Compositions – Magnetic – With wax – bitumen – resin – or gum
Reexamination Certificate
2002-04-02
2004-07-20
Sheehan, John P. (Department: 1742)
Compositions
Magnetic
With wax, bitumen, resin, or gum
C148S101000, C148S102000, C148S103000, C148S122000
Reexamination Certificate
active
06764607
ABSTRACT:
TECHNICAL FIELD
This invention relates to a corrosion-resistant R—Fe—B bonded magnet wherein are prevented the occurrence of flaws due to corrosion and the occurrence of flaws such as cracking, chipping, and swelling associated with the generation of white powder generated during the use of an R—Fe—B bonded magnet. Stated in greater detail, the present invention relates to a corrosion-resistant R—Fe—B bonded magnet wherein the occurrence of corrosion and white powder due to such as R hydroxides that cause cracking and chipping is prevented by causing an R compound such as an R oxide, R nitride, R carbide, or R hydride that becomes R(OH)
3
when it reacts with steam to be contained at 10 ppm or less and R(OH)
3
to be contained at from 1 ppm to 200 ppm in the powder for molding the magnet in a process wherein treatment is performed in a water vapor pressure atmosphere, or by also, after formation, coating the surface of the R—Fe—B bonded magnet with an organic resin, and to powder for molding such magnet and methods for manufacturing such magnet and powder.
BACKGROUND ART
By employing Fe and/or R (rare earth element Nd, Pr, or the like) that is an inexpensive abundant resource as the main components, R—Fe—B permanent magnets exhibit higher performance and can be fabricated at lower cost than conventional high-performance Sm—Co magnets. For that reason, these are being used today in the manufacture of sintered magnets and bonded magnets of various configuration and used in a wide range of applications.
In general, an R—Fe—B bonded magnet is fabricated by molding it after mixing a resin bonding agent into the powder for molding that bonded magnet. The powder for molding such an R—Fe—B bonded magnet is manufactured by an ingot pulverizing method, Ca reduction diffusion method, low-cost rapid quenching method, or, alternatively, by a hydrogenating treatment (HDDR method) wherewith a recrystallized fine structure is obtained and magnetic anisotropy can be effected.
It is known that the R—Fe—B bonded magnet described above is susceptible to a phenomenon whereby, during prolonged use in the atmospheric air, white powder is generated on the surface of and in the interior of the magnet, and that there are cases where, due to the volumetric expansion of that white powder, such defects as magnet cracking, chipping, or swelling occur.
This white powder generation phenomenon produces fatal defects in applications in motors and the like where exacting dimensional precision is demanded, which constitute important applications of bonded magnets, and in applications where cleanness is demanded, as in hard disk drives and the like.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide powder for molding an R—Fe—B bonded magnet, and an R—Fe—B bonded magnet, together with manufacturing methods therefore, wherewith, in the R—Fe—B bonded magnet, the white powder generation described above is prevented, and the occurrence of flaws such as cracking, chipping, and swelling associated therewith is prevented.
As a result of various studies on the causes of the volumetric expansion phenomenon associated with the generation of white powder generated in bonded magnets, the attention of the inventors was drawn to the fact that, by the admixture of slag into the raw material alloy during the melting-manufacture or heat treatment of raw material powder for bonded magnets, and surface reactants and the like, 1 to 200 ppm or so of R oxide, carbide, nitride, and hydride (R compounds) are produced, and to the fact that those various R compounds react with water vapor in the air and thus change to an R hydroxide.
In raw material powder for R—Fe—B bonded magnets, rapidly quenched powder produced by the rapid quenching method is obtained by rendering an alloy melt amorphous by rapid quenching by a quenching roller, and then performing a crystallizing heat treatment. Also, as for the hydrogenation treated powder, raw material powder obtained by an ingot pulverizing method or Ca reduction diffusion method or the like is subjected to a hydrogen occlusion treatment and dehydration treatment, and a fine recrystallized structure having magnetic anisotropy can be obtained.
When the rapidly quenched powders described above or a hydrogenation processed powder (HDDR), in particular, is used in raw material for R—Fe—B bonded magnets, these raw material powders are such that, due to the heat treatment during the manufacturing process described earlier, even if the contained R oxide or carbide or the like should become an R hydroxide that is stable in air, the R hydroxide will again change to an R oxide that is unstable in air in that heat treatment.
The inventors learned that, in a bonded magnet manufactured using the rapidly quenched powder or hydrogenation treated powder noted earlier, during long-term use, the R oxide and carbide and the like contained in the bonded magnet become causes of cracking, chipping, and swelling and the like in the bonded magnet by reacting with water vapor in the air and changing to an R hydroxide, whereupon white powder generation on the surface or in the interior of the bonded magnet occurs, and that white powder exhibits volumetric expansion.
Thereupon the inventors noted that, of the R compounds, the R hydroxide is the most stable in air at room temperature, and learned that, by causing the R compounds such as R oxide, carbide, nitride, and hydride present in the powder for molding bonded magnets to change to an R hydroxide beforehand, immediately prior to molding, and stabilizing them, and making the residual content of the R compounds 10 ppm or less, the volumetric expansion associated with the generation of white powder, which becomes a cause of cracking, chipping, and swelling and the like in R—Fe—B bonded magnets during use, can be prevented. They also learned that this prevention method can prevent the volumetric expansion associated with the generation of white powder even without effecting a coating.
The inventors also conducted studies on the corrosion that is a peculiar problem with R—Fe—B bonded magnets. Corrosion occurs when the R
2
Fe
14
B phase that strongly affects magnetic characteristics in bonded magnets is oxidized. Coating an organic resin onto the surface of the magnet is effective in preventing the corrosion that is generated in a conventional R—Fe—B permanent magnet. However, it was learned that, depending on the conditions of use, with the coating method noted above, pinholes develop unavoidably in the organic resin coating layer obtained by such coating application, resulting in the problem that the occurrence of corrosion cannot be prevented.
Thereupon, the inventors, as a result of further studies made on superior corrosion prevention and on preventing the volumetric expansion associated with white powder generation, learned that
1) after treating rare earth compounds that generate white powder such as R oxide, R nitride, R oxide, and R hydride that are unavoidably contained in raw material powder for R—Fe—B bonded magnets in a water vapor atmosphere under certain conditions, changing them to R hydroxides, and then mixing a binding agent resin into the molding powder, performing molding, and obtaining a bonded magnet of the prescribed shape and dimensions,
2) by coating a certain quantity of a fluorine resin and organic resin containing one or two or more types of a pigment or organic complex salt dye onto the surface of the bonded magnet,
3) the intrusion of moisture or the like from unavoidable pinholes occurring in the resin coating layer is prevented by a water repellancy imparted by the fluorine resin being contained, and
4) the penetration of the organic resin coating film by an oxide gas other than water is blocked by the pigment, or, alternatively, by the anticorrosive effect of the organic complex salt dye, white powder and corrosion generation can be simultaneously prevented, whereupon they perfected the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is characterized in that raw material powder for a
Dykema Gossett PLLC
Sheehan John P.
Sumitomo Special Metals Co. Ltd.
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