Metal treatment – Stock – Ferrous
Reexamination Certificate
2001-05-31
2003-06-03
Yee, Deborah (Department: 1742)
Metal treatment
Stock
Ferrous
C420S094000
Reexamination Certificate
active
06572714
ABSTRACT:
TECHNICAL FIELD
The present invention provides material having improved dorming property and excellent creep property and used for a mask of a cathode-ray tube (a Braun tube). An Fe—Ni based alloy is used for such mask. The present invention also provides a tension mask using this material and a color Braun tube using the above-mentioned tension mask.
BACKGROUND TECHNIQUE
The types of mask in a Braun tube are roughly classified into a shadow-mask type and an aperture-grill type. In the shadow-mask type, a dot or slot pattern is formed by etching, and press-forming is then carried out (hereinafter referred to as “the shadow-mask type by pressing”). In the aperture-grill type, a reed screen is formed by etching, and tension-application is then carried out. In the shadow-mask type by pressing, Fe-36% Ni alloy (Invar alloy) is generally used to improve the dorming property which is attributable to the thermal expansion of the shadow-mask. Important properties additionally required for the Fe—Ni based alloy are etching property, press formability and the like. On the other hand, a structural feature of the aperture-grill type is that the cathode-ray passing apertures are in the form of a reed screen. The dorming attributable to the thermal expansion of the mask is, therefore, unlikely to occur. Mild steel, which is less expensive than the Invar alloy, is, therefore, used, despite the high coefficient of thermal expansion of the mild steel. Each type has a merit and a demerit and is used in the market.
Recently, a type referred to as FTM (Flat Tension Mask), in which the respective merit of each type is employed, is newly under consideration. This type of mask is provided by the following method. A sheet etched in the form of dots or slots is not subjected to pressing but is subjected to application of vertical tension as in the aperture-grill type, and is supported on a frame member.
The description in Japanese Unexamined Patent Publication No. 10-50210, which belongs to the above-mentioned type, is cited now. As shown in
FIGS. 1 and 2
, the shadow mask
9
is provided inside the glass panel
2
which has an almost flat face screen plane
3
which is, in turn, provided in the flat-face type color cathode-ray tube
1
. Sheet springs
8
are welded on the outer side of the frame member
7
made of metal and are engaged with a panel pin
5
which supports the frame member
7
. The shadow mask
9
is, therefore, held in a predetermined position inside the glass panel
2
.
An electron gun (not shown) is provided in the neck portion of a funnel
6
of the color cathode-ray tube
1
and emits the electron beam
10
. The electron beam
10
, which has passed through the apertures of the shadow mask
9
extended on the frame member
7
, impinge upon the predetermined spots formed on the inner surface of a glass panel
2
.
Referring to
FIG. 1
, the first band frame portion
14
b
surrounds the beam selecting region
12
having an almost rectangular shape and forming a shadow mask. The second band frame portion
14
a
is additionally provided outside the first band frame portion
14
b
. The second band frame portion
14
b
and the first band frame portion
14
a
are connected at plural portions by the joint portions
14
c
. In a plurality of the outer regions
13
a
,
13
b
,
13
c
surrounded by the first band-frame portion
14
b
, the second band frame portion
14
a
, and the joint portions
14
c
, a number of small apertures are provided as in the beam-selecting region
12
. These small apertures have a slot shape or a round shape and are arranged in a predetermined pitch and pattern so as to enable the electron beam to pass therethrough. Small apertures are formed in the outer regions
13
a
,
13
b
and
13
c
. The flat member
11
to be used for a shadow mask, to which the tensional force is imparted, is welded on the frame member. Uniform tensional force is imparted to the entire beam-selecting region
12
during welding.
The second band frame portion
14
a
of the flat member
11
as described above is grasped on its four sides by a jig (not shown) and pulled outwards. The tensional force is thus applied to the entire face of the flat member
11
. Under such a condition, the first band frame portion
14
b
is positioned relative to and is welded on the frame member (
7
in FIG.
2
). Portions outside the welded portions of the flat member
11
, i.e., the outer regions
13
a
,
13
b
,
13
c
, the joint portions
14
c
and the second band frame portions
14
a
, are, subsequently cut off along the outer periphery
7
of the frame member
7
. By such method, a shadow-mask assembly (color-selecting electrode)
17
consisting of the frame member
7
and the shadow mask
9
as shown in
FIG. 3
is obtained. The color-selecting electrode
17
is mounted in the glass panel
2
.
The FTM type described hereinabove with reference to the publication ibid allegedly attains more flattening of a shadow mask as well as high luminance and high resolution as compared with the shadow-mask type by pressing. In addition, the vibration property of the FTM type is better than that of the aperture-grill type. No damper wires, which bridge the Fe—Ni alloy strips in the form of a stripe pattern, are necessary. In addition, the vertically pulling load can be lessened. The FTM system contributes, therefore, to cost reduction.
Since the shape of the cathode-ray passing apertures in FTM is different from that of the aperture-grill type, the thermal expansion occurring in the former type leads to the dorming phenomenon. It has, therefore, been contemplated to use as a mask the Fe—Ni based alloys, Invar alloy among them having a low coefficient of thermal expansion. It was found that the Invar alloy, which had been conventionally employed in the shadow-mask type by pressing, brought about in the FTM type, serious drawbacks such that heat treatments such as blackening and baking result in a decrease of tensional load of the shadow mask in the assembling process of the shadow mask to a level that wrinkles were formed on the shadow mask. The alloys used in the conventional shadow-mask type are tempered to improve the press formability. The conventional Invar alloy, however, turned out to be inappropriate for the FTM type. The present inventors investigated the reason for this in detail in the respective production steps of a mask, and discovered that it is related to the creep property of the mask material.
Namely, in the FTM type, the etched mask material is subjected to blackening, and then is welded on the frame material. Tension is then applied to impart a constant load. Baking is then carried out. The Invar alloy is pulled by a frame, that is, the tension is applied to the Invar alloy. It was discovered that the Invar alloy plastically deformed under heat, that is, a creep phenomenon occurred. When the creep phenomenon occurs, the mask is elongated and hence relaxation of the load applied upon tensioning occurs. Such various problems as wrinkle-formation on the mask, impairment of the vibration performance are, therefore, incurred.
DISCLOSURE OF INVENTION
Namely, the present invention solves the above-described problems and provides: (1) Fe—Ni alloy having improved dorming property and creep property and used for a shadow mask, which has the cathode-ray passing apertures, in the form of dots or slots formed by etching, and to which tension is then applied without undergoing press-forming (hereinafter referred to as “the tension mask”), said Fe—Ni alloy containing from 30% by weight (the percentage below is “weight %” unless otherwise specified) to 50% of Ni, the balance consisting of iron and unavoidable impurities, and having not less than 30% and not more than 57% of the final working degree; (2) Fe—Ni alloy used for the tension mask according to item (1), mentioned above, characterized by limiting the impurity components to 0.01% or less of C, 0.20% or less of Si, 0.5% or less of Mn, 0.015% or less of P, and 0.010% or less of S; (3) Fe—Ni alloy used for the tension mask according to item (1) or (2), mentioned ab
Kawahara Tetsuo
Taki Kazuhiro
Yuki Norio
Birch & Stewart Kolasch & Birch, LLP
Nippon Mining & Metals Co., Ltd.
Yee Deborah
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