Effects of additives on the orientation and strength of plastic ferrite magnet

In the manufacture of injection-bonded magnets from Sr-ferrite powder with nylon-12 resin, coupling agents and lubricant are normally added to improve the mechanical properties and to decrease abrasion by the injection molding machine. The effects of these additives on the particle orientation, compressive strength, and rheological behavior are investigated. Two coupling agents (one belonging to the silane series, the other to the titanate series) plus one lubricant have been added to the ferrite powders. Experimental results show that the lubricant can increase alignment by 14% and decrease compressive strength by 42%. The silane coupling agent induces 5.7% and 50.9% enhancement of alignment and compressive strength, respectively, and is better than the titanate coupling agent. In general, the best composition is 1.0 wt.% coupling agent combined with 0.5 wt.% lubricant C, yielding 82.7% alignment and 15.2 kg/mm² compressive strength