Method for manufacturing mold powder

Abstract

To provide a mold powder which contains glass powder as a silica raw material and can maintain good operability and steel quality without generating sintered masses or slag bears.SOLUTION: A mold powder contains, as main raw materials, a CaO-SiO2-based raw material and a silica raw material. The silica raw material contains glass powder, a content of the glass powder is 2.0 to 40.0 mass% and a particle size of the glass powder is less than 140 μm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a mold powder suitable for continuous casting of steel.

Background Art

[0002] In the continuous casting of steel, molten steel stored in a tundish is poured into a mold through a submerged nozzle, cooled and solidified, and a solidified shell (solidification shell) is continuously drawn downward from the mold using rolls to continuously produce slabs, blooms, billets, and other various shaped cast pieces. A powdery or granular mold powder is introduced onto the surface of the molten steel in the mold. The mold powder is melted by heat received from the molten steel (the molten mold powder is sometimes referred to as "powder slag", but hereinafter will be referred to as "molten slag"), forms a molten slag layer to cover the surface of the molten steel, and the molten slag flows into the space between the solidification shell and the mold, and is discharged and consumed in parallel with the solidification shell. The main roles of the mold powder from introduction to consumption are shown below. (1) Heat insulation of the molten steel surface (2) Prevention of oxidation of the molten steel surface (3) Absorption of non-metallic inclusions floating from the molten steel and purification of the molten steel (4) Ensuring lubrication between the solidification shell and the mold (5) Controlling the heat flux from the solidification shell to the mold

[0003] The mold powder is generally composed of a CaO-SiO2 base material raw material, a silica raw material, a flux raw material, and / or other raw materials. When introduced onto the surface of the molten steel in the mold, the components and raw materials are designed and adjusted to melt by heat received from the molten steel. If the selection, combination, content, etc. of the raw materials are inappropriate, the melting properties deteriorate, and sintered lumps and coarse lumps in a semi-molten state called slag bear may occur at the contact portion with the mold wall.

[0004] Sintered ingots and slag bears can cause significant deterioration in operability by leading to insufficient molten slag layer, obstruction of molten slag flow between the solidified shell and mold, insufficient heat retention due to slag exposure, abnormal flames due to gas leakage, and breakouts. Furthermore, they can cause inclusion defects and surface cracks in the cast slabs, negatively impacting steel quality. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-114110 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The CaO-SiO2 base material for mold powder is generally composed of minerals with relatively high melting points, such as tricalcium silicate, dicalcium silicate, and wollastonite. On the other hand, Patent Document 1 discloses glass powder as an example of a silica raw material for mold powder. Since glass powder has a relatively low melting temperature of about 800°C, it acts as a melting accelerator for mold powder. However, if there is a large difference in melting temperatures between the raw materials, the proportion of the so-called semi-molten layer, in which the liquid phase and unmolten raw material are mixed, increases, which can lead to the generation of sintered lumps and slag bears. However, Patent Document 1 does not disclose an appropriate method for incorporating glass powder.

[0007] This disclosure is made in view of the above circumstances, and its purpose is to provide a mold powder that contains glass powder as a silica raw material, does not generate sintered lumps or slag bears, and can maintain good operability and steel quality. [Means for solving the problem]

[0008] One aspect of this disclosure is, The main raw materials include CaO-SiO2 base material and silica raw material. The aforementioned silica raw material contains glass powder, The glass powder content is 2.0 to 40.0% by mass. The present invention relates to a mold powder characterized in that the particle size of the glass powder is less than 140 μm.

[0009] By using the mold powder according to one embodiment of this disclosure in continuous casting of steel, it is possible to maintain good operability and steel quality because sintered lumps and slag bears are not generated while containing glass powder as a silica raw material. [Modes for carrying out the invention]

[0010] Preferred embodiments of this disclosure will be described in detail below. It should be noted that these embodiments are not intended to unduly limit the scope of the claims of this disclosure, and not all configurations described in these embodiments are necessarily essential as solutions of this disclosure.

[0011] The mold powder of this embodiment contains a CaO-SiO2 base material and a silica material as the main raw materials. The silica material contains glass powder, with a glass powder content of 2.0 to 40.0% by mass and a glass powder particle size of less than 140 μm. By using the mold powder of this embodiment in continuous casting of steel, sintered lumps and slag bears are not generated while containing glass powder as the silica material, thus maintaining good operability and steel quality.

[0012] <Main raw materials> The CaO-SiO2 base material is not particularly limited as long as it is commonly used in mold powders, and examples include Portland cement, limestone, quicklime, synthetic calcium silicate, wollastonite, rinse slag, blast furnace slag, and dicalcium silicate. The CaO-SiO2 base material supplies the main components, CaO and SiO2. Silica raw materials other than glass powder are not particularly limited as long as they are commonly used in mold powders, and examples include silica sand, feldspar, silica, diatomaceous earth, perlite, fly ash, silica fume, and silica flower. The silica raw material adjusts the mass ratio (CaO / SiO2) of the mold powder.

[0013] <glass powder> The glass powder content is 2.0 to 40.0% by mass, more preferably 2.5 to 39.0% by mass. If the glass powder content is less than 2.0% by mass, the melting-promoting effect will not be obtained, and melting delay may occur, which is undesirable. On the other hand, if it exceeds 40.0% by mass, melting will be excessively promoted, and sintered lumps and slag bears may be generated, which is also undesirable.

[0014] The particle size of the glass powder is less than 140 μm, and more preferably less than 110 μm. If the particle size of the glass powder is 140 μm or larger, the localized pre-melting ratio will increase, which may worsen the melting properties and is undesirable. In this specification, a particle size of less than x μm means that the particles have passed through a sieve with a mesh size of x μm, and a particle size of x μm or more means that the particles have not passed through a sieve with a mesh size of x μm.

[0015] The form of the glass powder is not particularly limited as long as it is generally used for mold powder, and examples include powder, extruded granules, hollow spray granules, and agitated granulation. Powdered mold powder is obtained by mixing raw materials such as CaO-SiO2 base material and silica material in a mixer. Granular mold powder is further molded by adding binders as appropriate and using methods such as spray granulation, extrusion molding, or agitated granulation.

[0016] There are no particular restrictions on the type of glass powder, but recycled glass powder is preferred from an environmental protection standpoint, and waste glass from photovoltaic panels (PV) (hereinafter referred to as "photovoltaic panel glass") is particularly preferred. This reduces the consumption of fossil fuels and minerals, as well as the emission of CO2 and industrial waste. Photovoltaic panel glass is separated from PV and used as raw material after undergoing processes such as sorting, crushing, and classification. Photovoltaic panel glass is broadly classified into soda glass and borosilicate glass, both of which can be used as silica raw materials for mold powder. Soda glass, for example, contains SiO2: 68-75% by mass, Al2O3: 0-5% by mass, CaO: 5-15% by mass, MgO: 1-8% by mass, and Na2O: 11-18% by mass. Borosilicate glass, for example, contains SiO2: 30-50% by mass, Al2O3: 5-15% by mass, CaO: 5-15% by mass, MgO: 0-8% by mass, B2O3: 5-15% by mass, and SrO: 5-15% by mass.

[0017] <Auxiliary raw materials> The auxiliary raw materials other than the main raw materials are not particularly limited as long as they are commonly used in mold powder, and examples include flux raw materials, carbon raw materials, magnesia, alumina, etc. Examples of flux raw materials include fluoride salts such as sodium fluoride, lithium fluoride, cryolite, fluorite (calcium fluoride), and magnesium fluoride, carbonates such as sodium carbonate, lithium carbonate, potassium carbonate, manganese carbonate, aluminum carbonate, magnesium carbonate, and strontium carbonate, and boron raw materials such as boric acid, borax, and colemanite, which adjust the softening point, viscosity, and solidification temperature of the mold powder. Examples of carbon raw materials include coke, graphite, and carbon black, which adjust the melting rate of the mold powder. In this embodiment, the mold powder may contain a heat-generating material (reducing agent) such as a metal or alloy such as Si, Al, or Ca-Si to improve heat retention. When these heat-generating materials are included, an oxidizing agent may also be included to promote the reaction. [Examples]

[0018] The embodiments of this disclosure will be described in detail below.

[0019] <Sample Preparation> A CaO-SiO2 base material raw material, a silica raw material (excluding glass powder), glass powder, and auxiliary raw materials were mixed with a mixer to obtain a mold powder. Solar panel glass was used as the glass powder. 1.5 g of the mold powder was weighed and formed into a cylindrical briquette with an outer diameter of 10 mm using a briquette molding machine to obtain a sample. The raw material formulations of the mold powder are shown in Tables 1 and 2. [Table 1] [Table 2]

[0020] In Examples 1 to 3 and Comparative Examples 1 to 4 (Table 1), soda glass solar panel glass was used as the glass powder. Examples 1 to 3 are examples of the present invention. In Comparative Examples 1 and 2, the soda glass content is less than the range of the present invention, and in Comparative Example 3, the soda glass content is more than the range of the present invention. The particle size of the soda glass in Examples 1 to 3 and Comparative Examples 1 to 3 is less than 140 μm. Comparative Example 4 had the same raw material formulation as Example 2 except that the particle size of the soda glass was 140 μm or more. Note that the glass powder with a particle size less than 140 μm passed through a sieve with a mesh size of 140 μm, and the glass powder with a particle size of 140 μm or more did not pass through a sieve with a mesh size of 140 μm (the same applies hereinafter). The raw materials were adjusted so that the chemical compositions of Examples 1 to 3 and Comparative Examples 1 to 4 were the same.

[0021] In Examples 4 to 6 and Comparative Examples 5 to 8 (Table 2), borosilicate glass solar panel glass was used as the glass powder. Examples 4 to 6 are examples of the present invention. In Comparative Examples 5 and 6, the borosilicate glass content is less than the range of the present invention, and in Comparative Example 7, the borosilicate glass content is more than the range of the present invention. The particle size of the borosilicate glass in Examples 4 to 6 and Comparative Examples 4 to 7 is less than 140 μm. Comparative Example 8 had the same raw material formulation as Example 5 except that the particle size of the borosilicate glass was 140 μm or more. The raw materials were adjusted so that the chemical compositions of Examples 4 to 6 and Comparative Examples 5 to 8 were the same.

[0022] <Measurement and evaluation methods> The following measurements and evaluations were performed on the obtained samples.

[0023] A sample was inserted into a furnace capable of observing the melting process, such as a ring-shaped furnace using a high-purity silicon carbide heating element, and the melting process was observed while the temperature was increased at 5°C / min. The temperature at which the cylindrical shape clearly collapsed and deformed due to melting was defined as the softening point, and the temperature at which it became completely droplet-like was defined as the melting temperature. The melting temperature interval was calculated from the difference between these two temperatures.

[0024] The shorter the melting temperature range, that is, the closer the softening point and melting temperature, the faster the mold powder softens and melts, which is preferable as it reduces the generation of sintered lumps and slag bears. Therefore, the melting properties of the mold powder were evaluated as follows: excellent (◎) when the melting temperature range is 20°C or below, good (〇) when it is between 21 and 30°C, and poor (×) when it is 31°C or above.

[0025] <Measurement and evaluation results> The measurement and evaluation results are shown in Tables 1 and 2.

[0026] Table 1 shows that Examples 1-3 had short melting temperature intervals and good meltability. On the other hand, Comparative Examples 1-2, which had a low soda glass content, had high melting temperatures and long melting temperature intervals, and their meltability was poor (×). Comparative Example 3, which had a high soda glass content, had an excessively low softening point and a long melting temperature interval, and its meltability was poor (×). Comparative Example 4, which had a large soda glass particle size, also had a long melting temperature interval and its meltability was poor (×).

[0027] Examples 4-6 and Comparative Examples 5-8 (Table 2) used borosilicate glass for solar panel glass, but showed similar trends to those when soda glass was used (Table 1). Specifically, Examples 4-6 had a short melting temperature range and showed good meltability. On the other hand, Comparative Examples 5-6, which had a low borosilicate glass content, had high softening points and melting temperatures, and a long melting temperature range, resulting in poor meltability (×). Comparative Example 7, which had a high borosilicate glass content, had an excessively low softening point and a long melting temperature range, resulting in poor meltability (×). Comparative Example 4, which had a large borosilicate glass particle size, also had a long melting temperature range and poor meltability (×).

[0028] In Comparative Examples 1-2 and 5-6, where the glass powder content is less than 2.0% by mass, the melting-promoting effect of the glass powder is not obtained, and delayed melting is likely to occur. In Comparative Examples 3 and 7, where the glass powder content exceeds 40.0% by mass, melting is excessively promoted, and the generation of sintered lumps and slag bears is likely to occur. Therefore, a glass powder content of 2.0-40.0% by mass is preferred, and 2.5-39.0% by mass is considered more preferred. Furthermore, in Comparative Examples 4 and 8, where the glass powder particle size is 140 μm or larger, the localized pre-melting ratio is large, and deterioration of melting properties is likely to occur. Therefore, a glass powder particle size of less than 140 μm is preferred, and less than 110 μm is considered more preferred.

[0029] Although this embodiment has been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novelty and effects of this disclosure. Therefore, all such modifications are included within the scope of this disclosure. For example, any term that appears at least once in the specification together with a broader or synonymous term may be replaced with that different term anywhere in the specification. Furthermore, the configuration and operation of the manufacturing apparatus, etc., of this embodiment are not limited to those described in this embodiment and are capable of various modifications.

Claims

[Claim 1] CaO-SiO ２ The process includes mixing the base material and the silica material in a mixer. The silica raw material includes glass powder made from waste glass from solar power generation panels. The glass powder content is 2.0 to 40.0% by mass. A method for producing mold powder, characterized in that the particle size of the glass powder is less than 140 μm.

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