| Faraday, a British physicist and chemist, discovered electromagnetic inductionand proposed the field theory in 1831, which was when there was an alternatelychanged current through a coil there would be induction magnetic field. This is thebasic theory for studying induction heating. And after proposing theory of eddycurrent, it became possible to make induction heating applied in engineering. Now,with the improvement of science and technology, the induction heating techniquebecomes more and more mature and its excellence, including saving energy andresource, fast heat speed and good heat quality, simply operated, easy to beautomation, etc., has been known step by step, so that it is widely used in manyfields, for example, in the aspects of smelting, forging, welding, heat treatment. Asa branch of induction heating, power frequency induction heating technique playsmore and more important role. Nowadays power frequency induction heatingtechnique has been treated as important technique and some products have beenapplied in real. And with the improvement of numerical method, finite elementmethod, boundary element method and finite difference method have been used tosimulate the electromagnetic field, eddy current field and thermal field to enrichtheory and means of design.On the base of introducing basic knowledge about induction heating, combinedwith Jilin Province Science and Technology Bureau's science and technologydevelopment project 'Exploiture and Technology Study of Fast and UndamagedBearing Induction Heating Disassembling Equipment' and aimed at the question ofundamaged bearing inner's disassembling in the process of manufacture inChangchun Car Company, this dissertation studied the questions as followed.At the first, in the base of Maxwell equation, making simplified model ofinduction heating equipment as an example and using the asymptotic truncationtechnology of boundaries condition, this paper discussed two simplified eddycurrent models of sinusoidal steady-state magnetic field. One is the model ofaxisymmetric eddy current in vertical magnetic field excitation, and the other is themodel under transverse magnetic field excitation. In the analysis of axisymmetriceddy current, the variational finite element method and one order asymptoticboundary condition are used to set up the functional formulation. The integro-differential approach is adopted to replace the source current density with theexpression of the measurable current and the integral of coil eddy current. A finiteelement method with Galerkin's formulation is used to set up the eddy equation oflong structural conductor under the transverse magnetic field excitation.At the second, putting an eye to joule heat aroused from eddy current which canbe regarded as inside heat source to calculate thermal field. The result of thermalfield can be used to analyze thermal distributing and movement trend in differentpart of workpiece. Making the base of Joule Law and aimed at eddy equation, thecorresponding axisymmetric temperature field's deflection differential equation isset up in order to solve heat quantity. And considering heat exchange equation andits' boundary conditions, the distributing of thermal field is calculated. In the meanwhile, unsteady axisymmetric thermal field's equipollence value change questionsand the finite element's solution of transient state temperature field are alsodiscussed.At the third, introducing the use of ANSYS, a finite element analysis software,in simulating magnetic field, including the applied range, the type of elements usedin simulation, the basic step of simulation analysis and the questions which shouldbe noted when analyzing harmonic magnetic field. At the end, analyzing theproblem's model and listing the result.At the fourth, introducing the use of ANSYS in analyzing heat problem,including basic heat transmitting method: thermal conduct, convection andemission, and basic material attribute, such as enthalpy, specific heat, heatgeneration rate, etc.At the fifth, giving an example to explain how to use ANSYS to solvemagnetic-thermal coupling question. As a result, a simulation temperature variedwith time curve of inner bearing's outside surface and the internal surface isproduced.At the sixth, doing experiments with the designed equipment and measuringvalue in two different connections: triangle type connection and star typeconnection, making current and temperature as parameters. And drawing curvesdepending on data.This article presents the theories of eddy current field and the temperature fieldwhich are the basic theory used to design power frequency induction heatingequipment. These theories have very important significance for enhancing the workpiece's thermal efficiency and improving induction heating equipment. |
