Radially oriented ferrite magnets

A new manufacturing method, magnetic-field-free-process, to obtain radially oriented ferrite magnets was developed, utilizing the shape anisotropy of the particles of strontium magnetoplumbite, with the following properties : Br = 365mT, bHc = 225kA/m, iHc = 240kA/m, (BH)max = 24kJ/m³, density = 4950 kg/m³, flexural strength = 167MPa. The process consists of four steps, that is, powder preparation, rolling, winding, and sintering. The blended raw materials are calcined in two ways and mixed to a suitable ratio to attain the ´orientability´ of the particles. The prepared powder is kneaded with viscous organic binders to form a thixotropic article. By passing it through rolls, the alignment of the preferred direction of the magnetization of particles at right-angles to the plane of the rolling is obtained. The rolled strips are heated and wound on a mandrel. By this method radially oriented green cores are obtained. After the reduction of organic binders, they are fired in an oxidizing atmosphere. These radially oriented magnets which have high remanence, high coercivity and high mechanical strength, have wide application in the field of rotating machines such as stator or rotor magnets for small motors and generators.