Electromagnetic separation techniques in metal casting. II. Separation with superconducting coils

The second part of this paper is devoted to the use of dc superconducting coils for electromagnetic separation of small nonconducting inclusions in metal casting. We theoretically analyze two methods: 1) magnetohydrodynamic separation with an electric current induced by a mean flow (conical separator) and 2) electromagnetic separation with an externally injected electric current (helical separator). First, the paper develops a model of the conical separator proposed by Gillon and Pillin in 1998 and compares it with experiments. It states that the main reason for poor separation efficiency can be flow inhomogeneity and turbulence in the separation channel. Second, the paper introduces a model of the electromagnetic separator with an injected current. Such a model has a number of advantages including better performance and higher flow homogeneity. It is capable of separating of nonconducting inclusions on the order of 10 μm in size in a magnetic field of 8 T with a flow rate of 1 kg/s. Power efficiency of the electromagnetic separation is studied with respect to the accompanying Joule´s heating of molten metal. It is found that the electromagnetic separator with a superconducting coil and an injected current has the highest power coefficient, at least 100 times greater than the efficiency of conventional separation devices