Nd-Fe-B materials were applied widely in civil, aerospace and other fields. High properties Nd-Fe-B sintered magnets were required sustainably in the market. Most commercial magnets were cut from large blocks. Magnetic consistency was one of the fundamental market requirements. There were many reasons that affected the internal consistency of blank magnets. One of the reasons was that magnetic powders and chemical agents were mixed uneven. Nd-Fe-B powder was chemically active and easy to oxidize. The whole process of making powders was carried out in nitrogen atmosphere. There was no proper equipment, so it was very difficult to add chemical reagent evenly. The researchers were unable to research further due to inadequate equipment. In order to improve the magnetic properties and internal consistency of sintered blank magnets, new chemical reagent addition technology and new additive equipment should be developed. According to the characteristics of Nd-Fe-B powders preparation, at present, it was feasible to add multiple times and add less each time, and atomize the reagent to further improve the mixing uniformity. After a lot of experiments, new atomizing additive technology and the patented product "the auto fog-doser" were developed. The dosage, frequency, interval time and times were adjusted through the special programmable logic controller (PLC). Specially designed spiral-percussion nozzle and the corresponding pipeline combination improved the atomization effect of the reagent. The auto fog-doser worked synchronously with the jet-mill to realize that the whole surface of magnetic powder adsorbed chemical reagent. At the same time, the mixing time was reduced from 5 h to 1 h, which reduced the oxygen absorption of magnetic powder in this process. In actual operation, the spraying frequency was set for one or several times according to the fixed frequency of the jet-mill. The magnets were obtained by the dual-alloy technology and the commonly techniques of strip-casting, hydrogen crushing, jet-mill grinding, orientation molding and vacuum sintering. The cylindrical magnet of Φ10 mm×10 mm was gotten out in the center and eight apexes angle of the rectangular magnets; the magnetic properties were tested for calculating the change of different locations in the same magnets. The auto fog-doser was used in the magnets preparation process. The mixing uniformity of magnetic powder and chemical reagent was greatly improved with the increase of dosing frequency and the increase of the reagent layers. The remanence Br increased from 1.403 T to 1.426 T, with an increase of 1.64%. The maximum magnetic energy product (BH)max increased from 394.66 to 406.99 kJ•m-3, with an increase of 3.12%. The coercivity Hcj decreased from 1377.9 to 1373.1 kA•m-1, with an decrease of 0.35%. The changes of magnetic properties of the cylindrical Φ10 mm×10 mm in the center and eight apex angles of the rectangular magnets were: ΔBr=0.77%, ΔHcj=0.76%, Δ(BH)max=0.84%, the values were all less than 1%. The internal magnetic properties of the magnet had good consistency. The new atomizing additive technology and the patented product "the auto fog-doser" could improve the mixing uniformity of magnetic powder and chemical reagent. The mixing time was reduced from 5 to 1 h to better protect the magnetic powder. Nd-Fe-B sintered magnets with better internal consistency and higher magnetic properties were obtained: Br increased 1.64%, (BH)max increased 3.12%, Hcj decreased 0.35%. The change values of magnetic properties in the same magnet were all less than 1%. The internal magnetic properties of the magnet had good consistency. The internal magnetic properties consistency improvement of the blank was significant for small commercial magnets. The auto fog-doser had been applied in Nd-Fe-B sintered magnets fields. © Editorial Office of Chinese Journal of Rare Metals. All right reserved.
