Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
2001-11-20
2004-09-14
Reichard, Dean A. (Department: 2831)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
C445S027000, C445S044000
Reexamination Certificate
active
06790115
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an arc tube, and a method of fabricating the arc tube for a discharge lamp in which a cylindrical shroud glass is welded on and integrated with an arc tube main body having a sealed glass bulb that serves as a discharge portion and is formed at a portion of the main body along the longitudinal direction thereof.
2. Description of the Related Art
Conventionally, as shown in
FIG. 12
, an arc tube is configured in a manner that a cylindrical shroud glass
8
for shielding ultraviolet rays is welded on and integrated with an arc tube main body
1
having a sealed glass bulb
2
which serves as a discharge portion and is formed at a portion of the main body along the longitudinal direction thereof, and the sealed glass bulb
2
is covered by the shroud glass
8
. Reference numerals
8
a
,
8
b
depict welding portions of the shroud glass
8
.
Electrodes a, a are provided in an opposite manner within the sealed glass bulb
2
sandwiched between the pinch seal portions
3
a
,
3
b
, and lead wires c, c coupled to molybdenum foils b, b are drawn from the pinch seal portions
3
a
,
3
b
at both ends of the glass bulb, respectively. Cylindrical portions
4
a
,
4
b
as non-pinch seal portions are formed at the front and rear portions of the pinch seal portions
3
a
,
3
b
so as to be extracted therefrom, respectively.
The shroud glass
8
cuts ultraviolet rays in a wavelength range that may be harmful to the human body among light emitted from the sealed glass bulb
2
.
A sealed space
7
, formed by the shroud glass
8
and surrounding the arc tube main body
1
, suppresses devitrification generated at the arc tube. That is, since the lamp room in which the arc tube is disposed communicates with the outside of the lamp room through an air hole performing breathing operation, and the atmosphere within the lamp room contains a lot of moisture, the moisture causes the devitrification generated at the arc tube. Therefore, the arc tube main body
1
is covered by the sealed space
7
so that the arc tube main body
1
does not contact the atmosphere containing the moisture, thereby suppressing the generation of the devitrification.
In order to fabricate the arc tube shown in
FIG. 12
, first, the rod-shaped arc tube main body
1
having cylindrical portions
4
a
,
4
b
formed at both ends thereof is fabricated. Thereafter, the arc tube main body
1
is inserted within a shroud glass tube
9
, then the front and rear end sides of the shroud glass tube
9
are heated to be molten and softened. After that, the softened portions are deformed by using forming rolls in a direction for reducing the diameter of the shroud glass tube (a direction shown by the arrows in
FIG. 12
) and pressed against the pinch seal portions
3
a
,
3
b
of the arc tube main body
1
at the inside of the glass tube and welded at the pinch seal portions. Then, the shroud glass tube
9
is cut at predetermined portions as necessary.
However, according to the conventional arc tube described above, there arises a problem that the devitrification phenomenon occurs despite the fact that the shroud glass
8
(the shroud glass tube
9
) is welded to the arc tube main body
1
to form the sealed space
7
.
The inventors of the present invention inspected the cause of the occurrence of the devitrification phenomenon and determined that the cause resides in the sectional shape of the arc tube main body (the pinch seal portions
3
a
,
3
b
) for welding the shroud glass
8
thereon. That is, although the cross section of the shroud glass tube
9
is cylindrical, the cross section of the pinch seal portion
3
a
(
3
b
) is rectangular as shown in FIG.
13
(
a
) since it is typically pinched by a pincher. Thus, in the welding process of the shroud glass, as shown by a phantom line in FIG.
13
(
a
), when the shroud glass tube
9
, which is molten and softened and pressed in the direction for reducing the diameter thereof along its radius direction, contacts closely to the surface (flat surface) of the pinch seal portion
3
a
, an opening S extending in the axial direction along the contact surface is formed (see FIG.
13
(
b
)). As a result, the atmosphere (moisture) within the lamp room enters into the sealed space
7
around the arc tube main body
1
from the opening S formed at the welded portion, thereby causing devitrification.
SUMMARY OF THE INVENTION
The inventors of the present invention have determined that an opening is not formed at the contact surface between the arc tube main body
1
and the shroud glass
8
when the welded portion of the shroud glass at the arc tube main body
1
is formed in a circular shape in its cross section.
Accordingly, an object of the present invention is to provide an arc tube for a discharge lamp and a method for fabricating the arc tube in which the welded portion of the shroud at an arc tube main body is formed in a circular shape in its cross section thereby preventing the forming of an opening at the contact surface between the arc tube main body and the shroud glass.
In order to attain the aforesaid object, an arc tube for a discharge lamp according to the present invention is arranged in a manner such that the arc tube includes an arc tube main body at which a sealed bulb, for example, a glass bulb, serving as a discharge portion sandwiched by front and rear pinch seal portions is formed at a portion of a tube along a longitudinal direction thereof, and a cylindrical shroud which is welded on and integrated with the arc tube main body so as to cover the sealed bulb to form an airtight sealed space around the arc tube main body,
the front and rear end portions of the shroud are welded on shroud weld portions with circular cross sections provided at front and rear end sides of the arc tube main body, respectively. In the embodiments described herein, the shroud may be formed of glass, and the arc tube body may be formed from a glass tube. of course, other materials known to those skilled in the art may be substituted without departing from the scope of the present invention.
A method of fabricating an arc tube for a discharge lamp according to the present invention includes an arc tube main body fabricating process for fabricating an arc tube main body at which a sealed glass bulb serving as a discharge portion sandwiched by front and rear pinch seal portions is formed at a portion of a glass tube along a longitudinal direction thereof, and a shroud glass welding process for welding and integrating a cylindrical shroud glass on and with the arc tube main body so as to cover the sealed glass bulb, wherein
in the arc tube main body fabricating process, shroud glass welded portions with circular cross sections are formed on front and rear end sides of the arc tube main body, respectively, and
in the shroud glass welding process, the arc tube main body is inserted into the shroud glass tube, predetermined positions of the shroud glass having been heated, molten and softened are modified in a direction of reducing diameters thereof, and the predetermined positions are welded on the shroud glass welded portions on the front and rear end sides of the arc tube main body, respectively.
At the time of welding the shroud glass to the arc tube main body, the predetermined positions of the shroud glass tube having been heated, molten and softened are modified inside so as to reduce their diameter in a radial direction. As shown in
FIG. 9
(a diagram showing a state where the shroud glass is shrink-sealed) in an embodiment of the invention, each of the outer peripheral surfaces of the shroud glass welded portion of the arc tube main body (a shrink seal portion
15
a
and a cylindrical portion
14
a
) and the inner peripheral surface of the molten diameter-reduced area of the shroud glass tube
20
may have a circular shape almost matching to each other. Thus, the inner peripheral surface of the molten diameter-reduced portion of the shroud glass tube
20
is molten and welded on the outer peripheral surface
Fukai Kunio
Nagata Akihiro
Estrada Angel R.
Koito Manufacturing Co. Ltd.
Reichard Dean A.
Sughrue & Mion, PLLC
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