Elements of Design of Magnetic Separation Equipment

Abstract

The design of a magnetic circuit for a magnetic separator is based on the need to optimize the magnetic force required to separate eciently, and selectively, particles of dierent magnetic susceptibilities. As transpires from eq. (1.8), the magnetic force is the product of the magnetic field strength and of the field gradient. The desired magnetic field strength, the field gradient and their combination are a function of the type of material to be separated, mode of separation, required metallurgical performance and economic criteria. In this chapter the basic design criteria and techniques of the generation of the magnetic field and its gradient, as used in magnetic separation, will be reviewed. Magnetic circuit design has been traditionally dicult because of the usual non-analytic nature of the solutions for fields emanating from arbitrary sources. Further, unlike currents in electric circuits, magnetic flux is not confined to the wires but passes through various components of the circuit, including the air. Over the years, several analytical techniques have been used to give approximate solutions to magnetic design problems. In the simplest cases, the analytical solution can be exact, but in general for any practical problem, analytical solutions lead to large errors. Most designs are optimized by measurement and extrapo-lation, and experience of working with a particular type of a magnetic circuit is important. The advent of powerful computational techniques, such as finite element analysis, allows us to find accurate solutions for two-or three-dimensional field distributions in complex geometries, which in turn may be used to predict device performance with similar precision. However, these modelling techniques 251