US 3162933 A
Description (OCR text may contain errors)
Dec. 29, 1964 A. M. TRAX ETAL 3,162,933
METHOD OF PROCESSING CATHODE RAY TUBES Filed April 12, 1963 2 Sheets-Sheet 1 z; 6 Z INVENTORS gf flaw M. 7X24X @ZkMif-f Mom/764E- M Q it may Dec. 29, 1964 A. M. TRAX ETAL 3,162,933
METHOD OF PROCESSING CATHODE RAY TUBES Filed April 12, 1963 2 Sheets-Sheet 2 INVENTORS won/am 72 4M United States Patent 3,162,33 B'EETHOD 6F PROCESSWG QATHGDZE RAY TUBES Alan M. Trax and James J. Monagie, Marion, Ind, assignors to Radio Corporation of America, a corporation of Deiaware Filed Apr. 12, 1963, Ser. No. 272,619 3 Claims. (Ci. 29-4555) This invention relates to cathode ray tubes and particularly to a method of rendering the tube substantially immune or less susceptible to violent implosion.
In order to prevent tube implosion, it has been proposed by the prior art to reduce the tensile stress in the hoop area of a cathode ray bulb (that area adjacent the faceplate) by applying a tensioned compression band of a material of high tensile strength, e.g. steel, around the hoop area. The prior art has suggested bands fabricated from lengths of metal strapwhose ends are bolted together, lapped over and crimped together similar to the strapping of shipping crates, or lapped over and welded together. Such compression bands are, for example, disclosed in US. Patent 2,785,820, issued to H. B. Vincent et 211.
Both crimped and bolted bands are objectionable because they require the use of a protruding element at the joint of the strap ends. Such protruding elements often interfere with the mounting of the tube in a chassis or cabinet. Moreover, crimped and bolted fastenings sometime slip or relax when placed under prolonged tensions and thus lose the protective quality which they are designed to provide. The conventional crimped fastener also results in a weakening of the strap because of a cut which is made int-o the strap to produce the crimped seal. For these reasons welded bands are preferred.
However, in the case of welded bands, the prior art teaching has been limited to first forming a length of strap into a band and lapping and welding the ends together while the band is completely separated from the tube. The welded band is then heated to expand it, and while expanded, is slipped over the tube and allowed to cool and contract to provide its ultimate tensioned condition; Such welded bands are objectionable because of the inherently poor control of the amount of ultimate tension produced in the band when it shrinks onto the tube. Because such bands are made to a fixed predetermined size and then applied to the tube, the tension which is produced in the band when it shrinks depends upon the perimeter of the tube to which it is applied. Since perimeters vary from tube to tube, the resulting tension produced in prior art welded bands vary. Often the ten sion of the band is outside the allowable limits.
It is therefore an object of this invention to provide a new and improved method of rendering a cathode ray tube implosion resistant by applying a welded band to the tube but at the same time avoiding the above-described objections of the prior art.
Another object is to provide a method for applying a welded implosion prevention band to the tube with a good control of the final tension achieved.
According to the invention a metal strap is first heated to expand it and is then wrapped around both the envelope of a cathode ray tube and a welding electrode, lapped over itself at the electrode, and mechanically tensioned. The hot strap is then welded :at the lap, the electrode withdrawn from between the strap and the tube, and the strap cooled.
Since the welded band is made on the tube, it is custom sized to the tube. Accordingly, the ultimate tension produced in the band can be established accurately in a desired range. Even though a welding electrode is inserted between the strap and the tube in order to make the weld, and even though removal of the electrode may 3,l2,933 Patented Dec. 2%, 1964:
result in a relaxation of the mechanically applied strap tension, suprisingly, this does not prevent the obtaining of a highly tensioned band.
In the drawings:
FIGURE 1 is a top plan view partly in section of a cathode ray tube incorporating the invention;
FIGURE 2 is a front elevation view of the tube of FIGURE 1; and
FIGURE 3 is a front elevation view of a portion of the tube of FIGURES 1 and 2 illustrating the welding step of the invention.
The invention may be embodied in a cathode ray tube which includes: a pair of contoured metallic rim plates disposed under the welded compression band, and a coating of fiberglass cloth bonded to the funnel of the tube bulb with a suitable resin. However, the welded compression band applied by the method herein described can also be used, for example, in combination with a sheet of plastic material draped over the faceplate of thetube as described by Harrison in US. Patent 2,828,799, issued April 1, 1958, or in combination with a fitted glass cap bonded to the faceplate of a tube as described by Hedler et al. in US. Patent 3,075,870, issued January 29, 1963, or by itself. The purpose of the welded band is to relieve tensile stress in the bulb by circumferentially compressing the bulb to within some prescribed lirnits.
Referring to l IGURES 1 and 2, a cathode ray tube 10 is shown which includes an evacuated envelope (bulb) 11. The envelope 11 comprises a faceplate 12, a neck 14, and an interconnecting funnel 15. The funnel 15 includes a substantially rectangularly-shaped cylindrical hoop section 16 adjacent to the faceplate 12. The neck 14 is closed at its distal end with a stern 3.7. A phosphor screen 18 is disposed on the internal surface of the laceplate 12, and an electron gun 19 is disposed in the neck 14.
Atmospheric pressure pressing against the external surface of the faceplate 12, may exert two or three tons total force against the faceplate. This force tends to push the faceplate 12 into the hoop 16 in a manner similar to a cork being pushed into a bottle. A a result, circumferential tensile stresses as high as 1000 pounds per square inch are created in the hoop 16.
A stress reducing means for the tube 10 is provided in the form of a tensioned compression band 20 which encircle the hoop'16. A pair of semi-encircling metallic rim plates 22, which are contoured to the shape of the bulb 11, are pnovided as a foundation for the'band 20 to uniformly distribute tothe hoop 16 any non-uniform contact which the band 2t) might otherwise make with the hoop. As shown in FIGURE 2 the ends of each of the rim plates 22 terminate adjacent to each other in the vicinity of the central portion of one of the short sides 24 of the rectangular hoop 16. However, other rim plate structures can be used. For example, the rim plates may be L-shaped with their ends terminating adjacent to each other at two of the corner of the hoop 16.
The band 20 comprises a length 'of metal strap which is wrapped tightly around both the hoop 16 and the rim plates 22, and has its ends overlapped and welded together. The welded lap 25 may, as shown in FIGURE 2, be positioned centrally of one of the long sides 26 of the rectangular hoop 16. The band 20 may, for example, comprise carbon steel strapping, work hardened to about 100,000 p.s.i. tensile strength and have a light zinc plating thereon to retard oxidation and facilitate weldability. The strap may be from /2 to inch wide and from 20 to 23 mils thick. However, such strap composition and dimensions are not critical.
The tapered portion 28 of the funnel 15 is covered by a fitted piece of fiberglass cloth 30 which is bonded to the funnel with a suitable resin such as an epoxy. The fiberglass cloth 30 extends axially along the bulb 11 from closely adjacent to the rim plates 22 back to that portion of the tube where a magnetic deflection yoke would conventionally be mounted. The cloth 3% is provided with an opening therein exposing a high voltage contact terminal 32 of conventional design.
To apply the welded band 20 ,to the tube envelope 11, a length of suitable strapping is heated to a preselected temperature to thermally expand it. A preferred method of heating the strap is to pass an electrical current through the strap. It has been found that a heating of about of the length of the strap required to encircle the envelope 11 is sufficient to produce the desired elongation thereof. In preferred strap heating schedules for 16, 19 and 23 inch (diagonal dimension of faceplate) cathode ray tubes, straps have been suitably heated from 50 C. up to several hundred degrees centigrade with currents of 50 to 300 amperes from a 10 volts A.C. supply. If desired, a temperature detection device such as a surface pyrometer may be used to determine when the strap has reached a suitable temperature. The temperature to which any particular strap is raised is dependent not only upon the ultimate tension which it is desired to produce in the wedled band 20, but also upon the amount of mechanical tensioning which is subsequently produced in the strap when it is wrapped around the envelope ll. As an alternative to direct electrical resistance heating, the strap heating can be provided by: disposing a coil of metal strapping in an oven; by passing the strapping through a heated tube or torch flame located between the supply reel and the machine used to apply and weld the strap; or by heating the entire strapping and welding machine as well as the supply coil of strapping therein.
After the selected length of strap is heated to elongate over the rim plates 22, and pulled tightly to mechanically tension the strap about the envelope 11. The strap is lapped over itself and welded together at the lap to form the completed band 20. The mechanical tension produced in the band can, if desired, be quite low. The mechanically produced tension need only be high enough to custom size the band to the particular envelope around which it is being applied and need only be suifcient to produce in combination with the subsequent thermal shrinkage of the band the desired ultimate tension.
The mechanical tensioning and welding of the strap may be performed by any suitable strapping and welding machine. One such suitable machine having hydraulically powered tensioning means is marketed by Acme Steel Company and identified as Type Fl. In this particular machine, for example, a banding operation is performed as illustrated in FIGURE 3. The envelope 11 and the rim plates 22 are placed in position on the machine against a pair of welding electrodes 34 and a pair of strap gripper seats 35. The end section of a supply reel of metal strapping is fed out, and a pair of leads from an electrical power supply-are connected to spaced points thereon. Current is passed through the strapping between the spaced points to heat it. The strapping is then positioned around the envelope and lapped over itself opposite the electrodes 34. The end of the heated strap is gripped by a first gripper 36 adjacent to the lap and then is tensioned with a predetermined force by an electric clutch and/or a hydraulically powered second gripper 37. The tensioned strap is gripped by a third gripper 38, and is then severed just beyond the lap by a cutter 39. A shorting block 40 is then clamped against the lapped strap opposite the electrodes 34 and the welds are made.
As shown in FIGURE 3, the presence of the welding electrodes 34 and of the strap gripper seats 35 between the band 20 and the envelope 11 result in the band 20 being slightly lifted out of contact with the rim plates 22. After the welding of the strap is completed, the electrodes 34 and the strap seats 35 are forced from between'the still hot band 20 and the r m plates 22 thereby allowing the .it by thermal expansion, it is placed around the hoop 16 i example, where a tension of approximately 1200 pounds has been mechanically produced in the band for a 19 inch tube, the relaxation may be to a tension as low as 350 pounds. However, the band is now permitted to cool and contract and thus tighten about the envelope 11. More over, since the band 20 has been fabricated on the envelope 1i and thereby custom sized to it, the ultimate band tension can be consistently established from tube to tube to within a desired range.
Experience has shown that for 16 inch bulbs, an ultimate band tension of from 200' to 300 pounds is desirable, for 19 inch tubes from 600 to 800 pounds is desirable, and for 23 inch tubes 800 to 1000 pounds is desirable. Suitable band tensions have been obtained for 19 some tubes accurately controlled final strap tensions of about 1200 pounds have consistently been obtained by the practice of this invention.
In the implosion-proofing of the tube 10 of FlGURES l and 2, the fiberglass cloth 30 may be'bonded to the funnel 12 either before or after the band 20 is applied to the envelope ll. The fiberglass cloth 3%? may simply be cut and fitted to the funnel l2 and an epoxy resin sprayed, brushed, or rolled onto the cloth. The particular choice and application of fiberglass cloth and bonding resin is neither critical nor does it form a part of this invention, and therefore need not be further described herein. I
What is claimed is:
1. In the method of rendering a cathode ray tube implosion resistant by applying a metal band therearound, the steps of:
(a) heating a metal strap,
(12) wrapping said strap around said tube and lapping v the ends of said strap over each other,
(0) mechanically tensioning said heated strap to custom size it to said tube,
(d) welding the ends of said heated strap together at said lap to form a continuous band around said tube, and
(e) cooling said band to shrink it and thereby further tension it around said tube.
2. In the method of rendering a cathode ray tube implosion resistant, the steps of fabricating and applying a tensioned metal compression band around said tube, said steps comprising:
(a) heating a metal strap to elongate it by thermal expansion,
(b) wrapping the elongated strap around said tube and over a welding electrode which is adjacent to said tube with the ends of said elongated strap lapped over each other at said electrode,
(c) mechanically tensioning said elongated strap and welding its lapped ends together to form a continuous elongated band around said tube,
(d) withdrawing said electrode after the Welding from between said elongated band and said tube, and
(e) cooling said elongated band to shorten it and there- 'by further tension it around said tube.
3. The method of processing a cathode ray tube having a faceplate, a neck, and an interconnecting funnel to render it implosion resistant, said method comprising the steps of:
(a) bonding a fiberglass cloth to a first portion of said funnel spaced from said faceplate,
5 6 (b) fitting a pair of semi-encircling rim plates around cooling said band to shrink it and thereby further a second portion of said funnel adjacent to said facetension 1t around said tube. Plate References Cited in the file of this patent (c) wrapping a heated metal strap around sald tube UNITED STATES PATENTS over said run plates, 5 F (d) mechanically tensioning said strap and lapping M3514 Dllecy y 1, 1956 the ends of Said Strap Over each other, 2,785,820 V1ncent et al. Mar. 19, 1957 (e) welding said lapped ends together to form a con- FOREIGN PATENTS timwus band around said tube and 753,696 Great Britain July 25, 1956