Magnetic Materials Seminar
Presented by: International Magnaproducts, Inc.
Agenda
I. Brief Intro to IMI
II. History of Permanent
VI. Testing Methods
VII. Magnetizing Methods
Magnet Materials
VIII. Conclusion
III. Overview of Magnetic
IX. Questions
Terms
IV. Basic Physics and
Fundamentals
V. Material Characteristics
International Magnaproducts, Inc.
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Warehouse Facilities
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30,000 sq. ft.
15
Primary Materials
10
5
0
2000
Bonded Magnets
Ceramics
Alnico
Sintered NdFeB (licensed)
SmCo
Ferrite Compounds
Magnetizers, Demagnetizers,
Test Equipment
1999
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1998
•
20
1997
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Valparaiso, IN
Broomfield, CO
25
1996
•
Created by Don Coleman
in 1982
Locations
1995
•
Value-Added Services
•
•
•
•
•
•
Quality Control and Testing
Warehousing
Magnetizing and Demagnetizing
Powder Processing
Technical Support
Engineering/Design Support
IMI, Cont’d
• Primary
Customers
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Eastman Kodak –Delphi Automotive
–Honeywell Microswitch
Seagate
–Hi-Stat
Ametek
Fisher & Paykel –BEI Kimco
–General Electric
MPC
General Motors –Lear Corporation
–Breed Automotive
Hamlin
Woodward Inc –Cherry Electrical
Strattec (Briggs&Stratton)
History of Permanent Magnets
Magnet Timeline (Year vs. MGOe)
NdFeB
SmCo 2-17
2000
1990
1980
1970
SmCo 1-5
1960
1950
1940
1930
1920
1910
Ferrites
Alnico
MK Steel
1900
60
50
40
MGOe 30
20
10
0
Basic Physics and Fundamentals
Magnetic Version of Kirchof’s Voltage Law
•
Sum of all MMF (Hl) drops around a closed circuit is equal to the current enclosed (Ni)
(also known as Ampere’s Law)
•
Static gap problem: HmLm + HFeIFe + HgIg = 0
•
Since HFe = OmHmLm = HgIg
Magnetic Version of Ketchoff’s Current Law
•
Flux (Uo=BA) entering any cross section of spave is equal to the flux leaving it.
•
Static gap problem: BmAm = BgAg (=BFeAFe)
Hysteresis Graphs
Two Basic Types Useful to Designers:
Normal demag curve -
Used by the designer to calculate the flux density
in the air gap or the flux in aparticular portion of
the magnetic circuit.
Intrinsic demag curve -
Used by the designer to evaluate the effect of
any demagnetization influence on the magnet in
its magnetic circuit.
Properties that can be found from these curves:
Residual flux density
Intrinsic coercive force
Normal coercive force
Normal energy product
Calculations of Load Lines
Def: This is the relationship between B in the magnet and H in the magnet, as dictated by
the magnetic circuit.
Since M in the air gap is zero, Bg = µ0 Hg
Subsituting BmAm = µ HgAh
Solving and subsituting: BmAm = -µ HmLmAgNg
Dividing by –0AmHm: BmIµ0Hm = -lmAgIAmLg
How to Read a Hysteresis Loop of a Permanent Magnet
Basic Magnetic Quantities
B (Magnetic Induction):
Defined by the force moving on a charge
F = qov x B (general)
Magnetic Dipoles:
Origin - Current loop m=iA
Atom m=gJµB
Potential Energy - U = -m•B
Torque: τ = m X B
The magnetic moment is defined as j = µ0m, in which
case J and H appear in the energy and torque equations.
Magnetic Quantities, Cont’d
M (magnetization):
Def - Dipole moment per unit volume
J = Bi = µ0m(Magnetic polarization)
H (magnetic field strength):
Br (Remanence):
H=1/ µB(B-M)
Def - The induction remaining after a saturation magnetizing
field is reduced to zero (internal)
Since H = 0, Br = Bir
iHc (Intrinsic Coercivity):
Def - the negative field required to reduce Bi to zero,
after the application of a saturating magnetizing
field.
Differentiates permanent magnets from other magnets.
Magnetic Quantities, Cont’d
Hc (Coercivity):
Def - The negative magnetic field required to reduce b to zero,
after application of saturating magnetizing field.
(BH)Max:
Def – Maximum product of (BdHd) which can be obtained on the
demagnetization curve. Incdicates the energy that a magnetic material can supply to an
external magnetic circuit when operation at any point on it’s demagnetization curve.
Rev. Temp. Coeff: A number which describes the change in a magnetic property
with a change in temperature. It is usually expressed as the percentage change per unit of
temperature. Both Br & Hc affected.
Curie Temp.: The transition temperature above which a material loses it’s permant
magnet properties. Due to metallurgical change in material.
Magnetic Quantities, Cont’d
Irreversible Temp. Loss:
Irreversible changes in the magnetic state can be
caused by spontaneous reversals of magnetization in individual Weiss domains brought about
by thermally induced fluctuations in the internal magnetic field.
Reversible Changes:
Temperature fluctuations also result in reversible changes in
the magnetic flux density in the permanent magnet.
Magnetic Quantities, Cont’d
MMPA Def:
A permanent magnet is a body that is capable of maintaining a magnetic
field at other than cryogenic temperature with no expenditure of power.
What does this mean?
Even in the case of low coercivity of Alnico magnets, the
flux density loss over many, many years amounts to only a few percent.
Irreversible and reversible losses of magnetic properties
Types of Magnetic Materials
Not Ordered
• Diamagnetic
• Atoms have no permanent magnetic moment, only induce moment(Farady’s Law)
• Small negative magnetization at normal H (10kOe)
• Paramagnetic
• Atoms have no permanent magnetic moment, no interatomic interaction
• Small positive magnetization at nomal H (10kOe)
Magnetic Materials, cont.
Magnetically Ordered
• Antiferromagnetic
• Atoms have permanent moment, strong interatomic interaction
• Two equal and opposite sublattices, spontaneous magnetization is zero
• Small positive magnetization at normal H (10kOe)
• Ferromagnetic
• Atoms have permanent moment, strong interatomic interaction
• All atomic moments are coupled parallel, large spontaneous magnetization
• Very large positive magnetization at normal H (10kOe)
• Ferrimagnetic
• Atoms have permanent moment, strong interatomic interaction
• Two unequal and opposite sublattices, large spontaneous magnetization
• Large positive magnetization at normal H (10kOe)
Diagrams of Magnetic Materials
Antiferromagnetic
Ferromagnetic
Ferrimagnetic
Domain Wall Movement
•The spontaneous alignment of atomic magnetic moments in ferromagnetic
materials is generally limited to certain regions known as Weiss domains
•The transition zones between these regions in which the atomic magnetic moments
rotate from one preferred direction into another, are known as Bloch Walls.
•Initial magnetization  Rotational process  Saturation
•Saturation is reached when all magnetic moments are arranged parallel to the
external magnetic field. B then increases only proportionally to field strength H.
Domain Wall Movement
Initial State
Weak magnetic
field applied
Increasing field
makes one domain
Material has
reached saturation
Testing Permanent Magnets
Testing, cont.
Typical Methods:
•Fluxmeter: used for measuring magnetic flux. As the flux changes, a voltage is
induced; the resultant current causes the coil of the fluxmeter to be deflected.
•Gaussmeters: 4 types are rotating magnet, Hall effect, rotating coil, and nuclear
magnetic resonance. Measures surface Gauss of permanent magnets
•MagScan: Real-time magnetic field scan analyzing. Flatbed or rotary scanning
machines can be utilized.
Standard Test Methods
•Open Circuit test:
• any method that is used to test a magnet in free space after it has been
magnetized.
•Generated voltage test:
• Useful to test production magnets and associated magnetic circuits intended
for us in DC motors and generators.
•Pull test:
•Mechanical text that involves measuring the mechanical force required to pull
the pole face of a permanent magnet from a piece of steel or from another
magnet when opposite poles are in line.
•Torque test:
•Rotational mechanical force required to overcome the force resulting from
the magnetic attraction between magnetic poles of two magnets through a
specified air gap is measured.
Permanent Magnet Materials
• Most Commonly Used Materials
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AlNiCo
Ferrites
Samarium Cobalt
Neodymium-Iron-Cobalt
Bonded Materials
• Ferrite
• Neo
• SmCo
de
AlNiCo Magnets
(BH)Max
Br
Hc
Hci
1.7 MGOe
5.5 MGOe
5.3MGOe
5.0 MGOe
1.5 MGOe
3.9 MGOe
4.0 MGOe
4.5 MGOe
7.5kG
12.8kG
8.2kG
7.2kG
7.1kG
10.9kG
7.4kG
6.7kG
560 Oe
640 Oe
1650 Oe
1900 Oe
550 Oe
620 Oe
1500 Oe
1800 Oe
580 Oe
640 Oe
1860 Oe
2170 Oe
570 Oe
630 Oe
1690 Oe
2020 Oe
Density
7.1
7.3
7.3
7.3
6.8
6.9
7.0
7.0
g/cm
g/cm3
g/cm3
g/cm3
g/cm3
g/cm3
g/cm3
g/cm3
3
Tc
810C
860C
860C
860C
810C
860C
860C
860C
Tmax
450C
525C
550C
550C
450C
525C
550C
550C
Attributes: High flux, high Curie temp., very temperature stable (-.02%/ºC)
Detriments: Difficult to mount, low Hc
Cast and Sintered AlNiCo Processes
Casting
Sintering
Melting (1400 - 1500C)
Die Pressing (Approx. 5kbar)
Casting
Sintering (1250 - 1400C)
Homogenizing (1200 - 1300C)
Isotropic Magnets
Cooling from 1300 to 600C (1-20 min)
Tempering 550-700C (1-20h)
Anisotropic Magnets
Cooling in magnetic field
Isothermal magnetic field treatment (TTc)
Tempering 550-700C (1-20h)
Grinding, Magnetizing, Testing
Ferrite Materials
Grade
(BH)Max
Br
Hc
Hci
Density
1
5
7
8
1.05 MGOe
3.40 MGOe
2.75MGOe
3.50 MGOe
2.3kG
3.8kG
3.4kG
3.8kG
1860 Oe
2400 Oe
3250 Oe
2950 Oe
3250 Oe
2500 Oe
4000 Oe
3050 Oe
4.9 g/cm3
4.9 g/cm3
4.9 g/cm3
4.9 g/cm3
Attributes:
Tc
450C
450C
450C
450C
800C
800C
800C
800C
Low costs, moderately high Hc & Hci, very high electrical resistance, “most flux for
bucks.
Detriments:
Tmax
Moderately low Curie temp., poor temperature stability (-.2%/C)
Ferrite Production Process
SmCo Grades
Grade
(BH)Max
Br
Hc
Hci
Density
SmCo 1-5
18 MGOe
20 MGOe
26 MGOe
28 MGOe
30 MGOe
8.7kG
9.0kG
10.6kG
11.0kG
11.3kG
8600 Oe
8900 Oe
7000 Oe
7000 Oe
10,000 Oe
9000 Oe
8500 Oe
5000 Oe
5000 Oe
7000 Oe
8.5 g/cm
8.5 g/cm3
8.5 g/cm3
8.5 g/cm3
8.5 g/cm3
SmCo 2-17
Attributes:
3
Tc
750C
750C
825C
825C
825C
250C
250C
300C
300C
300C
High magnetic characteristics, high Curie temp, very temperature stable, high
energy for low volume, can be machined easily to very small sizes.
Detriments:
Tmax
High costs, very brittle
SmCo Production
Alloy Production
Milling < 5µm
Magnetic Orientation
Pressing
Sintering 1200°C
Heat Treatment
900 - 400 °C
Machining and
Magnetizing
Nd-Fe-B Materials
Grade
(BH)Max
Br
Hc
Hci
Density
Tc
Tmax
30
35
38
45
28-32 MGOe
33-36 MGOe
36-39MGOe
43-47 MGOe
12.0kG
12.5kG
12.9kG
13.9kG
11,000 Oe
11,800 Oe
12,300Oe
13,500 Oe
12,000 Oe
12,000 Oe
12,000 Oe
11,000 Oe
7.4 g/cm3
7.4 g/cm3
7.4 g/cm3
7.4 g/cm3
310C
310C
310C
310C
150C
150C
150C
150C
Attributes:
Detriments:
High energy for size, more economical than SmCo, no cobalt, very high Hc and Hci.
Poor temperature coefficient (-.13%/C), material will oxidize if not coated, low
Curie temperature.
Sintered Neodymium-Iron-Boron
Alloy Production
Milling < 5µm
Magnetic Orientation
Pressing
Sintering 10301100°C
Heat Treatment
900 - 600 °C
Machining and
Magnetizing
Other magnetic materials on the market
MA: (BH)Max = 1.3 – 5.5 MGOe, Br = 2700-5500G, Hc = 1800-2500 Oe
Curie Temp = 300 C, Max. Work Temp = 500 C
Attributes: Easily machineable, extremely durable, various mag. patterns
Detriments: Very high cost.
SmFeN: (BH)Max = 12.9 MGOe, Br = 11.5 kG, Hc = 600-700 Oe
Max Work Temp. = 100 C
Attributes: Highest mag. Properties of bonded magnets
Detriments: Low maximum working temp. = 100 C
Formag: (BH)Max = 4.5-6.0 MGOe, Br=11.5 – 12.5 kG, Hc = 600-700 Oe
Curie temp = 640 C, Max Work Temp = 460 C
Attributes: Excellent temp. and mechanical strength, no voids or piping
Detriments: Rods or pins are main configuration
Compression Molding
Advantages:
Good shaping/tolerances
Low Tooling
Highest (BH)Max
Disadvantages:
Some tolerance restrictions in one
dimension.
Not fully 3-D capable
Characteristics: (BH)Max = 12, 13 MGOe
Br = 7.6, 7.g kG
Hc = 5.9, 6 kOe
Hci = 10.8, 12 kOe
Calendering Process
Advantages:
No tooling
Continuous sheet available
Low cost process
Disadvantages:
Almost exclusively ferrite
Temp limitations
Max. thickness of sheets
Characteristics: (BH)Max = up to 1.6 MGOe
Br = 2610 g
Hc = 2150 Oe
Hci = 2650 Oe
Extrusion Molding
Advantages:
Excellent for long/continuous product
Relatively low tooling cost
Mechanical or magnetic alignment
Disadvantages:
Temperature capability
“Profile” or sheet only
Max. thickness of sheets
Characteristics: (BH)Max = 10.0 MGOe
Br = 7.0 kG
Hc = 5.7 kOe
Hci = 10.8 kOe
Max/Min Width = up to 4” wide
Max/Min Thick = up to .250”
Injection Molding
Advantages:
Excellent shaping/tolerances
Utilize all powders
Over/Insert - molding
Disadvantages:
High tooling cost
Restricted performance
Approx. 35% binder
Characteristics: (BH)Max = 2.2 MGOe
Br = 3000 G
Hc = 2250 Oe
Hci = 3300 Oe
Max/Min O.D. = up to 6.00”
Rare Earth Characteristics(Inj. Molding)
Property
SmCo 2-17
Nd-Fe-B
Br
6.8 kG
6.6 kG
Hc
6.2 kOe
5.1 kOe
Hci
12.0 kOe
10.0 kOe
(BH)Max
10.5 MGOe
8.5 MGOe
Multi-Component Injection Molding
Multi component injection molding (MCIM) or Co-injection is a manufacturing method by which
several non-similar polymers can be bonded together inside of an injection molding machine
thereby eliminating the need for mechanical assembly.
Advantages
Disadvantages
MCIM, cont’d.
MCIM, cont’d.
Q & A Session
Various Coatings for Magnets
• Reasons to coat:
– Neo easily corrodes
– Keep magnetic
material
in/envorinment out
– Keep unwanted
component interaction
to a minimum
– In some cases
coatings add physical
“strength” to a
magnet.
• Typical Coating
Categories:
– Organic (E-coat, Parylene)
– Metallic deposits (Ni, Al,
Sn)
• Potting compounds/resins
– Plastic moldings
Coatings, cont’d
• Important traits to
know:
–
–
–
–
–
–
–
–
Film thickness
hardness
color
durability
solvent resistance
cleanliness
cost
glueability
• Application methods:
– encapsulating, spray, dip,
dip and spin, electrocoat,
electroplate, electroless
plate, vacuum deposition
– Testing methods: visual,
adhesion testing, solvent
resistance,
environmental exposure
testing, thickness testing
Coatings, cont’d
• E-Coating:
– Typical thickness
(15-25 microns)
– Durability (Pencil
2H-4H)
– Salt spray (96
hours)
• Nickel Plating:
– Typical thickness (1050 microns)
– Durability (????)
– Salt spray (480 hours)
Coatings, cont’d
Conclusion & Additional Questions
Conversions
Quantity
Symbol
Magnetic Flux
CGS Unit
Conversion
factor
SI Unit
MAXWELL
10-3
WEBER
Magnetic Induction
B
GAUSS
10-4
TESLA
Magnetomotive
force
F
GILBERT
(OERSTED-CM)
103/4µ
AMPERE-TURN
OERSTED
103/4µ
1A/m = 12.57*10-3
AMPERE-METER
MEGAGAUS SOERSTED
103/4µ
1 A/m = 0.1257*103
GOe
JOULE/METER3
Magnetic Field
Strength
Energy Product
H
BdHd
More Conversions