Compositions – Magnetic – With wax – bitumen – resin – or gum
Patent
1998-03-10
1999-12-14
Koslow, C. Melissa
Compositions
Magnetic
With wax, bitumen, resin, or gum
252 6255, 264429, 264427, 264319, 264327, 26432817, 26432819, H01F 4102, H01R 108
Patent
active
060012722
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of manufacturing a rare earth bonded magnet by binding magnet powder containing rare earth elements by a binder, a composition for use in the manufacture of a rare earth bonded magnet, and to a rare earth bonded magnet.
BACKGROUND ART
Bonded magnets are manufactured from mixtures (compounds) of magnetic powders and binding resins (organic binders), by pressure-molding the mixtures into desired magnet shapes. Among such bonded magnets, a special type of bonded magnet referred to as a rare earth bonded magnet is made up from a magnet powder which is composed of a magnetic material containing a rare earth element or elements. Methods of manufacturing rare earth bonded magnets are disclosed, for example, in Japanese Patent Publication No. 53-34640, Japanese Patent Publication No. 46-31841, Japanese Patent Publication No. 04-74421, Japanese Patent Laid-Open No. 59-136907, Japanese Patent Laid-Open No. 59-213104, Japanese Patent Laid-Open No. 02-153509, Japanese Patent Laid-Open No. 60-211908, Japanese Patent Laid-Open No. 60-216523, Japanese Patent Laid-Open No. 61-164215, Japanese Patent Laid-Open No. 59-103309 and Japanese Patent Laid-Open No. 03-108301.
The methods of manufacturing rare earth bonded magnets are broadly sorted into compaction molding, injection molding and extrusion molding.
In compaction molding, the aforesaid compound is packed in a press mold and compacted at a room temperature so as to form a green body. Subsequently, when the binding resin is a thermosetting resin, the resin is hardened, whereby a magnet is obtained. This method enables the molding to be carried out with smaller amount of binding resin than other methods, resulting in a smaller resin content in the product magnet, thus advantageously contributing to improvement in the magnetic characteristics of the magnet.
Extrusion molding is a method in which heated molten compound extruded from an extruder die is solidified by cooling and then cut at a desired length, whereby a magnet is obtained. This method in one hand offers an advantage in that it permits easy production of thin-walled or elongated magnet by virtue of a comparatively large molding versatility on the shape of product magnet, but on the other hand suffers from a problem in that it requires, in order to ensure a sufficiently high fluidity of the molten compound during the molding, a greater amount of binding resin to be used as compared with the compaction molding method, with the result that the magnetic characteristics are impaired due to increased resin content in the product magnet.
In injection molding, the aforesaid compound, which has been heated and molten to exhibit sufficiently high fluidity, is poured into a mold so as to form a magnet of a desired shape. This method offers molding versatility on the magnet shape even greater than that offered by the extrusion molding method, enabling easy fabrication of magnets having irregular configurations. However, this method requires higher level of fluidity of the molten compound and, hence, a greater content of the binder resin than required in the extrusion molding method, resulting in poor magnetic characteristics of the product magnet due to increased content of the binder resin in the product magnet.
Among these methods, the compaction molding method enables production of magnets having superior magnetic performance as compared with other methods. Manufacture of bonded magnets by the known compaction molding method, however, suffers from the following disadvantages.
Firstly, it is to be pointed out that rare earth bonded magnets manufactured by this method tend to exhibit high porosity, which reduces mechanical strength and corrosion resistance of the product magnet. Hitherto, therefore, countermeasures have been taken in the compaction molding, such as use of high-pressure molding technique which employs a compaction pressure as high as 70 kgf/mm.sup.2 and anti-corrosion coating on the molded product. Elevated compaction pressure, however, heavily
REFERENCES:
patent: 5051200 (1991-09-01), Srail et al.
patent: 5176842 (1993-01-01), Kuwazawa et al.
Ikuma Ken
Shinohara Takatomo
Shiohara Kiyoshi
Koslow C. Melissa
Seiko Epson Corporation
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