Method and apparatus for producing granulated powder of rare earth alloy and method for producing rare earth alloy sintered compact

#The present invention relates to a method and machine of making a rare-earth alloy granulated powder and a method of making a rare-earth alloy sintered body.

#A rare-earth alloy sintered magnet (permanent magnet) is normally produced by compacting a powder of a rare-earth alloy, sintering the resultant powder compact and then subjecting the sintered body to an aging treatment. Permanent magnets currently used extensively in various applications include rare-earth-cobalt based magnets and rare-earth-iron-boron based magnets. Among other things, the rare-earth-iron-boron based magnets (which will be referred to herein as “R—Fe—B based magnets”, where R is one of the rare-earth elements including Y, Fe is iron, and B is boron) are used more and more often in various electronic appliances. This is because an R—Fe—B based magnet exhibits a maximum energy product, which is higher than any of various other types of magnets, and yet is relatively inexpensive.

#An R—Fe—B based sintered magnet includes a main phase consisting essentially of a tetragonal R2Fe14B compound, an R-rich phase including Nd, for example, and a B-rich phase. In the R—Fe—B based sintered magnet, a portion of Fe may be replaced with a transition metal such as Co or Ni and a portion of boron (B) may be replaced with carbon (C). An R—Fe—B based sintered magnet, to which the present invention is applicable effectively, is described in U.S. Pat. Nos. 4,770,723 and 4,792,368, for example.

#FIG. 1(a) schematically illustrates the structure of a granulated powder according to a preferred embodiment of the present invention, and FIGS. 1(b) and 1(a) schematically illustrate the structures of conventional granulated powders for the purpose of comparison.

#FIG. 2 schematically illustrates a granulating machine 20 for making an R—Fe—B based alloy granulated powder according to a preferred embodiment of the present invention.

#FIG. 3 schematically illustrates a granulating machine 100 for making an R—Fe—B based alloy granulated powder according to another preferred embodiment of the present invention.

#Hereinafter, a method of making a granulated powder and a method of making a rare-earth alloy sintered body according to preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of preferred embodiments, the features of the present invention will be described as being applied to a method of making a sintered magnet of an R—Fe—B based alloy powder prepared by a strip casting process, which exhibits excellent magnetic properties but low flowability. However, the present invention is in no way limited to those specific preferred embodiments. Thus, a rare-earth alloy powder made by any other method may also be used instead.

#A method of making an R—Fe—B based alloy sintered body according to a preferred embodiment of the present invention includes the steps of: making an R—Fe—B based alloy powder (which will be referred to herein as a “material powder” or “primary particle powder”); generating remanent magnetization in the material powder; granulating the powder by utilizing agglomeration force produced by the remanent magnetization of the material powder; making a compact by pressing the R—Fe—B based alloy powder, including the granulated powder, with a magnetic field applied thereto; and sintering the compact. By magnetizing the resultant sintered body by a known method, an R—Fe—B based sintered magnet can be obtained. It should be noted that the magnetizing process step may be carried out at any arbitrary point in time after the sintering process. For example, the user of the sintered magnet may perform the magnetizing process step just before he or she uses the sintered magnet. Even a non-magnetized one will also be referred to herein as a “sintered magnet”.

#In a method of making an R—Fe—B based alloy sintered body according to a preferred embodiment of the present invention, the powder is granulated by utilizing the agglomeration force produced by the remanent magnetization of the material powder. Accordingly, it is possible to either reduce the amount of a granulating agent to be added or use a binder with low binding force than a conventional one. Furthermore, even the addition of the granulating agent itself may be omitted.