AC magnetic characteristics of cores made from pressed rectangular steel particles

This paper describes a new material and method of processing that yields pressed. compacts magnetically suitable for a variety of AC applications. Small rectangular plain-carbon steel particles ranging in size from 1.5 × 0.25 × 0.15 mm to 3.8 × 0.61 × 0.15 mm are decarburized, individually insulated and uniaxially pressed using typical powder metallurgical techniques. The magnetic properties of compacted ring specimens were measured. The AC losses and permeability of the pressed compacts are strongly dependent upon pressing pressure and particle geometry. Increased compact density lowers the iron losses. Variations of iron loss among the various particle geometries are caused by changes in particle shape anisotropy. At 60 Hz the losses are somewhat higher than those of Conventional carbon steel laminations while at higher frequencies the compact losses are lower. This loss trend is due to the small eddy current contribution to the loss. Permeability also depends upon compact density and particle geometry. Increased density not only lowers the induction within each particle for a fixed overall compact induction, but also decreases the magnetostatic energy within the compacts. Both effects result in the increase in permeability with increased density. The smaller the demagnetizing factor of the individual particles, the higher is the permeability. Iron loss and permeability respond differently to particle geometry; hence, selection of the best particle size will depend upon which of the two characteristics is most important for the particular magnetic circuit involved.