Measurement of the pig iron and slag level in the blast furnace is essential to operate the furnace stably because an increase of these liquids level can cause fluctuations of the pressure in the furnace or the temperature of the furnace which are related to the furnace condition and may finally result in reduced productivity or serious trouble.The conventional method is the EMF (electromotive force) measurement correlated with the liquid level. It can be thought that a voltage generated electrochemically (as in a battery) by the reduction reaction of iron oxides. However some reports said that EMF sometimes loses correlation with the liquid level because of thermal influence.In this paper a new method is proposed using a quite small electrical resistance measurement of the hearth of a blast furnace which contains pig iron and molten slag. Accordingly the four point contact method was adopted and a pseudo random signal as a current pattern was fed to improve the S/N ratio.Measurements were done at plural positions along the circumference of the blast furnace. However when the current signal is independently fed at each position, spike noises are generated. These noises are originated in the induced voltage which is generated at neighbor positions when the polarity of the current changes. But finally this noise problem can be solved by feeding synchronized current and measuring the signal on the noiseless timing.The measurement results indicated that the level in the hearth is not necessary identical at all positions.KEY WORDS: blast furnace; pig iron; molten slag; level measurement; electrical resistance; pseudo random signal. BackgroundStability is extremely important in blast furnace operation, as the blast furnace is the first upstream process in steel production. Nevertheless, increase of the pig iron and molten slag level prevents stable operation. Pig iron descends, and then accumulates in the blast furnace hearth. And also, molten slag descends to the hearth. However, the molten slag accumulates over the pig iron because its density is lower than that of iron.Pig iron and molten slag are drained from one of plural tap holes (in the case of large blast furnaces) by turns at regular intervals. However, molten slag has poor drainage due to its relatively higher viscosity, and under special conditions when the temperature in the furnace is lower than usual, the viscosity of the molten slag increases, making tapping even more difficult. In the worst case, an excessive rise of the pig iron and molten slag level can cause serious trouble in which the molten slag melts the tuyeres. This type of trouble does not have only an adverse influence on operation over an extended time, but is also a problem for safety. Therefore, when the pig iron and molten slag level rises, pig iron and molten slag are drained from plural tap holes at the same time, enabling control of the productivity of pig iron and molten slag in order to keep the appropriate level and realize stable operation.The conventional method of measuring the...
The signal amplitude and the phase of acoustically stimulated electromagnetic (ASEM) response have been investigated in steel. In the ASEM method, magnetization is temporally modulated with the radio frequency (rf) of irradiated ultrasonic waves through magnetomechanical coupling. The first-harmonic components of the induced rf dipolar magnetic fields are detected using a resonant loop antenna. The signal amplitude of ASEM waves is determined by the magnitude of local piezomagnetic coefficients on an acoustically excited spot. Here, we divided the ASEM waves into the “in-phase” and “quadrature” components by phase-sensitive detection (PSD). On the basis of the linear response theory, we provided the theoretical formalism of ASEM response by introducing local complex piezomagnetic coefficients, dloc = d′ + id′′. We investigated the magnetic field (H) dependence of the individual components on the different surface conditions of steel plates. The in-phase component [∝ d′(H)] shows a hysteresis loop on the machined surface of a steel plate, in which d′(H) switches sign at two finite field values, ±H0. The inversion of magnetization associated with the applied static fields is thus definitely observed in the PSD measurements. In addition, we measured the hysteresis behaviors on a steel surface with a thin mill scale (iron oxide layers). The hysteresis loop broadens and a significant contribution of the quadrature component [∝ d′′(H)] is found. We discuss the origin of the hysteresis behaviors of d′ and d′′ using the Debye relaxation model.
Acoustically stimulated electromagnetic (ASEM) waves in thin steel sheets have been investigated for flaw detection. In the ASEM wave technique, magnetization is temporally modulated at the radio frequency (rf) of the irradiated ultrasonic waves through magnetomechanical coupling. The induced rf magnetic fields are detected by a resonant coil antenna and spatial images are obtained by scanning the ultrasound focal spot. In this work, we detected artificial defects (through holes) in thin steel sheets. Specific patterns of magnetic flux density caused by the hole were observed. By improving the sensitivity with a small coil antenna, we visualized a through hole 0.1 mm in diameter with a lift-off of 10 mm.
Articles you may be interested inApplication of MMC model on simulation of shearing process of thick hot-rolled high strength steel plate AIP Conf.Abstract. Recently, steel can manufacturing requires higher quality because otherwise minute non-metallic inclusions in thin sheets cause cracks and result in a burst during pressurization after the pressing process. Quality testing systems have already been installed in the final process in steel plants, but if there were another inspection in an earlier step, for example, at the hot strip mill, the mass manufacture of nonconforming products could be avoided and maintaining quality control would be more efficient. In order to detect inclusion defects in hot-rolled steel plates, the authors developed a new technique for MFLT (Magnetic Flux Leakage Testing) using different magnetizing forces. According to an analysis of the noise factors in MFLT, it was found that the signals generated from the scale layer on a steel surface are dominant. A different magnetizing force method is the used to decrease this overpowering noise level in MFLT. In this paper, it was confirmed that inclusions larger than 160 in diameter and less than 0.45mm in depth can be detected utilizing this method.
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