Rotary anode for an x-ray tube

Abstract

There is provided a rotary anode (100) for an X-ray tube. The rotary anode comprises: an anode disc (102) of refractory material comprising an anterior surface and a posterior surface, the anterior surface having an annular focal track region (106); a supportive backpack (104) comprising an anterior surface and a posterior surface, the anterior surface of the supportive backpack being fixedly attached to the posterior surface of the anode disc; and a stress-relieving cavity structure (108) formed in the rotary anode, wherein the stress-relieving cavity structure comprises a slot (110) for relieving thermomechanical stress in the annular focal track region, wherein the slot extends from the anterior surface of the anode disc towards the posterior surface of the supportive backpack, passing wholly through the anode disc and partially but not wholly through the supportive backpack. In this way, the cavity structure permits relaxation of the anode disc in the annular focal track region so as to mitigate or avoid cracking while reducing or minimizing its detrimental effect on the structural integrity of the supportive backpack.

Description

FIELD OF THE INVENTION

[0001] The invention relates to a rotary anode for an X-ray tube, to an X-ray tube comprising the rotary anode, and to a method for manufacturing the rotary anode.BACKGROUND OF THE INVENTION

[0002] Thermomechanical stresses on the anode disc of an X-ray tube can lead to mechanical failure. The current way of mitigating this problem is to form radial slots in the anode. The slots are typically formed in the metal body of the anode as well as its graphite backpack so as to penetrate the entire thickness of the metal body as well as that of the graphite backpack. An axial bore is formed at the inner end of each slot to relieve notch stress. Preferably, the axial bores are located in colder parts of the anode, away from the focal track, an arrangement which is more readily achievable with larger anodes than with smaller anodes, since, in the latter case, the length of the slots becomes so large relative to the radius of the disc as to compromise mechanical stability of the graphite backpack.

[0003] US4,255,685 describes an arrangement in which the slot extends partway through the metal disc in an axial direction before turning in a radial direction towards the outer circumference of the metal disc. In this arrangement, the slot does not relieve thermomechanical stress in the graphite backpack.SUMMARY OF THE INVENTION

[0004] The invention is defined by the independent claims. Advantageous embodiments are defined in the dependent claims. To better address one or more of the above concerns, there is provided, in a first aspect of the invention a rotary anode for an X-ray tube. The rotary anode comprises: an anode disc of refractory material comprising an anterior surface and a posterior surface, the anterior surface having an annular focal track region; a supportive backpack comprising an anterior surface and a posterior surface, the anterior surface of the supportive backpack being fixedly attached to the posterior surface of the anode disc; and a stress-relieving cavity structure formed in the rotary anode, wherein the stress-relieving cavity structure comprises a slot for relieving thermomechanical stress in the annular focal track region, wherein the slot extends from the anterior surface of the anode disc towards the posterior surface of the supportive backpack, passing wholly through the anode disc and partially but not wholly through the supportive backpack.

[0005] Stated differently, the slot does not completely penetrate the thickness of the supportive backpack. In this way, the cavity structure permits relaxation of the anode disc in the annular focal track region so as to mitigate or avoid cracking while reducing or minimizing its detrimental effect on the structural integrity of the supportive backpack.

[0006] The anode disc refractory material may comprise a refractory metal, such as tungsten or molybdenum. The refractory material may comprise an alloy, such as Titanium Zirconium Molybdenum (TZM), Tungsten Rhenium etc.

[0007] The slot may be at least partially bounded in the interior of the rotary anode by a rounded portion of the stress-relieving cavity structure for relieving notch stress in the slot. In this way, cracking at the limitation of the slot can be mitigated or prevented.

[0008] For ease of manufacture, the rounded portion of the stress-relieving cavity may be formed by at least one bore made in the rotary anode. In particular, the rounded portion of the stress-relieving cavity may comprise at least one of an axial bore formed in the anode disc and a radial bore formed in the supportive backpack. The axial bore may extend wholly through the anode disc and partially but not wholly through the supportive backpack. Alternatively, the axial bore may extend wholly through the anode disc and wholly through the supportive backpack. The radial bore may extend from the outer circumferential surface of the supportive backpack towards a central or bulk region of the rotary anode, passing partially or wholly through the supportive backpack.

[0009] For reducing its impingement on mechanical stability, a diameter of the axial bore may be less than half of a diameter of the anode disc.

[0010] The cavity structure may further comprise a chamfered surface in one or both of the posterior surface of the anode disc and the anterior surface of the supportive backpack, that is, at an intersection of the anode disc with the supportive backpack, for absorbing solder or braze. In particular, the anode disc may comprise at least one chamfered surface at its intersection with the supportive backpack. Additionally, or alternatively, the supportive backpack may comprise at least one chamfered surface at its intersection with the anode disc. In this way, disadvantageous filling of the cavity structure by solder or braze can be mitigated or avoided.

[0011] In a second aspect, there is provided an X-ray tube comprising the rotary anode of the first aspect.

[0012] In a third aspect, there is provided a method for manufacturing the rotary anode of the first aspect. The method comprises: obtaining an anode disc of refractory material comprising an anterior surface and a posterior surface, the anterior surface having an annular focal track region; obtaining a supportive backpack comprising an anterior surface and a posterior surface; fixedly attaching the anterior surface of the supportive backpack to the posterior surface of the anode disc; and forming a stress-relieving cavity structure in the rotary anode, wherein the stress-relieving cavity structure comprises a slot for relieving thermomechanical stress in the annular focal track region, wherein the slot extends from the anterior surface of the anode disc towards the posterior surface of the supportive backpack, passing wholly through the anode disc and partially but not wholly through the supportive backpack. The cavity structure or any part thereof can be formed in the anode disc or in the supportive backpack prior to or after soldering or brazing.

[0013] The term "anterior" means facing an electron beam in use of the X-ray tube or towards the front. Correspondingly, "posterior" means facing away from the electron beam or towards the rear.

[0014] The term "axial" is used herein to denote not only a direction parallel with the axis of rotation of the anode but any direction extending from the anterior side towards the posterior side or vice versa. The term "radial" is used herein to denote not only a direction parallel with the radius of the disc but any direction extending from the outer circumference of the anode towards its central or bulk region or vice versa. Thus, the terms "axial" and "radial" are not to be understood in a strict geometric sense and may furthermore be applied to straight or curved paths.

[0015] The term "bore" means any hole or groove made or enlarged by drilling, cutting, or removing material.

[0016] The term "notch stress" as used herein refers to a stress concentration caused by irregular geometry which interrupts the flow of stress, and which can result in the initiation and growth of fatigue cracks.

[0017] The indefinite article "a" or "an" does not exclude a plurality. In addition, the articles "a" and "an" as used herein should generally be construed to mean "one or more" unless specified otherwise or clear from the context to be directed to a singular form.

[0018] Unless specified otherwise, or clear from the context, the phrases "one or more of A, B and C", "at least one of A, B, and C", and "A, B and / or C" as used herein are intended to mean all possible permutations of one or more of the listed items. That is, the phrase "A and / or B" means (A), (B), or (A and B), while the phrase "A, B, and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

[0019] The term "comprising" does not exclude other elements or steps. Furthermore, the terms "comprising", "including", "having" and the like may be used interchangeably herein.

[0020] The above-described aspects will become apparent from, and elucidated with, reference to the detailed description provided hereinafter.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] A detailed description will now be given, by way of example only, with reference to the accompanying drawings, in which: Fig. 1A is a cross-sectional view of a rotary anode comprising one example of a stress-relieving cavity structure; Fig. 1B is a perspective view of one segment of the rotary anode shown in Fig. 1A; Fig. 1C is a side view of the segment shown in Fig. 1B; Fig. 2A is a cross-sectional view of a rotary anode comprising another example of a stress-relieving cavity structure; Fig. 2B is a side view of the segment shown in Fig. 2A; Fig. 3 is a cross-sectional view of a rotary anode comprising yet another example of a stress-relieving cavity structure; and Fig. 4 is a flowchart representing a method for manufacturing a rotary anode as described herein. DETAILED DESCRIPTION OF EMBODIMENTS

[0022] Figs. 1A-1C illustrate a rotary anode 100 comprising an anode disc 102 and a supportive backpack 104. The anode disc 102 is made of a refractory material (e.g., comprising molybdenum, tungsten, TZM) and comprises an anterior surface and a posterior surface, the anterior surface having an annular focal track region 106 thereon. The supportive backpack 104 comprises an anterior surface and a posterior surface, the anterior surface of the supportive backpack 104 being fixedly attached to the posterior surface of the anode disc 102, for example by brazing or soldering. The supportive backpack 104 may be made of graphite or other materials like carbon-fiber-carbon composites (CFC), silicon carbide (SiC), or other ceramic materials with suitable material characteristics.

[0023] A stress-relieving cavity structure 108 is formed in the rotary anode 100. The stress-relieving cavity structure 108 comprises a slot 110 for relieving thermomechanical stress in the annular focal track region 106. The slot 110 extends from the anterior surface of the anode disc towards the posterior surface of the supportive backpack 104, passing wholly through the anode disc 102 and partially but not wholly through the supportive backpack 104. The slot 110 furthermore extends from an outer circumferential surface of the anode disc 102 towards a central region of the anode disc 102. The slot 110 is bounded in the interior of the rotary anode 100 by a rounded portion of the stress-relieving cavity structure 108 for relieving notch stress in the slot 110. In the example shown, the rounded portion of the stress-relieving cavity 108 comprises an axial bore 112 and a radial bore 114. The slot 110 is bounded at its central or medial end by the axial bore 112, and bounded at its posterior end by the radial bore 114. The axial bore 112 extends wholly through the anode disc 102 and partially but not wholly through the supportive backpack 104, so far as to intersect the radial bore 114. The radial bore 114 extends from the outer circumferential surface of the supportive backpack 104 towards a central region of the rotary anode 100, passing partially through the supportive backpack 104, so far as to intersect the axial bore 112. The slot 110 communicates with the axial bore 112 and with the radial bore 114. The bores 112, 114 may be made for example by drilling or milling. Although only one slot is illustrated, it will be appreciated that the rotary anode 100 may comprise a number of slots distributed along its circumference, numbering for example between 2 and 48, or more preferably between 6 and 16 slots. The slot 110 in this non-limiting example has a slot width in the range 0.1 mm - 2 mm. The bores 112, 114 in this non-limiting example have a diameter between 0.1 mm-10 mm (e.g. identical to the slot width).

[0024] Figs. 2A and 2B illustrate a rotary anode 100 comprising another example of the stress-relieving cavity structure 108, which differs from that described and illustrated with reference to Figs. 1A-1C in two respects. Firstly, the radial bore 114 is formed somewhat deeper in the supportive backpack 104. Secondly, the cavity structure 108 further comprises chamfered surfaces at the intersection of the anode disc 102 with the supportive backpack 104 for absorbing solder or braze. In the example shown, both the anode disc 102 and the supportive backpack 104 comprise chamfered edges 116 on both lateral sides of the slot 110.

[0025] Fig. 3 illustrates another example of the cavity structure 108 in which the radial bore 114 has a non-circular cross section, to illustrate that the form and dimension of the bores 112, 114 are variable and may change along their length.

[0026] In other variants, the slots 110 may be formed at an angle with respect to the axis of rotation and / or with respect to the strictly geometric radial direction. In place of straight slots, curved, spiral, or S-shaped slots may be formed. The length of the radial bore 114 is variable: it can end before the interior end of the slot 110, at the same level, or it can extend farther, even passing completely through the supportive backpack 104. Slot width and length may vary within a slot and / or between slots.

[0027] Fig. 4 is a flowchart representing a method for manufacturing a rotary anode as described herein.

[0028] In S1, an anode disc of refractory material comprising an anterior surface and a posterior surface is obtained, the anterior surface having an annular focal track region.

[0029] In S2, a supportive backpack comprising an anterior surface and a posterior surface is obtained.

[0030] In S3, the anterior surface of the supportive backpack is fixedly attached to the posterior surface of the anode disc.

[0031] In S4, a stress-relieving cavity structure is formed in the rotary anode, wherein the stress-relieving cavity structure comprises a slot for relieving thermomechanical stress in the annular focal track region, wherein the slot extends from the anterior surface of the anode disc towards the posterior surface of the supportive backpack, passing wholly through the anode disc and partially but not wholly through the supportive backpack.

[0032] The skilled person will appreciate that also other orders of the above method steps are conceivable within the scope of the invention. For example, step S2 may precede step S1

[0033] Proposed herein is thus a new geometry of slots in rotary anodes that have graphite backpacks, solving the problem of forming the slots without overly reducing mechanical stability of the graphite backpack due to the introduction of the slots, in particular for smaller diameter anodes which operate at higher anode rotation frequencies.

[0034] Thermomechanical simulations of the arrangements described herein demonstrate that stresses can be mitigated to a tolerable level while the supportive backpack 104 remains stable enough to endure high anode rotation frequencies and thermomechanical loads.

[0035] Arrangements disclosed herein may find application in any X-ray tube including those intended for computed tomography or interventional guided therapy.

[0036] The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features.

[0037] It has to be noted that embodiments of the invention are described with reference to different categories. In particular, some examples are described with reference to methods whereas others are described with reference to apparatus. However, a person skilled in the art will gather from the description that, unless otherwise notified, in addition to any combination of features belonging to one category, also any combination between features relating to different category is considered to be disclosed by this application. However, all features can be combined to provide synergetic effects that are more than the simple summation of the features.

[0038] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art, from a study of the drawings, the disclosure, and the appended claims.

[0039] Measures recited in mutually different dependent claims may advantageously be combined.

[0040] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. Rotary anode (100) for an X-ray tube, the rotary anode comprising: an anode disc (102) of refractory material comprising an anterior surface and a posterior surface, the anterior surface having an annular focal track region (106); a supportive backpack (104) comprising an anterior surface and a posterior surface, the anterior surface of the supportive backpack being fixedly attached to the posterior surface of the anode disc; and a stress-relieving cavity structure (108) formed in the rotary anode, wherein the stress-relieving cavity structure comprises a slot (110) for relieving thermomechanical stress in the annular focal track region, wherein the slot extends from the anterior surface of the anode disc towards the posterior surface of the supportive backpack, passing wholly through the anode disc while passing partially but not wholly through the supportive backpack.

2. Rotary anode as claimed in claim 1, wherein the slot (110) is at least partially bounded in the interior of the rotary anode (100) by a rounded portion of the stress-relieving cavity structure (108) for relieving notch stress in the slot.

3. Rotary anode as claimed in claim 2, wherein the rounded portion of the stress-relieving cavity (108) is formed by at least one bore (112, 114) made in the rotary anode (100).

4. Rotary anode as claimed in claim 2 or 3, wherein the rounded portion of the stress-relieving cavity (108) comprises at least one of an axial bore (112) formed in the anode disc (102), and a radial bore (114) formed in the supportive backpack (104).

5. Rotary anode as claimed in claim 4, wherein the axial bore (112) extends wholly through the anode disc (102) and partially but not wholly through the supportive backpack (104).

6. Rotary anode as claimed in claim 4, wherein the axial bore (112) extends wholly through the anode disc (102) and wholly through the supportive backpack (104).

7. Rotary anode as claimed in any of claims 4-6, wherein the radial bore (114) extends from an outer circumferential surface of the supportive backpack (104) towards a central region of the rotary anode (100), passing partially or wholly through the supportive backpack (104).

8. Rotary anode as claimed in any of claims 4-7, wherein a diameter of the axial bore (112) is less than half of a diameter of the anode disc (102).

9. Rotary anode as claimed in any preceding claim, wherein the cavity structure (108) further comprises a chamfered surface (116) in one or both of the posterior surface of the anode disc (102) and the anterior surface of the supportive backpack (104) for absorbing solder or braze.

10. Rotary anode as claimed in any preceding claim, wherein the cavity structure (108) is configured to permit relaxation of the anode disc (102) in the annular focal track region (106) so as to mitigate or avoid cracking while reducing or minimizing its detrimental effect on structural integrity of the supportive backpack (104).

11. X-ray tube comprising the rotary anode (100) as claimed in any preceding claim.

12. Method for manufacturing a rotary anode (100) for an X-ray tube, the method comprising: obtaining (S1) an anode disc (102) of refractory material comprising an anterior surface and a posterior surface, the anterior surface having an annular focal track region (106); obtaining (S2) a supportive backpack (104) comprising an anterior surface and a posterior surface; fixedly attaching (S3) the anterior surface of the supportive backpack to the posterior surface of the anode disc; and forming (S4) a stress-relieving cavity structure (108) in the rotary anode, wherein the stress-relieving cavity structure comprises a slot (110) for relieving thermomechanical stress in the annular focal track region, wherein the slot extends from the anterior surface of the anode disc towards the posterior surface of the supportive backpack, passing wholly through the anode disc and partially but not wholly through the supportive backpack.

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