Television – Cathode-ray tube burn-in prevention
Reexamination Certificate
2002-03-13
2003-08-19
Wong, Don (Department: 2821)
Television
Cathode-ray tube burn-in prevention
C313S634000
Reexamination Certificate
active
06608645
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a weight reduction of a funnel for a cathode ray tube used in TV receivers.
In general, a cathode ray tube for use in the TV receiver has a front panel portion, a backward funnel portion and a neck portion incorporating an electron gun. Referring now to FIG.
3
A and
FIG. 3B
, the funnel portion comprises a yoke portion a at the smaller open-end side and a body portion b at the larger open-end side. The cross-section of the body portion b perpendicular to its centerline X has a substantially rectangular shape having the major axis L, the minor axis S and the diagonal axis D.
In the conventional funnel F′ for the cathode ray tube, which is T(Lh), T(Sh) and T(Dh) in thickness along the major axis L, the minor axis S and the diagonal axis D at an arbitrary height h, there is a relation, T(Sh)<T(Lh) <T(Dh), in general. Conventionally, the thickness of each region has been determined (see
FIG. 4
) according to T(&thgr;h), for example in the first quadrant of 0≦&thgr;≦90°, so that T(&thgr;h)=T(Lh)+(T(Dh)−T(Lh))sin
2
((90°×&thgr;)/ d°) in the L(0°)≦&thgr;≦D(d°) region, while T(&thgr;h)=T(Sh)+(T(Dh)−T(Sh))sin
2
((90°×(90°−&thgr;))/(90°−d°) in the D(d°)≦&thgr;≦s(90°) region.
The thickness distributions in the second (90°≦&thgr;≦180°), third (180°≦&thgr;≦270°) and fourth (270°≦&thgr;≦360°) quadrants have been determined following the above two equations to present a symmetric thickness distribution.
On the other hand, the weight of the cathode ray tube increases as the size of the TV receiver increases. It becomes thus necessary to reduce its weight for easier transport and handling. For weight reduction, the cathode ray tube should be made thinner. However, if its thickness is simply reduced, its mechanical strength deteriorates and will not meet the requirements for safety.
If the thickness is simply reduced, the moldability deteriorates as well. That is, the funnel for the cathode ray tube is manufactured by press molding, namely, by charging a predetermined amount of molten glass (hereafter, gob) in a bottom mold and then pressing a plunger against the gob in the bottom mold. When the gob is pressed by the plunger, it extends into the gaps between the bottom mold and the plunger until the top end of the molten glass reaches the shell mold that is prepared to form the larger open-end of the funnel. During this process of pressing, since the minor axis side and the major axis side of the funnel body are away from the centerline at different distances, the times for molten glass to reach from the major axis side and the minor axis side to the larger open-end through the gaps between the bottom mold and the plunger are different from each other. That is, it takes more time for the glass to reach the larger open-end from the major axis side than from the minor axis side.
In general, as described above, the molten glass on the minor axis side first reaches the larger open-end and then the glass on the major axis side is extended to the larger open-end. Thus the glass on the minor axis side, which has already reached the larger open-end, receives an excessive force that may cause cracks. Since it takes more time for glass extension on the major axis side than on the minor axis side, the temperature of glass is likely to fall on the major axis side and wrinkles may be produced in the vicinity of the larger open-end. Meanwhile, if the pressing force is lowered to prevent cracks on the minor axis side, the glass may not reach the larger open-end completely and dents (unfilled portions) may be left in the extended glass.
Such molding defects like crack, wrinkle and dent are produced even when the aspect ratio is 4:3, if one tries to simply reduce the thickness of the funnel body. When the aspect ratio is larger, for example, 16:9, this phenomenon becomes more apparent.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a funnel for a cathode ray tube that will lead to reduced weight with no deterioration in mechanical strength or moldability.
To attain the above object, the present invention provides a funnel for a cathode ray tube comprising a yoke portion at a smaller open-end side and a body portion at a larger open-end side. In this funnel, an arbitrary transverse cross-section (Ph) perpendicular to a centerline X of the body portion is substantially rectangular having a major axis L, a minor axis S and a diagonal axis D. With the transverse cross-section (Ph) being virtually divided into four 90°-quadrants around the center line X, a thickness distribution for at least one of the quadrants is provided by |T(Dh)−T(Lh)|≦0.3 mm and T(Dh)>T(Sh), |T(&thgr;h)−T(Lh)|≦0.3 mm and |T(&thgr;h)−T(Dh)|≦0.3 mm in the 0°≦&thgr;≦d° region, and |T(&thgr;h)−T(Sh)|≦0.3 mm in the (d+&agr;)°≦&thgr;≦90° region where 0°<&agr;<(90−d)°; where &thgr; (0≦&thgr;≦90°) is an angle measured from the major axis L in each quadrant, T(Lh) is a thickness of the region on the major axis L(&thgr;=0°), T(Sh) is a thickness of the region on the minor axis S(&thgr;=90°), T(Dh) is a thickness of the region on the diagonal axis D(&thgr;=d°), and T(&thgr;h) is a thickness of the region at an arbitrary angle (&thgr;). The arithmetic symbol “||” represents the absolute value.
Since the thickness of the funnel of the region on the major axis L is the same as that of the prior art, there is no decrease in mechanical strength. In the thickness configuration according to the present invention, the thickness is maintained substantially uniform over the region extending from the major axis L through the diagonal axis D by keeping the difference in thickness between the regions on the major axis L and on the diagonal axis D within 0.3 mm, and further the thickness of the region extending from 90°−(d+&agr;)° through the minor axis S is maintained substantially uniform by keeping the difference in thickness from the region on the minor axis S within 0.3 mm. Then it becomes possible to reduce the funnel weight. The smaller the above &agr; is, the more the above uniform thickness region may expand. As a result, the funnel becomes further lighter.
In the above configuration of the present invention, it is allowed that T(Dh)−T(Sh)≧0.8 mm. As described earlier, the time required for glass extension on the major axis side differs from that on the minor axis side when forming the funnel. However, if the thickness on the major axis L is made larger at least 0.8 mm than that on the minor axis S, the glass extension on the major axis side is accelerated and thus the delay in arriving time of glass extending from the major axis side to the larger open-end becomes smaller. As a result, molding defects such as crack, wrinkle and dent are prevented, and there is no deterioration in moldability. This thickness design is particularly effective to the funnel of the cathode ray tube where the aspect ratio is large, 16:9, and the difference in distance from the major axis and the minor axis is large.
In the present configuration, the angle, &agr;, can be 10°≦&agr;<(90−d)°. If &agr; is 10° or smaller, it becomes difficult to make a gradual decrease in thickness from the thickness T(Dh) on the diagonal axis to the thickness T(Sh). As &agr; approaches (90−d)°, the funnel becomes lighter. Thus the angle &agr; should be as small as possible within the (90−d)° range.
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patent: 2002-63858 (2002-06
A Minh Diu
J.C. Patents
Nippon Electric Galss Co., Ltd.
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