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.

Compression Molding NdFeB Magnet
GradeResidual InductionCoercive Force Intrinsic Coercive ForceMax Energy
Product
Average ReverslMax
Working Temp.
Curie
Temp.
BrHcbHc(BH)maxTmTc
mTkGskA/mkOekA/mkOekJ/m3MGOe%/°C°C°C
BN-2300-4003.0-4.0240-3203.0-4.0480-6406.0-8.024-323.0-4.0-0.11160300
BN-4400-5004.0-5.0240-3203.0-4.0560-7207.0-9.032-484.0-6.0-0.11160300
BN-6500-6005.0-6.0320-4004.0-5.0560-7207.0-9.048-606.0-7.5-0.11160300
BN-8600-6806.0-6.8360-4404.5-5.5640-8008.0-10.060-727.5-9.0-0.11160300
BN-8H600-6506.0-6.5400-4805.0-6.01040-136013.0-17.064-728.0-9.0-0.10180350
BN-8L600-6806.0-6.8400-4805.0-6.0640-8008.0-10.064-728.0-9.0-0.11160300
BN-8SR620-6806.2-6.8400-4805.0-6.0800-112010.0-14.068-768.5-9.5-0.10180350
BN-10680-7306.8-7.3400-4805.0-6.0640-8008.0-10.076-849.5-10.5-0.10160350
BN-10H700-7507.0-7.5440-5205.5-6.5640-8008.0-10.080-8810.0-11.0-0.10160350
BN-12720-7707.2-7.7440-5205.5-6.5720-8009.0-10.080-8811.0-12.0-0.10160350
Injection Molding NdFeB Magnet
GradeResidual InductionCoercive Force Intrinsic Coercive ForceMax Energy ProductAverage ReverslMax Working Temp.Density
BrHcbHcj(BH)maxTm
mTkGskA/mkOekA/mkOekJ/m3MGOe%/°C°Cg/cm3
BZ-3200-3002.0-3.0160-2402.0-3.0480-6406.0-8.012-241.5-3.0-0.111203.9-4.4
BZ-4350-4503.5-4.5240-3203.0-4.0560-7207.0-9.024-363.0-4.5-0.111204.2-4.9
BZ-5450-5504.5-5.5304-3603.8-4.5640-8008.0-10.036-444.5-5.5-0.111204.5-5.1
BZ-6500-6005.0-6.0328-3844.1-4.8640-8008.0-10.044-525.5-6.5-0.111204.7-5.2
BZ-7550-6505.5-6.5344-4004.3-5.0640-8008.0-10.052-606.5-7.5-0.121204.7-5.3
BZ-5H(SR)450-5504.5-5.5320-4004.0-5.0880-112011.0-14.036-444.5-5.5-0.111804.8-5.3
BZ-6H(SR)500-6005.0-6.0320-4004.0-5.0880-112011.0-14.044-525.5-6.5-0.111804.9-5.4
Injection Molding Ferrite Magnet
GradeResidual InductionCoercive Force Intrinsic Coercive ForceMax Energy ProductDensity
BrHcbHc(BH)max
mTkGskA/mkOekOekA/mkJ/m3MGOeg/cm3
BZ-F1.5220-2402.2-2.4160-1672.00-2.10231-2402.90-3.0011.6-12.41.45-1.553.25
BZ-F1.9270-2902.7-2.9180-1862.25-2.33216-2282.70-2.8514.8-15.61.85-1.953.63
BZ-F2.0280-2902.8-2.9184-2002.30-2.50216-2462.70-3.1015.6-16.41.95-2.053.70
BZ-F2.1280-2902.8-2.9190-2042.38-2.55224-2492.80-3.1216.4-17.22.05-2.153.75
BZ-F1.7 (PPS)250-2602.5-2.6167-1752.10-2.20208-2162.60-2.7013.6-14.01.70-1.753.56

The max working temperature of PA6 magnet is 150˚C
The above-mentioned data of magnetic properties and physical properties are given at room temperature.
The max working temperature of magnet is changeable due to length-diameter ratio, coating thickness and another environment factors.

Compression molding magnet uses a solid binder (e.g. a plastic or thermosetting epoxy) plus the magnetic material. The end material is isotropic – the magnetising coil fixture design determines the magnetic pattern it takes.
Compression molding bonded magnet is cost effective when higher volumes are required compression molded magnets are best produced in tens or hundreds of thousands of magnets per production run.

Advantages

  • A higher ratio of magnetic material powder to binder gives higher magnetic performance than the injection molded magnets (higher magnetic loading)
  • NdFeB, SmCo, Alnico and Ferrite versions possible
  • Hybrid versions as well (e.g. Ferrite+NdFeB) with combined properties
  • Good tolerances – secondary machining not needed
  • Low electrical conductivity, low eddy currents

Disadvantages

  • The compression bonding process is limited to simpler shapes such as rectangles, rings, arcs and cylinders. A consistent cross sectional area is required along the pressing direction
  • Possible tooling charges for production and magnetizing

Typical Applications

  • Motors
  • Position sensors
  • Hybrid performance components

Injection molding magnet uses a solid binder (e.g. a plastic or thermosetting epoxy) plus the magnetic material but gives a greater variety of shapes and complexity of shapes compared to compression bonded. The end material is isotropic – the magnetising coil fixture design determines the magnetic pattern it takes.

Overmolding is possible with injection molding process.

Injection molded magnets are produced in tens or hundreds of thousands of magnets per production run.

Advantages of Injection Molded Magnet

  • More complex shapes are possible
  • Overmold, insert mold, etc all possible
  • NdFeB, SmCo, Alnico and Ferrite versions possible
  • Hybrid versions as well (e.g. Ferrite+NdFeB) with combined properties
  • Low electrical conductivity, low eddy currents
  • Good tolerances. More resistant to chipping than compression bonded

Disadvantages of Injection Molded Magnet

  • Injection molded magnets offer lower magnetic performance than the compression bonded magnets (due to lower magnetic loading)
  • Possible tooling charges for production and magnetizing

Typical Applications of Injection Molded Magnet

  • Motors
  • Sensors
  • Injection molded rotor assemblies
  • Insert molded magnetic components
  • Overmolded magnetic components

Some Physical Properties of Bonded NdFeB Magnets

ParameterUnitValue
Density (ρ)g/cm34.0-6.5
Curie Temperature (Tc)ºC300-350
Recoil Permeability (μrec)1.20
Rockwell Hardness (HR)MPa35-45
Compressive Strenght (σbc)MPa800-1000
Tensile Strength (σb)MPa200
Thermal Expansivity (α)10-6/ºC1-2

Note:
∗ The above data are only for reference, specific magnets maybe have different values.

Bonded NdFeB magnets, neodymium iron boron, rare earth permanent magnets, Bonded Ferrite magnets Shape:

Ring Magnets

Abnormal Shape Magnets

Magnetic Assemblies with Metal

Rotor Assemblies

Arc/Segment Magnets

Block/Rectangular Magnets

Note: ∗ Other shapes of bonded NdFeB magnets can also be tailored according to customers’ specific requirements.

LECMAG’s Bonded Magnets (Polymer Bonded Magnets, Compression Molded Magnets, Injection Molded Magnets) Display

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