A continuous casting production method of tinplate

Abstract

The application provides a continuous casting production method of tinplate, which comprises the steps of dynamic control of a pulling speed, linkage control of cooling, dynamic adjustment of an insertion depth of a submerged nozzle and dynamic argon blowing, wherein the pulling speed control is based on the maximum section steel flow, the target pulling speed is calculated reversely according to the actual section, and the steel flow of each section is constant; the cooling water flow is compensated in linkage with the increment of the pulling speed, and the bulging of the shell is inhibited; the insertion depth of the nozzle adopts a one-way increasing insertion mode from shallow to deep in multiple stages; and the argon blowing flow is adjusted in stages according to the fluctuation of the crystallizer liquid level. The application can reduce the nozzle clogging area by more than 50%, the standard rate of liquid level fluctuation is increased to 95%, the continuous casting castability and the surface quality of the casting blank are significantly improved, and the application is suitable for the efficient and stable continuous casting production of tinplate and other aluminum-containing steels.

Description

Technical Field

[0001] This invention relates to the field of continuous casting technology in iron and steel metallurgy, and specifically to a continuous casting production method for tinplate. Background Technology

[0002] Tinplate, also known as tin-plated sheet or tinplate, is a metal packaging material made by coating a layer of tin onto a low-carbon aluminum-killed steel substrate. As an important low-carbon aluminum-containing steel sheet, tinplate is widely used in food packaging, electronic equipment, and other fields, requiring extremely high surface quality and internal cleanliness. During continuous casting, a certain amount of aluminum needs to be added to the molten steel for deep deoxidation and grain refinement. However, the addition of aluminum inevitably reacts with dissolved oxygen in the molten steel, generating a large number of dispersed solid aluminum oxide inclusions.

[0003] These inclusions are the main cause of decreased continuous casting playability and defects in the quality of cast billets. For example... Figure 1 As shown, these solid Al2O3 inclusions readily adsorb, accumulate, and sinter on the stopper rod head, the upper nozzle bowl, and the inner wall of the submerged nozzle during the flow of molten steel, forming dense nodules. This nodulation process leads to a series of chain reactions. For example, turbulent flow occurs as nodules block the molten steel channel, reducing the effective cross-sectional area of ​​the nozzle and causing asymmetrical flow of molten steel, resulting in flow deviation. This deviation directly impacts the protective slag layer in the crystallizer, causing violent fluctuations in the liquid surface. Slag entrapment and secondary oxidation occur because violent liquid surface fluctuations disrupt the uniform coverage of the protective slag layer, causing the protective slag to be entrapped into the molten steel, forming a "slag entrapment" defect. Simultaneously, the exposed molten steel comes into contact with air and undergoes secondary oxidation, further increasing the number of inclusions. Finally, billet defects result from some nodules peeling off under high shear force and entering the crystallizer with the steel flow. These nodules are captured by the solidification front, ultimately forming large clusters of inclusions in the billet, leading to product scrap.

[0004] To address the aforementioned issues, existing technologies have proposed various solutions. For example, Chinese patent CN121491298A, a method for improving the castability of aluminum-containing steel in continuous casting, focuses on reducing the formation of Al2O3 inclusions at the source by precisely controlling the acid-soluble aluminum content in the molten steel and the superheat of the tundish. However, this solution does not fully consider the migration and deposition behavior of already formed inclusions inside the nozzle, nor does it address the dynamic process adaptability issues when the casting cross-section changes (such as slab width adjustment). Therefore, its effect on improving castability is limited.

[0005] Another approach, exemplified by Chinese patent CN117226084A, describes a method for reducing alumina inclusions in molten steel in the tundish. This method leverages the charged physical properties of Al2O3 inclusions in molten steel, applying an external electric field to force the inclusions to migrate and deposit towards the nozzle wall, thereby purifying the molten steel. While this method holds significant theoretical potential, its application in actual industrial continuous casting production is limited by issues related to electrode arrangement, insulation safety, and stability under harsh high-temperature environments, resulting in very few cases and significant challenges in widespread adoption.

[0006] Therefore, it is evident that a pressing technical problem to be solved is how to dynamically suppress the deposition of Al2O3 inclusions in the nozzle by optimizing the fluid dynamics and thermodynamics conditions during the continuous casting process without requiring large-scale electrification of existing equipment. Summary of the Invention

[0007] The purpose of this invention is to provide a continuous casting production method for tinplate. By dynamically controlling the casting speed, the amount of steel flowing through each section is kept to the maximum. The drag force of the high-velocity molten steel effectively prevents inclusions from adhering to the nozzle wall. At the same time, combined with dynamic argon blowing and a unidirectional increasing strategy for nozzle insertion depth, the area of ​​nodule formation on the side hole of the submerged entry nozzle is reduced by more than 50%, which greatly extends the number of consecutive casting furnaces, reduces the frequency of nozzle replacement, and improves operational efficiency.

[0008] To achieve the above objectives, the present invention proposes the following technical solution:

[0009] A continuous casting production method for tinplate includes the step of casting molten tinplate using a continuous casting machine, wherein the continuous casting production method comprises:

[0010] Dynamic control steps for casting speed: The maximum allowable cross-sectional thickness A × width B of the continuous casting machine and the maximum steel throughput S0 corresponding to the maximum cross-section are used as the reference. The reference casting speed corresponding to the maximum steel throughput S0 is V0.

[0011] When the actual production cross-section is changed to thickness C × width D, the target pulling speed V is calculated according to the following formula:

[0012] V = (A×B) / (C×D) × V0 or V = S0 / (ρ×C×D), where ρ is the density of molten steel;

[0013] The continuous casting machine is controlled by the target casting speed V to keep the steel throughput of the continuous casting machine at each production section at the maximum steel throughput S0.

[0014] Cooling linkage control steps: Based on the increment of the target casting speed V relative to the reference casting speed V0, the cooling water volume of at least one cooling zone of the continuous casting machine's cooling system is increased in a linkage compensation manner to suppress billet bulging caused by the increase in casting speed.

[0015] As a preferred embodiment of the present invention, in the cooling linkage control step, adjusting the cooling water volume in the crystallizer cooling zone of the continuous casting machine according to the increment of the target casting speed V relative to the reference casting speed V0 includes:

[0016] Adjust the actual cooling water volume L of the narrow side and the actual cooling water volume W of the wide side of the crystallizer cooling zone; wherein...

[0017] ;

[0018] ;

[0019] Wherein, L0 and W0 are the reference cooling water volumes for the narrow and wide sides of the crystallizer cooling zone given by the system under the reference pulling speed V0, respectively; m and n are fixed compensation coefficients, with m ranging from 0.2 to 0.6 and n ranging from 0.2 to 0.6.

[0020] As a preferred embodiment of the present invention, in the cooling linkage control step, adjusting the cooling water volume of the foot roll section cooling zone of the continuous casting machine according to the increment of the target casting speed V relative to the reference casting speed V0 includes:

[0021] Adjust the actual cooling water volume Z of the narrow side and the actual cooling water volume K of the wide side of the cooling zone of the foot roller section; wherein...

[0022] ;

[0023] ;

[0024] Wherein, Z0 and K0 are the reference cooling water volumes of the narrow and wide sides of the cooling zone of the foot roller section given by the system under the reference pulling speed V0, respectively; m and n are fixed compensation coefficients, with m ranging from 0.2 to 0.6 and n ranging from 0.2 to 0.6.

[0025] As a preferred embodiment of the present invention, in the cooling linkage control step, adjusting the cooling water volume of the secondary cooling zone of the continuous casting machine according to the increment of the target casting speed V relative to the reference casting speed V0 includes:

[0026] Adjust the actual cooling water volume Q in zone 1 of the secondary cooling zone and the actual cooling water volume G in zone 2 of the secondary cooling zone; where...

[0027] ;

[0028] ;

[0029] Wherein, Q0 and G0 are the reference cooling water volumes of Zone 1 and Zone 2 of the two cooling zones given by the system under the reference pulling speed V0, respectively; m is a fixed compensation coefficient, with a value of 0.2 to 0.6.

[0030] As a preferred embodiment of the present invention, it further includes a step of dynamically adjusting the insertion depth of the immersion nozzle:

[0031] During the casting process, the submersible nozzle is inserted into the liquid surface of the crystallizer in a multi-stage, progressively increasing manner, and the insertion depth of the submersible nozzle changes unidirectionally from shallow to deep throughout the entire process.

[0032] As a preferred technical solution of the present invention, the insertion depth of the bottom end of the immersion nozzle below the liquid surface of the crystallizer is set to a plurality of preset depth intervals that increase progressively, and each preset depth interval is executed sequentially in time order.

[0033] At least three preset depth ranges are set;

[0034] The initial insertion depth of the first preset depth range is 100mm;

[0035] The insertion depth increment between two adjacent preset depth intervals is 30–50 mm;

[0036] The duration of each preset depth interval is 2 to 4 hours.

[0037] As a preferred embodiment of the present invention, it further includes a dynamic argon blowing step: during the continuous casting process...

[0038] During the first to fourth heats of molten steel casting, the argon blowing flow rate should be controlled at 6 to 10 L / min.

[0039] During the 5th to 8th heats of molten steel casting, the argon blowing flow rate should be controlled at 5 to 6 L / min.

[0040] After casting the 8th heat of molten steel, the argon blowing flow rate was controlled at 3-5 L / min.

[0041] As a preferred embodiment of the present invention, it further includes a dynamic argon blowing step:

[0042] During continuous casting, the argon blowing flow rate is divided into multiple stages and gradually reduced according to the real-time liquid level curve of the crystallizer, with the lowest flow rate reduced to 3 L / min.

[0043] As a preferred embodiment of the present invention, it further includes a steel molten metal source purification step:

[0044] A high-basicity covering agent is applied to the surface of the molten steel in the tundish to form a molten covering agent layer. The binary basicity of the high-basicity covering agent, CaO / SiO2, is 2.0 to 4.0.

[0045] During continuous casting, the high-basicity covering agent is added to the casting zone of the tundish once every two heats of molten steel; and the high-basicity covering agent is added to the impact zone of the tundish once every one heat of molten steel.

[0046] Carbonized rice husks are sprinkled on the surface of the molten covering agent layer to form an insulation layer;

[0047] The superheat of the molten steel in the tundish is controlled at 30±7℃.

[0048] As a preferred embodiment of the present invention, the immersion nozzle includes a vertical section and a double-sided concave-bottom nozzle formed at its bottom.

[0049] The angle of inclination of the central axis of the side opening of the double-sided concave bottom water nozzle relative to the horizontal plane is set to 20° to 30°.

[0050] As can be seen from the above technical solutions, the technical solution of the present invention provides a continuous casting production method for tinplate, which has the following beneficial effects compared with the prior art:

[0051] (1) By dynamically controlling the casting speed according to the cross-section, the steel flow rate inside the nozzle is stabilized, effectively suppressing inclusion deposition: When the production cross-section changes, this invention uses the steel throughput under the maximum cross-section as a benchmark to back-calculate the target casting speed required for the new cross-section, so that the steel throughput under each cross-section remains constant, thereby ensuring that the steel flow rate inside the submerged entry nozzle does not decrease due to the narrowing of the cross-section. The stable high-velocity steel generates a continuous drag force, effectively preventing Al2O3 inclusions from adhering to and sintering on the nozzle wall. Combined with the dynamic argon blowing and the unidirectional increasing strategy of nozzle insertion depth, the nodule area of ​​the submerged entry nozzle side hole is reduced by more than 50%, significantly extending the number of continuous casting furnaces, reducing the nozzle replacement frequency, and improving the efficiency and safety of continuous casting operations.

[0052] (2) Effectively control the fluctuation of the liquid level in the crystallizer and improve the surface quality of the billet: When the casting speed is increased, the cooling water volume of the crystallizer, foot roll section and secondary cooling zone is compensated in conjunction to suppress the bulging of the billet shell; the water inlet insertion method from shallow to deep and the staged argon blowing adjustment method are used in combination. After implementation, the compliance rate of the liquid level fluctuation of the crystallizer is less than ±3mm increased from 86% to more than 95.6%, which significantly reduced slag entrapment and secondary oxidation defects.

[0053] (3) Dynamically adapts to cross-sectional changes and has strong process stability: The casting speed calculation formula based on the maximum steel throughput can quickly adapt to cross-sections of different thicknesses and widths without manual intervention; the cooling water volume is automatically compensated with the increase of casting speed to ensure uniform solidification of the billet at high casting speed and avoid internal quality hazards such as bulging and cracks.

[0054] (4) Source purification and process control work together to improve the cleanliness of molten steel: High alkalinity covering agent is used in combination with carbonized rice husk for heat preservation, and combined with superheat control to adsorb Al2O3 inclusions for a long time; dynamic argon blowing is adjusted in stages according to the liquid level fluctuation, which not only ensures the effect of bubble capture of inclusions, but also avoids excessive disturbance of the liquid surface, ensuring the cleanliness of molten steel from the source to the end.

[0055] (5) Safe and reliable, easy to promote industrialization: No need to carry out large-scale electrification transformation of existing continuous casting equipment. It can be implemented by simply optimizing process parameters and control logic. It is compatible with existing secondary control systems, has low cost, quick results, and good industrial application prospects.

[0056] It should be understood that all combinations of the foregoing concepts and the additional concepts described in more detail below can be considered part of the inventive subject matter of this disclosure, provided that such concepts do not contradict each other.

[0057] The foregoing and other aspects, embodiments, and features of the teachings of the present invention will be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the invention, such as features and / or beneficial effects of exemplary embodiments, will become apparent from the following description or may be learned through practice of specific embodiments according to the teachings of the present invention. Attached Figure Description

[0058] The accompanying drawings are not drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the invention will now be described by way of example and with reference to the accompanying drawings, wherein:

[0059] Figure 1 Images showing the nodule formation at the submerged entry gate in traditional tinplate casting processes;

[0060] Figure 2 This image shows the nodulation condition of the submerged entry nozzle in the tinplate continuous casting production method of the present invention. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0062] The terms "first," "second," and similar words used in the specification and claims of this patent application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, unless the context clearly indicates otherwise, the singular forms of "an," "a," or "the," etc., do not indicate a quantity limitation, but rather indicate the presence of at least one. Terms such as "comprising" or "including" mean that the element or object preceding "comprising" encompasses the features, wholes, steps, operations, elements, and / or components listed following "comprising" or "including," and do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or collections thereof. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0063] This invention provides a continuous casting production method for tinplate. The specific implementation method of this invention will be described in detail below using a slab continuous casting machine as an example.

[0064] The continuous casting system of this invention adopts a top-down tower-style three-dimensional layout, forming a vertical conveying system for molten steel in the forming channel. The main components of the system, arranged from top to bottom by height, are: tundish, stopper rod and top nozzle, submerged entry nozzle, crystallizer, and cooling zone. Specifically, the tundish is located at the top, serving as a buffer tank for the molten steel. A stopper rod, capable of vertically raising and lowering, is suspended inside the tundish. A steel outlet is located at the bottom of the tundish, and the top nozzle is embedded and fixed within it. The lower end of the stopper rod is directly opposite the top inlet of the top nozzle, and its raising and lowering motion precisely controls the opening of the top nozzle, achieving stepless adjustment of the molten steel flow rate. The lower end of the top nozzle is sealed to the upper end of the submerged entry nozzle via a quick-change nozzle mechanism, forming a rigid flow channel. The term "top" in "top nozzle" refers to its position relative to the submerged entry nozzle below, not the direction of water flow; molten steel flows entirely through this top nozzle, unrelated to cooling water.

[0065] The crystallizer is located directly below the submerged entry nozzle. In the pouring state, the vertical section of the submerged entry nozzle penetrates downwards through the protective slag layer of the crystallizer, causing the double-sided concave-bottom nozzle to be submerged below the surface of the molten steel inside the crystallizer. Thus, the path formed by the inner cavity of the tundish, the gap between the stopper rod and the upper nozzle, the submerged entry nozzle cavity, and the molten steel in the crystallizer constitutes a closed molten steel transport channel, preventing contact between the molten steel and air throughout the entire process. The entire tundish, stopper rod, upper nozzle, and submerged entry nozzle are placed on a controllable, longitudinally lifting platform, through which the depth of the submerged entry nozzle inserted below the surface of the molten steel in the crystallizer is adjusted.

[0066] Specifically, the submerged entry nozzle includes a vertical section and a double-sided concave-bottom nozzle formed at its bottom. The structure of this double-sided concave-bottom nozzle is as follows: a closed cavity is formed at the bottom of the vertical section, with the bottom surface of the cavity recessed downwards, forming a basin-like structure. A pair of side openings are formed on the opposite sides of the cavity wall. After molten steel flows down from the vertical section, it first impacts the concave surface of the cavity for buffering and diversion, and then flows out horizontally or inclined downwards through the side openings. This structure avoids the molten steel vertically impacting the mold wall, thus facilitating the formation of a stable double circulation flow.

[0067] Furthermore, to ensure that the molten steel, after being buffered by the aforementioned concave cavity and diverted by the side opening, can form an ideal double-circulation flow pattern within the crystallizer, this invention precisely defines the outflow angle of the side opening. The angle of inclination of the central axis of the side opening relative to the horizontal plane is set to 20°–30°. The selection of this angle range directly determines the impact depth and backflow intensity of the diverted stream after it flows towards the narrow face of the crystallizer. When the angle is less than 20°, the outflow direction is too horizontal, and the upward backflow is prone to directly impacting the meniscus, leading to increased liquid surface fluctuations and even slag entrainment; when the angle is greater than 30°, the downward penetration depth is too large, which can easily carry inclusions and superheated molten steel into the depths of the liquid phase cavity, hindering the floating of inclusions and affecting the uniform growth of the solidified billet shell. By controlling the side opening angle within this specific range of 20°–30°, the momentum and energy distribution of the upward and downward backflows are precisely balanced, thereby ensuring a "shallow and active" double-circulation flow pattern and further enhancing the beneficial effects of the aforementioned concave bottom diversion structure on avoiding vertical impacts and stabilizing the flow field.

[0068] Under normal circumstances, during the settling and flowing process of molten steel in the tundish, the surface of the liquid is covered with a traditional covering agent of ordinary acidity or low alkalinity. Some of the large, easily floating deoxidation product Al2O3 inclusions carried in the molten steel float to the steel-slag interface under the action of buoyancy, and are absorbed by the covering agent through physicochemical processes, completing the initial purification. However, the fine, dispersed Al2O3 particles, due to insufficient buoyancy, will still enter the next process with the steel flow.

[0069] During actual casting, as the residence time of molten steel in the tundish increases, traditional covering agents continuously absorb Al2O3 inclusions floating in the molten steel, leading to a deterioration in their composition and physical properties. The basicity of the covering agent decreases significantly, while the viscosity increases, resulting in a rapid decline in its ability to chemically dissolve and physically capture Al2O3. This not only makes it difficult to effectively absorb inclusions that float to the surface later, but also means that already captured inclusions may be re-entered into the molten steel due to flow field disturbances.

[0070] To address this deficiency, this invention employs a composite covering method at the source, combining a high-alkalinity covering agent with carbonized rice husk insulation. The high-alkalinity covering agent itself possesses sufficient CaO content, maintaining the alkalinity of the covering agent system within an effective range even after absorbing a certain amount of Al2O3, thus ensuring continuous and stable chemical adsorption capacity. Simultaneously, the carbonized rice husk layer on top of the covering agent provides excellent heat insulation, delaying the deterioration of the covering agent's physical properties due to temperature drops. Therefore, this invention fundamentally overcomes the technical bottleneck of traditional covering agents experiencing performance degradation due to the absorption of impurities, achieving longer-lasting and more thorough source purification of Al2O3 impurities.

[0071] Specifically, to achieve long-term Al2O3 absorption, the binary basicity (CaO / SiO2) of the high-basicity covering agent of this invention is controlled between 2.0 and 4.0. When the basicity is below 2.0, the system's basicity decreases too rapidly after Al2O3 absorption, quickly losing its chemical adsorption capacity; when the basicity is above 4.0, the covering agent's melting point is too high, easily forming a crust on the molten steel surface, affecting the heat insulation and oxygen barrier effects. The basicity mentioned in this invention refers to binary basicity, i.e., the mass percentage ratio of CaO / SiO2.

[0072] The carbonized rice husks used in this invention are commercially available products, with a preferred fixed carbon content of 40%–60%, a particle size range of 1–8 mm, and a bulk density of 0.10–0.20 g / cm³. If rice husks that have undergone carbonization treatment at 700–900℃ are used, their heat retention and anti-sintering properties are even better.

[0073] The composite covering method of the present invention can be implemented according to the following steps: First, a certain amount of the above-mentioned high alkalinity covering agent is uniformly added to the surface of the molten steel in the tundish to form a molten covering agent layer with a thickness of 20-50mm; after the covering agent layer is spread and partially melted, a layer of carbonized rice husk is uniformly sprinkled on its surface to form a heat insulation layer with a thickness of 10-30mm, which constitutes the composite covering structure.

[0074] In the tundish metallurgical process, the flow behavior and surface stability of molten steel exhibit significant regional differences. The interior of the tundish is typically divided into functionally distinct zones by baffles. The area directly below the long nozzle of the ladle is the impact zone, where molten steel is injected at high speed from the ladle. This zone experiences extremely high turbulent kinetic energy, resulting in dramatic vertical fluctuations and horizontal tumbling of the surface, creating a strong wave dynamic. Conversely, the area above the nozzle of the tundish, after being rectified by the baffles, is the casting zone. In this zone, the molten steel flow velocity is significantly reduced, the flow is stable, and the surface remains relatively calm.

[0075] Due to the fundamental differences in the aforementioned flow states, the consumption rate of the covering agent varies drastically across different zones. In the impact zone, the violent turbulence of the liquid surface causes the molten covering agent layer to be continuously impacted, broken, washed away to the surrounding area, or entrained by the molten steel. Simultaneously, the continuous and violent impact of the high-temperature molten steel accelerates the melting of the covering agent, resulting in extremely rapid consumption and a high likelihood of localized thinning of the covering agent layer or even exposure of the molten steel. Once the molten steel in the impact zone is exposed, not only does heat dissipation intensify, but it also causes severe secondary oxidation and nitrogen absorption, deteriorating the cleanliness of the source molten steel.

[0076] In the casting zone, due to the stable liquid level, the covering agent is mainly consumed by relatively slow melting and aging after adsorbing inclusions, and the loss rate is much lower than that in the impact zone.

[0077] In response to the above findings, this invention breaks with the traditional practice of uniformly replenishing the covering agent in the tundish, proposing a differentiated replenishment method based on the regional liquid level fluctuation characteristics. For the impact zone, which experiences extremely rapid loss, a high-basicity covering agent is added after every heat of molten steel is poured to ensure that this area is always fully covered under high-temperature, high-turbulence conditions, preventing exposed molten steel. For the casting zone, which experiences slower loss, a high-basicity covering agent is added after every two heats of molten steel are poured, ensuring effective coverage while avoiding waste and temperature drop caused by over-replenishment. Thus, by precisely matching the replenishment frequency with the regional loss characteristics, continuous and effective coverage of the entire tundish liquid level can be achieved with minimal covering agent usage, ensuring the cleanliness of the molten steel from the source.

[0078] Furthermore, in some specific embodiments of the present invention, the superheat of the molten steel in the tundish is controlled at 30±7℃, that is, 23~37℃. This superheat design, on the one hand, works synergistically with the high-alkalinity covering agent and the carbonized rice husk insulation layer to ensure that the covering agent forms a stable liquid active slag layer to efficiently adsorb Al2O3 inclusions; on the other hand, it ensures that the molten steel has sufficient fluidity and temperature buffer when entering the top nozzle, suppressing the non-equilibrium precipitation and deposition of residual inclusions on the inner wall of the top nozzle from a kinetic perspective, thereby achieving effective control of top nozzle nodule formation throughout the entire casting process.

[0079] The pre-purified molten steel enters a narrow flow channel formed by the stopper rod head and the top inlet of the upper nozzle. This flow channel experiences abrupt changes in cross-section, a sharp increase in molten steel velocity, and dead zones. Combined with the localized temperature drop caused by the contact between the molten steel and the stopper rod and upper nozzle, residual Al2O3 inclusions in the molten steel readily precipitate and deposit as non-metallic inclusions at this location. Therefore, this area is a sensitive initiation site for nodule formation. Al2O3 adheres and accumulates on the inner wall of the upper nozzle and the stopper rod head, gradually reducing the effective flow area. This not only decreases the molten steel throughput, but the nodules formed may also suddenly detach under the scouring effect of the molten steel, becoming a source of large foreign inclusions in subsequent processes.

[0080] After the molten steel flows out of the inlet, it immediately enters the vertical section of the submerged entry nozzle, which is sealed to it. The steel flows vertically downwards along the pipe cavity, which is made of refractory material. During the downward transport of the molten steel, heat is continuously dissipated, and the velocity gradient at the flow boundary layer causes more fine Al2O3 particles to migrate and adhere to the pipe wall. The nodule formation phenomenon on the inner wall of the vertical section is also significant. The nodules grow along the wall, causing flow field distortion and increasing the risk of blockage at the bottom outlets on both sides of the submerged entry nozzle due to the narrowing of the channel.

[0081] The deposition and detachment of Al2O3 inclusions in molten steel on the inner wall of an immersion nozzle are essentially controlled by the dynamic competition between two opposing forces: adhesion and drag force from the molten steel. Adhesion (including the resultant force of van der Waals forces and interfacial tension) drives Al2O3 inclusions to adhere to the nozzle wall and tend towards stable deposition; while the drag force of the molten steel acts on the already attached or in the process of attaching Al2O3 inclusions, attempting to wash them away. Under the same inclusion size and morphology, the faster the molten steel flow rate, the greater the drag force acting on the inclusions, and the more difficult it is for the inclusions to deposit stably. Theoretical studies show that for an ideal spherical Al2O3 inclusion with a diameter of 5 μm, its depositional wall boundary velocity is approximately 0.6 m / s. When the local molten steel flow velocity is less than the critical velocity, the dragging force is insufficient to overcome the adhesion force, and the inclusions have a high probability of adhering and gradually sintering and depositing; when the local molten steel flow velocity is greater than the critical velocity, the dragging force dominates, the inclusions cannot remain stably on the wall and flow downstream with the molten steel.

[0082] To overcome the aforementioned shortcomings, this invention employs a dynamic speed control method. This method maximizes the competitive relationship between drag force and adhesion force by adjusting process parameters such as casting speed, ensuring that the molten steel flow rate within the entire casting channel remains at a high level. This, in turn, minimizes the deposition of Al2O3 inclusions on the inner wall of the nozzle. In short, this method requires maintaining a "constant maximum steel throughput" to maximize flow rate and prevent nozzle blockage.

[0083] The specific implementation method is as follows: A×B represents the maximum allowable cross-sectional thickness (m) × width (m) of the continuous casting machine, and the casting speed V0 (m / min) corresponding to the maximum allowable steel throughput S0 at the continuous casting machine's production rhythm is used as the benchmark. When the production cross-section changes from thickness (m) × width (m) to C×D, to ensure that the molten steel flow velocity (dragging force) inside the submerged entry nozzle does not decrease, the target casting speed V (m / min) corresponding to the new cross-section should be calculated based on the maximum steel throughput S0. The calculation formula is as follows:

[0084] ;

[0085] or:

[0086] .

[0087] In the above formula, A is the maximum allowable cross-sectional thickness (m) of the continuous casting machine, B is the maximum allowable cross-sectional width (m); C is the actual production cross-sectional thickness (m) of the continuous casting machine, D is the actual production cross-sectional width (m); ρ is the density of molten steel (kg / m³). 3 S0 is the maximum allowable steel throughput of the continuous casting machine (kg / min), and V0 is the casting speed (m / min) under the maximum steel throughput S0 reference.

[0088] It should be noted that all cross-sections involved in this invention are based on the opening size at the bottom of the crystallizer.

[0089] This dynamic speed control method ensures that the linear velocity of molten steel inside the submerged nozzle channel remains at a high level under different cross-sections. This not only utilizes the drag force of the high flow velocity to prevent inclusions from approaching and adhering to the wall, but also breaks the blown argon bubbles into smaller, more dispersed particles, which is beneficial for adsorbing more small inclusions and preventing excessive disturbance and slag entrapment at the steel-slag interface caused by large bubbles.

[0090] Furthermore, due to the adoption of the aforementioned dynamic casting speed control method, the target casting speed V in actual production will change relative to the reference casting speed V0, and is mostly increased. The increased casting speed reduces the residence time of the billet in the crystallizer and the fan-shaped section, resulting in a thinner billet shell. This increases the risk of billet shell bulging due to the static pressure of the molten steel, especially in narrow areas. Billet shell bulging directly causes abnormal fluctuations in the liquid level of the crystallizer, becoming a contributing factor to quality defects such as slag entrapment. Therefore, this invention also provides a cooling water volume control method linked to the dynamic changes in casting speed.

[0091] Specifically, the core of this cooling control method lies in introducing a cooling increment model based on changes in casting speed and including fixed compensation, on the basis of the reference water volume in each cooling zone, to enhance the cooling intensity under high casting speed conditions and suppress billet bulging. This cooling increment model is described as follows: when the casting speed is adjusted from the reference casting speed V0 to the target casting speed V, the increase ratio of the narrow-face cooling water volume and the increase ratio of the wide-face cooling water volume in each cooling zone are determined according to the following rules.

[0092] (1) For the cooling zone of the crystallizer, the increase ratio of cooling water volume in the narrow face and the increase ratio of cooling water volume in the wide face are respectively:

[0093] ,

[0094] .

[0095] Therefore, after obtaining the increase ratio of the narrow-face cooling water volume and the wide-face cooling water volume, when the pulling speed is adjusted from the reference pulling speed V0 to the target pulling speed V, the actual cooling water volume L of the narrow face and the actual cooling water volume W of the wide face in the crystallizer cooling zone are respectively:

[0096] ,

[0097] .

[0098] In the above formula, L0 and W0 are the reference cooling water volumes for the narrow and wide sides of the crystallizer cooling zone given by the system under the corresponding reference pulling speed V0, respectively; m and n are fixed compensation coefficients, with m ranging from 0.2 to 0.6 and n ranging from 0.2 to 0.6. m and n can be equal or unequal.

[0099] (2) For the cooling zone of the foot roller section, the increase ratio of cooling water volume on the narrow side and the increase ratio of cooling water volume on the wide side are respectively:

[0100] ,

[0101] .

[0102] Therefore, after obtaining the increase ratio of cooling water volume in the narrow face and the increase ratio of cooling water volume in the wide face, when the pulling speed is adjusted from the reference pulling speed V0 to the target pulling speed V, the actual cooling water volume Z of the narrow face and the actual cooling water volume K of the wide face in the foot roll section cooling zone are respectively:

[0103] ,

[0104] .

[0105] In the above formula, Z0 and K0 are the reference cooling water volumes of the narrow and wide sides of the cooling zone of the foot roller section given by the system under the corresponding reference pulling speed V0, respectively; m and n are fixed compensation coefficients, with m ranging from 0.2 to 0.6 and n ranging from 0.2 to 0.6. m and n can be equal or unequal.

[0106] (3) For the two cooling zones, the increase percentage of cooling water volume in Zone 1 and Zone 2 of the two cooling zones are respectively:

[0107] ,

[0108] .

[0109] Therefore, after obtaining the increase ratio of cooling water volume in Zone 1 of the secondary cooling system and the increase ratio of cooling water volume in Zone 2 of the secondary cooling system, when the pulling speed is adjusted from the reference pulling speed V0 to the target pulling speed V, the actual cooling water volume Q in Zone 1 of the secondary cooling system and the actual cooling water volume G in Zone 2 of the secondary cooling system are respectively:

[0110] ,

[0111] .

[0112] In the above formula, Q0 and G0 are the reference cooling water volumes for Zone 1 and Zone 2 of the second cooling zone given by the system under the corresponding reference pulling speed V0, respectively; m is a fixed compensation coefficient, with a value of 0.2 to 0.6.

[0113] The cooling capacity of other cooling zones in the secondary cooling area can be determined according to the system's preset parameters.

[0114] In traditional continuous casting processes, the stability of the flow field within the crystallizer is highly susceptible to the condition of the submerged entry nozzle. When Al2O3 inclusions in the molten tinplate deposit on the inner wall of the submerged entry nozzle, it often leads to blockage of one side of the nozzle. This asymmetrical blockage prevents the molten steel from being discharged evenly from both side holes, instead creating an "eccentric jet," where the vast majority of the molten steel is ejected at high speed from the unobstructed side hole. This eccentric flow completely disrupts the originally symmetrical and stable circulating flow field inside the crystallizer, causing violent turbulence on one side of the liquid surface while the other side tends to stagnate.

[0115] Based on the aforementioned flow deviation, the "from deep to shallow" adjustment process in traditional dynamic slag-changing line operation is the direct cause of catastrophic fluctuations in the liquid level. The so-called dynamic slag-changing line is an operation that periodically raises and lowers the submerged entry nozzle (Sub-submerged nozzle) to extend its lifespan. However, when the Sub-submerged entry nozzle has already experienced flow deviation due to bridging, if it is raised from a deep insertion position to a shallow insertion position according to traditional practice (i.e., from deep to shallow), the distance between the side opening of the Sub-submerged entry nozzle and the liquid surface of the crystallizer is drastically shortened. At this time, the energy of the eccentric jet, which could be buffered and absorbed in the deep molten steel, will directly impact the protective slag layer above without attenuation in the shallow insertion state. This powerful impact will instantly shatter and disperse the protective slag layer, causing violent churning and extreme fluctuations in the liquid level of the crystallizer. This not only disrupts the stability of the automatic liquid level control system but also causes severe slag entrapment and secondary oxidation of the molten steel, and may even force the continuous casting machine to slow down or stop, severely restricting smooth production.

[0116] While a fixed single-slag-line operation maintains a constant depth of the submerged entry nozzle below the molten metal surface throughout the casting process, ensuring a consistent relative position between the nozzle's side opening and the molten metal surface, the flow pattern (flow field) of the molten steel within the mold is relatively stable, which is beneficial for maintaining the stability of automatic molten metal surface control. However, its fatal flaw lies in the extremely short service life of the submerged entry nozzle. The slag-line location (the interface between the molten steel and the nozzle) is subjected to the most intense thermal shock, chemical erosion (from the molten protective slag), and mechanical scouring. When the nozzle remains fixed at the same depth, these destructive effects concentrate in the same horizontal annular area on the outer wall of the nozzle, causing rapid consumption of the refractory material and the formation of deep grooves. This makes the nozzle highly susceptible to breakage at this point, leading to catastrophic steel leakage. Therefore, while a fixed single-slag-line operation ensures short-term flow field stability, it comes at the cost of sacrificing continuous casting time and operational safety, failing to meet the demands of efficient industrial production.

[0117] Given the extremely high risk associated with the aforementioned "deep-to-shallow" slag line operation during nodule formation, this invention abandons the traditional reciprocating pattern of slag line depth adjustment and proposes a safer and more reliable method for dynamically adjusting the insertion depth of the submersible nozzle. It creatively employs a multi-segment, unidirectional insertion method that proceeds only from shallow to deep. Preferably, n segments are used, where n ≥ 3.

[0118] The specific implementation method is as follows: at different stages of the casting cycle, the lifting platform that carries the intermediate tundish drives the submerged nozzle to move down as a whole, so that the insertion depth of the submerged nozzle below the liquid surface of the crystallizer increases in a step-like manner, and the whole process only has a unidirectional change from shallow to deep, and the retraction action from deep to shallow is strictly prohibited.

[0119] Specifically, the process is divided into three stages. The initial stage involves a shallow insertion depth, for example, set at 100mm. As casting progresses, the submerged entry nozzle is lowered by a certain distance every 2-4 hours, with each stage's movement controlled within the range of 30-50mm, ultimately achieving a deeper, predetermined insertion depth. The time interval is determined by the erosion life of the single slag line of the submerged entry nozzle for this steel grade, ensuring that each slag line is fully utilized.

[0120] Above the molten steel surface in the crystallizer, a layer of molten protective slag covers the area. Within this region, the molten steel undergoes final physical purification. Fine Al₂O₃ inclusions not completely removed by the tundish covering agent rise to the steel-slag interface in the upper reflux zone of the crystallizer, where they are effectively absorbed by the liquid protective slag, marking the final stage of inclusion removal. Bubbles precipitated in the molten steel collide with and adhere to the Al₂O₃ inclusions, using buoyancy to accelerate their separation. However, to generate sufficient dispersed bubbles for efficient inclusion capture, argon gas needs to be blown into the molten steel; but a constant and excessively high argon blowing rate can exacerbate surface disturbance in the crystallizer during the later stages, potentially leading to slag entrapment. To address this contradiction, this invention proposes a dynamic argon blowing method, adjusting the argon flow rate in stages during continuous casting based on the degree of nozzle nodule formation and surface fluctuation characteristics.

[0121] The first to fourth heats are classified as the early stage of casting. During this stage, the nozzle clogging is relatively light and the liquid level fluctuation in the crystallizer is stable. At this time, a higher argon blowing rate is adopted to utilize the large volume of air to generate a large number of fine and dispersed bubbles, which enhances the collision, adhesion, and flotation removal of inclusions. The argon blowing flow rate is controlled at 6 to 10 L / min.

[0122] During the 5th to 8th heats, which is the middle stage of casting, as the casting time increases, the degree of nodule formation on the inner wall of the nozzle gradually worsens, and the liquid surface in the crystallizer shows regular fluctuations or low-frequency oscillations. At this time, the argon blowing flow rate should be appropriately reduced to 5-6 L / min to maintain a certain bubble capture capacity while suppressing excessive impact of the airflow on the liquid surface.

[0123] After the 8th heat, the casting process enters the later stage. During this stage, more nodules form at the nozzle, and the liquid level in the crystallizer fluctuates violently with irregular spikes or large drifts. At this time, the argon blowing flow rate is actively reduced to 3-5 L / min to maintain only basic metallurgical functions, prioritizing the stability of the liquid level and the safety of casting, and avoiding slag entrapment caused by gas flow escape.

[0124] Furthermore, during continuous casting, the argon blowing flow rate can be divided into multiple stages based on the real-time characteristics of the crystallizer level curve, adopting a strategy of gradual reduction, down to a minimum of 3 L / min. This maximizes the role of bubbles in capturing inclusions while maintaining liquid level stability, effectively balancing the dual requirements of inclusion removal and slag prevention.

[0125] In practice, the liquid level sensor in the crystallizer collects the liquid level signal in real time, and the PLC system generates a liquid level curve in time series.

[0126] Identifying each stage based on the liquid level profile, including:

[0127] Early stage of casting: For the first to fourth heats, the argon blowing flow rate is controlled at 6 to 10 L / min to generate a large number of diffuse bubbles to efficiently capture inclusions.

[0128] Mid-casting: Corresponding to the 5th to 8th heats, the argon blowing flow rate is appropriately reduced to 5 to 6 L / min, while maintaining the bubble capture capacity and beginning to suppress the impact of the airflow on the liquid surface.

[0129] Later stage of casting: After the 8th heat, the argon blowing flow rate is actively reduced to 3-5 L / min to suppress excessive disturbance to the liquid surface caused by the gas flow aggregation and escape.

[0130] Example 1

[0131] This embodiment provides a continuous casting production method for tinplate. The dynamic control method for casting speed is as follows: taking the maximum allowable casting speed of 1.30 m / min for the largest cross-section (1125 mm × 220 mm) as a benchmark, the target casting speed V (m / min) to be executed for different cross-sections C (mm) × D (mm) is calculated as follows:

[0132] .

[0133] It should be noted that when applying the above formulas for calculations, the units of each parameter should first be converted to a consistent unit system. Conversions between units of length, time, speed, etc., are standard skills for those skilled in the art and will not be elaborated upon here.

[0134] Based on the above formulas, the pulling speeds for some typical cross-sections in production are given in Table 1 below.

[0135] Table 1

[0136] 1125 220 1.30 1040 220 1.41 990 220 1.48 940 220 1.56 890 220 1.64

[0137] The dynamic adjustment method for the insertion depth of the submerged nozzle in this embodiment is as follows: At least three slag lines are set in the vertical section of the submerged nozzle. During the casting process, a three-stage insertion method is adopted, with the depth only progressing from shallow to deep, without any process from deep to shallow. Each insertion depth increment is 40mm, and the dwell time at each depth position is 2 hours.

[0138] The dynamic control method for cooling in this embodiment is to increase the cooling water volume of the crystallizer, the cooling water volume of the foot roller section, the cooling quantity of the second cooling zone 1, and the cooling water volume of the second cooling zone 2 according to the target pulling speed V and the reference pulling speed V0. According to Table 1, V0 in this embodiment is 1.3 m / min.

[0139] In this embodiment, the values ​​of m and n are both 0.4 in the increase ratio of cooling water volume in the crystallizer cooling zone and the foot roller section cooling zone; the value of m in the first and second cooling zones is 0.3.

[0140] The dynamic argon blowing method in this embodiment is as follows: the argon blowing flow rate between the stopper rod, the inlet, and the slide plate is divided into two stages: in the early stage when the nodulation is mild and the liquid level fluctuation in the crystallizer is stable, the argon blowing rate is 8 L / min; in the middle and later stages when the liquid level fluctuation in the crystallizer is unstable, the argon blowing rate is 4 L / min. The distinction between the two stages in this embodiment is based on the real-time liquid level curve of the crystallizer.

[0141] like Figure 1 The image shows the nozzle clogging situation after 11 heats of molten steel were continuously cast using the traditional process. Severe clogging is observed at the side openings, reducing the side hole area by nearly two-thirds. The traditional process controls the casting speed by maintaining a fixed speed regardless of cross-sectional changes. Even when the width decreases and conditions allow for speed increases, the casting speed remains constant at the lowest permissible speed of 1.30 m / min for the maximum cross-section (1125 mm × 220 mm).

[0142] This embodiment provides a method for continuous casting of tinplate, in which the casting speed is dynamically controlled: based on the maximum allowable casting speed of 1.30 m / min for a maximum cross-section of 1125 mm × 220 mm, the target casting speed is dynamically set to 1.30–1.64 m / min within an adjustable width range of 890–1125 mm and a thickness of 220 mm. After continuously casting 11 heats of molten steel under these process conditions, the nodule formation on the side hole of the submerged entry nozzle is as follows. Figure 2 As shown, the area of ​​the side opening is only slightly reduced. In comparison, it can be seen that using this invention reduces the area of ​​the side hole nodules by more than 50%, effectively ensuring the flowability of molten steel.

[0143] Meanwhile, in this embodiment, the compliance rate of liquid level fluctuation in the crystallizer being less than ±3mm is 95.6%, which is 9.6 percentage points higher than the 86% of the existing system process, and the liquid level control accuracy is significantly improved.

[0144] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A continuous casting production method for tinplate, comprising the step of casting molten tinplate using a continuous casting machine, characterized in that, The continuous casting production method includes: Dynamic control steps for casting speed: The maximum allowable cross-sectional thickness A × width B of the continuous casting machine and the maximum steel throughput S0 corresponding to the maximum cross-section are used as the reference. The reference casting speed corresponding to the maximum steel throughput S0 is V0. When the actual production cross-section is changed to thickness C × width D, the target pulling speed V is calculated according to the following formula: V = (A×B) / (C×D) × V0 or V = S0 / (ρ×C×D), where ρ is the density of molten steel; The continuous casting machine is controlled by the target casting speed V to keep the steel throughput of the continuous casting machine at each production section at the maximum steel throughput S0. Cooling linkage control steps: Based on the increment of the target casting speed V relative to the reference casting speed V0, the cooling water volume of at least one cooling zone of the continuous casting machine's cooling system is increased in a linkage compensation manner to suppress billet bulging caused by the increase in casting speed.

2. The continuous casting production method for tinplate according to claim 1, characterized in that, In the cooling linkage control step, the cooling water volume in the crystallizer cooling zone of the continuous casting machine is adjusted according to the increment of the target casting speed V relative to the reference casting speed V0, including: Adjust the actual cooling water volume L of the narrow side and the actual cooling water volume W of the wide side of the crystallizer cooling zone; wherein... ； ； Wherein, L0 and W0 are the reference cooling water volumes for the narrow and wide sides of the crystallizer cooling zone given by the system under the reference pulling speed V0, respectively; m and n are fixed compensation coefficients, with m ranging from 0.2 to 0.6 and n ranging from 0.2 to 0.

6.

3. The continuous casting production method for tinplate according to claim 1, characterized in that, In the cooling linkage control step, the cooling water volume in the foot roll section cooling zone of the continuous casting machine is adjusted according to the increment of the target casting speed V relative to the reference casting speed V0, including: Adjust the actual cooling water volume Z of the narrow side and the actual cooling water volume K of the wide side of the cooling zone of the foot roller section; wherein... ； ； Wherein, Z0 and K0 are the reference cooling water volumes of the narrow and wide sides of the cooling zone of the foot roller section given by the system under the reference pulling speed V0, respectively; m and n are fixed compensation coefficients, with m ranging from 0.2 to 0.6 and n ranging from 0.2 to 0.

6.

4. The continuous casting production method for tinplate according to claim 1, characterized in that, In the cooling linkage control step, the cooling water volume in the secondary cooling zone of the continuous casting machine is adjusted according to the increment of the target casting speed V relative to the reference casting speed V0, including: Adjust the actual cooling water volume Q in zone 1 of the secondary cooling zone and the actual cooling water volume G in zone 2 of the secondary cooling zone; where... ； ； Wherein, Q0 and G0 are the reference cooling water volumes of Zone 1 and Zone 2 of the two cooling zones given by the system under the reference pulling speed V0, respectively; m is a fixed compensation coefficient, with a value of 0.2 to 0.

6.

5. The continuous casting production method for tinplate according to claim 1, characterized in that, It also includes a dynamic adjustment step for the insertion depth of the submersible nozzle: During the casting process, the submersible nozzle is inserted into the liquid surface of the crystallizer in a multi-stage, progressively increasing manner, and the insertion depth of the submersible nozzle changes unidirectionally from shallow to deep throughout the entire process.

6. The continuous casting production method for tinplate according to claim 5, characterized in that, The insertion depth of the bottom end of the immersion nozzle below the liquid surface of the crystallizer is set to multiple preset depth intervals that increase progressively, and each preset depth interval is executed sequentially in time order. At least three preset depth ranges are set; The initial insertion depth of the first preset depth range is 100mm; The insertion depth increment between two adjacent preset depth intervals is 30–50 mm; The duration of each preset depth interval is 2 to 4 hours.

7. The continuous casting production method for tinplate according to claim 1, characterized in that, It also includes a dynamic argon blowing step: in the continuous casting process, During the first to fourth heats of molten steel casting, the argon blowing flow rate should be controlled at 6 to 10 L / min. During the 5th to 8th heats of molten steel casting, the argon blowing flow rate should be controlled at 5 to 6 L / min. After casting the 8th heat of molten steel, the argon blowing flow rate is controlled at 3-5 L / min.

8. The continuous casting production method for tinplate according to claim 1, characterized in that, It also includes a dynamic argon blowing step: During continuous casting, the argon blowing flow rate is divided into multiple stages and gradually reduced according to the real-time liquid level curve of the crystallizer, with the lowest flow rate reduced to 3 L / min.

9. The continuous casting production method for tinplate according to claim 1, characterized in that, It also includes the steel molten steel source purification process: A high-basicity covering agent is applied to the surface of the molten steel in the tundish to form a molten covering agent layer. The binary basicity of the high-basicity covering agent, CaO / SiO2, is 2.0 to 4.

0. During continuous casting, the high-basicity covering agent is added to the casting zone of the tundish once every two heats of molten steel; and the high-basicity covering agent is added to the impact zone of the tundish once every one heat of molten steel. Carbonized rice husks are sprinkled on the surface of the molten covering agent layer to form an insulation layer; The superheat of the molten steel in the tundish is controlled at 30±7℃.

10. The continuous casting production method for tinplate according to claim 5, characterized in that, The immersion nozzle includes a vertical section and a double-sided concave-bottom nozzle formed at its bottom; The angle of inclination of the central axis of the side opening of the double-sided concave bottom water nozzle relative to the horizontal plane is set to 20° to 30°.

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