US2502070A

US2502070A - Getter for induction flashing

Info

Publication number: US2502070A
Application number: US71732A
Authority: US
Inventors: Zed J Atlee; Dunmore W Dunk
Original assignee: Dunlee Corp
Current assignee: Dunlee Corp
Priority date: 1949-01-19
Filing date: 1949-01-19
Publication date: 1950-03-28
Anticipated expiration: 1967-03-28

Description

March 28, 1950 '2. J. ATLEE El AL GETTER FOR INDUCTION FLASHING Filed Jan. 19, 1949 "IPiL cl?! INVENTORS Zea J/lf/ee Dwmrofe W. Dun/1 /MM W if o ncy5 Patented Mar. 28 1950 GETTER FOR INDUCTION FLASHING Zed J. Atlee, Des Plaines, and Dunmore W. Dunk,

Lincolnwood, 111., assignors to Dunlee Corporation, Chicago, 111., a corporation of Illinois Application January 19, 1949, Serial No. 71,732

8 Claims. 1

The present invention relates to thermionic tubes, such as X-ray generators, rectifier tubes and the like and more particularly to gettering means incorporated therein.

An important object of the present invention is to provide a new and improved arrangement for gettering means within thermionic tubes.

A further object of the invention is to provide an X-ray generator, with an element containing gettering material which is so mounted that, when flashed, a more efficient disposition of the gettering material is obtained than in the case of similar devices as previously manufactured.

Another object of the invention is to provide a new and improved mounting arrangement for an element containing gettering material within a tube of the class described whereby, upon flashing of the element, the gettering material is substantially confined within a predetermined end portion of the tube envelope.

A still further object of the invention is to provide a new and improved mounting arrangement in X-ray generators and the like devices for the element containing the gettering material whereby the element may be flashed more readily by inductive heating than in the case of tubes as heretofore manufactured and without unduly heating adjacent parts of the tube.

A further important object of the invention is to provide a simple and inexpensive mounting arrangement within X-ray generators and like devices for the element. containing the gettering material whereby, upon flashing of the element, the disposition of the gettering material will be restricted to electrically unstressed portions of the tube envelope.

A still further object of the invention is to provide an X-ray generator with a combined glass-to-metal seal shield and support for an element containing gettering material.

For a consideration of what is believed novel and inventive, attention is directed to the following description in which the foregoing and numerous other important objects and advantages of the invention will become apparent, and which description, taken together with the accompanying drawing, discloses a preferred embodiment of the invention.

Referring to the drawing, Fig. 1 is a partial, sectional view taken substantially longitudinally through an X-ray generator provided with gettering means in accordance with the present in vention; r

Fig. 2 is an enlarged fragmentary sectional view illustrating one of the details of the present relatively inemcient because of the high teminvention; and

Fig. 3 is a plan view illustrating the getter rin incorporated in the present invention.

Referring now to the drawings, in Fig. 1 is shown a portion of a thermionic tube which, in this instance, is an X-ray generator, having a cathode unit I0, and an anode unit H, the two electrode units being enclosed within a glass envelope i2. In accordance with present uniform practice in the industry, the anode electrode III is shown mounted upon the end of a reentrant cylindrical portion [3 of the envelope by means of a glass-to-metal seal indicated at It.

In order to protect the seal Hi from the detrimental efifects of impingement of stray electrons thereupon, a cylindrical metal skirt i5 is preferably mounted upon the anode and which skirt extends in spaced elation around the cylindrical portion I3 and the seal [4. The end of the skirt l5 nearest the active ends of the electrodes fits snugly around the base of the anode unit It and is suitably secured thereto such as by the set screws [6.

The structure as thus far described is in accordance with present common practice in X-ray generatormanufacture. It is, furthermore, common practice to provide a gettering means in a high vacuum tube for rendering innoxious the traces of gas remaining in the tube after the usual exhausting procedure, or as a final step thereof after the tube has been sealed off. It is the purpose of the present invention, however, to provide a more efiicient arrangement of the gettering means than has been employed heretofore.

We are aware of the fact that it has been proposed heretofore to arrange getter elements inside of a glass-to-metal seal shield associated with one of the electrode units, and specific reference is made to the structures shown in Patents 2,260,927, Atlee, and 2,445,257, Atlee. The mounting arrangements for the getter elements as shown in these patents are inherently relatively expensive and, moreover, they cannot be flashed by inductive heating without causing undue heating of remaining metal parts and particularly the metal seal members. Accordingly it was necessary to bring out leads for the getter elements and which were flashed by passing a current flow therethrough from a source of energy connected to the lead terminals. Furthermore, because of the particular arrangement of the getter elements as shown, the gettering material, after flashing of the element, is deposited upon the metal surfaces of the seal shield and other parts so that the material is rendered perature to which these parts are heated during normal operation of the tubes.

In the prior Patent 2,242,160, Atlee, is shown a getter element supported by insulators upon a bracket and which is, in turn, supported upon the end of the seal shield, the getter element being positioned in the end pocket of the envelope whereby, following flashing of the element, the gettering material is deposited upon the inner surface of the glass envelope. While a more efiicient deposition of the gettering material is obtained in this case than in the case of the prior art patents mentioned in the paragraph above, the supporting arrangement for the getter element is relatively complicated and expensive. It will be noted that special guard means are required for preventing passage of gettering material into the main portion of the envelope to the vicinity of the active ends of the electrodes. While such a mounting for the getter element may be employed in the case of tubes having relatively large envelopes, the space requirements are such that it is impractical, if not impossible, to use such an arrangement in tubes of small dimensions. This is true also in the case of getter arrangements shown in the first mentioned patents.

In accordance with the present invention, we mount a getter element in the form of a ring directly upon one of the electrode structures in such a manner so that it may readily be heated inductively by means of high frequency energy without causing undue heating of the remaining parts of the tube. Moreover, the getter ring is so mounted that, upon flashing, the gettering material is deposited upon the inner surface of the end pocket of the envelope for the most efficient functioning thereof. Furthermore, the getter ring is so mounted upon the electrode structure that the structure, itself, forms a barrier, or guard, confining the gettering material to the region of the end pocket and precluding passage of the gettering material toward and deposition thereof upon electrically stressed portions of the envelope. It is not necessary to bring out any leads to external terminals for the getter element nor is it necessary to provide any special bracket or other supporting means therefor. Furthermore, the mounting arrangement of the present invention is extremely compact so that its space requirements are practically nil; and, since no extra parts are required for supporting the getter element, substantial savings in cost of manufacture are effected.

Referring again to the drawing, we provide a getter element in the form of a split ring shown at l! and which, in turn, is mounted within an annular groove is provided on the inner wall of the skirt l5 adjacent the free end thereof. The getter element ll preferably consists of a length of tubula wire filled with a suitable gettering material such as barium, magnesium and, preferably, a mixture of such metals. Ihe wire is of a length slightly less than the inner circumference of the groove l8 and is initially rolled to a diameter somewhat greater than the outside diameter of the skirt !5 as indicated in Fig. 3. For assembly of the getter element, the free ends of the wire are pressed together to a position indicated by dotted lines in Fig. 3 and, following insertion of the ring into the end of the skirt, the wire will expand due to its inherent resiliency and fit snugly within the groove 58. One side of the getter wire is ground away so as to produce a reduced section 2! and the ring is preferably so assembled within the skirt I5 that the reduced side of the ring faces toward the bottom of the groove [8.

In conditioning the X-ray tube for operation, it is necessary to remove all of the gas present within the envelope as well as the occluded gas contained in the electrodes and in the material of the envelope itself. The occluded gases are removed by baking or otherwise heat treating the entire device at a temperature slightly less than the softening point of the glass while keeping the exhaust means in operation. After all of the gas, including the occluded gases and oth-- er impurities, have thus been removed from the envelope, the exhaust connection may be sealed off and, as a final step, the getter element is flashed in order to form end products of the gettering material and any trace of gas or other impurities remaining in the envelope are rendered innocuous thereby.

With the getter element arranged as described, it may readily be flashed by inductive heating by passing high frequency electric energy through an externally arranged coil indicated at 22. Attention is directed to the fact that, for flashing the getter ring ll, only the free end of the skirt 15 need be positioned Within the induction coil 22. Because of the fact that the metal skirt i5 is electrically conductive, it will be heated by the '2 electrical currents induced therein and which heat is rapidly transmitted to the getter ring ll. Of course, some heat will be generated within the getter ring by electrical induction. Because of the fact that the skirt l5 surrounds the seal M, the metal part thereof is substantially shielded from inductive currents so that it is not heated to an extent likely to cause softening of the glass joined thereto and impairment of the seal.

Particular attention is directed to the fact that the free end of the skirt 15 faces and extends into the pocket 24 formed between the reentrant portion l3 and the adjacent outer wall portion 25 of the envelope. This end of the skirt is particularly well suited for supporting the getter element for the reason that the adjacent envelope walls defining the pocket 2 5 are electrically unstressed and hence are relatively cool throughout the operation of the tube. This is particularly true in the event that the tube is of the oil immersion type, such as an X-ray generator adapted to be mounted within an enclosing housing containing either oil or gaseous dielectric cooling medium. Upon fiashing of the getter ring H, the gettering material escaping through 5 the thin Wall section 2| of the tubular wire in volatilized form condenses upon contact with the relatively cool surfaces of the inner walls of the envelope defining the pocket 24 as indicated by the dotted area. In the manufacture of tubes in accordance with the present invention, the deposition of the gettering material is strictly confined within the area of the pocket M as indicated by a relatively sharp line of demarcation at the end of the deposit substantially in the radial plane of the free end of the skirt l5 and as indicated by the edge of the deposit 26.

An important feature of the present invention resides in the fact that the flashing of the getter, and. the extent thereof, can be closely observed by watching the density of the deposit upon the inner walls of the pocket 24 during the flashing operation. Excessive heating of the tube parts can be easily avoided by noting carefully when the getter commences to flash and discontinuing further heating after a deposit of desired density the tube and which are absorbed by the deposit of gettering material so long as the tube walls on which the deposit is formed are maintained relatively cool. The portion of the tube defining the pocket 24 is remote from both the filament and the anode target so that it is one of the coolest parts of the tube.

While the invention has been described with reference to the getter ring mounted on the inner side ofa glass-to-metal shield skirt, it is to be understood that this shield skirt merely forms a convenient mounting in a tube of the class described. Insofar as the present invention is concerned, the shield skirt, in effect, merely provides a barrier extending between the getter ring and the central portion of the tube whereby the gettering material volatilized from the .ring upon flashing thereof is retained entirely within the end pocket 24 and permits deposition of the gettering material upon the envelope side walls thereof. It is understood that the volatilized gettering material escaping from the getter ring disperses in a straight line; and, for this reason, it is necessary that the getter ring be arranged only slightly inwardly from the free end of the skirt l5. It is, of course, not essential that the ring be mounted within a groove I8 as shown; but this is preferred merely for reasons of space factor, simplicity, ease of construction and also the ease with which it may be flashed without unduly heating remaining adjacent parts of the tube.

While the invention has been described with particular reference to a certain embodiment thereof, it is desired that it be understood that various changes and modifications may be made without departing from the spirit and scope of the invention. It is desired, therefore, that it be expressly understood that the illustrated embodiment is merely by way of exemplification rather than by way of limitation.

What we claim as our invention is:

I. In an X-ray generator having a pair of spaced apart electrode units enclosed within a glass envelope, the invention comprising a metallic, cylindrical glass-to-metal seal shield mounted by one end on one of said units, the inner wall of said shield being provided with an annular groove and an annular getter ring mounted within said groove and retained in position thereby.

2. In an X-ray generator having a pair of spaced apart electrode units enclosed within a glass envelope, the invention comprising a metallic, cylindrical, glass-to-metal seal shield mounted by one end on one of said units, the space within said shield being in open communication with the remaining space within said envelope only by way of the free end of said shield, the inner wall of said shield being provided with an annular groove adjacent the free end thereof and a split metallic annular getter ring mounted within said groove and retained in position by the resiliency of said ring.

3. In an X-ray generator having a pair of spaced apart electrode units enclosed within a glass envelope, said envelope including a reentrant sleeve portion defining a pocket in one end of said envelope, one of said units being mounted on the end of said sleeve, a glass-tometal seal between said one unit and said sleeve portion, the invention comprising a cylindrical metal skirt annularly secured at one end to the base portion of said one electrode unit, the free end of said skirt extending around said seal in spaced relation therewith, the inner wall of said skirt being provided with an annular groove adjacent the free end thereof, an annular getter element comprising a metal sheath containing gettering material, said getter element being mounted within said groove and retained therewithin by the resiliency thereof.

4. In an X-ray generator comprising a pair of spaced apart electrode units enclosed within a glass envelope, said envelope including a reentrant sleeve portion defining a pocket in one end of said envelope, one of said units being mounted on the end of said sleeve, a glass-tometal seal between said one unit and said sleeve portion, the invention comprising a cylindrical, metal skirt annularly secured at one end to the base portion of said one electrode unit, the inner wall of said skirt being provided with a recess, and a getter element comprising a metal sheath containing a gettering material mounted within said recess.

5. In an X-ray generator having a pair of spaced apart electrodes enclosed within a glass envelope, a glass-to-metal seal mounting one of said electrodes in one end of said envelope, the invention comprising a cylindrical, metal, seal shield mounted by one end on said one electrode, an annular getter element secured to the inner surface of said shield adjacent the free end thereof, said getter element being arranged in contacting relation with the surface of said shield substantially throughout the full length of said element.

6. In an X-ray generator having anode and cathode electrodes enclosed within a glass envelope, said envelope including a reentrant sleeve portion defining a pocket in one end of said en velope, one of said electrodes being mounted on the end of said sleeve, a seal between said one electrode and said sleeve portion, the invention comprising a cylindrical, metal skirt annularly secured at one end to the base portion of said one electrode, the free end of said skirt extending around said seal in spaced relation therewith, an annular getter element comprising a sheath filled with gettering material mounted directly upon the end portion of said skirt and concentrically therewith, the diameter of said skirt being greater than the diameter of said element whereby said skirt provides a barrier for precluding passage of gettering material from the region of said pocket to the remainder of the space within said envelope upon the flashing of said element, said getter element being exposed in straight line relation with the inner walls of said envelope defining said pocket whereby, upon flashing of said element, gettering material therefrom will deposit upon the inner walls of said pocket.

7. In a thermionic tube having anode and cathode electrode units enclosed within a glass envelope, said envelope including a reentrant sleeve portion defining a pocket in one end of said envelope, one of said units being mounted on one end of said sleeve, said one unit including a cylindrical, metal member having a diameter greater than said sleeve portion, the invention comprising a getter ring consisting of a metallic sheath filled with gettering material, said ring being adapted to be flashed by inductive heating from a source of energy arranged externally of said tube, means mounting said ring upon said member in thermally and electrically conductive relation with respect thereto, said ring having a diameter substantially greater than the diameter of said sleeve portion but less than the diameter of said membeiysaid ring being mounted concentrically with said sleeve portion and said 1nemher, said ring being exposed in direct line relation to the inner surface of said envelope pocket, said member defining a barrier between said ring and the inner wall surfaces of said envelope beyond the region of said pocket whereby, upon flashing of said ring by inductive heating, said gettering material is deposited upon the walls of said envelope pocket, the barrier formed by said member precluding passage of gettering material from said pocket to the remaining space within said envelope.

8. In a thermionic tube having anode and cathode electrode structures enclosed within a glass envelope, said envelope including a reentrant sleeve portion defining a pocket in one end of said envelope, one of said structures being mounted on the end of said sleeve portion, an annular glass-to-metal seal between said one structure and said sleeve portion, the invention comprising an annular metal member adjacent said seal forming a part of said one structure having an outside diameter greater than the diameter of said seal, an annular getter element consisting of a length of hollow wire filled with gettering material, said getter element being adapted to be flashed by inductive heating through means of high frequency energy supplied from externally of said tube, said getter element having a diameter less than that of said member and greater than that of said seal, means mounting said getter element on said member closely adjacent thereto on the side thereof facing said pocket, said element being exposed in straight line relation with respect to the envelope surface defining said pocket, said member defining a barrier between all portions of said element and the space within said envelope on the opposite side of said member with respect to said element whereby, upon flashing of said element, all gettering material therefrom will be retained within said pocket.

ZED J. ATLEE.

DUNMORE W. DUNK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,260,927 Atlee Oct. 28, 1941 2,275,864 Record Mar. 10, 1942 2,341,941 Mouromtsefi et al. Feb. 15, 1944