Brief Introduction of Tundish Level Control System
Brief Introduction of Tundish Level Control System
Automatic equipment for continuous casting
tundish molten steel level control system
The tundish is the intermediate container between the ladle and the mold. The purpose of using the tundish is to reduce the static pressure of molten steel, stabilize the steel stream, and reduce the impact and agitation of the steel stream on the molten steel in the mold. When the molten steel stays in the tundish, non-metallic inclusions have the opportunity to partially float. Distributing molten steel to each mold of the multi-strand continuous casting machine and storing a certain amount of molten steel to realize sequential casting.
With the improvement of the quality requirements of the casting billet, the tundish is regard as the key link in the continuous casting system, and its metallurgical effect has been paid more and more attention by people. In the production process of the continuous casting machine, in order to improve the quality of the casting billet, the overall process of the continuous casting tundish has been optimized, and good results have been achieved. In view of the problems existing in the continuous casting tundish, the following reforms are mainly carried out: increasing the capacity of the tundish, covering the surface of the molten steel with non-oxidizing thermal insulation slag, adding a rectifier in the tundish to change the flow field of the molten steel in the tundish, using an alkaline tundish lining, and realizing the automatic control of molten steel level in tundish. One of the functions of the tundish is to uniformize the temperature and composition of the molten steel, maintain a certain residence time of the molten steel in the tundish, and promote the floating of non-metallic inclusions in the molten steel, which can’t be realized if the molten steel level of the tundish is too low or fluctuating.
In addition, during the pouring process, there is a layer of scum on the molten steel surface in the tundish. If the molten steel level is too low or fluctuates frequently, the ladle injection will impact the molten steel in the tundish and cause agitation, which is easy for these inclusions to be drawn into the nozzle and injected into the mold, affecting the quality of the billet. At the same time, if the liquid level is too low, it will cause the big impact of the steel flow on the bottom of the ladle, which will inevitably aggravate the erosion of the refractory material at the injection point in the bottom of the ladle, pollute the molten steel, affect the quality of the continuous casting slab and reduce the service life of the tundish.
Therefore, the continuous casting machine should try to maintain a certain and stable liquid level in the tundish during the pouring process. In the recent years, with the development of continuous casting technology and the requirements of molten steel purification, tundish pouring using the tundish level control system has appeared, which undoubtedly played a positive role in the uniformity and purification of molten steel.
The composition of the system
1． Weighing system of tundish weight: including weighing pressure head, anti-heat and anti-shock device, electronic weighing device, digital display device and weighing module board.
2． Ladle slag detection system: including slag detection sensor, special measurement cable, preamplifier, and central processing unit.
3． Infrared auxiliary measurement system: infrared position measurement probe, infrared measurement conversion device.
4． Control PLC and model: including ladle casting strand control PLC, operation station, tundish volume model, tundish liquid level control algorithm.
5． Control execution unit: including drive conversion module board, electric/hydraulic servo control module, ladle sliding nozzle mechanism.
6． Operation instruction unit: including large-screen display instrument and on-site operation instruction box.
The system introduction
1． The tundish weighing system includes 4 sets of weighing sensors and heat and shock-proof devices for sensors, which are distributed on the tundish carriage evenly. The actual weight of the tundish can be measured through the average stress calculation, and the signal is transmitted to the weighing module board through the high-temperature cable. The weighing module board needs to remove tare according to the communication signal with PLC and the in-position signal of the tundish car. At the same time, a large-screen indicator is used on the continuous casting operation platform to display the real-time net weight of molten steel in the tundish, and the weighing module board and the large-screen indicator communicate with each other through the ProfiBUS bus.
2． The ladle slag detection system in continuous casting is used to detect the slag content of ladle nozzles in the steelmaking and continuous casting process, so as to improve the cleanliness of tundish molten steel and obtain the best yield of ladle molten steel. It can reduce the impact on the cleanliness of the finished steel due to the entering of steel slag into the tundish, and the impact of the tundish, which can increase the number of continuous casting heats. The ladle slag detection system includes a coil for detecting slag, which is installed on the reference plate of each ladle nozzle mechanism. When the ladle is turned over to the continuous casting platform, it is connected to the ladle detection system installed on the continuous casting platform by the measuring high temperature signal cable, and the slag content of the ladle nozzle is detected during the whole process of ladle pouring, and according to the technological design, the nozzle mechanism of the ladle is automatically closed or an alarm signal is provided to guide the operation at the end of pouring.
3． The infrared auxiliary measurement system uses infrared measurement probes to conduct online detection of the surface height of the molten steel in the tundish, and sends the measurement parameters to the PLC as a reference factor for system detection to evaluate and correct the calculated data and ensure the accurate tundish level in the whole the pouring process.
4． The control PLC adopts the same series PLC of the user as the main system, and is connected to the whole continuous casting PLC system to realize the data exchange of ladle casting strand control. According to the tundish volume model, the system calculates the level height of molten steel in the tundish in real time. The operation station inputs the tundish level height and control mode required by the user. The system will calculate and control the sliding nozzle of the ladle in real time according to the input parameters and the liquid level control model of the tundish, the opening of ladle nozzle and the steel strand model.
At the start of the first heat and the end of the last heat of each tundish pouring process, a unique control model is used to realize the smooth change of the ladle casting strand and the tundish molten steel. In the process of opening and closing each ladle, a unique control mode is used to ensure the stability of the molten steel level in the tundish.
To achieve the above operations, the system needs to introduce the signals of the weight of molten steel in the ladle, the drawing speed, and the position of the tundish carriage.
5． The control execution unit converts the control signal output by the control PLC into the drive signal of the servo control module through the drive conversion module board, so as to control the opening of the sliding nozzle of the ladle.
6． The system is equipped with a large-screen indicator to indicate the weight of the molten steel in the ladle and the tundish in real time during the pouring process, and a set of indicating operation boxes to indicate and control the liquid level of the molten steel in the tundish at the pouring position of the ladle. The large-screen indicator communicates with the PLC through the ProfiBUS bus.
The technical indexes
l Weighing sensor：configured according to the user's tundish volume
l Weighing sensor protection device: designed according to the weighing sensor and the tundish structure
l Weighing error: 0.5
l Slag sensor: >400 heats
l Slag detection accuracy: 5% (duty cycle)
l Slag signal transmission: >2000m
l Slag sensor temperature: <900℃
l The measurement range of the liquid level in the tundish: 0--100%
l The control range of the liquid level in the tundish: 20%--100%
l The control accuracy of the liquid level in the tundish: ±5mm
l System response time: 100ms (excluding mechanical equipment)
l System power supply: AC. 220V±20V
l System operating temperature: <45℃
The equipment list