Preparation of Bonded Magnets - Preparation Process and Process Classification

Bonded magnets are a complex composed of magnetic powders, adhesives and appropriate additives. The magnetic properties of bonded magnets are mainly determined by the average performance of each magnetic powder with negligible interaction. Although some studies try to use low-melting point metals or alloys as adhesives, the adhesives used to form mass-produced bonded magnets are all polymer materials.

Differences between bonded and sintered magnets

Different from sintered magnets, the single powder particles of bonded magnets must have high enough coercivity. If the phase composition and microstructure required by high coercivity are seriously damaged in the pulverizing process, a good bonded magnet cannot be made, because the damage of grain boundary phase and particle oxidation have greatly reduced its coercivity.

Another major difference between bonded magnets and sintered magnets is that magnetic properties are greatly reduced. We know that the maximum magnetic energy product of a magnet is proportional to the square of its remanent magnetic field, and the remanent magnetic field is proportional to the saturation magnetic induction intensity, orientation and volume filling rate of magnetic powder in the magnet. Adhesives and additives occupy a considerable volume (nearly 20%) in the bonded magnet. Moreover, many bonded magnets are not oriented. Even if oriented magnets are, their orientation is difficult to reach the same level as sintered magnets. Therefore, the performance of bonded magnets with the same volume is far less than that of sintered magnets.

Advantages of bonded magnets

Bonded magnets occupy an important position in the field of rare earth permanent magnet due to their good consistency of performance, accurate size, complex shape, high material utilization rate and easy integration with metal/plastic parts. The most important type of isotropic bonded magnet is made of rapidly quenched NdFeB magnetic powder.Preparation technology and advantages and disadvantages of bonded magnets.

According to the different processing characteristics of polymer materials, the forming of bonded magnets can be divided into compression, injection, extrusion and calendering.