Bonded Magnets


Bonded Magnet (Polymer bonded magnets) is one of the most important magnetic materials. It opened a new world of application possibilities. Thermo-elastomer and thermo-plastic resins can be blended together with a variety of magnetic powders to form injection molded, compression and flexible magnets.

Bonded NdFeB magnet is composed with compression NdFeB magnet, injection NdFeB magnet and flexible NdFeB magnet. Since its birth in the middle of 1980’s, the demand of bonded NdFeB magnet has been dramatically increasing for the industries of automatic control, automobile, 3C products (computer, communication & consumer electronics) and household electric appliance with virtues as follows:

  • Offering new and cost-effective solutions for design and manufacture with availabilities of typical toughness of plastic, diverse and complex geometry, preferred magnetizing pattern, as well as more assembling methods.
  • Extensive choice of property range 1.0—11.5 MGOe.
  • Much better resistance of corrosion than sintered NdFeB magnet.
  • Free-machining by direct molding with net shape and close-tolerance
  • Minimizing figure and weight of application due to its comparatively stronger magnetic property and lower density.

Bonded magnet materials can be made from Ceramic, NdFeB, or SmCo powders which are combined with a variety of plastic binders (Matrix). They can be either Injection Molded or Compression Bonded into complex magnet shapes with finished dimensions. Bonded magnet materials have a moderate resistance to corrosion and a low tolerance to heat because of the binder material. Bonded magnet materials are commonly used in automotive parts because they lend themselves to large production quantities and complex shape can be produced at a low cost.

Injection molded magnets can be formed into complex shapes and be insert molded directly onto other components to produce assembly parts. Compression bonded magnets offer higher magnetic output than injection-molded magnets, but are limited to more simple geometries.

Forming methods of Bonded Magnets

Bonded Magnets are formed by either injection molding or compression molding.

Injection molding provides flexible shapes and compression molding provides higher magnetic properties.


Injection Molded:

  • Binder Types / Nylon / PPS / Polyamide.
  • Temperature Range -40c – 180c
  • Very Tight tolerances off tool ( 0.002 -0.003 Typical )
  • Very good mechanical strength

Compression Bonded:

  • Higher Magnetic Strength due to higher magnetic particle density.
  • Epoxy Binder / Resistant to normal industrial solvents and automotive fluids
  • Epoxy Coat after manufacturing to prevent oxidation
  • Temperature Range -40c – 165c
  • “Tight” tolerances off tool
  • Good mechanical strength

Typical Bonded Magnet Applications:

  • Sensors
  • Brushless DC Motors

General Bonded Magnet Applications:

  • Materials are isotropic and can be magnetized in any direction
  • Wide range of existing tool sizes are available in rings, discs and rectangles
  • Exsisting Multipole magnetizing fixtures for quick prototyping
  • Easily machined
  • Existing Multipole rings simplify assembly verse arc sepments

Surface Treatment:

In blending process, NdFeB alloy powder is embedded in epoxy resin or other thermal plastics what are solvent resistant against normal industrial and automotive fluids. Therefore bonded NdFeB magnet is more stable than sintered NdFeB magnet. However if the magnet is working in hot, moist and other corrosive environment, then coating is very necessary. Normally compression NdFeB magnet should have surface treated for protection purpose, meanwhile injection and calender bonded NdFeB magnet are no need to be coated due to high volume fraction of binder.

Temperature Character:

Both magnet remanence and coercive force will be decreased when the temperature on bonded NdFeB magnet is increased. Irreversible and reversible flux loss will take place at the same time. Temperature change will also obviously take effect on swelling, shrinkage, hardness, strength etc physical characters of bonded NdFeB magnet. As a composite, the maximum working temperature of bonded NdFeB magnet is not merely determined by the type of NdFeB alloy powder but also influenced by the used binder. The recommended working temperature of nylon 12 (PA12), nylon 6 (PA6), epoxy resin and PPS are respectively up to 100℃, 120℃, 180℃, 200℃ for continuously working.


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