US3508105A

US3508105A - Getter arrangement for cathode-ray tubes

Info

Publication number: US3508105A
Application number: US704712A
Authority: US
Inventors: Nicholas P Pappadis
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1968-02-12
Filing date: 1968-02-12
Publication date: 1970-04-21
Anticipated expiration: 1987-04-21

Description

April 21, 1970 N. -P. PAPPADIS GETTER ARRANGEMENT FOR CATHODE-RAY TUBES Filed Aug. 12. 1968 co oSmccoo uwx wm II-X INVENTOR.

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United States Patent 3 508 105 GETTER ARRANGEMENT FOR CATHODE-RAY TUBES Nicholas P. Pappadis, Chicago, Ill., assignor to Zenith Radio Corporation, a corporation of Delaware Filed Feb. 12, 1968, Ser. No. 704,712 Int. Cl. H01 19/ 70, 7/18 US. Cl. 313-178 2 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The present invention is directed to an improved getter arrangement for cathode-ray tubes and, while of general applicability, is especially beneficial to color picture tubes and, for convenience, will be described in that connection.

Color television tubes as currently manufactured include a gun mount which is usually a delta array of three guns positioned within the neck of the tube envelope. A tri-color screen is supported at the opposite end of the envelope and an aperture mask positioned very close to the screen permits color selection by providing that the electron beam issued from each gun of the mount, in passing through the apertures of the mask, is able to impinge upon a single assigned one of the three color phosphors customarily constituting a tri-color screen. This structure is, of course, very well known.

It is also well known that the efiiciency of operation and the emission life of such tubes depend to a great extent upon the degree of evacuation of the envelope. The life of the cathode varies inversely with the number of gas molecules remaining in the envelope since bombardment of the cathode by residual gas molecules which may become positively ionized by impact with other particles causes deterioration of the electron emissive cathode surface. In the fabrication of such tubes a mechanical pump in combination with a molecular pump is ordinarily employed to remove gas from the envelope. Additionally, a getter substance, usually one of the alkaline earth metals such as barium is employed to absorb gas molecules remaining after the mechanical evacuation process has been completed. Alkaline earth metals have been found to have the property of absorbing large quantities of gas molecules and preventing their accumulation within the envelope. The amount of gas absorbed is proportional to the area covered with the material. In the usual case, the getter material is supported in a position where it may be flashed upon an inner surface of the tube in any of a number of ways known in the art as, for example, by induction heating with a radio-frequency electromagnetic field or current flashing by causing a flow of current through the getter material.

It is, of course, necessary that the getter container be positioned to accomplish its desired function and yet avoid shadowing or other adverse efiects on the tube operation. Accordingly, it has been the practice to utilize a ring-shaped getter container supported on the free end of a spring extending from the end of the gun mount that faces the screen and projecting a considerable distance into the bell of the envelope. The supporting spring is 3,508,105 Patented Apr. 21, 1970 configured to conform with the portion of the envelope over which it extends and it positions the getter ring so that upon being flashed the vapors are directed away from the gun mount and toward the screen. This has the advantage of protecting the electron guns from getter deposits which may lead to stray emission, arcing and other operating defects. It also provides the advantage of depositing the gettering material over a larger area thus greatly increasing the gettering efiiciency.

In the past, however, the getter ring was backed by a ceramic disk and as the gun mount with the appended antenna getter was inserted into the envelope, the ceramic and the supporting spring contacted or scraped against the aquadag coating which would flake and result in unwanted particulate matter within the envelope. It also had the disadvantage that the ceramic constituted a heat sink requiring more power to flash the getter than otherwise.

Accordingly, it is an object of the invention to provide an improved getter arrangement for a cathode-ray tube which avoids disadvantages of the prior art.

It is another specific object of the invention to provide a getter arrangement Which minimizes flaking of the aquadag coating as the gun mount to which the getter is appended is positioned within the tube envelope.

It is still a further object of the invention to provide an improved getter arrangement which reduces the power requirements for flashing the getter.

SUMMARY OF THE INVENTION An improved getter arrangement, embodying the present invention and for use in cathode-ray tubes of the type under considerationcomprises an elongated spring secured at one end to the gun mount of the tube and projecting from the neck of the envelope into the bell portion thereof. This spring has a length very much greater than its width and an unflexed configuration conforming approximately to that of the section of the envelope subtended by the spring. The container for the getter, which is usually a ring-shaped channel, is secured to the opposite end of the spring and has a base facing the envelope. A sled is secured to that base, extends to the envelope and constitutes the only contact between the getter and the envelope. The sled has at least one curvilinear runner configured to make substantially point contact with the envelope as the gun mount and getter arrangement are inserted into position within the envelope.

BRIEF DESCRIPTION OF THE DRAWING The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE 1 is a fragmentary view, partially in cross section, of a tri-color cathode-ray tube embodying a getter arrangement constructed in accordance with the in- Vention;

FIGURE 2 is a view taken along section line 22 of FIGURE 1;

FIGURE 3 is a view showing the operation of inserting the gun mount and getter arrangement into the envelope; and

FIGURE 4 is a cross sectional view taken along section line 44 of FIGURE 3.

3 DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now more particularly to FIGURE 1, there is shown so much of the structure of a tri-color picture tube as necessary for an understanding of a getter arrangement constructed in accordance with the invention for use in that tube. The tube envelope has the usual cylindrical neck extending from a bell-shaped portion 11 which is closed at its other end by a faceplate 12. A tri-color screen 13, which may be backed by a reflecting layer 14 of aluminum, is deposited on the faceplate in 'well-known manner. Usually, the screen is a multiplicity of triads each of which is formed of a dot of green, a dot of blue and a dot of red emitting phosphor. The details of such a screen and the process of depositing the screen with its backing layer onto the faceplate form no part of the present invention and, since they may be formed by processes well understood in the art, they need not be considered further.

The usual shadow mask 15 is supported within the tube envelope in close proximity to screen 13 to achieve color selection. Usually, it is a metallic structure having a generally dome-like configuration and provided with a field of apertures, one for each triad of screen 13.

At the opposite end of the envelope there is a gun mount 20. It is an array of three electron guns arranged in a delta pattern and geometrically converged, that is to say, angularly disposed to the end that three beams issuing from the guns converge at shadow mask 15 at least at the central portion of the mask. Each of the three guns is similar in construction, comprising a cathode for emitting electrons, grids for forming the electrons into a beam and modulating the beam in accordance with luminance and chrominance information and other electrodes for focusing and accelerating the beams through the shadow mask to the tri-color screen. Here again, the gun mount is thoroughly conventional and, per se, is no part of the subject invention so that further detailed description is believed to be unnecessary. The end of tube neck 10 terminates in the usual base 16 having terminal pins through which electrical connections are readily made to the electrodes of the three guns and to the heaters of the several cathodes. The final element of the gun mount closest to screen 13 is a convergence cylinder 21 which supports convergence pole pieces 22.

There are two such pole pieces provided for each beam' and supported by cylinder 21 so that each pair is disposed on opposite sides of the path of travel of an assigned one of the three beams.

Dynamic convergence windings (not shown) are supplied with convergence signals of both the line and field scanning frequencies so that fields established between the pairs of convergence pole pieces may displace the beams as required to maintain their convergence at all points of the scanning raster. Of course, a scanning raster is developed by means of a yoke (not shown) normally positioned about the tube envelope where the bell and neck join. Scanning signals of line and field frequencies are applied to the yoke in the usual fashion for the purposes of deflecting the three beams concurrently across screen 13.

It is also commonplace to provide a conductive coating 17 of colloidal graphite or aquadag as a convenient means for providing a connection from a high voltage terminal (not shown) normally provided in the bell of the envelope to the final anode of the electron guns. This connection is completed from coating 17 to the gun electrodes through the usual snubber springs 23, which, in addition to extending the high voltage to the final anodes of the guns, also center and position the gun mount centrally of the tube axis. As thus far described, the color picture tube of FIGURE 1 is completely conventional in design, construction and operation. The remainder of this description will be confined to its getter arrangement.

This arrangement comprises an elongated spring '30 secured at one end to convergence cylinder 21 of the gun mount and projecting therefrom into the bell-shaped portion 11 of the envelope The spring has a length very much greater than its width and it also has an unflexed configuration conforming approximately to that section of the envelope which it subtends when the gun mount is secured in position within neck 10. The length of the spring permits a getter container 31 which is secured to the opposite or free end of spring 30 to be positioned well within envelope section 11 and yet, due to the configuration of spring 30, be in close proximity to the tube wall. This is highly desirable because the getter is then out of the beam paths as necessary to avoid shadowing even though a wide deflection angle is employed. Container 31 is conveniently in the form of a ring-shaped channel having a closed base which faces the envelope but otherwise open to receive a charge of getter material 32. I

A sled is secured to the base of the getter ring, extending to and constituting the only contact between the getter and the envelope. The sled has at least one, but preferably two curvilinear runners 33 configured to make substantially point contact with the tube envelope as the gun mount and getter arrangement are inserted into position within the envelope.

Structural details of the getter arrangement are clearly shown in FIGURE 2 from which it is apparent that getter ring 31 is secured to spring 30 by means of a metal strap 34 having a width small compared to that of spring 30. Strap 34 is aflixed to the free end of spring 30 by a weld indicated by the cross on the drawing so that the strap, in effect, constitutes an extension of spring 30. The strap has a similar weld to one point on the base of the metallic getter ring 31. The two runners 33 of the sled have identical configuration and are spaced parallel to one another at opposite ends of a brace 35 the central part of which is also welded to strap 34. Dimensionally, the inner diameter of the getter ring is large compared to the width of strap 34 and the spacing of runners 33 is approximately equal to the outside diameter of the getter ring. It will be observed in FIGURE 1 that the free ends 36 of runners 33 are located, due to the configuration of the runners, in a plane located between the base of the getter ring and the wall of the envelope. The length of the runners is chosen so that these free ends 36 extend slightly beyond the getter ring in the general direction of the gun mount. In this way, the runners are shielded and receive no deposit of getter material when the getter has been flashed which is a distinct advantage since getter deposited on the runners will have poor adherence and may readily flake off, giving rise to distinct possibilities of short circuits, arcing and low emission Within the tube.

The gun mount with the described getter arrangement attached is inserted into the tube initially as indicated in FIGURES 3 and 4. The runners 33 which are spaced apart considerably less than the neck diameter of the tube make point contacts with the neck and deflect spring 30 so that the only contact of the getter structure and is supporting spring with the internal surface of the tube envelope is that afforded by the runners. The gun mount is then moved to the right in the view of FIGURE 3 until it arrives in its final position indicated in FIGURE 1.. Throughout this entire movement, it is only the small contact of runners 33 that engages the Walls of the envelope and, therefore, there is a minimum scraping of conductive coating 17. As the gun mount arrives at its final position, getter ring 31 and runners'33 will have passed from neck 10 into the bell 11 permitting spring 30"t0 return toward its unflexed configuration. This positions the getter ring close to the tube wall but at the same time prevents spring 30 from rubbing against coating 17 as the final position of FIGURE 1 is reached.

One structural form of getter arrangement employed successfully in a 25-inch color picture tube was comprised of components having the following dimensions:

Spring 30.008 Inconel No. 600, radius of 2 inches arc length of 4 inches and width .203 inches.

Getter ring 31-.006" thick non-magnetic stainless steel, .985" ring, outside diameter .759", inside ring diameter, depth .085.

Brace 35.045 inch stainless steel with 1.045 inches.

Runners 33.045 inch stainless steel, arc length .451 inch,

radius of .138 inch.

Strap 34.015 x .070" non-magnetic stainless steel,

1.130" long with .125 radius on one end.

The described getter has improved heat transfer characteristics in that there are essentially only two point contacts made to the tube envelope and but a single contact between spring 30 and getter ring 31. In addition to greatly reducing the possibility of flaking conductive coating 17 as the gun mount and getter are installed within the envelope, the arrangement with its improved heat transfer properties permits the getter to be flashed with substantially less power, nearly half that required in the prior art device where the getter ring is backed by a disk of ceramic which tends to serve as a heat sink. Since the power requirement is reduced, there is much less likelihood of softening the getter structure which avoids the possibility of shadowing effects attributable to distortion of the getter when it is flashed. The getter ring faces away from the gun mount so that when the getter is flashed not only is the gun mount protected against unwanted deposits of getter but also there is a large area, namely the inner walls of bell section 11, upon which the vapor may deposit to provide a large gettering area.

While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. In a cathode-ray tube having an envelope with a cylindrical neck portion extending from a bell-shaped portion and further having a gun mount positioned within said neck portion, an improved getter arrangement which comprises:

an elongated spring secured at one end to said gun mount and projecting therefrom into said bell-shaped portion of said envelope, said spring having a length very much greater than its width and an unflexed configuration conforming approximately to that of the section of said envelope subtended. by said spring;

an annular getter container having a radius small compared to that of said neck portion, secured to the opposite end of said spring and having a base facing said section of said envelope;

and a sled secured to said base, extending to said envelope, and constituting the only contact between said getter and said envelope, said sled comprising a support fixed to said base centrally of said container in a plane disposed transversely of said spring and further comprising a pair of similar runners of arcuate configuration individually having a length at least approximately equal to said radius of said container, secured at one end to said support and extending in parallel to one another in the direction of said gun mount on opposite sides of said container and spaced away from the base thereof to make substantially point contact with said envelope as said gun mount and getter arrangement are inserted into position within said envelope.

2. A getter arrangement in accordance with claim 1 in which said runners are formed of arcuate sections of a wire, in which the free end of each of said runners is positioned in a plane between the base of said container and said envelope.

References Cited UNITED STATES PATENTS 2,843,777 7/1958 Szegho 313 X 3,381,805 5/1968 Della Porta et a1. 3l3174 X 3,385,420 5/1968 Della Porta 206-.4 3,390,758 7/1968 Reash et a1. 206-.4

JAMES W. LAWRENCE, Primary Examiner P. C. DEMEO, Assistant Examiner U.S. Cl. X.R. 2060.4