Application of automatic detection technology of ladle slag in heavy rail production

Application of automatic detection technology of ladle slag in heavy rail production

1. Introduction

    With the increase of heavy rail steel production and the development of new products of Hesteel Handan Steel, higher requirements are put forward for molten steel quality. Research has found that ladle slag is becoming more and more the main constraint factor for improving molten steel quality. In the first-line on-site operation, it is difficult for operators to close the ladle nozzle immediately after slag is discharged, so slag enters the tundish and then enters the crystallizer. At the same time, if the operator closes the nozzle too early due to concerns about slag discharge, it will cause too much residual steel in the ladle, reduce the molten steel recovery rate, and increase costs. In order to further improve the quality of heavy rail steel and the qualified rate of flaw detection, and optimize the comprehensive economic and technical indicators, Hesteel Handan Steel No. 1 Steelmaking Plant carried out project research and adopted the automatic slag detection and control system on the heavy rail production line.

2. System detection principle and composition

    During the casting process, the vibration of the support arm of the large ladle long nozzle manipulator is closely related to the slag content in the molten steel flowing in the long nozzle. In the process of molten steel flowing from the ladle into the tundish, the long nozzle and the manipulator support arm connected to it will produce strong vibration. The larger the nozzle opening, the greater the molten steel flow, and the more intense the vibration. The specific gravity of slag is about 1/3 of molten steel, so by detecting the vibration signal generated by the flow of slag and pure molten steel on the long nozzle operating arm, the change of the flow state of molten steel in the long nozzle can be indirectly monitored. The vibration type ladle slag automatic detection system is used to detect slag, which is a non-contact detection method with great market competitiveness.

3. Signal processing and state recognition technology of the system
    The environmental conditions at the continuous casting site are complex, in order to avoid false alarms caused by interference from vibration factors around the system. The system introduces a vector quantization (VQ) technology, and obtains its typical characteristic vector according to the vibration differences generated by the three states of pure molten steel flow, molten steel mixed with slag flow, and full slag flow in the long nozzle of the ladle, as shown in Figure 2. After the system extracts the features of the vibration signal in real time, it uses artificial intelligence network and Fourier transform technology to quickly identify and compare the real-time acquired signal with three feature vectors, and finally realizes the judgment of the molten steel state based on the real-time vibration signal, and completes a series of automatic controls for the slag discharge of the large ladle.

4. Realize automatic control of the tundish liquid level
    The tundish liquid level automatic control unit (ACMU) is an auxiliary module of the slag discharge detection system. It is interconnected with the slag discharge detection system to automatically control the opening of the sliding water inlet of the large ladle to stabilize the tundish liquid level at a reasonable level. When the tundish liquid level is at a reasonable level, the large ladle operator can start the tundish liquid level automatic control system through the water inlet opening operation box. After that, the tundish liquid level will be maintained at the liquid level at the time of starting the automatic control until the system detects the slag discharge of the large ladle. When the system detects the slag discharge and issues an audible and visual alarm, the tundish liquid level automatic control unit can automatically close the tundish water inlet, or it can be manually closed by the tundish operator.

5. Application effect

5.1 Automatic detection of slag success rate
    The slag detection system has been used for a total of 2225 ladles, and the alarm signal was not issued for 9 times due to untimely connection of molten steel (the molten steel ladle was in the detection period when it was placed, causing abnormal vibration interference signal). The success rate of detection is: (2225-9)/2225=99.59%

5.2 Increase the number of continuous casting furnaces
    It is difficult to close the nozzle just after slag is placed by manual judgment of slag release and water nozzle closing, which often leads to a large amount of highly corrosive ladle slag entering the tundish. These slags seriously corrode the refractory materials, often leading to aggravated erosion of the stopper rod and water nozzle (sometimes the stopper rod position can be lowered by 6-8mm/furnace, while the normal drop is about 1mm per heat), and also has a great impact on the working layer, thus becoming a key factor restricting the increase in the number of continuous casting furnaces. The slag entering the crystallizer will significantly change the various performance indicators of the crystallizer protective slag, resulting in various quality defects and even causing accidents such as steel leakage.

After the slag detection system was put into use, the slag of the ladle was effectively controlled, the abnormal erosion of refractory materials was greatly reduced, and the number of continuous casting heats was greatly increased. At present, the maximum number of continuous casting furnaces for heavy rail production has increased from 12 heats to 15 heats.

5.3 Improve the qualified rate of heavy rail flaw detection

    According to statistics, after the slag detection equipment was applied in the production of heavy rail steel, the internal quality of the steel ingot was significantly improved, the flaw detection failure caused by internal inclusions was effectively controlled, and the qualified rate of heavy rail flaw detection was increased from 92% to more than 98%.

6. Conclusion
    Since the ladle slag detection system was put into use in the heavy rail production line of Hegang Handan Steel, the amount of slag in the ladle has been well controlled, the automation level of production has been improved, the number of continuous pulling furnaces and the purity of molten steel have been increased, and the qualified rate of heavy rail flaw detection has been improved, which provides a favorable guarantee for the upgrading and quality improvement of heavy rail steel production. Ladle slag detection has become one of the important technologies for molten steel quality control.

Source: Today Steel