Five Kinds of Ferrite Magnet Manufacturing Process(2)

2. Hard magnetic ferrite

Hard magnetic ferrite can be called permanent magnet material, mainly: magnetic leadstone Ba - ferrite, Sr - ferrite, Pb - ferrite, and spinel type CO - ferrite, etc.

The production of hard magnetic ferrite requires not only high purity of raw material and precise composition of formula, but also moderate grain size, uniform distribution, reasonable orientation and dense structure of magnet.

The prefiring temperature of hard magnetic ferrite is generally 1100 ~ 1300℃. Sintering temperature in 1150 ~ 1250℃ oxidation atmosphere. Such as Ba - ferrite is the raw material in the temperature of 1100 ~ 1200℃ pre-sintering, forming in the temperature of 1150 ~ 1250℃ sintering. Co - ferrite is prefired at a temperature of about 900℃, and then decompressed at a temperature of 1100℃, after the magnetic field is applied at a temperature between 300℃ Curie temperature, and then slowly cooled and made.

The sintering density of ferrite is related to the size of the residual magnetic induction intensity. The denser the ferrite, the greater the residual magnetic induction intensity. Although the increase of sintering temperature can increase the density of the magnet, it will cause the grain size of the magnetic phase to grow, which is unfavorable to the magnetic induction intensity. The correct method is to introduce additives to accelerate the sintering speed, improve the density, but also effectively inhibit the growth of the magnet grain. Commonly used admixtures are: Al2O3, AS2O3 and Bi2O3, etc.

3. Pressure magnetic ferrite

The pressure magnetic ferrites are mainly Ni-containing ferrites, and Ni - Zn, Ni - Cu, Ni - Mg ferrites are widely used. The density of ferrite is directly related to the magnetic properties of ferrite. In the production process, the density of ferrite can be increased by increasing the forming pressure, increasing the firing temperature, introducing additives and high temperature prefiring. For example, in Ni-Zn pressomagnetic ferrite, increasing the content of Zn or replacing Ni with a little Cu as flux is conducive to improving the density of ferrite.