Bonded Ferrite magnet is a mature and reliable permanent magnetic material. With advantages such as structural stability, controllable magnetism, and competitive costs, bonded ferrite magnets remain a significant player in the global magnetic materials market.
Definition of Bonded Ferrite Magnets
Bonded ferrite magnets are composite permanent magnetic materials made by mixing ferrite magnetic powder with organic or inorganic binders. Its core characteristic lies in combining the magnetic properties of ferrite with the shaping capabilities of the binder, producing magnets with complex shapes through specific processes such as molding, injection, and extrusion.
This material possesses both magnetism and a certain degree of flexibility or machinability, making it suitable for applications requiring high complexity in shape, dimensional precision, and moderate magnetic performance.
Advantages of Bonded Ferrite Magnets
| Impact Resistance: It is less prone to breakage or chipping upon impact. Various shapes, such as rings, sheets, bars, raised profiles, and holes, can be formed by selecting appropriate shaping methods.
| High Dimensional Precision: The shaped products generally do not require further processing due to high dimensional accuracy.
| High Electrical Resistance: Due to the magnetic powder being coated in a resin binder, it exhibits high resistance.
Disadvantages of Bonded Ferrite Magnets
| Lower Magnetic Performance: Since the binder occupies a certain volume and itself lacks magnetism, bonded ferrite exhibits relatively lower magnetic performance compared to sintered ferrites.
| Thermal Expansion and Heat Resistance: It has a greater thermal expansion and relatively poor heat resistance.
Types of Bonded Ferrite Magnets
| Calendered Ferrite Magnets: Magnetic powder is mixed with synthetic rubber (such as neoprene) or thermoplastic elastomers (such as PVC) and calendered into sheets. Calendered ferrite, also known as rubber magnetic, typically has a binder content of 35-45% (by volume fraction) and is usually oriented mechanically. Its orientation is lower than that of injection-molded magnets, and the products are sheet-like, easy to cut, and flexible.
| Injection-Molded Ferrite Magnets: Magnetic powder and thermoplastic resin (such as nylon) are blended, extruded, and pelletized to create granules, which are then injection molded. The binder content is 30%-45% (by volume fraction), and the maximum magnetic energy product is relatively moderate, allowing for various shaped magnets or integrated multi-pole magnetic rings.
| Extruded Ferrite Magnets: Magnetic powder is mixed with thermoplastic resin (such as nylon) or thermoplastic elastomers (such as PVC) for blending, pelletizing, and extruding. By adjusting the mold shape of the extruder’s die, long strip products of various shapes can be continuously extruded and cut for use.
Production Process of Bonded Ferrite Magnets
The preparation process for bonded ferrite magnets differs from that of sintered ferrite magnets. Bonded ferrite is made by mixing magnetic powder, binder, and additives, followed by granulation, shaping, and curing to create magnets of specific sizes and shapes.
| Calendering Ferrite Magnets: After drying the magnetic powder in the oven, binders and coupling agents are added and mixed in a high-speed stirrer. This mixture is then fed into a kneader for processing and sheet formation, followed by pressing to achieve specific sizes and quality standards between two counter-rotating rollers, and finally cooled to form.
Injection-Molded Ferrite Magnets: Magnetic powder and binder are homogenously mixed, then heated, compacted, and mixed in an injection machine. The resulting hot melt is injected into a mold cavity under high pressure, cooled, and shaped to form magnets with defined appearances.
| Extrusion Ferrite Magnets: Magnetic powder, binder, and additives are mixed, then melted and plasticized in a screw, and extruded at the machine head. The formed products are shaped, cooled, drawn, and cut to create the final product.
Applications of Bonded Ferrite Magnets
| Magnetic Advertising Materials: Calendered rubber magnetic sh&eets can be cut and adhered flexibly, offering a low cost and eco-friendliness.
| Magnetic Toys: For example, magnetic puzzles and magnetic teaching boards are produced from flexible magnets made through calendering, making them safe and durable.
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