Method for maintaining cleanliness of molten steel during ladle change in continuous casting steelmaking plant

Abstract

This invention pertains to a method for maintaining the cleanliness of molten steel during ladle changes in continuous casting steelmaking equipment, within the field of continuous casting steelmaking technology. The method involves raising the tundish pouring level to 1.05–1.15 times the normal pouring level. Once the tundish reaches the target level, pouring is stopped, and a ladle change is performed. During the period of cessation of pouring molten steel into the tundish, the relationship between the lowest pouring level and the continuous molten steel output per minute is: (Tundish pouring level at the stop - lowest pouring level at the time of ladle change) / continuous molten steel output per minute at the stop = 1–4. After the ladle change, pouring resumes, and the tundish is brought back to the normal pouring level by controlling the steel flow rate through the ladle nozzle, completing the ladle change operation. The required rate of increase in the tundish level during this process is 4%–8% of the normal pouring level per minute. This method for maintaining the cleanliness of molten steel during ladle changes in continuous casting steelmaking equipment reduces the impact of the steel flow on the molten steel in the tundish, thus maintaining the cleanliness of the molten steel during the ladle change process.

Description

Technical Field

[0001] This invention belongs to the field of continuous casting steelmaking technology, and more specifically, relates to a method for maintaining the cleanliness of molten steel when changing ladles in continuous casting steelmaking equipment. Background Technology

[0002] Unsteady-state casting process control is one of the core aspects of continuous casting process control. During the ladle casting process in a continuous casting machine, a ladle is suspended on one of the booms of the ladle turntable. After the molten steel in the ladle is poured, another ladle is suspended on the boom on the other side of the turntable. Then, the turntable is rotated to exchange the positions of the two booms, and the other ladle continues casting into the tundish, thus enabling continuous production. The disadvantage of this casting mode is that the process of exchanging the positions of the two booms takes time, and the process of reopening the tundish nozzle after the exchange also takes time, resulting in a time interval between the casting of the two ladles. During this time, the tundish continues to output molten steel, injecting it into the casting crystallizer. The molten steel level in the tundish drops significantly, and the tundish is in an unsteady-state casting state during this process. To reduce quality problems caused by casting at low liquid levels in the tundish, it is generally considered to quickly return to the normal liquid level for casting. However, quickly restoring the liquid level in the tundish requires increasing the amount of molten steel poured into the tundish from the ladle, which causes violent agitation of the molten steel in the tundish, resulting in slag entrainment and secondary oxidation, which seriously reduces the cleanliness of the molten steel and the quality of the cast billet.

[0003] To address the issues of slag entrapment and secondary oxidation in molten steel caused by large fluctuations and rapid rises and falls in the tundish level during continuous casting ladle changes due to unsteady casting, the main focus is on controlling the rate of molten steel level rise in the tundish during ladle changes, reducing the impact of the steel flow on the molten steel, and minimizing the agitation of the molten steel in the tundish. Because achieving a good match between the tundish level rise rate, the molten steel level, and the continuous casting speed is difficult, large-sized inclusions in the steel are frequently found, leading to a decrease in yield. Currently, relevant patent literature on the problem of unsteady casting during continuous casting ladle changes includes: a method for maintaining the cleanliness of molten steel during ladle opening (CN105921734B), a casting equipment and method capable of maintaining a steady tundish liquid level (CN107598145 A), "Control and Optimization of Unsteady Casting in Continuous Casting," and "Experimental Analysis of the Behavior of Drainage Sand During Ladle Changes," etc. Through research on the above-mentioned technical solutions, the main problems with existing technical solutions are:

[0004] 1) A method for maintaining the cleanliness of molten steel during the initial pouring of a continuous casting ladle (CN105921734B) mainly focuses on reducing the entry of diverting sand into the impact zone. It does not address the issues of slag entrapment and secondary oxidation of molten steel caused by rapid fluctuations in the tundish liquid level. 2) A casting equipment and method capable of maintaining a stable tundish liquid level (CN107598145 A) provides a novel device that can indeed solve the problem of tundish liquid level fluctuations during ladle changes. However, this method involves two impact zones, and the change in the position of these zones during ladle changes also causes fluctuations in the flow field, constituting unsteady casting. Furthermore, modifying the casting platform to use this equipment incurs costs. 3) Literature such as "Control and Optimization of Unsteady Continuous Casting" proposes that solving unsteady continuous casting is a systematic task, requiring control of parameters such as the casting liquid level, ladle flow rate, and slag discharge. The proposed solutions are rather conceptual and do not offer specific solutions to the unsteady casting problems caused by rapid fluctuations in the liquid level during ladle changes.

[0005] In summary, this technology does not involve the technical solution of this application. Summary of the Invention

[0006] The technical problem this invention aims to solve is to address the shortcomings of existing technologies by providing a simple and effective method to resolve issues such as excessive slag entrapment and secondary oxidation of molten steel caused by the rapid rise and fall of molten steel level in the tundish during ladle changing. This method reduces the impact of the steel flow on the molten steel in the tundish, mitigates steel quality problems caused by unsteady casting during ladle changing, and maintains the cleanliness of molten steel during ladle changing in continuous casting steelmaking equipment.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] This invention relates to a method for maintaining the cleanliness of molten steel during ladle changes in continuous casting steelmaking equipment. The steps of this method are as follows:

[0009] S1. During continuous casting, when the molten steel is close to the ladle replacement, the tundish level is raised to 1.05 to 1.15 times the normal level.

[0010] S2. After the tundish reaches the target liquid level, stop pouring and perform a ladle replacement operation. During the period of ladle replacement and cessation of pouring molten steel into the tundish, the relationship between the lowest liquid level in the tundish and the continuous molten steel output per minute of the tundish is: (Tundish liquid level at which pouring is stopped - lowest liquid level at the time of ladle replacement) / molten steel output per minute of the tundish at the time of stoppage = 1~4;

[0011] S3. After the tundish is filled with molten steel and the tundish is changed, the casting begins. By controlling the amount of steel flowing through the ladle nozzle, the tundish is brought back to the normal casting level, and the ladle change operation is completed. During this process, the tundish level rise rate is controlled to be 4% to 8% of the normal casting level per minute.

[0012] The normal casting liquid level in the intermediate ladle is 600-1200 mm.

[0013] During the continuous casting process in step S1, when the molten steel from the stopped furnace is close to the ladle change, the tundish level is raised to 1.05 to 1.15 times the normal level. The required rate of increase of the tundish level is 1.0% to 3.5% of the normal level per minute.

[0014] When pouring begins after changing the ladle between steps S2 and S3, the actual liquid level in the tundish should be controlled at 75% to 88% of the normal pouring level.

[0015] The continuous casting process employs a multi-machine round billet continuous casting machine.

[0016] The large-scale turntable is equipped with a first boom and a second boom. A steel ladle is placed on one side of the first boom and another steel ladle is placed on one side of the second boom.

[0017] The large package turntable is a rotatable structure.

[0018] The working principle and beneficial effects of the technical solution adopted in this invention are as follows:

[0019] The method for maintaining the cleanliness of molten steel during ladle changes in continuous casting steelmaking equipment, as described in this invention, aims to maintain the cleanliness of molten steel during ladle changes and reduce slag entrapment and secondary oxidation problems caused by excessively rapid fluctuations in the tundish liquid level during ladle changes. The improvement of this method involves the control process of the tundish liquid level during ladle changes, matching the adjustment of process parameters such as casting speed, tundish liquid level, and filling flow rate. Through these improvements, the problems existing in the prior art are effectively solved, reducing the impact of the steel flow on the molten steel in the tundish, significantly reducing steel quality problems caused by unsteady casting during ladle changes, reducing product scrap due to large-size inclusions in the steel, and improving the yield. Attached Figure Description

[0020] The following is a brief explanation of the contents depicted in the accompanying drawings and the markings therein:

[0021] Figure 1 A comparative table showing the embodiments and comparative examples of the method for maintaining the cleanliness of molten steel during ladle replacement in continuous casting steelmaking equipment according to the present invention; Detailed Implementation

[0022] The following description, with reference to the accompanying drawings, provides a more detailed explanation of the specific embodiments of the present invention, including the shape and structure of each component, the relative positions and connections between the parts, the functions and working principles of each part:

[0023] As attached Figure 1 As shown, this invention relates to a method for maintaining the cleanliness of molten steel during ladle changes in continuous casting steelmaking equipment. The steps of this method are as follows:

[0024] S1. During continuous casting, when the molten steel is close to the ladle level, the tundish level is raised to 1.05–1.15 times the normal level. S2. After the tundish level reaches the target height, casting is stopped, and the ladle is changed. During the period of ladle change and cessation of molten steel pouring into the tundish, the relationship between the lowest tundish level and the tundish's continuous molten steel output per minute is: (Tundish level at the stop of pouring - lowest level at the time of ladle change) / tundish's continuous molten steel output per minute at the stop of pouring = 1–4. S3. After the ladle is filled with molten steel and the ladle is changed, pouring resumes. By controlling the steel flow rate through the ladle nozzle, the tundish level is brought back to the normal level, completing the ladle change. During this process, the tundish level rise rate is controlled to be 4%–8% of the normal level per minute. The normal tundish level is 600–1200 mm. The above steps address the shortcomings of existing technologies, and an improved technical solution is proposed. To maintain the cleanliness of molten steel during ladle changes in continuous casting and reduce excessive slag entrapment and secondary oxidation caused by the intense mixing of molten steel and slag above the molten steel surface due to rapid fluctuations in the tundish liquid level during the ladle change process, the improvement of the method in this invention involves the control of the tundish liquid level during the ladle change process, matching the adjustment of process parameters such as casting speed, tundish liquid level, and ladle filling flow rate. Through the above improvements, the problems existing in the prior art are effectively solved, the impact of the steel flow on the molten steel in the tundish is reduced, the quality problems of molten steel caused by unsteady casting during ladle changes are greatly reduced, the product scrap caused by large inclusions in the steel is reduced, and the yield is improved. The method for maintaining the cleanliness of molten steel during ladle replacement in continuous casting steelmaking equipment, as described in this invention, has simple steps and effectively solves the problems of excessive slag entrapment and secondary oxidation of molten steel caused by the intense agitation between the molten steel and the slag above the molten steel surface due to the rapid rise and fall of the tundish liquid level during ladle replacement. It reduces the impact force of the steel flow on the molten steel in the tundish, reduces the quality problems of molten steel caused by unsteady casting during ladle replacement, and maintains the cleanliness of molten steel during continuous casting ladle replacement.

[0025] During the continuous casting process in step S1, when the molten steel is close to being replaced with a ladle, the tundish level is raised to 1.05 to 1.15 times the normal level. The rate of increase in the tundish level is controlled to be 1.0% to 3.5% of the normal level per minute. This step controls the rate of increase in the tundish level, solves the problems in the existing technology, and ensures the cleanliness of the molten steel.

[0026] After step S2 and before step S3, when pouring begins after changing the ladle, the actual liquid level in the tundish should be controlled at 75% to 88% of the normal pouring level. This structure controls the actual liquid level in the tundish when pouring begins after changing the ladle, comparing the actual level with the normal pouring level, thus solving a technical problem.

[0027] The continuous casting utilizes a multi-machine round billet continuous casting machine. A first and second boom are mounted on the ladle turntable. A ladle is positioned on one side of the first boom, and another ladle is positioned on one side of the second boom. The ladle turntable is a rotatable structure. In this configuration, during the ladle casting process, one ladle is suspended on one boom of the ladle turntable. Once the molten steel in the ladle is poured, the other ladle is suspended on the boom on the other side of the turntable. The turntable is then rotated, exchanging the positions of the two booms, and the other ladle continues casting into the tundish, enabling continuous production.

[0028] The method of the present invention will be further described in detail below with reference to specific embodiments:

[0029] The invention is further illustrated using an example of a 120-ton ladle, a 5-strand, 5-move round billet continuous casting machine, a cross-sectional diameter of 600mm, and a casting speed of 0.28m / min. During production, 72 heats across 6 casting cycles were conducted. The first 4 cycles (48 heats) served as the example, and the last 2 cycles (24 heats) served as the comparative examples. The main process control procedures for ladle changing in the example are as follows:

[0030] 1. During continuous casting, when the molten steel for a heat is close to the ladle change, the tundish level should be raised to 1.05–1.15 times the normal level. The rate of increase should be controlled at 1.0%–3.5% per minute. 2. The normal tundish level is 600–1200 mm. 3. Once the tundish level reaches the target height, casting should be stopped, and the ladle change should be performed. During the period of cessation of molten steel casting, the relationship between the lowest tundish level and the continuous molten steel output per minute is: (Tundish level at cessation of casting - lowest level at ladle change) / continuous molten steel output per minute at cessation of casting = 1–4. 4. When the heat resumes after the ladle change, the tundish level should be controlled at 75%–88% of the normal level. 5. After changing the ladle and starting pouring, the steel flow rate through the ladle nozzle is controlled to bring the tundish back to the normal pouring level, completing the ladle changing operation. During this process, the rate of increase in the tundish level should be controlled to be 4%–8% of the normal pouring level per minute. A comparative table of embodiments and examples of the method for maintaining molten steel cleanliness during ladle changing in continuous casting steelmaking equipment described in this invention is attached. Figure 1 As shown.

[0031] From the appendix Figure 1 The results show that the method of maintaining the cleanliness of molten steel during ladle replacement in the continuous casting steelmaking equipment of the present invention can significantly reduce the impact force of the steel flow on the molten steel in the tundish. It can also greatly reduce the excessive slag entrapment and secondary oxidation of molten steel caused by the rapid rise and fall of the tundish liquid level during the ladle replacement process, which leads to intense mixing between the molten steel in the tundish and the slag above the molten steel surface. This reduces the product rejection caused by large inclusions in the steel and improves the yield.

[0032] The method for maintaining the cleanliness of molten steel during ladle changing in continuous casting steelmaking equipment, as described in this invention, aims to maintain the cleanliness of molten steel during ladle changing and reduce excessive slag entrapment and secondary oxidation of molten steel caused by the intense agitation between the molten steel and the slag above the molten steel surface due to rapid fluctuations in the tundish liquid level during the ladle changing process. The improvement of this method involves the control process of the tundish liquid level during ladle changing, matching the adjustment of process parameters such as casting speed, tundish liquid level, and filling flow rate. Through these improvements, the problems existing in the prior art are effectively solved, reducing the impact of the steel flow on the molten steel in the tundish, significantly reducing the steel quality problems caused by unsteady casting during ladle changing, reducing product scrap due to large inclusions in the steel, and improving the yield.

[0033] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any improvements made by adopting the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A method for maintaining the cleanliness of molten steel during ladle changing in continuous casting steelmaking equipment, characterized in that: The steps of the method for maintaining the cleanliness of molten steel when changing ladles in continuous casting steelmaking equipment are as follows: S1. During continuous casting, when the molten steel is close to the ladle change, raise the tundish level to 1.05 to 1.15 times the normal level. S2. After the tundish reaches the target liquid level, stop pouring and perform a ladle replacement operation. During the period of ladle replacement and cessation of pouring molten steel into the tundish, the relationship between the lowest liquid level in the tundish and the continuous molten steel output per minute of the tundish is: (Tundish liquid level at which pouring is stopped - lowest liquid level at the time of ladle replacement) / molten steel output per minute of the tundish at the time of stoppage = 1~4; S3. After the tundish is filled with molten steel and the ladle is changed, pouring begins. By controlling the amount of steel flowing through the ladle nozzle, the tundish is brought back to the normal pouring level, completing the ladle change operation. During this process, the tundish level rise rate is controlled to be 4% to 8% of the normal pouring level per minute. During the continuous casting process in step S1, when the molten steel from the stopped furnace is close to the ladle change, the tundish level is raised to 1.05 to 1.15 times the normal level. The required rate of increase in the tundish level is 1.0% to 3.5% of the normal level per minute. When starting casting after changing the ladle between steps S2 and S3, the actual liquid level in the tundish should be controlled at 75% to 88% of the normal casting level.

2. The method for maintaining the cleanliness of molten steel during ladle changing in continuous casting steelmaking equipment according to claim 1, characterized in that: The normal casting liquid level in the intermediate ladle is 600~1200mm.

3. The method for maintaining the cleanliness of molten steel during ladle changing in continuous casting steelmaking equipment according to claim 1 or 2, characterized in that: The continuous casting process employs a multi-machine continuous casting machine.

4. The method for maintaining the cleanliness of molten steel during ladle changing in continuous casting steelmaking equipment according to claim 1 or 2, characterized in that: The large-scale turntable is equipped with a first boom and a second boom. A steel ladle is placed on one side of the first boom and another steel ladle is placed on one side of the second boom.

5. The method for maintaining the cleanliness of molten steel during ladle changing in continuous casting steelmaking equipment according to claim 4, characterized in that: The large package turntable is a rotatable structure.

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