Accurate reduction control method for realizing bloom continuous casting static soft reduction based on primary mode

Abstract

The invention provides a precise reduction control method for achieving bloom continuous casting static soft reduction based on a first-level mode, and belongs to the technical field of continuous casting. The method comprises the following steps: determining the rolling reduction of each reduction roller according to the requirements of a reduction process; determining the total rolling reduction of each rolling reduction roller based on the rolling reduction of each rolling reduction roller; and each reduction roller performs static soft reduction based on the total reduction amount. According to the method, a dynamic reduction online model can be replaced, the reduction process is accurately executed, the dependence of reduction operation on a secondary model is reduced, and the maintenance workload of a reduction system is reduced. According to the method, the casting blank internal defect that the execution effect of the pressing process is uncertain and unsatisfactory due to the fact that calibration is not timely or inaccurate can be eliminated, and the execution effect of the pressing process can be completed by maintaining the minimum normal pressing action. The method can improve the production efficiency and reduce the production cost. In addition, the method is simple, convenient and easy to implement, and can be popularized, applied and implemented on similar bloom continuous casting machines in a large scale.

Description

Technical Field

[0001] This invention relates to the field of technology, and in particular to a method for precise control of static light pressure in continuous casting of large billets based on a first-level mode. Background Technology

[0002] During continuous casting, high-carbon alloy steel billets, due to their high carbon and alloy element content and wide two-phase region, are prone to defects such as center segregation, shrinkage cavities, and porosity during solidification. The larger the cross-sectional size, the longer the solidification time, and the more severe the defects. Center segregation is difficult to eliminate during subsequent heating and rolling processes, and its inheritance to the finished product significantly degrades mechanical and service properties. Light reduction technology applies external force at the end of billet solidification to compensate for the volume shrinkage of the liquid phase and promote the flow of solute-rich liquid between dendrites, thereby improving center segregation and shrinkage cavities. Practice has proven that this technology can stably improve the internal quality of large square high-carbon steel billets and is a key technology for the continuous casting of high-value-added billets in special steel. Its implementation includes static and dynamic light reduction under closed-loop control: static light reduction sets the reduction amount based on the fixed position of the straightening machine; dynamic light reduction calculates the solid fraction in real time through a secondary model and dynamically allocates the reduction amount, but requires frequent equipment adjustments, increasing maintenance complexity.

[0003] The current mainstream solution employs a combined control of the pressing equipment system and a secondary pressing model: the secondary model dynamically issues the pressing amount based on the temperature field calculation results, and the equipment system executes the process; if the secondary system fails (such as server crash, network interruption, or model maintenance), it switches to the primary static light pressing mode to maintain production. Static light pressing requires manual, gradual pressing between the straightening machines (e.g., pressing on machine #1, then pressing on machine #2 when the billet arrives), but the actual pressing amount is easily reduced due to the elastic rebound of the billet, resulting in insufficient total pressing amount. In addition, domestic systems typically use machine #1 as the measuring roller, and subsequent stands adjust the roller gap accordingly, increasing equipment costs and maintenance burden.

[0004] Using a combination of existing mainstream reduction equipment systems and a two-stage reduction model to perform light reduction is more conducive to ensuring stable control of the internal quality of the billet. However, this method involves a large workload for system maintenance and requires highly skilled maintenance personnel. The model itself has high requirements for the execution accuracy and calibration of the equipment system. The server of the two-stage system is also prone to failure in environments with severe dust and noise pollution, resulting in occasional unusable two-stage models. For these reasons, many large billet continuous casting machines in China are equipped with secondary cooling dynamic water distribution and light reduction technology, but few have achieved good results. In addition, for large billets, due to the stability of the solidified liquid core, the process parameters fluctuate little during normal continuous casting (except for the first furnace and the tail casting). Considering all the above, using a single-stage static roll gap control reduction can effectively and stably control the internal quality of the billet. In existing domestic single-level static roll gap control, manual, gradual pressing is necessary to ensure stable execution of the pressing process. For example, after the pressing roller of the #1 straightener performs the pressing amount, when the thinned billet reaches the pressing roller of the #2 straightener, the #2 straightener then performs the pressing amount, and so on, gradually executing the pressing amounts executed by all the straightener pressing rollers to complete the pressing process. However, with this control method, due to the inherent elastic rebound of the billet during the pressing process, when the billet reaches the #2 pressing roller after the #1 pressing roller has performed the pressing amount, the billet thickness is not the thickness after pressing, but rather greater. This causes the pressing amount to be incomplete. When multiple straightener pressing rollers are stacked, the total pressing amount is significantly reduced, making it impossible to correctly execute the pressing process and thus failing to guarantee the internal quality target of the billet.

[0005] Therefore, a simple and efficient static light reduction control method based on the first-level mode is needed for continuous casting of large billets. Summary of the Invention

[0006] In view of this, the present invention provides a precise reduction control method for static light reduction of large billets in continuous casting based on a first-level mode. It improves upon the shortcomings of the existing technology by starting from the underlying logic of the technical defects and eliminating the problem of inadequate reduction due to the elastic rebound of the billet in the existing first-level static reduction process.

[0007] Therefore, the present invention provides the following technical solution: A method for precise reduction control in static light-pressure continuous casting of large billets based on a first-level mode includes: The pressing amount of each pressing roller is determined according to the pressing process requirements; The total pressing amount of each pressing roller is determined by the pressing amount of each pressing roller; Each pressing roller performs static light pressing based on the total pressing amount: The first pressing roller in this round performs its corresponding total pressing amount to obtain the billet; when the billet reaches the next pressing roller, the next pressing roller performs its corresponding total pressing amount; this process continues until the last pressing roller in this round performs its corresponding total pressing amount, at which point the pressing round ends.

[0008] Furthermore, the pressing process requirements include: The target reduction amount for this round of pressing, the pressing roller performing the pressing in this round, and its corresponding reduction amount.

[0009] Further, determining the total pressing amount of each pressing roller by measuring the pressing amount of each pressing roller includes: The total reduction is the sum of the reductions of all the pressing rollers arranged sequentially along the material feeding direction before this pressing roller.

[0010] Furthermore, the static light pressing of each pressing roller based on the total pressing amount also includes: Calibrate the reference roll gap for each pressing roll to perform pressing; The difference between the reference roll gap of each pressing roll and the total pressing amount is used as the target roll gap; Each pressing roller performs static light pressing based on the target roll gap.

[0011] Furthermore, at the start of the first-stage static pressing, the current actual roll gap of all pressing rolls is recorded as the reference roll gap for each pressing roll to perform pressing.

[0012] Furthermore, after each pressing roller completes its corresponding total pressing amount, the solidification end position of the current billet is detected, and the target pressing amount for the next round of pressing is adjusted according to the detection result.

[0013] Advantages and positive effects of the present invention: (1) This method can replace the dynamic pressing online model, accurately execute the pressing process, reduce the dependence of pressing operation on the secondary model, and reduce the maintenance workload of the pressing system.

[0014] (2) This method can eliminate the internal defects of the billet that result in uncertain or unsatisfactory execution of the pressing process due to untimely or inaccurate calibration. Maintaining the minimum normal pressing action is sufficient to achieve the execution effect of the pressing process.

[0015] (3) This method can improve production efficiency and reduce production costs. In addition, this method is simple and easy to implement, and can be widely promoted and applied on similar large billet continuous casting machines. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart of a method for precise reduction control under static light pressure in continuous casting of large billets based on a first-level mode, as described in this embodiment of the invention. Figure 2 This is a low-magnification cross-sectional view of a BU billet that was not processed using this method in an embodiment of the present invention; Figure 3 This is a low-magnification view of the longitudinal section of a BU billet that was not produced using this method in an embodiment of the present invention; Figure 4 This is a low-magnification cross-sectional view of a BU billet using this method in an embodiment of the present invention; Figure 5 This is a low-magnification view of the longitudinal section of a BU billet using this method in an embodiment of the present invention; Figure 6 This is a comparison chart of the carbon segregation index distribution along the longitudinal section centerline of the billet using this method and the carbon segregation index distribution along the longitudinal section centerline of the billet without this method in this embodiment of the invention. Detailed Implementation

[0018] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0019] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0020] This invention provides a precise reduction control method for static light reduction in large billet continuous casting based on a single-level mode. By using a straightening machine to stably execute the light reduction process, it avoids inaccurate reduction caused by roll gap variations, maximizing the stable control of the billet's internal quality. Simultaneously, it significantly reduces the maintenance of the straightening machine's mechanical equipment, automation and hydraulic equipment and systems, improving production efficiency and lowering production costs. Furthermore, this invention eliminates the need for measuring rolls, allowing more straightening machines to participate in light reduction, saving costs. It is simple and easy to implement, and can be widely promoted and applied to similar large billet continuous casting machines.

[0021] The steps of this method include: S1. At the start of the first-stage static pressing, record the current actual roll gap of all tension levelers as the reference roll gap for each pressing roll to perform pressing. S2. Obtain the total reduction amount of each pressing roller according to the pressing process; S3. The target roll gap for each roll is the reference roll gap of this roll minus the total reduction of this roll. S4. Based on the target roll gap of each roll, perform the pressing process step by step: First, the first pressing roller in the pressing process is executed. After the billet pressed down by the pressing roller reaches the next pressing roller, the next pressing roller is executed. This process is repeated until all pressing roller actions in the pressing process are completed.

[0022] The recording and calculation of the reference roll gap, total reduction, and target roll gap should prioritize the reduction rolls that perform the reduction process, rather than all tension levelers, to simplify data processing as much as possible.

[0023] Example A steel plant has a five-machine, five-strut R16 full-arc 300mm×360mm cross-section large square billet casting machine, equipped with 9 tension levelers. The maximum reduction per roll is 6mm, and the maximum total reduction is 30mm. The arrangement of the tension levelers is shown in Table 1. It can simultaneously perform primary static light reduction and dynamic light reduction through a secondary cooling dynamic water distribution and light reduction control system.

[0024] In this embodiment, the secondary system server suddenly failed and could not perform the secondary compression, so the primary static compression method of this method was adopted.

[0025] Table 1

[0026] The specific operating conditions are as follows: The production process of high-carbon alloy steel BU (with a main C content of 1.0%, a Mn content of 1.0%, and a Cr content of 0.56%) involves continuous casting process parameters such as a casting speed of 0.75 m / min, a secondary cooling water ratio of 0.18 L / Kg, and a suitable central solid fraction of 0.3~0.75 under light pressure. According to the secondary dynamic water distribution solidification model, the corresponding compressible straightening machines for this working condition with a central solid fraction of 0.3~0.75 are No. 2~6 straightening machines, with a total reduction of 14 mm and single roll reductions of 1 mm, 3 mm, 5 mm, 3 mm, and 2 mm, respectively.

[0027] According to this method, the specific process data is shown in Table 1. Before performing the first-stage static pressing, the actual roll gap values ​​of each straightening machine are read, as shown in "Actual Roll Gap Values" of the pressing execution data in Table 2. It can be seen that under normal circumstances, as the billet gradually solidifies and shrinks, the roll gap values ​​of each roll should gradually decrease. However, the roll gap values ​​of the No. 4 pressing roll and the No. 8 pressing roll do not conform to the rule. This is mostly due to the fact that they have not been calibrated for a long time, resulting in errors in the roll gap values, which cannot truly reflect the actual billet thickness. Moreover, the No. 4 pressing roll has a large error and is located in the pressing process to be performed. The correct execution of the process proves that this method greatly reduces the accuracy requirements of the pressing equipment. As long as the operation is normal, it is sufficient. This is the advantage of this method.

[0028] Based on the actual roll gap, the reference roll gap for each pressing roll is obtained. Since only pressing rolls #2 to #6 are lightly pressed in this pressing process, the "reference roll gap" shown in Table 2 is formed first. The tension leveler, which does not participate in the pressing, is not involved in the recording and subsequent algorithm and execution.

[0029] The total reduction of each roll is determined from the pressing process, as shown in Table 2, "Total Reduction of Each Roll". Based on this, the target roll gap is determined, as shown in Table 2, "Target Roll Gap". The pressing process is then performed sequentially according to the target roll gap to complete the pressing process. At this point, regardless of the actual roll gap value of the cast billet after pressing by roll #3 when it reaches roll #4, the target roll gap of 307.5mm is always achieved. The same principle applies to the others. From the target roll gap perspective, roll #4 performs a reduction of -0.1mm relative to roll #3, but the actual total reduction is 9mm. This ensures the pressing process is executed even when the roll gap of the straightening machine is inaccurate, maximizing the pressing effect.

[0030] Table 2

[0031] Figure 2 and Figure 3 Low-magnification views of the cross-section and longitudinal section of the BU billet that were not prepared using this method. Figure 4 and Figure 5 This method is used to obtain low magnification images of the cross-section and longitudinal section of the BU billet.

[0032] Comparison of the cross-section at low magnification shows that the center segregation of the cast billet cross-section obtained by applying this method is reduced and shrinkage cavities are eliminated, and the center is more compact. Comparing the longitudinal section of the billet at low magnification, it can be seen that the center segregation line of the billet using this method is significantly improved, the included angle of the V-shaped segregation becomes larger and less clear, and the segregation channel is basically eliminated.

[0033] according to Figure 6 A comparison of the carbon segregation index distribution along the longitudinal section centerline of the BU slab shows that, after adopting this method, the carbon segregation index along the longitudinal section centerline of the BU slab changed from 0.88~1.09 to 0.98~1.04, which is significantly improved and more uniform.

[0034] The existing method calculates the reduction amount based on the roll gap value before reduction, without considering the billet rebound after the previous roll's reduction. This results in inaccurate total reduction. This method, however, calculates the total reduction amount of each roll based on the original roll gap, ensuring the effectiveness of the reduction process. It maximizes the accuracy of the reduction equipment system under minimal requirements, significantly reduces maintenance workload, and guarantees the internal quality of the billet.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for precise press-down control of static light press-down of bloom continuous casting based on a first-order model, characterized in that, The method comprises the following steps: determining the reduction amount of each reduction roller according to the reduction process requirements; determining the total reduction amount of each reduction roller through the reduction amount of each reduction roller; each reduction roller performs static light reduction based on the total reduction amount; the first reduction roller in the current round of reduction performs its corresponding total reduction amount to obtain a casting blank; when the casting blank reaches the next reduction roller, the next reduction roller performs its corresponding total reduction amount; and the process is repeated until the last reduction roller in the current round of reduction performs its corresponding total reduction amount, and the current round of reduction ends.

2. The method of claim 1, wherein, The reduction process requirements comprise: the target reduction amount of the current round of reduction, the reduction roller in the current round of reduction, and the corresponding reduction amount.

3. The method of claim 1, wherein, The determination of the total reduction amount of each reduction roller through the reduction amount of each reduction roller comprises: The total reduction amount is the sum of the reduction amounts of all reduction rollers arranged in sequence along the material feeding direction before the reduction roller.

4. The method of claim 1, wherein, Each reduction roller performs static light reduction based on the total reduction amount, which further comprises: calibrating the reference roll gap of each reduction roller for reduction; taking the difference between the total reduction amount and the reference roll gap of each reduction roller as the target roll gap; each reduction roller performs static light reduction based on the target roll gap.

5. The method of claim 4, wherein, At the start time of the first-stage static reduction, the actual roll gap of each reduction roller at that moment is recorded as the reference roll gap of each reduction roller for reduction.

6. The method of claim 1, wherein, After each reduction roller completes its corresponding total reduction amount, the solidification end position of the current casting blank is detected, and the target reduction amount of the next round of reduction is adjusted according to the detection result.

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