Automatic control technology for pulling speed of automobile sheet

Abstract

The invention discloses an automatic control technology for the pulling speed of an automobile sheet, which mainly aims at a pulling speed control stage in a pouring process, namely an automatic control process when the pulling speed is 0.8 m / min or above, and specifically comprises the following steps of: S1, calculating a target pulling speed by combining a superheat degree with a section parameter; and S11, calculating the degree of superheat. And S12, the target pulling speed is determined by combining the superheat degree with the section. And S2, a control method for increasing the speed in the stable pouring process when the pulling speed of the automobile sheet is larger than 0.8 m / min is adopted. And S3, the target pulling speed is recalculated 10 minutes after the pulling speed is increased to the target pulling speed, and the pulling speed is increased and decreased according to the target pulling speed. According to the automatic control technology for the pulling speed of the automobile sheet, the operation difference of four workers is solved, the pulling speed is controlled in a standardized mode, response is fast, the cold-rolled steel quality judgment changing rate of the automobile sheet is reduced, and the influence of pulling speed fluctuation on quality is reduced. The control of the automatic pulling speed model of the automobile sheet has great reference significance on the use of other steel types and casting machines, and the market popularization and application prospects are very wide.

Description

Technical Field

[0001] The present invention relates to the field of iron and steel metallurgy industry, and particularly to an automatic control technology for the drawing speed of automotive sheets. Background Art

[0002] During the normal casting process of continuous casting in steelmaking, it is often necessary to adjust the casting speed of the continuous caster according to production requirements. The casting speed control of the continuous caster is a key process parameter that determines the quality of the cast slab. In addition to the production rhythm, the influencing factors of casting speed control are related to the superheat of the tundish, the slab section, and production operations such as changing the nozzle, changing the tundish, starting casting, and ending casting. Manual casting speed control has disadvantages such as large fluctuations in casting speed, inaccurate and untimely adjustment. The on-site operators manually control the casting speed. Due to differences in each person's operating habits, for example, in the process of increasing the speed at the start of casting and when changing the nozzle, and decreasing the speed, a standardized operation cannot be formed, and the time interval for increasing the speed cannot be evenly controlled, resulting in inconsistent speeds of increasing the speed, which affects the quality of the cast slab. When manually controlling the casting speed, there needs to be a post worker on the casting platform at all times. Once an abnormal situation occurs, the post worker needs to handle it emergently on-site. If the handling is not timely, it will lead to quality accidents or production accidents. According to the standardized requirements of on-site operations, the operation process is modeled, and an automatic casting speed control model in various situations is established, and finally automatic starting casting and automatic casting speed control of continuous casting are realized. Currently, in the casting process of automotive sheets in steel mills, the casting speed control generally adopts manual adjustment by workers according to process requirements, and the problems brought by the operation differences between people cannot be completely eliminated, and quality problems often occur due to unreasonable casting speeds. Summary of the Invention

[0003] In order to meet different requirements in the casting process of automotive sheets, solve the operation differences among the four shifts of workers, standardize the control of the casting speed, respond quickly, reduce the rejudgment rate of the cold rolling quality of automotive sheets, and reduce the influence of casting speed fluctuations on quality, an automatic control technology for the casting speed of automotive sheets is provided.

[0004] In the casting speed control stage of the continuous casting production process of automotive sheets, it can be generally divided into 4 stages: casting start casting speed control, casting process casting speed control, end casting process casting speed control, and casting speed control in abnormal processes such as changing the nozzle. Casting start casting speed control stage: the process of increasing the casting speed of the first ladle in the tundish from 0 to 0.8 m / min; Casting process casting speed control stage: the process of increasing the casting speed to the target casting speed after the casting speed reaches 0.8 m / min and the casting speed control process before the end of casting; End casting process casting speed control stage: the casting speed control process of the last ladle cast in the tundish; Casting speed control stage in abnormal processes such as changing the nozzle: the entire casting process, including the stages from casting start to end of casting, the casting speed process of abnormal rapid speed reduction during nozzle change, red card, and production process.

[0005] The automatic control technology for the drawing speed of automotive sheets of the present invention is directed at the drawing speed control stage during the casting process, that is, the automatic control process when the drawing speed is 0.8 m / min or above, including: Data acquisition: Determine the production parameters related to steelmaking continuous casting to be collected, including tundish temperature, drawing speed, cross-section, steel throughput, slab length, slab position, ladle tonnage, tundish tonnage, production logistics. Determine the frequency and time of data acquisition, and decide the time interval of data acquisition according to the real-time and variable nature of the steelmaking process.

[0006] S1. Calculation of the target drawing speed by combining the superheat degree with the cross-section parameters of the cast slab S11. Calculation of the superheat degree Calculation of the superheat degree during the speed increase process: Based on the actual superheat degree measured during the casting process, temperature correction control is added. After the ladle starts pouring, When the ladle tonnage ≥ 200 t, when the measured actual superheat degree ≥ 26 °C, the superheat degree used for calculating the target drawing speed is the actual measured superheat degree plus 5 °C; when the measured actual superheat degree < 26 °C, the superheat degree for calculation is the actual measured superheat degree; When the ladle tonnage < 200 t, when the measured actual superheat degree ≥ 28 °C, the superheat degree for calculation is the actual measured superheat degree plus 3 °C; when the measured actual superheat degree < 28 °C, the superheat degree for calculation is the actual measured superheat degree; Calculation of the superheat degree during the speed decrease process: The superheat degree for calculation is the actual measured superheat degree during the casting process, without temperature correction; S12. Determination of the target drawing speed by combining the superheat degree with the cross-section of the cast slab Based on the nominal width issued in the casting plan, from the quality perspective, to prevent large changes in the flow field due to width adjustment + drawing speed, the drawing speed is not increased or decreased during the width adjustment process, and it is adjusted according to the target drawing speed calculation method 2 minutes after the width adjustment ends; 1) When the cross-section of the cast slab is [900, 1550] mm, When the superheat degree is ≤ 30 °C, the target drawing speed is 1.6 m / min, When the superheat degree is (30, 35] °C, the target drawing speed is 1.5 m / min, When the superheat degree is (35, 40] °C, the target drawing speed is 1.3 m / min, When the superheat degree is (40, 45] °C, the target drawing speed is 1.1 m / min, When the superheat degree > 45 °C, the target drawing speed is 1.0 m / min or a final casting application is submitted; 2) When the cross-section is (1550, 1900] mm When the superheat degree is ≤ 30 °C, the target drawing speed is 1.6 m / min, When the superheat is in the range of (30, 35] °C, the target casting speed is 1.4 m / min, When the superheat is in the range of (35, 40] °C, the target casting speed is 1.2 m / min, When the superheat is in the range of (40, 45] °C, the target casting speed is 1.1 m / min, When the superheat > 45 °C, the target casting speed is 1.0 m / min or an end-casting application is submitted; 3) When the slab section is in the range of (1900, 2150] mm When the superheat is ≤ 30 °C, the target casting speed is 1.5 m / min, When the superheat is in the range of (30, 35] °C, the target casting speed is 1.5 m / min, When the superheat is in the range of (35, 40] °C, the target casting speed is 1.3 m / min, When the superheat is in the range of (40, 45] °C, the target casting speed is 1.1 m / min, When the superheat > 45 °C, the target casting speed is 1.0 m / min or an end-casting application is submitted; S2. Control method for speed increase during stable casting when the casting speed of automotive sheet > 0.8 m / min 1) When the cast slab section ≤ 1200 mm, constant casting speed control is carried out, and the control is carried out according to the target casting speed of up to 1.6 m / min When the section ≤ 1200 mm, after maintaining at 0.8 m / min for 1 min, it accelerates at 0.5 m / min 2 and increases the speed by 0.1 m / min each time, then maintains for 30 s and continues to increase the speed, repeating the speed increase process until the target casting speed; the target casting speed is calculated according to the above S1; 2) When the section > 1200 mm, constant steel-passing amount control is carried out, and the control is carried out according to the target of the maximum steel-passing amount (3.5 t / min); When the section is in the range of (1200, 1500] mm, after maintaining at 0.8 m / min for 1 min, it accelerates at 0.5 m / min 2 and increases the speed by 0.1 m / min each time, then maintains for 30 s and continues to increase the speed, repeating the speed increase process until the target casting speed; the target casting speed is calculated based on the section, superheat and steel-passing amount together; When the section is in the range of (1500, 2150] mm, after maintaining at 0.8 m / min for 1 min, it accelerates at 0.5 m / min 2 and increases the speed by 0.1 m / min each time, then maintains for 50 s and continues to increase the speed, repeating the speed increase process until the target casting speed; the target casting speed is calculated based on the section, superheat and steel-passing amount together; The method for calculating the target casting speed based on the cross-section, superheat degree, and steel passing volume together is as follows: The A casting speed is the target casting speed calculated according to S1; the B casting speed is: the maximum steel passing volume (3.5 t / min) / (cross-section * thickness * density); for the decimal casting speed convention calculated by the steel passing volume and cross-section, when the last two digits after the decimal point are 0.10 - 0.13, it is uniformly set to 0.1, when the last two digits after the decimal point are 0.14 - 0.16, it is uniformly set to 0.15, and when the last two digits after the decimal point are 0.17 - 0.19, it is uniformly set to 0.2; when A ≤ B, the target casting speed is A, and when A > B, the target casting speed is B; when the logistics cannot meet the continuous casting speed requirement, manually input the maximum steel passing volume for corresponding calculation; S3. Recalculate the target casting speed 10 minutes after accelerating to the target casting speed, and adjust the casting speed up and down accordingly.

[0007] Furthermore, when the automotive sheet is the outer panel, the method for adjusting the casting speed up and down in S3 is as follows: Accelerating: When the target casting speed - actual casting speed ≤ 0.2 m / min, control the acceleration at 0.05 m / min for each slab; when the target casting speed - actual casting speed > 0.2 m / min, then control the acceleration to be completed on one slab, and follow the acceleration standard. If the acceleration is within the last 2 m of the slab, then control it all on the next slab; Decelerating: When the actual casting speed - target casting speed ≤ 0.1 m / min, control the deceleration at 0.05 m / min for each slab; when the actual casting speed - target casting speed > 0.1 m / min, then control the deceleration to be completed on one slab.

[0008] Furthermore, when the automotive sheet is other than the inner panel, the method for adjusting the casting speed up and down in S3 is as follows: Accelerating: When the target casting speed - actual casting speed ≤ 0.2 m / min, control the acceleration at 0.1 m / min for each slab; when the target casting speed - actual casting speed > 0.2 m / min, then control the acceleration to be completed on one slab, and follow the acceleration standard. If the acceleration is within the last 2 m of the slab, then control it all on the next slab; Decelerating: When the actual casting speed - target casting speed ≤ 0.1 m / min, control the deceleration at 0.1 m / min for each slab; when the actual casting speed - target casting speed > 0.1 m / min, then control the deceleration to be completed on one slab.

[0009] The beneficial effects of the present invention are: The automatic control technology for the casting speed of automotive sheets in the present invention solves the operation differences among four shifts of personnel, standardizes the control of the casting speed and enables rapid response, reduces the rejudgment rate of the cold-rolled steel quality of automotive sheets, and reduces the impact of casting speed fluctuations on quality. The automatic casting speed model control for automotive sheets has great reference significance for the use of other steel grades and continuous casting machines, and its market promotion and application prospects are very broad. Specific embodiments

[0010] When the automatic control method of the casting speed in the casting process of automotive sheet is used for the GA outer sheet of automotive sheet on the No. 1 machine in the steelmaking plant of Baosteel Zhanjiang Iron and Steel Co., Ltd., for the casting speed control stage in the casting process, that is, the automatic control process when the casting speed is 0.8 m / min and above, it includes: Data acquisition: Determine the production parameters related to continuous casting in steelmaking, including tundish temperature, casting speed, cross-section, steel passing volume, slab length, slab position, ladle tonnage, tundish tonnage, production logistics, determine the frequency and time of data acquisition, and determine the time interval of data acquisition according to the real-time and variability of the steelmaking process.

[0011] S1. Calculation of the target casting speed by combining the superheat degree with the cross-section parameters S11. Calculation of the superheat degree Calculation of the superheat degree during the speed increase process: Based on the actual superheat degree measured during the casting process, temperature correction control is added. After the ladle starts casting, When the ladle tonnage ≥ 200 t, when the measured actual superheat degree ≥ 26 °C, the superheat degree used for calculating the target casting speed is the actual measured superheat degree plus 5 °C; when the measured actual superheat degree < 26 °C, the superheat degree for calculation is the actual measured superheat degree; When the ladle tonnage < 200 t, when the measured actual superheat degree ≥ 28 °C, the superheat degree for calculation is the actual measured superheat degree plus 3 °C; when the measured actual superheat degree < 28 °C, the superheat degree for calculation is the actual measured superheat degree; Calculation of the superheat degree during the speed decrease process: The superheat degree for calculation is the actual measured superheat degree during the casting process, and no temperature correction is performed; S12. Determination of the target casting speed by combining the superheat degree with the cross-section Based on the nominal width issued in the casting plan, from the quality perspective, to prevent large changes in the flow field of width adjustment + casting speed and affect the quality, the casting speed is not raised or lowered during the width adjustment process, and it is adjusted again according to the target casting speed calculation method 2 minutes after the width adjustment ends; 1) When the cross-section of the cast slab is [900, 1550] mm, When the superheat degree is ≤ 30 °C, the target casting speed is 1.6 m / min, When the superheat degree is (30, 35] °C, the target casting speed is 1.5 m / min, When the superheat degree is (35, 40] °C, the target casting speed is 1.3 m / min, When the superheat degree is (40, 45] °C, the target casting speed is 1.1 m / min, When the superheat degree > 45 °C, the target casting speed is 1.0 m / min or a final casting application is submitted; 2) When the cross-section is (1550, 1900] mm When the superheat is ≤ 30°C, the target casting speed is 1.6 m / min. When the superheat is in the range of (30, 35]°C, the target casting speed is 1.4 m / min. When the superheat is in the range of (35, 40]°C, the target casting speed is 1.2 m / min. When the superheat is in the range of (40, 45]°C, the target casting speed is 1.1 m / min. When the superheat > 45°C, the target casting speed is 1.0 m / min or an end-casting application is submitted. 3) When the slab cross-section is in the range of (1900, 2150] mm When the superheat is ≤ 30°C, the target casting speed is 1.5 m / min. When the superheat is in the range of (30, 35]°C, the target casting speed is 1.5 m / min. When the superheat is in the range of (35, 40]°C, the target casting speed is 1.3 m / min. When the superheat is in the range of (40, 45]°C, the target casting speed is 1.1 m / min. When the superheat > 45°C, the target casting speed is 1.0 m / min or an end-casting application is submitted. S2. Control method for speed increase during stable casting when the casting speed of automotive sheet > 0.8 m / min 1) When the cross-section of the cast slab ≤ 1200 mm, constant casting speed control is carried out, and the control is carried out according to the target casting speed of up to 1.6 m / min. When the cross-section ≤ 1200 mm, after maintaining at 0.8 m / min for 1 min, the speed is increased at an acceleration of 0.5 m / min 2 Each time the speed is increased by 0.1 m / min and then maintained for 30 s before continuing to increase the speed. The above speed increase process is repeated until the target casting speed; the target casting speed is calculated according to S1. 2) When the cross-section > 1200 mm, constant steel passing amount control is carried out, and the control is carried out according to the target of the maximum steel passing amount (3.5 t / min). When the cross-section is in the range of (1200, 1500] mm, after maintaining at 0.8 m / min for 1 min, the speed is increased at an acceleration of 0.5 m / min 2 Each time the speed is increased by 0.1 m / min and then maintained for 30 s before continuing to increase the speed. The above speed increase process is repeated until the target casting speed; the target casting speed is calculated based on the cross-section, superheat, and steel passing amount together. When the cross-section is in the range of (1500, 2150] mm, after maintaining at 0.8 m / min for 1 min, the speed is increased at an acceleration of 0.5 m / min 2 Each time the speed is increased by 0.1 m / min and then maintained for 50 s before continuing to increase the speed. The above speed increase process is repeated until the target casting speed; the target casting speed is calculated based on the cross-section, superheat, and steel passing amount together. The method for calculating the target casting speed based on the cross-section, superheat, and steel throughput together is as follows: The A casting speed is the target casting speed calculated according to S1; the B casting speed is: the maximum steel throughput (3.5 t / min) / (cross-section * thickness * density); for the decimal casting speed convention calculated by steel throughput and cross-section, when the last two decimal places are 0.10 - 0.13, it is uniformly set to 0.1, when the last two decimal places are 0.14 - 0.16, it is uniformly set to 0.15, and when the last two decimal places are 0.17 - 0.19, it is uniformly set to 0.2; when A ≤ B, the target casting speed is A, and when A > B, the target casting speed is B; when the logistics cannot meet the continuous casting speed requirement, the maximum steel throughput is manually input for corresponding calculations; S3. Recalculate the target casting speed 10 minutes after reaching the target casting speed, and adjust the casting speed up or down accordingly. The adjustment method is as follows: Speed increase: When the target casting speed - actual casting speed ≤ 0.2 m / min, control the speed increase at 0.05 m / min per slab; when the target casting speed - actual casting speed > 0.2 m / min, control the speed increase to be completed on one slab, and follow the speed increase standard. If the speed increase is within the last 2 m of the slab, all control will be carried out on the next slab; Speed decrease: When the actual casting speed - target casting speed ≤ 0.1 m / min, control the speed decrease at 0.05 m / min per slab; when the actual casting speed - target casting speed > 0.1 m / min, control the speed decrease to be completed on one slab.

[0012] This automatic control method for the casting speed during the automotive sheet casting process eliminates the quality problems caused by the differences among the four shifts. The rejudgment rate of the steel quality of the GA outer panel of the automotive sheet has decreased from 2.2% before use to 1.5%.

[0013] The above content is only used to illustrate the technical solution of the present invention. Any simple modification or equivalent replacement of the technical solution of the present invention by those of ordinary skill in the art shall not depart from the essence and scope of the technical solution of the present invention.

Claims

1. An automated control technology for the drawing speed of automotive sheets, characterized in that: The automatic control process with a casting speed of 0.8 m / min or above includes: S1. Calculation of the target casting speed by combining the superheat with the cross-sectional parameters of the cast slab S11. Calculation of superheat Calculation of superheat during the speed-up process: Based on the actual superheat measured during the casting process, temperature correction control is added. After the tundish starts pouring, When the tundish tonnage ≥ 200 t, when the measured actual superheat ≥ 26 °C, the superheat used for calculating the target casting speed is the actual measured superheat plus 5 °C; when the measured actual superheat < 26 °C, the superheat for calculation is the actual measured superheat; When the tundish tonnage < 200 t, when the measured actual superheat ≥ 28 °C, the superheat for calculation is the actual measured superheat plus 3 °C; when the measured actual superheat < 28 °C, the superheat for calculation is the actual measured superheat; Calculation of superheat during the speed-down process: The superheat for calculation is the actual superheat measured during the casting process without temperature correction; S12. Determination of the target casting speed by combining the superheat with the cross-section of the cast slab Based on the nominal width issued in the casting plan, the casting speed is not increased or decreased during the width adjustment process, and it is adjusted again according to the target casting speed calculation method 2 minutes after the width adjustment ends; 1) When the cross-section of the cast slab is [900, 1550] mm, When the superheat ≤ 30 °C, the target casting speed is 1.6 m / min, When the superheat is (30, 35] °C, the target casting speed is 1.5 m / min, When the superheat is (35, 40] °C, the target casting speed is 1.3 m / min, When the superheat is (40, 45] °C, the target casting speed is 1.1 m / min, When the superheat > 45 °C, the target casting speed is 1.0 m / min or a final casting application is submitted; 2) When the cross-section is (1550, 1900] mm When the superheat ≤ 30 °C, the target casting speed is 1.6 m / min, When the superheat is (30, 35] °C, the target casting speed is 1.4 m / min, When the superheat is (35, 40] °C, the target casting speed is 1.2 m / min, When the superheat is (40, 45] °C, the target casting speed is 1.1 m / min, When the superheat > 45 °C, the target casting speed is 1.0 m / min or a final casting application is submitted; 3) When the cross-section is (1900, 2150] mm When the superheat ≤ 30 °C, the target casting speed is 1.5 m / min, When the superheat is (30, 35] °C, the target casting speed is 1.5 m / min, When the superheat is (35, 40] °C, the target casting speed is 1.3 m / min, When the superheat is (40, 45] °C, the target casting speed is 1.1 m / min, When the superheat > 45 °C, the target casting speed is 1.0 m / min or a final casting application is submitted; S2. Control method for speed-up during the stable casting process when the casting speed of automotive sheet > 0.8 m / min When the cross-section of the cast slab ≤ 1200 mm, constant casting speed control is carried out, and the control is carried out according to the target casting speed of up to 1.6 m / min When the cross-section ≤ 1200 mm, after maintaining at 0.8 m / min for 1 min, the speed is increased at an acceleration of 0.5 m / min 2 , and each time the speed is increased by 0.1 m / min and then maintained for 30 s before continuing to increase the speed. The speed increase process is repeated until the target drawing speed; the target drawing speed is calculated according to S1 described above; When the cross-section > 1200 mm, constant steel throughput control is carried out, and the control is carried out according to the target of the maximum steel throughput (3.5 t / min); When the cross-section is (1200, 1500] mm, it maintains at 0.8 m / min for 1 min and then accelerates at an acceleration of 0.5 m / min. It increases the speed by 0.1 m / min each time, maintains for 30 s after each increase, and then continues to increase the speed. The speed increase process is repeated until the target drawing speed is reached; the target drawing speed is calculated based on the cross-section, superheat degree, and steel passing volume together. 2 When the cross-section is (1200, 1500] mm, it maintains at 0.8 m / min for 1 min and then accelerates at an acceleration of 0.5 m / min. It increases the speed by 0.1 m / min each time, maintains for 30 s after each increase, and then continues to increase the speed. The speed increase process is repeated until the target drawing speed is reached; the target drawing speed is calculated based on the cross-section, superheat degree, and steel passing volume together. When the cross-section is (1500, 2150] mm, it is maintained at 0.8 m / min for 1 min and then accelerated at an acceleration of 0.5 m / min. Each time it is accelerated by 0.1 m / min, it is maintained for 50 s and then continues to accelerate. The acceleration process is repeated until the target drawing speed is reached; the target drawing speed is calculated based on the cross-section, superheat, and steel passing volume together. 2 When the cross-section is (1500, 2150] mm, it is maintained at 0.8 m / min for 1 min and then accelerated at an acceleration of 0.5 m / min. Each time it is accelerated by 0.1 m / min, it is maintained for 50 s and then continues to accelerate. The acceleration process is repeated until the target drawing speed is reached; the target drawing speed is calculated based on the cross-section, superheat, and steel passing volume together. The method for calculating the target casting speed based on the cross-section, superheat, and steel passing volume together is as follows: The A casting speed is the target casting speed calculated according to S1; the B casting speed is: the maximum steel passing volume (3.5 t / min) / (cross-section * thickness * density); for the decimal casting speed convention calculated by the steel passing volume and cross-section, when the last two decimal places are 0.10 - 0.13, it is uniformly set to 0.1, when the last two decimal places are 0.14 - 0.16, it is uniformly set to 0.15, and when the last two decimal places are 0.17 - 0.19, it is uniformly set to 0.2; when A ≤ B, the target casting speed is A, and when A > B, the target casting speed is B; when the logistics cannot meet the continuous casting speed requirement, the maximum steel passing volume is manually input for corresponding calculations. S3. Recalculate the target casting speed 10 minutes after accelerating to the target casting speed, and adjust the casting speed up or down accordingly.

2. The automatic control technology for the drawing speed of automotive sheets according to claim 1, characterized in that: When the automotive sheet is the outer panel, the method for adjusting the casting speed up or down in S3 is as follows: Accelerating: When the target casting speed - actual casting speed ≤ 0.2 m / min, control the acceleration at 0.05 m / min for each slab; when the target casting speed - actual casting speed > 0.2 m / min, control the acceleration to be completed on one slab, and follow the acceleration standard. If the acceleration is within the last 2 m of the slab, then control it all on the next slab. Decelerating: When the actual casting speed - target casting speed ≤ 0.1 m / min, control the deceleration at 0.05 m / min for each slab; when the actual casting speed - target casting speed > 0.1 m / min, control the deceleration to be completed on one slab.

3. The automated control technology for the drawing speed of automotive sheets according to claim 1, characterized in that: When the automotive sheet is other than the inner panel, the method for adjusting the casting speed up or down in S3 is as follows: Accelerating: When the target casting speed - actual casting speed ≤ 0.2 m / min, control the acceleration at 0.1 m / min for each slab; when the target casting speed - actual casting speed > 0.2 m / min, control the acceleration to be completed on one slab, and follow the acceleration standard. If the acceleration is within the last 2 m of the slab, then control it all on the next slab. Decelerating: When the actual casting speed - target casting speed ≤ 0.1 m / min, control the deceleration at 0.1 m / min for each slab; when the actual casting speed - target casting speed > 0.1 m / min, control the deceleration to be completed on one slab.