Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Patent
1988-10-31
1992-06-30
Sheehan, John P.
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
148120, 148302, H01F 102
Patent
active
051259885
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a rare earth-iron permanent magnet composed mainly of rare earth elements and iron, and also to a process for producing the same.
BACKGROUND ART
The permanent magnet is one of the most important electrical and electronic materials used in varied application areas ranging from household electric appliances to peripheral equipment of large computers. There is an increasing demand for permanent magnets of high performance to meet a recent requirement for making electric appliances smaller and more efficient than before.
Typical of permanent magnets now in use are alnico magnets, hard ferrite magnets, and rare earth-transition metal magnets. Much has been studied on rare earth-cobalt permanent magnets and rare earth-iron permanent magnets, which belong to the category of the rare earth-transition metal magnets, because of their superior magnetic performance. Rare earth-iron permanent magnets are attracting attention on account of their lower price and higher performance than rare earth-cobalt permanent magnets which contain a large amount of expensive cobalt.
Heretofore, there have been rare earth-iron permanent magnets produced by any of the following three processes. metallurgy. (See Japanese Patent Laid-open No. 46008/1984.) with a resin. Thin ribbons are produced by rapidly quenching the molten alloy using an apparatus for making amorphous ribbons. (See Japanese Patent Laid-open No. 211549/1984.) (2) above) under mechanical orientation by the two-stage hot pressing method. (See Japanese Patent Laid-open No. 100402/1985.)
The present inventors previously proposed a magnet produced from a cast ingot which has undergone mechanical orientation by the one-stage hot working. (See Japanese Patent Application No. 144532/1986 and Japanese Patent Laid-open NO. 276803/1987.) (This process is referred to as process (4) hereinafter.)
The above-mentioned process (1) includes the steps of producing an alloy ingot by melting and casting, crushing the ingot into magnet powder about 3 .mu.m in particle size, mixing the magnet powder with a binder (molding additive), press-molding the mixture in a magnetic field, sintering the molding in an argon atmosphere at about 1100.degree. C. for 1 hour, and rapidly cooling the sintered product to room temperature. The sintered product undergoes heat treatment at about 600.degree. C. to increase coercive force.
In the above-mentioned process (2) rapidly cooled thin ribbons of R--Fe--B alloy are produced by a melt-spinning apparatus at an optimum substrate velocity. The rapidly cooled thin ribbon is about 30 .mu.m thick and is an aggregation of crystal grains 1000.ANG. or less in diameter. It is brittle and liable to break. It is magnetically isotropic because the crystal grains are distributed isotropically. To make a magnet, this thin ribbon is crushed into powder of proper particle size, the powder is mixed with a resin, and the mixture undergoes press molding.
According to the above-mentioned process (3), the thin ribbon obtained by the process (2) undergoes mechanical orientation by a two-stage hot pressing in vacuum or an inert gas atmosphere. Thus there is obtained a anisotropic R--Fe--B magnet. In the pressing stage, pressure is applied in one axis so that the axis of easy magnetization is aligned in the direction parallel to the pressing direction. This alignment process brings about anisotropy. This process is executed such that the crystal grains in the thin ribbon has a particle diameter smaller than that of crystal grains which exhibit the maximum coercive force, and then the crystal grains are designed to grow to a optimum particle diameter during hot-pressing.
The above-mentioned process (4) is designed to produce and anisotropic R--Fe--B magnet by hot-working an alloy ingot in vacuum or an inert gas atmosphere. The process causes the axis of easy magnetization to align in the direction parallel to the working direction, resulting in anisotropy, as in the above-mentioned process (3). However, process (4) differs from pr
REFERENCES:
patent: 4767474 (1988-08-01), Fujimura et al.
patent: 4773950 (1988-09-01), Fujimura et al.
patent: 4902361 (1990-02-01), Lee et al.
Akioka Koji
Kobayashi Osamu
Shimoda Tatsuya
Seiko Epson Corporation
Sheehan John P.
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