What is the bonding process of NdFeB magnets?

The bonding process of NdFeB magnets is an important part of magnet preparation. Generally, four kinds of manufacturing processes are used. They are calendering process, injection molding process, extrusion forming process and die forming process.

Calendering process

In the calendering process, the magnetic powder and adhesive are evenly mixed in a volume ratio of about 7:3, rolled to the required thickness, and then manufactured into finished products through fixed telephone treatment. Generally, vinyl and NBR are used as the adhesive to bond with ferrite or part and a small amount of ndfeb. In general, no surface treatment is required, and the surface is protected or decorated with film. Nickel plating is required for NdFeB. In order to maintain its flexibility, the bonded magnet usually uses magnetic powder with particle size of 1-1.5 μ m, and the amount of bonding is also large. Therefore, most of the process uses ferrite magnetic powder, and the products are all plates of various thickness, and then cut into other shapes with a cutter. Because it is easy to bend, it can be easily made into multipolar magnetic ring with low raw material and manufacturing cost. It can be widely used in micro motor, press plate of printer, large billboard and children’s toys. The maximum energy product (BH) max of the bonded magnet made by this process is 4-6.4kj/m3 (isotropic). In order to improve the magnetic properties, appropriate amount of NdFeB magnetic powder can be added to obtain practical bonded magnet (BH) max = 9.6-11.2kj/m3, which is the same as the anisotropic bonded magnet made by this process.

Injection molding

In injection molding, the magnetic powder and adhesive are mixed, heated, mixed, granulated and dried, and then the spiral guide rod is sent to the heating chamber for heating, injected into the mold cavity for molding, and the finished product is obtained after cooling. Nylon 6, polyamide, polyester and PVC are usually used with 20% ~ 30% (volume fraction) addition and rigid bonded permanent magnet with complex shape. No surface treatment is needed for ferrite, SmCo magnet and NdFeB magnet. For injection molding process, in order to ensure the fluidity of magnetic powder and the strength of magnet, more binder should be added. Therefore, the magnetic properties of bonded magnet are basically the same as that of calendering process. The injection molding process can produce anisotropic magnets, that is, adding a certain constant magnetic field or pulse magnetic field when the particles are injected into the mold to improve the magnetic properties of the bonded magnets. The products are mainly used in instruments, such as speedometer, fuel meter, current and voltage meter of automobile, ship and airplane.

Extrusion forming

Extrusion molding is basically the same as injection molding, the only difference is that the heated pellets are extruded into the mold through a cavity for continuous molding. In the same way, nylon 6, polyamide, polyester and polyethylene are used to produce thin-walled cylindrical or ring-shaped magnets, such as ferrite, SmCo magnet and NdFeB magnet, which are difficult to be realized by other processes. The extrusion process is suitable for manufacturing thin-walled annular bonded magnets with thin sheet or high height. The magnetic properties are (BH) max = 3.2-4.8kj/m3 (isotropic). The products are mainly used in gaskets, small advertising signs and motors. Due to the limitation of technology and production equipment, rolling, injection and extrusion processes are mostly used for ferrite magnetic powder, and the magnetic properties of products are relatively low.

Die forming

The magnetic powder and adhesive are mixed in proportion, granulated and added with a certain amount of coupling agent, then pressed in the mold, and cured at 120 ° to 150 ° to obtain the final product. The permanent magnets with large size and simple shape can be bonded by using solid epoxy resin or phenolic resin with 1% ~ 5% addition. Cathodic electrophoresis, spraying, evaporation and other methods are generally used for coating protection. Molding is the most widely used technology at present, especially after the emergence of fast quenched NdFeB permanent magnetic powder, it has been developed rapidly. For the same material, the magnetic properties of the magnet obtained by molding are the best due to the small amount of bonding. Almost all bonded co-fe-b permanent magnets are made of rapidly quenched magnetic powder (a small amount of magnetic powder produced by HDDR process), and the process is basically molded, with the highest magnetic properties. (BH) max = 64-96kj / m3 (isotropic), the application market is very broad.
Source: China Permanent Magnet Manufacturer www.rizinia.com