US3851204A

US3851204A - Rotatable anode for x-ray tubes

Info

Publication number: US3851204A
Application number: US00337311A
Authority: US
Inventors: F Rollfinke
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1973-03-02
Filing date: 1973-03-02
Publication date: 1974-11-26
Anticipated expiration: 1991-11-26
Also published as: DE2409526A1; NL7401850A; FR2220094B1; NL176621C; AT340008B; FR2220094A1; DE2409526C2; NL176621B; ATA156074A

Abstract

An anode is disclosed of the rotatable type adapted for use in an X-ray generating tube, wherein the anode is of circular disclike configuration having an annular focus area on each of its sides adjacent the periphery, these focus areas being inclined symmetrically to the central plane of the disc whereby the disc may be turned side-for-side in a single beam X-ray tube to expose a fresh target surface after one surface has been pitted or burned, or may be used in an X-ray tube having provision for dual beams in which case the target areas of the anode may be employed simultaneously to produce a reinforced beam or, alternatively, singly in sequence to reduce the frequency of disassembling the tube to effect replacement of the anode.

Description

United States Patent [191 Rollfinke 1 1 ROTATABLE ANODE FOR X-RAY TUBES [75] Inventor: Fred J. Rollfinke, Carlisle, Pa.

[73] Assignee: General Electric Corporation,

Milwaukee, Wis.

22 Filed: Mar. 2, 1973 211 Appl.No.:337,31l

{521 US. Cl 313/330, 313/56, 313/60 1 [51] Int. Cl. H01j 35/08 [58] Field of Search 313/330, 56, 60

[56] References Cited UNITED STATES PATENTS 2,274,865 3/1942 Machlett 313/330 X 2,336,271 12/1943 Machlctt et a1 313/330 X 2,350,642 6/1944 Schwarzer 313/60 X [451 Nov. 26, 1974 Primary Examiner-James W. Lawrence Assistant ExaminerSaxfield Chatmon, Jr.

Attorney, Agent, or Firm-Thomas J. Bird, Jr.; Frank L. Neuhauser 5 7] ABSTRACT An anode is disclosed of the rotatable type adapted for use in an X-ray generating tube, wherein the anode is of circular disc-like configuration having an annular focus area on each of its sides adjacent the periphery, these focus areas being inclined symmetrically to the central plane of the disc whereby the disc may be turned side-for-side in a single beam X-ray tube to expose a fresh target surface after one surface has been pitted or burned, or may be used in an X-ray tube hav ing provision for dual beams in which case the target areas of the anode may be employed simultaneously to produce a reinforced beam or, alternatively, singly in sequence to reduce the frequency of disassembling the tube to effect replacement of the anode.

4 Claims, 4 Drawing Figures PATENTEL HSVZE 1974 FIG. 2

ROTATABLE ANODE FOR X-RAY TUBES This invention relates to anodes for Xray generating tubes and is particularly concerned with a type of anode adapted to be rotated within the X-raytube. The invention is characterized by an anode configuration designed to provide improvements in physical and mechanical properties and operating capabilities of the anode, and hence of the X-ray tube, in comparison to anodes heretofore used.

The invention is directed more particularly to solid single metal as well as bimetal or composite metalnonmetal rotated anodes in which an anode disc, or at least a portion of it, is composed of different materials in order to take advantage of different properties of those materials. Difficulty has been experienced with the use of prior bimetal rotatable disc anodes owing to distortion occasioned by difference in thermal expansion between the metals, with resulting distortionin the X-ray beam. It is accordingly a purpose of the present invention to obviate this difficulty and to achieve an improved structure from forging asymmetrical shape.

Heretofore, two general types of rotatable anodes for X ray use have been available. In the more common type, the anode is in the form of a circular plate or disc of shallow concavo-convex shape. The anode disc is mounted on a rotating shaft supported within the glass envelope of the tube with the convex surface of the disc facing a cathode supported in spaced relation thereto. The peripheral margin of the convex surface of the disc opposing the cathode constitutes the target or focus area and is bombarded by electrons given off by the cathode when the tube in in operation. This focus area is tilted to the path of electrons impinging upon it so that X-ray emanations produced by the bombardment will be directed or beamed laterally (radially from the disc) to intercept the subject which is to be examined. The convexity of the disc thus effectively provides the target tilting mentioned above with a minimum amount of material in the disc. This minimal material feature is desirable both from an economic standpoint, as the better target metals are quite expensive, as well as for functional reasons. The other type of rotated anode previously used is generally cylindrical with a conical or frusto-conical closed end which serves as the focus area. In both prior types of anodes it is possible to use only one surface as the focus area, and when this surface becomes exhausted or unuseable due to erosion, coarsening, distortion, etc., the tube must be disassembled and the anode replaced or reconditioned.

It is accordingly an object of the present invention to extend the useful life of a rotatable disc anode by so designing it that two focus or target surfaces are provided, one on each face of the disc adjacent its periphery with these faces disposed symmetrically to the central plane on the disc. Thus when one target surface has become corroded or unuseable due to electron bombardment, the disc may be removed from the rotating shaft and turned side-for-side and replaced on the shaft to bring the other target surface into position for use. The operating life of the anode is thereby effectively doubled before it must be replaced or reconditioned. If two cathodes are assembled in an X-ray tube, double life can be achieved by using the second cathode with the second focus path without having to remove and reassemble the target. Distortion problems experienced with bimetal anodes are also largely avoidedby thesymmetry of design of the disclosed anode. It is alsopossible to arrange to use both target surfaces of this anodesimultaneously to produce two X-ray beams'onameinforced X-ray beam where need for such arises.

The invention is illustrated by the embodiment shown in the accompanying drawinganddescribedin detail hereinafter. In the drawing,

FIG. 1 is an elevational view, partly in:section,'. of a; typical X-ray generating tube incorporating a rotatable anode of the present invention;

FIG. 2 is a plan view on an enlarged'scalelooking at the face of the rotatable anode shown in. FIG. 1;

FIG. 3 is an edge or side view of the anodeseen'in FIG. 2; and

FIG. 4 is a cross sectional view of the anode taken on line 44 of FIG. 2.

The X-ray tube 10 seen in FIG. 1 consistsbasically of a glass or other envelope 12 containing a cathode unit 14 which is heated by a suitable filament 16 to cause the emission of electrons. There is also disposed: within envelope 12 an anode unit ls comprisinga rotor and bearing support for ashaft 20 andaa circular anode disc 22 mounted on the end of the shaft. The peripheral. 7

margin of the anode disc is disposed opposite cathode 14. Anode unit 18 incorporates suitable inductive or magnetic means (not shown) by which to effect rotation of shaft 20 upon' applicationof a suitable rotating electromagnetic field externally encircling, the neck portion of the tube. The tube is supplied with relatively low voltage filament current at terminals 24, one of which also may serve as the cathode terminal. The rotatable anode disc is connected to terminal 26 for application thereto of high voltage potential. In the operation of the tube, anode disc 22 is driven by unit 18 at high r.p.m., and a high rectified voltage is applied between cathode 14 and the anode 22 through the aforesaid terminals 24, 26, to cause electrons emitted'by the cathode to be attracted to and impinge upon the surface of rotating disc anode 22. Impingement of the electrons upon the face of the disc produces the X-ray I emanations which are projected laterally through the side wall of envelope 12 of the tube 10 and focused on the subject to be examined. Most of the energy of the accelerated electrons striking the rotating anode disc 22 is converted to heat, with the result that the anode disc soon reaches a very high temperature. If the temperature becomes too high, the disc becomes burned and the X-ray emanations produced are scattered rather than beamed or directed in a desired path. The use of refractory metals, their alloys and other materials having high melting points is accordingly dictated for fabrication of the anode disc 22 if it is to have any reasonable or practical life. Molybdenum may be used for example, as well as other metals such as tungsten and rhenium which have still higher melting points and are thus desirable on that account. However, these latter metals do not have as good thermal dissipating properties and have the added disadvantage of substantially greater expense, especially in the case of rhenium. It is for this reason that bimetallic rotatable anode discs are frequently used, wherein the focus area of the rotating anode disc is formed of one of the extremely high-melting refractory metals or alloys able to withstand great temperatures, while the balance and generally the major portion of the rotating disc anode is formed of a lower cost but still relatively high melting materials such as molybdenum or graphite which has better thermal properties.

Referring to FIGS. 2, 3 and 4, anode disc 22 comprises a relatively thin substantially flat circular disc having an axial aperture 30 by which the disc is adapted to be mounted on the end of shaft 20. Disc 22 is of uniform configuration on each of its opposite faces whereby the central plane normal to the aperture 30 constitutes a plane of symmetry, as indicated by the dashed line marked S in FIG. 4. The peripheral margins of disc 22 are beveled, forming annular, substantially planar faces 32 which are equally inclined to the plane of symmetry. These faces constitute the target or focus areas of the anode, and increments of these faces are progressively exposed to electron ,bombardment from the cathode during rotation of the disc. As already mentioned, such bombardment produces X-ray emanations from the target surface, which emanations are then directed radially outward laterally of the X-ray tube. To effect this properly, the target faces 32 are disposed at a base angle which varies from around 5 to measured between the projection of an element or generatrix of revolution of the face and the aforesaid plane of symmetry S.

In the specific example here illustrated, the target surfaces 32 at each side of disc 22 are formed of thin layers or laminations of a highly refractory metal such as tungsten or tungsten-rhenium alloy, while the central major portion of the disc is formed of a high melting material such as molybdenum, molybdenum alloys, or graphite. It is of course possible to use an all tungsten, an all rhenium, or an all refractory metal alloy disc, and fabrication of the disc by forging any of these metals or alloys affords a particularly desirable anode structure.

Rotatable anode discs are generally 3 to 6 inches in diameter and from about Va to of an inch thick. These dimensions are dictated to a large degree by practical considerations involving the balancing of heat capacity with heat dissipating capabilities, compactness and maneuverability of the X-ray apparatus. Other dimensions may be used.

It will be apparent that with an anode of the design here described, when one of the target surfaces 32 becomes exhausted, the anode unit may be removed from the tube to allow disc 22 to be taken off of shaft 22 and turned side-for-side so as to bring the opposite target surface 32 opposite cathode 14 when the members are reassembled in the tube. In addition, with a rotated anode disc of this configuration it is possible to provide a second cathode in the X-ray located adjacent the opposite target face, whereby both the target faces may be used simultaneously to produce a reinforced X-ray beam, or individually to produce a separate beam.

Other symmetrical configurations of the anode disc are possible in place of the mutually inclined planar faces 32. For example such faces may be stepped, curvo-conical or the inclination may be reversed so that they are mutually inclined away from each other in the radial outward direction, depending of course on the design of the X-ray tube in which such rotated anodes are employed, or may have different inclinations.

What is claimed is:

l. A rotatable anode for an X-ray tube comprising:

a circular disc mountable for rotation about an axis;

said disc having oppositely disposed continuous annular faces adjacent its periphery;

said annular faces being mutually and symmetrically inclined toward a plane through and disc perpedicular to said axis.

2. A rotatable anode as defined in claim 1', wherein said annular faces are mutually inclined towards each other in the radial outward direction.

3. A rotatable metal anode as defined in claim 1, wherein at least the major portion of said disc is formed of a material selected from the group consisting of molybdenum, graphite, tungsten, tungsten alloys, and molybdenum alloys, and wherein said mutually inclined annular faces are formed of a metal selected from the group consisting of tungsten and tungsten-rhenium alloys.

4. A rotatable metal anode as defined in claim 3,

wherein said disc is forged of said metals and alloys.

* l l l

Claims

1. A rotatable anode for an X-ray tube comprising: a circular disc mountable for rotation about an axis; said disc having oppositely disposed continuous annular faces adjacent its periphery; said annular faces being mutually and symmetrically inclined toward a plane through said disc perpedicular to said axis.

2. A rotatable anode as defined in claim 1, wherein said annular faces are mutually inclined towards each other in the radial outward direction.

4. A rotatable metal anode as defined in claim 3, wherein said disc is forged of said metals and alloys.