EP0169117A1 - Rotary anode X-ray tube and method for mounting the rotary anode on a supporting axis - Google Patents

Abstract

The present invention relates to an X-ray tube with a rotating anode and a method of fixing a rotating anode to a support axis contained in such a tube. Said rotating anode (5) is fixed to said support axis (4) by means of a deformed means (21), disposed between said rotating anode (5) and said support axis (4), concentrically with the latter, and acting like a cable gland.

Description

The invention relates to an X-ray tube with a rotating anode usable in the general field of radiology, and particularly well suited in cases where the rotating anode is subjected to significant accelerations. It also relates to a method for fixing a rotary anode on a support axis.

The rotating anodes of X-ray tubes are generally disc-shaped. The disc is fixed on an axis itself connected to a rotor, the assembly being driven in rotation by a rotating magnetic field to which the rotor is subjected.

The rotating rotating anode is subjected to very high stresses, both thermal and mechanical.

Indeed, X-rays are obtained under the effect of electronic bombardment of a small surface of the anode, and a very small part of the electrical energy, used to accelerate the electrons, is transformed into X-rays. The rest of this energy is dissipated as heat in the rotating anode. Also, the rotating anode is subjected to very significant thermal shocks and can reach very high temperatures. Mechanical stresses are linked in particular to high rotational speeds and to significant accelerations to which the rotating anode may be subjected.

Generally the anode is fixed to the axis which connects it to the rotor, by fixing means acting by clamping. It commonly happens that under the effect of the constraints mentioned above, the rotating anode tends to loosen and to move by turning, relative to its support axis. This can result in a haze or an imbalance of the anode-rotor rotating assembly, with the appearance of vibrations and risks of mechanical rupture.

The problem thus posed, which is the fixing of the rotating anode to the axis which connects it to the rotor, exists with all types of anodes rotating.

But this problem is even more critical in the case of graphite anodes, due on the one hand to the differences in expansion coefficients of the graphite and of the support axis, and on the other hand to the coefficient of friction of the graphite which is a material with a lubricating tendency.

• - a) des clavettes engagées dans l'anode et dans l'axe support, selon des axes transversaux à ce dernier. Cette solution est peu efficace dans le cas des anodes en graphite en raison du caractère friable du graphite ;
• - b) des axes supports munis de bcssages excentrés ; l'inconvénient de cette solution est qu'elle laisse subsister un jeu mécanique très important entre le disque d'anode et l'axe support ;
• - c) une solution très différente consiste à braser l'anode sur son axe support. Cette solution assure une bonne liaison entre l'anode et son axe support, bien qu'elle constitue une opération délicate à mettre en oeuvre. En outre, elle peut limiter les performances du tube à rayons X en dégradant la qualité du vide qui existe dans ce dernier, si la température de fonctionnement conduit les matériaux de brasure à avoir une tension de vapeur trop élevée. Il est à remarquer d'autre part, que cette fixation par brasure exclut tout démontage ;
• - d) une demande de brevet européen publiée sous n° 0 055 828 décrit la réalisation, dans un même bloc de graphite, du disque d'anode et de son axe support, afin de rejeter la liaison graphite- métal dans une zone de température moins élevée, étant plus éloignée du disque d'anode. Cette configuration, outre son prix de revient très élevé, reste très fragile mécaniquement, du fait notamment de la faible résistance mécanique du graphite ;
• - e) une demande de brevet français publiée sous le n° 2 467 483 décrit une réalisation dans laquelle, une douille en graphite pyrolitique est brasée dans le corps du disque d'anode en graphite. Mais cette solution est également très coûteuse étant de réalisation délicate et mécaniquement fragile.

To date, different methods are used to try to overcome this difficulty. We can cite :

• - a) keys engaged in the anode and in the support axis, along axes transverse to the latter. This solution is not very effective in the case of graphite anodes because of the brittle nature of graphite;
• - b) support axes provided with eccentric bcssages; the drawback of this solution is that it leaves a very significant mechanical clearance between the anode disc and the support axis;
• - c) a very different solution consists in brazing the anode on its support axis. This solution provides a good connection between the anode and its support axis, although it is a delicate operation to implement. In addition, it can limit the performance of the X-ray tube by degrading the quality of the vacuum which exists in the latter, if the operating temperature leads the brazing materials to have a too high vapor pressure. It should also be noted that this fixing by soldering excludes any disassembly;
• - d) a European patent application published under No. 0 055 828 describes the production, in the same block of graphite, of the anode disc and its support axis, in order to reject the graphite-metal bond in a temperature zone lower, being further from the anode disc. This configuration, in addition to its very high cost price, remains very fragile mechanically, due in particular to the low mechanical strength of graphite;
• - e) a French patent application published under No. 2,467,483 describes an embodiment in which, a pyrolitic graphite sleeve is brazed in the body of the graphite anode disc. But this solution is also very expensive being of realization delicate and mechanically fragile.

This enumeration of different methods, all aimed at achieving the fixing of the rotating anode on its support axis, shows that the problem posed by this fixing is of great importance for all manufacturers of X-ray tubes. It also shows that To date, the problem posed by this fixation has not been resolved to everyone's satisfaction.

The present invention relates to an X-ray tube with a rotating anode, in which the fixing of the rotating anode disc on its support axis is ensured in a reliable manner, by means which are simple and easy to implement, and which also allow disassembly of the anode disc. The invention also relates to a method of fixing a rotating anode to a support axis.

According to the invention, an X-ray tube with a rotating anode, comprising a rotor and a support axis arranged and secured along a longitudinal axis around which said rotating anode is rotated, said rotating anode comprising a first and a second face, opposite , between which it comprises a through hole arranged along said longitudinal axis, said support axis being engaged in said through hole, is characterized in that it further comprises at least one deformed element contained in a housing concentric with said support axis, said housing being produced between said support axis and a wall of said through hole, so as to secure said rotary anode on said support axis.

• - la figure 1 montre partiellement, selon une vue en coupe, un tube à rayons X selon l'invention ;
• - la figure 2 montre plus particulièrement, selon une vue en coupe également, des moyens caractéristiques de l'invention contenus dans un encadré montré sur la figure 1 ;
• - les figures 3 et 4 représentent respectivement des moyens contenus dans l'encadré des figures 1 et 2, selon une première et une seconde variante de l'invention.

The invention will be better understood from the following description, given solely by way of example, and made with reference to the four accompanying drawings, among which:

• - Figure 1 partially shows, in a sectional view, an X-ray tube according to the invention;
• - Figure 2 shows more particularly, in a sectional view also, characteristic means of the invention contained in a box shown in Figure 1;
• - Figures 3 and 4 respectively represent means contained in the box of Figures 1 and 2, according to a first and a second variant of the invention.

FIG. 1 shows an X-ray tube 1 comprising, in an envelope 2, a rotor 3, a support axis 4, a rotating anode 5. The X-ray tube 1 being, with the exception of means serving to fix and to block the rotating anode 5 relative to the support axis 4, of a conventional type, the other means with which the X-ray tube 1 is traditionally provided are not shown.

The rotor 3 and the support axis 4 are arranged and secured along a longitudinal axis 6, around which they cause the rotation of the anode 5, according to arrow 9 for example. In the nonlimiting example of the description, the rotating anode 5 is formed by a graphite disc 11, on which is deposited a layer of tungsten 8. The rotating anode 5 has an axis of symmetry coincident in the figure with the longitudinal axis 6, along which it is crossed, between its first and second faces 12, 13, opposite, by a through hole 10 having in the example described a circular section (not shown).

The support axis 4 has a shoulder 16 from which its end 7 is engaged in the through hole 10 of the rotating anode 5, along the longitudinal axis 6; the second face 13 of the rotating anode 5 being in abutment on the shoulder 16.

The rotating anode 5 is fixed on its support axis 4 by means of a deformed element 21, arranged concentrically with the support axis 4 and contained in a housing 20 arranged between the support axis 4 and a wall 22 of the through hole 10. In the nonlimiting example described, the housing 20 is constituted by a groove, also concentric with the support axis 4, produced by the wall 22 of the through hole 10 and open, on the one hand on the first face 12 of the anode rotating 5, and open on the other hand on the support axis 4.

The housing 20 thus comprises a first wall 24, formed by the support axis 4 itself and, a second wall 25 opposite the first; this second wall belonging to the rotating anode 5.

The second wall 25 can be parallel to the first wall 24 au, thus in the example described, be inclined relative to the latter; the groove constituting the housing 20 then being a conical groove.

The deformed element 21 is constituted by a deformable element such as a closed or not ring, or a clamping ring, having before deformation a diameter (not shown in FIG. 1) equal to or greater than an average width L of the housing 20 , considered between its two walls 24, 25. The clamping rod constituting the deformed element 20 is made of a refractory material, at low vapor pressure, and fairly plastic such as tantalum or niobium.

The deformed element 21 surrounds the support axis 4 at the level of the first wall 24, and determines between this first wall 24 and the second wall 25, belonging to the rotating anode 5, forces (not shown) which effect the blocking of the rotating anode 5 relative to the support axis 4.

According to the same principle of fixing the rotating anode 5, on the support axis 4, the housing 20 and the deformed element 21 which it contains can be arranged on the side of the second face 13, towards the shoulder 16, where they are represented in FIG. 1, respectively identified 20a and 21a. In this case, the housing 20a is open on the side of the second face 13; the deformed element 21 enclosing the support axis 4 in the same manner as in the case of the previous example.

These two methods of fixing the rotating anode 5 on its support axis 4 can be used either separately or simultaneously. In this first version of the X-ray tube shown in FIG. 1, the end 7 of the support shaft 4 also comprises a thread 14, on which is aimed an axial nut 15. The nut 15 and the thread 14 also constitute a means of fixing the rotating anode 5 on its support axis 4, which also plays a role in the process according to which the deformation of the deformable element takes place or clamp ring from which the deformed element 21 is obtained.

In the nonlimiting example shown in FIG. 1, the nut 15 comprises on a lower face 26, a ring 27 also concentric with the support axis 4. According to the method of the invention, which will be explained further below of the description relating to FIG. 2, when the nut 15 is tightened on the thread 14 until it is locked on the first face 12 of the rotating anode 5, by means of a washer 30, the ring 27 enters the housing 20 bearing on the clamping ring 21; thus, when the nut 15 is used, the tightening ring 21 is inserted into the groove or housing 20, and comes to grip the support shaft 4 while being deformed, the assembly acting in the manner of a cable gland.

Similarly, if the rotating anode 5 has on the side of its second face 13 a housing 20a, provided with a clamping ring 21a, and that on the other hand the shoulder 16 also has a second ring 27a acting as the first ring 27, the tightening of the nut 15 causes the tightening rod 21a to be pushed into the groove or housing 20a; the clamping rod 21a as in the previous example, enclosing the support axis 4 while deforming.

It should be noted that the first or the second ring 27, 27a are not necessary to obtain the deformation of the tightening ring 21, 21a if, for example, the diameter of the tightening ring 21, 21a is such that before to be deformed, it protrudes from the plane of the first or second face 12, 13; this being further explained with reference to FIG. 2, which repeats elements contained in a box 50 that comprises FIG. 1.

FIG. 2 illustrates the method of the invention, applicable to the fixing of a rotating anode 5 on a support axis 4. The rotating anode 5 being of the type comprising, between these opposite faces 12, 13 and, along an axis of symmetry 31 perpendicular to its plane, a through hole 10; the through hole 10 being intended to receive the end 7 of the support axis 4, the axis of symmetry 31 then being coincident with the longitudinal axis 6 of the support axis 4.

• - à usiner l'anode tournante 5 pour réaliser au moins un logement 20 ouvert sur l'une des faces 12, 13, la première face 12 par exemple comme montrée dans l'exemple non limitatif de la figure 2 ;
• - puis, ayant par exemple engagé l'extrémité 7 de l'axe support 4 dans le trou débouchant 10, à placer le jonc de serrage 21 dans le logement 20 ; il est à remarquer que dans cette phase du procédé, le jonc 21 est en butée dans le logement 20 contre les parois 24, 25 de ce dernier, et comporte une partie 32 en dépassement par rapport au plan de la première face 12.

From such a rotating anode, the method consists:

• - to machine the rotating anode 5 to produce at least one housing 20 open on one of the faces 12, 13, the first face 12 for example as shown in the nonlimiting example of FIG. 2;
• - Then, having for example engaged the end 7 of the support axis 4 in the through hole 10, to place the clamping rod 21 in the housing 20; it should be noted that in this phase of the process, the rod 21 abuts in the housing 20 against the walls 24, 25 of the latter, and comprises a part 32 projecting from the plane of the first face 12.

The clamping ring 21 thus being in abutment, the next phase of the process consists in deforming the clamping ring 21 so as to increase the surface area and the force according to which, on the one hand, it is in contact and encloses the support axis 4 , that is to say the first wall 24, and on the other hand that it is in contact with the rotating anode 5, that is to say the second wall 25; this deformation of the clamping rod 21, which can even bring it into contact with the bottom 33, of the housing 20.

In the nonlimiting example of a first version of the method of the invention, the deformation of the clamping rod 21 is obtained by tightening the nut 15, on the thread 14. In the nonlimiting example described , the nut 15 is supported on the part 32 of the clamping ring 21 by means of the washer 30, and when the nut 15 is used until the washer 30 is brought into contact with the upper face 12 , the clamping rod 21 sinks into the housing 20 and encloses the support shaft 4 while being deformed; the clamping ring then has an appearance similar to that already shown in FIG. 1.

At this level of the process, the rotating anode 5 is fixed to the support axis 4 in a manner already considerably improved compared to the prior art. In order to further improve this fixation, the method of the invention also makes it possible to strengthen the connection between the deformed element 21 and the support axis 4, by producing a sort of weld between the latter.

To this end, the method also consists in heating the support axis 4 and the deformed element 21 to bring them to a temperature of the order of 1500 ° C; trials have shown good results at from 1200 ° C, and have shown that it is desirable not to exceed 1600 ° C.

This heating is preferably located on the part of the anode-support axis assembly 5-4, located around the through hole 10. Such localized heating can be obtained for example, under the effect of an electronic bombardment produced by means classics (not shown).

The support axes for rotating anodes, such as the support axis 4 are generally made of molybdenum or an alloy based on molybdenum. The heating of the support axis 4 and of the deformed element 21 makes it possible to favor phenomena of interdiffusion between the molybdenum and the material of which the deformed element 21 is made, tantalum by free. This interdiffusion constitutes a kind of weld which considerably increases the adhesion of the deformed element 21 to the support axis 4.

FIG. 3 illustrates another version of the method of the invention, in which the deformation of the deformable element or clamping rod 21 is obtained using a tool 35, and or the pitch of screws 14 and 1 'nut 15 are deleted.

In this version of the method, the clamping rod 21 being placed in the housing 20 in abutment on the first and second walls 24, 25, it is then pressed into the housing 20 using the tool 35, so as to obtain its deformation as in the previous example, but under the effect of a momentary action of the tool 35. The tool 35 may for example comprise a third ring 36, concentric with the support axis 4 and disposed in abutment on the part 32 projecting from the clamping rod 21. The third ring 36 can be surmounted, as in the nonlimiting example described, by a solid part 37, on which is momentarily applied, axially, a force F necessary for the 'depression and deformation of the deformable element or clamping rod 21; this force F can be produced using traditional means known to those skilled in the art, such as a press for example (not shown).

At this stage of the process of the invention, the rotating anode 5 is fixed on its support axis 4, in a secure manner, only by the action of the deformed element 21 or clamping rod, the screw pitch 14 and the 'nut 15 being deleted. It should be noted that this removal of the thread 14 and of the nut 15 represents, with the X-ray tube 1 of the invention, a significant reduction in cost, taking into account the machining difficulties for producing a no screw 14 and a nut 15, and the waste that these machinings cause.

The connection between the support axis 4 and the deformed element 21 can also be further improved, thanks to localized heating as has been explained in the previous example and which makes it possible to produce a sort of weld between the support pin 4 and the deformed element 21.

In this case, the tool 35 must remain in place during this heating, so that the force F continues to be exerted during the interdiffusion phenomena between the material of the support axis 4 and the material of the deformed element. 21.

In order to oppose a possible tearing of the rotating anode 5 relative to the support axis 4, along the longitudinal axis 6, the support axis 4 and the second wall 25 of the housing 20 may include streaks (not shown), made for example during their. machining.

In this spirit, as shown in the nonlimiting example of FIG. 4, the support shaft 4 comprises, at the level of the housing 20, a second groove 38 which constitutes a part of this housing 20. Under the thrust of the force F, the deformed element 21 or clamping rod also penetrates into this groove 38 of which it takes the form; flanks 39, 40 of the groove 38 thus constitute stops which oppose the tearing of the rotating anode 5, along the longitudinal axis 6. It should be noted that the housing 20 may also include a second groove 38 in the case of the examples shown in Figures 1, 2 and 3.

The X-ray tube and the method of the invention apply in all cases of X-ray tubes with a rotating anode, and more particularly in cases where the rotating anode is subjected to significant accelerations, and also in cases where the rotating anode is constituted by a graphite disc.

Claims (21)

1. X-ray tube with a rotating anode, comprising a rotor (3) and a support axis (4) arranged and secured along a longitudinal axis (6) around which said rotating anode (5) is rotated, said rotating anode comprising a first and a second face (12, 13), opposite, between which it has a through hole (10) disposed along said longitudinal axis (6), said support axis (4) being engaged in said through hole (10), characterized in that it comprises at least one deformed element (21) contained in a housing (20) concentric with said support shaft (4), said housing (20) being produced between said support axis (4) and a wall (22) of said through hole (10), so as to secure said rotary anode (5) on said support axis (4). 2. X-ray tube according to claim 1, characterized in that it further comprises an axial nut (15), screwed onto said support axis (4) and tightened on said first face (12) of the rotating anode ( 5). 3. X-ray tube according to one of the preceding claims, characterized in that said housing (20) is constituted by a conical groove. 4. X-ray tube according to one of the preceding claims, characterized in that said housing (20) is formed in the wall (22) of said through hole (10). 5. X-ray tube according to one of the preceding claims, characterized in that said housing (20) comprises a second groove (38) produced in said support axis (4). 6. X-ray tube according to claim 2, characterized in that the nut (15) comprises a first ring (27) bearing on the deformed element (21). 7. X-ray tube according to one of the preceding claims, characterized in that said housing (20) is open on the first face (12) of the rotating anode (5). 8. X-ray tube according to one of claims 1 to 7, characterized in that said housing (20) is open on the second face (13) of the rotating anode (5). 9. X-ray tube according to one of the preceding claims, characterized in that the support axis (4) has a shoulder (16) on which the second face (12) of the rotating anode (5) abuts. , and in that said shoulder (16) comprises a second ring (31) bearing on the deformed element (21). 10. X-ray tube according to one of the preceding claims, characterized in that the deformed element (21) is made of a refractory material and at low vapor pressure. 11. X-ray tube according to claim 10, characterized in that the deformed element (21) is made of tantalum. 12. X-ray tube according to claim 10, characterized in that the deformed element (21) is made of niobium. 13. Method for fixing a rotary anode to a support axis, said rotary anode (5) comprising an axis of symmetry (31) according to which it is pierced with a through hole (10), said support axis (4) being intended to be engaged in the through hole (10) along a longitudinal axis (6) coincident with said axis of symmetry (31), characterized in that it consists in producing, between said support axis (4) and a wall (22 ) of said through hole (10), a housing (20) concentric with said support axis (4), then engaging said support axis (4) in said through hole (10) and placing in said housing (20) a deformable element ( 21), then finally to deform said deformable element (21) so that the latter encloses said support axis (4) and ensures the locking of said rotary anode (5) relative to said support axis (4). 14. A fixing method according to claim 13, characterized in that it consists in deforming said deformable element (21) by pressing it into said housing (20) by tightening an axial nut (15), left permanently . 15. Fastening method according to claim 13, characterized in that it consists in deforming said deformable element (21) by pushing it into said housing (20) under the effect of a force (F) applied momentarily using a tool (35). 16. Fastening method according to one of claims 13 to 15, characterized in that it consists in heating said deformed element (21) and said support axis (4) to bring them to a temperature between 1 200 and 1 600 °, so as to favor interdiffusion effects between the material of the support axis (4) and the material of the deformed element (21) in order to increase the adhesion of said deformed element (21) on said support axis (4). 17. The fixing method according to claim 16, characterized in that said deformed element (21) and said support shaft (4) are brought to a temperature of 1500 °. 18. The fixing method according to claim 15 and one of claims 16 or 17, characterized in that it consists in maintaining the application of said force (F) during said heating of said deformed element (21) and of said support shaft. (4), and releasing the application of said force (F) after the application of said heating. 19. A fixing method according to claim 1, characterized in that said housing (20) is formed in the wall (22) of the through hole (10). 20. A fixing method according to claim 1, characterized in that said housing (20) is made in the form of a conical groove. , 21. A fixing method according to one of claims 19 or 20, characterized in that it consists in producing a second groove (38) in the support axis (4), opposite said housing (20).

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