Banded-type implosion protection cathode ray tubes

In a cathode ray tube reinforced by an annular reinforcing band mounted on the face plate of the tube by shrink fit, the opposite ends of the band are coupled together by interfitting members which accurately determine the peripheral length of the reinforcing band.

BACKGROUND OF THE INVENTION 
This invention relates to a banded-type implosion protection cathode ray 
tube reinforced by a band which is applied by shrink fit. 
To improve safety of a cathode ray tube against explosion, a reinforcing 
band is generally applied around the periphery of a face plate 
constituting a portion of the bulb of the cathode ray tube. Among various 
methods of applying the reinforcing band may be mentioned shrink fit 
method. According to this method, an annular reinforcing band 1 shown in 
FIG. 1 is heat expanded and then applied onto the periphery of the face 
plate 2a of the bulb 2. Then the reinforcingd band 1 is cooled to room 
temperature, thus causing it to tightly clamp the face plate with desired 
clamping force. 
However, the periphery of the face plate 2a and the reinforcing band 1 have 
certain manufacturing error or tolerance so that, in order to smoothly fit 
the reinforcing band and cause it to manifest the desired clamping force 
with a small heat expansion thereof, it is necessary to manufacture the 
outer peripheral length of the face plate and the inner peripheral length 
of the reinforcing band with highly accurate manufacturing tolerances. 
Where the relationship between the inner and outer peripheral lengths is 
not adequate, insufficient clamping force or incapability of applying the 
reinforcing band would result. The prior art reinforcing band has been 
manufactured by welding together opposing ends of a metal strip so that 
the inner peripheral length of a completed annular reinforcing band was 
not always accurate. 
Further, in the prior art banded-type implosion protection cathode ray tube 
as shown in FIGS. 2A and 2B, a plurality of mounting lugs 3 are provided 
between the outer periphery of the face plate 2a and the reinforcing band 
1. Due to the thickness of the mounting lugs 3, gaps 4 are formed between 
the face plate and the reinforcing band, thus decreasing the clamping 
force. Accordingly, in the prior art construction, shims are inserted into 
the gaps for the purpose of preventing the decrease in the clamping force. 
However, insertion of thin shims is not only troublesome but also 
displaces the mounting lugs 3. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide an improved 
banded-type implosion protection cathode ray tube provided with a shrink 
fit reinforcing band having an accurate peripheral length so that it can 
be accurately mounted and can produce sufficient clamping force. 
Another object of this invention is to provide a cathode ray tube having a 
novel reinforcing band that can improve the mounting accuracy of the 
mounting lugs and the mounting operation thereof. 
According to this invention, there is provided a banded-type implosion 
protection cathode ray tube of the type wherein an annular reinforcing 
band having at least one joint is mounted on the periphery of the face 
plate of the cathode ray tube by shrink fit, wherein there is provided 
interfitting means formed at the joint of the band and adapted to 
determine the peripheral length of the reinforcing band.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A reinforcing band 10 shown in FIGS. 3 and 4 comprises an annular or 
rectangular portion 11 and four mounting lugs 12 extending outwardly from 
the rectangular portion 11 at four corners of the face plate 8 see (FIG. 
1). Preferably, the mounting lugs 12 are integral with the portion 11. One 
end of the reinforcing band is provided with openings 14 and the other end 
is provided with projections 15 fitted in the openings 14, both the ends 
overlapping with each other to form one paired joint 13. As shown in FIG. 
5, it is necessary to bend a mounting lug 12 away from the side surface of 
the annular portion with a radius of curvature r layer than the thickness 
t of the band. If this radius of curvature were too small, the mounting 
lug might break or it would be impossible to maintain the desired 
accuracy. If the width of the bent portion of the mounting lug were too 
large, the edges of the bent portion would be excessively elongated at the 
time of bending so as to form cracks, thus decreasing the mechanical 
strength. According to this invention, for the purpose of solving this 
problem, the width of the bent portion of the mounting lug is decreased 
and the lug is bent at a portion remote from the side of the reinforcing 
band 11 by a distance corresponding to a height h which is 1.5 mm along 
with other dimensions as exemplified later in relation to a 5.5-inch 
cathode ray tube. 
Although the reinforcing band can be formed into an annular configuration 
having a desired peripheral length by forming only one opening 14 for 
receiving one projection 15, according to this invention, two openings 14 
and two projections 15 are formed so as to prevent overlapped portions of 
the joint from pivoting about one of the projections with consequent 
displacement in the lateral direction. Accordingly, one of the openings 14 
may be elongated or may have a play in the longitudinal direction of the 
reinforcing band. 
The reinforcing band is manufactured as follows. Thus, as shown in FIG. 6, 
a reinforcing band is stamped out from a steel sheet with openings 14, 
projections 15 and mounting lugs 12 at the desired positions and with 
desired dimensions. Then the mounting lugs are bent at right angles with 
respect to the band and the band is sequentially bent into rectangular 
form by utilizing the mounting lugs as reference points. Then the 
projections are inserted into openings 14 and the opposite ends of the 
band are welded together at the joint 13. 
Since the peripheral length of the completed reinforcing band can be 
determined from the positions of the stamped openings and projections, it 
is possible to have accurate peripheral length thus making it easy to 
mount the reinforcing band and to create sufficient clamping force. 
Moreover, as the mounting lugs are formed integral with the reinforcing 
band, the positional accuracy of the lugs can be improved. 
One example of the dimensions of a reinforcing band for use in the 5.5-inch 
cathode ray tube is as follows. 
l.sub.1 =393 mm, l.sub.2 =110.5 mm, l.sub.3 =86.12 mm 
W=11 mm (see FIG. 6); diameter of the opening 
14=3 mm, and diameter of the projection 15=2 mm. 
FIGS. 7A, 7B, 8A and 8B show modified interfitting members. In the case 
shown in FIGS. 7A and 7B, the projections 15 take the form of rings while 
in the case shown in FIGS. 8A and 8B, one connecting portion is provided 
with notches 16 while the other connecting portion is formed with bent up 
portions 17 received in the notches 16. These notches and bent up portions 
are formed at portions shown by dotted lines in FIG. 6. In each case, 
these interfitting members can be formed with high accuracies by stamping. 
According to this invention, the width of the neck 18 which connects the 
mounting lug 12 to the band 11 is decreased so that even when the lug is 
bent at this neck, there is no fear of forming cracks on both sides of the 
bent portion. Moreover, it is possible to smoothly bend the corner 
portions 19 of the reinforcing band along the outside surface of the tube. 
With this construction it is possible to more uniformly clamp the tube by 
the reinforcing band. As shown in FIG. 9, the side edges of the neck 18 
may be inclined and the opening 20 of the lug 12 may be a notch instead of 
a circular opening. 
One example of the dimensions of a reinforcing band for use in the 5.5-inch 
cathode ray tube is shown in FIG. 10. The reinforcing band was prepared 
from a steel sheet having a thickness of 0.8 mm and the inner peripheral 
length after welding was 390.7 mm. Various dimensions are: R=12.46 mm, 
W.sub.2 =12 mm, W.sub.3 =8 mm, W.sub.4 =6 mm, l.sub.4 =9.9 mm. 
In the embodiment described above, the reinforcing band has only one 
(paired) joint 13. However, it is also possible to manufacture the band 
from two U-shaped pieces which are joined at two portions. 
According to this invention it is possible to accurately manufacture the 
reinforcing band, to readily mount it around the face plate and to create 
uniform clamping force.