Multipole ring magnet is infinitely a preferred path for rotating machinery and magnetic coupling device compared with traditional splicing several arc magnets. Besides polar anisotropic ring magnet which made by multipole orientation technology, radial ring magnet, which also known as radially oriented ring magnet, is the most common and mature solution to produce multipole ring magnet. Radial ring magnet can be manufactured by either powder metallurgy process or hot deformation process, then powder metallurgy process can be further classified to earlier repulse orientation technology and Chinese unique rotating orientation technology according to the detailed generation mode of radially orientation magnetic field. Hot-pressed radial ring magnets exhibit much better performance in comparison with rotating oriented ring magnet:
a. Hot deformation process can generate anisotropy along the radial vector of the ring without applying radially orientation magnetic field, which totally different from powder metallurgy process.
b. Hot-pressed ring magnet is more tailored for the small-sized, high L/D ratio, or thin-walled ring magnet.
c. The density of rotating oriented ring magnet even lower than routine sintered Neodymium magnet, therefore, its corrosion resistance cannot compare with full-density hot-pressed magnet which has the lower content of Nd-rich phase and the nanocrystalline structure.
d. Rotating oriented ring magnet is always subject to inevitable cracking and deformation which caused by internal stress, thus exhibit lower mechanical strength than hot-pressed magnet.
e. Hot-pressed ring magnet is very beneficial to save rare earth resources and control product costs, its rare earth element amounts are lower 2% than rotating oriented ring magnet under the same magnetic performance requirement and need less heavy rare earth elements (HREEs) to improve thermal ability. In addition, hot deformation process is a kind of near net-shape technology, which has relatively higher material utilization rate.
f. Hot-pressed magnet has been proven to offer reliable guarantee to motor performance. The relevant testing results indicate that magnetic field strength waveform of rotating oriented ring magnet exhibit abnormal dispersion, then magnetization pattern of rotating oriented ring magnet also reflect weird spiral shape.
Analysis of such abnormal waveform and magnetization pattern in rotating oriented ring magnet can beunfolded via below sketch conversion.
For rotating orientation technology, there are always 10 – 20 degree deviation angles between ideal and practical orientation direction due to its own technical defects, then above abnormal waveform is more obvious when multipole ring magnet has larger pole width.
