Rotating anode x-ray tube

[57] ABSTRACT

This invention relates to an X-ray tube of the rotatinganode type which includes a disk which is resiliently mounted upon a shaft and also contains an electron impinging portion thereupon. The anode is provided with a plurality of recesses therewithin which produces the advantages which will be hereinafter summarized.

Claims, 11 Drawing Figures

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PATENTED AUG 71973

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ROTATING ANODE X-RAY TUBE

DESCRIPTION OF THE INVENTION

Generally, in rotating anode X-ray tubes which are presently known the electron impinging portion is placed at the greatest possible distance from the center of rotation so that the surface of the anode has the highest possible velocity at the point where the electron beam impinges thereupon. This permits the anode to be subjected to high load. As is also generally known, as the impinging electrodes strike the electrode impinging portion, the anode material heats up and expands. This, of course, will produce mechanical strains with regard to the other portion of the anode which are colder than the electrode impinging portion. Thus the anode has a tendency to break. In addition, of course, when a rotating anode ruptures the centrifugal force involved will cause the broken parts to fly apart and thus further dangers are produced. Where anodes are made of tungsten or molybdenum metal the metal involved is very brittle if it is not heated to at least 200° C. Where graphite anodes are used, their tensile strength is very low even though they have high heat capacitance and high ability to radiate heat.

In the anodes utilized heretofore, in order to increase the strength of the anode, the heating stresses have been distributed over longer time intervals so that the differences in thermal expansion between portions of the anode subjected to electron impingement and nonelectron impingement do not exceed the stress resistance of the material involved. In the case of known anode materials the thermal conductivity is between 0.3 to 0.6 cm times the square root of the time of loading in seconds. Thus, in one second, a heat migration of a maximum of 3 - 6 mm is obtained. Thus an anode of a radius of 5 cm requires 20 - 40 seconds before it is warmer than 200° C in all places. If the above limits are exceeded, of course, the anode will rupture but this can also be avoided if the entire thermal load is maintained below the breaking limit. This causes the additional disadvantage, however, that the exposure time must be lengthened. There is also a disadvantage that, where high temperature differences are involved, warp of the anode will occur making the anode unsuitable for proper use.

It has also been proposed to provide the electron impinging portion of the anode upon the surface of the ring. By the use of a ring, because the heat conduction paths are short, several of the above-mentioned disadvantages have been avoided. However, the ring only has a small surface area and therefore has poorer heat conduction and heat radiation.

I have avoided the disadvantages Of the prior structure by providing a rotating anode which includes rotating means and a disk portion which contains the electron impinging portion thereupon. The disk is provided with recesses which at least penetrate partially through the thickness of the disk and thus the direct connection between the axis of the disk and the electron impinging portion is interrupted. As a result the deformation stresses are moderated because of the fact that the disk is now somewhat resilient. Thus, substantially greater temperature differentials can be utilized without fracture of the anode. On the other hand the heat conductance and thermal capacity of the anode is retained since a large heat conductance area is pro2 vided. Also the heat radiating surface of the anode is increased so that faster cooling thereof is provided.

The recesses can be made in various shapes as indicated in the drawings. One of the preferred shapes is that of a sunburst. The recesses can be cut into the disk by various ways including the use of electron beams. Embossing systems can also be used. The part of the anode which lies between the electron impinging portion and the axis of rotation can also be given resilient properties by providing the anode plate with recesses which lie on concentric circles on the axis of rotation and extend from both the upper and lower surfaces. Such a construction provides for a resilience transverse to the radial direction. The recesses can also be cut into the support as interrupted lines. If this structure is utilized the adjacent recesses are so arranged that the parts which remain are always located at the place where a recess is provided in the adjacent circle to assure radial mounting.

The anodes can consist either of a homologous material such as tungsten, tantalum or carbon. Or, alternatively, it is possible to make the anodes of composite material. For example, a disk-shaped graphite anode could be coated on the electron impinging portion with a metal such as tungsten. It is also possible to insert a metal ring into a graphite dish. A particularly good anode is obtained if the graphite plate is first provided with spokes which extend up to the edge thereof. The plate is then prestressed by reducing its circumference. The groove for the insertion of the ring is then provided and the ring introduced therein. After this is done the stress on the plate is released and the ring is firmly clamped into position.

The above sets forth the proposed objects and advantages of this invention and a brief description thereof. Other objects and advantages of this invention will become apparent to the reader of this specification as the description proceeds.

The invention will now be further described by reference to the accompanying drawings which are made a part of this specification.

IN THE FIGURES

FIG. 1 is a side elevational view of an X-ray tube having the rotating anode of this invention with portions of the anode plate partially broken away to show details of construction.

FIG. 2 is a bottom plan vfew of the anode plate of the tube of FIG. 1.

FIG. 3 is a cross-sectional view of an anode plate of an alternative form of this invention in which the plate consists of a single material and the openings are arranged in the form of a sunburst.

FIG. 4 is a top plan view of the anode plate shown in FIG 3·

FIG. 5 is a view similar to that of FIG. 3 but showing a further alternative form of this invention wherein the anode plate is of heavy metal and the openings therewithin are concentric to one another.

FIG. 6 is a top plan view of the form of invention shown in FIG. 5.

FIG. 7 is a top perspective view of a further alternative form of this invention wherein the anode consists of individual spoke-shaped members which are held together on the outer periphery by a heavy metal rim which also constitutes the electron impinging portion.

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FIG. 8A is a fragmentary cross-sectional view of a portion of an anode plate wherein the electron impinging portion lies on a thin ring which is located on a graphite base and provided with concentric annular grooves on the top and bottom.

FIG. 8B is a view similar to that of FIG. 8A but showing the position of the annular grooves when differential heating is applied to the anode plate.

FIG. 9 is an isometric view of a further alternative form of anode plate and associated structure with portions thereof broken away.

FIG. 10 is a top plan view of one of the sections of the anode plate shown in FIG. 9.

The invention will be further described by reference to the specific form thereof as shown in the accompanying drawings. In this connection, however, the reader is cautioned to note that such specific form of this invention as set forth in the specification herein is for illustrative purposes and for purposes of example only. Various changes and modifications could obviously be made within the support and scope of this invention.

Now referring to the specific form of this invention as shown in the drawings herein, there is shown in FIG. 1 an X-ray tube 2 which is surrounded by a glass vacuum element 1. The cathode 3 is spaced from the rotating anode 4. Cathode combination 3 includes mount 5 with shielding 6 covering the conventional cathode construction (not shown). Anode 4 includes a rotor 7 which carries shaft 8 at its upper end. Between elements 11 and 12 is clamped an anode plate 9. It is thus seen that when rotor 7 turns anode plate 9 will also turn. Rotor 7 can, of course, be turned by a conventional stator which which is placed on the outside of tube 2. The rotation can be accomplished, for example, by complementary magnetic means arranged upon the rotor and stator.

Referring specifically to anode plate 9 (which preferably has a diameter of 100 mm) there is shown a graphite portion 10 which has a preferred thickness of 15 mm. Shaft 8 passes through an opening substantially centrally located within plate 9 and plate 9 is clamped in position between elements 11 and 12. A ring 13 is provided within a groove 14 located within anode plate 9. Ring 13 is preferably made of tungsten. The two concentric circles shown as 15 and 16 on ring 13 constitute electron impinging portions which are the portion of the anode upon which the electron beam from the cathode will impinge. It is noted that element 10 is provided with a plurality of recesses 17 and 18 which are preferably in the form of a sunburst and extend from the inner surface to the outer edge of element 10. Thus element 10 includes a plurality of sectors 20 which are connected with one another through spoke elements 19. Specifically, in the form of invention shown in FIGS. 1 and 2 there are a total of nine sectors 20 formed within member 10. Since ring 13 must be held securely in position it has a diameter of about 1 mm, smaller than that of the recess in which it is clamped. The ring 13 is then held in position by pressure. An additional holding action is provided in that the edge 21 of ring 13 is inclined outwardly toward shaft 8 and the upper diameter of ring 13 is larger than the lower diameter. A preferred manner of inserting ring 13 into groove 13 is to reduce the circumference of body 10 so that the ring 13 can be inserted despite its smaller inside diameter. Such a method can be easily accomplished by the utilization of a band which can be tight4 ened by imposing pressure around the circumference of the disk. Once the ring has been inserted the band can then be released so that spokes 19 can spring outwardly and will insure the proper support of ring 13.

In order to produce a beam between anode and cathode high voltage is applied to lines 22, 23, 24 and element 25. The heating voltage for the cathode within screen 6 is connected between line 23 and one of lines 22 and 24. Thus there is produced two spaced electron beams which are adapted to individually strike impinging portions 15 and 16 which lie on the surface of ring 13. In the preferred modification shown paths 15 and 16 are concentric to one another and differ by their inclination with respect to the axis of rotation of the anode plate with elements 16 being inclined outwardly by 17.5° with respect to the perpendicularity of the axis of rotation and the inner portion 16 is inclined outwardly by 10°.

In operation the device of FIGS. 1 and 2 produces generation of X-rays which then strike ring 13 along the electron impinging portions. The tensile and shear stresses which occur by reason of the electron impingement are taken up by recesses 17 and 18 which are provided in anode plate 9 and these stresses will then be eliminated by reason of the provision of the structure shown. In addition, of course, the fact that element 10 is made of graphite radiates the heat far better than any metallic element.

In FIGS. 3 and 4 there is shown an alternative structure of the anode disk portion. Here a plate 26 is provided which is equivalent in function to anode 9. Plate 26 consists of molybdenum and is coated with a 1.5 mm thick layer of an alloy of 90 percent tungsten and 10 percent rhenium along the electron impinging portions 27 and 28 which correspond to electron impinging portions 15 and 16 in FIG. 1. It is noted that there are provided 12 recesses in plate 26 which between them define spoke members 30 and these elements permit the differential expansion forces to be converted to bending forces and thus will note cause the disk to fracture.

In FIGS. 5 and 6 there is a further alternative structure of anode plate 9 shown. Here the analogous plate is designated 31 and consists of an allow which contains 0.1 percent yrridium plus 99.9 percent tungsten. This plate is 4 mm thick and contains 4 concentric rows of recesses 32, 33, 34 and 35 which have a width of 3 mm. The parts between the recesses then act as holding spokes. The electron impinging portion is indicated by reference character 36 and is inclined 12° downwardly with respect thereto perpendicular to the axis of rotation. Thus, again, the tensile and shear stresses produced during operation of the anode involved are converted into flexural stresses.

A further alternative construction shown in FIG. 7 includes a mounting plate 38 which includes a plurality of elements 39 which become wider from the axis of rotation toward the edge and are spaced from one another through slots 40. These elements 39 are held together by the ring 42 which is clamped around their lateral edges. In this construction it is noted that the electron impinging portion lies upon the outer element of ring 41 and the cathode 42 is placed on the side of the anode 37. Thus the electron impinging in the direction shown by the arrow 43 in FIG. 7 produces a beam of X-rays 44.

In FIGS. 8A and 8B there is shown a construction which can be provided in order to save weight. In such

3,751,702 a construction the ring could be easily deformed reversibly during heating upon production of the beam, thereby making the anode angle smaller. Thus there are produced not only tensile forces in a radial direction but also a bending force in the mount 46 which is made of graphite. In order to avoid breaking of mount 46 a plurality of annular grooves 47 and 48 are cut therewithin and are staggered with respect to one another on the upper and lower sides. Thus, when stresses are produced which lead to bending stresses grooves 47 then close somewhat at their upper end and grooves 48 widen somewhat at their lower end.

This position is shown in FIG. 8B.

In FIGS. 9 and 10 a further alternative construction is shown wherein the anode plate is composed of individual members 49-54 which are held to one another in pie-sliced relationship by ring 55. Each of these members 49-54 are provided with a plurality of recesses which extend transversely from either end. Element 54 is specifically shown in FIG. 10 and includes the recesses 57-60 which extend alternatively from opposite sides. It is obvious that this construction of members 49-54 will hold ring 55 resiliently on shaft 56. Here the electron impinging portion is also an outer periphery of ring 55 and the electrons are produced from coil 61 of cathode 62.

The foregoing sets forth the manner in which the objects of this invention are achieved.