Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
1999-11-08
2001-08-28
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
Reexamination Certificate
active
06280275
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for welding a shadow mask, and more particularly, to a method for welding a shadow mask in a flat CRT(Cathode Ray Tube).
2. Description of the Related Art
Recently, CRTs used as TV receivers or image displays have been provided with a flat surface which can eliminate image distortion, minimize reflection of external light, and maximize a visual area. As shown in
FIG. 1
, a conventional flat CRT is provided with a panel
1
having an inside surface coated with a fluorescent material
1
a
, an inner shield (not shown) fixed to the inside surface of the panel
1
to provide shielding from external magnetic fields, a funnel
5
sealed to an inside surface periphery of the panel
1
by frit glass, and a neck portion
5
a
positioned at a rear of the funnel. An electron gun
6
is provided in the neck portion
6
for emitting three colored electron beams of R, G, B. A deflection yoke (or deflection coil)
7
is provided on an outer circumference of the neck portion
5
a
for deflecting the electron beams in horizontal or vertical direction. The panel
1
is provided with safety glass
2
fixed to a front surface thereof by resin to prevent bursting of the cathode ray tube, and a rail
3
is fixed to an inside surface of the panel
1
. A shadow mask
4
is attached to the rail
3
for selecting a color from the electron beam. The rail
3
, a rectangular frame, is used to attach the shadow mask
4
to the inside surface of the panel
1
with an appropriate distance between the shadow mask
4
and the panel
1
. The rail
3
has a side facing the panel
1
with a groove
3
a
formed therein containing frit glass, and a contact surface
3
b
on the other side thereof contacting the shadow mask
4
. When molten frit glass fills the groove
3
a
, and the rail
3
is attached to the inside surface of the panel
1
, the rail
3
is fixed to the inside surface of the panel
1
when the molten frit glass solidifies. The shadow mask
4
is then placed on the contact surface
3
b
while the shadow mask
4
is subjected to a tensile stress and is bonded to the rail
3
by welding. Since the shadow mask
4
for use in a conventional flat CRT is formed of a thin plate (around 0.1 mm thick), the use of resistance welding is not desirable because the resistance welding causes a large mechanical deformation in the shadow mask and forms a large heat-affected zone. Therefore, laser beam welding is used to weld the shadow mask in a flat CRT, which provides fast and high quality welding, with a relatively small deformation and heat-affected zone of the object being welded.
However, despite of the use of laser welding, the shadow mask
4
may still be damaged and deformed during the welding, as follows.
In laser beam line welding, the thin plate may be pushed forward in the direction that the welding is progressing, causing the plate to be welded at a position deviated from a desired position. In order to avoid such a defect when a spot welding is used, there may be plastic deformation caused by thermal stress in the vicinity of welding spot if the welding is carried out without accurately calculating a size of the welding spot and a distance between the welding spot. The plastic deformation causes of distortion because of a difference of thermal expansion coefficients when heating occurring during fabrication of the flat CRT dissipates.
Even though laser welding is employed, welding the shadow mask
4
and the rail
3
by the aforementioned one run welding causes many defects, and results in low productivity since a high level of skill is required to prevent the defects.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method for welding a shadow mask that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method for welding a shadow mask in a flat CRT, which can prevent deformation or damage of the shadow mask, to provide an accurate welding.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the method for welding a shadow mask in a flat cathode ray tube includes: (1) applying an initial tensile force to a shadow mask for preventing deformation, and (2) fastening the shadow mask to a rail by welding, wherein fastening the shadow mask to a rail includes performing a primary spot welding having relatively long primary welding spot intervals between welding spots, and performing a secondary spot welding having secondary welding spot intervals between welding spots shorter than the primary welding spot intervals.
The primary and secondary spot weldings are performed using laser welding.
Preferably, the primary welding spot interval in the primary spot welding is set to be a min. {fraction (1/200)} to max. {fraction (1/100)} of the width/length of the rail/shadow mask, and more preferably, the primary welding spot interval in the primary spot welding is {fraction (1/150)} to {fraction (1/125)} of the width/length of the rail/shadow mask.
The secondary welding spot interval in the secondary spot welding is set to be a min. {fraction (1/600)} to max. {fraction (1/300)} of a width/length of the rail/shadow mask.
The welding spot diameter according to the present invention is set, (also taking a thickness of the shadow mask into consideration) to provide an adequate welding strength to the welding spot.
Specifically, the diameter of the welding spot in the primary and secondary spot welding is set to be approx. 10~30 times of a thickness of the shadow mask.
Accordingly, the aforementioned method for welding a shadow mask of the present invention can provide adequate welding strength and accuracy without causing deformation, thereby reducing defective welding and improving productivity.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 4828523 (1989-05-01), Fendley et al.
patent: 4834686 (1989-05-01), Kautz et al.
LG Electronics Inc.
Ramsey Kenneth J.
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