US3560788A

US3560788A - R-f energizable, pan-shaped getter for television tube

Info

Publication number: US3560788A
Application number: US782862A
Authority: US
Inventors: Clair Reash; Vincent Pietrasz
Original assignee: Union Carbide Corp
Current assignee: SAES Getters SpA
Priority date: 1968-12-11
Filing date: 1968-12-11
Publication date: 1971-02-02
Anticipated expiration: 1988-02-02

Abstract

A getter device for mounting in an electron tube to be flashed by induction heating from a circular coil positioned externally of the tube, the getter being a pan-shaped container having a vertical sidewall formed around a circular floor member, with an annular portion of the floor member adjacent the sidewall having a greater thickness than the central core portion of the floor member.

Description

United States Patent Inventors Clair Reash Fairview Park; Vincent Pietrasz, Cleveland, Ohio App]v No 782,862 Filed Dec. 11, 1968 Patented Feb. 2, 1971 Assignee Union Carbide Corporation New York, N.Y. a corporation of New York R-F ENERGIZABLE, PAN-SHAPED GETTER FOR TELEVISION TUBE 6 Claims, 4 Drawing Figs.

US. Cl 313/174, 206/04; 313/180 Int. Cl H0lj 19/70 Field of Search 313/174, 180; 206/04; 316/14, 25

[56] References Cited UNITED STATES PATENTS 2,060,861 11/1936 Glans 206/04 2,077,961 4/1937 Smith 206/04 2,093,273 9/1937 Haslaver 313/180X 3,381,805 5/1968 Della Porta et a1. 313/174X 3,385,420 5/1968 Della Porta 206/04 3,390,758 7/1968 Reash et al. 206/04 3,422,299 l/l969 Morehead .1 313/174 Primary Examiner- Roy Lake Assistant Examiner-Palmer C Demeo Attorneys- Paul A. Rose, Thomas I. OBrien, Harrie M.

Humphreys and Leo A. Plum ABSTRACT: A getter device for mounting in an electron tube to be flashed by induction heating from a circular coil positioned externally of the tube, the getter being a pan-shaped container having a vertical sidewall formed around a circular floor member, with an annular portion of the floor member adjacent the sidewall having a greater thickness than the central core portion of the floor member.

PATENTEDFEB 2|9n $560,788

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ATTORNEY R-F ENERGIZABLE, PAN-SHAPED GETTER FOR TELEVISION TUBE This invention relates to a high yield getter device for use in electron tubes and particularly in television picture tubes.

The use of the getter materials in the manufacture of electronic tubes is well-known. A commonly used getter construction consists of a container, such as an annular U-shaped receptacle, with the getter material pressed into the container. This assembly is mounted in an electron tube, for example a television picture tube. After the tube is evacuated, the residual gases left in the tube are removed by heating the getter container and material therein to a high temperature, suitably by induction heating, whereupon the getter material is flashed or vaporized. The vaporized getter material absorbs or reacts with the residual gases and removes them as low vapor pressure solid condensates and continues to adsorb any further liberated gases throughout the life of the tube.

Usually the getter material comprises a mixture or alloy of metals such as, for example, barium and aluminum. It is the barium component of this mixture which comprises the reactive material. The cleanup of residual gases in the larger sized television picture tubes, and particularly color tubes, requires a relatively large amount of active barium material. For example, color tubes having three electron guns and a metal shadow mask have been considered in the past to require a yield of 125 to 175 mg. of barium. Since the barium-aluminum powder mixture might have contained up to about 50 percent aluminum, the total amount of gettering powder mixture in the container before flashing could be from 250 to 350 mg. It

has also been found desirable to employ exothermic getten'ng powders in color television picture tubes. An exothermic gettering powder can comprise a barium-aluminum alloy or mixture plus about an equal weight of powdered nickel. The nickel reacts exothermically with the aluminum upon heating to supply additional heat for evaporating the barium as well as to assist in forming a solid residue of the unflashed material which remains in the container.

A typical channel ring exothermic getter used in color television tubes may contain, for example, 500 mg. of a 25 percent barium 25 percent aluminum 50 percent nickel exothermic alloy yielding about 125 mg. of barium when fully flashed. The getter container itself may comprise a U-shaped channel formed into a ring of about 25 mm. outside diameter and having a channel width of about 0.1 inch. To fulfill a need for a barium yield greater than 125 mg., getter containers of the above dimensions can be filled with an increased amount of barium-aluminum-nickel alloy, say 600 mg. instead of 500 mg., and a barium yield of about 150 mg. will be obtained. Ifa barium yield significantly in excess of this amount is required, then the length of the channel, and hence the diameter of the ring would have to be increased; or the width or height of the channel would have to be increased. Because of the manner of utilizing the getter container in the tube and because of the getter flashing conditions, it has been found impractical to significantly increase either the diameter of the container or the width or height of the channel for the reasons set out hereafter.

An electron tube, particularly a television picture tube, generally comprises a neck portion in which are located the electron gun or guns and auxiliary equipment; an enlarged bulb portion which terminates in a generally flat viewing screen; and a funnel portion joining the neck and bulb portions. The getter container is often mounted in the funnel portion of the tube. This is accomplished by mounting the getter container at the end of a springlike metallic strip support arm or antenna, the other end of which is fixed to a wall of the electron gun in the neck portion of the tube. The spring is biased to force the getter container against the wall of the tube in the funnel portion, out of the path of the electron tube. An RFinduction heating unit comprising a coil spirally wound in a conical shape which approximates the curve of the tube wall in the funnel area is positioned near this wall of the glass tube opposite the getter container. After the tube is partially evacuated by vacuum pumping and sealed, the coil is energized causing an induced current to flow in the getter container. heating the container and flashing the getter material.

In order to mount the getter container in the funnel portion of the tube, it is necessary to pass the container through the neck portion of the tube into the funnel section. The diameter of this passageway is limited by an internal ridge often found in the tube at the juncture of the neck and funnel portions due to flow of the fused glass during the joining of the neck and funnel portions. It has been found inconvenient to use getter containers over 25 mm. outer diameter because of this passageway limitation. This is especially the case in regard to the insertion in the tube of getter containers which have understructures designed to support the container off the wall of the tube to prevent direct contact of the heated container with the cooler walls of the tube 05 that cracking of the tube will not occur.

It is therefore not generally feasible to increase the barium capacity of getter containers of the channel ring type merely by increasing their outer diameter. Additionally, while the capacity of a channel ring getter container can be increased, by widening the channel, it has been found that such containers do not flash effectively because of an incomplete coupling of the RF field to the inner portions of the widened channel member. For example, a getter capacity of about 1000 mg. can be obtained by increasing the channel width of a 25 mm. container from 0.1 inch to 0.15 inch. However, since the spirally wound coil has an open core, there is a lesser concentration of flux generated at the inner wall of a 0.15 inch wide channel with the result that a lesser heating current is induced in the getter and an incomplete flashing of barium takes place, These problems regarding limitations on the size and configuration of getter containers apply to even the large 25 inch color tubes. At the same time, there is a demand for getters of significantly greater barium yield than the presently available getters for use in these large 25 inch tubes whereby the life of such tubes can be increased by providing additional getter material therein.

In copending application Ser. No. 783,029, entitled High Yield Getter Device, filed simultaneously with this application, there is disclosed a high yield getter comprising a metallic pan-shaped container having a vertical sidewall formed around the perimeter of a floor member with getter material pressed into the space formed by said sidewall and floor member, and an auxiliary heating means at least partially buried in said pressed getter material for conducting heat into the mass of said pressed getter material. The auxiliary heating means disclosed there can comprise a perforated metallic member, for example a disc-shaped piece of screen, buried in the mass of pressed getter material intermediate the top and bottom surfaces thereof with the getter material present in the perforations of said metallic member. This getter container will have a greater mass than the prior art liow yield getter containers and accordingly would require a higher power output to fully heat the container an flash the getter material.

It is the primary object of this invention to provide an improved getter of the pan-shaped container variety whereby additional heating efficiencies are achieved in high yield getters.

According to the present invention, an improved high yield getter is provided for mounting in an electron tube against an inner wall thereof and containing getter material to be flashed by induction heating of said getter by a circular RF field produced by an induction coil positioned externally of said tube wall and opposite said mounted getter, said getter comprising a metallic pan-shaped container having a vertical sidewall formed around a circular floor member with an annular portion of the floor member adjacent the sidewall being of a greater mass, i.e., having a greater thickness, than that of the central core of said floor member, getter material pressed into the space formed by said sidewall and floor member, and in a more specific embodiment, a perforated metallic member at least partially buried in said pressed getter material.

In a specific embodiment of the invention the pan-shaped getter container comprises a circular flange-shaped member having a vertical leg forming the sidewall of the container and a horizontal leg forming an annular shelf, a flat circular floor member resting on and connected to said shelf, getter material pressed into the space formed by said circular flange and floor member, and an auxiliary heating means such as a disc-shaped piece of metallic screen at least partially buried in said pressed getter material.

In the Drawings:

FIG. 1 is a schematic view of the neck and funnel portions of a television picture tube, in cross section, including the getter device of this invention mounted in the antenna position and showing the positioning of the heating coil;

FIG. 2 is a plan view of a high yield getter container of this invention showing the flange-shaped member and flat circular floor member with a screen in place on the floor member but prior to filling of the container with getter material;

FIG. 3 is an end view of the getter container of FIG. 2;

FIG. 4 is a sectional view along the line 4-4 of FIG. 2, but showing the getter container with getter material pressed into the container.

Referring to FIG. 1 there is shown a portion of a typical glass television picture tube. Such a tube may be viewed as having three main parts: a neck portion 11; a funnel portion 12; and the bulb or main tube, only a portion 13 of which is shown. The central axis Q. of the tube extends through these parts. It is of course understood that the division of a tube into such parts is arbitrary and it is not meant here that the getter of this invention can only be used in a funnel portion of a tube. Under suitable circumstances the getter of this invention could be mounted nearer to the gun in the neck of the tube or further into the bulb of the tube as desired. Additionally, it is to be understood that the getter of this invention can be used in other types of electron tubes than the television picture described herein and can also be used in other types of evacuated vessels.

More specifically, an electron gun 14 (or guns in the case of a color tube) is shown positioned in the neck of the tube. An antenna spring or support arm 15 is shown fixed at one end 16 to the sidewall of the gun and having mounted on its opposite end 17 the getter container 18. The support arm 15 is a piece of thin, flexible, flat metal strip such as for example stainless steel or a nickel-base alloy, biased to urge the getter container 18 against the wall 19 of the tube and out of the path of the electron beam. The getter container is supported in a position out of direct contact with the glass wall of the tube by a support member such as 20, otherwise the glass wall might crack if it were contacted directly by the hot getter container.

An RF induction heating coil 21 is shown positioned near the outer wall of the funnel portion of the tube. The coil and getter container must be arranged symmetrically so that the heating currents induced in the getter container are uniform and symmetrical. The RF field generated by this coil can be viewed as comprising elliptical flux lines, the long sides of which loop through the open central core of the coil, being more concentrated at the inner periphery of the individual windings of the coil and increasingly less dense nearer the center axis of the coil. The flux lines then flow around the outside of the coil. Referring again to FIG. 1, the arrow 22 represents the central axis of the coil as well as the getter container. Portions of the elliptical flux lines are represented schematically by the lines 23. Because of the nature of the high frequency RF coil, the diameter of its smallest winding being greater than the diameter of the getter container, and because of the interposition of the getter container in the RF field, the flux lines in the vicinity of the getter container are most concentrated at the periphery of the circular container, as're'presented by the lines 23. The heating currents induced in the getter container are therefore most concentrated in circular patterns near the periphery of the container where these outer portions of the getter container intercept the flux lines. The central portion of the getter container is thus not heated as effectively as the outer portion. However, the vertical sidewall and central core portion of the floor member will abstract heat from the highlyheated peripheral portion of the floor member, thereby preventing the rapid heating of the getter material itself and at the same time requiring the use of excess power in the induction coil to fully heat the getter material.

Referring now to FIGS. 2 through 4, an improved getter is shown which overcomes the above-disclosed difficulties. As seen there, the getter container 24 has a continuous vertical sidewall 25 formed around a circular floor member 26 forming a pan-shaped receptacle into which getter material may be pressed. The getter container has a central core portion 27 and an annular portion 28 encircling this core portion. The annular portion 28 is seen in FIG. 4 to have a greater thickness than the central core portion 27.

In the embodiment shown, the annular portion 28 has a greater thickness than the core portion because of the following considerations: the getter container 24 comprises a circular flange-shaped member 29 made up of a circular vertical sidewall 30 and at right angles thereto, a horizontal annular shelf 31. The flange member 29 thus forms a partially floored container having a central opening coextensive with the central core portion 27. A flat circular floor member 32 having a diameter slightly smaller than the inner diameter of the flange rests on the shelf 31 and is welded thereto at several points around the shelf, thus forming with the flange 29 a pan-shaped receptacle for holding getter material. A screen 33 of the type previously described is shown positioned in the receptacle. FIG. 4 shows the case where the screen was welded in place to the floor member 32 and then getter material 34 was pressed into the container over the screen. The getter material 34 could also have been pressed into the container and then the screen 33 pressed into the getter material.

A getter container of this type, having an outer diameter of 25 mm., may have a flange member made from 0.012 inch thick stock, and have a shelf width sufficient to leave a central opening 27 of about one-half the outer diameter, in the embodiment shown about 14 mm. The flat floor member can be about 0.003 inch in thickness.

The thickness of the container floor will thus be about 0.015 inches at its outer portions around the shelf 28, and about 0.003 inches at its central portion 27. This arrangement of a heavier peripheral member arranged around a lighter core member will allow for more effective heating of the getter material for the following reasons: as explained previously the flux generated by the circular induction coil will be densest at the periphery of the container, i.e., in the shelf region where the greatest concentration of flux exists. The greater thickness of metal in the shelf region provides additional mass for receiving induced currents from the RF field. In other words, a higher heating current will flow in the thicker material of the shelf region 28 than would be the case if the container floor were thinner in this region. At the same time, because the flux concentration is least in the central region 27 of the container, there is no need to have the floor member in this region as thick as it is in the shelf region. The container floor member need only be thick enough to structurally bridge the open core 27 and hold the pressed getter material. While the container floor member also serves to transmit heat to the central mass of getter material, no problems are encountered due to the use of the thinner member 32 because the screen 33, being buried in the getter material, more efficiently contacts and conducts heat into this central mass of getter material. By using this arrangement of a heavy flange member, thin floor member and the screen member, an efficient use of materials is accomplished, free of waste, and designed to most effectively provide large amounts of gettering material. In addition, because the getter container has its mass so positioned relative to the induction coil that the zones of high flux concentration coincide with the areas of high mass in the container, the power supplied to the coil to accomplish the flashing of the getter material is most effectively and economically utilized. If the container were entirely formed from 0.015 inch thick stock. then larger amounts of power would be required to heat the extra mass of metal in the sidewalls and central core portion of the floor member.

The screen 33 serves as an auxiliary heating means during the getter flashing operation as follows. when the induction coil is energized and the getter container heated, the portions of the screen which are near the periphery of the getter container, i.e., in the shelf region 28, take heat from this outer annular portion of the container and conduct it radially inward into the mass of getter material near the center 27 of the container. As a result, this central mass of getter material receives more heat than if there were no screen present. While the container floor member 32 also conducts heat from the shelf region in towards its center, this member only contacts and heats the bottom surface of the packed mass of getter material. The screen 33, being buried in the mass of getter material, contacts additional portions of the mass of getter material and transmits heat to these regions as well. The getter material in the center of the container is thus heated to a flashing temperature and the barium vapor is discharged in a substantially uniform pattern over most areas of the container.

The screen 33 is a metallic mesh of interwoven metal wires. Other types of perforated members may be used as the auxiliary heating means. They need only be metallic to conduct the heat to the central mass of getter material, and should have perforations so as to allow getter material to be in close contact with this heating member andso that the member does not occupy too much of the space in the container which is primarily intended to hold getter material. The auxiliary heating member should extend from the peripheral areas of the getter container in the shelf region to the center of the con tainer. In this way, the auxiliary heating member can take heat from the shelf region where the RF flux is densest and where the mass of the container is greater, whereby the heating effect is greatest; and transmit such heat to the central mass of the getter container where the flux density is least and where the induction heating is lowest. It is not necessary that the auxiliary heating member actually contact the floor member to be heated, since this member will be heated by the hot getter material in the shelf region.

Another advantage of the use of a screen member buried in the getter powder, is that the screen serves to hold the pressed getter material together as a coherent mass, particularly during and after flashing. The screen acts as a reinforcing means and holds the getter residue in the container after flashing, preventing the ejection of any solid particles into the tube interior where such foreign bodies might interfere with operation of the electronic system.

The auxiliary heating member, as well as the getter container itself, should generally be of a metal which will not melt as a result of the getter heating operation, and additionally should be nonmagnetic. Stainless steel mesh, for example S5304, is a suitable material for the screen. The flange 29 and insert floor member 32 can also be stainless steel members of this type.

The getter container also has support structure for mounting in the tube comprising a mounting bar 35 which extends across the underside of the container and which may be welded to the shelf portion 31 of the floor member at

points

36 and 37. A wire support member 20 may be welded at its midpoint 38 to the underside of the mounting bar 35. The antenna support arm 15 is connected at its end 17 to the projecting tab 39 on the mounting bar and the getter container mounted in the tube with the wire support member 20 resting on the tube wall.

The getter device described herein can hold large amounts of getter material. For example a 25 mm. outside diameter container of the type described herein can hold 2000 mg. or more of getter material, either barium-aluminum-nickel exothermic material, barium-aluminum endothermic material, or any other desired getter material. The improved getter containers of this invention providefor the effective and economical heating and efficient flashing of such large amounts of getter material.

While the improved getter containers of this invention have been described with regard to their use in large electron tubes, for example, 25 inch color T.V. tubes, it is understood that such containers can be produced in various sizes and capacities for use in T.V. picture tubes of any diameter as well as any other evacuated device which requires a getter container of high capacity and having efficient heating capabilities.

I claim: I

1. An improved high yield circular pan-shaped getter for mounting in the funnel portion of an electron picture tube against an inner wall thereof and for discharging active getter material into the tube interior when the circular getter is heated by a circular coil positioned externally of said tube wall and arranged coaxially with said mounted getter and energized to create an RF field having flux lines more concentrated at the periphery of the circular getter container than at the central core portion of the getter container, said getter comprising a metallic circular pan-shaped container having a vertical sidewall formed around the perimeter of a circular floor member and having powdered getter material pressed into the space formed by said sidewall and floor member, and with an annular portion of the floor member adjacent the sidewall having a greater thickness than that of the central core portion of the floor member, whereby a greater mass of metal is positioned near the periphery of the circular getter container where the RF flux of the electric field generated by the circular coil is greatest so as to maximize the heating of the getter material in the container.

2. The getter of claim 1 in which the getter container comprises a circular flange-shaped member having a vertical leg forming the sidewall of the container and a horizontal leg forming an annular shelf, and a flat circular floor member resting on and connected to said shelf.

3. The getter of claim 2 in which the diameter of the floor member is just sufficiently smaller than the inner diameter of the sidewall to allow the floor member to fit snugly into the space formed by said sidewall and to rest on the annular shelf.

4. The getter of claim 2 in which a perforated metallic member is at least partially buried in said pressed getter material.

5. The getter of claim 2 in which the thickness of the horizontal annular shelf portion of the circular flange-shaped member is greater than the thickness of the flat circular floor member.

6. The getter of claim 4 in which the perforated metalic member is a disc-shaped piece of metallic screen.