JPS6131589B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an X-ray anode and a method for manufacturing the same;
In particular, the improved crystal structure of the cast copper material allows for high loads
The purpose of the present invention is to provide an anode that contributes to high quality and long life of wire tubes and a method for manufacturing the same.

Generally, for example, a fixed anode X-ray tube is constructed as shown in FIG. 1, in which an anode base 2 is disposed on one side of an envelope 1 made of glass and supported by a sealing ring 3 made of metal. In the other side of the envelope 1, a cathode filament 5 is connected to a filament terminal 7 passing through a cup 6, facing the anode 2. The cup 6 is then supported by a support ring 8 attached to the envelope 1.

In such an X-ray tube, during operation, the cathode filament 5 is heated by a current applied from the filament terminal 7 and emits electrons. These electrons are accelerated by the high voltage applied to the anode substrate 2 while being focused by the cup 6, and collide with the target 4 with a desired distribution and energy, so that the target 4 generates X-rays.

Usually, the target is heated to a high temperature by electron bombardment from the cathode filament 5, so a refractory metal such as tungsten is used, and the anode base 2 is made of copper, which has good thermal conductivity, to release the heat of the target 4. . In addition, heat is transferred from the target 4 to the anode substrate 2.
To effectively release the target 4 and the anode base 2
It is necessary to strengthen the close contact between the two.

Conventionally, in order to satisfy such conditions, vacuum casting has been widely used as a method for attaching the target 4 to the anode substrate 2. That is, the target 4 is fixed in a cylindrical body to be heated (not shown), and the copper material placed therein is melted under high vacuum or low pressure reducing atmosphere at high temperature to melt the target 4 and the base. stick. Since the copper crystal grains of the anode thus formed are gradually aged under vacuum, they generally tend to become coarse.

Recent X-ray tubes are required to have a large load, and as a result, the power load tends to increase further. In such an X-ray tube, it is expected that the temperature of the target will rise very sharply, so for example, as shown in FIG.
A plurality of cut holes 12 are provided in the tube, and a fitting nozzle (not shown) is used to spray cooling oil into the cut holes 12 during operation of the X-ray tube. The oil is forced to cool by circulating it through a heat exchanger to achieve a cooling effect. Nevertheless, such high-load X-ray tubes tend to have a short lifespan due to failure of the vacuum seal during initial use. In view of these circumstances, the inventor's investigation revealed that this was due to a breakdown of the vacuum seal due to a crack in the crystal grain boundaries of the anode substrate. As mentioned above, the vacuum casting method for producing high quality anodes with good target adhesion strength and heat conduction tends to produce coarse crystals because the anodes are slowly cooled under vacuum. As shown in FIG. 2, dendritic grain boundaries 13 are formed, and these grain boundaries 13 penetrate from the cut hole 12 on the atmosphere side to the target 10 side on the vacuum side.
In a high-load X-ray tube, for example, when a high load of about 4KW is applied intermittently to a focal area of about 50 mm ² , the surface of the target 10 momentarily reaches a temperature of around 1000°C, and the copper member 11 from the target 10 reaches a temperature of 700°C. The temperature rises to around ℃. Therefore, when the high-load X-ray tube is in use, the copper member 11 near the back of the target 10 is
It will be subjected to intermittent thermal cycles of around 700°C, and large thermal stress will be applied to this area. This thermal stress is so strong that it is observed that recrystallization progresses significantly on the back side of the target or along the grain boundaries 13 after a thermal cycle of 100 to 200 hours. Weak dendritic grain boundaries13
progresses to a crack in the initial stage of use, and the anode 9
leads to vacuum destruction. Furthermore, if the copper member 11 is provided with cut holes 12 to improve the cooling effect, the length of the grain boundaries 13 will be shorter, promoting vacuum breakdown. In this way, the high-load X-ray tube
Intermittent thermal stress applied to the anode causes grain boundary cracks, resulting in leakage defects and a short life in the initial use stage. In addition, the inventor has analyzed and confirmed that the amount of molten gas impurities (oxygen, nitrogen, etc.) at the grain boundaries of the copper member by the above-mentioned anode manufacturing method is less than a few ppm, and there is no possibility that impurities are present. It was found that this was not the cause of grain boundary cracks.

The present invention was made in consideration of the above-mentioned situation, and aims to improve the crystal structure of a cast copper material for an anode of an X-ray tube.

That is, an anode in which crystal grain boundaries that cause anode cracking and vacuum-tight failure due to the strong thermal stress of intermittent thermal cycles are not generated, and more specifically, an anode in which at least the portion surrounding the target member is substantially monocrystalline. The present invention provides an anode made of a copper material that is particularly suitable for high-load use and can be expected to have high quality and a long life, and a method for manufacturing the same.

Hereinafter, an X-ray tube anode and a method for manufacturing the same according to the present invention will be explained. FIG. 3 shows the apparatus used for this purpose, FIG. 4 is a cross-sectional view of 14 parts of the vacuum container, and FIG. 5 is a partial longitudinal sectional view of 14 parts of the vacuum container. In this device, a heating vacuum container 14 made of a quartz bell jar is placed on a flange 16 with its open end interposed through a packing 15. The flange 16 is also connected to an oil rotary pump 19 via an exhaust conduit 17 and a valve 18. Vacuum container 14
Inside, a plurality of casting vessels or heated cylindrical bodies 21 made of a refractory metal such as graphite are installed in a circular shape via a hollow cylindrical bisque baking stand 20 placed on a flange 16 . Note that the code 21a
is the bottom of the cylindrical body 21 and is fixed together with the same graphite. A gas introduction hole 22 is provided on the top surface of the bisque baking table 20, and several exhaust holes (not shown) are provided on the side surface. Also exhaust pipe 17
A hydrogen introduction nozzle 23 is provided, which penetrates the bottom of the tank, passes through the exhaust conduit 17, and has one end protruding into the hollow clay baking table 20, and the other end is connected to a high-purity hydrogen gas supply source 25 via a minute leak valve 24. small conduit 2
6 is provided. Casting and melting is performed, for example, by a high frequency induction heating coil 27.

As shown in FIG. 5, a target member 28 made of a predetermined material such as tungsten and a copper member 29 are installed inside the heated cylindrical body 21. Further, the cylindrical body 21 to be heated is placed in the vacuum container 14 in a circular shape as shown in FIG. This cylindrical body 21 to be heated, that is, the casting container, has a recess in a part of its internal space, and in this embodiment, the bottom is tapered and the tapered edge portion 30 forms the recess. This taper is formed to approximately correspond to the taper angle of the X-ray tube anode target surface. Then, the vacuum container 14 and the bisque baking table 20
Install them all in a radial direction, that is, facing outward, with respect to the center of the That is, the tapered edge portion 30 corresponding to the tapered edge portion (11a in FIG. 2) of the finished cast anode is aligned in the outward direction of the cylinder.

A single crystal of an X-ray tube anode substrate is obtained using the above apparatus. The main points are as follows. The first is reduction purification of the cast member using high-purity hydrogen gas.

Second, in order to eliminate supercooling, suppress nucleation, and promote crystal growth, the molten copper material is gradually cooled at a very low rate before and after the solidification crystallization temperature (1083°C). Furthermore, the third feature is to utilize the unique shape of the X-ray tube anode to create a tapered edge portion 30 in the internal space of the casting container, which corresponds to the portion that forms the tapered edge portion of the finished casting anode.
During solidification and crystallization, nucleation and crystal growth occur from this tapered edge portion 30 by arranging it in the outward direction of the cylinder of the vacuum container, as if a seed crystal were placed in this portion and used as a nucleus. The objective is to create conditions that cause the copper liquid to solidify on top of the copper liquid.

Next, an embodiment of the method for manufacturing an X-ray tube fixed anode according to the present invention will be described.

(b) As shown in FIGS. 3 to 5, a heated cylindrical body 21 housing a target member and a copper member inside.
is installed, operate the oil rotary pump 19 and open the valve 18 to drain the inside of the vacuum container
Exhaust to 10 ^-1 to 10 ^-2 Torr.

(b) Next, while keeping the oil rotary pump 19 in operation, open the minute leak valve 24, introduce hydrogen, and adjust the inside of the vacuum vessel 14 to 8 to 10 Torr. In this way, a circulation path is created in which the hydrogen gas displaces and cleans the impure gas in the vacuum container 14 and is discharged by the oil rotary pump 19.

(c) Next, the cylindrical body 21 to be heated is heated by the high frequency induction heating coil 27 installed outside the vacuum vessel 14 according to the temperature raising step shown in FIG.

The melting and slow cooling steps shown in FIG. 6 can be roughly divided into three regions as shown in the figure.

Area A is the preliminary degassing step, which is 800 to 900
The heating cylinder 21 and other members are maintained at a temperature of 0.degree. C. and cleaned by reduction. In particular, it is necessary to allow sufficient time to remove impurities from the surfaces of the tungsten target member and copper member. This makes it possible to suppress the generation of impurity seeds that tend to accelerate the formation rate of nuclei during solidification and crystallization in region C.

In region B, when the members and others are clean, the heating temperature is increased to a copper melting casting temperature of 1200 to 1300°C. In this process, intense gas release occurs from the anode material, but by keeping the hydrogen gas introduced for 5 to 10 minutes, the oxygen in the molten copper can be actively removed as water by the dissolved hydrogen gas. After this, when the introduction of hydrogen is stopped, the hydrogen dissolved in the anode material is quickly discharged. When hydrogen is discharged, the vacuum pressure should be approximately 10 ^-2 Torr or less.

Next, region C is an extremely important step in single crystallization. In other words, the solidification and crystallization temperature of copper (1083
℃) is gradually cooled at a temperature decreasing rate of 5℃/min or less. This process specifically eliminates supercooling, reduces the nucleation rate to almost zero, and promotes crystal growth. The slow cooling rate can be achieved by gradually lowering the high frequency output.

Now, by aligning the part 30 corresponding to the tapered edge part of the finished cast anode using the unique shape of the X-ray tube anode in the outward direction of the circumference, the temperature can be lowered by using a cylindrical vacuum vessel and induction heating in this slow cooling process. Because the temperature is lowered, the temperature at the periphery drops faster than at the center, albeit slightly.Moreover, since the taper edge has a smaller heat capacity than other parts, the temperature drops the fastest, and it is possible to limit the location of nuclei generation here. can. Therefore, solidification crystallization starts from this portion, extends around the target member, and further progresses to the entire anode, ensuring that a single crystal structure is obtained. The inventor has determined that the diameter of the anode substrate is 38 mm, the length is 100 mm, the diameter of the tungsten target member is 25 mm, the thickness is 2 mm, and the taper angle (angle with respect to the central axis).
succeeded in molding a single-crystal anode body at approximately 70°C. If the taper angle is approximately 80℃ or less,
This could be obtained with sufficient reproducibility.

(d) After solidification and crystallization, rapid cooling is performed using nitrogen gas in region D below approximately 900°C. This can also shorten the process, and after cooling, the anode is taken out from the vacuum vessel 14, the cast anode is extracted from the heated cylindrical body 21, and finished into the desired anode shape.

The above-mentioned hydrogen introduction pressure needs to be at least several Torr in order to prevent oxidizing gas from penetrating into the anode material and to create a reducing atmosphere. Also, considering the safe operation of the oil rotary pump, hydrogen consumption, and prevention of cavities caused by impure gas in the molten copper material,
The upper limit hydrogen pressure is preferably kept at several tens of Torr.

The slower the slow cooling rate, the better; however, from an industrial standpoint, ie, from the standpoint of mass production, the upper limit for single crystallization is 5° C./min or less.

The embodiment shown in FIGS. 7 to 9 is a case in which a casting container 21 for accommodating a copper material has one hole-shaped recess 30 formed at the corner of the inner bottom. That is, this container 21 has a recess 30 formed in its flat bottom, and this recess 30 is heated to the vacuum container 1.
4. When installed inside, all are placed facing outward. Even when this is used, the concavity of this example corresponds to the tapered edge part of the above-mentioned example, and the molten copper material begins to crystallize from the concave part of the container and progresses throughout the container to obtain a single crystal. .

In this way, a tapered edge part or a hole-shaped recess as shown in Figs. A single crystal of copper can be obtained with good reproducibility by positioning it toward the point where the temperature distribution is lowest and slowly cooling it. In the present invention, the area around the target member, that is, the vicinity of the target surface of the anode substrate may have a substantially single-crystal structure. It is not necessary that the entire anode body be made of single crystal.

The single-crystal copper anode fixed to the X-ray tube produced in this way was able to prove its single-crystal structure in chemical etching, X-ray diffraction, and Laue photographic images.

The anode substrate made of single crystal copper has a face-centered cubic lattice structure and is symmetrical about three axes, so there is no anisotropy in heat conduction and thermal expansion coefficient, and it is suitable for use as an X-ray tube anode. It has better thermal conductivity than crystalline materials, can completely solve the grain boundary cracks caused by thermal stress in X-ray tube anodes, and has sufficient adhesion to target materials for practical use. This makes it possible to realize high-quality, long-life, high-load X-ray tube anodes with good reproducibility.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an X-ray tube, Fig. 2 is a partial cross-sectional view of a conventional anode, Fig. 3 is a device used in the present invention, Fig. 4 is a cross-sectional view of a vacuum vessel section, and Fig. 5 6 is a partial longitudinal cross-sectional view of the vacuum container part, FIG. 6 is a process diagram showing the temperature rise and fall steps of the process of the present invention, and FIG.
The drawings are longitudinal cross-sectional views of essential parts showing another embodiment, FIG. 8 is a cross-sectional view taken along line 8--8 in FIG. 7, and FIG. 9 is a schematic cross-sectional view corresponding to FIG. 2. 2...Anode, 4...Target, 14...Heating vacuum vessel, 21...Heated cylindrical body (casting container), 23...Hydrogen introduction nozzle, 28...Target member, 29...Copper member, 11a... ...Tapered edge part of the base body, 30... Recessed part in the casting container.

Claims (1)

[Scope of Claims] 1. In an X-ray tube anode in which a target member is cast into an anode base made of copper, the anode base portion surrounding the target member is substantially made of a copper material having a single crystal structure. An X-ray tube anode featuring: 2. In a method for manufacturing an X-ray tube anode in which a target member is cast into an anode base made of copper, there is a step of heating and melting the copper material in a reduced pressure reducing gas atmosphere, and then a temperature range in which the molten copper material is solidified and crystallized. A method for producing an anode for an X-ray tube, comprising the step of slowly cooling the anode at a temperature decreasing rate of 5° C./min or less. 3. The manufacturing method according to claim 2, in which a container having a recess in a part of the internal space is used as the casting container for accommodating the copper material. 4. The manufacturing method according to claim 3, wherein the recess is a tapered edge formed by shaping the bottom of the container into a tapered shape. 5 A casting container with a dent in a part of the internal space,
A plurality of cast members are placed in a circle in a vacuum heating container, a target member and a copper material are housed in each casting container, and each casting container is placed with its recess facing toward the outside of the heating container. The manufacturing method according to claim 2, characterized in that: