AlNiCo Magnets

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    AlNiCo MagnetsTypes Features Applications

    Manufacturing

    Process Magnetizing

    Graphical

    Representation

    Properties

    Alnico is an alloy produced by

    mixing aluminum, nickel andcobalt with certain addition of

    other metals like copper, ironand titanium. Capable of

    producing strong magneticfield, it has an excellent linear

    temperature characteristics and

    has wide industrialapplications.

    Types of Alnico MagnetsOn the basis of manufacturing

    process and application alnicocan be grouped into following

    types:

    y Cast Alnico

    y Sintered Alnico

    y Bar Alnico

    Features

    y Alnico's are the strong

    magnets which canproduce strong

    magnetic fields.

    y Excellent resistance to

    corrosion

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    y They have superiorthermal stability

    y These magnets havesome of the highest

    curie points of anymagnetic material

    ranging around 800oC

    y Some type of Alnico's

    are isotropic

    y They have high

    magnetic flux density

    ApplicationsAlnico magnets have

    applications in the followingareas:

    y Electric motorsy Electric guitar pickupsy Sensors

    y Loudspeakersy Cow magnets

    y Automotive andelectronic sensors

    y Actuatorsy Hall effect sensors

    y Magnetrony Reed switches

    y TWT amplifiersy Communication

    Manufacturing ProcessCasting or sintering process is

    applied for making alnicomagnets. The first step

    involves the pouring of molten

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    metal alloys into moulds. Laterit is passed through various

    heat cycles. The resultantmagnets have rough surface

    which after machining gives a

    glossy look.

    Sintered magnets are produced

    by compacting fine alnicopowder in a press, and then

    sintering the compactedpowder into a solid magnet.

    Alnico magnets can only be

    magnetized only in the fieldhaving magnetizing fields of

    about 3 kOe.S

    ince thesemagnets have low coercivity

    they, must be protected fromthe adverse repelling fields as

    this could partiallydemagnetize the magnets.

    MagnetizingAfter the tolerancemagnetizing is effected. As

    alnico magnets are brittle,theymust be protected from

    hard blows and handled withcare. It should be magnetized

    in a proper magnetic field andmust be prevented from the

    repelling fields as it is prone todemagnetization.

    Graphical Representation of

    Manufacturing Process

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    Properties

    Physical Properties

    Curie temperature 860

    Max.OperatingTemp.

    525-550

    Resistivity 47-54

    Hardness520-630

    Density g/cm36.9-

    7.3

    Rev. Recoil

    Permeability

    1.7-

    4.7

    Saturation Field

    Strength kOe2.7-6.3

    Temp.Coefficient of

    iHc

    -0.01-

    0.03

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    Design Guide

    Contents

    Introduction Manufacturing Methods

    Modern Magnet Materials Coatings

    Units Of Measure Assembly Considerations

    Design Considerations Magnetization

    Permanent MagnetStability

    Measurement And Testing

    Physical Characteristics

    AndHandling And Storage

    Machining Of PermanentMagnets

    Quick ReferenceSpecification Checklist

    1.0 Introduction

    Magnets are an important part of our daily lives, serving as essentialcomponents in everything from electric motors, loudspeakers, compucompact disc players, microwave ovens and the family car, toinstrumentation, production equipment, and research. Their contributoften overlooked because they are built into devices and are usually osight.

    Magnets function as transducers, transforming energy from one form another, without any permanent loss of their own energy. Generalcategories of permanent magnet functions are:

    Mechanical to mechanical - such as attraction and repulsion.

    Mechanical to electrical - such as generators and microphones

    Electrical to mechanical - such as motors, loudspeakers, chargparticle deflection.

    Mechanical to heat - such as eddy current and hysteresis torque

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    devices.

    Special effects - such as magneto resistance, Hall effect devicesmagnetic resonance.

    The following sections will provide a brief insight into the design andapplication of permanent magnets. The Design Engineering team at MSales & Manufacturing will be happy to assist you further in yourapplications.

    2.0Modern Magnet Materials

    There are four classes of modern commercialized magnets, each basetheir material composition. Within each class is a family of grades witown magnetic properties. These general classes are:

    Neodymium Iron Boron

    Samarium Cobalt

    Ceramic

    Alnico

    NdFeB and SmCo are collectively known as Rare Earth magnets becauthey are both composed of materials from the Rare Earth group ofelements. Neodymium Iron Boron (general composition Nd2Fe14B, oftabbreviated to NdFeB) is the most recent commercial addition to the of modern magnet materials. At room temperatures, NdFeB magnets the highest properties of all magnet materials. Samarium Cobalt ismanufactured in two compositions: Sm1Co5 and Sm2Co17 - often referas the SmCo 1:5 or SmCo 2:17 types. 2:17 types, with higher Hci valoffer greater inherent stability than the 1:5 types. Ceramic, also knowFerrite, magnets (general composition BaFe2O3 or SrFe2O3) have beencommercialized since the 1950s and continue to be extensively used tdue to their low cost. A special form of Ceramic magnet is "Flexible"material, made by bonding Ceramic powder in a flexible binder. Alnicomagnets (general composition Al-Ni-Co) were commercialized in the 1and are still extensively used today.

    These materials span a range of properties that accommodate a wide

    variety of application requirements. The following is intended to give broad but practical overview of factors that must be considered in selthe proper material, grade, shape, and size of magnet for a specificapplication. The chart below shows typical values of the key characterfor selected grades of various materials for comparison. These valuesdiscussed in detail in the following sections.

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    Table 2.1Magnet Material Comparisons

    Material Grade Br Hc Hci BHmax Tmax (Deg C)*

    NdFeB 39H 12,800 12,300 21,000 40 150

    SmCo 26 10,500 9,200 10,000 26 300

    NdFeB B10N 6,800 5,780 10,300 10 150

    Alnico 5 12,500 640 640 5.5 540

    Ceramic 8 3,900 3,200 3,250 3.5 300

    Flexible 1 1,600 1,370 1,380 0.6 100

    * Tmax (maximum practical operating temperature)is for reference only. The maximum practical operating temperature of

    any magnet is dependent on the circuit the magnet is operating in.

    3.0 Units ofMeasure

    Three systems of units of measure are common: the cgs (centimeter, gram,second), SI (meter, kilogram, second), and English (inch, pound, second)

    systems. This catalog uses the cgs system for magnetic units, unlessotherwise specified.

    Table 3.1 Units ofMeasure Systems

    Unit Symbol cgs System SI System English SystemFlux maxwell weber maxwellFlux Density B gauss tesla lines/in2Magnetomotive Force F gilbert ampere turn ampere turnMagnetizing Force H oersted ampere turns/m ampere turns/inLength L cm m inPermeability of a vacuum v 1 0.4 x 10-6 3.192

    Table 3.2Conversion FactorsMultiply By To obtaininches 2.54 centimeterslines/in

    20.155 Gauss

    lines/in2

    1.55 x 10-5

    Tesla

    Gauss 6.45 lines/in2Gauss 0

    -4Tesla

    Gilberts 0.79577 ampere turns

    Oersteds 79.577 ampere turns /m

    ampere turns 0.4 Gilbertsampere turns/in 0.495 Oerstedsampere turns/in 39.37 ampere turns/m

    Click here for an interactive version of this conversion table.

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    4.0 Design Considerations

    Basic problems of permanent magnet design revolve around estimating thedistribution of magnetic flux in a magnetic circuit, which may includepermanent magnets, air gaps, high permeability conduction elements, andelectrical currents. Exact solutions of magnetic fields require complex

    analysis of many factors, although approximate solutions are possible basedon certain simplifying assumptions. Obtaining an optimum magnet designoften involves experience and tradeoffs.

    4.1 Finite Element Analysis

    Finite Element Analysis (FEA) modeling programs are used to analyzemagnetic problems in order to arrive at more exact solutions, which can thenbe tested and fine tuned against a prototype of the magnet structure. UsingFEA models flux densities, torques, and forces may be calculated. Resultscan be output in various forms, including plots of vector magnetic potentials,

    flux density maps, and flux path plots. The Design Engineering team atMagnet Sales & Manufacturing has extensive experience in many types ofmagnetic designs and is able to assist in the design and execution of FEAmodels.

    4.2The B-H Curve

    The basis of magnet design is the B-H curve, or hysteresis loop, whichcharacterizes each magnet material. This curve describes the cycling of amagnet in a closed circuit as it is brought to saturation, demagnetized,saturated in the opposite direction, and then demagnetized again under theinfluence of an external magnetic field.

    The second quadrant of the B-H curve, commonly referred to as the"Demagnetization Curve", describes the conditions under which permanent

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    magnets are used in practice. A permanent magnet will have