Download study on metal melti study on metal melting at high frequency ng at

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.
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Buletinul AGIR nr. 4/2012 ● octombrie-decembrie
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CNAE
2012 - 2012
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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;
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STUDY ON
MELTING AT
AT HIGH
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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
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2012 - 2012
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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
ONMETAL
METALMELTING
MELTINGAT
ATHIGH
HIG FREQUENCY
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STUDY
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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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Buletinul AGIR nr. 4/2012 ● octombrie-decembrie
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NATIONAL
CONFERENCE
OF ELECTRICAL
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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.
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