EP2803076B1 - Rotary x-ray anode comprising a grinded structure which is radially aligned in at least a certain proportion and fabrication method - Google Patents

Description

The present invention relates to an X-ray rotary anode having an annular focal track, the focal track surface having a directional abrasive structure.

X-ray anodes are used in X-ray tubes to generate X-rays. X-ray devices with such X-ray rotary anodes are used in particular in the medical field in diagnostic imaging. In use, electrons are emitted from a cathode of the x-ray tube and accelerated in the form of a focused electron beam onto the rotated x-ray rotating anode. Much of the energy of the electron beam is converted into heat in the X-ray rotary anode, while a small portion is emitted as X-radiation. The locally released amounts of heat lead to a strong heating of the X-ray rotary anode.

Due to the electron beam, an annular path (focal path) is scanned in use due to the rotational movement of the x-ray rotary anode. In general, X-ray rotary anodes in the region of the focal track on a trained on a support body focal point coating. Due to the cyclic, thermomechanical load in the focal spot (point of impact of the electron beam on the X-ray rotary anode) occur in the region of the focal point surface cyclic compressive / tensile stresses, which in turn lead to plastic deformation in the region of the focal point surface as well as in the body of the X-ray rotary anode , Compressive stresses arise as a result of the expansion of the volume element acted upon by the electron beam in relation to the comparatively colder environment. Tensile stresses occur due to the plastic deformation taking place at high temperatures and due to the contraction of the previously strongly heated volume element occurring during the subsequent cooling. As a result, a network of micro and macrocracks forms on the focal surface. In some cases, cracks with widths of more than 100 μm are formed. Such macrocracks are particularly detrimental to the dose yield and thus on the picture quality. Furthermore, there is a risk of crack propagation deep into the body of the X-ray rotary anode, thereby increasing the risk of material eruption or breakage of the X-ray rotary anode.

In the DE 10 2007 024 255 A1 It is proposed to introduce a pattern into the focal track surface by electrochemical etching. The DE 103 60 018 A1 describes an X-ray rotary anode, in which at least partially defined micro-slots are arranged in the respective surface. In both variants, the focus is on the fact that the effect of expansion joints is essentially achieved by the defined structures in which the relative arrangement and dimensions of the individual grooves or slots is predetermined. In particular, a controlled expansion and a controlled release of the elastic energy should be made possible. Furthermore, at the DE 10 2007 024 255 A1 also described that the surface structure of a controlled microcracking can serve. The introduction of such defined structures is complex and associated with high costs. In the JP 2005/158589 A the post-processing of the focal point of a built-in and rotating X-ray rotary anode is described by means of loops in order to correct any existing imbalance.

Accordingly, the object of the present invention is to provide an X-ray rotary anode which is inexpensive to manufacture and in which the occurrence of fatigue in use can be suppressed as effectively as possible. The object is also to provide a corresponding method for producing an X-ray rotary anode.

According to the present invention, there is provided an X-ray rotary anode having an annular groove in which the groove surface has a directional abrasive structure. Across the circumference of the annular kerf and across the radial extent of the kerf, the orientation of the abrasive structure relative to a tangential reference direction in the respective surface portion is each inclined at an angle in the range of 15 ° to 90 ° inclusive.

In particular, the X-ray rotary anode has these features before it is first installed in an X-ray tube and exposed therein to an electron beam. After prolonged periods of use aging effects can occur, which - as described - lead to modifications of the focal surface.

Compared to the known from the prior art solutions of introducing defined slot structures or defined patterns, the introduction of a directed abrasive structure with significantly less effort is involved, especially since it is in view of achieving a very smooth surface in the region of the focal line anyway advantageous smoothing in a final surface processing step by grinding. A final surface-machining step, in part in the (internal) state of the art in the production of X-ray rotary anodes, involves grinding the focal surface and surrounding areas such that a rotating abrasive wheel is circumferentially passed over the focal surface, that the orientation of the abrasive structure is tangential. Accordingly, the production of X-ray rotary anodes according to the invention can be realized largely without additional effort by aligning the grinding direction relative to the respective tangential reference direction according to the claimed angular range in the final surface processing step.

Another advantage of the aligned abrasive structure over the above-described provision of defined slot structures or defined patterns, which are intended to serve primarily as expansion joints, is that evenly distributed over the focal surface a plurality of cracking bacteria is provided. In addition, since the individual grooves of an abrasive structure run comparatively pointedly to the groove bottom, a pronounced increase in stress occurs in this region under tensile stresses, which promotes crack initiation. Upon the occurrence of tensile stresses in the focal surface, accordingly, at a plurality of locations (and not only at predefined positions) provides the possibility of forming microcracks, and the kerf surface can respond to the tensile stresses by forming a network of finely divided microcracks. A formation of wide cracks is thereby avoided. The latter are more likely to benefit from the provision of only a limited number of defined slots or other defined structures. Furthermore, an advantage over the provision of defined slot structures or defined patterns is that a comparatively smooth track surface can be provided so that the self-absorption losses are negligible.

In the context of the above-stated problem, previous X-ray rotary anodes, which (according to the internal state of the art) had a circumferentially oriented abrasive structure, were examined in detail. It could be found after prolonged periods of use of the same that, although a relatively fine network of circumferentially oriented microcracks is formed, which increases with increasing use time to the effect that the accumulated crack widths increase. In the radial direction, however, significantly fewer and significantly wider cracks occur. Depending on the microstructure of the focal track, these can also run irregularly (eg zig-zag-shaped) close to the radial direction and release significantly more energy during formation per crack event. On the one hand, this leads to a high dose loss, since the cracks with increasing width act as more and more efficient electron traps. Furthermore, the likelihood of particle release from thermal and mechanical insulation of grains increases at acute-angle crack intersections, which carries the risk of image-disturbing high voltage instabilities. From the analyzes of the crack patterns, it can be deduced that the scorching marks, due to the stress exaggeration occurring there in response to the compressive / tensile stress in the focal point and the thermal and plastic deformation of the body of the X-ray rotary anode, form the formation of microcracks which run along the alignment of the abrasive screeds to promote.

It has been found that by the inventive construction of the X-ray rotary anode in which the orientation of the abrasive structure is inclined relative to a tangential reference direction in the respective surface portion each with an angle in the range of 15 ° to 90 ° inclusive, the formation of wide and particularly critical, in the radial direction cracks can be prevented. The respectively locally occurring strain in the region of the focal track surface can be determined by simulation and, accordingly, the orientation of the abrasive structure can be chosen such that it runs in each case substantially perpendicular to the orientation of the maximum local strain. In this case, the claimed angular range has been found to be an advantageous area.

In the present context, the term "focal path" refers to the surface section of the x-ray rotary anode which is intended to be scanned with an electron beam (and over which the electron beam is correspondingly guided in use). Accordingly, the focal path can form a surface section of a separate, generally ring-shaped, focal-path lining. However, it can also be formed directly on a (in this case substantially monolithic) body of the X-ray rotary anode. In general, further layers, add-on parts, etc., such as a graphite ring, etc., may also be provided on the x-ray rotary anode, in particular on the side remote from the focal track. The term "directional abrasive structure" generally refers to surface texturing formed by a uniformly distributed family of individual grooves whose arrangement and dimensions (length, width, depth) are statistically distributed and which are oriented substantially along a preferred direction are (ie, which are substantially parallel to each other). In the process, a substantially smooth surface is achieved overall. The directional abrasive structure is so far undefined that the position and dimensions of the individual grooves are not predetermined, in particular non-periodic or otherwise regular. The directional abrasive structure can be achieved by a relative movement between that for introducing the abrasive structure The abrasive article such as a grinding wheel, polishing pad and inserted mechanical polishing agent, brush) and the focal surface can be created along the desired orientation. The directional abrasive structure is introduced in particular by a grinding process. "Grinding" refers to a machining, path-controlled manufacturing process for machining surfaces with abrasives. In principle, however, there are also other possibilities for introducing the directional abrasive structure, such as, for example, by directional polishing (with a mechanical polishing agent) or by directional brushing.

The tangential reference direction is determined locally at the relevant surface section at which the orientation of the abrasive structure is to be determined. A tangential direction (or circumferential direction), a radial direction and an axial direction are defined at the respective point to be characterized on the X-ray rotary anode by the ring shape of the focal track. The angle between the tangential reference direction and the orientation of the abrasive structure is measured in the plane formed by the focal surface in this local area (tangent plane at the measurement point). It should be noted that the focal surface in the respective local area can also be inclined to a radial direction, which is the case in particular in a frustoconical focal track. Alternatively, the focal path may extend only in the plane spanned by the radial directions. Furthermore, it should be noted that the orientation of the abrasive structure relative to the tangential reference direction can also vary over different, radial positions, and in this case also continuously in the claimed angular range (from 15 ° to 90 °, in particular from 35 °). 70 °). It can alternatively remain constant. Furthermore, both the variant is included, that the tangential reference direction is clockwise, as well as the variant that the tangential reference direction runs counterclockwise (in plan view of the X-ray rotary anode). According to the present invention, at least in one of these two possibilities, the angle of the alignment Abrasive structure to the tangential reference direction respectively in the desired angular range (eg 15 ° - 90 °) are. Depending on the application and the direction of rotation of the X-ray rotary anode in use, differences may arise as to whether the angle is set relative to a tangential reference direction running in the clockwise direction or relative to a counterclockwise tangential reference direction. Which variant (depending on the particular application as well as the direction of rotation of the X-ray rotary anode in use) is preferable is to be determined in individual cases by experiments.

It has been found that the formation of wide, radial cracks, which is perceived as particularly disadvantageous, can be avoided all the more effectively the greater the angle of inclination of the orientation of the grinding structure relative to the tangential reference direction. Accordingly, the inclination angle is preferably in a range of from 30 ° to 90 ° inclusive. According to a further development, the orientation of the abrasive structure relative to a tangential reference direction in the respective surface section is inclined over the circumference of the annular focal track and beyond the radial extent of the focal track, in each case at an angle in the range of 60 ° to 90 ° inclusive. This variant is particularly advantageous if, in particular, strains in the tangential direction (or circumferential direction) are to be compensated for in the relevant X-ray rotary anode. By an angle of orientation in the range of at least 35 ° to a maximum of 70 ° relative to the tangential reference direction tensile stresses can be effectively compensated both in the radial and in the tangential direction. An optimum angle range can be determined in each case specifically as a function of the geometry and the materials used of the particular X-ray rotary anode type. Such a determination can be done in particular simulation-based.

According to a development, the course of the directed abrasive structure is substantially rectilinear. Also considered to be "substantially rectilinear" is such a course, in which the course is due to the (small) curvature of the surface of the focal track or due to the radially outward occurring expansion is slightly curved. Such a rectilinear course of the abrasive structure can be achieved by a corresponding orientation of the grinding direction of the abrasive (or possibly also the direction of movement of a polishing body or a brush) relative to the tangential reference direction. Furthermore, it can be provided that the X-ray rotary anode is segmented in the region of the focal point surface in such a way that in the circumferential direction in each case segments adjoin one another with a parallel orientation of the abrasive structure within the respective segment. This can be achieved in the context of production in particular by introducing an abrasive structure on a circumferential segment of the X-ray rotary anode with a desired orientation and then subsequently rotating the X-ray rotary anode through an angle section to again produce an abrasive structure with the desired (same orientation) relative to the associated tangential reference direction to bring.

According to a further development, the angle between the orientation of the abrasive structure and a tangential reference direction in the respective surface section decreases along a radial direction from the inside to the outside over the radial extent of the focal track. This is advantageous, inter alia, with regard to simple production. Such an abrasive structure can be introduced, in particular, by rotating the X-ray rotary anode during the introduction of the abrasive structure, while the direction of movement of the abrasive (or possibly also the direction of movement of a polishing body or a brush) is exclusively radial or optionally additionally tangential and / or axial Share has.

According to a development, the mean roughness Ra in the region of the abrasive structure is in a range of from 0.05 μm to 0.5 μm inclusive. On the one hand, this area still provides a sufficiently smooth surface with regard to the dose yield, while on the other hand it offers sufficient crack germs for the formation of a fine crack network. Depending on the application and operating conditions, different areas can be used be suitable. In particular, in certain applications, a comparatively smooth surface is desired, so that the mean roughness Ra is preferably in a range of from 0.05 μm to 0.15 μm inclusive. For many applications, a mean range of from 0.15 μm to 0.3 μm inclusive of the mean roughness Ra is suitable. Furthermore, in certain applications, a comparatively high roughness may also be permissible or desired, so that an abrasive structure having an average roughness Ra of 0.3 μm to 0.5 μm inclusive is suitable. In order to determine the average roughness depth, a measuring section running in a straight line and substantially perpendicular to the orientation of the grinding structure is used. The profile is measured with a touch probe with a feed rate of 0.5 mm / s over a measuring length of 15 mm. The first and the last 2.5 mm of the measured section are not evaluated but only the middle part of 10 mm length. As part of the evaluation of the measurement data, a filter according to ISO 16610-31 is used. The average roughness Ra is determined in accordance with DIN EN ISO 4287: 2010-07.

According to a development, the abrasive structure extends beyond the region of the focal path. In particular, the abrasive structure extends both radially inwardly and radially outwardly beyond the region of the focal path. This takes into account that considerable thermal loads and also deformation of the entire body of the X-ray rotary anode occur even in the area adjoining the focal point. This development makes it possible to support the formation of a fine fracture network in this area as well.

In accordance with a further development, the fuel track material in the region of the focal track is formed by tungsten or by a tungsten-based alloy. In particular, only one formed on a support body Brennbahnbelag from the materials mentioned is formed. With a tungsten-based alloy, reference is made in particular to an alloy containing tungsten as the main constituent, ie to a higher proportion (measured in weight percent) than each, the other Has elements. In particular, the focal lane is formed from a tungsten-rhenium alloy which may have a rhenium content of up to 26% by weight (wt%: wt%). In particular, the rhenium content is in a range of 5 to 10 wt.%. The materials mentioned are advantageous in view of the high, thermal loads and with regard to the highest possible emissivity of X-radiation.

According to a further development, the body of the X-ray rotary anode is formed completely or alternatively only the carrier body of the X-ray rotary anode (on which a focal point lining is formed) made of molybdenum or a molybdenum-based alloy (eg TZM or also MHC). These materials have proven particularly useful in view of the high thermal and mechanical loads. A molybdenum-based alloy is particularly referred to an alloy containing molybdenum as the main constituent, i. to a higher proportion (measured in weight percent) than any other containing element. In particular, the molybdenum-based alloy may have a content of at least 80 wt.% (Wt.%: Wt.%) Of molybdenum, in particular of at least 98 wt.% Of molybdenum. In this context, MHC is a molybdenum alloy which has an Hf content of 1.0 to 1.3% by weight (Hf: hafnium), a C content of 0.05-0.12% by weight, has an O content of less than 0.06 wt% and the remaining portion (other than impurities) molybdenum.

In accordance with a further development, the x-ray rotary anode has a carrier body and a focal point coating formed on the carrier body, on which the focal path runs. In this way, on the one hand, the materials can be adapted specifically to the requirements existing in the region of the focal point (high dose yield, high thermal load capacity) and, on the other hand, specifically to the requirements existing in the region of the carrier body (high mechanical strength, high thermal resistance, good heat dissipation). In particular, the generally ring-shaped formed Brennbahnbelag extends on both sides (ie radially inward and radially outward) beyond the focal distance. If laterally (radially inward and / or radially outward) to the surface of the focal point lining in the same plane and the surface of the support body is followed, it is preferred that the abrasive structure - in particular on both sides (ie, radially inward and radially outward) - extends beyond the focal length. As a result, a uniform transition between the track surface and carrier body is achieved on the surface. According to a further development, it is provided that the carrier body is formed from molybdenum or a molybdenum-based alloy (eg TZM, MHC, etc.) and that the focal path is formed from tungsten or a tungsten-based alloy.

The present invention further relates to a method for producing an x-ray rotary anode in which a directed abrasive structure is introduced at least in the region of an annular focal path of the x-ray rotary anode such that over the circumference of the annular focal track and over the radial extent of the focal track, the orientation of the abrasive structure is inclined relative to a tangential reference direction in the respective surface portion in each case with an angle in the range of 15 ° inclusive including 90 °.

The inventive method is characterized by the fact that an X-ray rotary anode can be provided by simple, inexpensive and reproducible feasible process steps, in which the occurrence of fatigue phenomena in the region of the focal surface can be significantly delayed. In particular, by means of the method according to the invention, it is possible to produce X-ray rotary anodes with the features explained above and in the following description part. Accordingly, reference is also made with respect to the inventive method to the explained to the X-ray rotary anode advantages. Furthermore, in the method according to the invention, the refinements and variants explained with reference to the x-ray rotary anode can also be realized in a corresponding manner, which may possibly be feasible by a corresponding adaptation of the method steps.

If the x-ray rotary anode has a carrier body and a focal point coating formed thereon, then in principle it is also possible to first introduce the abrasive structure into the focal point coating and then attach the focal point coating to the carrier body (for example by soldering). However, it is preferred that the abrasive structure is introduced into the focal track only when the track surface is already firmly connected to the carrier body (for example, by the carrier body and the fuel track are produced by powder metallurgy in the composite, or by the track coating by a vacuum plasma spraying on the carrier body is applied). In the preferred variant, the occurrence of edges in the transition region between the track surface and carrier body can be avoided.

According to a further development, the step of introducing the abrasive structure forms the last, in the region of the focal point surface material-removing machining step in the production of the X-ray rotary anode.

As already explained above, the abrasive structure is introduced in particular by directional grinding, directional polishing and / or directional brushing. In this case, grinding is preferred. In particular, an abrasive (e.g., grinding wheel) coated with abrasive grains (e.g., silicon carbide or diamond) is used for grinding. Such an abrasive is particularly suitable for a tungsten or tungsten based alloy (e.g., tungsten-rhenium alloy) trace material.

According to a development, an abrasive body is moved to introduce the abrasive structure such that its abrasive surface at least proportionally moves in the radial direction, and further that the abrasive body and the focal path are moved relative to each other in the circumferential direction (continuously during the introduction of the abrasive structure or intermittently by an angle section each between the processing steps). In particular, in order to realize the relative movement in the circumferential direction, the x-ray rotary anode is rotated about its axis of symmetry. As already above is explained so manages a relatively simple and inexpensive introduction of the abrasive structure.

Further advantages and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying figures.

Fig. 1:

eine schematische Querschnittsansicht einer Röntgendrehanode;

Fig. 2:

eine schematische Draufsicht einer erfindungsgemäßen Röntgendrehanode gemäß einer ersten Ausführungsform von oben; und

Fig. 3:

eine schematische Draufsicht einer erfindungsgemäßen Röntgendrehanode gemäß einer zweiten Ausführungsform von oben.

From the figures show:

Fig. 1:

a schematic cross-sectional view of an X-ray rotary anode;

Fig. 2:

a schematic plan view of an inventive X-ray rotary anode according to a first embodiment from above; and

3:

a schematic plan view of an inventive X-ray rotary anode according to a second embodiment from above.

In Fig. 1 is shown schematically the structure of a Röntgendrehanode -2-. The X-ray rotary anode -2- is rotationally symmetrical to a rotational axis of symmetry -4- formed. By the rotation symmetry axis -4- is simultaneously an axial direction -6-, each of which runs through the relevant point to be characterized and parallel to the axis of rotation of symmetry -4-determined. Perpendicular to the axial direction -6- extend the tangential direction -8- (in the present case opposite to the clockwise direction), which forms a tangent to the circumference in the respective point, and the radial direction -10-, perpendicular to the tangential -8- and the axial direction -6- stands. The X-ray rotary anode -2-has a plate-shaped carrier body -12- which can be mounted on a corresponding shaft. On the cover side, an annular focal lamination -14- is applied on the carrier body -12-. The portion over which the annular focal lamination -14- extends, has the shape of a truncated cone (a flat cone). The inclination of the surface of the Brennbahnbelags -14- is in Fig. 1 represented by the dashed line 15. The inclination is for example 12 ° relative to the radial direction -10-. The Brennbahnbelag -4- covers at least the region of the support body -12-, which is intended for scanning with an electron beam and thus the Burning lane -16- forms. In the present case, the focal-web covering -14-extends on both sides (ie both radially inward and radially outward) over the section of the focal-16, which in Fig. 1 schematically indicated by the curly bracket, out.

The following are with reference to the Figures 2 and 3 two embodiments of the present invention explained. It is in the Figures 2 and 3 in each case a schematic plan view of a Röntgendrehanode -2- shown. The X-ray rotary anode -2- is in accordance with the in Fig. 1 illustrated Röntgendrehanode -2- constructed and for the same components again the same reference numerals are used. In the Figures 2 and 3 is the tangential reference direction -8- for two different radial positions (for two, each lying on a horizontal, radial direction -10-, to be characterized points) located.

At the in Fig. 2 1, a directional abrasive structure -18- is provided which extends over the entire, inclined surface of the focal-web covering -14-. At individual peripheral portions of the focal web covering -14-, the orientation of the abrasive structure -18- is shown schematically as individual lines -20-. The lines -20- merely represent the orientation of the abrasive structure and do not represent individual grinding marks. The latter are namely, as explained above, statistically distributed and have different dimensions. Only its course extends essentially along the illustrated lines -20-. The abrasive structure -18-the in Fig. 2 illustrated, the first embodiment has a curved orientation. Along a radial direction -10- from inside to outside over the extension of the focal-web covering -14-, the angle between the orientation of the abrasive structure -18- and a tangential reference direction -8- in the respective surface section decreases. An introduction of such an abrasive structure -18- can be done in particular by rotating the X-ray rotary anode -2- during the introduction of the abrasive structure -18-, while the direction of movement of the abrasive is exclusively radial or optionally additionally tangential and / or axial portion (e.g., incorporation using a 5-axis grinder). Such a direction of movement of the abrasive can be done in particular by rotation of a cup wheel with a corresponding orientation of the axis of rotation.

At the in Fig. 3 illustrated, a second embodiment, a directed abrasive structure -22- is provided, which in turn extends over the entire inclined surface of the Brennbahnbelags -14-. The abrasive structure -22- is formed such that in the circumferential direction in each case segments with a parallel within the respective segment alignment of the abrasive structure -22- join each other. As in the case of the first embodiment, the orientation of the abrasive structure within the respective segment is shown schematically as individual lines -24- at individual circumferential sections of the focal-web covering -14-. The directional abrasive structure -22- of the Fig. 3 illustrated second embodiment has within the respective segment on a substantially rectilinear course. Due to the increase in the circumference along the radial direction -10- from the inside to the outside, the individual segments in the radially inner region are each narrower than in the radially outer region. Over the (relatively small) radial extent of the focal -16- across (see. Fig. 1 ), the orientation of the abrasive structure -22- remains substantially constant relative to the tangential reference direction -8-.

It has been found that by providing the abrasive structure according to the invention with an orientation in a range of from 15 ° to 90 ° inclusive relative to the tangential reference direction in the use of the X-ray rotary anode, a substantially finer and more uniform crack network is formed than after the (internal) state the technique with an orientation of the abrasive structure in the tangential direction. In this case, an angle in the range of up to and including 70 ° has proven to be particularly advantageous, in which the microcracks induced by the abrasive structure with their cumulative crack width are the total deformation of the focal path in use both in the radial direction and in the tangential direction compensate. This results in the place of a ramified network of intersecting or nested tangential and radial cracks a uniform, essentially along the alignment of the abrasive structure extending flock of fine microcracks. As a result, the load capacity and the life of the X-ray rotary anodes according to the invention are increased.

A further advantage is that due to the formation of fine microcracks the X-ray rotary anodes according to the invention, in addition to the increase in bursting safety and high-voltage stability, also have a significantly slower dose drop over the life of the X-ray rotary 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 in use to a reduction of the self-absorption of the X-radiation and thus to a comparatively high dose yield.

Embodiment:

X-ray rotary anodes with a tungsten-rhenium alloy (10 wt.% Rhenium, 90 wt.% Tungsten) hardfacing firmly bonded to the molybdenum alloy support body were first pre-smoothed by precision turning. After the fine turning of the focal point lining, a directional grinding structure was introduced with a fine-grained diamond grinding wheel. The cup diamond wheel had a grade of D76 indicated by the standard issued by FEPA (Fédération Europeene des Fabricants de Produits Abrasifs). To introduce the abrasive structure, an arrangement was chosen in which the axis of rotation of the cup diamond grinding wheel was aligned substantially perpendicular to the focal surface (relative to the point of contact of the cup wheel with the focal path) and with respect to the radial direction substantially center of the focal path. The arrangement was further chosen such that an annular grinding surface formed on the face side of the cup diamond grinding wheel, which is oriented perpendicular to the axis of rotation (the cup diamond grinding wheel), is rotated on a peripheral portion (the rotating one Pot-type diamond grinding wheel) engaged in the raceway surface while the opposite peripheral portion was spaced from the focal line. In order to introduce the abrasive structure, the cup diamond grinding wheel and the x-ray rotating anode in this arrangement were respectively rotated about their axes of rotation using oil as the lubricant. The inclination of the orientation of the introduced abrasive structure relative to the tangential reference direction depends on the relative speeds of the focal path relative to the grinding surface of the cup diamond wheel. In particular, the rotational speed of the cup diamond grinding wheel must be sufficiently high relative to the rotational speed of the X-ray rotating anode to achieve a tendency of the orientation of the grinding structure relative to the tangential reference direction. In the present case, the X-ray rotary anode was rotated at 100 revolutions per minute, with the focal length extending over a radius of about 75 mm to about 100 mm of the X-ray rotary anode, and the cup diamond grinding wheel had a speed of 20 m / s in the area of the grinding surface ( Meters / second). The resulting abrasive structure was substantially rectilinear, with a slight curvature due to the radius (62.5 mm in the present case) of the cup diamond wheel. The orientation of the abrasive structure was approximately 85 ° -90 ° relative to the tangential reference direction (ie, approximately radial). The mean roughness of the directional abrasive structure was Ra = 0.25 μm.

The present invention is not limited to the above-explained embodiments. In particular, as is known in the art, the outer shape and structure of the X-ray rotary anode may deviate from the X-ray rotary anode -2- shown in the figures. In particular, it can also be provided that the focal-path covering covers only a part of the frustoconical section and adjoins the surface of the support body radially inwardly and / or radially outwardly in the same plane on the surface of the focal-path covering. In this case, the respective (inclined) surface portions of the carrier body may be provided with an abrasive structure. Furthermore, it is also possible that the X-ray rotary anode has no separate focal track coating and the focal path on a substantially monolithic body (apart from attachments such as a graphite ring, etc.) is formed. Furthermore, in the context of production, in addition to the described production steps, provision may be made for the surface in question to be smoothed as far as possible prior to the introduction of the abrasive structure in order to eliminate as far as possible the influences of existing structures on the surface. Such smoothing can be done for example by mechanical polishing and / or electropolishing. Furthermore, there is also the possibility to bring in two sets of grooves, which intersect each other. In particular, the X-ray rotary anode can only be coarsely pre-rotated in the circumferential direction in order to introduce relatively coarse grooves which are aligned in the circumferential direction. The mean roughness obtained by rough turning may be, for example, Ra = 2 μm. Subsequently, the directional abrasive structure according to the invention, which extends at least predominantly in the radial direction, can be introduced in such a way that the grooves resulting from the turning at least partially remain intact. In this way, grooves and thus directed cracking nuclei are provided, which have at least two different orientations at the respective surface sections and accordingly support the formation of a fine crack network.

Claims (12)

1. A rotating x-ray anode with an annular focal track (16), the surface of the focal track having a directed ground structure (18; 22), wherein over the circumference of the annular focal track (16) and over the radial extent of the focal track (16), the alignment of the ground structure (18; 22) is inclined in relation to a tangential reference direction (8) in the respective surface portion in each case by an angle in the range from and including 15° up to and including 90°.
2. The rotating x-ray anode as claimed in claim 1, wherein over the circumference of the annular focal track (16) and over the radial extent of the focal track (16), the alignment of the ground structure (18; 22) is inclined in relation to a tangential reference direction (8) in the respective surface portion in each case by an angle in the range from and including 35° up to and including 70°.
3. The rotating x-ray anode as claimed in claim 1 or 2, wherein the directed ground structure (22) has in each case an essentially straight course.
4. The rotating x-ray anode as claimed in claim 1 or 2, wherein 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) in the respective surface portion decreases over the radial extent of the focal track (16).
5. The rotating x-ray anode as claimed in one of the preceding claims, wherein in the region of the ground structure (18; 22), the mean surface roughness Ra lies in a range from and including 0.05 µm up to and including 0.5 µm, a measuring section that runs straight and essentially perpendicularly to the alignment of the ground structure being used for the determination of the mean surface roughness.
6. The rotating x-ray anode as claimed in one of the preceding claims, wherein the ground structure (18; 22) extends beyond the region of the focal track (16).
7. The rotating x-ray anode as claimed in one of the preceding claims, wherein the material of the focal track in the region of the focal track (16) is formed by tungsten or by a tungsten-based alloy.
8. The rotating x-ray anode as claimed in one of the preceding claims, wherein said anode has a carrier body (12) and a focal track layer (14), which is formed on the carrier body (12) and on which the focal track (16) runs.
9. A method for producing a rotating x-ray anode (2), wherein a directed ground structure (18; 22) is introduced at least in the region of an annular focal track (16) of the rotating x-ray anode (2) in such a way that, over the circumference of the annular focal track (16) and over the radial extent of the focal track (16), the alignment of the ground structure (18; 22) is inclined in relation to a tangential reference direction (8) in the respective surface portion in each case by an angle in the range from and including 15° up to and including 90°.
10. The method as claimed in claim 9, wherein the step of introducing the ground structure (18; 22) forms the last working step involving removal of material in the region of the surface of the focal track, in the production of the rotating x-ray anode (2).
11. The method as claimed in claim 9 or 10, wherein the ground structure (18; 22) is introduced by grinding.
12. The method as claimed in one of claims 9 to 11, wherein to introduce the ground structure (18; 22), a grinding body is moved in such a way that its grinding surface moves at least partly in the radial direction (10), and in that furthermore the grinding body and the focal track (16) are moved in relation to one another in the circumferential direction.

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