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Plastic-bonded magnets

Plastic-bonded magnets are particle composites with permanent-magnet powder embedded in a plastic binder. Hard ferrite (HF), various SmCo and NdFeB powders and, to a very little extent, AINiCo alloys are used as magnetic powder. For embedding the magnetic particles, thermoplastic binders as, for instance, polyamide (PA) or polyphenyl sulfide (PPS) and duroplasts like epoxy resins are used. Depending on the material composition and production process, isotropic and anisotropic magnets with differing magnetic and mechanical specifications are available. Since not only the type of magnet or plastic material, but the filling and alignment degree, too, determine the composite's properties, the outcome is widely varying magnetic parameters and an outstanding variety in types and shapes.

The rigid plastic-bonded magnets have two production processes. Injection molding is the most frequently used. Compression molding is used especially for plastic-bonded rare-earth magnets.

First of all, a compound is mixed from the magnet powders and plastics. In the injection-molding process, hard ferrite or rare-earth powders are embedded into thermoplastics and granulated. The granulate is processed on injection-molding machines into magnet moldings. In compression molding technology, only of economic relevance for manufacturing plastic-bonded rare-earth magnets, suitable powder mixtures are processed in tools and presses. NdFeB powder is combined with duroplastic resins. In the compression tools, the compound mixtures are subsequently molded into the most frequently used shapes as blocks, disks, rings, flat sections and segments. After shaping, a thermal hardening phase follows, making the pressed material mechanically stable. This is followed by the finishing and surface cleaning stages. Depending on customer demands, the parts are magnetized and the surface marked or coated.

Plastic-bonded hard ferrite magnets In the manufacturing process for rigid plastic-bonded hard ferrite magnets, particles with permanent magnetic properties from barium or strontium ferrite are embedded into a thermoplastic. The volume of the hard ferrite powder is a decisive factor in the magnetism achieved. Due to this "thinning effect," plastic-bonded hard ferrite magnets cannot reach the magnetic values of the input (solid) material. Plastic-bonded magnets will have weaker magnetic properties at the same volume than sintered isotropic magnets. Higher magnetic values can be achieved with anisotropic plastic-bonded hard ferrite magnets, however not reaching the level of sintered anisotropic hard ferrite magnets. The ferrite/plastic mixing ratio will also influence the magnet's elasticity and hardness.

Plastic-bonded NdFeB magnets Magnets based on neodym-iron-boron are among the newest generation of permanent magnet materials. Plastic-bonded NdFeB magnets are especially used in applications where hart ferrite magnets cannot meet magnetic specifications or where sintered rare-earth magnets are not used for economic or production-related reasons. Further advantages are that plastic-injected magnets based on NdFeB are generally magnetically isotropic and hence can be magnetized in any direction with any number of poles. Due to the higher filling degree and hence higher density achievable with this technique, the compression-molded grades have high magnetism compared with the injection-molded varieties. The higher energy product thus allows smaller component shapes when compared to hard ferrites. As a rule, anisotropic magnets are produced in this manufacturing process with remanences of up to 0.8 T.

Our Product Range:

Our range comprises a wide selection of plastic-bonded hard ferrite and NdFeB materials with differing magnetic properties. They permit material selection tailored to individual application requirements.

We would be pleased to provide detailed advice.

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