Resin-bonded Magnets

Traditionally, resin-bonded permanent magnets have mainly been prepared by the compression molding method, or by the injecrion molding method. In the compression molding method, epoxy resins have been used. 

Binder resins for the injection molding method are poly(amide)s and ethylene vinyl acetate copolymers, and more recently poly(ether ether ketone) (PEEK) and PPS, because of their superior properties. Crystalline resins such as PPS or PEEK require a high temperature for fusion molding of 350°C or higher, so that there is a disadvantage in that the magnetic powder of the rare earth is likely to be oxidized by the molding process. 

With soluble polymers, it is possible to disperse the magnetic material in a polymeric solution and precipitate the dispersion in a non-solvent. Or else, the solvent can be evaporated in vacuo. This process of manufacture can be conducted at lower temperatures. PEN types are highly suitable as soluble polymers for preparing such resin-bonded magnets, still having good properties. A suitable solvent is NMP, appUed at ca. 190 C. 

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FIGURE 12 Preparation and recycling processes of epoxy resin bonded magnets (Yamashita et al., 2001). 

Enthalpy of sublimation, 328-329 Epoxy-resin-bonded magnet, pyrolysis of, 182 Erbium (Er)... 

Finally, metal- and resin-bonded composites are also classified as particulate composites. Metal-bonded composites included structural parts, electrical contact materials, metal-cutting tools, and magnet materials and are formed by incorporating metallic or ceramic particulates such as WC, TiC, W, or Mo in metal matrixes through traditional powder metallurgical or casting techniques. Resin-bonded composites are composed of particulate fillers such as silica flour, wood flour, mica, or glass spheres in phenol-formaldehyde (Bakelite), epoxy, polyester, or thermoplastic matrixes. 

Fig. 3.33. Hysteresis loops of mechanically alloyed resin-bonded (MM1) and compacted and hot die-upset anisotropic (MM3) NdI6Fe76B8-type magnets. The MM3 magnet was measured parallel and perpendicular to the press direction [3.80]...

The resultant powders are mixed with resin to prepare bonded magnets. This type of magnet is called MQ-1, and is magnetically isotropic. They have been used in a wide variety of industrial applications, and still have a large market. 

Cho H J and Ahn C H, Microscale resin-bonded permanent magnets for magnetic micro-electro-mechanical systems applications , J Appl Phys, 2003 93 (10) 8674-8676. 

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