8/7/2019 AlNiCo Magnets

1/18

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

8/7/2019 AlNiCo Magnets

2/18

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

8/7/2019 AlNiCo Magnets

3/18

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

8/7/2019 AlNiCo Magnets

4/18

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

8/7/2019 AlNiCo Magnets

5/18

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

8/7/2019 AlNiCo Magnets

6/18

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.

8/7/2019 AlNiCo Magnets

7/18

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.

8/7/2019 AlNiCo Magnets

8/18

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

8/7/2019 AlNiCo Magnets

9/18

magnets are used in practice. A permanent magnet will have