Powder metallurgy processes – Forming articles by uniting randomly associated metal particles – Consolidation of powders
Reexamination Certificate
1999-03-01
2001-07-17
Jenkins, Daniel (Department: 1742)
Powder metallurgy processes
Forming articles by uniting randomly associated metal particles
Consolidation of powders
Reexamination Certificate
active
06261515
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains generally to magnetic materials, and more particularly to a method for producing rare-earth magnets that have improved magnetic properties.
2. Description of the Background Art
Rare earth magnets are utilized in a wide variety of applications, ranging from motors, magnetic bearings, magnetic couplings, speakers, microphones, signal recording devices, instrumentation, switches, and relays to charged particle beam guidance, nuclear magnetic resonance image-forming equipment and particle accelerators.
A class of rare earth magnets, composed of a formulation of neodymium (Nd), iron (Fe) and boron (B), are the most powerful magnets available. They have high residual inductance (Br), high maximum energy product (BH
max
) and relatively high intrinsic coercivity (H
ci
). These magnets, known as the neodymium-iron-boron Rare earth magnets (Nd
2
Fe
14
B), provide the best magnetic properties in terms of high energy product. With its excellent magnetic properties, abundant raw material for its manufacture, and a relatively low manufacturing cost, use of the Nd
2
Fe
14
B rare earth magnets in applications requiring high magnetic properties are becoming almost universal. Rare earth-containing magnets are typically produced by crushing a rare earth-containing alloy into magnetic powder, forming and molding the magnetic powder into magnetic bodies (known as green compacts), sintering and heat-treating the green compacts.
Due to it's active chemical nature, however, neodymium is easily oxidized to form Nd
2
O
3
. Research has shown that the oxidation of neodymium in the magnet is seriously destructive to the properties of rare earth-containing magnets. The oxygen content of neodymium-iron-boron rare earth magnets is the key factor affecting the magnet's properties. Nd
2
O
3
, which is formed through the reaction of neodymium with O
2
, has anti-magnetic characteristics and detrimental to the overall magnetic properties of Nd
2
Fe
14
B rare earth magnets. Thus, reducing the oxygen content in the magnet effectively improves the magnetic properties of neodymium-iron-boron rare earth magnets because the Nd
2
O
3
content is correspondingly reduced. Reducing the percentage of Nd
2
O
3
in the major phase of Nd
2
Fe
14
B will also result in a reduction of volume and weight of the magnet, thus allowing for miniaturization at a very economical cost without sacrificing performance.
Accordingly, there is a need for a cost-effective method for manufacturing rare earth containing magnets that consistently reduces and/or controls the ability of oxygen-containing sources to react with the magnetic powder during the manufacture of the rare earth containing magnet. The present invention satisfies this need, as well as others, and generally overcomes the deficiencies found in the background art.
BRIEF SUMMARY OF THE INVENTION
The present invention pertains to a method for producing rare earth-containing magnets that results in the magnet having substantially enhanced magnetic properties. This innovative production method reduces the ability of the rare earth element, namely neodymium, dysprosium, or a combination of neodymium and dysprosium, to react with oxygen-containing sources prior to and during the molding, aligning in a magnetic field and compressing steps of the manufacturing process by isolating the magnetic powder and the formed magnet from oxygen-containing sources, wherein the humidity level and the oxygen content, is minimized and controlled.
The method of the present invention is based on the fact that environmental humidity oxidizes with neodymium in a rare earth-containing magnet to form Nd
2
O
3
. Nd
2
O
3
is generally formed in two ways: (1) by chemical reaction between neodymium and oxygen from the surrounding air, and (2) by chemical reaction between neodymium and H
2
O present in environmental humidity.
Besides neodymium, the iron in rare earth-containing magnets also react with oxygen. Iron can be oxidized through direct contact with oxygen in the surrounding air and also through chemical reaction with H
2
O present in environmental humidity during the manufacturing process. Therefore, the reduction of environmental humidity during the manufacture of the rare earth-containing magnet is essential in reducing anti-magnetic Nd
2
O
3
along with all other oxidized phases of the magnet.
The method for producing rare earth magnets according to the present invention generally comprises the steps of vacuum-packing magnetic powder into sealed packages, forming and molding the magnetic powder in an isolated environment wherein the humidity level within the isolated environment is maintained consistently below 40% and the oxygen content is maintained below 1%, aligning magnetically the formed magnet while the formed magnet is isolated from direct contact with the surrounding environment and compressing the formed magnet while the formed magnet is isolated from direct contact with the surrounding environment.
The present invention is easily incorporated into existing methods for manufacturing rare earth-containing magnets, which typically include the steps of crushing or pulverizing a rare earth-containing alloy into a magnetic powder, forming and molding the magnetic powder, magnetically aligning the molded and formed magnetic powder, compressing the magnetic powder to form a magnetic body or green compact, and sintering and heat treating the green compact.
The isolated environment generally comprises an enclosure, operating portals, an inlet/outlet window, molding bases and pressure-sealed molding covers disposed within the enclosure, a humidity meter, means for supplying inert gas into the enclosure and desiccating agents disposed between the inert gas supply means and the enclosure, along with desiccating agents within the enclosure.
As a result of reducing the humidity level and oxygen content throughout the forming and molding step, and isolating the green compact from the surrounding environment during magnetic alignment and compression, oxidation of the magnetic powders and green compacts is minimized, and the magnetic properties of the rare earth magnet are substantially improved, such that the maximum energy product ((BH)
m
) is increased by at least 3-5 MGOe and the intrinsic coercivity (H
ci
) is increased by at least 2-4 KOe and the working temperature is increased approximately 30° C. to 50° C. Rare earth magnets produced according to this invention have a composition of major phase, Nd
2
Fe
14
B≧96% (which contains <0.6% oxygen by weight); rich neodymium phase <3%; and rich boron phase <1%.
An object of the invention is to provide a method for producing rare earth-containing magnets that have a reduced oxygen content.
Another object of the invention is to provide a method for producing rare earth-containing magnets that minimizes and controls the humidity level and oxygen content of the manufacturing environment during forming and molding.
Another object of the invention is to provide a method for producing rare earth-containing magnets that isolates the formed magnet during aligning and compressing of the magnetic body.
Still another object of the invention is to provide a method for producing rare earth magnets that minimizes the oxidation of the formed magnet during sintering.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.
REFERENCES:
patent: 4402770 (1983-09-01), Koon
patent: 4588439 (1986-05-01), Narasimhan et al.
patent: 4597938 (1986-07-01), Matsuura et al.
patent: 4601875 (1986-07-01), Yamamoto et al.
patent: 4684400 (1987-08-01), Ritsko et al.
patent: 4802931 (1989-02-01), Cro
Dai Zhiliang
Fang Fu
Ren Guangzhi
Chan Law Group LC
Jenkins Daniel
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