WO2013014123A1

WO2013014123A1 - X-ray tube and method for the production thereof

Info

Publication number: WO2013014123A1
Application number: PCT/EP2012/064396
Authority: WO
Inventors: Norbert Huber; Martin Kautz; Jochen SCHÄFER
Original assignee: Siemens Aktiengesellschaft
Priority date: 2011-07-27
Filing date: 2012-07-23
Publication date: 2013-01-31
Also published as: DE102011079878A1

Abstract

The invention relates to an x-ray tube for producing x-ray radiation, comprising an anode (4), which comprises a phase-change material, PCM (11), for cooling, and to a method for producing the x-ray tube. The phase-change material (11) is arranged in the anode material and can, for example, be introduced into the anode (4) by pouring the phase-change material in the liquid form.

Description

description

The present invention relates to an X-ray tube for generating X-ray radiation having an anode comprising a phase change material for cooling, and to a method of manufacturing the X-ray tube. When generating X-rays with X-ray tubes, a large part of the electrical energy used is converted into heat energy. This accumulates at the anode and must be ^removed . The operation of an X-ray tube is diskonti ^¬ ously. There is a change between set-up times, which for example for the introduction of the body to be examined and for

Adjustment of the apparatus are necessary, and times of taking x-rays. The energy introduced during the generation of X-rays is released only gradually by heat conduction and by heat radiation, for which reason e.g. Rotary anodes in operation get very hot. Set-up times are usually long enough to ensure system cooling.

High peak temperatures, however, can lead to problems, even to the destruction of the X-ray tube. Therefore, high peak temperatures should be avoided. This results in a significant constructive effort to avoid unacceptably high thermal stresses and thermal overheating / destruction in the anode and a strong limitation in terms of material selection. Among other things, expensive materials like TZM, a titanium-zirconium-molybdenum alloy, have to be used.

Another problem is possible power outages. at

Power failure during or immediately after a treatment or

Examination, ie after a heat supply, there is the danger to destroy the tube due to high temperatures due to insufficient cooling. There is insufficient cooling also the risk of damage up to the destruction of the liquid metal bearing at the anode foot. Here, the temperatures Tempe ^¬ must be kept safely below 400 ° C. In general, the intensity, duration and frequency of the possible X-ray sequences that characterize the X-ray system depend on the heat dissipation and the heat buffering of the rotating anode plate. The temperatures in the anode should be kept as low as possible, eg by improving the cooling concepts. As already described, the possibilities are limited. For a power failure or failure of the cooling system, a battery is provided in the system, which provides sufficient energy for driving a coolant pump briefly until the start of the emergency power supply. As a result, it is possible to try to distribute the heat flowing away in the direction of the anode axis as long as possible to the entire system. Another Mög ^¬ friendliness is the rotating anode plate with a large heat capacity equip. This can be done, for example, by increasing the radius of the turntable or by applying graphite to the turntable for better heat dissipation. However, this increases the effort and costs. One possible solution to the problem is the use of phase change materials. From the prior art, for example DE10064341C2, the cooling of X-ray tubes via phase change materials is known. A phase change material in thermal contact with the material will be seen the anode of the X-ray tube ge ^¬ introduced at one side of the X-ray tube in a container. The phase change material decreases during operation, the ent ^¬ standing heat partially and releases it into the Rüst ^¬ times to the environment. Phase change or phase change materials, hereinafter also referred to as PCM (phase change material) are latent heat storage. Such a latent heat storage is characterized in that the PCM, for example, paraffin, a suitable salt or metal, at a certain Grenztempe ^¬ temperature which is usually higher for paraffin at, for example, about 50 ° C and salts or metals (greater than 500 ° C), performs a phase transformation. During the phase change, which is usually is the phase transition between the solid and the liquid state, the temperature of the PCM remains virtually constant despite heat, because the input power that speaks ent ^¬ the Schmelzentalphie is required for the phase transition , The the latent heat storage supplied during the phase transition of the PCM heat is so zwischenge ^¬ stores in the latent heat storage and only released at a reversal of the phase transformation. When power is applied, the PCM will not rise above the threshold temperature until the phase conversion of the PCM is completed and power is maintained. To ensure good cooling with PCM according to the prior art, heat-conducting ribs are necessary.

A disadvantage of the use of heat-conducting, however, is that they lead to a difference in density, which may result in problems with the Ro ^¬ tation of the anode. The one-sided attachment of the phase change material with heat conducting ribs to the anode can lead to imbalances in rotation of the anode, to the destruction of the X-ray tube. The structure of the X-ray tube with phase change material in a container, which consists of a different material than the anode itself, and with heat conducting ribs is complicated. The use of different materials leads to mechanical stresses when thermally expanded. These can lead to the destruction of the structure. Furthermore, space is lost for phase change material by the heat conducting ribs.

The object of the present invention is therefore to provide an X-ray tube for generating X-ray radiation and a method for the production thereof, which reduce or completely overcome the abovementioned problems. In particular, it is the object of the present invention to provide an X-ray tube specify, which has a simple structure, is simple and inexpensive to manufacture, and reliable in operation ^¬ sig and durable works.

The stated object is achieved with respect to the X-ray tube for generating X-radiation with the features of claim 1 and with respect to the method for producing the X-ray tube with the features of claim 9.

Advantageous embodiments of the inventive X-ray tube for generating X-radiation and the method for producing the X-ray tube will become apparent from the respectively associated ^¬ dependent subclaims. The features of the main claim with features of the subclaims and features of the claims can be combined with each other who the.

The X-ray tube according to the invention for generating X-radiation ^¬ comprises an anode with a phase change material to cool the anode. The phase change material is disposed in Ano ^¬ denmaterial or integrated.

The arrangement of the phase change material in the anode Mate rial can be dispensed with a container for the phase change material. The increased contact surface between phase change material and anode material compared to the previously described prior art, in which the phase change material is attached only on one side of the anode, made ^¬ light good heat transfer from the anode material to Pha ^¬ senwechselmaterial and thus allows for thermal fins to without. As a result, with the same mass additionally attached to the anode, it is possible to use more phase change material, which results in improved cooling. By way case of the heat-conducting ribs and the container for Befestigun the phase change material, the structure of the X-ray tube is simplified and saved costs. The arrangement of the phase ^¬ change material not unilaterally on the outside of the Ano ^¬ denmaterials, but reduced or avoided inside During rotation of the anode during operation of the X-ray tube imbalances, which can damage the X-ray tube to destruction.

The phase change material can be a highly heat-conductive phase change material. Possible materials are aluminum, or copper, or brass, or silicon or alloys comprising aluminum, and / or copper, and / or brass, and / or silicon. The use of highly heat-conductive phase change material additionally improves the cooling effect during operation. The anode material may include or may be a titanium-zirconium-molybdenum alloy. In contrast to conventional prior art PCMs, which include paraffin or salts, materials such as aluminum, copper, or brass are better able to conduct heat and have a high enthalpy of fusion. As a result, much amount of heat stored ^¬ and the low density of eg aluminum leads to ver ^¬-reduced problems with the rotation of the anode.

Inside the anode, a cavity may be formed, the phase change material is disposed in wel ^¬ cher. For filling the cavity and for compensating material expansions in operation, an opening of the cavity to the surroundings of the anode can be provided. The cavity in the anode material forms a Be ^¬ ratio for the phase change material, which is not exposed to mechanical stresses in relation to the anode, since no different materials meet. This increases the stability and life of the X-ray tube. Span ^¬ tion between the phase change material and anode material are degraded au¬ usually at phase change of the phase change material au ^¬ . Volume changes of the Phasenwechselmate ^¬ rials can be compensated through the opening.

The cavity can have different forms, for example a cuboid volume, or a rotationally symmetric Volu ^¬ men, in particular a cylindrical volume. A zylin ^¬ derförmige cavity may be easier herzustel ^¬ len may. A rotationally symmetric, in particular a cylinder derförmige cavity can form a common axis with the Rotati ^¬ onsachse the anode, which unbalances during rotation of the anode can be further reduced by different mass distributions or avoided.

The anode may be composed of at least two parts, in particular of just two parts which are mutually connected ^¬ ver. The at least or exactly two parts together enclose a cavity in which the phase change material is arranged. By the construction of two parts, the Ka ^¬ tivity is easy to produce in the interior of the anode. Alternatively, however, the cavity can also be introduced in a one-piece anode, for example as a bore, milling or by spark erosion.

In the case of a two-part or multi-part anode, the at least two parts can be joined together, for example, by a welded connection, in particular by a friction-welded connection. The cavity can be produced by spark erosion from the anode material, but also by other methods such as milling, or the parts can already be produced in the form of depressions during casting, for example, which then result in the cavity. The phase change material can comprise in particular greater than 5 to 1 on ^¬ for an anode material Volu ^¬ menverhältnis greater than 1 to 10. The more phase change material is present, the more heat can be dissipated or cached during operation of the X-ray tube and the better the cooling works. However, in prior art x-ray tubes, the amount of phase change material is severely limited because it is limited by the size of the container and the heat conducting structure, such as cooling fins, and can lead to imbalances in the molten state.

The inventive method for producing the above-described X-ray tube comprises that the Phasenwechselmate ^¬ rial in liquid form, in particular by casting in the anode is introduced. This allows a very uniform distribution Ver ^¬ the phase change material in the cavity and complete filling of the cavity. As a result, imbalances can be rented and the cavity can be filled to a maximum with phase change material, which means that a lot of phase change material is available as a thermal buffer.

The phase change material can be introduced in liquid form via a bore into the interior of the anode. The bore can be used to compensate for changes in volume of the phase change material in the operation of the X-ray tube and allows ei ^¬ ne simple introduction into the cavity even with an assembled anode of individual parts.

The phase change material may only be in contact with a Ano ^¬ denmaterial, in particular with a titanium zirconium molybdenum alloy, to reduce stresses in thermally-induced volume changes. In that no other materials are in contact out of phase change material and Ano ^¬ denmaterial, ie no materials of Be ^¬ holds isses or cooling fins, and in that the phase change material in the liquid state to no mechanical stresses leads to the anode material can not Proble ^¬ me as Chipping or bending caused by mechanical stresses at contact points of materials with different thermal expansion coefficients.

The advantages associated with the method of manufacturing the x-ray tube are analogous to the advantages previously described with respect to the x-ray tube and vice versa.

Preferred embodiments of the invention with advantageous developments according to the features of the dependent claims are explained in more detail with reference to the figures, but without being limited thereto. It is shown in the figures:

Fig. 1 shows an X-ray tube according to the prior art in

Longitudinal section, and

Fig. 2 in an enlarged view a partial

Longitudinal section through the anode of FIG. 1 and associated with the latent heat accumulator, and Fig. 3 is a longitudinal section through the anode of a fiction, modern ^¬ X-ray tube with PCM inside.

Fig. 1 shows an X-ray tube according to the prior Tech ^{¬ technology} , the vacuum housing 1 in a schematically indicated manner (bearings L i and L ₂ ) is rotatably mounted about a rotation axis D.

The vacuum housing 1 is formed with respect to the rotational axis D wesent ^¬ union rotationally symmetrical. In the interior of the vacuum housing 1, an electron emitter 2 with focusing electrode 3 is arranged, which is heated by a heating current in a known manner, not shown, during operation of the x-ray tube and emits an electron beam, designated by E in FIG. 1, of preferably circular cross-section. In the operation of the X-ray tube, the electron beam E strikes an anode 4, since an acceleration voltage, the so-called tube voltage, is applied between the anode 4 and the electron emitter 2, which is not shown in detail in a manner known per se , The electrons of the electron beam E accelerated by the tube voltage strike the anode 4 with such energy that X-radiation emanates from the point of incidence of the electron beam E referred to below as the focal spot BF.

In FIG. 1, the wall thickness of the vacuum housing 1 which originates from the focal spot BF and is reduced by an annular area serving as a beam exit window 5 is replaced. X-ray radiation illustrated by some arrows designated R.

Incidentally, the anode 4 forms a wall of the vacuum housing 1, that is, its bottom, so to speak.

In order to achieve that the focal spot BF is formed during operation of the X-ray tube at the desired location on the anode 4 from ^¬ and despite the rotation of the X-ray tube remains stationary, is a to the vacuum housing 1 stationary relative, that is, not rotating with the vacuum housing 1, a deflection system 6 is provided, which contains in the case of the described Ausführungsbei ^¬ game in a known, not shown manner with appropriate currents supplied coils for egg NEN a focusing and, secondly, provide the required From ^¬ steering the electron beam e.

As can be seen from FIG. 2, the anode 4 has a main body 9, which is formed, for example, from molybdenum, and provided with a focal path 10 in that region in which it is swept by the electron beam E because of the rotation of the x-ray tube is, for example, formed of a tungsten-rhenium alloy. Alternatively, the focal track 10 may be dispensed with using anode materials of e.g. Titanium-zirconium-molybdenum alloys.

In order to be able to dissipate into ^¬ brought loss of heat in the anode 4 during operation of the X-ray tube, the outside of the anode 4 is designated with a whole by 7, is provided in Fig. 1 only schematically indicated latent heat accumulator, the means for biasing associated with a gaseous cooling medium are, in Fig. 1 by a latent heat ^¬ memory with ambient air acting blower 8 are illustrated veraulicht.

The latent heat storage 7 serves as a buffer for the heat loss incurred during operation of the x-ray tube, so that a continuous removal of the costs incurred on the anode 4 heat loss is not necessary. Thus, there is the possi ^¬ ability to dispense with a liquid cooling medium to dissipate the heat loss on the anode 4 and ^{stattdes ¬} sen ^cached in the latent heat storage 7 heat loss by means of a gaseous cooling medium, namely the latent heat storage 7 by means of the blower 8 supplied ^¬ led Ambient air to dissipate.

By omitting a liquid cooling medium are then ^¬ vermie with commonly associated high frictional losses ^¬.

As already mentioned, the latent heat storage ^device 7 contains PCM 11, which in the case of the exemplary embodiment described is accommodated in a cup-shaped housing 12 which is open towards the anode 4.

In order to ensure a good thermal coupling of the anode 4 with the PCM 11 contained in the latent heat storage 7, a heat conducting body 13 is seen on the outside of the anode 4, which consists in the case of the described embodiment of copper. The heat-conducting body 13 is connected by soldering or welding areally with the anode 4, which he is facilitated when the two surfaces to be joined are planar as in the case of the illustrated embodiment.

In order to further improve the heat transfer between anode 4 and PCM 11, the heat-conducting body 13 preferably has annular ribs, one of which is designated 14 in FIG. 2, which engage the PCM 11.

In order to improve the removal of heat stored in the latent heat storage 7 by the air flow generated by the blower 8, the latent heat storage 7, as indicated in Fig. 2 ge dashed lines may be provided on its side facing away from the anode 4 end face with a heat sink 15. The latent heat accumulator 7 and optionally the heat sink 15 and the heat conducting body 13 with the ribs 14 are, by the way, as well as the anode 4 and the x-ray tube formed substantially rotationally symmetrical to the rotation axis D.

FIG. 3 shows a longitudinal section through the anode 4 of an X-ray tube according to the invention with PCM 11 in the interior, ie in a cavity 18 in the anode 4. The anode 4 is constructed from two parts which are mechanically fixed together by a welded joint 16 are connected liquid-tight. In the two parts of the anode 4 is on the Sei ^¬ te on which they are welded together, congruent ^¬ same and mirror inverted introduced a recess, wel ^¬ che the cavity 18 result. The wells can eg

be introduced by milling or by spark erosion in the surface.

The cavity 18 is fluid-tight with the exception of one or more ^¬ ter holes 17, which are designed to introduce the PCM 11 from the outside of the anode 4 to the cavity 18 through. Under bore 17 is hereinafter generally an opening to understand, which can be generated not only by drilling, but also eg by milling or spark erosion. Through the bores, after the parts of the anode 4 have been assembled, the PCM 11 can be introduced, for example, by pouring in liquid form until the cavity 18 is completely filled with PCM 11. The introduced PCM 11 can first solidify after insertion. During operation of the X-ray tube, the material then liquefies again and spreads evenly over the circumference, which counteracts a possible imbalance. In Ent ^¬ are unbalance by the Borungen 17 may include additional balancing holes, which are not shown in the figures for simplicity, are introduced into the anode 4 for compensating for or reducing the imbalance.

The bore is obliquely upwards in the direction of the electron emitter 2, not shown in FIG. 3, with an inclination in the direction of the axis of rotation D. Due to the inclination of the Bore 17 in the direction of rotation axis D and the formation upwards, against the direction of gravity, the PCM 11 also remains in liquid form upon rotation of the anode in the cavity 18. The bore 17 can remain open and to compensate for volume changes of the PCM 11 in the cavity 18 serve, without the liquid PCM 11 expires.

In embodiments of the anode 4 from a material such as a titanium-zirconium-molybdenum alloy, can be dispensed with an internal web 10 of another as the anode material ^¬ the. When using highly heat-conductive PCM, in particular aluminum, or copper, or brass, or silicon or their alloys, can be dispensed with an additional cooling or a higher performance can be achieved because it has sufficient heat capacity with sufficiently large cavity 4 to the completely absorbed in the operation of the X-ray tube Wär ^¬ memege and deliver it again during breaks. It can also be dispensed with the use of Wärmeleitkörpern 13 and heat sinks 15 and on containers such as the housing 12, by introduction and direct arrangement of hochwärmeleitfähigem PCM in the cavity 18 in the interior of the anode. 4

The X-ray tube according to the invention can be accommodated in a protective housing in a manner known per se, wherein the protective housing contains no liquid, but instead flows through a gaseous cooling medium, in particular the ambient air, wherein the flow is, for example, by a blower is maintained. Alternatively, the X-ray tube according to the invention may be housed in an oil bath or in a flow-through of oil vessel in a known per se and not Darge ^¬ imputed manner. The x-ray tube may comprise a stationary anode or a rotary anode.

The advantages of the embodiment of the X-ray tube according to the invention can be summarized as follows: Lower temporal peak temperatures in the anode 4, thus lower material load.

Less design and manufacturing ^effort in comparison ^¬ to the prior art, for example, by dispensing with heat-conducting body 13, no third material necessary.

Due to the small density e.g. of aluminum reduce the centrifugal forces.

The elimination of the heat-conducting ribs 14 leaves a larger volume for the PCM material 11.

If necessary accounts elaborately produced Deh ^¬ voltage joints such as the turntable, since severe temperature fluctuations and related material distortions can be avoided.

The effective thermal conductivity of the fuel ring to the remaining anode plate is significantly increased by free convection of the liquid PCM material.

Incidentally, the invention can also be applied to those X-ray tubes in which the electron emitter is rotatably supported relative to the vacuum housing in a manner known per se from US ^Pat . No. 5,046,186 and is held stationary by suitable measures relative to the vacuum housing. The invention can also be applied to other types of x-ray tubes.

The X-ray tube according to the invention should not be limited only to the described in Fig. 3 embodiment, son ^¬ countries may also have features which have been for example described above under the prior art. Any combination of described embodiments is encompassed by the invention.

Claims

claims

1. X-ray tube for generating X-radiation (R) with an anode (4), which comprises a phase change material (11) for cooling, characterized in that the phase change ^¬ selmaterial (11) is arranged in the anode material.

2. X-ray tube according to claim 1, characterized in that the phase change material (11) is a highly heat-conductive phase change material (11), in particular aluminum, or

Copper, or brass, or silicon or alloys comprising aluminum, and / or copper, and / or brass, and / or silicon.

3. X-ray tube according to one of the preceding claims, ^¬ characterized in that the anode material comprises a titanium-zirconium-molybdenum alloy or that the anode material is a titanium-zirconium-molybdenum alloy.

4. X-ray tube according to one of the preceding claims, characterized in that in the interior of the anode (4) a covity (18) is formed, in which the phase change material (11) is arranged, in particular with an opening for Umge ^¬ tion of the anode (4) for filling the cavity (18) and for equalizing material expansions.

5. X-ray tube according to claim 4, characterized in that the cavity (18) has a cuboidal volume or that the cavity (18) has a rotationally symmetrical volume up, in particular a cylindrical volume.

6. X-ray tube according to one of the preceding claims, ^¬ characterized in that the anode (4) consists of at least two parts, in particular of exactly two parts which are interconnected and together enclose a cavity (18), in which the phase change material (11) is arranged.

7. X-ray tube according to claim 6, characterized in that the at least two parts of the anode (4) are joined together by a welding ^¬ connection (16), in particular by a Reibschweißverbindung and / or the cavity (18) produced by spark erosion of the anode material is.

8. X-ray tube according to one of the preceding claims, ^¬ characterized in that the phase change material (11) to the anode material has a volume ratio greater than 1 to 10, in particular greater than 1 to 5.

9. A method for producing an X-ray tube according to one of the preceding claims, characterized in that the phase change material (11) is introduced in liquid form, in particular by casting in the anode (4).

10. The method according to claim 9, characterized in that by introduction in liquid form, the phase change material (11) evenly distributed in a cavity (18) in the interior of the anode (4), to avoid imbalances.

11. The method according to claim 9 or 10, characterized in that the phase change material (11) is introduced in liquid form via a bore (17) into the interior of the anode (4).

12. The method according to claim 11, characterized in that the bore (17) serves to compensate for volume changes of the phase change material (11) during operation of the X-ray tube.

13. The method according to any one of claims 9 to 12, characterized in that the phase change material (11) exclusively ^{¬ is} in contact with an anode material, in particular with a titanium-zirconium-molybdenum alloy, for the reduction of stresses in thermally induced volume changes ,