Permanent magnets can indeed be manufactured using rubber as a binder or matrix material. Such magnets are commonly referred to as rubber-bonded permanent magnets, elastomer-bonded magnets, or rubber composite magnets.
One method for producing rubber-bonded permanent magnets involves mixing hard magnetic powders with rubber. The rubber serves as a binder or polymeric matrix that binds the magnetic particles together. Commonly used hard magnetic powders include anisotropic strontium ferrite powder and isotropic neodymium-iron-boron (Nd-Fe-B) alloy powder. Other types of hard magnetic materials such as barium ferrite or samarium-cobalt (Sm-Co) may also be used. The elastomers or rubbers employed as binders vary widely, including natural rubber, sulfur-crosslinked nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), or silicone.
Compared to sintered or cast magnets, rubber-bonded magnets offer several advantages. One key benefit is the ability to customize their physical properties. By adjusting the type and content of hard magnetic powder, as well as processing parameters of the binder material, the magnetic and mechanical properties of the permanent magnets can be tailored.
Production methods for rubber-bonded permanent magnets include compression molding or injection molding. These materials are typically prepared by calendaring processes to create a mixture of powder and rubber. The mixture is then cured through a vulcanization process (usually involving high temperature and pressure) to form the final shape. The final step involves magnetizing the sample.
The particle size of the hard magnetic powder influences the mechanical properties of the product. For instance, increasing the mass fraction of hard ferrite or Nd-Fe-B may degrade mechanical properties, though this effect largely depends on particle size. In studies involving nanoscale magnetic particles, increasing the magnetic powder mass fraction has been shown to improve mechanical properties instead.
Rubber-bonded permanent magnets are significant due to their flexibility and ability to be molded into complex shapes. Their flexibility and elasticity serve as additional, critical parameters. Their applications are extensive and continually expanding. The automotive industry represents one sector with growing applications for rubber-bonded permanent magnets. Examples include their use in rotational magnetic encoders for anti-lock braking systems (ABS) and detection mechanisms. They are also employed in crankshafts to transmit speed and acceleration data to engine management systems. For ABS systems, permanent magnets are often shaped into rings and attached to steel bases, magnetized with multiple alternating poles. These ring magnets require varying dimensions and magnetic characteristics to accommodate different automotive ABS systems.
In conclusion, permanent magnets can utilize rubber as a binder. By blending hard magnetic powders (such as strontium ferrite or Nd-Fe-B) with rubber and employing processes like calendaring and vulcanization, rubber-bonded permanent magnets can be produced. These magnets exhibit flexibility and moldability, making them suitable for diverse applications.
