US2804564A - Getter structure - Google Patents

Description

Aug. 27, 1957 w. M. COUCH, JR

GETTER STRUCTURE Filed April 28, 1954 FIG.|

INVENTOR.

WIL'LIAM M. GOUGH,JR-.

ATTORNEY llnited States Patent 2,804,564 Patented Aug. 2'7, 1957 GETTER STRUCTURE William M. Couch, Jn, New Canaan, Conn, assignor to Maehlett Laboratories, Incorporated, Springtlale, Conn, a corporation of Connecticut Application April 28, 1954, Serial No. 426,228

4 Claims. (Cl. 313-180) This invention relates to a novel getter structure for us in vacuum tubes. More specifically, this invention relates to the physical mounting of the getter structure to avoid its breakage and the loss of metallic gettering particles into the envelope.

Metallic particles which are permitted to become loose within a vacuum envelope can be the source of a great deal of difficulty. If they reach the active electrode surfaces, they may prove contaminating to the electrode materials or exhibit properties which are undesirable for the particular electrode involved. Even where they do not reach the electrodes, however, such particles may have deleterious effects. For instance, in high voltage tubes such as X-ray tubes and X-ray valves, such particles accumulating on an envelope portion may acquire a charge which in turn may result in the bombardment and puncture of the envelope.

It has become common to employ getter wire which consists of a core of metallic particles of barium or other getter material within a tubular metallic sheath. Such getter wire is commonly manufactured in long lengths or coils of wire which may be cut to suitable lengths for use in a particular tube. Where the getter wire is cut, the core of particles is exposed. Loose particles from the ends of such getter wire have heretofore fallen out into the vacuum envelope during the manufacture, storage or use of a tube and have proved harmful to the performance of the tube or shortened the life of the tube.

The present invention prevents the loss of metallic particles from the ends of getter wire into the vacuum envelope. Such loss of particles is prevented by closing the ends of the getter wire. Rather than using soldering techniques or other techniques involving heat which might adversely effect the later performance of the getter, the present invention employs a mechanical expedient which is most effective yet cannot prove harmful to the getter. This expedient is the use of cup-like members the sidewalls of which snugly engage the ends of the getter wire.

In the prior art the getter element has often served as its own heating element. Frequently the getter wire has broken before it has served all of its useful life. When the getter wire has broken, it has, of course, been impossible for it to conduct or function further as its own heater. Further activation of the getter has thus been impossible. As a result of this getter failure, tube life has been decreased due to gassiness. Of more immediate consequence, however, has been the lose of getter particles into the vacuum envelope out of the broken getter wire.

In the present invention a heater element is provided which is separate from and in addition to the getter Wire itself. This heater element is placed in close proximity to the getter so that it will function efficiently to cause the blowing of the getter at an appropriate time. The heater wire is advantageously composed of a refractory wire of relatively small diameter compared with the getter wire and is advantageously wound in a generally helical form around the getter wire. The heater wire is much less likely to break than is the getter wire itself, despite its smaller diameter. Thus the heater wire mechanically reinforces the getter against breakage as well as spares the getter wire the additional burden of acting as its own heater. Accordingly, the getter Wire is permitted to function efficiently over the entire useful life of the getter material which it contains.

For a better understanding of the present invention reference is made to the following drawings:

Fig. 1 illustrates a vertical section of a portion of a vacuum envelope in the region of the stem press showing the method of mounting the getter structure, which is shown in elevation;

Fig. 2 is an enlarged plan view from above of the getter structure illustrated in Fig. l;

of Fig. 1;

Fig. 4 illustratesin cross-section the construction of the getter wire employed in the getter of the present invention.

Referring now to Fig. 1, it may be seen that the getter structure is supported upon a pair of lead-in Wires 10 and 11 which penetrate stem press 12. Press 12 terminates a reentrant portion 13 of a vacuum envelope. The vacuum envelope may be of any conventional type and its shape and size will, of course, depend upon the nature of the tube and the size, shape and relationship of the electrodes employed therein.

Also penetrating press 12 are leads l4 and 15 which provide leading-in connections for the filament. Outside of the vacuum envelope, leads 10, 11, 14 and 15 are terminated in flexible leads 10, 11', 14 and 15', respectively.

Within the vacuum envelope leads 10 and 11 are terminated in wide spaced parallel portions. Extending between these parallel portions of leads 10 and 11 is a getter wire 20. The getter wire 20 is entwined with a heater wire 21 of refractory metal which follows a general helical path around the getter wire 20. Enclosing the ends of getter wire 20 are cup-like members 22 and 23 which advantageously are composed of pieces of nickel tubing closed at one end by squeezing together and sealed by welding. Actually the cups are made sufficiently large to enclose several turns of the heater wire. The snug engagement of the heater wire which is in turn wrapped tightly about the getter wire, prevents the loss of getter particles from cups 22 and 23.

In addition to enclosing the ends of getter wire 29, cup- like members 22 and 23 serve as conductors. As conductors their snug engagement of heater wire 21 mechanically provides good electrical contact between the heater wire 21 and its enclosing cup. Since the getter wire is preferably arranged in a semicircular pattern as shown, it is possible to complete the electrical path through the heater wire by welding Wire 10 to cup 23 and wire 11 to cup 22. It will be noted from Fig. 2 that in the semi-circular pattern shown, the respective cup members are fixed to the outside of lead supports 10 and 11. U-shaped baffle member 24 is arranged with its side walls parallel with the longitudinal axis of cups 22 and 23 and the parallel portions of leads 11 and 12. The bottom of U-shaped baffle member 24 is arranged parallel to the diameter of the semi-circle formed by getter wire 20 and parallel to the parallel portions of the supports 10 and 11. Baflle member 24 is supported and held in place by welding it to cup-like member 22. It should be noted that cup-like member 23 is definitely out of contact with bafiie member 24.

Fig. 3 is a side elevational view of the getter structure Referring to Fig. 4 the cross-section of a preferred getter wire construction is illustrated. In this instance, the getter wire is composed of a core 30 of granular or powdered getter material, such as barium or its compounds, and a nickel sheath 31. One wall 31a of nickel sheath 31 is weakened by thinning it down. When a getter wire such as wire 20 is cut, loose particles from 'the getter core 30 are exposed and subject to loss out of the ends of the getter wire. Not only is this getter material lost and hence useless as far as getter purposes are concerned, it frequently becomes distributed. In its distributed form it may be a contaminant, free in the vacuum envelope to settle on the active electrodes and disturb tube characteristics. Use of snug fitting cups 22 and 23 prevents loss of gettering material into the vacuum envelope. These cup members 22 and 23 may be made of nickel tubing or the like which is highly conductive and easily welded to support conductors and 11 and baffle member 24. Likewise, nickel is capable of making good electrical contact with the wire, whether or not it is welded to heater wire 21.

In order to activate the getter of this invention it is necessary to apply a voltage between flexible leads 10' and 11 so that a current may have a path, for instance, through leads 10' and 10 to cup 23; through heater element 21 to cup 22; and thence back through conductor 11 and to flexible lead 11. When a current is applied to heater element 21 the resulting heat will cause the getter, particularly if it is barium, to rupture the thin wall 31a of nickel sheath 31. Preferably this thin wall faces bafile member 24, so that when the getter is fired or blown the metallic barium will be deposited on the baffle instead of on some other less desirable area within the vacuum envelope.

With this structure the getter wire may be heated again and again, whereas when the getter wire is itself used as the conductor, it may easily break from repeated heating or mechanical shock. The refractory heater wire is strong, and the vaporization of the barium will not affect its inherent strength and other physical qualities.

It is, of course, possible to use a getter of the present invention in a shape other than that illustrated. For instance, it can be arranged in a straight line or in an S-shape or in any other convenient shape. In the event that the shape is modified, it may be necessary to employ a different type of baffle structure, or arrange the getter in another location so that the getter material as it is blown will not interfere with the tubes functioning.

Although as previously explained it is not desirable to do so, it is possible in the practice of this invention to use the getter wire as its own heater, and thus eliminate heater element 21. Likewise, it is possible to eliminate cup members 22 and 23 and just use a getter element with a helical heater winding wrapped thereabout.

Many other modifications of the present invention will occur to those skilled in the art. All such modifications within the terms of the claims are intended to be within the scope of spirit of the present invention.

I claim:

1. A getter structure for use within a vacuum envelope comprising a wire embodying an imperforate sheath enclosing a supply of gettering material, the sheath having a wall portion thinned down to weaken it, cup-like members enclosing the ends of said Wire, a refractory metal heater element wire wrapped generally helically around the wire, leads connected to the heater element wire, through which leads a current may be applied to said heater element, and a shield opposite the weakened wall portion of the sheath for accumulation of gettering material thereon upon rupture of the weakened wall.

2. A getter structure for use within a vacuum envelope comprising a getter wire embodying an imperforate sheath enclosing a supply of gettering material, the sheath having a wall portion thinned down to weaken it, cup-like members enclosing the ends of said wire, a heater element wire wrapped around the sheath, leads connected to the respective ends of the heater element wire, through which leads a current may be applied to the heater element wire, and a substantially U-shaped shield opposite the weakened wall of the sheath, the getter wire being formed to a generally semi-circular pattern and being disposed in a plane substantially perpendicular to the bottom of the shield and with its diameter substantially parallel to the bottom of the shield.

3. A gettering device for use within the envelope of a vacuum tube, the device comprising a substantially U- shaped holder mounted in the envelope, a getter wire mounted within the holder and carrying a heater element,

the getter wire embodying a supply of gettering material enclosed by an imperforate metal sheath having a substantially thin wall portion, and leads connected to the heater element through which current may be applied to heat the heater element and consequently heat the gettering material, the thin wall portion of the sheath being directed toward the bottom of the holder whereby upon rupture of the thin wall portion by heated gettering material the holder will collect thereupon gettering material escaping from the sheath.

4. A gettering device for use within the envelope of a vacuum tube, the device comprising a holder mounted in the envelope and embodying a relatively flat baflle portion having parallel end portions disposed at substantially right angles to the bafile portion forming a U-shaped structure, a getter wire mounted on the holder and comprising a supply of gettering material enclosed by an imperforate metal sheath have a thin wall portion directed toward the baffle portion of the holder, metal cuplike members mounted on the ends of the getter wire with one of the cuplike members connected to one of the end portions of the holder supporting the getter wire in position of use, a heater wire encircling the getter wire, and leads connected to the ends of the heater wire whereby current may be applied to heat the heater wire and cause the gettering material to rupture the thin wall of the sheath and be deposited on the baffle portion of the holder.

References Cited in the file of this patent UNITED STATES PATENTS 286,916 Fitz Gerald Oct. 16, 1883 1,712,370 White May 7, 1929 2,273,637 Glover Feb. 17, 1942 2,528,547 Reilly et al. Nov. 7, 1950 2,657,452 Veenemans et a1. Nov. 3, 1953

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