Study On The La-Zn Substitution Of Sr-ferrite Powders For Injection Molding

Bonded ferrite magnet is still the most widely-used as permanent magnets.Injection molding is an important method to manufacture bonded ferrite magnet.Bonded ferrite by injection molding has widely used in the rotor of micro motor,printer magnetic stick, sensor and so on. Improving property of the magnet is the keydevelopment project of the manufactures. The Bras the major performmce of bondedmagnet is mainly influenced by the magnetic property, volume fraction andorientation of the ferrite particals. This paper aims to control grain size of ferritepowders by La-Zn substitution, enhance magnetic property and seek ways tomanufacture high-performance ferrife powder for injection molding.In this paper, we adopted ceramic technology to manufacture ferrite powders bymixing the raw materials, sintering, rude breaking, fine grinding, annealing andsurface treatment. Then the ferrite powder was mixed with nylon, extruded andinjected after. The property of the magnet and MFR （Melt Flow Rate） of thecompound were tested. Some test methods, such as particle size distribution tester,presser, SEM, XRD and VSM were used to study the powder characteristics and finalproperties of magnets.Several kinds of powders with different characteristics were made of the rawmaterials under three different sintering conditions. The average particles diameter,particle size distribution and CD （Compression Density） of the ferrite powderinfluence the MFR of the compound and orientation of the particles in the magnet.The particle size distribution and compression density of the ferrite powder is effectedby the size of the crystal witch formed durring sinterring.The series of Sr_1-xLa_xFe_12-xZn_xO₁₉（x=0～0.3）were manufactured. The researchindicates that the Brof the magnets produced by injection molding reaches itsmaximum value and decline later. When x≤0.2, the Hcjof magnets increases alongwith doping amount adding.And the series of Sr_0.85La_0.15Fe_11.85Zn_0.15O₁₉and SrFe₁₂O₁₉were manufacturedunder the sintering temperature of950-1250℃. The research showes that La-Znsubstitution can restrain the crystal growth. Compared with the SrFe₁₂O₁₉powder.The Sr_0.85La_0.15Fe_11.85Zn_0.15O₁₉powder showes some advantages such as narrowparticle size distribution, small APD, higher Hcjand higher σs, but also showes somedisadvantages such as lower CD and lower MFR of the compound durring injection,and which needs to controlling.