Methods for controlling molten steel level in the tundish during the casting process of a continuous casting machine

Abstract

This invention provides a method for controlling the molten steel level in the tundish during the casting process of a continuous casting machine, as well as the continuous casting machine itself. The invention employs a weight detection unit to monitor the weight of the molten steel in the tundish in real time, and determines the level based on the molten steel weight W and a target weight W0 in the tundish. Z0 The differences between them, the rate of change of the weight of molten steel in the ladle over time, the number of castings N, and the casting speed V 拉速 A time pulse signal is generated, which controls the opening of the ladle nozzle and adjusts the flow rate of molten steel in the tundish, thereby achieving dynamic control of the molten steel level in the tundish. This helps maintain a stable tundish level, which in turn benefits the stability of continuous casting production and the quality of the cast billet.

Description

Technical Field

[0001] This invention belongs to the field of continuous casting technology in the metallurgical industry, specifically relating to a method for controlling the molten steel level in the ladle during the casting process of a continuous casting machine and the continuous casting machine itself. Background Technology

[0002] In continuous casting, the ladle is located above the tundish, and the crystallizer is located below the tundish. Molten steel flows into the tundish through the ladle nozzle and then into the crystallizer through the tundish nozzle for billet casting. The flow rate of molten steel in the ladle can be controlled by adjusting the opening of the ladle nozzle. The tundish, as the transition vessel between the ladle and the crystallizer, affects the stability of the entire continuous casting process and the quality of the cast billet. A stable tundish level maintains a stable flow rate of molten steel into the crystallizer, thus facilitating stable casting speed. A low tundish level may cause flow interruption, forming cold shuts and affecting billet quality. A high tundish level may cause overflow, posing a hazard to equipment and personnel. Therefore, tundish level control is a critical process in continuous casting, significantly impacting billet quality, production safety, and cost reduction.

[0003] Given a fixed weight of molten steel in the ladle, the main factors affecting the molten steel level in the tundish include the ladle nozzle opening, tundish equipment dimensions, casting flow rate (N), and casting speed (V). 拉速 Currently, the control of molten steel level in the ladle often requires manual intervention. Operators rely on their own experience to visually assess the molten steel level in the ladle and then control the sliding gate. This operational experience is not easy to describe precisely, and the various signal quantities and evaluation indicators cannot be quantitatively represented. Summary of the Invention

[0004] In view of the above-mentioned technical status, the present invention provides a method for controlling the molten steel level in the tundish during the casting process of a continuous casting machine. This method can dynamically control the molten steel level in the tundish, thereby maintaining a stable tundish level, which is beneficial to the stability of continuous casting production and the quality of the cast billet.

[0005] The technical solution of the present invention is: a method for controlling the molten steel level in the tundish during the casting process of a continuous casting machine, wherein molten steel flows into the tundish through the ladle nozzle and into the crystallizer billet through the tundish nozzle;

[0006] A ladle weight detection unit is set up to monitor the weight of molten steel in the ladle in real time, obtaining the ladle steel weight W and the target value W. Z0 The difference between them, and the rate of change of the weight of molten steel in the ladle over time (i.e., the rate of change of the weight of molten steel in the ladle);

[0007] Based on the weight W of molten steel in the ladle and the target value W of molten steel in the ladle Z0 The differences between them, the rate of change of molten steel weight in the ladle, the number of castings N, and the casting speed V拉速 A time pulse signal is generated, the sign of which is determined by the weight W of the molten steel in the ladle and the target weight W of the molten steel in the ladle. Z0 The sign of the difference between them is controlled by the duty cycle of the time pulse signal, which is determined by the casting flow number N and the casting speed V. 拉速 And control of the weight change rate of molten steel in the ladle;

[0008] The opening degree of the water inlet is controlled by the time pulse signal.

[0009] As a preferred implementation method, the weight W of molten steel in the ladle and the target value W of molten steel in the ladle are... Z0 When the difference between them is negative, the time pulse signal is a positive pulse signal. The time pulse signal controls the increase of the ladle nozzle opening, i.e., the ladle nozzle opens, thus increasing the ladle nozzle opening. The weight of molten steel in the tundish W and the target weight of molten steel in the tundish W... Z0 When the difference between them is positive, the time pulse signal is a negative pulse signal. The time pulse signal controls the reduction of the opening of the large water inlet, that is, the large water inlet performs a contraction action, so that the opening of the large water inlet is reduced.

[0010] Preferably, the opening of the water inlet is controlled by the pulse width of the time pulse signal.

[0011] Preferably, the period of the time pulse is determined by the weight W of the molten steel in the ladle and the target weight W of the molten steel in the ladle. Z0 The difference between them is controlled. As a further preferred embodiment, the rate of change of molten steel weight in the ladle is less than the threshold value V for the rate of change of molten steel weight in the ladle. 变化率阈值 At that time, the duty cycle of the time pulse is zero, that is, the opening of the main water inlet does not change, and the V 变化率阈值 Adjustable.

[0012] As a preferred implementation, an execution unit is provided for adjusting the opening of the ladle nozzle; the weight W of the molten steel in the ladle detected by the tundish weight detection unit is transmitted to the control unit, where the control unit obtains the molten steel weight W and the target value W of the molten steel in the ladle. Z0 The difference between the values ​​and the rate of change of the weight of the molten steel in the tundish over time are used to generate a time pulse signal. This time pulse signal is used as the control signal of the execution unit to control the opening of the ladle nozzle, thereby adjusting the flow rate of the molten steel in the tundish and achieving the purpose of dynamically controlling the molten steel level in the tundish.

[0013] As a preferred implementation method, fuzzy control theory is used to generate time pulse signals. That is, the basic theory of fuzzy mathematics is applied to the relationship between the weight W of molten steel in the ladle and the target weight W of molten steel in the ladle. Z0 The differences between them, the rate of change of molten steel weight in the ladle, the number of castings N, and the casting speed V 拉速The process involves fuzzification, representing the data using fuzzy sets, storing it in the PLC (Programmable Logic Controller) program, and then processing it according to fuzzy rules to output the time pulse signal, thereby achieving dynamic control of the opening degree of the main water inlet.

[0014] The casting number N refers to the number of billets that can be cast simultaneously on a continuous casting machine, and N is a positive integer.

[0015] The duty cycle of the pulse is determined by the casting flow rate N and the casting speed V. 拉速 Control of the weight change rate of molten steel in the ladle, the larger the casting flow rate N, the larger the duty cycle, and the casting speed V. 拉速 The larger the value of the molten steel, the larger the duty cycle and the greater the rate of change in the weight of the molten steel in the ladle. Conversely, the smaller the casting flow rate N, the smaller the duty cycle and the smaller the casting speed V. 拉速 The smaller the duty cycle, the smaller the rate of change in the weight of molten steel in the ladle, and the smaller the duty cycle.

[0016] Preferably, the sprue nozzle is slidable. More preferably, the sliding speed of the sprue nozzle is constant, and the pulse width of the pulse is used as the sliding time of the sprue nozzle. As one implementation, a hydraulic cylinder is installed at the sprue nozzle to drive its sliding motion.

[0017] As a preferred implementation, based on the weight W of the molten steel in the ladle and the target weight W of the molten steel in the ladle... Z0 The deviation of the molten steel weight in the tundish can be divided into four zones: dead zone, micro-control zone, medium control zone, and fast control zone.

[0018] Within the dead zone, the weight W of the molten steel in the ladle and the target weight W of the molten steel in the ladle are... Z0 The deviation is within the range of a, that is, W Z0 -a≤W≤W Z0 +a, a>0;

[0019] In the micro-control zone, the deviation between the weight W of the molten steel in the ladle and the upper and lower limits of the dead zone is within the range of ba, that is, W Z0 -b≤W≤W Z0 -a、W Z0 +a≤W≤W Z0 +b, b>a, when the weight of the molten steel in the ladle is in this zone, the ladle nozzle opening is controlled by the time pulse to make the molten steel level in the ladle change towards the dead zone;

[0020] In the central control zone, the deviation between the weight W of molten steel in the ladle and the upper and lower limits of the weight in the micro-control zone is within the range of cb, that is, W Z0 -c≤W≤W Z0 -b、W Z0 +b≤W≤W Z0+c, c>b; when the weight of the molten steel in the ladle is in this zone, the ladle nozzle opening is controlled by the time pulse to make the molten steel level in the ladle change towards the dead zone;

[0021] In the fast control zone, the deviation of the molten steel weight W from the upper and lower limits of the control zone is outside the range c, i.e., W ≤ W Z0 -c、W Z0 +c≤W, when the weight of the molten steel in the ladle is in this zone, the opening of the ladle nozzle is controlled by the time pulse to cause the molten steel level in the ladle to change towards the dead zone.

[0022] When the weight of molten steel in the ladle is located in the dead zone, preferably, if the rate of change of the weight of molten steel in the ladle is less than or equal to the threshold value V of the rate of change of the weight of molten steel in the ladle. 变化率阈值 When no time pulse signal is generated, or the period of the generated time pulse signal can be considered to be 0, the ladle nozzle opening does not change, that is, the opening is constant, and the molten steel level in the tundish is the ideal level; if the weight change rate of the molten steel in the ladle is greater than V... 变化率阈值 At that time, the opening of the ladle nozzle is controlled by the time pulse, so that the molten steel level in the tundish changes towards the ideal level shown.

[0023] When the weight of the molten steel in the ladle is within the fast control zone, to avoid problems such as overflow or flow interruption due to a low level control rate, it is preferable to control the opening of the ladle's sliding gate to allow the molten steel level in the ladle to change rapidly and restore the ideal level. At this time, the casting flow rate N and casting speed V can be used as a reference. 拉速 The control of the weight change rate of molten steel in the ladle controls the duty cycle of the time pulse, while the period of the time pulse is controlled according to the weight change rate of molten steel in the ladle. The combined effect of these two factors ensures a smooth adjustment process.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] This invention employs a weight detection unit and a control unit. The weight detection unit monitors the weight W of the molten steel in the ladle in real time, and the control unit determines the weight based on the weight W of the molten steel in the ladle and the target weight W. Z0 The differences between them, the rate of change of the weight of molten steel in the ladle over time, the number of castings N, and the casting speed V 拉速 A time pulse signal is generated, which controls the opening of the ladle nozzle and adjusts the flow rate of molten steel in the tundish, thereby achieving dynamic control of the molten steel level in the tundish. This helps maintain a stable tundish level, which in turn benefits the stability of continuous casting production and the quality of the cast billet. Attached Figure Description

[0026] Figure 1 This is a curve showing the change of the weight of molten steel in the tundish and the control signal of the ladle nozzle over time in an embodiment of the present invention. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are still within the protection scope of the present invention.

[0028] Example 1:

[0029] During the casting process, molten steel flows into the tundish through the ladle nozzle and then into the crystallizer to cast the billet through the tundish nozzle.

[0030] In this embodiment, a ladle weight detection unit and a control unit are set up. The ladle weight detection unit monitors the weight of the molten steel in the ladle in real time, obtains the weight W of the molten steel in the ladle, and transmits it to the control unit. The control unit processes the data to obtain the weight W of the molten steel in the ladle and the target value W of the weight W of the molten steel in the ladle. Z0 The difference between the values ​​and the rate of change of the molten steel weight in the ladle over time, based on the molten steel weight W in the ladle and the target value W in the ladle. Z0 The differences between them, the rate of change of the weight of molten steel in the ladle over time, the number of castings N, and the casting speed V 拉速 A time pulse signal is generated, the sign of which is determined by the weight W of the molten steel in the ladle and the target weight W of the molten steel in the ladle. Z0 The sign of the difference between them is controlled by the duty cycle of the time pulse signal, which is determined by the casting flow rate N and the casting speed V. 拉速 Control of the rate of change in the weight of the intermediate package.

[0031] In this embodiment, the sprue nozzle is slidable, and an actuator is installed at the sprue nozzle to drive its sliding motion. In this embodiment, the actuator is a hydraulic cylinder, and the sliding speed of the sprue nozzle driven by the hydraulic cylinder is constant. In other embodiments, the actuator may employ other methods.

[0032] In this embodiment, the control unit uses fuzzy control theory to generate time pulse signals, that is, it uses the basic theory of fuzzy mathematics to compare the weight W of the molten steel in the ladle with the target weight W. Z0 The differences between them, the rate of change of molten steel weight in the ladle, the number of castings N, and the casting speed V 拉速 The data is fuzzified, represented by a fuzzy set, stored in the PLC program, and then processed according to fuzzy rules to output a time pulse signal.

[0033] In this embodiment, the control unit generates a time pulse signal to form control signals under different operating conditions. The control signals are isolated by a signal isolator and output to the execution unit for control, so as to control the ladle nozzle opening and adjust the molten steel inlet flow rate in the tundish, thereby achieving the purpose of dynamically controlling the molten steel level in the tundish and maintaining the stability of the tundish level, which is beneficial to the stability of continuous casting production and the quality of the billet.

[0034] In this embodiment, the weight of molten steel in the ladle is divided into four zones: dead zone, micro-control zone, intermediate control zone, and fast control zone.

[0035] Within the dead zone, the weight W of the molten steel in the ladle and the target weight W of the molten steel in the ladle are... Z0 The deviation is within the range of a, that is, W Z0 -a≤W≤W Z0 +a. In the dead zone, if the rate of change of molten steel weight in the ladle is less than or equal to V. 变化率阈值 At the ideal liquid level state, the ladle nozzle does not operate and the opening is constant; if the rate of change of molten steel weight in the ladle is greater than V... 变化率阈值 At that time, the PLC uses fuzzy control theory to compare the weight W of the molten steel in the ladle with the target value W. Z0 The differences between them, the rate of change of molten steel weight in the ladle, the number of castings N, and the casting speed V 拉速 The process generates a time pulse signal, which controls the sliding time of the hydraulic cylinder driving the ladle nozzle, thereby controlling the opening of the ladle nozzle and causing the molten steel level in the tundish to change towards the ideal level state within the dead zone.

[0036] In the micro-control zone, the deviation between the weight W of molten steel in the ladle and the upper and lower limits of the dead zone is within the range of ba, that is, W Z0 -b≤W≤W Z0 -a、W Z0 +a≤W≤W Z0 +b. In the micro-control area, the PLC uses fuzzy control theory to control the weight W of the molten steel in the ladle and the target value W. Z0 The differences between them, the rate of change of molten steel weight in the ladle, the number of castings N, and the casting speed V 拉速 The process generates a time pulse signal, which controls the sliding time of the hydraulic cylinder driving the ladle nozzle, thereby controlling the opening of the ladle nozzle and causing the molten steel level in the tundish to change towards the dead zone.

[0037] In the central control zone, the deviation between the weight W of molten steel in the ladle and the upper and lower limits of the weight in the micro-control zone is within cb, that is, W Z0 -c≤W≤W Z0 -b、W Z0 +b≤W≤W Z0 +c. In the central control area, the PLC uses fuzzy control theory to compare the weight W of the molten steel in the ladle with the target value W. Z0 The differences between them, the rate of change of molten steel weight in the ladle, the number of castings N, and the casting speed V 拉速 The process generates a time pulse signal, which controls the sliding time of the hydraulic cylinder driving the ladle nozzle, thereby controlling the opening of the ladle nozzle and causing the molten steel level in the tundish to change towards the dead zone.

[0038] In the fast control zone, the deviation of the molten steel weight W from the upper and lower limits of the central control zone is outside the range c, that is, W ≤ W Z0 -c、W Z0 +c≤W. In the fast control zone, the system controls the opening of the ladle's sliding gate to cause a rapid change in the molten steel level in the tundish to restore the ideal level. Under this high inertia condition, the absolute value of the rate of change of molten steel weight in the tundish increases, meaning the difference in molten steel inflow and outflow per unit time increases. At this point, the casting flow rate and casting speed V can be used as a reference. 拉速 The duty cycle of the time pulse for adjusting the rate of change of molten steel weight in the ladle is determined, and the molten steel weight W in the ladle is adjusted based on the target value W. Z0 The difference between the values ​​controls the period of the time pulse. The combined effect of the two produces a certain pulse width, which can make the adjustment process smooth and avoid problems such as overflow or flow interruption caused by a low liquid level control rate.

[0039] A specific control process, such as Figure 1 As shown, the details are as follows:

[0040] (1) In the initial stage, that is, during the period from 0 to t0, the control system is not started, the ladle sliding gate is fully open, and the weight of molten steel in the tundish increases.

[0041] (2) At time t0, the control system starts and enters the automatic control mode; during the time period from t0 to t3, the time pulse is obtained by performing fuzzy processing on the parameters of change in molten steel weight in the ladle, change rate of molten steel weight in the ladle, number of castings and casting speed, and this pulse is used as the sliding time of the sliding gate with constant sliding speed driven by the hydraulic cylinder, that is, the opening of the sliding gate is controlled by the pulse width.

[0042] During the time period t0 to t3, the weight W of molten steel in the ladle and the target value W of molten steel in the ladle are compared. Z0 The difference between them is positive, and the pulse signal is a negative pulse signal. The negative pulse signal controls the reduction of the opening of the large water inlet, that is, the large water inlet performs a contraction action, so that the opening of the large water inlet is reduced.

[0043] It is in the fast control zone during the t0 to t1 period, in the medium control zone during the t1 to t2 period, and in the micro control zone during the t2 to t3 period;

[0044] Furthermore, the pulse width gradually decreases during the t0 to t3 period, meaning the contraction stroke gradually decreases.

[0045] (3) During the t3 to t4 period, the liquid level is in the dead zone and the opening of the main water inlet does not move;

[0046] (4) At time t4, due to the increase in casting speed, the weight of molten steel in the tundish fluctuates, and the opening of the ladle nozzle needs to be increased. That is, a positive pulse signal is issued to control the opening of the ladle nozzle to increase, that is, the ladle nozzle opens.

[0047] During the t4 to t5 period, the large package sliding gate is opened in the micro-control zone.

[0048] (5) When the liquid level is in the dead zone between t5 and t6, the main water inlet does not operate.

[0049] At time t6, due to the closure of a certain casting stream, the weight of the molten steel in the tundish increases, requiring the ladle nozzle to be contracted, i.e., a negative pulse signal is emitted.

[0050] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the spirit of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them. It is neither necessary nor possible to provide a complete list of all embodiments here. These obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A method for controlling the molten steel level in the tundish during the casting process of a continuous casting machine, wherein molten steel flows into the tundish through the ladle nozzle and then into the crystallizer through the tundish nozzle to form the billet; its characteristics are: A ladle weight detection unit is set up to monitor the weight of molten steel in the ladle in real time, obtaining the ladle steel weight W and the target value W. Z0 The difference between them, and the rate of change of the weight of molten steel in the ladle over time; Based on the weight W of molten steel in the ladle and the target value W of molten steel in the ladle Z0 The differences between them, the rate of change of molten steel weight in the ladle, the number of castings N, and the casting speed V 拉速 A time pulse signal is generated, the sign of which is determined by the weight W of the molten steel in the ladle and the target value W of the weight W of the molten steel in the middle ladle. Z0 The sign of the difference between them is controlled by the duty cycle of the time pulse signal, which is determined by the casting flow number N and the casting speed V. 拉速 And control of the weight change rate of molten steel in the ladle; The opening degree of the water inlet is controlled by the time pulse signal.

2. The control method as described in claim 1: the weight W of molten steel in the ladle and the target value W of molten steel in the ladle. Z0 When the difference between them is negative, the time pulse signal is a positive pulse signal, and the opening degree of the large water inlet is increased by controlling the time pulse signal. Weight of molten steel in the tundish W and target value of molten steel in the tundish W Z0 When the difference between them is positive, the time pulse signal is a negative pulse signal, and the opening degree of the large water inlet is reduced by controlling the time pulse signal.

3. The control method as described in claim 1: controlling the opening degree of the water inlet by the pulse width of the time pulse signal.

4. The control method as described in claim 1: the period of the time pulse is determined by the weight W of the molten steel in the ladle and the target weight W of the molten steel in the ladle. Z0 The size of the difference between them is controlled.

5. The control method as described in claim 1: An execution unit is provided for adjusting the opening degree of the main water inlet; The molten steel weight signal detected by the ladle weight detection unit is transmitted to the control unit, where the control unit obtains the molten steel weight W and the target molten steel weight W. Z0 The difference between them and the rate of change of the weight of molten steel in the ladle are used to generate time pulse signals; The time pulse signal is used as the control signal of the execution unit to control the opening degree of the water inlet.

6. The control method as described in claim 1: The time pulse signal is generated using fuzzy control theory.

7. The control method as described in claim 6: the large water inlet is slidable.

8. The control method as described in claim 7: the sliding speed of the large nozzle is constant, and the pulse width of the time pulse is used as the sliding time of the sliding nozzle.

9. The control method as described in claim 5: the large water inlet is slidable; the execution unit includes a hydraulic cylinder, which drives the large water inlet to slide.

10. The control method as described in claim 1: based on the weight W of molten steel in the ladle and the target weight W of molten steel in the ladle. Z0 The deviation of the molten steel weight in the tundish can be divided into four zones: dead zone, micro-control zone, medium control zone, and fast control zone. Within the dead zone, the weight W of the molten steel in the ladle and the target weight W of the molten steel in the ladle are... Z0 The deviation is within the range of a, that is, W Z0 -a≤W≤W Z0 +a; In the micro-control zone, the deviation between the weight W of the molten steel in the ladle and the upper and lower limits of the dead zone is within the range of ba, that is, W Z0 -b≤W≤W Z0 -a、W Z0 +a≤W≤W Z0 +b; In the central control zone, the deviation between the weight W of molten steel in the ladle and the upper and lower limits of the weight in the micro-control zone is within the range of cb, that is, W Z0 -c≤W≤W Z0 -b、W Z0 +b≤W≤W Z0 +c; In the fast control zone, the deviation of the molten steel weight W from the upper and lower limits of the control zone is outside the range c, i.e., W ≤ W Z0 -c、W Z0 +c≤W; The opening of the ladle nozzle is controlled by the time pulse, causing the molten steel level in the tundish to change towards the dead zone.

11. The control method as described in claim 10: In the dead zone, if the rate of change of molten steel weight in the ladle is less than or equal to the threshold value V of the rate of change of molten steel weight in the ladle... 变化率阈值 At this time, no time pulse signal is generated, the ladle nozzle opening does not change, and the molten steel level in the tundish is at the ideal level; if the weight change rate of the molten steel in the ladle is greater than V... 变化率阈值 At that time, the opening of the ladle nozzle is controlled by the time pulse, so that the molten steel level in the tundish changes towards the ideal level.

12. The control method as described in claim 10: the weight of the molten steel in the ladle is located in the fast control zone, based on the casting flow rate and casting speed V. 拉速 The duty cycle of the control time pulse is generated based on the change rate of the molten steel weight in the ladle, and simultaneously based on the molten steel weight W in the ladle and the target molten steel weight W. Z0 The difference between them controls the period of the control time pulse.

13. A continuous casting machine, including a ladle, an tundish, and a crystallizer, characterized by: During the casting process, the method for controlling the molten steel level in the ladle adopts the method described in any one of claims 1 to 12.

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