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Comparison of Sintered NdFeB and Bonded NdFeB Properties

August 08,2023


NdFeB magnets can be divided into bonded NdFeB and sintered NdFeB. The difference between the two is mainly in the process.Bonded NdFeb is made by adding NdFeb magnetic powder to the binder. Lamination is actually injection molding, while sintering is vacuum heating at high temperatures! Sintered NdFeB permanent magnet materials use powder metallurgy technology. The molten alloy is powdered and pressed in a magnetic field to form a briquette. The briquettes are sintered in an inert gas or vacuum to achieve densification, and aging heat treatment is often required to increase the coercivity of the magnet.


1.Sintered NdFeB magnets.

Sintered NdFeB magnets are produced using a powder metallurgy process. First, the molten alloy is powdered and pressed into briquettes in a magnetic field, and then the briquettes are sintered in an inert gas or vacuum to achieve densification.Generally, only magnet blanks can be produced after sintering, which are then machined (e.g., wire cutting, slicing, grinding, etc.) to make magnets of various shapes.


Sintered NdFeB permanent magnets are widely used in electronics, motors, medical equipment, toys, packaging, hardware machinery, aerospace and other fields. The more common ones are permanent magnet motors, speakers, magnetic separators, computer disk drives, magnetic resonance imaging equipment instruments and so on.

Compared with bonded NdFeB magnets, sintered NdFeB magnets have high processing costs, high losses during processing and poor dimensional accuracy. But its advantages are also obvious. At present, the (BH)max of sintered NdFeB magnets can reach more than 50M, while bonded magnets are generally below 10M.


2.Bonded NdFeB magnets.

Bonded NdFeB magnets consist of Nd2Fe14B, a synthetic magnet. Bonded NdFeB magnets are magnets made from fast quenching NdFeB powder and binder by "molding" or "injection molding".

Bonded NdFeB has the advantages of low cost, high dimensional accuracy, large freedom of shape, good mechanical strength, light weight, etc. It is widely used in the fields of office automation equipments, electrical installations machinery, audio-visual equipments, instruments, small motors, measuring instruments and so on. Machinery, cell phones, CD-ROM, DVD-ROM drive motor, hard disk spindle motor HDD, other miniature special DC motors and automation instrumentation and other fields.

Compared with sintered NdFeB magnets, bonded NdFeB magnets can be molded in one go without secondary processing, and can be made into complex magnets of various shapes, which is incomparable with sintered magnets. With the help of bonded NdFeB magnets, one can greatly reduce the size and weight of motors.


3.What are the specific differences between bonded NdFeB and sintered NdFeB in terms of production and processing technology, density, magnetic properties, surface treatment, price, etc.?

Comparing the densities of the two, bonded NdFeB has a density of about 6 g/cm³, and sintered NdFeB has a density of about 7.5 g/cm³.

Bonded NdFeB materials contain less neodymium compared to magnets and therefore do not perform as well as sintered NdFeB. Thin-walled magnetic rings are generally bonded NdFeB.

There are two types of surface treatment: sintered NdFeB is usually galvanized or nickel-plated, and bonded NdFeB is usually black epoxy resin.