Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2001-03-26
2003-10-21
LaVilla, Michael (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S684000, C428S332000, C428S680000, C428S692100, C428S693100, C029S017200, C029S017300, C072S365200, C072S379200, C148S100000, C420S008000
Reexamination Certificate
active
06635361
ABSTRACT:
This application is the United States national phase application of International Application PCT/JP00/05374 (not published in English) filed Aug. 10, 2000.
TECHNICAL FIELD
The present invention relates to a steel sheet used for a magnetic shielding component which is set inside or outside a color cathode ray tube, encircling the electron path along the electron beam, i.e. a magnetic shielding steel sheet for a color cathode ray tube.
BACKGROUND ART
A basic arrangement of color cathode ray tubes comprises an electron gun for emitting electron beam and a phosphor screen for emitting light to develop an image when scanned by the electron beam. The electron beam may however be undesirably deflected by the effect of geomagnetism, hence causing color deviation in the image. For preventing such deflection, internal magnetic shields (also termed inner shields or inner magnetic shields) are installed. Additionally, external magnetic shields (also termed outer shields or outer magnetic shields) are provided outside the color cathode ray tube, in some cases. For simplicity, those inner magnetic shields and outer magnetic shields are referred to as magnetic shields hereinafter.
Recently, as commercial TV sets have been enlarged or widened in the screen size, the flight path length and scanning length of the electron beam increase significantly and thus TV sets have become more susceptible to the effect of geomagnetism. In other words, a deviation of the landing point on the phosphor screen of the electron beam from the designated point, which is caused by the effect of geomagnetism (thus termed a geomagnetic drift), maybe increased more than ever before. Since higher definition in the still image is requested in a cathode ray tube used for a personal computer display, it is most crucial to reduce such color deviation caused due to the geomagnetic drift.
In this circumstance, steel sheets used for the magnetic shields are often evaluated on the basis of known parameters including the magnetic permeability in a low magnetic filed equivalent substantially to the geomagnetism, the coercive force, and the remanent flux density.
One of technologies for improving the characteristics of steel sheet for magnetic shields is disclosed in Japanese Patent Disclosure (KOKAI) No. 3-61330 where the ferrite grain size number in a specific composition steel is defined to not larger than 3.0 to improve the magnetic properties. It is also described in the same disclosure that the required magnetic permeability of not less than 750 G/Oe and the required coercive force of not more than 1.25 Oe are mentioned as examples of preferable magnetic properties for a cold-rolled steel sheet for magnetic shields.
Alternatively, disclosed in Japanese Patent Disclosure (KOKAI) No. 5-41177 is a technique for producing an inner magnetic shield using of a magnetic material of which the remanent flux density is not less than 8 kG.
In Japanese Patent Disclosure (KOKAI) No. 10-168551, an improved magnetic shielding material which is used a specific composition steel of which the grain size of the product is kept small and having the coercive force of not less than 3 Oe and remanent flux density of not less than 9 kG, and a manufacturing method thereof are disclosed.
As those conventional technologies are unsatisfactory in the magnetic shielding effect, they may hardly overcome degradation in the image quality caused by color deviation pertinent to advanced commercial TV sets with the enlarged and/or widened screens. It is highly desired to provide improved steel sheets for magnetic shielding which have a higher level of the magnetic shielding effect.
In an article, Transaction (in Japanese) of the Institute of Electronics, Information, and Communication Engineers, vol. J79-C-II No. 6, p. 311-319, June 1996, the relationship between anhysteretic magnetic permeability and magnetic shielding effect is described, and it is pointed out that the higher the anhysteretic magnetic permeability is, the higher the magnetic shielding effect becomes.
The article, however, only describes the relationship between anhysteretic magnetic permeability and magnetic shielding effect, and it fails to disclose which type of steel sheet has a higher level of the anhysteretic magnetic permeability.
DISCLOSURE OF THE INVENTION
The present invention has been carried out in view of the above circumstances. Its object is to provide a steel sheet for magnetic shields which has a higher level of the anhysteretic magnetic permeability and is capable of decreasing the color deviation caused by geomagnetic drift to yield an image of higher definition, and a manufacturing method thereof.
According to an aspect of the present invention, there is provided a steel sheet for magnetic fielding containing 0.15% by weight or less of C and having a thickness of 0.05-0.5 mm and an anhysteresis magnetic permeability of 7500 or higher.
According to another aspect of the present invention, there is provided a steel sheet for magnetic shielding consisting essentially of 0.005-0.025% by weight of C, less than 0.3% by weight of Si, 1.5% by weight or less of Mn, 0.05% by weight or less of P, 0.04% by weight or less of S, 0.1% by weight or less of Sol.Al, 0.01% by weight or less of N, 0.0003-0.01% by weight of B, and the balance of Fe, wherein the thickness ranges 0.05-0.5 mm, a coercive force is less than 3.0 Oe, and an anhysteresis magnetic permeability is 8500 or higher.
According to further aspect of the present invention, there is provided a method of producing a magnetic shielding steel sheet comprising the steps of: hot-rolling a steel slab containing 0.15% by weight or less of C and then cold-rolling the hot-rolled steel sheet; annealing the cold-rolled steel sheet; and skin-pass rolling the steel sheet at a reduction of 1.5% or less, if necessary.
According to still further aspect of the present invention, there is provided a method of producing a magnetic shielding steel sheet comprising the steps of: hot-rolling a steel slab, which contains 0.005-0.025% by weight of C, less than 0.3% by weight of Si, 1.5% by weight or less of Mn, 0.05% by weight or less of P, 0.04% by weight or less of S, 0.1% by weight or less of Sol.Al, 0.01% by weight or less of N, 0.0003-0.01% by weight of B, directly or after a re-heating process, at a finishing temperature higher than the transformation temperature of Ar3; coiling the hot-rolled steel sheet at a temperature of 700° C. or lower; pickling the coiled hot-rolled steel sheet; cold-rolling the pickled hot-rolled steel at a reduction of 70-94%; and continuously annealing the cold-rolled steel sheet at a temperature in the range of 600-780° C.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will now be described in more detail.
In general, in a color cathode ray tube, demagnetization is carried out for adjusting the effect of external magnetic field to a constant condition under the operating circumstance. Such demagnetization is generally implemented by a method of applying an alternating current to the demagnetizing coils mounted outside the cathode ray tube when the TV set is switched on or in other opportunities. The method permits the demagnetization process in the geomagnetism, whereby the magnetic shields in the cathode ray tube can remain more highly magnetized than those perfectly demagnetized followed by magnetization by the geomagnetism. This allows the magnetic shields to have a higher level of the shielding effect than the condition of firstly perfectly demagnetized and successively magnetized by the geomagnetism. Accordingly, as described in the article, Transaction (in Japanese) of the Institute of Electronics, Information, and Communication Engineers, vol. J79-C-II No. 6, p. 311-319, June 1996, the steel sheet suitable for magnetic shielding is the steel sheet having high “anhysteretic magnetic permeability” which is determined by dividing remanent flux density after the demagnetization process in the geomagnetism, by geomagnetic field. In view of the above aspects, the inventors have examined the anhyst
Hiratani Tatsuhiko
Kodama Satoshi
Matsuoka Hideki
Mitsuzuka Ken-ichi
Sugihara Reiko
Frishauf Holtz Goodman & Chick P.C.
LaVilla Michael
NKK Corporation
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