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Magnetic Materials Seminar

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.

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Magnetic Materials Seminar

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  1. Magnetic Materials Seminar Presented by: International Magnaproducts, Inc.

  2. 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

  3. 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

  4. Value-Added Services • Quality Control and Testing • Warehousing • Magnetizing and Demagnetizing • Powder Processing • Technical Support • Engineering/Design Support

  5. 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

  6. History of Permanent Magnets NdFeB SmCo 2-17 SmCo 1-5 Ferrites Alnico MK Steel

  7. 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)

  8. 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

  9. 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

  10. How to Read a Hysteresis Loop of a Permanent Magnet

  11. 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.

  12. Magnetic Quantities, Cont’d M (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.

  13. 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.

  14. 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.

  15. 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

  16. 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)

  17. 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)

  18. Antiferromagnetic Ferromagnetic Ferrimagnetic Diagrams of Magnetic Materials

  19. 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.

  20. Domain Wall Movement Weak magnetic field applied Increasing field makes one domain Material has reached saturation Initial State

  21. Testing Permanent Magnets

  22. 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.

  23. 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.

  24. Most Commonly Used Materials AlNiCo Ferrites Samarium Cobalt Neodymium-Iron-Cobalt Bonded Materials Ferrite Neo SmCo Permanent Magnet Materials

  25. AlNiCo Magnets Attributes: High flux, high Curie temp., very temperature stable (-.02%/ºC) Detriments: Difficult to mount, low Hc

  26. Casting Sintering Die Pressing (Approx. 5kbar) Casting Sintering (1250 - 1400C) Homogenizing (1200 - 1300C) Isotropic Magnets Cooling from 1300 to 600C (1-20 min) Isothermal magnetic field treatment (TTc) Tempering 550-700C (1-20h) Tempering 550-700C (1-20h) Grinding, Magnetizing,Testing Melting (1400 - 1500C) Anisotropic Magnets Cooling in magnetic field Cast and Sintered AlNiCo Processes

  27. Ferrite Materials 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)

  28. Ferrite Production Process

  29. 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

  30. Alloy Production Milling < 5µm Sintering 1200°C Magnetic Orientation Pressing Heat Treatment 900 - 400 °C Machining and Magnetizing SmCo Production

  31. Nd-Fe-B Materials 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.

  32. Alloy Production Milling < 5µm Magnetic Orientation Pressing Heat Treatment 900 - 600 °C Machining and Magnetizing Sintered Neodymium-Iron-Boron Sintering 1030-1100°C

  33. 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

  34. 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

  35. 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

  36. 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”

  37. 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”

  38. Rare Earth Characteristics(Inj. Molding)

  39. 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.

  40. MCIM, cont’d.

  41. MCIM, cont’d.

  42. Q & A Session

  43. 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 Various Coatings for Magnets

  44. 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

  45. 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

  46. Coatings, cont’d

  47. Conclusion & Additional Questions

  48. Conversions

  49. More Conversions

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