Magnetic flux controllers are widely used in induction heating systems for concentration, shielding or redistribution of the magnetic field which generates power in the part to be heat-ed. Controllers help to obtain accurate heat pattern control, improve parameters of inductors and performance of the entire installation. In melting systems, especially in the case of vacu-um, cold crucible and other specialty furnaces, the magnetic control can provide large energy savings, magnetic field shielding, shorter melting cycles and optimized field distribution for enhancement of the metallurgical processes. Magnetic flux control, i.e. modification of the magnetic field distribution and intensity, may be accomplished by variation of shape and po-sitioning of the induction coil turns, by insertion of non-magnetic shields (Faraday rings) or the magnetic templates that may be called magnetic controllers. Each method of magnetic control has its own advantages, drawbacks and limitations. Induc-tion coil designers pay main attention to optimization of active conductors (turns), their size, number and position. They try to avoid using additional components for the magnetic flux control in order to simplify design and reduce costs. This approach is understandable but it is correct only partially. Today’s competitive market with new materials and technologies, more strict demands to the product quality, safety and ergonomic requirements forces us to review the existing design guidelines and traditions. The main tool for that is computer simulation which can predict not only the process parameters but also life time of tooling (inductors) and service properties of the final products. In some cases it is difficult or even impossible to meet specifications of heating without application of magnetic controllers. Effects of using magnet-ic controllers, design guidelines and results prediction with the help of computer simulation are described in this presentation. Several case stories are based on more than 20 years of R&D and practical experience of sci-entists and practitioners at Fluxtrol, Inc. Presented material may be interesting not only for the induction heating community but also for all people using AC magnetic fields in techno-logical processes.

1. Magnetic Flux Control
for Induction Heating
Installations
Dr. Valentin Nemkov
Director of Research
Fluxtrol, Inc., USA
Webinar
May 20, 2015

2. Dr. Valentin Nemkov May 20, 2015
Outline
o What is magnetic flux control?
o Magnetic controllers
o Materials for magnetic flux control
o Temperature management
o Protection
o Selected applications
• Heat treating and brazing
• Melting installations
• Shielding
• Conclusions
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3. Dr. Valentin Nemkov May 20, 2015
Magnetic Flux Control
Magnetic flux control is modification of magnetic flux
value and distribution in the induction system by proper
arrangement of “active” components of the coil.
A common practice is to create a coil by optimization of
the coil turns’ size and position.
Some non-magnetic conductive components (usually
copper ring, called Faraday rings) are used for shielding
purposes. Their use always reduces the induction coil
power factor and efficiency. They are often called “robber
rings”.
Quite opposite, magnetic components can improve the
coil efficiency and power factor. We’ll consider here
magnetic components.
Depending on application, they are called “concentrators”,
“cores”, “shunts”, “diverters”, “impeders”, etc.
Generally, let us call them “magnetic controllers”.
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Photo courtesy of Induction Tooling, USA

4. Dr. Valentin Nemkov May 20, 2015 4
Often time the coil designers are not well familiar with
magnetic controllers and try to avoid using them as
unreliable cost-adding components.
Optimal magnetic flux control can give users the following
technical benefits:
• Achieve optimal power and temperature distribution in
the part
• Heat required areas faster thus increasing production rate
• Improve parameters of inductors and the whole
installation performance
• Shield specific areas from unwanted heating or field
exposure
• Save energy in traditional and innovative applications
• Control residual stresses and reduce distortions.
Benefits of Magnetic Flux Control

5. Dr. Valentin Nemkov May 20, 2015
Concentrator provides several effects:
• Higher power in the part for the same
coil current
• Power concentration under the coil
face resulting in better utilization of
the induced power
• Elimination of external fields.
But… concentrator pushes the coil current
to one side of the coil tubing resulting in
higher coil losses
Computer analysis can predict all the
results. But before using computer analysis
it is useful to make preliminary evaluation
based on magnetic circuit idea. Power distribution on the part surface
Effects of Magnetic Flux Concentrator
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6. Dr. Valentin Nemkov May 20, 2015
Magnetic Circuit
Any induction heating device has at least three
closed loops.
• The first loop is a coil winding that carries
current Ic generating magnetic field
• The second loop (or set of loops) is the loop(s)
of induced eddy currents Iw
• The third loop is formed by closed magnetic
lines that show magnetic field distribution in
space. Field is characterized by a vector of flux
density B and a value of magnetic flux Φ.
Some induction devices have “materialized”
closed magnetic loop such as transformer type
induction heaters (right bottom) or channel
melting furnaces. In majority of induction systems
the magnetic flux flows along the “return path” in
the air.
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7. Dr. Valentin Nemkov May 20, 2015
Magnetic Flux Circuit: Example of internal (ID) coil
IN = Φ (Zm + Rm)
Φ – magnetic flux
IN – ampere turns of the coil
Rm – magnetic resistance (reluctance) of return path,
in this case of a space inside the coil
Zm – magnetic impedance of the “active zone”;
Zm = RmsZmw/(Rms + Zmw)
Rms – magnetic resistance of a gap
Zmw - magnetic impedance of the work piece
Rm = L/(μrμ0S), with L and S – length and area of
return path, μr- permeability of material
Magnetic controllers reduce Rm permeability times;
ideally Rm => 0.
It minimizes ampere-turns to IN = Φ Zm
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Here the return path is in a narrow space inside the coil: installation of the
magnetic core is very beneficial.

8. Dr. Valentin Nemkov May 20, 2015
Materials for Magnetic Flux Control
There are three groups of materials: steel or alloy laminations, ferrites and
Soft Magnetic Composites (SMC) also known as MagnetoDielectrics (MDM)
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9. Dr. Valentin Nemkov May 20, 2015
Electrical steel (Laminations):
• Best magnetic properties (high Bs, low losses)
at low and middle frequencies
• High temperature resistance
• Unlimited dimensions (sheets and strips)
• Lower price for stock material
• Limited frequency range (up to 20 kHz)
• Limited machinability (stamping or laser
cutting)
• Very bad performance in 3D fields
• Laborious assembling especially at higher
frequencies
Laminations are the main material for magnetic
flux control in induction applications at low
frequencies (50 Hz - 10 kHz)
Materials for Magnetic Flux Control
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10. Dr. Valentin Nemkov May 20, 2015
Ferrites:
• Very high permeability in weak fields
• Can work at high frequencies
• Low losses in selected grades
• Chemically inert
• Low price in mass production (electronics, etc.)
• Low saturation flux density (0.3-0.45 T)
• Low Curie temperature (~ 250 C) with magnetic
properties reduction starting at 150 C
• Poor thermal conductivity
• Very poor mechanical properties
– Very hard
– Brittle
– Non machinable with conventional tools
• Sensitive to mechanical and thermal shocks
• Inconsistent in dimensions (large tolerances)
Variety of ferrites is being used in induction
technology in standard shapes for HF transformers,
chokes, HF welding impeders, etc.
Materials for Magnetic Flux Control
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11. Dr. Valentin Nemkov May 20, 2015
Materials for Magnetic Flux Control
Soft Magnetic Composites:
• Very wide frequency range (50 Hz – 13.56 MHz)
• Good magnetic and thermal properties
• High saturation flux density (up to 1.7T)
• Excellent machinability and versatility
• Good performance in 3D fields
• Limited dimensions (compared to steels); max size
of Fluxtrol material plate 222 x 165 mm
• Higher stock price than laminations
Combination of laminations in large regular areas and
SMC in 3D and complex geometry areas is very
promising for induction installations of low and
middle frequencies
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12. Dr. Valentin Nemkov May 20, 2015
SMC Ferrotron 559H
Ferrotron 559H is the main HF SMC
• Proved frequency range – up to 13.56 MHz
• Max permeability 19
• Good electric strength
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13. Dr. Valentin Nemkov May 20, 2015
SMC Fluxtrol 100
Fluxtrol 100 is the main SMC for low and middle
frequencies (up to 50 kHz)
• Max permeability 130
• High thermal conductivity, 150% of stainless steel
• Good mechanical strength and machinability
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14. Dr. Valentin Nemkov May 20, 2015
Concentrator Permeability Influence
A – side areas, B – work area
Gap 4 mm; Coil face width 19 mm
Frequencies 3 and 10 kHz
Workpiece:
• Flat body composed of a central part B
and two side areas
• Materials – magnetic or non-magnetic
steel
Conditions:
• Linear single-turn inductor
• Same temperature under the coil face
• Same heating time
Considered parameters:
1. Current demand
2. Power demand
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15. Dr. Valentin Nemkov May 20, 2015
Concentrator Permeability Influence
Simulation and practical tests proved that the concentrator permeability of 20 – 60
(depending on many factors) is sufficient for induction systems with open magnetic circuits.
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16. Dr. Valentin Nemkov May 20, 2015
Experiments confirmed the identity of a heat pattern created by “vertical
loop” inductor with concentrators made of laminations (left) and SMC (right)
Experimental Confirmation of Heating Intensity
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SMC

17. Dr. Valentin Nemkov May 20, 2015
Temperature map of scanning
system. Temperature scales are
different for a coil and a work piece
Management of Magnetic Controller Temperature
Temperature depends on many factors:
• Coil design
• Controller material
• Application technique
• Heating regime (frequency, power, duty
cycle, etc.)
• Environment
Methods to manage temperature:
• Favorable coil design
• Magnetic material selection
• Gluing technology (thin thermally
conductive epoxy, etc.)
• Additional cooling plates
• Internal cooling of the controller
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Controllers are heated by magnetic losses and by heat transfer from the hot part.

18. Dr. Valentin Nemkov May 20, 2015
Program Flux 3D allows us to input formulae for losses Pv vs. B and f directly
into the program. If field has two components B1 and B2, it is possible to take
into account material anisotropy using a vector of magnetic loss power density
Pv = (c1B1
a + c2B2
a) fb
Max T = 127 C
Temperature distribution
in the coil with concentrator
Prediction of Magnetic Controller Temperature
Magnetic field lines and
flux density color map
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19. Dr. Valentin Nemkov May 20, 2015
Protection of Magnetic Controllers
Microsample of SMC with
zirconia coating
Sample of SMC with alumina
coating
Ceramic coating (Al2O3, ZrO2, etc.) effectively
protects the coil face from mechanical and
thermal damage and from electric discharge in
case of occasional touch of the hot parts.
Ceramic coating
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20. Dr. Valentin Nemkov May 20, 2015
Protection of Magnetic Controllers
SMC Controllers with thin Teflon coating for
service in special environments
Different plastic coatings allow the magnetic flux controllers work in aggressive
atmospheres, clean rooms, biomedical and food packaging applications
Plastic coating
Sample with Nylon coating applied
by fluidized bed technology
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21. Dr. Valentin Nemkov May 20, 2015
ImpregnationImpregnation is a saturation of surface layer of
metallic and composite materials by special
epoxy resins. It results in the following:
• Clean surface with sealed pores
• Better mechanical strength
• Reduced corrosion
• Prevention of water and aggressive fluids
penetration inside the material
SMC controllers may be used as structural elements, for quenchant supply, etc.
They may be attached to the chamber walls, shield frame, etc., using stainless steel inserts.
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Mechanical Attachment

22. Dr. Valentin Nemkov May 20, 2015
Magnetic Flux Control in Induction Heat Treating
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23. Dr. Valentin Nemkov May 20, 2015
Effect of Concentrator on Hair-pin Coil Performance
Computer simulation (Elta program) and
process demonstration with a coil driven by
robot along the water cooled plate
Performance of hair-pin coils can be
greatly improved by magnetic
concentrator.
• Concentrators improve coil
efficiency and power factor
• Local installation of the
concentrator redistributes power
along the coil length
• Effectively control the
temperature pattern.
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24. Dr. Valentin Nemkov May 20, 2015
Crankshaft Hardening
Crankshafts were the first parts being hardened by induction in early 1930s.
Big improvements in this technology have been made recently.
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25. Dr. Valentin Nemkov May 20, 2015
Rotational Hardening of Crankshafts
Optimized induction coil; SMC are made in sections in
order to tolerate the coil turn movement due to
heating and strong electromagnetic forces
Hardness pattern
Magnetic controllers help to obtain required hardness depth and pattern
and improve coil efficiency
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26. Dr. Valentin Nemkov May 20, 2015
Bare clamshell coil causes significant
unintended heating of the crankshaft web.
C-shaped controller or even thin (1.5 mm !)
side magnetic shields save energy, eliminate
unintended heating, improve heat pattern
control and reduce the part distortion.
Shielding in Induction Hardening Processes
In induction heating systems magnetic
shields can provide the following effects:
• Improve the process efficiency
• Protect certain areas of the part from
unintended heating
• Prevent the installation components
(frame, machine parts) from heating
• Eliminate influence of the coil’s
magnetic field on sensors and control
system elements
SM composites are excellent materials for
shielding in induction heating systems
due to their versatility.
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27. Dr. Valentin Nemkov May 20, 2015
Non-rotational Crankshaft Hardening Coil
Side shields play three roles: crankshaft web shielding, accurate control of heat
pattern and coil efficiency improvement
SharP-C inductor, courtesy of INDUCTOHEAT Inc.
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Fluxtrol
SMC shields

28. Dr. Valentin Nemkov May 20, 2015
Power Distribution Control
Magnetic controllers, locally
placed on a coil for single-
shot hardening of shaft,
provide effective heat
pattern control.
This horse-shoe coil was designed for brazing
an output pipe to aluminum heat exchanger. In
addition to big improvement in coil efficiency,
the magnetic controller precisely distributes
power between three components of the joint
guaranteeing high quality of brazing.
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29. Dr. Valentin Nemkov May 20, 2015
Goals of magnetic flux control:
• Improvement of furnace parameters
(efficiency, power factor)
• Optimal distribution of power and ED forces
in the melt
• Induction coil shielding:
- reduction of losses in the furnace
structure or chamber
- field reduction on work places (Maximum
Permissible Exposure levels compliance)
Magnetic Control in Coreless Melting Furnaces
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30. Dr. Valentin Nemkov May 20, 2015
Magnetic Flux Control in Cold Crucible Furnaces
Faraday Ring
Cold Crucible
Mock-up
at Fluxtrol, Inc.
Dimensions of mock-up:
Crucible ID 60 mm, OD 82.5 mm,
length 67 mm, number of fingers 8
Coil ID 84 mm, length 54 mm
Load – Stainless steel 304, Dia. 52 mm,
length 57 mm, Frequency 10 kHz
Cold Crucible Furnaces (CCF) for
melting metals have very low electrical
efficiency (25-50%) because the
crucible “fingers” obstruct magnetic
field penetration to the melt surface.
Intensive experimental and theoretical
study at Fluxtrol, Inc. showed that
magnetic controllers can strongly
improve the furnace parameters and
power distribution along the melt.
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31. Dr. Valentin Nemkov May 20, 2015
Magnetic Circuit of CCF
Magnetic flux lines for optimized
system (2D simulation)
Scheme of magnetic circuit :
1 – melt; 2 – fingers (axial component); 3 – gap;
4 – external return path; 5 – top and bottom
rings; 6 – top and bottom inserts
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32. Dr. Valentin Nemkov May 20, 2015
3D Study of CCF: Model and Current Distribution
“Fingers”
Faraday Ring
Coil Turns
3D Model
A – No magnetic controllers
B – All set of magnetic
components (top and
bottom rings, shunts and
inserts)
For the same power in the melt, magnetic
controllers reduced the coil current
demand almost 1.8 times and total furnace
power – 2.5 times. Experiments confirmed
these findings.
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33. Dr. Valentin Nemkov May 20, 2015
Magnetic Field Distribution along the Load
Current in the coil is held constant (200 A)
There is good agreement between the experimental and 3D simulated results
Flux density is doubled when all forms of flux controllers were used.
Effectiveness of magnetic control strongly depends upon the CCF type and design!
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34. Dr. Valentin Nemkov May 20, 2015
CC Melter with Bottom Pouring of Ti Alloys
Ames Lab, Iowa State University
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Ti-6Al-4V powder
New induction coil with magnetic
circuit:
• Increased efficiency from 31 to 47%
• Increased volume of material poured
from the crucible
• Improved matching of the furnace
and reduced losses in supplying
circuitry.

35. Dr. Valentin Nemkov May 20, 2015
Shielding in Special Melting Installations
In melting furnaces working in a vacuum or protective atmosphere, magnetic
shielding not only improves the furnace efficiency and reduces the coil current, but
also eliminates losses in the chamber. It allows a designer to reduce the chamber
dimensions or increase the melting unit size for the same chamber.
Ceramic-lined induction coil with
side and bottom SMC shields for
melting radioactive materials in
glove box
Magnetic flux line and power density map in a
melting system without and with magnetic shields.
With the same total coil power, power in the melt
increased 2.7 times
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36. Dr. Valentin Nemkov May 20, 2015
Melting Coil Shielding for Special Furnaces
If possible, the best solution is installation of magnetic shunts directly onto the
coil turns using epoxy gluing, mechanical attachment or both.
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37. Dr. Valentin Nemkov May 20, 2015
Bare Inductor, efficiency 85% Two Faraday Rings, efficiency 72%
Shielding in Open Induction Installations
Open induction installations may create strong magnetic fields in surrounding
environment. The main goal of shielding is to limit magnetic field on work places
below Maximum Permissible Exposure level.
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38. Dr. Valentin Nemkov May 20, 2015
2
1
3
In open furnaces, magnetic shielding protects the frame components from unintended
heating and strongly reduces the magnetic field on workplaces without impairing the
coil efficiency .
Magnetic flux line and power density
distribution in induction system without
shielding and with a shield made of magnetic
shunts and two Faraday rings.
Electromagnetic shield design:
1- Coil turns; 2- Faraday ring;
3 - Magnetic shunts
Electrical efficiency 84%
Shielding in Open Melting Installations
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39. Dr. Valentin Nemkov May 20, 2015
Hm,
A/m
External Magnetic Field Strength
Maximum Permissible Exposure level for 3 kHz (A in amplitude):
International Standard (ICNIRP 2010) - 113 A/m; USA (IEEE C95.1) - 163 A/m
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40. Dr. Valentin Nemkov May 20, 2015 40

41. Dr. Valentin Nemkov May 20, 2015
Magnetic field lines in end area Losses in winding sections with and without poles for
the same load power
Simulation of Crucible Furnace
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42. Dr. Valentin Nemkov May 20, 2015
Case
Load
power
kW
Frequency
Hz
Furnace
A
Coil
Losses
kW
Faraday
Rings
kW
Furnace
Power
kW
Efficiency,
%
Furnace
kVAR’s
With MP 4110 286 24040 850 6 5000 82.2 47800
W/O MP 4110 291 25320 1155 36 5366 76.6 50350
Difference 0 - -1280 -305 -30 -366 +5.6 -2,550
Induction Furnace Parameters Change
Economical effect evaluation:
- Annual energy savings due to magnetic poles (3000 hrs/year) is 1,120 MWhr
- Annual savings on energy (price 0.1 $/kWhr) is app. $112,000
- Reduction in cooling water demand (TBD)
- Possible savings in capital investments:
- $5,000 due to reduced capacitors battery (reactive power saving 2.55 MVAr)
- $36,600 due to smaller inverters (rated power may be reduced by 366 kW)
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43. Dr. Valentin Nemkov May 20, 2015
Conclusions
• Magnetic flux control in systems for induction heating,
melting and EM processing of materials is used for a very
long time but is still underevaluated(to my opinion)
• New materials and computer simulation allow us to
optimize magnetic circuits and meet strict demands of
industry
• Both Laminations and Soft Magnetic Composites may be
used at lower frequencies (up to 20 kHz)
• For higher frequencies SMC may be effectively used with
some competition from ferrites
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44. Dr. Valentin Nemkov May 20, 2015
Optimized coil for
axle scan hardening
THANK
YOU!
For more information contact the author vsnemkov@fluxtrol.com
and visit website www.fluxtrol.com
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