Magnetic Materials Seminar Presented by: International Magnaproducts, Inc.

Magnetic Materials Seminar

Presented by: International Magnaproducts, Inc.

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

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’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)

Antiferromagnetic

Ferromagnetic

Ferrimagnetic

Diagrams of Magnetic Materials

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 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

– 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)

Ferrite Production Process

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

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 (10-50

microns)– Durability (????)– Salt spray (480 hours)

Coatings, cont’d

Conclusion & Additional Questions

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

More Conversions