Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Reexamination Certificate
1999-09-30
2001-08-21
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
C148S540000
Reexamination Certificate
active
06277211
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to processes for reducing the oxygen content and/or improving the metal yield in alloys and permanent magnets having a rare-earth iron-boron composition, and to alloys and magnets produced by such processes.
BACKGROUND OF THE INVENTION
Rare earth-iron-boron based magnets, such as the well known Nd—Fe—B magnets, are used in numerous applications, including computer hardware, automobiles, consumer electronics and household appliances. In particular, magnets using rare earth elements, such as Nd or Pr, are useful primarily because of their superior magnetic properties, as manifested by their large coercivity, remanence, magnetization, and maximum energy product. The primary disadvantage of such magnets is that because of the cost of scarce rare earth metals, such as Nd or Pr, they are relatively expensive to make.
There are several known methods to fabricate rare earth-iron-boron magnets. In such methods, the constituent metals are melted together and subsequently solidified. Solidification is achieved by different techniques which include cooling, melt spinning, and annealing. The solidified alloy may take the form of an ingot, ribbon, flakes, or powder. Methods for fabricating magnets include sintering, hot pressing, hot deformation, and bonding. The process for making a sintered permanent rare earth magnet is well known and is described in, for example, U.S. Pat. Nos. 4,770,723, 4,792,368 and 5,645,651, which are incorporated herein by reference. The processes for making a hot-pressed or hot-deformed magnet are also well known and are described in, for example, U.S. Pat. Nos. 4,792,367 and 4,844,754, where are incorporated herein by reference. The process for making a bonded magnet is well known and is described in, for example, U.S. Pat. No. 4,902,361, which is incorporated herein by reference.
The oxygen content of the alloy or magnet affects its magnetic properties. A high oxygen content in the alloy causes a decline in the coercivity of the permanent magnet, preventing it from obtaining a high energy product. It is therefore desirable to have a process by which rare earth-iron-boron alloys and magnets are produced which limits their oxygen content. It is also desirable to have a process by which the metal yield from rare earth-iron-boron alloys is improved without adversely affecting the magnetic properties of the powder or magnet that may be formed.
SUMMARY OF THE INVENTION
The present invention is directed to a process for preparing a rare earth-iron-boron alloy that results in reduced oxygen content and/or greater yield. The process comprises the steps of preparing a melt having a composition comprising a rare earth, boron, iron, and copper; and solidifying the melt. In different embodiments, the melt further comprises cobalt, dysprosium, and/or gallium.
Preferably, the melt comprises approximately 15 to 34 weight percent of the rare earth, 0.8 to 1.4 weight percent of boron, and balanced with iron; the rare earth preferably consists of Nd and Pr. Cu is preferably included in the melt in the form of pure Cu, and preferably in a proportion less than 0.2 weight percent. In specific embodiments of the invention, the step of solidifying comprises cooling or melt spinning.
The present invention is further directed to a rare earth-iron-boron alloy produced according to this process. As used herein, the term “rare earth-iron-boron alloy” encompasses an alloy in any form, including, without limitation, forms where the alloy is particulate, powdered (i.e. with a particle size less than 400 microns), flaked, ribboned, and cast as an ingot.
The invention is further directed to a process for preparing a permanent rare earth-iron-boron magnet that comprises the steps of preparing a melt having a composition comprising a rare earth, boron, iron, and copper; solidifying the melt; and fabricating the permanent rare earth-iron-boron magnet from the solidified melt. Different embodiments for preparing a permanent magnet include aspects that correspond to those recited above for preparing a rare earth-iron-boron alloy.
The invention is also directed to a permanent rare earth-iron-boron magnet made by this process. As used herein, the phrase “permanent rare earth-iron-boron magnet” encompasses any permanent magnet, including a magnetic particle, a magnetic powder, a magnetic flake, a bonded magnet, and a fully dense isotropic or anisotropic magnet. Such magnets include, without limitation, sintered, hot-pressed, hot-deformed, and bonded magnets.
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Dickey Robert Eugene
Panchanathan Viswanathan
Magnequench Inc.
Oltmans Andrew L.
Pennie & Edmonds LLP
Sheehan John
LandOfFree
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