Neodymium bonded magnets (Nd-Fe-B)

Neodymium bonded magnets (Nd-Fe-B), just as neodymium sintered magnets, achieved a big market success. In the production process, Nd2Fe14B based compound magnetic powder is bonded with a plastic. A type of the bonding plastic is selected according to the foreseen method of magnets forming. For high-pressure moulding (pressing) applied are chemically set plastics, e.g. epoxy resin, whereas for injection moulding, thermoplastic, e.g. nylon. Magnets manufactured by use of both methods are characteristic of big repeatability of magnetic properties, very tight dimensional tolerance and good quality of surface. A type of the applied bonding plastic determines maximum working temperature Tmax of the magnets. It is about 120 °C in case of epoxy resin, and about 80 °C in case of nylon.

Bonded NdFeB magnets

Neodymium bonded magnets can be produced as isotropic or anisotropic ones. However generally, those are isotropic magnets, which highest energy density (BH)max and remanence Br are about twice as big as that of the strongest ferrite magnets. In case of anisotropic Nd-Fe-B bonded magnets, said values are about four times bigger. Both said types of the magnets show very high values of coercive force jHc, which makes possible to install them under strong demagnetizing fields. Due to the fact that Nd-Fe-B powder grains are air-tightly closed in a plastic matrix, the magnets are characteristic of high corrosion resistance.

The following are the most important qualities of neodymium bonded magnets: big repeatability of magnetic properties, possibility of production of complicated and repeatable shapes without expensive mechanical working, high corrosion resistance and very high values of coercive force jHc.

Neodymium bonded magnets are, above all, installed in small motors and generators, counters, censors, electronic devices, mechanical toys, separators, holders (grips), converters and many other mass-produced devices (equipment), applied in a restricted range of temperatures.

Magnetic properties typical for neodymium bonded magnets:

Material
symbol

emanence
(Br)

Coercive
force
(bHc)

Coercive
force
(jHc)

Energy
density
(BH) max

[kGs] [kOe] [kOe] [kJ/m3] [MGsOe]

W4

4,0 - 5,0

4,0 - 4,5

  7,0 -  9,0

32 -  40

  4,5 -   5,0

W6

5,0 - 6,0

4,0 - 4,5

   7,0 -   9,0  

40 -  60

  5,5 -   7,5

W8

6,0 - 6,7

4,5 - 5,5

  8,0 - 10,0 

64 -  72

  8,0 -   9,0

W8H

5,6 - 6,6

5,0 - 5,8

13,0 - 17,0

60 -  72

  7,5 -   9,0

W10

6,6 - 7,0

5,0 - 5,5

  8,0 - 10,0 

72 -  80

  9,0 - 10,0

W10H

6,9 - 7,3

5,0 - 6,0

  9,5 - 10,0 

80 -  88

10,0 - 11,0

W12

7,2 - 8,0

5,2 - 6,0

  9,0 - 11,0 

88 -  96

11,0 - 12,0

W12D

7,2 - 8,0

5,6 - 6,5

  9,0 - 12,0 

88 -100

11,0 - 12,5


Other physical properties typical for neodymium bonded magnets:

Symbol
of material

Coefficient
temperature
of remanecence 
TK (Br)

Coefficient
temperature
of coercive force 
TK (Br)

Density

Brinell hardness

Resistivity

Max. working
temp.

[%/oC] [%/oC] [g/cm3] [HB] [Ohm cm] [oC]
W4 -0,10 -0,4 4,5-5,5  40-45 14000 150
W6 -0,10 -0,4 5,3-5,8 40-45 14000 150
W8 -0,10 -0,4 5,6-6,0 35-38 14000 140
W8H -0,13 -0,4 5,6-6,0 35-38 14000 140
W10 -0,10 -0,4 5,8-6,1 35-38 14000 140
W10H -0,10 -0,4 6,0-6,2 35-38 14000 150
W12 -0,10 -0,4 6,2-6,6 35-38 14000 150
W12D -0,07 -0,4 6,2-6,6 35-38 14000 160