Rotating X-ray anode with an at least partly radially aligned ground structure

Abstract

A rotating x-ray anode has an annular focal track. The surface of the focal track has a directed ground structure. Over the circumference of the annular focal track and over the radial extent of the focal track, the alignment of the ground structure is inclined relative to a tangential reference direction in the respective surface portion in each case by an angle that lies in the range from 15, including, up to and including 90. A corresponding method for producing a rotating x-ray anode is described.

Claims

1. A rotating x-ray anode, comprising: an annular focal track having a surface formed with a directed ground structure; an alignment of the directed ground structure, over a circumference of said focal track and over a radial extent of said focal track, being inclined in relation to a tangential reference direction at a respective surface portion by an angle in a range from 15 to 90, wherein the range includes 15 and 90; and wherein the directed ground structure is a surface structuring that is formed by a uniformly distributed array of individual striae or individual grooves that are aligned along a preferential direction, and wherein the individual striae or individual grooves have a randomly distributed arrangement and randomly distributed dimensions.

2. The rotating x-ray anode according to claim 1, wherein, over the circumference of said annular focal track and over the radial extent of said focal track, the alignment of the ground structure is inclined in relation to the tangential reference direction in the respective surface portion in each case by an angle in a range from 35 to 70, wherein the range of 35 to 70 includes 35 and 70.

3. The rotating x-ray anode according to claim 1, wherein the directed ground structure in each case has a substantially straight course.

4. The rotating x-ray anode according to claim 1, wherein, along a radial direction from inside to outside, the angle between the alignment of the ground structure and the tangential reference direction in the respective surface portion decreases over the radial extent of said focal track.

5. The rotating x-ray anode according to claim 1, wherein, in a region of the ground structure, a mean surface roughness Ra lies in a range from 0.05 m to 0.5 m, wherein the range from 0.05 m to 0.5 m includes 0.05 m and 0.5 m, wherein a measuring section that runs straight and substantially perpendicularly to the alignment of the ground structure is used for determining the mean surface roughness.

6. The rotating x-ray anode according to claim 1, wherein the ground structure extends beyond a region of said focal track.

7. The rotating x-ray anode according to claim 1, wherein a material of said focal track at said focal track is tungsten or a tungsten-based alloy.

8. The rotating x-ray anode according to claim 1, wherein said anode has a carrier body and a focal track layer, which is formed on said carrier body and on which said focal track runs.

9. A method of producing a rotating x-ray anode, the method comprising: introducing a directed ground structure into at least a region of an annular focal track of the rotating x-ray anode such that, over a circumference of the annular focal track and over a radial extent of the focal track, an alignment of the ground structure is inclined in relation to a tangential reference direction in the respective surface portion in each case by an angle in a range from 15 to 90, wherein the range includes 15 and 90; and wherein the directed ground structure is a surface structuring that is formed by a uniformly distributed array of individual striae or individual grooves that are aligned along a preferential direction, and wherein the individual striae or individual grooves have a randomly distributed arrangement and randomly distributed dimensions.

10. The method according to claim 9, wherein the step of introducing the ground structure is a last working step involving removal of material in the region of the surface of the focal track, in a production of the rotating x-ray anode.

11. The method according to claim 9, wherein the introducing step comprises grinding the ground structure into the x-ray anode.

12. The method according to claim 9, wherein the step of introducing the ground structure comprises moving a grinding body such that a grinding surface thereof moves at least partly in the radial direction, and that furthermore the grinding body and the focal track are moved in relation to one another in the circumferential direction.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) Further advantages and expedient aspects of the invention emerge from the following description of exemplary embodiments with reference to the accompanying figures, in which:

(2) FIG. 1 shows a schematic cross-sectional view of a rotating x-ray anode;

(3) FIG. 2 shows a schematic plan view of a rotating x-ray anode according to the invention, as provided by a first embodiment, from above; and

(4) FIG. 3 shows a schematic plan view of a rotating x-ray anode according to the invention, as provided by a second embodiment, from above.

DESCRIPTION OF THE INVENTION

(5) In FIG. 1, the structure of a rotating x-ray anode -2- is schematically represented. The rotating x-ray anode -2- is formed rotationally symmetrically in relation to an axis of rotational symmetry -4-. Determined at the same time by the axis of rotational symmetry -4- is an axial direction -6-, which respectively runs through the point to be characterized that is concerned and parallel to the axis of rotational symmetry -4-. Running perpendicularly to the axial direction -6- are the tangential direction -8- (depicted in the present case as counter to the clockwise direction), which respectively forms a tangent to the circumference at the point concerned, and the radial direction -10-, which is perpendicular to the tangential direction -8- and the axial direction -6-. The rotating x-ray anode -2- has a disk-shaped carrier body -12-, which can be mounted on a corresponding shaft. Applied to the carrier body -12- on the top side is an annular focal track layer -14-. The portion over which the annular focal track layer -14- extends has the form of a truncated cone (of a flat cone). The inclination of the surface of the focal track layer -14- is represented in FIG. 1 by the dashed line 15. The inclination is, for example, 12 in relation to the radial direction -10-. The focal track layer -4- covers at least the region of the carrier body -12- that is intended for scanning with an electron beam, and consequently forms the focal track -16-. In the present case, the focal track layer -14- extends on both sides (i.e. both radially inwardly and radially outwardly) beyond the portion of the focal track -16- that is schematically indicated in FIG. 1 by the curly bracket.

(6) Two embodiments of the present invention are explained below with reference to FIGS. 2 and 3. A schematic plan view of a rotating x-ray anode -2- is respectively represented here in FIGS. 2 and 3. The rotating x-ray anode -2- is in this case constructed in a way corresponding to the rotating x-ray anode -2- represented in FIG. 1, and the same reference numerals are in turn used for the same components. In FIGS. 2 and 3, the tangential reference direction -8- is depicted for two different radial positions (for two points to be characterized, in each case lying on a horizontally running radial direction -10-).

(7) In the case of the first embodiment, represented in FIG. 2, a directed ground structure -18- is provided, extending over the entire inclined surface of the focal track layer -14-. At individual circumferential portions of the focal track layer -14-, the alignment of the ground structure -18- is schematically depicted as individual lines -20-. The lines -20- are merely used here to indicate the alignment of the ground structure and do not represent individual grinding striae. This is so because, as explained above, the latter are randomly distributed and have different dimensions. It is just that the course of said striae extends essentially along the indicated lines -20-. The ground structure -18- of the first embodiment, represented in FIG. 2, has a curved alignment. Along a radial direction -10- from inside to outside, the angle between the alignment of the ground structure -18- and a tangential reference direction -8- decreases over the extent of the focal track layer -14- in the respective surface portion. Such a ground structure -18- can be introduced in particular by the rotating x-ray anode -2- being rotated during the introduction of the ground structure -18-, while the direction of movement of the grinding means is exclusively radial or possibly additionally has a tangential and/or an axial component (for example introduction by using a five-axes grinding machine). Such a direction of movement of the grinding means may be obtained in particular by rotation of a cup wheel with corresponding alignment of the axis of rotation.

(8) In the case of the second embodiment, represented in FIG. 3, a directed ground structure -22- is provided, in turn extending over the entire inclined surface of the focal track layer -14-. The ground structure -22- is formed in such a way that segments with a parallel alignment of the ground structure -22- within the segment concerned respectively adjoin one another in the circumferential direction. At individual circumferential portions of the focal track layer -14-, the alignment of the ground structure within the respective segment is schematically depicted as individual lines -24- in a way corresponding to the first embodiment. The directed ground structure -22- of the second embodiment, represented in FIG. 3, has within the respective segment an essentially straight course. On account of the enlargement of the circumference along the radial direction -10- from the inside outward, the individual segments are in each case narrower in the radially inner region than in the radially outer region. Over the (relatively small) radial extent of the focal track -16- (cf. FIG. 1), the alignment of the ground structure -22- in relation to the tangential reference direction -8- remains essentially constant.

(9) It has been found that the provision of the ground structure according to the invention with an alignment in a range from and including 15 up to and including 90 in relation to the tangential reference direction has the effect that a much finer and more uniform crack network is formed during the use of the rotating x-ray anode than according to the (internal) prior art with an alignment of the ground structure in the tangential direction. An angle in the range from and including 35 up to and including 70, in which the microcracks induced by the ground structure with their accumulated crack width compensate for the overall deformation of the focal track occurring during use, both in the radial direction and in the tangential direction, has been found to be particularly advantageous here. This produces a uniform array of fine microcracks, running essentially along the alignment of the ground structure, instead of a branching network of tangential and radial cracks intersecting one another or running into one another. As a result, the load-bearing capacity and the lifetime of the rotating x-ray anodes according to the invention are increased.

(10) It is also advantageous that, on account of the formation of the fine microcracks, the rotating x-ray anodes according to the invention have in addition to the increase in bursting resistance and high-voltage stability also a significantly slowed decline in dose over the lifetime of the rotating x-ray anode. This is attributed to the following effects: on the one hand, the crack widths and crack depths are reduced; on the other hand, the microcracks have a radial component. Both effects contribute during use to a reduction in the self-absorption of the x-radiation, and consequently to a comparatively high dose yield.

Exemplary Embodiment

(11) Rotating x-ray anodes with a focal track layer of a tungsten-rhenium alloy (10% by weight rhenium, 90% by weight tungsten), which was firmly connected to the carrier body of a molybdenum alloy, were first pre-smoothed by fine turning. After the fine turning of the focal track layer, a directed ground structure was introduced with a fine-grained diamond cup grinding wheel. The diamond cup grinding wheel had a grain size of D76, given in accordance with the standard issued by the FEPA (Fdration Europene des Fabricants de Produits Abrasifs [Federation of European Producers of Abrasives]). To introduce the ground structure, an arrangement in which the axis of rotation of the diamond cup grinding wheel was aligned essentially perpendicularly to the surface of the focal track (with respect to the point of contact of the cup wheel with the focal track) and essentially in the middle of the focal track with respect to the radial direction was chosen. The arrangement was also chosen in such a way that an annular ground surface, formed on the end face of the diamond cup grinding wheel and aligned perpendicularly to the axis of rotation (of the diamond cup grinding wheel), engaged in a grinding manner in the surface of the focal track during the rotation of said wheel on a circumferential portion (of the rotating diamond cup grinding wheel), while the opposite circumferential portion was kept at a distance from the focal track. To introduce the ground structure, in this arrangement the diamond cup grinding wheel and the rotating x-ray anode were respectively rotated about their axes of rotation, with oil being used as a lubricant. The inclination of the alignment of the introduced ground structure in relation to the tangential reference direction depends on the relative speeds of the focal track in relation to the ground surface of the diamond cup wheel. In particular, the rotational speed of the diamond cup grinding wheel must be sufficiently high in relation to the rotational speed of the rotating x-ray anode in order to achieve an inclination of the alignment of the ground structure in relation to the tangential reference direction. In the present case, the rotating x-ray anode was rotated at 100 revolutions per minute, with the focal track extending over a radius of about 75 mm to about 100 mm of the rotating x-ray anode, and the diamond cup grinding wheel having a speed of 20 m/s (meters/second) in the region of the ground surface. The ground structure obtained thereby was aligned essentially straight, having a slight curvature on account of the radius (in the present case 62.5 mm) of the diamond cup grinding wheel. The alignment of the ground structure was inclined about 85-90 in relation to the tangential reference direction (i.e. ran approximately radially). The mean roughness of the directed ground structure was Ra=0.25 m.

(12) The present invention is not restricted to the exemplary embodiments explained above. In particular, the outer form and the structure of the rotating x-ray anode, as known in the art, may deviate from the rotating x-ray anode -2- represented in the figures. In particular, it may also be provided that the focal track layer covers only part of the frustoconical portion and the surface of the focal track layer is adjoined radially inwardly and/or radially outwardly in the same plane by the surface of the carrier body. In this case, the (inclined) surface portions concerned of the carrier body may also be provided with a ground structure. Furthermore, it is also possible that the rotating x-ray anode does not have a separate focal track layer and the focal track is formed on an essentially monolithic body (apart from attachments such as for example a graphite ring, etc.). Furthermore, in addition to the production steps described, it may be provided within production that the surface concerned is smoothed to the greatest extent possible before the introduction of the ground structure, in order to eliminate as far as possible the influences of existing structures on the surface. Such smoothing may be performed for example by mechanical polishing and/or electropolishing. Furthermore, there is also the possibility of introducing two arrays of striae, which cross one another. In particular, the rotating x-ray anode may first be coarsely pre-turned in the circumferential direction, in order to introduce relatively coarse striae that are aligned in the circumferential direction. The mean surface roughness obtained by the coarse turning may for example be around Ra=2 m. The directed ground structure according to the invention, which extends at least predominantly in the radial direction, may then be introduced in such a way that the striae resulting from the turning are at least partially retained. In this way, striae, and consequently directed crack nuclei, that have at least two different alignments on the respective surface portions, and accordingly support the formation of a fine crack network, are provided.