US2311724A

US2311724A - X-ray tube

Info

Publication number: US2311724A
Application number: US390321A
Authority: US
Inventors: Zed J Atlee
Original assignee: General Electric X Ray Corp
Current assignee: General Electric X Ray Corp
Priority date: 1941-04-25
Filing date: 1941-04-25
Publication date: 1943-02-23
Anticipated expiration: 1960-02-23
Also published as: GB556787A; FR940157A; BE477898A

Description

Feb. 23, 1943. y z J. ATLEE x-RAY TUBE Fiied April 25. 1941 ks@ www. www@ w QM Nw mmv x 1 mm. wm, N Q/ mw 1N@ mw m. mm m s m E Nw m NM@ N @E NM1. Q, mmm@ @u w. n@ fliili-- w. @m .wm n@ .IIL Y 4/NH Patented Feb. 23, 1943 X-RAY TUBE Zed J. Atlee, Elmhurst,

Electric X-Ray Corpor poration of New York Application April 25, 1941, Serial No. 390,321

7 Claims.

This invention relates in general to rotatable devices and has more particular reference to rotatable structures enclosed in sealed envelopes, the invention pertaining especially to an improved rotatable anode structure for use in X- ray tubes.

An important object of the present invention is to provide a rotating structure of the character mentioned, having magnetic driving means formed and arranged therein and operable to rotate the structure; a further object being to form the driving means as a permanent magnet built into the rotating structure and the mounting on which it is carried; a still further object being to utilize the unbalancing of a magnetic eld through thermal inversion to develop driving torque.

Another important object is to provide an improved magnetic drive for the rotating anode in an X-ray tube; a further important object being to provide for driving the anode of an X-ray tube by establishing a magnetic field at the anode and by unbalancing the iield by heating a portion of the anode lying in said eld above the magnetic inversion temperature of the anode material.

Another important object resides in providing an improved mounting structure for a rotary device of the character mentioned; a further object being to form the mounting as a hollow pedestal within which is journaled a turnable spindle carrying the rotatable device, whereby the pedestal may form a stationary mounting for carrying the magnetic driving means and other auxiliary equipment in position to co-operate with the rotary structure; a further object being to turnably support the carrying spindle inpreferably roller bearings disposed on the pedestal; and a still furtherobject being to provide means on the pedestal for lubricating the bearings therein and to control the application of lubricant from a control station outwardly of the device.

These and numerous other important objects, advantages, and inherent functions ofthe invention will become apparent as the invention is more fully understood from the following description, which, taken in conjunction with the accompanying drawing, discloses a preferred enibodiment of the invention.

Referring to the drawing:

Figure 1 is a sectional view taken longitudinally through an X-ray generator provided with a rotating anode embodying my present invention;

Figure 2 is a sectional view taken substantially along the line 2 2 in Figure 1; and

Figure 3 is a graphical representation illus- Ill., assignor to General ation, Chicago, Ill., a cor- (Cl. Z-148) trating loss of magnetism with rise in temperature of iron, nickel and cobalt.

To illustrate my invention, I have shown on the drawing an X-ray generator Il comprising spaced-apart cathode and anode means I3 and l5 enclosed within a preferably glass envelope Il. The anode l5 is of the rotating type, being turnably supported for rotation on mounting means I9 which, in turn, is supported on the envelope I'l at one end thereof. The anode, of course, may be rotatably supported on the mounting means in any suitable fashion, and although the structure and arrangement of the anode mounting does not necessarily limit the broader aspects of the present invention, certain features of the mounting facilitate-and co-operate to advantage in conjunction with the magnetic driving means.

As shown, the mounting means I9 comprises a pedestal having a stem-like portion 2l extending outwardly of the envelope and a portion 29 extending within the envelope. The anode l5 is rotatably mounted on the portion 29, and the pedestal is sealed to the envelope at the re-entrant portion 23, which denes an opening in which the pedestal extends. As illustrated, the pedestal is provided with an annular shoulder 3l carrying, sealed thereon, a plate or disk 32 having a cylindrical rim 33 sealed at one end to the disk 32, the opposite end of the rim providing an annular edge forming a glass-to-metal seal 34 with the envelope at the inner end of the reentrant portion 23. This seal supports the pedestal and the anode thereon.

It should be understood that X-ray generators functionV to producevX-rays in response to the -activation of the anode by'electronic action established by the operation of-the cathode -|3, said electronic action consisting of the'impinge- -ment of electrons emitted by the cathode upon a vtarget 4| forming a part of the anode I'5. Electronic impingement onthe target results inthe generation of relatively large quantities of heat at the target, which is dissipated thence through the body of the anode l5. In operation, the temperature of the anode at the Zone of electron impingernent on the target 4l may momentarily be of the order in excess of 750 centigrade.

It should be understood, also, that X-ray generators are conditioned for operation by exhausting from the envelope substantially all gaseous and other impurities by evacuating the envelope, as by means of a molecular exhaust pump, and nally sealing the envelope in evacuated condition.

pass away from the zone in which subjected to electronic bombardment.

As shown in the drawing, the anode I5 comprises a cylindrical body 39 having an open end receiving and embracing the pedestal portion 29. The opposite end of the anode body is enclosed and is formed with an axial head or neck 25, which affords a mounting for the annular target member 4I. The target member, as shown, comprises an annular ring of suitable material, such as tungsten, which is embedded and secured in the preferably copper body of the anode at the end of the neck 25. The target ring extends outwardly of the head to form an annular grove vor space 42 with the closed end of the cylindrical body 30. The anode also carries a ring 44 of magnetic material, such as iron, nickel, cobalt, or alloys thereof, which is fastened securely in the anode structure and forms a part thereof, said ring 44 extending in the groove 42 immediately behind and adjacent to, and in intimate thermal contact with the target ring 4 I.

In order to provide for driving the anode I5 on the pedestal, I provide means forming a magnetic circuit on the stationary and rotatable por- Y tions of the anode structure, said magnetic circuit comprising a magnet 81 fastened on the stationary pedestal in position to magnetically cooperate with the ring 44 on the rotatable anode I5.

As shown, the magnet 81 comprises a bar of permanently magnetized material characterized by the ability to retain magnetic properties at the operating temperature of the device. Alnico is a suitable material for the purpose. The permanent magnet 81 is anchored at one end on a mounting piece 89 which seats upon the pedestal portion 29 adjacent the seal ring 32, the parts being rigidly held together and in operating position, as by means of holding screws 9|. The bar magnet 81 extends from its mounting along the side of the anode body 30 and is formed, at its end remote from the mounting 89, with a shoe 93 which extends in the annular groove or space 42 immediately adjacent and in magnetic 'relationship with the ring 44. Theishoe 93 may, of course, be formed as an integral part of the magnet 81, or may conveniently comprise a sepa'- rately formed member of sofi; ironsecured to the bar 81, as by means of fastening screwsv 95. The shoe 93, however, is formed and arranged to make` a small gap clearance with the ring 44. It will be noted that the shoe 93 faces that portion of the ring 44 which underlies the focal spot or zone of electron impact upon the target ring 4I. When the generator is in operation, electron impact on the target 4I raises the temperature of thev ring 4I at the focal spot and thus raises the temperature of the adjacent portions of the magnetic ring 44 opposite the shoe 93.

Iron, nickel, cobalt, and alloys thereof, all possess magnetic inversion characteristics when vheated above a characteristic temperature or socalled Curie point, each material having its own characteristic inversion temperature, as.`

shown in Figure 3, illustrating the loss of magnetsm with rise in temperature of iron, nickel and cobalt. The inversion temperature of any material having magnetic inversion characteristics is extremely critical, as indicated by vertical lines in Figure 3, so that by utilizing the momentary heating of the target at the focal spot above inversion temperature of the material of the ring 44, an unbalanced magnetic field may be created which allows the stationary magnet 81 to exert a rotating torque upon the anode. As the material of the target 4I moves out of the electron stream, the temperature of the target and of the ring 44 will fall rapidly as heat is dissipated into the body of the anode, so that the material of the ring 44, which at any instant is not in line with the focal spot, will have regained magnetism and be able to form apart of the magnetic cirpedestal portion'29.

cuit and go through the same cycle repeatedly as the material ofthe ring 44 is advanced into position opposite the focal spot.

The pedestal portion 29 extends within the cylindrical body of the anode and carries-anode bearings comprising, in the illustrated embodiment, a pair of roller bearings 43 and 45 in spaced-apart position on the pedestal portion 29. Each bearing comprises an outer race secured preferably in the hollow pedestal, and an inner race secured on and thereby supporting a spindle 41, suitable roller members being conventionally retained between the inner and outer race portions of the bearings.

The spindle 41 may, of course, be secured in the bearings in any suitable or preferred fashion, although I have shown the same as being formed with" threaded portions receiving clamping nuts for clampingly securing the inner bearing races in spaced relationship on the spindle 41, the outer races of the bearings 43 and 45 being secured in the cavity 35, the outer race ofthe bearing 43 being secured in a seat 49 formed near the bottom of the cavity, said race being held in said seat by a spacing tube 5I, one end of which engages the outer race of the bearing 43 to hold it on the seat 49. The other end of the tube 5I forms a seat for receiving the outer race of the bearing 45, which is held in place by a clamping tube 53 having a iiange portion. 55 secured to the inner end of the pedestal portion 29 as by means of holding screws 51. The spindle 41 is thus journaled for rotation in the bear# ings 43 and 45 which are mounted on the pedestal portion 29. The stem 41 has an end formed with a ange 59 outwardly of the open end vof the The anode I5 is secured on said ange 59 by means of an annular mounting frame 6I, which is formed at one end for clamping on the flanged end of the stem 41. To this end, the frame 6I has an end wall 63 formed with an opening dened by a lboss for receiving the end of the stem 41 outwardly of the flange 59, the frame 6I being secured on the stem 41 by means of a bolt 61 threading into the stem 41 and having ahead overlying the boss 65 to thereby clamp the wall E3 upon the ange 59. The frame 6I comprises cylindrical portions preferably formed integrally with the wall 63 and extending thence outwardly of and encircling the pedestal portion 29, said frame 6I having an enlarged annular portion 69 adapted snugly to extend within the cylindrical portion 39 of the anode I5, which is formed with a shoulder 1I defin- -ing a seat for receiving the frame portion 59, the

anode being anchored onthe frame as by means of holding screws 12.

In order to lubricate the bearings, I provide for the application thereto of a lubricating medium whichhas a vapor pressure suiciently low so that it will not evaporate from the bearing under the conditions of temperature and pressure prevailing within the envelope. To this end, I may utilize, as a lubricating medium, a material such as barium, caesium, strontium, cadmium, chromium, copper, silver, aluminum, iron or nickel, which have a vapor pressure of the desired order whereby the lubricating medium may not migrate from a treated bearing operating under low pressure and high temperature conditions. In practicing this phase of my present invention, I provide for applying the selected lubricating medium in film-like form upon the bearings after the same have been assembled in place and the envelope evacuated. The selected material or materials are applied upon the bearing surfaces by vaporizing the same and directing the vaporized material upon the bearing surfaces to be treated, whereby to condense the vapor as a thin film upon the working surfaces of the bearings. The deposited material forms an alloy with the material of the bearings, which may be any suitable ferrous material, whereby is formed an alloy film having desired lubricating properties.

As shown in the drawing, the pedestal portion 29 and the spacing tube 5| are cut away to form openings 'l3 and l5, respectively, adjacent the bearings 43 and 45. In these openings are disposed loops 11 and 19 of hollow wire containing lubricating material, said loops 11 and 'I9 being disposed with weakened wall portions facing the bearings 43 and 45. One end of each loop is electrically connected, as at 8|, on the pedestal portion 29, the other end of each loop being electrically connected, as at 82, with conductors 83 which extend outwardly of the envelope through ducts formed in the plate 32, the conductors being hermetically sealed and electrically insulated in said ducts by glass-to-metal seals 85. By connecting a`suitable source of electrical potential between the outwardly exposed end 2l of the pedestal and either or both of the conductors 83, an electrical heating current may be caused to flow through the wire in order to raise the temperature thereof to a point at which the lubricating material therein may be vaporized, and, as

heretofore described, expelled through the weakened wall portion of the loops and onto the bearings. The bearings may thus be lubricated, and the quantity of lubricating material applied to each bearing may be regulated by controlling the activating current delivered through each loop. Each loop, furthermore, may be supplied with suilicient lubricating medium to enable re-lubrication of the bearings from time to time during the service life of the device.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregc-ing 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 form herein disclosed being a preferred embodiment for the purpose of illustrating the invention; but I do not herein claim the novel means for and method of lubricating the bearings since the same forms the subject matter of my copending applications for United States Letters Patent Serial No. 284,273 led July 13, 1939 for Anti-friction process and product, which issued August 18, 1942 as United States Letters Patent No. 2,293,037; Serial No. 364.005 filed' November 2, 1940 for X- ray generator lubricating structure which issued August 18, 1942 as United States Letters Patent No. 2,293,527; and Serial No. 366,978 filed November 25, 1940 for Method of conditioning X- ray generators which issued May 13, 1941 as United States Letters Patent No. 2,242,101.

The invention is hereby claimed as follows:

1. An X-ray tube having a sealed envelope, a rotarystructure in said envelope comprising a support member, a rotary member on said support member, and magnetic means on said support and rotary members in position to establish an unbalanced magnetic eld tending to rotate said rotary member on said support member in response to the application of heat to said magnetic means.

2. An X-ray tube having a sealed envelope, a rotary structure in said envelope comprising a support member, a rotary member on said support member, magnetic means on said rotary member, a permanent magnet on said support member in position to co-operate with said magnetic means whereby to turn the rotary member on the support member through the creation of an unbalanced magnetic eld when said magnetic means is heated above its magnetic inversion temperature.

3. An X-ray tube having a sealed envelope, a support member and a rotary member thereon in said envelope, an annular ring of magnetic material on said rotary member, and a permanent magnet on said support member having a portion extending adjacent and in magnetic cooperation with said ring whereby to rotate the rotary member when a portion of said ring is heated above the magnetic inversion temperature of the material thereof.

4. An X-ray tube having a sealed envelope, a support member and a rotary member thereon within said envelope, annularly disposed magnetic means on said rotary member, and a magnet on said support member in position to cooperate with said annularly disposed magnetic means, said magnetic means being normally magnetic but yielding its magnetism when heated to a critical inversion temperature whereby to establish an unbalanced magnetic field exerting a turning torque upon said rotary member upon heating portions of said magnetic means.

5. An X-ray tube having a sealed envelope, a support member and a rotary anode member thereon within said envelope, annularly disposed magnetic means on said rotary member, a magnet on said support member in position to cooperate with said annularly disposed magnetic means, and an electron emitting cathode positioned to direct electrons on said anode member at a focal zone through which said anode member including said annularly disposed magnetic means may progressively rotate whereby to progressively heat said magnetic means, said magnetic means being normally magnetic but yielding its magnetism when heated to a critical inversion temperature whereby to establish an unbalanced magnetic. eld exerting a turning torque upon said rotary member upon heating portions of said magnetic means within said focal zone.

6. An X-ray tube having a sealed envelope, a rotary structure in said envelope comprising a support member, a rotary member on said support member, and magnetic means on said suppc rt and rotary members in position to establish die and including hollow portions embracing the support member and spaced outwardly thereof, said spindle being supported in bearing means in said cavity, and magnetic means on said support member and rotary means in position to establish an unbalanced magnetic eld tending to rotate said rotary means on said support member in response to the application of heat to said magnetic means.

ZED J. ATLEE.y