| Molten steel liquid level in tunish is an important information during continuous casting production. And during pouring, the real-time measurement of molten steel liquid level has many effects on controlling pouring stability, improving quality of casting billet, preventing breakout and increasing the lifetime of refractory material on tundish and so on. Especially, on premise of guaranteeing casting quality, the accurate molten steel liquid level information can be applied to reduce the surplus molten steel in the tundish as much as possible, hence, metallurgical enterprise should benefit from increasing of steel yielding rate. Hence, it is of practical significance to study the liquid level measurement of molten steel in the tundish.At present, molten steel liquid level measurement in tundish is a difficult problem which has not been solved. It is found that not only the mould power, including covering flux and impurities between the slags and the molten steel, but also the tundish in high-temperature, multiple-dust and strong interference, cause difficulties to the liquid level measurement in tundish. Hence, some methods, such as ultrasonic, eddy current, microwave and vision and so on, can not be applied to molten steel liquid level measurement.Because it is hard to apply the liquid level measurement of tundish for practical engineering, a new molten steel liquid level measuring method based on vision detection was put forward in this paper. In addition, the article also has research on setting up and analyzing of the mechanism model, extracting accurate temperature, locating temperature gradient of feebleness objective, correcting distortion on measuring system and carrying on the experiment in the metallurgical field and so on. In summary, some works and innovation are presented as followed:1. Molten steel liquid level measuring method based on vision detectionThe principle of the method, researched in this paper, is that a measuring bar which is made of refractory material was inserted into molten steel in tundish to percept for the temperature.And as air layer, flux slag layer and molten metal layer which have different temperature change velocity to each other, locates in the tundish, after heat balance, the temperature distribution of the measuring bar will appears of catastrophe point at the interface between the air layer, the flux slag layer and the molten metal layer. Then, the molten steel liquid level can be obtained from the two interfaces by visual detection.In order to analyzing the feasibility of the method in theory, a numerical calculation is carried out through the3d unsteady heat-transferring modeling, based on the finite element analysis. Then, compared with the result of the temperature measured on the filed, the calculating temperature on the modeling is showed that there are some catastrophe points of longitudinal temperature distrubition in the interface between the air layer, the flux slag layer and the molten metal layer. Therefore, the method provides the theoretical basis for measuring the molten steel liquid level in the papers.Besides, after analyzing the measuring parameters of the system at actual condition, the resolution of system spatial, varied from0.4mm/pixel to2mm/pixel, meets accuracy requirements of metallurgical field.2. Extracting temperature of measuring bar reliably and locating interface of temperature gradientThe conventional image segmentation method is inapplicable to deal with the separation between measuring bar, background and noise. However, according to the characteristics of measuring images, the improved segmentation method on ostu image of particle swarm, given in this paper, can realize the optimal segmentation between them. Simultaneously, the optimal segmentation threshold must be obtained reasonably and quickly from the improved adaptive step searching for particle swarm method which connects with information entropy. Finally, as the speed of searching for threshold can be2.4times as high as the iterative method, the improved segmentation method will achieve to extracting the temperature on the measuring bar feasibly.As feebleness objective, interface between the flux slag layer and the molten metal layer covered up by complicated noise and interference may not be located reliably, the thesis establishes feebleness objective location method based on image information and mechanism modeling. And according to the criterion for objection feature, obtained from simulating through the mechanism model, the false feature forming for complicated noise, interference in image can be restrained. So the feebleness objective is searched, extracted and located. And the accuracy rate about the interface location is up to about95%.3. Correcting molten steel liquid level measuring system and testAn improved correcting method of monocular vision distortion is put forward in this paper. It is used to not only extract the control point automatically and accurately but also build up the modeling, which connected with the bilinear interpolation operation, of polynomial mapping between distorted images and original ones. Considering correcting precision and complexity of operation, the five degree polynomial is the best of all. After analyzing the result, it is found that the error caused by distortion is about20mm between the measuring liquid level and actual ones before distortion correction, but0.4mm after distortion correction. Simultaneously, it uses the relationship between reference object and its image correct measuring paramaters which may be vary in dynamic measuring. Deviation of the measuring result is less than2.5mm after paramater-correction. In order verify accuracy of the molten steel liqiud level measuring method, compared the level measuring results with hand-measured results, it is found that the average deviation is about4.3mm.As well, the results obtained from the mechanism modeling and test in the industrial field suggest that the method proposed in this paper can reliably be used to liquid level measure on the spot. In addition, in order to meet to industrial application, the measure principle can also popularize to other molten metal liquid level. So molten steel liquid level measure method based on temperature has wide application prospect and popularization value. |
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