The effect of processing parameters on magnetic properties of an epoxy resin-bonded isotropic Nd-Fe-B magnet

Ring-shaped epoxy resin-bonded magnets were fabricated using an isotropic nano-crystalline melt spun Nd-Fe-B powder. The magnets were produced from a mixture of the isotropic powder and some epoxy resins as binders, using a compression-molding technique. The morphology and average particle size of the powders were examined using an SEM. The magnetic properties of the magnets were evaluated using a hysteresis loop tracer. The effects of milling time, binder type and content, hardener amount, lubricant percentage, pressing pressure, and curing temperature and time on magnetic properties of magnets were studied. It was found that the magnetic properties of the bonded magnets were the best in an as-received condition of ribbons, and any particle size reduction by milling results in reduction in permanent magnetic properties. The best magnetic properties were attained for the bonded magnets produced using a two-component air-dried liquid epoxy resin. The optimized binder content, lubricant percentage, pressing pressure, curing temperature and time in these magnets were as: 3 wt%, 0.4 wt%, 900 MPa, room temperature and 24 h, respectively. The optimal magnetic properties were as follows:B-r = 7 kG,H-cJ = 9.10 kOe and (BH)(max) = 11.5 MGOe. However, the best thermal stability was obtained when the bonded magnets were produced using a solid powder epoxy resin with a special aromatic hardener.