Improvement of the Overall Performance of Magnetic Powder Cores by Optimising the Coupling Agent Content
Magnetic powder cores,also known as soft magnetic composite materials(SMCs),consist of metal magnetic powders coated with an insulating layer formed through a specific pressing process.In engineering applications,magnetic powder cores may be subjected to issues such as cracking,reduced magnetic permeability,and diminished mechanical strength.The insulation coating of the magnetic powder core includes inorganic and organic coatings.Coupling agents,a type of polymer composite additive,have both inorganic and organophilic molecular groups,allowing them to modify the surface of the magnetic powder and serve as a"bridge"between the inorganic and organic coating layers.The gap between academic and industrial research on the cracking and expansion coefficients of magnetic powder cores leads to a poor understanding of the underlying mechanisms.The moldability,magnetic properties,and mechanical properties of carbonyl iron powder(CIP)magnetic powder cores(including magnetic rings,magnetic discs,and molding inductors)with different contents of the KH550 silane coupling agent were investigated in this study.Scanning electron microscopy(SEM),thermomechanical analysis(TMA),and LCR techniques were used for analysis.The SEM images of the magnetic powder core sections indicate that increasing the amount of coupling agent reduces powder agglomeration,which increases the area percentage of the nonmagnetic phase and porosity.With an increase in the coupling agent content,the area percentage of the nonmagnetic phase increased from 18.4％to 31.4％.Notably,the magnetic disc experimental outcomes,influenced by the coupling agent content,thickness,molding pressure,and curing rate,revealed that a higher curing rate,increased thickness,and higher molding pressure made the magnetic discs more susceptible to cracking.However,coupling agents can reduce the cracking tendency of the molding inductors and magnetic rings,thereby enhancing their moldability.The density of the magnetic discs is influenced by both the molding pressure and coupling agent content.When the coupling agent content remains constant,an increase in the molding pressure results in increased density.However,for discs subjected to identical molding pressures,a higher coupling agent content corresponded to a reduced density.Density of the magnetic discs with 0.1 wt.％coupling agent content are abnormal.The TMA showed that the coupling agent can stabilize the resin on the magnetic powder surface and facilitate powder particle rearrangement during curing,thereby increasing the core expansion coefficient.Magnetic powder cores with 0 wt.％and 0.1 wt.％coupling agents have negative expansion coefficients,leading to potential shrinkage and cracking.In contrast,the cores with 0.3 wt.％,0.5 wt.％,and 0.7 wt.％coupling agents yielded an increased expansion coefficient during resin curing,thereby effectively reducing the core's cracking tendency.However,increasing the coupling agent content can affect the magnetic properties of the core.As the non-magnetic phase and porosity change,the density and magnetic permeability of the magnetic powder core initially increase and subsequently decrease.Similarly,the core loss and quality factors exhibit opposite trends.As the porosity increases,it induces additional coercivity proportional to the square root of the specific pore surface area,consequently leading to increased core loss.The core loss first decreases and then increases,and the quality factor increases before eventually decreasing.This paper also demonstrates that the meshing capability of magnetic powders directly affects their mechanical properties.As the coupling agent content increases,the mechanical strength of the magnetic powder core improves and then declines.Given the moldability of the core and other characteristics,the ideal coupling agent content is 0.3 wt.％.This study explored the effect of the coupling agent on the expansion coefficient of magnetic powder core during curing and unveiled its influence on other properties,laying a robust theoretical foundation for the application of high-performance magnetic powder cores.
carbonyl iron powderKH550 coupling agentexpansion coefficientmagnetic powder coremolding inductor
NETL
NSTL
万方数据
