WO1998045870A1

WO1998045870A1 - Cathode-ray tube having a shrink fit band

Info

Publication number: WO1998045870A1
Application number: PCT/US1998/006284
Authority: WO
Inventors: Harry Robert Swank
Original assignee: Thomson Consumer Electronics, Inc.
Priority date: 1997-04-10
Filing date: 1998-03-31
Publication date: 1998-10-15
Also published as: MY126507A; CN1146953C; KR20010006098A; CN1252165A; AU6789698A; KR100496483B1; TW525832U; JP2001519084A

Abstract

A shrinkfit band (18) for a CRT (10) comprises a strip of metal having two ends (20, 22). At least one end (20) of the band is in contact with the CRT. The ends (20, 22) are joined by at least one connective joint (24) to form a loop. The loop is disposed around the CRT. The band is improved over prior bands by spacing an inside tail end (27) of the band a sufficient distance (d3) away from the connective joints to prevent an inward curl of the inside tail end (27).

Description

CATHODE-RAY TUBE HAVING A SHRINK FIT BAND

This invention relates generally to cathode-ray tubes (CRT's) having implosion protection bands and, more particularly, to such tubes having shrinkfit bands. BACKGROUND OF THE INVENTION

An implosion protection band of the shrinkfit type is manufactured by forming a strip of metal, preferably steel, into a loop having the same configuration as the faceplate panel to be protected. The two ends of the strip are joined together on one side of the band, for example by welding or crimping. In some instances, the band is made from two strips of metal joined on two sides to form the loop, or by joining a short metal connecting plate to the ends of a metal strip to form the loop. The periphery of the loop is slightly smaller than the periphery of the faceplate panel. The loop is heated to a sufficient temperature to cause the loop to expand to dimensions permitting the loop to be slipped around the sides of the faceplate panel. As the band cools, the loop shrinks and tightly surrounds the panel, thereby applying a compressive force to the panel. In order to conserve material and to reduce the cost of the shrinkfit band, the ends of the strip typically extended not more than 12.7 mm (0.5 inch) from the connective joint that secures the ends together. Because the end of the strip adjacent to the glass sidewall of the faceplate panel extends only about 12.7 mm from the connective joint, the opposing forces acting on the joint tend to rotate the inside tail end of the strip, which is in contact with the glass sidewall of the faceplate panel, causing the inside tail end of the strip to curl inwardly and contact the mold match line of the faceplate panel producing a pronounced high pressure area extending from the ultimate connective joint to the tail paralleling the end of the strip. This high pressure area produces a high "line" of pressure where the inside tail end of the strip contacts the glass, causing occasionally scratching, or otherwise damaging the glass and increasing the possibility of tube failure. The mold match line is a convex seam formed where the two parts of the faceplate panel mold are joined. Panels damaged in such a way cannot be reused after salvage unless the damaged areas are polished out.

SUMMARY OF THE INVENTION A shrinkfit band for a CRT comprises a strip of metal having two ends, at least one end of the band is in contact with the CRT. The ends are joined by at least one connective joint to form a loop. The loop is disposed around the CRT. The present shrinkfit band is improved by spacing an inside tail end of the band a sufficient distance away from the connective joint to prevent an inward curl of the inside tail end. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in greater detail, with relation to the accompanying drawings, in which:

Fig. 1 is a perspective view of a CRT and shrinkfit band according to the present invention;

Fig. 2 is a front view of a closure side of the present shrinkfit band; Fig. 3 is an edge view of the closure showing a plurality of connective joints of the novel band made according to the present invention;

Fig. 4 is a view of the inner surface of the novel band of Fig. 3, showing a pressure pattern caused by the location of the connective joints of the closure relative to the inside tail end of the band, and the resultant effect on a protective tape overlying the inner surface of the band;

Fig. 5 is an edge view of a prior band showing the curl induced by the proximity of the connective joints of the closure relative to the inside tail end of the band;

Fig. 6 is a view of the inner surface of the prior band of Fig. 5, showing the pressure pattern induced by the location of the connective joint relative to the tail of the band, and the effect of the resultant curl on the protective tape overlying the inner surface of the prior band;

Fig. 7 an edge view of a second embodiment of the novel band showing a connecting plate extending between the two ends of the band; and

Fig. 8 is a view of the inner surface of the novel band and connecting plate of Fig. 7, showing the pressure patterns.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With respect to Figs. 1 - 4, a CRT 10 comprises an evacuated envelope 12 having a faceplate panel 14 joined by a frit seal, not shown, to a funnel 16. A shrinkfit band 18, in the form of a loop with cold dimensions slightly smaller than the periphery of the panel 14, is fitted around a sidewall 19 of the panel by heating the band within the range of 300° to 500° C, to cause it to expand, and then allowing it to cool. The tension of the cooled band 18 applies a compressive force to the sidewall of the panel. The redistribution of forces decreases the probability of an implosion of the tube by minimizing tension in the corners of the panel. The band 18 is formed by joining together a first end 20 and a second end 22 of at least one steel strip with a plurality of connective joints 24 to form a closure 26. The connective joints 24 may be formed either by welding or crimping. As illustrated in Figs. 3 and 4, the connective joints 24 are shown as being crimped. In crimping, at least one connective joint 24, and preferably a plurality of connective joints, aligned in rows, are formed by drawing and extruding the strip to mechanically interlock the ends thereof to form the loop. Crimping is further described in U.S. Pat. No. 4,459,735, issued to Sawdon on July 17, 1984. The welded connecting joints 24 also are formed in rows of about 4 connective joints each.

With reference to Fig. 2, the band 18 has a width, W, of 47.62 mm and a thickness within the range of 2.18 to 2.38 mm. A plurality of openings 28 are formed, for example, by lancing the band 18 adjacent to one edge 30. A narrow strip 32 of band material bridges the openings 28. The strip 32 is formed out of the plane of the band 18 to provide a support for a degaussing coil mounting clip, not shown. A plurality of mounting lugs 34 are attached to the band at each of the corners. The openings 28 adjacent to the corners also include a slot 36 which communicates with the opening 28 and provides a means for ensuring that the tension on the closure 26 does not exceed the design limit. This feature of the band 18 is described more completely in U.S. Pat. No. 5,181,123, issued to Swank on Jan. 19, 1993. In the prior art, as shown in Figs 5 and 6, the shrinkfit band 118 has a closure 126 which includes a contacting end 120 that is overlapped by a top end 122. The distance, d,, from the connective joint 124 adjacent to an inside tail end 127 of the contacting end 120 is not greater than 12.7 mm (0.5 inch). The distance, d₂, from the connective joint 124 adjacent to an outside tail end 129 of the top end 122 also is 12.7 mm. Tension forces, T, are exerted on the connective joints 124 of the band 118, when it is installed on the CRT, not shown. These forces cause a rotation around the connective joints 124, but the effect of that rotation is most pronounced at the inside tail end 127 of the band. As shown in Figs. 5 and 6, the contacting end 120 curls inwardly, toward the sidewall of the CRT, not shown, to the extent that the inside tail end 127 cuts through a fiber tape 40 that is disposed between the band 118 and the CRT. A pressure pattern 142 is impressed into the tape 40 and indicates the area of the band 118 that is subjected to the greatest pressure. The curl formed by the inside tail end 127 of the band 118 is sufficient, in some instances, to cut the tape 40 and scratch or otherwise damage the glass of the sidewall of the CRT 10.

In one preferred embodiment, shown in Figs. 3 and 4, the present band 18 is formed so that the distance, d₃, from the connective joints 24 adjacent to an inside tail end 27 of the first end 20 the band is at least 19 mm (0.75 inch). The distance, d₂, from an outside tail end 29 of the second end 22 of the band 18 to the nearest connective joints 24 remains unchanged at 12.7 mm. The fiber tape 40 disposed between the band 18 and the CRT shows a pressure pattern 42 similar in shape to the pressure pattern 142; however, the pressure pattern 42 differs in that the area of greatest pressure is substantially elongated between the nearest connective joints 24 and the inside tail end 27 of the band 18. The extended distance, d₃, between the nearest connective joints 24 and the inside tail end 27 dissipates the rotational effects caused by the tension, T, and prevents the inside tail end 27 from curling inwardly toward the sidewall of the CRT. The elimination of the curl at the inside tail end 27 is easily discerned by inspection of the band 18 and tape 40.

A second embodiment of the present invention is shown in Figs. 7 and 8. In this embodiment, a shrinkfit band 218 comprises a first strip of metal having a first end 220 and a second end 222 joined together by a connecting strip of metal 223 attached to each of the ends 220 and 222 by a plurality of connective joints 224 to form a closure 226. The shrinkfit band 218 is disposed around the sidewall of the CRT, not shown, with inside tail ends 227 and 229 of the first and second ends 220 and 222, respectively, in contact with the sidewall of the CRT. The inside tail ends 227 and 229 are spaced from the nearest of the plurality of connective joints 224 by a distance, d₃, of at least 19 mm which is sufficient to prevent the inward curl of each of the inside tail ends against the sidewall of the CRT. The extended distance between the nearest connective joints 224 and the inside tail ends 227 and 229 dissipates the rotational effects caused by the tension force, T, and prevents the inside tail ends 227 and 229 from curling inwardly toward the sidewall of the CRT. The fiber tape 40 disposed between the band 218 and the CRT shows a pair of pressure pattern 242 and 244 that are substantially identical in shape to each other and to the pressure pattern 42, shown in Fig. 4. The elimination of the curl is easily discerned by inspection of the band 218 and tape 40 which shows no evidence of being cut by the inside tail ends 227 and 229.

Claims

1. A shrinkfit band (18; 218) for a CRT (10), comprising a strip of metal having two ends (20, 22; 220, 222) joined together by at least one connective joint (24; 224) to form a loop disposed around said CRT, at least one of said ends (20; 220, 222) of said strip having an inside tail end (27; 227, 229) that is in contact with said CRT; characterized by said inside tail end (27; 227, 229) being spaced from said connective joint (24; 224) by a distance (d₃) sufficient to prevent an inward curl of said inside tail end against said CRT (10).

2. The shrinkfit band (18; 218) described in claim 1, characterized by said inside tail end (27; 227, 229) of said strip being spaced at least 19 mm from said connective joint (26; 226).

3. A shrinkfit band (18) for a CRT (10), comprising a strip of metal having a first end (20) and a second end (22) overlapping said first end, said first and second ends being joined together by a plurality of connective joints (24) to form a closure (26), said band being disposed around a sidewall (19) of a faceplate panel (12) of said CRT with said first end of said strip being adjacent to said sidewall; characterized by an inside tail end (27) of said first end (20) of said strip being spaced from the nearest of said connective joints (24) by a distance (d₃) sufficient to prevent an inward curl of said inside tail end against said sidewall (19) of said CRT (10).

4. The shrinkfit band (18) described in claim 3, characterized by said inside tail end (27) of said first end (20) of said strip being spaced at least 19 mm from the nearest connective joint (24).

5. A shrinkfit band (218) for a CRT (10), comprising a first strip of metal having a first end (220) and a second end (222) joined together by a connecting strip (223) of metal attached to said first and second ends by a plurality of connective joints (224) to form a closure (226), said band being disposed around a sidewall (19) of said CRT with said first and second ends of said first strip of metal being in contact with said CRT; characterized by said first and second ends (220, 222) of said first strip of metal having each an inside tail end (227, 229), the inside tail ends (227, 229) being spaced from the nearest of said plurality of connective joints (224) by a distance (d₃) sufficient to prevent an inward curl of said inside tail ends (227, 229) against said sidewall (19) of said CRT (10).

6. The shrinkfit band (218) described in claim 5, characterized by said inside tail ends (227, 229) of said first and second ends (220, 222) of said first strip being spaced at least 19 mm from the nearest connective joints (224).