Arc segment magnet, ring magnet and method for producing such magnets

Abstract

A thin arc segment magnet made of a an R- T - B based, rare earth sintered magnet substantially comprising 28-33 weight % of R and 0.8-1.5 weight % of B, the balance being substantially Fe T, wherein R is at least one rare earth element including Y, and T is Fe or Fe and Co, which has an oxygen content of 0.3 weight % or less, a density of 7.56 g/cm 3 or more, a coercivity iHc of 1.1 MA/m (14 kOe) or more at room temperature, and an orientation Br/4πI max of 96% or more in an anisotropy-providing direction at room temperature can be produced by using a slurry mixture formed by introducing fine alloy powder of the above composition into a mixture liquid comprising 99.7-99.99 parts by weight of a mineral oil, a synthetic oil or a vegetable oil and 0.01-0.3 parts by weight of a nonionic surfactant and/or an anionic surfactant.

1. A thin arc segment magnet having a thickness of 1-4 mm and made of a  an R- T - B - based,  rare earth sintered magnet having a main component composition comprising 28-33 weight % of R and 0.8-1.5 weight % of B, the balance being substantially Fe  T, wherein R is at least one rare earth element including Y, and T is Fe or Fe and Co, said arc segment magnet having an oxygen content of 0.3 weight % or less, a carbon content of  0 . 10  weight %  or less and a nitrogen content of  0 . 15  weight  %  or less  based on the total weight of the magnet, a density of 7.56 g/cm 3  or more, a coercivity iHc of 1.1 MA/m (14 kOe) or more at room temperature, and an orientation Br/4πI max  of 96% or more in an anisotropy-providing direction at room temperature, Br being a residual magnetic flux density, and  4 πI max    being a maximum value of  4 πI in a curve of  4 πI - H curve, wherein  4 πI is the intensity of magnetization, and H is the intensity of a magnetic field.    
     
     
       2. The arc segment magnet according to  claim 1 , having parallel anisotropy. 
     
     
       3. The arc segment magnet according to  claim 1 , having an axial length of 40-100 mm. 
     
     
       4. The arc segment magnet according to  claim 1 , having a ratio I(105)/I(006) of 0.5-0.8, wherein I(105) represents the intensity of an X-ray diffraction peak from a (105) plane, and I(006) represents the intensity of an X-ray diffraction peak from a (106) plane. 
     
     
       5. A radially anisotropic, arc segment magnet having an inner diameter of 100 mm or less and made of a  an R- T - B - based,  rare earth sintered magnet having a main component composition comprising 28-33 weight % of R and 0.8-1.5 weight % of B, the balance being substantially Fe  T, wherein R is at least one rare earth element including Y, and T is Fe or Fe and Co, said arc segment magnet having an oxygen content of 0.3 weight % or less, a carbon content of  0 . 10  weight %  or less and a nitrogen content of  0 . 15  weight  %  or less  based on the total weight of the magnet, a density of 7.56 g/cm 3  or more, a coercivity iHc of 1.1 MA/m (14 kOe) or more at room temperature, and an orientation [Br///(Br//+Br⊥)]×100 (%) of 85.5% or more at room temperature, said orientation being defined by a residual magnetic flux density Br// in a radial direction and a residual magnetic flux density Br⊥ in an axial direction perpendicular to said radial direction. 
     
     
       6. The arc segment magnet according to  claim 5 , wherein it is as thin as 1-4 mm. 
     
     
       7. The arc segment magnet according to  claim 5 , wherein it is as long as 40-100 mm in an axial direction. 
     
     
       8. A radially anisotropic ring magnet having an inner diameter of 100 mm or less and made of a  an R- T - B - based,  rare earth sintered magnet having a main component composition comprising 28-33 weight % of R and 0.8-1.5 weight % of B, the balance being substantially Fe  T, wherein R is at least one rare earth element including Y, and T is Fe or Fe and Co, said ring magnet having an oxygen content of 0.3 weight % or less, a carbon content of  0 . 10  weight %  or less and a nitrogen content of  0 . 15  weight  %  or less  based on the total weight of the magnet, a density of 7.56 g/cm 3  or more, a coercivity iHc of 1.1 MA/m (14 kOe) or more at room temperature, and an orientation [Br///(Br//+Br⊥)]×100 (%) of 85.5% or more at room temperature, said orientation being defined by a residual magnetic flux density Br// in a radial direction and a residual magnetic flux density Br⊥ in an axial direction perpendicular to the radial direction. 
     
     
       9. The ring magnet according to  claim 8 , having portions bonded by sintering. 
     
     
       10. A method for producing a  an R- T - B - based,  rare earth sintered magnet having a main component composition comprising  28 - 33  weight %  of R and  0 . 8 - 1 . 5  weight  %  of B, the balance being substantially T, wherein R is at least one rare earth element including Y, and T is Fe or Fe and Co, said rare earth sintered magnet having an oxygen content of  0 . 3  weight  %  or less, a carbon content of  0 . 10  weight  %  or less and a nitrogen content of  0 . 15  weight  %  or less based on the total weight of the magnet, a density of  7 . 56  g/cm   3    or more, and a coercivity iHc of  1 . 1  MA/m or more at room temperature, said method  comprising the steps of finely pulverizing an alloy for said R- T - B - based,  rare earth sintered magnet to an average particle size of 1-10 μm in a non-oxidizing atmosphere; introducing the resultant fine powder into a mixture liquid comprising 99.7-99.99 parts by weight of at least one oil selected from the group consisting of a mineral oil, a synthetic oil and a vegetable oil and 0.01-0.3 parts by weight of a nonionic surfactant and/or an anionic surfactant; subjecting the resultant slurry mixture to molding in a magnetic field; and carrying out oil removal, sintering and heat treatment in this order. 
     
     
       11. The method for producing a  an R- T - B - based,  rare earth sintered magnet according to  claim 10 , wherein the molding in a magnetic field is compression molding, and the compressed green body preferably has a density distribution of 4.3-4.7 g/cm 3  to provide a  an R- T - B - based,  rare earth sintered magnet having a main phase composed of an R 2 T 14 B intermetallic compound, wherein R is at least one rare earth element including Y, and T is Fe or Fe and Co . 
     
     
       12. A method for producing a thin arc segment magnet having a thickness of 1-4 mm and made of a  an R- T - B - based,  rare earth sintered magnet having a main component composition comprising 28-33 weight % of R and 0.8-1.5 weight % of B, the balance being substantially Fe  T, wherein R is at least one rare earth element including Y, and T is Fe or Fe and Co, said arc segment magnet having an oxygen content of 0.3 weight % or less, a carbon content of  0 . 10  weight %  or less and a nitrogen content of  0 . 15  weight  %  or less  based on the total weight of the magnet, a density of 7.56 g/cm 3  or more, a coercivity iHc of 1.1 MA/m (14 kOe) or more at room temperature, and an orientation Br/4πI max  of 96% or more in an anisotropy-providing direction at room temperature, Br being a residual magnetic flux density, and  4 πI max    being a maximum value of  4 πI in a curve of  4 πI - H curve, wherein  4 πI is the intensity of magnetization, and H is the intensity of a magnetic field,  said method comprising the steps of finely pulverizing an alloy for said R- T - B - based,  rare earth sintered magnet to an average particle size of 1-10 μm in a non-oxidizing atmosphere; introducing the resultant fine powder into a mixture liquid comprising 99.7-99.99 parts by weight of at least one oil selected from the group consisting of a mineral oil, a synthetic oil and a vegetable oil and 0.01-0.3 parts by weight of a nonionic surfactant and/or an anionic surfactant; subjecting the resultant slurry mixture to molding in a magnetic field; and carrying out oil removal, sintering and heat treatment in this order. 
     
     
       13. A method for producing a radially anisotropic, arc segment magnet having an inner diameter of 100 mm or less and made of a  an R- T - B - based,  rare earth sintered magnet having a main component composition comprising 28-33 weight % of R and 0.8-1.5 weight % of B, the balance being substantially Fe  T, wherein R is at least one of  rare earth elements  element including Y, and T is Fe or Fe and Co, said arc segment magnet having an oxygen content of 0.3 weight % or less, a carbon content of  0 . 10  weight %  or less and a nitrogen content of  0 . 15  weight  %  or less  based on the total weight of the magnet, a density of 7.56 g/cm 3  or more, a coercivity iHc of 1.1 MA/m (14 kOe) or more at room temperature, and an orientation [Br///(Br//+Br⊥)]×100 (%) of 85.5% or more at room temperature, said orientation being defined by a residual magnetic flux density Br// in a radial direction and a residual magnetic flux density Br⊥ in an axial direction perpendicular to said radial direction, said method comprising the steps of finely pulverizing an alloy for said R- T - B - based,  rare earth sintered magnet to an average particle size of 1-10 μm in a non-oxidizing atmosphere; introducing the resultant fine powder into a mixture liquid comprising 99.7-99.99 parts by weight of at least one oil selected from the group consisting of a mineral oil, a synthetic oil and a vegetable oil and 0.01-0.3 parts by weight of a nonionic surfactant and/or an anionic surfactant; subjecting the resultant slurry mixture to molding in a magnetic field; and carrying out oil removal, sintering and heat treatment in this order. 
     
     
       14. A method for producing a radially anisotropic ring magnet having an inner diameter of 100 mm or less and made of a  an R- T - B - based,  rare earth sintered magnet having a main component composition comprising 28-33 weight % of R and 0.8-1.5 weight % of B, the balance being substantially Fe  T, wherein R is at least one rare earth element including Y, and T is Fe or Fe and Co, said ring magnet having an oxygen content of 0.3 weight % or less, a carbon content of  0 . 10  weight %  or less and a nitrogen content of  0 . 15  weight  %  or less  based on the total weight of the magnet, a density of 7.56 g/cm 3  or more, a coercivity iHc of 1.1 MA/m (14 kOe) or more at room temperature, and an orientation [Br///(Br//+Br⊥)]×100 (%) of 85.5% or more at room temperature, said orientation being defined by a residual magnetic flux density Br// in a radial direction and a residual magnetic flux density Br⊥ in an axial direction perpendicular to the radial direction, said method comprising the steps of finely pulverizing an alloy for said R- T - B - based,  rare earth sintered magnet to an average particle size of 1-10 μm in a non-oxidizing atmosphere; introducing the resultant fine powder into a mixture liquid comprising 99.7-99.99 parts by weight of at least one oil selected from the group consisting of a mineral oil, a synthetic oil and a vegetable oil and 0.01-0.3 parts by weight of a nonionic surfactant and/or an anionic surfactant; subjecting the resultant slurry mixture to molding in a magnetic field; and carrying out oil removal, sintering and heat treatment in this order.