Television – Video display – Cathode-ray tube
Reexamination Certificate
2000-04-14
2003-09-23
Kelley, Chris (Department: 2613)
Television
Video display
Cathode-ray tube
C348S825000, C348S836000
Reexamination Certificate
active
06624855
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a safety band for a CRT(Cathode Ray Tube), and in particular to a safety band for a CRT which is capable of enhancing a stability of use by providing a straight line shape safety band having a reinforced anti-explosive characteristic for each panel in a cathode ray tube in which a flat type panel and an effective screen expanded panel, which attract a big attention, are adapted.
2. Description of the Background Art
The CRT(Cathode Ray Tube) is directed to a display apparatus which is widely used for a television set, an oscilloscope, a radar system, etc.
In the above-described cathode ray tube, there are provided fluorescent pixels which are a light emitting device for converting a received electrical image data into a visual data, and a graphite which is a light absorbing material. A color image which is reproduced by impacting an electronic beam onto a fluorescent film formed of an aluminum film for enhancing a luminance, so that a human can view a color image.
As shown in
FIG. 1
, the conventional CRT includes a panel
1
installed on a front surface, and a conical funnel
2
melted at a rear end of the panel
1
for thereby forming a vacuum container of a CRT.
An electron gun
5
is installed at an end portion having a small diameter among the portions of the funnel
2
, namely, in the interior of a neck portion
3
. A deflection yoke is installed at an outer portion near the neck portion
3
for deflecting the emitted electron beam
4
onto the whole portions of a screen by generating a fin cushion shaped horizontal deflection magnetic field and a barrel shaped vertical deflection magnetic field.
In addition, a fluorescent film
6
is formed on an inner surface of the panel
1
, and a shadow mask
7
which operates for a function of a section-based electrode of the electron beam
4
at a certain distance from the fluorescent film
6
is stably engaged by a frame
8
installed therein.
In the above-described conventional cathode ray tube, the electron beam
4
outputted from the electron gun
5
is deflected onto a certain portion of the screen by the vertical and horizontal deflection magnetic fields and continuously passes through a plurality of through holes(not shown) formed at the shadow mask
7
and impacts the fluorescent film
6
for thereby implementing a certain image.
In addition, the interior of the conventional CRT has a vacuum state therein by the panel
1
and the funnel
2
. A certain stress occurs at the panel
1
by an external atmospheric pressure. As shown in
FIG. 2
, a compression pressure occurs at the front surface of the panel based on the structural characteristic of the CRT, and a tension stress occurs at a side wall of the panel
1
.
Therefore, in a state that the compression stress and the tension stress are formed based on the vacuum, when an external impact is applied to the CRT, a certain exploding phenomenon that the panel
1
or the funnel
2
is exploded may occur. The above-described exploding phenomenon cause a malfunction of the CRT and a user may be damaged.
Since the glass which is a material of the panel
1
is weak against a tension stress compared to the compression stress, the side wall of the panel
1
is weaker than the front portion of the same.
Here, the above-described exploding phenomenon is classified into four steps. The above-described steps will be explained with reference to FIG.
3
D.
First, in a first step which is an initial crack forming step, when a certain portion of the CRT is impacted by an external impact source
10
, as shown in
FIG. 3A
, a small crack occurs at the panel
1
.
Namely, when the strength of the impact portion exceeds a certain level against the external impact source
10
, a small crack occurs by the compression and tension stresses. The impact energy is spread over the CRT At this time, the crack grows at a structurally weal portion of the CRT or at a skirt which receives a concentrated stress.
In a second step which is a crack growing step, as shown in
FIG. 3B
, a crack “c” grows in the direction skirt of the panel
1
, and the crack grows in a radial or conical shape.
The thusly formed creaks are grown over the entire portions of the CRT. At this time, the crack is increased more at the skirt portion to which the tension stress is applied, so that the skirt portion is expanded.
In a third step, as shown in
FIG. 3C
, the panel or the funnel
2
are depressed. The crack “c” is extended from the outer surface to the inner surface of the panel
1
, so that the surface of the panel
1
or the funnel
2
is depressed.
As the skirt portion is expanded, the cracks are increased, and then a glass(the surface of the panel) is depressed due to a pressure difference between the inner and outer portions of the CRT.
In a fourth step, as shown in
FIG. 3D
, the particles are spread. When the CRT is inwardly depressed, a certain kinetic energy is generated, and the particles collide with each other, so that the particles are outwardly spread.
In a usual case, the surface portion is depressed, and then a certain impact is applied to the funnel
2
, and at the final stage, the particles are spread.
As described above, since the exploding phenomenon causes a malfunction of the CRT or a certain damage to a user, so that a safety band
11
is used for preventing the above-described exploding phenomenon.
FIG. 4
is a view illustrating a comparison of the stress before and after the safety band is engaged to the CRT In
FIG. 4
, the left side illustrates a stress distribution before the safety band is engaged, and the right side illustrates a stress distribution after the safety band is engaged.
Namely, it is possible to enhance a strength of the lateral side by engaging the safety band to the side wall of the panel
1
for thereby preventing an exploding phenomenon.
In detail, when a certain impact is applied to the surface of the CRT a transform stress which expands the side wall portions of the panel
1
, namely, a tension stress occurs. In this case, since the side wall portions of the panel
1
is compressed by the safety band
11
, so that the cracks “c” which pass through the lateral sides and surfaces are prevented for thereby decreasing the speed of the crack “c”.
As the safety band
11
is engaged, since a vacuum transformation stress affects the vacuum transformation stress, the direction of the main stress of the surface of the panel
1
is changed, and the growing direction of the crack “c” is changed for thereby preventing an explosion.
The safety band
11
surrounds a mold match line which is naturally formed when installing the panel
1
. As shown in
FIGS. 5A through 5C
, the safety band
11
may be formed in a straight line shape
11
a
, an overlapped shape
11
b
, a bent shape
11
c
, etc.
The advantages and disadvantages of each of the safety band
11
a
,
11
b
and
11
c
are compared in the following Table 1.
TABLE 1
Straight
line type
Overlapping type
Bent type
Anti-explosion
∘
∘
⊚
characteristic
Processing
⊚
&Dgr;
x
characteristic
Unit cost
⊚(1)
&Dgr;(1.5~1.8 times)
x(more than 2.2
times)
Co-usability of
⊚(simple)
&Dgr;(more
x(very
band facility
complicated)
complicated)
Welding method
Dot welding
Dot welding
Inverter welding
Use of welding
No
Yes
Yes
plate
Cost of facility
⊚(1)
&Dgr;(1.5~2 times)
x(more than 2.5
times)
Productivity per
⊚(4800 units)
&Dgr;(2400 units)
x(below 2000 units-
day(29-inch)
estimated)
where
⊚represents an excellent,
∘represents good,
&Dgr;represents a common, and
xrepresents bad.
As shown in Table 1, in the case of the bent type band
11
c
, the anti-explosion characteristic is excellent. However, the bent type band
11
c
has a bad processing characteristic, a unit cost, a facility co-usability, a welding method, a welding plate use, a facility investment cost, a productivity per day, etc. compared to the other types. In the case of the straight line type band
11
a
, the above-described characteristics except fo
Kelley Chris
LG Electronics Inc.
Wong Allen
LandOfFree
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