US2704169A - Electronic tube - Google Patents

Description

March 15, 1955 H, |$HLER E1'AL 2,704,169

' ELECTRONIC- TUBE Filed May 17, 1951 United States Patent ELECTRONIC TUBE Harry K. Ishler, Lansdale, and Joseph J. Grabiec, Philadelphia, Pa., assignors to Philco Corporation, Philadelphia, Pa., acorporation of Pennsylvania Application May 17, 1951, Serial No. 226,758

Claims. (Cl. 220-2.2)

The present invention relates to electronic tubes and, particularly, to cathode ray tubes of the kind commonly used in television systems. Specifically, the in vention has to do with the exhaust tubulation with which the tube envelope is supplied to provide a duct for evacuating the tube in the final stages of its manufacture.

A tubulation of the above mentioned kind must be of substantial length in order to accommodate the fitting adapted to connect the tube to the exhausting machine. Also, the tubulation must be long enough to provide ample space between said fitting and the body of the tube so that a suflicient portion of the tubulation remains exposed for association with the equipment adapted to pinch-off the tubulation and to seal the tube.

In accordance with generally known manufacturing procedures, the tubulation is made of an elongated tubular member either of glass or of metal, and such a tubulation is mounted on the tube envelope either by a glass-to-glass seal or by a metal-to-glass seal. the latter case, the tubulation generally consists of a piece of copper tubing brazed to a coupling element made of an alloy containing chromium which is especially suited for sealing to glass. Also, in accordance with said known procedures, it is customary to mount the elongated tubulation on the tube envelope prior to processing the tube, for the reason that impurities which may contaminate the fluorescent screen of the tube and otherwise affect proper operation of the tube, are apt to result from the sealing operation, and for the further reason that washing of the tube envelope before its actual processing which includes application of the fluorescent screen material, is depended upon to remove such impurities. An elongated tubulation projecting from the tube envelope is in constant danger of being damaged and is likely to subject the envelope, as well as the glass-to-glass or metal-to-glass seal, to undue stresses which can and often do cause a defective seal. Moreover, a finished electronic tube which is provided with a tubulation of the herein mentioned known variety and which is rendered useless due to damaged tubulation, cannot be effectively salvaged because salvage of such a tube necessitates repetition of the glass-to-glass or metal-to-glass sealing operation and, since the interior of the finished tube cannot be rewashed without danger of destroying the effectiveness of the coated internal surfaces and the electronic gun structure of the tube, it becomes practically impossible to remove contaminating impurities which may result from the repeated sealing operation. Thus, glass or metal tubulations heretofore in common use, have certain objectionable features which give rise to handling difliculties and problems and which may bring about undue waste of time and material in manufacturing the tube, and it is an important object of the invention to provide a novel tubulation structure which overcomes these difficulties and solves these problems, and which is capable of effecting significant manufacturing economies.

Other and more specific objects of the invention have to do with the provision of an exhaust tubing assembly which most advantageously adapts itself to efficient production line procedure, which effectively reduces the possibilities of slow air leaks occurring at the seal between the tubulation and the tube envelope,

2,704,169 Patented Mar. 15, 1955 2 which makes it possible to mount a major portion of the tubulation after the cathode ray tube has been fully constructed and immediately before exhausting is carried out, and which makes feasible the salvage of tubes should said major portion become damaged. 7

-According to a broader aspect of the invention, the novel tubulation or exhaust tubing assembly includes two main sections, one of which is considerably shorter than the other. The shorter section is adapted to be coupled first with the tube envelope and then with the longer section. The tubulation sections are advantageously made up of separate metallic parts or pieces, each of which has peculiar characteristics whereby the shorter section can be readily sealed to the tube envelope and the longer section can be effectively brazed to the shorter section without danger of deleteriously affecting the seal between said shorter section and the tube envelope. According to a narrower aspect of the invention, the exhaust tubulation comprises three metallic pieces adapted for rigid connection with each other in generally concentric relationship. One of these pieces has the general form of a. centrally apertured flanged or dish-shaped button adapted to occupy an opening in the tube envelope; another of said pieces has the general form of a short tubular element adapted for connection with said button to project perpendicularly therefrom in line with the aperture thereof; and the remaining or third piece has the general form of an elongated tubular member adapted for connection with said short tubular element to extend concentrically therefrom. An important and significant advantage of the above stated arrangement, is that the cathode ray tube can be fully assembled before the longer tubing section is added to the shorter section to complete the exhaust tubulation. As a result, assembly of the tube is considerably facilitated due to the fact that the shorter section which is initially coupled to the tube envelope, presents no serious hindrance to the handling of the tube. Also, the fact that the elongated tubular member is brazed to the. shorter tubular section rather than directly to the button at the tube envelope, is singularly important because it permits removal and replacement of the elongated member without disturbing the metal-to-glass seal, in the event of damage to said member or to the brazed joint between said member and the shorter t bulation section.

The novel features of the invention and the manner in which the above mentioned and other objects and advantages are best achieved, will clearly appear from the following description of the embodiment shown in the accompanying drawing, in which:

Figure 1 is an elevational view of a cathode ray tube provided with an exhaust tubulation constructed in accordance with the invention, a portion of the tube envelope being broken away to illustrate internal structure;

Figure 2 is an enlarged sectional view taken substantially along line 2-2 of Figure 1; and

Figure 3 is an exploded view, in perspective,- illustrating the parts of the exhaust tubulation, shown in Figure 2.

With more particular reference to the drawing, the cathode ray tube illustrated in Figure l is fully assembled and ready to be evacuated and sealed off. As shown, the tube envelope, generally designated at 10, is constructed of glass and comprises an enlarged bulbous portion 11 and an elongated neck portion 12.

"The bulbous portion is provided with a flattened face 13, the internal surface of which is coated with a fluorescent substance 14 forming a luminescent screen.

of a layer of conductive material a which serves as a high potential anode.

The procedure commonly followed in processing a tube of the above described variety generally includes, as successive steps,'washing the tube envelope, applying the fluorescent screen substance to the face of the tube, coating the bulbous and neck portions of the tube with conductive material, inserting and mounting the gun structure within the tube envelope, evacuating the tube and activating the cathode of the gun structure and, thereafter, sealing the tube. In order to carry out the evacuation and sealing operations, the tube envelope is ordinarily provided with an elongated exhaust tubulation of suitable material, such as glass or copper. According to common practice, the tubulation is sealed to the glass of the tube envelope, at the glass fusion ternperature, prior to the processing of the tube, so as to 1nsure that the washing of the tube will remove impurities likely to accumulate within the tube envelope as a result of the coupling of the tubulation with said envelope, which impurities are apt to have deleterious eifects on the fluorescent screen, as well as on the proper operation of the cathode ray tube. It will be understood that an elongated tubulation projecting for a substantial distance from the tube, not only complicates handling of the tube but, further, creates a condition in which the tubulation, during the entire processing of the tube, is in constant danger of being broken or damaged.

In accordance with the present invention, the tubulation is constructed of two distinct main sections generally indicated at 18 and 19, respectively. The section 18, which is of a length considerably shorter than the length of section 19, is adapted to be aflixed to the tube envelope prior to the initial processing of the tube, that is, prior to the washing operation, whereas the other or longer section 19 is adapted to be added to said shorter section after the tube has been completely processed except for exhausting and finally sealing the tube. In this manner, the shorter section of the tubulation which is mounted directly on the tube envelope, presents no serious hindrance to handling of the tube during its processing, since most of the handling is done without the presence of the elongated tubulation.

In the illustrated embodiment, and as can be best seen in Figure 2, the shorter section 18 is made up of two pieces, one piece being in the form of a flanged or generally dish-shaped metal button 18a, the other piece being in the form of a short tubular metal element 18b. The flanged or dish-shaped button is provided with a central aperture 20, and the short tubular element has one of its ends, as indicated at 21, joined with said button so that said element extends substantially perpendicularly to said button and in line with the aperture in the latter. The flanged or dished portion of button 18a is configured to fit snugly within an opening 22 in the tube envelope into which said button is fixedly secured by means of a metal-to-glass seal. The longer section 19 consists of a single piece in the form of an elongated tubular metal member which (see Figure 2) has one end portion fixedly joined, as indicated at 23, to the free end portion of element 18b of the short tubulation section, so that said member extends contiguously and concentrically with respect to said short section.

According to the invention, the three metal pieces which are shown separately in Figure 2 and which, when assembled, constitute the complete tubulation as illustrated in Figures 1 and 2, are of such a character that the button 18a and the tubular element 18b can be adequately welded together, that said button 18a can be efiectively sealed onto the tube envelope, that said short tubular element and the elongated tubular member 19 can be readily brazed without danger of deleteriously affecting the metal-to-glass seal, and that said elongated tubular member can be conveniently cold-worked to effect pinch-off and to provide a hermetic seal, as is represented in broken lines at 24 in Figure 2. Thus, in accordancewith the invention, the metal employed for the button 18a should have substantially the same coefiicient of thermal expansion as glass; the metal employed for the short tubular element 18b should have a low coefficient of thermal conductivity so that the elongated member 19 can be brazed to said element without unduly increasing the temperature gradient at the metalto-glass seal; and the metal employed for the elongated tubular member 19a should be susceptible of cold-working, to provide the final seal by mere mechanical pinching operation. While any suitable metal having the above mentioned general properties may be used, 1t has been found that, in practice, the requirements of the invention are best achieved when the button 181: is made of chromium-nickel-iron alloy, when the tubular element 18b is made of nickel, and when the tubular member 19 is made of oxygen-free high-constructivity copper. A suitable alloy for the button is available on the market and is known as Allegheny #4 Alloy which is composed, substantially. of 6% chromium, 42% nickel and 52% iron. The chromium-nickel-iron alloy is such that it matches the glass customarily used in the manufacture of the tube envelope and, accordingly, assures a good vacuum seal all around the disk 18a; the nickel insures against corrosion, is unaffected by oxidation of the mentioned alloy, has an electrical resistance sufiiciently high to insure a good projection-welded joint, and has a melting point high enough to insure against the occurrence of leaks, at said welded joint, due to application of heat when effecting the metal-to-glass seal; and the cooper is not only best suited to ready brazing operation but, further, is most adaptable to coldworking.

In carrying out the invention, the short tubulation section 18 is assembled by projection welding the nickel tubular element 18b to the preformed alloy button 18a. The button is then oxidized and, if desired, glazed by application of a thin coat of glass similar to that used in making the tube envelope. The short tubulation section is then mounted on the tube envelope. This is accomplished b inserting the button into the opening provided in the tube envelope and sealing said button to the glass of the tube, in the customary manner. It is to be noted that the wall which defines the opening in the tube envelope is inwardly slanted and that the marginal surface of the button is correspondingly tapered, so that proper seating of said button within said opening is assured. The tube with the short tubulation section at tached thereto, is then put through the hereinbefore mentioned processing steps, that is, the tube is washed, the fluorescent and the conductive coatings are applied to the appropriate internal surfaces of the tube, the electron gun structure is mounted in the neck portion of the tube and connected with the terminals on the supporting cap, and said cap is afiixed to the end of said neck portion. At this point in the processing of the tube, the copper elongated tubular member 19 is, in accordance with the invention, added onto the mentioned shorter section by engaging and brazing one end portion of said member with the projected end portion of the nickel short tubing element 18b. The tube envelope is then evacuated and the cathode of the electron gun is activated, after which the tube is finally sealed by mechanically pinching the copper tubulation section. This is conveniently accomplished by means of steel mandrels operated to apply from 3500 to 5000 lbs. total pressure on opposite sides of the copper tubing. In practlce, the copper tubing is pinched off at a point in prox1m1ty to the short tubulation section which can then advantageously serve as the high voltage contact terminal, the connection between said short section and the internal conductive coating being accomplished by the mere expedient of applying said coating so that it extends over the inner marginal edge of the coupling but- It will be appreciated that, in accordance with the invention, the interposition of the nickel element 18b WhlCh 1s capable of being readily welded to the alloy button 18a and to which the copper tubing sections 19 can be adequately brazed, is an important feature of the above described novel tubulation assembly. It will be understood that if the cooper section were brazed dlrectly to the alloy button, after sealing of the button to the glass of the tube and after otherwise processing the tube, then the heat necessary to eifect the brazed oint, is apt to cause fracture of glass and contamination of the fluorescent screen. If, alternatively, the copper section is brazed to the alloy button prior to sealing the latter to the glass of the tube and before processing the tube, then the heat necessary to effect the metal-toglass seal, is llkely to create leaks at the brazed joint, as well as to contaminate the fluorescent substance when applled internally, to the face of the tube. Accordingly, the nickel element 18b, in the hereinbefore described arrangement, has a twofold advantage: firstly, it makes it possible fully to assemble the tube without having to contend with a long tubulation projecting from the tube envelope; secondly, it makes it possible to complete the tubulation by addition of a readily workable tubular copper section without danger of contaminating the tube or of occasioning leaks in the tube structure.

We claim:

1. In combination with the envelope of an electronic tube having an exhaust opening, a tubulation for evacuating and finally sealing said envelope, comprising a tubulation section consisting of two pieces, one piece made of metallic alloy adapted to be sealed to the tube envelope, the other piece made of metal adapted to be welded to said one piece and capable of being heated without substantially increasing the temperature gradient at the seal between said one piece and the tube envelope, a second tubulation section consisting of a single piece made of metal adapted to be brazed to said other piece of the first mentioned tubulation section and susceptible of being pinched to effect final sealing of the tube envelope, a sealed joint connecting said one piece of the first mentioned tubulation section with the tube envelope at its said opening, a welded joint interconnecting said two pieces of the first mentioned tubulation section, and a brazed joint connecting said second tubulation section with said other piece of said first mentioned tubulation section.

2. In combination with the glass envelope of an electronic tube having an exhaust opening, a tubulation for evacuating and finally sealing said glass envelope, comprising a tubulation section consisting of two pieces, one piece made of alloy having the same coefiicient of thermal expansion as the glass of the tube envelope and adapted to be joined to the latter by a metal-to-glass seal, the other piece made of metal adapted to be welded to said one piece and capable of being heated without substantially increasing the temperature gradient at said metal-to-glass seal, a second tubulation section consisting of a single piece made of metal adapted to be brazed to said other piece of the first mentioned tubulation section and susceptible of being pinched to efiect final sealing of the tube envelope, a metal-to-glass seal connecting said one piece of the first mentioned tubulation section with the tube envelope at its said opening, a welded joint interconnecting said two pieces of the first mentioned tubulation section, and a brazed joint connecting said second tubulation section with said other piece of said first mentioned tubulation section.

3. In combination with the envelope of an electronic tube having an exhaust opening, a tubulation for evacuating and sealing said envelope, comprising a centrally apertured button-like piece, a generally tubular element extending from said piece in line with the aperture therein, an elongated generally tubular member projecting concentrically from said element and as a continuation thereof, a hermetic seal between said piece and the tube envelope as its said opening, a welded joint between one end portion of said member and the apertured portion of said piece, and a brazed joint between one end portion of said element and the other end portion of said member, said element having a low coefficient of thermal conductivity to prevent undue increase of the temperature gradient at said seal due to application of heat in providing said brazed joint.

4. In combination with the glass envelope of an electronic tube having an exhaust opening, a tubulation for evacuating and sealing said glass envelope, comprising a centrally apertured button-like piece, a generally tubular element extending from said piece in line with the aperture therein, an elongated generally tubular member projecting concentrically from said element and as a continuation thereof, a metal-to-glass seal between said piece and the glass of the tube envelope at its said opening, a welded joint between said piece and member and a brazed joint between said element and said member, said element having a low coefiicient of thermal conductivity to prevent undue increase in the temperature gradient at the metal-to-glass seal due to application of heat in providing said brazed joint.

5. In combination with the glass envelope of an electronic tube having an exhaust opening, a tubulation for evacuating and sealing said glass envelope, comprising a centrally apertured button-like piece made of chromiumnickel-iron alloy, a generally tubular element made of nickel and extending from said piece in line with the aperture therein, an elongated generally tubular member made of copper projecting concentrically from said element and as a continuation thereof, a metal-to-glass seal between said piece and the glass of the tube envelope at its said opening, a welded joint between one end portion of said element and the apertured portion of said piece, and a brazed joint between the other end portion of said element and one end portion of said member.

References Cited in the file of this patent UNITED STATES PATENTS 1,613,461 Johnson Jan. 4, 1927 1,940,870 Litton Dec. 26, 1933 2,137,097 Sateren Nov. 15, 1938 2,275,864 Record Mar. 10, 1942 2,279,831 Lempert Apr. 14, 1942 2,291,973 Marshall Aug. 4, 1942 2,441,841 Phelps May 18, 1948 2,479,032 Thibieroz Aug. 16, 1949 2,506,633 Engstrom May 9, 1950 2,570,425 Bocciarelli Oct. 9, 1951 OTHER REFERENCES Product Engineering of July, 1947, Methods for Placing Brazing, page 124.

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