Note: Descriptions are shown in the official language in which they were submitted.
RCA 85,570 2 ~ 3
IMPROVED SHRINK FIT lMPLOSIQN PROTECT~ON BAND
This invention relates generally to implosion
protection bands for cathode ray tubes (CRT) and particularly to
an improved shrink fit implosion protection band.
Cathode ray tubes are evacuated to a very low internal
pressure and accordingly are subject to the possibility of
implosion, due to the stresses produced by atmospheric pressure
acting on all surfaces of the tube. This problem has been
addressed in the art by providing CRTs with implosion protection
bands. Such bands are used to apply a compressive force to the
sidewalls of the CRT faceplate panel, to redistribute some of the
panel forces. The redistribution of the panel forces decreases the
probability of an implosion of the tube by minimizing tension in
the corners of the faceplate. Additionally, in the event of an
implosion, the redistributed stresses cause the imploding glass to
be directed toward the back of the cabinet in which the tube is
mounted, thereby substantially reducing the probability of
someone in the vicinity of the imploding tube being injured.
2 0 Implosion protection bands of the shrink fit type
typically are manufactured by forming a strip of s~eel into a loop
having the same configuration as the faceplate to be protected and
joining the two ends of the strip on one side of the band. In some
instances, the band is made by joining two identical strips on two
sides of the loop. For both types of bands, the periphery of the
loop is slightly smaller than the periphery of the faceplate panel.
The loop is heated to approximately 300 to 500C, and the
coefficient of expansion of the material causes the loop to expand
to dimensions permitting the loop to be slipped around the sides
3 0 of the panel. As the band cools, it shrinks and tightly surrounds
the panel, thereby applying the necessary implosion protection
compression to the panel sidewalls. The compressive force can be
accurately controlled by controlling the yield point and thickness
of the band, because the coefficient of expansion of the banding
3 5 material is known.
The panels are produced by rnolding glass in a two
part mold. Accordingly, the sidewall of every panel has a seam,
commonly called the mold match line, which is formed where the
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two parts of the mold meet. Additionally, the sidewalls of the
panel are thicker where they join the front of the panel than they
are at the open end which mates with the funnel. The angled
sidewalls improve the molding process and ease extraction of the
S molded glass panel from the mold. For this reason, glass forward
of the mold match line is offset and lies at a small angle with
respect to the portion of the sidewall which joins the faceplate.
This angle typically is in the order of 5.5, for example.
The best results from implosion protection bands are
obtained when the implosion protection band overlies the mold
match line of the panel, with the first edge of the band as far
forward as possible without extending beyond the sidewall at the
corner of the panel. For this reason, when a shrink fit type
implosion protection band is used, the band typically lies flat
against the angular sidewall of the panel and therefore the edge of
the band which extends beyond the mold match line does not
always contact the side of the panel. The best implosion
protection and the ultimate adherence of the implosion protection
band to the panel therefore are not obtained. For this reason,
2 0 there is a need for a shrink fit implosion protection band which
ensures that both edges of the implosion protecting band contact
the sides of the faceplate panel being protected. The present
invention fulfills this need.
According to the present invention, a shrink fit
2S implosion protection band for a CRT faceplate panel having a
convex mold match line, which forms an angle ~, extending around
the sidewall of the panel, includes a bend formed at an angle ~
completely around the circumference of the implosion protection
band. The angle 0 overlies the mold match line and ensures
3 0 contact between both edges of the implosion protection band and
the faceplate panel.
In the drawings:
FIGURE 1 is a top view of a shrink fit implosion
protection band in accordance with ~he invention.
3 S FIGURE 2 is a cross section taken along line 2-2 of
FI&URE 1.
FIGURE 3 is a side view of the preferred embodiment
of FIGURE 1.
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2~29~3
FIGURE 4 is a cross section, partially broken away, of
the side of a CRT faceplate panel.
FIGURE 1 is a preferred embodiment of the inventive
implosion protection shrink fit band 10. The band 10 is
5 substantially rectangular in configuration and has rounded
corners 11. The long side dimension of the shrink band 10 is
designated A, and the short side is designated B. For present
standard tube sizes, the long side-short side ratio is 4:3. For this
ratio, the periphery of the implosion protection band is designed
10 to be 6 to 8 millimeters shorter than the periphery of the panel to
be protected, and the sides therefore are l.S to 2 mm shorter than
those of the glass panel. Also, the inside radius r of the four
corners l 1 is substantially equal to the outside radius of the
corners of the faceplate. During heating, the band 10 expands and
15 can easily be passed over the faceplate and aligned with the mold
match line of the panel. The corners seat first during cooling and,
because they are the first contact points, the band seats and
adheres well to the panel while the rest of the band settles against
the glass sidewalls. As the band cools, almost all forces are
2 0 directed through the band into the blend areas where the straight
walls blend into the curved corners. The force is thus transferred
to the panel corners and onto the faceplate of the panel in a ratio
proportional to the sine of the angle of the band, with respect to
the corner of the panel, times the tension of the band. Because
2 5 the corners of the band are locked in place, there is no movement
and the long sides of the band can initially adjust themselves and
balance the forces. A substantial portion of the strain is thus
concentrated in the corner blend areas, and these forces exceed
the yield point of the band metal, thereby placing a controlled
3 0 compressive force on the corners of the band and through the
band onto the corners of the panel. These compressive forces
offset tension forces which are produced on the faceplate corners
by atmospheric pressure when the tube is evacuated.
Mounting lugs 12 are attached to the corners of the
3 5 band lO and are used to mount the tube in the decorative cabinet
of the television receiver in which the tube is used. Eyelets 13 are
provided at various locations along the band 10. The eyelets 13
RCA 85,570 2~95~
are used to mount other components of the television receiver,
such as electronic components, degaussing coils and ground straps.
FIGURE 2 is a cross section of the band 10 taken along
line 2-2 of FIGURE 1. The band 10 has a bend 14 which displaces
one edge of the band at an angle ~ away from the plane of the
band. The bend 14 extends completely around the band 10 at a
bend area 22. The advantages of the bend 14 can be appreciated
from FIGURE 4, which is a broken away cross section of the panel
to be protected. The process of manufacturing the faceplate panel
16 utilizes a two piece mold in which glass is molded to form the
panel. Because the mold is a two piece mold, a mold match line 17
is formed around the complete periphery of the panel 16 at the
point where the two pieces of the mold meet. Also, the outside
surface 18 of the open portion where the panel 16 joins a funnel
l S (not shown) is disposed at an angle ,B with respect to the upper
sidewall surface 19 which joins the faceplate 16. The angle ~
typically is 5.5 and is utilized because it eases the manufacturing
processes; for example, it makes it easier to remove the molded
panel from the mold.
2 0 In the prior art, when a shrink band was placed
around the panel 16, the band laid flat against the angled portion
18 of the panel 16, thereby leaving a small space between the
band 10 and the upper sidewall surface 19 of the panel 16. With
the invention, the angle ~ of bend 14 in the band 10 exceeds the
angle ~ by 0.5 to 3.5 degrees. Accordingly, when the band cools
both the edges 20 and 21 of the band 10 contact the surfaces 18
and 19, respectively, of the panel 16. As the band continues to
cool, it shrinks to the shape of the panel 16, so that almost the
entire surface of the band is tightly drawn against the surfaces 18
3 0 and 19 of the panel 16. Accordingly, when the band is applied to
the panel 16, the bend area 22 of the band 10 is aligned with the
mold match line 17 of the panel 16, so that the band 10 overlies
the match line 17.
In FIGURE 3, the bend 14 extends the complete length
3 5 of the minor side of the band 10, and, as stated above, extends
comple~ely around the band 10. The overlapped ends of the band
are joined together, by welding or in some other known
convenient way, as indicated at 23. The band lû can be formed
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~rom two identical pieces in the manner shown at joints 24 and 25
in FIGURE 1 or, alternatively, from a single strip of material and
joined on one side, as indicated in FIGURE 3.
After the band 10 is joined into a single loop, it is
S stretched at least 1 to 1.5% to ensure that the yield point of the
band is reached during the cooling process. The stretching can be
done simply by using dies in the corners 11, which have the same
radius r as the inside corners of the faceplate to ensure that the
corners of the band are made to the desired radius. The corner
10 dies are spread in directions parallel to the diagonals of the
faceplate and for the distance required to achieve the desired 1 to
1.5% stretch, using hydraulic jacks, or other equipment available
in the art.
