No abstract

For real-time and precise measurement of molten steel level in tundish during continuous casting, slag level and slag thickness are needed. Among which, the problem of slag thickness measurement has been solved in our previous work. In this paper, a systematic solution for slag level measurement based on laser triangulation is proposed. Being different from traditional laser triangulation, several aspects for measuring precision and robustness have been done. First, laser line is adopted for multi-position measurement to overcome the deficiency of single point laser range finder caused by the uneven surface of the slag. Second, the key parameters, such as installing angle and minimum requirement of the laser power, are analyzed and determined based on the gray-body radiation theory to fulfill the rigorous requirement of measurement accuracy. Third, two kinds of severe noises in the acquired images, which are, respectively, caused by heat radiation and Electro-Magnetic Interference (EMI), are cleaned via morphological characteristic of the liquid slag and color difference between EMI and the laser signals, respectively. Fourth, as false target created by stationary slag usually disorders the measurement, valid signals of the slag are distinguished from the false ones to calculate the slag level. Then, molten steel level is obtained by the slag level minus the slag thickness. The measuring error of this solution is verified by the applications in steel plants, which is ±2.5 mm during steady casting and ±3.2 mm at the end of casting.

This paper proposes a molten steel level measuring method in a tundish. This method is based on the temperature attenuation characteristic of the temperature tube. Our previous work focused on the temperature distribution of the temperature tube which can be used for molten steel level measurement. In some continuous casters, sticky slag adheres to the tube, thus, blocking the temperature information on the tube. To avoid this problem of lacking true temperature, we analyzed the principle of adhesion and conclude that the adhesive slag thickness of the tube is influenced by whether that part of the tube contacts the slag or the molten steel prior to being lifted. Consequently, for detecting the adhesive slag thickness online with available pyrometer, a heat transfer model is established. Through analysis of the model, it was revealed that the thickness of the adhesive slag remarkably influences the measurable maximum curvature time of the temperature attenuation. In addition, this maximum curvature time is insensitive to other irrelevant factors such as initial temperature and ambient temperature. Therefore, the maximum curvature time of the temperature attenuation of the adhesive slag indirectly indicates the molten steel level. Finally, the experiments prove the feasibility and the sound accuracy of this method with the maximal error being 3 mm. This method is not only suited for the molten steel level measurement, but also applicable to other non-destructive measurement of coating layer thickness.