Machine pressure casting composite structure converter tapping hole brick and preparation method thereof

Abstract

The invention discloses a machine pressure casting composite structure converter tapping hole brick and a preparation method thereof, and belongs to the field of refractory materials. The tapping hole brick is of a radial composite structure and comprises a mechanical pressing forming outer layer and a casting forming inner layer from outside to inside. The outer layer is made of a magnesia carbon material, 97 fused magnesite is used as aggregate, and the carbon content is 10-18%; the inner layer is made of a carbon-free aluminum magnesium material, 99 macrocrystalline fused magnesite is used as an aggregate, and the carbon content is less than or equal to 0.5%. The preparation method comprises the following steps: firstly, carrying out mechanical pressing and curing on an outer-layer green body, carrying out interface pretreatment, pouring an inner-layer material by taking the outer-layer green body as a mold, and carrying out curing and drying to obtain a finished product. Through innovative compounding of a material system and a forming process, the outer layer has excellent thermal shock resistance, and the inner layer has extremely high density, high-temperature strength and erosion resistance, so that the problems of carbon oxidation and molten steel recarburization are fundamentally avoided, the service life of the tapping hole is remarkably prolonged, and the tapping hole is particularly suitable for clean steel smelting.

Description

Technical Field

[0001] This invention belongs to the field of refractory materials, and more specifically, relates to a converter tapping brick and its preparation method, particularly a converter tapping brick with a composite structure of a machine-pressed carbon-bonded outer layer and a carbon-free castable inner layer. Background Technology

[0002] In converter steelmaking, the taphole is subjected to rapid temperature changes, oxidizing atmospheres, intense scouring by molten steel, and chemical erosion by slag. Magnesia-carbon bricks, due to their excellent slag resistance and thermal shock stability, have long been the mainstream material for converter tapholes. However, traditional magnesia-carbon taphole bricks have an inherent contradiction: the graphite (typically with a carbon content of 15%-20%) introduced to ensure thermal shock stability is easily oxidized during blowing and tapping, leading to the formation of a loose decarburized layer on the working surface, reduced structural strength, and subsequent rapid erosion by the molten steel flow. This is the primary reason limiting their lifespan. Furthermore, high carbon content also leads to increased carbon content in the molten steel, failing to meet the smelting requirements for clean steel and ultra-low carbon steel.

[0003] Castable refractories, as materials formed through flow filling, hydration bonding, and drying sintering, possess unique advantages such as uniform molding structure, extremely dense microstructure after sintering, and high high-temperature strength. However, their thermal shock resistance is generally inferior to that of carbon-containing magnesia-carbon bricks. Currently, there are no successful precedents for combining machine-pressed magnesia-carbon bricks with carbon-free castable refractories through a specific process for manufacturing converter tapholes. The technical challenge lies in solving the problem of firmly bonding two materials with different materials, different bonding systems, and different thermal expansion characteristics, avoiding interfacial delamination due to incompatibility under high-temperature use. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention is proposed.

[0005] The purpose of this invention is to overcome the shortcomings of existing converter tapping bricks, such as limited service life due to carbon oxidation, inability to simultaneously achieve excellent thermal shock resistance and extremely high corrosion resistance, and inability to avoid carbonization of molten steel. The invention provides a novel structural design, a strong bond, and a significantly extended service life, which is especially suitable for high-quality steel smelting. It also includes a method for preparing the same pressurized cast composite converter tapping brick.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a machine-pressed cast composite structure converter tapping brick, which is a hollow ring structure, comprising an integrally formed machine-pressed outer layer and a cast inner layer from the outside to the inside; wherein, the machine-pressed outer layer is a magnesia-carbon material with a carbon content of 10%~18%; and the cast inner layer is a carbon-free alumina-magnesia material with a carbon content ≤0.5%.

[0007] Furthermore, in the radial direction of the steel outlet brick, the thickness of the machine-pressed outer layer accounts for 60% to 85%; and the thickness of the cast-molded inner layer accounts for 15% to 40%.

[0008] Furthermore, the machine-pressed outer layer is composed of an outer layer composite material and a molding binder, wherein the composition and mass fraction of each raw material in the outer layer composite material are as follows:

[0009] 45-65 parts of 97% fused magnesia particles;

[0010] 10-20 parts of 97% fused magnesia fine powder;

[0011] 8-18 parts of flake graphite;

[0012] 1-4 parts of aluminum-tungsten alloy;

[0013] 1-3 parts of metallic silicon powder;

[0014] Boron carbide 0.5 to 2 parts.

[0015] Furthermore, the cast inner layer is composed of an inner layer castable mixture, wherein the composition and mass fraction of each raw material in the inner layer castable mixture are as follows:

[0016] 40-60 parts of 99% large-crystal fused magnesia particles;

[0017] 10-20 parts of tabular corundum particles;

[0018] 5-15 parts of α-Al₂O₃ micro powder;

[0019] 8-15 parts of 99% large-crystal fused magnesia fine powder;

[0020] 3-8 parts of pure calcium aluminate cement;

[0021] 1-3 parts of silica micro powder;

[0022] Boron nitride powder 0.5~2 parts.

[0023] Furthermore, the molding binder is liquid phenolic resin, and its addition amount is 3% to 5% of the total mass of the outer composite material.

[0024] Furthermore, the particle size of the 97 fused magnesia particles (outer layer) includes a four-stage mixture of fine powders with particle sizes of 3~1mm, 1~0.5mm, 0.5~0.1mm and <0.1mm.

[0025] Furthermore, the particle size of the 99 large crystalline fused magnesia particles (inner layer) includes a three-stage mixture of 3~1mm, 1~0.5mm, and 0.5~0mm.

[0026] Furthermore, the fixed carbon content of the flake graphite is ≥98%, and the particle size is 100 mesh; the B4C content in the boron carbide is ≥95%.

[0027] A method for preparing the above-mentioned machine-pressed composite structure converter tapping brick is characterized by the following steps: first, a machine-pressed outer layer blank is prepared, and after curing, it is used as a mold skeleton to inject the mixed inner layer casting material into it, which is then vibrated and molded. Finally, the finished product is obtained by curing, drying, and heat treatment in sequence.

[0028] Furthermore, the specific steps are as follows:

[0029] Step 1, outer layer mixing and molding: Weigh each raw material of the outer layer composite material according to the weight ratio, preheat to 30~40℃, add liquid phenolic resin, and mix in a mixer for 15~25 minutes; press the mixed mud into a ring-shaped outer layer blank under a pressure greater than 150MPa.

[0030] Step 2, outer layer curing: After the outer layer blank is air-dried under natural conditions for 8 to 12 hours, it is placed in a drying kiln and heated to 110°C at a heating rate of 5 to 10°C / hour and held for 12 to 24 hours. Then it is heated to 180 to 220°C at the same rate and held for 12 to 24 hours to complete the curing.

[0031] Step 3, Interface pretreatment: The inner surface of the cured outer layer blank is mechanically sandblasted or cut to form a rough bonding surface;

[0032] Step 4, Inner Layer Castable Preparation and Casting: Weigh each raw material of the inner layer castable according to the weight ratio, dry mix evenly, add an appropriate amount of water (usually 4.5%~6.5%), wet mix for 5~10 minutes until uniform; pour the mixed castable into the cavity of the pretreated outer layer blank, place it on a vibrating table and vibrate to compact it.

[0033] Step 5, Curing and Drying: After casting, cure for 24 to 48 hours at a temperature of 15~25℃ and humidity >90%; after demolding, place the composite green body in a drying kiln and slowly heat it to 110℃ at a heating rate not exceeding 10℃ / hour and hold it for no less than 24 hours, then raise it to 200~250℃ and hold it for 12~24 hours to ensure that the inner layer is fully dried and obtains initial strength;

[0034] Step 6, Processing and Inspection: After drying, the composite steel outlet bricks undergo necessary dimensional precision machining and surface cleaning. Once they pass inspection, they become finished products.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] 1. By combining the outer layer of machine-pressed magnesia-carbon bricks with the inner layer of carbon-free alumina-magnesia castable, the outer layer leverages the high thermal conductivity, low elastic modulus, and excellent thermal shock resistance of magnesia-carbon bricks to effectively absorb and buffer thermal and mechanical stresses within the converter. The inner layer utilizes high-purity, large-crystal fused magnesia aggregates and the carbon-free, highly dense structure of the castable after sintering, fundamentally eliminating carbon oxidation problems and providing erosion resistance, scour resistance, and high-temperature strength far exceeding those of traditional pressed bricks. The synergy between the two results in a breakthrough improvement in service life.

[0037] 2. The inner layer of this invention is made of carbon-free material, which completely avoids the problem of carbon increase in molten steel caused by the presence of graphite, and is particularly suitable for smelting high-quality steels such as clean steel and ultra-low carbon steel.

[0038] 3. Through specific interface pretreatment (roughening) and composite drying process, a strong mechanical engagement and ceramic bond are ensured between the machine-pressed outer layer and the cast inner layer, resulting in high interface strength and preventing delamination or peeling during use.

[0039] 4. The inner layer material design of this invention realizes a "multi-level self-repair and reinforcement" mechanism, which is the core of achieving an ultra-long lifespan:

[0040] Level 1 Protection: Rapid Sealing of the Glass Phase. Silica micropowder and B2O3 (generated by the oxidation of boron carbide and boron nitride) in the inner layer material form a low-melting-point borate glass phase at high temperatures. This liquid phase can rapidly wet, spread, and migrate into the pores and microcracks of the working surface, achieving "physical sealing" and immediately blocking the intrusion of oxygen and molten slag.

[0041] Secondary strengthening: whisker bridging and structural enhancement. Simultaneously, under high temperature and the action of specific additives (such as Al and Si), aluminum borate whiskers and spinel phases are generated in situ within the system. These whiskers act as "bridging" links between particles and across cracks, consuming crack propagation energy and significantly improving the material's toughness, high-temperature strength, and thermal shock resistance, thus achieving "structural repair."

[0042] Level 3 reinforcement: In-situ hard phase enhances wear resistance. High-hardness, high-melting-point phases such as tungsten borides and oxides generated by additives such as aluminum-tungsten alloys at high temperatures are dispersed in the matrix, forming an "in-situ hard phase," which greatly improves the inner working surface's resistance to molten steel erosion and wear.

[0043] 5. This invention ensures the long-term stability of the composite structure through a dual interface bonding mechanism of "mechanical interlocking and ceramic bonding". The roughened interface of the machine-pressed outer layer provides a strong "mechanical anchoring" foundation for the casting of the inner layer; while under the heat treatment during drying and first use, the components at the interface of the inner and outer layers diffuse into each other, generating in situ "ceramic bonding phases" such as magnesium aluminum spinel, realizing the transition from physical bonding to chemical bonding, making the interface strength even higher than that of the material bulk, and completely eliminating the risk of delamination.

[0044] 6. The preparation process of this invention combines the advantages of "green manufacturing" and "low cost". The core of the entire process is "machine pressing-casting-low temperature heat treatment", which eliminates the need for expensive hot pressing sintering or ultra-high temperature treatment, significantly reducing energy consumption. At the same time, the outer layer uses 97 electrofused magnesia, achieving optimized cost control while ensuring performance, which is in line with the green and environmentally friendly industrial development direction. Detailed Implementation

[0045] The following detailed description of exemplary embodiments of the invention, while described in sufficient detail to enable those skilled in the art to practice the invention, should be understood that other embodiments may be implemented and various changes may be made to the invention without departing from its spirit and scope. The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and does not limit the description of the features and characteristics of the invention, in order to suggest the best mode for carrying out the invention and sufficient to enable those skilled in the art to practice it. Therefore, the scope of the invention is defined only by the appended claims.

[0046] Example 1

[0047] This embodiment describes a machine-pressed composite structure converter taphole brick with an outer layer to inner layer thickness ratio of 70:30. The specific preparation steps are as follows:

[0048] Step 1, Outer Layer Mixing and Molding: Weigh the outer layer raw materials (using 97 fused magnesia) according to the proportions in Example 1 in Table 1, preheat to 35°C, add 4 parts of liquid phenolic resin, and mix in a high-speed mixer for 18 minutes. Press the mixed mud into a ring-shaped outer layer blank under a pressure of 180 MPa.

[0049] Step 2, outer layer curing: After the outer layer blank is naturally air-dried for 10 hours, it is placed in a drying kiln and heated to 110℃ at 8℃ / hour and held for 16 hours, and then heated to 200℃ at 8℃ / hour and held for 16 hours.

[0050] Step 3, Interface pretreatment: Use a sandblasting machine to uniformly sandblast the inner surface of the cured outer layer blank.

[0051] Step 4, Inner Layer Casting: Weigh all raw materials of the inner layer castable (except water, and use 99 large crystal fused magnesia as aggregate) according to the proportions in Example 1 in Table 1, dry mix for 3 minutes, then add 5.5 parts water, and wet mix for another 8 minutes. Pour the mixed castable into the pretreated outer layer cavity and vibrate it on a vibrating table for 3 minutes until fully compacted.

[0052] Step 5, Curing and Drying: Curing at 20℃ and >95% humidity for 36 hours. After careful demolding, the composite preform is heated to 110℃ at 8℃ / hour and held for 36 hours, then heated to 220℃ at 5℃ / hour and held for 18 hours.

[0053] Step 6, Processing: After drying, the steel outlet brick is ground on the outer circle and the end face is machined. After cleaning the surface, the finished product is obtained.

[0054] Example 2

[0055] This embodiment of a machine-pressed cast composite structure converter tapping brick has an outer layer to inner layer thickness ratio of 75:25. Its composition and mass fraction are as shown in Table 1 of Example 2 (outer layer 97 sand, inner layer 99 large crystal sand), and the preparation method is the same as in Example 1.

[0056] Example 3

[0057] This embodiment of a machine-pressed cast composite structure converter tapping brick has an outer layer to inner layer thickness ratio of 65:35. Its composition and mass fraction are as shown in Table 1 of Example 3 (outer layer 97 sand, inner layer 99 large crystal sand), and the preparation method is the same as in Example 1.

[0058] Comparative Example

[0059] A traditional one-time machine-pressed monolithic magnesia-carbon brick (using 97 electrofused magnesia) was used as a comparative example, and its composition ratio is shown in Table 1.

[0060] Table 1 is a list of the components of the low-carbon composite converter taphole bricks described in various embodiments of the present invention.

[0061]

[0062] Table 2 shows the performance parameters of the steel taphole bricks obtained from Examples 1-3 and the comparative example.

[0063]

[0064] The data in Table 2 show that the composite taphole bricks prepared in Examples 1-3 of this invention have excellent bulk density and room temperature / high temperature strength due to the use of 99% large-crystal fused magnesia as the main aggregate in the inner layer, and extremely low apparent porosity. While maintaining excellent thermal shock resistance, the slag erosion resistance is greatly improved, which is ultimately reflected in the field service life, which is more than 60% longer than that of traditional products.

Claims

1. A machine-pressed cast composite structure converter tap hole brick, which is a hollow ring structure, characterized in that, The tapping brick comprises an integrally combined machine-pressed outer layer and a cast inner layer from outside to inside in the radial direction; The machine-pressed outer layer is a magnesia-carbon material with a carbon content of 10-18% by mass percentage; The cast inner layer is a carbon-free alumina-magnesia material with a carbon content of ≤0.5% by mass percentage.

2. The machine-poured composite structure converter tap brick of claim 1, wherein: In the radial thickness of the tapping brick, the thickness ratio of the machine-pressed outer layer is 60-85%, and the thickness ratio of the cast inner layer is 15-40%.

3. Machine pressed cast composite structure converter tap hole brick according to claim 1 or 2, characterized in that: The machine-pressed outer layer is composed of an outer layer composite material and liquid phenolic resin as a forming binder, wherein the composition and mass fraction of each raw material of the outer layer composite material are as follows: 97 fused magnesia particles: 45-65 parts; 97 fused magnesia fine powder: 10-20 parts; Flaky graphite: 8-18 parts; Aluminum-tungsten alloy: 1-4 parts; Metallic silicon powder: 1-3 parts; Boron carbide: 0.5-2 parts.

4. The machine-poured composite structure converter tap brick of claim 1, wherein: The cast inner layer is composed of an inner layer castable mixture, wherein the composition and mass fraction of each raw material of the inner layer castable mixture are as follows: 99 large-crystal fused magnesia particles: 40-60 parts; Tabular corundum particles: 10-20 parts; α-Al2O3 micro powder: 5-15 parts; 99 large-crystal fused magnesia fine powder: 8-15 parts; Pure calcium aluminate cement: 3-8 parts; Silicon dioxide micro powder: 1-3 parts; Boron nitride powder: 0.5-2 parts.

5. The machine-poured composite structure converter tap brick of claim 3, wherein: The addition amount of the liquid phenolic resin is 3-5% of the total mass of the outer layer composite material.

6. The machine-poured composite structure converter tap brick of claim 4, wherein: The particle size of the 99 large-crystal fused magnesia particles includes three levels of 3-1 mm, 1-0.5 mm, and 0.5-0 mm.

7. The method of making a machine pressed cast composite structure converter tap hole brick according to any one of claims 1-6, characterized in that, The method comprises the following steps: Step a: after mixing the outer layer composite material with the binder, a ring-shaped machine-pressed outer layer blank is obtained by machine pressing; Step b: the machine-pressed outer layer blank is subjected to solidification treatment; Step c: the mixed inner layer castable is injected into the cavity of the solidified machine-pressed outer layer blank, and vibration forming is performed to obtain a composite blank; Step d: the composite blank is sequentially subjected to curing and drying treatment to obtain a finished product.

8. The machine-poured composite structure converter tap brick of claim 7, wherein: Before step c, an interface pretreatment step is further included, that is, the inner surface of the solidified machine-pressed outer layer blank is subjected to mechanical sand blasting or cutting processing to form a rough bonding surface.

9. The machine-poured composite structure converter tap brick of claim 7, wherein: The solidification treatment in step b includes heat preservation of the outer layer blank at a temperature of 180-220°C; and the drying treatment in step d includes heat preservation of the composite blank at a temperature of 200-250°C.

10. The machine-poured composite structure converter tap brick of claim 7, wherein: The inner layer castable in step c is wet mixed by adding water with a mass percentage of 4.5-6.5%; and the curing treatment in step d is performed under the conditions of a temperature of 15-25°C and a humidity of >90% for 24-48 hours.

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