Segregation of Nd-Fe-B powders during injection molding of gears with magnetic properties
Waldemar Kaszuwara, Bartosz Michalski, Łukasz Ciupiński, Andrzej Skalski, Lech Paszkowski, Dionizy Biało
Quarterly No. 2, 2012 pages 93-97
DOI:
keywords: Nd-Fe-B magnets, polymer bonded magnets, hard magnetic composite
abstract The possibility of producing polystyrene-bonded micro-magnets with the use of two commercial nanocrystalline Nd-Fe-B powders (delivered by the Magnequench Co) was examined. The micro-magnets were formed by the injection method to obtain gear-shaped samples. The powders were produced by two different methods, namely the crushing of a rapidly cooled ribbon (MQP-16-7) or spraying (MQP-S). Depending on the production method, the powders differ in their particle shapes: the former method gave flaky particles whereas the latter - spherical particles. The particle shape has an essential effect upon the technological properties of the powder. The gear-shaped micro-magnets with a diameter of 2.6 mm were examined by X-ray tomography. An analysis of the 3D images has shown that during their injection with polystyrene, the powders undergo segregation. The largest particles of the MQP-S powder (spherical) are located at the greatest distance from the injection point which was positioned in the axis of the gear. They are also relatively numerous near the side surfaces of the gear. The filling ratio of this composite decreases as we pass along the radius of the gear. Taking into account the fact that the properties of the sprayed powders depend on their particle size, these observations will permit the of designing pieces with a gradient of magnetic properties. In the gears produced from the powder with flake-shaped particles, the flake surfaces tend to position themselves perpendicularly to the gear radius. The shape, therefore, of the powder particles determines the anisotropy of their distribution within the product. This observation can be utilized in the design of bonded magnets.