Sintered Multipole Ferrite Ring Magnet Research

Technology research on sintered ferrite multipole ring magnet with diametrical magnetic orientation

It has been half a century since the permanent ferrite magnet was discovered. The production technologies are developed towards a mature level which brings a higher quality and a larger production scale. Now it has become one of the magnetic materials which have the biggest consumption and widest applications.

In recent years, based on the traditional dry press compacting technology, together with advanced powder making technology, diametrical magnetization direction technology and delicate molding technology, a new sintered ferrite multipole ring magnets with diametrical magnetization direction was developed and become the staring flower in the big family of magnetic materials.

The sintered ferrite multipole ring magnets with diametrical magnetization direction are mainly used in key parts in various delicate transducers, micro synchro motors, DC magnetic field orienting systems and in those occasions where the precise positioning in driven apparatus is required it plays an very important role, such as printer, computerized tooling machines, industrial valves and direction / driving / antenna control system in the aviation industry.

Technological characteristics of sintered ferrite multipole ring magnets with diametrical magnetization direction

As we mention above the sintered ferrite multipole ring magnets with diametrical magnetization direction are mainly used in all kinds of micro synchro motors. Because the application domain of motors requires reliable, stable and precise function in system operation, so the magnets as the key parts of motors, have very high technology requirements. Generally speaking, the magnets require the following technical requirements:

  • High magnetic properties: Taking the 24-pole ring magnet of D23*D16*20(mm) as example, the surface magnetic flux density Bb should be above 180mT to ensure enough force and reliable operation of the whole system.
  • Average deployment of the roles. One requirement is the difference of surface magnetic flux density should be controlled under a range of 3-5%. The other requirement is the angles between roles one another should be equal to ensure a stable and precise positioning function.
  • Strict requirements on the dimension and tolerance. This point is far beyond the common sintered permanent magnets. It is mainly for the purpose of the assembly of whole machine system and meets the requirements of stable operating and low noise.

Craft features

Anisotropic multipole ferrite ring production flowchart

anisotropic multipole ferrite ring production flowchart

The flowchart of the production of the sintered anisotropic multipole ferrite ring magnet with diametrical magnetization direction is shown as above. The flowchart is longer than that of common ferrite magnets. Especially the complicated processing procedures in the dry press compacting and the crafts in each procedure are changeable. Any slight change will have a important import on the magnetic properties of final products.

To sum up, the sintered multipole ferrite ring magnets with diametrical magnetization direction require high technologies, complicated crafts. It has high requirements on the raw materials, equipments, staff and working conditions and environments. The investment of production line is higher than common ferrite production liner, but it has high extra value and return value.

Production equipments

  1. Powder making system:

    The system consists of a series of wet powder crushing equipments, wet prepress compacting equipments, dry and crushing powder making equipments. Compared with traditional powder making system, this system adds wet prepress procedures which show the advance in the powder making. The powder made by this system has better magnetization direction and flexibility. The table below shows the comparison of magnetic properties of multipole ring magnets made by traditional technology and by the modern technology.

  2. No.
    Magnetic property Bb(mT)
    note
    max
    min
    1
    200
    190
    advanced milling technology
    2
    178
    162
    traditional milling technology

  3. Dry shaping system:
  4. The dry shaping processing of the sintered ferrite multipole ring magnets with diametrical magnetization direction is the main distinction in technology with normal ferrite magnets. The system includes highly precise hydraulic press, mold stand system of diametrical orientation, high-pressure impulse magnetizing and demagnetizing and strong wind cooling dust-filtering apparatus. It can ensure the consistent size, equal density and good magnetization direction fixing efficiency for the press compacting multipole ring magnet flan.

  5. Grinding processing system:
  6. Due to the special applications, the whole machine system using the sintered ferrite multipole ring magnets with diametrical magnetization direction has a strict requirement on the dimension and tolerance of multipole ring magnets, including vertical degree, co-axial degree, circle degree, and jumping, etc. All of there is far beyond the requirements on common permanent ferrite magnets.

  7. Magnetizing inspection system:

    The magnetizing and inspection of the sintered ferrite multipole ring magnets with diametrical magnetization direction is also an important procedure. Although multipole ring magnets have a good dimension and Hcj property, if the magnetizing is improper, it can’t get an efficient application. The factors that whether the polarity strength of multipole ring magnets is equal and whether the pole distribution is equal, disregarding the influential factors in the dry press compacting, will on some extend decide the magnetic property of final ring magnets. The inspection system is the eye of the production course.

Conclusions

  1. The production technology of the sintered ferrite multipole ring magnets with diametrical magnetization direction is different from that of common ferrite products. The advance powder making method is the key point and special molds guarantee the good quality.
  2. The production of the sintered ferrite multipole ring magnets with diametrical magnetization direction has a strict requirement on the working environment (humility and temperature).
  3. Because the sintered ferrite multipole ring magnet with diametrical magnetization direction is the essential part of delicate motors, it requires strict quality control system and delicate tooling instruments.