JP5561760B2 - Target, X-ray tube and target manufacturing method - Google Patents

Description

  The present invention relates to a target, an X-ray tube including the target, and a method for manufacturing the target.

  The X-ray tube apparatus includes an X-ray tube. The X-ray tube is configured to generate an X-ray by colliding an electron beam with an anode target. Such an X-ray tube apparatus is used in many applications such as a medical diagnostic apparatus, an industrial nondestructive inspection apparatus, and a material analysis apparatus. Hereinafter, a rotary anode type X-ray tube device and a rotary anode type X-ray tube will be described as representative devices.

  In a rotating anode X-ray tube, electrons emitted from the cathode are accelerated and focused by a potential gradient between the fixed cathode and the rotating anode target, and typically have an energy of 20 to 150 keV, and the target of the rotating anode target. Colliding with the surface, this forms a focal point on the target surface that becomes the X-ray generation source.

  When an electron beam with high energy collides with the focal point, the electron beam is rapidly decelerated by the target material, so that X-rays are emitted from the focal point. The target surface is made of a refractory metal such as tungsten or a tungsten alloy. The target surface is formed on a substrate (target body) made of a refractory metal such as molybdenum or molybdenum alloy. The rate of conversion to X-rays is only about 1% of the kinetic energy of the electrons that strike the anode target. The remaining energy is converted to heat.

  Since the anode target stores the generated heat, a heat capacity is required. This can be achieved by increasing the volume of the metal substrate in order to obtain a large heat capacity, but in general, a heat storage body made of graphite (graphite), which is a heat-resistant material having a lower specific gravity, is brazed to the metal substrate. Yes.

  As the graphite (graphite) material, an isotropic graphite material in which many graphite crystals having various crystal orientations are gathered is generally used (see, for example, Patent Documents 1 and 2). The heat stored in the heat storage body made of graphite (graphite) is released from the surface of the graphite (graphite) having a relatively high radiation rate by the heat radiation action. For this reason, a heat storage body made of graphite (graphite) can be named a heat radiating body, and is hereinafter referred to as such.

  By the way, the heat dissipating body using graphite has a drawback that fine wear powder (graphite particles) is embedded on the surface by mechanical removal processing of the heat dissipating body. Such mechanical removal processing is usually performed twice, that is, a process of manufacturing the heat dissipating body with graphite and a final finishing process as an anode target after the heat dissipating body is brazed to the metal substrate. . Although the embedded fine wear powder is removed to some extent by the cleaning process, it is not sufficiently removed and tends to remain on the surface of the radiator.

  Fine abrasion powder is the first surface of the radiator due to the centrifugal force that works when the anode target built into the X-ray tube rotates at high speed and the electrostatic force that works when a high voltage is applied to the X-ray tube. Leave. The fine abrasion powder that has detached from the surface of the radiator becomes a conductive foreign substance in the vacuum space of the X-ray tube, which causes discharge in the X-ray tube.

  Therefore, as a measure to prevent the embedded fine abrasion powder from detaching from the surface of the radiator, as a final finishing process of the anode target, hydrocarbon gas is decomposed in an active direct current glow discharge to heat the surface of the radiator. A method for forming a decomposed carbon film is disclosed (for example, see Patent Document 3).

Japanese Patent Publication No. 3-64448 JP 2002-154874 A Japanese Patent No. 2791977

  However, when the pyrolytic carbon film is formed as described above, the manufacturing cost increases, and further, the gas occluded in the radiator is confined firmly. If the gas is confined in the radiator, the anode target itself cannot be sufficiently heated even after passing through the heated gas extraction step in vacuum or the evacuation step of the X-ray tube. For this reason, the gas confined in the radiator is gradually released into the vacuum space when the X-ray tube is used, and eventually causes a discharge in the X-ray tube. As a result, there has been a problem that the life of the X-ray tube is shortened.

  The present invention has been made in view of the above points, and its object is to provide a target that can suppress the manufacturing cost, does not confine gas in the radiator, and has no wear powder on the exposed surface of the radiator. Another object of the present invention is to provide a method for manufacturing an X-ray tube and a target.

In order to solve the above problems, a target according to an aspect of the present invention is:
A heat sink formed of near net and isotropic graphite;
A target body that has a target surface that emits X-rays upon incidence of electrons, is formed of a metal having a specific gravity greater than that of isotropic graphite, and the heat radiator is joined by brazing. It is characterized by being able to rotate around the center.

Moreover, the X-ray tube which concerns on the other aspect of this invention is
A heat sink made of isotropic graphite and made of isotropic graphite, and a target surface that emits X-rays upon incidence of electrons, and is made of a metal having a specific gravity greater than that of isotropic graphite. A target body whose body is joined by brazing, and a target that is rotatable about a rotation axis;
An electron emission source that emits electrons to irradiate the target;
And a vacuum envelope containing the target and the electron emission source.

Moreover, the method for manufacturing a target according to another aspect of the present invention includes:
In the method of manufacturing a target that can rotate around a rotation axis,
Near-net molding a mixture of one or more types of carbon-based powder material,
Forming a radiator with isotropic graphite obtained by heating and firing the near-net shaped mixture,
A target body that has a target surface that emits X-rays when electrons are incident and is made of a metal having a specific gravity greater than that of isotropic graphite,
The radiator is joined to the target body by brazing.

  According to the present invention, a manufacturing cost can be suppressed, a gas is not confined in the radiator, a target having no abrasion powder on the exposed surface of the radiator, an X-ray tube including the target, and a method for manufacturing the target are provided. can do.

FIG. 1 is a sectional view showing a rotary anode type X-ray tube apparatus according to an embodiment of the present invention. 2 is a cross-sectional view showing the rotary anode type X-ray tube shown in FIG. FIG. 3 is an enlarged cross-sectional view showing the anode target shown in FIG. FIG. 4 is a flowchart showing a method for manufacturing the anode target. FIG. 5 is a cross-sectional view showing a radiator of the anode target.

  Hereinafter, a rotating anode type X-ray tube apparatus and an anode target manufacturing method used in the X-ray tube apparatus according to embodiments of the present invention will be described in detail with reference to the drawings. First, the configuration of the X-ray tube apparatus will be described.

  As shown in FIG. 1, a rotary anode type X-ray tube apparatus includes a rotary anode type X-ray tube 1, a stator coil (electromagnetic coil) 6 that generates a magnetic field as a rotation drive mechanism, an X-ray tube 1 and a stator. A housing 2 that houses the coil 6, an insulating oil 3 as a coolant filled in the housing 2, and a cooling unit 30 are provided.

  As shown in FIGS. 1 and 2, the X-ray tube 1 includes an anode target 10 as a target, a cathode 18, a vacuum envelope 17, a rotating body 13, and a fixed body 15.

  The rotating body 13 is formed in a cylindrical shape, and one end thereof is closed. The rotating body 13 extends along a rotation axis a that is a central axis of the rotating operation of the rotating body. The rotating body 13 can rotate around the rotation axis a. The rotating body 13 is made of a material such as Fe (iron) or Mo (molybdenum).

  The fixed body 15 is formed in a column shape. The diameter of the fixed body 15 is smaller than the inner diameter of the rotating body 13. The fixed body 15 is provided coaxially with the rotating body 13 and extends along the rotation axis a. The fixed body 15 is made of a material such as Fe or Mo. One end portion of the fixed body 15 is located on the closed one end portion side of the rotating body 13, and the other end portion of the fixed body 15 protrudes to the outside of the rotating body 13 and is exposed.

  The rotating body 13 and the fixed body 15 are provided with a gap of about 20 to 30 μm from each other. The fixed body 15 supports the rotating body 13 in a rotatable manner. Although not shown, the gap between the rotating body 13 and the fixed body 15 is filled with a metal lubricant. The rotating body 13, the fixed body 15 and the metal lubricant form a radial sliding bearing.

  A seal portion 16 is provided at the other end of the rotating body 13 that is opened. The seal portion 16 is fixed to the other end portion of the rotating body 13 with a fixing screw. The seal portion 16 is formed in an annular shape, and is provided with a gap around the entire side surface of the fixed body 15. The seal part 16 regulates a relative shift in the direction along the rotation axis a of the rotating body 13 and the fixed body 15.

  The clearance (clearance) between the seal portion 16 and the fixed body 15 is set to a value that can maintain the rotation of the rotating body 13 and suppress the leakage of the metal lubricant. From the above, the gap is slight. Further, in the direction along the rotation axis a, the fixed body 15, the seal portion 16, and the metal lubricant form a thrust bearing.

As shown in FIGS. 2 and 3, the anode target 10 is disposed to face one end of the rotating body 13 in the direction along the rotation axis a. The anode target 10 includes a radiator 12 and a target body 11.
The heat dissipating body 12 is formed of graphite (isotropic graphite) that is near-net molded and exhibits mechanical, electrical, and thermal isotropy. The radiator 12 is formed in an annular shape. The exposed surface of the radiator 12 is not subjected to mechanical removal processing or film formation processing.

  The target body 11 has a target surface 11a that emits X-rays when electrons are incident thereon. The target main body 11 has an annular shape and is formed of a metal having a specific gravity greater than that of isotropic graphite. Here, the target body 11 is made of a molybdenum alloy, and the target surface 11a is made of a tungsten alloy. A heat radiator 12 is joined to the target body 11 by brazing. Here, the target main body 11 and the heat radiating body 12 are joined by the zirconium brazing 20.

  The anode target 10 is fixed by a nut 14 to one end of the rotating body 13 that is closed. The anode target 10 is provided coaxially with the rotating body 13 and the fixed body 15. The anode target 10 is in an equilibrium state around the rotation axis a, and can rotate around the rotation axis a.

  As shown in FIG. 2, the cathode 18 is disposed so as to face the target surface 11 a of the anode target 10 at an interval. The cathode 18 is attached to the cathode structure 19. The cathode 18 has a filament 18 a as an electron emission source that emits electrons irradiated to the anode target 10.

  As shown in FIGS. 1 and 2, the vacuum envelope 17 is formed in a cylindrical shape. The vacuum envelope 17 is made of metal and glass. In the vacuum envelope 17, the diameter of the part facing the anode target 10 is larger than the diameter of the part facing the rotating body 13. The vacuum envelope 17 is joined to the other end portion of the fixed body 15 and the cathode assembly 19 so as to maintain the airtight state of the vacuum envelope 17. The vacuum envelope 17 has an X-ray emission window 17 a that emits X-rays in the vicinity of the target surface 11 a facing the cathode 18. The vacuum envelope 17 is hermetically sealed and accommodates the rotating body 13, the fixed body 15, the anode target 10, the cathode 18, and the like. The inside of the vacuum envelope 17 is maintained in a vacuum state.

  The stator coil 6 is provided to face the side surface of the rotating body 13 and surround the outside of the vacuum envelope 17. The stator coil 6 rotates the rotating body 13. By supplying a predetermined current to the stator coil 6, the rotating body 13 is rotated at a predetermined speed, and the anode target 10 is rotated at a predetermined speed.

  The housing 2 has an X-ray emission window 2 a that emits X-rays in the vicinity of the target surface 11 a facing the cathode 18. The housing 2 contains an X-ray tube 1 and a stator coil 6 and is filled with insulating oil 3.

The cooling unit 30 includes a cooler (heat exchanger) 31 and a pump (insulating oil circulation pump) 32. The insulating oil 3 supplied into the housing 2 is cooled by the cooler 31. The pump 32 circulates the insulating oil 3 through the cooler 31 and circulates in a circulation path formed in the housing 2 through an inlet and an outlet provided in the housing 2. Thereby, the heat generated in the X-ray tube 1 is released to the outside of the housing 2 through the insulating oil 3.
As described above, the rotary anode type X-ray tube apparatus is configured.

Next, a method for manufacturing the anode target 10 will be described.
As shown in FIG. 4, when the manufacture of the anode target 10 is started, first, in step S1,
A mixture in which a powder material containing one or more kinds of carbon as a main component is prepared. Here, a mixture obtained by mixing and kneading coke, carbon black, and binder pitch is prepared.

  Subsequently, in step S2, the mixture is dried, and in step S3, the dried mixture is pulverized. Next, in step S4, the finely pulverized mixture is subjected to near-net molding by cold isostatic pressing. Thereby, the said mixture can be formed in a desired shape previously.

  Thereafter, in step S5, the molded product made of the above mixture is fired at a temperature of 800 to 1200 ° C. in a vacuum atmosphere or in an inert atmosphere to carbonize the molded product. Subsequently, in step S6, the molded product is graphitized at a temperature of 2500 to 3000 ° C. in a vacuum atmosphere or an inert atmosphere. As shown in FIG. 5, the heat radiator 12 is thereby formed from isotropic graphite. As described above, the radiator 12 can be formed of isotropic graphite obtained by heating and firing the molded product.

  Next, as shown in FIG. 3 to FIG. 5, after preparing the target body 11 having the target surface 11 a and formed of the molybdenum alloy, in step S <b> 7, using the zirconium brazing 20, the heat sink 12 is applied to the target body 11. Are joined by brazing. Thereby, the anode target 10 that can rotate around the rotation axis a is completed, and the manufacture of the anode target 10 is completed.

  According to the rotating anode type X-ray tube apparatus and the anode target 10 manufacturing method configured as described above, the anode target 10 is a near net molded radiator 12 formed of isotropic graphite, a target A target body 11 having a surface 11a, made of a molybdenum alloy having a specific gravity greater than that of isotropic graphite, and having a radiator 12 joined by brazing, and is rotatable about a rotation axis a.

  Since the heat radiating body 12 is joined to the target body 11, the allowable heat input of the anode target 10 can be increased, and the heat capacity of the anode target 10 can be increased. Since the specific gravity of graphite is about one fifth of the specific gravity of molybdenum, it is possible to increase the heat capacity while suppressing the weight of the anode target 10.

  Since the radiator 12 is near-net molded, the exposed surface of the radiator 12 need not be subjected to mechanical removal processing, and the manufacturing time and manufacturing cost can be suppressed as compared with the case where mechanical removal processing is performed. it can. Since there is no wear powder that becomes conductive foreign matter in the vacuum space of the X-ray tube 1 on the exposed surface of the radiator 12, it is possible to prevent discharge that may occur in the X-ray tube when wear powder exists. Can do.

  Furthermore, since it is not necessary to perform film formation processing on the surface of the radiator 12, the manufacturing time and the manufacturing cost can be suppressed. Further, since the heat radiating body 12 can be formed without confining gas inside, it is possible to prevent discharge that may occur in the X-ray tube when gas is discharged from the heat radiating body 12.

  From the above, the manufacturing cost can be suppressed, the gas is not confined in the radiator 12, and the anode target 10 having no abrasion powder on the exposed surface of the radiator 12, the X-ray tube 1 including the anode target 10, An X-ray tube device and a method for manufacturing the anode target 10 can be obtained. And the X-ray tube 1 and X-ray tube apparatus which can suppress generation | occurrence | production of a discharge defect over a long period can be obtained.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiments. For example, some components may be deleted from all the components shown in the embodiment.

  For example, before joining the heat radiating body 12 to the target body 11, the surface of the heat radiating body 12 may be mechanically removed to form a flat joint surface 12S. By flattening the bonding surface 12S of the radiator 12, the adhesive strength between the target body 11 and the radiator 12 can be improved.

  After joining the heat radiating body 12 to the target body 11, mechanical removal processing may be performed on a part of the surface of the target body 11. When the anode target 10 is not in an equilibrium state about the rotation axis a, the anode target 10 can be adjusted to be in an equilibrium state about the rotation axis a by the above method. Since the place where the mechanical removal process is performed is the target body 11 having a large specific gravity, the surface of the target body 11 may be slightly removed.

  The target body 11 is not limited to a molybdenum alloy, but may be formed of a metal having a specific gravity greater than that of isotropic graphite. The brazing material used when joining the target main body 11 and the heat radiating body 12 is not limited to the zirconium brazing 20 and can be variously modified.

  The X-ray tube and the X-ray tube apparatus of the present invention can be variously modified without being limited to the X-ray tube and the X-ray tube apparatus, and various rotary anode type X-ray tubes and X-ray tube apparatuses can be used. Can be applied.

  DESCRIPTION OF SYMBOLS 1 ... X-ray tube, 10 ... Anode target, 11 ... Target main body, 11a ... Target surface, 12 ... Radiation body, 12S ... Joining surface, 13 ... Rotating body, 15 ... Fixed body, 17 ... Vacuum envelope, 18 ... Cathode, 18a ... filament, a ... rotating shaft.

Claims (7)

A heat sink formed of near net and isotropic graphite;
A target body that has a target surface that emits X-rays upon incidence of electrons, is formed of a metal having a specific gravity greater than that of isotropic graphite, and the heat radiator is joined by brazing. A target characterized by being able to rotate around the center.   The target according to claim 1, wherein a joining surface of the heat radiating member joined to the target body is flat.   2. The target according to claim 1, wherein a part of the surface of the target body is subjected to mechanical removal processing. A heat sink made of isotropic graphite and made of isotropic graphite, and a target surface that emits X-rays upon incidence of electrons, and is made of a metal having a specific gravity greater than that of isotropic graphite. A target body whose body is joined by brazing, and a target that is rotatable about a rotation axis;
An electron emission source that emits electrons to irradiate the target;
An X-ray tube comprising: a vacuum envelope containing the target and an electron emission source. In the method of manufacturing a target that can rotate around a rotation axis,
Near-net molding a mixture of one or more types of carbon-based powder material,
Forming a radiator with isotropic graphite obtained by heating and firing the near-net shaped mixture,
A target body that has a target surface that emits X-rays when electrons are incident and is made of a metal having a specific gravity greater than that of isotropic graphite,
A method of manufacturing a target, comprising joining the heat radiating body to the target body by brazing. The surface of the formed radiator is subjected to mechanical removal processing to form a flat joint surface,
The method for manufacturing a target according to claim 5, wherein when joining the heat radiating body to the target body, a joining surface of the heat radiating body is joined to the target body.   The method for manufacturing a target according to claim 5, wherein after the radiator is joined to the target body, a mechanical removal process is performed on a part of the surface of the target body.

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