Cooling roll, ribbon-shaped magnetic materials, magnetic powders and bonded magnets

Abstract

Disclosed herein is a method of manufacturing a magnetic material which can provide a bonded magnet having excellent magnetic properties and having excellent reliability. A melt spinning apparatus 1 is provided with a tube 2 having a nozzle 3 at the bottom thereof, a coil 4 for heating the tube and a cooling roll 5 having a circumferential surface 53 in which gas expelling grooves 54 are formed. A melt spun ribbon 8 is formed by injecting the molten alloy 6 from the nozzle 6 so as to be collided with the circumferential surface 53 of the cooling roll 5, so that the molten alloy 6 is cooled and then solidified. In this process, gas is likely to enter between a puddle 7 of the molten alloy 6 and the circumferential surface 53, but such gas is expelled by means of the gas expelling grooves 54.

What is claimed is:  
     
         1 . A method of manufacturing a magnetic material in which a molten alloy is collided to a circumferential surface of a cooling roll to be cooled and then solidified to produce a ribbon-shaped magnetic material having an alloy composition represented by the formula of R x (Fe 1−y Co y ) 100−x−z B z  (where R is at least one rare-earth element, x is 10-15 at %, y is 0-0.30, and z is 4-10 at %), wherein the method is characterized by use of a cooling roll having gas expelling means provided in a circumferential surface of the cooling roll for expelling gas entered between the circumferential surface and a puddle of the molten alloy.  
     
     
         2 . The method as claimed in  claim 1 , wherein the cooling roll includes a roll base and an outer surface layer provided on an outer peripheral portion of the roll base, and said gas expelling means is provided in the outer surface layer.  
     
     
         3 . The method as claimed in  claim 2 , wherein the outer surface layer of the cooling roll is formed of a material having a heat conductivity lower than the heat conductivity of the structural material of the roll base at or around a room temperature.  
     
     
         4 . The method as claimed in  claim 2 , wherein the outer surface layer of the cooling roll is formed of a ceramics.  
     
     
         5 . The method as claimed in  claim 2 , wherein the outer surface layer of the cooling roll is formed of a material having a heat conductivity equal to or less than 80 W m −1 ·K −1  at or around a room temperature.  
     
     
         6 . The method as claimed in  claim 2 , wherein the outer surface layer of the cooling roll is formed of a material having a coefficient of thermal expansion in the range of 3.5-18[×10 −6 K −1 ] at or around a room temperature.  
     
     
         7 . The method as claimed in  claim 2 , wherein the average thickness of the outer surface layer of the cooling roll is 0.5 to 50 μm.  
     
     
         8 . The method as claimed in  claim 2 , wherein the outer surface layer of the cooling roll is manufactured without experience of machining process.  
     
     
         9 . The method as claimed in  claim 1 , wherein the surface roughness Ra of a portion of the circumferential surface where the gas expelling means is not provided is 0.05-5 μm.  
     
     
         10 . The method as claimed in  claim 1 , wherein the gas expelling means includes at least one groove.  
     
     
         11 . The method as claimed in  claim 10 , wherein the average width of the groove is 0.5-90 μm.  
     
     
         12 . The method as claimed in  claim 10 , wherein the average depth of the groove is 0.5-20 μm.  
     
     
         13 . The method as claimed in  claim 10 , wherein the angle defined by the longitudinal direction of the groove and the rotational direction of the cooling roll is equal to or less than 30 degrees.  
     
     
         14 . The method as claimed in  claim 10 , wherein the groove is formed spirally with respect to the rotation axis of the cooling roll.  
     
     
         15 . The method as claimed in  claim 10 , wherein the at least one groove includes a plurality of grooves which are arranged in parallel with each other through an average pitch of 0.5-100 μm.  
     
     
         16 . The method as claimed in  claim 10 , wherein the groove has openings located at the peripheral edges of the circumferential surface.  
     
     
         17 . The method as claimed in  claim 10 , wherein the ratio of the projected area of the groove or grooves with respect to the projected area of the circumferential surface is 10-99.5%.  
     
     
         18 . The method as claimed in  claim 1 , further comprising a step of milling the ribbon shaped magnetic material.  
     
     
         19 . A ribbon-shaped magnetic material which is manufactured by the method described in any one of  claims 1  to  17 .  
     
     
         20 . The ribbon-shaped magnetic material as claimed in  claim 19 , wherein the average thickness thereof is 8-50 μm.  
     
     
         21 . A powdered magnetic material which is manufactured by the method described in  claim 18 .  
     
     
         22 . The powdered magnetic material as claimed in  claim 21 , wherein the powdered magnetic material is subjected to at least one heat treatment during or after the manufacturing process thereof.  
     
     
         23 . The powdered magnetic material as claimed in  claim 21 , wherein the mean particle size of the powder is 1-300 μm.  
     
     
         24 . The powdered magnetic material as claimed in  claim 21 , wherein the powdered magnetic material mainly has a R 2 TM 14 B phase (where TM is at least one transition metal) which is a hard magnetic phase.  
     
     
         25 . The powdered magnetic material as claimed in  claim 24 , the volume ratio of the R 2 TM 14 B phase with respect to the whole structural composition of the powdered magnetic material is equal to or greater than 80%.  
     
     
         26 . The powdered magnetic material as claimed in  claim 24 , wherein the average grain size of the R 2 TM 14 B type phase is equal to or less than 500 nm.  
     
     
         27 . A bonded magnet which is manufactured by binding the powdered magnetic material as claimed in any one of  claims 22  to  26  with a binding resin.  
     
     
         28 . The bonded magnet as claimed in  claim 27 , wherein the intrinsic coercive force (H CJ ) of the bonded magnet at a room temperature lies within the range of 320-1200 kA/m.  
     
     
         29 . The bonded magnet as claimed in  claim 27 , wherein the maximum magnetic energy product (BH) max  of the bonded magnet is equal to or greater than 40 kJ/m 3 .