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Alnico Magnets

Alnico Permanent MagnetsCast Alnico 5 is the most commonly used of all the cast Alnicos. This material is used extensively in rotating machinery, meters, instruments, sensing devices and holding applications, to name a few.

Excellent temperature stability, high residual induction and relatively high energies characterize Alnico materials, composed primarily of alloys of Aluminum, Nickel and Cobalt. They are manufactured through either a casting or sintering process. Cast magnets may be manufactured in complex shapes, such as horseshoes, not possible with other magnet materials. Sintered Alnicos offer slightly lower magnetic properties but better mechanical characteristics than cast Alnicos.

Alnico is hard and brittle. Machining or drilling cannot therefore be accomplished by ordinary methods. Holes are usually cored in at the foundry and magnets are cast close to final size and then finish machined to closer tolerances.

Alnico has a low coercive force and is easily demagnetized if not handled with care. For optimum performance of Alnico 5, the magnetic length should be approximately 5 times the pole diameter or equivalent diameter. For example, a 0.250" diameter magnet should be about 1.250" long.

Because of its higher coercivity, Alnico 8 may be used in shorter lengths and in disc shapes.

Common Applications for Alnico Magnets

  • Actuators
  • Alternators
  • Automotive Parts
  • Bearings
  • Clutches
  • Coin Acceptors
  • Controls
  • Cow Magnets
  • Door Catches
  • Education
  • Electric Motors
  • Generators
  • Guitar Pickups
  • Heat Treatment Jigs and Recovery
  • Magnetrons
  • Meters
  • Microphones
  • Relays
  • Sensors
  • Traveling Wave Tubes

Manufacturing Methods

Pressing and Sintering

Sintered magnets are manufactured by compacting fine Alnico powder in a press and then sintering the compacted powder into a solid magnet.

Cast

Cast magnets are manufactured by pouring a molten metal alloy into a mold and then further processing it through various heat-treat cycles. The resulting magnet has a dark gray exterior appearance and may have a rough surface. Machined surfaces have a shiny appearance similar to steel.

Assemblies

Assemblies can be fabricated by adhering magnets with adhesives to suit a range of environments, by mechanically fastening magnets, or by a combination of these methods. Due to the relatively brittle nature of these magnet materials, press fits are not recommended.

Surface Treatments

The corrosion resistance of Alnico is considered excellent and no surface treatments are required. However, Alnico magnets are easily plated for cosmetic reasons if required.

Machining

Alnico is hard and brittle, and prone to chipping and cracking. Special machining techniques must be used to machine this material. Holes must be made by EDM methods. We are fully equipped to machine these materials to your blueprint specifications.

Magnetizing and Handling

Alnico magnets require magnetizing fields of about 3 kOe. Because of their relatively low coercivities, special care should be taken to assure that these magnets are not subjected to adverse repelling fields, since these could partially demagnetize the magnets. Magnetized magnets should be stored with keepers to reduce the possibility of partial demagnetization. If Alnicos are partially demagnetized, they may be easily remagnetized.

Temperature Effects

Up to about 1000 F, changes in magnetization are largely reversible and re-magnetizable, while changes above this are largely structural and not fully reversible or re-magnetizable.

Approximately 90% of room temperature magnetization is retained at temperatures of up to 1000 F.

Material Characteristics

Cast Alnico materials commonly contain casting voids and hairline cracks within the material. These can be exposed by finish machining. The following is an extract from MMPA standards regarding such imperfections: "These are materials used primarily for their magnetic capabilities as permanent magnets without regard to mechanical properties. These materials, prepared by good metallurgical practice, by their very nature will unavoidably contain a degree of physical imperfection. It is not generally recommended that these materials be used for structural or decorative purposes unless the physical requirements of the magnet are previously suitably specified".

Properties of Cast Alnico Magnets

Grade
(Equivalent
MMPA Class)
Br
mT (Gs)
Hc
kA/m (Oe)
(BH)max
kJ/m3 (MGOe)
Density
g/cm3
Temp Coefficient
Near Br %/k
(Near Hcj %/k)
Curie Temp
Tc
Max Working
Temp
Tw
Remark
LN10
(ALNICO 3)
600 (6000)40 (500)10 (1.20)6.9-0.03 (-0.02)810 ℃ (1490 °F)450 ℃ (842°F)Isotropic
LNG13
(ALNICO 2)
700 (7000)48 (600)12.8 (1.60)7.2-0.03 (-0.02)810 ℃ (1490 °F)450 ℃ (842°F)Isotropic
LNGT18
(ALNICO 8)
580 (5800)100 (1250)18 (2.20)7.3-0.025 (+0.02)860 ℃ (1580 °F)550 ℃ (1022°F)Isotropic
LNG37
(ALNICO 5)
1200 (12000)48 (600)37 (4.65)7.3-0.02 (+0.02)850 ℃ (1562 °F)525 ℃ (977°F)Anisotropic
LNG40
(ALNICO 5)
1250 (12500)48 (600)40 (5.00)7.3-0.02 (+0.02)850 ℃ (1562 °F)525 ℃ (977°F)Anisotropic
LNG44
(ALNICO 5)
1250 (12500)52 (650)44 (5.50)7.3-0.02 (+0.02)850 ℃ (1562 °F)525 ℃ (977°F)Anisotropic
LNG52
(ALNICO 5DG)
1300 (13000)56 (700)52 (6.50)7.3-0.02 (+0.02)850 ℃ (1562 °F)525 ℃ (977°F)Anisotropic
LNG60
(ALNICO 5-7)
1350 (13500)59 (740)60 (7.50)7.3-0.02 (+0.02)850 ℃ (1562 °F)525 ℃ (977°F)Anisotropic
LNGT28
(ALNICO 6)
1000 (10000)57.6 (720)28 (3.50)7.3-0.02 (+0.03)850 ℃ (1562 °F)525 ℃ (977°F)Anisotropic
LNGT36J
(ALNICO 8HC)
700 (7000)140 (1750)36 (4.50)7.3-0.025 (+0.02)860 ℃ (1580 °F)550 ℃ (1022°F)Anisotropic
LNGT60
(ALNICO 9)
900 (9000)110 (1380)60 (7.50)7.3-0.025 (+0.02)860 ℃ (1580 °F)550 ℃ (1022°F)Anisotropic
LNGT38
(ALNICO 8)
800 (8000)110 (1380)38 (4.75)7.3-0.025 (+0.02)860 ℃ (1580 °F)550 ℃ (1022°F)Anisotropic
LNGT40
(ALNICO 8)
820 (8200)110 (1380)40 (5.00)7.3-0.025 (+0.02)860 ℃ (1580 °F)550 ℃ (1022°F)Anisotropic
LNGT72
(ALNICO 9)
1050 (10500)112 (1400)72 (9.00)7.3-0.025 (+0.02)860 ℃ (1580 °F)550 ℃ (1022°F)Anisotropic

Properties of Sintered Alnico Magnets

Grade
(Equivalent
MMPA Class)
Br
mT (Gs)
Hcb
kA/m (Oe)
Hcj
kA/m (Oe)
(BH)max
kJ/m3 (MGOe)
Density
g/cm3
Curie Temp
Tc
Max Working
Temp
Tw
Remark
SLN8
(ALNICO 3)
520 (5200)40 (500)43 (540)8-10 (1.0-1.25)6.7760℃ (1400 °F)450℃ (842 °F)Isotropic
SLNG12
(ALNICO 2)
700 (7000)40 (500)43 (540)12-14 (1.5-1.75)7810℃ (1490 °F)450℃ (842 °F)Isotropic
SLNGT18
(ALNICO 8)
600 (6000)95 (1200)107 (1350)18-22 (2.25-2.75)7.2850℃ (1562 °F)550℃ (1022 °F)Isotropic
SLNGT28
(ALNICO 6)
1000 (10000)56 (700)57 (710)28-30 (3.5-3.8)7.2890℃ (1634 °F)525℃ (977 °F)Anisotropic
SLNG34
(ALNICO 5)
1100 (11000)50 (630)51 (640)34-38 (3.5-4.15)7.2890℃ (1634 °F)525℃ (977 °F)Anisotropic
SLNGT31
(ALNICO 8)
780 (7800)104 (1300)106 (1130)33-36 (3.9-4.5)7.2850℃ (1562 °F)550℃ (1022 °F)Anisotropic
SLNGT38
(ALNICO 8)
800 (8000)123 (1550)126 (1580)38-42 (4.75-5.3)7.2850℃ (1562 °F)550℃ (1022 °F)Anisotropic
SLNGT42
(ALNICO 8)
880 (8800)120 (1500)122 (1530)42-48 (5.3-6.0)7.25850℃ (1562 °F)550℃ (1022 °F)Anisotropic
SLNGT38J
(ALNICO 8HC)
730 (7300)151 (1900)163 (2050)38-40 (4.75-5.0)7.2850℃ (1562 °F)550℃ (1022 °F)Anisotropic
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