Developed in the 1930’s, Alnico magnets have several attributes that continue to make them the workhorse of the permanent magnet industry in the 21st Century. Their name is derived from the primary chemical composition of the alloy; AlNiCo - Aluminum, Nickel, and Cobalt, [balance is Fe (Iron)].
Their compact crystalline structure yields relatively high density resulting in good mechanical strength and good maximum energy products. Having the lowest temperature coefficient of Br [TcBr] for any commercial magnet material (-0.02%/°C), results in exceptional uniformity of magnetic properties over a wide temperature range. Approximately 90% of room temperature magnetization is retained at temperatures up to 538°C. Cast Alnico magnets offer the highest operating temperature of any magnet material; up to 450 - 550°C. Because of their good chemical structure, they exhibit excellent corrosion resistance, and can be cast into a variety of shapes.
In 2005 an R & D program was begun to develop improved structural strength, high energy grades of Cast Alnico 9. Generally, optimum properties of Cast Alnico magnets are achieved with columnar or single crystal structure with the direction of magnetization parallel to the columnar grain axis. However, this has not been the case for Alnico 5-7 and Alnico 9 which are particularly crack-prone due to their columnar structure. This research led to the development of our superior grades of Cast Alnico 9 with improved physical strength, extended temperature and time stability, and the highest energy product and coercive force of any alnico materials in the world [BHmax up to 11.5 MGOe]!
Sintered Alnico magnets are mechanically the strongest of the Alnico series, and with the benefit of close tolerance pressing they are ideally suited for small complex shapes, typically with minimal finish grinding.
Compression Molded [Bonded] Alnico – A fairly recent addition to the traditional Cast and Sintered Alnico line is the Isotropic “Bonded” Alnico magnet. Using thermo-elastomeric [polyethylene, polyurethane], thermoplastic [nylon, PPS], or epoxy based binders, the Alnico powder is carefully blended with the binder, and other chemicals, and pressed in a mold. In addition to pressing complex shapes, like gear teeth, extremely tight dimensional tolerances may be held without secondary finishing. Insert molding can reduce overall system cost. Density is 79% of that for Sintered Alnico because of dilution by the binder; the maximum operating temperature is limited by binder and reactivity of the powder to between 80° and 200°C.
These magnets resist chipping, and permit complex magnetizing patterns.
As noted above, Cast Alnico offers excellent magnetic uniformity and temperature stability up to its’ maximum operating temperature. The temperature coefficient of Br is -0.02%/°C resulting in exceptional uniformity of magnetic properties up to the maximum operating temperature [approximately 96% of room temperature magnetization is retained at temperatures up to 220°C].
Applications include magnetic suspension bearings for kWh meters, high stability magnetic sensors for use with both reed switches and Hall Effect devices, brush-less DC motor magnets and linear actuators, Waveguide components, and D’Arsonval meter movements to name a few, as well as other devices which require magnetic calibration.