Alnico magnets are manufactured by a cast or sintered process. Production level cast Alnico magnets are produced by conventional foundry methods using resin bonded sand molds. The magnetic characteristics for some exotic grades of Alnico magnets are achieved during the casting operation and are due to the unique crystalline grain orientation developed during the process. Sintered Alnico is a powdered metal and it is manufactured by compacting finely milled Alnico powder in a metallic mold. The resulting geometry is not fully dense and it must be sintered in a furnace to achieve a solid state. Properties of all anisotropic or oriented cast and sintered Alnico magnet alloys are optimized during a heat treatment process. The direction of orientation is determined in this phase of the manufacturing process which involves heating the alloy above its curie temperature, then cooling at a controlled rate in the presence of a directional magnetic field. Some cast and sintered Alnico magnets are isotropic or un-oriented and they skip the orientation process. These grades of Alnico magnets usually have lower energy products compared to the anisotropic grades, but they lend themselves to specialized magnetizing. The surfaces of cast Alnico magnets are usually dark grey, have wide tolerances, and have a rough finish. Critical dimensions are abrasively cut or ground in order to maintain close tolerances and improve the fit and finish. Sintered Alnico magnets usually require minimal grinding because they can be produced with tighter dimensional tolerances. It is usually desirable to have features developed in the casting or sintering operations because conventional machining methods are difficult to employ when fabricating Alnico magnets. According to our customer.
