• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.49 no.10
• /
• pp.652-658
• /
• 2000

In many cases, ferrite magnets of ferrite bonded magnets used in inner-rotor type small brushless DC(BLDC) motors do not have rotor core. The magnetization directions of permanent magnets do not have only parallel or radial direction. In this case, the characteristics of magnets are different from cored type ones which have uniform magnetization direction. In this paper, the magnetization directions and intensities of a ferrite magnet and a ferrite bonded magnet are analyzed by finite element analysis for magnetization procedure. The characteristics of inner-rotor type BLDC motor are analyzed by using the analyzed results. The validity of the method is verified by comparing the analyzed results with measured ones.

• Electrical & Electronic Materials
• /
• v.10 no.5
• /
• pp.440-446
• /
• 1997

This research has been performed for the fabrication of high quality ferrite plastic magnet. The magnetic properties of S $r_{5.9}$F $e_2$ $O_3$ ferrite bonded magnets by injection moulding with a variety of applied magnetic field were investigated. 0.3wt% CaCO3, 0.2wt% $SiO_2$, 0.5wt% $Al_2$ $O_3$and 0.5wt% N $a_2$ $SiO_3$are added in order to improve the magnetic properties of Sr-ferrite plastic magnets during the powder fabrication. For carbon coating on chemical compound specimen, 5wt% polyvinyl alcohol is added, and then calcinated under $N_2$ environment of 12$25^{\circ}C$. The particle size is distributed from 0.9~1.2${\mu}{\textrm}{m}$ which approximates to the single domain. The obtained Sr ferrite powder is well mixed with silane coupling and calcium stearate of 1wt%. Nest, the specimen is pelleted after kneading each of them with polyamidel2 as a binder. When the temperature of injection and mould were 25$0^{\circ}C$ and 8$0^{\circ}C$ respectively at injection pressure of 200kgf/$\textrm{cm}^2$, the degree of orientation was 85.3% under the applied magnetic field of 12kOe. As the results, when the packing density of Sr ferrite powder was 90wt%, the magnetic properties of Sr ferrite bonded magnet were follows : $_{B}$ $H_{c}$=2.41kOe, Br=3.1kG, (BH)$_{max}$=2.21MgOe. Especially, the Sr-ferrite bonded magnet with 10wt% N $d_2$F $e_{14}$B additive were as follows : $_{B}$ $H_{c}$=2.57kOe, Br=3.14kG and (BH)$_{max}$=2.39MGOe.GOe.GOe.GOe.e.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.59 no.12
• /
• pp.2173-2178
• /
• 2010

The magnetization directions of a polar magnetized ferrite bonded magnet are analyzed by finite element method (FEM). The influence of the width of SmCo magnets for magnetic field generation is investigated. The surface flux densities of the polar anisotropic magnets are analyzed and compared according to the pole number and thickness of the magnets. And the electromotive force (EMF) values of brushless DC motors with the magnets are investigated. The validity of the analysis method is verified by comparing the analyzed results with measured ones.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.23 no.12
• /
• pp.988-995
• /
• 2010

In this study the (Alnico, Sm-Co) bonded magnets were fabricated by mixing the Sm-Co added alnico alloy powders with epoxy resin and binder, appropriately. Also, the hybrid ring magnets of (Alnico, Sm-Co)/Sr-ferrite were fabricated by coupling the Sr-ferrite composite layer with an (Alnico, Sm-Co) magnet. The magnetic properties of (Alnico, Sm-Co) ring magnets were varied with the amount of Sm-Co powders. The addition of Sm-Co powders increased a remanent induction($B_r$) and coercive force($_BH_C$), while decreasing a surface flux density and repulsive distance. The surface flux density and repulsive distance for the (Alnico, Sm-Co) ring magnet increased with a magnetizing voltage up to about 160 V and reached an apparent saturation point. Also, the measurements of temperature and moisture characteristics showed that the surface flux densities of N-S poles and repulsive distance decreased a little within 4% after 10 days passed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1997.11a
• /
• pp.120-123
• /
• 1997

In this paper, we deal with the effect on magnetic properties when Nd is added to Sr ferrite bonded magnet. First, we choose SrO$_{n}$.Fe$_2$O$_3$(n=5.9), which is nonstoichiomatric composition, as specimen ferrite. Then, we add 5wt% polyvinyl alcohol and calcinate at 12$25^{\circ}C$ under $N_2$ environment for carbon coating on chemical compound specimen. After that we obtain 1.2${\mu}{\textrm}{m}$ single domain powder through grinding process for 18 hours. The single domain Sr ferrite Powder is well mixed with silage coupling and calcium stearate of 1wt% Then, it is kneaded by using polyamide12 as a binder and is pelleted. After adding Nd-Fe-B powder to the pelleted specimen, we injection-mould it under magnetic field by using anisotropic mould. Especially, when we add l3wt% Nd-Fe-B powder to the polyamide12, we obtain excellent magnetic propertiecs which are $_{B}$H$_{C}$=2.65KOe, Br=3.16KG and (BH)$_{max}$=2.61MGOeOeOeOeOe

• Journal of Magnetics
• /
• v.9 no.4
• /
• pp.105-108
• /
• 2004

The attempt for the addition of double-phase nanocomposite $Nd_2Fe_{14}BFe_3B$ powders, respectively, into several $RE_2Fe_{14}B$(RE=Pr, Nd) powders with high magnetic properties was carried out. The powders were compounded and compressed to take shape bonded magnets. By means of investigating the variation of compound magnet $B_r$, the interaction between magnetic powders was revealed. The result shows that not chemical just but physical interaction exists between elements. The compound effect of $Nd_2Fe_{14}BFe_3B$-ferrite bonded magnets was detailed studied. The functional relation was revealed between magnetic properties and ferrite content. That is $Y = 5.42 x^2 -11.34x + 6.62$. The variation of $_iH_c$ temperature coefficient ${\beta}_{iHc}$ with ferrite content was investigated. Following the ferrite content increased, ${\beta}_{iHc}$ and $h_{irr}$ were obviously decreased, compression-resistant strength was enhanced.

• Proceedings of the KIEE Conference
• /
• 2004.10a
• /
• pp.110-112
• /
• 2004

The magnetization directions of a polar anisotropic ferrite-bonded magnet are analyzed by finite element method (FEM). The influence of the width of Sm-Co magnets for magnetic field generation is investigated. The surface flux densities of the polar anisotropic magnets are analyzed and compared according to the pole number and thickness of the magnets. And the electromotive force (EMF) values of brushless DC motors with the magnets are investigated.

• Proceedings of the Korean Magnestics Society Conference
• /
• 1996.05a
• /
• pp.44-45
• /
• 1996

• Journal of the Korean Magnetics Society
• /
• v.6 no.5
• /
• pp.310-316
• /
• 1996

In this study magnetic properties of anisotropic ferrite bonded magnets produced by extrusion molding with a variety of magnetic field, extrusion mold temperature and extrusion rate were investigated. X-ray diffraction study showed the alignment of magnetic powder was decreased by molten flow in extrusion mold. When the temperature of extrusion mold was $20^{\circ}C$, the degree of alignment as much as 82% could be achieved under the applied magnetic field of 4 kOe. The bonded magnets having the remanence of 2.2 kG was able to fabricated by extrusion molding when the packing density of Sr-ferrite powder was 50 vol%.

• Journal of the Korean Magnetics Society
• /
• v.21 no.4
• /
• pp.147-150
• /
• 2011

Since their discovery in the early 1980's, the market for bonded rare earth magnets has shown steady growth. Today these magnets are widely used for our daily life such as computer peripherals, automotive, consumer electronics, and office automation. However, the price increases of rare-earths started from the $2^{nd}$ half of 2010 became even worse in 2011. During $2^{nd}$ quarter of 2011, almost all of rare-earths showed unprecedented vertical price increases, and it brought significant impact to the related industry in terms of the price and supply. This will ask the fundamental change in the policy of the bonded rare earth industry to expand its market share, which has been highly dependent on the replacement of ferrite magnets via relatively higher performance compared to the price at certain applications. In order to achieve the sustainable growth of bonded rare-earth magnets in the future, it needs to change the current paradigm and setup the new business model. This article includes a brief summary of the rare earth price trend and the applications of the rare-earth bonded magnets. The efforts to improve the performance and diversify the applications for future growth have been also presented.