What is the difference between bonded and sintered neodymium magnets?

2026-01-05

Bonded and sintered neodymium (NdFeB) magnets are the two most common types of rare-earth magnets. While they share the same base chemistry—Neodymium, Iron, and Boron—their manufacturing processes, physical properties, and performance levels are fundamentally different.

Here is a technical comparison to help you understand which is best for your specific application.

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1. Manufacturing Process

The primary difference lies in how the magnetic particles are held together.

Sintered Neodymium Magnets: These are produced via a powder metallurgy process. Raw materials are melted, cast into a strip, and then milled into a microscopic powder. This powder is then compacted in a magnetic field to align the particles and "sintered" (heated in a vacuum furnace) until the particles fuse into a solid, dense block.

Bonded Neodymium Magnets: These are made by mixing "quick-quenched" NdFeB powder with a polymer binder (such as epoxy or nylon). The mixture is then formed into shapes through compression molding or injection molding. Unlike sintered magnets, they do not require high-heat fusion.

2. Magnetic PerformanceThe "strength" of a magnet is measured by its Maximum Energy Product (BHmax), typically in MegaGauss Oersteds (MGOe).

Sintered NdFeB

Magnetic Strength (BH_max)：35 – 55+ MGOe

Structure：100% Magnetic material

Magnetic Density：High (~7.5 g/cm³)

Bonded NdFeB

Magnetic Strength (BHmax)：6 – 12 MGOe

Structure：Mixed with non-magnetic binder

Magnetic Density：Lower (~6.0 g/cm³)

Sintered magnets are significantly more powerful because they are fully dense. Bonded magnets have lower performance because the non-magnetic binder "dilutes" the magnetic material.

3. Shape, Precision, and Machining

Bonded Magnets (The "Precision" Choice): Because they are molded, bonded magnets can be formed into highly complex shapes (thin-walled rings, gears, or intricate rotors) with extremely tight tolerances. They often require no secondary machining.

Sintered Magnets (The "Power" Choice): These are brittle and hard, like ceramics. They are typically produced as simple blocks or discs and must be sliced or ground using diamond-coated tools to reach final dimensions. They are prone to chipping and cracking.

4. Magnetization Patterns

Bonded Magnets: Most are isotropic, meaning they can be magnetized in any direction after they are molded. This allows for complex multi-pole magnetization (e.g., 12 or 24 poles on a single small ring), which is ideal for small motors and sensors.

Sintered Magnets: These are usually anisotropic, meaning they have a "preferred" direction of magnetization determined during the pressing stage. While they are much stronger, multi-pole magnetization on a single piece is technically difficult and expensive.

5. Corrosion Resistance and Coating

Bonded Magnets: The epoxy or plastic binder acts as an internal shield. While they still require a coating (like black epoxy) for harsh environments, they are naturally more resistant to corrosion than sintered types.

Sintered Magnets: Sintered NdFeB is highly susceptible to oxidation (rusting). They almost always require a protective surface treatment, such as Nickel-Copper-Nickel (NiCuNi), Zinc, or Gold plating.

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