1. Delivery of permanent magnets:
Handling magnetized magnets may cause major problems for transport and assembly. They might cause injury due to dangerous forces, attract dirt or may hard to be kept in their assembly location.
Thus the easy handling of unmagnetized magnets during transport and assembly often requires a magnetizytion of the fully assembled magnet system.
Possible reasons for the magnetization of magnet assemblies are:
- Easier handling and packaging
- Reduction of dirt attrction (e.g. iron dust)
- Reduced risc of injury
- In some magnet system the magnetic layout requires iron return paths for the stability of the magnets. This may be of high relevancy for AlNiCo or Colbald alloys.
- Better profitability in case of high quantities
Most of the permanent magnets are not magnetized directly after production. Sinter magnets for example are demagnetized completely due to the high sinter temperature. They have to be magnetized afterwards by application of a high external field.
Some plastic bonded magnets may be magnetized directly in the injection mold. However it often still is helpful to strengthen some weakly magnetized portions by application of a higher external field of an impuls magnetizer.
A permanent magnet is magnetized by application of a strong outer magnetic field. This magnetic field forces the spins of the atomic electrons stepwise into its own direction. With increasing outer field the magnet will trace the new curve. If the outer field strength is bigger than the saturation field strength all the spins have been oriented with the field. A high magnetization will not be possible from there on.
In case of permenent magnets this is an irreversible process. The magnet remains magnetized when the outer field goes back to zero. It will go back to the remanence point Br.
3. Creation of outer field:
Normally the outer field is generated in coils which are connected to impulse magnetizers. Magnets with lower saturation field strength might also be magnetized by other permanent magnets or DC magnetizers.
The required duration of the magnetizing does not play a roll in this case. The required time to turn an electron spin is in the nano seconds range.
It is more time critical to have the field proceed to the magnet, which itself may be conductive or it may be shielded by conductive materials.
Therefore the pulse frequency and shape has to be well consided when using an impulse magnetizer. Limiting are:
- Heat up of the magnetizing coil in slow pulses faster pulses
- Eddy currents slower Pulses