Funnel structure for cathode ray tube

Details Funnel structure for cathode ray tube Funnel structure for cathode ray tube

2002-11-07

2004-06-01

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Envelope

C220S00210A

Reexamination Certificate

active

06744193

ABSTRACT:

This nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2002-0026924 filed in Korea on May 15, 2002, which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode ray tube, and in particular to a funnel structure for a cathode ray tube which is capable of preventing breakage by stress concentration.
2. Description of the Prior Art
In general, a cathode ray tube materializes an optical screen by converting an electric signal into an electron beam and emitting the electron beam onto a fluorescent surface. Because the cathode ray tube has excellent display quality in contradiction to a price, it is widely used.
The cathode ray tube will be described in detail with reference to accompanying drawings.
FIG. 1
is a longitudinal-sectional view illustrating a general cathode ray tube.
In the general cathode ray tube, a front glass as a panel
1
is combined with a rear glass as a funnel
5
, and it is sealed in a high vacuum state.
And, the cathode ray tube includes a fluorescent surface
3
coated onto the internal surface of the panel
1
and performing a certain luminescent material function; an electron gun
13
emitting an electron beam
14
for making the fluorescent surface
3
fluoresce; a deflection yoke
10
installed at the outer circumference of the funnel
5
and deflecting the electron beam
14
so as to be scanned appropriate to an area of the fluorescent surface
3
; a shadow mask
6
installed with a distance from the fluorescent surface
3
; and a reinforcing band
15
installed at the side circumference of the panel
1
and dispersing stress occurred on the panel
1
and the funnel
5
.
The panel
1
has a curved inner surface and a substantially flat outer surface.
The funnel
5
performs a vacuous body function with a certain space formed by being combined with the panel
1
and the electron gun
13
and fixedly supports the deflection yoke
10
and the electron gun
13
.
The funnel
5
is largely divided into a body portion
51
at which the panel
1
is installed, a yoke portion
52
at which the deflection yoke
10
is installed and a neck portion
53
at which the electron gun
13
is installed.
Herein, a line of demarcation between the body portion
51
and the yoke portion
52
is called a TOR (top of round)
7
, a line of demarcation between the yoke portion
52
and the neck portion
53
is called a neck seal
9
, and an imaginary line as a base of the total length of the funnel
5
is called a reference line
8
.
In addition, a portion at which the panel
1
and the funnel
5
are combined with each other is called a sealing surface
4
, twice of an angle
18
of a cross point between a center axis
12
of the funnel
1
and the reference line
8
to an imaginary line connecting the cross point with an effective surface end
17
of the shadow mask
6
is called a deflection angle.
In the above-described cathode ray tube, because the cathode ray tube has a large width comparably, it is difficult to secure an installation space, in addition, it is heavy. In more detail, with a recent slim-lightweight trend in electronic equipment, in order to slim down the cathode ray tube, a method of reducing the total length of the panel
1
and a method of reducing the total length of the funnel
5
can be used.
Herein, when the total length of the panel
1
is reduced, by vacuuming after an exhaust process, high tensile stress is occurred on the sealing surface
4
at which the panel
1
and the funnel
5
are combined with each other. In addition, because a space for combining the reinforcing band
15
is reduced, stress dispersion efficiency of the reinforcing band
15
is lowered.
In the meantime, when the total length of the funnel
5
is reduced, relatively high stress occurs on the funnel
5
having a thickness smaller than that of the panel
1
. In particular, because high tensile stress occurs on the sealing surface
4
at which the panel
1
and the funnel
5
are combined with each other, breakage may easily occur in production process.
Therefore, tensile stress in vacuum has to be thoroughly considered, in general, a limit stress value of the funnel
5
is not greater than 12 MPa in designing. In more detail, when stress value of the funnel
5
is not less than 12 MPa, a crack may occur even in a small impact, the stress may proceed the crack, and accordingly implosion of the funnel
5
may occur.
In the meantime, in order to reduce the stress concentration, a thickness of the body portion
51
of the funnel
5
can be increased, in that case, a thickness difference between the yoke portion
52
and the body portion
51
is increased, in a temperature lowering process in fabrication of the funnel
5
, a crack may occur by a heat capacity difference due to the thickness difference between the body portion
51
and the yoke portion
52
.
In addition, when the thickness of the yoke portion
52
is increased inwardly, a BSN (beam shadow neck) in which the electron beam
14
is covered by interference of the internal surface of the yoke portion
52
occurs, a screen quality of the cathode ray tube is lowered.
Therefore, in lowering the stress concentration according to the sliming-down of the funnel
5
, the method of increasing the thickness of the funnel
5
is not preferable. Instead, it is most preferable to use a method of optimizing a shape of the funnel
5
.
Accordingly, in order to optimize a shape of the funnel
5
, a shape of the funnel
5
will be described with reference to
FIGS. 2A and 2B
.
FIGS. 2A and 2B
illustrate a stress occurred around the TOR (top of round)
7
at which the sealing surface, the body portion
51
and the yoke portion
52
of the yoke portion
52
meet, before anything else, principal factors in determining a funnel shape will be described.
In more detail, a length of an evaluation line
21
connecting the outer end of the sealing surface
4
at which the panel
1
meets the funnel
5
with the outer end of the TOR
7
at which the body portion
52
meet the yoke portion
52
is defined as b. A length from a point on the evaluation line
21
, which meets a vertical line
22
having a maximum length from the outer surface of the funnel
5
to the evaluation line
21
, to the outer end of the sealing surface
4
is defined as a. And, a maximum length of the vertical line
22
is defined as H.
As depicted in
FIG. 2A
, in the funnel shape such as
FIG. 2
(hereinafter, it is referred to as A type), because an a value and a H value was relatively small, stress around the yoke portion
52
of the funnel
5
was dispersed.
However, in the A type, in the vacuum state after combining the funnel
5
with the panel
1
, stress concentration not less than 12 MPa occurred on the sealing surface
4
.
In more detail, in the A type funnel, as depicted in
FIG. 2A
, when a maximum stress on a funnel minor axis was measured, a maximum stress around the yoke portion
52
was 6.3 MPa, however, a maximum stress on the sealing surface
4
was 15.3 MPa.
In the meantime, as depicted in
FIG. 2B
, in the funnel shape such as
FIG. 2B
(hereinafter, it is referred to as B type), because an a value and a H value were relatively big, stress around the sealing surface
4
of the funnel
5
was dispersed.
However, in the B type, stress concentration not less than 12 MPa occurred around the TOR
7
at which the body portion
51
met the yoke portion
52
.
In more detail, in the B type funnel shape, as depicted in
FIG. 2B
, when a maximum stress of the funnel minor axis was measured, a maximum stress on the central portion of the sealing surface was 11.5 MPa, however, a maximum stress around the yoke portion was 21.1 MPa.
The stress concentration occurred in the A type and B type funnels may cause breakage with crack in fabrication of the cathode ray tube, and accordingly an yield rate may be lowered.
Accordingly, it is required to research a measure which is capable of lowering stress concentration and securing impact resistance of the

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