RARE-EARTH VACODYM·VACOMAX permanenti/Magneti... · Alongside analytical processes, we utilize sophisticated computer programs to analyze and design magnet systems. These include

ADVANCED MATERIALS – THE KEY TO PROGRESS

RARE-EARTHPERMANENT MAGNETS

VACODYM · VACOMAX

page1. Introduction 4

2. Product Range 6

3. Applications 9

4. Materials and Magnetic Properties 144.1 Characteristic Properties 144.2 Material Grades 184.3 Temperature Dependence and

Magnetic Losses 394.4 Magnetization of RE Magnets 40

5. Corrosion Behaviour, Surface Protectionand Coatings 425.1 Corrosion Behaviour 425.2 Surface Protection 435.3 Types of Coating 445.4 Description of the Coatings 44

6. Forms of Supply 486.1 Types of Magnetization 486.2 Dimensional Tolerances 48

7. Glueing RE Magnets 51

8. Integrated Management System 518.1 Quality Management 518.2 Technial terms and Conditions of Sale 528.3 Environmental and Safety Management 53

9. Safety Guidelines 54

10. Appendix: 5510.1 Technical Principles and Terms 5510.2 Conversion Table Celsius – Fahrenheit 57

11. Ductile Permanent Magnet alloys andMagnetically Semi-hard Materials 58

RARE EARTH PERMANENT MAGNETS2

CONTENTS

3RARE EARTH PERMANENT MAGNETS

RARE-EARTHPERMANENT MAGNETS

VACODYM · VACOMAXVACUUMSCHMELZE GmbH & Co. KG (VAC)is one of the world’s leading producersof special metallic materials with exceptionalphysical properties and resulting products.The company has a staff of approximately3.000, is represented in 40 countries spreadacross all continents and currently achieves a turnover of more than € 270 million.The headquarters, including operational headquarters of VAC is in Hanau, Germany.The company also has production plants inSlovakia and China.


1. INTRODUCTION

In addition to permanent magnets, the product range inclu-des soft magnetic materials, semi-finished products andparts, inductive components, magnetic shieldings andvarious other materials with special physical properties.Apart from the rare-earth permanent magnets, the spectrumincludes, ductile permanent magnets and magneticallysemi-hard materials. The latter are characterized by low-costforming capabilities and adjustable permanent magnet pro-perties.

We have been working on the magnetic properties of speci-al metallic materials and their applications for over 70 years.In 1973 we had already started producing permanent mag-nets on a rare-earth-cobalt base using powder metallurgicalmethods. By finding optimum solutions in close cooperationwith our customers we have contributed strongly to thewidespread use of this new material group – available underthe trade name VACOMAX®.

VACODYM® * is our trade name for neodymium-iron-boronmagnets. VACODYM has been produced on an industrialscale since 1986. Our materials have the highest energydensity available to date. All processing steps from meltingthe alloy under vacuum through to coating the finished partsare performed at our works ensuring optimum material pro-perties throughout the entire production process. As marketleader in Europe today, we belong to the worldwide top-ran-king producers of rare-earth permanent magnets.

The magnetic properties are largely determined by the pre-material and the production process. Magnets can be pro-duced in three different ways. These three methods areidentified by the letters HR, TP, or AP in the alloy code. HR(high remanence) refers to the isostatically pressed mag-nets, as in the past. In the die pressed design we differen-tiate between TP (transverse pressed) and AP (axial pres-sed). Details on the available forms of supply are given inSection 6.

Intensive development work has continually adapted ourrange of VACODYM alloys to the demands of the market.The focus being on the magnetic properties and especiallyon improving corrosion resistance, which was realized in thenewly developed “8-Series” consisting of VACODYM 837,

® = registered trademark of VACUUMSCHMELZE*) = licensor NEOMAX Co. Ltd. (Japan)


854, 863, 872 and 890. This new series of alloys and the“6-Series” consisting of VACODYM 633, 655, 669, 677 and688 already successfully launched on the market magnetsparticularly suitable for use in motor applications are availa-ble. These can be used under normal ambient conditionswithout any extra surface coating.

For systems we developed a group of alloys for applicationtemperatures up to 150°C – the so-called “7-Series” ofVACODYM 722, 745, 764 and 776, which are characterizedby particularly high remanence in-duction values. If the bestpossible corrosion resistance is an additional issue the highremanent qualities of VACODYM 837 and 854 from the “8-Series” are a further option.

Economic production processes, modern inspection techni-ques and a certified quality management system complyingwith DIN EN ISO 9001, ISO TS 16949 and DIN EN ISO 14001are as much a matter of course as staff training sessionsand an active environmental protection policy.

By continuing to build on our long established foundations,we aim to remain your reliable and competent partner.

Fig 1:

Development of energy densities (BH)max of permanent magnets

and their potential.

0

100

200

300

400

500

600

700

800

1880 1900 1920 1940 1960 1980 2000 2020 2040 2060

Year

Steel

AlNiCo

Ferrite

SmCo5

Sm2Co17

NdFeB

Future possibilitiesof new materials

(BH)max = 485 kJ / m3

(Theoretical limits NdFeB)

(BH)max

[kJ/m3]


2. PRODUCT RANGE

The product range of our rare-earth magnets covers a carefully balanced program of materials with different mag-netic properties. As a result, it is relatively easy to select a material suitable for any specific application.

VACODYM is the permanent magnet material offering thehighest energy densities currently available. The excellentmagnetic properties of this material group can be traced to the strongly magnetic matrix phase Nd2Fe14B featuringvery high saturation polarization and high magnetic anisotro-py. A ductile neodymium-rich bonding phase at the grainboundaries provides these magnets with good mechanicalproperties. Fig. 2 gives an overview of the typical propertiesof our VACODYM-magnets.

VACOMAX is our permanent magnet material of rare-earthsand cobalt. These magnets feature especially high coercivi-ties with simultaneously high saturation and excellent temperature and corrosion stability. In Fig. 3 the typicaldemagnetization curves of VACODYM and VACOMAX arecompared with the classical permanent magnet materialsAlNiCo and hard ferrite.

VACUUMSCHMELZE has many years of experience in the production of permanent magnets and the design ofmagnetic circuits. Alongside analytical processes, we utilizesophisticated computer programs to analyze and designmagnet systems. These include 2D- and 3D-field cal-culations with finite element methods. Their use has substantially shortened the design phase of assemblies.As a result, besides single magnets, we are supplying anincreasing number of finished magnet assemblies to custo-mer’s specifications.

Detailed information on these is given in our PD-004 leaflet.

1,00

1,05

1,10

1,15

1,20

1,25

1,30

1,35

1,40

1,45

1,50

800 1200 1600 2000 2400 2800 3200

coercivity, HcJ (kA/m)

rem

anen

ce, B

r (T

)

VACODYM

863 TP

837 TP

633 TP

655 TP

677 TP

688 TP

872 TP

890 TP

854 TP

669 TP

745 TP

764 TP

776 TP

Fig. 2:

Remanence Br and coercivity HcJ of

transverse field pressed VACODYM

magnets


Fig. 3:

Typical demagnetization curves

of VACODYM and VACOMAX in

comparison with AlNiCo and Ferrite

at room temperature

The use of soft magnetic materials as system components,e.g. VACOFLUX® and VACOFER®, enables us to meet custo-mers’ specifications at a high quality level. In many casesoptimum assembly and magnetization of the systems is onlypossible when the magnets and the other system compo-nents are sourced and put together at the magnet producer.

Magnets made of VACODYM and VACOMAX are producedpowder metallurgically by sintering. The main processingsteps are given in Fig. 4. Depending on size, shape, toleran-ces, batch size and magnetic requirements, the parts are either cut from isostatically pressed blocks or are die-pressed. When diepressing, the powder particles are aligned

by strong magnetic fields parallel (axial field for AP-grades)or perpendicular (transverse fields for TP-grades) to thedirection of pressing depending on the geometry of the part.Isostatically or transverse-field pressed parts have an appro-ximately 5 – 8% higher remanence compared to axial-fieldpressed magnets.


Fig. 4: Production steps of rare-earth magnets

Melting of the Alloyunder Vacuum

Crushing

Milling

Alignment in Magnetic Field

Pressing

Sintering, Annealing

Machining, Coating

Magnetizing

die pressedisostatic

Transverse Field (TP) Axial Field (AP)


3. APPLICATIONS

Compared to conventional magnet materials, such as AlNiCoor hard ferrite, magnets of VACODYM and VACOMAX displaya number of excellent magnetic properties. Users benefitimmensely from their merits:

– Energy densities up to tenfold those of AlNiCo and hardferrite not only enable a reduction in magnet volume (see Fig. 5), but also the miniaturization of systems and whole subassemblies, saving the costs for return paths,coils etc.

– Existing magnet systems can be improved in many cases. In general, when using VACODYM or VACOMAX we recommend the previous systems to be re-designed.

– New design ideas can be utilized and new fields of applications are opened:

MOTORS AND GENERATORS

Servomotors, DC motors, linear motors and heavy-dutymotors (e.g. motors for ships’ propulsion and wind turbinegenerator systems) utilize predominantly VACODYM mag-nets. In the case of high temperatures VACOMAX is thematerial of choice. A further important application is smallpower and fractional horsepower motors, e.g. bell typearmature and dental motors.

Fig. 5:Example illustrating the volume reduction achieved with VACODYM andVACOMAX: each magnet is designed to produce a field of 100 mT at thereference point P = 5 mm from the surface of the pole

Assemblies for motors

Rotor of a servomotor


Synchronous coupling with

VACODYM-magnets

Sensor for electronic vehicle stabilization program (ESP)

– Sensor (module in plastic housing with customer specific connectors)

– module cap: inner (with magnet) and outer view

Producer: Robert Bosch GmbH

AUTOMOTIVE ENGINEERING AND SENSORSSensors to measure engine, gear and wheel rotary speed(e.g. ABS systems), accelerations (e.g. ESP, airbag) or positions (e.g. throttle valve, injection systems, camshaft,crankshaft, fuel gauges) are equipped with VACOMAX orVACODYM magnets, depending on the requirements fortemperature and corrosion stability.

VACODYM magnets, in particular, should be considered foractuators in engine management, small motors (e.g. steeringboost), generators and for noise reduction.

Synchronous motors as main drives in electro and hybridvehicles are also equipped with VACODYM magnets.

MRI (MAGNET RESONANCE IMAGING)In precise analysis equipment in medical engineering moreand more permanent magnet systems with high remanentVACODYM grades are used besides superconducting andother electrically excited systems. The main advantages arethe very low energy consumption, savings in weight and amaintenance-free construction.

MAGNETIC COUPLINGSMagnetic couplings are preferred in automation and chemi-cal processing technology as they ensure a permanent hermetic separation of different media. Owing to increasedtemperature requirements, VACOMAX magnets are used fornumerous applications. VACODYM is recommended forlower application temperatures.

Field line characteristic (Finite elements calculation)


A dipole with a diameter of 1.5 m is the heart of a particle detector named

„Alpha Magnetic Spectrometer“ (AMS). It is manufactured from approx.

5000 rectangular magnets made of VACODYM 510 HR and operates

successfully aboard the ISS space station since 1998.


BEAM GUIDING SYSTEMS, WIGGLERS AND UNDULATORS

Permanent magnetic beam guiding systems require very little maintenance and no power supply. Systems usingVACODYM or VACOMAX magnets have proved imperative in all applications where high field strengths have to beachieved in special reaction chambers, e.g. in sputteringdevices, travelling wave tubes, wigglers, undulators andmulti-pole devices as well as particle detectors.

To meet these requirements, we produce defined and carefully balanced compatible sets of magnets exhibitingmagnetic properties to tight tolerances, such as the anglebetween the preferred magnetic direction and the geometryof the parts. Economic manufacturing processes are avail-able to produce parts with a large volume, in particular, wecan produce large magnet cross sections with pole surfacesup to approx. 110 cm2.

15 m long undulator system with magnets of VACODYM and polepieces of

VACOFLUX for the TESLA Test Facility at DESY in Hamburg.


PERMANENT MAGNET BEARINGSDifferent magnetic bearing principles have been developedfor turbo-molecular pumps, centrifuges etc. These employring magnets magnetized in either axial or radial direction.The material is selected according to customer’s specifica-tions.

HOLDING SYSTEMSClamping plates and vibration dampers for machine tools areone of the main fields of application for holding systems.These normally require maximum holding forces and call forVACODYM. We supply ready-to-use holding assemblies withpot-shaped iron return passes as well as single magnets.

MEASURING INSTRUMENTSIn this field the applications range from electronic scalesthrough pulse meters to NMR-analysis equipment.Depending on the construction principle systems usingarmatures or rotors fitted with VACODYM or VACOMAX magnets are selected.

SWITCHES AND RELAYSFor the widely varying designs of Hall switches, polarizedrelays, revolution counters etc., magnets or magnet ass-emblies incorporating VACODYM or VACOMAX are useddepending on the specification.

Mass spectrometer from INFICON GmbH with magnet assembly made ofVACOMAX


Table 1: CHARACTERISTIC PROPERTIES OF VACODYM AT ROOM TEMPERATURE (20°C)

4.1 CHARACTERISTIC PROPERTIES4. MATERIALS AND MAGNETIC PROPERTIES

1) Coding based on IEC 60404-8-1, the magnetic values usually exceed the IEC values

Pressing Material Code1) Remanence Coercivitydirection

Br Br HcB HcB

typ. min. typ. min.Tesla kG Tesla kG kA/m kOe kA/m kOe

HR VACODYM 722 HR 380/87,5 1,47 14,7 1,42 14,2 915 11,5 835 10,5

VACODYM 745 HR 370/111,5 1,44 14,4 1,40 14,0 1115 14,0 1065 13,4

VACODYM 510 HR 360/95,5 1,41 14,1 1,38 13,8 980 12,3 915 11,5

VACODYM 633 HR 315/127,5 1,35 13,5 1,29 12,9 1040 13,1 980 12,3

VACODYM 655 HR 280/167 1,28 12,8 1,22 12,2 990 12,4 925 11,6

VACODYM 677 HR 240/223 1,18 11,8 1,12 11,2 915 11,5 850 10,7

TP VACODYM 745 TP 355/111,5 1,41 14,1 1,37 13,7 1090 13,7 1035 13,0

VACODYM 764 TP 335/127,5 1,37 13,7 1,33 13,3 1060 13,3 1005 12,6

VACODYM 776 TP 305/167 1,32 13,2 1,28 12,8 1020 12,8 970 12,2

VACODYM 837 TP 335/127,5 1,37 13,7 1,33 13,3 1060 13,3 1010 12,7

VACODYM 854 TP 310/167 1,32 13,2 1,28 12,8 1020 12,8 970 12,2

VACODYM 863 TP 295/200 1,29 12,9 1,25 12,5 995 12,5 950 11,9

VACODYM 872 TP 280/223 1,25 12,5 1,21 12,1 965 12,1 915 11,5

VACODYM 890 TP 250/263 1,19 11,9 1,15 11,5 915 11,5 865 10,9

VACODYM 633 TP 305/127,5 1,32 13,2 1,28 12,8 1020 12,8 970 12,2

VACODYM 655 TP 280/167 1,26 12,6 1,22 12,2 970 12,2 925 11,6

VACODYM 669 TP 255/200 1,22 12,2 1,17 11,7 940 11,8 875 11,0

VACODYM 677 TP 240/223 1,18 11,8 1,13 11,3 915 11,5 860 10,8

VACODYM 688 TP 225/262,5 1,14 11,4 1,09 10,9 885 11,1 830 10,4

AP VACODYM 745 AP 325/111,5 1,34 13,4 1,31 13,1 1025 12,9 970 12,2

VACODYM 764 AP 305/135,5 1,30 13,0 1,27 12,7 995 12,5 955 12,0

VACODYM 776 AP 280/167 1,26 12,6 1,22 12,2 965 12,1 915 11,5

VACODYM 837 AP 300/135,5 1,30 13,0 1,26 12,6 995 12,5 950 11,9

VACODYM 854 AP 275/167 1,26 12,6 1,21 12,1 965 12,1 905 11,4

VACODYM 863 AP 250/200 1,21 12,1 1,17 11,7 925 11,6 875 11,0

VACODYM 872 AP 235/223 1,17 11,7 1,13 11,3 890 11,2 845 10,6

VACODYM 890 AP 210/263 1,11 11,1 1,07 10,7 845 10,6 795 10,0

VACODYM 633 AP 280/135,5 1,26 12,6 1,22 12,2 965 12,1 915 11,5

VACODYM 655 AP 255/167 1,20 12,0 1,16 11,6 915 11,5 865 10,9

VACODYM 669 AP 225/200 1,16 11,6 1,12 11,2 885 11,1 820 10,3

VACODYM 677 AP 215/223 1,13 11,3 1,08 10,8 860 10,8 805 10,1

VACODYM 688 AP 200/262,5 1,08 10,8 1,03 10,3 830 10,4 770 9,7


2) The maximum application temperature is governed by the layout of the system. The approx. values given refer to magnets operating in working points of B/μoH = -1 (max. energy product).Users are recommended to consult VAC on any application of VACODYM involving temperatures above 150 °C.

Energy density Temperature coefficient Density Max.20-100 °C 20-150 °C continuous

TemperatureHcJ (BH)max (BH)max TK (Br) TK (HcJ) TK (Br) TK (HcJ) Tmax

2)min. typ. min. typ. typ. typ. typ. typ.kA/m kOe kJ/m3 MGOe kJ/m3 MGOe %/°C %/°C %/°C %/°C g/cm3 °C °F

875 11 415 53 380 48 –0,115 –0,77 7,6 50 120

1115 14 400 50 370 47 –0,115 –0,73 7,6 70 160

955 12 385 48 360 45 –0,115 –0,79 7,5 60 140

1275 16 350 44 315 40 –0,095 –0,65 –0,105 –0,55 7,7 110 230

1670 21 315 40 280 35 –0,090 –0,61 –0,100 –0,55 7,7 150 300

2230 28 270 34 240 30 –0,085 –0,55 –0,095 –0,50 7,7 190 370

1115 14 385 48 355 45 –0,115 –0,73 7,6 70 160

1275 16 360 46 335 42 –0,115 –0,70 –0,125 –0,59 7,6 100 210

1670 21 335 42 310 39 –0,110 –0,61 –0,120 –0,55 7,6 140 280

1275 16 360 46 335 42 –0,110 –0,62 –0,120 –0,54 7,6 110 230

1670 21 335 42 310 39 –0,105 –0,60 –0,115 –0,53 7,7 150 300

2000 25 315 40 295 37 –0,100 –0,56 –0,110 –0,51 7,7 170 340

2230 28 300 38 280 35 –0,095 –0,53 –0,105 –0,49 7,7 190 370

2625 33 270 34 250 31 –0,090 –0,50 –0,100 –0,46 7,7 220 430

1275 16 335 42 305 39 –0,095 –0,65 –0,105 –0,57 7,7 110 230

1670 21 305 39 280 35 –0,090 –0,61 –0,100 –0,55 7,7 150 300

2000 25 290 36 255 32 –0,085 –0,57 –0,095 –0,51 7,7 170 340

2230 28 270 34 240 30 –0,085 –0,55 –0,095 –0,50 7,7 190 370

2625 33 250 32 225 28 –0,080 –0,51 –0,090 –0,46 7,8 220 430

1115 14 340 43 325 41 –0,115 –0,73 7,6 80 180

1355 17 325 41 305 38 –0,115 –0,69 –0,125 –0,58 7,6 110 230

1670 21 305 38 280 35 –0,110 –0,61 –0,120 –0,55 7,6 150 300

1355 17 325 41 300 37 –0,110 –0,62 –0,120 –0,54 7,6 120 250

1670 21 305 38 275 35 –0,105 –0,60 –0,115 –0,53 7,7 160 320

2000 25 280 35 250 32 –0,100 –0,56 –0,110 –0,51 7,7 180 360

2230 28 260 33 235 30 –0,095 –0,53 –0,105 –0,49 7,7 200 390

2625 33 235 29 210 26 –0,090 –0,50 –0,010 –0,46 7,7 230 440

1355 17 305 38 280 35 –0,095 –0,64 –0,105 –0,57 7,7 120 250

1670 21 275 35 255 32 –0,090 –0,61 –0,100 –0,55 7,7 160 320

2000 25 255 32 225 28 –0,085 –0,57 –0,095 –0,51 7,7 180 360

2230 28 240 30 215 27 –0,085 –0,55 –0,095 –0,50 7,7 200 390

2625 33 225 28 200 25 –0,080 –0,51 –0,090 –0,46 7,8 230 440


Table 2: CHARACTERISTIC PROPERTIES OF VACOMAX AT ROOM TEMPERATURE (20°C)

Material Remanence CoercivityCode1)

Br Br HcB HcB HcJ

typ. min. typ. min. min.Tesla kG Tesla kG kA/m kOe kA/m kOe kA/m kOe

VACOMAX 240 HR 1,12 11,2 1,05 10,5 730 9,2 600 7,5 640 8,0

200/64

VACOMAX 225 HR 1,10 11,0 1,03 10,3 820 10,3 720 9,0 1590 20,0

190/159

VACOMAX 225 TP 1,07 10,7 1,03 10,3 790 9,9 720 9,0 1590 20,0

190/159

VACOMAX 225 AP 1,04 10,4 0,97 9,7 760 9,6 680 8,5 1590 20,0

170/159

VACOMAX 200 HR 1,01 10,1 0,98 9,8 755 9,5 710 8,9 995 12,5

180/100

VACOMAX 170 0,95 9,5 0,90 9,0 720 9,0 660 8,3 1195 15,0

160/120

VACOMAX 145 S 0,90 9,0 0,85 8,5 660 8,3 600 7,5 1990 25,0

140/2001) Coding based on IEC 60404-8-1, the magnetic values usually exceed the IEC values

Material Curie- Specific Specific Thermal Coefficient of thermal Young’s Bending Compressive Vickers- Stress

temp. electr. heat con- expansion modulus strength strength hardness crack

resistance ductivity 20-100 °C resistance

II c � c KIC

°C �mm2/m J/(kg · K) W/(m·K) 10-6/K 10-6/K kN/mm2 N/mm2 N/mm2 HV N/mm3/2

VACODYM 310–370 1,1–1,7 350–550 5–15 4–9 -2–0 140–170 120–400 600–1250 500–700 80–180

VACOMAX Sm2Co17 800–850 0,65–0,95 300–500 5–15 8–12 10–14 140–170 80–150 400–900 550–750 30–60

VACOMAX SmCo5 700–750 0,4–0,7 300–500 5–15 4–10 10–16 100–130 90–180 600–1100 500–700 40–80

Table 3: CHARACTERISTIC PROPERTIES OF VACODYM AND VACOMAX AT ROOM TEMPERATURE (20°C)


Energy density Temperature coefficient Density Max.20-100 °C 20-150 °C continuous

temperature(BH)max (BH)max TK (Br) TK (HcJ) TK (Br) TK (HcJ) T2)max

typ. min. typ. typ. typ. typ. typ.kJ/m3 MGOe kJ/m3 MGOe %/°C %/°C %/°C %/°C g/cm3 °C °F

240 30 200 25 –0,030 –0,15 –0,035 –0,16 8,4 300 570

225 28 190 24 –0,030 –0,18 –0,035 –0,19 8,4 350 660

215 27 190 24 –0,030 –0,18 –0,035 –0,19 8,4 350 660

200 25 170 21 –0,030 –0,18 –0,035 –0,19 8,4 350 660

200 25 180 23 –0,040 –0,21 –0,045 –0,22 8,4 250 480

180 23 160 20 –0,040 –0,21 –0,045 –0,22 8,4 250 480

160 20 140 18 –0,040 –0,14 –0,045 –0,15 8,4 250 480

2) Prior to using VACOMAX above 200 °C we recommend customers contact VAC.

Material Hmag min.

kA/m kOe

VACODYM 2500 31

VACOMAX 225 3650 46

VACOMAX 240 2000 25

VACOMAX 145/170/200 2000 25

Table 4: INNER MAGNETIZING FIELD STRENGTHOF VACODYM AND VACOMAX


4.2 MATERIAL GRADES

VACODYM and VACOMAX are anisotropic materials with areversible permeability µrev < 1.1 at the working point. Theexact value depends on the material grade and the magnetgeometry.

VACODYM and VACOMAX do not feature open porosity,i.e. the pores are not connected to one another. Thereforeboth materials can be utilized for vacuum applications.

The following pages show demagnetization curves of diffe-rent grades at various temperatures. Additionally, the typicalirreversible losses are given as a function of temperature atdifferent loadlines. These charts are based on HR- or TP-gra-des. Axial field pressed magnets have slightly reduced los-ses under comparable conditions.

The measured curves refer to magnets whose minimumdimensions are >10 mm perpendicular to the direction ofmagnetization and > 5 mm parallel to it. Smaller dimensionsmay deviate from the curves shown.


4.2.1 SINTERED MAGNETS ON A Nd-Fe-B BASE

VACODYM 722

Typical demagnetization curvesB(H) and J(H) at different temperatures

Typical irreversible losses at different workingpoints as a function of temperature

VACODYM 722 HR

-0,5

20° C 60° C 80°C 100° C

120° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo ·H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0


VACODYM 745 HR

-0,5

20° C

120° C

60° C 80° C 100° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 745 AP

-0,5

20° C

120° C

60° C 80° C 100° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 745




VACODYM 764 TP

-0,5 20°C C 120° C

150° C

80° C60°C 100°C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 764 AP

-0,520°C 80° C60°C 100°C 120° C

150° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 764




VACODYM 776 TP

-0,5

20° C

120° C 150° C

180° C

100° C60° C 80° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VVAACCOODDYYMM 777766 AAPP

-0,5

20° C

120° C 150° C

180° C

80° C60° C 100° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

-10

-5

0

0 50 100 150 200

VACODYM 776 TP

B/μ0 · H =

°C

-20 -0,5 -1

irrev

ersi

ble

loss

es (

%)

Temperature

VACODYM 776




VACODYM 510 HR

-0,5

20° C

120° C

60°C 80°C 100° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 510




VACODYM 633 HR

-0,5 20° C 120° C

150° C

80° C 100° C60° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 633 AP

-0,5 20° C 120° 150° C100° C80° C60° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 633




VACODYM 655 HR

-0,5

20° C

120° C 150° C

180° C

100° C60° C 80° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 655 AP

-0,5

20° C

120° C 150° C

180° C

80° C60° C 100° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 655




VACODYM 669 TP

-0,5

20° C

120° C 150° C 180° C80° C 100° C

210° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 669 AP

-0,5

20° C

150° C

180° C

80° C 100° C

210° C

120° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 669




-2

VACODYM 677 HR

-0,5

20° C

120° C 150° C 180° C

210° C

100° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 677 AP

-0,5

20° C

150° C 180° C

210° C

100° C 120° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 677




-2

VACODYM 688 TP

-0,5

20° C

120° C 150° C 180° C 210° C

240° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

-2

VACODYM 688 AP

-0,5

20° C

120° C 150° C 180° C 210° C

240° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 688




VACODYM 837 AP

-0,520°C 60°C 80° C 100°C 120°C 150° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 837 TP

-0,520° C 80° C60°C 100°C 120°C 150° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

-10

-5

0

50 100 150 200 250

VACODYM 837 TP

-1 -2

°C

- 0,5B/µ0 · H = 0

irrev

ersi

ble

loss

es (

%)

Temperature

VACODYM 837




VACODYM 854 TP

-0,5

20° C

120° C 150° C 180° C80° C60° C 100° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 854 AP

-0,5

20° C

120° C 150° C 180° C80° C60° C 100° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

-10

-5

0

50 100 150 200 250

VACODYM 854 TP

-1 -2

°C

- 0,5B/µ0 · H = 0

irrev

ersi

ble

loss

es (

%)

Temperature

VACODYM 854




VACODYM 863 AP

-0,5

20° C

150° C180° C

80° C 100° C

210° C

120° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 863 TP

-0,5

20° C

120° 150° C 180° C80° C 100° C

210° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

-10

-5

0

50 100 150 200 250

VACODYM 863 TP

B/ 0 · H = 0 - 0,5 -1 -2

°C

irrev

ersi

ble

loss

es (

%)

Temperature

VACODYM 863




-2

VACODYM 872 AP

-0,5

20° C

120° 150° C 180° C

210° C

100° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

VACODYM 872 TP

-0,5

20° C

120° 150° C 180° C

210° C

100° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

-10

-5

0

50 100 150 200 250

VACODYM 872 TP

B/ 0 · H = 0 - 0,5 -1 -2

°C

irrev

ersi

ble

loss

es (

%)

Temperature

VACODYM 872




-2

VACODYM 890 AP

20° C

120° 150° C 180° C 210° C

240° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

-2

VACODYM 890 TP

-0,5

20° C

120° 150° C 180° C 210° C

240° C

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

-2 0 - 18 -16 -14 -12 -10 -8 -6 -4 -2 0

-8

-6

-4

-2

4

10

12

14

16

T kG

J,B

kOe

B/ μo · H

kA/m -1400 -1200 -1000

-1,0 -1,5 -2,0 -4,0

H

0-800 -600 -400 -200

8

6

2

0

-10

-5

0

50 100 150 200 250

VACODYM 890 TP

B/ 0 · H = 0 - 0,5 -1 -2

°C

irrev

ersi

ble

loss

es (

%)

Temperature

VACODYM 890




4.2.2 SINTERED MAGNETS ON A Sm2Co17 BASE

VACOMAX 240




AP

VACOMAX 225




4.2.3 SINTERED MAGNETS ON A SmCo5 BASE

HR

VACOMAX 200




VACOMAX 170




VACOMAX 145




4.3 TEMPERATURE DEPENDENCE ANDMAGNETIC LOSSES

The magnetic properties of permanent magnets are gover-ned by the application temperature. The typical demagneti-zation curves of VACODYM and VACOMAX at different tem-peratures are shown on the relevant alloy pages (see pages19-38). When selecting a material and the dimensions of amagnet, the characteristic magnetic values and the tempe-rature dependence must be considered (see section 10.1 ofappendix ”Technical Principles and Terms”).

The temperature dependence of the demagnetization curvescauses changes in the flux density, commonly referred to asmagnetic losses. These losses fall into two main categories:Reversible losses and irreversible losses. The latter resultfrom demagnetization of small areas of the magnet in oppo-sing fields and/or a rise in temperature, as well as changesin the micro-structure.

Reversible changes in the flux density are attributed to thetemperature dependence of the saturation polarization andare solely a function of alloy composition. They are describedby the temperature coefficient of the remanence; the meanvalue for each material is given in Table 1 and 2, resp. If anapplication calls for temperature compensation, we recom-mend the use of a magnetic shunt made of THERMOFLUX®.This achieves temperature coefficients l TC l <0.01%/K insystems with slightly reduced flux values in the range from20° to 100°C.

Irreversible losses owing to demagnetization processes aredependent on the load line of the magnet and the maximumapplication temperature. The typical irreversible losses to beexpected for the various material types at different load linesB/µoH are given in the applicable data sheets.

Irreversible changes can largely be avoided by means of astabilization process (aging). To obtain the optimum stabili-zation conditions for each application users should contactVAC. As a rule, it is adequate to heat the magnets to slight-ly above the maximum application temperature for approxi-mately one hour. This pre-treatment achieves good stabiliza-tion but at the expense of the flux density which is reducedaccordingly by the irreversible changes.

The losses caused by magnetization reversal in small areasof the magnet can be eliminated by remagnetization.

The maximum continuous application temperatures are pri-marily restricted by the reduction in the magnetic properties(see Tables 1 and 2).

To avoid undesired irreversible changes in the microstructu-re which cannot be remedied by remagnetization, VACODYMmagnets must not be heated to above 350°C and VACOMAXmagnets not above 400°C.

Chemical reactions with the immediate atmosphere or con-tact materials (e.g. glues) must be prevented. This appliesespecially to reactions with potential hydrogen production(see section 5.1). Radioactive radiation for a longer time cancause irreversible magnetic losses.

VACOMAX can be used at temperatures down to that ofliquid helium. When using VACODYM below approx. 150 Kour technical staff should be consulted.


4.4 MAGNETIZATION

Full magnetization is the precondition for achieving the typi-cal magnetic values that are listed in Table 1 resp. 2 for thevarious materials. The required minimum field strengths ofthe inner magnetizing field Hmag are obtained from the mag-netization behaviour of the material in question. They areshown in Table 4, page 17, and in Fig. 6. To achieve theinternal magnetizing field Hmag, the given external field Hext

must be increased by the value of the demagnetizing field Ha

which is determined by the working point:

l Hext l = l Hmag l + l Ha l

(See Section 10.1 of appendix “Technical Principles andTerms”.)

Due to the high coercivities of VACODYM and VACOMAX themagnets can also be magnetized outside the system. As aresult, handling the magnets and assembly of systems ismore difficult but the actual magnetization is far easier. WithVACODYM 510, 722/745 and also VACOMAX 240, caremust be taken to ensure that the working point of the mag-net is sufficiently above the “knee” of the B(H) -demagneti-zation curve (see section 10.1 of appendix “TechnicalPrinciples and Terms”).

Prior to magnetizing VACODYM and VACOMAX in a systemwe advise users to contact VAC.

Magnets made of VACODYM and especially of VACOMAXcan only be completely reversed in exceptionally high mag-netic fields (> approx. 120 kOe).

Fig. 6:Demagnetization curves of VACODYM and VACOMAX as a function of magnetization field strenght Hmag.The magnetization behaviour of VACODYM and VACOMAX of the SmCo5 type (Figs. a and b) is based on the so-called nucleation mechanism. This easy magnetiza-tion is only possible from the thermally demagnetized state.The pinning mechanism is characteristic for the VACOMAX type Sm2Co17 (Figs. c and d). VACOMAX 240 is very easy to magnetize compared with VACOMAX 225. Thisis achieved by a special heat treatment.

a)Magnetizing field strength(kA/m)


Magnetizing field strength(kA/m)




5. CORROSION BEHAVIOUR, SURFACEPROTECTION AND COATINGS

5.1 CORROSION BEHAVIOUR

Due to their strongly negative electrochemical standardpotential (E0 = –2.2 to –2.5 V) rare-earth (RE) elementsbelong to the group of non-precious and thus highly reacti-ve elements.

Their chemical reactivity is similar to that of alkaline earthmetals, like magnesium. Under normal conditions, the REmetals react slowly. Under conditions at higher temperaturesand the presence of water or humidity, the reaction is morerapid, RE-hydroxide is formed and hydrogen is set free. Thereleased hydrogen can then react with the free RE metal for-ming RE metal hydrides.

By adding an adequate amount of more noble elements suchas, for example, cobalt, the reaction with water can bealmost suppressed. The reaction rate is negligible.

This is the back-ground to VACOMAX (SmCo5 or Sm2Co17)only exhibiting a slight surface discolouration when exposedto high humidity (e.g. >80 % relative humidity) and increa-sed temperature (e.g. >80°C). No significant amount of cor-rosion products was measured even after long exposure(e.g. >1000 h).

The situation is in general different with Nd-Fe-B magnets.The individual magnet grains are held together mechanical-ly and fixed to each other by the so-called neodymium-richphase. This phase represents up to 5 % of the total volumeof the material and from a chemical point of view behaveslike pure neodymium. As a result, a relatively rapid intergra-nular decomposition of the magnet (see Fig. 7) sets in underhigh humidity and temperature (e.g., in the so-called HASTHighly Accelerated Stress Test acc. IEC 68-2-66 at 130°C /

95 % humidity and 2.6 bar). This in turn leads to a high corrosion rate and debris, which is neodymium hydroxide,and also to magnet dust (loose Nd-Fe-B grains). Sections5.2 to 5.4 describe means of protecting these materialseffectively in corrosive operating conditions.

The second generation of VACODYM materials such as forexample the 6-series and 8-series alloys no longer featurethis corrosion mechanism.

Additions of carefully selected suitable materials (includingcobalt) to the neodymium-rich phase have improved theircorrosion behaviour and systematically stopped intergranu-lar corrosion in a warm, humid atmosphere. The corrosionbehaviour of such VACODYM alloys is similar to that of pureiron materials (steel). In the HAST test even after severalweeks exposure the corrosion rate can hardly be measured.There is merely a dark grey shimmer to the material sur-face.

In cases where the humidity turns to condensation, VACO-DYM materials gradually begin to rust, similarly to partsmade of iron (red rust). Here the corrosion products aremainly non-magnetic metal oxides or hydroxide. In applica-tions where dew formation occurs regularly (condensation),and/or the parts are to be used in water or other corrosivemedia, we recommend coating.


5.2 SURFACE PROTECTION

Permanent magnets made of VACODYM and VACOMAX canbe used in normal ambient conditions (such as room temperature, humidity up to 50 %, no condensation) withoutspecial additional surface protection. However, the magnetsurface has to be coated for many applications. There arethree main reasons for this:

CORROSION PROTECTIONRE-permanent magnets are frequently exposed to chemical-ly aggressive media such as acids, alkaline solutions, salts,cooling lubricants or harmful gases and have to be pro-tected. In the case of VACODYM high humidity, dew forma-tion or sweat is already sufficient to cause corrosion. We the-refore recommend to handle VACODYM-magnets with suitedgloves on principle.

PROTECTION AGAINST MAGNETIC PARTICLESVACODYM and VACOMAX are sintered materials, thus it can-not be excluded that magnetic particles are found on thesurface. In certain applications (e.g. systems with small wor-king air gaps) loose magnetic particles may affect the func-tion and/or destroy the magnet assembly. Coating ensuresthat the magnets can be cleaned thoroughly and will be freeof all deposits.

HANDLING PROTECTIONMagnets are frequently mechanically stressed duringassembly or operation in an assembly. In some circumstan-ces, this may lead to chipping, sharp edges are a particularrisk.

Each application of VACODYM and VACOMAX must be chek-ked as to whether coating is necessary and how the surfaceis to be protected. We have tested the behaviour of our per-manent magnets under widely varying conditions and will bepleased to advise you on the appropriate coating for yourapplication.

8XX

6XX

VACODYM 7XX

Wei

ght l

oss

Exposure time (days)

Fig. 7:Weight loss of VACODYM magnets in a HAST-Test similar to IEC 68-2-66(130 °C; 95 % relative humidity; 2.6 bar in vapour)


5.3 TYPES OF COATINGS

The coatings can be divided into two basic groups: metallicand organic. To meet special requirements and on request,double coatings of metal/metal & metal/varnish and a num-ber of special coatings are available.

METALLIC COATINGSAs a rule, galvanic processes are used for metallic coating.Apart from our standard nickel or tin coating, on request weoffer double coating nickel + tin. In addition IVD (Ion VapourDeposition)-Aluminium coating is also possible.When selecting the type of metallic coating, the possibility ofgalvanic element formation in the assembly must be takeninto account, as long as dew formation cannot be excluded.

ORGANIC COATINGSFor this case we offer different spray coatings with excellentcorrosion protection characteristics. Cost-effective alternati-ves to metallic coatings are especially aluminium spray coa-tings as well as the newly developed VACCOAT epoxy resincoating.

5.4 DESCRIPTION OF THE COATINGS

The majority of all applications are covered by our coatings”galvanic tin”, ”galvanic nickel”, ”electro-painting” and ”IVDaluminium coating” as well as the recently introduced VACCOAT® spray coatings introduced. The properties of thecoatings complement one another.

All galvanic coating processes and the spray coatings areapplied at VACUUMSCHMELZE. The described properties canonly be achieved in a carefully controlled system which takesinto consideration the microstructure of the magnets, themechanical processing/machining, cleaning and coating.

IVD aluminium coating is performed by a subcontractorselected and qualified by VAC with great care. Appropriatequality assurance measures ensure continuity of quality inseries production.

Using the latest automating technology, all other coatings areapplied by VAC in-house cost-effectively and with highreproducibility as well as quality.

GALVANIC TIN

Galvanic tin coating provides good corrosion protectionagainst atmospheric influences, humidity as well as weakacids and alkaline solutions.

The tin coating applied at VAC is dense and free of intercon-nected pores. The typical coating thickness range for mag-nets is 15–30 µm. The finish of tin coating is silvery-whiteand slightly glossy.

No phase transitions occur between –40°C and the meltingpoint of 232°C. The deposition process is optimized by VACfor RE magnets especially to preclude hydrogen damage tothe surface of the magnet during coating positively.

Small parts can be coated economically in a barrel. Largerparts are galvanized in a rack. The decision on which methodto use is governed by the weight of the part and/or the geo-metry (typical nominal values: <25 g barrel; >25 g rack).

The special merits of tin coatings are their high resistance toenvironmental influences (e.g. 85°C/85 % relative humidity)as generally specified for electronic applications. Tin is high-ly ductile and is almost free of internal stresses over a widecoating thickness range, moreover the process is highly reli-able. There is no risk of cracking or flaking. Mechanicalstress does not lead to chipping but merely to deformation ofthe tin coating so that the magnetic material is still protec-ted safely.

After thorough cleaning the tin coating is free of all residuesand thus provides an ideal surface for many adhesives.


GALVANIC NICKEL

Galvanic nickel coatings can be used as an alternative to tinor as double coating in combination with tin.

On VACODYM, its protection is superior to a comparablecoating thickness of tin. The minimum coating thickness thatwe recommend for protection against corrosion is 10 µm fornickel coating in comparison with 15 µm for tin coating.

Galvanic nickel coatings are hard, abrasion-proof and can becleaned without difficulty and without residues. Thereforethese coatings have prevailed today, especially for cleanroom applications.

VAC has a special nickel coating process which suppliesoptically attractive semibright coatings. Compared withcustomary bright nickel methods, such as are frequentlyused for rare earth magnets, our process has the followingadvantages:

a) The coatings have high ductility and therefore show aclearly lower tendency to mechanical damage in the edgearea on impact of shock. This leads to more reliable pro-duction both in the plating process and during assembly.Even parts of 50 g in weight can still be coated by barrel pla-ting with suitable geometry. Coating in a rack is possible forheavier parts.

b) When glued, clearly better adhesive strengths are achie-ved than with bright nickel coating because of the increasedsurface roughness.

c) The process exhibits a very homogenous coating thickness distribution over a wide current density range, sothat the so-called “dog-bone-effect” (excessive coatingbuild-up in the edge/corner area) is minimized. Dimensionaltolerances for thin flat parts of ±50 µm (including machining)can thus be achieved reliably in production (comparable withgalvanic tin coating).

d) The risk of stress cracks under thermal loading is low.The reasons for this are the better ductility as well as theextremely low internal stresses of the coating.

All these properties make galvanic nickel a universal coatingfor RE permanent magnets covering many applications.

DOUBLE COATING NICKEL + TIN

Especially high corrosion resistance is attained when tin coating is applied on top of a layer of nickel. The lifetime ofthis double coating under environmental test conditions (e.g.85/85 test) is twice that of nickel or tin coatings of the samethickness. The surface properties are equivalent to those oftin coating.

IVD ALUMINIUM

IVD (= ion vapour deposition) aluminum ensures excellentcorrosion protection both in a humid climate and in exposu-re to salt spray. The cathodic protection by the aluminumcoating enables, for example, continuous use in water.Further, owing to the electrochemical protection provided bythe aluminium small imperfactions in the coating do notaffect the corrosion resistance in any perceivable way.

Since aluminum can be used in principle up to approx.500°C, all applications of RE permanent magnets are thuscovered.

The corrosion resistance of this coating is improved furtherby subsequent surface passivation.

Because of the high ductility of the coating, mechanicalloads only cause deformation of the coating similar to thatwith tin, without the protective effect being impaired bydamage to the coating. In comparison to electroplated zinclayers, which are also used as cathodic protection for Nd-Fe-B, the IVD-aluminium has the following advantages:

– extremely high temperature resistance– no hydrogen embrittlement during coating process– no formation of loose white rust in corrosive atmosphere– very good HAST resistance.

Small parts (up to 25 g) are coated in a cost effective barrelprocess. Heavy parts are handled as rack goods. Process-included contact marks are prevented by special handling.


ALUMINIUM SPRAY COATING VACCOATThe stove-enamel finish filled with aluminium flakes showssimilar resistance to climatic or salt spray tests like IVD alu-minium. Even magnets with a coating thickness of only 5 µmwithstand longterm autoclave and salt spray tests.

Compared to other spray coatings our new coating providesa superior edge protection. The coating is suitable for appli-cations up to utilization temperatures of up to 180°C in con-tinuous application.

Due to the excellent hardness of this stove – enamel finish(typical 6-8 H pencil hardness) Al-spray coating is not sensitive to mechanical damage. For parts > 10 g thecoating is applied in an automatic spray coating machinewhich ensures high reproducibility and process safety aswell compliance with strict dimensional tolerances. An auto-matically controlled and very cost-effective barrel-platingprocess is available for small parts.

The Aluminium spray coating is also of great benefit in thecoating of complete magnet systems. As a rule, any residu-al adhesive can be permanently covered by our spray coa-ting. In contrast to IVD aluminium coating this coating is notelectrically conductive.

EPOXY SPRAY COATING VACCOATThis coating recently developed in-house sets new stan-dards regarding corrosion protection, temperature resi-stance, coating application and the subsequent processingof coated magnets into systems. When cured VACCOAT20011 provides high-grade corrosion protection on VACODYM. At the same time when the coating film is not yet

cured it can be a high-strength adhesive. A high-strengthadhesive bond forms during stoving giving a shear strengthof typically >15 N/mm2. At the same time the system is pro-tected effectively from corrosion by the coating. The attai-ned corrosion protection is comparable to aluminium spraycoating. The stoved coating has a pencil hardness of at least4H and can be thermally stressed to approx. 200°C.Optically high-quality finish layers of between 5 µm and 40µm can be applied in one operation. The coating colour isselectable (the standard colour is black). The coating is abra-sion-resistant and exhibits very good electrical insulationbehaviour. Similarly to aluminium spray coating the layerscan be applied to the magnets either in a continuous auto-matic process or in a barrel-plating process.

Micrograph of coverage with VACCOAT 10047 at the edge of a magnet


TEMPORARY CORROSION PROTECTION/SURFACE PASSIVATIONTo protect uncoated magnets temporarily, e.g. during trans-port or storage, we have developed a passivation method.This protects our RE-magnets, including the more corrosionsensitive VACODYM, sufficiently against temporary environ-mental influences such as a rise in humidity. With this standard procedure our magnets can be stored under normal ambient conditions providing condensation can beexcluded.

PROPERTY PROFILE OF DIFFERENT COATINGSTable 5 compares the properties of the most important coatings and should be used as a guideline when selectingsurface protection for an application. It gives the minimumlayer thickness of the various coatings and ensures adequa-te corrosion protection in the majority of applications. Tomeet more stringent requirements on corrosion protection,the layer thickness must be adjusted accordingly. Pleasenote that improper handling may well harm the coating.

Table 5: SURFACE COATINGS

Surface Method Min. layer Colour Hardness Resistance Temperature Typical

thickness for to range application

corrosion examples

protection

tin (Sn) galvanic > 15 µm silver HV 101) humid atmosphere, < 160 °C electric motors,bright solvents sensor technology

mechanical engineering

nickel (Ni) galvanic > 10 µm silver HV 3501) humid atmosphere, < 200 °C clean-rooms,semibright solvents, small-sized motors,

cooling lubricants linear motors,UHV undulators

Ni +Sn galvanisch Ni > 5 µm silver HV 101) humid atmosphere, < 160 °C hot water meters,Sn > 10 µm bright solvents, use in fuel (biodiesel)

cooling lubricants,salt spray test

Aluminium IVD > 5 µm silver semibright HV 201) humid atmosphere, < 500 °C electric motors,passivated (chromium VI salt spray test, sensor technology,

free), yellow solvents aeronautic semibright applications(yellow chromated)

aluminium automatic > 5 µm yellow > 4H2) humid atmosphere, < 180 °C electric motors,spray coating spray coating semibright spray test, generators,VACCOAT toxic gas test, sensor technology,10047 solvents linear motors,

motorcars

epoxy automatic > 10 µm black3) 4H2) humid atmosphere, < 200 °C segmented magnet spray coating spray coating salt spray test, systems, electric motors,VACCOAT toxic gas test, linear motors,20011 solvents motorcars

1) Vickers hardness (nominal values) 2) Pencil hardness 3) other colours possible


For shaped parts with more complex geometry we usuallygive a maximum and a minimum envelope curve; the con-tour of the die-pressed part is within this curve.

The length tolerances for parts cut from blocks (TP resp. HRquality) are ±0.1 mm. On request even tighter tolerancescan be met by grinding. If no tolerances are specified, wesupply according to DIN ISO 2768 mK.

6. FORMS OF SUPPLY

6.1 TYPES OF MAGNETIZATION

Magnets made of VACODYM and VACOMAX can be suppliedin the magnetized or non-magnetized state. Normally thepoles are not marked.

Owing to the magnetic anisotropy of VACODYM and VACO-MAX the parts are magnetized along certain preferred direc-tions relative to the geometry of the part. The most commonpole configurations are shown on the right.

Our experts with in-depth know-how will be pleased to ans-wer any questions on magnetization techniques. For the deli-very of magnetized parts we have developed various packa-ging methods which can – if necessary and in compliancewith the rigorous IATA regulations – be modified to meetindividual customers’ requirements for airfreight.

6.2 DIMENSIONAL TOLERANCES

The pole surfaces of die-pressed sintered magnets made ofVACODYM or VACOMAX usually have to be ground. The tole-rance after grinding is normally ±0.05 mm; values of ±0.02mm are possible.

The dimensions perpendicular to the direction of pressingare largely determined by the dies and do not normally requi-re machining (netshape). Typical tolerances for the sides ofdie pressed parts are:

Nominal dimensions perpendicular Tolerance (mm)*to the direction of pressing (mm)

up to 7 ±0,10 . . . ±0,20

7 – 15 ±0,15 . . . ±0,30

15 – 25 ±0,25 . . . ±0,40

25 – 40 ±0,30 . . . ±0,60

40 – 60 ±0,45 . . . ±0,90

60 –100 ±0,80 . . . ±1,50

100 –150 ±1,50 . . . ±2,50

* precise data on request

Pole arrangementstop view side view

for rods:and rings:axial

for rings:radial

for rings:diametral

for segments:diametral

NETSHAPE PARTSBy leaving out the grinding process, particularly competitve-ly priced magnets with a pole surface of up to approx. 6 cm2

can be die-pressed. Perpendicular to the direction of pres-sing, these netshape magnets exhibit the tolerances as sta-ted. In the direction of pressing due to special die-pressingand sintering methods, thickness tolerances of typically± 0.2 mm are met at individually measured points withoutsubsequent grinding. Preferred shapes are cuboids and seg-ments with typical thicknesses in the range of 2.2 to 8.0mm. Our experts will gladly assist in the layout of the mag-net geometry and the tolerance of netshape magnets.

Should these surfaces require machining the general tole-rances to DIN EN 2768 mK can usually be met.


(LxW)

(LxW)

(LxW)

(LxW)

DIMENSIONS OF DIE-PRESSED VACODYM AP-MAGNETS(AXIAL-FIELD PRESSED)CRITERIA FOR ECONOMIC MAGNET GEOMETRIES

Shape Type Sketch Dimensions Dimensions Remarkseconomic possible economic

Ring AP D �120 mm D �180 mm onlyd �3 mm 1 mm �T �70 mm thickness T ground(D-d)/2 = w �3 mm A <15000 mm2

d/D �0,6D/10 �T �D/2A <9500 mm2

Disk AP D �100 mm D �140 mm onlyD/10 �T �D/2 1 mm �T �70 mm thickness T ground

Cuboid AP L �120 mm L �150 mm onlyLxW �9500 mm2 LxW �15000 mm2 thickness T groundT �55 mm 1 mm �T �70 mmT �0,15 �� L/W �5Re �0,1 ��

Loaf AP L �120 mm L �150 mm thicknessW �50 mm 2 mm �H �55 mm T and width W groundT �0,6 H2 mm �H �20 mm0,5 �L/W �5Re �0,1 ��

Arc- AP L �120 mm L �150 mm thicknessSegment W �50 mm 1,5 mm �T �50 mm T and width W ground

2 mm �T 20 mm ß �150°ß �80° W �70 mm0,5 �L/W �3Re �0,1 ��

Shaped AP W �45 mm H, W �150 mm onlyPart H �35 mm A �15000 mm2 thickness T ground

A �1500 mm2 1 mm �T �70 mmW/H �31,5 mm �T �30 mmT �0,1 ��ARe �0,1 ��A



Cuboid TP W �70 mm W �110 mm Thickness T(HR) 2 mm �T �100 mm 1 mm �T �140 mm cut or ground

10 mm �H �55 mm TxW � 13000 mm2

W/H �2,5 H �80 mmRe �0,1 ��(TxW)

Ring TP 8 mm �D �70 mm 6 mm �D �120 mm only outer diameter D ground(diametral) d �3 mm d �1 mm

(D-d)/2 = w �2 mm w �1,5 mm0,1 �d/D �0,65 0,1 �d/D �0,83 mm �H �55 mm 2 mm �H �80 mmH �5w H �8w

Disk TP 8 mm �D �70 mm 5 mm �D �120 mm only outer diameter D ground(diametral) 5 mm �H �55 mm 2 mm �H �80 mm

H �D/4

DIMENSIONS OF DIE-PRESSED VACODYM TP-MAGNETS(TRANSVERSE FIELD PRESSED)CRITERIA FOR ECONOMIC MAGNET GEOMETRIES


Cuboid HR W �110 mm W �110 mm unprocessed with aT �250 mm T �800 mm 6 mm � contour tolerance,A �7000 mm2 A �7000 mm2 Re approx. 5 mm

Disk, HR D �70 mm D �90 mm unprocessed with arod L �250 mm L �800 mm 6 mm � contour tolerance

Analogue shapes and dimensions also available in VACOMAX with moderate restrictions (appropriate to the magnet quality).

DIMENSIONS OF ISOSTATICALLY-PRESSED VACODYM HR-MAGNETS(UNTREATED, UNPROCESSED)CRITERIA FOR ECONOMIC MAGNET GEOMETRIES


7. GLUEING RE MAGNETS

The majority of RE magnets produced by VAC are assembledinto magnet systems using adhesives. When selecting anadhesive the following should be considered:

– static and dynamic load– thermal load (time-span/frequency/temperature range)– thermal expansion of both partners– size of glueing area– corrosive load

(resistance of adhesive to atmosphere and chemicals)– quality of glueing surfaces (coating, roughness etc.)– material matching regarding electrochemical potentials

(corrosion due to voltaic cell formation)– thickness of glueing gap

In the following we offer some advice on adhesives andaccumulated bonding methods for magnets based on theexperience at VAC over the years:

a) Adhesives with acid content must not be used with REmagnets, particularly not with VACODYM. Acidic products inconnection with humidity lead to rapid decomposition of themagnet material at the interface adhesive/magnet and willdamage the bond. Such adhesive must even be avoidedwhen magnets are coated and especially if varnished.

b) When bonding large surfaces with iron or other substra-tes the coefficients of thermal expansion of the RE magnetmaterials must be taken into account. In particular, in con-nection with VACODYM, which has a negative coefficient ofthermal expansion (-1 x 10-6/K) perpendicular to the direction of magnetization, and thus, as a rule, parallel to thebonding surface, stresses build up due to strains resultingfrom fluctuations in temperature which the bond mustabsorb. Our team of magnet experts will be pleased to advise you on this matter.

c) When preparing the RE magnets for bonding, sand blasting should be avoided. This processing step might leadto a loosening of the microstructure on the surface of thesintered magnets. Our permanent magnets are supplied inthe state ”ready for bonding”. The passivation applied aftercleaning provides a suitable base for most adhesives.However, if a pre-treatment step directly prior to bonding isconsidered important then we recommend users subse-quently clean the bonding surface with a solvent, such asacetone or benzine.

d) An adhesive selected for an uncoated magnet is notautomatically suitable for a coated magnet. For surfaceswhich are particularly difficult to bond, e.g. nickel plating, themarket offers tailor-made adhesives. With painted magnets care must be taken to ensure that the adhesivedoes not attack the painting or cause blisters. VAC have in-depth experience with a large number of adhesives and themost commonly used surfaces, and will be pleased to helpcustomers select the right adhesive for their application.

8. INTEGRATED MANAGEMENT SYSTEM

Documentation of the quality, environmental and industrialsafety management system in a corporate quality manage-ment system was integrated in the financial year 2003.Currently it is based on the following set of standards:

• DIN EN ISO 9001:2000• ISO/TS 16949:2002• DIN EN ISO 14001:2005• OHSAS 18001:1999• ISO/IEC 17025:2005

8.1 QUALITY MANAGEMENT

Quality is an essential aspect of our corporate policy. In orderto reliably realise the high quality of our products and services based on a quality management system certified inaccordance with DIN EN ISO 9001 and ISO/TS 16949 we setgreat store by close cooperation of all operational divisions.Further development of our Total Quality Management(TQM), introduced as early as 1994, has been continual, andit is orientated towards business excellence models and ourcorporate goals.


The most important target of all our quality management-related actions is fulfilling all customers‘ expectations andgreat customer satisfaction, both internally and externally.

To further optimise VAC-internal processes – with the primary objective of further reducing costs – the Six-Sigmaanalysis was introduced in all our operations in the fiscalyear 2002.

We achieved the product quality demanded by our customers by the definition and implementation of targetedQM measures during product and process planning, strictlycontrolled raw material procurement and test sequencesintegrated in the process using a statistical process control(SPC). Compliance with relevant process feasibilities (cpk-values) is a matter of course for us as is documenting theessential magnetic and geometric properties. For complexetasks or for especially stringent requirements we define aquality assurance programme jointly developed with ourclients. By qualified technical advice we help to design andrealise quality and cost-effective products and services; atthe request of our customers we also conclude quality assu-rance agreements (QAA).

8.2 TECHNICAL TERMSAND CONDITIONS OF SALE

Like most other permanent magnet materials, sintered magnets of rare earth alloys are brittle. Although VACODYMis mechanically more stable than VACOMAX, for this material it is also impossible to exclude that magnets exhibitfine hair-line cracks or chipped edge defects. This does notsignificantly influence the magnetic or mechanical propertiesof the concerned parts.

The exchange of critical samples has in serial productionproved itself for the test and definition of the visual quality ofmagnets. Unless we have a special agreement with ourcustomers, in our quality inspection we allow mechanicalsurface damages (flaking, edge and corner chippings) up toa total of max. 2% per pole surface. The permissible chippings are to be defined jointly with the customer or usingcritical samples for small magnets with a pole surface of<20 mm2. Up to a third of the concerned cross-sectionalarea of fine hair-line cracks will not be rejected as long asthe mechanical stability in accordance with the intended useis met.


Under normal manufacturing conditions, slight amounts ofmagnetic dust and material debris may adhere to finished, inparticular to uncoated and magnetized parts. If this is notacceptable, a coating resp. individual packing is to be pro-vided.

The final inspection of our magnets and assemblies is normally based on a standardized fixed sampling rate.Unless otherwise agreed with customers we test to DIN ISO2859-1, AQL 0.65 with the c = 0 acceptance number. Byconsistently employing the latest quality assurance techni-ques we are frequently able to agree to even tighter toleran-ces on request. For instance, for products for the automoti-ve industry an additional process capability value of cpk

> 1.33 is specified for geometric characteristics.

Acceptance conditions for special magnetic properties callfor clearly defined test procedures and reference samples.A further prerequisite, in particular for VACOMAX, is that theparts are supplied in the magnetized state.

With miniature magnets – dimensions less than approx.2 mm – reduced magnetization is to be expected owing tosurface effects and depending on the position of the workingpoint. If you require more information, please contact us.

8.3 ENVIRONMENTAL AND SAFETY MANAGEMENT

We are committed to protecting our environment and tousing the available natural resources as economically aspossible. This principle applies to our production processesas well as to our products. Already at the development stageof our products we take potential damage to the environ-ment into consideration. It is our aim to avoid or reduce to aminimum any harmful effects – our precautions frequentlyexceed those stipulated by law.

VAC environmental management assures that the standardof EN ISO 14001 is effectively put into practice. Technicaland organisational means for this purpose are regularlyaudited and are subject to continuous improvement.

A further goal in the design of our products, processes andworkplaces is the health and safety protection of our staffand our partners based on OHSAS 18001. Here the appli-cable laws, standards and regulations are taken intoaccount together with state-of-the-art expertise on occupa-tional medicine and industrial science.


9. SAFETY GUIDELINES FOR HANDLINGMAGNETS MADE OF VACODYM AND VACOMAX

Magnetized rare-earth magnets of VACODYM and VACOMAXexhibit high field and exert strong, attractive forces on ironand other magnetic parts in their vicinity. Consequently, theymust be handled with care to avoid damage. Owing to theirstrong magnetic forces there is a risk of injury when hand-ling larger magnets. They should always be manipulatedindividually or with the aid of jigs. We recommend protectivegloves be worn as well as for handling of uncoated VACO-MAX and Ni-coated parts, especially for people with allergiesto metals.

The high fields can change or damage the calibration of sensitive electronic devices and measuring instruments.Please note that magnetized magnets must be kept at a safedistance (e.g. over 2 m) from pacemakers, computers,monitors and all magnetic data storage media (such as floppy disks, credit cards, audio and video tapes etc.).

On impact rare-earth magnets may develop large sparks.Never handle them in an explosive atmosphere.

Unprotected VACODYM and VACOMAX magnets must not beexposed to hydrogen. Its adsorption destroys the microstruc-ture and leads to disintegration. The only effective protectionis gas-proof encapsulation of the magnets.

Machining magnets requires special safety precautions forthe grinding slurry. Especially for VACOMAX legal regulationsregarding the handling of Co-containing dust have to beobserved. The EG Safety Data Sheets provide more compre-hensive information on the safety aspects involved whenhandling VACODYM and/or VACOMAX magnets.


10. APPENDIX

10.1 TECHNICAL PRINCIPLES AND TERMS

10.1.1 HYSTERESIS LOOP

The behaviour of a magnetic material in a magnetic field ischaracterized by the correlation between magnetic flux den-sity (induction) B and magnetic field strength H (B(H) hysteresis loop). The same correlation can be described bythe polarization J (J(H) hysteresis loop, Fig. I). The flux den-sity B and the polarisation J are given by

B = µ0H + J.

The first quadrant of the hysteresis loop describes the magnetization behavior of the material: when applying amagnetic field H the flux density B of a non-magnetizedmaterial varies along the virgin curve (cf. Fig. I).

When all magnetic moments are oriented parallel to theexternal magnetic field, the polarization J is at its maximumvalue, the saturation polarization Js (J = Js = const.). The fluxdensity B however, continues to increase linearly with thefield strength H.

The minimum field strength required to attain saturationpolarization is referred to as the saturation field strength Hs.If – in the magnetized state – the magnetic field strength isreduced, the flux density changes in accordance with thehysteresis loop and at H = 0 attains residual flux density(remanence) Br (intersection of the hysteresis loop with ordi-nate). In the strongly anisotropic RE permanent magnetsdescribed here the remanence Br is in the same order ofmagnitude as the saturation polarization Js:

Br ≈ Js

10.1.2 DEMAGNETIZATION CURVE

The second quadrant of the hysteresis loop describes thedemagnetization behaviour of the material. The most impor-tant characteristic terms of permanent magnets which areoperated exclusively in opposing fields (see “working point”for further details) are determined from the demagnetizationcurve.

The most important characteristic terms of a permanentmagnet are:

– RemanenceThis is obtained as described above from the inter-section of the hysteresis loop and the ordinate (at H = 0 we have Br = Jr).

– CoercivityThe field strengths at which the flux density B or the polarization J reach zero are referred to as coercivities of flux density HcB or polarization HcJ respectively (intersection of the hysteresis loop B(H) and J(H) withthe abscissa).

– Energy DensityThe product of the related values from flux density B and field strength H can be attained from any pointalong the demagnetization curve (see Fig. II). This product represents the energy density and passes through a maximum value between remanence and coercivity, the maximum energy density (BH)max. As a rule this value is used to grade permanent magnet materials.

– Working PointThe magnetic field originating from the poles of a permanent magnet has a demagnetizing effect as it is in the opposing direction to polarization J. The operatio-nal state of a permanent magnet is consequently always in the range of the demagnetization curve.The pair of values (Ba, Ha) applying to the relevant operational state is referred to as working point P.The position of P depends on the geometry of the magnet or in magnetic circuits with soft magnetic flux conductors on the ratio of air-gap length to magnet length. P is obtained from the intersection of the working or shearing lines with the B(H) curve (see Fig. III).

The best use of a permanent magnet in static systems is when the working point P lies in the (BH)max point.Shearing in the magnetic circuit should practically be selected so that the working point is just at this position or, preferably, just above it, i.e. is in slightly lower opposing field strengths.


For dynamic systems with changing operating straight lines (e.g. motors) shearing should be selected so that the permanent magnet’s working point remains within the straight line range of the demagnetiza-tion curve. The reason is to ensure great stability from outside field and temperature influences (see Fig. III p. 57). The working point shifts to a higher opposing field strengths, e.g. from P1 to P2 if the air gap in a magnet system is increased. If the change is reversed the original working point P1 can only be reproduced ifP2 is within the linear section of the demagnetizationcurve. However, if P2, as shown in Fig. III, is below theknee of the demagnetization curve irreversible lossesarise. The working point shifts to P3 on an inner returnpath with a correspondingly lower flux density. The riseof this return path is referred to as permanent perme-ability.

10.1.3 INFLUENCE OF TEMPERATURE

The demagnetization curves of permanent magnets are tem-perature dependent.

This dependence is characterized by the temperature coeffi-cients of the remanent flux density TC(Br) and the coercivityTC(HcJ):

A change in temperature causes the working point to shift onthe working line (see Fig. IV p. 57). As long as the workingpoint stays within the linear region of the demagnetizationcurve, the changes in flux density are reversible, i.e. aftercooling the flux density returns to its original value. In allother cases any change in flux density is irreversible (irre-versible magnetic losses) and can only be cancelled out byremagnetization.

To avoid irreversible changes in the flux density through temperature fluctuations, the working point must remain

within the linear section of the demagnetization curve overthe entire temperature range in which the magnet is to beused.

A permanent magnet can be completely demagnetized byheating to temperatures above the Curie temperature Tc.After cooling to the initial temperature the old state of mag-netization can be reproduced by magnetizing again providingheating has not caused changes in the microstructure. It fol-lows that thermal demagnetization is only possible withmagnets made of VACODYM. Here the Curie temperature iswithin a range where changes in the microstructure do notoccur. In contrast thermal demagnetization may not be performed on VACOMAX because the range of Curie tem-perature in these alloys is substantially higher and at morethan 700°C phase transitions occur which may destroy the permanent magnet properties irreversibly.

TK(Br) = ––– · ––– · 100 (%/K)

TK(HcJ) = ––– · ––––– · 100 (%/K)

1 dBr

Br dT

1 dHcJ

HcJ dT

Unit and SI-units1) ConversionSymbol table

flux density B T (Tesla) 1 T = 1 Vs/m2 = 10 kG (Induktion) (Kilogauss)

Polarization J T (Tesla) s. flux density B

Magnetic field A/m 1 A/cm = 0,4 � Oe strenght H � 1,257 Oe (Oersted)

Energy density kJ/m3 1 kJ/m3 = 0,126 106 MGOe(BH)max

Max. energy product

Magnetic Wb (Weber) 1 Wb = 1 Vs = flux � 108 Mx (Maxwell)

1) Basic units in SI-systems: meter, kilogram, second, Ampere. The units Gauss, Oested or Maxwell in the conversation table refer to the cgs- or Gaussian system with the basic units centimeter, gram and second.

10.1.4 MAGNETIC SIZES AND UNITS

The most important magnetic sizes, their units and conver-sions are as follows:


10.2 CONVERSION TABLE CELSIUS – FAHRENHEIT

°C °F °C °F °C °F °C °F °C °F °C °F–20 : – 4 50 : 122 120 : 248 190 : 374 260 : 500 330 : 626–10 : 14 60 : 140 130 : 266 200 : 392 270 : 518 340 : 644

0 : 32 70 : 158 140 : 284 210 : 410 280 : 536 350 : 66210 : 50 80 : 176 150 : 302 220 : 428 290 : 55420 : 68 90 : 194 160 : 320 230 : 446 300 : 57230 : 86 100 : 212 170 : 338 240 : 464 310 : 59040 : 104 110 : 230 180 : 356 250 : 482 320 : 608

Fig. I Fig. III

Fig. II Fig. IV

virgin cu

rve


Material CROVAC CROVAC CROVAC CROVAC MAGNETO- VACOZET SEMIVAC SENSOR-12/160 16/160 12/500 16/550 FLEX 35U 258 90 VAC

Main components FeCrCo CoFeV CoFeNi FeCrCoNiMo FeNiAlTi

Variant isotrop • •

anisotrop • • • • • •

Forms of wire • • •

supply strip • • • • • • •

wire • •

strip • • • • •

Remanence (T) 0,85-0,95 0,80-0,90 1,15-1,25 1,10-1,20 0,80-0,90 1,30-1,50 0,90-1,30 1,30-1,60

Coercivity(kA/m) 36-42 39-45 47-55 53-61 25-30 2,0-3,2 4-10 1,5-2,6

Coercivity tolerance(kA/m) +/- 2 +/- 2 +/- 3 +/- 3 +/- 1,5 +/- 0,15 +/- 0,5 +/- 0,15

Energy density(BH)max (kJ/m3) 13 15 35 37 12 2,5 5 3

Density (g/cm3) 7,6 8,1 8,1 7,85 7,65

Curie temperature (°C) 640 700 800 700 630

Max. applicationtemperature (°C) 480 500 400 450 300

TK (BR) -25°C - 250°C (%/K) – 0,03 -0,01 – – –

Therm. expansion(RT-100°C) (10-6/K) 10 11 11 – –

El. resistivity(�mm2/m) 0,7 0,65 0,15 – –

Vickers hardness HV as rolled 330 480 400 – –

soft annealed 230 – – – –

hard treated 480 900 600 700 600

Tensile strenght RM as rolled (MPa) 1150 1850 1700 – –

soft annealed (MPa) 620 – – – –

heart treated (MPa) – – 1500 – –

Elongationas rolled (%) 2 1,5 3 – –

soft annealed (%) 20 – – – –

heart treated (%) – – 0,5 – –

The elongation is given for AL50 (strips) rsp. AL100 (wire).The above mechanical properties are given as related values.

A detailed description of these materials is included in our leaftet PD-003, which is available on request.

11. DUCTILE PERMANENT MAGNET ALLOYS AND SEMI-HARD MATERIALS(MAGNETIC AND MECHANICAL PROPERTIES)


VACUUMSCHMELZE SALES OFFICE SINGAPORE

300 BEACH ROAD#31-03 THE CONCOURSESINGAPORE 199555PHONE +65 6391 2600FAX +65 6391 [email protected]

VAC SALES USA LLC

2935 DOLPHIN DRIVE SUITE 102 42701 ELIZABETHTOWN KY / USA PHONE +1270 769-1333 FAX +1270 765 3118 [email protected]

ADVANCED MATERIALS – THE KEY TO PROGRESS

PD 002 - VACODYM/VACOMAX · EDITION 2007

Published by VACUUMSCHMELZE GmbH & Co. KG, Hanau© VACUUMSCHMELZE 2007. All rights reserved.

As far as patents or other rights of third parties are concerned, liabilityis only assumed for products per se, not for applications, processes andcircuits implemented within these products. The information describesthe type of product and shall not be considered as assured characte-ristics. Terms of delivery and rights to change design reserved.

VACUUMSCHMELZE GMBH & CO. KG

GRÜNER WEG 37D-63450 HANAU / GERMANYPHONE +49 6181 38 0FAX +49 6181 38 [email protected]

Documents

RARE-EARTH VACODYM·VACOMAX permanenti/Magneti... · Alongside analytical processes, we utilize sophisticated computer programs to analyze and design magnet systems. These include