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Rare Earth Magnets

Rare Earth Magnets Neodymium Iron Boron (Ndfeb)

Neodymium magnets (Nd-Fe-B) are composed of neodymium, Iron, Boron and a few transition metals. Samarium Cobalt magnets (SmCo) are composed of samarium, cobalt and iron. These rare earth magnets are extremely strong for their small size, metallic in appearance and found in such simple shapes as rings, blocks and discs.


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Manufacturing Rare Earth Magnets :

In general, the elements are melted together and milled into a power that is dry-pressed to shape in the presence of a magnetic field. The material is then inte-red, aged, ground to dimension, magnetizem and tested. They are called "rare earth" magnets because the elements of neodymium and samarium are classified as such in the lanthanides section of the Periodic Table of the Elements.

Neodymium magnets (Nd-Fe-B) are composed of neodymium, Iron, Boron and a few transition metals. Samarium Cobalt magnets (SmCo) are composed of samarium, cobalt and iron. These rare earth magnets are extremely strong for their small size, metallic in appearance and found in such simple shapes as rings, blocks and discs.

Manufacturing Rare Earth Magnets

In general, the elements are melted together and milled into a power that is dry-pressed to shape in the presence of a magnetic field. The material is then inte-red, aged, ground to dimension, magnetizem and tested. They are called "rare earth" magnets because the elements of neodymium and samarium are classified as such in the lanthanides section of the Periodic Table of the Elements.

Neodymium Attributes of Neodymium
  • Very high resistance to demagnetization
  • High energy for size
  • Good in ambient temperature
  • High priced
  • Material is corrosive and should be coated for long term maximum energy output
  • Low working temperature for heat applications Application of Neodymium

Magnetic separator, linear actuators, microphone assemblies, servo motors, DC motors (automotive starters), Computer rigid disc drives, hammer bank printers, and speakers.

Samarium Attributes of Samarium
  • High resistance to demagnetization
  • High energy (magnetic strength is strong for its size)
  • Good temperature stability
  • Expensive material (cobalt is market price sensitive
Applications of Samarium :
  • Computer disc drives
  • Sensors
  • Traveling wave tubes
  • Linear actuators
  • Satellite systems
  • Motors where temporary stability is vital
Applications of Samarium :
Rare Earth Tolerances

For as pressed material, tolerance on the thickness (direction of magnetization) is +/- .127mm. Other Dimensions are +/- 2.5% or +/-.254mm, whicherer is greater.

According to Magnet Materials Producers Association (MMPA) standards, visual imperfections such as hairline cracks, porosity and minor chips are commonly found in sintered metallic magnets. A chipped edge is considered acceptable if no more than 10% of the surface is missing. Cracks are acceptable as long as they do not extend across more then 50% of of pole surface.

Rare Earth Machining

Since rare earth magnet material is prone to chipping and cracking, it does not lend itself to conventional machining methods. It can, however, be abrasively ground, but only with the use of liberal amounts of coolant. The coolant minimizes heat fracturing and the risk of fires caused by oxidized grinding dust.

Rare Earth Magnetizing and Handling

Rare earth magnets are very brittle and very strong magnetically. Therefore, it is crucial to handle these magnets with extreme care to avoid personal injury and damage to the magnets. Fingers can be severely pinched between attracting magnets. Magnets can be chip if allowed to "Jump at" an attracting object. It is highly recommended that when constructing rare earth magnetic assemblies, they be magnetized after assembly.

Typical magnetic and Physical Properties of Rare Earth Magnet Material :
Magnetic Properties For Nd-Fe-B Magnets
Properties Unit Remanence Br Coercive force Hcb Intrinsic Coercive force Hcj Max.Energy Product(BH) max Temperature Coefficient(20°C-TW) Density D Curie Temperature Max Working Temperature TW
αBr αHcj
Grade kGs T kA/m KOe KOe kA/m MGOe KJ/m³ -%°C -%°C g/cm³ °C °C
N35 11.7-12.1 1.7-1.21 >=10.9 >=868 >=12 >=955 33-36 263-287 0.12 0.6 >=7.4 310 80
N38 12.1-12.5 1.21-1.25 >=11.3 >=899 >=12 >=955 36-38 287-303 0.12 0.6 >=7.4 310 80
N40 12.5-12.8 1.25-1.28 >=11.6 >=923 >=12 >=955 38-41 303-326 0.12 0.6 >=7.4 310 80
N42 12.8-13.2 1.28-1.32 >=11.6 >=923 >=12 >=955 41-43 326-342 0.12 0.6 >=7.4 310 80
N45 13.2-13.8 1.32-1.38 >=11.0 >=876 >=12 >=955 43-46 342-366 0.12 0.6 >=7.4 310 80
N48 13.8-14.2 1.38-1.42 >=11.0 >=876 >=12 >=955 46-49 366-390 0.12 0.6 >=7.4 310 80
N50 13.9-14.6 1.39-1.46 >=10.5 >=836 >=12 >=955 47-51 374-406 0.12 0.6 >=7.4 310 80
N52 14.2-14.7 1.42-14.7 >=10.5 >=836 >=12 >=955 49-53 399-422 0.12 0.6 >=7.4 310 80
35M 11.7-12.1 1.17-1.21 >=10.9 >=868 >=14 >=1114 33-36 263-287 0.11 0.6 >=7.4 320 100
38M 12.1-12.5 1.21-1.25 >=11.3 >=899 >=14 >=1114 36-38 287-303 0.11 0.6 >=7.4 320 100
40M 12.5-12.8 1.25-1.28 >=11.6 >=923 >=14 >=1114 38-41 303-326 0.11 0.6 >=7.4 320 100
42M 12.8-13.2 1.28-1.32 >=12.0 >=955 >=14 >=1114 41-43 326-342 0.11 0.6 >=7.4 320 100
45M 13.2-13.8 1.32-1.38 >=12.0 >=955 >=14 >=1114 43-46 342-366 0.11 0.6 >=7.4 320 100
48M 13.8-14.2 1.38-1.42 >=12.0 >=955 >=14 >=1114 46-49 366-390 0.11 0.6 >=7.4 320 100
35H 11.7-12.1 1.17-1.21 >=10.9 >=868 >=17 >=1353 33-36 263-287 0.11 0.6 >=7.4 320-340 120
38H 12.1-12.5 1.21-1.25 >=11.30 >=899 >=17 >=1353 36-38 287-303 0.11 0.6 >=7.4 320-340 120
40H 12.5-12.8 1.25-1.28 >=11.6 >=923 >=17 >=1353 38-41 303-326 0.11 0.6 >=7.4 320-340 120
42H 12.8-13.2 1.28-1.32 >=12.00 >=955 >=17 >=1353 41-43 326-342 0.11 0.6 >=7.4 320-340 120
45H 13.2-13.8 1.32-1.38 >=12.00 >=955 >=17 >=1353 43-46 342-366 0.11 0.6 >=7.4 320-340 120
48H 13.8-14.2 1.38-1.42 >=12.00 >=955 >=17 >=1353 46-49 366-390 0.11 0.6 >=7.4 320-340 120
33SH 11.3-11.7 1.13-1.17 >=10.50 >=835 >=20 >=1592 31-33 247-263 0.10 0.6 >=7.4 340-400 150
35SH 11.7-12.1 1.17-1.21 >=10.9 >=868 >=20 >=1592 33-36 263-287 0.10 0.6 >=7.4 340-400 150
38SH 12.1-12.5 1.21-1.25 >=11.30 >=899 >=20 >=1592 36-38 287-303 0.10 0.6 >=7.4 340-400 150
40SH 12.5-12.8 1.25-1.28 >=11.6 >=923 >=20 >=1592 38-41 303-326 0.10 0.6 >=7.4 340-400 150
42SH 12.8-13.2 1.28-1.32 >=12.00 >=955 >=20 >=1592 41-43 326-342 0.10 0.6 >=7.4 340-400 150
30UH 10.8-11.3 1.08-1.13 >=10.20 >=812 >=25 >=1990 28-31 223-247 0.10 0.6 >=7.4 340-400 180
33UH 11.3-11.7 1.13-1.17 >=10.50 >=835 >=25 >=1990 31-33 247-263 0.10 0.6 >=7.4 340-400 180
35UH 11.7-12.1 1.17-1.21 >=10.90 >=868 >=25 >=1990 33-36 263-287 0.10 0.6 >=7.4 340-400 180
38UH 12.1-12.5 1.21-1.25 >=11.30 >=899 >=25 >=1990 36-39 287-303 0.10 0.6 >=7.4 340-400 180
30EH 10.8-11.3 1.08-1.13 >=10.20 >=812 >=30 >=2387 28-31 223-247 0.10 0.6 >=7.4 340-400 200
33EH 11.3-11.7 1.13-1.17 >=10.50 >=835 >=30 >=2387 31-33 247-263 0.10 0.6 >=7.4 340-400 200
35EH 11.7-12.1 1.17-1.21 >=10.90 >=868 >=30 >=2387 33-36 263-287 0.10 0.6 >=7.4 340-400 200

NOTE:
  • The above-mentioned data of magnetic parameters and physical properties are in room temperature.
  • The maximum working temperature of magnet is changeable due to ratio length and diameter and environmental factors.
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