Improvement of the filler orientability during injection molding of multi-polar SmCo-magnets by premagnetization

The magnetic properties of rare earth fillers (RE), e.g. Samarium Cobalt (SmCo), are remarkably high, if compared to ferrites. Nevertheless, they have very high magnetizing fields, which lead to poor orientability of the filler particles in the magnetic field during processing by injection molding. As a result, SmCo-filled polymers cannot be applied for the production of multi-polar magnets, because the multi-polar magnetic field in the mold is too low to orient the filler particles. This paper deals with the new method for the production of multi-polar SmCo magnets that integrates premagnetization of the filler in the hot runner system of the injection mold. The method developed separates the magnetizing process from the orienting process of the particles. First the magnetic compound is molten in the plastification unit of the injection molding machine. Then the molten compound is magnetized in the hot runner system by a very strong magnetic coil, and is finally injected into the cavity with its multi-pole field integrated. The procedure presented considerably enhances orientability. Also, the properties of multi-pole magnets improve significantly thanks to premagnetization.