GB2238656A

GB2238656A - Shrink fit implosion protection band

Info

Publication number: GB2238656A
Application number: GB9025823A
Authority: GB
Inventors: Harry Robert Swank
Original assignee: Thomson Consumer Electronics Inc
Current assignee: Technicolor USA Inc
Priority date: 1989-11-30
Filing date: 1990-11-28
Publication date: 1991-06-05
Also published as: CA2029553A1; KR940000304B1; IT9022150A0; TR24817A; GB9025823D0; IT9022150A1; CN1019433B; KR910010611A; JPH03187136A; CN1052219A; PL288019A1; DE4037874A1

Abstract

A shrink fit implosion protection band (10), Fig. 1, for a CRT faceplate planel (16), Fig. 2, includes an angle theta extending the full circumference of the band, such that in use the bend area 22 overlays the panel mould match line (17) and ensures that both edges (20, 21) of the band contact the faceplate after the band has shrunk into position. Preferably the angle theta of the band 10 exceeds the angle beta formed in the faceplate at the mould match line 17 by 0.5 DEG to 3.5 DEG . <IMAGE>

Description

1 SHRINK FIT IMPLOSION PROTECTION BAND This invention relates generally to

implosion protection bands for cathode ray tubes (CRT) and particularly to shrink fit implosion protection band.

Cathode ray tubes are evacua:ted 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 paiiel 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.

Implosion protection bands of the shrink fit type typically are manufactured by forming a strip of steel 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 500"C, and the coefficient of expansion of the material causes the loop to expand to dimensions permitting the loop to be slipped around the sides 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 material is known.

The panels are produced by molding 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 2 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 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 0 C, 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, 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 implosion protection band for a CRT faceplate panel having a convex mold match line, which forms an angle 0, extending around the sidewall of the panel, includes a bend formed at an angle 0 completely around the circumference of the implosion protection band. The angle 0 overlies the mold match line and ensures 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 the invention.

FIGURE 2 is a cross section taken along line 2-2 of T FIGURE 1.

of FIGURE 1.

FIGURE 3 is a side view of the preferred embodiment 3 FIGURE 4 is a cross section, partially broken away, of the side of a CRT faceplate panel.

FIGURE I is a preferred embodiment of the inventive implosion protection shrink fit band 10. The band 10 is 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 to be 6 to 8 millimeters shorter than the periphery of the panel to be protected, and the sides therefore are 1.5 to 2 mm shorter than those of the glass panel. Also, the inside radius r of the four corners 11 is substantially equal to the outside radius of the corners of the faceplate. During heating, the band 10 expands and can easily be passed over the faceplate and aligned with the mold match line of the panel. The comers 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 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 comers 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 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 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 band 10 and are used to mount the tube in the decorative cabinet of the television receiver in which the tube i-, used. Eyelets 13 are provided at various locations along the band 10. The eyelets 13 4 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 0 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 (not shown) is disposed at an angle P with respect to the upper sidewall surface 19 which joins the faceplate 16. The angle P typically is 5.5' and is utilized because it eases the manufacturing ZP processes; for example, it makes it easier to remove the molded panel from the mold.

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 0 of bend 14 in the band 10 exceeds the angle P 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 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 of the minor side of the band 10, and, as stated above, extends completely 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 10 can be formed :Y Q from 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 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 comer 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.

1 6

Claims

1. A shrink fit implosion protection band for a CRT faceplate panel having a convex mold match line extending around the sidewall of said panel, said mold match line forming an angle P in said sidewall, comprising a bend formed at an angle 0 to displace one edge of said bend away from the plane of said band, toward said sidewall, and extending completely around the circumference of said band, said angle 0 overlying said mold match line for ensuring contact between both edges of said band and said panel.

2.

said angle P.

The -band of claim 1, wherein said angle 0 exceeds

3. The band of claim 1, wherein said angle 0 exceeds said angle P by 0.50 to 3.50.

4. The band of claim 1, 2 or 3, wherein the faceplate and said implosion protection band have rounded corners, and the inside radius of the band corners is substantially equal to the outside radius of the faceplate corners.

5. The band of claim 1, 2 or 3, wherein said angle 0 is in the proximity of the front edge of said band.

6. A protection band substantially as hereinbefore described with reference to the drawings.

-

7. A cathode ray tube having a protection band according to any preceding claim.

Published 1991 at7be Patent 0171ce. State House. 66/71 High Holborn. EondonWCIR47P. Further copies may be obtained from Saks Branch, Unit 6. Nine Mile Point Cwmfelinfach. Cross Keys. Newport NPI 7HZ. Printed by Multiplex techniques ltd, St Mary Cray, Kent.

1 W