Effect of the Insulating Layer on the Properties of SMC Inductors

In inductor applications, different soft magnetic materials are used depending on the frequency range. Owing to powder metallurgy technology and to the increase in the implementation of innovative multifunctional materials, it is possible to find an alternative to the traditional magnetic materials of the inductance application sector. This study concerns a deep analysis related to soft magnetic composite materials. The insulating layer's effect is investigated to explore the applicability of such materials to the inductor sector. Four coatings systems are selected and two types of samples are prepared in the shape of a toroid and a rod, which are tested in different operating conditions. The rod inductors are also compared with a traditional one, based on soft ferrite materials. This work aims to integrate data coming from different measuring devices: the useful small-signal measurements of an RLC meter are completed by large-cycle data measured through a hysteresigraph. Different parameters are considered for the investigation: magnetic permeability (maximum and initial), iron losses at different induction peak values, and inductor quality factor are the most important. The obtained results prove that each analysis type is not fully reliable without the other in determining the coatings' effects on the SMC inductors' performance. In the end, it is demonstrated that SMC inductances can be successfully applied in a particular frequency range

Effect of granulometry and oxygen content on SMC magnetic properties

The interest around the adoption of Soft Magnetic Composite materials (SMC) in the realization of electric machines, or parts of electric machines, is continuously increasing. The main reason lies on the opportunity to realize magnetic circuits following a 3D design procedure, which is not allowed with the adoption of the traditional lamination sheets. This is not the only reason, as a lot of research is being carried out on the losses distribution in the magnetic material, particularly as function of the frequency. In this paper different iron powders have been analyzed to investigate the impact of the granulometry on the SMC performance; in particular the grain size and the oxygen content have been considered variable parameters. The materials, prepared, compacted and tested in our laboratories, have been characterized to obtain the magnetic characteristic and information about the iron losses

Study of an Impact Mill-Based Mechanical Method for NdFeB Magnet Recycling

Nowadays, the circular economy is gaining more and more attention in sectors where the raw material supply is critical for both cost and geo-political reasons. Moreover, the environmental impact issue calls for recycling. From this perspective, the recovery of rare earth elements represents a strategic point. On the other hand, the high cost and the dangerous standard recovery methods that apply to NdFeB magnets limits options for traditional recycling. A new mechanical method is proposed, not requiring hydrogen, high temperature, or chemical processes, but instead using an impact mill designed to operate in vacuum. A traditional impact mill operating in a glove box filled with Ar atmosphere has also been used for comparison. The obtained NdFeB powders were analyzed in terms of magnetic properties and chemical composition, particularly in terms of the oxygen content

Overview of SMC characterization for their adoption in electromechanical systems

Electrical machines designers have shown in the last decade an increasing interest towards new materials that could represent a valid alternative to those commonly adopted in the realization of magnetic circuits. It is the case of parts or components realized with magnetic powders in place of laminated steels, or bonded magnets in place of sintered ones. The focus of the paper is about the realization of magnetic circuits by means of the powder metallurgy technique, adopting the so called “Soft Magnetic Composites”, or SMC, opening to the possibility of realizing by compression complex shapes otherwise impossible to be even considered. The impact of these new materials and their increasing adoption in the electrical machines scenario, has put in evidence the necessity of analyzing their realization process and providing the characterization of the obtained SMCs. The paper will first of all face the problem of describing the influence of the production process parameters, starting from the selection of the possible and more suitable binders, their percentage, the mold pressure, the curing temperature. Then the attention will move on the analysis of all the tests required to get a complete information of the obtained material. In particular, the characterization regards the magnetic behavior and the energetic performance, together with measurements of the conductivity, and the evaluation of the mechanical characteristics. The magnetic and energetic characterization, realized with the “transformer approach”, requires toroidal specimens with two coils wound on the magnetic structure to provide the magnetizing field and to detect the resulting effect. Considering that these materials will be part of devices always more subjected to power electronic supplies, the tests must be conducted in a wide frequency range (55000 Hz) and with different waveforms, in particular the sinusoidal and the triangular wave. The resulting information is a complete characterization of whatever SMC material under the point of view of the B(H) curve, the hysteresis cycle, the magnetic permeability and the specific losses. The analysis of the cited quantities can be performed as a post process activity, providing interesting results regarding the relationship of specific behaviors as a function of the supply frequency. In a world always more and more oriented to energy-saving procedures, significant importance will be addressed to the dissipation aspects, and the analysis of the losses separation should become a primary parameter to be considered in the choice of the most suitable material. A novel thermographic approach for the analysis of the energetic behavior of magnetic materials is also introduced and presented. The methodology allows the identification of possible structural defects, information useful to introduce process modifications. Last but not least, the mechanical properties. The normally adopted laminated steels do not have any problem of mechanical resistance; a deeper penetration of SMC materials will be possible if they will reach similar mechanical behavior. The tests to be conducted according to typical standards are “Transverse Rupture Strength” (or TRS), with a three point bending test, and tensile strength test. The paper also describes the realization steps of several prototypes of electrical machines, both radial and axial flux: from dimensional calculus to the experimental validation, all the phases are described in detail

Study of the Adoption of Different Bonded Magnets in Assisted Reluctance Machines

The possibility of using permanent magnets in assisted reluctance machine has been studied. The adoption of bonded magnets seems a very promising solution for such machine typology. In this context, different types of bonded magnets have been analyzed and compared taking into account several parameters, such as the torque and the power factor, and considering as reference case the Synchronous Reluctance Machine. Also, the comparison with traditional permanent magnets has been performed. The magnetic properties obtained from magnetic characterization have been reported and compared. Furthermore, the simulation results have been used to get a wide and detailed evaluation to choose the better solutions

New SMC Materials for Small Electrical Machine With Very Good Mechanical Properties

A new technology may be proposed for the realization of the magnetic parts of electromechanical devices, mainly for small electric machines. Such a technology provides the substitution of the traditional magnetic sheets with parts obtained by molding special magnetic powders [soft magnetic composites (SMC)]. The advantages may be constituted not only by economical reasons, but mostly by the possibility to realize parts having shapes otherwise impossible with the traditional lamination. Some commercial products are available in the market as “ready to press” powders, but their mechanical properties are in general not sufficient. To investigate the possibility to obtain good mechanical properties maintaining the magnetic characteristics of a selected commercial insulated iron powder compound, the authors have conducted a research activity based on the use of special iron powders and a selected epoxy resin as binder. The paper describes the activity carried out for the realization of SMC by mixing iron powders and Epoxy resin with different binder percentages and molding pressures. The obtained results have to be considered very satisfactory and suggest to continue the research argument to explore the possibilities of further improvements

Multiple Layer Magnetic Materials for Variable Flux Permanent Magnet Machines

This paper investigates the potentialities in simultaneous compaction of different types of permanent magnet materials, in order to build multi-layered magnets for electrical machine application. In particular, bonded magnet and hybrid magnet powders are used for building two-layer samples, which pave the way for the construction of special electrical machines having complex shapes, such as the variable flux permanent magnet machines. In this study, samples of innovative double layer magnet are built by means of single press and next magnetization procedure. Then, the ‘layered’ magnets have been experimentally characterized, focusing the attention on two diverse arrangements: the so-called parallel and series configurations

Effect of the Temperature on the Magnetic and Energetic Properties of Soft Magnetic Composite Materials

In recent years, innovative magnetic materials have been introduced in the field of electrical machines. In the ambit of soft magnetic materials, laminated steels guarantee good robustness and high magnetic performance but, in some high-frequency applications, can be replaced by Soft Magnetic Composite (SMC) materials. SMC materials allow us to reduce the eddy currents and to design innovative 3D magnetic circuits. In general, SMCs are characterized at room temperature, but as electrical machines operate at high temperature (around 100 C), an investigation analysis of the temperature effect has been carried out on these materials; in particular, three SMC samples with different binder percentages and process parameters have been considered for magnetic and energetic characterization

Rapid Characterization Method for SMC Materials for a Preliminary Selection

In electrical machines, laminated steels are commonly adopted as soft magnetic materials, while for permanent magnets, sintered ferrites and NdFeB are the most common solutions. On the other hand, the growing demand for volume reduction with the increment of efficiency leads to the necessity of exploring other magnetic materials able to face the challenge better than the traditional ones. Bonded magnets have been used to replace sintered magnets, obtaining a better use of space and particular magnetic properties. Instead, for the magnetic circuit, Soft Magnetic Composites (SMC) allow realizing very complex magnetic design (3D path for flux) with iron loss reduction at medium-high frequencies, especially for the eddy currents loss contribution. On the other hand, SMC materials have such drawbacks as low mechanical properties and high hysteresis losses. For this reason, in this work, different studies considering several variables have been carried out. SMCs were produced through a moulding process; inorganic and organic layers to cover ferromagnetic particles were used, adopting different coating processes. Particular tests have been performed for a quicker and more indicative overview of the materials obtained. The single sheet tester (SST) is easier than traditional toroidal methods; on the other hand, the multiplicity of variables affects the SMC materials and their process. For this reason, coercivity and conductibility tests permit rapid measurement and provide a direct classification of the produced SMCs, providing the main information needed to select suitable materials. Results highlighted that choosing the more appropriate SMC material is possible after using these simple preliminary tests. After these tests, it was possible to argue that with 0.2 wt% of phenolic resin as the organic layer (and compaction pressure of 800 MPa), it is possible to produce a good SMC. On the other hand, the SMC with 0.2 wt% of epoxy resin (and compaction pressure of 800 MPa) gives a minor coercivity value. Additionally, despite the SMC with the inorganic layer, 0.2 wt% of nano-ferrites showing the best coercivity values (specifically for vacuum treatment at 600 °C), their resistivity was unsatisfactory

APPLICAZIONE DELLA TECNICA DI IMPACT MILL PER LA PRODUZIONE DI MATERIALI SOFT MAGNETIC COMPOSITE

Lo sviluppo dei materiali Soft Magnetic Composite (SMC) rappresenta una soluzione innovativa per diversi settori applicativi, in particolare nel campo delle macchine elettriche e nell’ambito delle telecomunicazioni. Se da un lato l’impiego dei tradizionali lamierini permette in generale una progettazione 2D dei circuiti magnetici, obbligando i produttori ad adottare geometrie semplici, dall’altro i materiali SMC offrono invece la possibilità di realizzare dei nuclei magnetici aventi forme complesse tramite la metallurgia delle polveri. Inoltre, gli SMC presentano delle perdite energetiche inferiori ai tradizionali lamierini e proprietà magnetiche costanti a medio-alte frequenze d’esercizio. In questo lavoro si propone l’adozione di un nuovo rivestimento isolante sulle polveri ferromagnetiche, realizzato usando la tecnica di impact mill. Le polveri ferromagnetiche vengono ricoperte con particelle di silicio e ferrite, materiali in grado di essere sottoposti a processi o trattamenti termici ad alte temperature. Questi nuovi materiali SMC, sono stati interamente preparati e in seguito caratterizzati dal punto di vista delle proprietà magnetiche e delle perdite nel ferro. Infine, la qualità del rivestimento è stata indagata per mezzo della microscopia elettronica a scansione (SEM)