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HOME : PRODUCTS : PERM MAGNETS : BONDED : COMPRESSION BONDED
COMPRESSION MAGNETS
The family of PLASTIFORM® brand bonded magnets (injection molded, compression bonded, and flexible) represent one of the more important groups of magnetic materials available today. They can be tailored to suit a wide range of magnetic and physical strength, size, shape, and temperature characteristics. Compression bonded magnets are well-suited where maximum magnetic strength is required but physical strength can be slightly compromised, and where the profile shape is not complex. Another advantage over injection molded magnets is that tooling costs are relatively low making compression bonded a better choice than injection where volumes are low. With relatively little automation, compression bonded also lends itself well to high volume manufacturing (millions of magnets per year).
MATERIALS
Magnetic powders appropriate for compaction pressing include the many neodymium-iron-boron (NdFeB) grades as well as crushed and powdered samarium cobalt (SmCo). Ferrite is not useful due to the ultra-fine particle size. Combinations of NdFeB grades may also be used to create a specific set of magnetic characteristics.
The NdFeB materials used in this process are isotropic materials which do not require magnetic alignment of the powder during processing. The pressed product is extremely uniform in all directions. Uniformity of final magnetization is totally a function of the magnetizing equipment.
Almost all manufacturers use an epoxy binder. Various other additives are used to improve adhesion to the magnetic powder, corrosion resistance, flowability for improved die-fill, etc. The epoxies are quite resistant to solvents, but may suffer some softening and swelling if exposed for more than a short time. There is also considerable open porosity. To reduce corrosion of the rare earth materials, it may be necessary to apply a coating to the magnet.
TOLERANCES
Magnet dimensions in the X-Y plane are established by the die, by handling out of the die and by cure expansion. They are generally rated at +/-0.003 in. Closer tolerances can be negotiated. Tolerances in the pressing direction (axial length) are more problematic, and depend on many factors including part length, wall thickness, magnet shape and magnetic material. Please consult the factory for specifics.
TEMPERATURE CHARACTERISTICS
The epoxies used for bonded magnets are capable of use at or above 180°C. Maximum use temperature is almost totally a function of two items: 1) the combination of intrinsic coercivity and reversible temperature coeficient which, for any permeance coefficient, causes large irreversible losses at elevated temperatures and 2) degradation of the rare earth powder due to corrosion. Materials are available which perform satisfactorily at and above 165°C. Maximum temperature ratings are available in the catalog. Plastiform technical personnel will be glad to assist in the choice of material for your applications.
Please also visit the sections on Injection Molded and Flexible Bonded magnets.
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