US2549614A - Rotary anode x-ray tube - Google Patents

Description

April 17, 1951 A. H. LEIGHTON ROTARY ANODE X-RAY TUBE File oct. 27, 1948 Patented Apr. 17, 1951 UNITED ROTARY ANODE X-RAY TUBE Alexander HQ Leighton, Minneapolis, Minn., Vas- A signor' to Westinghouse Electric Corporation,

East Pittsburgh, Pa., a.v corporation of Pennsylvania Application October 27, 1948, Serial No. 56,706 Y 4'C1aims, (Cl. Z50-148) Y vThe present invention relates to X-ray tubes v and more particularly to such tubes provided with a rotary anode.Y l

Rotary anode X-'ray tubes have known to the art and possess the advantage that the electron beam impinges upon substantially the. entire surface of the tungsten target due to rotationof the .anode which thus prolongs the life of the target andA hence the entire tube. In

addition, since the electron beam is concentratedV only for a brief interval of time at one spot of the tungsten target during its rotation, a rotary anode V2i-ray tube can withstand a somewhat greater energy loading than a conventional stationary anode X-ray tube which thus results in a greater intensity of the generated X-rays.

Despite these advantages,'however, one serious problem with rotary anode X-ray tubes has been ,insulating material circulating through Vstationary parts of the anode. n

It is accordingly the primary object of the present invention to provide an X-ray tube having a rotary anode wherein the heat radiating area of the anode is increased as well as the length of its thermal conducting path thus decreasing the temperature of the bearings for the anode during operation of the tube;

Another object of the present invention is th provision of an X-ray tube having a rotary anode formed of plates to increase the heat radiating surface of the anode so that a larger percentage of the heat generated during operation of ,the tube is dissipated by radiation from the anode thus decreasing the amountof heat dissipated through conduction to the bearings for the anode.

Still further objects of the present invention will become obvious to those skilled inthe art by Y reference to the accompanying drawing where- Figure l is a fragmentary View in cross section of a rotary anode X-ray tube constructed in accordance with the presentinvention,

long been providing the anode with a metallic cylindrical member the lower periphery 8 of which is sealed to the upper peripheral edge of the reentrant stem. To effect such seal the cylindrical member 7 is formed of ametalhaving substantially the samev coefficient of expansion as the vitreous envelope material, such, for example, as an alloy of cobalt,v nickel, and iron, and commercially known as KovanA ,Y Extending coaxially of the cylindrical member 'I is the anode 'conducting support 9, which may be formed of a good heat and electrical conducting material, Asuch as copper, and having a flanged portionl ID, the under surface of which is welded or similarly secured to the Vupper periphery of the cylindrical metallic member I to form an hermetic seal therewith. A rotor supporting shaft I2 threadedly engaged the conducting support 9 and may be held against unloosening by a set screw I3. A pairof ball bearings I4 are carried by this supporting shaft I2 and are held in spaced relation with respect to ea'ch other by a sleeve or the like I5.

The rotor proper of the rotary anode comprises a hollow shell I6 frictionally engaging the ball races I4 and held in such position by a threaded retaining ring I'I, with the latter being lockedafin place by a set screw or the like I8. Although this shell I6 is formed of a good heat and electrically conducting material, such as copper or the like, its outer surface is provided with an annular Yring or spaced laminations I9 of a magnetic material, such as iron, so as to cause rotationof the shell I6 about the ball races I4 under vthe influenceof a magnetic field generated by the 22l of good heat and electric conductivity. Riveted; welded, or otherwise secured to this stud is Figure 2'is a sectionalview takenv onthe'line Y II'-II of Figure 1, l

' Figure 3 is an elevational view of a modification which the rotary anode of the present invention may take, and

Figure 4 is a sectional view taken on the line `IV-IV of Figure 3.

' Referring now to the drawings in detail the X-ray tube as shown in Figure l comprises an evacuated vitreous envelope 5 provided with a reentrant stem B to which the anode electrode is hermetically sealed. kThis is accomplished by a metallic plate or preferably adisk 23 of substantial diameter and relatively small cross section, thus providing considerable heat radiating area from its surface, while at the Sametime allowing heat to be conducted to the shell by' the stud 22. supported through a plurality of spacing rivets or the like 25, from the disk 23 and the refractory metal'target 26, preferably of tungsten, is supported from the second disk 24 by a central stud 21 riveted or otherwise secured to both the target 26 and second disk 24. It will be noted that the central rivet 21 is of somewhat larger diameter than the rivets 25 supporting the disk 24, for the purpose of better heat conduction, so that the heat generated at the tungsten target 26 is con- AVduct'edvthrough the central rivet 2l to the disk 2,4 for dissipation through radiation therefrom due toY its relatively large surface area. Sincethe surface, of thedisk Mitself is in- A second metallic disk 24 is in turn suflicient to radiate alll of the heat some will flow to the disk 23 both by radiation and conduction through the studs 25, so that the radiat-` ing surface of the disk 23 is thus added to that of the disk 24 for the rapid dissipation'of the heat. Naturally some heat will also be conducted by the stud 22 to the shell i6 and, thence by the sleeve l and ball bearings to the rotor shaft l2 and anode conducting support 9, exteriorly of the tube 5 to the atmosphere. However, due to the area of the disks 23 and 24 the greater dissipation of the heat will be by radiation to the walls of the X-ray tube 5 and thence to the atmosphere, while the amount finally conducted through the ball bearings l will be conned to a relatively small amount.

In order to still further decrease the amount of` heat finally conducted by the ball bearingsA i4 the number of disks employed may be increased as shown in the modificationv of Figure 3, where two additional disks 28 and 29 are employed thus doubling the radiating surface area over that illustrated in Figure l. Of course the number of disks can be increased, being limited only by the spacing required between the tungsten target and the thermionic cathode 30,' and the length of the X-ray tube, l

It thus becomes obvious to those skilled in the art that an X-ray tube of the rotary anode type is herein provided in Which the heat radiating surface of the anode is so increased, as well as the thermal conductive path thereof, that the temperature to which the bearings is subjected during operation of the tube is decreased substantially to a minimum. Moreover, by providing the anode with a plurality of disks having a substantially large surface area compared with their cross section, the greater percentage of the heat generated at the anode targetis dissipated by radiationA through the tube Walls, thus confining the heat dissipated by conduction through the metallic parts of the anode to a very small amount which prolongs the useful life of the X- ray tube yet allows a greater energy loading without deleterious eiiects ensuing.

Although two embodiments of the present invention have been shown and described, itis to be understood that still further modifications thereof may be made without departing from the spirit and scope of the appended claims.

Iv claim:

l. A rotary anode X-ray tube comprising an evacuated vitreous envelope provided with a metallic anode and a cathode therein, said anode having a target at which heat is generated-during operation of said X-ray tube and including a rotatable member journalled for rotation, about the longitudinal axis of said tube, and'said anode comprising a series of annular spaced metallic disks completely spaced fromv each other to expose their entire respective plane surfaces and supported from' each other by a connecting member independent of said rotatable member for increasing the heat dissipated by radiation from the anode surface and to decrease the anode heat dissipated by conduction to a minimum.

2. A rotary anode X-ray tube comprising an evacuated vitreous envelope provided with a metallic anode and a cathodetherein, said anode having a target at whichheat is generated during operation of said X-ray tube and including; a rotatable member journalled` for rotation about the longitudinalaxis of said tube, and said anode comprising a series .of superimposed, annular disksA ofLrelatiyely; large surface. area .angularly disposed with respect to the axis of' rotation of said anode and completely spaced from each other to expose their entire respective plane surfaces and supported from each other by uprights of small cross sectional area entirely independent of saidrotatable member for increasing the anode heat dissipated by radiation from the anode surface and to decrease the anode heat dissipated by conduction through the metallic anode to a minimum.

3. A rotary anode X-ray tube comprising an evacuated vitreous envelope provided with a metallic anode and a cathode therein, said anode having a target at which heat is generated during operation of said X-ray tube and including arotatable member journalled for rotation about the longitudinal axis of said tube, said rotatable member comprising a metallic shell frictionally engaging a pair of bearings and provided with a stud of smaller diameter than said shell and disposed coaxially of the axis of said tube, and said anode including a series of annular'disks of relatively large surface areas completely spaced from each other to exp-ose their entire respective plane surfaces With the first disk in the series being supported by saidstud and the remainder of said disks being supportedv from each other independently of said stud, for increasing the anode heat dissipated by radiation from the anode surface and to decrease the anode heat dissipated by conduction through said metallic shell to the frictionally engaged bearings.

4. A rotary anode X-ray tube comprising an evacuated vitreous envelope provided with a metallic anode and a cathode therein, said anode having a target at which heat is generated during operation of said X-ray tube and including a rotatable member journalled for rotation about the longitudinal axis of said tube, said rotatable member comprising a metallic shell frictionally engaging a pair of bearings and provided with a stud of smaller diameter than said shell and disposed coaxially of the axis of said tube,` and said anode including a series of annular disks of relatively largeV surface areas completely spaced from eachother to expose their entire respective plane surfaces with the first disk in the series being supported byk said stud and the remainder of said disks being supported from each other by radiallyv disposed studs independent of the stud of said shell, for increasing the anode heat dissipated by radiation from the anode surface and to decrease the anode heat dissipated by conduction through said metallic shell to the frictionally engaged bearings,v and said anode target being connected by a metallic stud of larger diameter than said radially disposed studs to the last of' said disks in the series remote from said metallic shell.

ALEXANDER H. LEIGHTON.

REFERENCES CITED The following references are of record inthe le of this patent:

UNTED STATES PATENTS Number y Name l Date 2,030,561 Andrew Feb. 1l, 1936 2,111,412 Ungelenk Mar. l5, 19.38 2,274,865 Machlett Mar. 3,1942

FOREIGN PATENTS Number Country Datev 64,830 Denmark Sept. 30, 1946 400,022; GreatBritain Oct. 19, 1933

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