| In continuous casting of steel, mold flux infiltrates into the gap between the solidifying shell and mold, and forms a flux film consisting of solid layer (adjacent to the mold) and liquid layer(adjacent to the shell). The heat transfer from the shell to the mold is controlled by the solid flux film and the lubrication between shell and mold is controlled by the liquid layer. Strand lubrication and heat transfer control are probably the two most critical functions of a mold flux. The first function is depended on the heat transfer performance of the flux. When casting cracking sensitivity steels, such as middle carbon steels, in order to prevent the formation of surface longitudinal cracking, it is necessary to adjust the heat transfer performance of the flux, increase thermal resistance, minimize and uniform heat flux. So mold flux selection based on heat transfer performance is very important to assure continuous casting process and enhance the surface quality of the slab. But so far, the equipment, which is much similar to the practice, can simulate mold/strand heat transfer, and measure the thermal performance of mold flux, has not been developed.This paper has studied the development of thermal characteristic analyzer for mold flux, and measured the thermal performance of mold fluxes for middle carbon steel and low carbon using this analyzer.The thermal characteristic analyzer consisted of detection system and key mechanical devices. Detection system included the flow detection and temperature detection. Key mechanical devices included heating element, copper gauge head, slip device, elevation and subsidence device. Copper gauge head was used to simulate mold, and heating element was used to simulate solidifying shell. Heating element design, including material design and shape design, was the key to develop thermal characteristic analyzer. By analyzing and comparing the optional materials, 0Cr21A16Nb Fe-Cr-Al alloy was chosen as a heating element. When material was fixed, the shape of heating element determined the temperature distribution and service life. The paper decided the overall shape was grooved plate, and after several design and trials, the final dimension was that: plate's length=200mm, width=80mm, thickness=5mm; the groove is square, length=34mm, depth=3mm; ab=ef=79mm, bc=ed=22mm, ce=42mm, mn=1mm. The element's temperature distribution was reasonable, and life was more than 30 times.The influence of flow on difference in temperature of cooling water was studied. The result indicated that as flow increasing, the difference in temperature of cooling water was distinctly decrease, but when flow increased to a certain magnitude, the cooling intensity did not increase any more. The paper determined the flow of cooling water was 80l/h, under this condition, the difference in temperature was 6℃, which was similar to the practice.The heat transfer performance of mold flux was measured by thermal characteristic analyzer, and the results showed that the temperature of under surface of copper gauge head was 161.3-193.8℃, which was closed to the temperature of hot surface of mold when continuous casting; Heat flux was 0.682-0.971MW/m~2, which had some differences with practice, but on the whole, the thermal characteristic analyzer could simulate the transverse heat transfer in the mold, and the design was reasonable. The results also showed the heat flux decreased by 26.97% when using mold flux for middle carbon steel.Mold fluxes for middle carbon steel and for low carbon steel were done 8 repeatability experiments respectively. The results indicated the test data was some reproducibility, and under different factors it was comparability through analysis of variance. Taking into consideration the actual conditions, the data measured by thermal characteristic analyzer was relative reliable, and the analyzer could be used to research the influence of chemical composition on thermal performance of mold flux.Under the experiment conditions, the thermal resistance of XLZ-13 was 14.152-17.264m~2K/W, the thermal resistance of MXB2D1 was 9.916-10.581m~2K/W. |
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