By adding magnetic fillers to polymers, polymer-bonded magnets can be injection molded with a multipolar structure, according to a paper by Stefan Eimeke, a researcher at the Institute of Polymer Technology at the University of Erlangen-Nuremberg in Erlangen, Germany.
For making magnets, injection molding has several advantages over traditional sintering techniques, such as better dimensional stability, more freedom to design complex shapes and cost reduction in the one-step proc¼ess, Eimeke's paper said.
The key is the use of permanent magnets incorporated inside the mold to both orient and magnetize the metal fillers inside the melt. The orientation changes from pole to pole, based on the placement of the in-mold permanent magnets, he said.
Institute of Polymer Technology researchers studied how several variables affect the orientation, including changes in melt temperature, viscosity, part thickness, flow length and the type of steel used. One conclusion: the magnetic conductivity of the permanent magnets is stronger on thin parts than thicker parts.