A process control method for reducing residual steel pouring into the tundish during multi-machine, multi-flow continuous casting.

Abstract

This invention relates to a process control method for reducing residual steel in the tundish during multi-machine, multi-flow continuous casting, belonging to the field of continuous casting technology in the metallurgical industry. The technical solution is as follows: (1) The bottom of the tundish is a stepped bottom structure, the through hole on the baffle wall is 8-15mm away from the bottom of the impact zone, and a fusible baffle is provided inside the baffle wall; (2) When the last heat of the next casting cycle reaches the middle stage, the continuous casting speed is reduced; (3) Before the last heat of the next casting cycle is refined and discharged from the station, the discharge temperature is increased; (4) When the flow is closed, the side flows that are far from the impact zone of the tundish are closed first, and then the flow is closed from the outside to the inside, and finally the flow in the center position is closed; (5) The billet is assembled during the period between the middle stage of the last heat of the next casting cycle and the closing of the ladle. According to the billet length requirements, the side flows that have been cut into whole lengths by the billet flame cutting machine are stopped. The beneficial effects of this invention are: effectively reducing residual steel in the tundish, improving the quality of molten steel at the end of the casting cycle, and reducing the consumption of steel materials.

Description

Technical Field

[0001] This invention relates to a process control method for reducing excess steel poured into the tundish during multi-machine, multi-flow continuous casting, belonging to the field of continuous casting technology in the metallurgical industry. Background Technology

[0002] Tundish filler residue in continuous casting refers to the amount of molten steel remaining in the tundish after each casting cycle. It is a crucial indicator affecting steel consumption and a key factor in evaluating the economic efficiency of modern continuous casting machines. When the molten steel level around the tundish submersible nozzle drops below the critical eddy current height, eddies form in the nozzle area, causing slag and covering agent from the tundish surface to enter the crystallizer, resulting in slag entrapment in the billet. To prevent slag entrapment during the later stages of casting, steel companies typically ensure the molten steel level in the tundish is above the critical eddy current height when casting is stopped. Higher tundish filler residue leads to lower steel yield and significant waste of production costs. Especially in today's challenging market environment, reducing tundish filler residue, further reducing costs and increasing efficiency, and minimizing steel consumption are critical.

[0003] Multi-strand continuous casting refers to the simultaneous production of multiple strands of billets on a single continuous casting machine using a separate crystallizer vibration device and straightening machine for each strand. Continuous casting machines with 3 to 8 strands (3 to 8 machines) are widely used, primarily for square and round billets. During production, if one or two strands in a multi-strand continuous casting machine malfunction and stop casting, the remaining strands can generally continue casting a ladle of molten steel. Multi-strand continuous casting machines typically use a long tundish with multiple nozzles equal to the number of strands to allow simultaneous injection of molten steel into each strand's crystallizer. The molten steel travels a long distance within the long tundish, resulting in significant temperature loss and temperature differences between strands. The outermost nozzle has a lower temperature, making it prone to clogging. The more strands and the longer the tundish, the more common it is to have several strands stop casting simultaneously, leading to low billet yield and a large amount of residual molten steel in the tundish.

[0004] Currently, domestic and international research on reducing residual steel in continuous casting tundishes mainly focuses on optimizing the tundish structure. For example, Chinese patent application No. 201720407283.0 discloses a tundish for reducing residual steel in continuous casting. This method reduces residual steel in the tundish by opening through holes on the dam inside the tundish and by making the bottom of the tundish bottom in the pouring zone lower than the bottom of the pouring zone. It is mainly aimed at one casting per machine.

[0005] Chinese patent application No. 200710010179.9 discloses a method for reducing excess molten steel in continuous casting tundishes. It mainly involves changing the properties of the molten steel slag in the tundish and increasing its basicity and viscosity to lower the liquid temperature around the casting gate, reduce the amount of slag, promote the solidification of the molten steel in the tail billet section, and reduce excess molten steel. This method mainly reduces excess steel through slag deformation, which is difficult to control. In continuous casting cycles with fewer furnace runs, there is less slag, and it is impossible to change the basicity and viscosity of the slag to achieve the purpose of reducing excess steel. Summary of the Invention

[0006] The purpose of this invention is to provide a process control method for reducing the amount of residual steel poured into the tundish during multi-machine, multi-flow continuous casting, which effectively reduces the amount of residual steel poured into the tundish, improves the quality of molten steel at the end of casting, reduces the consumption of steel materials, and solves the problems existing in the background technology.

[0007] The technical solution of this invention is:

[0008] A process control method for reducing residual steel in the tundish of multi-machine, multi-flow continuous casting, characterized by control according to the following requirements:

[0009] (1) The bottom of the tundish is a stepped bottom structure. The bottom of the impact zone is 2-10 mm higher than the bottom of the side flow casting zone, and the bottom of the side flow casting zone is 5-15 mm higher than the bottom of the center flow casting zone. The bottom of the impact zone is located in the middle of the bottom of the tundish. The bottom of the center flow casting zone is the bottom of the two flow zones that are close to the bottom of the impact zone. The bottoms of the other zones are the bottoms of the side flow casting zones. There are baffles on both sides of the bottom of the impact zone. There are through holes on the baffles. The through holes are 8-15 mm away from the bottom of the impact zone. There are fusible baffles inside the baffles that match the through holes.

[0010] (2) When the last heat of the next casting is poured to the middle stage, reduce the continuous casting speed so that the center flow speed is the minimum speed and the side flow speed is the minimum speed ±0.1m / min;

[0011] (3) Before the last heat of steel is refined and discharged from the station, the pouring time of the last heat is calculated according to the length of this pouring, and the temperature at the station is increased according to the temperature drop during the extended pouring time. The temperature increase range is calculated as 0.5-1℃ / min.

[0012] (4) When closing a flow, prioritize closing the edge flows that are far from the impact zone of the middle pack, then close them sequentially from the outside to the inside, and finally close the flow at the center position;

[0013] (5) The billet assembly begins during the period between the middle of the last casting and the closing of the ladle. The billet is sized according to the billet requirements. The side stream that has passed through the billet flame cutting machine to form a whole sized piece is stopped. The billet assembly method is as follows: Assume that the distance from the billet cutting machine to the crystallizer outlet is N meters and the billet sized requirement is n meters. If N / n is an integer, the stream is stopped. If N / n is a decimal, the stream is not stopped. The stream is stopped when the size of the billet after passing the cutting position and the size of the billet before the cutting are added together to make up the sized piece.

[0014] The above-mentioned process control method for reducing the amount of residual steel poured into the tundish in multi-machine, multi-flow continuous casting refers to the long nozzle of the continuous casting machine corresponding to the bottom of the impact zone, the bottom of the center flow pouring zone corresponding to the center position flow of the continuous casting machine, the center position flow being the two flows on the left and right adjacent to the bottom of the impact zone, and the bottom of the side flow pouring zone corresponding to other flows of the continuous casting machine, referred to as side flows.

[0015] In the above-mentioned process control method for reducing the amount of residual steel poured into the tundish during multi-machine, multi-flow continuous casting, the fusible baffle is a low-carbon steel plate with a thickness of 1-3mm.

[0016] In the above-mentioned process control method for reducing the amount of residual steel poured into the tundish during multi-machine, multi-flow continuous casting, the fusible baffle is prefabricated inside the retaining wall.

[0017] The tundish structure employed in this invention limits the height of the slag retaining wall through-holes primarily to reduce the height of molten steel within the impact zone retaining wall during the last pour, thereby reducing excess steel. Adding fusible baffles to the retaining wall through-holes mainly prevents impurities from the first pour of molten steel from being washed into the stopper rod pouring zone during the initial pouring. By adding fusible baffles, the molten steel level is already higher than the retaining wall through-holes when the baffles melt, preventing slag from entering the tundish stopper rod pouring zone and causing inclusions in the cast billet. A stepped ladle bottom is adopted, with the ladle bottom around the impact zone of the long nozzle higher than that of the side-flow tundish. This is mainly to ensure that molten steel around the impact zone enters the casting area and raises the molten steel level in the tundish at the end of the casting stop. The bottom of the side-flow tundish is higher than that of the center-flow ladle because the side-flow molten steel is the first to stop casting and its temperature is generally lower. After the side-flow molten steel stops casting, the lower-level molten steel enters the bottom of the center-flow tundish, raising the molten steel level in the center-flow tundish. The molten steel in the center position has a higher temperature and stops casting last, thus minimizing the amount of molten steel remaining in the tundish.

[0018] Controlling the casting speed mainly involves reducing the casting speed in the last furnace to lower the critical height for vortex formation, while also providing sufficient time for manual billet assembly.

[0019] Controlling overheating is mainly because the last heat of casting requires a long time to pour out the molten steel in the tundish, and the casting speed needs to be reduced, which will cause the temperature of the continuous casting tundish to drop. Increasing the outlet temperature raises the tundish temperature, laying the foundation for reducing the casting speed and reducing excess steel in the later stages.

[0020] Manual billet assembly prioritizes assembling billets at the side flow stage, primarily because the temperature of the molten steel at the side flow stage is lower, making it prone to nozzle clogging. Additionally, the bottom of the tundish at the side flow stage is higher than that at the center flow stage, allowing the molten steel to flow towards the center flow stage after stopping pouring at the critical vortex height, thus ensuring that the entire tundish is filled with molten steel as completely as possible. Furthermore, due to the limitations of computer-aided billet tracking and the complexity of actual production changes, manual billet assembly is more flexible and can fully utilize the remaining molten steel in the tundish to produce qualified billets of specified lengths.

[0021] The beneficial effects of this invention are: it effectively reduces the amount of residual steel poured into the tundish, improves the quality of molten steel at the end of the pouring process, reduces steel material consumption, and lowers the production costs for enterprises. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the intermediate package structure of the present invention;

[0023] In the diagram: 1. Ladle; 2. Long nozzle; 3. Tundish; 4. Stopper rod; 5. Fusible stopper and through hole; 6. Tundish submersible nozzles (7, 8, 9, 10, 71, 81, 91, 101); 11. Bottom of ladle in the far-flowing pouring area of ​​the impact zone; 12. Bottom of ladle in the near-nozzle pouring area of ​​the impact zone; 13. Bottom of ladle in the impact zone; 14. Bottom of ladle in the impact zone. Implementation

[0024] The invention will be further described below with reference to the accompanying drawings and examples.

[0025] A process control method for reducing residual steel pouring into the tundish during multi-machine, multi-flow continuous casting, wherein control is carried out according to the following requirements:

[0026] (1) The bottom of the tundish is a stepped bottom structure. The bottom of the impact zone is 2-10 mm higher than the bottom of the side flow casting zone, and the bottom of the side flow casting zone is 5-15 mm higher than the bottom of the center flow casting zone. The bottom of the impact zone is located in the middle of the bottom of the tundish. The bottom of the center flow casting zone is the bottom of the two flow zones that are close to the bottom of the impact zone. The bottoms of the other zones are the bottoms of the side flow casting zones. There are baffles on both sides of the bottom of the impact zone. There are through holes on the baffles. The through holes are 8-15 mm away from the bottom of the impact zone. There are fusible baffles inside the baffles that match the through holes.

[0027] (2) When the last heat of the next casting is poured to the middle stage, reduce the continuous casting speed so that the center flow speed is the minimum speed and the side flow speed is the minimum speed ±0.1m / min;

[0028] (3) Before the last heat of steel is refined and discharged from the station, the pouring time of the last heat is calculated according to the length of this pouring, and the temperature at the station is increased according to the temperature drop during the extended pouring time. The temperature increase range is calculated as 0.5-1℃ / min.

[0029] (4) When closing a flow, prioritize closing the edge flows that are far from the impact zone of the middle pack, then close them sequentially from the outside to the inside, and finally close the flow at the center position;

[0030] (5) The billet assembly begins during the period between the middle of the last casting and the closing of the ladle. The billet is sized according to the billet requirements. The side stream that has passed through the billet flame cutting machine to form a whole sized piece is stopped. The billet assembly method is as follows: Assume that the distance from the billet cutting machine to the crystallizer outlet is N meters and the billet sized requirement is n meters. If N / n is an integer, the stream is stopped. If N / n is a decimal, the stream is not stopped. The stream is stopped when the size of the billet after passing the cutting position and the size of the billet before the cutting are added together to make up the sized piece.

[0031] The bottom of the impact zone corresponds to the long nozzle of the continuous casting machine, the bottom of the center flow pouring zone corresponds to the center position flow of the continuous casting machine, the center position flow consists of the two flows on the left and right that are adjacent to the bottom of the impact zone, and the bottom of the side flow pouring zone corresponds to the other flows of the continuous casting machine, which are called side flows.

[0032] The fusible baffle is a low-carbon steel plate with a thickness of 1-3mm.

[0033] The fusible baffle is prefabricated inside the retaining wall. Example 1

[0034] See attached document Figure 1 The continuous casting machine is an eight-strand continuous casting machine. When building the tundish before each casting, the distance between the through hole of the tundish retaining wall and the bottom of the impact zone is 8mm. A fusible baffle with a thickness of 1mm is added to the through hole of the tundish retaining wall. The bottom of the impact zone is 210mm higher than the bottom of the side flow casting zone, and the bottom of the side flow casting zone is 5mm higher than the bottom of the center flow casting zone.

[0035] Before the last heat of molten steel leaves the station, the refining worker calculates the pouring time for the last heat based on the length of this pouring, and increases the exit temperature by 1℃ / min according to the extended stop time.

[0036] When the last batch is poured to the middle stage, reduce the overall casting speed of the continuous casting, so that the center flow casting speed is the minimum casting speed of 0.8 m / min and the side flow casting speed is 0.9 m / min;

[0037] When the last batch is poured to the middle stage, the operator begins to assemble the billets. Prioritize assembling the billets and shutting off the side streams 7 and 71, which are farther away from the impact zone of the tundish. Then assemble the billets and stop pouring streams 8 and 81. Close them off one by one from the outside to the inside. Finally, close the central streams 10 and 101.

[0038] The distance from the billet cutter to the crystallizer outlet of the continuous casting machine is 25 meters, and the billet length requirement is 12.5 meters. The result of 25 / 12.5 is an integer of 2. Therefore, when observing the 7th and 71st streams, if the head of the billet in the 7th stream reaches the position of the flame cutter, then stop casting for that stream. Similarly, shut down streams 71, 8, 81, 9, 91, 10 and 101 in sequence.

[0039] After the casting was completed, the 10th stream was shut off last. There were 6 tons of steel remaining in the tundish and slag was removed. All streams except the 10th stream successfully assembled billets. The last billet of the 10th stream was 0.2 meters long. Example 2

[0040] See attached document Figure 1 The continuous casting machine is an eight-strand continuous casting machine. When building the tundish before each casting, the distance between the through hole of the tundish retaining wall and the bottom of the impact zone is 15mm, and a 3mm fusible baffle is added to the through hole of the tundish retaining wall. The bottom of the impact zone is 10mm higher than the bottom of the side flow casting zone, and the bottom of the side flow casting zone is 15mm higher than the bottom of the center flow casting zone.

[0041] Before the last heat of molten steel leaves the station, the refining worker calculates the pouring time for the last heat based on the length of this pouring, and increases the temperature at the station by 0.5℃ / min according to the extended stop time.

[0042] When the last batch is poured to the middle stage, reduce the overall casting speed of the continuous casting, so that the center flow casting speed is the minimum casting speed of 0.8 m / min and the side flow casting speed is 0.8 m / min;

[0043] When the last batch is poured to the middle stage, the operator begins to assemble the billets. Prioritize assembling the billets and shutting off the side streams 7 and 71, which are farther away from the impact zone of the tundish. Then assemble the billets and stop pouring streams 8 and 81. Close them off one by one from the outside to the inside. Finally, close the central streams 10 and 101.

[0044] The distance from the billet cutter to the crystallizer outlet of the continuous casting machine is 25 meters, and the billet length requirement is 10 meters. The result of 25 / 10 is 2.5, which is not an integer. Therefore, it is necessary to observe. When the billet head of either stream 71 or 7 passes the cutter by 5 meters, stop casting for it. If it is found that the billet head of stream 71 reaches the flame cutter position 5 meters before it, then stop casting for stream 71. In the same way, shut down streams 7, 8, 81, 9, 91, 10 and 101 in sequence.

[0045] After pouring was completed, the 101st stream was shut off last, and 3 tons of steel remained in the tundish before slag removal. All streams except the 101st stream successfully assembled billets, and the 10th stream produced a 0.15-meter tail billet. Example 3

[0046] See attached document Figure 1The continuous casting machine is an eight-strand continuous casting machine. When building the tundish before each casting, the distance between the through hole of the tundish retaining wall and the bottom of the impact zone is 10mm, and a fusible baffle is added to the through hole of the tundish retaining wall by 2mm. The bottom of the impact zone is 6mm higher than the bottom of the side flow casting zone, and the bottom of the side flow casting zone is 8mm higher than the bottom of the center flow casting zone.

[0047] Before the last heat of molten steel leaves the station, the refining worker calculates the pouring time for the last heat based on the length of this pouring, and increases the temperature at the station by 0.6℃ / min according to the extended stop time.

[0048] When the last batch is poured to the middle stage, reduce the overall casting speed of the continuous casting, so that the center flow casting speed is the minimum casting speed of 0.8 m / min and the side flow casting speed is 0.7 m / min;

[0049] When the last batch is poured to the middle stage, the operator begins to assemble the billets. Prioritize assembling the billets and shutting off the side streams 7 and 71, which are farther away from the impact zone of the tundish. Then assemble the billets and stop pouring streams 8 and 81. Close them off one by one from the outside to the inside. Finally, close the central streams 10 and 101.

[0050] The distance from the billet cutter to the crystallizer outlet of the continuous casting machine is 25 meters. The billet length requirement is 11 meters. 25 / 11 results in an integer of 2 with a remainder of 3 meters. To reach the required length of 11 meters, 8 meters are needed. Therefore, when assembling the billets, observe the 7th and 71st streams. If the head of the billet in the 7th stream reaches 8 meters after the flame cutter, stop pouring for that stream. Similarly, shut down streams 71, 8, 81, 9, 91, 10, and 101 in sequence.

[0051] After pouring was completed, the 10th stream was shut off last, and 4 tons of steel remained in the tundish before slag removal. All streams except the 101st stream successfully assembled billets, and the 10th stream's tail billet was 0.25 meters long.

Claims

1. A process control method for reducing residual steel pouring into the tundish during multi-machine, multi-flow continuous casting, characterized in that: Control should be implemented according to the following requirements: (1) The bottom of the tundish is a stepped bottom structure. The bottom of the impact zone is 2-10 mm higher than the bottom of the side flow casting zone, and the bottom of the side flow casting zone is 5-15 mm higher than the bottom of the center flow casting zone. The bottom of the impact zone is located in the middle of the bottom of the tundish. The bottom of the center flow casting zone is the bottom of the two flow zones that are close to the bottom of the impact zone. The bottoms of the other zones are the bottoms of the side flow casting zones. There are baffles on both sides of the bottom of the impact zone. There are through holes on the baffles. The through holes are 8-15 mm away from the bottom of the impact zone. There are fusible baffles inside the baffles that match the through holes. (2) When the last heat of the next casting is poured to the middle stage, reduce the continuous casting speed so that the center flow speed is the minimum speed and the side flow speed is the minimum speed ±0.1m / min; (3) Before the last heat of steel is refined and discharged from the station, the pouring time of the last heat is calculated according to the length of this pouring, and the discharge temperature is increased according to the extended time of the stop pouring. The temperature increase range is calculated according to 0.5-1℃ / min. (4) When closing a flow, prioritize closing the edge flows that are far from the impact zone of the middle pack, then close them sequentially from the outside to the inside, and finally close the flow at the center position; (5) The billet assembly begins during the period between the middle of the last casting and the closing of the ladle. The billet is sized according to the billet requirements. The side stream that has passed through the billet flame cutting machine to form a whole sized piece is stopped. The billet assembly method is as follows: Assume that the distance from the billet cutting machine to the crystallizer outlet is N meters and the billet sized requirement is n meters. If N / n is an integer, the stream is stopped. If N / n is a decimal, the stream is not stopped. The stream is stopped when the size of the billet after passing the cutting position and the size of the billet before the cutting are added together to make up the sized piece.

2. The process control method for reducing residual steel pouring into the tundish during multi-machine, multi-flow continuous casting according to claim 1, characterized in that: The bottom of the impact zone corresponds to the long nozzle of the continuous casting machine, the bottom of the center flow pouring zone corresponds to the center position flow of the continuous casting machine, the center position flow consists of the two flows on the left and right that are adjacent to the bottom of the impact zone, and the bottom of the side flow pouring zone corresponds to the other flows of the continuous casting machine, which are called side flows.

3. The process control method for reducing residual steel pouring into the tundish during multi-machine, multi-flow continuous casting according to claim 1, characterized in that: The fusible baffle is a low-carbon steel plate with a thickness of 1-3mm.

4. The process control method for reducing residual steel pouring into the tundish during multi-machine, multi-flow continuous casting according to claim 3, characterized in that: The fusible baffle is prefabricated inside the retaining wall.

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