SSTUDY ON METAL MELTING AT HIGH FREQUENCY STUDY ON … · STUDY ON METAL MELTING AT HIGH FREQUENCY Buletinul AGIR nr. 4/2012 octombrie-decembrie 1 TUDY ON METAL MELTI SSTUDY ON METAL

STUDY ON METAL MELTING AT HIGH FREQUENCY

Buletinul AGIR nr. 4/2012 ● octombrie-decembrie 1

STUDY ON METAL MELTISTUDY ON METAL MELTISTUDY ON METAL MELTISTUDY ON METAL MELTING AT HIGH FREQUENCYNG AT HIGH FREQUENCYNG AT HIGH FREQUENCYNG AT HIGH FREQUENCY

Prof. Eng. Ioan RUJA, PhD1, Prof. Eng. Constantin MARTA, PhD

1,

Eng. Aurel MIDAN2, Eng.Marius TUFOI

1

1University „Eftimie Murgu” of Reşiţa, România,

2U.C.M. of Reşiţa, România

REZUMAT. REZUMAT. REZUMAT. REZUMAT. În cadrul lucrării În cadrul lucrării În cadrul lucrării În cadrul lucrării se prezintă o instalaţie care permite topirea metalelor în câmp electromagnetic la frecvenţe se prezintă o instalaţie care permite topirea metalelor în câmp electromagnetic la frecvenţe se prezintă o instalaţie care permite topirea metalelor în câmp electromagnetic la frecvenţe se prezintă o instalaţie care permite topirea metalelor în câmp electromagnetic la frecvenţe cuprinse între 200÷300 KHz.cuprinse între 200÷300 KHz.cuprinse între 200÷300 KHz.cuprinse între 200÷300 KHz.. . . . Topirea prin inducţie, în levitaţie prezintă interes datorită posibilităţii de a obţine metale mai Topirea prin inducţie, în levitaţie prezintă interes datorită posibilităţii de a obţine metale mai Topirea prin inducţie, în levitaţie prezintă interes datorită posibilităţii de a obţine metale mai Topirea prin inducţie, în levitaţie prezintă interes datorită posibilităţii de a obţine metale mai pure şi cu proprietăţi mecanice, tpure şi cu proprietăţi mecanice, tpure şi cu proprietăţi mecanice, tpure şi cu proprietăţi mecanice, tehnologice şi electrice care le fac mai performante faţă de metalele obţinute prin topire în ehnologice şi electrice care le fac mai performante faţă de metalele obţinute prin topire în ehnologice şi electrice care le fac mai performante faţă de metalele obţinute prin topire în ehnologice 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 rezonainstalaţiile clasice. Instalaţia cuprinde două părţi: convertorul static de frecvenţă şi circuitul oscilant LC care la rezonainstalaţiile clasice. Instalaţia cuprinde două părţi: convertorul static de frecvenţă şi circuitul oscilant LC care la rezonainstalaţiile clasice. Instalaţia cuprinde două părţi: convertorul static de frecvenţă şi circuitul oscilant LC care la rezonanţă nţă nţă nţă determină topirea şi levitaţia metdetermină topirea şi levitaţia metdetermină topirea şi levitaţia metdetermină topirea şi levitaţia metaluluialuluialuluialului.... Cuvinte cheie:Cuvinte cheie:Cuvinte cheie:Cuvinte cheie: încălzire , , , , inducţie, convertor static de frecvenţă, rezonanţă, topire ABSTRACT. ABSTRACT. ABSTRACT. ABSTRACT. The paper presents an installation allowing the melting of metals in electromagnetic field at frequencies The paper presents an installation allowing the melting of metals in electromagnetic field at frequencies The paper presents an installation allowing the melting of metals in electromagnetic field at frequencies The paper presents an installation allowing the melting of metals in electromagnetic field at frequencies ranging between 200÷300 KHz.ranging between 200÷300 KHz.ranging between 200÷300 KHz.ranging between 200÷300 KHz.. . . . Melting by iMelting by iMelting by iMelting by induction, in levitation, presents a special interest due to the possibility to nduction, in levitation, presents a special interest due to the possibility to nduction, in levitation, presents a special interest due to the possibility to nduction, in levitation, presents a special interest due to the possibility to obtain purer metals with higherobtain purer metals with higherobtain purer metals with higherobtain purer metals with higher----performance mechanic, technologic and electric properties compared to the metals performance mechanic, technologic and electric properties compared to the metals performance mechanic, technologic and electric properties compared to the metals performance mechanic, technologic and electric properties compared to the metals obtained by melting in classic installations. The installation cobtained by melting in classic installations. The installation cobtained by melting in classic installations. The installation cobtained by melting in classic installations. The installation comprises two parts: the static frequency converter and the LC omprises two parts: the static frequency converter and the LC omprises two parts: the static frequency converter and the LC omprises two parts: the static frequency converter and the LC oscillating circuit, which, at resonance, triggers the metal melting and levitation. oscillating circuit, which, at resonance, triggers the metal melting and levitation. oscillating circuit, which, at resonance, triggers the metal melting and levitation. oscillating circuit, which, at resonance, triggers the metal melting and levitation. Keywords:Keywords:Keywords:Keywords: heating, induction, static frequency converter, resonance, melting

1. INTRODUCTION

The penetration depth of the electromagnetic field in

metals is given by the relation (1).

f⋅⋅=

πµ

ρδ (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]:

2

45.6

d

ff c

⋅

⋅=

π (2)

where: d [m] is the diameter of the sample;

µ [H/m] is the environment magnetic

permeability;

f [Hz] is frequency of oscillator.

rµµµ ⋅=0

(3)

At series or parallel resonance of an LC circuit the

following relation is valid [1], [2]:

CLf r

⋅⋅⋅=

π2

1 (4)

where: fr is the resonance frequency, [Hz];

L is the coil inductance, [H];

C [F] is the condenser capacity.

Fig. 1. Explanation at series resonance frequency

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.

I U

f 0 fr

Buletinul AGIR nr. 4/2012 ● octombrie-decembrie_____________________________________________________________________________________

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NATIONAL CONFERENCE OF ELECTRICAL DRIVES – CNAE 2012


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 ,

CLf r

⋅⋅⋅=

π2

1,

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:

CX c

⋅=

ω

1 (5)

LX L ⋅= ω (6)

LR RX = (7)

L

L

LX

XQ = (8)

( )CLLS XXRZ −+= (9)

Fig. 3. Physical modelling of the series RLC circuit

Z

UI = (10)

By neglecting RL, (RL=0) and setting the condition

XC=XL,, the following results:

CLf r

⋅⋅⋅=

π2

1 ,

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;

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STUDY ON METAL MELTING AT HIGH 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

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197



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

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STUDY ON METAL MELTING AT HIG 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 ***

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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.



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.


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,



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.

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SSTUDY ON METAL MELTING AT HIGH FREQUENCY STUDY ON … · STUDY ON METAL MELTING AT HIGH FREQUENCY Buletinul AGIR nr. 4/2012 octombrie-decembrie 1 TUDY ON METAL MELTI SSTUDY ON METAL