THEORETICAL INVESTIGATION ON BY-ONLY-CURRENT ELECTROMAGNETIC SEPARATION OF INCLUSION FROM MOLTEN METALS

The electromagnetic field under applied AC and DC current in round and rectangular pipe was systematically investigated, then a concept of 'equivalent current density' was proposed for evaluating the inhomogeneous electromagnetic pinch force, and the mono-component removal efficiency and the overall removal efficiency of inclusion were formulated. It is founded that flat pipe is superior to round pipe for the electromagnetic removal of inclusion, and DC current can get a higher removal efficiency than A C current due to absence of skin phenomenon. Under usual condition, a removal efficiency of 52% for 10μm inclusion or more than 92% for 20μm inclusion can be achieved by imposing a current density of 3×106A/m2 in a flat pipe.

Purification technology of molten aluminum

Various purification methods were explored to eliminate the dissolved hydrogen and nonmetallic inclusions from molten aluminum alloys. A novel rotating impeller head with self-oscillation nozzles or an electromagnetic valve in the gas circuit was used to produce pulse gas currents for the rotary impeller degassing method. Water simulation results show that the size of gas bubbles can be decreased by 10%20% as compared with the constant gas current mode. By coating ceramic filters or particles with active flux or enamels, composite filters were used to filter the scrap A356 alloy and pure aluminum. Experimental results demonstrate that better filtration efficiency and operation performance can be obtained. Based on numerical calculations, the separation efficiency of inclusions by high frequency magnetic field can be significantly improved by using a hollow cylinder-like separator or utilizing the effects of secondary flow of the melt in a square separator. A multi-stage and multi-media purification platform based on these methods was designed and applied in on-line processing of molten aluminum alloys. Mechanical properties of the processed scrap A356 alloy are greatly improved by the composite purification.

In-situ A1/24Si Functional Graded Materials Prepared by Electromagnetic Separation

Cylinder-like in-situ AI/24Si FGMs were produced by using electromagnetic separating process. Si primary phase reinforced layer with volume fraction as high as 16 pct was formed at the outer region of the cylinder-like samples where the local hardness and wear resistance were enhanced remarkably. Moreover, both of strength and ductility in the inner region provided insurance of reliable strength for this as-cast gradient material. It indicated that general mechanical properties such as good wear resistance at the outer region and good ductility in the central part could be obtained with the optimized redistribution of the Si primary particles under the electromagnetic force.

Removal of SiC particles from solar grade silicon melts by imposition of high frequency magnetic field

Non-metallic particles and metallic impurities present in the feedstock affect the electrical and mechanical properties of high quality silicon which is used in critical applications such as photovoltaic solar cells and electronic devices. SiC particles strongly deteriorate the mechanical properties of photovoltaic cells and cause shunting problem. Therefore, these particles should be removed from silicon before solar cells are fabricated from this material. Separation of non-metallic particles from liquid metals by imposing an electromagnetic field was identified as an enhanced technology to produce ultra pure metals. Application of this method for removal of SiC particles from metallurgical grade silicon （MG-Si） was presented. Numerical methods based on a combination of classical models for inclusion removal and computational fluid dynamics （CFD） were developed to calculate the particle concentration and separation efficiency from the melt. In order to check efficiency of the method, several experiments were done using an induction furnace. The experimental results show that this method can be effectively applied to purifying silicon melts from the non-metallic inclusions. The results are in a good agreement with the predictions made by the model.

REMOVE INCLUSIONS FROM ALUMINUM MELT INELECTROMAGNETIC FIELD

Electromagnetic separation of non-metallic inclusions from Al-Si melt is studied by theoretical analysis and experiments on self-designed electromagnetic separation apparatus. Metallographs and LECO Image Analysis System were used to analyze the content of alumina in aluminum alloy before and after electromagnetic separation. It is seen that removal effciency increases with the increase of electromagnetic force (EMF) and diameter of inclusion particles while decreases with the increase of melt velocity and height of separator. All alumina particles with diamete of 14μm have been removed successfully from the melt.

Electromagnetic Separation of Nonmetallic Inclusions From Liquid Steel by High Frequency Magnetic Field

The currernt work is to investigate the removal of nonmetallic inclusionsfrom liquid steel using electromagnetic separation.In experiments,a certain amount of aluminum was added to the molten steel in a crucible to generate aluminum inclusions.A layer of aluminum clusters were observed close to the wall of the crucible.Three dimensional electromagnetic field and fluid flow simulation indicated that particles moved to the wall of the crucible by the EM force and were entrapped at the inside wall of the crucible.

The Droplet Evolution Trend and Purification Efficiency in ESR Process by Superimposing a Static Magnetic Field

The paper investigated the refinement effect on droplet size of Electroslag Remelting(ESR)Process by superimposing a transverse static magnetic field through physical simulation method.A transparent experimental model is built to visualize the ESR process under magnetic field,especially focusing on the formation and departure process of droplets on electrode tip.The results show that due to the interaction between alternating current and external transverse magnetic field,the resulting electromagnetic oscillation in the molten droplet and slag bath refined droplets remarkably, the higher the magnetic field intensity,the smaller the droplet size.However,there exists a suitable frequency of 10Hz for the current which will achieve an optimal effect of droplet's dispersing and refinement.Based on the theory of electromagnetic separation,a new mechanism of removing nonmetallic inclusions in ESR process is proposed.By a simplified circuit model,the inclusion removal efficiency is calculated and it proves that the refinement of droplets under magnetic field could increase the removal efficiency of nonmetallic inclusions in ESR significantly.

Development of Clarification Technology for Molten-Al by a Combination of Cyclone and Electromagnetic Separation

Aluminum has high recyclability and promising future,so aluminum recycling is important for the future society.However aluminum recycling has some problems;one problem is inclusions remaining in final aluminum products.In this study,we have proposed a new separation process of inclusion particles from molten aluminum;it is the electromagnetic cyclone separator,which consists of the liquid cyclone and the electromagnetic separator.We carried out water model experiments,in which the magnetic separation was used instead of the electromagnetic separation.A theoretical model to estimate the separation efficiency was developed and the results agreed with the water model experiments.The theoretical model was used to estimate the separation performance of the electromagnetic cyclone separator for molten aluminum,and it was predicted that the separator was effective clarification process for aluminum recycling.

Separation of Particles From Molten Aluminum With High Frequency Electromagnetic Field

The currentstudy is to investigate the separation of non-metallic inclusions from molten aluminum with 53-63 kHz high frequency electromagnetic filed.In the experiments,aAl-SiC composite material- pure aluminum with a certain amount of dispersed SiC particles with 10-20 μm diameter- was used.Both laboratory experiments and numerical simulation were performed.It was observed that SiC particles were pushed to the boundary layer of the aluminum close to the wall of the crucible,and the thickness of the particle layer was approximately 1.0-1.5 mm and the area fraction of the particle layer was 9-15%of the entire horizontal cross section area.With separation time going on,the accumulation layer became thinner,and the accumulation layer density became higher.The numerical simulation indicated that the magnetic flux density is larger at top and bottom than other locations and very small at the center of the crucible,and the EM force mainly acted on the outside 0.004 m layer of the melt due to the effect of the skin effect.There were recirculation eddies at the top and bottom and close to the corner where the EM force was the largest.The speed of the flow was 11-13 mm/s at the corner of the top and bottom and was as small as 1 mm/s at the center of the crucible. Both the numerical simulation and the experimental observation showed that the top free surface was not flat, approximately 1.0 mm high at the center of the top surface by numerical simulation and 4.0 mm by the experimental observation.More particles were entrapped at the lower part of the crucible.