Stock material or miscellaneous articles – All metal or with adjacent metals – Foil or filament smaller than 6 mils
Reexamination Certificate
2001-09-21
2002-07-09
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Foil or filament smaller than 6 mils
C428S611000, C428S577000, C428S900000, C428S928000, C428S638000, C148S100000, C148S121000, C148S304000, C148S306000, C148S307000, C148S403000, C336S229000, C336S232000, C336S234000, C029S605000, C029S609000
Reexamination Certificate
active
06416879
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an amorphous. alloy thin strip used for wound cores of power transformers, high frequency transformers and the like.
2. Description of the Related Art
The methods to continuously produce thin metal strips and wires by rapidly cooling an alloy in a molten state include methods such as the centrifugal rapid cooling method, the single roll method, the twin roll method and the like. These methods rapidly solidify molten metal to produce thin metal strips and wires by ejecting it through an orifice or the like onto the inner or outer surface of a metal drum rotating at high speed. Further, it is possible to produce amorphous alloys similar to liquid metal and obtain materials excellent in magnetic or mechanical properties by properly selecting the composition of the alloys.
The amorphous alloys are considered promising as industrial materials for widely varied uses owing to their excellent properties. Among the amorphous alloys, an Fe-based amorphous alloy thin strip, for example an Fe-Si-B amorphous alloy thin strip, is used for the cores of power transformers, high frequency transformers and the like by virtue of its low core loss, high saturation magnetic flux density, high magnetic permeability and other advantages.
However, although an Fe-Si-B amorphous alloy thin strip has a better core loss compared with a silicon steel sheet, its saturation magnetic flux density B
s
is inferior. This is because, when the content of Fe is increased for enhancing the saturation magnetic flux density, the ability of the alloy to form an amorphous state is deteriorated and stable production of the amorphous alloy thin strip becomes difficult. If it is possible to increase the saturation magnetic flux density while maintaining the amorphous state forming ability, downsizing of cores becomes viable and the degree of freedom in the design of cores for transformers and the like is increased, which will bring about great advantages. In response to the above needs, the following technologies have been proposed.
Japanese Unexamined Patent Publication No. H5-40703, for instance, discloses an amorphous alloy thin strip having a composition, in atomic %, of (Fe
a
Si
b
B
c
C
d
)
100−X
Sn
X
, where: a=0.80 to 0.86, b=0.01 to 0.12, c=0.06 to 0.16, d=0.001 to 0.04, a+b+c+d=1, and X=0.05 to 1.0. This technology makes it possible to improve the amorphous state forming ability even in a high Fe range by an addition of Sn, but the saturation magnetic flux density actually obtained is 1.73 T at most.
Japanese Unexamined Patent Publication No. H6-220592, as another example, discloses an amorphous alloy thin strip having a composition, in atomic %, of Fe
a
Co
b
Si
c
B
d
M
X
, where: 60≦a≦83, 3≦b≦20, 80≦a+b≦86, 1≦c≦10, 11≦d≦16, 0.1≦X≦1.0 when M is Sn, 0.1≦X≦2.0 when M is Cu or 0.01≦X≦0.07 when M is S, and a+b+c+d+X=100. A large saturation magnetic flux density is obtained by this technology thanks to the Co addition of Co. However, Co is a very expensive element and, although Fe-based amorphous alloy thin strips containing Co are used for some high-grade uses, the technology has the shortcoming of high material cost.
Besides these, Japanese unexamined Patent Publication No. H6-264197 discloses an amorphous alloy thin strip having a composition, in atomic %, of Fe
X
B
Y
Si
Z
Mn
a
, where: 80<X≦83, Y=6 to 11, Z=8 to 13, a=0.5 to 3. In this technology, the insulation film treatment property of the material is enhanced by an addition of Mn, but the alloy cannot attain the magnetic flux density of 1.7 T.
Thus, it has been impossible to produce a practically applicable and low-cost Fe-based amorphous alloy thin strip having a high saturation magnetic flux density by any conventional technology.
As described above, it has been difficult to stably obtain an amorphous alloy thin strip in an as cast or as annealed condition, because, when the content of Fe of an Fe-based amorphous alloy thin strip is increased aiming at enhancing the saturation magnetic flux density, the amorphous state forming ability of the alloy is deteriorated and crystallization proceeds locally.
When fabricating a wound core or a laminated core transformer using an amorphous alloy thin strip, it is a normal practice to form a core by laminating a multiplicity of thin strips and to anneal the core under a direct current magnetic field applied in the direction of its magnetic circuit. The annealing is done to lower strain in the strips and create magnetic anisotropy in the direction of the applied magnetic field. However, when the annealing temperature is too low, it becomes difficult to lower the strain and create the magnetic anisotropy.
When the annealing temperature is too high, in contrast, the thin strips crystallize and the excellent soft magnetic property intrinsic to the amorphous material disappears. For this reason, there is an optimum temperature in the annealing of a core.
The heavier the core and the larger its volume, the more a temperature unevenness is apt to be generated at different portions of the core during heating after it is charged into a heat treatment furnace. When a sufficient time is secured for the heating and cooling processes, the temperature unevenness is minimized, but this lowers productivity.
Various methods have been proposed to improve the annealing process such as: a method to minimize the temperature difference in a core during cooling by attaching heat insulating materials to the inner and outer surfaces of the core (Japanese Unexamined Patent Publication No. S63-45318); a method to immerse a core in a bath of an ultra-heat-resistant insulating oil kept at an annealing temperature (Japanese Unexamined Patent Publication No. S60-255934); a method to immerse a core in a molten tin bath kept at an appropriate temperature not exceeding the glass-transition temperature and then in a cooling liquid bath (Japanese Unexamined Patent Publication No. S62-294154); etc.
These methods improve the annealing process. However, these method did not improve the thin strips quality nor their magnetic properties even when there occurs a temperature unevenness among different portions of a core.
As a technology to improve the thin strip proper, on the other hand, Japanese Unexamined Patent Publication No. S57-185957 proposes a method to add 1 to 10 atomic % of P, as a substitute of expensive B, to an amorphous alloy thin strip containing, in atomic %, 1 to 5% of B and 4 to 14% of Si. P in this patent publication is meant as an element to enhance the amorphous state forming ability as do B, Si and C.
Further, Japanese Unexamined Patent Publication No. H8-193252 discloses, for the purpose of reducing the use of expensive B, an alloy having a composition, in atomic %, of 6 to.10% of B, 10 to 17% of Si, 0.02 to 5% of P and the balance consisting of Fe. P in the composition of this patent publication is meant to improve the surface roughness of the strip.
As another example, Japanese Unexamined Patent Publication No. H9-202951 discloses an alloy, having a composition, in atomic %, of 76 to 80% of Fe, 6 to 10% of B, 8 to 17% of Si, 0.02 to 2% of P and 0.2 to 1.0% of Mn, aimed at improving the magnetic properties and workability in a condition of a high Si content and a B content of 10 atomic % or less. The effect of P in the alloy composition of this patent publication is limited only to the improvement of the amorphous state forming ability and the addition of Mn is indispensable for suppressing the crystallization caused by the multi-element composition.
Japanese Unexamined Patent Publication No. H9-268354, aiming at improving the magnetic properties even in a low B content range of 10 atomic % or less through an appropriate control of the surface roughness of a strip, discloses an alloy having a composition, in atomic %, of 6 to 10% of B, 10 to 17% of Si as a preferable content range,
Sakamoto Hiroaki
Sato Yuichi
Dicus Tamra L.
Jones Deborah
Kenyon & Kenyon
Nippon Steel Corporation
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