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Understand the Radiation Magnetic Ring in One Article

At present, most of the mainstream permanent magnet brushless motors use surface-mounted or embedded magnetic tiles to form a ring-shaped magnetic circuit. However, the spliced magnetic ring has shortcomings such as high processing accuracy of magnetic tiles, difficulty in assembly, poor stability of magnetic pole transition, and serious motor noise. Moreover, this structure requires a frame structure of soft magnetic material to fix the magnetic tiles, which affects assembly efficiency.

The radiating magnetic ring is a type of specially oriented annular permanent magnet that is magnetized in the radial direction around the magnetic ring. It can be widely used in servo motors, magnetic transmissions, magnetic bearings, sensors and other fields instead of spliced magnetic rings.

Common magnetization methods
Common magnetization methods

Main advantages of radiation magnetic rings

  1. The radiating ring is an integral magnetic ring, with better control of dimensional accuracy and simplified assembly process;
  2. The surface field is sinusoidal, evenly distributed, and the transition area between magnetic poles is small, so the motor operates stably and has low noise;
  3. The magnetization methods and magnetic field distribution are diverse. It can be unipolar radiation, multi-pole direct charging and multi-pole oblique magnetization. The magnetic circuit design is more flexible.

Radiation magnetic rings can be divided into magnetic field-oriented and pressure-oriented magnetic rings according to the orientation mode. Among them, sintered or bonded magnetic rings are mostly magnetic field-oriented, and hot-pressed/heat-deformed magnetic rings are mostly pressure-oriented.

According to the material, it can be divided into: ferrite permanent magnet rings, rare earth permanent magnet rings and other permanent magnet rings. Among them, rare earth permanent magnet rings mainly include samarium cobalt permanent magnet rings and neodymium iron boron permanent magnet rings. The ones with the highest magnetic properties are sintered or hot pressed/heat deformed NdFeB magnetic ring. According to the shape, those with an inner and outer diameter ratio less than 0.7 are thick-walled rings, and those with an inner and outer diameter ratio greater than 0.9 are thin-walled rings.

Radiation Magnetic Ring

Due to the relatively mature bonding process and low price, the output of bonded NdFeB radiation rings accounts for the largest proportion. However, the density and performance of bonded magnetic rings are low, and high-end application scenarios are limited. For high-performance sintered and hot-pressed/heat-deformed NdFeB radiation magnetic rings, there are large differences in the shrinkage ratio and thermal expansion coefficient in the directions of the easy magnetization axis and the difficult magnetization axis of NdFeB grains. Therefore, it is easily broken during the preparation, magnetization and assembly processes, the yield is low, and the price is generally high.

Japan carried out the development of radiant ring equipment and processes earlier, and its equipment accuracy and stability, as well as product brands, have great advantages. The research on radiant rings in China started relatively late, but many companies and scientific research institutes are now able to stably supply radiant ring products of various sizes and brands.

Radiation Magnetic Ring

Size of the radiation magnetic ring

  1. The bonded radiation magnetic ring is less limited by size;
  2. Thermal pressure radiation rings are mostly thin-walled magnetic rings, with diameters mostly below 30mm and wall thickness below 3mm;
  3. Sintered radiation magnetic rings can produce products with a maximum outer diameter greater than 200mm, a wall thickness exceeding 5mm, and a height less than 50mm. However, due to qualification rate and cost constraints, most of the products on the market are small-diameter magnetic rings with an outer diameter less than 100mm.

Purchasing personnel can make reasonable choices based on comprehensive factors such as product size, performance and cost-effectiveness.