Research Of Electromagnetic Elimination Of The Molten Metal With High Frequency Magnetic Field

Electromagnetic Elimination (EME), which is a new technique of purification, has become one of research focuses because of its non-pollution, high-efficiency and independence on the difference of the density between the melt and nonmetallic inclusions. High frequency magnetic field purification, which is one method of the EME, is the main study hot due to its convenient application.In this paper, a calculation model of EME with high frequency magnetic field has been set up on the base of Maxwell equations. The elimination time and efficiency can be calculated by discrete and summation. With the model, the influence of parameters, such as dimension of non-metallic inclusion, diameter of tubule, magnetic induction intensity of molten metal surface on the elimination time and efficiency can be analyzed. The best elimination frequency of the high frequency magnetic field has also been calculated. The calculation results show that when the magnetic induction intensity in the molten metal surface is 0.06T and the distance from non-metallic inclusion to the melt Surface is 4mm, the non-metallic inclusions with the diameter 10μm canbe eliminated in 20s and the elimination efficiency is about 96%. The elimination efficiency with the 30μm non-metallic inclusions is about 99% when the elimination time is 5.7s while the elimination efficiency with the 100μm non-metallic inclusions can reach 99% in 0.56s. The electromagnetic body force in the molten metal can get the maximum value when f=1/(4πσμx~2). With the increase of frequency, elimination time can be decreased while it increases with the frequency when the value of frequency is more than 1／(4πσμx~2).The effects of magnetic induction intensity and the acting time on the turbulence in the molten metal have been analyzed with the finite element software calculation and the experiment research. It can be seen that with the increase of magnetic induction intensity and the force time, the turbulent flow of melt becomes intense. The simulation results of electromagnetic separation with multi-tubule show that the magnetic induction intensity in the inner molten metal can be obviously affected by the width of the gap between the exterior molten metal. The experiment results also show that electromagnetic separation with multi-tubule is feasible. The influence of the diameter of the inclusion, the elimination time and magnetic induction intensity on the elimination results have been verified with the experiments. It can be seen from the experiment results that alumina inclusions with diameter 5～15μm dispersed in the molten metal can not be separated effectively on the current experiment conditions, while alumina inclusions with diameter 30～200μm in the molten aluminum can be separated when the diameter of the tubule is 10mm, the magnetic induction intensity 0.04T and the separation time 1s. When the elimination time exceeds 3s, there are few alumina inclusions larger than 30μm in the inner of the molten aluminum. The same results can be acquired if acting the 0.06T magnetic induction intensity more than 1s. The optimum temperature range to separate primary silicon in the A1-18wt%Si alloy with high frequency magnetic field has been obtained with the experiments. The experiment results show that the primary silicon can be better separated in 5s when the temperature range of the alloy is from 600℃to 620℃and the magnetic induction intensity is 0.04T.In order to explore the practicability of EME with high frequency magnetic field, the continuous multi-elimination equipment has been set up. The high frequency magnetic field is applied around the ceramic foam filter. The continuous elimination results with the Al-10wt%Mg alloy show that without magnetic force, the percentage composition of oxygen in the alloy is decreased from 0.0009% to 0.0004% after twice elimination and the elimination efficiency is 55.6%. When the magnetic induction intensity around the ceramic foam filter is 0.04T, the percentage composition of oxygen is decreased from 0.0014% to 0.0003% and the elimination efficiency is 78.6%, it is 23.6% higher than that without high frequency magnetic field. The continuous elimination results with the molten aluminum containing 30～200μm alumina inclusions show that the average elimination efficiency is 96.9% when the magnetic induction intensity is 0.04T. It increases to 97.3% when the magnetic induction intensity is increased to 0.06T, and the later is 1.15% higher than that with caremic foamfiller only. In the paper, the influence of the turbulence on the elimination efficiency of the ceramic foam filter has been investigated, it is seen that with the increase of the turbulence, the elimination efficiency of the ceramic foam filter can be decreased seriously.