Electron gun and method for manufacturing the same

The present invention relates to an electron gun retaining a cathode and a plurality of electrodes with a pair of bead glasses and a method for manufacturing the same, wherein each of the bead glasses are provided with a convex portion at a position where a bead support for an electrode is buried on a side of the electrodes, each of bead bases of a beading apparatus on which the bead glasses are disposed is formed with a concave portion at a position corresponding to the convex portion of the bead glass, the bead glasses disposed on the bead bases are heated and softened, the bead supports for the cathode and the plurality of electrodes are buried and secured in the bead glasses, and the bead glasses each include convex portions on a side opposite to the electrodes. In accordance with the present invention, recesses and projections over the surfaces of the bead glasses on the electrode sides are reduced in size, thereby further increasing a supporting strength of the electrodes, preventing withstand voltage deterioration of the electron gun, and maximizing a yield in a manufacturing process of the electron gun.

BACKGROUND AND RELATIVE ART 
The present invention relates to an electron gun and a method for 
manufacturing the same, and more particularly, to a beading method for 
burying a plurality of electrodes in bead glasses and an electron gun 
manufactured by this method. 
In general, an electron gun is composed of a plurality of electrodes. An 
inline-type electron gun has such a particular construction that a 
plurality of electrodes are buried and securely held in bead glasses in 
order to precisely manufacture an assembly of the red, green and blue 
electrodes in order. 
Referring to FIG. 4, a beading apparatus for burying the plurality of 
electrodes in the bead glasses is so arranged that bead base 3 each 
including a stopper 2 for supporting the bead glass 1 are respectively 
fixed on the top ends of two arms 4, which two arms 4 are in turn arranged 
to be brought into an opening/closing movement by an arm driving means not 
shown while each of them are being swirled or moved in parallel relation 
with each other, or while they swirls and moves in parallel 
simultaneously. The beading apparatus also includes a heating means (not 
shown) for heating and softening the bead glasses 1 which are supported by 
the bead bases 3. 
The bead glasses 1 are mounted on the bead bases 3, prior to being heated 
and softened at a temperature in the vicinity of a melting point of 
approximately 1200.degree. C. The bead glasses 1 are then pressed against 
the ends of the plurality of electrodes 6 assembled on a beading jig 5 so 
as to bury these ends of the electrodes thereinto. Succeedingly, the bead 
glasses are brought back into a condition that they are at a normal 
temperature, thereby completing fixture of the plurality of electrodes in 
the bead glasses. 
The same kind of apparatus as the above is disclosed in Japanese Utility 
Model Laid-open Publication No. 52-42052. 
In a certain conventional bead glass 1, there is provided a rectangular 
parallelepiped glass 10 as shown in FIG. 10A or a glass 11 of FIG. 11A 
having a convex portion 11a on the side which is not in contact with a 
G.sub.4 -electrode as shown in FIG. 11A. In a case of the glass 10 of FIG. 
10A, a bead base 3 having a flat surface where the glass is mounted, is 
employed as shown in FIG. 10B. On the contrary, in a case of the glass 11 
of FIG. 11A, a bead base 3 provided with a concave portion 3a for 
receiving the convex portion 11a of the glass 11 is employed as shown in 
FIG. 11B. When the glasses 10 of FIG. 10A are applied to a beading process 
as described in FIG. 4 by means of the bead bases 3 shown in FIG. 10B, an 
electron gun illustrated in FIG. 10C can be obtained. Similarly, the 
glasses 11 of FIG. 11A are applied to the beading process by means of the 
bead bases 3 shown in FIG. 11B in order to manufacture an electron gun 
illustrated in FIG. 11C. 
Additionally, in FIGS. 10C and 11C, a reference numeral 20 designates a 
cathode body structure, and reference numerals 21 to 26 designate G.sub.1 
-electrode, G.sub.2 -electrode, G.sub.3 -electrode, G.sub.4 -electrode, 
G.sub.5 -electrode and G.sub.6 -electrode, respectively. 
SUMMARY OF THE INVENTION 
As be clearly understood from FIGS. 10C and 11C, the electron gun 
manufactured by the above-mentioned conventional art has such a 
construction that when a bead support portion 24a for the thick plate-like 
G.sub.4 -electrode is buried in the inner surfaces of the melted bead 
glasses, the surfaces are largely concaved, owing to surface tensions of 
the bead glasses 10, 11 softened at a high temperature and characteristics 
of surfaces of the metallic cathode body structure 20 and the electrodes 
21 to 26, and that the portions of the bead glasses extruded by burying 
the bead support portion 24a in the bead glasses are formed into large 
projections 30, 31 on the surfaces of the electrode sides. The thicknesses 
of bead support portions for the cathode structure body 20, the G.sub.1, 
G.sub.2, G.sub.3 -electrodes 21, 22, 23, and the G.sub.5 and G.sub.6 
-electrodes 25 and 26 are thin, and the extents of recesses and 
projections of the bead glasses caused by burying the bead supports in the 
bead glasses remain small in size, thereby resulting in no problem. 
As mentioned above, if the recesses and the projections 30, 31 are largely 
extended, a strength for supporting the electrodes is often weakened. The 
electrodes cannot be thus rigidly retained with certain space-intervals 
therebetween. This causes a deterioration in a focus performance of the 
electron gun. In the knocking process during manufacture of color 
cathode-ray tubes, because the anode electrodes are subjected to a high 
voltage of 60.about.70 kV, if the recesses and the projections 30, 31 are 
largely formed at an extent as described above, unfavorable sparks are 
frequently generated close to the anode electrodes via the projections 
from the low-voltage electrodes, and a failure of the electron gun in the 
withstand voltage deterioration is thus inevitable. This failure decreases 
a yield in the manufacturing process of the electron gun. 
An object of the present invention is to provide an electron gun and a 
method for manufacturing the same, in which the recesses and the 
projections on the surfaces of the bead glasses on the electrode sides are 
reduced in size. 
The above object is achieved by providing each bead glass with a convex 
portion on a portion where a bead support for at least one electrode is 
buried on the electrode side, providing each bead base of a beading 
apparatus where the bead glass is disposed, with a concave portion on a 
portion corresponding to the convex portion of the bead glass, burying and 
securing bead supports for a cathode and a plurality of electrodes in the 
bead glasses after heating and softening the bead glasses disposed on the 
bead bases, and forming a convex portion on a side of each bead glass 
opposite to the electrode. 
When the bead supports for the electrodes are buried in the heated and 
softened bead glasses, portions of the glasses extruded by the bead 
support which corresponds to the concave portions of the bead bases are 
received in the concave portions of the bead bases, so that the extents of 
the projections of the glasses can be minimized. Further, since the convex 
portion defined on the electrode side of each bead glass serves to fill up 
the recess on the interface where the bead support is buried, the recess 
is also reduced in size. 
The above and other objects, features and advantages of the present 
invention will become more apparent from the following description when 
taking in conjunction with the accompanying drawings in which preferred 
embodiments of the present invention are shown by way of illustrative 
examples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of the present invention will be described hereinafter 
with reference to FIGS. 1 to 3. Reference numerals used in the first 
embodiment will be applied to the same members in FIGS. 10 to 11 as those 
in FIGS. 1 to 3, and accordingly, the parts explained in FIGS. 1 to 3 are 
unnecessary to be explained again. 
As shown in FIG. 1, a bead glass 12 before being subjected to a beading 
process is provided with a convex portion 12a on an inner surface thereof 
corresponding to a G.sub.4 -electrode 24, which will be shown in FIG. 3. 
As shown in FIG. 2, a bead base 3 is formed with a concave portion 3a on a 
portion thereof which corresponds to the convex portion 12a of the bead 
glass. 
A beading process is carried out by a method similar to the method having 
been described with reference to FIG. 4, while employing the bead glasses 
12 and the bead bases 3 which are arranged in the above-mentioned manner. 
As a result, an electron gun having a structure, as shown in FIG. 3, can 
be obtained. Specifically speaking, when bead supports for a cathode 20 
and electrodes 21 to 26 are buried in the bead glasses 12 having been 
heated and softened, portions of the glasses extruded by a bead support 
24a are inevitably extruded into the concave portions 3a of the bead bases 
3. Convex portions 12b are thus formed on the outsides of the bead glasses 
12. In this case, the configurations having a recess and projections 32, 
33 on the buried interface of each bead glass 12 in the vicinity of the 
bead support 24a are observed, but the portion of the glass extruded by 
the bead support 24a flows into the concave portion 3a of the 
corresponding bead base 3, as described above, so that an extent of the 
projection is minimized. At the same time, since the convex portion 12a 
formed on the bead glass on the electrode side serves to fill up the 
recess on the buried interface of the bead glass 12, the size of the 
recess is minimized. 
In the first embodiment described above, although the convex portions 12a 
of the bead glasses 12 and the concave portions 3a of the bead bases 3 are 
formed on the portions corresponding to the bead support 24a of the 
G.sub.4 -electrode 24, there of course may be provided with convex and 
concave portions on remaining portions in alignment with the bead supports 
of the other electrodes. 
Alternatively, FIGS. 5 to 8 show a second embodiment. In the illustrated 
second embodiment, each bead glass can be provided with two convex 
portions in contrast to the first embodiment. Referring to FIG. 5, a bead 
glass 12 prior to a beading process includes two convex portions 12a and 
12c on the inner surface of the bead glass corresponding to the 
electrodes. Referring to FIG. 6, a bead base 3 is formed with two concave 
portions 3a and 3c each of which corresponds to the respective two convex 
portions of the bead glass. FIG. 7 illustrates a modification of the 
second embodiment in FIG. 5, in which a bead base 3 is formed with a 
concave portion 3a which is large enough to receive both two convex 
portions of the bead glass. 
An electron gun according to the second embodiment and its modification is 
manufactured by the similar process to the first embodiment of the 
invention. FIG. 8 illustrates the manufactured electron gun having the 
above-mentioned structure of the second embodiment and its modification. 
When manufacturing the electron gun, as shown in FIG. 9, a depth D of the 
bead support 24a for the G.sub.4 -electrode 24 which is buried in the bead 
glass is preferably predetermined in a range between 30% and 70% with 
respect to a total thickness T of the bead glass. In other words, the 
following relation can be derived: 
EQU 0.3.ltoreq.D/T.ltoreq.0.7 
In case of D/T&lt;0.3, a strength for supporting the electrodes is weakened, 
and on the contrary, in case of D/T&gt;0.7, the bead glasses often tend to 
crack. 
According to the present invention, minimization of the recess and 
projection on the buried interface of the bead glass on its electrode side 
causes the supporting strength of the electrodes to be further improved, 
so that the electrodes can be retained with certain intervals 
therebetween, thereby increasing a focus performance of the electron gun. 
Further, in the knocking process during manufacture of color cathode-ray 
tubes, the electron gun is protected from the withstand voltage 
deterioration caused by produced spark, whereby a yield in the 
manufacturing process of the electron gun is maximized.