摘要:

The stiffness of magnetic bearings composed of only two permanent magnet rings is limited. To increase this stiffness, stacked structures are used. Conventional stacking is obtained by placement of the magnetizations in opposition. This article presents another type of stacking with rotating magnetization direction (RMD), which improves the stiffness by about a factor of 2 in comparison with the conventional stack.

ISSN:0021-8979    

DOI:10.1063/1.349857

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

It is necessary to get higherc‐axis alignment of Nd2Fe14B grains in Nd‐Fe‐B magnets for higher‐energy products. During the hot working process, where melt‐spun flakes were hot pressed followed by die‐upsetting, hot‐pressed bodies showed roughly isotropic structure whilec‐axis alignments were developed during die‐upsetting. In this report, we studied the relationship between the reductions during upsetting and the degree of thec‐axis alignments and also tried to get the formula of this relationship. We prepared samples having different reductions and evaluated remanence,c‐axis alignment and strains of each flake in the samples.c‐axis alignments were evaluated using x‐ray diffraction.1Strains were measured using the sizes of each deformed melt‐spun flake. In the range of 50%–70% reduction, remanence was lower in the surface layer than in the center. The difference in remanence in these two regions became smaller as the reduction became larger. The distribution ofc‐axis alignments and strains showed similar phenomena. Then we could propose the following formula showing the relationship between reduction andc‐axis alignment: (&sgr; − &sgr;0)/(&sgr;i− &sgr;0) = (1 − &egr;z)4, where &sgr; is standard deviation ofcaxis alignment and &sgr;0, &sgr;idenotes the &sgr; value at enough large strain and initial value of &sgr;, respectively. &egr;zmeans strain parallel to pressing axis.

ISSN:0021-8979    

DOI:10.1063/1.349832

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

By simultaneous additions of Co and V or of Co and Mo the temperature stability of sintered Nd‐Fe‐Al‐B magnets can be improved.1–3A partial substitution of Nd by Dy increases the coercivity by 1.4 kA/cm per wt. % Dy in the alloy, which results in strong coercivities at high temperatures. At 150 °C, for instance, coercivities of about 9 kA/cm can be achieved. The magnetizing behavior is determined by nucleation of reversed domains. A complete magnetization requires a magnetizing field strength of about 25 kA/cm and does not depend on the coercive field strength. Although in Nd‐Dy‐Fe‐Co‐Mo‐B magnets the Nd‐rich Fe eutectic and the Nd1.1Fe4B4boride are replaced by the Nd3Co compound and the Mo2FeB2boride, respectively, the corrosion is similar to sintered Nd‐Dy‐Fe‐B magnets. The corrosion rate at the 85 °C–85% relative humidity test is much more determined by the surface treatment of the magnets.

ISSN:0021-8979    

DOI:10.1063/1.349833

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The advent of neodymium iron boron rare‐earth permanent magnet material has afforded the opportunity to construct linear machines of high force to weight ratio. The paper describes the design and construction of an axial flux machine and rotating drum test rig. The machine occupies an arc of 45° on a drum 1.22 m in diameter. The excitation is provided by blocks of NdFeB material which are skewed in order to minimize the force variations due to slotting. The stator carries a three‐phase short‐chorded double‐layer winding of four poles. The machine is supplied by a PWM inverter the fundamental component of which is phase locked to the rotor position so that a ‘‘dc brushless’’ drive system is produced. Electromagnetic forces including ripple forces are measured at supply frequencies up to 100 Hz. They are compared with finite‐element analysis which calculates the force variation over the time period. The paper then considers some of the causes of ripple torque. In particular, the force production due solely to the permanent magnet excitation is considered. This has two important components each acting along the line of motion of the machine, one is due to slotting and the other is due to the finite length of the primary. In the practical machine the excitation poles are skewed to minimize the slotting force and the effectiveness of this is confirmed by both results from the experiments and the finite‐element analysis. The end effect force is shown to have a space period of twice that of the excitation. The amplitude of this force and its period are again confirmed by practical results.

ISSN:0021-8979    

DOI:10.1063/1.349834

出版商:AIP    

年代:1991

数据来源: AIP