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STUDY ON METAL MELTING AT HIGH FREQUENCY MELTING NG AT HIGH FREQUENCY STUDY ON METAL MELTI Prof. Eng. Ioan RUJA, PhD1, Prof. Eng. Constantin MARTA, PhD1, Eng. Aurel MIDAN2, Eng.Marius TUFOI1 1 University „Eftimie Murgu” of Reşiţa, România, 2U.C.M. of Reşiţa, România REZUMAT. În cadrul lucrării se prezintă o instalaţie care permite topirea metalelor în câmp electromagnetic la frecvenţe cuprinse între 200÷300 KHz.. KHz.. Topirea prin inducţie, în levitaţie prezintă interes datorită posibilităţii de a obţine metale mai pure şi cu proprietăţi mecanice, tehnologice tehnologice şi electrice care le fac mai performante faţă de metalele obţinute prin topire în instalaţiile clasice. Instalaţia cuprinde două părţi: convertorul static de frecvenţă şi circuitul oscilant LC care la rezonanţă rezonanţă determină topirea şi levitaţia metalului metalului. alului. Cuvinte cheie: încălzire , inducţie, convertor static de frecvenţă, rezonanţă, topire ABSTRACT. The paper presents an installation allowing the melting of metals in electromagnetic field at frequencies ranging between 200÷300 KHz.. KHz.. Melting by induction, induction, in levitation, presents a special interest due to the possibility to obtain purer metals with higherhigher-performance mechanic, technologic and electric properties compared to the metals obtained by melting in classic installations. The installation comprises comprises two parts: the static frequency converter and the LC oscillating circuit, which, at resonance, triggers the metal melting and levitation. Keywords: heating, induction, static frequency converter, resonance, melting 1. INTRODUCTION fr = The penetration depth of the electromagnetic field in metals is given by the relation (1). ρ δ= µ ⋅π ⋅ f (1) where: δ is the penetration depth; ρ is electrical resistivity; µ is the metal magnetic permeability; f is the frequency of the induced current. whereas the critical frequency is given by the formula [2]: fc = 6.45 ⋅ f π ⋅d2 1 (4) 2 ⋅π ⋅ L ⋅ C where: fr is the resonance frequency, [Hz]; L is the coil inductance, [H]; C [F] is the condenser capacity. U I (2) where: d [m] is the diameter of the sample; µ [H/m] is the environment magnetic permeability; f [Hz] is frequency of oscillator. 0 fr f Fig. 1. Explanation at series resonance frequency µ = µ0 ⋅ µr (3) At series or parallel resonance of an LC circuit the following relation is valid [1], [2]: The melting equipment uses static converters realised with commandable semi-conductor devices (silicon controlled rectifiers, nMOS transistors, IGBT ), commanded by PWM signals (Pulse-Width Modulation) [3], [5], [6]. The obtaining of the PWM signal is presented in fig.2. _____________________________________________________________________________________ Buletinul AGIR nr. 4/2012 ● octombrie-decembrie 1 Buletinul AGIR nr. 4/2012 ● octombrie-decembrie 195 NATIONAL CONFERENCE OF ELECTRICAL DRIVES CNAE 2012 - 2012 _____________________________________________________________________________________ CONFERINŢA NAŢIONALĂ DE ACŢIONĂRI ELECTRICE, ediţia–XVI, SUCEAVA 1 ω ⋅C (5) XL =ω⋅L (6) X R = RL (7) XL XL (8) Xc = QL = Z S = RL + ( X L − X C ) (9) Fig. 2. Generation of PWM signal a) composing of two signals (a sinusoidal and a triangular one); b) shape of the PWM signal and wave shape of the voltage / current from the exit ofa frequency static converter commanded by PWM. With the help of a mono-phase frequency static converter one may generate an alternative voltage wave with variable frequency. This voltage is applied to a series LC circuit with a certain configuration. Inside the coil with L inductivity one introduces the metal (Φ) to be melted [7]. By modifying the frequency of the Uinv voltage wave from the exit of the static converter and my altering the modulation degree (m=AS/AD) we can obtain the resonance of the series LC circuit. We can obtain the resonance of the LC circuit which, operating at frequencies with the resonance , f r = 1 , 2 ⋅π ⋅ L ⋅ C determines the maximum transfer of active energy from the source to the metallic material subjected to heating. In this work experiments were performed with an induction heating system made by authors and has examined the results measured with the simulated. The main contributions of the authors are: - implementation of simulators with the scheme fig. nr.4 ; - realization of the capacitor and the coil from the power circuit LC - sizing and adjustment of the elements from the electrical diagram; interpretation of the partial results - adaptation of the scheme for melting steel sample. 2. MODELLING In the case of the series RLC circuit we have: Fig. 3. Physical modelling of the series RLC circuit I= U Z (10) By neglecting RL, (RL=0) and setting the condition XC=XL,, the following results: f r = 1 , 2 ⋅π ⋅ L ⋅ C i.e. at the resonance frequency, the value of the current through the circuit is maximum. The maximum current induced in the metal present inside the coil triggers the increase of the metal temperature and its heating up to melting. Between the source and resonant circuit the exchange of reactive energy is zero (cos φ=1). The diagram of the installation is presented in Fig.4 The technical characteristics of the main elements from the diagram are: - Q3-Q4- BUH100G - Q8-Q11-n MOS transistors, IRF 540; - the matching impedance, Zm is an impedance made of three-five pieces of toroidal barrel-shaped coil, connected in parallel, with ferrite core, (N1=26 wires); - capacities C6=C7= 0.68 µF; _____________________________________________________________________________________ Buletinul AGIR nr. 4/2012 ● octombrie-decembrie 2 196 Buletinul AGIR nr. 4/2012 ● octombrie-decembrie STUDY ON MELTING AT AT HIGH _____________________________________________________________________________________ STUDY ON METAL METAL MELTING HIGH FREQUENCY FREQUENCY - Ls=0,55 µH; - C10= 0,5 µF; - D1 and D2- drivers of the TL494NC type; - TS, separation transformer with ferrite core. The Zm impedance is a matching impedance by which one maximises the power transfer from source to charge. It should observe the condition: ZSsource=ZLcharge where: ZSsource is the exit impedance of the source; ZLcharge is the entry impedance of the charge; Fig. 4. Electric diagram of the heating installation 3. EXPERIMENTAL RESULTS Fig.5 presents a view of the experimental installation. Fig. 5. View of the experimental installation _____________________________________________________________________________________ Buletinul AGIR nr. 4/2012 ● octombrie-decembrie 3 Buletinul AGIR nr. 4/2012 ● octombrie-decembrie 197 NATIONAL CONFERENCE OF ELECTRICAL DRIVES CNAE 2012 - 2012 _____________________________________________________________________________________ CONFERINŢA NAŢIONALĂ DE ACŢIONĂRI ELECTRICE, ediţia–XVI, SUCEAVA Fig.6 shows the wave shape of the voltage, which commands the two transistors and in In fig.7 we see the wave shape of the voltage on charge. Fig. 6. The UGS command voltage of the two transistors Fig.6 The wave shape of the voltage, which commands the two transistors. Fig.7 The wave shape of the voltage on charge _____________________________________________________________________________________ Buletinul AGIR nr. 4/2012 ● octombrie-decembrie 4 198 Buletinul AGIR nr. 4/2012 ● octombrie-decembrie STUDY ONMETAL METALMELTING MELTINGAT ATHIGH HIG FREQUENCY _____________________________________________________________________________________ STUDY ON FREQUENCY Fig. 8. a). Condenser b). Coil. Fig. 9. The steel sample at the temperature of a) 715°C, b) 925 °C and c) 1112°C 4. CONCLUSIONS Following the experiments performed until the present the following conclusions could be drawn: For the power installations P> 2 KW we need transistors with IDS >100 A; The C10 capacity must resist to high currents, ICS> 350 A at fr >300KHz; A correct dimensioning of Zm impedance is necessary; The use of the semi-commanded rectifier supposes an appropriate filtering of the rectified voltage. BIBLIOGRAPHY [1] Irshad Khan, Automatic frequency control of a induction furnace, 2000, Cape Technikon These Dissertation. http//dk.cput.ac.za/td_ctech/58.. [2] Gerard Develey, Chauffage par induction electromagnetique: principes, 2009 [3] Soshin Chikazumi , Physics of Ferromagnetism , Oxford Science Publications, Oxford University Press; New York, 1997. [4] Ben-Yaakov, Sam and Gregory Ivensky, Passive Lossless Snubbers for High Frequency PWM Converters, Seminar 12, APEC 99. [5] Balogh Laszlo, Practical Considerations for MOSFET Gate Drive Techniques in High Speed, Switch-mode Applications, Seminar APEC99. March 1999. [6] *** http://www.fluxeon.com *** [7] *** www.neon-john.com *** _____________________________________________________________________________________ Buletinul AGIR nr. 4/2012 ● octombrie-decembrie 5 Buletinul AGIR nr. 4/2012 ● octombrie-decembrie 199 NATIONAL CONFERENCE OF ELECTRICAL DRIVES CNAE 2012 - 2012 _____________________________________________________________________________________ CONFERINŢA NAŢIONALĂ DE ACŢIONĂRI ELECTRICE, ediţia–XVI, SUCEAVA About the authors Prof. Eng. Ioan RUJA, PhD University “Etimie Murgu” of Reşiţa email:[email protected] Is a professor at University “Etimie Murgu” of Reşiţa. Teaching disciplines: Electric drives systems and motion controls. He has published four book specialist, has over 30 patents and innovative certificates, has published over 100 papers. The research topics in electric drives systems, power electronics and motion controls. Conf. Eng. Constantin MARTA, PhD. University “Etimie Murgu” of Reşiţa email:[email protected] Is a professor at University “Etimie Murgu” of Reşiţa. Teaching disciplines: metallurgy, steel and iron elaboration. He has published five book specialist, has over 5 patents and innovative certificates, has published over 75 papers. The research topics in metallurgy, CAD, CAE and FEM analyze. Eng. Aurel MIDAN, U.C.M. Reşiţa S.A. email:[email protected] Graduated at the Technical University of Timişoara, Faculty of Metallurgy Engineering. After finishing University he started to work in steel and iron eleboration and casting The research topics: power electronics, circuits design, CAD, CAE , CAM. Eng. Marius TUFOI, University “Etimie Murgu” of Reşiţa email:[email protected] Graduate of the Engineering Faculty of “Etimie Murgu“ University of Reşiţa, Faculty of Electrical Engineering. After finishing University he started to work in motion controls, CAD, CAM and and FEM analyze . The research topics in power electronics and circuits design. _____________________________________________________________________________________ Buletinul AGIR nr. 4/2012 ● octombrie-decembrie 6 200 Buletinul AGIR nr. 4/2012 ● octombrie-decembrie