Download C. Role of Work Coil

International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Design and Performance of Induction Hardening
Machine
Hnin Wai Wai Hlaing, Nang Saw Yuzana Kyaing

Abstract— The induction hardening machine utilized in the
industrial application. In this machine, work coil and work piece
are the main portion of the system. As the work coil is the heart
of the machine, an excellent coil design reduces power
requirement and causes good efficiency. This paper shows the
design of work coil, magnetic field intensity and heat
requirement in the work piece. Increasing number of work coil
turns is increasing power requirement for the same shape and
size of work piece. Unlikely the induction melting, the surface
hardening system needs the high frequency depends upon the
permeability of work piece. This paper describes the results by
increasing frequency, changing work piece size.
current is passed. Because of the electrical conductivity of the
metals, current is induced primarily near surface of the part.
As the result of the flow current and the resistance of the
material, heat energy is developed in the work piece. And the
work piece is hardened electrically
Alternating magnetic flux
Induce current in
work piece
Current in coil
Index Terms— Induction hardening, Magnetic field intensity,
Multi-turns Helical coil, Stationary hardening method.
Figure 1 Basic Induction Heating System
I. INTRODUCTION
II. DIFFERENT TYPES AND METHODS OF INDUCTION
HARDENING
In induction hardening system, the essential requirements
are the coil called work coil and the alternating current
supply. The work coil may be wound the material to be
hardened called work piece or it may be near by the work
piece and work coil is applied by the high-frequency current.
The flow of current in the work coil produces a magnetic field
or flux that surrounds each turns of work coil and this flux
passes through air or any metal that is within or near the work
coil. The alternating current causes the flux to change or the
alternating magnetic field. And the change of flux induces a
voltage within the work piece. Due to this induced voltage,
the induce current is flown through the work piece. Since this
heat is caused by the induction of current, the process is called
induction heating. And as the induction hardening is the
branch of the induction heating system, the process of
induction hardening is the same as that of induction heating.
But the applied frequency of induction hardening system is
higher than induction melting system. Basic induction heating
system is shown in figure (1) [1].
As the most important one in a hardening machine is the
available of high- intensity heat energy the short operation
time, to fulfill the requirement the induction type hardening
machine called induction hardening machine is used. This
type of hardening system is the system of heating by electric
energy. The process of induction hardening machine is that in
which the component to be hardened is surrounded by a
suitable-shaped coil through which high frequency electric
Manuscript received Oct 15, 2011.
Hnin Wai Wai Hlaing, Department of Electrical Power Engineering,
Mandalay Technological University, (e-mail: [email protected]).
Mandalay, Myanmar, 09-422488194
Nang Saw Yuzana Kyaing, Department of Electrical Power
Engineering,
Mandalay
Technological
University,
(e-mail:
[email protected]). Mandalay, Myanmar
A. Type of Hardening
There are two types of hardening depending upon the depth
of heating zone. They are through hardened and surface
hardened.
(i)Though Hardened
In the form of through hardened, heat treated is in such a
way that the inside of the work piece is hard as the outside.
Therefore, not only is the surface resistance to wear, but the
entire part is more able to resist bending or twisting without
failure. The heating cycle is long compared with surface
hardening, and the frequency required is less than another.
(ii)Surface Hardened
It is also called case hardening. In this hardening, the core
of work piece remains malleable whilst the outside surface
attains the desired hardness value. The high frequency is
required and the heating cycle is very short [2].
B. Method of Hardening
There are two methods of hardening. They are stationary
hardening method and scanning method.
(i)Stationary Hardening Method
It is also called one-shot hardening method and in this
method, heating and quenching are done at the same position.
There is no movement of work piece or work coil during
operation period. This method can be applied for both
revolving of hardening work piece and stationary of
hardening material.
(ii)Scanning Hardening Method
In this method, heating is done partly and heat portion is
hardened, and heating inductor travels through longish
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
direction of work piece successively. This can be applied for
revolving of work piece, stationary of work piece, work coil
remains stationary and work piece travels, and work coil
travels.
C. Role of Work Coil
The work coil is the heart of induction hardening system. It
is the main part of the system that transfers the electric energy
to the heat energy. So, to be the maximum transfer of heat
energy to the work piece the role of work coil is very
important. The work coil is generally formed to be the largest
possible number of magnetic flux lines inserted in the work
piece at the area to be heated. The denser the flux at this point,
the higher will be the current generated in the work piece.
As the current generated in the work piece causes the heat
energy, the heating rate and the depth of heat penetration
absolutely depend upon the work coil. The work coil faces
various types, sizes and shapes of work pieces for a wide
variety of heating operation. So, the formation of work coil is
the most important one for the whole system to be a good
efficiency.
1. Types of Conductor
To form a work coil, a suitable length of conductor must be
wound in the shape of a coil or desired pattern in accordance
with the natures of work piece. It carries a huge current for all
time of operation. So to be a good conductor, the material
used as a conductor must afford a continuous passage of
electrical current, even when subjected to a difference of
electrical potential. The greater density of current for a given
potential is the more effective the conductor. The material
with high conductivity or low resistivity is used as a conductor
for the induction hardening system.
During operation, as the work coil is adjacent to the heated
work piece, it is heated by the radiation and convection of heat
from the work piece. And due to the self-resistivity of
conductor must be less. Table 1 shows the conductivity of
some materials. According to the table the conductivity of
silver is rather higher than that of copper. But it is more
expensive and the melting point of it is lower than that of
copper. So as its high conductivity the use of copper is
suitable for induction hardening process. [4]
Table 1. Specification of Work Coil
Specification
Value
Material
Copper
Resistivity
1.7×10-8 (at 293.15K)
Permeability
1
Melting temperature
2. Multi Turns Helical Coil Type
The copper conductor is wound or formed either
symmetrical in contour or shaped to suit the outline of the part
to be heated. This type is suited to surface heating of shaft and
bars. The shape of helical coil mainly depends on the shape of
work piece. So, the coil may be in the shape of round,
rectangular, formed, spiral helical and others. Of all, the
round coils are commonly used and suitable for several
shapes of work piece [3].
Figure. 2 Multi Turns Helical Coil Type
III. DESIGN CALCULATIONS
A. Power Required for Heat Developed in Work Piece
The electric power required for an induction heating
process is generally related to the heat developed on the work
piece and the heat transmitted to the surrounding area.
Therefore, the required power is the sum of heat absorbed by
the work piece and dissipated heat to nearby. The temperature
rise of a work piece depends upon the heat it receives, its mass
and the nature of the material. The relationship between these
quantities is as follow. [5]
Total energy required to melt metal,
Q1  m.S. Δ .1 t
(1)
Where,
Q1= heat absorbed in the work piece, W
Δθ  change in temperature, K
Cp= specific heat of melting metal
m= mass of work piece
t=melting time, sec
The radiation power varies greatly over the heating cycle.
Radiation loss becomes appreciable when the surface
temperature exceeds a few hundred degrees.
By the Stefan-Boltzman law, the radiation heat loss is
Table 2. Specification of work piece
Specification
Value
Material
1040 carbon steel
Resistivity (Ωm)
12.7×10-8 (at 293.15K)
115.6×10-8 (at 1253.15K)
Permeability (H/m)
1
Specific Heat (J/kg.K)
434 (at 300K)
1169 (at 1000K)
Melting Temperature (K) 1794026
Hardened Temperature 1116.48- 1172.03
(K)
Density (kg/m3)
7861.13
Q2 = ε.C.Asw.(θ4-θ40)
(2)
Where,
Q2 = power loss caused by radiation, W
ε = emissivity
C= constant, which depends upon the nature of the body
surface, W/m2.K4
Asw = surface area of work piece, m2
The heat loss by conduction through the air from the work
piece to the adjacent work coil can be shown by the Fourier’s
law as follows.
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Q3 
k A sw ( 4   4 0 )
 3
Cp
Lc 
2
rout
N2
0.0254(9rout  10lc )
Where,
Q3 = heat loss caused by conduction, W
k = thermal conductivity of work piece, W/m.K
Cp = coupling distance, m
Therefore, the required electric power to develop the
desired temperature on work piece for some times can be
expressed as follows.
Where, Lc= inductance of work coil, µH
rout= outer radius of work coil, m
The DC resistance of conductor,
Ph = Q1+Q2+Q3
Where,
Rdc=DC resistance of work coil, Ω
ρ= resistivity of conductor, Ω.m
A= cross sectional area of conductor, m2
The resistance of conductor is,
(4)
Where,
Ph = electric power due to heat energy in the work piece, W
R dc 
ρlc
Ac
(9)
(10)
B. Length of Conductor Required for Work Coil
Rc 
C p= 0.5dc
, Cd = 0.5Cp
Where,
Cp = pitch of coil windings, m
d c  diameter of conductor, m
lw
d c  Cp
rc = radius of conductor, m
δc = depth of current penetration in the conductor, m
(5)
(6)
Where,
Din = inner diameter of work coil, m
dw = diameter of work piece, m
Dout  Din  2dc
(7)
Volume of work piece is,
Vw = mass× density
Vw = length×cross sectional area, Acw
(13)
Surface area of work piece
(8)
Asw = 2π rw lw
Where, lc= length of conductor , m
llead = length of work coil lead, m
rin= inner radius of work coil, m
The conductor with 0.00635 m in diameter is chosen to be
used as work coil. Therefore, the coil pitch is 0.003175 m and
the coupling distance is 0.001588 m and length of conductor
is 1.3623 m.
D. Depth of penetration in conductor and work piece
C. Inductance and Resistance of Work Coil and Work Piece
Where,
tc= minimum thickness of conductor, m
 c  depth of current penetration in the conductor, m
The inductance of work coil is,
(12)
Where, Rw= resistance of work piece, Ω
rw= radius of work piece ,m
δw=depth of heated ,m
Vw = rwπ(2πδw-δw2)
The total length of conductor for work coil,
2
N 2 2πrw
θ w lw δw
Assume that the length of work piece is equal to the radius of
work piece.
Where,
Dout = outer diameter of work coil, m
dc  diameter of work piece, m
lc  2lead  N 2π  rin   (1.5  d c )2
The resistance of work piece is,
Rw 
N= number of turns of work coil
lw= length of work piece to be hardened, m
Inner diameter of work coil is
Din  d w  2Cp
(11)
Where,
Rc = resistance of work coil, ohm
Cd =coupling distance, m
Number of work coil is
N =
lc rc
ρA c 2δc
(14)
The depth of current penetration in conductor is,
δc 
ρ
, t c  2δc
πfμ 0μ r
(15)
µr= relative permeability of conductor, H/m
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
µ0=permeability of free space = 4π ×10-7, H/m
f=applied frequency, Hz
The depth of hardness in the work piece is
ρw
πfμ wμ 0
δw 
(16)
Where,
δw = death of hardness, m
µw = permeability of work piece, H/m
ρ w = resistivity of work piece, mho/m
E. Work Coil Current and Magnetic Field Intensity in the
Work Piece
Table 4. Results for Work Piece
Specification
Value
Material
1040 carbon steel
Shape
cylindrical
Nature of surface
Uniform
Diameter (m)
0.000802
Depth of Hardness (m)
0.07314
Length (m)
0.03657
Cross Sectional Area
0.0001823
Surface Area (m2)
0.008403
Volume (10-6 m2)
6.665
Resistance of work Piece (A)
0.1449
Induced Current (A)
195.3524
The different results are observed by changing number of
turns, changing work piece size and changing frequency for
the same size of work piece.
The magnetic flux density in the work piece is,
Bw=µHw
(17)
The magnetic field intensity in the work piece is,
Hw 
Ew
2π  f A cw μ w
(18)
Where,
Acw = cross sectional area of work piece, m2
The induced voltage is,
Ew = Iw Rw
(19)
Where ,
Iw = induced current in the work piece, A
The work coil current is,
Table 5. Results by Changing Number of Turns
N=5
N=4
N=3
N=2
f (kHz)
50
50
50
50
δw(mm)
0.802
0.802 0.802
0.802
Q1
5000
5000
5000
5000
Ph
5585
5529
5442
5375
dc (mm)
5.38
6.35
8.84
1.27
lc (m)
0.0404 0.038 0.3978
0.381
1
rout (m)
0.0433 0.044 0.0476
0.0525
5
Rw (Ω)
0.2264 0.144 0.0815
0.0362
9
L (µH)
2.326
1.596 0.9723
0.5078
6
H (A-turn/m 21439
17065 12698
8413
Øw(µweb)
113
90
67
44
0.25
Resistance of work Piece (ohm)
Inductance of work coil (×10-4 H)
H l
Ic  w c
N
(20)
0.2
Magnetic Field Intensity (×105 A turn/m)
Magnetic Flux Density (×10-3 web)
Where,
lc = length of work coil, m
N = number of turns
0.15
0.1
IV. DESIGN RESULTS
The design Results are mainly divided into two parts. They
are the results for work coil and work piece.
0.05
0
Table 3. Results for Work Coil
Specification
Value
Shape
Round
Number of Turns
4
Inner Diameter (m)
0.07632
Outer Diameter (m)
0.08902
Length (m)
0.0381
Coil Pitch (m)
0.03175
Coupling Distance (m)
0.01588
Resistance of Work Coil (Ω)
0.003955
Inductance of Work Coil (µH) 1.5966
Current (A)
16205523
2
3
4
Number of Turns (N)
5
Figure 3. Different results by changing numbers of turns
Table 6. Results by Changing Work Piece Size
rw = lw
1.5rw = lw
2rw = lw
N
4
4
4
f (kHz)
50
50
50
Ph (W)
5529
5479
5415
rw (m)
0.03657
0.0299
0.0259
lw (m)
0.03657
0.04485
0.0518
dc (m)
0.00635
0.00762
0.01016
lc (m)
0.0381
0.04572
0.06096
rout (m)
0.04451
0.03943
0.0386
Rw (Ω)
0.1449
0.0966
0.0724
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
L (µH)
H (A-turn/m)
Øw(µweb)
1.5966
17065
90
1.2058
20749
73
0.9806
23807
63
0.12
Length of Work Piece (m)
Diameter of Conductor (m)
Length of conductor (m)
0.1
0.08
0.06
0.04
0.02
0
0.03657
0.0299
Radius of Work Piece (m)
0.0259
Figure 4. Different results on the diameter as well as length of
conductor and length of work piece by changing size of work
piece.
Table 7. Results by changing Frequency for the Same Size of
Work Piece
f (kHz)
10
50
100
4
4
4
δw (m)
0.001793
0.000802
0.0005672
14.705
6.665
4.729
Vw(×10 m)
REFERENCES
[1]
[2]
N
-6
designs for the various types of cylindrical shape of work
piece with multi-turn helical coil. Changing number of turns
causes different power requirement on the same shape and
size of work piece. The inductance of work coil and resistance
of work piece are directly proportional to the number of turns.
The more turns, the more magnetic field intensity and
magnetic flux density. In this design, the size of work piece is
considered with three states. The length and diameter of
conductor depends on the size of work piece. In the first state,
total power requirement and magnetic flux density are highest
but magnetic field intensity is the lowest. The second state is
not suitable for multi-turn coil. Frequency changes mainly
cause the various depth of hardness and heat absorbed on the
work piece. The more frequency, the less depth of hardness,
but the more heat absorbed. In this system, the work piece is
not needed to rotate because the uniform heat causes the
surface. In conclusion, the length of work piece and the radius
of work piece should be equal to get the much flux density in
the work piece, and to achieve the much inductance in the
work coil.
[3]
[4]
Q1
11031
5000
3547
Ph
11560
5529
4077
Rw (Ω)
0.0647
0.1449
0.2049
H (A-turn/m
82495
17056
8713
Øw(µweb)
435
90
46
[5]
Plonsey, Principles and Application of Electromagnetic
Field, Springer, Berlin, (1971).
Davise, A. 1995.Surface Hardening by Means of
Electrical Induction. March 2005
http://www.cihinuction.com
Curits, F.W.1944. High Frequency Induction Heating. 1st
ed. New York: McGraw-Hill Book Company, Inc.
Zinn, S., and Semiatin, S.L.1988.Coil Design and
Fabrication: Basic Design and Modifications. July 2005
http://www.amerithem.com/technotes.html
Pender, H., and Del Mar, W.A. No Date. Electrical
Engineering Handbook 4th ed. Wiley Engineering
Handbook Series.
18
Depth of hardness in work piece (×10-4m)
16
Volume of Work Piece (×10-6)
Heat Absorbed on Work Piece (kJ)
14
Electric Power due to Heat Energy (kW)
12
10
8
6
4
2
0
10
50
Applied Frequency (kHz)
100
Figure 5. Various results due to the changing frequency.
V. CONCLUSION
This design is very useful in surface hardening machine
because the size of work piece can be changed. This paper
5
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