Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2001-06-05
2003-06-24
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C445S047000, C445S036000, C445S037000, C313S403000
Reexamination Certificate
active
06583545
ABSTRACT:
INDUSTRIAL FIELD
The present invention relates to a material for an aperture grille for use in a color picture tube, a production method therefor, an aperture grille and a color picture tube installed incorporating the aperture grille.
The present invention particularly relates to a material for an aperture grille material for use in a color picture tube having excellent tensile strength, excellent high temperature creep strength and excellent magnetic characteristic, a method for producing the color picture tube, an aperture grille made thereof, and a color picture tube incorporating this aperture grille.
BACKGROUND OF THE INVENTION
It has been required for material of an aperture grille used for a color picture tube to have tensile strength of at least 60 kgf/mm
2
, since the aperture grille is welded on a frame under loading large amount of tensile strength during a step of producing the aperture grille. Regarding material of an aperture grille presently used for a color picture image, a low carbon steel sheet which is hard-treated has been employed.
In a conventional art, an aperture grille is thermally treated so as to become a black aperture grille after the aperture welded on a frame. In such a case, the above thermal treatment is operated at 455° C. less than a recrystallization temperature of steel sheet for a short time, i.e. 15 minutes so as to maintain a condition in which each a tape constituting a black aperture grille is not loosed and its tensile force keeps on being loaded.
However, in the case that a thermal treatment for blackening is operated under the above condition, it can not be avoid for occurring a recovery phenomenon of the steel. The tape is extended by recovering the steel. The phenomenon causes a reason why the tape is twisted or broken. Regarding material of an aperture grille for a color picture tube, it is required material having tensile strength equal or more than 60 kgf/mm
2
and creep strength equal or less than 0.4% while a thermal treatment for blackening is operated at 455° C. for 15 minutes.
A color picture tube comprises an electron gun and a luminescent screen for converting electron beams to an picture image. In order to avoid earth magnetism for deflecting the electron beam, it is necessary for an inside portion of the color picture tube to have a characteristic as magnetic shield material. Therefore, it is required material having large magnetic flux density (Br), small coercive force (Hc) and a high ratio (Br/Hc) of the magnetic flux density with respect to the coercive force.
However, regarding a low carbon steel sheet for which a strength process and a thermal treatment for blackening are processed so as to obtain a high yield strength described above, the magnetic flux density is relatively small, that is, not more than 8 KG and the coercive force is relatively large, that is, about 5 oersted (Oe). Accordingly the ratio of Br/Hc is relatively small, that is, about 1.6. Such an amount is insufficient as magnetic shield material.
In a conventional art, regarding a method for improving a tensile yield strength of a low carbon steel sheet, there is a solid solution strengthen method affected by carbon and nitrogen. However, if amounts of carbon and nitrogen in the steel is increased, carbide and nitride are increased. Thereby, it is apt to be prevented magnetic domain walls from moving so that magnetic characteristics are deteriorated. Although there is a method for precipitating carbide or others in a steel sheet as a method for improving a creep strength, a diameter of almost grains of the precipitates is large and belonged in a size of micron order and a movement of the magnetic domain walls is prevented so that the magnetic characteristic is largely deteriorated. Such a method is not applied to a present method for producing material of an aperture grille used for a color picture tube.
To resolve the technical drawbacks described above, the inventors have already recommended precipitation-strength type low alloy steel with copper and phosphor. The steel with additive of copper and phosphor is material having high strength and high magnetic characteristic. The technical concepts thereof will be disclosed hereinafter.
In the case of adding copper in an extremely low carbon steel, a micro copper phase (&egr; phase) having a size of nano meter (nm) is precipitated by an precipitation treatment. In the case of adding phosphor, solid solution strength thereof is affected by adding phosphor is utilized so that tensile strength of the material can be equal or more than 60 kg/mm
2
and the material can have excellent magnetic characteristics having the ratio Br(KG)/Hc(Oe) equal or more than 2.5 when the steel is heated by the precipitation process.
A steel sheet with additive of copper and/or phosphor is high quality material of an aperture grille for a color picture tube as described above. However, it is recognized that hot roll cracking phenomenon is occurred during a hot rolling step in a method for producing the material. As the result, the yield for producing a steel sheet is rarely reduced.
A purpose of the present invention is to provide material of an aperture grille used for a color picture tube having excellent tensile strength and excellent high temperature creep characteristic, wherein various characteristics of a steel sheet with additive of copper and phosphor can be maintained and a high yield level can be maintained.
DISCLOSURE OF THE INVENTION
An invention recited in claim 1 relates to material of an aperture grille used for a color picture tube comprising copper of 0.05 to 2.5 wt %, wherein the material is characterized of further including nickel of 0.01 to 1.75 wt %.
An invention recited in claim 2 relates to material of an aperture grille used for a color picture tube comprising copper of 0.05 to 2.5 wt % and phosphor of 0.001 to 0.4 wt %, wherein the material is characterized of further including nickel of 0.01 to 1.75 wt %.
An invention recited in claim 3 relates to a method for producing material of an aperture grille used for a color picture tube, wherein said method is characterized of comprising a step of a precipitation treatment in a temperature range of 300 to 700° C. after cold rolling a low carbon alloy hot rolled steel including copper of 0.05 to 2.5 wt % and nickel of 0.01 to 1.75 wt %.
An invention recited in claim 4 relates to a method for producing material of an aperture grille used for a color picture tube, wherein said method is characterized of comprising a step of a precipitation treatment in a temperature range of 300 to 700° C. after cold rolling a low carbon alloy hot rolled steel including copper of 0.05 to 2.5 wt %, nickel of 0.01 to 1.75 wt % and phosphor of 0.001 to 0.4 wt %.
An invention recited in claim 5 relates to a method for producing material of an aperture grille used for a color picture tube, wherein said method is characterized of comprising a step of cold rolling low carbon alloy hot rolled steel including copper of 0.05 to 2.5 wt % and nickel of 0.01 to 1.75 wt %, a step of secondary cold rolling after intermediate annealing in a temperature range of 500° C. to 800° C., and a step of a precipitation treatment in a temperature range of 300 to 700° C.
An invention recited in claim 6 relates to a method for producing material of an aperture grille used for a color picture tube, wherein said method is characterized of comprising a step of cold rolling low carbon alloy hot rolled steel including copper of 0.05 to 2.5 wt %, nickel of 0.01 to 1.75 wt % and phosphor of 0.001 to 0.4 wt %, a step of secondary cold rolling after intermediate annealing in a temperature range of 500° C. to 800° C., and a step of an elution treatment in a temperature range of 300 to 700° C.
An invention recited in claim 7 relates to an aperture grille used for a color picture tube made of a low carbon alloy steel sheet including copper of 0.05 to 2.5 wt % and nickel of 0.01 to 1.75 wt %.
An invention recited in claim 8 relates to an aperture grille used for a color picture tube made of a low carbon alloy
Ide Tsuneyuki
Okayama Hironao
Sigemasa Susumu
Tahara Yasuo
Browdy and Neimark , P.L.L.C.
Toyo Kohan., Ltd.
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