Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Background of the Invent _n
The presen-t invention relates to a p:icture tube com-
prising a faceplate, a funnel, and a neck provided with an
implosion proof facility.
In the course of their development, picture tLbes
for monochrome and color television sets have been made much
more implosion-proof by improvements in their shape. The risk
of destruction as a result of bumps on the glass body of the
tube has been greatly reduced. It is known, however, -that
the implosion of a picture tube presents quite di-fferent dangers
to the surroundings depending on where the fracture begins.
It is, therefore, disadvantageous if the funnel section of
the tube is too resistant compared -to the faceplate or panel
section, for the fragments of the front glass panel can -then
be reflected from he funnel in the forward direction. It
hasl therefore, been proposed to reduce the resistance to the
impac-t of fragments and, thus, eliminate the risk of reflec--
tion by means of a ring o:E predetermi.ned breaking points around
the funnel section, so that no fragments of the glass panel
will be thrown back toward the viewer. However, this measure
acts on the implosion process relatively late, namely when
the panel fragments strike the wall of the funnel.
Summary of the Invention
It is, therefore, an object o.E the presen-t invention
to provide a more effective means for reducing the danger of
implosion in a picture -tube.
According to the invention, the implosi.on process
is influenced from the very beginning by a few sharply defined
and irregularly distributed obstacles to thi? s11ock waves occur-
ring in the Eunne1 wall wh:ict1 cbst.1c:1es i.l1 Ll~e L`0~.`11~ cil- a plu~--
ali-ty oE wal.l-th:i.ck1le~ss ancl~o~~ wa11.-~ t-e~:ial irre~Ju1.1~:1.y
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distributed inhomogeneities in the funnel wall. As impacts
on the tube cause an accumulation of eneryy o~ the inhomoyene-
i-ties, the inhomogeneities a-t the neck-to-funnel transition
cause cracks to start at those points. Such a crack will immed-
iately proceed to the tube neck and, thus, result in relatively
safe devacuation of the tube. In an preferred embodiment,
each inhomogeneity has a circumscribed circle thereabout,
measured in the surface of the funnel, which is 0.001 to 0.1
-times the funnel circumference at that point.
The shock waves caused in the glass wall by impacts
delivered to the tube envelope are reflected by the inhomogene-
ities. Excessive internal stresses are caused in the glass
envelope particularly if the inhomogeneity is located at a
vibration antinode of the envelope.
The location of these vibration areas depends on
the point of impact, so that several inhomogeneities will advan-
tageously be irregularly distributed over the surface of the
Eunnel in such a way that the distance from one inhomogeneity
to one or more further inhomogeneities, measured in the surface
of the funnel, is at least equal to half the length of the
circumference of an inhomogeneity.
To safely keep any undesirable fracture yrow-th at
an inhomoyeneity to a subcritical ra-te, inhomogeneities are
advantageously provided at points of the tube which are substan-
tially free of tensile strain.
The neck-to-funnel and funnel-to-faceplate transition
zones are less resistant, so that the inhomogeneities will
advantageously be spaced at least the length of their circum-
ference from the cylindrical portion of the neck and from the
line at which the facepla-tc? and tlle ~ullnel ale -joined.
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The inhomogeneities should be bounded so that a maxi-
mum gradient of internal stress can occur at their boundaries.
Therefore, the inhornogenei-ties
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include combinations of line-shaped depressions and/or elevations in/of the glass
wall, i.e., are I-, I-, V-, Y- or X-shaped.
Such inhomogeneities can be implemented, for example, with metallic
inclusions in the glass wall of the funnel. They may also be ground or cut into
the inside or outside of the glass wall, or they may be obtained by thermally
or chemically introducing internal stresses into the glassA
The desired effects were proved by implos;on tests as specified by
VDE (Association of German ~lectrical Engineers) and Underwriters Laboratories
Inc. The crack started at the inhomogeneity and travelled to the neck of the
tube. There, devacuation was consequently initiated, so that the pressure e~erted
in the front panel would no longer be sufficient to accelerate any fragments
of glass if a crack had formed there.
This result was obtained with a 1 mm deep I-shaped depression in
the inside surface of the funnel of an A55-14X color picture tube. The length
of this depression was about 20mm.
Brief Descri~tion of the Drawin~
Above mentioned and other features and objects of this invention
will become more apparent by reference to the following description taken in
conjunction with the ~ccompanying drawing, in which:
Fig. 1 shows the basic shape of the discontinuities, herein called
"inhomogeneities", in the wall of the glass envelope;
Fig. 2 shows cross sections through portions of the glass envelope
where inhomogeneities, namely ribs, steps and depressions, are formed in the
wall;
Fig. 3 shows corresponding inhomogeneities which are subsequently
attached to or formed in the wall;
Fig. 4 shows an inhomogeneity introduced into the wall of the envelope;
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Fig. 5 shows an inhomogeneity and its circumscribed circle (broke
line) which is to be understood as the circumference U of the inhomogeneity;
Fig. 6 illustrates the proportions of the arrangement of inhomoge-
neities on the funnel of the picture tube; and
Fig. 7 indicates the formation of a crack in the presence of an in-
homogeneity according to the invention.
Description of the Preferred Embodiment
The implosion of a picture tube involves relatiYely little danger if
eracks form at the neck-to-cone transition at least simultaneously but if possible
earlier than in other areas. In that case, the vacuum in the tube will be reduced
from the rear before fragments of the front glass panel are accelerated by the
violent devacuation.
The invention, therefore, mal~es use of the inhomogeneities shown
in Figs. 1 to 4, which serve to eonvert the energy of an impact on the glass en-
velope into internal stresses at the desired point of the envelope, the internal
stress being essential to produee an effective reflection. The obstacle may be
a mass excess, a mass deficiency or a deformation. If the obstacle is represented
by a foreign-body inclusion, an added advantage is gained if the thermal expan-
sion of the inclusion is chosen so that if the tube is greatly over-heated, internal
stresses will also be produced at the inhomogeneity located at the small funnel
end; this inhomogeneity will then initiate the implosion at the desired point.
As shown in Fig. 3, an inhomogeneity of a different material may also be soldered
on, for example. All measures of Figs. 1- 4 rnay be taken on the inside or outside
wall of the tube.
In the course of the development of television tubes, the risk of
destruction due to external loading has been greatly reduced. The funnel-to-
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neck transition and the seal area between the front panel and the funnel are,of course, more sensitive than the other tube areas. Therefore, as shown in Fig.
~i, the inhomogeneities should be spaced about 1- 2 U apart, where U is the cir-
cumference of an inhomogeneity (see Fig. 5). Within the remaining area of the
funnel surface, two or more inhomogeneities, also of different kind, may be
provided, for the propagation paths of the vibration energy are different at
different points, particularly on the front panel surface, and after a few reflections
nodes and antinodes of the glass envelope vibrations are formed in the different
areas. As experiments have shown, the crack formed at an inhomogeneity travels
into the relatively easily separating neck-to-funnel transition area as desired.
Advantageously, the inhomogeneity points in the direction of the
tube neck.
While I have described above the principles of my invention in con-
nection with specific apparatus, it is to be clearly understood that this description
is made only by way of e2cample and not as a limitation to the scope of my in-
vention as set forth in the objects thereof and in the accompanying claims.
