X-RAY ANODE

Abstract

An x-ray anode has an emission layer and a carrier with carrier material to support the emission layer. The carrier material is a metallized carbon fiber material with a portion in which the fibers are specifically directed. A high heat dissipation from the emission layer and a coefficient of heat expansion of the carrier that is advantageous for bonding with the emission layer are achieved.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section through an x-ray anode with an emission layer and a carrier containing a directed carbon fiber material.

FIG. 2 is a diagram with preferred directions in which carbon fibers of the carbon fiber material are aligned.

FIG. 3 shows a further x-ray anode with another carrier.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an x-ray anode 2 executed as a rotary anode that, for example, can be inside of a housing (not shown) of a rotating radiating tube. The rotary anode 2 has an emission layer 4 and a carrier 6 bearing the emission layer 4, which carrier 7 is thermally connected with a coolant circuit (not shown) and—like the emission layer 4—is rotationally symmetrical relative to a rotation axis 8. It have a cylindrical metallic core 10, a metallic housing 12 made from molybdenum with an outer wall 14 and an end wall 16 and a rotationally symmetrical ring 18 with a carrier material that is formed from a metallized carbon fiber material 20 with five directed portions 22, 24, 26, 28, 30. Each of the portions 22, 24, 26, 28, 30 comprises carbon fibers with an average length of 2 mm, of which over 95% are aligned in a predetermined preferred direction associated with the respective portion 22, 24, 26, 28, 30, with a deviation of at maximum ±5°. Essentially all carbon fibers of the carrier material are aligned in a predetermined, preferred direction in this manner.

The carbon fibers are divided into two carbon fiber types that differ in terms of their properties. The type 1 is characterized by a high heat conductivity in the axial direction. The type 2 shows a large coefficient of heat expansion in the radial direction and its carbon fibers are less sensitive to brittleness and scoring than the carbon fibers of the type 1. The heat conductivity of the type 2 in the axial direction is less than that of the type 1 and essentially plays no role. Some properties at room temperature are, in detail:

	Heat conductivity	Coefficient of heat expansion
	(Wm−1K−1)	(ppm/K)
Type 1	axial	400 to 1900	−1.0 to 0
	radial	5 to 40	5 to 20
Type 2	axial	20 to 200	−1.0 to 0
	radial	5 to 20	5 to 20

The carbon fibers in the portion 22 are exclusively carbon fibers of the type 1 and are aligned parallel to the rotation axis 8 and thus towards the emission layer 3. The task to dissipate as much heat as possible from the emission layer 4 per unit of time is assigned to them. The carbon fibers of the portions 24, 26, 28, 30 are exclusively carbon fibers of the type 2 to which the task is assigned to ensure a desired coefficient of heat expansion in the radial direction 34 (FIG. 2). They are aligned helically around the rotation axis 8, the helical shape being accomplished by a number of carbon fibers arranged next to one another and after one another and not by individual carbon fibers alone. The carbon fibers of the portions 26 and 28 are arranged in the direction of a clockwise threading and the carbon fibers of the portions 24 and 30 are arranged in the direction of a counter-clockwise threading such that a meshwork of carbon fibers respectively results via the helical tracks of the portions 24, 26 and of the portions 28, 30 running opposite one another.

To explain the alignments, FIG. 2 schematically shows the axial direction 32 of the x-ray anode 2 that is parallel to the rotation axis 8, the tangential direction 34 around the rotation axis 8 (by which should also be understood the azimuthal direction within the x-ray anode 2) and two preferred directions 36, 38 that are applied as helical directions. The carbon fibers of the portions 26, 28 are arranged with a maximum deviation of ±5° in the preferred direction 36 that exhibits a helical angle α₂ of 17° relative to the tangential direction 34 and is a clockwise helical direction. The carbon fibers of the portions 24, 30 are arranged with a maximum deviation of ±5° in the preferred direction 38 that exhibits a helical angle α₂ of likewise 17° relative to the tangential direction 34 and is a counter-clockwise helical direction. The axial direction 32 corresponds to a third preferred direction 40 in which the carbon fibers of the portion 22 are likewise aligned with a maximum deviation of ±5°.

Due to the large difference of the coefficient of heat expansion of the carbon fibers of the type 2 in the axial and radial direction of the carbon fibers, the coefficient of heat expansion of the carrier material in the radial direction of the x-ray anode 2 can be adjusted within predetermined limits, dependent on the helical angles α₁, α₂ of the carbon fibers of the portions 24, 26, 28, 30, and be adapted to the coefficient of heat expansion of the emission layer 4 or another layer. The coefficient of heat expansion of the carrier material in the radial direction of the x-ray anode 2 is hereby additionally dependent on the quantity of the carbon fibers of the portions 22, 24, 26, 28, 30 relative to the quantity of the metal surrounding the carbon fibers. In the exemplary embodiment shown in FIG. 1, the carbon fibers occupy ⅔ of the volume and the metal ⅓ of the volume of the carrier material. The housing 12 is not designated as a carrier material. This volume ratio can be adjusted dependent on the requirements of the x-ray anode 2. A volume portion of 50% to 90% of the carbon fibers has proven to be advantageous.

To achieve a particularly good head dissipation from the emission layer 4, the carrier 6 is provided with a first carbon fiber-containing layer 42 situated next to the emission layer 4, under which first carbon fiber-containing layer 42 is arranged a second carbon fiber-containing layer 44 further removed from the emission layer 4, which second carbon fiber-containing layer 44 exhibits a higher carbon fiber proportion than the first layer 42. The carbon fibers of the type 2 imparting mechanical stability and setting the coefficient of heat expansion are reduced in the upper layer 42 so that the heat conductivity can ensue there undisturbed by the carbon fibers of the portion 22 and the metal.

During an x-ray operation electrons are accelerated from a cathode (not shown) onto the x-ray anode 2 and strike (as indicated by an arrow 46) in a radial outer region of the x-ray anode 2 on the emission layer 4. During this the x-ray anode 2 rotates with a frequency of 250 Hz around the rotation axis 8. By the rotation the electrons strike on a focal ring of the emission layer 4 that lies above the outer ring 18. In the focal ring x-ray radiation and a large amount of heat are generated by braking processes, which heat heats the emission layer 4. The heat is transferred through the thin end wall 16 to the carrier material of the outer ring 18 and is primarily conducted away from the emission layer 4 by the carbon fibers of the portion 22 that are parallel to the rotation axis 8. This emission layer 4 expands due to the heating of the emission layer 4. The carbon fibers of the portions 22, 24, 26, 28, 30 are thus selected in terms of quantity and arrangement such that the carrier material exhibits a coefficient of heat expansion adapted to the emission layer 4 in the radial direction, which coefficient of heat expansion is equal to that of the emission layer 4 in a range of 0.5×0⁻⁶/° K. The carbon fibers of the portions 24, 26 additionally provide for a mechanical stability that protects the x-ray anode 2 from out-of-balances even at high rotation speeds. Since the carbon fibers do not creep up to a temperature of 2200° C., a long-term stability is provided with regard to the geometry and an out-of-balance development is countered. The quantities of the carbon fibers of the portions 24, 26 relative to the portions 28, 30 can be varied depending on the requirement for heat expansion and mechanical stability.

To produce the x-ray anode 2, the core 10 is centered in the housing 12 so that an annular interstice is formed between core 10 and outer wall 14. A plurality of layers of carbon fiber material 20 in tissue or meshwork form are subsequently applied on the outer wall 14 and on the core 10, which layers form the portions 24, 26 and a part of the portion 22. The carbon fibers that form the portions 28, 30 and the further part of the portion 22 can then be placed inside in a loose meshwork. The carbon fibers can be inserted as tissue or meshwork mats in which the carbon fibers are already arranged in the desired preferred directions 36, 38, 40. A number of mats differing from one another are placed inside one another in alternation in order to form the meshwork with the helical tracks running opposite one another. To make wetting of the carbon fibers with metal easier, these are coated with Cr carbide, W carbide or Mo carbide or a combination of at least two of these carbides or with cobalt.

After completion of the meshwork, this is impregnated with a metal with very good heat conductivity, for example copper or silver. The metal now metalizing the current deflector 20 hereby serves as a solder to bond the carrier material with the end wall 16 of the housing 12 on which the emission layer 4 is applied. As an alternative or for further improvement of the wetting, the metal can be provided with a slight alloying of an additive metal that is a carbide creator and/or improves the bonding with the carbon fibers or the carbides and the soldering process with the end wall 16. To avoid voids (hollow spaces) in the carrier material, the carrier material is isostatically pressed with the liquid metal while hot.

FIG. 3 shows an alternative x-ray anode 48 with an emission layer 4 on a carrier 50 whose carrier material comprises carbon fiber material 56 with three directed portions 22, 52, 54. The subsequent specification is essentially limited to the differences with regard to the exemplary embodiment in FIGS. 1 and 2 to which reference is made with regard to constant features and functions. Essentially constant components are in principle numbered with the same reference characters. The carbon fiber material 56 includes carbon fibers of the portion 22 that are executed and aligned just like the carbon fibers of the portion 22 in FIG. 1. The portions 52, 54 of the carbon fiber material 56 are aligned analogous to the portions 28, 30 and are respectively held together in a tissue or mesh mat made from carbon fiber material 56 that is wound in spirals around the rotation axis 8. The carbon fibers of the portion 52 are those of the type 1 and the carbon fibers of the portion 54 are those of the type 2.

To produce the x-ray anode 48, the emission layer 4 is provided with a metallic layer 58 that acts as a solder given a casting of metal 60 that should saturate the carbon fiber material 56. The carbon fiber material 56 made from two mats wound expanding in the radial direction is applied on this layer 58 with, if applicable, a preliminary auxiliary housing. The mats respectively comprise a layer made from carbon fibers of the portion 22 aligned in the axial direction in the carrier 50, which carbon fibers are aligned with a helical angle α₁, α₂ of respectively 19° relative to the tangential direction 34. Given a rolling of both mats, a repeating layer series of four layers results, namely a layer with portion 22, a layer with helically-arranged carbon fibers of the portion 52, again a layer with portion 22 and a layer with carbon fibers of the portion 54 arranged helically in the opposite direction, such that the carbon fibers of the portions 52, 54 form a mesh in helical form running in opposite directions. The carbon fibers can be coated with a carbide or metal and are subsequently saturated with the metal 60 as described with regard to FIG. 1. The carbon fiber material 56 is bonded with the emission layer 4 via the at least partial melting of the layer 58. Homogeneous material properties that promote a durable high stability of the carrier 50 result via the regular order of the layers made from carbon fibers of the type 1 and the type 2.

Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.

Claims

1. An x-ray anode comprising: an emission layer;a carrier layer comprised of carrier material on which emission layer is supported; andsaid carrier material comprising metallized carbon material with at least a portion of fibers therein being oriented in a specified direction.

2. An x-ray anode as claimed in claim 1 wherein said fibers in said metallized carbon fiber material are oriented in a direction toward said emission layer.

3. An x-ray anode as claimed in claim 1 wherein said metallized carbon fiber material comprises carbon fibers saturated with metal.

4. An x-ray anode as claimed in claim 1 wherein said metallized carbon fiber material comprises at least a first carbon fiber type and a second carbon fiber type differing from said first carbon fiber type.

5. An x-ray anode as claimed in claim 4 wherein said first carbon fiber type has a higher heat conductivity then said second carbon fiber type, and wherein said second carbon fiber type has at least one of a higher mechanical flexibility and a lower brittleness than said first carbon fiber type.

6. An x-ray anode as claimed in claim 4 wherein the fibers of said first carbon fiber type are oriented in a first specified direction and wherein the fibers of said second carbon fiber type are oriented in a second specified direction differing from said first specified direction.

7. An x-ray anode as claimed in claim 1 wherein said x-ray anode is rotatable around a rotation axis, and wherein said fibers of said first carbon fiber type and said fibers of said second carbon fiber type respectively form helical tracks proceeding in opposite directions around said rotation axis.

8. An x-ray anode as claimed in claim 1 wherein said portion of said metallized carbon material having fibers oriented in said specified direction comprises a rolled mat.

9. An x-ray anode as claimed in claim 1 wherein said x-ray anode is rotatable around a rotation axis, and wherein said portion of said metallized carbon fiber material having said fibers oriented in said specified direction forms a helical track around said rotation axis.

10. An x-ray anode as claimed in claim 1 wherein said carrier comprises a first carbon fiber-containing layer situated next to said emission layer, and a second carbon fiber-containing layer spaced from said emission layer, said first carbon fiber-containing layer comprising a lower carbon fiber proportion than said second carbon fiber-containing layer.

11. An x-ray anode as claimed in claim 1 wherein said carrier material is cast on said emission layer.

12. An x-ray anode as claimed in claim 11 wherein said metallized carbon fiber material comprises solder that bonds said carrier material with said emission layer.

13. An x-ray anode as claimed in claim 12 wherein said metallized carbon fiber material comprises a metal that chemically interacts with said carbon and said solder.

14. An x-ray anode as claimed in claim 1 wherein said carrier material has a coefficient of expansion adapted to a coefficient of expansion of said emission layer in a radial direction of said x-ray anode.