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Agenda
I. Brief Intro to IMI
II. History of Permanent
Magnet Materials
III. Overview of Magnetic
Terms
IV. Basic Physics and
Fundamentals
V. Material Characteristics
VI. Testing Methods
VII. Magnetizing Methods
VIII. Conclusion
IX. Questions
International Magnaproducts, Inc.• Created by Don Coleman
in 1982
• Locations– Valparaiso, IN
– Broomfield, CO
• Warehouse Facilities– 30,000 sq. ft.
• Primary Materials– Bonded Magnets
– Ceramics
– Alnico
– Sintered NdFeB (licensed)
– SmCo
– Ferrite Compounds
– Magnetizers, Demagnetizers, Test Equipment
0
5
10
15
20
25
1995
1996
1997
1998
1999
2000
Value-Added Services
• Quality Control and Testing
• Warehousing
• Magnetizing and Demagnetizing
• Powder Processing
• Technical Support
• Engineering/Design Support
IMI, Cont’d• Primary
Customers– Eastman Kodak– Seagate– Ametek– Fisher & Paykel– MPC– General Motors– Hamlin– Woodward Inc– Strattec (Briggs&Stratton)
–Delphi Automotive–Honeywell Microswitch–Hi-Stat–BEI Kimco–General Electric–Lear Corporation–Breed Automotive–Cherry Electrical
History of Permanent Magnets
0102030405060
MGOe
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
Magnet Timeline (Year vs. MGOe)
MK SteelAlnico
FerritesSmCo 1-5
SmCo 2-17
NdFeB
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
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’dM (magnetization): Def - Dipole moment per unit volume
J = Bi = µ0m(Magnetic polarization)
H (magnetic field strength): H=1/ µB(B-M)
Br (Remanence): 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 MaterialsNot 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)
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.
Initial StateWeak magnetic
field applied Increasing field makes one domain
Material has reached saturation
Domain Wall Movement
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
– AlNiCo– Ferrites– Samarium Cobalt– Neodymium-Iron-Cobalt– Bonded Materials
• Ferrite• Neo• SmCo
AlNiCo Magnets(BH)Max Br Hc Hci Density T c Tmax
1.7 MGOe 7.5kG 560 Oe 580 Oe 7.1 g/cm3 810C 450C5.5 MGOe 12.8kG 640 Oe 640 Oe 7.3 g/cm3 860C 525C5.3MGOe 8.2kG 1650 Oe 1860 Oe 7.3 g/cm3 860C 550C5.0 MGOe 7.2kG 1900 Oe 2170 Oe 7.3 g/cm3 860C 550C1.5 MGOe 7.1kG 550 Oe 570 Oe 6.8 g/cm3 810C 450C3.9 MGOe 10.9kG 620 Oe 630 Oe 6.9 g/cm3 860C 525C4.0 MGOe 7.4kG 1500 Oe 1690 Oe 7.0 g/cm3 860C 550C4.5 MGOe 6.7kG 1800 Oe 2020 Oe 7.0 g/cm3 860C 550C
Attributes: High flux, high Curie temp., very temperature stable (-.02%/ºC)
Detriments: Difficult to mount, low Hc
Casting Sintering
Melting (1400 - 1500C) Die Pressing (Approx. 5kbar)
Casting Sintering (1250 - 1400C)
Homogenizing (1200 - 1300C)
Isotropic Magnets Anisotropic Magnets
Cooling from 1300 to 600C (1-20 min) Cooling in magnetic field Isothermal magnetic field treatment (TTc)
Tempering 550-700C (1-20h) Tempering 550-700C (1-20h)
Grinding, Magnetizing, Testing
Cast and Sintered AlNiCo Processes
Ferrite MaterialsGrade (BH)Max Br Hc Hci Density T c Tmax
1 1.05 MGOe 2.3kG 1860 Oe 3250 Oe 4.9 g/cm3 450C 800C5 3.40 MGOe 3.8kG 2400 Oe 2500 Oe 4.9 g/cm3 450C 800C7 2.75MGOe 3.4kG 3250 Oe 4000 Oe 4.9 g/cm3 450C 800C8 3.50 MGOe 3.8kG 2950 Oe 3050 Oe 4.9 g/cm3 450C 800C
Attributes: Low costs, moderately high Hc & Hci, very high electrical resistance, “most flux for
bucks.
Detriments: Moderately low Curie temp., poor temperature stability (-.2%/C)
Grade (BH)Max Br Hc Hci Density T c Tmax
SmCo 1-5 18 MGOe 8.7kG 8600 Oe 9000 Oe 8.5 g/cm3 750C 250C20 MGOe 9.0kG 8900 Oe 8500 Oe 8.5 g/cm3 750C 250C
SmCo 2-17 26 MGOe 10.6kG 7000 Oe 5000 Oe 8.5 g/cm3 825C 300C28 MGOe 11.0kG 7000 Oe 5000 Oe 8.5 g/cm3 825C 300C30 MGOe 11.3kG 10,000 Oe 7000 Oe 8.5 g/cm3 825C 300C
SmCo Grades
Attributes: High magnetic characteristics, high Curie temp, very temperature stable, high
energy for low volume, can be machined easily to very small sizes.
Detriments: High costs, very brittle
Alloy Production Milling < 5µm
Magnetic Orientation Pressing
Heat Treatment 900 - 400 °C
Sintering 1200°C
Machining and Magnetizing
SmCo Production
Nd-Fe-B MaterialsGrade (BH)Max Br Hc Hci Density T c Tmax
30 28-32 MGOe 12.0kG 11,000 Oe 12,000 Oe 7.4 g/cm3 310C 150C35 33-36 MGOe 12.5kG 11,800 Oe 12,000 Oe 7.4 g/cm3 310C 150C38 36-39MGOe 12.9kG 12,300Oe 12,000 Oe 7.4 g/cm3 310C 150C45 43-47 MGOe 13.9kG 13,500 Oe 11,000 Oe 7.4 g/cm3 310C 150C
Attributes: High energy for size, more economical than SmCo, no cobalt, very high Hc and Hci.
Detriments: Poor temperature coefficient (-.13%/C), material will oxidize if not coated, low
Curie temperature.
Alloy Production Milling < 5µm
Magnetic Orientation Pressing
Heat Treatment 900 - 600 °C
Sintering 1030-1100°C
Machining and Magnetizing
Sintered Neodymium-Iron-Boron
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 MoldingAdvantages:
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 ProcessAdvantages:
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 MoldingAdvantages:
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 MoldingAdvantages:
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 MoldingMulti 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
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 (10-50
microns)– Durability (????)– Salt spray (480 hours)
ConversionsQuantity Symbol CGS Unit
Conversion factor
SI Unit
Magnetic Flux MAXWELL 10-3 WEBER
Magnetic Induction B GAUSS 10-4 TESLA
Magnetomotive force
FGILBERT
(OERSTED-CM)103/4µ AMPERE-TURN
Magnetic Field Strength
H OERSTED103/4µ
1A/m = 12.57*10-3AMPERE-METER
Energy Product BdHdMEGAGAUS S-
OERSTED
103/4µ
1 A/m = 0.1257*103
GOeJOULE/METER3
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