Ferrite Permanent Magnet Technology
These affordable magnets are widely used in many electronic devices and products, such as loudspeakers, household appliances, toys and medical instruments
Chemical composition and working principle
Ferrite permanent magnets are made of ferrimagnetic materials. In a magnetic field, the atoms in these ferrimagnetic materials can adopt and maintain an orderly arrangement. Once they become magnetized, they possess a high magnetic remanence even after the external magnetic field is removed. There are two commonly used ferdmagnetic materials. ferroxdure (BaFe12O19) and ferrostrontium (SrFel2Ol9). The latter has a higher magnetizability, but costs about 50% more.
Manufacture of ferrite permanent magnets
a) Preparation of powder material:
The proper starting ingredients are mixed thoroughly, ground and made into small balls, which are then heated in a high temperature furnace. The heated ball are then @her finely ground into a powder material.
Two methods of shaping are most widely used: dry pressing and magnetic field assisted pressing. In dry pressing, the powder material is mixed with binder and compressed in a mold to give (Square) magnet blanks. In magnetic field assisted pressing, the powder material is suspended in water and the suspension is compressed in a mold under a magnetic field to give -9i@magnet blanks. In addition to these, magnetic field assisted injection molding has also been developed.
After being dried, the product blanks are sintered in a high temperature continuous furnace.
d ) Polishing
Sintered (Square) magnet blanks are then polished, ultrasonically cleaned and dried in a stove while sintered 4ktk magnet blanks require mechanical grinding to achieve precise sizes, followed by ultrasonic cleaning and drying in a stove.
e) Magnetization and final product QC
Ferrimagnetism materials are usually magnetized in a magnetic field with special equipment. The final product QC includes measurements of product size and major magnetic properties with special instruments.