Please activate JavaScript!
Please install Adobe Flash Player, click here for download

discovered 02_2012

discovered 02.12 FOCUS WWW.Hzdr.DE calculations. For the first time ever our results take into account the electrical conductivity of the mold wall as an important variable for the flow of the molten metal.“ Sven Eckert and his team are planning further experiments on the effects of electromagnetic brakes, for example with different mold volumes and forms. But they are also considering new innovative electromagnetic stirrers. While today‘s electromagnetic brakes control the flow of the liquid steel at the entrance to the mold, in the future magnetic stirrers could be used in the lower part of the strand. Through electromagnetic agitation in the solidification zone the grain structure of the metal can be positively altered and non- homogeneous material can be avoided. But to get back to the electromagnetic brakes, which themselves also consume energy: Sven Eckert is already dreaming of the day when the brakes will only be switched on when absolutely necessary. For this, one would have to be able to look in real time at the molten metal and be able to measure the flow, but at 1,500 degrees Celsius any material that comes in direct contact with the molten metal simply disintegrates. For this reason innovative measuring techniques are also on the research and development agenda. A new magnetic method has already been patented, which works from the outside without coming into contact with the molten metal. Magnetic fields can influence the flow of conductive liquids, but the reverse is also the case, because any current distorts a magnetic field in a specific way. This flow-dependent distortion can be measured outside of the molten steel. In this way the MHD team (in particular Frank Stefani and Thomas Wondrak) managed to successfully develop the first tomographs that were able to compute and make visible the flow of the liquid from external magnetic field signals. The technology is known as CIFT (Contactless Inductive Flow Tomography). The first projects with industry using the CIFT technology have been extremely promising, so the goal now is to develop a sensor on the basis of CIFT for molten steel. In the future this kind of sensor will only switch on the electromagnetic brakes when a steady flow of the liquid metal threatens to become turbulent. Furthermore, the most innovative idea is one of planning a sensor-actuator system, i.e. a magnetic sensor and magnetic brake combined as one system that constantly monitors the molten steel during the real casting process and is able to intervene and control it as needed. Metal production and processing assume a crucial position when looking at the proportion of energy costs of the gross value of production in the processing trade. This point was also mentioned in the July 2011 Federal Government’s sixth energy research program with the goal of “coming up with innovative developments to considerably slow down energy consumption in the German metal-producing industry“. Sven Eckert and his team want to further explore the use of magnetic fields in steel casting in order to make an important contribution to Germany’s new energy turnaround. LITERATURE K. Timmel, S. Eckert, G. Gerbeth: “Experimental investigation of the flow in a continuous-casting mold under the influence of a transverse, direct current magnetic field”, in Metallurgical and Materials Transactions B, vol. 42B (2012), p. 68 - 80 (DOI 10.1007/s11663-010-9458-1) Contact _ Institute of Fluid Dynamics at HZDR Dr. Gunter Gerbeth MULTIMAG: This facility is used in model experiments for optimizing crystal growth processes. Here, the scientist’s face is being reflected onto the gallium indium zinc-filled container’s free surface. Image credit: Rainer Weisflog