Bonded Neodymium-Iron Boron Magnets
For a more flexible alternative to sintered neodymium, consider using bonded neodymium magnets for your application. Bonded neodymium powder is used to create these magnets. Powder is melted and mixed with a polymer. Components are then pressed or extruded to create the product. Bonded Neodymium magnets can be magnetized into complex patterns with multiple poles. Though much weaker than Sintered Neodymium magnets, Bonded neodymium magnets give greater flexibility in terms of shapes that can be made. They are also lighter than Samarium Cobalt, and have a lower acceptable temperature (coercivity). Nevertheless, they offer excellent value for applications that require a smaller magnet or utilize radial rings.
Bonded Neodymium magnets are made of the powerful Nd-Fe-B material mixed into an epoxy binder. The mix is approximately 97 vol% magnet material to 3 vol% epoxy. The manufacturing process involves combining Nd-Fe-B powder with an epoxy binder and compressing the mixture in a press and curing the part in an oven. Since the material is formed by compression bonding, the dimensions typically vary .002″ or better for a given run.
Bonded neodymium-iron-boron (NdFeB) magnets are strong magnets which are used for various applications. Epoxy coating is mostly common used for bonded NdFeB magnets; electroless nickel plating is also used to prevent corrosion. Isotropic bonded NdFeB material can be magnetized in any direction, or with multiple poles.
Bonded Nd-Fe-B material is isotropic, so it can be magnetized through any direction, including multi-polar arrangements. Because the material is in an epoxy binder, it can be machined on a mill or lathe. However, the material will not support a thread, so holes cannot be tapped. Bonded Nd-Fe-B material is often used to substantially reduce the size of designs that used ceramic magnet materials. Significant size reductions can be achieved because the material is approximately three times stronger than ceramic magnet material. In addition, since the material is isotropic, it can be magnetized multi-polar, such as a N-S-N-S pattern on the outer diameter of a ring.
Types of Bonded Neodymium Magnets
Maximum Working Temperature
Although the Curie temperature for NdFeB material is about 310 ºC for 0% cobalt material to greater than 370 ºC for 5% cobalt, some irreversible loss of output may be expected at even moderate temperatures. Neo magnets also have a moderately high Reversible Temperature Coefficient of Induction which reduces total magnetic output as temperature rises. Selection of neo magnets instead of SmCo, is a function of the maximum temperature of the application, required magnetic output at typical working temperature and total cost of the system.
Neo magnets also have some limitations due to their corrosion behavior. In humid circumstance, a protective coating or plating is highly recommended. Coatings which have been applied successfully include; e-coating, powder coating, nickel plating, zinc plating, parylene and combinations of these coatings.