Magnetization Process

 

Machining of Magnets

 

 

 

 

Sintered Samarium Cobalt and Ferrite magnets exhibit small cracks within the 

material that occur during the sintering process. Provided that the cracks do not 

extend more than halfway through a section, they do not normally affect the 

operation of the magnet. This is also true for small chips that may occur during 

machining and handling of these magnets, especially on sharp edges. Magnets 

may be tumbled to break edges. This is done to avoid "feathering" of sharp 

edges due to the brittle nature of magnets and is also done for better adhesion of 

plating or coatings. Because of these inherent material characteristics, it is not 

advisable to use any permanent magnet material as a structural component of an 

assembly.  

 

Neodymium magnets are more durable compared to Samarium Cobalt and 

Ferrite magnets, however they are still brittle and they should be handled with 

care. Since permanent magnets are produced of brittle material, they should not 

be used as bearing components of an assembly.  

 

Sintered Neodymium, Samarium Cobalt and Ferrite magnets are machined by 

grinding, which may affect the magnet cost. Maintaining simple geometries and 

wide tolerances is therefore desirable from an economic point of view. Generally, 

tolerances less than ±.005” will result in higher costs, regardless of the size of the 

part. Rectangular or round sections are preferable to complex shapes. Square 

holes and very small holes (less than .250”) are difficult to machine and should 

be avoided.  

  

Cast Alnico magnets exhibit porosity as a natural consequence of the casting 

process. This may become a problem with small shapes which are machined out 

of larger castings. The voids occupy a small portion of the larger casting, but can 

account for a large portion of the smaller fabricated magnets. This may cause a 

problem where uniformity or low variation is critical, ant it may be advisable either 

to use a sintered Alnico, or another material.  

 

 

 

 

 

 

 

 

 

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Handling Of Magnets 

 

 

 

 

 

 

•

  Personnel wearing pacemakers must not handle magnets.  

•

  Magnets should be kept away from sensitive electronic equipment, computer 

disks, and credit cards with magnet stripes.  

•

  Modern magnet materials are extremely strong magnetically and somewhat 

weak mechanically. Therefore, packaging is an important issue. 

•

  Any person required to handle magnets should be appropriately trained about 

the potential dangers of handling magnets.  

•

  Injury is possible to personnel, and magnets themselves can easily get 

damaged if allowed to snap towards each other, or if nearby metal objects are 

allowed to be attracted to the magnets.  

•

  Materials with low coercive forces such Alnico must be carefully handled and 

stored when received in a magnetized condition. When stored, these magnets 

should be maintained on a "keeper", which provides a closed loop protecting 

the magnet from adverse fields. Bringing together like poles in repulsion can 

lead to irreversible, although remagnetizable, losses.  

•

  Samarium Cobalt magnets must be carefully handled and stored due to the 

extremely brittle nature in the material.  

•

 Uncoated 

Neodymium 

magnets 

should be stored in a way to minimize the risk 

of corrosion. 

•

 Magnetized 

magnets 

are 

considered Hazardous Materials when transporting 

by air and the stray flux must meet IATA guidelines. 

•

  NdFeB materials, when in powder form, can ignite from static charges   

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Magnetization Process

 

 

 

 

 

To make a magnet "magnetic" it must be exposed to a strong external magnetic 

field. This field reorganizes the magnet’s domain structure and leaves the 

magnet with a remanent magnetization (Br). If a magnet is isotropic, the 

remanent magnetization has the same direction as the external field. Meanwhile, 

an anisotropic magnet can only be magnetized in its anisotropy direction. 

 

The most common method of magnetizing is to let a very short current pulse go 

through a conductor or a coil. The short pulse is generated from a magnetization 

machine, which is basically a powerful capacitor together 

with a controller. Different materials require different 

lengths of current pulse. The resistivity of a material 

provides a prediction of what the magnetization pulse 

should look like. A material with high resistivity can be 

magnetized with a pulse of a few micro seconds, while a 

more conductive material may need several hundreds of 

a second longer pulse. Also, the volume of a magnet is of 

importance for the length of the current pulse.  

 

During the magnetizing process, Eddy Currents are produced in an electrical 

conducting material. Eddy Currents create a magnetic field which is in the 

opposite direction of the applied field.  

 

Besides various pulse lengths, different materials need different strengths of the 

magnetizing field. Coercive force (intrinsic) is the property of the material that 

decides what magnetic field strength that is needed for the magnetization. Axial 

and diametrical magnetization can be made in standard inductors, i.e. solenoids. 

However, radial, multiple pole, or any other complex magnetization has to be 

done in a specially built magnetization fixture.  

 

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