NdFeB Family Big Decryption: Sintering - Bonding - Hot Pressing(1)

NdFeB permanent magnet products can be divided into sintered NdFeB, bonded NdFeB and hot pressed NdFeB according to the different production process. Due to the different production process, they have great differences in the magnetic properties of products, post-processing and application. In the early stage, we have made a systematic introduction to sintered NdFeB. Next, we will introduce bonding and hot pressing NdFeB, as well as the comparison of three different NdFeB products in performance and application.

Bonded NdFeB

Bonded magnets appeared around the 1970s, when SmCo magenets had reached commercialization, sintered NdFeB permanent magnets market situation is very good, but it is difficult to precision machining into special shape, and in the process of processing is prone to cracking, damage, edge, Angle and other problems, in addition, it is not easy to assemble, so that its application is limited. To solve this problem, permanent magnets are crushed, mixed with plastic and pressed into shape in a magnetic field, which is probably the most primitive way of making bonded magnets. Bonded NdFeB magnets are widely used because of their advantages such as low cost, high dimensional accuracy, large freedom of shape, good mechanical strength and light weight.

Production process

Bonded NdFeB magnet is made of permanent magnet powder and rubber or hard lightweight plastic and other bonding materials mixed, according to user requirements directly shaped into a variety of shapes of permanent magnet parts.

The preparation of magnetic powder is the key process of processing NdFeB permanent magnet. The properties of magnetic powder directly affect the magnetic properties of permanent magnet. The methods for preparing NdFeB magnetic powders include mechanical crushing, frit quenching, HDDR, gas spray and mechanical alloying. At present, the mainstream technology uses HDDR method, which is the preparation of high-performance rare earth permanent magnet powder through the process of hydrogenation-decomposation-dehydrogenation-recombination: first, the alloy is broken into coarse powder, loaded into a vacuum furnace, crystallization treatment at a certain temperature, the alloy absorbs hydrogen and disproportionates, and then the hydrogen is extracted to recombine into rare earth permanent magnet powder with very small grains. By this method, fine grains with an average particle size of 0.3μm can be obtained, and magnetic powders with high coercivity can be obtained.

At present, there are 4 kinds of bonding NdFeB pressing process: calendering, injection molding, extrusion molding and die molding, among which calendering and injection are more mainstream.