional double-layer heat-insulating covering agents during steelmaking.

Description

Technical Field

[0001] This application relates to the field of intermediate package covering agent technology, and specifically discloses a double-layer intermediate package covering agent pellet. Background Technology

[0002] With the continuous improvement of steel production technology, the requirements for auxiliary materials used in steelmaking are also becoming increasingly stringent. The initial function of tundish covering agents was simply heat preservation to prevent excessive temperature drop in molten steel during transportation or pouring. However, with the increasing demands for steel quality, molten steel heat preservation covering agents have gradually developed into multifunctional products. Specific functions include heat preservation, preventing secondary oxidation of molten steel by the atmosphere, adsorbing floating inclusions in the steel, and avoiding steel contamination by not reacting with the molten steel.

[0003] Alkaline covering agents have more advantages than acidic and neutral covering agents, but their heat preservation effect is poor. Therefore, most steel plants use double-layer heat preservation covering agents, which have a double-layer structure. The bottom layer is generally alkaline slag, which forms a liquid slag layer to adsorb impurities when used. The top layer is generally carbonized rice husk to enhance heat preservation.

[0004] However, since the tundish covering agent is a consumable, as production progresses, the carbonized rice husks will continuously melt and enter the lower layer, reducing the alkalinity of the lower layer of alkaline slag and potentially increasing the carbon content of the molten steel. In addition, conventional tundish covering agents are in bulk and are added manually in whole bags, which requires a lot of manpower and poses safety risks. Furthermore, the burning of woven bags produces a large amount of smoke and dust, causing environmental pollution, and the bulk fine powder material is removed by dust collectors, resulting in material waste. Therefore, in view of these issues, the inventors have provided a double-layer tundish covering agent pellet to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of potential quality hazards in molten steel caused by the melting of rice husks in traditional double-layer insulation coverings during steelmaking.

[0006] To achieve the above objectives, the basic embodiment of the present invention provides a double-layer intermediate liner covering agent pellet, comprising the following components by mass percentage: limestone 30%–37%, dolomite 18%–28%, lightly calcined magnesia powder 10%–15%, expanded perlite 22%–30%, expanded graphite 1%–4%, binder 1%–3%, and magnesium chloride 2%–4%.

[0007] The principle and effect of this basic scheme are as follows:

[0008] 1. Compared with the prior art, the double-layer tundish covering agent pellets in this invention add limestone, and the main component of limestone is CaO, which can decompose at high temperature, promote the decomposition and melting of the pellets, improve the uniformity of the slag surface, and at the same time provide a lower molten layer with better adsorption of inclusions in the molten steel, while removing S and P in the steel and reducing the secondary oxidation of the molten steel.

[0009] 2. Compared with the prior art, the double-layer tundish covering agent pellets of the present invention add lightly calcined dolomite, whose main components are CaO and MgO. The use of lightly calcined dolomite further increases the CaO content in the covering agent pellets. The hydration degree of MgO is less than that of CaO, which can better solve the problem of wet pelletizing of raw materials. At the same time, it adjusts the viscosity of the slag surface to increase the uniformity of the slag surface, and adds sintered magnesium powder to provide the overall basicity of the pellets and enhance the ability of the molten layer to adsorb inclusions in the molten steel.

[0010] 3. Compared with the prior art, the addition of expanded perlite in this invention enables the covering and formation of a molten layer, which improves the problem of easy crusting of alkaline covering agents. Moreover, expanded perlite, as a high-efficiency thermal insulation material, has low thermal conductivity and density, and can float to the surface to form a transitional thermal insulation layer.

[0011] 4. Compared with the prior art, the present invention adds expandable graphite, which reduces the thermal conductivity of the insulation layer when heated and expands, thereby improving the overall insulation performance of the covering agent.

[0012] Furthermore, the limestone has a particle size range of 0.149–3 mm, the dolomite has a particle size range of 0.074 mm–5 mm, the lightly calcined magnesia powder has a particle size range of <0.074 mm, the expanded perlite has a particle size range of 1–3 mm, the expanded graphite has a particle size range of <0.074 mm, the binder has a particle size range of <0.044 mm, and the magnesium chloride has a particle size range of <0.074 mm.

[0013] Furthermore, the limestone contains, by mass, ≥50% CaO, ≤2% H2O, and ≤5% SiO2.

[0014] Furthermore, the lightly calcined dolomite contains, by mass, ≥40% Ca, ≥26% MgO, and ≤5% H2O.

[0015] Furthermore, the sintered magnesium powder contains, by mass, ≥90% MgO, ≤4% SiO2, ≤1.6% CaO, and ≤0.5% H2O.

[0016] Furthermore, the expanded perlite contains, by mass, 68%-73% SiO2, 11%-15% Al2O3, ≤1% H2O, and has a thermal conductivity of 0.045 ≤ 0.055.

[0017] Furthermore, the expandable graphite contains ≥99% C by mass and has an expansion ratio of 200–250 mm / g.

[0018] Furthermore, the binder is a commonly available starch-cellulose compound, and the magnesium chloride is a white powder containing ≥92% MgCl2 by mass.

[0019] Furthermore, the double-layer intermediate baggage covering agent pellets contain ≤2% moisture by weight. The moisture content in the double-layer intermediate baggage covering agent pellets is controlled by the magnesium chloride hydration reaction. The magnesium chloride hydration reaction releases heat and removes moisture, thereby achieving the purpose of controlling the moisture content.

[0020] Furthermore, the alkalinity range of the double-layer tundish covering agent pellets is 1 to 1.2, and the mass percentage of CaO+MgO in the double-layer tundish covering agent pellets is greater than 40%, and the mass percentage of SiO2 is ≥20%. Detailed Implementation

[0021] Example 1:

[0022] A double-layer intermediate liner pellet comprises the following components by mass percentage: limestone 33%, dolomite 21%, lightly calcined magnesia powder 12%, expanded perlite 28%, expanded graphite 1%, binder 2%, and magnesium chloride 3%.

[0023] The particle size ranges as follows: limestone (0.149–3 mm), dolomite (0.074 mm–5 mm), lightly calcined magnesia (<0.074 mm), expanded perlite (1–3 mm), expanded graphite (<0.074 mm), binder (<0.044 mm), and magnesium chloride (<0.074 mm).

[0024] Limestone contains ≥50% CaO, ≤2% H2O, and ≤5% SiO2 by weight; lightly calcined dolomite contains ≥40% CaO, ≥26% MgO, and ≤5% H2O by weight; expanded perlite contains 68%-73% SiO2, 11-15% Al2O3, and ≤1% H2O by weight, with a thermal conductivity of 0.045 ≤ 0.055; expandable graphite contains ≥99% C by weight, with an expansion ratio of 200-250 mm / g; the binder is starch and cellulose; magnesium chloride is a white powder containing ≥92% MgCl2 by weight.

[0025] The pellets of the double-layer tundish covering agent are ellipsoidal in size (φ40×40mm). The moisture content of the double-layer tundish covering agent pellets is ≤2% by mass. The moisture content in the double-layer tundish covering agent pellets is controlled by the magnesium chloride hydration reaction. The magnesium chloride hydration reaction releases a large amount of heat, which is used to control the moisture content. The alkalinity range of the final double-layer tundish covering agent pellets is 1 to 1.2. The mass percentage of CaO+MgO in the double-layer tundish covering agent pellets is greater than 40%, and the mass percentage of SiO2 is ≥20%.

[0026] In this scheme, limestone is obtained through mining and its main component is CaO. It can decompose at a high temperature of 850℃, which promotes the decomposition and melting of pellets, improves the uniformity of the slag surface, and provides alkalinity so that the lower molten layer can better adsorb inclusions in the molten steel, remove S and P from the steel, and reduce the secondary oxidation of the molten steel.

[0027] Lightly calcined dolomite mainly consists of CaO and MgO. Using lightly calcined dolomite further increases the CaO content in the covering agent pellets. Since MgO has a lower degree of hydration than CaO, it can better solve the problem of wet pelletizing of raw materials. At the same time, it can adjust the viscosity of the slag surface to increase the uniformity of the slag surface.

[0028] Sintered magnesium powder, whose main component is MgO, can provide basicity and enhance the ability of the molten layer to adsorb inclusions in molten steel.

[0029] Expanded perlite's main components are SiO2 and Al2O3. SiO2, along with CaO and MgO from limestone and lightly calcined dolomite, forms a SiO2-CaO-MgO slag system. This slag system falls within the range of liquid slag components present at the tundish steelmaking temperature. The raw material ratio is designed based on this slag system, allowing the covering agent to form a molten layer and mitigating the problem of easy crusting with alkaline covering agents. A small amount of Al2O3 can adsorb inclusions and float to the surface, improving the slag's viscosity. Furthermore, expanded perlite, as a highly efficient thermal insulation material, has low thermal conductivity and density, allowing it to float to the surface and form a transitional insulation layer.

[0030] Expandable graphite is a product that undergoes acidification or electrochemical treatment and begins to expand significantly at around 120°C. Its expansion rate is temperature-dependent, expanding slowly at low temperatures and rapidly at high temperatures. At temperatures above 800°C, it can expand rapidly and instantaneously. During this thermal expansion, not only does its volume increase, but it also releases a large amount of gas, propelling the covering agent to quickly cover the molten steel surface. This creates numerous voids and pores in the insulation transition layer, forming a "blackbody" effect that significantly reduces the thermal conductivity of the insulation layer. The interaction between expanded perlite and expanded graphite improves the insulation capacity of the covering agent pellets. Simultaneously, introducing a small amount of carbon can prolong the melting time of the covering agent, thereby controlling the thickness of the molten layer and reducing the amount of covering agent pellets used, saving costs for steel mills.

[0031] The binder is produced by a manufacturer with comprehensive technology, providing initial strength to the pellets and preventing secondary breakage.

[0032] Magnesium chloride can release heat during hydration in the pelletizing stage, accelerating the evaporation of moisture from the pellets. Simultaneously, it combines with MgO in lightly calcined dolomite and sintered magnesia powder to form magnesite cement, increasing the later-stage strength of the pellets and preventing breakage when added to the silo. Furthermore, magnesium chloride can improve the melting point of the pellets, allowing them to decompose rapidly after being added to molten steel, quickly covering the surface of the molten steel and effectively reducing secondary oxidation. The content of each added component is shown in the table below:

[0033]

[0034] The physicochemical properties of the double-layer thermal insulation covering agent pellets are shown in the table below:

[0035]

[0036] The preparation method of the double-layer thermal insulation covering agent pellets adopts the currently mature cold pressing process: automatic batching—stirring—bulking—natural drying for 72 hours. Samples were taken and tested to determine the physicochemical properties of the double-layer thermal insulation covering agent pellets for application. Specific test data are shown in the table below.

[0037]

[0038] The test results were qualified, and the product was put into practical application in the steelmaking plant. The amount of tundish covering agent added per ton of steel was determined to be 1.1 kg / t (steel). The method of adding covering agent pellets is as follows: when the first ladle is poured, 200 kg is added to the ladle pouring hole and the two-strand pouring hole respectively. When each subsequent ladle is poured, 30-40 kg is added to the ladle pouring material and the two-strand pouring hole respectively.

[0039] Description of effects: Adding the coating in pellet form significantly reduces smoke and dust. The pellets melt rapidly, ensuring the molten steel temperature in the tundish remains above the target temperature during ladle pouring, meeting production requirements. Furthermore, compared to previous covering agents, where slag sometimes adhered to the tundish walls, making slag removal difficult, this situation has been significantly improved after using these covering agent pellets; the tundish walls are now virtually slag-free.

[0040] Example 2:

[0041] The only difference from Example 1 is that: limestone 32%, dolomite 20%, lightly calcined magnesia powder 13%, expanded perlite 28%, expanded graphite 2%, binder 2%, and magnesium chloride 3% were pelletized and tested. The test results are shown in the table below. The test results are qualified. It was added to the steel plant for practical application. The amount of tundish covering agent added per ton of steel was determined to be 1.13 kg / t (steel). The method of adding covering agent pellets is as follows: when the first ladle is poured, 200 kg is added to both the ladle pouring hole and the two-strand pouring hole. When each subsequent ladle is poured, 30-40 kg is added to both the ladle pouring hole and the two-strand pouring hole. The test results are shown in the table below.

[0042]

[0043]

[0044] Description of effects: Adding the coating in pellet form significantly reduces smoke and dust. The pellets melt rapidly, ensuring the molten steel temperature in the tundish remains above the target temperature during ladle pouring, meeting production requirements. Furthermore, compared to previous covering agents, where slag sometimes adhered to the tundish walls, making slag removal difficult, this situation has been significantly improved after using these covering agent pellets; the tundish walls are now virtually slag-free.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A double-layer intermediate packing covering agent pellet, characterized in that: The composition includes the following components by mass percentage: limestone 30%–37%, dolomite 18%–28%, lightly calcined magnesia powder 10%–15%, expanded perlite 22%–30%, expanded graphite 1%–4%, binder 1%–3%, and magnesium chloride 2%–4%.

2. The double-layer intermediate packing covering agent pellets according to claim 1, characterized in that, The limestone has a particle size range of 0.149–3 mm, the dolomite has a particle size range of 0.074 mm–5 mm, the lightly calcined magnesia powder has a particle size range of <0.074 mm, the expanded perlite has a particle size range of 1–3 mm, the expanded graphite has a particle size range of <0.074 mm, the binder has a particle size range of <0.044 mm, and the magnesium chloride has a particle size range of <0.074 mm.

3. The double-layer intermediate packing covering agent pellets according to claim 2, characterized in that, The limestone contains, by mass, ≥50% CaO, ≤2% H2O, and ≤5% SiO2.

4. The double-layer intermediate packing covering agent pellets according to claim 2, characterized in that, The lightly calcined dolomite contains, by mass, ≥40% Ca, ≥26% MgO, and ≤5% H2O.

5. A double-layer intermediate packing covering agent pellet according to claim 2, characterized in that, The lightly calcined dolomite contains, by mass, ≥40% Ca, ≥26% MgO, and ≤5% H2O.

6. The double-layer intermediate packing covering agent pellets according to claim 2, characterized in that, The expanded perlite contains 68%-73% SiO2, 11%-15% Al2O3, ≤1% H2O by mass, and has a thermal conductivity of 0.045 ≤ 0.

055.

7. The double-layer intermediate packing covering agent pellets according to claim 2, characterized in that, The expandable graphite contains ≥99% C by mass and has an expansion ratio of 200–250 mm / g.

8. A double-layer intermediate packing covering agent pellet according to claim 2, characterized in that, The binder is starch plus cellulose, and the magnesium chloride is a white powder containing ≥92% MgCl2 by mass.

9. A double-layer intermediate packing covering agent pellet according to claim 8, characterized in that, The pellets of the double-layer tundish covering agent are ellipsoidal in size of φ40×40mm. The moisture content of the double-layer tundish covering agent pellets is ≤2% by mass. The moisture content of the double-layer tundish covering agent pellets is controlled by magnesium chloride hydration reaction.

10. A double-layer intermediate packing covering agent pellet according to any one of claims 1 to 9, characterized in that, The alkalinity range of the double-layer tundish covering agent pellets is 1 to 1.2, and the mass percentage of CaO+MgO in the double-layer tundish covering agent pellets is greater than 40%, and the mass percentage of SiO2 is ≥20%.

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