Environmental Engineering Reference
In-Depth Information
Table 5.1 Performance of popular permanent magnet types
Type
Remnant
B r (T)
Coercive
H c (kA/m)
Energy
(MGOe)
Recoil
permeability (#)
Alnico 5
1.35
58.9
7.5
17
Alnico 6
1.05
62
31
13
Alnico 9
1.06
119.3
9
7
Ceramic 5
0.38
190.8
3.4
1.1
Ceramic 6
0.32
190.8
2.5
1.1
Ceramic 8
0.40
222.6
4.1
1.1
Magnequench I
0.68
390
9.8
1.22
Magnequench II
0.8
517
13
1.15
Magnequench III
1.31
979
42
1.06
NeoMax 27H
1.1
811
28
1.05
NeoMax 35
1.25
882
36
1.05
10 4 = Gauss (G).
Conversion: ( H c in A/m)/79.6 = Oersted (Oe); ( B r in T)
B r , and coercive force, H c , at a permeance coefficient that falls on the magnet recoil
line. Table 5.1 lists magnetic properties of magnets.
Permeance coefficient ( P c )
Also referred to as the operating slope or the load line.
The slope of the load line is the permeance coefficient ( P c )
Slope of the normal curve as
it passes through the B -axis is
called the recoil permeability,
m r
B -axis
(Gauss or
Tesla)
Demag curve
second quadrant
Operating point
Intrinsic curve
B r
Typical values of m r for
sintered NdFeB are 1.05.
Bonded NdFeB range from
1.12 to 1.70.
B d
Normal curve
H -axis
(Oersteds or
A/m)
H d
H ci
H c
Figure 5.1 Illustration of permanent magnet intrinsic and normal curves
The better grades of permanent magnets used for electric machines tend to
have recoil permeability approach the permeability of air (1.0), which is why the
best motor magnets are the RE neodymium types such as NeoMax 27H. Figure 5.1
illustrates this situation for RE magnets.
In summary, we can say the following about permanent magnets:
Alnico for highest temperature stability
Ceramic for best energy at lowest cost
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