US2692958A - X-ray tube - Google Patents

Description

Oct. 26, 1954 M. J. zuNlcK ETA'. 2,692,958

X-RAY TUBE Filed Aug. 18, 1952 .I 7 MloHAEL .ZHLVJVKICl 52 W//VA JOHN E. lLLmewoRTH ATTORNEY Patented Oct. 26, 1954 X-RAY TUBE Michael J. Zunick, Greenfield, and John E. Illingworth, Waukesha, Wis., assigner-s to General Electric Company, a corporation of New York Application August 18, 1952, Serial No. 304,966

9 Claims. (C1. 313-32) The present invention relates in general to vacuum sealing, and has more particular reference to means for and method of insuring vacuum tightness at relatively thin sections in metal castings, the invention more especially pertaining to the assurance of vacuum tightness in the evacuated envelopes of electron iiow devices, such as X-ray generating tubes, more particularly at thin wall sections of cast metal comprising portions of the anode of the now device and forming portions or its evacuated envelope. The invention comprises subject matter divided from a co-pending application for United States Letters Patent, Serial No. 248,766, filed September 28, 1951.

An X-ray generator tube comprises an electron iiow device embodying an electron emitting cathode, an anode forming an electron target, and a sealed and evacuated envelope enclosing the anode and cathode in spaced apart facing relationship within the envelope. X-rays are produced in such a tube by applying electrical potential be tween the anode and cathode for electron driving purposes, in order to impel electrons, emitted at the cathode, tovvardand upon the electron target portions of the anode, at relatively high velocity, in order to constitute the anode target portions as an X-ray source. The anode and cathode are commonly sealed in openings formed in the envelope, in fashion disposing portions of the anode and cathode structure in said openings, thereby constituting such portions as parts of the sealed and evacuated envelope.

Impingement of electrons on the anode target results in the generation of substantial quantities of heat `which, especially in high powered tubes, tends to deteriorate and ultimately to destroy the target. In the interests of eiiicient X-ray production, the generator tube is usually operated under load conditions producing, in the target, high temperatures of the order of the melting| temperature of the target material; and various expediente are employed for cooling the anode target in order to hold the same at a temperature, during operation of the tube, safely below the temperature at which the target would melt or become otherwise damaged or burned.

Water, oil and air are commonly employed as media for transferring heat away from the anode targets of X-ray generating tubes, Where air is employed as a cooling medium, it is common to provide the anode structure with an extension protecting outwardly of the envelope and carrying heat radiating .ns or other heat dissipating so that anode heat may be conducted from the target, through the body of the anode to the radiating fins, and dissipated thence to circumtively large quantities of anode heat generated in high power tubes when in operation. Accordingly, for high power tube cooling purposes, it is common to continuously deliver a cooling medium, such as oil or water, through a chamber formed in the anode structure immediately behind the target, the medium being circulated between the chamber and anexternal cooler to thus absorb heat from the target into the circulating medium and then extract the heat from the medium outwardlyof the generator and dissipate it to atmosphere. The medium thus circulated in the chamber formed in the anode structure, immediately behind. the target, is normally under pressure of the orderof atmospheric pressure, as distinguished from the low pressure conditions within the evacuated envelope, so that the sectional thickness of the target portions of the anode structure, at said chamber, are required to be vacuum tight in order to preserve the evacuated condition Within the generator envelope.

It is desirable, however, to make the said target portions as thin as possible, in the interests of rapid heat dissipation from the anode target to the circulating medium in the chamber. Anode structures, however, are commonly made of cast metal, usually copper, the target usually comprising a button of refractory material, such as tungsten, embedded in the copper anode structure adjacent the cooling chamber. It has been found necessary, in the past, to design X-ray tube anodes with Walls of thicknesses of the order of not less than S/s" of cast metal, behind the target button and between it and the cooling chamber, because of the relatively coarse granular structure obtained during the casting operation, which tends to open up along the grain boundaries of the constituent material during subsequent heat processing of the casting.

An important object of the present invention is to substantially reduce the sectional thickness in metal castings, as between the target button and the cooling chamber in an X-ray anode structure, while maintaining adequate vacuum tightness at such section of reduced thickness; a further ob ject being to provide an X-ray anode structure embodying minimal Wall thickness immediately behind the target button, in the interests of rapid heat dissipation.

Another important object is to accomplish minimal sectional thickness in cast metal structures,

while maintaining vacuum tightness therein, by incorporating, in the structure, a relatively thin layer or sheet of relatively dense material, such as molybdenum, as a vacuum maintaining insert in the structure at the place or station where vacuum tightness is desired.

Another important object is to incorporate, in a casting comprising a thin cast metal section, a thin plate or shell of dense, substantially impervious material, in order to render the thin cast metal section vacuum tight; a further object being to incorporate such shell or layer in the casting during the formation thereof as such, by applying the shell or plate as an insert in the casting mold and casting the metal into the mold in position to envelop and embed the insert in the cast metal.

Another important object is to provide an X-ray tube anode comprising a metal casting carrying a target button embedded therein at a relatively thin wall portion which defines a coolant circulating chamber in the structure, the casting incorporating a thin layer of molybdenum enveloped in the casting between the button and the cooling chamber.

The foregoing and numerous other objects, advantages and inherent functions of the invention will become apparent as the same is more fully understood from the following description which, taken in conjunction with the accompanying drawings, discloses preferred embodiments of the invention for the purpose of demonstrating the same.

Referring to the drawings:

Fig. 1 is a sectional view of an X-ray generating tube having an anode structure of cast metal, having a thin Wall section containing a vacuum maintaining insert in accordance with the present invention;

Fig. 2 is an enlarged sectional view taken through the anode structure shown in Fig. 1;

Fig. 3 is a sectional view taken substantially along the line 3 3 in Fig. 2;

Fig. 4 is a sectional View taken through another anode structure embodying the invention;

Fig. 5 is a sectional view taken substantially along the line 5-5 in Fig. 4;

Fig. 6 is an exploded View illustrating the manner of mounting the pre-formed target button and the vacuum sealing shell or layer as inserts in an anode casting mo-ld; and

Fig. 7 is a sectional view showing another anode structure embodying the invention.

To illustrate the invention, the drawings show an X-ray generating tube II comprising a cathode I2 embodying an electron emitting element I3', an anode I4 forming an electron target I5, and a sealed evacuated envelope enclosing and supporting the anode and cathode in spaced apart facing relationship within the tube. While the invention is not necessarily limited to any particular form, construction or configuration of the envelope, or of the cathode I2, the envelope, as shown, may comprise a tubular glass element I6 having reentrant end portions I1 and II, forming openings at the opposite ends of the envelope. These end portions may be circumferentially sealed respectively to the anode and cathode structures, in order to hermetically seal the envelope at said openings and to mechanically support the anode and cathode structures respectively upon the reentrant portions I'I and I'I, so that the anode and cathode structures seal said openings and form parts of the envelope structure within the reentrant portions I'I and I1.

The emitting element I3 may comprise a filament suitably supported on and insulated from the cathode structure I2, the lament being connected with lead conductors I8 adapted for connection with a suitable power source outwardly of the envelope, for the purpose of energizing the filament for electron emission. The filament may be connected with the lead conductors I8 through suitable envelope seals, preferably formed in the envelope forming parts of the cathode structure, at the inner end of the reentrant portion I1.

It will, of course, be understood that the generator tube II may be operated for the production of X-rays at the target I5, by energizing the filament I3 for electron emission, as by connecting the conductors I8 with a suitable source of emitter energizing power, While simultaneously applying electron driving potential between the cathode and the anode target, as by connecting the anode and one of the conductors I8 with a suitable source of electron driving potential outwardly of the envelope. To this end, the necessary electrical connection with the ano-de may be made at or through the outwardly exposed envelope forming parts thereof disposed within the reentrant portion II.

Electrons emitted by the lament I3, when energized, may travel as an electron beam I9 from the filament I3 under the influence of the anodecathode electron driving potential, and impinge upon the facing surface of the target I5, thereby constituting the target as a source of X-rays which may be projected thence as an X-ray beam 20.

The present invention is not necessarily limited to any particular anode shape, style or configuration. The anode may comprise a body 2l formed of cast metal, such as copper, into which is set a target button 22 of suitable refractory target material, such as tungsten. Behind the target button 22, the body 2E may form a Wall 2I defining a cavity 23 for the circulation of a cooling fluid in heat exchange relationship with the button 22, through the wall 2 I', for the continuous cooling of the target, the sectional thickness of the cast *metal wall 2I behind the button 22 being of the order of or less, which is ordinarily insufficient to provide vacuum tightness in a cast metal Wall of such thickness. In order to insure vacuum tightness in said relatively thin section of cast metal behind the button 22, a layer 24 of dense, impervious sheet material is embedded in the wall 2 I As shown more particularly in Figs. 1, 2 and 3, the layer 2li may comprise a cup-shaped element having a bottom wall 25 extending in the wall 2|' immediately behind the target button 22, the vertical spacement between the facing surfaces of the button 22 and the wall 25 being of the order of alf", or less.

'I'he member 24 preferably comprises molybdenum and has Wall thickness of the order of from 0.005 to 0.010 so that the combined thickness of copper, molybdenum, and the material of the target 2 I, between the cathode facing surface of the target button and the chamber 23, is of the order of 1/8, or less, of which distance the thickness of the target button accounts for about e' The anode structure, also, if desired, may be formed with staggered partition forming ns 2'6 and 25 extending in the chamber '23. These fins may be integral with the side and bottom walls of the cavity 23 and may include a pair of spaced apart lateral ns 25 extending from one side of the cavity toward the opposite side thereof, as

shown more kparticularlyv in Fig.k 3 of the drawings, and a central, fin 26 spaced from and extending medially between said lateral ns from the. opposite side of the cavity `2'3. These may serve to strengthen the wall structure, and will also serve as defiecting baiiles for cooling fluid circulated iny the chamberBS,A asy hereinafter more fully described.

The anode structure may also include a sleevelike extension 27, one rend of which may be brazed or otherwise sealingly secured on the casting 2 as .at 28, in open communication with the cavity 23. The opposite or open end of the member 21 may be tted with a. `cover member 23 carrying the outer end of a. tube or pipe 30 in position extending outwardly of the cover member 29` for connection with a source of cooling fluid. 'I'he inner end of the pipe. 30, may be sealed,` as. at 3i.in an opening 32 formed lin a. preferably metal disk 33.

This disk may besized to extend snugly with-in` the cavity :23. in position overlying the wallv remote edges of the-1311s 26 and 2.6.', the opening 32. being disposed opposite the wall remote end of the iin. '26. 4outwardly of the fins 26, Athe disk 33 may be. formed with a pair ofcut-out openings 34; and the end closure member v29. may be formed with an outlet opening 35. A. suitable cooling duid may be delivered, as by means of a pump or other circulating device, through the pipe 3b from a source ofsu-ch iluid disposed outwardly of Athe X-ray generator tube. The cooling uid may pass thencev through the` opening. 32 into the cooling chamber 23. Such duid may travel in the chamber 23 through the channels. deiined by and between the baiiles 26 and 26 in heat exchange relationship `withv the target button through its supporting wall portions of the anode. The cooling fluid may be discharged from the chamber 23 through theY openings 34 into the sleeve-like member 2l, and may pass thence through the outletI opening 35 which-if desired, may be 4connected withtheex* ternal sourceof cooling fluid, preferably through suitable means for cooling the fluid for'recircula-l tion to the chamber 23.

In order to seal the anode in the envelope-member 6, the body 2| of the anode may be formed with a peripheral shoulder 33 upon. which is sealed, as by welding or brazing, a cup-shaped seal member 3.1 having annular skirt portions forming a :lip adapted vto form a circumferential glass-to-metal seal 38 with the reentrant envelope portion H, at the inner end thereof. The anode may thus be sealingly mounted. .and supported on the envelope lmember i6 so that the seal `member 3l, as well as portions of the anode including the target supporting Wall portions 2l may form portions of the envelope structure closing the opening formed at the Ainner end of the reentrant portion lf'l.

The present invention, of course, is not necessarily limited to the form and arrangement of theparts of the Ianode structure. As shown more particularly in Figs. 4 vand 5 of the drawings, the body2| may be formed with a single medial partition wall 26 formed integral Withvthe opposite side Walls of the chamber 23 and dividing it `into a pair or compartments on opposite sides of the partition, said partition wall having an edge spaced from the bottom 25 of the cupshaped member to define a slot or opening 23" between said edge and the bottom of the cup. This slot serves to interconnect the compartments 23'I and to assure that the cooling medium, in

flowingfin `thechamber from one compartment tov the other, will pass immediately behind Vthe target, in emcentheat exchange relation therewith.

The disk 33, which covers the open side of the chamber 23, in Figs. 4 and 5', may be formed with inlet and outlet openings 32 and 34 disposed therein in position respectively communicating with thel compartments 23 on opposite'sides of the walls 26", the inlet pipe 30 being sealed in the opening 32, at the inner end of said pipe. The 'disk 33 also Amay be sealed at kits edges to the `inner end Yof the sleeve-like extension '21, which, in turn, may be sealed in the body 2| 'as at 28, and a sealing skirt 31, making a glass-tometal seal 3'8 with a reentrantv glass envelope portion il, vmay be sealed, as at 36, upon peripheral shoulder portions of the body 2l.

An enclosingm preferably sheet metal, shell All may be applied upon the-body 2| and secured in position, as by crimping the peripheral portions M v4of the shell into locking engagement in circumferential grooves v42 `formed in the body 2|. The shell 40 may include skirt portions 43 extending around and enclosing the glass-metal `seal 33. to protectv the sam-e from stray electron impingement. The shell may Aalso be formed with portions 44 enclosing the targetend of the anode, such portions being formed with an opening A45 in alinement with and between the elec.- tron emitting elementof the cathode and the anode targetformedfby the button 22.

It is, of course, also possible to incorporate structures embodying the present invention in other types-of anodes, including anodes for use in X--ray generators of thesort shown in United States Letters Patent No. 2,356,645, issued August 22, 1944, on the invention of Z. J. Atlee and H.. W.

Brackney. Such ananode is shown in section, in.

Fig. 7, and may comprise a tubular metal sleeve 46, forming av portion of the envelope of the generator tube, a target structure 4l being sealed in theiend ofthe tube in position to be bombarded by electrons emitted by a cathode enclosed in and supported by the tube envelope at the target remote end of. the tube 43. The cathode is thus in position to emit an electron beam longitudinally through the. tube 43 for limpingernent upon the target. As. shown in Fig. 7, the target structure 41. may comprise. a body 2| of-cast metal, such as copper,I in which a target button 22 of refractory material, such as tungsten, is set, the structure including a disk or plate 25 of dense, impervious material, such as molybdenum, enfeloped in and supercially integrated with the copper body of the target structure behind the target button 22. the body 2Jl including an outwardly extending peripheral flange d8 to facilitate the sealing of the target structure TI in the end of the tube 4E, as by Welding or brazing the tube end, to said flange.

Anode structures embodying the present invention, regardless of their shape or conguration, may be formed' by placing the target button 22 and the member 25, whether formed as a cup or as a plate, as inserts in a suitable casting mold in which the inserts'may be anchored. To this end, as shown more particularly in Fig. 6 of the drawings, the target button 22 may be anchored on a mounting plate 451, preferably comprising graphite,l by means of molybdenum anchoring pins 5t, said pins having ends secured in openings 5l in the anchor plate. The member 25, whether the same comprises a flat plate as shown in Fig. 7, or the bottom of a cup-shaped member of the sort shown in'Figs. 3 ande, may be Vanchored on the mountingv plate 49 in stacked relationship `v'vith respect to the button 22, as by means of molybdenum anchoring pins 52, the same having ends adapted to be secured in openings 53 formed in the mounting plate 49, at the edge of the button 22 and intermediate the openings 5l.

When the parts are so mounted, it will be seen that the member 25 is supported in spaced parallel relationship above the target button 22, the vertical distance between the facing surfaces of the member 25 and the button 22 being equal to the diameter of the hooked disk retaining ends of the pins 50. The inserts 22 and 25, thus anchored on the mounting'plate 49, may be fastened in a suitable mold shaped in conformity with the desired shape of the anode body 2 l, and copper may then be cast into the mold, upon the so mounted insert elements 22 and 25 in order to embed and envelop said elements in the casting in proper relative position therein, the button 22, in effect, being brazed to and upon the member 25, by the intervening cast material which enters between the space defined by the hooked portions of the anchor pins 50, between the facing surfaces of the elements 22 and 25. The copper thus becomes superiicially integrated with the material of the elements 22 and 25 at the copper enveloped surfaces thereof. The casting operation is preferably accomplished under vacuum conditions. After the casting operation has been completed and the anode structure removed from the mold, the mounting disk t9 may be stripped from the casting and the projecting ends of the pins 50 and 52 may be removed, leaving portions of the anchoring members 50 and 52 embedded in the cast material in the edges of the target button.

It will be seen from the foregoing that the present invention provides a novel method of insuring vacuum tightness in the metal casting comprising the thin wall section 2| which extends behind the target button 22 and between it and the chamber 23, such wall section comprising a part of the evacuated envelope of the X-ray tube. This is accomplished by embedding in said section a relatively thin layer of dense, impervious material, such as molybdenum. The resulting .structure is not only vacuum tight at said thin Wall section, but said Wall section, being thin, allows for the rapid transfer of heat from the target `button 22 to the cooling fluid in the chamber 23.

X-ray anodes incorporating the novel features of the present invention not only show improved and efficient anode cooling characteristics; but the incorporation of integral coolant guiding baffies, such as the bailies 26 and 26', in the anode structure eliminates the necessity of assembling relatively more expensive conventional cooling coils in the chamber 23, the guiding baiiies 26 and 26', together with the inexpensive cover disk 33, being a cost reducing improvement in iiuid cooled X-ray tube anodes.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacrificing any of its attendant advantages, the forms herein being preferred embodiments forthe purpose of illustrating the invention.

The invention is hereby claimed as follows:

l. An X-ray tube comprising an anode, a cathode and a sealed and evacuated envelope enclosing and supporting said anode and cathode in spaced apart facing relationship therein, said anode comprising a metal casting having a relatively thin wall portion forming an electron target on one side thereof in position facing said cathode, said wall portion defining a chamber in the anode structure on the opposite side of said Wall portion, means for connecting said chamberl with a source of fluid cooling medium disposed outwardly of the envelope, and a thin layer of dense impervious material embedded in and supercially integrated with the constituent metal of said Wall to render the same vacuum tight, between said chamber and said electron target. l

2. An X-ray tube comprising an anode, a cathode and a sealed and evacuated envelope enclosing and supporting said anode and cathode in spaced apart facing relationship therein, said anode comprising a metal casting having a relatively thin Wall portion forming an electron target on one side thereof in position facing said cathode, said Wall portion defining a chamber in the anode structure on the opposite side of said wall portion, means for connecting said chamber with a source of fluid cooling medium disposed outwardly of the envelope, and a thin layer of molybdenum embedded in and superficially integrated With the constituent metal of said wall to render the same vacuum tight, between said chamber and said electron target.

3. An X-ray tube comprising an anode, a cathode and a sealed and evacuated envelope enclosing and supporting said anode and cathode in spaced apart facing relationship therein, said anode comprising a copper casting having a relatively thin wall portion forming an electron target on one side thereof in position facing said cathode, said Wall portion dening a chamber in the anode structure on the opposite side of said Wall portion, means for connecting said chamber with a source of fluid cooling medium disposed outwardly of the envelope, and a thin layer of molybdenum embedded in said Wall to render the same vacuum tight, between said chamber and said electron target.

4. An X-ray tube comprising an anode, a cathode and a sealed and evacuated envelope enclosing and supporting said anode and cathode in spaced apart facing relationship therein, said anode comprising a metal casting having a relatively thin wall portion forming an electron target on one side thereof in position facing said cathode, said wall portion defining a chamber in the anode structure on the opposite side ofl said Wall portion, means for connecting said chamber with a source of fiuid cooling medium disposed outwardly of the envelope, and a thin layer of dense impervious material embedded in and superficially integrated with the constituent metal of said wall to render the same vacuum tight, between said chamber and said electron target, said casting including an integral fin forming a partition dividing said chamber into compartments communicating one with another betvveenan edge of the fm and a spaced Wall of the chamber.

5. An X-ray tube comprising an anode, a cathode and a sealed and evacuated envelope enclosing and supporting said anode and cathode in spaced apart facing relationship therein, said anode comprising a metal casting having a relatively thin wall portion forming an electron tarside of said wall portion, means for connecting said chamber with a source of uid cooling medium disposed outwardly of the envelope, and a thin cup-shaped element of molybdenum embedded in and superficially integrated with the constituent metal of said casting at said wall and in the portions of the casting which denne the side walls of said chamber 'to render the anode vacuum tight,` between said chamber and said electron targetf` 6. An X-ray'tube comprising an anode, a cathode and a sealed and evacuated envelope enclosing and supporting said anode and cathode in spaced apart facing relationship therein, said anode comprising a metal casting having a relatively thin wall portion, a button of refractory metal embedded in said wall portion and exposed on one side thereof in position forming an electron target facing said cathode, said wall portion dening a chamber in the anode structure on the opposite side of said wall portion, means connecting said chamber with a source or" fluid cooling material outwardly of the envelope, and a thin layer of dense impervious metal embedded in and superfcially integrated with the constituent metal of said wall to render the same vacuum tight, said button and layer being integrally joined hy and with the intervening metal of said wall portion.

'7. An X-ray tube comprising an anode, a cathode and a sealed and evacuated envelope enclosing and supporting said anode and cathode in spaced apart facing relationship therein, said anode comprising a cuprous metal casting having a relatively thin wall portion forming an electron target on one side thereof in position facing said cathode, said Wall portion defining a chamber in the anode structure on the opposite side of said wall portion, means for connecting said chamber with a source of fluid cooling medium disposed outwardly of the envelope, and a thin layer of molybdenum embedded in said wall to render the same vacuum tight, between said chamber and said electron target, said casting including an integral fin forming a partition dividing said chamber into compartments communicating one with another between an edge of the fin and a spaced wall of the chamber.

8. An X-ray tube comprising an anode, a oathode and a sealed and evacuated envelope enclosing and supporting said anode and cathode in spaced apart facing relationship therein, said anode comprising a cuprous metal casting having a relatively thin wall portion forming an electron target on one side thereof in position facing said cathode, said wall portion dening the bottom of a chamber in the anode structure on the opposite side of said wall portion, means for connecting said chamber with a source of uid cooling medium disposed outwardly of the envelope, and a thin cup-shaped element of molybdenum embedded in said casting at said wall and in the portions of the casting which dene the side walls of said chamber to render the anode vacuum tight, between said chamber and said electron target.

9. An X-ray tube comprising an anode, a cathode and a sealed and evacuated envelope enclosing and supporting said anode and cathode in spaced apart facing relationship therein, said anode comprising a cuprous metal casting having a relatively thin wall portion, a button of refractory metal embedded in said Wall portion and exposed on one side thereof in position forming an electron target facing said cathode, said wall portion defining a chamber in the anode structure on the opposite side of said Wall portion, means connecting said chamber with va source of uid cooling material outwardly of the envelope, and a thin layer of molybdenum embedded in said Wall to render the same vacuum tight, said button and layer being integrally joined by and with the intervening metal of said wall portion.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,994,140 McEuen Mar. 12, 1935 2,053,327 Ehrke Sept. 8, 1936 2,098,315 Sharp Nov. 9, 1937 2,125,896 Driggs et al. Aug. 9, 1938 2,506,327 Harrington May 2, 1950

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