Influence of a dielectric type on dielectromagnetics properties
Tomasz Janta, Bogumił Węgliński Politechnika Wrocławska, Instytut Maszyn, Napędów i Pomiarów Elektrycznych, ul. Smoluchowskiego 19, 50-372 Wrocław
Annals 3 No. 7, 2003 pages 165-171
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abstract Magnetic powder composites gather lately special meanings as materials for magnetic cores of electric devices. Special interest is focused on dielectromagnetics. Changes of selected mechanical, electric and magnetic properties of dielectromagnetics, executed at use of different kinds of dielectrics are presented in the paper. Various epoxy resins in quantities 0.5% by weight were used as dielectrics. It includes: Amicon SE 617, Araldit K-600 and epoxy resin which was used up till now: Epidian 101 in powder form and as diluted in acetone in proportion 10 ml/g of resin. In comparative aims one executed compacts from iron powder without addition of dielectric. This iron powder was the same as used as a base for other presented dielectromagnetics. Dielectromagnetics for tests were compacted in form of ring samples with dimensions φ50xφ60x5 mm. Applied compacted pressure was 800 MPa and samples were cured at temperature 200oC in the course of 2 hours. The greatest values of density (Fig. 2) were obtained for composite executed without addition of dielectric. Quite large values one can observe for Amicon and Epidian resins diluted in acetone. Decidedly the greatest values of resistivity (Fig. 3) were obtained for Epidian in acetone. It proves uniform distribution of dielectric layers on surfaces of iron powder. Thus this is the most effective manner of magnetic particles insulating. Use of remaining dielectrics, which are in form of very tiny powder, does not cause so good insulation of magnetic particles. Resistivity of the composite without a dielectric is of course very small. Lack of a dielectric causes, that bending strength of such composite (Fig. 4) is not big (around 70 MPa). The greatest value of bending strength (around 120 MPa) was obtained at use Epidian in acetone. Sticking ability of Araldit is not satisfactory (bending strength about 80 MPa), what can be a result of greater sizes of its grains if compare with remaining dielectrics (Amicon and Epidian). Distribution of dielectromagnetics energy losses at induction 0.5 and 1 T for frequencies 50 and 200 Hz are presented in Figures 5-8. Values of losses correspond with resistivity of executed composites. The lowest losses were obtained for dielectromagnetics with Amicon, while a little bit higher for Epidian in acetone. Generally values of losses for different dielectrics little differ from oneself. At higher value of magnetic induction (Figs 7 and 8), differences of losses for tested dielectromagnetics wear away, especially for frequencies 200 Hz (Fig. 8). Magnetization characteristics (Figs 9 and 10) show practically similar, if not saying identical courses for executed dielectromagnetics, both at 50 and 200 Hz. Worse characteristic exhibits dielectromagnetic with addition of Epidian in acetone. Courses of magnetizing characteristics translate oneself on values of permeability (Figs 11-14). Research showed that, within the range of examined frequencies 50÷200 Hz, kind of applied dielectric does not have significant influence on magnetic proprieties of tested dielectromagnetics. It can have more essential influence on such proprieties as mechanical strength or resistivity. Key words: powder metallurgy, soft magnetic materials, dielectromagnetics, dielectrics, properties