Metal treatment – Stock – Magnetic
Reexamination Certificate
1998-12-22
2001-11-06
King, Roy (Department: 1742)
Metal treatment
Stock
Magnetic
C148S110000, C148S309000, C148S306000, C420S078000
Reexamination Certificate
active
06312531
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to a magnetic composite article using soft magnetic powder of Fe—Al—Si system alloy that is employed in transformer-cores of power supplies, choke coils, or magnetic heads, and a manufacturing method of the same.
2. Background Art
Electric appliances and electronic devices have been downsized, which entails a demand for small and efficient magnetic articles. Ferrite cores and dust cores are thus employed as choke coils that are used at a high frequency band. The ferrite core has a problem of a low saturation-magnetic-flux-density, while the dust core formed by compacting magnetic powder has a substantially higher saturation-magnetic-flux-density than the ferrite core. The dust core has thus an advantage over the ferrite core in the way of downsizing appliances and devices.
On the other hand, the dust core is inferior to the ferrite core in regard to permeability and power loss. Because of these points, when the dust core is used as a choke coil or an inductor, a great amount of core loss raises the core temperature, which is an obstacle to downsizing.
The core loss of dust core comprises, in general, hysteresis loss and eddy current loss. The eddy current loss increases in proportion to the square of the frequency and the square of the size of eddy current i.e. the square of path length of the eddy current. Therefore, the magnetic-powder-surface is coated with insulating resin so that the dust core restrains itself from producing eddy current.
The dust core is formed generally with the compacting pressure of not less than 5 ton/cm
2
. Its magnetostrictive is increased, while the permeability is lowered through this process. As a result, the hysteresis loss is increased. In order to release the magnetostrictive, a heat treatment has been applied to the dust core after the compacting. Some of the heat treatments are disclosed e.g. in the Japanese Patent Application Non-examined Publication Nos. H06-342714, H08-37107, and H09-125108.
However, a conventional dust core using powder of Fe—Al—Si system alloy has a drawback that the core loss increases in step with temperature rising. To be more specific, when a temperature coefficient of the core loss is positive around the room temperature, the transformer or choke coil produces heat due to the core loss during its active use. Its temperature thus rises and the core loss further increases, which induces a greater heat. This vicious circle is repeated to provoke a thermo-run-away.
In order to avoid the thermo-run-away, it is therefore crucial that the dust core should have a temperature characteristic such that the core loss is minimized at 80° C.-100° C. in an active use.
In general, the Fe—Al—Si system alloy shows its maximum permeability steeply around the composition of Si=9.6%, Al=5.5%, and the remainder of Fe (the figures are wt %) where the crystal magnetic anisotropy K≈0 and magnetostricitve constant &lgr;≈0, as shown in
FIGS. 2 and 3
. The composition within this range is generally called “sendust”. This maximum permeability was taken into consideration, and the magnetic composite articles employing the powder of Fe—Al—Si system alloy have been proposed, and some of them are disclosed in the patent gazettes of the Japanese Patent Application Non-examined Publication Nos. H06-342714, H08-37107 and H09-125108. However, no description about the relation between the core loss and the temperature characteristic is found in any of these proposals.
The temperature characteristic of the core-loss is determined by behavior of the hysteresis loss, i.e. the temperature characteristic of permeability. Ferrite in the conventional manner has shown its maximum permeability at a given temperature and shown also its minimum loss at the same point. This is because the crystal magnetic anisotropy K shows “0” at the given temperature, where magnetic domain walls can move with ease, and therefore, the hysteresis loss decreases. A conventional “sendust” dust-core employing the soft magnetic powder of Fe—Al—Si system alloy increases its core-loss monotonously as shown in
FIG. 1
when the temperature is not lower than the room temperature. Therefore, this dust-core has been evaluated not good for a large-power transformer.
DISCLOSURE OF THE INVENTION
The present invention addresses these problems and aims to provide magnetic composite article having excellent characteristics such as a high permeability and a low-core-loss. A magnetic composite article according to the present invention employs soft magnetic powder of Fe—Al—Si system alloy, of which magnetostrictive constant &lgr; is positive at the room temperature so that a temperature coefficient of the core loss at the room temperature is negative. The soft magnetic powder employed in the article preferably comprises 4.5%≦Al≦8.5%, 7.5%≦Si≦9.5%, and the remainder of Fe, (the figures are wt %). This structure realizes a core having a low core-loss even at a high frequency, an excellent temperature characteristic such that the temperature coefficient of the core loss is negative, and an excellent permeability.
However, according to the present invention, in a case of the magnetic composite article employing the soft magnetic powder of Fe—Al—Si system alloy, the crystal magnetic anisotropy K does not govern the temperature characteristic contrary to the established theory, but the magnetostricitive constant &lgr; that has not drawn attention hitherto governs it. Further, the following fact is found. That is, when the magnetostrictive constant &lgr; takes positive value at the room temperature (around 20-30° C.), the temperature coefficient of the core-loss has a negative inclination. In particular, when employing the soft magnetic powder of Fe—Al—Si system alloy that comprises 4.5%≦Al≦8.5%, 7.5%≦Si≦9.5%, and the remainder of Fe (the figures are wt %), the inventors can obtain an excellent temperature characteristic such as a high permeability and a low core-loss. Preferably the soft magnetic powder that comprises 5.0%≦Al≦6.5%, 8.2%≦Si≦9.2% and the remainder of Fe is used, whereby the more effective result is obtained.
REFERENCES:
patent: 4299622 (1981-11-01), Kimira et al.
patent: 4985089 (1991-01-01), Yoshizawa et al.
patent: 5073214 (1991-12-01), Hirota et al.
patent: 5466306 (1995-11-01), Mishima et al.
patent: 5466539 (1995-11-01), Takayama
patent: 5580399 (1996-12-01), Tamai et al.
patent: 5651841 (1997-07-01), Hideharu et al.
patent: 06342714 (1994-12-01), None
patent: 08037107 (1996-02-01), None
patent: 9-125108 (1997-05-01), None
M. Takahashi, et al. “Magnestostriction Constants for FDe-Al-Si (SENDUST) Single Crystals with D03 Ordered Structure” IEEE Transactions on Magnetics . . . vol. 23, No. 5, Sep. 1987, pp. 3523-3535.
T. Tanaka, et al., “Temperature dependence of the effective permability of the resin-molded Senduct alloys” Journal of Applied Physics . . . vol. 57, No. 1 Apr. 15, 1985, pp. 4252-4254.
Matsutani Nobuya
Mido Yuji
Onishi Kazuaki
Coy Nicole
King Roy
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
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