Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2000-08-17
2002-10-01
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C148S327000, C148S325000, C148S326000
Reexamination Certificate
active
06459195
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an Fe—Cr—Ni alloy suitable as material for electron gun parts, such as electrodes for electron gun parts, which has improved punching properties, and in particular, has superior linearity at the boundary of a shearing surface and a fracture surface at a punched surface.
FIG. 1
shows a cross section of a color cathode ray tube of the shadow mask type already known in the art. A panel
1
is coated on the back side with a phosphor film
2
that generates the three primary colors red, green, and blue. An electron gun
4
that emits electron beams
3
is housed in the neck. The electron beams
3
are deflected in scanning by a deflection yoke
5
. The reference numeral
6
indicates a shadow mask and the reference numeral
7
indicates a magnetic shield.
FIGS. 2A and 2B
are perspective and cross sectional views, respectively, of a grid electrode
10
as an example of a punched part to be fitted in the electron gun
4
. The electrode
10
acts to control electrons emitted from a cathode in the electron gun, and acts to form electron beams and to modulate electron current. The electrode has small holes
10
a
,
10
b
, and
10
c
made by coining and punching so as to allow red, green, and blue color-generating beams, respectively, to pass through them.
In general, the electron gun electrodes for use in cathode ray tubes and the like are completed by press punching, with or without coining, a sheet of nonmagnetic stainless steel about 0.1 to 0.7 mm thick. The press punching among these processings, however, presents a burr formation problem. That is, as materials are punched with a pattern of through holes for passing beams therethrough, for example,
10
a
,
10
b
, and
10
c
each, burrs B are formed on the edges
10
e
of the holes where punches have forced slugs down and cut them off from the blank (see FIG.
2
). The burrs have adverse effects on the control of the electron beams, sometimes causing total failure of the electron guns. Therefore, it has been desired to remove burrs.
Although barrel polishing or chemical polishing has been applied after press punching for removing burrs, these optional processings increase the production cost. Furthermore, in barrel polishing, the burrs fall and project into the transmission hole for the beams, and it has therefore been desired that the burrs not remain after press punching.
Improvements in the punching properties of nonmagnetic stainless steel have hitherto been proposed. Japanese Patent Application, First Publication, No. 268352/97 proposes to form a work hardening layer in a surface portion. However, the mere hardening of the surface portion cannot continuously propagate cracks formed by shearing in the thickness direction of the sheet, and is not sufficient to control of burrs in press punching the transmission holes for electron beams.
Japanese Patent Application, First Publication, No. 176571/96 proposes to specify the S content within 0.0010 to 0.050% thereby dispersing S or S compounds along grain boundaries or within grains in the alloy stock. Japanese Patent Application, First Publication, No. 12690/99 proposes to combine specifying the S content and surface hardening. However, the mere addition of S, a free-cutting element, in a specified percentage cannot be deemed adequate for the control of burrs in the case of production processes. Addition of S for a free-cutting element increases the thickness fraction of fracture surface in a punched surface. However, the boundary of the shearing surface and the fracture surface waves as shown in
FIG. 3B
, and the parallel portion of the transmission hole for electron beams is shortened as shown in
FIG. 4
, and the punching properties are therefore not sufficient for electrodes required to have the most precise specifications for fine control of electric field. It should be noted that the surface hardening may be an adverse effect for drawing which is performed to a certain extent through working of electron gun electrodes, in addition to increase in the of steps and production cost.
BRIEF SUMMARY OF THE INVENTION
This invention has an object to solve the aforementioned problems of the prior art and to provide an Fe—Cr—Ni alloy for electron gun electrodes and an Fe—Cr—Ni alloy sheet for electron gun electrodes which are improved in punching properties, in particular, in the linearity at the boundary of the shearing surface and the fracture surface in the punched surface.
The inventors have intensively studied the influences of inclusions and the distribution thereof for the purpose of reducing the thickness fraction of the fracture surface in punched surfaces and improving the linearity at the boundary of a shearing surface and a fracture surface in a punched surface. As a result, the inventors have found that materials, which can satisfy the most precise specifications for electron beam transmission holes of electron gun electrodes without formation of burrs, can be produced by restricting the average distance in the thickness direction of the sheet between inclusions to the specific value or less according to the length of the inclusions and by restricting the inclusions within the specific compositions.
In particular, it has been demonstrated that although inclusions typified by MnS effectively contribute to initiation and propagation of cracks in shearing, cracks initiate too quickly and the width of the shearing surface is narrow compared to other portions if the length of the inclusion is too long, and as a result, this causes a wave at the boundary of a shearing surface and a fracture surface in a punched surface of transmission holes. Furthermore, the inventors have found that the linearity at the boundary of a shearing surface and a fracture surface in a punched surface is good even if inclusions with lengths of 100 &mgr;m or more exist by forming inclusions with lengths of 10 &mgr;m or more and less than 100 &mgr;m and with an average distance therebetween in the thickness direction of 100 &mgr;m or less, and by forming inclusions with lengths of less than 10 &mgr;m and with an average distance therebetween in the thickness direction of 20 &mgr;m or less when the thickness of the sheet is in the range of 0.1 to 0.7 mm.
Furthermore, the inventors have found that the linearity at the boundary of a shearing surface and a fracture surface in a punched surface can be further improved by specifying the chemical composition of inclusions with lengths of less than 10 &mgr;m in 40≦SiO
2
≦100, 0≦Al
2
O
3
≦40, and 0≦Mn≦30 by atomic %.
The average distance between inclusions in the thickness direction is measured by the method described below. First, a sheet rolled to a thickness of 0.1 to 0.7 mm is cut along the rolling direction, and the cross section along the rolling direction is specularly polished and then electropolished in phosphoric acid so as to facilitate distinction of inclusions. When an average distance in the thickness direction between inclusions with lengths of 10 &mgr;m or more and less than 100 &mgr;m is measured, a region defined by the thickness of the sheet and length of 100 &mgr;m in the rolling direction is set, and the number of inclusions, which have lengths of 10 &mgr;m or more and less than 100 &mgr;m and at least a portion thereof overlaps with the region, is counted. The average distance is obtained by dividing the number of inclusions with thickness of the sheet. In the case of inclusions with length of less than 10 &mgr;m, a region defined by the thickness of the sheet and length of less than 10 &mgr;m in the rolling direction is set, and the number of inclusions, which have lengths of less than 10 &mgr;m and at least a portion thereof overlaps with the region, is counted. The average distance is obtained by dividing the number of the inclusions with the thickness of the sheet. The average distances are measured at ten random portions, and the average thereof is obtained as an average distance of inclusions with lengths of 10 &mgr;m or more and less than 100 &mgr;m or an averag
Arent Fox Kintner & Plotkin & Kahn, PLLC
Berck Ken A.
Nippon Mining & Metals Co., Ltd.
Patel Vip
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