Magnetics Business & Technology - Spring 2016 - (Page 14)

FEATURE ARTICLE Insulated Iron Powders, SMC, Current State and Future Possibilities By Dr. Kalathur Narasimhan | P2P Technologies Insulated iron or iron-silicon for soft magnetic powder composites (SMC) are a niche unique to powder metallurgy. This method uses pure iron powder with a highly insulating coating to provide a soft magnetic ferrous material that is suitable for a variety of electromagnetic applications. These coated powders offer 3D flux carrying capability compared to traditional lamination steels where flux is maximized in the rolling direction. This technology has been in commercial use since introduced in the early 1990s, but has only enjoyed limited applications. Recent improvements in the material systems and forming processes have enabled making this technology more attractive choice for some electronic and electric motor applications. Although an attractive material, insulated composites have not displaced mainstream lamination steels in electric induction motors. This is because of insulating coating creates a distributed air gap in the material. This has the effect of lowering the saturation induction and permeability of the material. Mechanical strength, as measured by a three point bend method, is about 100 MPa, requiring additional means of strengthening, such as resins. In general, the higher the frequency the lower the core loss of insulated iron composites compared to lamination steels (see Figure 1). This figure shows the core losses as a function of frequency for AncorLam, an insulated iron powder for SMC applications made by Hoeganaes Corp., and typical lamination steel. At lower frequencies the lamination steel has lower losses than AncorLam. As the frequency increases the losses increase at a greater rate for the lamination steel. At lower frequencies the core loss is dominated by hysteresis losses, which are higher for insulated iron composites. At higher frequencies, the eddy current losses are lower for insulated iron composites as the eddy currents are localized to the particle surface compared to lamination steels where the eddy currents are generated at the larger surface of the steel. Data from past studies show that AncorLam type materials compete well in AC applications operating at frequencies >400 Hz with lamination steel thicknesses >0.35 mm5. Table 1. Within these limitations there is room for material and process optimization for specific applications. To this end a family of insulated composite material is available. Typically the particles size and coating type is modified to meet specific application types. In general, applications that need higher permeability have coarser particles and less insulation. Applications that need to operate at higher frequencies use finer particles (designation F) and or increased insulation (designated as HR). See Table 1 on the effect of particle size on permability. A generic summary of materials and application types is presented in Table 2. The specific magnetic performance of each grade is summarized in Table 3. Table 2. Typical applications with suggested material type. Figure 1. Core loss of insulated composite and lamination steel as a function of frequency. 14 Magnetics Business & Technology * Spring 2016 The typical production process involves compacting the insulated iron particle and curing at a temperature that increases the mechanical strength without destroying the insulation. An insulated iron composite powder is compacted into the desired shape. The green part is then cured in N2 at 450°C resulting in the final cured component. The curing has the benefits of increasing mechanical strength of the compact and it also partially stress relieves the iron improving magnetic response, specifically the hysteresis losses. www.MagneticsMagazine.com http://www.MagneticsMagazine.com

Table of Contents for the Digital Edition of Magnetics Business & Technology - Spring 2016

Editor's Choice
Permanent Magnets in a Changing World Market
Design Considerations Using Permanent Magnets
Insulated Iron Powders, SMC, Current State and Future Possibilities
Research & Development
The Design of a Permanent Magnet Motor for a Direct Drive Fan Application
Tailoring of Pole Shapes of Multipolar Injection Molded Magnets
Electromagnetics
Industry News
Marketplace / Advertising Index
Spontaneous Thoughts: Seventeen Mistakes People Make with Permanent Magnets

Magnetics Business & Technology - Spring 2016