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Volume 53, Issue 7
July
Displaying 1-12 of 12 articles from this issue
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Paper
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—Two-dimensional Simulations—Fujio Tsumori, Keiichiro Hayakawa2006 Volume 53 Issue 7 Pages 559-564
Published: 2006
Released on J-STAGE: January 18, 2007
JOURNAL OPEN ACCESSAn attempt is made to a new compaction model, which may agree well with experimental result when the particles are very adhesive. Adhesion force by liquid bridge between particles is incorporated in the present simulation. The simulation of two particles' collision is first performed, and then movements of free falling 1000 particles are calculated. When two particles collide with one another, they stick together. When 1000 particles fall by the gravity, they form clusters. Then, simulations of compaction of 1000 particles are carried out by the present model and the conventional model in which adhesion force of liquid bridge is not considered. In the early stage of these simulations, particles stick together continuously in present model while particles move apart from each other after a brief moment of collision in conventional model. It causes higher compressive stress and less homogeneous distribution in the present model. Furthermore, simulations of unloading in these two models are compared. In the present model, compact body keeps the shape after unloading while particles part each other in the conventional model. Thus, the effect of adhesion of particles is found very clearly in these simulations.View full abstractDownload PDF (718K) -
—Three-dimensional Simulations and Model Experiment—Fujio Tsumori, Keiichiro Hayakawa2006 Volume 53 Issue 7 Pages 565-570
Published: 2006
Released on J-STAGE: January 18, 2007
JOURNAL OPEN ACCESSAn attempt is made to a new compaction model, which may agree well with experimental result when the particles are very adhesive. In our previous report1), we proposed a new model, in which adhesion force by liquid bridge is considered, for two-dimensional DEM simulations, and the effect of adhesion of particles is found clearly. But in three-dimensional space, particles have more freedoms of movement and it is unable to simulate the movement of particles completely with two-dimensional simulations. In this paper, the simulation model is expanded to three-dimension, and compared with the experimental results. Filling and compaction simulations are carried out in three-dimensional space. In the compaction simulation in the mold with a step, particles are agglomerated and make clusters. The behavior of particles in the compaction process in the mold with a step is also observed with micro-focus X-ray CT system. The behavior of particles observed in the experiment is similar to the simulated results, and the simulated changes of relative density in the higher and lower sections of the mold make a good agreement with the experimental results.View full abstractDownload PDF (1035K)
Special Issue:High Quality Permanent Magnets and Their Applications
Summarization
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Hiroshi Yamamoto2006 Volume 53 Issue 7 Pages 572
Published: 2006
Released on J-STAGE: January 18, 2007
JOURNAL OPEN ACCESSDownload PDF (103K)
Review
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Yuji Kaneko, Futoshi Kuniyoshi2006 Volume 53 Issue 7 Pages 573-578
Published: 2006
Released on J-STAGE: January 18, 2007
JOURNAL OPEN ACCESSAs NdFeB sintered magnets have been improved not only in magnetic properties but also in cost-performance, they have been remarkably expanding in the global markets. Especially, motor applications by using NdFeB sintered magnets are rapidly increasing because improvements in motor efficiency are urgent to reduce CO2 exhaust gas. Market demands for these magnets are focused on (1) higher energy products, (2) higher thermal stability and reliability, (3) sales price reduction. Therefore, it is very important to investigate how to realize an excellent alignment of 2-14-1 grains in sintered magnet and how to increase coercive force with a minimum content of Dy through the powder metallurgical process. In this paper, the market trend of NdFeB sintered magnets is introduced and the latest investigation on high performance NdFeB sintered magnets are described.View full abstractDownload PDF (739K)
Paper
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Rintaro Ishii, Toshio Miyoshi, Hirokazu Kanekiyo, Satoshi Hirosawa2006 Volume 53 Issue 7 Pages 579-583
Published: 2006
Released on J-STAGE: January 18, 2007
JOURNAL OPEN ACCESSWe investigated influences of various elements (Ti, Nb, Zr, Mo, Ta, Hf, W, V, Cr) on magnetic properties of Fe-B/Nd2Fe14B based Nd-Fe-B-Ti-C nanocomposite magnets in order to obtain larger coercivity for high temperature applications. As a result, addition of Cr was found to be most effective to enhance coercivity dramatically. Thermal flux losses of high-coercivity (HcJ=1609kA/m) Nd-Fe-B-Ti-C-Cr nanocomposite magnet at 473K are less than 2%.View full abstractDownload PDF (642K) -
Fumitoshi Yamashita, Shuichi Sato, Masaki Nakano, Hirotoshi Fukunaga2006 Volume 53 Issue 7 Pages 584-589
Published: 2006
Released on J-STAGE: January 18, 2007
JOURNAL OPEN ACCESSThe magnetic properties of radially-anisotropic ring-shaped magnets deteriorate when their diameter decreases, so the miniaturization of their magnet motors becomes difficult. In order to overcome this difficulty, we developed a self-organization technique of binder for anisotropic rare-earth bonded-magnets. By using this technique, we controlled the flexibility of perpendicularly-anisotropic rigid sheet-shaped magnets (approximately 1 mm in thickness), transformed them into various specific shapes, and succeeded in preparing radially-anisotropic ring-shaped magnets. In this contribution, we report a new technique which enables us to prepare an composite bonded magnet with a two-layered structure. In the magnet prepared by the developed technique, the direction of easy magnetization varies from the circumferential direction to the radial direction without deterioration of the degree of alignment. Consequently, the multi-polar magnetized magnets observed a smooth flux waveform and the initial irreversible flux loss reduction compared with that of conventional radially anisotropic magnets.View full abstractDownload PDF (801K) -
Hiroshi Yamamoto, Naohiro Mitani2006 Volume 53 Issue 7 Pages 590-596
Published: 2006
Released on J-STAGE: January 18, 2007
JOURNAL OPEN ACCESSExperiments were carried out to investigate the effects of composition, heat-treatment and nitrogenation conditions on the magnetic properties of Sm-Fe-Co-Cr-Y-N compounds with the TbCu7-type structure. The optimum preparation conditions of the compounds were as follows: composition: {Sm10(Fe0.9Co0.1)89.4Cr0.3Y0.3}86.6N13.4, roller velocity: 50 m/s, heat treatment: 680°C for 60 min in high-purity Ar gas, and nitrogenation condition: 420°C for 10 h in high-purity N2 gas. Typical magnetic properties of the obtained compound powders were as follows: Jr=0.98 T, HcJ=765.1 kA/m, HcB=545.4 kA/m, (BH)max=138.5 kJ/m3 (17.4 MGOe), and Tc=523°C. It was found that this sample was an exchange spring magnet from recoil loops of the hysteresis curve, X-ray diffraction patterns and σ-T (Magnetization-Temperature) curve. The value of (BH)max for a compression-molded isotropic bonded magnet prepared by using {Sm10(Fe0.9Co0.1)89.4Cr0.3Y0.3}86.6N13.4 powder was 96.2 kJ/m3 (12.1 MGOe), when the density of bonded magnet was 6.05 Mg/m3. And the average reversible temperature coefficient of Jr was α(Jr)ave.=−0.05 %/°C, the temperature coefficient of HcJ in the range from 25°C to 125°C obtained by a linear extrapolation was α (HcJ)=−0.40 %/°C.View full abstractDownload PDF (666K) -
Tetsuji Saito, Hisanobu Sato, Masato Fukui, Hiroyuku Takeishi2006 Volume 53 Issue 7 Pages 597-601
Published: 2006
Released on J-STAGE: January 18, 2007
JOURNAL OPEN ACCESSSm2Fe17 nitrided powder was consolidated into bulk material at room temperature in an ambient atmosphere by the compression shearing method. The resultant bulk material retained the original Sm2Fe17N3 phase structure without any appreciable decomposition of the Sm2Fe17N3 phase. The bulk material had a density equivalent to 92.7% of the X-ray density of the Sm2Fe17N3 phase. The bulk materials produced at 473 K in nitrogen atmosphere by the compression shearing method had virtually the same density as that produced at room temperature in an ambient atmosphere, but exhibited a maximum energy product of 65.7 kJm−3 with a coercivity of 892 kAm−1.View full abstractDownload PDF (1204K) -
Hiroshi Yamamoto, Hiroaki Nishio, Yoshihito Sawayama2006 Volume 53 Issue 7 Pages 602-609
Published: 2006
Released on J-STAGE: January 18, 2007
JOURNAL OPEN ACCESSAn experiment was carried out to investigate the effect of Ba-Stearate as a reducing agent on the magnetic and physical properties of anisotropic BaFe2-W type ferrite magnets. It was found that the magnetic properties of BaO·8.5Fe2O3 were improved by adding 0.3 wt% of Ba-Stearate, 0.5 wt% of SiO2, and 0.5 wt% of CaO together. The optimum conditions for making magnets were as follows; Chemical composition: Ba1.029Ca0.127Si0.097C0.053Fe2+2.456Fe3+15.392O27, semisintering condition: 1350°C×4.0 h in nitrogen gas atmosphere, drying condition: 180°C×2.0 h in air, sintering condition: 1160°C×1.5 h in nitrogen gas atmosphere. Magnetic and physical properties of a typical sample were Jm = 0.46 T, Jr = 0.43 T, HcJ = 182.3 kA/m, HcB = 177.2 kA/m, (BH)max = 33.8 kJ/m3, Tc = 495°C, HA = 1332 kA/m and KA = 2.65×105J/m3. The lattice constants of this compound were a = 5.883×10−10m, c = 32.92×10−10m, and c/a = 5.596.View full abstractDownload PDF (816K) -
Hiroshi Yamamoto, Masaki Isono2006 Volume 53 Issue 7 Pages 610-616
Published: 2006
Released on J-STAGE: January 18, 2007
JOURNAL OPEN ACCESSSingle phase Ba-Pr-Co M-type ferrite fine particles were prepared by controlling the chemical coprecipitation method and subsequent heat treatment. The chemical reagents used for this experiment were BaCl2·2H2O, FeCl3·6H2O, PrCl3·7H2O and CoCl2·6H2O. The chemical coprecipitation compositions were chosen according to the formula {(BaO)·n/2(Fe2O3)}100−x−y(Pr2O3)x(CoO)y, where n was fixed at 10.5, x was varied between 1.0 and 12.0, y between 2.0 and 10.0. A water solution containing Ba2+, Fe3+, Pr3+ and Co2+ was poured into a solution of NaOH (pH=13.0). The precipitated products were boiled at 100°C for 2h, and they were carefully washed with pure water for 24h. The washing was repeated 5 times and the products were then filtered and dried at 80°C for 12h. The obtained fine particles were heated at a temperature between 950 and 1100°C for 2h in air to get single phase Ba-Pr-Co M-type ferrite fine particles. The most prominent magnetic properties have been observed for the sample with the preparation composition of {(BaO)·5.25(Fe2O3)}92.0(Pr2O3)4.0(CoO)4.0 ; they are as follows: σs=83.1×10−6 Wb·m/kg (66.1 emu/g), σr=41.0×10−6 Wb·m/kg (32.6 emu/g), HcJ=467.8 kA/m (5.88 kOe), α(σr)=−0.19 %/°C, α(HcJ)=0.07 %/°C and Tc=450°C.View full abstractDownload PDF (680K) -
Hiroshi Yamamoto, Hiroaki Nishio, Kenji Kanaya2006 Volume 53 Issue 7 Pages 617-624
Published: 2006
Released on J-STAGE: January 18, 2007
JOURNAL OPEN ACCESSAn experiment was carried out to investigate the effect of Cr substitution on the magnetic and physical properties of Co-Ni spinel ferrite fine particles by the chemical coprecipitation method without post annealing. The chemical coprecipitation compositions were chosen according to the formula (CoO)0.5(NiO)0.5−x(Cr2O3)0.5x·n/2(Fe2O3), where x varied between 0 and 0.2, and n between 2.0 and 2.5. Good magnetic properties were achieved with materials of composition (CoO)0.5(NiO)0.35(Cr2O3)0.075·(Fe2O3). The typical magnetic properties were saturation magnetization σs=33.9×10−6 Wb·m/kg, coercivity HcJ=549.3 kA/m, K1=7.6×104 J/m3, K2=−36×104 J/m3, and anisotropy field HA=5.57 MA/m. Furthermore, the particles were tried to etch in the diluted sulfuric acid solution (concentration 0.5∼2.0%, etching time 6∼30 h) for the purpose of removing super paramagnetic fine particles. Good magnetic properties were achieved with materials of concentration 1.5% and etching time 24h. The typical magnetic properties were σs=91.99×10−6 Wb·m/kg, HcJ=1.39 MA/m, K1=22.8×105 J/m3, and K2=−128.6×105 J/m3. The value of HA can not measured because a measurement magnetic field was not enough.View full abstractDownload PDF (1162K) -
Takashi Honda, Souichi Hatanaka, Jiro Yamasaki2006 Volume 53 Issue 7 Pages 625-629
Published: 2006
Released on J-STAGE: January 18, 2007
JOURNAL OPEN ACCESSAn electromagnetic micromotor based upon a friction drive features relatively high torque at low speeds without reduction gears. In this paper, we have redesigned the motor structure to reduce the thickness below 3 mm and examined its basic characteristics. The motor has a single-phase, two-pole axial gap structure. The stator is a thin excitation coil with a ferrite core. The rotor consists of a NdFeB magnet, 5 mm in diameter and 1 mm in thickness, with three inclined elastic legs, and is magnetically fixed on the stator. When an alternating current is applied to the coil, the rotor oscillates axially according to the change in the attractive force and hops on the stator. Thus the axial oscillation of the rotor is converted into the rotary movement through the friction of the legs. We constructed the motors using a commercial NdFeB magnet and a surface-modified one. As a result, the torque of the motor using the surface-modified NdFeB magnet was much larger than that of the commercial motor. The maximum starting torque obtained here reached approximately 0.11 mNm, which is several times as large as those of commercial DC motors of this volume.View full abstractDownload PDF (611K)
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