Economic and technical advantages have also been found in the production of components for magnetic applications.
- Small permanent magnets of the Alnico, Cunife or Cunico types can be pressed and sintered to final shape and size, showing equivalent magnetic properties but finer grain structures and better mechanical strengths than similar cast materials.
- Soft magnetic sintered products in iron, silicon-iron and iron with about 5% of phosphorus are widely used in the manufacture of pole pieces and armatures for dc application.
- The use of sintered high-permeability laminated components in nickel-iron and permalloy-type materials for transformer applications is increasing, and with the direct rolling of powders into thin strips, further applications will undoubtedly follow.
a. Cores for self-inductance
Probably one of the most important uses of metal powders for magnetic purposes is
- the production of cores for self-inductance coils in high-frequency communication equipment.
The cores are produced by compressing insulated metal powders.
- Sintering in the accepted sense is not required, although a thermal stabilisation
- or stress-relieving treatment is usually carried out to obtain optimum magnetic
- Purity and close control of compositional limits is very necessary, and electrolytic
- or carbonyl powders and pre-alloyed permalloy-type powder are widely used
- as raw material.
Another class of magnetic materials which are processed by powder metallurgy methods are the ferrites or magnetic oxides. The combination of ferric oxide with bivalent oxides of magnesium, nickel, manganese, copper, zinc, etc, produces materials having a wide range of both soft and permanent magnetic properties.
The 'soft ferrite' has found the widest application in the manufacture of cores for radio and television and other applications such as ABS sensor rings,computer printers and armatures. Increased miniaturisation of personal hi-fi and telecommunication equipment has seen a surge in production of sintered rare earth-cobalt magnets in recent years, as well as the introduction of Fe-Nd-B magnets.
China is now the main source of all these products