Papers by Keyword: Magnetic Stirring

Abstract: A segmented 3-D coupled electromagnetic-thermal solute transportation model, aimed to better understand the macro-segregation formation in the strand during a popular continuous casting (CC) process, has been developed. Based on the model validation by industrial tests, the effect of M-EMS and F-EMS running parameters on the segregation distribution were subsequently carried out. It is shown that the simulated solute segregation profile in the W-shape along the casting thickness direction is in a good agreement with the measured profile. In the initial solidification shell with thickness in 0.020 m, the solute segregation degree changes from a positive value to a negative with the increasing distance from strand surface because of the washing effect induced by the impact flow from the nozzle side port and M-EMS. Here, the minimum degree of carbon segregation decreases from 0.976 to 0.875 with the increasing stirring current from 100A to 550A. As the stirring current of F-EMS decreases from 630A to 200A, the minimum segregation degree locating at 0.109 m distance from strand surface increases from 0.805 to 0.967. The carbon segregation degree at the strand center first decreases from 1.10 to the minimum value of 1.06 at the case of 350 A/4 Hz because of the concentration equilibrium for the local decreasing negative segregation induced by F-EMS, and then increases to 1.16 due to the local poor stirring.

Abstract: Two samples of ZnO doped Ba with the chemical composition, 97ZnO-3BaO, have been prepared via oxalate co-precipitation. During precipitation the first sample, A, was stirred by magnetic stirrer while the second sample, B, was stirred via 40KHz ultrasonic wave. The obtained powders were decomposed at 400°C for 3h, then pressed and sintered at 1200°C for 1.5h. Then XRD, SEM and J-E measurements were performed and analysed. The grain sizes of the obtained ceramics were (0.5-2.26) µm and (80-119) nm for samples A and B, respectively. The J-E measurements revealed that the obtained ceramic has voltage switching characteristics, and that the switching voltage could be controlled by the stirring process.

Abstract: Experiments were performed for visual observation and investigation of liquid Gallium flow at a temperature of 40oC in a rotating magnetic field. Two different measuring methods were developed to determine the revolution number of rotating melt. In both cases the frequency of magnetic induction was 50, 100 and 150 Hz and the values of magnetic induction could be changed between 0 and 70 mT. The magnetic Taylor number changed between 0 and 3.54x107 during the experiments.

Abstract: In order to minimize the occurrence of hot-cracking phenomena in laser welding of hotcracking sensitive aluminum alloy sheets, it is a common technique to introduce silicon-containing filler wire into the weld metal. However, to achieve an optimum result, a homogenous distribution of not less than 2 % of silicon throughout the weld metal is strongly recommendable. Under certain circumstances, this may be a difficult task. One potential solution to achieve sufficient dilution and, consequently, a very homogenous silicon distribution might be the application of alternating magnetic fields. In foundry technology, the use of magnetic fields to influence melt flow is a wellestablished method. For TIG welding, a process called magnetic stirring was first investigated in the 1970s. It was sufficiently demonstrated by the help of an alternating magnetic field coaxial with the arc axis, that, among other effects, the degree of dilution can be increased and a refined grain structure is achieved. Since the late 1990s, some efforts have been taken to apply constant magnetic fields to laser welding processes. However, neither alternating fields nor potential effects on dilution have been in the focus of these investigations. To help this situation, basic studies on magnetically influencing melt flow during laser welding of aluminum have been conducted. To that end, alternating fields have been coaxially applied with magnetic flux densities up to 60 mT and frequencies in the range of 0 to 20 Hz. It was demonstrated by the help of a specially developed method that, depending on the parameters chosen, such fields are indeed capable of influencing melt flow and weld pool dilution, thus “stirring” the weld metal.