Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Reexamination Certificate
2001-09-14
2003-10-21
Jenkins, Daniel J. (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
C148S101000, C419S023000, C419S033000, C419S036000
Reexamination Certificate
active
06635120
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing a sintered rare earth magnet having a low oxygen content and high density and orientation, and to a high-performance, ring-shaped, R-T-B-based, sintered magnet having a lower oxygen content, a higher density and higher orientation in a polar anisotropic or radially dipolar direction than those of the conventional sintered magnets.
BACKGROUND OF THE INVENTION
R—Fe—B based, sintered magnets, wherein R is at least one of rare earth elements including Y, are produced by coarsely pulverizing R—Fe—B-based alloys of desired compositions, finely pulverizing them in an inert gas such as nitrogen, etc., molding the resultant fine R—Fe—B-based alloy powder having an average particle size of 1-10 &mgr;m in a magnetic field, sintering the resultant green body, and then heat-treating the resultant sintered magnet. To provide the R—Fe—B-based, sintered magnets with improved residual magnetic flux density Br and maximum energy product (BH)
max
, it is extremely important that the R—Fe—B-based, sintered magnets have reduced oxygen content. In view of this fact, the applicants previously discovered mineral oils and synthetic oils having a function to prevent the oxidation of the fine R—Fe—B-based alloy powder, and proposed a process for producing high-performance, R—Fe—B-based, sintered magnet having a low oxygen content and a high density, which comprises a introducing the fine R—Fe—B-based alloy powder into the above mineral or synthetic oil to form a slury, molding the slurry, degreasing the resultant green body, and then sintering and heat-treating it (see Japanese Patent 2,731,337, etc.).
This production process is advantageous in that the fine power and the green body are covered with the above oil to protect them from the air, thereby substantially suppressing their oxidation. Thus, the R—Fe—B-based, sintered body obtained by degreasing and sintering has as low an oxygen content as corresponding to that of the coarse R—Fe—B-based alloy powder before fine pulverization. Because this production process suffers from little decrease in the percentages of the R elements in the R—Fe—B-based alloy due to oxidation during sintering, a rare earth-rich phase forming a grain boundary phase is well kept in the resultant R—Fe—B-based, sintered body. Therefore, the R content in the green body can be set small, leading to decrease in excess R-rich phase and rare earth oxides and thus increase in a volume ratio of R
2
Fe
14
B-type crystal grains (main phase), which constitute a ferromagnetic phase, than he conventional sintered magnets. Therefore, this production process can provide a sintered magnet with remarkably improved Br and (BH)
max
.
However, there is recently strong demand to miniaturize and reduce in weight magnet-comprising electric appliances such as VCMs, CD pickups, motors for domestic electric appliances, etc., resulting in increasingly higher demand to miniaturize and reduce in weight sintered rare earth magnets used in these electric appliances. Though the process of Japanese patent 2,731,337 was considered satisfactory to this demand, higher Br and (BH)
max
than those achieved by Japanese patent 2,731,337 are now demanded. The inventors' research has revealed that there is room for improving the magnetic orientation of the slurry.
OBJECT OF THE INVENTION
Accordingly, an object of the present invention is to provide a method for producing a sintered rare earth magnet having a low oxygen content and high density and orientation.
Another object of the present invention is to provide a polar anisotropic or radially bipolar, R-T-B-based, sintered ring magnet having low oxygen content and high density and orientation.
SUMMARY OF THE INVENTION
The method for producing a sintered rare earth magnet comprising the steps of finely pulverizing a coarse rare earth magnet alloy powder to an average particle size of 1-10 &mgr;m in a non-oxidizing atmosphere; introducing the resultant fine rare earth magnet alloy powder into a non-oxidizing liquid comprising at least one oil selected from the group consisting of mineral oils, synthetic oils and vegetable oils, and at least one lubricant selected from the group consisting of esters of aliphatic acids and monovalent alcohols, esters of polybasic acids and monovalent alcohols, esters of aliphatic acids and polyvalent alcohols and their derivatives to prepare a slurry; molding the slurry; degreasing the resultant green body; sintering the degreased green body; and then heat-treating the green body.
A weight ratio of the lubricant to the fine rare earth magnet alloy powder is preferably 0.01/99.99 to 0.5199.5.
The sintered rare earth magnet may further comprise 0.01-0.2 weight % of Ga, 0.01-0.3 weight % of Al, and 0.01-0.8 weight % of Nb.
The polar anisotropic ring magnet having is constituted by an R—Fe—Co—Cu—B-based, sintered magnet comprising 28-33 weight % of R, wherein R is at least one rare earth element including Y, 50 atomic % or more of R being occupied by Nd, 0.8-1.5 weight % of B, 0.5-5 weight % of Co, and 0.01-0.3 weight % of Cu, the balance being substantially Fe and inevitable impurities; the amount of oxygen inevitably contained being 0.3 weight % or less based on the total weight of the ring magnet; the ring magnet having a density of 7.56 g/cm
3
or more; and a ratio of I (105)/I (006) being 0.5-0.8, wherein I (105) and I (006) are X-ray diffraction peak intensity measured with respect to (105) and (006) planes, respectively, at a middle position on an outer surface between magnetic poles of the ring magnet. With I(105)/I (006)=0.5-0.8, the sintered magnet has higher Br and (B) than those of the conventional sintered magnets.
The radially dipolar ring magnet of the present invention is constituted by an R—Fe—Co—Cu—B-based, sintered magnet comprising 28-33% by weight of R, wherein R is at least one rare earth element including Y, 50 atomic % or more of R being occupied by Nd, 0.8-1.5% by weight of B, 0.5-5 weight % of Co, and 0.01-0.3 weight % of Cu, the balance being substantially Fe and inevitable impurities; the amount of oxygen inevitably contained being 0.3 weight % or less based on the total weight of the ring magnet; the ring magnet having a density of 7.56 g/cm
3
or more and an intrinsic coercivity iHc of 1.1 MA/m (14 kOe) or more at room temperature; and the degree of orientation expressed by [(Br//) 1 (Br//+Bri⊥)]×100(%) being 85.5% or more, wherein Br// is a residual magnetic flux density in an orientation direction at room temperature, and Br⊥ is a residual magnetic flux density in a longitudinal direction perpendicular to the orientation direction.
The thin, sintered arc segment magnet having a thickness of 1-4 mm according to the present invention is constituted by an R′—Fe—B-based, sintered magnet comprising 28-33 weight % of R′, wherein R′ is at least one of rare earth elements including Y, 50 atomic % or more of R′ being occupied by Pr, 0.8-1.5 weight % of B, 5 weight % or less of Co, and 0.3 weight % or less of Cu, the balance being substantially Fe and inevitable impurities; the amount of oxygen inevitably contained being 0.3 weight % or less based on the total weight of the arc segment magnet; the arc segment magnet having a density of 7.50 g/cm
3
or more, a coercivity iHc of 1.1 MA/m (14 kOe) or more at room temperature, and orientation (Br/4&pgr;I
max
) of 96% or more in an anisotropy direction.
The thin, sintered arc segment magnet preferably has parallel anisotropy and a length of 40-100 mm. Further, a ratio of I (105)/I (006) is preferably 0.5-0.8, wherein I (105) and I (006) are X-ray diffraction peak intensity measured with respect to (105) and (006) planes, respectively, using CuK&agr;1-ray (&lgr;=0.15405 nm). With I (105)/I (006)=0.5-0.8, the thin, sintered arc segment magnet has higher Br and (BH than those of the conventional sintered magnets.
The radially anisotropic, sintered arc segment magnet having an inner diameter of 100 mm or less according
Tokoro Hisato
Uchida Kimio
Hitachi Metals Ltd.
Jenkins Daniel J.
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