Method and apparatus for producing magnetic rare earth alloy powder, method for producing bonded magnet, method for producing rare earth sintering magnet, and method and apparatus for improving purity of inert gas

Abstract

Rare earth magnetic alloy fine powders are manufactured by placing a mixture of a rare earth metal and a transition metal as raw materials in a crucible, induction heating it in an Ar gas atmosphere, melting metal elements contained in the above mixture, injecting an Ar gas at a predetermined pressure from above the molten alloy to expel the above molten alloy in a downward direction from the nozzle port of the above crucible, and applying a jet stream of an inert gas to the above expelled molten alloy to collide the above expelled molten alloy with the above inert gas so as to scatter the above molten alloy and solidify it by quenching. A rare earth bond magnet and a rare earth sintered magnet are produced using rare earth magnetic alloy fine powders obtained by the above process, which is rarely oxidized on the surface, almost spherical and uniform in diameter.

What is claimed is:  
     
         1 . A process for producing rare earth magnetic alloy powders, comprising the steps of: 
 injecting an inert gas from above a rare earth magnetic alloy molten in a crucible to expel the molten alloy from a nozzle port formed in the bottom of the crucible; and    blowing a cooling gas against the expelled molten alloy to produce fine powders of the alloy.    
     
     
         2 . The process for producing rare earth magnetic alloy powders according to  claim 1 , wherein the cooling gas is any one of Ar gas, Ne gas and He gas or a mixture thereof.  
     
     
         3 . The process for producing rare earth magnetic alloy powders according to  claim 1  or  2 , wherein the cooling gas is blown against a position away from the center of the expelling direction of the molten alloy.  
     
     
         4 . The process for producing rare earth magnetic alloy powders according to any one of  claims 1  to  3 , wherein the cooling gas is blown from two or more different directions.  
     
     
         5 . The process for producing rare earth magnetic alloy powders according to any one of  claims 1  to  4 , wherein the cooling gas is blown against two or more positions in the falling direction of the molten alloy.  
     
     
         6 . The process for producing rare earth magnetic alloy powders according to  claim 4  or  5 , wherein the blowing directions of the cooling gas are perpendicular to each other when seen from the nozzle port side of the crucible.  
     
     
         7 . The process for producing rare earth magnetic alloy powders according to any one of  claim 4  to  6 , wherein the angle formed by the blowing direction of the cooling gas and the expelling direction of the molten alloy is 20 to 45°.  
     
     
         8 . The process for producing rare earth magnetic alloy powders according to any one of  claims 1  to  7 , wherein the cooling gas is mixed with Zn vapor.  
     
     
         9 . The process for producing rare earth magnetic alloy powders according to any one of  claims 1  to  7 , wherein Zn vapor is supplied to the delivery passage of the molten alloy.  
     
     
         10 . The process for producing rare earth magnetic alloy powders according to any one of  claims 1  to  9 , wherein the cooling gas is heated and blown.  
     
     
         11 . The process for producing rare earth magnetic alloy powders according to any one of  claims 1  to  10 , wherein a heater is mounted around the delivery passage of the molten alloy.  
     
     
         12 . The process for producing rare earth magnetic alloy powders according to any one of  claims 1  to  11 , wherein the shape of the nozzle for jetting out the cooling gas is conical.  
     
     
         13 . The process for producing rare earth magnetic alloy powders according to  claim 12 , wherein the apex angle of the conical nozzle is 20 to 40°, and the length of the nozzle is set such that the ratio of the opening diameter D of the outlet to the opening diameter d of the inlet satisfy the relationship 20<(D/d)<60.  
     
     
         14 . The process for producing rare earth magnetic alloy powders according to any one of  claims 1  to  13 , wherein the nozzle for jetting out the cooling gas is connected to an ultrasonic transducer in order to apply ultrasonic waves to the expelled molten alloy.  
     
     
         15 . The process for producing rare earth magnetic alloy powders according to  claim 14 , wherein the barrel of vibration of the ultrasonic waves is situated in the delivery passage of the molten alloy.  
     
     
         16 . The process for producing rare earth magnetic alloy powders according to any one of  claims 1  to  15 , wherein a liquid pool portion is formed in the nozzle for jetting out the cooling gas, and the molten alloy in the liquid pool portion is expelled while vibration is applied thereto.  
     
     
         17 . The process for producing rare earth magnetic alloy powders according to any one of  claims 1  to  16 , wherein an induction magnetic field is applied to the molten alloy to be expelled from the nozzle.  
     
     
         18 . A process for producing rare earth magnetic alloy powders, comprising the steps of: 
 injecting an inert gas from above a rare earth magnetic alloy molten in a crucible to expel the molten alloy from a nozzle formed in the bottom of the crucible; and    colliding the expelled molten alloy with the wing portions of a rotating cooling drum having a plurality of wing portions extending in an axial direction on the flank to produce fine powders of the alloy.    
     
     
         19 . The process for producing rare earth magnetic alloy powders according to  claim 18 , wherein the falling speed of the molten alloy and the pitch, projection height and moving speed of the wing portions are set such that the falling distance of the molten alloy expelled while the wing portions move one pitch becomes shorter than the projection height of the wing portions.  
     
     
         20 . The process for producing rare earth magnetic alloy powders according to any one of  claims 1  to  19 , wherein the rare earth magnetic alloy is R—Fe alloy (R is at least one rare earth metal).  
     
     
         21 . The process for producing rare earth magnetic alloy powders according to any one of  claims 1  to  19 , wherein the rare earth magnetic alloy is R—Fe—B alloy.  
     
     
         22 . The process for producing rare earth magnetic alloy powders according to  claim 21 , wherein the rare earth magnetic alloy is NdFeB alloy.  
     
     
         23 . The process for producing rare earth magnetic alloy powders according to any one of  claims 20  to  22 , wherein the rare earth magnetic alloy is an iron-rich rare earth magnetic alloy.  
     
     
         24 . The process for producing rare earth magnetic alloy powders according to any one of  claims 20  to  22 , wherein the rare earth magnetic alloy is an iron-poor rare earth magnetic alloy.  
     
     
         25 . The process for producing rare earth magnetic alloy powders according to  claim 24 , wherein a cooling gas containing iron powders is blown against the expelled molten alloy to produce fine powders of the alloy.  
     
     
         26 . The process for producing rare earth magnetic alloy powders according to  claim 25 , wherein the iron powders are needle-like iron powders obtained by reducing goethite.  
     
     
         27 . The process for producing rare earth magnetic alloy powders according to  claim 1  or any one of  claims 3  to  17 , wherein SmFe alloy is molten in place of the rare earth magnetic alloy, and an N 2  gas is blown against the expelled molten alloy to nitride and finely powder the alloy in order to produce SmFeN magnetic alloy powders.  
     
     
         28 . The process for producing rare earth magnetic alloy powders according to  claim 27 , wherein the SmFeN magnetic alloy powders are produced in an N 2  gas atmosphere.  
     
     
         29 . An apparatus for producing rare earth magnetic alloy powders, comprising: 
 a crucible having a nozzle in the bottom;    a jet gas feeder for injecting a high-pressure inert gas from above a rare earth magnetic alloy molten in the crucible; and    a cooling drum positioned below the molten alloy expelled from the nozzle, wherein    the cooling drum is turned, and a plurality of wing portions extending in an axial direction are provided on the flank of the cooling drum to quench and solidify the molten alloy by colliding it against the flank of the cooling drum.    
     
     
         30 . The apparatus for producing rare earth magnetic alloy powders according to  claim 29 , wherein wavy irregularities extending in an axial direction are formed on at least the faces on a side corresponding to the drum rotating direction of the wing portions.  
     
     
         31 . The apparatus for producing rare earth magnetic alloy powders according to  claim 29  or  30  which further comprises means of applying a jet stream of cooling water to the contact portion with the molten alloy of the drum.  
     
     
         32 . The apparatus for producing rare earth magnetic alloy powders according to any one of  claims 29  to  31 , wherein a collision board is placed in the scattering direction of the molten alloy collided with the drum.  
     
     
         33 . An apparatus for producing rare earth magnetic alloy powders, comprising: 
 a crucible having a nozzle in the bottom;    a jet gas feeder for injecting a high-pressure inert gas from above a rare earth magnetic alloy molten in the crucible; and    a cooling gas feeder, having a jet nozzle, for blowing a cooling gas against the expelled molten alloy, wherein    the nozzle is provided with actuators having an end movable in contact with the molten alloy in the nozzle.    
     
     
         34 . The apparatus for producing rare earth magnetic alloy powders according to  claim 33 , wherein a liquid pool portion is formed in the nozzle, and the ends of the actuators are movable in contact with the molten alloy in the liquid pool portion.  
     
     
         35 . The apparatus for producing rare earth magnetic alloy powders according to  claim 33  or  34 , wherein the liquid pool portion is substantially spherical.  
     
     
         36 . The apparatus for producing rare earth magnetic alloy powders according to any one of  claims 33  to  35 , wherein the actuators are driven by a magneto-distortion transducer or a quartz transducer having a piezoelectric effect.  
     
     
         37 . The apparatus for producing rare earth magnetic alloy powders according to  claim 36 , wherein the drive frequency of the actuators is 50 kHz to 5 MHz.  
     
     
         38 . A process for producing a rare earth bond magnet, comprising the steps of: 
 dispersing rare earth magnetic alloy fine powders manufactured by the process for producing rare earth magnetic alloy fine powders according to any one of  claims 1  to  28  in a binder to prepare a resin magnet composition; and    molding this resin magnet composition using a metal mold.    
     
     
         39 . The process for producing a rare earth bond magnet according to  claim 38 , wherein the rare earth magnetic alloy fine powders are heated at a predetermined temperature.  
     
     
         40 . The process for producing a rare earth bond magnet according to  claim 38  or  39 , wherein the resin magnet composition is molded while it is aligned in a magnetic field.  
     
     
         41 . The process for producing a rare earth bond magnet according to any one of  claims 38  to  40 , wherein the resin magnet composition is manufactured from almost spherical rare earth magnetic alloy fine powders as the fine powders.  
     
     
         42 . The process for producing a rare earth bond magnet according to  claim 41 , wherein the diameters of the rare earth magnetic alloy fine powders are in the range of 2 to 100 μm.  
     
     
         43 . The process for producing a rare earth bond magnet according to  claim 42 , wherein the diameters of the rare earth magnetic alloy fine powders are in the range of 2 to 30 μm.  
     
     
         44 . A process for producing a rare earth sintered magnet, comprising the step of: 
 sintering rare earth magnetic alloy fine powders manufactured by the process for producing rare earth magnetic alloy fine powders according to any one of  claims 1  to  28  at a predetermined temperature.    
     
     
         45 . The process for producing a rare earth sintered magnet according to  claim 44 , wherein the rare earth magnetic alloy fine powders are pressed and aligned in a magnetic field and then sintered.  
     
     
         46 . The process for producing a rare earth sintered magnet according to  claim 44  or  45 , wherein almost spherical rare earth magnetic alloy fine powders are used as the fine powders.  
     
     
         47 . The process for producing a rare earth sintered magnet according to  claim 46 , wherein the diameters of the rare earth magnetic alloy fine powders are in the range of 2 to 30 μm.  
     
     
         48 . A process for increasing the purity of an inert gas, comprising the step of passing the inert gas through an active metal to remove the residual oxygen contained in the inert gas.  
     
     
         49 . The process for increasing the purity of an inert gas according to  claim 48 , wherein the active metal has greater standard formation free energy for an oxidation reaction than hydrogen.  
     
     
         50 . The process for increasing the purity of an inert gas according to  claim 48 , wherein the active metal has greater standard formation free energy for an oxidation reaction than carbon.  
     
     
         51 . The process for increasing the purity of an inert gas according to any one of  claims 48  to  50 , wherein the active metal is any one of K, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, W and Pb, or a mixture thereof.  
     
     
         52 . The process for increasing the purity of an inert gas according to any one of  claims 48  to  51 , wherein the active metal is shaped like a mesh.  
     
     
         53 . The process for increasing the purity of an inert gas according to any one of  claims 48  to  51 , wherein the active metal is shaped like a honeycomb.  
     
     
         54 . The process for increasing the purity of an inert gas according to any one of  claims 48  to  51 , wherein the inert gas is let pass through a sintered body or porous body of the active metal.  
     
     
         55 . A process for producing rare earth magnetic alloy powders using an inert gas which is purified by the process of any one of  claims 48  to  54  as the cooling gas of  claim 1 .  
     
     
         56 . An apparatus for producing rare earth magnetic alloy powders, comprising: 
 a crucible having a nozzle in the bottom;    a jet gas feeder for injecting a high-pressure inert gas from above a rare earth magnetic alloy molten in the crucible; and    a cooling gas feeder, having a jet nozzle, for blowing a cooling gas against the expelled molten alloy, wherein 
 the cooling gas is let pass through a chamber containing an active metal.  
   
     
     
         57 . The apparatus for producing rare earth magnetic alloy powders according to  claim 55 , wherein at least two chambers through which the cooling gas passes are arranged parallel to each other and can be switched therebetween.  
     
     
         58 . The apparatus for producing rare earth magnetic alloy powders according to  claim 56 , wherein oxygen content detection means for detecting the content of the residual oxygen in the inert gas is mounted on a downstream side of the active metal in the chamber.