Phase transformations in Mn-Al permanent magnet alloys

Phase transformation studies have been made of the Mn-Al alloys with compositions near the equiatomic range with or without small amounts of carbon, copper and nickel, using differential thermal analysis, X-ray diffraction and optical and electron microscopy. The high temperature hexagonal phase obtained by quenching, transforms to the ferromagnetic phase between 500 and 550° C and on further heating transforms back to the hexagonal phase between 750 and 950° C. Also, on controlled cooling of the phase from about 900° C, the ferromagnetic phase is formed between 800 and 670° C. TEM studies have shown the presence of the B19 ordered phase, ferromagnetic phase and Mn₅Al₈ precipitates even in quenched alloys.     

Magnetic domain structure of isotropic MnAlC permanent magnet alloys

Observations of the magnetic domain structure were made on an isotropic MnAlC alloy (of the following composition: 73.0 wt% manganese, 26.4 wt% aluminium and 0.6 wt% carbon) homogenized at 1373 K for 1 h, quenched in water and tempered in the temperature range from 723 to 923 K. Observation of the magnetic domain structure was carried out by the Bitter powder pattern technique. It was found that the magnetic properties of the MnAlC alloy are closely related to the type of magnetic domain structure.     

烧结NdFeB永磁合金的腐蚀行为研究及进展

介绍了烧结NdFeB磁体的腐蚀机理和近年来NdFeB永磁材料防腐蚀研究的进展情况,着重评述了合金化法、防护涂层和放电等离子烧结NdFeB的特点及存在的问题,并提出了改进措施.     

The effect of boron on the magnetic properties of AlNiCo 5 permanent magnet alloys

The investigation of the effect of boron (0–1.0 wt%) on the magnetic properties of magnetically hard Alnico 5 alloy of equiaxial grain structure has shown that the addition of this element in the amount up to 0.003 wt% Increases the coercive force and maximum Magnetic energy product but decreases the remanent induction. The addition of boron > 0.003 wt% causes the decrease of those properties.     

Self-regulating permanent magnet linear motor

A new type of self-regulating permanent magnet linear motor (PMLM) is proposed. This PMLM utilizes chiefly permanent magnets and a ferromagnetic yoke for producing a force to propel a flying vehicle. A detailed structure and the theory of the proposed PMLM are given     

Magnetization changes for cobalt-rare-earth permanent magnet alloys when heated up to 650°C

Changes in magnetization with temperature are of concern to the engineer designing permanent magnet devices. Of particular interest are the reversible and irreversible losses which occur when a magnet is heated to a slightly elevated temperature. In this paper the nature of the irreversible magnetization losses which occur when Co-Sm and other cobalt-rare-earth permanent magnets are heated above room temperature are discussed. It is shown that the losses are dependent upon the operating point of the demagnetization curve, and also that post-sintering thermal processing can play a significant role in controlling the changes in magnetization with temperature. Data are given on the effect of composition and high-temperature aging and cooling rate on the irreversible losses. Measurements of demagnetization curves at temperatures up to 200°C are given for a Co-Sm magnet and the data is related to the irreversible losses.     

Fields in permanent magnet linear synchronous machines

The determination of electromagnetic fields in permanent magnet linear synchronous machines (PMLSM's) to form the basis for the evaluation of forces and parameters of PMLSM'S (to be presented in a subsequent paper) is discussed. Analytical techniques applied to permanent magnet rotary synchronous machines are modified and adapted to PMLSM's. Fields are determined analytically in a single-sided PMLSM, and computed results by the finite-element method are compared with those obtained experimentally. A good correlation between the results obtained by the three procedures-analytical, finite-element computational, and experimental-validates the approximations used in the analysis.     

A magnetic transducer with a permanent magnet

Conclusions At present the development of magnetic transducers of the type described is in its infancy.The investigation carried out cannot be considered as exhaustive, since a complete evaluation of the possibilities of the new system can only be made after considerable experimental material has been accumulated and the theory developed still further. The outlines method of designing magnetic transducers, however, may be found useful.     

Three-dimensional analytic model of permanent magnet axial fluxmachine

A three-dimensional (3-D) magnetic field problem in an axial flux machine with a toroidal winding is considered. The precise solutions generated by the integral transform and Fourier methods in elementary subregions are joined using the iterative Schwartz algorithm. The comparison between two dimensional and 3-D models is performed and a correction factor taking into account the radial variation of the magnetic flux is given     

各向异性纳米耦合永磁材料的制备

采用热变形和SPS-热变形两种方法,探讨制备高性能纳米双相耦合材料的可能性,发现(1)、采用热变形的方法,可以实现晶粒组织的纳米尺寸,为实现材料的耦合打下基础.(2)、采用SPS-热变形方法,可以制备出密度更高、各向异性显著的磁体.     

Recent advances in permanent magnet brushless DC motors

This paper deals with the latest developments in Permanent Magnet Brushless DC (PMBLDC) motor drives. A comprehensive account of the state-of-the-art on types of construction of the motor, closed loop controllers in position, speed and current/torque control and recent trends in inverters, sensors etc. are given. Techniques for mechanical sensors elimination are discussed in detail. Special efforts made to reduce torque ripples, noise and vibrations are described. The impact of microelectronics through integrated chips used in the control of PMBLDC motor drives is given. The increasing applications of this drive due to improved performance and its cost reduction are also enlisted.     

Superconducting bulk magnet for maglev vehicle: Stable levitation performance above permanent magnet guideway

High-temperature superconducting (HTS) maglev vehicle is well known as one of the most potential applications of bulk high-temperature superconductors (HTSCs) in transported levitation system. Many efforts have promoted the practice of the HTS maglev vehicle in people's life by enhancing the load capability and stability. Besides improving the material performance of bulk HTSC and optimizing permanent magnet guideway (PMG), magnetization method of bulk HTSC is also very effective for more stable levitation. Up to now, applied onboard bulk HTSCs are directly magnetized by field cooling above the PMG for the present HTS maglev test vehicles or prototypes in China, Germany, Russia, Brazil, and Japan. By the direct-field-cooling-magnetization (DFCM) over PMG, maglev performances of the bulk HTSCs are mainly depended on the PMG's magnetic field. However, introducing HTS bulk magnet into the HTS maglev system breaks this dependence, which is magnetized by other non-PMG magnetic field. The feasibility of this HTS bulk magnet for maglev vehicle is investigated in the paper. The HTS bulk magnet is field-cooling magnetized by a Field Control Electromagnets Workbench (FCEW), which produces a constant magnetic field up to 1 T. The levitation and guidance forces of the HTS bulk magnet over PMG with different trapped flux at 15 mm working height (WH) were measured and compared with that by DFCM in the same applied PMG magnetic field at optimal field-cooling height (FCH) 30 mm, WH 15 mm. It is found that HTS bulk magnet can also realize a stable levitation above PMG. The trapped flux of HTS bulk magnet is easily controllable by the charging current of FCEW, which implies the maglev performances of HTS bulk magnet above PMG will be adjustable according to the practical requirement. The more trapped flux HTS bulk magnet will lead to bigger guidance force and smaller repulsion levitation force above PMG. In the case of saturated trapped flux for experimental HTS bulk magnet, it is not effective to improve its maglev performances by increasing of charging magnetic field, when the guidance force at WH 15 mm is 5.7 times larger than that by DFCM of FCH 30 mm. So introducing HTS bulk magnet into the present maglev system is feasible and more controllable to realize stable levitation above applied PMG, which is an important alternative for the present HTS maglev vehicle.     

一种新型永磁球形步进电动机的研究

针对国际上新提出的一种永磁球形结构步进电动机进行了研究。首先运用积分方程法和三维有限元法进行了磁场计算,在此基础上应用麦氏张量法和虚位移法对其转矩特性进行求解,获得了电机的矩角特性,并通过不同的方法对比验证了计算结果的正确性。同时提出一种基于加权无向图的运动控制算法,通过对路径进行搜索,实现了对电机通电状态的有效控制,达到了沿着期望运动轨迹运动的目的。在对电机及其滑轨支架位置检测系统进行运动学分析的基础上,对电机实际步进运动过程和编码器输出进行了仿真研究,结果显示出了位置检测系统和控制算法的有效性。     

Designing printed circuit stators for brushless permanent magnet motors

Progress in a number of areas of technology has made printed circuit motors a serious contender for many applications. Modern cost effective neodymium magnets have allowed compact motor designs. Multi-layer circuit board production techniques have made the production of printed circuit coils cheaper and easier. However, in spite of the growing importance of printed circuit brushless motors, there is a lack of analytical tools to assist with their design. Geometrical analysis has been used to allow the plotting of printed circuit tracks to be carried out more systematically. The track plotting procedures have been linked with the finite element method to predict rotational electromotive force (EMF) waveforms. Six prototype motors were built and they were used to experimentally validate the method of predicting EMF waveforms. A general design algorithm is presented based on the suggested track plotting procedure and the EMF prediction technique.     

No-load magnetic-field distribution in a permanent magnet electrical machine

A numerical method for the calculation of a stationary two-dimensional magnetic field in a permanent magnet electrical machine at no-load is presented. The field approach based on Maxwell's equations is used to formulate the vector potential equation with variable tensor coefficients which holds for any point in the machine cross section perpendicular to the shaft axis. The partial differential equation is transformed into a finite-difference numerical algorithm. The set of nonlinear partial-difference equations is solved by the iterative line successive overrelaxation procedure. The method presented here is an extension of the Colorado method of Erdélyi and his associates for finding two-dimensional magnetic fields in electrical machines with electromagnetic excitation.     

A new permanent magnet material: Modified Ca ferrite

An experiment was carried out to investigate the preparation condition of anisotropic Ca system ferrite magnets with optimum magnetic and physical properties. Compositions were chosen according to the formula (CaO.nFe2O3)100-x(La2O3)x, wherexwas varied between 0 and 4.0, and n between 5.5 and 6.25. The optimum condition of making magnets and some properties of a typical specimen are as follows. The preparation condition: composition (CaO.6Fe2O3)97(La2O3)3, semisintering condition 1250°C × 1 h in O2gas, sintering condition 1275°C × 0.5 h in O2gas. Magnetic properties:4piI_{10}k = 4200G, 4πIr = 4100 G,IHC= 2100 Oe,BHC= 2050 Oe,(BH)_{max} = 3.5MG . Oe, Ku = 3.34 × 10⁶erg/cc, HA= 20.5 kOe,sigma_{s} = 64.8emu/g, Tc = 446°C.